JP5621380B2 - Cellulose ester and method for producing the same - Google Patents

Description

  The present invention relates to a method for producing a cellulose ester having a very low content of gelled foreign matter and a cellulose ester produced by the production method.

  Cellulose acetate films are used as films in various photographic materials and optical materials because of their toughness and flame retardancy. For example, a cellulose acetate film is a typical support for photographic light-sensitive materials. Cellulose acetate films are also used in liquid crystal display devices because of their optical isotropy.

  Such an optical film of cellulose acetate is required to have few optical defects that affect the transmission of light because its use is optical. And if it is the use of the conventional cellulose-ester film, even if it is a fine surface unevenness | corrugation, foreign material, or an optical defect which does not have a quality problem, it will become a problem in an optical film. In particular, when an optical film is used as a component of a liquid crystal display device, a so-called bright spot foreign substance or gel-like foreign substance that abnormally refracts transmitted light even if it is transparent becomes an optical defect and the quality. It becomes the problem above.

  In recent years, these liquid crystal display devices are used not only as display devices for personal computers but also as display devices for television receivers, DVDs, etc., or display devices for mobile phones and PDAs (mobile terminals). There are demands for fewer defects. That is, in recent years, display devices for personal computers, television receivers, and computer games have become larger and larger in screen, and the number of image forming elements (so-called dot number) has increased as symbolized by full high-definition LCD televisions. The area of the area per image forming element has become very small.

  With such technological trends, performance and properties required for polarizing plate protective films, antireflection film optical films, and stretched optical films used in liquid crystal display devices are diversifying. For one thing, there is a need to provide films with fewer optical defects per unit area.

  These foreign substances include black foreign substances, bright spot foreign substances, and gel-like foreign substances. The black foreign matter is caused by impurities and the like, and the bright spot foreign matter is mainly caused by cellulose ester or the like that is close to non-acetated acid, and the refractive index is different and the transmitted light is abnormally refracted. On the other hand, unlike the above-mentioned two foreign substances, the gel-like foreign substance is a foreign substance in which the detailed chemical structure and generation mechanism are not clarified and the amount present in the film is large.

  Black foreign matters are caused by impurities being mixed during the production of cellulose esters such as cellulose acetate and in the dissolving step, and bright spot foreign matters are caused by cellulose having a different degree of esterification.

  The black foreign matters and bright spot foreign matters as described above can be removed by filtering a solution (dope) in which cellulose acetate is dissolved during the production of the optical film with a filter paper or a metal filter. However, the gel foreign substance cannot be removed even if a fine filter paper or a metal filter is used because the shape is irregular.

On the other hand, Patent Documents 1 to 3 disclose a method of removing foreign matters by using silicon dioxide (diatomaceous earth) as a filter aid when producing a cellulose ester film. However, the above-mentioned patent document does not describe the adsorption capacity index such as the specific surface area and pore volume of silicon dioxide, and the ability to remove the gel-like foreign matter, and the effect of removing the gel-like foreign matter was not sufficient even if additional tests were conducted. . In general, the specific surface area of diatomaceous earth used as a filter aid is about 1 to 5 m ² / g, and when the silicon dioxide fine particles having a specific surface area larger than that are used as a filter aid, There is no description about the removal ability.

  Patent Document 1 describes that the filterability is improved by regulating the bulk density and the bright spot foreign matter is reduced, but there is no description of the gel-like foreign matter. Further, even if silicon dioxide fine particles having a bulk density within the specified range were used, the effect of removing gelled foreign matters was not sufficient.

  Patent Document 4 discloses the use of a filter aid substituted with a sulfone group or a carboxyl group. However, although these functional groups can remove impurities derived from alkaline earth, the effect of removing gel-like foreign matters has not been sufficient. As described above, it has been difficult to remove the gel-like foreign matters contained in the cellulose ester.

JP 2004-107629 A JP 2009-061618 A JP 2009-061619 A JP 2008-207366 A

  The present invention has been made in view of the above problems and situations, and a solution to the problem is to provide a method for producing a cellulose ester having a very low content of gel-like foreign matter and a cellulose ester produced by the production method. It is.

As a result of intensive studies, the inventors of the present invention have, in the method for producing a cellulose ester, treating a solution in which the cellulose ester is dissolved with silicon dioxide particles having a specific surface area of 30 to 1000 m ² / g to remove the silicon dioxide particles. It has been found that a cellulose ester in which gel-like foreign matters are remarkably reduced can be obtained by having the above.

  That is, the said subject which concerns on this invention is solved by the following means.

1. Gelatinous foreign matter comprising a step of treating cellulose ester with silicon dioxide particles having a specific surface area of 30 to 1000 m ² / g and removing the silicon dioxide particles from the treated cellulose ester . A method for producing a cellulose ester having a very low content .

  2. 2. The method for producing a cellulose ester according to item 1, wherein the pore volume of the silicon dioxide particles is in the range of 0.5 to 2.0 ml / g.

3. In the step of removing the silicon dioxide particles obtained by processing the cellulose ester, the first term or method for producing a cellulose ester according to the paragraph 2 which comprises using the silicon dioxide fine particles as a filter aid.

  By the said means of this invention, the cellulose ester manufactured by the manufacturing method of the cellulose ester with very little content of a gel-like foreign material and the said manufacturing method can be provided.

  Therefore, it is possible to provide an optical film having good contrast and few optical defects.

The method for producing a cellulose ester of the present invention comprises a step of treating the cellulose ester with silicon dioxide particles having a specific surface area of 30 to 1000 m ² / g, and removing the silicon dioxide particles from the cellulose ester after the treatment. It is characterized by having. This feature is a technical feature common to the inventions according to claims 1 to 4.

  As an embodiment of the present invention, it is preferable that the pore volume of the silicon dioxide particles is in the range of 0.5 to 2.0 ml / g from the viewpoint of manifesting the effects of the present invention. Furthermore, it is preferable to use silicon dioxide particles as a filter aid in the step of removing the silicon dioxide particles.

  According to the production method of the present invention, it is possible to obtain a cellulose ester having a very low content of gelled foreign matters.

  Hereinafter, the present invention, its components, and modes and modes for carrying out the present invention will be described in detail. In addition, in this application, "-" is used in the meaning which includes the numerical value described before and behind that as a lower limit and an upper limit.

<Silicon dioxide fine particles>
In the present invention, silicon dioxide fine particles having a specific surface area of 30 to 1000 m ² / g are used, but such a specific surface area cannot be achieved only by the surface outside the particle, and can be achieved even if the particle size is reduced to about 1 μm. I can't do it. That is, since the surface in the porous space inside the particles is necessary, the silicon dioxide fine particles used in the present invention are preferably porous.

  The silicon dioxide fine particles used in the present invention are silicon dioxide fine particles having an infinite number of silanol groups on the surface. This makes it possible to capture foreign matter with high polarity.

  Silicon dioxide can be classified into natural products and synthetic products, and can be further classified into crystalline and amorphous.

  Natural products use naturally occurring silicon dioxide as fine particles such as diatomaceous earth and activated clay. On the other hand, synthetic silicon dioxide fine particles are synthesized by a dry method or a wet method, and further classified into a precipitation method, a gel method, a sol-gel method, etc. in the wet method.

  The silicon dioxide fine particles in the present invention can be used equally for natural products and synthetic products, but amorphous silicon dioxide fine particles can be used preferably, and synthetic amorphous silicon dioxide fine particles are particularly preferred.

  The method for synthesizing the silicon dioxide fine particles used in the present invention is preferably synthesized by a wet method, and silicon dioxide fine particles synthesized by a sol-gel method are particularly preferred. Filterability is improved by using silicon dioxide fine particles synthesized by these methods.

If the silicon dioxide fine particles in the present invention have a specific surface area of 30 to 1000 m ² / g, gelled foreign substances can be removed. In view of filterability, the specific surface area is preferably 100~900m ² / g, more preferably 300~800m ² / g.

  The particle diameter of the silicon dioxide fine particles in the present invention is not particularly limited, but is preferably 1 to 100 μm, more preferably 2 to 50 μm, and most preferably 5 to 20 μm from the viewpoints of filterability and foreign matter removing ability. The above range is preferable because the filterability is improved by increasing the particle size, and the ability to capture foreign matter is improved by decreasing the particle size.

  The “pore volume” in the present invention refers to the volume of cavities existing in the fine particles, and the pore volume of the silicon dioxide fine particles in the present invention is preferably 0.5 to 2.0 ml / g. 0.8 to 1.8 ml / g is preferable and 1.0 to 1.5 ml / g is more preferable from the adsorbability of foreign matter.

  Although there is no restriction | limiting in particular in the usage-amount of the silicon dioxide fine particle in this invention, From a viewpoint of productivity and adsorption capacity, it is preferable that it is 0.1-500 mass% with respect to a cellulose ester, and 5-200 mass% is further. Preferably, 10 to 100% by mass is most preferable.

  The silanol groups present on the surface of the silicon dioxide fine particles used in the present invention may be surface-treated by reacting with other functional groups. Examples of functional groups that react with silanol groups include halogen, amino group, imino group, carboxyl group, hydroxyl group (hydroxyl group), alkoxyl group, acid chloride group, aldehyde group, epoxy group, alkoxysilyl group, and isocyanate group. Can be mentioned.

