KR101500599B1 - Retardation film and polarizing plate - Google Patents

Abstract

A problem to be solved by the present invention is to provide a retardation film which can easily and reliably adjust the retardation, can easily laminate and adhere, and has little change in retardation according to the conditions of use .
[MEANS FOR SOLVING PROBLEMS] A retardation film according to the present invention is a retardation film formed by stretching a sheet of an extrusion-molded cellulose acetate propionate resin. This retardation film has a retardation value measured with a ray of 448.1 nm as R448, a retardation value measured with a ray of 589 nm as R589, and a retardation value measured with a ray of 800 nm as R800, {( R800 / R589-R448 / R589) / (800-589) is preferably 0.001 or more and 0.003 or less.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a retardation film and a polarizing plate,

The present invention relates to a retardation film and a polarizing plate.

Conventionally, a retardation film formed by stretching a sheet made of polycarbonate or a sheet made of cycloolefin polymer is known. This retardation film is used, for example, in a polarizing plate. Specifically, a polarizing plate is produced by laminating and bonding the above retardation film to a polarizing sheet in which a polarizer protective film made of triacetyl cellulose or the like is laminated on both sides of the polarizer using a water-shed or the like.

The retardation film made of polycarbonate has a relatively high photoelastic coefficient of 60 or more and 80 or less of the resin, and when it is deformed by the temperature or humidity of the environment in which it is used, the refractive index changes and the retardation may change. For this reason, it is difficult to use the retardation film made of polycarbonate as a retardation film which is reluctant to change the retardation, for example, a retardation film laminated on a circularly polarizing plate for antireflection of an organic EL display.

Since the retardation film made of a cycloolefin polymer has high gas barrier properties but is low in moisture permeability, it can not be bonded using a water-based cloth comprising a cellulose-based resin as a main component, and therefore, there is a problem that lamination adhesion with a polarizer or the like is difficult.

Japanese Patent Application Laid-Open No. 2007-131681 proposes a retardation film made of cellulose acetate propionate. The retardation film of this publication is formed in a sheet form by casting a solution in which cellulose acetate propionate is dissolved in a solvent. For this reason, the solvent remains in the retardation film of this publication, and there is a problem that it is difficult to balance the retardation in the surface direction and the retardation in the thickness direction by the residual solvent.

Japanese Patent Application Laid-Open No. 2007-131681

(Summary of the Invention)

(Problems to be Solved by the Invention)

DISCLOSURE OF THE INVENTION The present invention has been made based on the above-described circumstances, and it is an object of the present invention to provide a liquid crystal display device which can easily and reliably adjust the retardation and can be easily laminated and bonded, And a retardation film with little change in retardation. Another object of the present invention is to provide a polarizing plate which has a retardation film which is reliably controlled in retardation, is easy to manufacture, and further has little change in optical characteristics due to the conditions of use.

The retardation film according to the present invention performed to solve the above problems is a retardation film formed by stretching a sheet of extruded cellulose acetate propionate resin.

A sheet of extruded cellulose acetate propionate is a retardation film formed by stretching in an oblique direction with respect to the sheet longitudinal direction.

Since the retardation film is made of cellulose acetate propionate, there is little change in retardation due to conditions of the use environment compared to a conventional polycarbonate sheet or the like. In addition, since the retardation film is stretched, the phase difference is prolonged. It is easy to balance the retardation in the surface direction and the retardation in the thickness direction, as compared with the production using a solution in which a conventional cellulose acetate propionate is dissolved in a solvent , And the retardation film has an appropriately balanced surface direction retardation and thickness direction retardation. In addition, this retardation film can be adhered using a water-based paint comprising a cellulose-based resin which is conventionally used, so that lamination adhesion with a polarizer or the like can be carried out easily and reliably.

In this retardation film, when the retardation measured with a light ray of 448.1 nm is represented by R448, the retardation measured by a ray of 589 nm is represented by R589, and the retardation measured by a ray of 800 nm is represented by R800,

(R800 / R589-R448 / R589) / (800-448) is preferably 0.001 or more and 0.003 or less.

As a result, the retardation in the plane direction measured by the light with high wavelength (800 nm) becomes larger than the retardation in the plane direction measured with the light with low wavelength (448.1 nm), and the increasing ratio is within the above numerical range, Direction retardation along the wavelength of the light ray can be exhibited and a desired retardation can be exhibited for a wide wavelength range.

