WO2011065124A1 - Production method for phase contrast film, and polarizer and liquid crystal display device using said film - Google Patents

Abstract

Disclosed is a production method for a phase contrast film that is resistant to high temperature and high humidity and has an excellent long-term storing capability. The phase contrast film production method is a method for producing, by means of solution casting, a phase contrast film having, as the main component, a thermoplastic resin with an elastic modulus of at least 1000 MPa at 80°C and 5% RH, wherein the elastic modulus (E1) at (Tg-10)°C and the elastic modulus (E2) at (Tg+10)°C satisfy formula (1) below, and is characterized by involving a process for extending the phase contrast film at an extension rate of 11 to 100% in the direction of conveyance of the film. (1) 500 ? E1/E2 ? 10

Description

Method for producing retardation film, polarizing plate using the film, and liquid crystal display device

The present invention relates to a method for producing a retardation film that is transparent, resistant to high temperature and high humidity, and excellent in long-term storage, and a polarizing plate and a liquid crystal display device using the film.

Demand for liquid crystal display devices is expanding for applications such as liquid crystal televisions and personal computer liquid crystal displays. Usually, 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, two polarizing plates provided on both sides thereof, and a retardation film for optical compensation. Each polarizing plate has a configuration in which a polarizer (also referred to as a polarizing film or a polarizing film) is sandwiched between two polarizing plate protective films.

As this polarizing plate protective film, a cellulose triacetate film is usually used, but by selecting a specific resin such as alicyclic polyolefin, cellulose acetate propionate, acrylic resin-cellulose ester resin mixed resin, etc. The function as a phase difference film is also given (patent documents 1 and 2).

The retardation of the retardation film is appropriately adjusted to a desired value by providing a stretching process in the normal film manufacturing process. In the stretching step, the phase difference is adjusted by appropriately combining stretching in the transport direction (also referred to as longitudinal stretching or MD stretching) and stretching in the direction perpendicular to the transport direction (also referred to as lateral stretching, width stretching, or TD stretching). In the hot melt casting method, stable stretching can be performed even when both the MD stretching and TD stretching have a large stretching ratio. However, in the solution casting method, if the stretching ratio of the MD stretching is increased, a slippage occurs. There existed a subject that flatness deteriorated or it was easy to fracture | rupture in a manufacturing process.

On the other hand, the flatness of the film is generally higher by the solution casting method than by the hot melt casting method. Therefore, in the retardation film in which the flatness is particularly important, the TD by the solution casting method is used. Adjustment of phase difference has been attempted with stretching as the main stretching (Patent Document 2).

Recent advances in technology have accelerated the increase in size of liquid crystal display devices and diversified uses for liquid crystal display devices. For example, it can be used as a large display installed on a street or in 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 that it is used outdoors, deterioration of the polarizer due to high temperature and high humidity becomes a problem, and the polarizing plate protective film that also serves as the retardation film has higher resistance to high temperature and high humidity and long-term use. Although retardation stability (also referred to as long-term storage stability) is required, the above retardation film is still insufficient.

JP 2007-2027 A JP 2009-179731 A

Accordingly, the present invention has been made in view of the above problems, and its object is to provide a method for producing a retardation film having high-temperature and high-humidity resistance and excellent long-term storage stability, and a polarizing plate and a liquid crystal using the film. It is to provide a display device.

In the present invention, it has been found that the above-mentioned problems can be solved by producing a retardation film mainly composed of a resin having a specific physical property under the conditions of the present invention.

The object of the present invention was achieved by the following.

1. A thermoplastic resin having an elastic modulus at 80 ° C. and 5% RH of 1000 MPa or more, an elastic modulus E1 at (Tg−10) ° C., and an elastic modulus E2 at (Tg + 10) ° C. satisfying the following formula (1): A method for producing a retardation film having a main component by a solution casting method, the method comprising a step of stretching a stretching ratio of 11 to 100% in a film transport direction.
(1) 500 ≧ E1 / E2 ≧ 10
2. 2. The method for producing a retardation film as described in 1 above, wherein the thermoplastic resin contains an acrylic resin as a main component.

3. 3. The retardation film as described in 1 or 2 above, wherein the thermoplastic resin contains an acrylic resin (A) and a cellulose ester resin (B) in a mass ratio of 95: 5 to 30:70. Manufacturing method.