  In the present invention, the content of silicon dioxide fine particles in the solution after removing the silicon dioxide fine particles is preferably 0.1% by mass or less based on the cellulose ester. By setting it to 0.1% by mass or less, generation of foreign matters due to aggregation of silicon dioxide fine particles can be suppressed.

As an index of the concentration of silanol on the surface of silicon dioxide that can be suitably used in the present invention, the following infrared absorption spectrum can be mentioned. In the infrared absorption spectrum of silicon dioxide, an absorption peak at 1800 cm ⁻¹ derived from a siloxane (Si—O—Si) bond, an absorption peak derived from a silanol group (Si—OH), and the like appear. The absorption peak derived from the silanol group is derived from an absorption peak in the vicinity of 3500 cm ⁻¹ derived from an associative silanol group in which adjacent silanols are associated by a hydrogen bond, and an isolated silanol group not causing such a hydrogen bond. There are two types of absorption peaks around 3750 cm ⁻¹ .

When the ratio of the peak intensity of 3500 cm ⁻¹ corresponding to the associative silanol group to the peak intensity of 1860 cm ⁻¹ derived from the siloxane bond is x, in the silicon dioxide used in the present invention, 0.5 <x < A range of 2.5 is preferred. When x is 0.5 or more, since the absolute amount of silanol groups that can remove the gel-like foreign matter is sufficient, the effect of removing the gel-like foreign matter is high. On the other hand, when x is 2.5 or more, the associating property between silanol groups is extremely advanced and the affinity with the gel-like foreign matter is reduced. Therefore, when x is in the above range, a sufficient effect of removing the gel-like foreign matter is obtained. Is expressed. A more preferable range is 1.0 <x <1.5.

Furthermore, when the ratio of the peak intensity of 3750 cm ⁻¹ derived from the isolated silanol group to the peak intensity of 3500 cm ⁻¹ derived from the associative silanol group is y, the range is 1.0 <y <9. preferable. When y is 1.0 or more, there is little associating property between silanol groups, and the affinity with gelled foreign matters is high. When y is 9 or more, since the absolute amount of silanol groups from which gel-like foreign matters can be removed is small, the removal effect is high when 1.0 <y <9. In the case of 1.1 <y <5, it is more preferable.

  The firing temperature when synthesizing the silicon dioxide fine particles used in the present invention is preferably about 200 to 350 ° C. When the firing temperature exceeds 350 ° C., the value of y may be too large, which is not preferable. Moreover, when the time of baking is too long, there exists a possibility that the value of x may become 0.5 or less. For example, when the firing temperature is 200 ° C., the firing time is suitably about 2 to 36 hours, and when the firing temperature is 300 ° C., the firing time is suitably about 0.1 to 24 hours.

The silicon dioxide fine particles used in the present invention are not particularly limited as long as the specific surface area is 30 to 1000 m ² / g. For example, silica gel MB-300, MB-500 manufactured by Fuji Silysia, Fuji Silica Gel AB type, Fuji silica gel type A, Fuji silica gel RD type, Merca Silica Gel 40, Silica Gel 60, Silica Gel 100, and the like.

  The silica gel subjected to chemical modification is an adsorbent having an alkyl group introduced on silica gel, and ODS (Octadecyl group-bonded silica gel) in which an octadecyl group of a long aliphatic chain is introduced is often used. Specific examples of the silica gel subjected to chemical modification include ODS-A and ODS-AQ manufactured by YMC. Is mentioned.

<Processing method>
In the treatment method in the present invention, silicon dioxide particles having a specific surface area of 30 to 1000 m ² / g may be dispersed, suspended and stirred in a solution in which cellulose ester is dissolved. The solution in which the cellulose ester is dissolved by pre-coating may be filtered. Further, it is possible to treat the molten cellulose ester by the same method.

As a method for removing silicon dioxide particles having a specific surface area of 30 to 1000 m ² / g used in the present invention, for example, known methods such as filtration, centrifugation, and decantation can be used. It is preferable to remove silicon dioxide particles having a specific surface area of 30 to 1000 m ² / g by filtration and centrifugal separation from the removal capability and production suitability.

  Various known filtration devices can be used for filtering the cellulose ester solution according to the present invention. That is, when roughly classified as a filter, it can be divided into a continuous filter and a batch pressure filter, and as a continuous filter, it can be divided into a belt type, a multiple disk type, a screw press type, a filter press type, etc. Examples of the batch pressure filter include a leaf type and a candle type.

  A filter press device, a paper filter device, a leaf filter device, a drum filter device, a precoat filter device, or the like can be used. The industrially most advantageous product is a filter press apparatus, and the filter press apparatus may be pre-coated and used. As an example of the filter press apparatus, 40 to 50 plates of about 60 cm square are used, and a net is attached to each plate, and a filter paper or cotton cloth is installed between the nets. A plurality of these filter press apparatuses may be used for filtration in multiple stages.

  As the filter medium used in the present invention, a sintered metal filter, a non-woven metal filter, a cotton cloth filter, a paper filter, or the like may be used.

  If it is a filter press type, the filter medium to be used can be a natural fiber or a synthetic fiber. In general, polypropylene, polyester (tetron), and nylon can be used as the material of the synthetic fiber used for the filter cloth. Vinylon, acrylic, saran, etc. can also be used depending on the solvent. Each of these materials has characteristics on the material and can be used according to the characteristics. If it is a natural fiber, cotton can be mentioned as a typical material. Monofilaments, multifilaments, spun yarns and the like can be used as the type of raw yarn used for the filter cloth. When a monofilament is used, the cake peelability is excellent and clogging is small, but there is a disadvantage that the fine particles are poorly captured. When multifilaments are used, the strongest filter cloth is obtained and the cake peelability is good. In the case of spun yarn, cake peeling is poor and clogging is slightly faster. The filter cloth weave includes plain weave, twill weave, and satin weave. In the case of plain weave, particles are easily collected but clogging is accelerated. In the case of twill weave, a filter cloth having a good balance between collection and clogging can be obtained. In the case of satin weaving, particles are less clogged, but the ability to collect particles is poor. In the present invention, plain or twill filter cloth is suitable.

For cotton filter, cotton flannel (No. 10B, 63 plain yarn 20th single yarn, 46 weft 10 single yarn), gold width (11, 100 plain weave 40 single yarn, 98 weft 40 single yarn) , Thick twill weave (26, twill, 12-3, 64, 12-4, 32) may be used. In the paper filter, filter paper (300 g / m ² ) or the like may be used. These filter media may be used in combination (for example, the first filter media is one cotton flannel filter paper, the second filter media is two cotton flannels, one gold width, and the third filter media is one cotton flannel one filter paper, one gold width).

  The retention particle size of the filter medium used in the present invention is preferably 1 to 50 μm. 2-20 micrometers is further more preferable, and 3-15 micrometers is the most preferable. By using such a filter medium, filterability is improved and productivity is improved.

  The pressure in the filtration step according to the present invention can be appropriately set in consideration of filtration efficiency. Specifically, the filter medium may be pressurized to 5 to 18 atmospheres (for example, 8 to 18 atmospheres, for example, 10 to 18 atmospheres). The cellulose mixed fatty acid ester composition obtained by dissolving cellulose ester in an organic solvent, filtering and drying may be a filament. In the step of dissolving the cellulose mixed fatty acid ester according to the present invention in an organic solvent and filtering, kaolin, titanium oxide, clay or the like may be used as a filter aid. The filtrate may be kept warm at about 40 to 50 ° C. The filter medium may be pressurized to 5 to 18 atmospheres (for example, 8 to 18 atmospheres, for example, 10 to 18 atmospheres). Filtration multiple times instead of once (for example, the first filter medium is one cotton flannel paper, the second filter medium is two cotton flanks, one gold width, the third filter medium is one cotton flannel, one filter paper, one gold width) In the same configuration, the first filtration may be performed at 12 to 18 atmospheres, the second filtration may be performed at 8 to 14 atmospheres, and the third filtration may be performed at 5 to 9 atmospheres). When the same filter medium configuration is used, the filtration pressure may be changed between the first time and the second time (for example, the second filtration is performed at a lower pressure).

In the step of removing silicon dioxide particles having a specific surface area of 30 to 1000 m ² / g in the present invention, it is preferable to pre-coat silicon dioxide fine particles on the filter medium as a filter aid, particularly when filtration is performed. The silicon dioxide fine particles used as a filter aid can be used without particular limitation, and natural diatomaceous earth, synthetic silica gel, and the like can be used. As a filter aid, for example, Celite (for example, Filter-Cel, Celite 505, Standard Super-Cel, Celite 512, Hyflo Super-Cel, Celite manufactured by Jones-Manville Sales Corp.). , Celite 503, Celite 535, Celite 545, Celite 560, etc.], Dikalites (Superref, UF, Speedflow, Special Speed, manufactured by Grefco, Inco, USA). Etc.], radio lights [(RADIOLITE # 100, RADIOLITE manufactured by Showa Chemical Industry Co., Ltd. 200, RADIOLITE # 500, RADIOLITE # 600, RADIOLITE # 700, RADIOLITE # 900, RADIOLITE # 1100, RADIOLITE #] 100), silica gel (silica gel MB-300, MB-500, Fuji Silica AB type, manufactured by Fuji Silysia) Fuji-silica gel A type, Fuji-silica gel RD type, Merca Silica Gel 40, Silica Gel 60, Silica Gel 100, etc.) The filterability is drastically improved by using a filter aid. The ability to remove foreign matter is also improved.

