JP6200868B2 - Manufacturing method of optical film - Google Patents

Description

  The present invention relates to an optical film manufacturing method and an optical film.

The demand for liquid crystal display devices is expanding in applications such as liquid crystal televisions and personal computer liquid crystal displays. In general, a liquid crystal display device is composed of a liquid crystal cell in which a transparent electrode, a liquid crystal layer, a color filter, etc. are sandwiched between glass plates, and two polarizing plates provided on both sides thereof. The element (also referred to as a polarizing film or a polarizing film) is sandwiched between two optical films (polarizing plate protective film). As the material of the optical film, various polymers are used. For example, acrylic resins such as polymethyl methacrylate (also referred to as PMMA) are used.
On the other hand, as a method for forming an optical film, the solution film forming method is excellent in thickness unevenness and surface smoothness of the obtained film. Therefore, as a method for manufacturing various optical films such as a polarizing plate protective film and a retardation film. Used in a wide range of fields. The solution film forming method is a film forming method in which a dope composition containing a polymer and a solvent is cast on a support to form a cast film, and a film is formed through a process of drying the solvent.
Patent Document 1 describes a method for producing an optical film by drying a film at a high temperature and then stretching the film as a method for producing an optical film using an acrylic resin by a solution casting method. Patent Documents 2 and 3 also describe methods for obtaining an optical film by drying an acrylic resin film at a high temperature.

JP 2007-118266 A International Publication No. 2009/150926 JP 2014-38180 A

  However, in the method for producing an optical film by the solution casting method described in Patent Documents 1 to 3, although the solvent can be dried in a short time, the productivity is lowered due to generation of wrinkles on the film during transportation. It was a problem. Moreover, there was room for improvement in the dimensional stability of the obtained optical film.

  The subject of this invention is providing the manufacturing method of the optical film which can dry a solvent for a short time, is hard to generate | occur | produce a wrinkle in a film during conveyance, and is excellent in productivity. Another object of the present invention is to provide an optical film having few wrinkles and excellent dimensional stability.

The above problem is solved by the following means.
The present invention relates to the following <1> to <4>, but other matters are also described for reference.

<1>
A method for producing an optical film by solution casting,
A step (1) of casting a dope composition containing a polymer and a solvent on a support to form a cast film, and drying the solvent;
The casting film is peeled off from the support within the range of 5 to 60% by mass of the solvent with respect to the total solid content of the casting film, and both ends in the width direction of the casting film are tentered. Step (2) of gripping with
The step (3) of shrinking the gripped cast film to 97% to 70% in the width direction at a temperature of Tg-30 ° C. to Tg + 20 ° C. with respect to the glass transition temperature Tg of the optical film, and the cast film Step (4) for obtaining an optical film by heat-treating at a temperature of Tg + 60 ° C. to Tg + 120 ° C. with respect to the glass transition temperature Tg of the optical film
In this order, the manufacturing method of an optical film.
<2>
After the step (4),
Step (5) of stretching the optical film to 105% to 300% in the width direction at a temperature lower than the heat treatment temperature in the step (4) by Tg + 10 ° C. to Tg + 100 ° C. with respect to the glass transition temperature Tg of the optical film.
The manufacturing method of the optical film as described in <1> containing.
<3>
The manufacturing method of the optical film as described in <1> or <2> in which the said polymer contains (meth) acrylic-type resin.
<4>
The manufacturing method of the optical film in any one of <1>-<3> in which the said dope composition contains a rubber elastic particle in the ratio of 1-50 mass parts with respect to 100 mass parts of said polymers.
<5>
The optical film manufactured with the manufacturing method of the optical film in any one of <1>-<4>.

  ADVANTAGE OF THE INVENTION According to this invention, a solvent can be dried in a short time, a wrinkle is hard to generate | occur | produce in a film during conveyance, and the manufacturing method of the optical film which is excellent in productivity can be provided. Moreover, according to this invention, an optical film with few wrinkles and excellent dimensional stability can be provided.

  Hereinafter, the contents of the present invention will be described in detail. The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments. In the specification of the present application, “to” is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value.

<Method for producing optical film>
The method for producing the optical film of the present invention comprises:
A method for producing an optical film by solution casting,
A step (1) of casting a dope composition containing a polymer and a solvent on a support to form a cast film, and drying the solvent;
The casting film is peeled off from the support within the range of 5 to 60% by mass of the solvent with respect to the total solid content of the casting film, and both ends in the width direction of the casting film are tentered. Step (2) of gripping with
The step (3) of shrinking the gripped cast film to 97% to 70% in the width direction at a temperature of Tg-30 ° C. to Tg + 20 ° C. with respect to the glass transition temperature Tg of the optical film, and the cast film Step (4) to obtain an optical film by heat-treating at a temperature of Tg + 60 ° C. to Tg + 120 ° C. with respect to the glass transition temperature Tg of the optical film.
In this order.

  Hereinafter, the present invention will be described in detail.

<Dope composition>
The dope composition is a composition containing at least a polymer and a solvent.

<Polymer>
The polymer is preferably a (meth) acrylic resin, a polycarbonate resin, a polystyrene resin, or a cyclic polyolefin resin, and can be selected from these resins and mixed resins of these plural types of resins.

  The (meth) acrylic resin is a concept including both a methacrylic resin and an acrylic resin. The (meth) acrylic resin also includes acrylate / methacrylate derivatives, particularly acrylate / methacrylate (co) polymers.

  The polymer preferably contains a (meth) acrylic resin, more preferably contains 30 to 100% by mass of (meth) acrylic resin, and 60 to 100% by mass of (meth) based on the total solid content of the polymer. It is more preferable that an acrylic resin is included, and it is particularly preferable that the resin is made of 100% by mass of (meth) acrylic resin.