4). The step of stretching in the transport direction has at least two steps, and the step of stretching in a direction perpendicular to the transport direction is between the two steps, of the at least two steps The production of the retardation film as described in any one of 1 to 3 above, wherein the stretch ratio M1 in the upstream process and the stretch ratio M2 in the downstream process satisfy the following formulas (2) and (3): Method.
(2) M1 ≧ M2, (3) M1 + M2 ≧ 11
5. 5. The method for producing a retardation film according to 4, wherein the following formula (4) is satisfied when a stretching ratio in the step of stretching in a direction perpendicular to the transport direction is T1.
(4) 15 ≧ (M1 + M2) /T1≧0.5
6). A polarizing plate using a retardation film produced by the method for producing a retardation film as described in any one of 1 to 5 above.

7. 7. A liquid crystal display device using the polarizing plate described in 6 above.

According to the present invention, it was possible to provide a method for producing a retardation film having high-temperature and high-humidity resistance and excellent long-term storage stability, and a polarizing plate and a liquid crystal display device using the film.

It is the schematic of the solution casting apparatus used for this invention.

The present invention has been found to solve the problems of the present invention by producing a retardation film containing a resin having a specific physical property as a main component under the conditions of the present invention.

The effect of the present invention is that a film excellent in flatness can be produced by the solution casting method, and the resin whose physical property (elastic modulus) changes remarkably across the glass transition temperature (hereinafter referred to as Tg) is the first MD. It is presumed that the strain generated in the stretching step is once eliminated by TD stretching, and even if the second MD stretching is performed, the absolute residual strain is reduced, so that the strain is exhibited.

In addition, since the main stretching direction and the film production direction coincide with each other, the strain relaxation of the film stored in the roll state hardly affects the change in the storage state of the retardation. I guess it is a factor.
<Thermoplastic resin>
The resin capable of exhibiting the effect of the present invention has an elastic modulus at 80 ° C. and 5% RH of 1000 MPa or more, and has an elastic modulus E1 at (Tg−10) ° C. and an elastic modulus E2 at (Tg + 10) ° C. It is a resin whose main component is a thermoplastic resin that satisfies the following formula (1).
(1) 500 ≧ E1 / E2 ≧ 10
Here, the main component means a resin constituting 50% by mass or more of the resin constituting the thermoplastic resin.

Examples of such resins include alicyclic polyolefins, acrylic resins, methyl methacrylate-styrene copolymers, and acrylic resin-cellulose ester resin mixed resins, and acrylic resin-cellulose ester resin mixed resins are particularly preferable.

More preferably, 20 ≦ E1 / E2 ≦ 400.

Note that the elastic modulus was conditioned at 23 ° C. and 55% RH for 24 hours, under the respective conditions (80 ° C. 5% RH, (Tg + 10) ° C. 5% RH, (Tg−10) ° C. 5% RH), JIS It measured according to the method of K7127. Tensillon made by ORIENTEC Co., Ltd. was used as the tensile tester, the test piece was 100 mm × 10 mm, the distance between chucks was 50 mm, and the test speed was 100 mm / min.

<Acrylic resin-cellulose ester resin mixed resin>
The acrylic resin-cellulose ester resin mixed resin of the present invention is characterized by containing the following acrylic resin (A) and cellulose ester resin (B) in a mass ratio of 95: 5 to 30:70.

<< Acrylic resin (A) >>
The acrylic resin (A) used in the present invention includes a methacrylic resin. The resin is preferably composed of 50 to 100% by mass of methyl methacrylate units and 0 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 (A) used in the retardation film of the present invention has a weight average molecular weight (Mw) of 75,000 to 1100000 from the viewpoint of mechanical strength as a film and fluidity when producing the film, 150,000 to 400,000.

The weight average molecular weight of the acrylic resin (A) of the present invention can be measured by gel permeation chromatography. The measurement conditions are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh 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 (A) of the present invention 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 can be used, 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.

By using this molecular weight, both heat resistance and brittleness can be achieved.

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

<Acrylic particles (C)>
In the present invention, acrylic particles (C) may be contained in the retardation film.

For example, when a predetermined amount of the prepared retardation film is collected, dissolved in a solvent, stirred, and sufficiently dissolved and dispersed, a PTFE membrane filter having a pore size smaller than the average particle size of the acrylic particles (C) is obtained. It is preferable that the weight of the insoluble matter that has been filtered and collected by filtration is 90% by mass or more of the acrylic particles (C) added to the retardation film.

The acrylic particles (C) used in the present invention are preferably acrylic particles (C) having a layer structure of two or more layers, and particularly preferably the following multilayered acrylic granular composite.

In the present invention, the method of blending the acrylic particles (C) with the acrylic resin (A) is not particularly limited. After the acrylic resin (A) and other optional components are previously blended, usually at 200 to 350 ° C. A method of uniformly kneading with a single-screw or twin-screw extruder while adding acrylic particles is preferably used.

