JP2013137394A - Method for manufacturing retardation film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing retardation films capable of suppressing fracture in handling in drawing a film or after the drawing and stably and continuously satisfying a relation of 0.92≤R/Re≤1.08.SOLUTION: A drawing step includes: a first drawing step of performing a uniaxial drawing process for a specific film before the drawing in one direction, the specific film before the drawing including a resin layer a1 containing polycarbonate, a resin layer b containing resin B having a negative intrinsic birefringence, and a resin layer a2 containing polycarbonate; and a second drawing step of performing a uniaxial drawing process in the direction orthogonal to the direction in which the uniaxial drawing step is performed in the first drawing step. A plane orientation coefficient represented by (nx+ny)/2-nz of a resin layer A1 and a resin layer A2 formed by drawing the resin layer a1 and the resin layer a2 by the drawing step respectively is defined to 0.017 or more.

Description

  The present invention relates to a method for producing a retardation film. More specifically, the present invention relates to a method for producing a retardation film having a highly controlled thickness and orientation degree and excellent strength.

  For example, a retardation film used for optical compensation of a liquid crystal display device is required to be capable of reducing a change in color tone of the display device depending on an observation angle, and various techniques have been developed conventionally. For example, Patent Document 1 proposes a retardation film in which a film made of a resin having a positive intrinsic birefringence value and a film made of a resin having a negative intrinsic birefringence value are bonded together. However, a resin having a negative intrinsic birefringence value usually has low strength and is brittle. Therefore, it has been pointed out that when a layer made of a resin having a negative intrinsic birefringence value is stretched and subjected to a retardation film stretching treatment, it is easily broken and the manufacturing efficiency is poor.

In order to prevent damage to a layer made of a resin having a negative intrinsic birefringence value, in Patent Document 2, a resin having a negative intrinsic birefringence value such as polystyrene and a resin having a positive intrinsic birefringence value such as polycarbonate are used together. A laminated film is obtained by extrusion or co-casting, and the film is stretched so that the retardation Re at an incident angle of 0 ° and the retardation R _{40 at an} incident angle of 40 ° have a relationship of 0.92 ≦ R ₄₀ /Re≦1.08. A manufacturing method for obtaining a satisfying retardation film has been proposed. According to this manufacturing method, a layer made of a resin having a negative intrinsic birefringence value can be protected by a layer made of a resin having a positive intrinsic birefringence value. Can be prevented.

JP 2008-216998 A JP 2009-192844 A

  However, as the retardation film, a film having a thinner film thickness is required as the display device becomes thinner. When the film thickness is reduced, the film may be broken not only at the time of stretching but also at the time of conveyance after winding or winding onto a roll, and a film having higher strength has been demanded.

  Further, in order to obtain a retardation film having a small film thickness, it is preferable to increase the stretching ratio. However, if the stretching ratio is increased, the retardation greatly fluctuates due to slight fluctuations in the film thickness, and the desired retardation is obtained. It was difficult to obtain a phase difference film.

The present invention was devised in view of the above problems, and can suppress breakage during handling of the film and during handling after stretching, and a relationship of 0.92 ≦ R ₄₀ /Re≦1.08 stably and continuously. It aims at providing the method which can manufacture the phase difference film which satisfy | fills.

As a result of intensive studies to solve the above problems, the present inventor sequentially biaxially stretches a specific pre-stretch film having a resin layer containing polycarbonate on both sides of a resin layer containing a resin having a negative intrinsic birefringence. When producing a retardation film satisfying the relationship of 0.92 ≦ R ₄₀ /Re≦1.08 by the above, it has been found that the above problem can be solved by setting the plane orientation coefficient of the resin layer containing the polycarbonate within a specific range. The present invention has been completed.

Thus, according to the present invention,
A resin layer A1 containing a polycarbonate-containing resin A1, a resin layer B containing a resin B provided on one surface of the resin layer A1 and having a negative intrinsic birefringence, and the resin in the resin layer B A resin layer A2 containing a resin A2 containing polycarbonate, provided on the surface opposite to the layer A1,
A retardation Re at an incident angle of 0 °, the retardation _{R 40} at an incident angle of 40 ° is a method for producing a retardation film which satisfies a relation of 0.92 ≦ _R 40 /Re≦1.08,
A resin layer a1 containing a polycarbonate-containing resin A1, a resin layer b containing a resin B provided on one surface of the resin layer a1 and having a negative intrinsic birefringence, and the resin in the resin layer b A resin layer a2 containing a resin A2 containing polycarbonate, provided on the surface opposite to the layer a1;
When the uniaxial stretching direction is the X axis, the direction perpendicular to the uniaxial stretching direction in the film plane is the Y axis, and the film thickness direction is the Z axis, the plane of incidence is perpendicular to the film plane and The phase of linearly polarized light in the XZ plane that is perpendicularly incident on the film surface and the plane of vibration of the electric vector in the YZ plane is delayed when uniaxially stretched in the X-axis direction at the temperature T1 and is different from the temperature T1. A film before stretching, which proceeds when uniaxially stretched in the X-axis direction at a temperature T2,
A first stretching step in which a uniaxial stretching process is performed in one direction at a temperature T1 or T2, and
By a stretching process having a second stretching process in which a uniaxial stretching process is performed at a temperature T2 or T1 different from the above in a direction orthogonal to the direction in which the uniaxial stretching process is performed in the first stretching process,
The plane orientation coefficient represented by (nx + ny) / 2-nz of the resin layer A1 formed by stretching the resin layer a1 and the resin layer A2 formed by stretching the resin layer a2 is 0.017. Including the steps described above,
A method for producing a retardation film is provided.
(However, nx and ny represent the refractive index in the main axis direction in the plane of the retardation film, and nz represents the refractive index in the thickness direction of the retardation film.)