<(Meth) acrylic resin>
[Constitutional unit of (meth) acrylic resin]
The (meth) acrylic resin preferably contains a methyl methacrylate unit (a), may be composed only of the methyl methacrylate unit (a), or an alkyl (meth) acrylate unit (b) other than methyl methacrylate. May be included. However, when the (meth) acrylic resin contains an alkyl (meth) acrylate unit (b) other than methyl methacrylate, the proportion is preferably less than 5% by mass. The (meth) acrylic resin may be a methyl methacrylate homopolymer without using other copolymerizable monomers.

  When the (meth) acrylic resin contains an alkyl (meth) acrylate unit (b) other than methyl methacrylate, examples of the alkyl (meth) acrylate unit (b) include the following.

(Alkyl (meth) acrylate units other than methyl methacrylate (b))
Examples of the alkyl (meth) acrylate unit (b) other than the aforementioned methyl methacrylate include, for example, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, benzyl acrylate, and the like. Acrylic acid esters (preferably alkyl acrylates having 1 to 18 carbon atoms); methacrylic acid esters such as ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, and benzyl methacrylate (Preferably an alkyl methacrylate having 2 to 18 carbon atoms in the alkyl number); May be used alone, or in combination of two or more kinds.

(Other structural units)
The (meth) acrylic resin may also contain structural units other than the alkyl (meth) acrylate units (a) and (b). Examples of such structural units include α, β-unsaturated acids such as acrylic acid and methacrylic acid, unsaturated group-containing divalent carboxylic acids such as maleic acid, fumaric acid, and itaconic acid, styrene, α-methylstyrene, and the like. Examples include aromatic vinyl compounds, α, β-unsaturated nitriles such as acrylonitrile and methacrylonitrile, maleic anhydride, maleimide, N-substituted maleimide, and glutaric anhydride. On the other hand, cellulosic resins are not included as other structural units.
One type of these structural units may be introduced alone into the (meth) acrylic resin, or two or more types may be combined and introduced into the (meth) acrylic resin.

  Among these, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, 2-ethylhexyl acrylate, and the like are preferable from the viewpoint of thermal decomposition resistance and fluidity of the copolymer. n-Butyl acrylate is particularly preferably used.

(Mass fraction of methyl methacrylate unit (a))
The (meth) acrylic resin is most preferably composed of a single methyl methacrylate unit (a) from the viewpoint of increasing the glass transition temperature and obtaining heat resistance. On the other hand, when the (meth) acrylic resin is a copolymer of the methyl methacrylate unit (a) and other structural units, the acrylic resin is imparted with properties other than the properties expressed by the methyl methacrylate unit (a). can do.
In the aforementioned (meth) acrylic resin, the content ratio of methyl methacrylate in the monomer component to be subjected to the polymerization step is preferably 95 to 100% by mass, more preferably, in order to sufficiently exhibit the effects of the present invention. It is 97-100 mass%, More preferably, it is 100 mass%.
By setting the ratio of methyl methacrylate to 95% by mass or more, an acrylic resin having high heat resistance can be obtained, and the heat resistance of the optical film can be improved.
The acrylic resin includes a methyl methacrylate unit (a), and the mass fraction of the alkyl (meth) acrylate unit (b) other than methyl methacrylate is preferably less than 5% by mass, and less than 3% by mass. More preferably, it is particularly preferably 0% by mass.

(Method for producing (meth) acrylic resin)
(Meth) acrylic resins that can be used in the present invention are commercially available or can be obtained by known synthesis methods.
As a method for producing a (meth) acrylic resin that can be used in the present invention, emulsion polymerization, solution polymerization, bulk polymerization, and suspension polymerization can be applied. Of these, emulsion polymerization and suspension polymerization are more preferred in producing the high molecular weight product of the present invention.
As the initiator for suspension polymerization, those used in usual suspension polymerization can be used, and examples thereof include organic peroxides and azo compounds.
As the suspension stabilizer, conventionally known ones can be used, and examples thereof include organic colloidal polymer substances, inorganic colloidal polymer substances, inorganic fine particles, and combinations of these with surfactants.

The (meth) acrylic resin contains a methyl methacrylate unit (a), the mass fraction of the alkyl (meth) acrylate unit (b) other than methyl methacrylate is less than 5% by mass, and the weight average molecular weight is 250,000- It is preferably 4 million, and the weight loss when heated at 140 ° C. for 1 hour is preferably 0.5% or less. In the acrylic resin having such a composition of the structural unit, in order to achieve both high weight average molecular weight and suppression of weight loss, it is preferable to perform the following method particularly when the acrylic resin is synthesized.
As a method that is preferably included during the synthesis of the (meth) acrylic resin, after the (meth) acrylic resin is obtained by a polymerization reaction, the reaction solution is filtered through a filter cloth in a suspension state, washed with methanol, The method of drying a filtrate can be mentioned. An example of the filter cloth is nylon filter cloth. By not drying the reaction solution as it is after the (meth) acrylic resin is obtained by the polymerization reaction, excess polymerization initiators can be removed, and both high weight average molecular weight and suppression of weight loss are achieved (meta) ) Acrylic resin can be obtained.

