JPWO2015111519A1 - Dope composition, optical film, method for producing optical film, polarizing plate and liquid crystal display device - Google Patents

Abstract

An acrylic resin having a weight average molecular weight Mw of 250,000 or more, a solvent having a mass ratio (A: B) of 85:15 to 50:50 of (A) methylene chloride and (B) an alcohol having 1 to 4 carbon atoms; The dope composition containing less than 0.5% by mass of the cellulose ester content with respect to the acrylic resin is obtained with a high viscosity, and streaks are unlikely to occur in the casting film when discharged from the casting die. Moreover, the obtained polymer film can be easily peeled from the metal support; optical film; method for producing optical film; polarizing plate; liquid crystal display device.

Description

  The present invention relates to a dope composition, an optical film, a method for producing the same, a polarizing plate, and a liquid crystal display device.

  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 optical element (polarizing plate protective film) is sandwiched between a child (also referred to as a polarizing film or a polarizing film). As this polarizing plate protective film, a cellulose triacetate film is usually used.

  On the other hand, with the recent advancement of technology, the enlargement of the liquid crystal display device is accelerated, and the use of the liquid crystal display device is diversified. For example, it can be used as a large display installed in a street or a store, or used as an advertising display in a public place using a display device called digital signage.

  In such an application, since it is assumed to be used outdoors, deterioration due to moisture absorption of the polarizing plate becomes a problem, and the polarizing plate protective film is required to reduce moisture permeability. However, it is difficult to sufficiently reduce the moisture permeability with a cellulose ester film such as a cellulose triacetate film that has been conventionally used, and there is a problem that the optical influence increases when the film thickness is increased in order to reduce the moisture permeability. there were. Furthermore, in recent years, there has been a demand for thinning of the apparatus, so that the thickness of the polarizing plate itself has also become a problem.

  On the other hand, as an optical film material with low moisture permeability, polymethyl methacrylate (hereinafter abbreviated as PMMA), which is a representative of acrylic resin, exhibits excellent transparency and dimensional stability in addition to low moisture permeability. Used in optical films.

  For example, Patent Document 1 discloses a polarizing plate protective film containing an acrylic resin and a cellulose ester. This polarizing plate protective film can reduce moisture permeability by mixing an acrylic resin with cellulose ester, and it is said that relatively good dimensional stability can be obtained even under high humidity conditions.

  By the way, a resin film made of an acrylic resin or the like is generally manufactured by a melt film forming method in which a resin is heated to a molten state to form a film.

  As the acrylic resin used in the melt film forming method, those having a weight average molecular weight of about 5 to 150,000 are usually used. The reason for this is that if the weight average molecular weight of the acrylic resin is less than 50,000, the resin film becomes fragile. Conversely, if the weight average molecular weight of the acrylic resin is greater than 150,000, fluidity cannot be obtained even when heated. This is because in either case, it is difficult to form a film.

  On the other hand, as a film forming method, a solution film forming method using a solution (dope composition) in which a resin is dissolved with a solvent is known.

  For example, in Patent Document 2, when an acrylic resin having a weight average molecular weight of 8 to 150,000 is formed into a film by a solution casting method, a polyethylene terephthalate (PET) film is dried until the acrylic film has a self-supporting property. Is described as a temporary support, and then a method for producing an acrylic film is described in which a film is obtained by peeling.

JP 2013-120278 A JP 2007-118266 A

  However, when the present inventors examined the conventional dope composition used by the solution casting method, the dope composition using an acrylic resin having a relatively small weight average molecular weight of 8 to 150,000 has a low viscosity and a low flow rate. It has been found that production problems such as streaks are likely to occur during discharge from the cutting edge of the extended die.

  In order to solve this, it is conceivable to increase the solid content concentration of the dope composition to increase the viscosity. In that case, since the solid content concentration of the dope composition becomes high, it takes time in the stage where the solid content is dissolved in a solvent to obtain a dope composition, which is disadvantageous for productivity. Further, when a solution film is formed from a high concentration dope composition, there is a problem that the obtained polymer film is difficult to peel off from the metal support.

  Therefore, in order to solve the problems of the prior art, the present inventors have obtained a high viscosity, hardly cause streaks in the casting film during discharge from the casting die, and have dried the casting film. The present inventors have studied for the purpose of providing a dope composition that can easily peel a polymer film obtained by drying to have a self-supporting property from a metal support. Furthermore, studies have been conducted for the purpose of providing an optical film having a good surface shape and excellent optical characteristics, a method for producing a highly productive optical film, and a polarizing plate and a liquid crystal display device including the optical film. It was.

As a result of intensive studies to solve the above problems, the inventors of the present invention have obtained the following findings (1) to (4).
(1) By making the weight average molecular weight of an acrylic resin 250,000 or more, the dope can be increased in viscosity at a relatively low concentration.
(2) When a mixed solvent of (A) methylene chloride and (B) an alcohol having 1 to 4 carbon atoms is used as a solvent and the concentration of the acrylic resin in the dope composition is lowered (that is, the proportion of the solvent is increased). In the process of drying the cast film, the difference in drying speed between methylene chloride and alcohol becomes more prominent, and the rate of slow drying alcohol increases.
(3) A cast film formed using a mixed solvent of (A) methylene chloride and (B) an alcohol having 1 to 4 carbon atoms is peeled off from the support when the ratio of the alcohol in the mixed solvent is high. Easy to do.
(4) When a mixed solvent of (A) methylene chloride and (B) C1-C4 alcohol is used and the dope composition contains a large amount of cellulose ester, the ratio of alcohol in the mixed solvent is high. When the polymer film is whitened, the whitening problem is eliminated when the composition is such that the cellulose ester content is less than 0.5% by mass with respect to the acrylic resin.

  Furthermore, the effect of facilitating peeling of the cast film with the alcohol of (3) above is that (B) the alcohol having 1 to 4 carbon atoms, whose content ratio is increased, is a metal support and acrylic in the cast film. It was also clarified that there is a high possibility that it is caused by inhibiting the hydrogen bond formed with the resin.

The above problem is solved by the following configuration.
[1] The mass ratio (A: B) of an acrylic resin having a weight average molecular weight Mw of 250,000 or more, (A) methylene chloride, and (B) an alcohol having 1 to 4 carbon atoms is 85:15 to 50:50. The dope composition which contains a certain solvent and whose content of a cellulose ester is less than 0.5 mass% with respect to the above-mentioned acrylic resin.
[2] When a solid content contained in the dope composition was mixed with a solvent having a mass ratio (A: C) of (A) methylene chloride and (C) methanol of 82:18, a mixture was prepared. The dope composition according to [1], wherein the solid content concentration when the complex viscosity at 22 ° C. of the mixture is 30 Pas · sec is 30% by mass or less.
[3] The dope composition according to [1] or [2], wherein the solid content concentration is 10% by mass or more and 30% by mass or less.
[4] Dope composition as described in any one of [1]-[3] whose content of the above-mentioned acrylic resin is 70 mass% or more with respect to solid content whole quantity.
[5] The solid content of the material other than the acrylic resin is 2% by mass or more based on the total solid content, and the equilibrium water content of the solid content of the material other than the acrylic resin is the equilibrium water content of the acrylic resin. Dope composition as described in any one of [1]-[4] smaller than a rate.
[6] An optical film having a polymer film obtained by forming the dope composition according to any one of [1] to [5].
[7] In a region 6 cm in diameter from an arbitrarily set center, the number of occurrences of stepped unevenness having a pitch of 0.5 to 2.0 cm and a thickness height difference of 2.0 to 3.0 μm is less than 10 [ 6].
[8] A dissolution step of preparing the dope composition according to any one of [1] to [5], and a casting step of casting the dope composition on a metal support to form a casting film. And a peeling step of drying the cast film to form a polymer film and peeling the polymer film from the metal support to obtain a polymer film.
[9] A polarizing plate having at least one optical film according to [6] or [7] as a polarizing plate protective film.
[10] A liquid crystal display device comprising the polarizing plate according to [9].

  According to the dope composition of the present invention, a high viscosity can be obtained, and streaks can be prevented from entering the casting film during ejection from the casting die. Further, whitening of the cast film during the drying process is suppressed, and the polymer film obtained by drying the cast film can be easily peeled from the metal support. Thereby, it is possible to efficiently obtain a polymer film having a uniform surface shape and excellent optical characteristics.

  Moreover, according to the optical film and the manufacturing method thereof of the present invention, since the above-described dope composition is used, an optical film having excellent optical characteristics can be obtained with high productivity.

It is a graph which shows the time-dependent change of the methanol content ratio in a drying process in four types of cast films which changed the weight average molecular weight of an acrylic resin. It is a graph which shows the relationship between the ratio of the component (volatile matter) volatilized in the drying process, and peeling load in four types of cast films from which the weight average molecular weight of an acrylic resin differs. It is the schematic of the film manufacturing line for enforcing the solution casting method.

