WO2013145560A1 - Method for producing optical film, optical film, polarizing plate, and liquid crystal display device - Google Patents

Abstract

The present invention relates to a method for producing an optical film that comprises an acrylic resin and a cellulose ester resin fulfilling the equations 2.3 ≤ X+Y ≤ 2.6 and 1.4 ≤ X ≤ 2.6 or an optical film that comprises a cellulose ester resin in which the degree of substitution of an acetyl group in a cellulose ester moiety is 2.0 to 2.5, said method being characterized in that the production is carried out by a solvent-casting film formation process using a dope that has a water content of 2.0 to 5.0 mass% during a period from the initiation of the production to a rising time at which a steady operation is initiated and has a water content of 0.6 to 2.0 mass% during a period in which the steady operation is carried out.

Description

Optical film manufacturing method, optical film, polarizing plate, and liquid crystal display device

The present invention relates to an optical film manufacturing method, an optical film manufactured by the manufacturing method, a polarizing plate using the optical film, and a liquid crystal display device.

In recent years, the development of thinner and lighter information devices equipped with liquid crystal display devices such as LCD TVs, notebook computers, car navigation systems, and mobile phones has been increasingly advanced. Along with this, there is an increasing demand for thinner protective films for polarizing plates used in liquid crystal display devices.

In general, a polarizing plate uses a transparent protective film bonded to both sides of a polarizer by a so-called aqueous adhesive in which a polyvinyl alcohol-based material is dissolved in water, and the transparent protective film has high moisture permeability. From this point, cellulose ester resin is used.

However, since a film containing a cellulose ester resin has a large dimensional change in a high temperature and high humidity environment, a film containing an acrylic resin having a low moisture permeability may be used as a transparent protective film.

When a film containing an acrylic resin and a cellulose ester resin is formed by the melt casting film forming method, if the temperature of the cooling roll is high, the acrylic resin has a thermoplasticity, and the film is peeled off at the time of peeling. Sticking and deformation will occur. In Patent Document 1, by adding a low molecular weight precipitant, the surface temperature of the cooling roll used in the melt flow salt film forming method can be set to a relatively high temperature, and the flatness of the film at the time of peeling. A technique for preventing defects is described.

However, since the technique is based on a manufacturing method using a melt casting film forming method, a film containing an acrylic resin and a cellulose ester resin or a film containing diacetyl cellulose is manufactured by a solution casting film forming method. Is not described.

However, even when a film is produced by a solution casting film forming method using a dope containing an acrylic resin and a cellulose ester resin or a dope containing diacetyl cellulose, the thermoplastic resin has a cause. It is difficult to peel the film from the support belt. In particular, when the film is peeled from the support belt at the time of start-up from the start of production to the steady operation, it becomes difficult to peel the film from the support belt due to the slow line speed. The film is easily broken.

Therefore, when the moisture content of the dope is increased, the peelability is improved when the film is peeled off from the support belt even at the time of start-up. However, when the moisture content of the dope is increased, contamination of the support belt during steady operation causes a haze when used in a polarizing plate, resulting in a problem that the panel contrast is lowered.

JP 2011-68005 A

The present invention has been made in view of such circumstances, and its purpose is to provide a low risk of film breakage at both the start-up and the steady operation from the start of production to the steady operation, and support. An object of the present invention is to provide a method for producing an optical film which does not cause body belt contamination. Furthermore, it is providing the optical film produced by the said manufacturing method, a polarizing plate using the same, and a liquid crystal display device.

As a result of intensive studies by the present inventors to achieve the above object, it is possible to obtain a method for producing an optical film that has high peelability from the support belt and does not cause stain on the support belt by the following configuration. The headline and the present invention were completed.

That is, in the method for producing an optical film according to one aspect of the present invention, an optical film containing an acrylic resin and a cellulose ester resin satisfying the following formulas (1) and (2), or the substitution degree of the acetyl group of the cellulose ester is In the method for producing an optical film containing a cellulose ester resin of 2.0 to 2.5, the water content is 2.0 to 5.0% by mass at the time of start-up from the start of production to steady operation. During operation, the dope having a moisture content of 0.6 to 2.0% by mass is produced by a solution casting film forming method.

Formula (1) 2.3 <= X + Y <= 2.6
Formula (2) 1.4 ≦ X ≦ 2.6
(In the above formula, X represents the degree of substitution of the acetyl group of the cellulose ester, and Y represents the degree of substitution of the propionyl group or butyryl group.)

According to the present invention, an object of the present invention is to provide a method for producing an optical film that has a low risk of film breakage and is less susceptible to substrate belt contamination. Furthermore, the optical film produced by the said manufacturing method, the polarizing plate using the same, Comprising: A polarizing plate and a liquid crystal display device with which generation | occurrence | production of haze hardly arises can be provided.

FIG. 1 is a schematic diagram showing a dope preparation step, a casting step, and a drying step of a solution casting film forming method.

Hereinafter, embodiments according to the present invention will be described, but the present invention is not limited thereto.

[Method for producing optical film]
The method for producing an optical film according to this embodiment includes an optical film containing an acrylic resin and a cellulose ester resin satisfying the following formulas (1) and (2), or a substitution degree of acetyl groups of the cellulose ester of 2.0 to In the method for producing an optical film containing a cellulose ester resin of 2.5, the moisture content is 2.0 to 5.0% by mass at the start-up from the start of production to steady operation, and the moisture content is obtained during steady operation. It is produced by a solution casting film forming method using a dope having a rate of 0.6 to 2.0% by mass.

Formula (1) 2.3 <= X + Y <= 2.6
Formula (2) 1.4 ≦ X ≦ 2.6
(In the above formula, X represents the degree of substitution of the acetyl group of the cellulose ester, and Y represents the degree of substitution of the propionyl group or butyryl group.)