The step of treating with silicon dioxide particles having a specific surface area of 30 to 1000 m ² / g in the present invention and removing the silicon dioxide particles from the cellulose ester after the treatment can be incorporated into a part of the cellulose production step. First, the cellulose production process will be described below.

[Activation process]
In the activation step, cellulose is treated with an activator to activate the cellulose. In the present invention, raw material cellulose is supplied in a slurry wet state.

  As the activator for activating cellulose, a solvent for acylation reaction (acylation solvent) is usually used. As the acylation solvent, organic carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid are used. Or an aliphatic carboxylic acid (linear or branched C1-6 alkanoic acid) such as valeric acid. These activators can be used alone or in combination of two or more.

  In the activation treatment, an aqueous medium containing water is used as the activator. This aqueous medium may be an aqueous medium containing an organic carboxylic acid. In consideration of substituting the aqueous medium from the cellulose raw material with the carboxylic acid used in the reaction prior to the reaction following the activation treatment, it is economical. It is preferable to use many organic carboxylic acids.

  The activation step is not limited to a single activation step, and may be constituted by a plurality of activation steps, and can be performed using activators having different acylation catalyst concentrations. For example, the acylating catalyst may be composed of a first activating step for activating cellulose with an activating agent and a second activating step for activating cellulose with an activating agent containing an acylating catalyst. You may comprise in the 1st process of processing cellulose with the activator with a low density | concentration, and the 2nd process of processing cellulose with the activator with the high density | concentration of an acylation catalyst.

  The amount of the activator used is, for example, about 25 to 150 parts by mass, preferably 30 to 125 parts by mass, and more preferably about 50 to 100 parts by mass (for example, 70 to 100 parts by mass) with respect to 100 parts by mass of cellulose. It may be.

  The activation treatment may be performed by treating cellulose with an activator, spraying the activator on cellulose, or immersing cellulose in the activator. Usually, raw material cellulose is often added to the activator to form a slurry. The activation treatment temperature can be selected from the range of 0 ° C to 100 ° C. In order to perform the activation treatment without applying an industrial load, it is usually 10 ° C to 40 ° C, preferably about 15 ° C to 35 ° C. It is. The activation treatment time can be selected in the range of 0.1 hours to 72 hours, and is usually about 0.1 hours to 3 hours, preferably about 0.2 hours to 2 hours.

  In the case of the present invention, when the solvent used for pulverizing the raw material cellulose is carboxylic acid, the activation process proceeds in the fine pulverization stage, so the standing time is short, and it is immediately put into the esterification reaction vessel. be able to.

  When a solution other than carboxylic acid such as water is used for pulverizing the raw material cellulose, the activation treatment is completed by washing with carboxylic acid several times, replacing with carboxylic acid, and allowing to stand.

[Esterification process]
The cellulose activated by the activation treatment is esterified with a carboxylic acid (containing at least one or more) having an acyl group having at least 2 carbon atoms and a carboxylic anhydride (containing at least one or more) in the presence of an acid catalyst. . As the acid catalyst, Lewis acid or strong acid can be used, but sulfuric acid is generally used.

  Usually, an acid anhydride [for example, an acid anhydride of a carboxylic acid having 2 or more carbon atoms (carboxylic anhydride)], for example, C2-6 alkanoic anhydride such as acetic anhydride, propionic anhydride, butyric anhydride, valeric anhydride, etc. Things can be used. A carboxylic acid having an acyl group having at least 2 carbon atoms (for example, at least a C2-6 carboxylic anhydride) is used. You may use these individually or in combination of 2 or more types. As long as it has an acyl group and is easily acylated, it is not limited to carboxylic acids, and organic acid halides can also be used.

  The amount of the acid catalyst (especially sulfuric acid) used in the esterification step is, for example, from 3 to 20 parts by mass, preferably from 5 to 18 parts by mass, more preferably from about 7 to 15 parts by mass with respect to 100 parts by mass of cellulose. It can be selected and is usually about 7 to 15 parts by mass.

  As the esterification solvent, an esterification solvent corresponding to at least an acyl group having 2 or more carbon atoms, for example, a carboxylic acid (acid anhydride) may be used, and for example, selected from acid anhydrides corresponding to C2-6 carboxylic acid A plurality of acid anhydrides having different carbon numbers may be used. For example, propionic anhydride and / or butyric anhydride and acetic anhydride may be used in combination.

  Preferred esterification solvents are C2-4 alkanecarboxylic anhydrides, for example, at least one selected from C2-4 carboxylic anhydrides (such as acetic anhydride or propionic anhydride), a combination of acetic anhydride and propionic anhydride, A combination of acetic anhydride and butyric anhydride, and a combination of acetic anhydride, propionic anhydride and butyric anhydride. In particular, a combination of acetic anhydride and propionic anhydride, and a combination of acetic anhydride and butyric anhydride are preferable. Acetic anhydride is more reactive than propionic anhydride and the like, and in the case of obtaining a cellulose mixed fatty acid ester having a low degree of acetyl group substitution, acetic anhydride is not used or the object of the present invention is not impaired. The esterification solvent having at least 3 carbon atoms and corresponding to the acyl group may be combined with a small amount of acetic anhydride.

  In the case of obtaining a cellulose ester having an acyl group having 3 or more carbon atoms, the esterification solvent may correspond to an acyl group having 3 or more carbon atoms, for example, propionic anhydride, if acylation or aging can be performed in the presence of acetic acid. What is necessary is just to comprise by butyric anhydride etc., and it does not necessarily need to contain the esterification solvent (acetic anhydride) corresponding to an acetyl group. In order to introduce an acetyl group, acetic anhydride is not necessarily used, and the reaction may be carried out in the presence of acetic acid.

  Such acetic acid may be present in the reaction system in the esterification step and the ripening step (particularly at least the ripening step), and may be composed only of acetic acid derived from the activation treatment. May be newly added, and may be used as an esterification solvent in an ordinary esterification step.

  In addition, when producing a cellulose ester using a plurality of esterification solvents, in the esterification step, a plurality of esterification solvents may coexist in the reaction system, and after esterifying cellulose with a specific esterification solvent The cellulose may be esterified with another esterification solvent. The usage-amount of the esterification solvent in an esterification process is 1.1-4 equivalent with respect to the hydroxyl group (hydroxyl group) of a cellulose, for example, Preferably it is 1.1-2 equivalent, More preferably, it is 1.3-1. About 8 equivalents.

  Only in the case of acetylation, when obtaining a cellulose ester having a small degree of acetyl substitution, the amount of acetic anhydride used in the esterification step is 0.5 equivalent or less (0 to 0) relative to the hydroxyl group (hydroxyl group) of cellulose. About 3 equivalents), 0.2 equivalents or less (0.01-0.1 equivalents), or substantially no use.

  In the esterification step, an esterification solvent (organic carboxylic acid such as acetic acid, propionic acid, butyric acid) is usually used as a solvent or diluent. The amount of the esterification solvent (carboxylic acid) used is about 50 to 700 parts by weight, preferably 150 to 600 parts by weight, and more preferably about 200 to 550 parts by weight with respect to 100 parts by weight of cellulose.

  In addition, esterification reaction can be performed at the temperature of about 0-50 degreeC, Preferably it is 5-45 degreeC, More preferably, it is about 10-40 degreeC. The esterification reaction may be performed at a relatively low temperature of 10 ° C. or less (0 to 10 ° C.) in the initial stage. The reaction time at such a low temperature may be, for example, 30 minutes or more, 40 minutes to 2 hours, preferably about 45 to 100 minutes) from the start of the esterification reaction. The esterification time at 10 to 50 ° C. is 10 minutes or longer and 20 to 90 minutes, preferably 30 to 80 minutes, 40 minutes to 75 minutes.

  When a uniform reaction system is formed, it can be determined that the esterification reaction has been completed.

  After completion of the esterification reaction, the hydrolysis reaction may be started, or the esterification solvent, the esterification solvent, and the acid catalyst may be left in the aging step as they are.

[Esterification reaction stopping step]
When the hydrolysis reaction is performed in order to deactivate the esterification solvent after the esterification reaction, it is sufficient if the esterification solvent can be deactivated, and usually at least water is often included. The quenching agent that promotes hydrolysis may be composed of at least one selected from water, an esterification solvent, an alcohol, and a neutralizing agent. More specifically, examples of the quenching agent include water alone, a mixture of water and carboxylic acid, a mixture of water and alcohol, a mixture of water and neutralizing agent, water, an organic carboxylic acid and alcohol, and the like. Examples thereof include a mixture with a hydrating agent.