[Weight average molecular weight of (meth) acrylic resin]
In the present invention, the “weight average molecular weight” is a weight average molecular weight measured by gel permeation chromatography.
The weight average molecular weight of the (meth) acrylic resin is preferably 250,000 to 4,000,000, more preferably 600,000 to 4,000,000, still more preferably 800,000 to 3,000,000, and 1,000,000 to 2 million is particularly preferable. When the weight average molecular weight of the (meth) acrylic resin is 250,000 or more, for example, when an optical film is produced by a solution casting method, the viscosity is relatively high even if the concentration of the (meth) acrylic resin is lowered. The solution (dope) can be obtained. As a result, streaks are prevented from appearing on the surface when the dope is discharged from the casting die, and a film having a good surface shape can be obtained. Further, by reducing the resin concentration of the dope (increasing the proportion of the solvent), the solvent component remains in the dried film, and the film can be easily peeled off from the support. It is done. On the other hand, when the weight average molecular weight of the (meth) acrylic resin is 4 million or less, there is an advantage that the (meth) acrylic resin can be easily synthesized or obtained.
Here, the “weight average molecular weight (Mw)” in the present invention can be measured under the conditions described in [Measurement Method] in the Examples. Specifically, it is as follows.
It is a weight average molecular weight measured under the following conditions by gel permeation chromatography.
Solvent Tetrahydrofuran apparatus name TOSOH HLC-8220GPC
Three columns TOSOH TSKgel Super HZM-H (4.6 mm × 15 cm) are connected and used.
Column temperature 25 ° C
Sample concentration 0.1% by mass
Flow rate 0.35ml / min
Calibration curve TSK standard polystyrene made by TOSOH Mw = 2800000-1050 calibration curves with 7 samples are used.

<Cellulose ester resin>
As the polymer, a cellulose ester resin may be contained particularly from the viewpoint of improvement in brittleness, heat resistance, and transparency when mixed with a (meth) acrylic resin. The proportion of the cellulose ester resin to be mixed with the (meth) acrylic resin is preferably 40% by mass or less with respect to the total solid content. In the cellulose ester resin, the total substitution degree (T) of acyl groups is preferably 2.0 to 3.0, and the substitution degree of acyl groups having 3 to 7 carbon atoms is preferably 1.2 to 3.0. . That is, the cellulose ester resin is a cellulose ester resin substituted with an acyl group having 3 to 7 carbon atoms. Specifically, propionyl, butyryl and the like are preferably used, and a propionyl group is particularly preferably used.

  The acyl substitution degree of the cellulose ester resin is such that the total substitution degree (T) is 2.0 to 3.0, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 3.0. Preferably, the total degree of substitution of acyl groups other than those having 3 to 7 carbon atoms, that is, acetyl groups or acyl groups having 8 or more carbon atoms, is more preferably 1.3 or less.

  In the present application, the “acyl group” is meant to include those further having a substituent. However, the carbon number of the acyl group includes a substituent of the acyl group.

  When the cellulose ester resin has an aromatic acyl group as a substituent, the number of substituents X substituted on the aromatic ring is preferably 0 to 5. Also in this case, it is necessary to pay attention so that the substitution degree of the acyl group having 3 to 7 carbon atoms including the substituent is 1.2 to 3.0. For example, since the benzyl group has 7 carbon atoms, when it has a substituent containing carbon, the benzyl group has 8 or more carbon atoms and is not included in the acyl group having 3 to 7 carbon atoms. Become.

  Further, when the number of substituents substituted on the aromatic ring is 2 or more, they may be the same or different from each other, but they may be linked together to form a condensed polycyclic compound (for example, naphthalene, indene, indane, phenanthrene, quinoline). , Isoquinoline, chromene, chroman, phthalazine, acridine, indole, indoline, etc.).

  The cellulose ester resin preferably has a structure having at least one kind of a substituted or unsubstituted aliphatic acyl group having 3 to 7 carbon atoms.

  The substitution degree of the cellulose ester resin is that the total substitution degree (T) of the acyl group is 2.00 to 3.00, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 3.0. preferable.

  Moreover, it is a preferable structure that the sum total of the substitution degree of other than an acyl group having 3 to 7 carbon atoms, that is, an acetyl group and an acyl group having 8 or more carbon atoms is 1.3 or less.

  The cellulose ester resin is preferably at least one selected from cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose propionate, and cellulose butyrate, particularly cellulose acetate propionate and cellulose Pionate is more preferred.

  Among these, particularly preferable cellulose ester resins are cellulose acetate propionate and cellulose acetate butyrate, and those having an acyl group having 3 or 4 carbon atoms as a substituent are preferable.

  The portion not substituted with an acyl group usually exists as a hydroxyl group. These can be synthesized by known methods.

  In addition, the substitution degree of an acetyl group and the substitution degree of other acyl groups are obtained by a method prescribed in ASTM-D817-96.

  The weight average molecular weight (Mw) of the cellulose ester resin is 75000 or more, particularly from the viewpoint of improving compatibility with (meth) acrylic resins and brittleness, and is preferably in the range of 75,000 to 300,000, It is more preferable that the value is within the range, and a value of 160000 to 240000 is particularly preferable.

<Additives>
Additives may be added to the dope composition of the present invention as long as the effects of the present invention are not impaired.

As additives, plasticizers, ultraviolet absorbers, antioxidants, brittleness improvers, optical enhancers, rubber elastic particles, and the like can be added.
The plasticizer has a function of improving the fluidity and flexibility of the dope composition used when manufacturing the optical film. Examples of the plasticizer include phthalate ester, fatty acid ester, trimellitic ester, phosphate ester, polyester, and epoxy.
Examples of the ultraviolet absorber include benzotriazole, 2-hydroxybenzophenone, and salicylic acid phenyl ester. For example, 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2- (3 Triazoles such as 5-di-t-butyl-2-hydroxyphenyl) benzotriazole, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone And the like are preferred.
Furthermore, various antioxidants, brittleness improvers, optical enhancers, rubber elastic particles, and the like can be added as additives in order to improve thermal decomposability and thermal colorability during molding.