  Hereinafter, the best mode for carrying out the present invention will be described in detail, but the present invention is not limited thereto. In the present specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value. Moreover, (meth) acryl represents methacryl or acryl. The acrylic resin used in the present invention means a (meth) acrylic resin and also includes a methacrylic resin.

<< Dope composition >>
The dope composition is cast on a support to form a cast film, and the cast film is dried to form a polymer film by peeling the polymer film from the metal support. It is.
In this specification, the cast membrane dried to have self-supporting property is called a polymer membrane.
In the dope composition of the present invention, the mass ratio (A: B) of acrylic resin having a weight average molecular weight Mw of 250,000 or more, (A) methylene chloride, and (B) alcohol having 1 to 4 carbon atoms is 85:15. The solvent which is -50: 50 is contained, and content of a cellulose ester is less than 0.5 mass% with respect to the above-mentioned acrylic resin.
Hereinafter, each component of the dope composition will be described. The dope composition includes a solid content including at least a resin component and an additive, and a solvent. Here, the solid content will be described first.

<Solid content>
[acrylic resin]
The acrylic resin used in the present invention includes a methacrylic resin. What consists of less than 5 mass% of methyl methacrylate units 50-100 mass% and another monomer unit copolymerizable with this is preferable. A homopolymer of methyl methacrylate may be used without using any other copolymerizable monomer. As other copolymerizable monomers, alkyl (meth) acrylate units (b) other than methyl methacrylate are preferred. More preferably, 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 less than 5% by mass.

  When the acrylate 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, cyclohexyl acrylate, and acrylic acid. Acrylic acid ester such as benzyl (preferably alkyl acrylate having 1 to 18 carbon atoms in alkyl); ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate Methacrylic acid esters such as benzyl methacrylate (preferably alkyl methacrylate having 2 to 18 alkyl carbon atoms); and the like. These may be used alone or in combination of two or more. Good.

(Other structural units)
The acrylic resin used in the present invention may also contain constituent 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 α, β-unsaturated nitriles such as aromatic vinyl compounds, acrylonitrile and methacrylonitrile, maleic anhydride, maleimide, N-substituted maleimide, glutaric anhydride, and lactone rings. One type of these structural units may be introduced alone into the acrylic resin, or two or more types of structural units may be combined and introduced into the 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 alkyl 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 alkyl resin is a copolymer of the methyl methacrylate unit (a) and other structural units, characteristics other than the characteristics expressed by the methyl methacrylate unit (a) can be imparted to the acrylic resin. .
In the aforementioned 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 97 to 100% by mass, in order to sufficiently exert the effects of the present invention. %, More preferably 100% by 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 of the present invention obtained using the dope composition of the present invention 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.

(Manufacturing method of acrylic resin)
The acrylic resin that can be used in the present invention is commercially available or can be obtained by a known synthesis method.
As the method for producing an acrylic resin that can be used in the present invention, emulsion polymerization, solution polymerization, bulk polymerization, and suspension polymerization can be applied. Among these, emulsion polymerization and suspension polymerization are more preferable in producing a high molecular weight acrylic resin that can be used in 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.

(Weight average molecular weight Mw of acrylic resin)
The acrylic resin (A) used in the dope composition of the present invention has a weight average molecular weight (Mw) of 250,000 or more. Since the acrylic resin is such a polymer, the viscosity of the dope composition can be sufficiently increased even when the concentration of the acrylic resin in the dope composition is relatively low. As a result, streaks are prevented from entering the surface of the casting film during discharge from the casting die, and a polymer film having a good surface shape can be obtained. On the other hand, in relation to the viscosity, the concentration of the acrylic resin can be lowered (the ratio of the solvent can be increased) while making the dope composition high viscosity, so that the effect of the present invention that facilitates film peeling can be achieved. Remarkably can be obtained. This effect will be described in detail later.

The weight average molecular weight (Mw) of the acrylic resin (A) is more preferably in the range of 250,000 to 2,200,000, particularly preferably in the range of 300,000 to 2,000,000, and 500,000 to 1,800,000. More preferably, it is in the range, and most preferably in the range of 1,000,000 to 1,800,000. The upper limit of the weight average molecular weight (Mw) of the acrylic resin (A) is preferably 2.5 million or less from the viewpoint of production. An acrylic resin having such a weight average molecular weight is higher than the weight average molecular weight of the acrylic resin used for melt film formation, and is suitable for solution film formation.
In the present invention, “weight average molecular weight (Mw)” refers to that measured by gel permeation chromatography under the following conditions.
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.

(Concentration of acrylic resin)
The concentration of the acrylic resin in the dope composition is preferably 8% by mass or more and 40% by mass or less. It is preferably 10 to 35% by mass, more preferably 12 to 33% by mass, still more preferably 14 to 30% by mass, particularly preferably 14 to 28% by mass, and 14 to 26%. Most preferably, it is mass%. By setting the concentration of the acrylic resin to 8% by mass or more, a high-quality polymer film with suppressed film thickness unevenness can be obtained. Moreover, the effect which makes easy film | membrane peeling by the below-mentioned alcohol can be acquired reliably by making the density | concentration of an acrylic resin into 40 mass% or less.

[Solid content other than acrylic resin]
The dope composition of the present invention may be added with a solid content such as a resin other than an acrylic resin and an additive as long as the function of the polymer film to be formed is not impaired. However, the dope composition of the present invention has a cellulose ester content of less than 0.5% by mass based on the above-mentioned acrylic resin. If the dope composition contains a large amount of cellulose ester, the cast film is whitened during the drying process of the cast film, and transparency is impaired. However, in the dope composition of the present invention, there is no problem even if cellulose is contained as long as it is a trace amount that does not impair the effect of the invention without impairing the transparency of the cast film. Specifically, in the dope composition The cellulose content with respect to the total solid content is less than 0.5% by mass, and it is more preferable that the content is not contained at all. This corresponds to “substantially free of cellulose ester”. When the cellulose ester content is less than 0.5% by mass with respect to the acrylic resin described above, whitening of the cast film during the drying process is suppressed, and a polymer film with reduced optical properties and moisture permeability is efficiently used. Can get well.
In the dope composition, the cellulose ester content relative to the acrylic resin is such that after the dope composition of the present invention is dried and formed into a polymer film, the cellulose ester content is 0 relative to the acrylic resin described above. It can be confirmed by less than 5% by mass. In the polymer film obtained by forming the dope composition of the present invention, the content of the cellulose ester relative to the acrylic resin has a peak area peculiar to the cellulose ester that does not appear in the acrylic resin by infrared spectrum measurement. It can be determined by quantifying.
In the present invention, the cellulose content was determined as follows.
After obtaining a film from a dope in which cellulose ester of 0.1, 0.3, 0.5, 1.0, and 2.0 mass% is mixed in advance with respect to the amount of acrylic resin, infrared of these films is obtained. The spectrum measurement was performed, and the height from the baseline of the peak at 1370 cm ⁻¹ which does not appear in the acrylic resin and is characteristic of the cellulose ester was determined. A calibration curve was created based on the peak height from this baseline, and the amount of cellulose ester was determined by measuring the infrared spectrum of the sample film. This measurement was performed with a NICOLET 6700 FT-IR infrared spectrometer.

When a resin other than an acrylic resin is added to the dope composition, even if the added resin is in a compatible state, it may be mixed without being dissolved unless it is whitened when a film is formed.
Moreover, additives other than the resin component may be added to the dope composition. Such additives include plasticizers, UV absorbers, thermal decomposability and thermal colorability during molding, transportability, and various antioxidants, brittleness improvers, and film balances to improve optical performance. Examples thereof include an additive for reducing the water content / moisture permeability and an optical developer.
The plasticizer has a function of improving the fluidity and flexibility of the dope composition. 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 Benzophenones such as
Examples of the antioxidant include phenolic and amine-based compounds such as hindered phenol having radical scavenging ability.
Examples of the brittleness improver include rubbery compounds that improve the brittleness of acrylic resins such as acrylic-butadiene rubber, and copolymers of MMA (methyl methacrylate) and butyl acrylate.
Additives that reduce the equilibrium water content / moisture permeability of the film include low molecular weight compounds, oligomers, and resins that are more hydrophobic than acrylic resins and have a low equilibrium water content. For example, phenol resin, phenol novolac resin, coumarone resin, norbornene resin, rosin resin, and other alicyclic polymers can be preferably used.

  When adding resin and additives other than an acrylic resin, it is preferable that the resin and additive are raw materials whose equilibrium moisture content is lower than an acrylic resin. Thereby, the equilibrium moisture content of the dope composition of the present invention is lowered, and further, the equilibrium moisture content of the optical film made of the dope composition of the present invention is lowered. As a result, the moisture permeability of the optical film of the present invention tends to be reduced and the moisture permeability tends to be reduced, and the polarizing plate and the liquid crystal display device using the optical film of the present invention are subject to variations in temperature and humidity due to environmental changes. In contrast, the display performance can be kept favorable.