In the method for producing an optical film in the present embodiment, a dope preparation step for adjusting the dope composition, a casting step for casting the dope composition on a support, and heating to remove a part of the solvent. Solution casting film forming method including a solvent evaporation step, a peeling step for peeling from the support, a drying / stretching step for drying and stretching the peeled film, and a winding step for winding the dried / stretched film Is used.

FIG. 1 is a diagram schematically showing a dope preparation step, a casting step, and a drying step of a solution casting film forming method according to an embodiment of the present invention.

In FIG. 1, each symbol represents the following member. 1 Melting pot, 2, 5, 11, 14, 43 Liquid feed pump 3, 6, 12, 15, 44 Filter, 4, 13, 42 Stock tank, 8, 16 conduit, 10 UV absorber charging pot, 20 Merge tube, 21 mixer, 30 die, 31 metal support, 32 web, 33 peeling position, 34 tenter device, 35 roll drying device, 37 take-up roll, 41 fine particle charging pot.

Hereinafter, each step of the solution casting film forming method in the present embodiment will be described.

(1) Dope preparation step In the dope preparation step, an acrylic resin, a cellulose ester resin, a peeling aid and other additives are stirred in an organic solvent mainly composed of a good solvent for an acrylic resin and a cellulose ester resin. It is a process of dissolving.

First, the adjustment of the moisture content of the dope will be described.

(Moisture content)
Further, in the dope preparation process of the present embodiment, the moisture content is 2.0 to 5.0 mass% at the start-up from the start of production to the steady operation, and the moisture content is 0.6 to 2.0 mass at the steady operation. Adjust to mass%.

As a method of setting the moisture content at the time of start-up within the range of 0.6 to 2.0% by mass with respect to the total amount of the dope, the moisture content in the dope is calculated from the sum of the moisture content in the resin and the moisture content in the alcohol. There is a method in which the rate is calculated and the shortage is mixed with a solvent and then blended as a dope.

Since the line speed is slow at the time of start-up, if the moisture content is less than 2.0% by mass with respect to the total amount of the dope, the peelability of the web from the support belt becomes low, and the film after drying breaks. It becomes easy to do. Once the film breaks, it must be started up again, and productivity deteriorates. In addition, if the water content is greater than 5.0% by mass, the solubility of the acrylic resin and cellulose ester resin in the solvent is deteriorated, and it does not move to the belt side together with the water molecules to which the peeling aid molecules are attached during the drying process. Therefore, the support belt is easily soiled.

Further, in the steady operation, when the moisture content is less than 0.6% by mass with respect to the total amount of the dope, the peelability of the web from the support belt is lowered and the dried state is the same as in the start-up. The film is easily broken. On the other hand, if the water content is higher than 2.0% by mass, the support belt is soiled after peeling.

As means for lowering the moisture content of the dope from the start-up to the steady operation, the predetermined acrylic resin, cellulose ester resin, and other additives are adjusted by in-line addition, the moisture content in the resin and alcohol The moisture content in the dope is calculated from the total moisture content in the dope, and the deficiency is adjusted by mixing in a solvent and then preparing as a dope.

Subsequently, each component added in the dope adjusting step will be described.

(acrylic resin)
The acrylic resin used in the present embodiment is not particularly limited, but is preferably composed of 50 to 99% by mass of methyl methacrylate units and 1 to 50% by mass of other monomer units copolymerizable therewith. .

Examples of other copolymerizable monomers include alkyl methacrylates having 2 to 18 alkyl carbon atoms, alkyl acrylates having 1 to 18 carbon atoms, alkyl acrylates such as acrylic acid and methacrylic acid. Saturated acids, maleic acids, fumaric acids, divalent carboxylic acids containing unsaturated groups such as itaconic acid, aromatic vinyl compounds such as styrene, α-methylstyrene, and nucleus-substituted styrene, α, β- such as acrylonitrile, methacrylonitrile, etc. Examples thereof include unsaturated nitrile, maleic anhydride, maleimide, N-substituted maleimide, and glutaric anhydride, and these can be used alone or in combination of two or more.

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.

The acrylic resin used in the optical film of the present embodiment preferably has a weight average molecular weight (Mw) of 80,000 to 1,000,000 from the viewpoint of mechanical strength as a film and fluidity when producing the film.

The weight average molecular weight of a resin such as an acrylic resin according to this embodiment can be measured by gel permeation chromatography. The measurement conditions are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (3 used by Showa Denko KK were connected)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Science Co., Ltd.)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0 ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 2,800,000-500 calibration curves with 13 samples were used. The 13 samples are preferably used at approximately equal intervals.

The production method of the acrylic resin in the present embodiment is not particularly limited, and any known method such as suspension polymerization, emulsion polymerization, bulk polymerization, or solution polymerization may be used. Here, as a polymerization initiator, a normal peroxide type and an azo type can be used, and a redox type can also be used. The polymerization temperature may be 30 to 100 ° C. for suspension or emulsion polymerization, and 80 to 160 ° C. for bulk or solution polymerization. Furthermore, in order to control the reduced viscosity of the produced copolymer, polymerization can be carried out using alkyl mercaptan or the like as a chain transfer agent.

A commercially available acrylic resin can also be used as the acrylic resin of the present embodiment. For example, Delpet 60N, 80N (Asahi Kasei Chemicals Co., Ltd.), Dialal BR52, BR80, BR83, BR85, BR88 (Mitsubishi Rayon Co., Ltd.), KT75 (Electrochemical Industry Co., Ltd.) and the like can be mentioned. .

In the present embodiment, one or more acrylic resins may be used. In this case, the weight average molecular weight of any acrylic resin is preferably about 80,000 to 1,000,000. By setting it as such molecular weight, coexistence of the heat resistance and brittleness of an optical film can be aimed at.

(Cellulose ester resin)
In this embodiment, cellulose acetate propionate satisfying the following formulas (1) and (2) is used as the cellulose ester resin contained in the optical film together with the acrylic resin.