  The step of obtaining the pre-stretch film preferably further includes a co-extrusion step of co-extruding the resin A1 containing polycarbonate, the resin B having a negative intrinsic birefringence value, and the resin A2 containing polycarbonate.

  The resin A1 or the resin A2 preferably contains an infrared absorber.

In the manufacturing method, the resin A1, the resin A2, and the resin B have different infrared absorption bands, respectively.
In the co-extrusion step, the film before stretching is obtained by co-extruding the resin A1, the resin B, and the resin A2 from the opening of the die having an opening whose size can be adjusted.
A measuring step of measuring the film thickness of each of the resin layer a1, the resin b, and the resin layer a2 of the pre-stretch film with an infrared film thickness meter;
It is preferable to have an opening adjustment step of adjusting the size of the opening of the die according to the measured film thickness of each layer.

According to the method for producing a retardation film of the present invention, the retardation at the time of conveyance after stretching or winding onto a roll is suppressed, and the retardation satisfies the relationship of 0.92 ≦ R ₄₀ /Re≦1.08. A film can be manufactured stably and continuously.

When the resin A1 and the resin A2 are the same resin, the glass transition temperature Tg _{A1 of} the resin A1 (or the resin A2) constituting the resin layer a1 (resin layer a2) is high, and the resin constituting the resin layer b Assuming that the glass transition temperature Tg _{B of B} is low, the temperature dependence of the retardation Δ when the resin layer a1 (resin layer a2) and the resin layer b of the laminate for producing a retardation plate are respectively stretched; An example of the temperature dependence of retardation (DELTA) when the laminated body for phase difference plate manufacture is extended | stretched is shown. It is a figure which shows typically the outline | summary of the manufacturing apparatus of the retardation film which concerns on one Embodiment of the manufacturing method of the retardation film of this invention.

  Hereinafter, the present invention will be described in detail with reference to embodiments and examples, but the present invention is not limited to the following embodiments and examples, and departs from the gist of the present invention and its equivalent scope. You may change arbitrarily and implement in the range which does not.

The production method of the present invention includes a resin layer A1 containing a resin A1 containing polycarbonate, a resin layer B containing a resin B provided on one surface of the resin layer A1 and having negative intrinsic birefringence, The resin layer B is provided on a surface opposite to the resin layer A1 and includes a resin layer A2 containing a polycarbonate-containing resin A2, and includes a retardation Re at an incident angle of 0 ° and an incident angle of 40 °. Retardation R ₄₀ is a method for producing a retardation film satisfying the relationship of 0.92 ≦ R ₄₀ /Re≦1.08.

  In the production method of the present invention, the pre-stretch film includes a resin layer a1 containing a resin A1 containing polycarbonate, and a resin B provided on one surface of the resin layer a1 and having negative intrinsic birefringence. A resin layer b and a resin layer a2 containing a resin A2 containing polycarbonate provided on a surface of the resin layer b opposite to the resin layer a1, the uniaxial stretching direction being the X axis and the uniaxial stretching direction; A linearly polarized film surface that is perpendicular to the film surface and has an electric vector vibration surface in the XZ plane, with the Y-axis being the direction perpendicular to the film plane and the Z-axis being the film thickness direction. The phase with respect to linearly polarized light that is perpendicularly incident on the plane and the plane of vibration of the electric vector is in the YZ plane is delayed when it is uniaxially stretched in the X-axis direction at the temperature T1, and the direction of the X-axis is Proceeds when the uniaxially stretched, using a pre-stretched film.

(Resin A1, A2)
Resin A1 and resin A2 used in the present invention are resins containing polycarbonate. Polycarbonate is a polymer excellent in retardation development, low temperature stretchability, and adhesion to other layers.

  Any polycarbonate can be used as long as it is a polymer having a repeating unit due to a carbonate bond (—O—C (═O) —O—). Moreover, what consists of one type of repeating unit may be used for a polycarbonate, and what combined two or more types of repeating units in arbitrary ratios may be used.

Examples of the polycarbonate include bisphenol A polycarbonate, branched bisphenol A polycarbonate, o, o, o ′, o′-tetramethylbisphenol A polycarbonate, and the like.
As the polycarbonate, one type may be used alone, or two or more types may be used in combination at any ratio.

  The resin A1 and the resin A2 may contain components other than polycarbonate as long as the effects of the present invention are not significantly impaired. For example, the resin A1 and the resin A2 may contain a polymer other than polycarbonate, a compounding agent, and the like.