  The solid content of the material other than the acrylic resin (addition amount of the solid content) is such that the content of the acrylic resin is 70% by mass or more with respect to the total solid content contained in the dope composition, that is, It is preferable that it is less than 30 mass% with respect to the total amount of solid content. In particular, when a solid content having an equilibrium water content smaller than that of the acrylic resin is added, the solid content (addition amount of the solid content) of the material is preferably 2% by mass or more based on the total solid content. The content is more preferably 2 to 28% by mass, and further preferably 5 to 25% by mass.

[Concentration of solid content in dope composition]
The concentration of the solid content in the dope composition is preferably 10% by mass or more, and more preferably 40% by mass or less. As a result, a high quality polymer film with reduced film thickness unevenness can be obtained. The concentration of the solid content in the dope composition is preferably 35% by mass or less, more preferably 33% by mass or less, still more preferably 30% by mass or less, and 28% by mass or less. Particularly preferred is 26% by mass or less. Thereby, the effect of facilitating film peeling by the alcohol described later can be obtained with certainty.

<Solvent>
[Mixed solvent of solvent (A) and solvent (B)]
The dope composition of the present invention contains a mixed solvent of (A) methylene chloride and (B) an alcohol having 1 to 4 carbon atoms as a solvent, and (A) methylene chloride and (B) an alcohol having 1 to 4 carbon atoms The mass ratio (A: B) is 85: 15-50: 50. In the following description, methylene chloride may be referred to as a solvent (A), and an alcohol having 1 to 4 carbon atoms may be referred to as a solvent (B).
With such a solvent composition, this dope composition has an effect that the polymer film obtained by drying the cast film can be easily peeled off from the metal support. This effect will be described with reference to FIGS.
FIG. 1 is a graph showing the change over time of the methanol content in the residual solvent (volatile matter) during the drying process for four types of cast films with different weight average molecular weights of acrylic resin.
FIG. 2 is a graph showing the relationship between the remaining solvent component (total volatile content) and the peeling load when peeling the polymer film from the metal support during the drying process. The amount of residual methanol was detected by gas chromatography.
The residual solvent amount (volatile matter) of the polymer film is defined by the following formula.
Residual solvent amount (volatile content) (%) = (weight of film containing solvent−weight of film after removing solvent by heating) / (weight of film after removing solvent by heating) × 100
The solvent was removed by heating at 140 ° C. for 1 hour.
Each cast film is cast on a metal support using a mixed solvent in which methylene chloride and methanol are mixed in a mass ratio of 82:18 as a solvent.
In such a casting film drying process, methylene chloride having a low boiling point volatilizes faster than alcohol having 1 to 4 carbon atoms. For this reason, as shown in FIG. 1, the content ratio of methanol in the mixed solvent increases with time. On the other hand, as shown in FIG. 2, as the volatile content due to drying increases, the peeling load between the metal support and the cast film once increases. However, when the volatile content further increases, the peeling load is reversed. The load decreases. There is a correlation between the decrease in peel load and the increase in methanol ratio.

[Peeling load]
The “peeling load” in the present specification is a region where the residual solvent (volatile content) in the casting film is 100% or less on the metal support, and the end from which the casting film has been peeled is suspended from the load cell. It is a value measured based on the tension required when peeling a cast film of a certain area from a metal support.
The peeling load is preferably 50 gf / cm or less, more preferably 30 gf / cm or less, and further preferably 15 gf / cm or less. When the peeling load is 50 gf / cm or less, the polymer film can be stably peeled from the metal support without applying an excessive force, and a polymer having excellent surface shape that prevents stepped unevenness. A film can be obtained.
Step unevenness means that when the peeling load between the polymer film and the metal support is large, the peeling point increases or decreases at the time of peeling, or the peeling load increases or decreases, resulting in the width direction of the finished film. This is a phenomenon in which a difference in film thickness occurs, resulting in stepped unevenness and causing a surface failure.

Thus, the dope composition of the present invention was obtained by drying the casting film because the content ratio of alcohol in the mixed solvent increased with time and the peeling load decreased in the drying process of the casting film. The polymer film can be easily peeled from the metal support. As a result, a polymer film having a good surface shape can be obtained efficiently. Such an effect of facilitating film peeling by alcohol is presumed to be due to the fact that alcohol has an action of inhibiting a hydrogen bond formed between the metal support and the acrylic resin.
Here, if a cellulose ester is contained in the dope composition, the cellulose ester becomes difficult to dissolve with an increase in the methanol ratio, causing a phenomenon that the cast film is whitened, resulting in a matte surface. As a result, the film surface shape (smoothness) is impaired. On the other hand, since the dope composition of the present invention does not contain a cellulose ester, such whitening is avoided, and the obtained polymer film has an excellent film surface shape.

(C1-C4 alcohol)
(B) The alcohol having 1 to 4 carbon atoms used for the mixed solvent is preferably methanol, ethanol, isopropanol, n-butanol, iso-butanol, sec-butanol, or tert-butanol, and methanol or ethanol is used. More preferably, methanol is most preferably used.

(Mass ratio A: B)
The mass ratio of (A) methylene chloride to (B) C1-C4 alcohol in the solvent (A: B) is (A) methylene chloride and (B) C1-C4 alcohol mass ratio is A: B. = 85: 15-50: 50. The mass ratio of A: B is preferably 84:16 to 55:45, and more preferably 83:17 to 60:40.

  When the mass ratio (A: B) is set so that the ratio of B is 15% by mass or more, the difference in the drying rate between the ethylene chloride and the alcohol can be made remarkable in the drying process of the cast film, and the peeling The alcohol content ratio of the polymer film at the time can be made higher. As a result, the polymer film can be more easily peeled from the support. Moreover, when the ratio of the mixed solvent is 50% by mass or less, whitening of the dope composition due to insoluble acrylic resin can be avoided, and the dope composition can be cast favorably. Here, in the dope composition of the present invention, since the weight average molecular weight of the acrylic resin is as large as 250,000 or more, a sufficient viscosity can be obtained even when the proportion of the mixed solvent is high (the acrylic resin concentration is low). it can. For this reason, it is possible to reliably suppress the streaks from entering the casting film at the time of discharging from the casting die while sufficiently enjoying the effect of facilitating film peeling by alcohol.

[Solvents other than solvent (A) and solvent (B)]
The dope composition of the present invention is a solvent (other than (A) and (B) other than (A) and (B) as long as the effect of the mixed solvent of (A) methylene chloride and (B) an alcohol having 1 to 4 carbon atoms is not hindered. Solvent). Any other solvent can be used without limitation as long as it dissolves the solid content used in the dope composition.

For example, methyl acetate, ethyl acetate, amyl acetate, acetone, 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 Examples include 3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane, and the like, and methyl acetate, ethyl acetate, and acetone can be preferably used.
When other solvents are used, the total mass of the mixed solvent of (A) methylene chloride and (B) an alcohol having 1 to 4 carbon atoms and the mass ratio of the other solvent is 99.9: 0.1 to 90 : 10, more preferably 99.9: 0.1 to 95: 5, and even more preferably 99.9: 0.1 to 98: 2.

<Characteristics of the dope composition>
[Solid content concentration when complex viscosity is 30 Pas · sec]
In the dope composition of the present invention, the solid content contained in the dope composition is mixed with a solvent in which the mass ratio (A: C) of (A) methylene chloride and (C) methanol is 82:18; When the complex viscosity at 22 ° C. of the mixture is 30 Pas · sec, the dope solid content concentration is preferably 30% by mass or less, and more preferably 25% by mass or less. The lower limit is preferably 10% by mass or more.
In the present invention, “complex viscosity” is a value measured using 1 mL of a sample solution as a rheometer (CLS 500) with a Steel Cone having a diameter of 4 cm / 2 ° (both manufactured by TA Instruments).
The complex viscosity of the dope composition in the present invention is preferably 1 to 100 Pa · s, more preferably 2 to 70 Pa · s, still more preferably 20 to 80 Pa · s, and further preferably 25 to 70 Pa · s. Most preferred. When the complex viscosity is in such a range, the solution casting suitability is further improved, and the whitening suppression effect of the film is further enhanced. The dope composition satisfying this condition can obtain a sufficient viscosity during casting even when the solid concentration is low (the ratio of the mixed solvent is high). For this reason, after the casting film is dried to the extent that it has self-supporting property, the film can be easily discharged at the time of discharge from the casting die while fully enjoying the effect of facilitating film peeling by alcohol when peeling from the metal support. It is also possible to reliably suppress streaks from entering the film.

<< Polymer Film Obtained by Forming Dope Composition >>
Since the polymer film obtained by forming the dope composition of the present invention has a uniform surface shape and high transparency and can be efficiently produced, it is useful for various applications. In particular, the polymer film can be suitably used as an optical film such as a polarizing plate protective film or an optical compensation film.
Hereinafter, an optical film (the optical film of the present invention) will be described as a suitable application of the polymer film obtained by forming the dope composition of the present invention.