Formula (1) 2.3 <= X + Y <= 2.6
Formula (2) 1.4 ≦ X ≦ 2.6
(In the above formula, X represents the degree of substitution of the acetyl group of the cellulose ester, and Y represents the degree of substitution of the propionyl group or butyryl group.)

The cellulose ester resin is preferably a cellulose ester that simultaneously satisfies the following formulas (1) ′ and (2) ′.

Formula (1) ′ 2.4 ≦ X + Y ≦ 2.5
Formula (2) ′ 1.5 ≦ X ≦ 2.5

Among them, cellulose acetate propionate having 1.5 ≦ X ≦ 2.5 and 0 ≦ Y ≦ 0.9 is preferable. The portion not substituted with an acyl group usually exists as a hydroxyl group. These can be synthesized by known methods.

These acyl group substitution degrees can be measured according to the method prescribed in ASTM-D817-96.

Further, when the cellulose ester resin is not used, diacetyl cellulose having an acetyl group substitution degree of 2.0 to 2.5 is used. In particular, diacetyl cellulose having a substitution degree of 2.1 to 2.3 is preferably used. When the total substitution degree is 2.5 or more, the mechanical strength of the film is increased, and when it is 2.0 or less, the solubility of the cellulose ester is improved or the generation of foreign matters is reduced.

The weight average molecular weight of the cellulose ester resin of the present embodiment is preferably 75000 or more, and may be about 1000000 as long as it is 75000 or more. However, in consideration of productivity, those of 75000 to 280000 are preferable, More preferred are 100,000 to 240,000.

In the acrylic resin-containing film of the present embodiment, it is preferable that the acrylic resin and the cellulose ester resin are contained in a compatible state. The physical properties and quality required for the acrylic resin-containing film are achieved by supplementing each other by dissolving different resins.

Whether the acrylic resin and the cellulose ester resin are in a compatible state can be determined by, for example, the glass transition temperature Tg.

For example, when the two resins have different glass transition temperatures, when the two resins are mixed, there are two or more glass transition temperatures for each resin because there is a glass transition temperature for each resin. When they are compatible, the glass transition temperature specific to each resin disappears and becomes one glass transition temperature, which is the glass transition temperature of the compatible resin.

The glass transition temperature referred to here is an intermediate value determined according to JIS K7121 (1987) by using a differential scanning calorimeter (DSC-7 manufactured by Perkin Elmer Co.) at a heating rate of 20 ° C./min. The point glass transition temperature (Tmg).

The total mass of the acrylic resin of this embodiment and the cellulose ester resin satisfying the above formulas (1) and (2), or the total mass of the cellulose ester resin in which the substitution degree of the acetyl group of the cellulose ester is 2.0 to 2.5 Is preferably 55% by mass or more, more preferably 60% by mass or more based on the total amount of the dope.

(Peeling aid)
In the dope adjusting step of the present embodiment, a peeling aid can be used as necessary, and an ionic surfactant is preferably used.

The reason why the ionic surfactant used in the present embodiment has a function as the peeling aid is as follows.

When producing a film containing an acrylic resin as in this embodiment, an interaction occurs between the acrylic resin and the support belt, and a dope is formed by casting a dope on the web (casting support). The film may be called “web”). This is because acrylic resin has high polarity. Therefore, when a dope composition containing such an ionic surfactant is cast on a support belt and dried, a part of the ionic interface in the dope composition (web) on the support belt is obtained. The activator molecules move to the surface on the side of the support belt together with the water molecules deposited by the polarity. As a result, the interaction between the ionic surfactant molecules unevenly distributed on the surface of the support belt and the surface of the support belt is reduced, and the peelability of the web can be improved.

The optical film of the present embodiment may contain resins and additives other than acrylic resin and cellulose ester resin within a range not impairing the effects of the present invention.

(Acrylic particles)
The dope composition in the method for producing an acrylic resin-containing film of the present embodiment preferably contains acrylic particles because the objective effect of the present invention is exhibited well and the pencil hardness is excellent.

The acrylic particles according to the present embodiment represent an acrylic component that exists in the state of particles (also referred to as an incompatible state) in the optical film containing the acrylic resin and the cellulose ester resin.

The acrylic particles used in the present embodiment are not particularly limited, but are preferably acrylic particles having a multilayer structure of two or more layers, and particularly preferably the following multilayer structure acrylic granular composite.

The multilayer structure acrylic granular composite is formed by laminating an innermost hard layer polymer, a cross-linked soft layer polymer exhibiting rubber elasticity, and an outermost hard layer polymer from the center to the outer periphery. It refers to a particulate acrylic polymer having a structure.

Commercially available acrylic particles can also be used as the acrylic particles of this embodiment. For example, Staphyloid AC-3355 (manufactured by Ganz Kasei Co., Ltd.), Delpet SRB215 (manufactured by Asahi Kasei Chemicals Co., Ltd.) and the like can be mentioned.

In the method for producing an optical film of the present embodiment, it is preferable to adjust the dope in such an amount that the content of acrylic particles is 0.05 to 45% by mass with respect to the total mass of the resin constituting the film. .

(Other additives)
In the dope composition of the present embodiment, a compound that can be added to a normal optical film, such as an ultraviolet absorber, an antioxidant, an antistatic agent, and particles, can be used.

(Organic solvent)
It is preferable that the organic solvent which forms the dope composition in the manufacturing method of the optical film of this embodiment is an organic solvent mainly having a good solvent for acrylic resin and cellulose ester resin. In particular, methylene chloride and a linear or branched aliphatic alcohol having 1 to 4 carbon atoms are preferably used. These simultaneously dissolve acrylic resin, cellulose ester resin, and other additives.

