JP2003251693A - Method for relaxation heat treatment of biaxially oriented polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for relaxation heat treatment of a biaxially oriented film which enables long-time continuous production of a film of a low heat shrinkage percentage having no flaw in the surface of the film. <P>SOLUTION: In the method for relaxation heat treatment of the biaxially oriented polyester film, the film is subjected to the relaxation heat treatment between a tenter and a pair of draw-off rollers subsequent to this, conveyed then by a plurality of groups of conveying rolls and wound up continuously by a winder. There is no nip roll for nipping the film over the whole width thereof in the take-up rollers and the groups of the conveying rolls. The surface temperature of the take-up rollers is 55-85°C, while the percentage of heat shrinkage of the wound film in the lengthwise direction under the condition of 150°C×30 minutes is 0.1-0.6%. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a relaxation heat treatment method for a biaxially stretched film, and more particularly to a relaxation heat treatment method for a biaxially stretched film capable of continuously producing a film having a low heat shrinkage ratio without scratches on the film surface for a long time. Regarding

[0002]

2. Description of the Related Art Biaxially stretched polyester films represented by polyethylene terephthalate films have been widely used as base films for films for optical applications such as touch panels and CRT displays, or as cover films for agricultural houses. In these base films, the agent coated on the film surface may be dried at 80 to 150 ° C in the post-treatment process of the user, and dimensional stability in a high temperature range where a heat load is applied, particularly low heat shrinkability is required. Sometimes.

In response to these requirements, as a relaxation heat treatment method for obtaining a low heat shrinkable film in the film forming process, a nip roller 9 is arranged on a take-up roller as shown in FIG.
There is known a method of loosening a film while separating the film tension between the upstream side and the downstream side of the roller. There is also known a method in which a film having no scratch on the film surface can be produced by reducing relative slip between the film and the take-up roller by the nip roller.

However, when a film having no optical defects is required for optical applications, oligomers are deposited and adhered on the film surface in a tenter, and the nip roller is contaminated with time when it is operated for a long time, resulting in roll surface. The problem that the film is scratched occurs because the oligomer attached to the film scrapes the film surface. In particular, in a film containing an ultraviolet absorber as a film component, oligomer deposition or sublimation in the tenter becomes conspicuous, which causes a problem.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a relaxation heat treatment method for a biaxially stretched film, which solves the above problems and can efficiently produce a film having a low heat shrinkage without scratches on the film surface. is there.

[0006]

According to the present invention, (1) a biaxially stretched polyester film is subjected to a relaxation heat treatment between a tenter and a pair of take-up rollers following the tenter, and then subjected to a plurality of heat treatments. A method of relaxing heat treatment of a film by transporting the film with a transport roll group and continuously winding the film with a winder, wherein the take-up roller and the transport roll group do not have a nip roll that nips the entire width of the film, Moreover, the surface temperature of the take-up roller is 55 to 85 ° C., and the heat shrinkage rate at 150 ° C. × 30 minutes in the longitudinal direction of the wound film is 0.1 to 0.6%.
Can be achieved by a relaxation heat treatment method for a biaxially stretched polyester film.

As a further preferred embodiment of the present invention,
(2) The take-up roller is a roll made of metal, the maximum height Rmax of the surface roughness thereof is 0.1 to 1.6 μm, and the traveling direction in which one surface of the film is in contact with the take-up roller. The length (L) (L) of the biaxially stretched polyester film according to (1) is 150 to 1500 mm, (3) the take-up roller has means for adjusting the temperature inside (1) or (2) A relaxation heat treatment method for a biaxially stretched polyester film, (4) a blade is inserted near both ends of the film on the downstream side of the stretching zone of the tenter to separate the film from the clip gripping portion (1) to ( In the relaxation heat treatment method for the biaxially stretched polyester film according to any one of 3) and (5) relaxation heat treatment, the relaxation rate of the film represented by the following formula (1) is 0.5.
The method for relaxing heat treatment of the biaxially stretched polyester film according to any one of (1) to (4), wherein

[0008]

## EQU00002 ## Relaxation rate (%) = (Vs-Vw) /Vs.times.100 (1) (In the formula (1), Vs is the running speed (m) of the tenter clip.
/ Min), Vw is the peripheral speed (m / min) of the take-off roller. (6) Relaxation of the biaxially stretched polyester film according to any one of (1) to (5), wherein the centerline surface roughness Ra of the wound biaxially stretched polyester film is 0.002 to 0.035 μm. Examples of the heat treatment method include (7) a relaxation heat treatment method for a biaxially stretched polyester film according to any one of (1) to (6), wherein the polyester constituting the biaxially stretched polyester film contains an ultraviolet absorber. it can.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to the drawings.