<Optical film>
The optical film of the present invention has at least one polymer film obtained by forming the dope composition of the present invention, and the high film obtained by forming the dope composition of the present invention. Although the structure which has only 1 layer of molecular films may be sufficient, the structure which has two or more layers may be sufficient, It is preferable that it is the structure which has only 1 layer of said polymer films.
The optical film of the present invention may have a multilayer structure having layers other than the above polymer film. A three-layer configuration in which the dope composition of the present invention is a central layer and an outer layer is provided on both sides, and a plurality of outer layers may be provided. In the case of a multilayer structure having two or more polymer films obtained by forming the dope composition of the present invention, each polymer film is obtained by forming the same dope composition. Alternatively, it may be obtained by forming different dope compositions. The optical film may be provided with a surface treatment or a functional layer described later on the surface of the polymer film. The optical film of the present invention preferably has a configuration having the above polymer film as at least one outermost layer (layer having an air interface).
Regarding the constitution of the dope composition used in this optical film, the description in the section <Dope composition> can be referred to. Moreover, this optical film can be manufactured by the following optical film manufacturing methods (the optical film manufacturing method of the present invention).

(Equilibrium moisture content of optical film)
In this specification, the “equilibrium moisture content” of an optical film refers to a moisture content (measured at a temperature of 25 ° C. and a relative humidity of 80% according to the Karl Fischer method for a 24 mm × 36 mm film sample cut from the optical film). This is a value calculated by dividing g) by the sample mass (g). Here, the equilibrium moisture content can be measured using a moisture measuring device (trade name CA-03, manufactured by Mitsubishi Chemical Corporation) and a sample drying apparatus (trade name VA-05, manufactured by Mitsubishi Chemical Corporation).
When the optical film of the present invention is used as a protective film for a polarizing plate, the adhesiveness with water-soluble thermoplastics such as polyvinyl alcohol is not impaired, so that the temperature is 25 ° C. and the relative humidity is 80% regardless of the film thickness. The equilibrium moisture content is preferably 0 to 4% by mass. More preferably, it is 0.1-3 mass%, and it is still more preferable that it is 0.5-2 mass%.

(Surface shape of optical film)
The optical film of the present invention preferably has a small maximum height difference (PV value) (step unevenness).
The maximum height difference (PV value) of the film thickness can be measured using, for example, a fringe analyzer, a laser displacement meter, a contact-type film thickness meter, or the like.
In the present specification, the “maximum height difference (PV value)” of the optical film is measured using a fringe analyzer FX-03 (manufactured by FUJINON) with a measurement area of 60 mm in diameter. The maximum difference in film thickness.
The optical film of the present invention preferably has a maximum height difference (PV value) of 3.0 μm or less, more preferably 1.1 μm or less, and particularly preferably 0.9 μm or less. preferable. Since the optical film of the present invention is composed of a polymer film obtained by forming the dope composition of the present invention, the maximum height difference (PV value) of the film thickness is surely 3.0 μm or less. Can be suppressed.

[Method for producing optical film]
The method for producing an optical film of the present invention is a method for producing an optical film by a solution casting method.
This production method includes a dissolution step (1) in which the dope composition of the present invention is dissolved in a solvent to prepare a dope, and a casting film in which the above-described dope composition is cast on a metal support to form a cast film. It includes at least a stretching step (2) and a peeling step (3) in which the cast film is dried and then peeled from the metal support to obtain a polymer film.
After the peeling step, a drying step of further drying the peeled polymer film to eliminate residual solvent (volatile matter) may be performed.
Moreover, you may perform the extending | stretching process (4) which extends | stretches a polymer film at least to a uniaxial direction or a biaxial direction after a peeling process.

These steps can be performed continuously by, for example, a film production line shown in FIG. However, the film production line used in the method for producing an optical film of the present invention is not limited to the one shown in FIG. The optical film in the present invention includes all the films after the peeling step.
The film production line 20 shown in FIG. 3 includes a stock tank 21, a filtration device 30, a casting die 31, a metal support 34 stretched over rotating rollers 32 and 33, a tenter dryer 35, and the like. . Further, an ear-cutting device 40, a drying chamber 41, a cooling chamber 42, a winding chamber 43, and the like are arranged.

  An agitator 61 that is rotated by a motor 60 is attached to the stock tank 21. The stock tank 21 is connected to the casting die 31 via the pump 62 and the filtration device 30.

  The width of the casting die 31 is preferably 1.1 to 2.0 times the width of the final film.

  A metal support 34 is provided below the casting die 31 so as to span the rotating rollers 32 and 33. The rotating rollers 32 and 33 are rotated by a driving device (not shown), and the metal support 34 travels endlessly with the rotation.

  In order to set the surface temperature of the metal support 34 to a predetermined value, it is preferable that the heat transfer medium circulation device 63 is attached to the rotary rollers 32 and 33. The metal support 34 preferably has a surface temperature that can be adjusted to -20 ° C to 40 ° C.

The metal support 34 preferably has a width in the range of 1.1 to 2.0 times the casting width of the dope composition 22. The length is preferably 20 m to 200 m, the film thickness is 0.5 mm to 2.5 mm, and the surface roughness is preferably polished to be 0.05 μm or less. The metal support 34 is preferably made of stainless steel, and more preferably made of SUS316 so as to have sufficient corrosion resistance and strength. Moreover, it is preferable to use the metal support 34 having an overall film thickness unevenness of 0.5% or less.
It is also possible to use the rotating rollers 32 and 33 directly as a support.

  The casting die 31, the metal support 34 and the like are accommodated in the casting chamber 64. The casting chamber 64 is provided with a temperature control facility 65 for keeping the internal temperature at a predetermined value, and a condenser (condenser) 66 for condensing and recovering the volatile organic solvent. A recovery device 67 for recovering the condensed and liquefied organic solvent is provided outside the casting chamber 64. Further, it is preferable that a decompression chamber 68 for controlling the pressure of the back surface of the casting bead formed from the casting die 31 to the metal support 34 is disposed, and this is also used in this embodiment. .

  Air blowing ports 70, 71, 72 are provided near the peripheral surface of the metal support 34 to evaporate the solvent in the casting film 69.

  The crossover portion 80 is provided with a blower 81, and the ear-cutting device 40 downstream of the tenter dryer 35 is used for finely cutting the waste at the side end (referred to as an ear) of the cut film 82. Crusher 90 is connected.

  The drying chamber 41 is provided with a number of rollers 91, and an adsorption / recovery device 92 for adsorbing / recovering the solvent gas generated by evaporation is attached. A forced static elimination device (static elimination bar) 93 for adjusting the charged voltage of the film 82 to a predetermined range (for example, −3 kV to +3 kV) is provided downstream of the cooling chamber 42. Furthermore, in this embodiment, a knurling application roller 94 for applying knurling to both edges of the film 82 by embossing is appropriately provided downstream of the forced static elimination device 93. Further, a winding roller 95 for winding the film 82 and a press roller 96 for controlling the tension at the time of winding are provided in the winding chamber 43.

Next, an example of a method for manufacturing the film 82 using the above-described film manufacturing line (referred to as a band manufacturing apparatus) 20 will be described below.
The dope composition 22 is always made uniform by the rotation of the stirrer 61. The dope composition 22 may be mixed with additives such as a retardation enhancer, a plasticizer, and an ultraviolet absorber during the stirring.

(1) Dissolution Step The dissolution step is a step for preparing the dope composition of the present invention. The dissolution step in the present invention is a step of dissolving a solid content such as acrylic resin in an organic solvent mainly containing methylene chloride while stirring to form a dope composition, or further mixing an additive solution. And a step of forming a dope composition.
Regarding the material of the dope composition, the description in the section of <Dope composition> can be referred to.

The dope composition can be prepared at a temperature of 0 ° C. or higher (ordinary temperature or high temperature). The dope composition of the present invention can be prepared using a dope preparation method and apparatus in a normal solvent cast method.
For dissolution of the polymer, a method carried out at normal pressure, a method carried out below the boiling point of methylene chloride, a method carried out under pressure above the boiling point of methylene chloride, JP-A-9-95544, JP-A-9-95557, or Various dissolution methods can be used, such as a cooling method as described in JP-A-9-95538 and a high-pressure method as described in JP-A-11-21379. From the viewpoint of dissolution efficiency, pressurization may be performed particularly above the boiling point of methylene chloride. In this case, the acrylic resin, the solvent (A) and the solvent (B) are put in a pressure vessel and sealed, and stirred while heating to a temperature not lower than the boiling point of the solvent at normal temperature and in a range where the solvent does not boil. To do.
The temperature for heating is usually 40 ° C. or higher, preferably 60 to 200 ° C., more preferably 80 to 110 ° C.
The concentration of the acrylic resin in the dope composition is preferably 10 to 35% by mass. It is preferable that an additive is added to the dope during or after dissolution to dissolve and disperse, and then filtered through a filter medium, defoamed, and sent to the next step with a liquid feed pump.

