WO2025164157A1 - Method for producing acrylic resin-containing film and multi-stage stretched acrylic resin-containing film - Google Patents

Abstract

The problems addressed by the present invention are to provide a method for producing an acrylic resin-containing film which is widened and thinned, does not crack, has high density, and can maintain functionality, and to provide a multi-stage stretched acrylic resin-containing film.　Provided is a method for producing an acrylic resin-containing film characterized by casting a dope containing an acrylic resin (A) and a cellulose ester resin (B) in a mass ratio of 95:5-30:70, stretching the acrylic resin-containing film in two stages in the widthwise direction, and having the longitudinal expansion/contraction rate A from the detachment position of the acrylic resin-containing film to a position immediately before the second widthwise stretching and the widthwise relaxation rate A after the second widthwise stretching satisfy the relationship -250<(expansion/contraction rate A/relaxation rate A)<550.

Description

Method for producing acrylic resin-containing film and multi-stage stretched acrylic resin-containing film

The present invention relates to a method for producing an acrylic resin-containing film and a multi-stage stretched acrylic resin-containing film. More specifically, it relates to a method for producing an acrylic resin-containing film that is wide and thin, crack-free, high-density, and capable of maintaining its functionality.

In recent years, in addition to the increasing size of TVs, there has been a demand for improved productivity through longer and wider film in order to reduce environmental impact. There is also a demand for resource conservation through thinner film.

Here, before the widened and thinned film is incorporated into a display device, a hard coat layer may be formed as a functional layer on the film, and this functional layer may be formed through a coating process. In the coating process, a coating liquid is first prepared and then allowed to penetrate into the film substrate, but if the coating liquid penetrates too far into the substrate, the thickness of the hard coat layer may not be sufficiently ensured.

This has led to problems such as the inability to fully fulfill the role of the functional layer, such as providing the film with excellent pencil hardness.

Furthermore, as mentioned above, if the coating liquid penetrates too deeply into the substrate, cracks can occur in the film substrate, causing problems such as these, and improvements were needed.

In response to the above-mentioned issues, Patent Document 1 discloses a method for efficiently producing an acrylic resin-containing film in which an acrylic resin and a cellulose ester resin are mixed in a specific ratio. While the acrylic resin-containing film produced by this method has excellent flexibility and surface properties, there is still room for improvement.

International Publication No. 2009-150910

The present invention was made in consideration of the above problems and circumstances, and its objective is to provide a method for producing an acrylic resin-containing film and a multi-stage stretched acrylic resin-containing film that can be made wider and thinner, crack-free, high-density, and maintain functionality.

In order to solve the above-mentioned problems, the present inventors have investigated the causes of the above-mentioned problems and have found that the above-mentioned problems can be solved by stretching an acrylic resin-containing film in multiple stages and controlling the longitudinal stretch rate and the widthwise relaxation rate so as to satisfy a specific relationship, thereby arriving at the present invention.
That is, the above-mentioned problems of the present invention are solved by the following means.

1. A method for producing an acrylic resin-containing film, comprising at least a casting step, a first conveying step, a first stretching step, and a second stretching step, in this order,
In the casting step, a dope containing an acrylic resin (A) and a cellulose ester resin (B) in a mass ratio of 95:5 to 30:70 is cast;
In the first stretching step, the acrylic resin-containing film is stretched in the width direction,
In the second stretching step, the acrylic resin-containing film is further stretched in the width direction,
An expansion/contraction rate A in the longitudinal direction from the peeling position of the acrylic resin-containing film in the casting step to a position immediately before stretching the acrylic resin-containing film in the width direction in the second stretching step, and a relaxation rate A in the width direction after stretching the acrylic resin-containing film in the width direction in the second stretching step satisfy the relationship of the following formula (1): -250<(expansion/contraction rate A/relaxation rate A)<550
A method for producing an acrylic resin-containing film, comprising:

2. A second conveying step is provided between the first stretching step and the second stretching step,
A conveying tension _T1 of the acrylic resin-containing film after drying the dope in the first conveying step and a conveying tension _T2 of the acrylic resin-containing film in the second conveying step satisfy the relationship of the following formula (2): 1.00<(conveying tension _T1 /conveying tension _T2 )<2.00.
2. The method for producing an acrylic resin-containing film according to claim 1.

3. The stretch rate A and the relaxation rate A satisfy the relationship of the following formula (3): Relaxation rate A<stretch rate A
2. The method for producing an acrylic resin-containing film according to claim 1.

4. When the acrylic resin-containing film is transported at an expansion/contraction rate a in the second transport step, the relationship of the following formula (4) is satisfied: 1.25<(expansion rate a/relaxation rate A)<5.5.
2. The method for producing an acrylic resin-containing film according to claim 1.

5. A multi-stage stretched acrylic resin-containing film containing at least an acrylic resin (A), a cellulose ester resin (B), rubber particles, and inorganic particles,
the multistage stretched acrylic resin-containing film contains the acrylic resin (A) and the cellulose ester resin (B) in a mass ratio of 95:5 to 30:70;
the total substitution degree (T) of the acyl groups of the cellulose ester resin (B) is in the range of 2.0 to 3.0, and the substitution degree of the acyl groups having 3 to 7 carbon atoms is in the range of 1.2 to 3.0; and
The multistage stretched acrylic resin-containing film has a film density in the range of 1.235 to 1.300 g/cm ³ .

The above-mentioned means of the present invention can provide a method for producing an acrylic resin-containing film and a multistage stretched acrylic resin-containing film that can be made wider and thinner, crack-free, have high density, and maintain functionality.
The mechanism by which the effects of the present invention are manifested or the mechanism of action is not clear, but is speculated as follows.

The method for producing an acrylic resin-containing film of the present invention comprises at least a casting step, a first conveying step, a first stretching step, and a second stretching step in this order, wherein in the casting step, a dope containing an acrylic resin (A) and a cellulose ester resin (B) in a mass ratio ranging from 95:5 to 30:70 is cast, in the first stretching step, the acrylic resin-containing film is stretched in the width direction, and in the second stretching step, the acrylic resin-containing film is further stretched in the width direction, and an expansion rate A in the longitudinal direction from a peeling position of the acrylic resin-containing film in the casting step to a position immediately before stretching the acrylic resin-containing film in the width direction in the second stretching step, and a relaxation rate A in the width direction after stretching the acrylic resin-containing film in the width direction in the second stretching step satisfy the relationship of the following formula (1): -250<(expansion rate A/relaxation rate A)<550
It is characterized by:

In conventional films, wide, thin films are stretched only once, which can cause voids to form in the film, particularly due to the influence of the stretch rate in the longitudinal direction, making it difficult for the film to maintain its dense state. This reduces the density of the film, which can lead to excessive penetration of the functional layer-forming coating liquid when a functional layer is formed on the film, making it difficult to ensure the function of the functional layer.

In a method for producing an acrylic resin-containing film that includes at least a casting process, a first conveying process, a first stretching process, and a second stretching process, in this order, the inventors control the longitudinal stretch rate and the widthwise relaxation rate to satisfy the relationship shown in formula (1) above.

When a film is stretched at high temperatures, the mobility of the resin contained in the film improves, thereby increasing its density. In the above manufacturing method, the amount of residual solvent in the film is reduced up to the second stretching step. When the amount of residual solvent has decreased, it is possible to increase the density of the film by further stretching it in the width direction, but at the same time, voids will also be created in the width direction.

In the present invention, after the film is stretched in the width direction in the second stretching step when the residual solvent has been reduced, the film is relaxed in the width direction, thereby filling the voids and increasing the density of the film. This allows the film to maintain its dense state.

From the above, it is inferred that the widened and thinned acrylic resin-containing film produced by the manufacturing method of the present invention does not develop cracks, has high density, and is able to maintain its functionality.

Schematic diagram showing the relationship between the state of the resin at the peeling position during the casting process and voids present in the film Schematic diagram showing the relationship between the state of the resin and voids present in the film immediately before stretching in the second stretching step. Schematic diagram showing the relationship between the state of the resin and voids present in the film immediately before stretching in the second stretching step. Schematic diagram showing the relationship between the state of the resin before the relaxation treatment in the second stretching step and voids present in the film. Schematic diagram showing the relationship between the state of the resin after the relaxation treatment in the second stretching step and voids present in the film A flowchart showing the flow of the film manufacturing process according to the present invention. Schematic diagram of a film manufacturing apparatus according to the present invention. Schematic diagram for explaining how a film is stretched by a tenter stretching device

The method for producing an acrylic resin-containing film of the present invention comprises at least a casting step, a first conveying step, a first stretching step, and a second stretching step, in this order, wherein a dope containing an acrylic resin (A) and a cellulose ester resin (B) in a mass ratio ranging from 95:5 to 30:70 is cast in the casting step, the acrylic resin-containing film is stretched in the width direction in the first stretching step, and the acrylic resin-containing film is further stretched in the width direction in the second stretching step, and the expansion rate A in the longitudinal direction from a peeling position of the acrylic resin-containing film in the casting step to a position immediately before stretching the acrylic resin-containing film in the width direction in the second stretching step and the relaxation rate A in the width direction after stretching the acrylic resin-containing film in the width direction in the second stretching step satisfy the relationship of formula (1).
This feature is a technical feature common to or corresponding to each of the following embodiments (aspects).

As an embodiment of the present invention, it is preferable that the conveying tension _T1 and the conveying tension _T2 satisfy the relationship of the formula (2) above, from the viewpoint of suppressing the generation of voids in the film and setting the stretching rate to an appropriate value.

From the viewpoint of further enhancing the effects of the present invention, it is preferable that the stretch rate A and the relaxation rate A satisfy the relationship expressed by formula (3).

From the perspective of controlling the film density within an appropriate range, it is preferable that the expansion/contraction rate a in the second conveying step and the relaxation rate A satisfy the relationship expressed by formula (4).

The multistage stretched acrylic resin-containing film of the present invention is a multistage stretched acrylic resin-containing film containing at least an acrylic resin (A), a cellulose ester resin (B), rubber particles, and inorganic particles, characterized in that the acrylic resin-containing film contains the acrylic resin (A) and the cellulose ester resin (B) in a mass ratio of 95:5 to 30:70, the total degree of substitution (T) of acyl groups of the cellulose ester resin (B) is in the range of 2.0 to 3.0, the degree of substitution of acyl groups having 3 to 7 carbon atoms is in the range of 1.2 to 3.0, and the film density of the acrylic resin-containing film is in the range of 1.235 to 1.300 g/ ^cm3 .

The present invention, its components, and the embodiments and modes for implementing the invention are described in detail below. Note that in this application, the symbol "to" is used to mean that the numerical values before and after it are included as both the lower limit and upper limit.

The advantages and features provided by one or more embodiments of the present invention will be more fully understood from the following detailed description and the accompanying drawings, which are for illustrative purposes only and are not intended to define the limits of the present invention.

1. Method for Producing Acrylic Resin-Containing Film The method for producing an acrylic resin-containing film of the present invention comprises, in this order, at least a casting step, a first conveying step, a first stretching step, and a second stretching step, wherein in the casting step, a dope containing an acrylic resin (A) and a cellulose ester resin (B) in a mass ratio ranging from 95:5 to 30:70 is cast, in the first stretching step, the acrylic resin-containing film is stretched in the width direction, and in the second stretching step, the acrylic resin-containing film is further stretched in the width direction, and an expansion rate A in the longitudinal direction from a peeling position of the acrylic resin-containing film in the casting step to a position immediately before stretching the acrylic resin-containing film in the width direction in the second stretching step, and a relaxation rate A in the width direction after stretching the acrylic resin-containing film in the width direction in the second stretching step satisfy the relationship of the following formula (1): Formula (1) -250<(expansion rate A/relaxation rate A)<550
It is characterized by:

The stretch rate A and the relaxation rate A satisfy the relationship of the following formula (3): Relaxation rate A<stretch rate A
This is preferable from the viewpoint of further enhancing the effects of the present invention.