FIG. 1 is a side view showing a relaxation heat treatment apparatus exemplifying one embodiment of the present invention. FIG. 2 is a side view showing a conventional relaxation heat treatment device. FIG. 3 is a plan view of FIG.

1-3, 1 is a tenter, 2a,
2b is a pair of take-up rollers, 3 is a temperature control device, 4 is a blade, 5 is a product film, 6 is a film edge, 7 is a cross guider, 8 is an edge nip roller, 9 is a nip roller, and Vs is a running tenter clip. The velocity, Vw is the peripheral velocity of the take-off roller, and L is the contact length.

In the relaxation heat treatment method of the present invention, the blades 4 are inserted into both ends of the biaxially stretched film in the tenter 1 to separate them from the clip, and the speed Vw of the take-up rollers 2a and 2b is slightly reduced from the running speed Vs of the tenter clip. It is possible to produce a film having a low heat shrinkage by relaxing by reducing At this time, by not using the nip roller 9 that nips the product portion 5 over the entire width, it is possible to remarkably reduce film scraping due to the oligomer. However, if the film is not simply nipped, slippage occurs between the film and the take-up roller and the film is damaged, so it is preferable to raise the temperature of the take-up roller to soften the film and improve the adhesion to the roller. The surface temperature of the pair of take-up rollers 2a and 2b is preferably 55 to 85 ° C, and 60 to 75 ° C.
Is more preferable. If it exceeds the upper limit, the film surface becomes rough due to overheating, and if it is lower than the lower limit, slippage occurs and the film is easily scratched. Further, the take-off roller is generally a metal roll, and in order to maintain abrasion resistance, a roller having a known surface treatment such as hard chrome plating can be used. The temperature of the take-up roller can be easily controlled by, for example, simply supplying and circulating hot water with a Unicon. The surface roughness of the take-up roller has a maximum height Rmax of 0.1 to 1.6 μm.
The range of m is good, and if it is larger than this range, the contact area between the film and the roll surface becomes small and slippage easily occurs,
On the other hand, if it is less than this range, it is difficult to finish the surface, and it is practically difficult to maintain the surface property when it is always used. Further, the contact length L is preferably in the range of 150 to 1500 mm, and in this range, the film and the roll can be taken up without slipping.

On the other hand, the relaxation rate of the film in the relaxation heat treatment is preferably 0.5 to 2.0%. If it is less than this range, there is almost no effect of relaxing to reduce the heat shrinkage rate of the film, and conversely from this range. If it is large, the film tends to have wrinkles, and the film 5 (of the product part) that is loosened and droops in the tenter may come into contact with an obstacle, the film may be violently violently caused by hot air, and the meandering may be maintained. Yes, film formation becomes unstable. The cross guider 7 can be used to support and lift the end portion of the sagging film, or a plurality of central portions if necessary, and further extend wrinkles. If the tenter is long, a cross guider, or simply a push-up roll may be provided inside the tenter. On the other hand, by using the edge nip roller 8, the meandering of the film 5 can be suppressed.

In the present invention, by cutting the vicinity of the film edge with the blade 4 in the tenter, the product portion 5 can be relaxed efficiently with a high relaxation rate. The blade 4 is preferably made of a super hard blade that is less likely to wear even during continuous operation, and preferably has a thickness of 50 to 250 μm and is hard to break. The heat relaxation treatment may be performed in a separately provided treatment facility after leaving the tenter.

The biaxially stretched polyester film of the present invention can be manufactured by a conventionally known method.
For example, after the polyester described below is dried, the polymer melting point Tm
To (Tm + 70) ° C., melted at a temperature of (Tm + 70) ° C., extruded from a die to a cooling drum, and rapidly cooled to have an intrinsic viscosity of 0.35 to 0.9 dl /
g of unstretched film is obtained, and the unstretched film is stretched in the machine direction at a temperature of (Tg−10) to (Tg + 70) ° C. (however, T
g is the glass transition temperature of polyester) and is 2.5 to
Draw at a draw ratio of 5.0 times, then T in the transverse direction with a tenter.
It can be produced by stretching at a temperature of g to (Tg + 70) ° C. at a draw ratio of 2.5 to 5.0, and further heat setting at a temperature of (Tg + 70) to Tm ° C. The polyethylene terephthalate film is preferably heat set at 190 to 240 ° C. The heat setting time is preferably 1 to 60 seconds. The film thickness after biaxial stretching is 50 to 25.
0 μm is preferable, and if it is thinner than this range, it is difficult to relax.
In the present invention, the biaxially stretched film has a center line roughness Ra of 0.002 to 0.035 μm, which is flat and has a small amount of added lubricant, and can exert a remarkable effect of eliminating scratches on the film. The effect can be more remarkably exhibited in a film containing a known additive that easily produces a sublimate such as.