In addition, a solution in which acrylic particles are dispersed in advance is added to and mixed with a solution (dope solution) in which acrylic resin (A) is dissolved, and acrylic particles (C) and other optional additives are dissolved and mixed. A method such as adding the solution in-line can be used.

As the acrylic particles (C) of the present invention, commercially available particles can also be used. For example, METABRENE W-341 (C2), Chemisnow MR-2G (C3), MS-300X (C4) (manufactured by Mitsubishi Rayon Co., Ltd.) "Kane Ace" manufactured by Kaneken Chemical Co., Ltd., "Paraloid" manufactured by Kureha Chemical Industry Co., Ltd., "Acryloid" manufactured by Rohm and Haas Co., Ltd. Parapet SA ″ and the like can be mentioned, and these can be used alone or in combination of two or more.

The retardation film of the present invention preferably contains 0.1 to 5% by mass of acrylic particles (C) with respect to the total mass of the resin constituting the film.

<< Cellulose ester resin (B) >>
The cellulose ester resin (B) of the present invention has a total substitution degree (T) of acyl groups of 2.0 to 3.0 and a substitution degree of acyl groups of 3 to 7 carbon atoms of 1.2 to 3.0. Preferably there is. That is, the cellulose ester resin (B) is a cellulose ester resin substituted with an acyl group having 3 to 7 carbon atoms. Specifically, propionyl, butyryl and the like are preferably used, and a propionyl group is particularly preferably used. .

When the total substitution degree of the acyl group of the cellulose ester resin (B) is less than 2.0, that is, when the residual degree of the hydroxyl groups (hydroxyl groups) at the 2, 3 and 6-positions of the cellulose ester molecule is more than 1.0. In this case, the resin is not sufficiently compatible with the acrylic resin (A), and haze becomes a problem.

In addition, even when the total substitution degree of the acyl group is 2.0 or more, if the substitution degree of the acyl group having 3 to 7 carbon atoms is less than 1.2, still sufficient compatibility cannot be obtained, Brittleness will decrease. For example, even when the total substitution degree of the acyl group is 2.0 or more, the substitution degree of the acyl group having 2 carbon atoms, that is, the acetyl group is high, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1. When it is less than 2, the compatibility is lowered and the haze is increased. Even when the total substitution degree of the acyl group is 2.0 or more, the substitution degree of the acyl group having 8 or more carbon atoms is high, and the substitution degree of the acyl group having 3 to 7 carbon atoms is less than 1.2. In such a case, the brittleness is lowered and desired characteristics cannot be obtained.

In the cellulose ester resin (B) of the present invention, the total substitution degree (T) is 2.0 to 3.0, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 3. If it is 0.0, there is no problem, but the total degree of substitution of acyl groups other than those having 3 to 7 carbon atoms, that is, acetyl groups or acyl groups having 8 or more carbon atoms, is preferably 1.3 or less.

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

When the cellulose ester resin (B) has an aromatic acyl group as a substituent, the number of substituents X substituted on the aromatic ring is preferably 0 to 5. Also in this case, it is necessary to pay attention so that the degree of substitution of the acyl group having 3 to 7 carbon atoms including the substituent is 1.2 to 3.0.

For example, since the benzyl group has 7 carbon atoms, when it has a substituent containing carbon, the benzyl group has 8 or more carbon atoms and is not included in the acyl group having 3 to 7 carbon atoms. Become.

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

In the cellulose ester resin (B), a structure having at least one kind of a substituted or unsubstituted aliphatic acyl group having 3 to 7 carbon atoms is used as a structure used in the cellulose resin of the present invention.

The substitution degree of the cellulose ester resin (B) of the present invention is such that the total substitution degree (T) of the acyl group is 2.00 to 3.00, the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 3 .0.

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

The cellulose ester resin (B) of the present invention is preferably at least one selected from cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose propionate, and cellulose butyrate, particularly cellulose acetate. Propionate and cellulose propionate are more preferable.

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

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

Incidentally, the substitution degree of the acetyl group and the substitution degree of other acyl groups were determined by the method prescribed in ASTM-D817-96.

The weight average molecular weight (Mw) of the cellulose ester resin (B) of the present invention is in the range of 75,000 to 320,000, particularly from the viewpoint of improving compatibility with the acrylic resin (A) and brittleness, and in the range of 100,000 to 24,000. Some are preferred, and those having 160000 to 240,000 are particularly preferred.

The weight average molecular weight can be measured by the above GPC method.