The solvent is preferably a mixed solvent having a ratio of methylene chloride to aliphatic alcohol (MA represented by the following formula (i)) of 15 to 30, and 20 to 25. If the MA is less than 15, the peel force increases and the drying property tends to be poor, and thus the productivity may be deteriorated. If the MA is greater than 30, the haze may be increased. is there.

Formula (i): MA = mass of aliphatic alcohol / (mass of aliphatic alcohol + mass of methylene chloride) × 100

When the aliphatic alcohol in the above range is contained in the dope composition, the drying efficiency is good in the evaporation step described later. In addition, a large number of voids are formed at locations where the aliphatic alcohol to be evaporated was present in the film, and the film can be made thin. As a result, it can be set as the film excellent in adhesiveness with a polarizer.

Examples of the linear or branched aliphatic alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Among these, ethanol is most preferable from the viewpoints of the stability of the dope, the boiling point being relatively low, and good drying properties.

For dissolution of acrylic resin and cellulose ester resin, a method carried out at normal pressure, a method carried out below the boiling point of the main solvent, a method carried out under pressure above the boiling point of the main solvent, JP-A-9-95544 and JP-A-9- Various dissolution methods can be used such as a method performed by a cooling dissolution method as described in JP-A-95557 or JP-A-9-95538, a method performed at high pressure as described in JP-A No. 11-21379, In particular, a method of pressurizing at a temperature equal to or higher than the boiling point of the main solvent is preferable.

The total of three types of acrylic resin, cellulose ester resin and acrylic particles in the dope is preferably in the range of 15 to 45% by mass. An additive is added to the dope during or after dissolution to dissolve and disperse, then filtered through a filter medium, defoamed, and sent to the next step with a liquid feed pump.

For the filtration, it is preferable to use a filter medium having a collected particle diameter of 0.5 to 5 μm and a drainage time of 10 to 25 sec / 100 ml. In this method, the aggregate remaining when the fine particles are dispersed and the aggregate generated when the main dope is added are only aggregated by using a filter medium having a collected particle diameter of 0.5 to 5 μm and a drainage time of 10 to 25 sec / 100 ml. Can be removed. In the main dope, the concentration of particles is sufficiently thinner than that of the additive solution, so that aggregates do not stick together at the time of filtration and the filtration pressure does not increase suddenly.

(Sapwood)
In many cases, the main dope may contain about 10 to 50% by mass of the recycled material. Since the return material contains acrylic particles, it is preferable to control the addition amount of the acrylic particle addition liquid in accordance with the addition amount of the return material. The return material is a product obtained by finely pulverizing the optical film, which is generated when the optical film is formed, and is obtained by cutting off both sides of the film, or by using an optical film original that has been speculated out due to scratches, etc. .

Large agglomerates are removed from the acrylic particle charging vessel 41 with a filter 44 and fed to the stock tank 42. Thereafter, the acrylic particle additive liquid is added from the stock tank 42 to the main dope dissolving kettle 1. Thereafter, the main dope solution is filtered by the main filter 3, and an ultraviolet absorbent additive solution is added in-line from 16 to this.

Also, those obtained by previously kneading and pelletizing acrylic resin and acrylic particles can be preferably used.

(2) Casting process An endless metal support belt 31, for example, a stainless support belt, which feeds the dope described above to a pressure die 30 through a liquid feed pump (for example, a pressurized metering gear pump) and transfers it infinitely, or This is a step of casting a dope from a pressure die slit to a casting position on a metal support such as a rotating metal drum.

¡Pressure dies that can adjust the slit shape of the die base and make the film thickness uniform are preferred. The pressure die includes a coat hanger die and a T die, and any of them is preferably used. The surface of the metal support is a mirror surface. In order to increase the film forming speed, two or more pressure dies may be provided on the metal support, and the 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.

Further, from the viewpoint of productivity, surface quality, peelability, etc., it is preferable that the line speed at the start-up is 4 to 27 m / sec and the line speed at the steady operation is 40 to 60 m / sec. Within such a range, the effects of the present invention can be further enhanced.

(3) Solvent evaporation step In this step, the web is heated on the casting support belt to evaporate the solvent.

In order to evaporate the solvent, there are a method of blowing air from the web side and / or a method of transferring heat from the back side of the support by a liquid, a method of transferring heat from the front and back by radiant heat, and the like. It is preferable because of good drying efficiency. A method of combining them is also preferably used. The web on the support belt after casting is preferably dried on the support in an atmosphere of 40 to 100 ° C. In order to maintain the atmosphere at 40 to 100 ° C., it is preferable to apply hot air at this temperature to the upper surface of the web or heat by means such as infrared rays.

(4) Peeling step In this step, the web in which the solvent has evaporated on the metal support belt is peeled off at the peeling position 33. The peeled web is sent to the next process.

The temperature at the peeling position on the metal support is preferably 10 to 40 ° C., more preferably 11 to 30 ° C.

The residual solvent amount at the time of peeling of the web on the metal support belt at the time of peeling is peeled in a state of 20 to 50% by mass depending on the strength of drying conditions, the length of the metal support, etc. It is preferable that it is 40 mass%. In the case of peeling when the residual solvent amount is more than 50% by mass, if the web is too soft, the flatness at the time of peeling tends to be impaired, and slippage and vertical stripes due to peeling tension tend to occur. Moreover, when it peels at the time of less than 20 mass%, there exists a possibility that the tear from an edge part may generate | occur | produce by excessive drying.

The residual solvent concentration (%) of the web is defined by the following formula (ii).

Formula (ii): Residual solvent concentration (%) = (Mass of cast film−Mass of dry film) / Mass of dry film × 100 (%)

In addition, the heat treatment for measuring the residual solvent amount represents performing heat treatment at 115 ° C. for 1 hour.

The peeling tension when peeling the metal support from the film is usually preferably 196 to 245 N / m. However, when wrinkles are likely to occur during peeling, peeling with a tension of 190 N / m or less is preferable. It is preferable to peel at a minimum tension of ˜166.6 N / m, and then peel at a minimum tension of ˜137.2 N / m, and particularly preferable to peel at a minimum tension of ˜100 N / m.