If the value of (stretch rate A/relaxation rate A) is -250 or less, the acrylic resin-containing film will shrink too much in the longitudinal direction, and the resin molecules in the acrylic resin-containing film will no longer be able to maintain a stable arrangement. As a result, voids will easily form in the acrylic resin-containing film.

Furthermore, wrinkles occur in the acrylic resin-containing film, and when a hard coat layer or the like is formed on the acrylic resin-containing film, the amount of coating liquid applied when forming the hard coat layer becomes excessive, impairing the functionality of the film.

In order to achieve a (stretch rate A/relaxation rate A) value of 550 or more, the acrylic resin-containing film must be stretched excessively, which requires the film to be manufactured under high temperature and high tension conditions. Films manufactured under such conditions are prone to breakage. There is also the risk of foaming, which can cause voids to form in the film.

(Stretch rate A)
The concept of the "stretchability ratio A" in the present invention will be explained below with reference to FIGS. 1, 2A and 2B.

Figure 1 is a schematic diagram showing the relationship between the state of the resin at the peel position in the casting process and voids present in the film. Before being stretched in the first stretching step, the relationship between the resin and voids in the film at the peel position in the casting process is assumed to be aligned as shown in Figure 1. Note that L _(MD)0 is the length in the longitudinal direction (machine direction, MD) of the film cut out at a specific portion at the peel position in the casting process.

2A and 2B are schematic diagrams showing the relationship between the state of the resin and voids present in the film immediately before stretching in the width direction in the second stretching step. The relationship between the resin and voids in the film immediately before stretching in the second stretching step is as shown in FIG. 2A or 2B. Note that L _(MD)A1 is the length of L(MD)0 extended in the longitudinal direction (machine direction, MD) of the film from the peeling position in the casting step to a position immediately before stretching in the width direction (TD) in the second stretching step. Furthermore, L _(MD)A2 is the length of L _{( MD)} 0 shortened in the longitudinal direction (machine direction, MD) of the film from the peeling position in the casting step to a position immediately before stretching in the width direction (TD) in the second stretching step.

Furthermore, if the expansion/contraction rate A is too small, i.e., if the film shrinks too much in the longitudinal direction (conveyance direction, MD), the resin particles will no longer be able to maintain a stable arrangement, making it more likely for voids to form.

[Calculation of expansion/contraction ratio A]
The expansion/contraction rate A [%] was calculated by the following formula.
Formula: Expansion/contraction rate A [%]={(V _W1 - V ₁ )/V ₁ }×100+{(V ₄ -V ₃ )/V ₃ }×100

The meanings of the symbols in the above formula are as follows:
V _W1 : Film winding speed in the second transport step (film winding speed by the winding device 8)
V ₁ : Belt speed in the casting section (speed of the support)
_V3 : Film unwinding speed in the second transport step _V4 : Film transport speed in the second stretching step

(Relaxation rate A)
The concept of the "relaxation rate A" in the present invention will be explained below with reference to FIGS. 3 and 4. FIG.

3 is a schematic diagram showing the relationship between the state of the resin before the relaxation treatment in the second stretching step and the voids present in the film. Details of the stretching in the second stretching step will be described later. Note that L _(TD)A0 is the length in the width direction (TD) of the film before the relaxation treatment in the second stretching step.

4 is a schematic diagram showing the relationship between the state of the resin after the relaxation treatment in the second stretching step and the voids present in the film, where L _(TD)A1 is the length in the width direction (TD) of the film after the relaxation treatment in the second stretching step.

If the relaxation rate A is small, the film density will be slightly low, but if the film is sufficiently stretched in the longitudinal direction (machine direction, MD) and the relaxation rate A is sufficient, the film density will be extremely good. Conversely, if the relaxation rate A is too large, the film density will be high, but the film will wrinkle and crack more easily, which will result in too much coating liquid seeping in when forming a hard coat layer or the like on the film, reducing functionality.

[Calculation of relaxation rate A]
The relaxation rate A [%] was calculated by the following formula.
Formula Relaxation rate A [%] = (L _(TD)A0 /L _(TD)A1 -1) x 100 [%]
(L _(TD)A1 : length in the width direction (TD) of the film after the relaxation treatment in the second stretching step, L _(TD)A0 : length in the width direction (TD) of the film before the relaxation treatment in the second stretching step)

(Types of film-forming methods)
The acrylic resin-containing film of the present invention can be produced by, for example, a solution casting film-forming method or a melt casting film-forming method.

The "solution casting film-forming method" is a film-forming method that involves the following steps: First, a dope is cast onto a moving support to form a casting film (web), which is then dried to a degree that allows it to be peeled off. The film is then peeled off from the support, and while transported by a transport roller, the peeled film is dried and stretched to form a long resin film.

The "melt casting film-forming method" is a film-forming method in which a composition containing a thermoplastic resin and additives is heated to a temperature at which the composition exhibits fluidity, and then the melt containing the fluid thermoplastic resin is cast.

Figure 5 is a flowchart showing the flow of the film manufacturing process according to the present invention. Note that this flowchart applies to both the solution casting film-making method and the melt casting film-making method, but the following description will be given assuming the solution casting film-making method is used.

(1.1) Casting process: S1
6 is a schematic diagram of a film manufacturing apparatus according to the present invention. In the casting process, a dope prepared by stirring at least a resin and a solvent in a stirring tank 1a of a stirring device 1 is sent to a casting die 2 through a conduit via a pressure-type metering gear pump or the like. The dope is cast from the casting die 2 onto a support 3 (casting belt) to form a casting film (web). The casting film (web) is then dried to a peelable degree, and then peeled off as a film from the support 3 (casting belt) by a peeling roller 4.

In order to increase the film-making speed of the raw film, two or more of the above-mentioned casting dies may be provided on the support, and the dope amount may be divided and layered. It is also preferable to obtain a raw film with a laminated structure by a co-casting method in which multiple dopes are cast simultaneously.

The support 3 is made of, for example, a stainless steel belt and is held in place by a pair of rollers 3a, 3b and several rollers positioned between them. In this case, it is preferable that the surface of the support be a mirror finish.

One or both of the rollers 3a and 3b are provided with a drive device that applies tension to the support 3, so that the support 3 is used in a tensioned state. The support 3 may also be a drum.

(Composition of resin in dope)
The dope is prepared so as to contain the acrylic resin (A) and the cellulose ester resin (B) in a mass ratio ranging from 95:5 to 30:70.

(Film peeling and stretch rate A)
The position where the film is peeled from the support 3 (casting belt) by the peeling roller 4 is defined as the peeling position, and the stretch ratio in the longitudinal direction (machine direction, MD) of the film from the peeling position to the position immediately before stretching the film in the width direction (TD direction) in the second stretching step described below is the stretch ratio A according to the present invention. The calculation method of the stretch ratio A is as described above.

(1.2) First conveyance step: S2
(Transport tension _T1 )
The first conveying step is a step of conveying the peeled film with a conveying roller 4 at a conveying tension T ₁ [N/m], and the conveying tension T ₁ [N/m] is controlled by the speed difference between the film conveying speed in the first conveying step and the film winding speed V _W1 in the winding device 8.

In the first conveying step, a drying device 5 may be provided at the position shown in Figure 6, and the film may be dried as needed while being conveyed.

The conveying tension _T1 can be measured, for example, by installing a tension meter at any position in the first conveying step in Figure 6, or at both ends of the film. It is also preferable to measure the conveying tension _T1 using a non-contact tension meter. For example, a non-contact web tension meter such as a Bellmatic non-contact web tension meter may be used, which can measure the conveying tension without contacting the film using air pressure by using an air turn bar supplied with air from a blower in the range of slight to low pressure.

(Temperature during film transport)
At this time, the glass transition temperature Tg [°C] of the resin (synthetic resin consisting of acrylic resin and cellulose ester resin) in the dope is calculated from the resin composition, and the temperature during transportation is determined to be (Tg-10)°C or lower, more preferably within the range of (Tg-40)°C to (Tg-60)°C.

(Stretch rate b)
The stretch rate b [%] in the first conveying step is also one of the factors that affect the effects of the present invention, and the stretch rate b [%] in the longitudinal direction (conveying direction, MD direction) of the film during conveying is a value calculated by the following formula.

Formula: Expansion/contraction rate b [%] = {(V ₂ - V ₁ )/(V ₁ )}×100 [%]

The meanings of the symbols in the above formula are as follows:
V ₁ : Belt speed in the casting section (speed of the support)
_V2 : Film transport speed in the first stretching step

(1.3) First stretching step: S3
The first stretching step is a step of stretching the above-mentioned film in the width direction. The stretching device 6 may be, for example, a tenter stretching device. Details of the tenter stretching device will be described later in the second stretching step. In this step, the relaxation rate B is calculated.

(Relaxation rate B)
Hereinafter, the concept of "relaxation rate B" in the present invention is omitted because it is the same as the above-mentioned "relaxation rate A." Therefore, only the method for calculating the relaxation rate B [%] will be described below. Note that if the relaxation rate B is high, the film density will be high. Also, if the relaxation rate B is low, the film density will be slightly low.

[Calculation of relaxation rate B]
The relaxation rate B [%] according to the present invention was calculated by the following formula.
Formula Relaxation rate B [%] = {(L _(TD)B0 -L _(TD)B1 )/L _(TD)B1 }×100[%]
(L _(TD)B1 : length in the width direction (TD) of the film after the relaxation treatment in the first stretching step, L _(TD)B0 : length in the width direction (TD) of the film before the relaxation treatment in the first stretching step)

(Second conveying process: 2nd MD)
In the second conveying step, the film stretched by the stretching device 6 is wound by the winding device 8 to produce a raw film. At this time, the film may be dried by providing a drying device 7, for example. Then, both ends of the film in the width direction are cut by a cutting section 13 consisting of a slitter before the film is wound by the winding device 8. Thus, the second conveying step according to the present invention includes the cutting and winding steps.

[Transport tension T2 _]
The raw film wound by the winding device 8 is unwound from the winding device 8 at a winding speed _V3 . The raw film is then transported in the second transport step with a transport tension _T2 [N/m]. The transport tension _T2 [N/m] is controlled by the speed difference between the film transport speed in the second transport step and the film winding speed _VW2 in the winding device 12. At this time, the film may be dried by providing a drying device 9, for example.

The conveying tension _T2 can be measured in the same manner as the conveying tension _T1 by installing a tension meter at any position in the second conveying step in FIG. 6 or at both ends of the film.

In the second conveying step, the amount of residual solvent is decreasing, so if the expansion/contraction rate a is too high, voids are more likely to occur.

[Temperature and expansion/contraction rate a during film transport]
At this time, the glass transition temperature of the resin calculated from the resin composition in the dope is used to determine the temperature during transport within the range of (Tg-10)°C to (Tg+20)°C. During transport, the stretch rate a of the film in the longitudinal direction (machine direction, MD) is measured.

[Calculation of expansion/contraction ratio a]
The stretch rate a [%] according to the present invention was a value calculated by the following formula.
Formula: Expansion/contraction rate a [%] = {(V _W1 - V ₂ )/V ₂ } x 100 + {(V ₄ - V ₃ )/V ₃ } x 100

The meanings of the symbols in the above formula are as follows:
V _W1 : Film winding speed in the second transport step (film winding speed by the winding device 8)
_V2 : Film transport speed in the first stretching step _V3 : Film unwinding speed in the second transporting step _V4 : Film transport speed in the second stretching step

[Relationship of conveying tension in the conveying process]
The conveying tension in the first conveying step is conveying tension _T1 , and the conveying tension in the second conveying step is conveying tension _T2 .

Here, it is preferable that the conveying tension _T1 and the conveying tension _T2 satisfy the relationship of the following formula (2) from the viewpoint of suppressing the generation of voids in the film and setting the stretching rate to an appropriate value.