(2) Casting process The casting process is a process of casting the above-mentioned dope composition on a metal support to form a cast film. The dope composition 22 is sent to the filtration device 30 by a pump (for example, a pressurized metering gear pump) 62 and filtered there, and then cast from the casting die 31 onto the metal support 34.
A casting bead is formed from the casting die 31 to the metal support 34, and a casting film 69 is formed on the metal support 34. The temperature of the dope composition 22 during casting is preferably −10 ° C. to 57 ° C.
The casting film 69 moves as the metal support 34 moves. A pressure die that can adjust the slit shape of the die base and facilitates uniform film thickness is preferred. The pressure die includes a coat hanger die and a T die, and any of them is preferably used. In order to increase the film forming speed, two or more pressure dies may be provided on the metal support, and the dope amount may be divided and stacked. Or it is also preferable to obtain the film of a laminated structure by the co-casting method which casts several dope simultaneously.

(3) Solvent drying and peeling process Next, the casting film 69 is continuously conveyed to the location where the air blowing port 73 is arranged in the upper part. Dry air is blown toward the casting film 69 from the nozzle of the air blowing port 73. The solvent evaporation process is a process in which the casting film is heated on the metal support and the solvent is evaporated until the casting film can be peeled from the metal support (until the casting film has a self-supporting property and becomes a polymer film). is there.
In order to evaporate the solvent, air is blown from the casting film side and / or heat is transferred from the back of the metal support by liquid, heat is transferred from the front and back by radiant heat, energy such as microwave and far infrared Although there is a method of applying a wire, the method of backside liquid heat transfer 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 a boiling point of methylene chloride or less.

The cast film 69 is peeled off from the metal support 34 while being supported by the peeling roller 75 as the polymer film 74 after becoming a polymer film having self-supporting property as a result of evaporation of the solvent by drying.
Here, the temperature at the peeling position on the metal support 34 is preferably −50 to 40 ° C., more preferably −30 to 35 ° C., and further preferably −10 to 30 ° C.

  The residual solvent amount (volatile content) at the time of peeling of the polymer film on the metal support at the time of peeling is in the range of 50 to 120% by mass depending on the strength of drying conditions, the length of the metal support, and the like. Peeling is preferable, but when peeling is performed when the amount of residual solvent (volatile matter) is larger, if the polymer film is too soft, the flatness is impaired when peeling from the metal support, and vertical streaks due to peeling tension occur. Therefore, the residual solvent amount (volatile content) at the time of peeling is determined in consideration of the economic speed and quality.

  The polymer film (wet film) 74 that has been peeled off under the above conditions is then transported through the transfer section 80 provided with a number of rollers, and the polymer film 74 is fed into the tenter dryer 35. In the transfer part 80, the drying of the polymer film 74 is advanced by blowing dry air of a desired temperature from the blower 81. At this time, the temperature of the drying air is preferably 20 ° C to 250 ° C.

  The polymer film 74 is preferably stretched in the width direction (TD direction) orthogonal to the transport direction (MD direction). By stretching in the width direction, unevenness generated at the time of drying and stripping on the support can be reduced, and a good surface shape can be obtained in the film plane. The draw ratio in the width direction is preferably 10% or more, more preferably 20% or more, and still more preferably 30% or more.

(4) Drying and stretching step The polymer film 74 sent to the tenter dryer 35 is dried while being transported while being gripped by clips at both ends. In this case, stretching in the width direction can be performed using a tenter dryer 35.
It is preferable to divide the inside of the tenter dryer 35 into temperature zones and adjust the drying conditions appropriately for each of the zones.
In this way, the polymer film 74 can be stretched in the width direction by the crossover 80 and / or the tenter dryer 35.
Stretching in the transport direction may be performed, and by making the rotational speed of the downstream roller faster than the rotational speed of the upstream roller at the crossover portion 80, the polymer film 74 is given draw tension in the transport direction. be able to.
Here, in the transfer part 80 and / or the tenter dryer 35, the polymer film 74 is dried without being stretched, and the residual solvent amount in the film is 3.0% by mass or less, preferably 1.0% by mass or less. More preferably, the stretching may be performed after the content is 0.5% by mass or less, more preferably 0.3% by mass or less, and particularly preferably 0.2% by mass or less.
In addition, when extending | stretching the polymer film which made the residual solvent amount 3.0 mass% or less, you may extend | stretch, after winding up once, without extending | stretching.
The polymer film to be stretched may be a dry film or a wet film, but is preferably a wet film. The stretching treatment may be performed in any one of the transport direction (MD) and the width direction (TD), and it is preferable to perform biaxial stretching in both the transport direction and the width direction. Each stretching may be performed in one stage or in multiple stages. In the case of biaxial stretching, it is preferable to perform stretching in the order of the transport direction and then the width direction.

  The stretching ratio in the width direction is preferably 110% to 500%, more preferably 120% to 400%, and particularly preferably 130% to 300%, when 100% is not stretched. preferable. Similarly, the draw ratio in the conveying direction is preferably 110% to 500%, more preferably 120% to 400%, and particularly preferably 130% to 300%.

  Here, the glass transition temperature of the unstretched polymer film after drying is the glass transition temperature of the aforementioned thermoplastic resin, preferably 90 to 200 ° C, more preferably 100 to 180 ° C. The temperature during stretching is preferably a temperature range of Tg ± 30 ° C. with respect to the glass transition temperature Tg of the unstretched polymer film after drying, more preferably a temperature range of Tg ± 25 ° C., and Tg ± 20 A temperature range of ° C is more preferred. Stretching in this temperature range has good film handling suitability, and a desired optical film can be produced without breaking the polymer film. By stretching at a temperature of (Tg-30 ° C.) or higher, the film can be prevented from being broken. Moreover, extending | stretching at the temperature below (Tg + 30 degreeC) can prevent extending | stretching by the dead weight of a film. Moreover, the increase in the total haze and internal haze due to phase separation in the film can be suppressed.

  As described above, the stretching treatment may be performed in a drying process after the polymer film 74 is formed and then passed through the crossing section 80 and the tenter dryer 35, or may be performed after the polymer film 74 is dried and wound up. . Casting conditions are preferably performed under such a condition that the film thickness is 10 to 200 μm when the film is produced unstretched, more preferably 10 to 150 μm, still more preferably 10 to 100 μm, and 10 to 10 μm. Most preferably, the conditions are 60 μm.

  The polymer film 74 is dried to a predetermined residual solvent amount (volatile content) by the tenter dryer 35, and then sent to the downstream side as a film 82. Both ends of the film 82 are cut at both edges by the edge-cutting device 40. The cut side end portion is sent to the crusher 90 by a cutter blower (not shown). The crusher 90 pulverizes the film side end portion into a chip. Since this chip is reused for the preparation of the dope composition, this method is effective in terms of cost. In addition, although it can also abbreviate | omit about the cutting process of this film both ends, it is preferable to carry out in any one from the above-mentioned casting process to the process of winding up the above-mentioned film.

  The film 82 from which both side ends have been removed is sent to the drying chamber 41 and further dried. The temperature in the drying chamber 41 is preferably in the range of 50 ° C to 160 ° C. In the drying chamber 41, the film 82 is conveyed while being wound around a roller 91, and the solvent gas generated by evaporation here is adsorbed and recovered by an adsorption recovery device 92. The air from which the solvent component has been removed is blown again as dry air inside the drying chamber 41. The drying chamber 41 is more preferably divided into a plurality of sections in order to change the drying temperature.

  The film 82 is cooled to approximately room temperature in the cooling chamber 42. A humidity control chamber (not shown) may be provided between the drying chamber 41 and the cooling chamber 42. When providing this humidity control chamber, it is preferable that air adjusted to a desired humidity and temperature is blown onto the film 82. Thereby, generation | occurrence | production of the curling of the film 82 and the winding defect at the time of winding can be suppressed.

  Further, in the present invention, it is preferable to provide a knurling roller 94 and to impart knurling to at least one end of the film 82 by embossing. 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 knurled only on one side or knurled on both sides.

(Take-up)
Finally, the film 82 is taken up by the take-up roller 95 in the take-up chamber 43. At this time, it is preferable to wind the sheet while applying a desired tension with the press roller 96. More preferably, the tension is gradually changed from the start to the end of winding. The film 82 to be wound is preferably at least 100 m in the transport direction. The width of the film 82 is preferably 600 mm or more, more preferably 1100 mm or more and 2900 mm or less, and further preferably 1800 mm or more and 2500 mm or less.

  In the solution casting method, when casting the dope composition, two or more kinds of dope compositions can be simultaneously laminated or sequentially laminated. Furthermore, you may combine both casting. 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. A multi-layer film can be obtained by co-casting. In this multilayer film, 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 metal support.