In this embodiment, the temperature at the peeling position on the metal support is preferably −50 to 40 ° C., more preferably 10 to 40 ° C., and most preferably 15 to 30 ° C.

(5) Drying and stretching step After peeling, a roll drying device 35 that transports the web alternately through a plurality of rolls arranged in the drying device, and / or a tenter stretching device 34 that clips and transports both ends of the web with clips. Use to dry the web.

The drying means is generally to blow hot air on both sides of the web, but there is also a means to heat by applying microwaves instead of wind. Too rapid drying tends to impair the flatness of the finished film. Drying at a high temperature is preferably performed from about 8% by mass or less of the residual solvent. Throughout, drying is generally performed at 40-250 ° C. In particular, drying at 40 to 160 ° C. is preferable.

When using the tenter stretching apparatus 34, it is preferable to use an apparatus that can independently control the film gripping length (distance from the start of gripping to the end of gripping) left and right by the left and right gripping means of the tenter. In the tenter process, it is also preferable to intentionally create sections having different temperatures in order to improve planarity. It is also preferable to provide a neutral zone between different temperature zones so that the zones do not interfere with each other.

The stretching operation may be performed in multiple stages, and it is also preferable to perform biaxial stretching in the casting direction and the width direction. When biaxial stretching is performed, simultaneous biaxial stretching may be performed or may be performed stepwise. In this case, stepwise means that, for example, stretching in different stretching directions can be sequentially performed, stretching in the same direction is divided into multiple stages, and stretching in different directions is added to any one of the stages. Is also possible. That is, for example, the following stretching steps are possible.

-Stretch in the casting direction-Stretch in the width direction-Stretch in the casting direction-Stretch in the casting direction-Stretch in the width direction-Stretch in the width direction-Stretch in the casting direction-Stretch in the casting direction

Also, simultaneous biaxial stretching includes stretching in one direction and contracting the other while relaxing the tension. The preferred draw ratio for simultaneous biaxial stretching can be in the range of x1.01 to x1.5 in both the width direction and the longitudinal direction.

When the tenter is used, the amount of residual solvent in the web is preferably 20 to 100% by mass at the start of the tenter, and drying is preferably performed while the tenter is applied until the amount of residual solvent in the web is 10% by mass or less. More preferably, it is 5% by mass or less.

When performing the tenter, the drying temperature is preferably 30 to 150 ° C, more preferably 50 to 120 ° C, and most preferably 70 to 100 ° C.

In the tenter process, it is preferable that the temperature distribution in the width direction of the atmosphere is small from the viewpoint of improving the uniformity of the film. The temperature distribution in the width direction in the tenter process is preferably within ± 5 ° C, and within ± 2 ° C. Is more preferable, and within ± 1 ° C is most preferable.

(6) Winding step This is a step of winding up the optical film by the winding roll 37 after the residual solvent amount in the web is 2% by mass or less, and the residual solvent amount is set to 0.4% by mass or less. A film having good stability can be obtained.

As a winding method, a generally used method may be used, and there are a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress, and the like.

[Optical film]
The optical film of this embodiment is manufactured by the said manufacturing method, and the substitution degree of the acetyl group of an acrylic resin and the cellulose ester resin which satisfy | fills following formula (1) and (2), or a cellulose ester is 2.0. Contains a cellulose ester resin of ~ 2.5.

When an acrylic resin and a cellulose ester resin satisfying the following formulas (1) and (2) are used for the optical film according to the present embodiment, the acrylic resin and the cellulose ester resin are mixed at a mass ratio of 95: 5 to 50:50. It is preferable to contain. In order to further enhance the effect of the present invention, an optical film containing the following acrylic resin and cellulose ester resin in a mass ratio of 80:20 to 60:40 is preferable.

Further, when the acrylic resin and the cellulose ester resin have a mass ratio of more than 95: 5, the brittleness improvement effect by the cellulose ester resin may not be sufficiently obtained. On the other hand, when the acrylic resin is less than 50:50, the high temperature and high humidity resistance may be insufficient.

In addition, it is preferable that the optical film of the present embodiment does not cause breakage such as breakage, that is, does not cause ductile breakage even when a large stress is applied to bend the film in two. The ductile fracture in the present application is caused by a stress that is greater than the strength of a certain material, and is defined as a fracture accompanied by significant elongation or drawing of the material before the final fracture. The fracture surface is characterized by numerous indentations called dimples.

The thickness of the optical film according to this embodiment is preferably 10 to 30 μm, more preferably 20 to 30 μm. If the optical film is thicker than the above region, the polarizing plate after polarizing plate processing becomes too thick, so that it is not suitable for the purpose of thin and light in liquid crystal displays used for notebook personal computers and mobile electronic devices. On the other hand, if it is thinner than the above region, the moisture permeability of the film is increased, and the ability to protect the polarizer from humidity may be reduced, which is not preferable.

The optical film according to the present embodiment has a tension softening point of 105 to 95 in consideration of use in a high-temperature environment such as a projector having a high haze and a high temperature such as a projector or an in-vehicle display device. The temperature is preferably 145 ° C., more preferably 110 to 140 ° C.

The optical film of the present embodiment preferably has a glass transition temperature (Tg) of 110 ° C. or higher. More preferably, it is 120 ° C. or higher. Especially preferably, it is 150 degreeC or more.

The glass transition temperature referred to here is an intermediate value determined according to JIS K7121 (1987) by using a differential scanning calorimeter (DSC-7 manufactured by Perkin Elmer Co.) at a heating rate of 20 ° C./min. Point glass transition temperature (Tmg).

Further, the optical film of the present embodiment preferably has a breaking elongation in at least one direction of 10% or more, more preferably 20% or more in the measurement based on JIS-K7127-1999.