Formula (2) 1.00<(conveying tension T ₁ /conveying tension T ₂ )<2.00

By making the conveying tension _T1 in the first conveying step greater than the conveying tension _T2 in the second conveying step, the stretch rate a in the longitudinal direction (conveying direction, MD direction) of the film in the second conveying step does not become too high.

In the second conveying step, the amount of residual solvent in the film is also decreasing, so the expansion/contraction ratio a does not become too high, thereby preventing the formation of voids in the film. Furthermore, since the conveying tension _T1 in the first conveying step is not too larger than the conveying tension _T2 in the second conveying step, the expansion/contraction ratio a does not become too low. This prevents the film density from becoming too high, and for this purpose, it is preferable to satisfy the relationship of the above formula (2).

(1.4) Second stretching step: S4
The second stretching step is a step in which the raw film transported in the second transport step is further stretched in the width direction by a stretching device 10. As the stretching device 10, for example, a tenter stretching device can be used. The speed at which the film is transported in the stretching device 10 is referred to as a transport speed _V4 in this specification. In this step, the raw film may also be subjected to a treatment such as drying, if necessary. The relaxation rate A in the width direction of the film is measured during this step.

(Relaxation rate A, stretch rate A, and stretch rate a)
The stretch ratio A according to the present invention is the stretch ratio in the longitudinal direction (machine direction, MD) of the film from the peeling position of the film in the casting step to the position immediately before stretching in the width direction in the second stretching step, and the stretch ratio A and the relaxation ratio A satisfy the relationship of the following formula (3): Relaxation ratio A [%] < stretch ratio A [%]
This is preferable from the viewpoint of further enhancing the effects of the present invention.

In addition to the above relationship, if the relaxation rate A in the width direction of the film is not too small, the occurrence of voids due to a decrease in the density of the film can be suppressed. Furthermore, if the relaxation rate A is not too large, the occurrence of wrinkles and cracks due to an increase in the film density can be suppressed.

Furthermore, the expansion/contraction rate a in the second conveying step and the relaxation rate A satisfy the relationship of the following formula (4): 1.25<(expansion/contraction rate a/relaxation rate A)<5.5.
This is preferable from the viewpoint of controlling the film density within an appropriate range.

(Tenter stretching device)
FIG. 7 is a schematic diagram for explaining how a film is stretched by a tenter stretching apparatus.

As shown in Figure 7, the tenter stretching device 14 is mainly divided into a width retention zone A, a stretching zone B, a film width retention zone C, and a stress relaxation zone D. Each zone is described below. Note that the "relaxation treatment" referred to in this specification is carried out in the stress relaxation zone D.

Width retention zone A: A zone in which the distance between the gripping clips of the film width (both base ends) from the entrance of the tenter stretching device 14 to the stretching start point a of the film is constant. Stretching zone B: A zone in which the distance between the gripping clips of the film width (both base ends) from the stretching start point a to the stretching end point b of the film in the tenter stretching device 14 increases in the traveling direction (transport direction). Film width retention zone C: A zone in which the film width is retained in a stretched state, in which the distance between the gripping clips of the film width (both base ends) after stretching from the stretching end point b of the film in the tenter stretching device 14 to the stress relaxation treatment start point c of the film is constant. Stress relaxation zone D: A zone in which the distance between the gripping clips of the film width (both base ends) from the stress relaxation treatment start point c to the stress relaxation treatment end point d of the tenter stretching device 14 narrows in the traveling direction (transport direction).

The above-mentioned "relaxation treatment" refers to a gripping pattern that narrows the film width in the direction of travel (conveyance direction, longitudinal direction, MD direction). The process of preventing film F from being stretched taut in the width direction, i.e., preventing stress from being applied to the film in the width direction, is called relaxation treatment, and this relaxation treatment is carried out while the film ends are being gripped.

The a, b, c, and d shown between each zone can be summarized as follows:

a) Starting point of film stretching, entrance of stretching zone b) End point of film stretching, entrance of film width retention zone c) Starting point of film stress relaxation treatment, entrance of stress relaxation zone d) End point of stress relaxation treatment, exit of stress relaxation zone

Other symbols in FIG. 7 are as follows:
F Film Hc Width of film at entrance of stress relaxation zone Hd Width of film at exit of stress relaxation zone 110 Housing 111 Clip 112 Rail

3 and 4, the relaxation rate A corresponds to "L _(TD)A0 " in Fig. 3 (the length in the width direction of the film before the relaxation treatment in the second stretching step) and "Hc" in Fig. 7. "L _(TD)A1 " in Fig. 4 corresponds to "Hd" in Fig. 7.

(1.5) Subsequent process (third conveying process: 3rd MD)
The raw film stretched and relaxed by the stretching device 10 in the second stretching step is transported in the third transport step. At this time, the film may be subjected to a drying treatment by providing a drying device 11, etc., as necessary.

(Cutting and winding process)
Thereafter, the film is processed by cutting both ends in the width direction by a cutting section 13 made of a slitter, and is wound into a roll by a winding device 12 at a winding speed _VW2 to produce a film.

2. Multistage Stretched Acrylic Resin-Containing Film The multistage stretched acrylic resin-containing film of the present invention is a multistage stretched acrylic resin-containing film containing at least an acrylic resin (A), a cellulose ester resin (B), rubber particles, and inorganic particles, characterized in that the acrylic resin-containing film contains the acrylic resin (A) and the cellulose ester resin (B) in a mass ratio of 95:5 to 30:70, the total degree of substitution (T) of acyl groups in the cellulose ester resin (B) is in the range of 2.0 to 3.0, the degree of substitution of acyl groups having 3 to 7 carbon atoms is in the range of 1.2 to 3.0, and the film density of the acrylic resin-containing film is in the range of 1.235 to 1.300 g/ ^cm3 . The film can be suitably produced by the above-mentioned production method.

(2.1) Film Density, Thickness and Length The multi-stage stretched acrylic resin-containing film of the present invention has a higher film density than that of conventional stretched films containing acrylic resins, and is in the range of 1.235 to 1.300 g/cm ³ .

Here, the term "multi-stage stretching" refers to stretching in multiple stages. Furthermore, the term "single-stage stretching" below refers to a single stretching event. Whether a resin film has been stretched can be confirmed, for example, by checking whether it has an in-plane slow axis (an axis extending in the direction in which the refractive index is greatest). Furthermore, whether a resin film has been stretched in multiple stages can be confirmed primarily by checking whether the film density is higher than that of conventional films.

Conventional stretched films containing acrylic resins are single-stage stretched films, and therefore the film density is only within the range of 1.180 to 1.235 g/cm ^3. However, the present invention is characterized in that the film density is controlled within the range of 1.236 to 1.300 g/cm ³ by multiple stretching steps.

The reason why the density of a film, such as the multi-stage stretched film of the present invention, increases is because the mobility of the resin contained in the film is improved by stretching the film at a high temperature. Furthermore, the density of the film is further increased by further stretching it in the width direction in the second stretching step, when the amount of residual solvent in the film manufacturing process has been reduced.

However, at the same time, voids are also generated in the width direction, and by filling these voids with a relaxation treatment in the width direction, stretching can be carried out without reducing density. This is thought to result in a wide, thin film that fully utilizes the effects of the functional layer formed on the film.

Furthermore, the stretching rate b in the longitudinal direction in the first conveying step is controlled by controlling the conveying tension _T1 in the first conveying step, which further enhances the effects of the present invention.

In addition, with regard to the longitudinal expansion rate b in the first conveying step, since the film contains a large amount of residual solvent, the mobility of the resin is high and the density of the film is likely to increase. Furthermore, by making the longitudinal expansion rate of the film in the first stretching step < (longitudinal expansion rate during the film peeling process), the film is more likely to become denser.

(Film density)
The density of a film can be measured, for example, by X-ray reflectivity (XRR). X-rays are totally reflected when they are incident on the film surface at a very shallow angle, and when the angle of incidence of the X-rays is equal to or greater than the critical angle of total reflection, the X-rays penetrate into the film, causing a decrease in reflectivity.

Reflectance profiles measured by the XRR method can be analyzed using dedicated reflectance analysis software. In this invention, when the angle at which reflectance begins to decrease is defined as θa, the surface density is defined as the density at which the fitting error between the measurement results and the calculation results is smallest within the 2θ range from 2θa to 2θa + 0.1°. In this case, fitting is performed with the surface roughness in the range of 0 to 1 nm.

Cut the substrate film into a piece measuring 30 mm x 30 mm, fix it to the sample stage, and measure it under the following measurement conditions.

<Measurement conditions>
・Device: Thin film X-ray diffraction device (ATX-G manufactured by Rigaku Corporation)
・Sample size: 30mm x 30mm
・Incidence X-ray wavelength: 1.5405Å
Measurement range (θ): 0 to 6°
・Analysis software: Reflectance analysis software GXRR (Rigaku Corporation)

(film thickness)
The effect of the present invention is more pronounced in the thin film region. The thickness of the film according to the present invention is preferably in the range of 5 to 80 μm, more preferably in the range of 30 to 60 μm.

There is no particular upper limit to the film thickness, but when the film is manufactured using the solution casting method, the upper limit is approximately 250 μm from the perspectives of coatability, foaming, solvent drying, etc. The film thickness can be selected appropriately depending on the application.

However, if the film is too thick, the amount of residual solvent will be large, and when that solvent evaporates, voids will be more likely to form, making it more important to control the range of (stretch rate A/relaxation rate A).

The film thickness can be measured using an inline retardation/film thickness measuring device RE-200L2T-Rth+film thickness (manufactured by Otsuka Electronics Co., Ltd.).

(film length)
The film according to the present invention can be stored by, for example, winding the film in a roll in a direction perpendicular to the width direction of the film to form a roll body.

The length of the film according to the present invention is not particularly limited, but can be, for example, approximately 100 to 10,000 m. Furthermore, the width of the strip-shaped laminated film is preferably 1 m or more, and more preferably within the range of 1.1 to 4 m. From the perspective of improving the uniformity of the film, it is more preferably within the range of 1.3 to 2.5 m.

(2.2) Resin The film according to the present invention contains at least an acrylic resin (A), a cellulose ester resin (B), rubber particles, and inorganic particles. The resin species of the resin composition in the dope used in the casting process for producing this film include at least the acrylic resin (A) and the cellulose ester resin (B). The resin composition may contain other resins besides the above-mentioned resin species, including rubber particles and inorganic particles. The particles may include other particles besides rubber particles and inorganic particles. The resin composition may also contain other components, such as various additives.

If the above film contains a resin other than the acrylic resin (A) and the cellulose ester resin (B), the added resins may be in a compatible state or may be mixed without dissolving. When using resins or additives other than the acrylic resin (A) and the cellulose ester resin (B), it is preferable to adjust the amount added so as not to impair the functionality of the film.

Furthermore, the density of the film can be affected by changing the amount of rubber particles or inorganic particles relative to the resin. For example, increasing the amount of rubber particles or inorganic particles relative to the resin promotes solvent diffusion, reducing the chance of density differences between the front and back of the film.

(Mass ratio and total mass)
In the multistage stretched acrylic resin-containing film of the present invention, the acrylic resin (A) and the cellulose ester resin (B) are contained in a compatible state in a mass ratio within the range of 95:5 to 30:70, preferably within the range of 95:5 to 50:50, more preferably within the range of 90:10 to 60:40.

If the mass ratio of acrylic resin (A) to cellulose ester resin (B) is greater than 95:5, the effects of cellulose ester resin (B) will not be fully achieved. If the mass ratio is less than 30:70, moisture resistance will be insufficient.

The total mass of the acrylic resin (A) and cellulose ester resin (B) in the acrylic resin-containing film is preferably 55% by mass or more of the acrylic resin-containing film, more preferably 60% by mass or more, and particularly preferably 70% by mass or more.

(compatible state)
In the multistage stretched acrylic resin-containing film of the present invention, the acrylic resin (A) and the cellulose ester resin (B) must be contained in a compatible state. For example, the physical properties and quality required for applications such as optical films are achieved by mutually compensating for each other through the compatibility of different resins.