<Rubber elastic particles>
In order to improve brittleness and impact resistance, the dope composition in the present invention preferably contains rubber elastic particles.
That is, in the method for producing an optical film of the present invention, the dope composition preferably contains rubber elastic particles in a proportion of 1 to 50 parts by mass with respect to 100 parts by mass of the polymer, and a proportion of 3 to 40 parts by mass. It is more preferable that it is contained at a ratio of 5 to 30 parts by mass. If the addition amount is 1 part by mass or more, a sufficient improvement effect on brittleness and impact resistance can be obtained, and if it is 50 parts by mass or less, the transparency of the optical film is not impaired.
As the rubber elastic particles, commercially available ones can be used, for example, Metablene W-341 (C2) manufactured by Mitsubishi Rayon Co., Ltd., “Kane Ace” manufactured by Kaneka Chemical Industry Co., Ltd. Examples include “Acryloid” manufactured by Andhers, “Staffyroid” manufactured by Gantz Kasei Kogyo, and “Parapet SA” manufactured by Kuraray. These may be used alone or in combination of two or more.
The particle diameter of the rubber elastic particles preferably used in the present invention is not particularly limited, but is preferably 10 nm or more and 10 μm or less, more preferably 20 nm or more and 1 μm or less, particularly Most preferably, it is 50 nm or more and 400 nm or less.

(solvent)
The solvent contained in the dope composition is preferably an organic solvent.
The organic solvent can be used without limitation as long as it dissolves the polymer and the additive added as necessary.

  For example, as a chlorinated organic solvent, methylene chloride and as a non-chlorinated organic solvent, methyl acetate, ethyl acetate, amyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane , Cyclohexanone, ethyl formate, 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3 , 3-hexafluoro-2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, Nitroethane can be mentioned, and methylene chloride, methyl acetate, ethyl acetate, acetone, and methyl ethyl ketone are preferred. Ku can be used.

In addition to the organic solvent, the dope composition preferably contains 1 to 40% by mass of a linear or branched aliphatic alcohol having 1 to 4 carbon atoms. When the ratio of alcohol in the dope composition is increased, peeling from the metal support is facilitated, and when the ratio of alcohol is small, there is also a role of promoting dissolution of the polymer in a non-chlorine organic solvent system.
In the present invention, when a plurality of solvents are used, the solvent having the highest weight ratio may be referred to as a main solvent.

  Examples of the linear or branched aliphatic alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, isopropanol, n-butanol, s-butanol, and t-butanol. Methanol is preferred because of the stability, boiling point and relatively good drying properties of these dope compositions.

Preparation of dope composition (dissolution process)
In the dissolution step, a dope composition is prepared by mixing and stirring a polymer, an organic solvent, and an additive added as necessary.

The dope composition can be prepared by a general method comprising processing at a temperature of 0 ° C. or higher (ordinary temperature or high temperature). Preparation of the dope composition of this invention can be implemented using the preparation method and apparatus of the dope composition in a normal solvent cast method. In the case of a general method, halogenated hydrocarbon (especially dichloromethane) and alcohol (especially methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, t-butanol, 1) -Pentanol, 2-methyl-2-butanol and cyclohexanol) are preferably used.
The polymer content in the dope composition is preferably 10 to 50% by mass, more preferably 10 to 40% by mass, and still more preferably 10 to 35% by mass. Arbitrary additives described later may be added to the organic solvent (main solvent).
The dope composition can be prepared by stirring the polymer, the organic solvent, and, if necessary, the additive. At this time, the mixture of each component may be added and dissolved in the stirring solvent, or each component may be sequentially added and dissolved in the stirring solvent, or a solution of each component is prepared in advance. The dope composition may be formed by mixing these solutions. For the dissolution of the polymer, a method carried out at normal pressure, a method carried out below the boiling point of the main solvent, a method carried out under pressure above the boiling point of the main solvent, JP-A-9-95544, JP-A-9-95557, or Various dissolution methods such as a method using a cooling dissolution method as described in JP-A-9-95538 and a method using a high pressure as described in JP-A-11-21379 can be used. A method of pressurizing at the above temperature is preferred.

The container for preparing the dope composition needs to be configured so that it can be stirred. Further, it is preferable that the container can be pressurized by injecting an inert gas such as nitrogen gas. Moreover, you may utilize the raise of the vapor pressure of the solvent by heating. Or after sealing a container, you may add each component under pressure.
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 a container. The prepared dope composition is cooled and then taken out from the container, or taken out and then cooled using a heat exchanger or the like.

  The manufacturing method of the optical film of this invention has process (1)-(4) in this order as mentioned above, respectively, process (1) is a casting process, process (2) is a peeling process, process (3), respectively. ) Is referred to as a preheating step, and step (4) is referred to as a heat treatment step. Moreover, you may have a process (5) after a process (4), and a process (5) is called an extending process.

Process (1) Casting process In the manufacturing method of this invention, a casting process is provided.
In the casting process, the dope composition prepared in the dissolving process is cast on a support to form a film, and this is dried to form a cast film. In this casting process, an endless metal belt (for example, a stainless steel belt or a rotating metal drum) that feeds the dope composition to a pressure die through a liquid feed pump (for example, a pressurized metering gear pump) and transfers it infinitely It is preferable that the dope composition be cast from a pressure die slit at a casting position on a support such as a process film. As the die, a pressure die that can adjust the slit shape of the die base portion and can easily make the film thickness uniform is preferable. The pressure die includes a coat hanger die and a T die, and any of them is preferably used. The surface of the metal support is a mirror surface. In order to increase the film forming speed, two or more pressure dies may be provided on the metal support, and the amount of the dope composition may be divided and overlaid. Alternatively, it is also preferable to obtain a cast film having a laminated structure by a co-casting method in which a plurality of dope compositions are cast simultaneously.
When casting the dope composition, two or more kinds of dope compositions may be simultaneously laminated or sequentially laminated. Further, these two co-castings may be combined. When performing simultaneous lamination and co-casting, a casting die to which a feed block is attached may be used, or a multi-manifold casting die may be used. It is preferable that at least one of the thickness of the layer on the air surface side and the thickness of the layer on the support side is 0.5% to 30% of the film thickness of the entire film. . Furthermore, when performing simultaneous lamination co-casting, it is preferable that the high-viscosity dope composition is wrapped with the low-viscosity dope composition when the dope composition is cast from the die slit to the support.
In this casting step, co-casting may be performed sequentially.