<Alicyclic polyolefin>
Examples of the alicyclic polyolefin include ZEONOR, ZEONEX (manufactured by ZEON Corporation), ARTON (manufactured by JSR Corporation), APPEL (manufactured by Mitsui Chemicals), and TOPAS (manufactured by Polyplastics Corporation). Can be used.

<acrylic resin>
As the acrylic resin, the above acrylic resin (A) can be used alone, or one obtained by copolymerizing maleic acid (for example, Delpet 980N (manufactured by Asahi Kasei Chemicals Corporation)) can be used. .

<Methyl methacrylate-styrene copolymer>
As the methyl methacrylate-styrene copolymer, for example, Dianal BR52 (manufactured by Mitsubishi Rayon Co., Ltd.) can be used.

<Other additives>
The retardation film of the present invention can contain a plasticizer, an ultraviolet absorber, a retardation control agent, a matting agent, and an antioxidant as other additives.

In addition, Tg (glass transition temperature) of the thermoplastic resin was measured by the following method.

A sample conditioned for 24 hours in an atmosphere of 23 ° C. and 55% RH is performed with a differential scanning calorimeter (DSC 6220, manufactured by Seiko Instruments Inc.). The film is heated from room temperature to 220 ° C. at a rate of 20 ° C./minute, once cooled to room temperature, then heated again under the same conditions, and the calorific value change obtained by the second temperature increase is used. Of the two inflection points of the temperature-heat generation curve, the high temperature side and the low temperature side are point A and B, respectively, and linear approximation is performed in each of the temperature range above point A and the temperature range below point B. Let Tg be the midpoint of each intersection with the straight line l1 passing through the inflection point between B. When the inflection point cannot be read, a line l2 obtained by linearly approximating only between the points A and B is used instead of l1.
<Manufacturing method>
The method for producing a retardation film of the present invention is a production method by a solution casting method, and is characterized by having a step of stretching 11 to 100% in the film transport direction.

Here, for example, when the stretch rate is 1000 mm before stretching but is 1100 mm after stretching, the stretch rate is 10% (stretch ratio 1.1 times).

Hereinafter, a preferred method for producing the retardation film of the present invention will be described.

1) Dissolution step In an organic solvent mainly composed of a good solvent for the acrylic resin (A) and the cellulose ester resin (B), the acrylic resin (A), the cellulose ester resin (B), the resin (D), It is a step of dissolving the additive while stirring to form a dope, or a step of mixing the additive solution with the acrylic resin (A) or cellulose ester resin (B) solution to form a dope.

For dissolving the acrylic resin (A) and the cellulose ester resin (B), 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 Various melting methods such as a method of performing a cooling dissolution method as described in JP-A-9-95557 or JP-A-9-95538, a method of performing at a high pressure as described in JP-A-11-21379, and the like. Although it can be used, a method in which pressure is applied at a temperature equal to or higher than the boiling point of the main solvent is particularly preferable.

The acrylic resin (A) and cellulose ester resin (B) in the dope are preferably in the range of 15 to 45% by mass in total. 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 fine particles is sufficiently thinner than that of the additive solution, so that the aggregates do not stick together during filtration and the filtration pressure does not increase rapidly.

FIG. 1 is a diagram schematically showing a dope preparation step, a casting step, and a drying step of a solution casting manufacturing method preferable for the present invention. Large agglomerates are removed from the acrylic fine particle charging vessel 41 by the filter 44 and fed to the stock vessel 42.

Thereafter, the acrylic fine particle additive solution is added from the stock kettle 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.

In many cases, the main dope may contain about 10 to 50% by weight of recycled material. Since the return material contains acrylic fine particles, it is preferable to control the addition amount of the acrylic fine particle addition liquid in accordance with the addition amount of the return material.

Recycled material is a product obtained by finely pulverizing a retardation film, which is generated when a retardation film is formed, and is obtained by cutting out both sides of the film, or a retardation film original that is speculated out due to scratches, etc. used.

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

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

¡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.

3) Solvent evaporation step In this step, the web (the dope is cast on the casting support and the formed dope film is called a web) is heated on the casting support to evaporate the solvent.

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, etc., but the back side liquid heat transfer method is dry. High efficiency and preferable.

Also, a method of combining them is preferably used. The web on the support 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 This is a step of peeling the web where the solvent has evaporated on the metal support at the peeling position (peeling roll 33).