  Examples of the neutralizing agent include bases that can neutralize part of the acid catalyst or esterification solvent, such as alkali metal compounds (hydroxides such as sodium hydroxide and potassium hydroxide, carbonates such as sodium carbonate and potassium carbonate, etc. , Organic acid salts such as sodium acetate and potassium acetate), alkaline earth metal compounds (eg, hydroxides such as calcium hydroxide, carbonates such as calcium carbonate, organic acid salts such as calcium acetate and magnesium acetate) And may be used alone or in combination of two or more. Examples of the alcohol include straight chain alcohols (ethanol, methanol, propanol, etc.). These alcohols can also be used alone or in combination of two or more.

  The ratio of water and esterification solvent or water and alcohol can be selected from the range of about 20 to 140 parts by mass of esterification solvent or alcohol with respect to 100 parts by mass of water, and usually 25 to 120 parts by mass, preferably 50. -100 mass parts.

  The hydrolysis after the esterification step and before the ripening step may contain a neutralizing agent in a ratio of partially neutralizing the acid catalyst or may not contain a neutralizing agent. The preferred deactivator may be water alone, but since water is a poor solvent for cellulose esters, there is a high possibility that cellulose esters other than the desired degree of substitution will precipitate. And a mixed solution is preferable.

  Since the reaction component contained in the raw material cellulose is not 100%, an unreacted component is included at this stage. Therefore, a process of filtering the reaction solution once may be introduced.

  This reaction stopping step can be omitted if necessary.

[Filtering process]
It is preferable to provide a filtration step between the esterification step and an aging step described later.

  The solution after completion of the esterification reaction contains unacetylated, low-acetylated components and impurities that did not react with the raw material cellulose. Time is further shortened, and specific cleavage of molecular chains and substituents occurring in the reaction solution is difficult to occur. The film surface quality of the film formed using the obtained cellulose ester is cellulose without filtration. Even better than the ester.

  Filter media used for filtration preferably have low absolute filtration accuracy. However, if the absolute filtration accuracy is too low, the filter media is likely to be clogged, and the filter media must be replaced frequently, resulting in reduced productivity. There is a problem of making it.

  The material of the filter medium is not particularly limited, and a normal filter medium can be used. However, a filter medium made of plastic such as polypropylene, polyester, and PTFE, a filter medium made of glass fiber, and a metal filter medium such as stainless steel fiber can be used. This is preferable because there is no dropout.

  Since the cellulose ester slurry contains an acid, a metal filter is easily corroded, and therefore, a filter made of glass fiber or plastic fiber is more preferable.

  When performing filtration using a metal filter between the esterification process and the aging process, it is possible to neutralize and deactivate sulfuric acid and carboxylic anhydride and then move to the filtration process without worrying about corrosion. Can be used.

  In the present invention, it is preferable to use a pressure filter equipped with the filter medium.

[Aging process]
In the ripening step, after the esterification reaction is almost completed, the acylation is performed to obtain a desired degree of substitution, and after the completion of the deacylation, a neutralizing agent is added to complete the series of reactions. .

  When the acid catalyst used for esterification is neutralized, the required amount of acid catalyst may be added again, or used in the aging process without neutralizing the acid catalyst (especially sulfuric acid) used in the esterification process. May be. An acid catalyst other than the acid catalyst used in the esterification may be added.

  If sulfuric acid is too much, the molecular weight may be reduced. Therefore, it is preferable to use the acid catalyst used in the esterification step as it is without adding an acid catalyst in the aging step.

  In addition, in the stage where the acid catalyst is neutralized later, the alkali metal or alkaline earth metal contained in the neutralizing agent is added in the neutralizing agent, and remains in the purified cellulose ester. It is preferable not to add sulfuric acid in the aging process because it can be an obstacle.

  In addition, a deacylation solvent (such as a mixed solution of water and carboxylic acid) may be newly added as necessary when aging.

  The reaction temperature during the aging step is preferably 20 to 90 ° C, preferably 25 to 80 ° C, more preferably 30 to 70 ° C. The aging reaction may be performed in a nitrogen atmosphere or in an air atmosphere. Also good.

  The aging reaction time can be selected from the range of 20 minutes or more and 25 minutes to 6 hours, preferably 30 minutes to 5 hours, and more preferably 1 to 3 hours.

[Neutralization process]
After the desired cellulose ester is obtained in the aging step, it is necessary to neutralize the acid catalyst used for deacylation. As the neutralizing agent, it is preferable to add a neutralizing agent composed of a base described in the esterification reaction stopping step.

  The reaction product (dope containing cellulose mixed fatty acid ester) is put into a precipitation solvent (water, aqueous acetic acid solution, etc.) to separate the cellulose mixed fatty acid ester, and free metal components and sulfuric acid components are removed by washing with water. May be. In addition, a neutralizing agent can also be used in the case of washing with water.

[Post-treatment process (precipitation, filtration, washing, drying)]
After neutralizing the acid catalyst in the neutralization step, the product is precipitated by precipitation.

  For precipitation, a mixed solution of water and carboxylic acid is preferably used. These precipitation solvents are not limited, and ketones, alcohols, ethers, esters and the like alone or water mixed solvents may be used.

  The process of filtering and washing the precipitated product is repeated until the free acid concentration is 500 ppm or less, preferably 300 ppm or less, and more preferably 150 ppm or less.

  Thereafter, the desired cellulose ester is obtained by drying with dry air.

  The cellulose ester treatment step in the present invention is preferably incorporated in the filtration step in the cellulose ester production. By incorporating it in the filtration step, it is possible to remove gel-like foreign matters without reducing productivity.

<Cellulose ester>
Although it does not specifically limit as a cellulose ester used for this invention, It is preferable that an ester group is a C2-C22 linear or branched carboxylic acid ester, Even if these carboxylic acid forms a ring. It may be an aromatic carboxylic acid ester. In addition, these carboxylic acids may have a substituent. The cellulose ester is particularly preferably a lower fatty acid ester having 6 or less carbon atoms.

  As a preferred cellulose ester, specifically, in addition to cellulose acetate, a propionate group or a butyrate group is bonded in addition to an acetyl group such as cellulose acetate propionate, cellulose acetate butyrate, and cellulose acetate propionate butyrate. Mention may be made of mixed fatty acid esters of cellulose. Of these, cellulose acetate propionate is particularly preferred.

  It is preferable that the cellulose acetate propionate used in the present invention satisfies the substitution degrees of the following formulas (1) and (2) at the same time.

Formula (1): 2.0 <= X + Y <= 2.9
Formula (2): 1.5 <= Y <= 2.7
(In the formula, X represents the degree of substitution of the acetyl group. Y represents the degree of substitution of the propionyl group.)
The measuring method of the substitution degree of these acyl groups can be measured according to ASTM-D817-96.

  The larger the total acyl group substitution degree, the better the dimensional change, haze, and water absorption.

  The cellulose ester that can be used in the present invention may be used by mixing resins having different degrees of substitution in order to obtain optical properties that meet the purpose. The mixing ratio is preferably 10:90 to 90:10 (mass ratio).

  The cellulose ester that can be used in the present invention can be used alone, but can also be used by mixing with two or more other resins. Examples of the resin to be mixed include acrylic resin, polyester resin, polycarbonate resin, polyamide resin, and vinyl resin. Among these, acrylic resins are preferably used.

  The mixing ratio of other resins that can be mixed with the cellulose used in the present invention is preferably 10:90 to 90:10 (mass ratio).

  The number average molecular weight of other resins that can be mixed with the cellulose used in the present invention is preferably in the range of 2000 to 150,000.

  The number average molecular weight of the cellulose ester used in the present invention is preferably in the range of 60,000 to 300,000 because the mechanical strength of the resulting film is strong. Furthermore, the thing of 70000-200000 is used preferably.

  The weight average molecular weight Mw and the number average molecular weight Mn of the cellulose ester and the resin to be mixed can be measured using gel permeation chromatography (GPC).

  An example of measurement conditions is as follows, but is not limited to this, and an equivalent measurement method can be used.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three products manufactured by Showa Denko KK)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corporation) Mw = 100000 to 500 calibration curves with 13 samples are used. Thirteen samples are used at approximately equal intervals.

  The cellulose used as a raw material for the cellulose ester used in the present invention is not particularly limited, and examples thereof include cotton linter, wood pulp, and kenaf. Moreover, the cellulose ester obtained from them can be mixed and used in arbitrary ratios, respectively.

  Cellulose esters such as cellulose acetate and cellulose acetate propionate used in the present invention can be produced by known methods. Specifically, it can be synthesized with reference to the method described in JP-A-10-45804.

[Cellulose ester solution]
The cellulose ester solution in the present invention may be prepared by dissolving the cellulose ester in a solvent, or may be adjusted to a liquid state by melting the cellulose ester.

  As the solvent for dissolving the cellulose ester, an organic solvent is preferably used. As described above, the cellulose ether acetate solution according to the present invention has an effect that it can be prepared using various kinds of organic solvents. That is, not only is it excellent in solubility in an organic solvent containing a halogen atom such as methylene chloride, but a solution can be prepared without using an organic solvent containing a halogen atom. However, the solution may of course be prepared using methylene chloride.