  Examples of polymers other than polycarbonate that may be contained in the resin A1 and the resin A2 include acrylic polymers such as polymethyl methacrylate; olefin polymers such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; Polyarylene sulfide such as polyphenylene sulfide; polyvinyl alcohol; cellulose ester; polyether sulfone; polysulfone; polyallyl sulfone; polyvinyl chloride; norbornene polymer; Moreover, the structural component of these polymers may be contained as a repeating unit in a part of polycarbonate. Furthermore, these may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. However, from the viewpoint of remarkably exhibiting the advantages of the present invention, the amount of the polymer other than polycarbonate is preferably small in the resin A1 and the resin A2, for example, 10 parts by weight or less is preferable with respect to 100 parts by weight of the polycarbonate. 5 parts by weight or less is more preferable, and 3 parts by weight or less is still more preferable. Among these, it is particularly preferable that no polymer other than polycarbonate is contained. In addition, it is preferable that the resin A1 and the resin A2 have a positive intrinsic birefringence value. Therefore, the polymer other than the polycarbonate is preferably a polymer having a positive intrinsic birefringence value.

  The compositions of the polymers used for the resin A1 and the resin A2 may be the same or different, but are preferably the same. By making the compositions of the polymers used for the resin A1 and the resin A2 the same, there is an advantage that it is possible to suppress the occurrence of bending or warping in the pre-stretch film or retardation film. Moreover, it becomes easy to control the plane orientation coefficient of the resin layer A1 and the resin layer A2 of the obtained retardation film. The resin A1 and the resin A2 may have completely the same composition, but the same polymer may be used and only the compounding agent blended in the polymer may be changed.

  Examples of the compounding agents that may be contained in the resin A1 and the resin A2 are: lubricants; layered crystal compounds; inorganic fine particles; antioxidants, heat stabilizers, light stabilizers, weathering stabilizers, UV absorbers and the like Agents; infrared absorbers; plasticizers; colorants such as dyes and pigments; antistatic agents; Among these, a lubricant and an ultraviolet absorber are preferable because they can improve flexibility and weather resistance. In addition, a compounding agent may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Further, the amount of the compounding agent can be appropriately determined within a range that does not significantly impair the effects of the present invention. For example, the total light transmittance in terms of 1 mm thickness of the multilayer film of the present invention can be maintained at 80% or more. It is good.

  Examples of the lubricant include inorganic particles such as silicon dioxide, titanium dioxide, magnesium oxide, calcium carbonate, magnesium carbonate, barium sulfate, and strontium sulfate; polymethyl acrylate, polymethyl methacrylate, polyacrylonitrile, polystyrene, cellulose acetate, cellulose acetate Organic particles such as pionate can be mentioned. Among these, organic particles are preferable as the lubricant.

  Examples of ultraviolet absorbers include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone ultraviolet absorbers, benzotriazole ultraviolet absorbers, acrylonitrile ultraviolet absorbers, triazine compounds, nickel complex compounds. And inorganic powders. Specific examples of suitable UV absorbers include 2,2′-methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol), 2- (2′-hydroxy-3′-tert-butyl-5′-methylphenyl) -5-chlorobenzotriazole, 2,4-di-tert-butyl-6- (5-chlorobenzotriazol-2-yl) ) Phenol, 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, 2,2 ′, 4,4′-tetrahydroxybenzophenone, and the like. Particularly preferred are 2,2′-methylenebis ( 4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol).

  In the present invention, it is preferable that the resin A1, the resin A2, and the resin B have different infrared absorption bands. Since the resin B usually includes a polymer different from the resin A1 and the resin A2, the resin B has an infrared absorption band different from that of the resin A1 and the resin A2. In order to make the resin A1 and the resin A2 have different infrared absorption bands, the composition of the polymer used for the resin A1 and the composition of the polymer used for the resin A2 may be different from each other. It is more preferable that A2 contains the above infrared absorber only on one side. Since only one of the resin A1 and the resin A2 contains the infrared absorber, the resin A1, the resin A2, and the resin B can have different infrared absorption bands.

In the present invention, the “infrared absorption band” refers to a region where the absorption rate in the infrared region (2 to 5 μm) is 5 to 60%, preferably 10 to 40%. The absorptivity in the infrared region can be measured using a commercially available spectrophotometer (for example, UV-Vis near-infrared spectrophotometer V-670 manufactured by JASCO Corporation).
In the present invention, “having different infrared absorption bands” means that (1) the absorption peak wavelengths are the same but the absorption bands are different; (2) the absorption bands are the same but the absorption peak wavelengths are different; (3) It means either when the absorption peak wavelength and the absorption band are different. Among (1) to (3), (2) and (3) are preferable, and (3) is more preferable.

  Since the resin A1, the resin A2, and the resin B have different infrared absorption bands, the film thickness of each layer of the retardation film obtained in the present invention and the unstretched film used for the production thereof is easily measured with an infrared film thickness meter. can do. Examples of the infrared film thickness meter include a regular reflection type, a diffuse reflection type, and a transmission type. The infrared film thickness meter is characterized by non-contact, high response speed, and continuous measurement. Therefore, in the case where the retardation film and the pre-stretch film are continuously manufactured, it is possible to perform feedback control of manufacturing conditions based on the film thickness measured in-line. If such feedback control is performed, the film thickness of each layer can be precisely controlled. Thereby, even if a draw ratio is high, the retardation film which has a desired retardation can be manufactured stably.