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

The amount of residual solvent at the time of peeling of the web on the metal support at the time of peeling is preferably 50 to 120% by mass depending on the strength of drying conditions, the length of the metal support, and the like. When peeling off at a time when the amount of residual solvent is larger, if the web is too soft, the flatness at the time of peeling will be impaired, and slippage and vertical stripes are likely to occur due to peeling tension, so the balance between economic speed and quality The amount of residual solvent is determined.

The amount of residual solvent in the web is defined by the following formula.

Residual solvent amount (%) = (mass before web heat treatment−mass after web heat treatment) / (mass after web heat treatment) × 100
Note that the heat treatment for measuring the residual solvent amount represents performing heat treatment at 115 ° C. for 1 hour.

The peeling tension at the time of peeling the metal support from the film is usually 196 to 245 N / m. However, if wrinkles easily occur at the time of peeling, it is preferable to peel with a tension of 190 N / m or less. 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 the present invention, 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.

The web peeled in the peeling step is the next step and is sent to the stretching step which is a feature of the present invention.

5) Stretching Step The stretching step of the present invention is characterized by having a step of stretching a stretching ratio of 11 to 100% in the transport direction. The stretching ratio of 11 to 100% in this conveying direction refers to the rate at which the web that has undergone the peeling process is stretched before winding, and the value calculated from the rotation speed of the peeling roll and the rotation speed of the winding roll. Using. For example, in FIG. 1, the rotation speed of the peeling roll 33 and the rotation speed of the take-up roll 42 are calculated.

The process of stretching in the transport direction (MD stretching process) has at least two stages, and the process of stretching in the direction perpendicular to the transport direction (TD stretching process) is between the at least two stages. Of the two stages, the stretching ratio M1 in the upstream process from the TD stretching process and all stretching ratios M2 in the downstream process from the TD stretching process are expressed by the following formulas (2) and (3). It is preferable that the above is satisfied.
(2) M1 ≧ M2, (3) M1 + M2 ≧ 11
Further, when the stretching rate in the step of stretching in the direction perpendicular to the transport direction (TD stretching step) is T1, it is more preferable that the following formula (4) is satisfied.
(4) 15 ≧ (M1 + M2) /T1≧0.5
As shown in FIG. 1, a first MD stretching step 34 and a second MD stretching step 39 are provided from the upstream process of the manufacturing process, and a TD stretching process 36 is provided therebetween. You may have the 3rd MD extending process or more further downstream of the 2nd MD extending process.

In the present invention, MD stretching is performed by adjusting the tension of a roll such as a transport roll.

The stretching ratio M1 in the first MD stretching process is calculated from the rotational speed of the peeling roll 33 and the rotational speed of the TD stretching process starting roll 37. Similarly, the stretching ratio M2 in the second MD stretching process is calculated from the rotational speed of the final roll 38 in the TD stretching process and the rotational speed of the take-up roll 42. The same applies when the third MD stretching step or more is included.

In the present invention, M1 ≧ M2 and M1 + M2 ≧ 11 are preferable, but M1 / M2 ≧ 1.5 to 3, and 30 ≧ M1 + M2 ≧ 12 are more preferable. Further, 30 ≧ M1 ≧ 10, 10 ≧ M2 ≧ 2 is preferable.

In the first MD stretching step, it is preferable that the residual solvent amount is in the range of 20 to 100% by mass, the temperature is in the range of 15 to 70 ° C., and the tension is 50 to 300 N / m.

In the second MD stretching step, it is preferable that the residual solvent amount is in the range of 1 to 30% by mass, the temperature is in the range of 50 to 160 ° C., and the tension is 50 to 300 N / m.

In the present invention, a TD stretching step is included after the first MD stretching step. TD stretching is preferably performed with a tenter stretching apparatus. The stretching ratio T1 in the TD stretching step is calculated by comparing the film (web) width in the TD stretching step starting roll 37 and the film (web) width in the TD stretching step final roll 38.

In the present invention, it is preferable that 15 ≧ (M1 + M2) /T1≧0.5, but more preferably 10 ≧ (M1 + M2) /T1≧0.6. 30 ≧ T1 ≧ 0.1 is preferable.

As the tenter stretching apparatus, 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 TD stretching step, it is also preferable to intentionally create compartments 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 residual solvent amount of the web in the TD stretching step is preferably 20 to 100% by mass at the start of stretching, and drying is preferably performed while applying a tenter until the residual solvent amount of the web becomes 10% by mass or less. More preferably, it is 5% by mass or less.

In the tenter stretching, the drying temperature is preferably Tg + 10 to Tg + 90 ° C., more preferably Tg + 15 to Tg + 70 ° C., and most preferably Tg + 20 to Tg + 50 ° C.