From casting die, decompression chamber, support structure, co-casting, peeling method, stretching, drying conditions for each process, handling method, curl, winding method after flatness correction, solvent recovery method, film recovery method The details are described in paragraphs [0617] to [0889] of JP-A-2005-104148.
The casting conditions of the present invention are preferably carried out under such conditions that when the optical film is unstretched, the film thickness of the optical film is 10 to 80 μm, and the conditions are 15 to 40 μm. Is more preferable. If the film thickness is thinner than this range, the strength of the cast film is lowered and the workability is deteriorated. On the other hand, if the film thickness is larger than this range, the solvent may remain in the optical film.

  Next, the cast film thus obtained is dried. At that time, heating is usually performed on the cast metal support, and the solvent is evaporated until the cast film becomes peelable from the metal support. To evaporate the solvent, there are a method of blowing air from the casting membrane side and / or a method of transferring heat from the back surface of the metal support by liquid, a method of transferring heat from the front and back by radiant heat, etc. This method is preferable because of good drying efficiency. A method of combining them is also preferable. In the case of backside liquid heat transfer, it is preferable to heat at or below the boiling point of the main organic solvent used in the dope composition or the lowest organic solvent.

Step (2) Peeling Step In the production method of the present invention, a peeling step is provided.
In the peeling step, the cast film formed in the casting step is peeled from the support. The peeled cast film is sent to the preheating process. The amount of residual solvent at the time of peeling of the cast film on the support is set according to the drying conditions, the length of the support, etc., but in the present invention, the solvent is peeled in the range of 5 to 60% by mass. Furthermore, it is preferable to peel in the range of 10-40 mass%. Here, the residual solvent amount is the content of the solvent with respect to the total solid content of the cast film, as represented by the following formula.
Residual solvent amount (% by mass) = [(MN) / N] × 100
Here, M is the mass at an arbitrary point of the casting membrane, and N is the mass when a mass M is dried at 130 ° C. for 3 hours.
In the present invention, the temperature at the peeling position on the metal support is preferably −50 to 40 ° C., more preferably 0 to 40 ° C., and most preferably 10 to 30 ° C.

Process (3) Preheating process In the manufacturing method of this invention, a preheating process is provided.
After the peeling step, it is preferable to heat the casting membrane in the preheating step using a tenter device that grips and conveys both ends of the casting membrane. As a heating means, hot air is generally blown on both sides of the polymer film, but there is also a means of heating by applying microwaves instead of wind.
The surface temperature of the film in the preheating step is preferably Tg-30 ° C to Tg + 20 ° C of the optical film, more preferably Tg-20 to Tg + 10 ° C, and particularly preferably Tg-10 to Tg + 5 ° C. Moreover, in the preheating step, the width direction of the film is contracted to 97% to 70% by adjusting the interval between the clips that hold both ends of the film. It is more preferable to contract to 95% to 75%, and it is even more preferable to contract to 90% to 80%.
Here, the shrinkage rate means that obtained by the following equation.
Shrinkage rate (%) = 100 × width after shrinkage / width before shrinkage By providing such a preheating step, a film having excellent dimensional stability can be obtained. Moreover, there is little generation | occurrence | production of a wrinkle, and a favorable planar film and a roll film with a favorable winding form can be obtained.

Step (4) Heat Treatment Step In the production method of the present invention, a heat treatment step is provided as a subsequent stage of the pre-heat treatment step.
The surface temperature of the cast film in the heat treatment step performed after the preheating step is preferably in the range of Tg + 60 ° C. to Tg + 120 ° C. with respect to the glass transition temperature (Tg) of the optical film, and Tg + 70 to Tg + 100 of the optical film. More preferably, it is in the range of ° C. By setting the heat treatment temperature within this range, the solvent can be sufficiently dried, a cast film and an optical film excellent in dimensional stability can be produced, and further, the transportability of the cast film is excellent.
The heat treatment is preferably performed for 10 seconds or longer. By setting the treatment time within this range, the solvent can be sufficiently dried, and cast films and optical films with excellent dimensional stability can be produced. From the viewpoint of optical film productivity, the heat treatment time is The shorter one is preferable, and it is preferably within 300 seconds.

Step (5) Stretching Step The optical film obtained through the heat treatment step is preferably stretched in the width direction. At this time, the residual solvent amount of the cast film is preferably less than 1%.
The draw ratio is preferably 105% to 300%, and more preferably 110% to 200%. If the draw ratio is 105% or more, a good surface shape is obtained, and if it is 300% or less, the optical film is less likely to break.
Here, “stretch ratio (%)” means that obtained by the following formula.
Stretch ratio (%) = 100 × Width after stretching / Width before stretching The surface temperature of the optical film in the stretching step is lower than the temperature in the heat treatment step, and is Tg + 10 ° C. to Tg + 100 ° C. of the optical film. Is preferable, and it is more preferable that it is Tg + 20-Tg + 60 degreeC. If it is Tg + 10 degreeC or more of an optical film, the dimensional stability of an optical film will not deteriorate, and the thing with favorable transparency of an optical film will be easy to be obtained.
If it is Tg + 100 ° C. or less of the optical film, wrinkles are less likely to occur after the tenter is detached, and the rolled form of the roll is difficult to deteriorate.
You may perform an extending | stretching process with respect to the optical film which wound up the extending | stretching process from the roll offline after winding an optical film once in a roll shape after performing a heat treatment process.
It is preferable that the surface temperature of the film is cooled to Tg or less before the optical film is detached from the tenter after the stretching step.
In order to prevent the film from fusing to the tenter gripping portion, the temperature of the gripping portion is preferably cooled to Tg or less.