  Examples of infrared absorbers include cyanine compounds, phthalocyanine compounds, nophthalocyanine compounds, naphthoquinone compounds, diimonium compounds, aminium compounds, anthraquinone compounds, and dithiol complexes. Among these, an aminium-based compound is preferable because it hardly overlaps with the infrared absorption peak of polycarbonate and has absorption at a general measurement wavelength of an infrared film thickness meter.

  When the resin A1 or the resin A2 contains an infrared absorber, the content of the infrared absorber is preferably 0.6 to 3.0% by mass, more preferably 1.0 to 2.0% by mass. If the content of the infrared absorber is less than the above range, it is difficult to control the amount of the infrared absorber added when mixing with the polycarbonate, and whether the change in the thickness of each layer is measured, It may not be possible to distinguish whether the variation in the amount of addition is being measured. On the other hand, if the content of the infrared absorber is larger than the above range, the film becomes more colored, or the extrusion stability when the infrared absorber and the polycarbonate are kneaded with a twin screw extruder or the like is produced. Low.

The glass transition temperature Tg _A1 of the resin _A1 and the glass transition temperature Tg _A2 of the resin A2 are usually 80 ° C. or higher, preferably 90 ° C. or higher, more preferably 100 ° C. or higher, still more preferably 110 ° C. or higher, particularly preferably 120 ° C. or higher. It is. With such a high glass transition temperature, orientation relaxation of the resin A1 and the resin A2 can be reduced. In addition, although there is no restriction | limiting in particular in the upper limit of Tg _A1 and Tg _A2 , Usually, it is 200 degrees C or less.

(Resin B)
Resin B used in the present invention is a resin having a negative intrinsic birefringence. The resin B is preferably a thermoplastic resin. Examples of polymers contained in the resin B include polystyrene polymers including homopolymers of styrene or styrene derivatives or copolymers with other monomers; polyacrylonitrile polymers, polymethyl methacrylate polymers, or these And a multi-component copolymer. Moreover, as said other monomer copolymerized to styrene or a styrene derivative, acrylonitrile, maleic anhydride, methyl methacrylate, and butadiene are mentioned as a preferable thing, for example. In addition, these polymers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Among these, a polystyrene polymer is preferable from the viewpoint of high retardation development, and a copolymer of styrene or a styrene derivative and maleic anhydride is particularly preferable from the viewpoint of high heat resistance.

  Resin B may contain a compounding agent. Examples thereof include the same compounding agents that may be contained in the resin A. The amount of the compounding agent can be appropriately determined within a range that does not significantly impair the effects of the present invention. For example, the total light transmittance at 1 mm thickness of the laminate for producing a retardation plate can be maintained within 80% or more. That's fine. In addition, a compounding agent may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The glass transition temperature Tg _B of the resin B is usually 80 ° C. or higher, preferably 90 ° C. or higher, more preferably 100 ° C. or higher, more preferably 110 ° C. or higher, particularly preferably 120 ° C. or higher. With such a high glass transition temperature, the relaxation of orientation of the resin B can be reduced. Although not particularly limited to the upper limit of the glass transition temperature Tg _B, usually it is 200 ° C. or less.

The breaking elongation of the resin B at the glass transition temperature Tg _A1 of the resin _A1 and the glass transition temperature Tg _A2 of the resin _A2 is preferably 50% or more, and more preferably 80% or more. The upper limit of the elongation at break of the resin B is not particularly limited, but is usually 200% or less. When the elongation at break is within this range, the multilayer film of the present invention can be stably produced by stretching. The elongation at break is determined by using a test piece type 1B test piece described in JISK7127 at a pulling speed of 100 mm / min.

The absolute value of the difference between the glass transition temperature Tg _A1 of the resin _A1 and the glass transition temperature Tg _A2 of the resin _A2 and the glass transition temperature Tg _B of the resin B is preferably greater than 5 ° C, more preferably 8 ° C or more. The temperature is preferably 40 ° C. or lower, more preferably 20 ° C. or lower. If the absolute value of the difference between the glass transition temperatures is too small, the temperature dependence of the retardation development tends to be small. On the other hand, if the absolute value of the difference between the glass transition temperatures is too large, it becomes difficult to stretch a resin having a high glass transition temperature, and the flatness of the retardation plate may be easily lowered. The glass transition temperatures Tg _A1 and Tg _A2 are preferably higher than the glass transition temperature Tg _B. Therefore, it is preferable that the resin A1 and the resin A2 and the resin B usually satisfy the relationship of Tg _A1 > TgB + 5 ° C. and Tg _A2 > TgB + 5 ° C.

(Film before stretching)
The film before stretching used in the production method of the present invention is provided on one surface of the resin layer a1 containing the resin A1, the resin layer a1 and the resin layer b containing the resin B, and the resin layer b. And a resin layer a2 containing the resin A2 is provided on the surface opposite to the resin layer a1.