In this retardation film, when the retardation measured with a light ray at 448.1 nm is represented by R448, the retardation measured with a light ray at 589 nm is represented by R589, and the retardation measured with a light ray at 800 nm is represented by R800,

(1-R448 / R589) / (589-448) is 0.0013 or more and 0.003 or less,

(R800 / R589-1) / (800-589) is preferably 0.0006 or more and 0.003 or less.

As a result, in the low-wavelength region (448.1 to 589 nm), the retardation in the plane direction measured by the high-wavelength (589 nm) ray becomes larger than the retardation in the plane direction measured with the low-wavelength (448.1 nm) Is within the above-mentioned numerical range, it is possible to exert the retardation in the plane direction with respect to the light beam in the low wavelength region according to the wavelength of the light beam. Further, the surface direction retardation measured by the high wavelength (800 nm) light ray in the high wavelength region (589 to 800 nm) is larger than the surface direction retardation measured by the low wavelength (589 nm) light ray, It is possible to exhibit the retardation in the plane direction with respect to the light of the high wavelength region according to the wavelength of the light. That is, by adopting the above-described configuration, a desired phase difference can be expressed over a wide wavelength range.

It is preferable that the ratio {(R800 / R589-1)} / {(1-R448 / R589}) is not less than 0.4 and not more than 1. In this manner, the rate of change of retardation in the surface direction in the low wavelength region (448.1 to 589 nm) (589 nm to 800 nm) of the retardation of the retardation in the plane direction is within the above-described numerical range, the ratio of the retardation of the surface direction retardation in the high wavelength region It is easy to develop a desired phase difference in a wide wavelength range.

In this retardation film, it is preferable that the retardation in the plane direction measured by a light beam having a wavelength of 589 nm is 130 nm or more and 150 nm or less. Thus, the retardation film can exert its function as a quarter wavelength plate.

In this retardation film, it is preferable that retardation in the thickness direction measured by a light beam having a wavelength of 589 nm is not less than 70 nm and not more than 300 nm. This makes it possible to easily and reliably hold the retardation in the thickness direction of the retardation film suitable for the surface retardation.

In this retardation film, it is preferable that the stretching magnification in the longitudinal direction of the sheet is 30% or more and 250% or less. This makes it possible to easily and accurately realize the retardation in a desired range.

In the polarizing plate according to the present invention,

The retardation film having the above structure,

A polarizer laminated and bonded to the retardation film through an adhesive layer

.

The polarizing plate has the above-described retardation film having the above-described structure, and thus has the advantage of the above-mentioned retardation film. That is, the polarizing plate has less change in optical characteristics due to a change in the use environment, and also has good balance between retardation in the plane direction and retardation in the thickness direction of the retardation film. Further, the polarizing plate is easily and reliably laminated and adhered to the polarizing plate by using an adhesive layer such as a water-based film containing a cellulose-based resin which is conventionally used.

INDUSTRIAL APPLICABILITY As described above, the retardation film of the present invention can easily and reliably adjust the retardation, can be easily laminated and adhered easily, and has little change in retardation due to conditions of use environment.

1 is a schematic front view of a retardation film according to an embodiment of the present invention.
Fig. 2 is a schematic explanatory view for explaining the stretching method in the production method of the retardation film of Fig. 1;
3 is a schematic front view of a polarizing plate using the retardation film of FIG.
4 is a graph showing the relationship between the wavelength of the transmitted light beam and the retardation in the plane direction of the retardation film of the embodiment of the present invention and the retardation film of Comparative Examples 1 and 2. Fig.
5 is a table comparing numerical values 1 to 4 on the basis of Fig.

(Mode for carrying out the invention)

Hereinafter, the embodiments of the present invention will be described, but first, the retardation film 1 of one embodiment of the present invention will be described.

≪ Phase difference film (1) >

The retardation film (1) of the present invention is formed by stretching a sheet of extruded cellulose acetate propionate in an oblique direction with respect to the longitudinal direction of the sheet. This sheet is formed by extruding a resin composition containing cellulose acetate propionate as a main component. Here, cellulose acetate propionate is obtained by replacing at least a part of the hydroxyl groups of cellulose with an acetyl group and a propionyl group.