In the stretching step, 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, and the temperature distribution in the width direction in each stretching step is preferably within ± 5 ° C., and ± 2 ° C. Is more preferable, and within ± 1 ° C. is most preferable.

6) Winding step This is a step of winding the phase difference film by the winder 42 after the residual solvent amount in the web is 2% by mass or less, and the residual solvent amount is 0.4% by mass or less. A film having good stability can be obtained.

As a winding method, a generally used one 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, etc., and these may be used properly.

The retardation film of the present invention is preferably a long film. Specifically, the retardation film shows a thickness of about 100 m to 5000 m, and is usually in the form of a roll. The film width is preferably 1.3 to 4 m, more preferably 1.4 to 2 m.

The thickness of the retardation film of the present invention is not particularly limited, but when used for a polarizing plate protective film described later, it is preferably 20 to 200 μm, more preferably 25 to 100 μm, and 30 to 80 μm. It is particularly preferred.
<Polarizing plate>
The polarizing plate used in the present invention can be produced by a general method. That is, it is preferable that an adhesive layer is provided on the back side of the retardation film of the present invention, and is bonded to at least one surface of a polarizer produced by immersion and stretching in an iodine solution.

Also, if necessary, surface treatment such as corona treatment can be performed. By performing the surface treatment, adhesion with the polarizer can be improved. The film may be used on the other surface, or another polarizing plate protective film may be used.

For example, commercially available cellulose ester films (for example, Konica Minoltack KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5, KV8UY-HA, KV8UX-RHA, KV8UX-RHA Co., Ltd.), cycloolefin films (for example, ZEONOR film (manufactured by ZEON Corporation), ARTON film (manufactured by JSR Corporation)) and the like are preferably used.

A polarizer, 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 known at present is a polyvinyl alcohol polarizing film, which is a polyvinyl alcohol. There are one in which iodine is dyed on a system film and one in which dichroic dye is dyed.

The polarizer is formed by forming a polyvinyl alcohol aqueous solution into a film and dyeing the film by uniaxial stretching or dyeing or uniaxially stretching, and then performing a durability treatment with a boron compound.

As the adhesive used in the adhesive layer, an adhesive layer having a storage elastic modulus at 25 ° C. in the range of 1.0 × 10 ⁴ Pa to 1.0 × 10 ⁹ Pa in at least a part of the adhesive layer is used. It is preferable to use a curable adhesive that forms a high molecular weight body or a crosslinked structure by various chemical reactions after the adhesive layer is applied and bonded.

Specific examples include, for example, urethane adhesives, epoxy adhesives, aqueous polymer-isocyanate adhesives, curable adhesives such as thermosetting acrylic adhesives, moisture curable urethane adhesives, polyether methacrylate types, Examples include anaerobic adhesives such as ester-based methacrylate type and oxidized polyether methacrylate, cyanoacrylate-based instant adhesives, acrylate-peroxide-based two-component instant adhesives, and the like.

The adhesive may be a one-component type, or a type in which two or more components are mixed before use. The adhesive may be a solvent system using an organic solvent as a medium, or an aqueous system such as an emulsion type, a colloidal dispersion type, or an aqueous solution type that is a medium containing water as a main component. It may be a solvent type.

The concentration of the adhesive solution may be appropriately determined depending on the film thickness after bonding, the coating method, the coating conditions, and the like, and is usually 0.1 to 50% by mass.
<Liquid crystal display device>
By incorporating the polarizing plate bonded with the retardation film of the present invention into a liquid crystal display device, various liquid crystal display devices with excellent visibility can be produced. The polarizing plate according to the present invention is bonded to a liquid crystal cell via the adhesive layer or the like.

The polarizing plate according to the present invention is a reflective type, transmissive type, transflective type LCD or TN type, STN type, OCB type, HAN type, VA type (PVA type, MVA type), IPS type, etc. Preferably used.

Especially in the case of a large-screen display device having a screen of 30 or more types, particularly 30 to 54 type, there is no white spot at the periphery of the screen and the effect is maintained for a long time. In addition, there was little color unevenness, glare and wavy unevenness, and the eyes were not tired even during long-time viewing.

<Production of retardation film>
<Preparation of Retardation Film 1 (hereinafter R1)>
(Dope solution 1 composition)
Dianar BR85 (Mitsubishi Rayon Co., Ltd.) 70 parts by mass CAP: cellulose acetate propionate (acyl group total substitution degree 2.75, acetyl group substitution degree 0.20,
Propionyl group substitution degree 2.55, Mw = 200000) 30 parts by mass Methylene chloride 300 parts by mass Ethanol 40 parts by mass The above composition was sufficiently dissolved while heating to prepare Dope Solution 1.