  The pre-stretch film may be provided with two or more resin layers a1, resin layers a2 and resin layers b, but the thickness of the retardation film obtained from the viewpoint of simplifying the control of retardation and the present invention. From the viewpoint of reducing the thickness, it is preferable to provide only one layer each.

In the production method of the present invention, as the pre-stretch film, the stretch direction in a certain direction (that is, the uniaxial stretch direction) is the X axis, the direction orthogonal to the uniaxial stretch direction in the film plane is the Y axis, and the film When the thickness direction is the Z axis, it is incident perpendicularly to the film surface of linearly polarized light (hereinafter referred to as “XZ polarized light” where appropriate) that is incident perpendicularly to the film surface and whose electric vector vibration surface is in the XZ surface. And the phase with respect to linearly polarized light (hereinafter referred to as “YZ polarized light” where appropriate) where the vibration plane of the electric vector is in the YZ plane
Delayed when uniaxially stretched in the X-axis direction at temperature T1,
When the uniaxial stretching is performed in the X-axis direction at a temperature T2 different from the temperature T1,
Satisfying the requirement (hereinafter referred to as “requirement P” as appropriate).

  The requirement P may be satisfied when at least one of the various directions in the plane of the unstretched film is taken as the X axis. Usually, since the film before stretching is an isotropic raw film, the above-mentioned requirement P is satisfied when one direction in the plane is the X axis, and any other direction is the X axis. The requirement P can be satisfied.

  In a film in which a slow axis appears in the X axis by uniaxial stretching, the phase of XZ polarized light is usually delayed from that of YZ polarized light. Conversely, in a film in which a fast axis appears on the X-axis by uniaxial stretching, the phase of XZ polarized light is usually advanced relative to that of YZ polarized light. The pre-stretch film used in the present invention is a multilayer film utilizing these properties, and is a film in which the appearance of the slow axis or the fast axis depends on the stretching temperature. The temperature dependence of the expression of such retardation can be adjusted, for example, by adjusting the relationship between the photoelastic coefficient of the resin A1, the resin A2, and the resin B and the film thickness ratio of each layer.

The in-plane retardation of a certain layer is the difference between the refractive index nx in the X-axis direction that is the stretching direction and the refractive index ny in the Y-axis direction that is perpendicular to the stretching direction (= | nx−ny |). It is a value obtained by multiplying the film thickness d. Moreover, the retardation of the multilayer film provided with resin layer A1, resin layer A2, and resin layer B is synthesize | combined from the retardation of each layer. Therefore, for example, in order to reverse the sign of retardation developed in the entire film by stretching at a high temperature T _H and a low temperature T _L , (i) the glass transition temperature of the stretching at a low temperature T _L the absolute value of the retardation high resin is expressed is smaller than the absolute value of the retardation expressing low resin glass transition temperature, a draw in (ii) a higher temperature T _H, low glass transition temperature resin is expressed It is preferable to adjust the film thickness of each layer so that the absolute value of retardation is smaller than the absolute value of retardation at which a resin having a high glass transition temperature is developed.

The temperature T1 is one of T _{H and} T _L , and the temperature T2 is either T _H or T _L that is different from T1. Moreover, it is preferable that the temperature satisfying the requirement P is at least (Tg ₁ −10) to (Tg _h +10) ° C. because the birefringence can be easily adjusted. Wherein in the resin constituting the laminated film, and the most glass transition temperature is lower Tg _l, most glass transition temperature is high Tg _h. That is, it is preferable that the temperatures T1 and T2 are included in the temperature range.

The expression of retardation when a pre-stretch film satisfying the requirement P is stretched will be specifically described with reference to the drawings. FIG. 1 shows that when the resin A1 and the resin A2 are the same resin, the glass transition temperature Tg _{A1 of} the resin A1 (or the resin A2) constituting the resin layer a1 and the resin layer a2 is high, and the resin layer b If the glass transition temperature Tg _B of the resin B constituting is assumed to lower, and the temperature dependence of the phase difference Δ at which the resin layer of the film prior to stretching a1 (resin layer a2) and a resin layer b stretched respectively, stretching An example of the temperature dependence of the phase difference Δ when the front film is stretched is shown. In the pre-stretching film as shown in FIG. 1, in the stretching at the temperature Tb, the negative retardation expressed in the resin layer b is larger than the positive retardation expressed in the resin layer a1, so that the entire retardation film is A negative phase difference Δ is developed. On the other hand, in the stretching at the temperature Ta, the negative phase difference expressed in the resin layer b is smaller than the positive phase difference expressed in the resin layer a1, and therefore the positive phase difference Δ is expressed as the entire retardation film. become. Therefore, by combining such stretching at different temperatures Ta and Tb, the phase difference generated by stretching at each temperature is synthesized to have a desired phase difference, and thus exhibit a desired optical function. A film can be realized stably.

  Thus, as the resin constituting each layer, resin A1 and resin that can cause a difference between the refractive index in the X-axis direction and the refractive index in the Y-axis direction in each layer by stretching in one direction (that is, uniaxial stretching) By selecting a combination of A2 and resin B and further adjusting the total film thickness of each layer in consideration of stretching conditions, a film before stretching that satisfies the requirement P can be obtained.