The average substitution degree (DSac + DSpR) of the acetyl group and / or the propionyl group in the cellulose acetate propionate is preferably 2.0 or more. When the average degree of substitution is less than the lower limit described above, the retardation film (1) having a larger retardation (absolute value) becomes shorter in shorter wavelengths, which may lower the display quality of the liquid crystal display device. The average substitution degree (DSac + DSpR) of the acetyl group and / or the propionyl group in the cellulose acetate propionate can be determined, for example, by the method described in ASTM-D817-96. The upper limit value of the average degree of substitution (DSac + DSpR) is 3, in which case all of the hydroxyl groups are acetylated or profiled.

The average substitution degree (DSac) of the acetyl group in the cellulose acetate propionate is preferably 0.1 or more and 1.6 or less, and the average degree of substitution (DSpR) of the propionyl group in the cellulose acetate propionate Is preferably 0.1 or more and 2.4 or less, more preferably 0.5 or more and 2.0 or less, and further preferably 1.0 or more and 2.0 or less.

The cellulose acetate propionate may have other substituents other than an acetyl group and a propionyl group. Examples of other substituents include ether groups such as butyrate and other ester groups, alkyl ether groups, and aralkylene ether groups.

The weight average molecular weight (Mw) of the cellulose acetate propionate is preferably 5,000 or more and 140,000 or less, more preferably 15,000 or more and 110,000 or less, and still more preferably 50,000 or more and 105,000 or less. When the weight average molecular weight of the cellulose acetate propionate exceeds the upper limit, the thermal fluidity at the time of extrusion molding is lowered, which may result in difficulty in thermoforming. On the other hand, when the weight average molecular weight of the cellulose acetate propionate is less than the above lower limit, there is a fear that the mechanical strength of the obtained film is lowered or the obtained film does not have a sufficient retardation. The weight average molecular weight (Mw) can be calculated by gel permeation chromatography (GPC).

The cellulose acetate propionate may be composed of a single compound, but in order to make it easy to adjust the optical properties such as in-plane retardation, a compound of a different kind of substitution degree of propionyl group or acetyl group may be used .

The cellulose acetate propionate can be prepared by a known method. For example, cellulose is treated with a gypsum soda solution to give an alkali cellulose, which is acylated with a mixture of acetic anhydride and propionic anhydride. The resulting cellulose ester has an average degree of substitution (DSac + DSpR) of approximately 3, but cellulose acylate propionate having an intended degree of substitution can be produced by partial hydrolysis of an acyl group. Also, the degree of propionyl substitution can be obtained by varying the ratio of acetic anhydride to propionic anhydride at the time of acylation.

The resin composition as the sheet-forming material may also contain other compounds other than the cellulose acetate propionate as the main component. Examples of other compounds include cellulose esters such as cellulose butyrate, and cellulose ethers such as methyl cellulose and ethyl cellulose. Of these, ethylcellulose which is excellent in the expression of the inward direction retardation and excellent in compatibility with cellulose acetate propionate is preferable. The blending amount of ethyl cellulose is preferably 1 part by mass or more and 10 parts by mass or less, more preferably 3 parts by mass or more and 8 parts by mass or less, and more preferably 6 parts by mass or more and 8 parts by mass or less, based on 100 parts by mass of cellulose acetate propionate desirable.

The resin composition preferably contains a plasticizer from the viewpoint of improving processing characteristics at the time of drawing. The plasticizer is not particularly limited, and examples thereof include diethyl phthalate, polyhydric alcohol compounds and the like. Of these, diethyl phthalate is preferable because it has good compatibility with cellulose acetate propionate and little influence on the surface direction retardation.

The content of the plasticizer is preferably 5% by mass or more and 20% by mass or less, more preferably 8% by mass or more and 16% by mass or less based on the whole resin composition. If the content of the plasticizer exceeds the upper limit, the mechanical strength may be lowered. On the other hand, when the content of the plasticizer is less than the above lower limit, the effect due to the addition of the plasticizer is not sufficiently exhibited, and the thermoforming and drawing process may not be improved.

The resin composition preferably contains a phosphite-based coloring preventing agent. By containing the phosphite-based coloring preventing agent, an excellent coloring preventing effect can be obtained even in a range where the molding temperature is high.