The upper limit of the elongation at break is not particularly limited, but is practically about 250%. In order to increase the elongation at break, it is effective to suppress defects in the film caused by foreign matter and foaming.

The optical film of the present embodiment preferably has a total light transmittance of 90% or more, more preferably 93% or more. Moreover, as a realistic upper limit, it is about 99%. In order to achieve excellent transparency expressed by such total light transmittance, it is necessary not to introduce additives and copolymerization components that absorb visible light, or to remove foreign substances in the polymer by high-precision filtration. It is effective to reduce the diffusion and absorption of light inside the film.

The optical film of the present embodiment preferably has a haze value (turbidity) of 1.0% or less, which is one of the indices indicating transparency, from the viewpoint of luminance and contrast when incorporated in a liquid crystal display device. More preferably, it is 0.5% or less.

In order to achieve such a haze value, it is effective to remove foreign substances in the polymer by high-precision filtration and reduce the diffusion of light inside the film.

When using acrylic particles, it is also effective to reduce the difference in refractive index between the acrylic resin and the acrylic particles.

In addition, since the surface roughness also affects the haze value as surface haze, the particle size and addition amount of acrylic particles may be suppressed within the above range, or the surface roughness of the film contact portion during film formation may be reduced. It is valid.

The total light transmittance and haze value of the optical film are values measured according to JIS-K7361-1-1997 and JIS-K7136-2000.

The optical film of the present embodiment can be preferably used as an optical film for optics as long as it satisfies the physical properties as described above, but by making the following composition, a film excellent in workability and heat resistance can be obtained. Obtainable.

〔Polarizer〕
A polarizing plate using the optical film according to the present embodiment will be described. The polarizing plate can be produced by a general method.

The back side of the optical film according to the present embodiment is subjected to alkali saponification treatment, and the treated optical film is immersed and stretched in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution on at least one surface. It is preferable to bond them together. The optical film may be used on the other surface, or another polarizing plate protective film may be used. In contrast to the optical film according to this embodiment, the polarizing plate protective film used on the other surface has an in-plane retardation Ro of 590 nm, an optical compensation film having a phase difference of 20 to 70 nm and Rt of 70 to 400 nm ( It is preferable to use a retardation film.

These can be produced, for example, by the methods described in JP-A Nos. 2002-71957 and 2003-170492. Alternatively, it is preferable to use a polarizing plate protective film that also serves as an optical compensation film having an optically anisotropic layer formed by aligning a liquid crystal compound such as a discotic liquid crystal. For example, the optically anisotropic layer can be formed by the method described in JP2003-98348A. Alternatively, a non-oriented film having a retardation Ro of 590 nm and 0 to 5 nm and an Rt of −20 to +20 nm described in JP-A-2003-12859 is also preferably used.

By using in combination with the optical film according to the present embodiment, a polarizing plate having excellent planarity and a stable viewing angle expansion effect can be obtained.

As a polarizing plate protective film used on the back side, as commercially available cellulose ester films, KC8UX2MW, KC4UX, KC5UX, KC4UY, KC8UY, KC12UR, KC4UEW, KC8UCR-3, KC8UCR-4, KC8UCR-5, KC4FR-1, KC4FR-1, -2, KC8UE, KC4UE (manufactured by Konica Minolta Opto Co., Ltd.) and the like are preferably used.

A polarizing film, which is a main component of a polarizing plate, is an element that transmits only light having a plane of polarization in a certain direction. A typical polarizing film currently known is a polyvinyl alcohol polarizing film, which is a polyvinyl alcohol film. There are films in which iodine is dyed on a system film and films in which a dichroic dye is dyed, but the present invention is not limited to this. As the polarizing film, a polyvinyl alcohol aqueous solution is formed and dyed by uniaxial stretching or dyed, or uniaxially stretched after dyeing, and then preferably subjected to a durability treatment with a boron compound. A polarizing film having a thickness of 5 to 30 μm, preferably 8 to 15 μm is preferably used. On the surface of the polarizing film, one surface of the optical film according to this embodiment is bonded to form a polarizing plate. It is preferably bonded with an aqueous adhesive mainly composed of completely saponified polyvinyl alcohol or the like.

(Image display device)

By incorporating a polarizing plate produced using the optical film according to the present embodiment into a display device, various image display devices having excellent visibility can be produced.

The optical film according to this embodiment is incorporated in the polarizing plate, and is a reflective type, transmissive type, transflective liquid crystal display device or TN type, STN type, OCB type, HAN type, VA type (PVA type, MVA type), It is preferably used in liquid crystal display devices of various driving systems such as IPS type and OCB type. The optical film according to the present embodiment is also preferably used for various image display devices such as a plasma display, a field emission display, an organic EL display, an inorganic EL display, and electronic paper.

This specification discloses various modes of technology as described above, and the main technologies are summarized below.

In the method for producing an optical film according to one aspect of the present invention, an optical film containing an acrylic resin and a cellulose ester resin satisfying the following formulas (1) and (2), or the substitution degree of the acetyl group of the cellulose ester is 2. In the method for producing an optical film containing a cellulose ester resin of 0 to 2.5, the water content is 2.0 to 5.0% by mass at the start-up from the start of production to the steady operation, and at the steady operation Is characterized in that it is produced by a solution casting film forming method using a dope having a water content of 0.6 to 2.0 mass%.

Formula (1) 2.3 <= X + Y <= 2.6
Formula (2) 1.4 ≦ X ≦ 2.6
(In the above formula, X represents the degree of substitution of the acetyl group of the cellulose ester, and Y represents the degree of substitution of the propionyl group or butyryl group.)

By having such a configuration, it is possible to manufacture an optical film that has a low risk of film breakage and is less likely to cause contamination of the support belt.