From casting die, decompression chamber, metal support structure, co-casting, peeling method, stretching, drying conditions of each process, handling method, curling, winding method after flatness correction, solvent recovery method, film recovery The method is described in detail in paragraphs [0617] to [0889] of JP-A-2005-104148.
In the above description, an example of the method for producing the optical film of the present invention has been described in an example in which the dope composition is cast on a band in the casting process. However, the method for producing the optical film of the present invention is a casting process. The same mechanism is established when the dope composition is cast on a drum. In this case, the apparatus and manufacturing conditions described in JP2013-82192A are preferably used.

[Thickness and characteristics of optical film]
Next, the film thickness and characteristics of the optical film of the present invention will be described. The optical film of the present invention preferably has excellent functions as a polarizing plate protective film and an optical compensation film by satisfying the following characteristics.

(Film thickness)
The film thickness of the optical film of the present invention is preferably 10 to 150 μm, more preferably 10 to 100 μm, and further preferably 10 to 60 μm.

(Glass-transition temperature)
In this specification, “glass transition temperature Tg” means that when a film sample is heated at a rate of temperature increase of 10 ° C./min using a differential scanning calorimeter (DSC), the measured temperature is from the baseline. It means the average value of the temperature that begins to change and the temperature that returns to the baseline again. Note that the change in the measured temperature from the baseline is due to the glass transition of the film.
The optical film of the present invention preferably has a glass transition temperature of 90 ° C. or higher, more preferably 90 to 200 ° C., and still more preferably 90 to 180 ° C.

[Application example of optical film]
The optical film of the present invention can be preferably used as, for example, a polarizing plate protective film and an optical compensation film for a liquid crystal display device. The optical compensation film is generally used for a liquid crystal display device and refers to an optical material that compensates for a retardation, and is synonymous with a retardation plate, an optical compensation sheet, and the like. The optical compensation film has birefringence and is used for the purpose of removing the color of the display screen of the liquid crystal display device or improving the viewing angle characteristics.

  The optical film obtained by forming the dope composition of the present invention may be an optical compensation film itself, or may be used as a support for the optical compensation film, and an optical anisotropic layer is provided thereon. Also good. The optically anisotropic layer is not limited to the optical performance or driving method of the liquid crystal cell of the liquid crystal display device in which the optical film of the present invention is used, and any optically anisotropic layer required as an optical compensation film Can be used together. The optically anisotropic layer used in combination may be formed from a composition containing a liquid crystalline compound or may be formed from a thermoplastic film having birefringence.

[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 in a low pressure gas of 10 ^{−3 to} 20 Torr, and plasma treatment under atmospheric pressure is also preferable. 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 the at least one surface of the above-mentioned polymer film. 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. The functional layer laminating method described above includes the co-flow with the dope composition of the present invention to form the above polymer film, or the above polymer film formed using the dope composition of the present invention. It is preferable to be coated on top.
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. The aforementioned monomers 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. .

Specific examples of the monomer having two or more (meth) acryloyl groups include (meth) acrylic alkylene glycols such as neopentyl glycol acrylate, 1,6-hexanediol (meth) acrylate, and propylene glycol di (meth) acrylate. Acid diesters;
(Meth) acrylic acid diesters of polyoxyalkylene glycols such as triethylene glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate;
(Meth) acrylic acid diesters of polyhydric alcohols such as pentaerythritol di (meth) acrylate;
(Meth) acrylic acid diesters of ethylene oxide or propylene oxide adducts such as 2,2-bis {4- (acryloxy · diethoxy) phenyl} propane and 2-bis {4- (acryloxy · polypropoxy) phenyl} propane ;
Etc.

  Furthermore, epoxy (meth) acrylates, urethane (meth) acrylates, and polyester (meth) acrylates are also preferably used as the photopolymerizable polyfunctional monomer.

Among these, esters of polyhydric alcohol and (meth) acrylic acid are preferable. A polyhydric alcohol means a dihydric or higher alcohol.
More preferably, a polyfunctional monomer having 3 or more (meth) acryloyl groups in one molecule is preferable. For example, pentaerythritol tetra (meth) acrylate, pentaerythritol tri (meth) acrylate, trimethylolpropane tri (meth) acrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, propylene oxide modified trimethylolpropane tri (meth) acrylate, Ethylene oxide modified tri (meth) acrylate phosphate, trimethylolethane tri (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, dipentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (Meth) acrylate, 1,2,3-cyclohexanetetramethacrylate, polyurethane polyacrylate, Li ester polyacrylate, caprolactone-modified tris (acryloyloxyethyl) isocyanurate.

  Furthermore, resins having three or more (meth) acryloyl groups, such as relatively low molecular weight polyester resins, polyether resins, acrylic resins, epoxy resins, urethane resins, alkyd resins, spiroacetal resins, polybutadiene resins, polythiol polyene resins And oligomers or prepolymers such as polyfunctional compounds such as polyhydric alcohols.

  As other polyfunctional monomers described above, for example, dendrimers described in JP-A-2005-76005 and JP-A-2005-36105 can be used.

As the polyfunctional monomer, esters of polyhydric alcohol and (meth) acrylic acid, and amides of polyhydric alcohol and isocyanate containing a plurality of (meth) acryloyl groups are also preferably used.
The polyhydric alcohol is not particularly limited, but is preferably an aliphatic alcohol, and more preferably an alcohol having a cyclic aliphatic hydrocarbon group. The aliphatic group of the monocyclic alicyclic alcohol is preferably a cycloalkyl group having 3 to 8 carbon atoms, and examples thereof include a cyclopentyl group, a cyclobutyl group, a cyclohexyl group, and a cyclooctyl group.
Examples of the aliphatic group of the polycyclic alicyclic alcohol include a group having a bicyclo, tricyclo, tetracyclo structure or the like having 5 or more carbon atoms, and a cycloalkyl group having 6 to 20 carbon atoms is preferable. Adamantyl group, norbornyl group, dicyclopentyl group, tricyclodecanyl group, tetracyclododecyl group, central skeleton of compounds described in claims of JP-A-2006-215096, compound described in JP-A-2001-10999 And the like. A part of carbon atoms in the cycloalkyl group may be substituted with a hetero atom such as an oxygen atom.
Among them, examples of the polycyclic alcohol include an adamantyl group, a norbornyl group, a dicyclopentyl group, a tricyclodecanyl group, a tetracyclododecyl group, and a central skeleton of the compound described in the claims of JP-A-2006-215096. Polyhydric alcohols having a central skeleton of the compounds described in JP-A No. 2001-10999 are particularly preferred from the viewpoint of reducing moisture permeability.

  Two or more kinds of polymerizable polyfunctional monomers may be used in combination. Polymerization of these monomers having an ethylenically unsaturated group can be carried out by irradiation with ionizing radiation or heating in the presence of a photo radical initiator or a thermal radical initiator. Among these, it is preferable to use a photopolymerization initiator. As the photopolymerization initiator, a photoradical polymerization initiator and a photocationic polymerization initiator are preferable, and a photoradical polymerization initiator is particularly preferable.

  Moreover, it is also preferable to use the above-mentioned polymerizable polyfunctional monomer in combination with a monofunctional monomer.

  As the monofunctional monomer, a monomer having one (meth) acryloyl group is preferable, and a monomer having one (meth) acryloyl group is usually obtained from a monovalent alcohol and acrylic acid.

The monohydric alcohol may be an aromatic alcohol or an aliphatic alcohol.
As monohydric alcohol, methyl alcohol, n-propyl alcohol, iso-propyl alcohol, n-butyl alcohol, tert-butyl alcohol, n-amyl alcohol, diacetone alcohol, 1-methoxy-2-propanol, furfuryl alcohol 2-octanol, 2-ethylhexanol, nonanol, n-decanol, undecanol, n-dodecanol, trimethylnonyl alcohol, benzyl alcohol, phenethyl alcohol, ethylene glycol monoisoamyl ether, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, Examples include ethylene glycol monohexyl ether.
Moreover, about the aliphatic part of aliphatic alcohol, cycloaliphatic may be sufficient. The cycloaliphatic may be monocyclic, polycyclic, or may be bridged in the case of polycyclic. As the monocyclic type, a cycloalkyl group having 3 to 8 carbon atoms is preferable, and examples thereof include a cyclopentyl group, a cyclohexyl group, a cyclobutyl group, and a cyclooctyl group. Examples of the polycyclic type include groups having a bicyclo, tricyclo or tetracyclo structure having 5 or more carbon atoms, and a cycloalkyl group having 6 to 20 carbon atoms is preferable, for example, an adamantyl group, norbornyl group, dicyclopentyl group. , Tricyclodecanyl group, tetracyclododecyl group, central skeleton of the compound described in the claims of JP-A-2006-215096, central skeleton of the compound described in JP-A-2001-10999, and the like. . A part of carbon atoms in the cycloalkyl group may be substituted with a hetero atom such as an oxygen atom.

  The monovalent alcohol, whether it is an aromatic alcohol or an aliphatic alcohol, preferably has 6 or more carbon atoms.

  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.