Both edges of the film obtained through the stretching process are cut at both edges by an edge-cutting device. It is preferable to give a knurling to both edges of the film from which both ends have been removed by embossing. The knurling is preferably applied to at least one end, and more preferably applied to both ends. The width of the knurling is preferably 3 mm to 50 mm, more preferably 5 mm to 30 mm, and the height is preferably 0.5 to 500 μm, more preferably 1 to 200 μm. This may be a single push or a double push.
Finally, the film is wound up. In this case, it is preferable to wind the sheet while applying a desired tension with a press roller. More preferably, the tension is gradually changed from the start to the end of winding. The film to be wound is preferably at least 100 m in the longitudinal direction (casting direction), more preferably from 100 to 10000 m, further preferably from 500 to 7000 m, and more preferably from 1000 to 6000 m. Even more preferred. The width of the film is preferably 600 mm or more, more preferably 1100 mm or more and 2900 mm or less, and still more preferably 1800 mm or more. Moreover, 5000 mm or less is preferable, 3000 mm or less is more preferable, and 2500 mm or less is still more preferable.

[Glass-transition temperature]
In the present specification, “glass transition temperature Tg” is a value obtained by measuring a film sample with a dynamic viscoelasticity measuring device (DMA). A dynamic viscoelasticity was measured by applying a tensile load to a 5 mm × 50 mm test piece under the conditions of a frequency of 1 Hz, a heating rate of 5 ° C./min, a measurement temperature range of 30 to 240 ° C., and a distance between chucks of 50 mm. At this time, the value of the inflection point of the storage elastic modulus E ′ was defined as “glass transition temperature Tg”.
The optical film of the present invention preferably has a glass transition temperature of 90 to 200 ° C, more preferably 100 to 190 ° C, and still more preferably 110 to 180 ° C.

[Configuration added to optical film]
The optical film of the present invention may have an additional configuration depending on its application. Examples of such a configuration include a surface treatment applied to the surface of the optical film and a functional layer provided on the surface of the optical film. Hereinafter, the surface treatment and the functional layer will be described.

(surface treatment)
The optical film of the present invention can achieve improved adhesion between the optical film and other layers (for example, a polarizer, an undercoat layer, and a back layer) by optionally performing a surface treatment. For example, glow discharge treatment, ultraviolet irradiation treatment, corona treatment, flame treatment, acid or alkali treatment can be used. The glow discharge treatment here may be low-temperature plasma that occurs under a low pressure gas of 10 ^{−3 to} 20 Torr, and plasma treatment under atmospheric pressure is also preferred. A plasma-excitable gas is a gas that is plasma-excited under the above conditions, and includes chlorofluorocarbons such as argon, helium, neon, krypton, xenon, nitrogen, carbon dioxide, tetrafluoromethane, and mixtures thereof. It is done. Details of these are described in detail in pages 30 to 32 in the Japan Institute of Invention Disclosure Technical Bulletin (Public Technical Number 2001-1745, published on March 15, 2001, Japan Institute of Invention), and are preferably used in the present invention. be able to.

(Functional layer)
Moreover, the optical film of this invention may laminate | stack a functional layer with a film thickness of 0.1-20 micrometers on at least one surface. The types of the functional layer include a hard coat layer, an antireflection layer (a layer having a refractive index adjusted such as a low refractive index layer, a medium refractive index layer, a high refractive index layer), an antiglare layer, an antistatic layer, an ultraviolet absorbing layer, A moisture permeation reducing layer is exemplified.
The functional layer described above may be a single layer or a plurality of layers. It is preferable that the functional layer is laminated by co-casting with the polarizing plate protective film of the present invention or coated on the polarizing plate protective film of the present invention.
When the functional layer is formed by coating and drying, it is preferable to use a monomer having an ethylenically unsaturated group as a binder. This monomer may be monofunctional or polyfunctional. Among them, it is preferable to use a polymerizable polyfunctional monomer, more preferably a photopolymerizable polyfunctional monomer, and particularly preferably a coating solution containing a monomer having two or more (meth) acryloyl groups. .

  In addition, an antireflection layer (a layer having a adjusted refractive index such as a low refractive index layer, a middle refractive index layer, or a high refractive index layer), an antiglare layer, an antistatic layer, an ultraviolet absorption layer, or a moisture permeability reducing layer is provided as a functional layer. Therefore, various additives may be added.

  The thickness of the functional layer is more preferably 0.01 to 100 μm, and particularly preferably 0.02 to 50 μm. Furthermore, as a functional layer which reduces a water vapor transmission rate, it is more preferable that it is 0.1-20 micrometers in thickness.