The polyester film in the present invention is a cotton-like saturated polyester synthesized from an aromatic dibasic acid or its ester-forming derivative and a diol or its ester-forming derivative. Specific examples of the polyester include polyethylene terephthalate, polyethylene isophthalate, polybutylene terephthalate, poly (1,4-cyclohexylene dimethylene terephthalate), polyethylene 2,6-naphthalene dicarboxylate and the like, and copolymers thereof. Alternatively, a blend of these with a small proportion of another resin is also included.

From the viewpoint of the slipperiness and processability of the film, polyester is added with lubricant such as calcium carbonate, kaolin, silica, titanium oxide, alumina, crosslinked polystyrene particles, and silicone resin particles, and / or
Fine particles of catalyst residue may be included. Further, other additives such as pigments, stabilizers, and ultraviolet absorbers can be contained as required.

In the present invention, the fact that there is no nip roller in the take-up roller and the plurality of conveying roll groups from the relaxation heat treatment to the winding by the winder is mainly used for the purpose of tension cutting. This means that a nip roller that nips the film product portion over almost the entire width is not used, and does not refer to a roller that nips the edge portion of the film with a narrow width.

[0019]

EXAMPLES The present invention will be further described below with reference to examples. The physical properties in the examples were measured by the following methods.

(1) Surface temperature of take-up roller The surface temperature of the take-up roller is controlled while the temperature of the take-up roller is stopped and the roll is stopped (ST-50- manufactured by Rika Kogyo Co., Ltd.).
500) and used as the roll temperature.

(2) MD heat absorption (heat shrinkage): 350 mm in the longitudinal (MD) direction of the film, 5 in the width direction.
A 0 mm sample is cut out, marked points are set at 300 mm intervals in the vicinity of both ends in the longitudinal direction of the sample, one end is fixed to an oven adjusted to a temperature of 150 ° C., and the other end is left free for 30 minutes. This is taken out, the gauge length is measured at room temperature (this length is referred to as S), and the MD heat absorption is obtained by the following formula (2).

[0022]

[Equation 3]   MD heat balance (%) = (300−S) / 300 × 100 (2)

(3) Number of scratches Biaxially stretched film is irradiated with halogen light in a dark room,
The number of scratches measuring 1 × 1 m square was counted. At this time, the scratches apparently formed during sampling (for example, scratches that seemed to flow laterally instead of in the longitudinal direction of the film) were excluded from the number.

(4) Evaluation The product level of the film was judged by the number of scratches on the film. The number of scratches is 1 / m ² or more ×: Product not acceptable level The number of scratches is 0 / m ² ○: Product level

(5) Surface Roughness (Centerline Surface Roughness Ra) Both front and back images of the film are measured with a surface roughness meter (Surfcom 111A, Tokyo Seimitsu Co., Ltd.), and the average value is calculated to obtain the surface roughness. Ra.

(6) Intrinsic viscosity The viscosity of the solution with an orthochlorophenol solvent is adjusted to 35 ° C.
It was measured and determined at.

(7) Glass transition temperature (Tg) According to JIS K2171, Therm manufactured by DuPont
al Analyst 2000 type differential calorimeter (DS
In C), it was measured at a temperature rising rate of 10 ° C./min.

[Example 1] Relaxation heat treatment was performed during film formation of a biaxially stretched film using the apparatus shown in FIG. First, polyethylene terephthalate (Tg: 70 ° C.) pellets (for film F) having an intrinsic viscosity of 0.65 dl / g to which a small amount of kaolin was added were dried at 180 ° C. for 4 hours, and then 2
It was supplied to an extruder heated to 70 to 300 ° C., and formed into a sheet by an extrusion molding die. Furthermore, while statically adhering and solidifying this film on a cooling drum having a surface temperature of 25 ° C. by air, while cooling the film with a cooling knife,
An unstretched film was obtained. This unstretched film is then
2. Preheat with a heating roll group at 5 ° C, and use the peripheral speed difference between a roll heated to 75 ° C and a pair of rolls whose temperature has been adjusted to 50 ° C while heating in an infrared heater in a non-contact manner in the longitudinal direction. The film was longitudinally stretched to 1 ×, then cooled with a roll group at 20 to 50 ° C., and led to a tenter 1. While holding both ends of the film with clips, it was laterally stretched 3.2 times in a hot atmosphere at 120 ° C.