  When the moisture permeability reducing layer is provided, the moisture permeability (C) of the optical film on which the moisture permeability reducing layer is laminated and the moisture permeability (D) of the optical film without the moisture permeability reducing laminate are C / D of 0. It should be 9 or less. More preferably, it is 0.85 or less, and more preferably 0.8 or less.

<< Polarizing plate >>
Next, the polarizing plate of the present invention will be described.
The polarizing plate of the present invention has at least one optical film of the present invention as a polarizing plate protective film. For the configuration of the optical film, the description in the section <Optical film> can be referred to. The polarizing plate is produced by, for example, a method in which the optical film of the present invention is treated with an alkali and bonded to both sides of a polarizer produced by immersing and stretching a polyvinyl alcohol film in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. There is. 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 for bonding 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 both sides of the polarizer, and further comprises a protective film on one side of the polarizing plate and a separate film on the opposite side. Is more preferable. The protective film and the separate film are used for the purpose of protecting the polarizing plate at the time of shipping the polarizing plate and at the time of product inspection. In this case, the protect film is bonded for the purpose of protecting the surface of the polarizing plate, and is used on the side opposite to the surface where the polarizing plate is bonded to the liquid crystal plate. Moreover, a separate film is used in order to cover the adhesive layer bonded to a liquid crystal plate, and is used for the surface side which bonds a polarizing plate to a liquid crystal plate.
In a liquid crystal display device, a substrate including a liquid crystal cell is usually disposed between two polarizing plates. The optical film of the present invention can be used as any protective film of two polarizing plates. Of the two polarizing plate protective films of the plate, it is preferably used as a polarizing plate protective film disposed on the liquid crystal cell side with respect to the polarizer.

<< Liquid Crystal Display >>
The liquid crystal display device of the present invention includes the polarizing plate of the present invention. The liquid crystal display device preferably includes a liquid crystal cell and the polarizing plate of the present invention disposed in at least one of the liquid crystal cells, and the optical film of the present invention contained in the polarizing plate is the outermost layer. It is more preferable that they are arranged in the.

(General liquid crystal display device configuration)
The liquid crystal display device includes a liquid crystal cell in which liquid crystal is supported between two electrode substrates, two polarizing plates disposed on both sides thereof, and at least one between the liquid crystal cell and the polarizing plate as necessary. It is preferable to have a configuration in which a single optical compensation film is disposed.
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 optical film of the present invention can be used for liquid crystal cells in various display modes. TN (Twisted Nematic), IPS (In-Plane Switching), FLC (Ferroelectric Liquid Crystal), AFLC (Anti-Ferroly Liquid Liquid Crystal), OCB (Optically QuantNW). Various display modes such as 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 optical film of the present invention is effective in any display mode liquid crystal display device. Further, it is effective in any of a transmissive type, a reflective type, and a 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.

<Preparation of material>
(acrylic resin)
The acrylic resin described below was used.

-Production Example 1-
An acrylic resin having a weight average molecular weight of 1,200,000 and an MMA ratio of 100% used in Examples 1 and 6 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 benzoyl peroxide were added and reacted at 85 ° C. for 6 hours. The obtained suspension was filtered with a nylon filter cloth, washed with water, and the filtrate was dried at 50 ° C. overnight to obtain the target polymer in the form of beads (92.0 g).

-Other production examples-
An acrylic resin having a weight average molecular weight of 800,000 and an MMA ratio of 100% used in Example 2 was synthesized in the same manner as in Production Example 1 except that the amount of benzoyl peroxide added was changed to 0.23 g.
An acrylic resin having a weight average molecular weight of 500,000 and an MMA ratio of 100% used in Example 3 was synthesized in the same manner as in Production Example 1 except that the amount of benzoyl peroxide added was changed to 0.36 g.
The acrylic resin having a weight average molecular weight of 300,000 and an MMA ratio of 100% used in Example 4 and Comparative Examples 3 and 4 was the same as in Production Example 1 except that the amount of benzoyl peroxide added was changed to 0.61 g. Synthesized.
The acrylic resin having a weight average molecular weight of 300,000 and MMA / styrene copolymer (80/20, polymerization ratio) used in Example 5 was changed to 80 g of methyl methacrylate and 20 g of styrene. The synthesis was performed in the same manner except that the amount of benzoyl oxide charged was changed to 0.6 g.
An acrylic resin having a weight average molecular weight of 200,000 and an MMA ratio of 100% used in Comparative Example 1 was synthesized in the same manner as in Production Example 1 except that the amount of benzoyl peroxide added was changed to 0.92 g.
An acrylic resin having a weight average molecular weight of 100,000 and an MMA ratio of 100% used in Comparative Example 2 was synthesized in the same manner as in Production Example 1 except that the amount of benzoyl peroxide added was changed to 1.83 g.

[Example 1]
<Dissolution process: preparation of dope composition>
The composition described below was put into a mixing tank and stirred at room temperature to dissolve each component to prepare a dope.

(Dope composition)
PMMA resin with a weight average molecular weight of 1,200,000 100 parts by mass Methylene chloride 350 parts by mass Methanol 77 parts by mass

  The prepared dope composition had a dope solid content of 19%, and the viscosity was measured to be 30 Pas · sec.

<Measurement of dope characteristics and evaluation of dope>
(Measurement method of dope solid content concentration when complex viscosity is 30 Pas · sec)
A dope composition was prepared in which the solid content concentration used in the dope composition prepared above was changed by 1% from 10% to 50%, and the solvent had a mass ratio of (A) methylene chloride and (C) methanol. A: C = 82: 18. The complex viscosity at 22 ° C. of this dope composition was measured by the above-described complex viscosity measurement method, and the dope solid content concentration at 30 Pas · sec was obtained.

(Turbidity)
The turbidity of the dope composition prepared above was visually evaluated by separating 50 mL of the sample solution into a 100 mL glass sample tube.
No turbidity: Evaluation was made based on a judgment criterion that the other side of the glass sample tube was visible and the turbidity was clearly transparent: the turbidity was white and the other side of the sample tube was not visible.

(Residual MeOH ratio measurement: gas chromatography volatile content measurement)
Using the dope composition prepared above, the amount of residual MeOH when the polymer film was stripped from the metal support with a residual volatile content of 50% was measured by the following method.
0.2 g of the peeled film was dissolved in 20 g of chloroform, and the methylene chloride concentration and the methanol concentration in the film were measured by gas chromatography. GC-2014 (manufactured by Shimadzu Corporation) is used for gas chromatography, a packed column 54 is used, the temperature raising condition is the vaporization chamber temperature 200 ° C., and the column temperature raising condition is 160 ° C. from the starting temperature to 3 ° C. The temperature was increased to 180 ° C./min. Methanol was detected at a retention time of 1.9 minutes, and methylene chloride was detected at a retention time of 5.5 minutes. A calibration curve was prepared with each solvent prepared to a specified concentration in advance, and the concentration was determined.
The residual methanol ratio was calculated | required from the amount of methylene chloride and methanol which remain | survived in the film obtained from the above, and the initial amount of methylene chloride and methanol at the time of dope preparation.

<Film formation of optical film>
(Casting process)
Using the film production line as shown in FIG. 3, the above prepared dope was uniformly cast from a casting die onto a stainless steel metal support having a width of 2000 mm to form a casting film.

(Peeling process)
When the residual solvent amount (volatile content) in the cast film reaches 50% by mass, it is stretched by 40% in the MD direction when peeling from the metal support, and stretched by 40% in the TD direction by a tenter and dried. Drying was performed at 140 ° C. in the zone.
A polymer film having a thickness of 40 μm was produced through the above steps. The single-layer film of the polymer film thus obtained was used as the optical film of Example 1.

[Evaluation of optical film]
(Glass-transition temperature)
When the glass transition temperature of the obtained optical film was measured with a differential scanning calorimeter (DSC) using a film sample 7 mm × 35 mm cut out from the optical film at a heating rate of 10 ° C./min, the glass of the sample film It was determined as the average value of the temperature at which the baseline derived from the transition begins to change and the temperature at which the baseline returns again.

(Equilibrium moisture content)
The equilibrium moisture content is measured by using a film sample 7 mm × 35 mm cut out from an optical film as a moisture meter and a sample drying apparatus “CA-03” and “VA-05” (both manufactured by Mitsubishi Chemical Corporation). Measured by the method. It was calculated by dividing the amount of water (g) by the sample mass (g).