<Polarizing plate>
The optical film of the present invention can be used as a polarizing plate protective film.
The polarizing plate can be produced by a general method. There is a method in which a polarizing plate protective film of the present invention is treated with an alkali and bonded to both surfaces of a polarizer produced by immersing and stretching a polyvinyl alcohol film in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. Instead of alkali treatment, easy adhesion processing as described in JP-A-6-94915 and JP-A-6-118232 may be performed. Further, the surface treatment as described above may be performed.
Examples of the adhesive used to bond the polarizing plate protective film treated surface and the polarizer include polyvinyl alcohol adhesives such as polyvinyl alcohol and polyvinyl butyral, vinyl latexes such as butyl acrylate, and the like.
The polarizing plate protective film and the polarizer may be bonded together with other adhesives or pressure-sensitive adhesives, or may be directly laminated without using any adhesives or pressure-sensitive adhesives.
The polarizing plate is preferably composed of a polarizer and a polarizing plate protective film that protects at least one surface thereof.
In a liquid crystal display device, a substrate including a liquid crystal cell is usually disposed between two polarizing plates, but the optical film of the present invention can be used as any protective film of the two polarizing plates. It is preferable that the optical film of this invention is used as a polarizing plate protective film arrange | positioned in the side far from a liquid crystal cell with respect to a polarizer among the two polarizing plate protective films of each polarizing plate.

<Liquid crystal display device>
The liquid crystal display device includes a liquid crystal cell and a polarizing plate disposed in at least one of the liquid crystal cells, and is the most visible layer of the polarizing plate protective film of the present invention contained in the polarizing plate. More preferably it is arranged.

(General liquid crystal display device configuration)
The liquid crystal display device includes a liquid crystal cell having a liquid crystal supported between two electrode substrates, two polarizing plates disposed on both sides of the liquid crystal cell, and, if necessary, at least between the liquid crystal cell and the polarizing plate. It is preferable to have a configuration in which one optical compensation film is arranged.
The liquid crystal layer of the liquid crystal cell is usually formed by sealing liquid crystal in a space formed by sandwiching a spacer between two substrates. The transparent electrode layer is formed on the substrate as a transparent film containing a conductive substance. The liquid crystal cell may further be provided with a gas barrier layer, a hard coat layer, or an undercoat layer (undercoat layer) (used for adhesion of the transparent electrode layer). These layers are usually provided on the substrate. The substrate of the liquid crystal cell generally has a thickness of 50 μm to 2 mm.

(Types of liquid crystal display devices)
The polarizing plate protective film can be used for liquid crystal cells in various display modes. TN (Twisted Nematic), IPS (In-Plane Switching), FLC (Ferroelectric Liquid Crystal), AFLC (Anti-Ferroelectric Liquid Crystal), OCB (Optically ComplySampB)
Various display modes such as Twisted Nematic), VA (Vertically Aligned), ECB (Electrically Controlled Birefringence), and HAN (Hybrid Aligned Nematic) have been proposed. In addition, a display mode in which the above display mode is oriented and divided has been proposed. The polarizing plate protective film is effective in any display mode liquid crystal display device. Further, it is effective in any of a transmissive, reflective, and transflective liquid crystal display device.

  Hereinafter, the present invention will be specifically described based on examples. The materials, reagents, amounts and ratios of substances, operations, and the like shown in the following examples can be appropriately changed without departing from the gist of the present invention. Therefore, the present invention is not limited to the following examples. In the following description, “MMA” represents methyl methacrylate, and “MA” represents methyl acrylate.

<Example 1>
(acrylic resin)
An acrylic resin (PMMA resin) having a weight average molecular weight of 1.3 million and an MMA ratio of 100% used in Examples and Comparative Examples was synthesized by the following method.
300 g of ion-exchanged water and 0.6 g of polyvinyl alcohol (saponification degree 80%, polymerization degree 1700) were added to a 1 L three-necked flask equipped with a mechanical stirrer, thermometer, and cooling tube and stirred to completely dissolve the polyvinyl alcohol. Thereafter, 100 g of methyl methacrylate and 0.15 g of azobisisobutyronitrile were added and reacted at 85 ° C. for 6 hours. The obtained suspension was filtered with a nylon filter cloth, washed with methanol, and the filtrate was dried at 50 ° C. overnight to obtain the desired polymer in the form of beads.

[Production of optical film]
(Dissolution process: preparation of dope composition)
The composition described below was put into a mixing tank and stirred while heating to dissolve each component to prepare a dope composition.

(Dope composition 1)
PMMA resin 100 parts by mass Rubber elastic particles 10 parts by mass Antioxidant 0.1 parts by mass Dichloromethane 383 parts by mass Methanol 57 parts by mass In addition, Kaneace M-210 (manufactured by Kaneka Corporation) was used as the rubber elastic particles. As the antioxidant, Sumilizer GS (manufactured by Sumitomo Chemical Co., Ltd.) was used.

(Measurement of glass transition temperature)
In order to measure the glass transition temperature of the film obtained from the above prepared dope composition, the obtained dope composition is cast on a glass plate, and the obtained cast film is dried at 140 ° C. for 40 minutes. Thus, a film having a thickness of 40 μm was produced.
Next, the glass transition temperature (Tg) of the obtained film was measured with a dynamic viscoelasticity measuring instrument (DVA-225 manufactured by IT Measurement Control Co., Ltd.) under the following conditions. A dynamic viscoelasticity was measured by applying a tensile load to a 5 mm × 50 mm test piece under the conditions of a frequency of 1 Hz, a heating rate of 5 ° C./min, a measurement temperature range of 30 to 240 ° C., and a distance between chucks of 50 mm. At this time, the value of the inflection point of the storage elastic modulus E ′ was defined as “glass transition temperature Tg”.

(Casting process, peeling process)
The above-prepared dope composition was uniformly cast from a casting die onto a stainless steel band (casting support). When the amount of residual solvent in the cast film reached 20% by mass, the cast film was peeled off as the cast film. Both ends in the width direction of the cast film thus peeled off were held with a tenter.