  The total film thickness of each layer of the pre-stretched film satisfying the requirement P varies depending on the resin used in each layer, but (total resin film a1 film thickness + total resin film a2 film thickness) / resin layer b film thickness Is preferably 1/4 to 1/20, more preferably 1/5 to 1/15. Even if any of the resin layers becomes too thick, the temperature dependence of retardation development tends to be reduced.

  The total thickness of the film before stretching is preferably 10 μm or more, more preferably 20 μm or more, particularly preferably 30 μm or more, preferably 500 μm or less, more preferably 400 μm or less, and particularly preferably 300 μm or less. If the pre-stretch film is thinner than the lower limit of the range, sufficient retardation tends to be difficult and mechanical strength tends to be weakened. If the film is thicker than the upper limit of the range, the flexibility is deteriorated and handling may be hindered. There is sex.

  The thickness ratio between the resin layer a1 and the resin layer a2 may be either thicker, but the thicker resin layer is used from the viewpoint of ensuring light leakage of the polarizing plate when combined with the polarizing plate in a liquid crystal display device. It is preferable that it is 1.5 times or more of the thickness of the thinner resin layer. Further, from the viewpoint of maintaining the accuracy of the thickness of the thinner resin layer, the thickness of the thicker resin layer is preferably 10 times or less than the thickness of the thinner resin layer.

(Production method of film before stretching)
There is no limitation on the production method of the film before stretching, for example, by a coextrusion method; a film lamination molding method such as dry lamination; a co-casting method; a coating molding method such as coating a resin solution on the resin film surface; It may be manufactured. Among these, the co-extrusion method is preferable from the viewpoint of manufacturing efficiency and preventing a volatile component such as a solvent from remaining in the film.

  When the coextrusion method is employed, the pre-stretched film is obtained, for example, by a coextrusion process in which a resin A1 containing polycarbonate, a resin B having a negative intrinsic birefringence value, and a resin A2 containing polycarbonate are coextruded. Examples of the co-extrusion method include a co-extrusion T-die method, a co-extrusion inflation method, and a co-extrusion lamination method. Among them, the co-extrusion T-die method is preferable. Further, the coextrusion T-die method includes a feed block method and a multi-manifold method, but the multi-manifold method is particularly preferable in that variation in thickness can be reduced.

  When the co-extrusion T-die method is employed, the melting temperature of the resin in the extruder having the T-die is preferably 80 ° C. or higher than the glass transition temperatures of the resin A1, the resin A2, and the resin B. More preferably, the temperature is higher than or equal to a higher temperature, more preferably lower than or equal to a temperature higher than 180 ° C., and more preferably lower than or equal to a temperature higher than 150 ° C. If the melting temperature in the extruder is excessively low, the fluidity of the resin may be insufficient. Conversely, if the melting temperature is excessively high, the resin may be deteriorated.

In the coextrusion method, the film-like molten resin extruded from the opening of the die is usually brought into close contact with a cooling roll (also referred to as a cooling drum). The method for bringing the molten resin into close contact with the cooling roll is not particularly limited, and examples thereof include an air knife method, a vacuum box method, and an electrostatic contact method.
The number of cooling rolls is not particularly limited, but is usually 2 or more. In addition, examples of the arrangement method of the cooling roll include, but are not particularly limited to, a linear type, a Z type, and an L type. Further, the way of passing the molten resin extruded from the opening of the die through the cooling roll is not particularly limited.

  The degree of adhesion of the extruded film-like resin to the cooling roll varies depending on the temperature of the cooling roll. When the temperature of the cooling roll is raised, the adhesion is improved. However, if the temperature is raised too much, the film-like resin may not be peeled off from the cooling roll, and there is a possibility that a problem of winding around the drum may occur. Therefore, the temperature of the cooling roll is preferably (Tg + 30) ° C. or less, more preferably (Tg-5) ° C. to (Tg−), where Tg is the glass transition temperature of the resin of the layer that is extruded from the die and contacts the drum. 45) Set to a range of ° C. By doing so, problems such as slipping and scratches can be prevented.

  It is preferable to reduce the content of residual solvent in the pre-stretched film obtained. As a means for that, (1) Residual solvent contained in Resin A1, Resin A2 and Resin B as raw materials is reduced; (2) Resin A1, Resin A2 and Resin B are spared before forming a multilayer film. And the like. For example, the preliminary drying is performed using a hot air dryer or the like in the form of pellets of the resin A1, the resin A2, and the resin B. The drying temperature is preferably 100 ° C. or more, and the drying time is preferably 2 hours or more. By performing preliminary drying, the residual solvent in the film before stretching can be reduced, and foaming of the extruded film-like resin can be prevented.

  In the pre-stretch film, the thickness variation of each layer is preferably 1 μm or less over the entire surface. Thereby, also in each layer of retardation film, the dispersion | variation in film thickness can be made into 1 micrometer or less on the whole surface, and the dispersion | variation in the color tone of a display apparatus provided with the said retardation film can be made small. In addition, the color tone change after long-term use of the retardation film can be made uniform.