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 belt casting apparatus. With the stainless steel band support, the solvent was evaporated until the residual solvent amount reached 100%, and it was peeled off from the stainless steel band support with a peeling roll at a peeling tension of 180 N / m.

The peeled web was MD stretched at a transport tension of 180 N / m while evaporating the solvent at 60 ° C. in the first MD stretching step, then slit to 1.6 m width, and transported to a tenter (TD stretching step). At this time, the stretching ratio M1 in the transport direction from the peeling roll to the TD stretching process starting roll was 15%.

Then, it was dried at a drying temperature of 145 ° C. (Tg + 25 ° C.) while being stretched 1.15 times in the width direction (stretching ratio T1: 15%) with a tenter. At this time, the residual solvent amount when starting stretching with a tenter was 10%.

After stretching with a tenter, after relaxing at 130 ° C in the second MD stretching step, it was dried while being transported with a number of rolls at 120 ° C with a transport tension of 100 N / m, slit to 1.5 m width, Was subjected to a knurling process having a width of 10 mm and a height of 5 μm, and wound around a core having an initial tension of 220 N / m and a final tension of 110 N / m, and an inner diameter of 15.24 cm, to obtain a retardation film R1. At this time, the stretching ratio in the transport direction from the TD stretching step starting roll to the take-up roll was 8%.

Hereinafter, the raw materials are changed as shown in Table 1, the peeling force and the transport tension at the time of film formation are adjusted, and the stretching ratio is set as shown in Table 1. A phase difference film sample was prepared. The materials used are as follows.

For comparison, A: Konica Minolta Tack KC8UX (manufactured by Konica Minolta Opto Co., Ltd.), B: Fujitac TD (manufactured by Fuji Film Co., Ltd.), C: Retardation film described in Example 101 of WO06 / 1323671, D: The retardation film described in Example 111 was used.

(Various resins)
Dianar BR85: Acrylic resin (Mitsubishi Rayon Co., Ltd.)
MS: Methyl methacrylate-styrene copolymer (mass ratio = 60: 40), Mw 100000
ARTON: Cyclic polyolefin ARTON-G7810 (manufactured by JSR Corporation)
Delpet 80N: Polymethylmethacrylate (Asahi Kasei Chemicals Corporation)
HAC: Manufactured as follows.

Methyl methacrylate 20 parts by weight Acrylamide 80 parts by weight Potassium persulfate 0.3 part by weight Ion-exchanged water 1500 parts by weight The above is charged into the reactor and the reactor is replaced with nitrogen gas. The reaction was allowed to proceed at 70 ° C. until converted to. The obtained aqueous solution was used as a suspending agent. A solution in which 0.05 part by mass of the above suspending agent is dissolved in 165 parts by mass of ion-exchanged water is supplied to a stainless steel autoclave having a capacity of 5 liters and equipped with a baffle and a foudra-type stirring blade, and the system is filled with nitrogen gas. It stirred at 400 rpm, replacing.

Next, a mixed substance having the following charge composition was added while stirring the reaction system.

Methacrylic acid 27 parts by weight Methyl methacrylate 73 parts by weight t-dodecyl mercaptan 1.2 parts by weight 2,2′-azobisisobutyronitrile 0.4 part by weight The temperature was raised to 70 ° C. and the internal temperature was 70 ° C. The time at which the polymerization was reached was set as the polymerization start time, and the polymerization was continued for 180 minutes.

Thereafter, the reaction system was cooled, the polymer was separated, washed, and dried according to the usual method to obtain a bead-shaped copolymer. The polymerization rate of this copolymer was 97%, and the weight average molecular weight was 130,000.

Add 0.2% by mass of additive (NaOCH ₃ ) to this copolymer and use a twin screw extruder (TEX30 (manufactured by Nippon Steel Co., Ltd., L / D = 44.5)) to add nitrogen from the hopper. While purging at a rate of 10 L / min, an intramolecular cyclization reaction is performed at a screw rotation speed of 100 rpm, a raw material supply rate of 5 kg / hour, and a cylinder temperature of 290 ° C. Resin HAC was obtained. The weight average molecular weight (Mw) of HAC was 130,000, and Tg was 130 ° C.