  Of these, halogenated solvents, ketone solvents, ester solvents and ether solvents are preferred. Ketones, esters and ethers may have a cyclic structure. The boiling point of the organic solvent is preferably less than 140 ° C, more preferably less than 100 ° C, and most preferably less than 70 ° C.

  Examples of organic solvents include dichloromethane (boiling point: 40 ° C.), acetone (boiling point: 56 ° C.), N-methylpyrrolidone (boiling point: 202 ° C.), tetrahydrofuran (boiling point: 65.4 ° C.), 1,4-dioxane ( Boiling point: 101.1 ° C), methyl acetate (boiling point: 57.8 ° C), ethyl formate (boiling point: 54 ° C), 2-methoxyethanol (boiling point: 124 ° C), acetic acid (boiling point: 118 ° C) Can do. Of these, dichloromethane, acetone, acetic acid, tetrahydrofuran and methyl acetate are particularly preferred. Two or more organic solvents may be used in combination. However, it can also be dissolved in a single solvent of methyl acetate. When two or more organic solvents are used in combination, the good solvent exemplified above and the other poor solvent may be used in combination. Examples of the poor solvent include lower alcohols having 1 to 4 carbon atoms (eg, methanol, n-butanol) and cyclohexane. When the good solvent and the poor solvent are used in combination, the proportion of the good solvent is preferably 50% by mass or more. More preferably, it is 70 mass% or more, Most preferably, it is 90 mass% or more.

  When heating, it is preferable to heat from the outside of the container. For example, a jacket type heating device can be used. The entire container can also be heated by providing a plate heater outside the container and piping to circulate the liquid. It is preferable to provide a stirring blade inside the container and stir using this. The stirring blade preferably has a length that reaches the vicinity of the wall of the container. A scraping blade is preferably provided at the end of the stirring blade in order to renew the liquid film on the vessel wall. Instruments such as a pressure gauge and a thermometer may be installed in the container. Each component is dissolved in a solvent in the container. The prepared dope is taken out of the container after cooling, or taken out and then cooled using a heat exchanger or the like. The concentration of cellulose ether acetate in the solution to be prepared is determined according to the use of the solution. The concentration in the solution is generally 5 to 50% by mass, preferably 10 to 40% by mass. When the cellulose ether acetate solution is used for film production, the viscosity of the solution is preferably in the range of 10,000 to 1,000,000 cP. Preparation of these cellulose ester solutions is described in JP-A-08-231761.

  When adjusting the cellulose ester solution in this invention by melt | dissolving a cellulose ester, as the melting temperature, 200-300 degreeC is preferable, 220-290 degreeC is more preferable, 230-280 degreeC is the most preferable. By making this temperature range, decomposition of the cellulose ester can be suppressed.

In the present invention, it is possible to produce an optical film by dissolving the cellulose ester in a solvent and filtering the silicon dioxide particles having a specific surface area of 30 to 1000 m ² / g. It can also be taken out as a solid by adding a poor solvent.

<Additives>
(Plasticizer)
The cellulose ester used in the present invention can contain a plasticizer. The plasticizer is not particularly limited, but is preferably a polycarboxylic acid ester plasticizer, a glycolate plasticizer, a phthalate ester plasticizer, a fatty acid ester plasticizer, a polyhydric alcohol ester plasticizer, or a polyester. It is selected from plasticizers, acrylic plasticizers and the like. Of these, when two or more plasticizers are used, at least one plasticizer is preferably a polyhydric alcohol ester plasticizer.

  The polyhydric alcohol ester plasticizer is a plasticizer comprising an ester of a dihydric or higher aliphatic polyhydric alcohol and a monocarboxylic acid, and preferably has an aromatic ring or a cycloalkyl ring in the molecule. Preferably it is a 2-20 valent aliphatic polyhydric alcohol ester.

  The polyhydric alcohol preferably used in the present invention is represented by the following general formula (a).

General formula (a): Ra- (OH) _n
(However, Ra represents an n-valent organic group, n represents a positive integer of 2 or more, and an OH group represents an alcoholic and / or phenolic hydroxyl group (hydroxyl group).)
Examples of preferred polyhydric alcohols include the following, but the present invention is not limited to these. Adonitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1,2-butanediol, 1,3- Butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol, 1,6-hexanediol, hexanetriol, galactitol, mannitol, 3-methylpentane- Examples include 1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, xylitol and the like. In particular, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane, and xylitol are preferable.

  There is no restriction | limiting in particular as monocarboxylic acid used for polyhydric alcohol ester, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid, etc. can be used. Use of an alicyclic monocarboxylic acid or aromatic monocarboxylic acid is preferred in terms of improving moisture permeability and retention.

  Examples of preferred monocarboxylic acids include the following, but the present invention is not limited thereto.

  As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-10. When acetic acid is contained, the compatibility with the cellulose ester is increased, and it is also preferable to use a mixture of acetic acid and another monocarboxylic acid.

  Preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanoic acid, undecylic acid, lauric acid, tridecylic acid, Saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, laccelic acid, undecylenic acid, olein Examples thereof include unsaturated fatty acids such as acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid.

  Examples of preferred alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or derivatives thereof.

  Examples of preferred aromatic monocarboxylic acids include those in which 1 to 3 alkoxy groups such as alkyl group, methoxy group or ethoxy group are introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, biphenylcarboxylic acid, Examples thereof include aromatic monocarboxylic acids having two or more benzene rings such as naphthalenecarboxylic acid and tetralincarboxylic acid, or derivatives thereof. Benzoic acid is particularly preferable.

  The molecular weight of the polyhydric alcohol ester is not particularly limited, but is preferably 300 to 1500, and more preferably 350 to 750. A higher molecular weight is preferred because it is less likely to volatilize, and a smaller one is preferred in terms of moisture permeability and compatibility with cellulose ester.

  The carboxylic acid used for the polyhydric alcohol ester may be one kind or a mixture of two or more kinds. Moreover, all the OH groups in the polyhydric alcohol may be esterified, or a part of the OH groups may be left as they are.

  The glycolate plasticizer is not particularly limited, but alkylphthalylalkyl glycolates can be preferably used. Examples of alkyl phthalyl alkyl glycolates include methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, octyl phthalyl octyl glycolate, methyl phthalyl ethyl Glycolate, ethyl phthalyl methyl glycolate, ethyl phthalyl propyl glycolate, methyl phthalyl butyl glycolate, ethyl phthalyl butyl glycolate, butyl phthalyl methyl glycolate, butyl phthalyl ethyl glycolate, propyl phthalyl butyl glycol Butyl phthalyl propyl glycolate, methyl phthalyl octyl glycolate, ethyl phthalyl octyl glycolate, octyl phthalyl methyl glycolate, octyl phthalate Ethyl glycolate, and the like.

  Examples of the phthalate ester plasticizer include diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dioctyl phthalate, dicyclohexyl phthalate, and dicyclohexyl terephthalate.

  Examples of the citrate plasticizer include acetyl trimethyl citrate, acetyl triethyl citrate, and acetyl tributyl citrate.

  Examples of fatty acid ester plasticizers include butyl oleate, methylacetyl ricinoleate, and dibutyl sebacate.

  Examples of the phosphate ester plasticizer include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate and the like.

  The polyvalent carboxylic acid ester compound is composed of an ester of divalent or higher, preferably divalent to 20 valent polyvalent carboxylic acid and alcohol. The aliphatic polyvalent carboxylic acid is preferably 2 to 20 valent, and in the case of an aromatic polyvalent carboxylic acid or an alicyclic polyvalent carboxylic acid, it is preferably 3 to 20 valent.

  The polyvalent carboxylic acid is represented by the following general formula (b).

General formula (b): Rb (COOH) _m (OH) _n
(Where Rb is an (m + n) -valent organic group, m is a positive integer of 2 or more and 6 or less, n is an integer of 0 or more and 4 or less, a COOH group is a carboxyl group, and an OH group is an alcoholic or phenolic hydroxyl group. Represents a group (hydroxyl group).
Examples of preferred polyvalent carboxylic acids include the following, but the present invention is not limited to these. Trivalent or higher aromatic polyvalent carboxylic acids such as trimellitic acid, trimesic acid, pyromellitic acid or derivatives thereof, succinic acid, adipic acid, azelaic acid, sebacic acid, oxalic acid, fumaric acid, maleic acid, tetrahydrophthal An aliphatic polyvalent carboxylic acid such as an acid, an oxypolyvalent carboxylic acid such as tartaric acid, tartronic acid, malic acid and citric acid can be preferably used. In particular, it is preferable to use an oxypolycarboxylic acid from the viewpoint of improving retention.

  There is no restriction | limiting in particular as alcohol used for the said polyhydric carboxylic acid ester compound, Well-known alcohol and phenols can be used. For example, an aliphatic saturated alcohol or aliphatic unsaturated alcohol having a straight chain or side chain having 1 to 32 carbon atoms can be preferably used. It is more preferable that it is C1-C20, and it is especially preferable that it is C1-C10. In addition, alicyclic alcohols such as cyclopentanol and cyclohexanol or derivatives thereof, aromatic alcohols such as benzyl alcohol and cinnamyl alcohol, or derivatives thereof can also be preferably used.