Examples of the phosphite-based coloring preventing agent include tetrakis (2,4-di-t-butylphenyl) [1,1-biphenyl] -4,4'-diylbisphosphonite, tetrakis , 6-di-t-butylphenyl) [1,1-biphenyl] -4,4'-diylbisphosphonite, tetrakis (2,6- (2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite, bis (2- Pentaerythritol diphosphite, bis (4-t-butyl-2-cumylphenyl) pentaerythritol diphosphite, bis (2,6- Di-t-butyl-6-methylphenyl) pentaerythritol diphosphite, and among these, pentaerythritol-based ones having excellent antifouling effect are preferable.

The blending amount of the phosphite-based coloring preventing agent is preferably 0.005 mass% or more and 0.5 mass% or less with respect to the whole resin composition. If the compounding amount of the phosphite-based coloring preventing agent exceeds the upper limit, there is a possibility that a sufficient effect on the added amount may not be obtained. On the other hand, when the amount of the phosphite-based coloring preventing agent is less than the lower limit described above, there is a fear that the coloring preventing effect is lowered.

The resin composition may contain other additives insofar as the effect of the present invention is not impaired. Examples of other additives include heat stabilizers, ultraviolet stabilizers, crystal nucleating agents, gloss removing agents, pigments, mold inhibitors, antibacterial agents, flame retardants, and hydrophilic agents.

The stretching magnification in the oblique direction of the sheet is preferably 30% or more and 250% or less, more preferably 40% or more and 220% or less, in the phase difference film (1) , More preferably 50% or more and 120% or less. If it is less than the lower limit value, there is a fear that the phase difference can not be sufficiently manifested. On the other hand, if the upper limit value is exceeded, there is a fear that the phase difference can not be controlled sufficiently. The stretching method in the oblique direction will be described later.

The retardation film (1) has a phase advance axis inclined at an angle of not less than 40 ° and not more than 50 ° with respect to the longitudinal direction of the sheet. Further, in the present invention, the inclination angle of the fast axis is not particularly limited, but it can be suitably used as a retardation film for a polarizing plate by setting the inclination angle to about 45 degrees.

The phase retardation film (1) has a retardation in the plane direction of 130 nm or more and 150 nm or less as measured by a light beam having a wavelength of 589 nm. In the present invention, the retardation in the plane direction is not necessarily limited to those in the above-mentioned range, but the retardation in the plane direction of the retardation film (1) can be suitably used as a 1/4 wave plate by setting the retardation in this range. In addition, the retardation in the plane direction (Re) is a numerical value obtained by the following equation.

Re = (ny-nx) xd

Here, nx is the refractive index of the fast axis (parallel to the plane direction) of the retardation film, and ny is the refractive index of the retardation film axis (parallel to the plane direction and perpendicular to the fast axis) , and d is the thickness of the retardation film.

The retardation film (1) has a retardation in the thickness direction of 70 nm or more and 300 nm or less as measured by a light beam having a wavelength of 589 nm. In the present invention, the retardation in the thickness direction is not necessarily limited to the retardation in the above-mentioned range. However, by setting the retardation in the thickness direction of the retardation film 1 in the above range, The balance can be easily and securely held. The retardation in the thickness direction (Rth) is a value obtained by the following equation.

Rth = ((nx + ny) / 2-nz) xd

Here, nz is the refractive index of the retardation film 1 in the thickness direction (direction perpendicular to the plane direction).

The retardation in the plane direction and the retardation in the thickness direction can be measured by using an automatic birefringence measuring apparatus (for example, trade name: KOBRA-WR manufactured by Oji Paper Co., Ltd.) (Nx, ny, nz) by measuring a three-dimensional refractive index by transmitting a light beam of a specific wavelength (for example, 589 nm) under the environment of an optical system

The retardation film (1) had a retardation in the plane direction measured with a ray of 448.1 nm as R448, a retardation in the plane direction measured with a ray of 589 nm as R589, and a retardation in the plane direction measured with a ray of 800 nm R800, it is preferable that the following conditions are satisfied.

The value obtained by dividing the difference between the ratios R800 / R589 and R448 / R589 of R800 and R448 to R589 by the wavelength change amount (800-448.1) of the measurement light (hereinafter sometimes referred to as numerical value 1) is 0.0008 or more . Specifically, it is preferable to satisfy the following formula (1).

식 (1)

Equation (1)

The left side (numerical value 1) of the above formula (1) means the rate at which the retardation in the plane direction measured by a light beam at a high wavelength (800 nm) becomes larger than the retardation in the plane direction measured with a light beam at a low wavelength (448.1 nm) When the numerical value 1 is equal to or more than the above lower limit value, the function as a 1/4 wavelength plate can be exerted in a wide wavelength range. It is more preferable that the lower limit value is 0.0009.