The biaxially stretched film was heat set as it was in a tenter at a temperature of 235 ° C., and both ends of the film were separated from the clips by the cemented carbide blade 4, and then the take-up speed was reduced by 1.4% to relax the film. Then, slowly cool it from 180 ℃ to 110 ℃, take it out from the tenter, support the both ends of the loosened product part with the cross guider 7, and cool the film cooled to 90 ℃ at room temperature with the take-up rollers 2a and 2b having the surface temperature of 65 ℃. It was taken up, conveyed by a plurality of roll groups without passing through a nip roller, and taken up by a winder. The take-up roller has a hard chrome-plated surface roughness with a maximum height Rmax of 0.
Using a 4 μm object, the contact length L between 2a and the film is 205
mm, the contact length L between the film and 2b was 580 mm. Obtained thickness 188 after continuous film formation for about 16 hours
The number of scratches and the MD heat absorption of the biaxially stretched film of μm were measured and shown in Table 1. The obtained film was a product-level defect-free low heat shrinkable film. The surface roughness R of the film
a was 0.010 μm.

[Examples 2 to 4] Film speed (thickness),
A biaxially stretched film was obtained in the same manner as in Example except that the kind of film and the roller temperature were changed as shown in Table 1. Table 1 shows the results of measuring the physical properties of the obtained film. The surface roughness Ra of the film of Example 4 was 0.015 μm.

The film G shown in Table 1 is as follows. Film G: 2,2 'as a small amount of lubricant and UV absorber
-Paraphenylenebis (3,1-benzoxazine-4
-ON) containing 0.5 wt% of polyethylene terephthalate film (intrinsic viscosity 0.65 dl / g, Tg: 7)
0 ° C).

Comparative Example 1 Film formation was carried out for 16 hours under substantially the same conditions as in Example 1 except that the take-up roll temperature was 50 ° C. The physical properties of the film obtained are shown in Table 1. As the film slipped between the take-up rolls, scratches were noticeable and outside the product level.

[Comparative Example 2] Nip roller 9 shown in FIG.
The film was formed for 16 hours under substantially the same conditions as in Example 3 except that was used. Table 1 shows the physical properties of the obtained film. The nip roll 9 became pure white, resulting in an extremely large number of scratches on the film surface.

[0034]

[Table 1]

[0035]

According to the present invention, it is possible to continuously produce a biaxially stretched film having a low heat shrinkage ratio without scratches on the film surface for a long time.

[Brief description of drawings]

FIG. 1 is a side view of a relaxation heat treatment apparatus showing one embodiment of the present invention.

FIG. 2 is a side view of a relaxation heat treatment apparatus showing a conventional form.

FIG. 3 is a plan view of a relaxation heat treatment apparatus showing one embodiment of the present invention.

[Explanation of symbols]

1: Tenter 2a: upstream take-up roller 2b: Downstream take-up roller 3: Temperature control device 4: Blade 5: Product film 6: Film edge 7: Cross guider 8: Edge nip roller 9: Nip roller Vs: Traveling speed of the tenter clip Vw: peripheral speed of take-off roller L: Contact length

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Claims (7)

[Claims] 1. A biaxially stretched polyester film is subjected to a relaxation heat treatment between a tenter and a pair of subsequent take-up rollers, and then the film is conveyed by a plurality of conveying roll groups and continuously wound by a winder. A method of relaxing heat treatment of a film by removing the film, wherein the take-up roller and the conveying roll group have no nip roll that nips the entire width of the film, and the take-up roller has a surface temperature of 5
5 to 85 ° C., 1 in the longitudinal direction of the wound film
A relaxation heat treatment method for a biaxially stretched polyester film, wherein the heat shrinkage ratio at 50 ° C x 30 minutes is 0.1 to 0.6%. 2. The take-up roller is a metal roll having a maximum surface roughness Rmax of 0.1 to 1.6.
The length (L) in the running direction in which one surface of the film is in contact with the take-up roller is 150 to 1500 mm.
The method for relaxing heat treatment of a biaxially stretched polyester film according to claim 1, wherein 3. The relaxation heat treatment method for a biaxially stretched polyester film according to claim 1, wherein the take-up roller has means for adjusting the temperature inside. 4. The biaxially stretched polyester film according to claim 1, wherein the film is separated from the clip gripping portion by inserting a blade near both ends of the film on the downstream side of the stretching zone of the tenter. Relaxation heat treatment method. 5. The biaxially stretched polyester film according to claim 1, wherein the relaxation rate of the film represented by the following formula (1) in the relaxation heat treatment is 0.5 to 2.0%. Relaxation heat treatment method. ## EQU1 ## Relaxation rate (%) = (Vs−Vw) / Vs × 100 (1) In the equation (1), Vs is the traveling speed (m / m) of the tenter clip.
Min) and Vw are the peripheral speed (m / min) of the take-off roller. 6. The centerline surface roughness Ra of the wound biaxially stretched polyester film is 0.002 to 0.035 μm.
The method for relaxing heat treatment of a biaxially stretched polyester film according to any one of claims 1 to 5, wherein 7. The relaxation heat treatment method for a biaxially stretched polyester film according to claim 1, wherein the polyester constituting the biaxially stretched polyester film contains an ultraviolet absorber.