Whether the acrylic resin (A) and the cellulose ester resin (B) are compatible with each other is determined by their glass transition temperatures (Tg).

When two resins are simply mixed, each resin has its own glass transition temperature, so the mixture has two glass transition temperatures. In contrast, when the two resins become compatible, the glass transition temperatures specific to each resin disappear, and there is a single glass transition temperature that becomes the glass transition temperature of the compatible resins.

In terms of heat resistance, the film preferably has a glass transition temperature (Tg) of 110°C or higher. More preferably, it is 120°C or higher. Especially preferably, it is 150°C or higher.

It is known that the glass transition temperature T _g1,2 of this miscible mixture can be approximated by the Gordon-Taylor equation (M. Gordon and J.S. Taylor, 2 J. of Applied Chem. 493-500 (1952)). The Gordon-Taylor equation is as follows:
Formula T _g1,2 = (w ₁ T _g1 +Kw ₂ T _g2 )/(w ₁ +Kw ₂ )
[Where, _w1 and _w2 are the mass fractions of components 1 (acrylic resin (A)) and 2 (cellulose ester resin (B)), _Tg1 and _Tg2 are the glass transition temperatures (Kelvin) of components 1 and 2, respectively. _Tg1,2 is the glass transition temperature of the mixture of components 1 and 2. K is a constant related to the free volume of the two resins.]

The "glass transition temperature" referred to here is determined using a differential scanning calorimeter (Perkin-Elmer DSC-7 model). Specifically, a sample is conditioned for 24 hours in an atmosphere of 23°C and 55% RH, and then measured in a nitrogen stream at a temperature rise rate of 20°C/min. The midpoint glass transition temperature (Tmg) is determined in accordance with JIS K7121 (1987).

The acrylic resin (A) and the cellulose ester resin (B) are preferably each an amorphous resin, and either one may be a crystalline polymer or a polymer that is partially crystalline. Furthermore, it is preferable that the acrylic resin (A) and the cellulose ester resin (B) are compatible with each other to form an amorphous resin.

In the present invention, "containing acrylic resin (A) and cellulose ester resin (B) in a compatible state" means that the respective resins (polymers) are mixed together, resulting in a compatible state. This does not include a state in which a mixed resin is formed by mixing an acrylic resin precursor such as a monomer, dimer, or oligomer with cellulose ester resin (B) and then polymerizing it.

For example, the process of obtaining a mixed resin by mixing a precursor of an acrylic resin, such as a monomer, dimer, or oligomer, with a cellulose ester resin (B) and then polymerizing it involves a complex polymerization reaction. Resins produced by this method are difficult to control, and the molecular weight is also difficult to adjust.

Furthermore, when resins are synthesized using this method, graft polymerization, crosslinking reactions, and cyclization reactions often occur, resulting in cases where the resin is insoluble in solvents or cannot be melted by heating. It is also difficult to elute the acrylic resin in the mixed resin and measure the weight-average molecular weight (Mw), making it difficult to control its physical properties, and the resin cannot be used to stably produce acrylic resin-containing films.

(2.2.1) Acrylic resin (A)
The acrylic resin (A) according to the present invention also includes a methacrylic resin. There are no particular limitations on the resin. The acrylic resin (A) is preferably one that contains 50 to 99% by mass of methyl methacrylate units and 1 to 50% by mass of other monomer units copolymerizable therewith.

Other copolymerizable monomers include, for example, alkyl methacrylates with alkyl carbon numbers of 2 to 18, alkyl acrylates with alkyl carbon numbers of 1 to 18, α,β-unsaturated acids such as acrylic acid and methacrylic acid, unsaturated group-containing dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid, aromatic vinyl compounds such as styrene and α-methylstyrene, α,β-unsaturated nitriles such as acrylonitrile and methacrylonitrile, maleic anhydride, maleimide, N-substituted maleimide, and glutaric anhydride. These can be used alone or in combination of two or more types of monomers.

Among these, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, 2-ethylhexyl acrylate, etc. are preferred from the standpoint of thermal decomposition resistance and fluidity of the copolymer. Furthermore, methyl acrylate and n-butyl acrylate are particularly preferred.

(Commercially available)
Commercially available acrylic resins can also be used as the acrylic resin of the present invention. Examples include Delpet 60N and 80N (manufactured by Asahi Kasei Chemicals Corporation), Dianall BR52, BR80, BR83, BR85, and BR88 (manufactured by Mitsubishi Rayon Co., Ltd.), and KT75 (manufactured by Denki Kagaku Kogyo Kabushiki Kaisha). Two or more types of acrylic resins can also be used in combination.

(Manufacturing method)
The method for producing the acrylic resin (A) in the present invention is not particularly limited, and the resin can be produced by a known method, such as suspension polymerization, emulsion polymerization, bulk polymerization, or solution polymerization.

(Weight average molecular weight)
The acrylic resin (A) according to the present invention preferably has a weight average molecular weight (Mw) in the range of 80,000 to 1,000,000, particularly from the viewpoint of improving brittleness as an acrylic film and improving transparency when it is mixed with the cellulose ester resin (B).

If the weight-average molecular weight (Mw) of the acrylic resin (A) is below 80,000, sufficient improvement in brittleness will not be achieved, and compatibility with the cellulose ester resin (B) will deteriorate. It is particularly preferable that the weight-average molecular weight (Mw) of the acrylic resin (A) be in the range of 100,000 to 600,000, and most preferably in the range of 150,000 to 400,000.

The weight-average molecular weight of the acrylic resin of the present invention can be measured by gel permeation chromatography (GPC). The measurement conditions are as follows:

<Measurement conditions>
Solvent: methylene chloride Column: Shodex K806, K805, K803G (manufactured by Showa Denko K.K.; three columns connected together were used)
Column temperature: 25°C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (GL Sciences)
Pump: L6000 (Hitachi, Ltd.)
Flow rate: 1.0ml/min
Calibration curve: A calibration curve was prepared using 13 samples of standard polystyrene STK standard polystyrene (manufactured by Tosoh Corporation) in the range of Mw = 500 to 2,800,000. It is preferable to use the 13 samples at approximately equal intervals.

(2.2.2) Cellulose ester resin (B)
The total substitution degree (T) of the acyl groups in the cellulose ester resin (B) according to the present invention is in the range of 2.0 to 3.0, and the substitution degree of the acyl groups having 3 to 7 carbon atoms is in the range of 1.2 to 3.0, thereby improving brittleness in particular and increasing transparency when the cellulose ester resin (B) is made compatible with the acrylic resin (A).

If the proportion of structurally bulky cellulose ester resin is too high compared to the acrylic resin, hydrogen bonding will result in a three-dimensional, stable arrangement, making it difficult to increase density even when the film is stretched or relaxed. Also, tiny voids are likely to form, which can cause excessive penetration of the coating solution when forming a hard coat layer, etc., resulting in reduced functionality.

The acyl group having 3 to 7 carbon atoms is an aliphatic acyl group having 3 to 7 carbon atoms, and a structure having at least one such aliphatic acyl group is preferred for use in cellulose ester resin (B). Two or more types of cellulose resins can also be used in combination.

Cellulose ester resin (B) is substituted with an acyl group having 3 to 7 carbon atoms. Specific examples of the acyl group that are preferably used include propionyl and butyryl groups, with propionyl being particularly preferred.

Specifically, it is preferably at least one selected from cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose propionate, and cellulose butyrate. In other words, it is preferably one having an acyl group having 3 or 4 carbon atoms as a substituent.

Among the above, cellulose acetate propionate and cellulose propionate are particularly preferred.

(Total degree of acyl substitution and number of carbon atoms)
The degree of acyl substitution can be determined by the method specified in ASTM-D817-96. When the total degree of acyl substitution is less than 2.0, that is, when the residual ratio of hydroxyl groups at the 2-, 3-, and 6-positions of the cellulose ester molecule exceeds 1.0, the acrylic resin (A) and the acrylic resin (B) are not sufficiently compatible with each other. This causes haze problems when used as a film. Haze (turbidity) is an index for determining transparency.

Furthermore, even if the total degree of substitution of the acyl groups is 2.0 or higher, if the degree of substitution of acyl groups with 3 to 7 carbon atoms is below 1.2, sufficient compatibility will not be achieved or brittleness will decrease. For example, even if the total degree of substitution of acyl groups is 2.0 or higher, if the degree of substitution of acyl groups with 2 carbon atoms, i.e., acetyl groups, is high and the degree of substitution of acyl groups with 3 to 7 carbon atoms is below 1.2, compatibility will decrease and haze will increase.

Furthermore, even if the total degree of substitution of acyl groups is 2.0 or more, if the degree of substitution of acyl groups with 8 or more carbon atoms is high and the degree of substitution of acyl groups with 3 to 7 carbon atoms is below 1.2, brittleness will deteriorate and the desired properties will not be achieved.

The acyl substitution degree of the cellulose ester resin (B) according to the present invention is acceptable as long as the total substitution degree (T) is 2.0 to 3.0 and the substitution degree of acyl groups having 3 to 7 carbon atoms is 1.2 to 3.0. However, it is preferable that the total substitution degree of acyl groups having carbon atoms other than 3 to 7, i.e., acetyl groups and acyl groups having 8 or more carbon atoms, is 1.3 or less.

Furthermore, it is more preferable that the total degree of substitution (T) of acyl groups in the cellulose ester resin (B) is in the range of 2.5 to 3.0.

The acyl group may be an aliphatic acyl group or an aromatic acyl group.

[Aliphatic acyl group]
When the acyl group is an aliphatic acyl group, it may be linear or branched and may further have a substituent. The number of carbon atoms of the acyl group in the present invention includes the number of carbon atoms of the substituent of the acyl group.

[Aromatic acyl group]
When the acyl group is an aromatic acyl group, the number of substituents X substituted on the aromatic ring is 0 to 3. In this case, care must also be taken to ensure that the degree of substitution of an acyl group having 3 to 7 carbon atoms, including the substituent, is 1.2 to 3.0. For example, since a benzoyl group has 7 carbon atoms, when it has a substituent containing carbon, the number of carbon atoms as a benzoyl group is 8 or more, and it is not included in the acyl group having 3 to 7 carbon atoms.

Furthermore, when the number of substituents substituted on an aromatic ring is two or more, they may be the same or different. They may also be linked to each other to form a condensed polycyclic compound (e.g., naphthalene, indene, indane, phenanthrene, quinoline, isoquinoline, chromene, chroman, phthalazine, acridine, indole, indoline, etc.).

(Synthesis method)
The portion not substituted with an acyl group is usually present as a hydroxyl group, and these can be synthesized by known methods.

(Weight average molecular weight)
The weight average molecular weight (Mw) of the cellulose ester resin (B) according to the present invention is preferably in the range of 75,000 to 300,000, particularly from the viewpoint of compatibility with the acrylic resin (A) and improvement of brittleness, more preferably in the range of 100,000 to 240,000, and particularly preferably in the range of 160,000 to 240,000.

If the weight average molecular weight (Mw) of the cellulose ester resin exceeds 75,000, the heat resistance and brittleness will be sufficiently improved.

(2.3) Particles The multistage stretched acrylic resin-containing film of the present invention contains at least rubber particles and inorganic particles. There are no particular restrictions on the particles contained, and particles other than the above-mentioned particles may also be contained.

(2.3.1) Rubber Particles The multistage stretched acrylic resin-containing film of the present invention contains at least rubber particles. The rubber particles are preferably contained in a range of 40 to 85% by mass, particularly when a (meth)acrylic resin or a styrene-(meth)acrylate copolymer is used. This provides toughness (flexibility) and improves the resistance to creases when the film is folded.