  When an oxypolycarboxylic acid is used as the polycarboxylic acid, the alcoholic or phenolic hydroxyl group (hydroxyl group) of the oxypolycarboxylic acid may be esterified with a monocarboxylic acid. Examples of preferred monocarboxylic acids include the following, but the present invention is not limited thereto.

  As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. It is more preferable that it is C1-C20, and it is especially preferable that it is C1-C10.

  Preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid, tridecylic acid, Saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, and laccelic acid, undecylenic acid, olein Examples thereof include unsaturated fatty acids such as acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid.

  Examples of preferred alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or derivatives thereof.

  Examples of preferred aromatic monocarboxylic acids include those in which an alkyl group is introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, and two or more rings such as biphenylcarboxylic acid, naphthalenecarboxylic acid, and tetralincarboxylic acid. Aromatic monocarboxylic acids possessed by them, or derivatives thereof.

  Of these monocarboxylic acids, acetic acid, propionic acid, and benzoic acid are particularly preferable.

  The molecular weight of the polyvalent carboxylic acid ester compound is not particularly limited, but is preferably in the range of 300 to 1000, and more preferably in the range of 350 to 750. The larger one is preferable in terms of improvement in retention, and the smaller one is preferable in terms of moisture permeability and compatibility with cellulose ester.

  The alcohol used for the polyvalent carboxylic acid ester may be one kind or a mixture of two or more kinds.

  The acid value of the polyvalent carboxylic acid ester compound is preferably 1 mgKOH / g or less, and more preferably 0.2 mgKOH / g or less. Setting the acid value in the above range is preferable because the environmental fluctuation of the retardation is also suppressed.

(Acid value)
The acid value in the present invention refers to the number of milligrams of potassium hydroxide necessary for neutralizing the acid (carboxyl group present in the sample) contained in 1 g of the sample. The acid value is measured according to JIS K0070.

  Examples of particularly preferred polyvalent carboxylic acid ester compounds are shown below, but the present invention is not limited thereto. For example, triethyl citrate, tributyl citrate, acetyl triethyl citrate (ATEC), acetyl tributyl citrate (ATBC), benzoyl tributyl citrate, acetyl triphenyl citrate, acetyl tribenzyl citrate, dibutyl tartrate, diacetyl dibutyl tartrate, Examples include tributyl trimellitic acid and tetrabutyl pyromellitic acid.

  The polyester plasticizer is not particularly limited, and a polyester plasticizer having an aromatic ring or a cycloalkyl ring in the molecule can be used. Although it does not specifically limit as a polyester plasticizer, For example, the aromatic terminal ester plasticizer represented by the following general formula (c) can be used.

General formula (c): B-COO-((G-O-) _m- CO-A-COO-) _n G-O-CO-B
(In the formula, B represents a benzene ring and may have another substituent. G represents an alkylene group having 2 to 12 carbon atoms, an arylene group having 6 to 12 carbon atoms, or an oxyalkylene having 4 to 12 carbon atoms. Group A represents an alkylene group having 2 to 10 carbon atoms or an arylene group having 4 to 10 carbon atoms, and m and n represent a repeating unit.)
The compound of the general formula (c) includes a benzene monocarboxylic acid group represented by BCOOH, an alkylene glycol group, an oxyalkylene glycol group or an aryl glycol group represented by HO— (GO—) ₁ H, HOCO-A It is synthesized from an alkylenedicarboxylic acid group or aryldicarboxylic acid group represented by —COO—H, and can be obtained by the same reaction as that of a normal polyester plasticizer.

  Examples of the benzene monocarboxylic acid component of the raw material of the polyester plasticizer include, for example, benzoic acid, para-tert-butyl benzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethyl benzoic acid, ethyl benzoic acid, normal propyl benzoic acid, There are aminobenzoic acid, acetoxybenzoic acid and the like, and these can be used as one kind or a mixture of two or more kinds, respectively.

  Examples of the alkylene glycol component of the polyester plasticizer include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,2-propane. Diol, 2-methyl 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2,2-diethyl- 1,3-propanediol (3,3-dimethylolpentane), 2-n-butyl-2-ethyl-1,3-propanediol (3,3-dimethylolheptane), 3-methyl-1,5-pentane Diol 1,6-hexanediol, 2,2,4-trimethyl 1,3-pentanediol, 2-ethyl 1,3-he There are sundiol, 2-methyl 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-octadecanediol, etc., and these glycols are used as one kind or a mixture of two or more kinds. used. In particular, an alkylene glycol having 2 to 12 carbon atoms is particularly preferable because of excellent compatibility with a cellulose ester.

  Examples of the oxyalkylene glycol component having 4 to 12 carbon atoms as the raw material for the aromatic terminal ester include diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol. , One or a mixture of two or more.

  Examples of the alkylene dicarboxylic acid component having 4 to 12 carbon atoms as the raw material for the aromatic terminal ester include succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid. These are used as one kind or a mixture of two or more kinds. Examples of the arylene dicarboxylic acid component having 6 to 12 carbon atoms include phthalic acid, terephthalic acid, isophthalic acid, 1,5-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, and the like.

  The polyester plasticizer has a number average molecular weight of preferably 300 to 1500, more preferably 400 to 1000. The acid value is 0.5 mgKOH / g or less, the hydroxyl (hydroxyl) value is 25 mgKOH / g or less, preferably the acid value is 0.3 mgKOH / g or less, and the hydroxyl (hydroxyl) value is 15 mgKOH / g or less. is there.

(Acrylic polymer)
The cellulose ester solution in the present invention can also contain a (meth) acrylic polymer as a plasticizer.

  The (meth) acrylic polymer is preferably a polymer Y having a weight average molecular weight of 500 or more and 3000 or less obtained by polymerizing an ethylenically unsaturated monomer Ya having no aromatic ring.

  The (meth) acrylic polymer includes at least an ethylenically unsaturated monomer Xa having no aromatic ring and a hydroxyl group (hydroxyl group) in the molecule, and ethylene having a hydroxyl group (hydroxyl group) without an aromatic ring in the molecule. The weight average molecular weight 500 obtained by polymerizing the polymer X having a weight average molecular weight of 3000 to 30,000 obtained by copolymerization with the unsaturated unsaturated monomer Xb and the ethylenically unsaturated monomer Ya having no aromatic ring More preferably, it is a mixture of the polymer Y of 3000 or less.

  More preferably, the polymer X is represented by the following general formula (X), and the polymer Y is represented by the following general formula (Y).

Formula (X):
_{- [CH 2 -C (Rc)} (CO 2 Rd) -] m - [CH 2 -C (Re) (CO 2 Rf-OH) -] n - [Xc] p -
General formula (Y):
_{Ry- [CH 2 -C (Rg)} (CO 2 Rh-OH) -] k - [Yb] q -
(In the formula, Rc, Re and Rg represent H or CH _3. Rd represents an alkyl group having 1 to 12 carbon atoms and a cycloalkyl group. Rf and Rh represent —CH ₂ — and —C ₂ H ₄ —. Or -C ₃ H _6- , Ry represents OH, H or an alkyl group having 3 or less carbon atoms, Xc represents a monomer unit that can be polymerized to Xa and Xb, and Yb can be copolymerized to Ya Represents a monomer unit, m, n, k, p and q represent molar composition ratios, provided that m ≠ 0, n ≠ 0, and k ≠ 0.
As addition amount of these plasticizers, it is preferable to contain 0.5-30 mass% with respect to the total mass of the said polymer (A) and a cellulose ester, It is preferable to contain especially 5-20 mass%. .

(UV absorber)
The cellulose ester solution in the present invention can also contain an ultraviolet absorber. The ultraviolet absorber is intended to improve durability by absorbing ultraviolet rays of 400 nm or less, and in particular, the transmittance at a wavelength of 370 nm is preferably 10% or less, more preferably 5% or less, and further Preferably it is 2% or less.

  The ultraviolet absorber is not particularly limited, and examples thereof include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, triazine compounds, nickel complex compounds, inorganic powders, and the like. It is done.

  For example, 5-chloro-2- (3,5-di-sec-butyl-2-hydroxyphenyl) -2H-benzotriazole, (2-2H-benzotriazol-2-yl) -6- (linear and side Chain dodecyl) -4-methylphenol, 2-hydroxy-4-benzyloxybenzophenone, 2,4-benzyloxybenzophenone, etc., and tinuvin 109, tinuvin 171, tinuvin 234, tinuvin 326, tinuvin 327, tinuvin 328, There are tinuvins such as tinuvin 928, all of which are commercially available from Ciba Japan and can be preferably used.

  The UV absorbers preferably used in the present invention are benzotriazole UV absorbers, benzophenone UV absorbers, and triazine UV absorbers, particularly preferably benzotriazole UV absorbers and benzophenone UV absorbers. .

  In addition, a discotic compound such as a compound having a 1,3,5-triazine ring is also preferably used as the ultraviolet absorber.