(Preheating process, heat treatment process, stretching process)
For the peeled cast film, under the conditions shown in Table 1, a preheating step (shrink in the width direction at the temperature shown in Table 1), a heat treatment step (heat treatment at the temperature shown in Table 1) with a tenter, and a stretching step ( The film was stretched in the width direction at the temperatures shown in Table 1. The roll appearance evaluation results and various physical properties of the obtained film are shown in Table 1.
In addition, the temperature described here is the surface temperature of the film in each process.
In each step, a PET film having an E thermocouple attached to the surface in advance was conveyed, and the surface temperature was measured using NR-1000 manufactured by Keyence Corporation.

<Roll appearance evaluation>
The obtained film was wound up as a 3900 m roll, and the roll appearance was visually evaluated.
A: No wrinkle generated B: Wrinkled at the end C: Folded starting from the wrinkle

<85 ° C, relative humidity 85%, dimensional change around 24 hours>
About the obtained film, 85 degreeC, relative humidity 85%, the dimensional change rate before and behind 24 hours, ie, the value of (L'-L0) / L0} * 100% was calculated | required about the width direction of the film. Here, the aforementioned L0 represents the film length (unit: mm) before passing for 24 hours at 85 ° C. and 85% relative humidity, and the aforementioned L ′ was allowed to pass for 24 hours at 85 ° C. and 85% relative humidity. Then, the film length (unit: mm) after 2 hours have passed in an environment of 25 ° C. and a relative humidity of 60%. The sample film used was 30 mm × 120 mm, and other conditions were as follows.
After conditioning for 2 hours or more in an atmosphere of 25 ° C. and a relative humidity of 60%, with an automatic pin gauge (manufactured by Shinbun Kagaku Co., Ltd.), holes with a diameter of 6 mm are arranged at intervals of 100 mm so as to be parallel to the 120 mm side of the film. Open and measure the original distance (L0) to a minimum scale of 1/1000 mm. Then, after 24 hours had passed at 85 ° C. and 85% relative humidity, after adjusting the humidity for 2 hours in an atmosphere of 25 ° C. and 60% relative humidity, the dimension L ′ of the punch interval was measured.

<Haze>
The haze was measured using a haze meter (NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd.). In addition, about the measurement, it measured based on JIS-K7105.

<Examples 2-12, Comparative Examples 1-6>
An optical film was prepared in the same manner as in Example 1 except that the conditions shown in Table 1 below were used in the preheating step, the heat treatment step, and the stretching step, and each evaluation item was measured in the same manner as in Example 1.
In Comparative Example 6, the optical film was broken and could not be evaluated.

<Example 13>
An optical film was prepared in the same manner as in Example 1 except that the dope composition was changed as follows. In the following dope compositions 2 to 6, the PMMA resin is the same as that of the dope composition 1, and the rubber elastic particles are all Kaneace M-210 (manufactured by Kaneka Corporation) to prevent oxidation. As the agent, all used were Sumilizer GS (manufactured by Sumitomo Chemical Co., Ltd.).
(Dope composition 2)
PMMA resin 100 parts by weight Antioxidant 0.1 part by weight Dichloromethane 426 parts by weight Methanol 64 parts by weight

<Example 14>
An optical film was prepared in the same manner as in Example 1 except that the dope composition was changed as follows.
(Dope composition 3)
PMMA resin 100 parts by weight Plasticizer 20 parts by weight Rubber elastic particles 10 parts by weight Antioxidant 0.1 part by weight Dichloromethane 426 parts by weight Methanol 64 parts by weight In addition, BisP-TMC (manufactured by Honshu Chemical Industry Co., Ltd.) is used as a plasticizer. It was.

<Example 15>
An optical film was prepared in the same manner as in Example 1 except that the dope composition was changed as follows.
(Dope composition 4)
PMMA resin 70 parts by mass CAP 30 parts by mass Antioxidant 0.1 part by mass Dichloromethane 348 parts by mass Methanol 52 parts by mass In addition, CAP482-20 (manufactured by Eastman Chemical Co., Ltd.) was used as CAP.

<Example 16>
An optical film was prepared in the same manner as in Example 1 except that the dope composition was changed as follows.
(Dope composition 5)
Polystyrene 100 parts by mass Antioxidant 0.1 part by mass Dichloromethane 234 parts by mass In addition, PSJ-polystyrene G9504 (manufactured by PS Japan Ltd.) was used as polystyrene.

Claims (4)

A method for producing an optical film by solution casting,
A casting step (1) in which a dope composition containing a polymer and a solvent is cast on a support to form a cast film, and the solvent is dried;
The cast film is peeled off from the support within a range of 5 to 60% by mass of the solvent with respect to the total solid content of the cast film, and both ends in the width direction of the cast film are tentered. Peeling process (2) gripped by
A preheating step (3) for shrinking the gripped cast film to 97% to 70% in the width direction at a temperature of Tg-30 ° C. to Tg + 20 ° C. with respect to the glass transition temperature Tg of the optical film; A heat treatment step (4) for obtaining an optical film by heat-treating the film at a temperature of Tg + 60 ° C. to Tg + 120 ° C. with respect to the glass transition temperature Tg of the optical film;
In this order, the manufacturing method of an optical film. After the heat treatment step (4),
Stretching step (5) for stretching the optical film to 105% to 300% in the width direction at Tg + 10 ° C. to Tg + 100 ° C. and lower than the heat treatment temperature in the step (4) with respect to the glass transition temperature Tg of the optical film.
The manufacturing method of the optical film of Claim 1 containing this.   The manufacturing method of the optical film of Claim 1 or 2 in which the said polymer contains (meth) acrylic-type resin. The manufacturing method of the optical film of any one of Claims 1-3 in which the said dope composition contains a rubber elastic particle in the ratio of 1-50 mass parts with respect to 100 mass parts of said polymers.