In the method for producing an optical film, it is preferable that a mass ratio of the acrylic resin to the cellulose ester resin is 80:20 to 60:40. According to such a configuration, the effect of the present invention can be further enhanced.

In the method for producing an optical film, it is preferable that the line speed at the start-up is 4 to 27 m / sec and the line speed at the steady operation is 40 to 60 m / sec. According to such a configuration, the effect of the present invention can be further enhanced.

Further, an optical film according to another aspect of the present invention is manufactured using the method for manufacturing an optical film.

According to such a configuration, it is possible to obtain an optical film having a high antistatic property that can be used for an optical film such as a protective film for a polarizing plate used in the liquid crystal display device.

The film thickness of the optical film is preferably 10 to 30 μm. According to such a configuration, an optical film excellent in adhesion with a polarizer or the like can be obtained.

The polarizing plate according to a further aspect of the present invention is characterized in that the optical film is used on at least one surface. According to such a configuration, since the above-described optical film having high antistatic property is used as the protective film for polarizing plate used in the liquid crystal display device, it is suitable for enlargement of the screen.

Further, a liquid crystal display device according to a further aspect of the present invention is characterized by using the optical film or the polarizing plate. According to such a structure, since the said polarizing plate is used for the polarizing plate used for the said liquid crystal display device, it is suitable for the enlargement of a screen.

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the examples.

[Example 1]
<Production of optical film K1 at start-up>
(Preparation of dope solution at startup)
BR85 (acrylic resin, manufactured by Mitsubishi Rayon Co., Ltd.) 70 parts by mass Cellulose ester (cellulose acetate propionate acyl group total substitution degree 2.75, acetyl group substitution degree 0.19, propionyl group substitution degree 2.56, Mw = 2000
00) 30 parts by mass Sodium dodecylbenzenesulfonate 0.5 parts by mass Methylene chloride 232.2 parts by mass Ethanol 44.1 parts by mass Water 2.9 parts by mass

In addition, the moisture content in the dope is calculated from the sum of the moisture content in the resin and the moisture content in the alcohol so that the moisture content at start-up is 1.5% by mass with respect to the total amount of the dope. It adjusted by preparing as a dope after mixing with a solvent.

(Preparation of dope solution for steady operation)
BR85 (acrylic resin, manufactured by Mitsubishi Rayon Co., Ltd.) 70 parts by mass Cellulose ester (cellulose acetate propionate acyl group total substitution degree 2.75, acetyl group substitution degree 0.19, propionyl group substitution degree 2.56, Mw = 2000
00) 30 parts by mass Sodium dodecylbenzenesulfonate 0.5 parts by mass Methylene chloride 232.2 parts by mass Ethanol 44.1 parts by mass Water 0.26 parts by mass

The composition of the K1 dope is calculated from the sum of the moisture content in the resin and the moisture content in the alcohol, and the moisture content in the dope is calculated. The moisture content during steady operation was adjusted to 0.8 mass% with respect to the total amount of dope by changing to the composition amount of the dope for handling.

(Optical film formation)
The produced dope solution was uniformly cast on a stainless steel band support at a temperature of 22 ° C. and a width of 2 m using a support belt casting apparatus. With the stainless steel band support, the solvent was evaporated until the residual solvent concentration (residual solvent amount) was 35% by mass, and peeling was performed from the stainless steel band support with a peeling tension of 162 N / m. The time required from casting to peeling was 150 seconds at the start-up and 90 seconds at the steady operation. The line speed was 27 m / sec at startup and 40 m / sec during steady operation.

The peeled acrylic resin-containing web was evaporated at 35 ° C., slit to 1.6 m width, and then dried at a drying temperature of 135 ° C. while being stretched 1.1 times in the width direction by a tenter. At this time, the residual solvent concentration when starting stretching with a tenter was 10% by mass.

After stretching with a tenter and relaxing at 130 ° C for 5 minutes, drying was completed while transporting the drying zone at 120 ° C and 130 ° C with a number of rolls, slitting to a width of 1.5 m, and 10 mm wide at both ends of the film. A 5 μm knurling process was performed, and the film was wound around a 6-inch inner diameter core with an initial tension of 220 N / m and a final tension of 110 N / m to obtain an optical film K1. The draw ratio in the MD direction (casting direction) calculated from the rotational speed of the stainless steel band support and the operating speed of the tenter was 1.1 times.

<Preparation of polarizing plate H1>
A 120 μm-thick polyvinyl alcohol film was uniaxially stretched (temperature: 110 ° C., stretch ratio: 5 times). This was immersed in an aqueous solution composed of 0.075 g of iodine, 5 g of potassium iodide and 100 g of water for 60 seconds, and then immersed in an aqueous solution of 68 ° C. composed of 6 g of potassium iodide, 7.5 g of boric acid and 100 g of water. This was washed with water and dried to obtain a polarizer.

Then, according to the following steps 1 to 5, a polarizer, the optical film K1, and Konica Minolta Tack KC4UY (cellulose ester film manufactured by Konica Minolta Opto Co., Ltd.) were bonded to the back side to prepare a polarizing plate H1.

Step 1: Soaked in a 2 mol / L sodium hydroxide solution at 60 ° C. for 90 seconds, then washed with water and dried to obtain an optical film saponified on the side to be bonded to the polarizer.

Step 2: The polarizer was immersed in a polyvinyl alcohol adhesive tank having a solid content of 2% by mass for 1 to 2 seconds.

Step 3: Excess adhesive adhered to the polarizer in Step 2 was gently wiped off and placed on the optical film treated in Step 1.

Step 4: The optical film, the polarizer, and the back side optical film laminated in Step 3 were bonded at a pressure of 20 to 30 N / cm ² and a conveyance speed of about 2 m / min.

Step 5: A sample obtained by bonding the polarizer, the optical film, and Konica Minolta Tack KC4UY prepared in Step 4 in a dryer at 80 ° C. was dried for 2 minutes, and a polarizing plate H1 corresponding to the optical film was prepared. .