Rubber particles are particles containing a rubbery polymer. The rubbery polymer is a soft crosslinked polymer with a glass transition temperature (Tg) of 20°C or less. Examples of such crosslinked polymers include butadiene-based crosslinked polymers, (meth)acrylic-based crosslinked polymers, and organosiloxane-based crosslinked polymers.

Among these, (meth)acrylic crosslinked polymers are preferred, and acrylic crosslinked polymers (acrylic rubbery polymers) are more preferred, from the viewpoint of having a small difference in refractive index from (meth)acrylic resins and being less likely to impair the transparency of the film. In other words, the rubber particles are preferably particles containing an acrylic rubbery polymer [a].

(Acrylic rubber-like polymer [a])
The acrylic rubber-like polymer [a] is a crosslinked polymer containing, as a main component, structural units derived from an acrylic acid ester. Here, "containing, as a main component," means that the content of structural units derived from an acrylic acid ester falls within the range described below.

The acrylic rubber-like polymer [a] is preferably a crosslinked polymer containing the following three structural units (1) to (3):
(1) A structural unit derived from an acrylic acid ester. (2) A structural unit derived from another monomer copolymerizable with the structural unit derived from an acrylic acid ester. (3) A structural unit derived from a polyfunctional monomer having two or more radically polymerizable groups (non-conjugated reactive double bonds) in one molecule.

Preferred acrylic esters include alkyl acrylate esters with alkyl groups having 1 to 12 carbon atoms, such as methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, sec-butyl acrylate, isobutyl acrylate, benzyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, and n-octyl acrylate. One type of acrylic ester may be used, or two or more types may be used.

[Structural units derived from acrylate esters]
The content of structural units derived from acrylate esters is preferably within a range of 40 to 80% by mass, more preferably within a range of 50 to 80% by mass, based on the total structural units constituting the acrylic rubber-like polymer [a1]. When the content of acrylate esters is within the above range, sufficient toughness is easily imparted to the film.

[Other copolymerizable monomers]
The other monomer copolymerizable with the structural unit derived from an acrylic acid ester is a monomer copolymerizable with an acrylic acid ester other than a polyfunctional monomer, i.e., the copolymerizable monomer does not have two or more radically polymerizable groups.

Examples of copolymerizable monomers include methacrylic acid esters such as methyl methacrylate; styrene, methylstyrene, and other styrenes; (meth)acrylonitriles; (meth)acrylamides; and (meth)acrylic acid. Among these, it is preferable that the other copolymerizable monomer include a styrene. The other copolymerizable monomer may be one type, or two or more types.

The content of structural units derived from other copolymerizable monomers is preferably within the range of 5 to 55% by mass, and more preferably within the range of 10 to 45% by mass, of all structural units constituting the acrylic rubber-like polymer [a].

[Polyfunctional Monomer]
Examples of polyfunctional monomers include allyl (meth)acrylate, triallyl cyanurate, triallyl isocyanurate, diallyl phthalate, diallyl maleate, divinyl adipate, divinyl benzene, ethylene glycol di(meth)acrylate, diethylene glycol (meth)acrylate, triethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tetra(meth)acrylate, dipropylene glycol di(meth)acrylate, and polyethylene glycol di(meth)acrylate.

The content of structural units derived from polyfunctional monomers is preferably within the range of 0.05 to 10% by mass, and more preferably within the range of 0.1 to 5% by mass, of all structural units constituting the acrylic rubber-like polymer [a].

If the content of the polyfunctional monomer is 0.05% by mass or more, the degree of crosslinking of the resulting acrylic rubber-like polymer [a] is easily increased, so the hardness and rigidity of the resulting film are not significantly impaired. If the content is 10% by mass or less, the toughness of the film is less likely to be impaired.

The monomer composition constituting the acrylic rubber-like polymer [a] can be measured, for example, by the peak area ratio detected by pyrolysis GC-MS.

The glass transition temperature (Tg) of the rubbery polymer is preferably 0°C or lower, and more preferably -10°C or lower. If the glass transition temperature (Tg) of the rubbery polymer is 0°C or lower, it can impart appropriate toughness to the film. The glass transition temperature (Tg) of the rubbery polymer is measured using the same method as described above.

〔others〕
The glass transition temperature (Tg) of the rubbery polymer can be adjusted by the composition of the rubbery polymer. For example, in order to lower the glass transition temperature (Tg) of the acrylic rubbery polymer [a], the following is preferable.

In the acrylic rubber-like polymer [a], it is preferable to increase the mass ratio of the acrylic acid ester with an alkyl group having 3 or more carbon atoms to the other copolymerizable monomer. Furthermore, it is preferable that the number of carbon atoms is within the range of 4 to 10.

The particles containing the acrylic rubber-like polymer [a] may be particles made of the acrylic rubber-like polymer [a]. Alternatively, they may be particles having a hard layer made of a hard crosslinked polymer (c) having a glass transition temperature of 20°C or higher, and a soft layer made of the acrylic rubber-like polymer [a] arranged around the hard layer (these are also referred to as "elastomers").

Furthermore, the particles may be made of an acrylic graft copolymer obtained by polymerizing a mixture of monomers such as methacrylic acid esters in at least one stage in the presence of an acrylic rubber-like polymer [a]. The particles made of an acrylic graft copolymer may be core-shell type particles having a core containing the acrylic rubber-like polymer [a] and a shell covering the core.

In this embodiment, when the film is not stretched, the shape of the rubber particles may be close to spherical. In other words, when observing the cross section or surface of the film, the aspect ratio of the rubber particles may be approximately 1 to 2.

The average particle size of the rubber particles is preferably in the range of 100 to 400 nm. If the average particle size of the rubber particles is 100 nm or more, it is easy to impart sufficient toughness and stress relaxation properties to the base film, and if it is 400 nm or less, the transparency of the base film is less likely to be impaired. From the same perspective, the average particle size of the rubber particles is more preferably in the range of 150 to 300 nm.

The average primary particle size of the rubber particles can be determined by measuring the dispersed particle size of the rubber particles in the dispersion liquid using a zeta potential/particle size measurement system (ELSZ-2000ZS, manufactured by Otsuka Electronics Co., Ltd.).

The amount of rubber particles contained is not particularly limited, but is preferably in the range of 0.5 to 20% by mass of the film, and more preferably in the range of 0.8 to 15% by mass.

(2.3.2) Inorganic Particles The film of the present invention contains particles of an inorganic compound, i.e., inorganic particles, which improve the transportability of the film. Examples of the inorganic compound in the inorganic particles include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, and calcium phosphate.

(2.3.3) Other Particles The film according to the present invention may contain, in addition to the inorganic particles, particles of organic compounds, i.e., organic particles. Examples of organic compounds that can be used include polytetrafluoroethylene, cellulose acetate, polystyrene, polymethyl methacrylate, polypropyl methacrylate, polymethyl acrylate, polyethylene carbonate, acrylic styrene-based resins, silicone-based resins, polycarbonate resins, benzoguanamine-based resins, melamine-based resins, polyolefin-based powders, polyester-based resins, polyamide-based resins, polyimide-based resins, polyethylene fluoride-based resins, and pulverized fractions of organic polymer compounds such as starch, as well as polymer compounds synthesized by suspension polymerization.

As a compound, those containing silicon are preferred because they reduce turbidity, with silicon dioxide being particularly preferred. Examples of such commercially available products include Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, and TT600 (all manufactured by Nippon Aerosil Co., Ltd.).

(2.4) Other Components There are no particular limitations on the other components as long as they do not impair the effects of the present invention, and examples thereof include plasticizers, ultraviolet absorbers, antioxidants, and flame retardants.

(Plasticizer)
In the film of the present invention, a plasticizer may be used in combination to improve the fluidity and flexibility of the composition. Examples of the plasticizer include phthalate esters, fatty acid esters, trimellitates, phosphate esters, polyesters, and epoxy plasticizers.

Among these, polyester and phthalate ester plasticizers are preferred. Polyester plasticizers are superior in non-migration and extraction resistance compared to phthalate ester plasticizers such as dioctyl phthalate, but are somewhat inferior in plasticizing effect and compatibility. Therefore, by selecting or combining these plasticizers depending on the application, they can be used in a wide range of applications.

Polyester plasticizers are the reaction products of mono- or tetracarboxylic acids and mono- to hexavalent alcohols, but the most commonly used are those obtained by reacting dicarboxylic acids with glycols. Representative dicarboxylic acids include glutaric acid, itaconic acid, adipic acid, phthalic acid, azelaic acid, and sebacic acid.

In particular, the use of adipic acid, phthalic acid, etc., results in products with excellent plasticizing properties. Examples of glycols include ethylene, propylene, 1,3-butylene, 1,4-butylene, 1,6-hexamethylene, neopentylene, diethylene, triethylene, and dipropylene glycols. These dicarboxylic acids and glycols may be used alone or in combination.

It is preferable to add 0.5 to 30 parts by weight of plasticizer per 100 parts by weight of the acrylic film of the present invention. If the amount of plasticizer added exceeds 30 parts by weight, the surface will become sticky, which is not practically preferable.

[Commercially available]
An example of a commercially available product is Monopet SB (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.).

(ultraviolet absorber)
The film according to the present invention preferably contains an ultraviolet absorber, and examples of the ultraviolet absorber that can be used include benzotriazole-based, 2-hydroxybenzophenone-based, and salicylic acid phenyl ester-based absorbers.

Examples include triazoles such as 2-(5-methyl-2-hydroxyphenyl)benzotriazole, 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole, and 2-(3,5-di-t-butyl-2-hydroxyphenyl)benzotriazole, and benzophenones such as 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, and 2,2'-dihydroxy-4-methoxybenzophenone.

Here, among UV absorbers, those with a molecular weight of 400 or more are less likely to volatilize due to their high boiling points and are less likely to scatter during high-temperature molding, so adding a relatively small amount can effectively improve weather resistance.

Ultraviolet absorbers with a molecular weight of 400 or more include benzotriazole-based absorbers such as 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]-2-benzotriazole and 2,2-methylenebis[4-(1,1,3,3-tetrabutyl)-6-(2H-benzotriazol-2-yl)phenol], and hindered amine-based absorbers such as bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate and bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate. Further examples include hybrid compounds having both hindered phenol and hindered amine structures in the molecule, such as 2-(3,5-di-t-butyl-4-hydroxybenzyl)-2-n-butylmalonate bis(1,2,2,6,6-pentamethyl-4-piperidyl) and 1-[2-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy]ethyl]-4-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy]-2,2,6,6-tetramethylpiperidine. These compounds can be used alone or in combination. Among these, 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]-2-benzotriazole and 2,2-methylenebis[4-(1,1,3,3-tetrabutyl)-6-(2H-benzotriazol-2-yl)phenol] are particularly preferred.

(antioxidant)
Furthermore, various antioxidants can be added to the film of the present invention to improve thermal decomposition and thermal discoloration during molding processing, and antistatic agents can be added to impart antistatic properties to the acrylic film.

(Flame retardant)
The film according to the present invention may use a flame-retardant acrylic resin composition containing a phosphorus-based flame retardant, which may be one or a mixture of two or more selected from red phosphorus, triaryl phosphate esters, diaryl phosphate esters, monoaryl phosphate esters, aryl phosphonic acid compounds, aryl phosphine oxide compounds, condensed aryl phosphate esters, halogenated alkyl phosphate esters, halogen-containing condensed phosphate esters, halogen-containing condensed phosphonic acid esters, halogen-containing phosphites, etc.

Specific examples include triphenyl phosphate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, phenylphosphonic acid, tris(β-chloroethyl)phosphate, tris(dichloropropyl)phosphate, and tris(tribromoneopentyl)phosphate.

(2.5) Uses The film according to the present invention can be used in the form of a film for the following uses, such as a liquid crystal display device.

Specific examples include polarizing plate protective films for liquid crystal display devices, retardation films, anti-reflection films, brightness enhancement films, hard coat films, anti-glare films, anti-static films, and optical compensation films for widening viewing angles.

Typical uses of the film according to the present invention include polarizing filter protective films, retardation films, and optical compensation films, among others.