The following evaluation was performed about the retardation film sample. The results are shown in Tables 1 and 2.
(Haze)
A film sample was conditioned in an air-conditioned room at 23 ° C. and 55% RH for 24 hours, and then one film sample was conditioned according to JIS K-7136 under the same conditions as a haze meter (NDH2000 type, manufactured by Nippon Denshoku Industries Co., Ltd.). ).
(Slip)
Regarding the produced retardation film, the film appearance was visually evaluated and evaluated according to the following criteria.
○: Very smooth flatness Δ: Slightly creased, wrinkled, and step can be confirmed ×: Clearly creased, wrinkled, and step can be confirmed (film thickness unevenness)
Under an atmosphere of 23 ° C. and 55% RH, the produced retardation film was divided into 10 equal parts with the width and each thickness was measured with a contact-type film thickness meter manufactured by Mitutoyo Corporation. When measuring the average thickness T _AVE , maximum thickness T _MAX , and minimum thickness T _MIN ,
The thickness unevenness was calculated as {(T _MAX −T _MIN ) / T _AVE } × 100, and evaluated as follows.
○: Thickness variation is 3% or less △: Thickness variation is 3% to 5%
X: Thickness unevenness is 5% or more (phase difference fluctuation)
Using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments Co., Ltd.), in a film that was allowed to stand for 24 hours in an environment of 23 ° C. and 55% RH, the retardation of the film at a wavelength of 589 nm was measured in the same environment. went.

The average refractive index and film thickness d of the film constituent material measured with an Abbe refractometer were input, and the values of in-plane retardation (Ro) and thickness direction retardation (Rth) were obtained. Further, the values of the three-dimensional refractive indexes nx, ny, and nz are calculated by the above device.
Formula (i) Ro = (nx−ny) × d
Formula (ii) Rth = ((nx + ny) / 2−nz) × d
(In the formula, the refractive index in the slow axis direction in the film plane is nx, the refractive index in the direction perpendicular to the slow axis in the plane is ny, the refractive index in the thickness direction is nz, and d is each thickness (nm). Represents.)
Subsequently, after 1000 hours of treatment at 40 ° C. and 95% RH, the measurement was performed in the same manner, and the fluctuation of the retardation value was evaluated in three stages according to the following criteria.
・ Ro variation ○: less than 1 nm Δ: 1 to less than 2 nm ×: 2 nm or more ・ Rth variation ○: less than 2 nm Δ: 2 to less than 5 nm ×: 5 nm or more

As is clear from Tables 1 and 2, it can be seen that the production method of the present invention is excellent in long-term storage at high temperature and high humidity.

DESCRIPTION OF SYMBOLS 1 Melting pot 3, 6, 12, 15 Filter 4, 13 Stock tank 5, 14 Liquid feed pump 8, 16 Conduit 10 Additive charging pot 20 Merge pipe 21 Mixer 30 Die 31 Metal support 32 Web 33 Peeling roll 34 First MD Stretching Step 35 First MD Stretching Final Roll 36 TD Stretching Step (Tenter Stretching)
37 TD stretching process starting roll 38 TD stretching process final roll 39 2nd MD stretching process 40 2nd MD stretching process starting roll 41 2nd MD stretching process final roll 42 Winding roll

Claims (7)

1. The main component is a thermoplastic resin having an elastic modulus at 80 ° C. and 5% RH of 1000 MPa or more, and an elastic modulus E1 at (Tg−10) ° C. and an elastic modulus E2 at (Tg + 10) ° C. satisfying the following formula (1) A method for producing a retardation film comprising a step of stretching a film with a stretching ratio of 11 to 100% in a film transport direction.
   (1) 500 ≧ E1 / E2 ≧ 10
2. The method for producing a retardation film according to claim 1, wherein the thermoplastic resin contains an acrylic resin as a main component.
3. 3. The retardation according to claim 1, wherein the thermoplastic resin contains the acrylic resin (A) and the cellulose ester resin (B) in a mass ratio of 95: 5 to 30:70. A method for producing a film.
4. The step of stretching in the transport direction has at least two steps, and the step of stretching in a direction perpendicular to the transport direction is between the two steps, of the at least two steps The retardation film according to any one of claims 1 to 3, wherein the stretch ratio M1 in the upstream process and the stretch ratio M2 in the downstream process satisfy the following formulas (2) and (3): Production method.
   (2) M1 ≧ M2, (3) M1 + M2 ≧ 11
5. 5. The method for producing a retardation film according to claim 4, wherein the following formula (4) is satisfied when a stretching ratio in the step of stretching in a direction perpendicular to the transport direction is T <b> 1.
   (4) 15 ≧ (M1 + M2) /T1≧0.5
6. A polarizing plate using a retardation film produced by the method for producing a retardation film according to any one of claims 1 to 5.
7. A liquid crystal display device using the polarizing plate according to claim 6.

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