[Examples 2 to 6 and Comparative Examples 1 to 3]
Hereinafter, the moisture content in the dope is calculated from the sum of the moisture content in the resin and the alcohol in the alcohol as shown in Table 1 for the moisture content at startup and steady operation. The optical films K2 to 9 are adjusted in the same manner as the optical film K1 except that the line speed during start-up and steady operation is adjusted as shown in Table 1 except that the line speed is adjusted as shown in Table 1. Was made.

Further, in the same manner as the polarizing plate H1, polarizing plates H2 to 9 corresponding to the optical films K2 to 9 were produced. The optical films K2 to K9 and the polarizing plates H2 to H9 were set as Examples 2 to 6 and Comparative Examples 1 to 3, respectively.

Here, the peelability evaluation of the optical films K1 to K9 and the belt dirt evaluation were performed using the following evaluation criteria.

(Rupture risk)
The risk of breakage of the optical film at the time of start-up was evaluated according to the following five levels.

5: Fracture probability is less than 10%.
4: The fracture probability is 10% or more and less than 30%.
3: The fracture probability is 30% or more and less than 50%.
2: The fracture probability is 50% or more and less than 70%.
1: Breaking probability is 70% or more.

(Solubility)
The solubility of the optical films K1 to K9 at the time of start-up was evaluated in five stages as follows.

5: Completely dissolved.
4: It seems that liquid haze is rising a little.
3: The liquid viscosity is high.
2: Liquid viscosity is high and haze is high.
1: Undissolved material remains.

(Belt dirt evaluation)
The belt contamination when the dope composition cast on the stainless steel band support was peeled off from the stainless steel band support was evaluated in five stages as follows.

5: None of the evaluators found any unevenness.
4: Although it may be slightly uneven by the evaluator, it is a level that can be used as a product without any problem.
3: A level that can be used as a product although there may be slight unevenness depending on the evaluator.
2: The level at which the evaluator slightly sees unevenness and cannot be used as a product.
1: Although it was faint in many evaluators, the nonuniformity was seen.

Here, the antistatic property and haze of the polarizing plates H1 to H9 were evaluated using the following evaluation criteria.

(Haze)
The haze of the polarizing plates H1 to H9 was evaluated in five stages as follows.

The measurement was performed according to JIS K-7136 using a haze meter (NDH2000 type, manufactured by Nippon Denshoku Industries Co., Ltd.).

5: 0.1% or less 4: 0.2% or less 3: 0.2-0.3%
2: 0.3-0.5%
1: 0.5% or more

As is apparent from the results in Table 1, the moisture content at the start-up is 2.0 to 5.0 mass% with respect to the total amount of dope, and the moisture content at the steady operation is 0.6 to 2.2. The optical films K1 to 6 obtained by the production methods of Examples 1 to 6 adjusted to 0% by mass have a low risk of breaking both at the time of start-up and at the time of steady operation. Dirt also became difficult to adhere. Further, in the polarizing plates H1 to 6 using the optical films K1 to 6, the generation of haze was sufficiently suppressed.

On the other hand, the optical film K7 in Comparative Example 1 manufactured with a dope having a moisture content at startup of less than 2.0% by mass resulted in a high risk of breakage. In addition, the optical film K8 in Comparative Example 2 manufactured with a dope having a water content of more than 5.0% by mass at the time of start-up is considered to have diffused water molecules to the support belt side, and thus the support belt becomes dirty. As a result, the polarizing plate H8 using K8 had haze.

Further, the optical film K9 in Comparative Example 3 using a dope in which the water content at startup and the water content during steady operation were both adjusted to 3.0% by mass was inferior to support belt contamination. Furthermore, when the polarizing plate H9 using the acrylic resin K9 was used as a polarizing plate, haze was generated.

This application is based on Japanese Patent Application No. 2012-69725 filed on March 26, 2012, the contents of which are included in this application.

In order to express the present invention, the present invention has been described appropriately and sufficiently through the embodiments with reference to the drawings and the like. However, those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized that it can be done. Therefore, unless the modifications or improvements implemented by those skilled in the art are at a level that departs from the scope of the claims recited in the claims, the modifications or improvements are not limited to the scope of the claims. To be construed as inclusive.

The present invention has wide industrial applicability in the technical field of optical films and manufacturing methods thereof.

Claims (7)

1. An optical film containing an acrylic resin and a cellulose ester resin satisfying the following formulas (1) and (2), or an optical film containing a cellulose ester resin having a substitution degree of acetyl group of cellulose ester of 2.0 to 2.5 In the film manufacturing method,
   Using a dope having a moisture content of 2.0 to 5.0% by mass at the start-up from the start of production to steady operation, and having a moisture content of 0.6 to 2.0% by mass during steady operation, A method for producing an optical film, which is produced by a solution casting film forming method.
   Formula (1) 2.3 <= X + Y <= 2.6
   Formula (2) 1.4 ≦ X ≦ 2.6
   (In the above formula, X represents the degree of substitution of the acetyl group of the cellulose ester, and Y represents the degree of substitution of the propionyl group or butyryl group.)
2. 2. The method for producing an optical film according to claim 1, wherein a mass ratio of the acrylic resin to the cellulose ester resin satisfying the formulas (1) and (2) is 95: 5 to 50:50. .
3. 3. The method for producing an optical film according to claim 1, wherein the line speed at the start-up is 4 to 27 m / sec and the line speed at the steady operation is 40 to 60 m / sec. .
4. An optical film produced by the method for producing an optical film according to any one of claims 1 to 3.
5. 5. The optical film according to claim 4, wherein the optical film has a thickness of 10 to 30 μm.
6. A polarizing plate using the optical film according to claim 4 on at least one surface.
7. A liquid crystal display device using the optical film according to claim 4 or 5, or the polarizing plate according to claim 6.

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