(2.5.1) Hard Coat Layer The film according to the present invention may have a hard coat layer formed on it in order to enhance functionality such as impact resistance and ease of handling.

As described above, the film according to the present invention is a multi-stage stretched film, and therefore has a film density in the range of 1.235 to 1.300 g/cm ^3. This differs from conventional single-stage stretched films, which have a film density in the range of 1.180 to 1.235 g/cm ³ , and results in superior film strength when a hard coat layer is formed.

The film strength after the hard coat layer has been formed can be confirmed by various known methods, such as measuring the pencil hardness in accordance with JIS K 5600 5-4 (Pencil Hardness Evaluation Method).

It is more preferable for the hard coat layer to contain ultraviolet-curable resin and silica particles, from the viewpoint of improving impact resistance and ease of handling. Furthermore, other additives can be further blended as needed, as long as the effects of the present invention are not impaired.

(Ultraviolet curing resin)
The ultraviolet curable resin preferably contains a component containing a monomer having an ethylenically unsaturated double bond. By irradiating ultraviolet light, a hard coat layer having excellent mechanical film strength (scratch resistance, pencil hardness) can be formed.

Examples of UV-curable resins include organic hard coat materials such as organic silicone, melamine, epoxy, acrylate, and polyfunctional (meth)acrylic compounds. Other examples include inorganic hard coat materials such as silicon dioxide.

Among these, (meth)acrylate-based and polyfunctional (meth)acrylic compound hard coat forming materials are preferred from the standpoint of good adhesive strength and excellent productivity. Here, (meth)acrylic refers to acrylic and methacrylic.

(Meth)acrylates include those having one, two, or three or more polymerizable unsaturated groups in the molecule, as well as (meth)acrylate oligomers containing three or more polymerizable unsaturated groups in the molecule.

For example, examples of polyfunctional acrylates that can be used include pentaerythritol polyfunctional acrylate, dipentaerythritol polyfunctional acrylate, pentaerythritol polyfunctional methacrylate, and dipentaerythritol polyfunctional methacrylate. (Meth)acrylates may be used alone or in combination of two or more types.

(Silica particles)
When the hard coat layer contains an ultraviolet curable resin and silica particles, the mass ratio of the silica particles to the ultraviolet curable resin (silica particles/ultraviolet curable resin) is preferably within the range of 10/90 to 50/50.

A ratio of 10/90 or more is preferred in terms of increasing the hardness of the hard coat layer, while a ratio of 50/50 or less is preferred in terms of not causing haze or deteriorating scratch resistance.

In order to achieve both haze and surface hardness, it is preferable for the silica particles to have an average primary particle size of 200 nm or less. The particle size is preferably in the range of 5 to 100 nm, and more preferably in the range of 10 to 50 nm.

Furthermore, although the surface hardness of silica particles increases even when the particle surface is untreated, silica particles that are partially coated with an organic component and have reactive polymerizable unsaturated groups on the surface introduced by the organic component are preferred. The average primary particle size of the silica particles preferably used in this embodiment is 5 to 200 nm, and examples of silica particles having such a particle size include silica particles having the above-mentioned reactive polymerizable unsaturated groups on their surface.

Publicly known silica particles that have not been surface-modified can be used. Furthermore, the shape of the particles may be spherical or irregular, and they are not limited to ordinary colloidal silica; they may be hollow particles, porous particles, core/shell particles, etc., although colloidal silica is preferred.

[Dispersion medium]
The dispersion medium for silica particles is preferably water or an organic solvent, and examples of the organic solvent include alcohols, ketones, aromatic hydrocarbons, amides, esters, ethers, etc. Among these, alcohols and ketones are preferred, and these organic solvents can be used alone or in combination.

Examples of alcohols include methanol, isopropyl alcohol, ethylene glycol, butanol, and ethylene glycol monopropyl ether. Examples of ketones include methyl ethyl ketone and methyl isobutyl ketone. Examples of aromatic hydrocarbons include toluene and xylene. Examples of amides include dimethylformamide, dimethylacetamide, and N-methylpyrrolidone. Examples of esters include ethyl acetate, butyl acetate, and gamma-butyrolactone. Examples of ethers include tetrahydrofuran and 1,4-dioxane.

[Commercially available]
Examples of commercially available colloidal silica include IPA-ST, IPA-ST-L, IPA-ST-ZL, MEK-ST-L, and MEK-ST-MS manufactured by Nissan Chemical Industries, Ltd.

Reactive silica particles are obtained by surface treating colloidal silica with an organic compound having a reactive polymerizable unsaturated group. In other words, the organic component that coats the surface of the silica particles here refers to the organic component derived from the organic compound having a reactive polymerizable unsaturated group used in the surface treatment.

[Organic compounds used in surface treatment]
The organic compound used for surface treatment to coat the surface of silica particles with an organic component is an organic compound having a polymerizable unsaturated group. The polymerizable unsaturated group is preferably any two or more of a hydroxy group, a carboxy group, an amino group, an epoxy group, an isocyanate group, a (meth)acryloyl group, and a vinyl group. Furthermore, a combination of a hydroxy group, a carboxy group, an isocyanate group, and a (meth)acryloyl group is particularly preferred. In the present invention, (meth)acrylate means methacrylate or acrylate.

Specific examples of organic compounds having a polymerizable unsaturated group include coupling agents such as 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, vinyltrichlorosilane, vinyltrimethoxysilane, and vinyltriethoxysilane; acrylic acid esters such as methyl acrylate, 2-ethylhexyl acrylate, methoxyethyl acrylate, butoxyethyl acrylate, butyl acrylate, methoxybutyl acrylate, and phenyl acrylate; methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, methoxyethyl methacrylate, ethoxymethyl methacrylate, phenyl methacrylate, and lauryl methacrylate; 2-(N,N-diethylamino)ethyl acrylate, 2-(N,N-dimethyl methacrylate), Examples of suitable esters include substituted amino alcohol esters of unsaturated substituted acids such as 2-(N,N-dibenzylamino)ethyl acrylate, 2-(N,N-dibenzylamino)methyl acrylate, and 2-(N,N-diethylamino)propyl acrylate; unsaturated carboxylic acid amides such as acrylamide and methacrylamide; compounds such as ethylene glycol diacrylate, propylene glycol diacrylate, propylene glycol diacrylate, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate, and triethylene glycol diacrylate; polyfunctional compounds such as dipropylene glycol diacrylate, ethylene glycol diacrylate, propylene glycol dimethacrylate, and diethylene glycol dimethacrylate; and/or polythiol compounds having two or more thiol groups in the branch (e.g., trimethylolpropane trithioglycolate, trimethylolpropane trithiopropylate, pentaerythritol tetrathioglycol, etc.).

In this way, using reactive silica particles with polymerizable unsaturated groups creates crosslinks between the binder resin and the silica particles, and between the silica particles themselves, resulting in improved hardness and prevention of particle shedding. Furthermore, using modified silica particles can also improve chemical resistance.

The organic component preferably covers almost the entire particle surface in order to suppress aggregation of the silica particles and to introduce many reactive functional groups onto the silica particle surface to improve the hardness of the hard coating layer. From this viewpoint, the organic component covering the silica particles is preferably contained in an amount of 1.00 × 10 ^-3 g/m ² or more in the reactive silica particles.

The proportion of the organic component coating can usually be determined as the constant mass loss when the dry powder is completely combusted in air, for example, by thermogravimetric analysis in air from room temperature to typically 800°C.

The amount of organic compound per unit area can be determined by the following method. First, the mass of the organic component divided by the mass of the inorganic component (mass of organic component/mass of inorganic component) is measured using differential thermal gravimetric analysis (DTG), and then the volume of the entire inorganic component is calculated from the mass of the inorganic component and the specific gravity of the silica used.

Furthermore, assuming that the silica particles before coating are spherical, the volume and surface area per silica particle before coating are calculated from the average particle size of the silica particles before coating, and the number of reactive silica particles is determined by dividing the volume of the entire inorganic component by the volume per silica particle before coating.

Furthermore, the amount of organic components per reactive silica particle is determined by dividing the mass of organic components by the number of reactive silica particles. Finally, the amount of organic components per unit area can be determined by dividing the mass of organic components per reactive silica particle by the surface area per silica particle before coating.

As a method for preparing reactive silica particles having at least a portion of their surface coated with an organic component and having polymerizable unsaturated groups on their surfaces introduced by the organic component, any conventionally known method can be used as appropriate, depending on the type of polymerizable unsaturated group to be introduced to the silica particles.

The reactive silica particles may be in powder form containing no dispersant, but it is preferable to use a solvent-dispersed sol of fine particles, as this allows the dispersion step to be omitted and increases productivity.

Commercially available reactive silica particles include MIBK-SD, MIBK-SDMS, MIBK-SDL, IPA-ST, and IPA-SDMS manufactured by Nissan Chemical Industries, Ltd.

The average primary particle size of silica particles can be determined by measuring the dispersed particle size of silica particles in a dispersion liquid using a zeta potential/particle size measurement system (ELSZ-2000ZS, manufactured by Otsuka Electronics Co., Ltd.).

(Other additives)
The hard coat layer may further contain other additives as needed, as long as the effects of the present invention are not impaired, such as a leveling agent, an ultraviolet stabilizer, an ultraviolet absorber, etc. Also, various known additives such as an antioxidant, a surfactant, an antistatic agent, etc. may be used.

[Leveling Agent]
The leveling agent is particularly effective in reducing surface irregularities when applying a coating liquid for forming a hard coat layer. As the leveling agent, for example, a silicone-based leveling agent such as dimethylpolysiloxane-polyoxyalkylene copolymer is suitable.

[UV stabilizer]
As the ultraviolet stabilizer, for example, a hindered amine-based ultraviolet stabilizer, which has high stability against ultraviolet rays, is preferably used. When the hard coat layer contains the ultraviolet stabilizer, radicals, active oxygen, etc. generated by ultraviolet rays are inactivated, and ultraviolet stability, weather resistance, etc. can be improved.

[Ultraviolet absorber]
Examples of the ultraviolet absorber include salicylic acid-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, triazine-based ultraviolet absorbers, benzoxazinone-based ultraviolet absorbers, etc. One or more types selected from these groups may be used.

Among these, triazine-based UV absorbers and benzoxazinone-based UV absorbers are preferred from the standpoint of dispersibility. Furthermore, polymers having UV-absorbing groups in the molecular chain are also suitable as the UV absorbers. By using such polymers having UV-absorbing groups in the molecular chain, it is possible to prevent deterioration of the UV absorption function due to bleeding out of the UV absorber, etc.

Examples of the above-mentioned ultraviolet absorbing group include a benzotriazole group, a benzophenone group, a cyanoacrylate group, a triazine group, a salicylate group, and a benzylidene malonate group. Of these, a benzotriazole group, a benzophenone group, and a triazine group are particularly preferred.

(Method of forming hard coat layer)
As a method for forming a hard coat layer on the film of the present invention in order to enhance functionality, for example, the following method can be mentioned.

First, a coating liquid for forming an active energy ray-cured material layer, i.e., a coating liquid for forming a hard coat layer, is prepared and applied to the film of the present invention. The coating liquid is then dried and cured to form a hard coat layer, which is an active energy ray-cured material layer.

The coating liquid for forming the hard coat layer is preferably a coating liquid containing, for example, an ultraviolet-curable resin and silica particles, and the coating liquid is preferably prepared using at least two solvents selected from alcohol, ester, ether, and ketone to reduce drying unevenness.

Examples of the above solvents include chlorinated solvents such as chloroform and dichloromethane; aromatic solvents such as toluene, xylene, benzene, and mixtures thereof; alcoholic solvents such as methanol, ethanol, isopropanol (IPA), n-butanol, and 2-butanol; methyl cellosolve, ethyl cellosolve, butyl cellosolve, ethylene glycol monomethyl ether, propylene glycol monomethyl ether (PGME), dimethylformamide, dimethyl sulfoxide, dioxane, cyclohexanone, tetrahydrofuran, acetone, methyl ethyl ketone (MEK), ethyl acetate, and diethyl ether.