The numerical value 1 is preferably 0.003 or less. When the numerical value 1 exceeds the upper limit value, the surface direction retardation of the high wavelength (800 nm) light becomes excessively large or the surface direction retardation of the low wavelength (448.1 nm) becomes too small, / 4 wave plate can not be exerted. Further, the upper limit value of the numerical value 1 is more preferably 0.002.

The value obtained by dividing the difference between the ratios of R800 and R589 (R800 / R589 and 1) to R589 by the wavelength change amount (800-589) of the measurement light (hereinafter sometimes referred to as the numerical value 2) is preferably 0.0006 or more Do.

Concretely, it is preferable to satisfy the following formula (2).

식 (2)

Equation (2)

The left side (numerical value 2) of the formula (2) means the rate at which the surface direction retardation increases in accordance with the wavelength of the light beam transmitted in the high wavelength region (589 to 800 nm) The function as a 1/4 wavelength plate can be exerted in the high wavelength region.

The numerical value 2 is preferably 0.003 or less. If the numerical value 2 exceeds the upper limit value, the function as a 1/4 wavelength plate may not be able to be exerted in the high wavelength region. Further, the upper limit value of the numerical value 2 is more preferably 0.002.

It is preferable that the value obtained by dividing the difference between the ratios of R448 and R589 (R448 / R589 and 1) to R589 by the wavelength change amount (589-448.1) of the measurement light (hereinafter sometimes referred to as the numerical value 3) is 0.0013 or more .

Specifically, it is preferable to satisfy the following formula (3).

식 (3)

Equation (3)

The left side (numerical value 3) of the formula (3) means the rate at which the surface direction retardation increases in accordance with the wavelength of the light beam transmitted in the low wavelength region (448.1 to 589 nm) The function as a 1/4 wavelength plate can be exerted in the low wavelength region. It is more preferable that the lower limit value is 0.0014.

Also, the numerical value 3 is preferably 0.003 or less. When the numerical value 3 exceeds the upper limit value, on the other hand, there is a possibility that the function as a quarter wave plate can not be exerted in a wide wavelength region in the low wavelength region. Further, the upper limit value of the numerical value 3 is more preferably 0.002 or less.

The ratio of the numerical value 2 to the numerical value 3 is preferably 0.4 or more.

Specifically, it is preferable to satisfy the following expression (4).

식 (4)

Equation (4)

The left side (numerical value 4) of the above equation (4) is the ratio of the rate of change of the surface direction retardation in the high wavelength region to the rate of change of the surface direction retardation in the low wavelength region (448.1 to 589 nm) The retardation in the surface direction in the low-wavelength region and the high-wavelength region becomes sufficiently large corresponding to the wavelength of the light transmitted therethrough, so that the function as a quarter-wave plate can be exerted in a wide range of wavelengths. It is more preferable that the lower limit value is 0.42.

The numerical value 4 is preferably 1 or less. If the numerical value 4 exceeds the upper limit value, the production becomes difficult. Further, the upper limit value of the numerical value 4 is more preferably 0.8 or less, and still more preferably 0.7 or less.

The lower limit value of the average thickness of the retardation film 1 is preferably 40 占 퐉 to 250 占 퐉, more preferably 40 占 퐉 to 200 占 퐉, and still more preferably 40 占 퐉 to 150 占 퐉. If the average thickness of the phase difference film (1) exceeds the upper limit value, there is a possibility that the demand for the lightness is adversely affected. On the other hand, when the average thickness of the retardation film 1 is less than the above lower limit value, there is a fear that a sufficient retardation can not be exhibited.

The average thickness of the sheet before stretching of the retardation film 1 is preferably 50 占 퐉 to 500 占 퐉, more preferably 100 占 퐉 to 300 占 퐉, and still more preferably 120 占 퐉 to 250 占 퐉. As a result, after stretching, the above-mentioned retardation film (1) having the average thickness can be produced.

The light transmittance of the retardation film 1 is preferably 85% or more, more preferably 90% or more. If the light transmittance of the retardation film 1 is less than the lower limit, the amount of light from the light source is lowered, which may lower the visibility of the screen.