  In order to make the variation in the film thickness of each layer 1 μm or less as described above, for example, (1) a polymer filter having an opening of 20 μm or less is provided in the extruder; (2) the gear pump is rotated at 5 rpm or more; (3) Arranging means around the die; (4) Air gap is 200 mm or less; (5) Edge pinning is performed when the film is cast on a cooling roll; and (6) Twin screw as an extruder An extruder or a screw type single-screw extruder may be used. Further, for example, the thickness of each layer can be reduced by measuring the film thickness of each layer during manufacturing and performing feedback control based on the film thickness as in the embodiment described later.

(Method for producing retardation film)
In the production method of the present invention, the resin layer A1 formed by stretching the resin layer a1 and the resin layer A2 formed by stretching the resin layer a2 in a stretching step of stretching the film before stretching. A step of setting the plane orientation coefficient represented by (nx + ny) / 2-nz to 0.017 or more.

(Plane orientation coefficient)
The plane orientation coefficient is an index indicating the orientation state of the molecular chain in the film. From the refractive index nx and ny in the principal axis direction in the plane of the retardation film and the refractive index nz in the thickness direction of the retardation film, the formula: It is a numerical value calculated according to (nx + ny) / 2−nz. The larger the plane orientation coefficient, the more the molecular orientation proceeds in the direction perpendicular to the thickness direction of the film.

  In the pre-stretched film, the molecular chain is not oriented, so there is no refractive index anisotropy, and the plane orientation coefficient is almost zero. In the production method of the present invention, the plane orientation coefficient is set to 0.017 or more by stretching the pre-stretched film. The upper limit of the plane orientation coefficient is preferably 0.025 because the film may be whitened if the orientation proceeds too much.

(Measurement method of plane orientation coefficient)
The plane orientation coefficient is 532 nm from the critical angle of the prism, the resin layer A1 and the resin layer A2 with respect to the resin layer A1 and the resin layer A2 of the retardation film by using a refractive index film thickness measuring device. It was calculated by measuring with.

(Stretching process)
In the production method of the present invention, the stretching step includes a first stretching step in which the film before stretching is uniaxially stretched in one direction at a temperature T1 or T2, and the uniaxial stretching process in the first stretching step. And a second stretching step in which a uniaxial stretching process is performed at a temperature T2 or T1 different from the above in a direction orthogonal to the direction in which the above is performed.

(First stretching process)
In the first stretching step, the film before stretching is uniaxially stretched in one direction at either the temperature T1 or T2. When the film is stretched at the temperature T1, the phase of the XZ polarized light with respect to the YZ polarized light is delayed in the pre-stretched film that satisfies the requirement P. On the other hand, when the uniaxial stretching is performed at the temperature T2, the phase of the XZ polarized light with respect to the YZ polarized light advances.

When the relationship between the glass transition temperatures is Tg _A > Tg _B , the temperature T1 is preferably higher than Tg _B, more preferably higher than Tg _B + 5 ° C., and preferably lower than Tg _A + 40 ° C. More preferably, it is lower than Tg _A + 20 ° C. Here, Tg _A represents a higher temperature of Tg _A1 and Tg _A2 . If the temperature T1 is higher than the lower limit of the temperature range, the retardation of the resin layer B can be stably stored in a desired range, and if the temperature T1 is lower than the upper limit of the temperature range, the resin layer A1 and the resin layer A2 This retardation can be stably contained within a desired range.
In this case the glass transition temperature relation is Tg _A> Tg _B, it is preferably carried out at a temperature T1 in the first stretching step.

When the relationship of glass transition temperature is Tg _B > Tg _A , the temperature T1 is preferably higher than Tg _A, more preferably higher than Tg _A + 5 ° C., and preferably lower than Tg _B + 40 ° C. More preferably, it is lower than Tg _B + 20 ° C. If the temperature T1 is higher than the lower limit of the temperature range, the retardation of the resin layer A1 and the resin layer A2 can be stably stored in a desired range, and if the temperature T1 is lower than the upper limit of the temperature range, the resin layer B This retardation can be stably contained within a desired range.
In this case the glass transition temperature relation is Tg _B> Tg _A, is preferably performed at a temperature T2 in the first stretching step.

  The uniaxial stretching process can be performed by a conventionally known method. For example, it is the MD direction (machine direction: flow direction of the film in the production line using the difference in peripheral speed between rolls, and usually coincides with the long direction of the long film, and is also called the vertical direction. ) In a TD direction (traverse direction; a direction parallel to the film surface and perpendicular to the MD direction. Usually coincides with the width direction, also referred to as the transverse direction). Examples thereof include a uniaxial stretching method. Examples of the uniaxial stretching method in the MD direction include an IR heating method between rolls, a float method, and the like. Of these, the float method is preferred because a retardation film having high optical uniformity can be obtained. On the other hand, as a method of uniaxially stretching in the TD direction, a tenter method can be mentioned.