When a solution prepared by dissolving at least two solvents from alcohols, esters, ethers, or ketones is cast onto a substrate, it is preferable that one of the solvents is a ketone. Among ketones, methyl ethyl ketone (MEK) is preferred from the viewpoint of the solubility of UV-curable resins.

The other type is preferably an ether. Among ethers, propylene glycol monomethyl ether (PGME) is preferred from the perspective of its high boiling point, slow drying time, and ability to suppress unevenness.

The coating liquid for forming the hard coat layer can be applied to the film of the present invention by any method, such as dipping, die coating, wire bar coating, or spraying, and the coating liquid can be dried using known methods after application.

The coating film of the hard coat layer-forming coating liquid can be cured by irradiating it with active energy rays. Examples of light sources for irradiating active energy rays (preferably ultraviolet rays) include low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, carbon arc lamps, metal halide lamps, and xenon lamps.

The amount of light emitted from the light source may be about 20 to 10,000 mJ/ ^cm2 , preferably in the range of 50 to 2,000 mJ/ ^cm2 . The irradiation time is preferably in the range of 0.5 seconds to 5 minutes, and from the viewpoint of work efficiency, a range of 3 seconds to 2 minutes is more preferable.

The dry layer thickness of the hard coat layer is preferably in the range of 2 to 15 μm, and more preferably in the range of 3 to 8 μm.

(2.5.2) Antireflection Layer When a functional layer such as the hard coat layer described above is formed on the film of the present invention, an antireflection layer can be coated on the functional layer to form an antireflection film having an external light antireflection function. In this case, the antireflection layer is formed by preparing a coating liquid for forming the antireflection layer using a solvent, applying the coating liquid, and drying and curing the coating liquid.

If necessary, a method may be used in which irregularities are formed on the surface of a mold without using a solvent, and then the irregularities of the mold are transferred onto the film using an ultraviolet-curing resin or thermoplastic resin to form an anti-glare (AG) layer, etc. (a method for forming an embossed AG layer).

The layer formed on the functional layer is not limited to the anti-reflection layer described above, and any known layer can be formed to suit various applications. For example, other layers such as a conductive layer may also be formed.

The anti-reflection layer is preferably laminated taking into consideration the refractive index, layer thickness, number of layers, layer order, etc. so that reflectance is reduced by optical interference. The anti-reflection layer is preferably composed of a low refractive index layer with a lower refractive index than the film used as the support, i.e., the film of the present invention on which the functional layer is formed, or a combination of a high refractive index layer and a low refractive index layer with a higher refractive index than the film of the present invention on which the functional layer is formed.

(Low refractive index layer)
The low refractive index layer preferably contains silica-based fine particles, and the refractive index thereof is preferably in the range of 1.30 to 1.45 when measured at 23° C. and at a wavelength of 550 nm.

The thickness of the low refractive index layer is preferably in the range of 5 nm to 0.5 μm, more preferably in the range of 10 nm to 0.3 μm, and most preferably in the range of 30 nm to 0.2 μm.

The composition for forming the low refractive index layer preferably contains at least one type of silica-based fine particle that has an outer shell layer and is porous or hollow inside. It is particularly preferred that the particles that have an outer shell layer and are porous or hollow inside are hollow silica-based fine particles.

The composition for forming a low refractive index layer may also contain an organosilicon compound represented by the following general formula (OSi-1), a hydrolyzate thereof, or a polycondensate thereof.
General formula (OSi-1): Si(OR) ₄
In the above general formula (OSi-1), R represents an alkyl group having 1 to 4 carbon atoms. Specifically, tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, etc. are preferably used.

Other additives may also be added, such as a solvent, a silane coupling agent, a curing agent, and a surfactant, as needed. The composition may also contain a thermosetting and/or photocurable compound primarily composed of a fluorine-containing compound containing 35-80% by mass of fluorine atoms and containing a crosslinkable or polymerizable functional group.

Specific examples include fluorine-containing polymers and fluorine-containing sol-gel compounds. Examples of fluorine-containing polymers include hydrolysates and dehydration condensates of perfluoroalkyl group-containing silane compounds (e.g., (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane). Other examples include fluorine-containing copolymers whose constituent units are fluorine-containing monomer units and crosslinking reactive units.

(High refractive index layer)
The refractive index of the high refractive index layer is preferably adjusted to be in the range of 1.4 to 2.2 when measured at 23° C. and a wavelength of 550 nm. The thickness of the high refractive index layer is preferably in the range of 5 nm to 1 μm, more preferably in the range of 10 nm to 0.2 μm, and most preferably in the range of 30 nm to 0.1 μm.

The refractive index can be adjusted by adding metal oxide fine particles, etc. Metal oxide fine particles with a refractive index in the range of 1.80 to 2.60 are preferred, and those in the range of 1.85 to 2.50 are even more preferred.

The type of metal oxide microparticles is not particularly limited, and metal oxides containing at least one element selected from Ti, Zr, Sn, Sb, Cu, Fe, Mn, Pb, Cd, As, Cr, Hg, Zn, Al, Mg, Si, P, and S can be used.

(2.5.3) Conductive Layer As a material for forming the conductive layer, a commonly known conductive material can be used, such as a metal oxide such as indium oxide, tin oxide, indium tin oxide, gold, silver, or palladium.

Using these materials, the conductive layer can be formed as a thin film on a film with a hard coat layer by vacuum deposition, sputtering, ion plating, solution coating, or other methods. It is also possible to form a conductive layer using an organic conductive material that is a π-conjugated conductive polymer.

In particular, conductive materials whose main component is indium oxide, tin oxide, or indium tin oxide, which have excellent transparency and conductivity and can be obtained at relatively low cost, are suitable for use.

The thickness of the conductive layer cannot be generalized as it varies depending on the material used, but it is preferable that the thickness be such that the surface resistivity is 1000 Ω or less, preferably 500 Ω or less. Taking economical efficiency into consideration, the thickness of the conductive layer is preferably 10 nm or more, more preferably in the range of 20 to 80 nm, and even more preferably 70 nm or less. Furthermore, in such a thin film, visible light interference fringes caused by uneven thickness of the conductive layer are less likely to occur.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these. In the examples, the terms "parts" and "%" are used, but unless otherwise specified, they represent "parts by mass" or "% by mass."

[Film Preparation]
Films [1] to [15] were produced by the solution casting film-forming method according to the following steps.

[A] Preparation of Film [1] (Preparation of Dope [D-1])
The following dope composition [1] was thoroughly dissolved under heating to prepare a dope [D-1].
<Dope composition [1]>
Acrylic resin (A) 65 parts by mass Cellulose ester resin (B) 35 parts by mass Methylene chloride 300 parts by mass Ethanol 40 parts by mass Rubber particles R1: 1 part by mass

The "acrylic resin (A)" in the dope composition [1] is "Dianal BR85" (acrylic resin) manufactured by Mitsubishi Rayon Co., Ltd. The weight-average molecular weight (Mw) is 280,000, and the proportion of methyl methacrylate (MMA) units in the acrylic resin molecule is in the range of 90 to 99% by mass.

The "cellulose ester resin (B)" in the dope composition [1] has acetyl and propionyl acyl groups. The total degree of substitution of the acyl groups is 2.75, the degree of substitution of acetyl groups (acyl groups with two carbon atoms) is 0.19, and the degree of substitution of propionyl groups (acyl groups with three carbon atoms) is 2.56, and the weight-average molecular weight (Mw) is 200,000.

The "rubber particles R1" in the dope composition [1] are "Kane Ace M210" (average primary particle diameter R: 200 nm) manufactured by Kaneka Corporation.

(Preparation of Dope [D-2]: Preparation of Dope for Film Formation)
Next, the dope composition [2] containing the dope [D-1] prepared by the above method was charged into a disperser to prepare an inorganic particle dispersion (M-1) as an additive.
<Dope composition [2]>
Inorganic particles [1] 4 parts by weight Dichloromethane 76 parts by weight Ethanol 10 parts by weight Dope [D-1] 10 parts by weight

The inorganic particles [1] are "Aerosil R812" (average primary particle size: 7 nm, apparent specific gravity: 50 g/L) manufactured by Nippon Aerosil Co., Ltd.

100 parts by mass of the above dope solution (D-1) and 0.75 parts by mass of the particle-free dispersion (M-1) were mixed to prepare a dope for film formation [D-2]. The above process was carried out using the stirring device 1 shown in Figure 6.

[A-1] Casting step The dope [D-2] was sent to the casting die 2 through a conduit via a pressure type metering gear pump. Then, the dope [D-2] was uniformly cast from the casting die 2 to a casting position on the support 3, which was an endless rotating stainless steel belt, at a temperature of 22°C and in a width of 2 m.

The dope [D-2] was heated on a stainless steel band support 3 until it became self-supporting, and then the solvent was evaporated and dried using a peeling roller 4 from the support 3 until the residual solvent content was reduced to 40% and it could be peeled off, forming a film.

Thereafter, the film was peeled off from the support with a peeling tension of 162 N/m while maintaining self-supporting property by a peeling roller 4. The support speed at this time was defined as a casting belt speed _V1 and was used to calculate the stretch ratio A.

[A-2] First conveying step: The solvent was evaporated from the above film at 35°C without holding the width, and the film was slit into a width of 1.6 m. The film was then conveyed while being treated at a high temperature to increase the density of the film. During this process, the film was conveyed while measuring the conveying tension _T1 with the non-contact web tension meter manufactured by Bellmatic.

(Transport tension T ₁ , expansion/contraction ratio b, temperature during transport)
Table I shows the conveying tension T ₁ [N/m], the stretch rate b [%] in the longitudinal direction (conveying direction, MD direction) of the film, and the temperature [°C] during conveying in the first conveying step.

The stretch rate b [%] in the longitudinal direction (machine direction, MD) of the film is calculated using the following formula:

Formula: Expansion/contraction rate b [%] = {(V ₂ - V ₁ )/(V ₁ )}×100 [%]

The meanings of the symbols in the above formula are as follows:
V ₁ : Belt speed in the casting section (speed of the support)
_V2 : Film transport speed in the first stretching step

[A-3] First Stretching Step Thereafter, the film was stretched in a stretching device 6 while being heated to 140°C. As the stretching device 6, a tenter stretching device 14 as shown in Figure 7 was used, and the film was stretched in the width direction in stretching zone B, and then subjected to relaxation treatment in stress relaxation zone D at 130°C for about 20 seconds at a relaxation rate B [%] (B = 2). The amount of residual solvent at this time was 10%.

[A-4] Second Conveying Step Thereafter, the film was heated on the dryer 7 while being conveyed, and the solvent was evaporated from the film. Then, both ends of the film in the width direction were cut at the cutting section 13 to produce a raw film, and the raw film was taken up around a core by the winding device 8 at a winding speed V _W1 (V _W1 =30 m/min).

(Relaxation rate B)
The relaxation rate B [%] in the first stretching step is shown in Table I. The relaxation rate B [%]
was calculated by the following formula:
Relaxation rate = (L _TDB0 /L _TDB1 -1) x 100 [%]
( _LTDB1 : length in the width direction of the film after the relaxation treatment in the first stretching step, _LTDB0 : length in the width direction of the film before the relaxation treatment in the first stretching step)

The wound raw film was unwound from the winding device 8 at a unwinding speed V ₃ (10 m/min), and transport was started.

(Transport tension _T2 , expansion/contraction ratio a, temperature during transport)
Table I shows the conveying tension T ₂ [N/m], the stretch rate a [%] in the longitudinal direction (conveying direction, MD direction) of the film, and the temperature [°C] during conveying in the second conveying step.

The transport tension _T2 was measured by a non-contact web tension meter manufactured by Bellmatic, in the same manner as the transport tension _T1 described above, while the film was transported in the second transport step.