The haze value of the retardation film (1) is preferably 2% or less, and more preferably 1% or less. If the haze value of the retardation film (1) exceeds the upper limit, the light transmittance may be lowered, and the clarity of the transmitted image may be lowered.

≪ Production method of retardation film (1)

The method for producing the retardation film (1) comprises a step of melting a sheet-forming material whose main component is cellulose acetate propionate, a step of extruding the molten sheet-forming material into a sheet form, a step of stretching the sheet- And a step of punching the stretched sheet-forming material into a rectangular shape.

The melting step and the extruding step can be performed by a conventionally known melt extrusion method. For example, the sheet forming material can be melted and extruded from a T die to form a sheet.

The stretching step is a step of continuously stretching the extruded sheet-forming material in an oblique direction with respect to the sheet longitudinal direction as described above. In this step, the stretching temperature is preferably 130 ° C or more and 170 ° C or less, and more preferably 140 ° C or more and 160 ° C or less. If the stretching temperature is lower than the above lower limit value, there is a fear that the sheet shape forming material is broken at the time of stretching. On the other hand, when the stretching temperature exceeds the upper limit value, there is a fear that a sufficient retardation can not be expressed by stretching.

In this stretching step, the sheet-forming material is stretched in the longitudinal direction (in the sheet longitudinal direction) and the sheet-forming material is stretched in the transverse direction (in the sheet width direction) . The stretching in the longitudinal direction and the transverse direction can be performed, for example, by the stretching device shown in Fig. The stretching device shown in Fig. 2 is characterized in that both end portions of the sheet-forming material 1a are respectively stuck to the chuck, the chucks at both ends are advanced in the sheet longitudinal direction faster than the sheet extrusion speed, And is elongated in the oblique direction with respect to the sheet longitudinal direction by accelerating the chucking speed.

Here, it is preferable that the stretching magnification is 30% or more and 250% or less as described above. The stretching magnification is a ratio of the distance between the pair of chucks after stretching relative to the distance between the pair of chucks before stretching (the widthwise length W1 (width) of the sheet-forming material 1a before stretching) (A value obtained by retracting the width W1 of the sheet-forming material before stretching from the length W2 in the oblique direction (fast axis direction) of the sheet material). Specifically, it can be obtained by the following expression (5).

식 (5)

Equation (5)

Further, in the present invention, the stretching method is not limited to the above-mentioned method. For example, the stretching method may be a stretching method in one direction (for example, the longitudinal direction) and then the other direction , It is also conceivable to employ a method of stretching in an oblique direction. In this case, the drawing magnification can be obtained by the equation (6).

식 (6)

Equation (6)

Further, in the present invention, the stretching step is provided continuously to the above-mentioned extrusion step. However, the present invention is not limited to this. For example, a sheet formed by extrusion and formed into a sheet- , And thereafter, a step of unwinding and stretching the sheet from the sheet roll fabric can be performed. In this case, it is preferable to carry out a step of preheating the sheet as the previous step of stretching.

In the punching step, the long side or short side of the rectangular shape to be punched is punched so as to be parallel to the longitudinal direction of the stretched sheet-forming material. Since the sheet-forming material is stretched in the oblique direction with respect to the longitudinal direction as described above, the fast axis of the punched sheet (the retardation film 1) is inclined in the oblique direction with respect to the sheet longitudinal direction.

≪ Production method of polarizing plate 10 >

Next, a method of producing the polarizing plate 10 using the retardation film 1 will be described.

The method for producing the polarizing plate 10 has a step of laminating and bonding the retardation film 1 to the polarizer 3. Here, conventionally known polarizers 3 can be used, and for example, a polyvinyl alcohol resin film is dyed with a dichromatic material (for example, iodine or dichromatic dye) and uniaxially stretched is used . The polymerization degree of the polyvinyl alcohol constituting the polyvinyl alcohol resin film is preferably 500 or more, more preferably 1000 or more. The polyvinyl alcohol resin film can be formed by a known method (for example, a soft method in which a resin solution is dissolved in water or an organic solvent, a casting method, etc.). The thickness (average thickness) of the polarizer 3 differs depending on the purpose or use of the liquid crystal display device or the like in which the polarizing plate 10 is used, but is typically 5 占 퐉 or more and 100 占 퐉 or less. The polarizer 3 may contain an optional component other than the polyvinyl alcohol resin and the dichroic substance so long as the polarizing function and optical transparency are not impaired. As a typical production method of the polarizer 3, a series of manufacturing steps including swelling, dyeing, crosslinking, stretching, washing and drying of a polyvinyl alcohol resin film is employed. In each treatment step except for the drying step, the treatment is carried out by immersing the polyvinyl alcohol resin film in a bath of the solution used in each step. The order, recovery, and execution of respective treatments of swelling, dyeing, crosslinking, stretching, washing and drying can be suitably set according to purposes, materials to be used and conditions. For example, the stretching treatment may be performed before the dyeing treatment, or may be performed simultaneously with the swelling treatment. It is also preferable to carry out the crosslinking treatment before and after the stretching treatment.