  The cellulose ester solution in the present invention preferably contains two or more ultraviolet absorbers. As the UV absorber, a polymer UV absorber can also be preferably used, and in particular, a polymer type UV absorber described in JP-A-6-148430 is preferably used.

  The method of adding the UV absorber can be added to the dope after dissolving the UV absorber in an alcohol such as methanol, ethanol or butanol, an organic solvent such as methylene chloride, methyl acetate, acetone or dioxolane or a mixed solvent thereof. Or you may add directly in dope composition.

  For an inorganic powder that does not dissolve in an organic solvent, a dissolver or a sand mill is used in the organic solvent and cellulose ester to disperse and then added to the dope.

  The amount of the UV absorber used is not uniform depending on the type of UV absorber, the operating conditions, etc., but when the dry film thickness of the optical film is 30 to 200 μm, it is 0.5 to 10 with respect to the polarizing plate protective film. % By mass is preferable, and 0.6 to 4% by mass is more preferable.

(Antioxidant)
Antioxidants are also referred to as deterioration inhibitors. When a liquid crystal image display device or the like is placed in a high humidity and high temperature state, the optical film may be deteriorated.

  The antioxidant has a role of delaying or preventing the optical film from being decomposed by, for example, the residual solvent amount of halogen in the optical film or phosphoric acid of the phosphoric acid plasticizer. It is preferable to contain.

  As such an antioxidant, a hindered phenol compound is preferably used. For example, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di- -T-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3 -(3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino)- 1,3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octa Sil-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide) 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxy Benzyl) -isocyanurate and the like.

  In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3 -(3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di- A phosphorus processing stabilizer such as t-butylphenyl) phosphite may be used in combination.

  The addition amount of these compounds is preferably 1 ppm to 1.0%, more preferably 10 to 1000 ppm in terms of mass ratio with respect to the total mass of the polymer (A) and the cellulose ester.

(Fine particles)
Fine particles can be added to the cellulose ester solution in the present invention after the treatment step of the cellulose ester solution.

  Examples of the fine particles include inorganic compounds such as silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, and aluminum silicate. And magnesium silicate and calcium phosphate. Further, fine particles of an organic compound can also be preferably used. Examples of organic compounds are polytetrafluoroethylene, cellulose acetate, polystyrene, polymethyl methacrylate, polypropyl methacrylate, polymethyl acrylate, polyethylene carbonate, acrylic styrene resin, silicone resin, polycarbonate resin, benzoguanamine resin, melamine resin Also, pulverized and classified products of organic polymer compounds such as polyolefin-based powders, polyester-based resins, polyamide-based resins, polyimide-based resins, polyfluorinated ethylene-based resins, and starches. Alternatively, a polymer compound synthesized by a suspension polymerization method, a polymer compound made spherical by a spray drying method or a dispersion method, or an inorganic compound can be used.

  Fine particles containing silicon are preferable in terms of low turbidity, and silicon dioxide is particularly preferable.

  The average primary particle diameter of the fine particles is preferably 5 to 400 nm, and more preferably 10 to 300 nm.

  These may be mainly contained as secondary aggregates having a particle size of 0.05 to 0.3 μm, and may be contained as primary particles without being aggregated if the particles have an average particle size of 100 to 400 nm. preferable.

  The content of these fine particles in the cellulose ester is preferably 0.01 to 1% by mass, particularly preferably 0.05 to 0.5% by mass.

  Silicon dioxide fine particles are commercially available under the trade names of, for example, Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600 (manufactured by Nippon Aerosil Co., Ltd.). it can.

  Zirconium oxide fine particles are commercially available, for example, under the trade names Aerosil R976 and R811 (manufactured by Nippon Aerosil Co., Ltd.) and can be used.

  Examples of the polymer include silicone resin, fluororesin, and acrylic resin. Silicone resins are preferable, and those having a three-dimensional network structure are particularly preferable. It is marketed by name and can be used.

  Among these, Aerosil 200V and Aerosil R972V are particularly preferably used because they have a large effect of reducing the friction coefficient while keeping the turbidity of the optical film low. In the said optical film, it is preferable that the dynamic friction coefficient of at least one surface is 0.2-1.0.

  Various additives may be batch-added to a dope that is a resin-containing solution before film formation, or an additive solution may be separately prepared and added in-line. In particular, in order to reduce the load on the filter medium, it is preferable to add a part or all of the fine particles in-line.

  When the additive solution is added in-line, it is preferable to dissolve a small amount of resin in order to improve mixing with the dope. A preferable amount of the resin is 1 to 10 parts by mass, and more preferably 3 to 5 parts by mass with respect to 100 parts by mass of the solvent.

  In order to perform in-line addition and mixing in the present invention, for example, an in-line mixer such as a static mixer (manufactured by Toray Engineering), SWJ (Toray static type in-tube mixer Hi-Mixer) or the like is preferably used.

<Method for producing optical film>
The cellulose ester in the present invention can be directly formed as an optical film after undergoing the treatment step.

  Hereinafter, the manufacturing method of the said optical film is demonstrated.

  The optical film can be preferably used regardless of whether it is a film produced by a solution casting method or a film produced by a melt casting method.

  The optical film is produced by dissolving a resin and additives in a solvent to prepare a dope, casting a dope onto an endless metal support that moves indefinitely, and drying the cast dope as a web. It is carried out by a step, a step of peeling from the metal support, a step of stretching or maintaining the width, a step of further drying, and a step of winding up the finished film.

  The process for preparing the dope will be described. It is preferable that the concentration of the resin in the dope is higher because the drying load after casting on the metal support can be reduced. However, if the concentration of the resin is too high, the load during filtration increases and the filtration accuracy deteriorates. As a density | concentration which makes these compatible, 10-35 mass% is preferable, More preferably, it is 15-25 mass%.

  As a method for dissolving the resin when preparing the dope described above, a general method can be used. When heating and pressurization are combined, it is possible to heat above the boiling point at normal pressure. It is preferable to stir and dissolve while heating at a temperature that is equal to or higher than the boiling point of the solvent at normal pressure and that the solvent does not boil under pressure, in order to prevent the generation of massive undissolved materials called gels and mamacos. Moreover, after mixing resin with a poor solvent and making it wet or swell, the method of adding a good solvent and melt | dissolving is also used preferably.

  The pressurization may be performed by a method of injecting an inert gas such as nitrogen gas or a method of developing the vapor pressure of the solvent by heating. Heating is preferably performed from the outside. For example, a jacket type is preferable because temperature control is easy.

  The heating temperature with the addition of the solvent is preferably higher from the viewpoint of the solubility of the resin, but if the heating temperature is too high, the required pressure increases and the productivity deteriorates. A preferable heating temperature is 45 to 120 ° C, more preferably 60 to 110 ° C, and still more preferably 70 to 105 ° C. The pressure is adjusted so that the solvent does not boil at the set temperature.

  Alternatively, a cooling dissolution method is also preferably used. For example, cellulose ester or the like can be dissolved in a solvent such as methyl acetate.

  Next, the solution in which the resin is dissolved is filtered using a suitable filter medium such as filter paper. As the filter medium, it is preferable that the absolute filtration accuracy is small in order to remove insoluble matters and the like, but there is a problem that the filter medium is likely to be clogged if the absolute filtration accuracy is too small. For this reason, a filter medium with an absolute filtration accuracy of 0.008 mm or less is preferable, a filter medium with 0.001 to 0.008 mm is more preferable, and a filter medium with 0.003 to 0.006 mm is still more preferable.

  There are no particular restrictions on the material of the filter medium, and ordinary filter media can be used. However, plastic filter media such as polypropylene and Teflon (registered trademark), and metal filter media such as stainless steel do not drop off fibers. preferable. It is preferable to remove and reduce impurities, particularly bright spot foreign matter, contained in the raw material resin by filtration.

  “Bright spot foreign matter” means that two polarizing plates are placed in a crossed Nicols state, an optical film or the like is placed between them, light is applied from one polarizing plate, and observation is performed from the other polarizing plate. It is a point (foreign matter) that the light from the opposite side appears to leak.

  “Gel-like foreign material” means that two polarizing plates are placed in a crossed Nicols state, an optical film or the like is placed between them, light is applied from one polarizing plate, and observation is performed from the other polarizing plate. In this case, the light from the opposite side does not leak, but it is observed as irregularities on the film surface and refers to a foreign material that is indefinite when viewed with a transmission microscope.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited at all by these Examples.

Synthesis of Silicon Dioxide Fine Particles No. 3 sodium silicate aqueous solution was diluted so that the SiO ₂ equivalent concentration was 5.1% by mass. While maintaining this at 42 ° C., with stirring, a 19% by mass aqueous sulfuric acid solution was added over 10 minutes until pH = 10 to obtain a partially neutralized silica slurry. While stirring this slurry, the temperature was raised to 70 ° C., and further 21% by mass of sulfuric acid was added over 60 minutes until pH = 6 to obtain a completely neutralized silica slurry. This slurry was washed with water, filtered to form a silica hydrogel, dried and fired to obtain silica gels having various physical properties shown in Tables 1 and 2. The specific surface area, pore volume, and surface silanol groups were controlled by adjusting sodium silicate aqueous solution and sulfuric acid aqueous solution, concentration, mixing ratio, etc., or aging treatment.