(Film surface)
Within a 6 cm diameter region in the film, the occurrence location (number of occurrences) of stepped unevenness having a pitch of 0.5 to 2.0 cm and a thickness difference of 2.0 to 3.0 μm was measured. A total of nine places were evaluated from the areas of 1 m in the longitudinal direction and 1 m in the width direction of the formed film, with three places at 50 cm intervals, and the number was averaged.
The thickness height difference was measured with a FUJINON fringe analyzer (FX-03) as the maximum height difference (PV value) within an area of 6 cm in diameter. At this time, the average refractive index of 1.49 of acrylic resin was used as the value of the refractive index to be input. The resolution of this apparatus is 512 × 512.
The film surface condition was evaluated according to the following criteria based on the obtained measurement values. In the present invention, A or B is an acceptable level, and is preferably A.
A: No stepped unevenness having a maximum height difference (P-V value) of 2.0 to 3.0 μm.
B: 1 to 3 stepped irregularities having a maximum height difference (PV value) of 2.0 to 3.0 μm were generated.
C: 4 to 15 stepped irregularities having a maximum height difference (PV value) of 2.0 to 3.0 μm were generated.
D: 16 or more stepped irregularities having a maximum height difference (P-V value) of 2.0 to 3.0 μm occurred.

(Examples 2-5, Comparative Examples 1-2)
As the composition of the dope composition, the resin and the solid content were changed as shown in Table 1, respectively, except that the dope solid content concentration was such that the viscosity of the dope was 30 Pas · sec. Optical films of Examples and Comparative Examples were produced and evaluated in the same manner.

(Example 6)
A dope composition was prepared in the same manner as in Example 1 except that 2.7 parts by mass of the following compound 1 was added as an ultraviolet absorber to 100 parts by mass of the acrylic resin, and an optical film was produced.
Compound 1

(Comparative Example 3)
(Dope composition)
PMMA resin having a weight average molecular weight of 300,000 100 parts by mass Methylene chloride 226 parts by mass Methanol 31 parts by mass

(Comparative Example 4)
(Dope composition)
PMMA resin having a weight average molecular weight of 300,000 100 parts by mass Methylene chloride 116 parts by mass Methanol 141 parts by mass

  The obtained results are shown in Table 1.

As shown in Table 1, the optical film of each example has an initial methanol ratio of more than 15%, so that the residual alcohol concentration at the time of peeling tends to increase, both of which have a small peel load, It was excellent in transparency. In each example, no streak was observed when the casting film was discharged from the casting die.
On the other hand, the optical films of Comparative Examples 1 and 2 in which the weight average molecular weight of the acrylic resin was less than 250,000 had many stepped irregularities on the surface and were inferior in flatness.
Further, in Comparative Example 3 in which the mass ratio of methanol is less than 15%, a large load is required when the polymer film is peeled off, and a part of the polymer film remains on the metal support to form a film surface (stepped shape). (Mura) was bad.
In Comparative Example 4 in which the mass ratio of methanol exceeded 50%, the dope was cloudy due to insufficient dissolution, and the viscosity could not be measured. An attempt was made to produce a film, but the film became whitened. The film remained partially peeled on the metal support, the peeling load was large, and the film surface (step unevenness) was also whitened, making measurement impossible.
In addition, in the dope composition used in each Example, content of the cellulose ester with respect to the above-mentioned acrylic resin was confirmed by the method as described in this specification. As a result, the cellulose ester was below the detection limit, and it was confirmed that the content of the cellulose ester was less than 0.5% by mass with respect to the acrylic resin described above.

(Comparative Example 5)
Furthermore, the cellulose ester 35 having an acetyl group substitution degree of 0.19 and a propionyl group substitution degree of 2.56 was added to 65 parts by mass of the PMMA resin having a weight average molecular weight of 1,200,000 used in Example 1 in accordance with JP2013-120278A. A dope composition was prepared in the same manner as in Example 1 except that the amount was in parts by mass. As a result, whitening derived from the cellulose ester was observed, and an optical film was produced. However, the film was turbid and the equilibrium moisture content was low. In the optical film of Example 1, the optical film of Comparative Example 5 was as high as 2.3% with respect to 1.5%, and as an optical film, the temperature and humidity were insufficient in wet heat durability against environmental changes.

<Preparation of polarizing plate>
After immersing Fujitac TD60UL (manufactured by FUJIFILM Corporation) in a 4.5 mol / L sodium hydroxide aqueous solution (saponification solution) adjusted to 37 ° C. for 1 minute, the film was washed with water, and then 0.05 mol / L. After being immersed in an aqueous sulfuric acid solution for 30 seconds, it was further passed through a washing bath. Then, draining with an air knife was repeated three times, and after dropping the water, it was retained in a drying zone at 70 ° C. for 15 seconds and dried to produce a saponified tack film.
Next, according to Example 1 of Japanese Patent Laid-Open No. 2001-141926, a circumferential speed difference was given between two pairs of nip rolls, and the film was stretched in the longitudinal direction to prepare a polarizer having a thickness of 20 μm.
On one side of the polarizer thus obtained, the above-mentioned saponified tack film was bonded with a 3% aqueous solution of PVA (manufactured by Kuraray Co., Ltd., PVA-117H) as an adhesive, and the other side of the polarizer was bonded. Using an acrylic adhesive on the surface, the optical film of each example was subjected to corona treatment by roll-to-roll so that the absorption axis of the polarizer and the longitudinal direction of the tack film and the optical film are parallel to each other. The polarizing plate was produced by bonding.
In addition, an optical film containing the ultraviolet absorber of Example 6 was used in place of the above-mentioned Fujitac TD60UL, and a polarizing plate was prepared by laminating the optical film of Example 1 with an acrylic adhesive on both sides of the polarizer.
All of the optical films of each Example had sufficient bonding properties with polyvinyl alcohol, and had excellent polarizing plate processing suitability.

(Display performance evaluation in IPS liquid crystal display device)
The polarizing plate sandwiching the liquid crystal cell is peeled off from a commercially available liquid crystal television (IPS mode slim type 42-inch liquid crystal television), and the above-prepared polarizing plate is placed on the liquid crystal cell side on the optical film side of each example. As shown in the figure, it was re-bonded to the liquid crystal cell via an adhesive. The reassembled LCD TV was held for 3 days in an environment of 50 ° C. and 80% relative humidity, then moved to an environment of 25 ° C. and 60% relative humidity, kept on in a black display state, and visually observed after 48 hours. Light unevenness was evaluated.
When observing luminance unevenness during black display when observed from the front of the apparatus, it was found that the unevenness was hardly visually recognized in an environment with an illuminance of 100 lx.

1 Series using acrylic resin with a weight average molecular weight of 1,200,000 2 Series using acrylic resin with a weight average molecular weight of 300,000 Series 4 using acrylic resin with a weight average molecular weight of 120,000 Use acrylic resin with a weight average molecular weight of 100,000 Series 20 Film production line 21 Stock tank 22 Dope composition 30 Filtration device 31 Casting dies 32, 33 Rotating roller 34 Metal support 35 Tenter dryer 40 Ear-cut device 41 Drying chamber 42 Cooling chamber 43 Winding chamber 60 Motor 61 Stirrer 63 Heat medium circulation device 64 Casting chamber 65 Temperature control facility 66 Condenser
67 Recovery Device 68 Decompression Chamber 69 Casting Films 70, 71, 72, 73 Blowing Port 74 Polymer Film 80 Crossing Portion 81 Blower 82 Film 90 Crusher 91 Roller 92 Adsorption Recovery Device 93 Forced Static Removal Device (Static Removal Bar)
94 Knurling roller 95 Winding roller 96 Press roller

Claims (10)

  An acrylic resin having a weight average molecular weight Mw of 250,000 or more, and a solvent having a mass ratio A: B of 85 to 15:50 of A methylene chloride and B 1-4 alcohol, The dope composition whose content is less than 0.5 mass% with respect to the said acrylic resin.   When the solid content contained in the dope composition was mixed with a solvent having a mass ratio of A methylene chloride and C methanol of A: C = 82: 18 to prepare a mixture, the complex viscosity at 22 ° C. of the mixture was 30 Pas. The dope composition according to claim 1, wherein the dope solid content concentration at 30 seconds is 30% by mass or less.   The dope composition according to claim 1 or 2, wherein the solid content concentration is 10% by mass or more and 30% by mass or less.   Content of the said acrylic resin is 70 mass% or more with respect to solid content whole quantity, Dope composition of any one of Claims 1-3.   The solid content of a material other than the acrylic resin is 2% by mass or more based on the total solid content, and the equilibrium moisture content of the solid content of the material other than the acrylic resin is smaller than the equilibrium moisture content of the acrylic resin. The dope composition of any one of 1-4.   The optical film which has a polymer film obtained by forming the dope composition of any one of Claims 1-5 into a film.   The number of occurrences of step-like unevenness having a pitch of 0.5 to 2.0 cm and a thickness height difference of 2.0 to 3.0 μm in an area of 6 cm in diameter from an arbitrarily set center is less than ten. Optical film. A dissolving step of preparing the dope composition according to any one of claims 1 to 5;
A casting step of casting a dope composition on a metal support to form a casting film;
A method for producing an optical film, comprising: drying a cast film to form a polymer film; and peeling the polymer film from the metal support to obtain a polymer film.   A polarizing plate having at least one optical film according to claim 6 as a polarizing plate protective film.   A liquid crystal display device comprising the polarizing plate according to claim 9.

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