In the lamination bonding step in the method for producing the polarizing plate 10, the polarizer 3 and the retardation film 1 are laminated and bonded with an adhesive. As the adhesive, conventionally known adhesives can be used. For example, a water-soluble adhesive is used and a water-repellent material mainly composed of a cellulose-based resin is suitably used.

≪ Polarizer (10) >

Next, the polarizing plate 10 using the retardation film 1 will be described with reference to FIG. The polarizing plate 10 shown in Fig. 3 has a polarizer 3 and the retardation film 1 laminated and bonded to both surfaces of a polarizer 3 laminated and adhered via an adhesive layer 5 made of the adhesive.

Here, the pair of the retardation films 1 laminated on both surfaces of the polarizer 3 are laminated and bonded to the polarizer 3 such that the fast axis directions of the retardation films 1 are mutually at a constant angle in plan view. Specifically, one of the retardation films 1 is laminated and adhered so that the fast axis direction thereof is inclined by + 45 ° with respect to the transmission axis direction of the polarizer 3, and the other retardation film 1 is laminated So that the fast axis direction is inclined at -45 DEG with respect to the transmission axis direction of the polarizer 3 in plan view. Therefore, the pair of the retardation films 1 are laminated and bonded to the polarizer 3 so that the fast axis directions of the pair of the retardation films 1 are at an angle of 90 degrees with respect to each other. It is preferable that a certain angle is not less than 80 DEG and not more than 100 DEG in terms of a plane formed by the fast axis direction of the pair of the phase difference films 1. It is also preferable that the absolute value of the angle obtained by the plane formed by the fast axis direction of the phase difference film 1 and the transmission axis direction of the polarizer 3 is 40 ° or more and 50 ° or less.

<Advantages>

Since the retardation film 1 has the above-described structure, it has the following advantages. That is, since the retardation film (1) is made of cellulose acetate propionate, the change of retardation due to the conditions of the use environment is less than that of a conventional sheet made of polycarbonate, and the polarizing plate (10) It is difficult for the optical characteristics to change.

Since the phase difference film (1) has a phase difference by being stretched, it is easy to balance the retardation in the plane direction and the retardation in the thickness direction as compared with the case where the film is produced by using a conventional solvent. Therefore, ) Can obtain a plane direction retardation and a thickness direction retardation of an appropriate balance. Therefore, such a retardation film can be easily and reliably produced, for example, as a retardation film functioning as a positive A plate, and can be easily and surely used as a retardation film serving as, for example, a negative C plate .

Further, the retardation film 1 can be adhered using a water-based cloth composed mainly of a cellulose-based resin which is conventionally used, and lamination adhesion with the polarizer 3 can be easily and reliably performed.

Further, the retardation film in this retardation film can be suitably used as a 1/4 wavelength plate in a wide range of wavelengths since the retardation in the plane direction is changed within the above range by the transmitted light rays (see formulas (1) to (4)).

Since the retardation film 1 can be produced by stretching in an oblique direction to realize a retardation and punching the stretched sheet at a long side or a short side parallel to the sheet longitudinal direction, The manufacturing process is less and the loss is less likely to occur, so that the cost can be reduced.

[Example 1]

Next, an embodiment of the retardation film according to the present invention will be described.

In this example, 5 parts by weight of TPP of Daihachi Kagaku Kogyo as a plasticizer, and 10 parts by weight of # 10 of Daihatsu Kagaku Kogyo Co., Ltd. were added to 100 parts by weight of a main component cellulose acetate propionate (average degree of substitution of propionyl group 2.0) To prepare a sheet-forming material. The sheet-forming material was melted and extruded through a T-die to obtain a sheet-shaped sheet-forming material. The sheet-forming material was stretched at a drawing temperature of 155 DEG C at a draw ratio of 165% to obtain a retardation film of this example. The average thickness of the retardation film was 145 탆 (240 탆 before stretching).