  The pore characteristics of silica gel were measured by a nitrogen adsorption / desorption method. Here, the specific surface area was determined by the BET method and the pore volume was determined by the BJH method. Infrared absorption spectra were measured with diffuse reflected light after the sample was diluted with KBr.

<Preparation of film 1>
Dissolve 10 parts by mass of cellulose acetate propionate having a degree of acetyl substitution of 0.19, a degree of propionyl substitution of 2.56, and a total degree of substitution of 2.75 with respect to 100 parts by mass of dichloromethane. Suspended and stirred. After 2 hours, stirring was stopped, and three filter papers with a retained particle size of 3 to 5 μm were stacked and filtered using a sealed pressure filter. After the filtrate was concentrated under reduced pressure, the solution was adjusted so that dichloromethane was 43 parts by mass and ethanol was 4 parts by mass with respect to 10 parts by mass of the cellulose ester. Film 1 was obtained by forming this solution into a film thickness of 40 μm.

<Production of Film 2 to Film 13>
Films 2 to 13 were produced in the same manner as the film 1 except that the silicon dioxide fine particles were changed to numbers 2 to 13.

<Preparation of film 14>
10 parts by mass of cellulose acetate propionate having an acetyl substitution degree of 0.78, a propionyl substitution degree of 1.86 and a total substitution degree of 2.64 are dissolved in 100 parts by mass of acetic acid. Suspended and stirred. After 2 hours, stirring was stopped, and three filter papers with a retained particle size of 3 to 5 μm were stacked and filtered using a sealed pressure filter. While maintaining the filtrate at 20 ° C., a solution of acetic acid / water = 1/1 was added dropwise, and 50 parts by mass of a solution of acetic acid / water = 1/1 was further added and stirred from where the powder precipitated in the solution. . After 1 hour, it was filtered, washed with pure and confirmed to have a pH = 7 and dried.

  After drying until the loss on drying was 0.1% by mass, the solution was adjusted so that the obtained cellulose ester powder had 43 parts by mass of dichloromethane and 4 parts by mass of ethanol with respect to 10 parts by mass. A film 14 was obtained by forming this solution into a film thickness of 40 μm.

<Preparation of film 15>
A film 15 was produced in the same manner as the film 14 except that acetic acid was changed to acetone.

<Preparation of film 16>
A film 16 was produced in the same manner as the film 14 except that acetic acid was changed to methyl acetate.

<Preparation of film 17>
A film 17 was produced in the same manner as the film 14 except that acetic acid was changed to tetrahydrofuran.

<Preparation of film 18>
Dissolve 10 parts by mass of cellulose acetate propionate having an acetyl substitution degree of 1.01, a propionyl substitution degree of 1.53, and a total substitution degree of 2.54 with respect to 100 parts by mass of dichloromethane. Suspended and stirred. After 2 hours, the stirring was stopped, three filter papers having a retained particle size of 3 to 5 μm were stacked, and 10 parts by mass of Celite 505 (Merck) was filled on the filter paper in the sealed pressure filter and filtered. After the filtrate was concentrated under reduced pressure, the solution was adjusted so that dichloromethane was 43 parts by mass and ethanol was 4 parts by mass with respect to 10 parts by mass of the cellulose ester. A film 14 was obtained by forming this solution into a film thickness of 40 μm.

<Preparation of films 19-20>
The film 19 and the film 20 were produced by the same method as the production of the film 18 except that the silicon dioxide fine particles were changed to numbers 19 to 20.

<Preparation of film 21>
<Manufacture of cellulose ester>
100 parts by mass of raw pulp (α-cellulose 93% or more) and 98 parts by mass of glacial acetic acid were put into a mixer and stirred to form a slurry, and then charged into a stone mill and pulverized at 40 ° C. for 30 minutes. The average pulverized particle size of the pulverized raw material pulp was 61 μm by microscopic observation.

  Next, 50 parts by mass of acetic acid was added to the pulverized raw material pulp, and an activation treatment was performed for 1.2 hours.

  The acetic acid-containing pulp is put into a reactor, and further 250 parts by weight of propionic anhydride, 420 parts by weight of propionic anhydride, and 9 parts by weight of sulfuric acid are added, and the temperature is gradually raised from room temperature to 40 ° C. while keeping the temperature at 40 ° C. The temperature was kept for 1 hour to allow the esterification reaction to proceed.

  Next, after neutralizing by adding 265 parts of 30% aqueous acetic acid solution in the primary neutralization step, 145 parts by mass of 80% aqueous acetic acid solution was added to hydrolyze the remaining carboxylic anhydrides in the aging step, The mixture was kept at 0 ° C. and stirred for 1 hour.

  Thereafter, to stop the reaction, 16 parts by mass of a 30% by mass aqueous magnesium acetate solution was added to neutralize the sulfuric acid.

  Next, 40 parts by mass of No. 21 silicon dioxide fine particles were added and stirred for 3 hours, and then the silicon dioxide fine particles were filtered by a pressure filter using a metal nonwoven fabric filter having a retention particle size of about 3 μm.

  The cellulose ester precipitated in the precipitation step was filtered off, washed 7 times with warm water of 50 ° C., and the remaining acetic acid aqueous solution was eluted, followed by drying at 70 ° C. for 3 hours, acetyl substitution degree 0.56, propionyl substitution A cellulose ester which is cellulose acetate propionate having a degree of 2.09 and a total degree of substitution of 2.65 was obtained. The weight average molecular weight (Mw) was 200,000 as a result of measurement using the following measurement method.

  The solution was adjusted such that dichloromethane was 43 parts by mass and ethanol was 4 parts by mass with respect to 10 parts by mass of the obtained cellulose ester. A film 21 was obtained by forming this solution into a film thickness of 40 μm.

<Production of films 22 to 25>
Films 22 to 25 were produced in the same manner as the production of film 1 except that the silicon dioxide fine particles were changed to numbers 22 to 25.

<Preparation of film 26>
10 parts by mass of cellulose acetate propionate having an acetyl substitution degree of 0.19, a propionyl substitution degree of 2.56, and a total substitution degree of 2.75 was dissolved in a solution of 43 parts by mass of dichloromethane and 4 parts by mass of ethanol. A film 25 was obtained by forming this solution into a film thickness of 40 μm.

<Preparation of film 27>
Silicon dioxide fine particles were changed to particles having a specific surface area of 4 m ² / gm, a pore volume of 0.4 ml / g, a silicon dioxide composition of 95%, an average particle size of 70 μm, a particle size standard deviation of 20 μm, and a bulk density of 0.45 g / cm ^3. A film 26 was produced in the same manner as in the production of the film 1 except that.

<Production of Film IR-1>
The film IR-1 was prepared in the same manner as the production of the film 1 except that the silicon dioxide fine particles were changed to the silicon dioxide fine particles IR-1 to IR-7 having the IR intensity ratio (infrared absorption intensity ratio) shown in Table 2. -Film IR-7 was produced.

<Evaluation method>
Measurement of amount of bright spot foreign matter Two polarizing plates are placed in an orthogonal state (crossed nicols) to block transmitted light, and the prepared sample is placed between the two polarizing plates. The polarizing plate used was a glass protective plate. Light was irradiated from one side, and the number of bright spots having a diameter of 0.01 mm or more per 100 cm ² was counted with an optical microscope (50 times) from the opposite side.

Measurement of the amount of gel-like foreign matters Gel-like foreign matters having a diameter of 0.02 mm or more per 100 cm ² were counted with an optical microscope (50 times). The gel-like foreign matters were counted after confirming that they were not bright spot foreign matters in the crossed Nicols state.

Evaluation of filterability Filtration time was measured when three sheets of filter paper having a retention particle size of 3 to 5 μm were stacked and filtered on a sealed pressure filter having a filtration area of 64 cm ² . A filtration rate of 50 ml / min or more was rated as ◎, 40-50 ml / min as ○, 20-40 ml / min as Δ, and 20 ml / min or less as x.

  The above evaluation results are shown in Tables 1 and 2.

  From the above results, it is possible to remove gel-like foreign matters by using the processing method according to the method for producing cellulose ester of the present invention. Moreover, when the IR intensity ratio (infrared absorption intensity ratio) of the silanol group is within a preferable range in the present invention, the ability to remove gel-like foreign matters is further excellent.

Claims (3)

Gelatinous foreign matter comprising a step of treating cellulose ester with silicon dioxide particles having a specific surface area of 30 to 1000 m ² / g and removing the silicon dioxide particles from the treated cellulose ester . A method for producing a cellulose ester having a very low content .   The method for producing a cellulose ester according to claim 1, wherein the pore volume of the silicon dioxide particles is in the range of 0.5 to 2.0 ml / g. In the step of removing the silicon dioxide particles obtained by processing the cellulose ester, cellulose ester The method according to claim 1 or claim 2, characterized by using silicon dioxide fine particles as a filter aid.