The stretch rate a [%] in the longitudinal direction (machine direction, MD) of the film is calculated using the following formula:

Equation: Expansion rate a [%] = [{(film winding speed V _W1 in the second conveying step) - (film conveying speed V ₂ in the first stretching step)}/(film conveying speed V ₂ in the first stretching step)] x 100 + [{(film conveying speed V ₄ in the second stretching step) - (film unwinding speed V ₃ in the second conveying step)}/(film unwinding speed V ₃ in the second conveying step)] x 100

[A-5] Second Stretching Step The unwound raw film was stretched in a stretching device 10. In this case, a tenter stretching device 14 as shown in FIG. 7 was used as the stretching device 10, and the raw film was stretched in the width direction while being transported in stretching zone B at a transport speed V ₄ (10 m/min), and then subjected to a relaxation treatment in stress relaxation zone D at 130°C for about 5 minutes at a relaxation rate A (A = 2 [%]). The amount of residual solvent at this time was 0.30 mass%.

[A-6] Third conveying step: The film was then dried in the drying device 11 at 120°C and 140°C while being conveyed by multiple rolls, and the raw film was processed by slitting it into a width of 1.5 m in the cutting section 13 to produce a film.

The film was wound around a core at a winding speed V _W2 (V _W2 =10 m/min) by the winding device 12 to produce a film [1]. The thickness of the film [1] at this time was 35 μm.

The film thickness was measured at 1,612 locations using an inline retardation/film thickness measuring device RE-200L2T-Rth+film thickness (manufactured by Otsuka Electronics Co., Ltd.). The traverse movement speed was 100 mm/sec. The average of the measured values was taken as the film thickness.

(Stretch rate A and relaxation rate A)
The stretch rate A [%] and relaxation rate A [%] are shown in Table I.

The expansion/contraction rate A [%] was calculated using the following formula.
Formula: Expansion/contraction rate A [%]={(V _W1 - V ₁ )/V ₁ }×100+{(V ₄ -V ₃ )/V ₃ }×100

The meanings of the symbols in the above formula are as follows:
V _W1 : Film winding speed in the second transport step V ₁ : Casting zone belt speed (support speed)
_V3 : Film unwinding speed in the second transport step _V4 : Film transport speed in the second stretching step

The relaxation rate A [%] was calculated by the following formula.
Relaxation rate = (L _(TD)A0 /L _(TD)A1 -1) x 100 [%]
(L _(TD)A1 : length in the width direction of the film after the relaxation treatment in the second stretching step, L _(TD)A0 : length in the width direction of the film before the relaxation treatment in the second stretching step)

[B] Preparation of films [2] to [15] Films [2] to [15] were prepared in the same manner as in the preparation of film [1], except that the mass ratio of acrylic resin (A) to cellulose ester resin (B) in the preparation of dope and the parameters in the preparation process of film were as shown in Table I.

[ evaluation ]
The evaluation was carried out by the following methods, and the evaluation results are shown in Table II.

A hard coat layer was formed on each of the prepared films [1] to [15] using the following method to form a hard coat film. The pencil hardness of the hard coat layer formed on the hard coat film was measured in accordance with JIS K 5600 5-4 (pencil hardness evaluation method).

[C] Formation of Hard Coat Layer [C-1] Preparation of Silica-Dispersed Methyl Ethyl Ketone Solution A Before preparing the coating liquid for forming a hard coat layer, a silica-dispersed methyl ethyl ketone solution A to be used in the preparation of the coating liquid for forming a hard coat layer was prepared by the following steps.

(Surface adsorbed ion removal process)
Water-dispersed colloidal silica "Snowtec N" (average particle size 12 nm, pH 9.0 to 10.0) manufactured by Nissan Chemical Industries, Ltd. was subjected to ion exchange for 3 hours using 500 g of cation exchange resin "Diaion SK1B" manufactured by Mitsubishi Chemical Corporation.

Next, ion exchange was carried out for 3 hours using 300 g of anion exchange resin "SA20A" manufactured by Mitsubishi Chemical Corporation, and then the mixture was washed with ion-exchange water.

As a result, an aqueous dispersion of silica fine particles [a1] having a solid content of 20 mass % and a Na ₂ O content of 5 ppm was obtained.

(Surface treatment process: introduction of monomer)
To 20 g of the silica fine particle aqueous dispersion [a1] obtained by the surface-adsorbed ion removal step, 300 ml of isopropanol, 4.0 g of 3,6,9-trioxadecanoic acid, and 4.0 g of methacrylic acid were added and stirred for 1 hour to prepare a mixed solution [b].

The above-prepared mixed solution [b] was stirred while being heated at 60°C for 6 hours, thereby obtaining silica microparticle dispersion [a2] in which methacryloyl groups had been introduced into the silica microparticles.

The distilled water, isopropanol, and methacrylic acid were removed from the resulting silica microparticle dispersion [a2] using a rotary evaporator, and methyl ethyl ketone was added without drying the mixture, followed by the addition of the same amount (100% by mass) of methacrylic acid used in the surface treatment.

This resulted in the preparation of silica-dispersed methyl ethyl ketone solution A with a solids content of 40% by mass.

Residual water and isopropanol were kept below 0.1% by mass.

The silica microparticles in silica-dispersed methyl ethyl ketone solution A were measured using a particle size analyzer (Microtrac, manufactured by Nikkiso Co., Ltd.), and the average primary particle size d55 was found to be 13 nm.

[C-2] Formation of hard coat layer (preparation of coating solution for forming hard coat layer)
A mixed solution [c] was prepared by mixing the following ultraviolet-curable resin, surfactant, silica-dispersed methyl ethyl ketone solution A (solid content 40% by mass), and propylene glycol monomethyl ether. Thereafter, the mixed solution [c] was stirred for 30 minutes to prepare a coating solution for forming a hard coat layer.

UV-curable resin "A-DPH" (manufactured by Shin-Nakamura Chemical Co., Ltd.) 60 parts by mass Surfactant "Surflon S-651" (manufactured by AGC Seimi Chemical Co., Ltd.) 0.1 parts by mass Silica dispersion methyl ethyl ketone solution A (solid content 40% by mass) 100 parts by mass Propylene glycol monomethyl ether (PGME) 40 parts by mass

(Application, drying, and curing of coating liquid for forming hard coat layer)
The coating solution for forming a hard coat layer was applied to one side of each of the prepared films [1] to [15] using a microgravure coating to a dry thickness of 5 μm, and then dried to form a coating film.

Next, the coating film was cured by irradiating it with ultraviolet light at a light intensity of 270 mJ/ ^cm2 using a high-pressure mercury lamp in the atmosphere, thereby forming a hard coat layer on each of the films [1] to [15].

[D] Specific Evaluation Method A dedicated device equipped with a 750 g weight and a test pencil of each hardness specified in JIS S 6006 was run over the hard coating layer formed on each of the films [1] to [15] at a speed of 0.75 mm/sec for a distance of 7 mm. The angle of the pencil relative to the running surface was 45±1°.

This procedure was repeated five times. The maximum hardness value at which there was one scratch or less was determined. A higher maximum value indicates a higher hardness. The hardness was then evaluated according to the following criteria. A, B, and C were considered acceptable, and were evaluated as levels that present no practical problems.

(Evaluation criteria)
A: Pencil hardness is 3H or more (passed).
B: Pencil hardness is 2H or more and less than 3H (pass).
C: Pencil hardness is H or more but less than 2H (pass).
D: Pencil hardness is less than H (failure).

[E] Overall Evaluation From Tables I and II, it can be seen that the examples in which a hard coat layer was formed on the substrate film of the present invention were only rated A, B, and C, and therefore present no practical problems.

Although embodiments of the present invention have been described and illustrated in detail above, the disclosed embodiments have been made for purposes of illustration and example only and are not intended to be limiting. The scope of the present invention should be interpreted by the terms of the appended claims.

We can provide a manufacturing method for an acrylic resin-containing film and a multi-stage stretched acrylic resin-containing film that can be made wider and thinner, crack-free, have high density, and maintain functionality.

1 Stirring device 1a Stirring tank 2 Casting die 3 Support (casting belt)
3a, 3b Roller 4 Peeling roller 5, 7, 9, 11 Drying device 6, 10 Stretching device 8 Winding device in second conveying step 12 Winding device in third conveying step 13 Cutting section 14 Tenter stretching device 110 Housing 111 Clip 112 Rail a Starting point of film stretching, entrance of stretching zone b Ending point of film stretching, entrance of film width retention zone c Starting point c of stress relaxation treatment on film, entrance of stress relaxation zone d Ending point of stress relaxation treatment, exit of stress relaxation zone F Film Hc Width of film at entrance of stress relaxation zone Hd Width of film at exit of stress relaxation zone L _(MD)0 Length in the longitudinal direction of the film obtained by cutting out a specific portion at the peeling position in the casting step L _(MD)A1 Length in the longitudinal direction of the film from the peeling position in the casting step to a position immediately before stretching in the width direction in the second stretching step L _{(MD) A0} : Length in the width direction of the film before the relaxation treatment in the second stretching step L _(TD)A1: Length in the width direction of the film after the relaxation treatment in the second stretching step F: Film S1: Casting step S2: First conveying step S3: First stretching step 2nd _MD
V _W2 : Film winding speed in the third transport step (film winding speed by the winding device 12)
V ₁ : Belt speed in the casting section (speed of the support)
_V2 : Film transport speed in the first stretching step _V3 : Film unwinding speed in the second transporting step _V4 : Film transport speed in the second stretching step

Claims (5)

A method for producing an acrylic resin-containing film, comprising at least a casting step, a first conveying step, a first stretching step, and a second stretching step, in this order,
In the casting step, a dope containing an acrylic resin (A) and a cellulose ester resin (B) in a mass ratio of 95:5 to 30:70 is cast;
In the first stretching step, the acrylic resin-containing film is stretched in the width direction,
In the second stretching step, the acrylic resin-containing film is further stretched in the width direction,
An expansion/contraction rate A in the longitudinal direction from the peeling position of the acrylic resin-containing film in the casting step to a position immediately before stretching the acrylic resin-containing film in the width direction in the second stretching step, and a relaxation rate A in the width direction after stretching the acrylic resin-containing film in the width direction in the second stretching step satisfy the relationship of the following formula (1): -250<(expansion/contraction rate A/relaxation rate A)<550
A method for producing an acrylic resin-containing film, comprising: a second conveying step between the first stretching step and the second stretching step;
A conveying tension _T1 of the acrylic resin-containing film after drying the dope in the first conveying step and a conveying tension _T2 of the acrylic resin-containing film in the second conveying step satisfy the relationship of the following formula (2): 1.00<(conveying tension _T1 /conveying tension _T2 )<2.00.
The method for producing an acrylic resin-containing film according to claim 1 . The stretch rate A and the relaxation rate A satisfy the relationship of the following formula (3): Relaxation rate A<stretch rate A
The method for producing an acrylic resin-containing film according to claim 1 . When the acrylic resin-containing film is transported at an expansion/contraction rate a in the second transport step, the relationship of the following formula (4) is satisfied: 1.25<(expansion rate a/relaxation rate A)<5.5.
The method for producing an acrylic resin-containing film according to claim 1 . A multi-stage stretched acrylic resin-containing film containing at least an acrylic resin (A), a cellulose ester resin (B), rubber particles, and inorganic particles,
the multistage stretched acrylic resin-containing film contains the acrylic resin (A) and the cellulose ester resin (B) in a mass ratio of 95:5 to 30:70;
the total substitution degree (T) of the acyl groups of the cellulose ester resin (B) is in the range of 2.0 to 3.0, and the substitution degree of the acyl groups having 3 to 7 carbon atoms is in the range of 1.2 to 3.0; and
The multistage stretched acrylic resin-containing film has a film density in the range of 1.235 to 1.300 g/cm ³ .