For the retardation film of this example, the retardation in the plane direction with respect to the transmitted light beam of each wavelength was measured with an automatic birefringence measuring apparatus (trade name: K0BRA-WR, manufactured by Oji Kessou Kiki Kiki Co., Ltd.) Lt; / RTI &gt; The results are shown in Fig.

As a comparative example, the retardation of the retardation film was measured under the same conditions as those described above for the retardation film (trade name: WRF-W manufactured by Dainippon Ink and Chemicals, Inc.). The results are shown in Fig.

In Fig. 4, the abscissa indicates the wavelength of the transmitted light ray when measured. The vertical axis represents the ratio of the retardation in the plane direction measured at the transmission light ray of each wavelength to the retardation in the plane direction measured at the wavelength 589 nm transmission ray.

4, as compared with the retardation film of the comparative example, the phase retardation film of the present example has the surface direction retardation sequentially increased as the transmitted light ray is shifted from a lower wavelength to a higher wavelength, / 4 function as a wave plate.

More specifically, as shown in Fig. 5, numerical value 1 (numerical value on the left side of the equation (1)) is about 0.00093 in the present embodiment and about 0.00079 in the comparative example. The numerical value 2 (the numerical value on the left side of the equation (2)) is about 0.00060 in the present embodiment and about 0.00051 in the comparative example. The numerical value 3 (numerical value on the left side of the equation (3)) is about 0.00143 in the present embodiment and 0.00120 in the comparative example. As described above, in this embodiment, the surface direction retardation gradually increases as the transmission light ray is shifted from a low wavelength to a high wavelength as compared with the comparative example, and the function as a quarter wavelength plate is exhibited in a wide wavelength region. In addition, the numerical value 4 (the numerical value in the equation (4)) was about 0.42 in the present embodiment and the comparative example.

[Other Embodiments]

Further, the present invention is not limited to the above-described embodiment, but can be practiced with various modifications and improvements. For example, the polarizing plate 10 of the above-described embodiment has a three-layer structure (excluding the adhesive layer 5) of a pair of retardation films 1 and a polarizer 3 interposed therebetween The polarizing plate 10 may have a two-layer structure of, for example, a polarizer 3 and the retardation film 1, and may have a three-layer structure as in the above embodiment, It is also possible to appropriately change the design so as to further laminate the protective film.

INDUSTRIAL APPLICABILITY As described above, the retardation film and the polarizing plate of the present invention can be suitably used in various fields such as a liquid crystal display device used for a mobile phone terminal, a PC monitor, a television, an electronic calculator, a clock,

1 phase difference film
1a sheet forming material
3 polarizer
5 Adhesive layer
10 Polarizer

Claims (8)

A sheet of an extruded cellulose acetate propionate resin is formed by stretching,
(DSac + DSpr) of the acetyl group and the propionyl group in the cellulose acetate propionate is not less than 2.0 and not more than 3.0, the average degree of substitution (DSac) of the acetyl group is not less than 0.1 and not more than 1.6, and the propionyl group Has an average degree of substitution (DSpr) of not less than 0.5 and not more than 2.0,
When the surface direction retardation measured with a light ray at 448.1 nm is represented by R448 and the surface direction retardation measured with a 589 nm ray is represented by R589 and the surface direction retardation measured with an 800 nm ray is represented by R800,
(1-R448 / R589) / (589-448) is 0.0013 or more and 0.003 or less,
(R800 / R589-1) / (800-589) is from 0.0006 to 0.003,
(R800 / R589-1) / (1-R448 / R589) is 0.4 or more and 1 or less. The retardation film according to claim 1, wherein (R800 / R589-R448 / R589) / (800-448.1) is 0.0008 or more and 0.003 or less. The retardation film according to claim 1, wherein the retardation in the plane direction measured by a light beam having a wavelength of 589 nm is 130 nm or more and 150 nm or less. The retardation film according to claim 1, wherein the retardation in the thickness direction measured by a light beam having a wavelength of 589 nm is 70 nm or more and 300 nm or less. The retardation film according to claim 1, wherein the stretching magnification in the stretching direction is 30% or more and 250% or less. A polarizing plate comprising the retardation film according to claim 1,
And a polarizer laminated and bonded to the retardation film through an adhesive layer. delete delete

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