  In the uniaxial stretching treatment, in order to reduce stretching unevenness and thickness unevenness, a temperature difference may be created in the TD direction in the stretching zone. In order to create a temperature difference in the TD direction in the stretching zone, for example, a known method such as adjusting the opening degree of the hot air nozzle in the TD direction or controlling the heating by arranging the IR heaters in the TD direction may be used. it can.

(Second stretching step)
After the first stretching step, the second stretching step is performed. In the second stretching step, the film stretched in one direction in the first stretching step is uniaxially stretched in a direction orthogonal to the direction in which the uniaxial stretching process was performed in the first stretching step.

In the second stretching step, uniaxial stretching is performed at a temperature T2 or T1 different from that in the first stretching step. In the second stretching step, when the relationship between the glass transition temperatures is Tg _A > Tg _B , it is preferable to perform the uniaxial stretching treatment at the temperature T2. When the relationship between the glass transition temperatures is Tg _A > Tg _B , the temperature T2 is preferably higher than Tg _B −20 ° C., more preferably higher than Tg _B −10 ° C., and Tg _B It is preferably lower than + 5 ° C. and preferably lower than Tg _B. By making the temperature T2 higher than the lower limit of the above range, the film can be prevented from being broken or clouded during stretching, and by making the temperature lower than the upper limit, the desired retardation can be stably expressed in the resin layer B. Can do.

When the relationship between the glass transition temperatures is Tg _B > Tg _A , the uniaxial stretching treatment is preferably performed at the temperature T1. When the relationship of glass transition temperature is Tg _B > Tg _A , the temperature T2 is preferably higher than Tg _A −20 ° C., more preferably higher than Tg _A −10 ° C., and lower than Tg _A + 5 ° C. it is preferred, it is preferably lower than the Tg _A. By making the temperature T2 higher than the lower limit of the above range, it is possible to prevent the pre-stretching film from being broken or clouded during stretching, and by making the temperature T2 lower than the upper limit, a desired retardation is obtained in the resin layer A1 and the resin layer A2. It can be expressed stably.

  The difference between the temperature T1 and the temperature T2 is usually 5 ° C. or higher, preferably 10 ° C. or higher. By increasing the difference between the temperature T1 and the temperature T2 as described above, a desired retardation can be stably expressed in the retardation film. In addition, although there is no restriction | limiting in the upper limit of the difference of temperature T1 and temperature T2, 100 degrees C or less is preferable from a viewpoint of industrial productivity.

  There exists a tendency for the plane orientation coefficient of the retardation film obtained to become large, so that extending | stretching temperature is low. Therefore, it is preferable that the temperature T1 and the temperature T2 are lower temperatures as long as the desired retardation can be stably expressed in the retardation film.

For the uniaxial stretching treatment in the second stretching step, a method similar to the method that can be adopted in the uniaxial stretching treatment in the first stretching step can be applied. However, the uniaxial stretching process in the second stretching process is preferably performed at a smaller stretching ratio than the uniaxial stretching process in the first stretching process. In the sequential stretching process, the final molecular orientation state is more strongly affected in the second stretching process than in the first stretching process. Therefore, the smaller the stretching ratio in the second stretching process, the more the retardation of the retardation film. This is because adjustment is easy. Specifically, the stretching ratio in the first stretching step is preferably 2 to 4 times, more preferably 3 to 4 times, and particularly preferably 3 to 3.5 times. The draw ratio in the second drawing step is preferably 1.1 to 2 times, more preferably 1.1 to 1.5 times, and particularly preferably 1.1 to 1.3 times.
Further, from the standpoint that the plane orientation coefficient is higher and 0.017 or more, it is preferable that the draw ratio is high in both the first stretching step and the second stretching step. Specifically, the product of the draw ratio in the first draw step and the draw ratio in the second draw step is preferably 3.6 or more, more preferably 3.8 or more, and even more preferably 4.0 or more. Select the stretch ratio. On the other hand, if the draw ratio is too high, it is difficult to adjust the optical properties in the stretching step, so the product of the draw ratio in the first drawing step and the draw ratio in the second drawing step is preferably 6.0 or less. .

  The combinations of the stretching directions in the first stretching process and the second stretching process are, for example, stretching in the MD direction in the first stretching process and stretching in the TD direction in the second stretching process, or stretching in the TD direction in the first stretching process. What is necessary is just to extend | stretch to MD direction at a 2nd extending | stretching process, or to extend | stretch to the diagonal direction substantially orthogonal to it by extending | stretching to an oblique direction at a 1st extending | stretching process. Especially, it is preferable to extend | stretch in a TD direction at a 1st extending | stretching process, and to extend | stretch to MD direction at a 2nd extending | stretching process. This is because the variation in the direction of the optical axis can be reduced over the entire width of the obtained retardation film by performing stretching in the MD direction in the second stretching step having a small stretching ratio.

(Feedback control based on film thickness)
By using the resin A1, the resin A2 and the resin B having different infrared absorption bands, the pre-stretch film obtained by the coextrusion method is in the process of in-line production using an infrared film thickness meter. Also, the film thickness of each layer can be measured. Therefore, the film thickness of each layer can be measured during the manufacturing, and the feedback control of the manufacturing conditions can be performed based on the measured film thickness. By performing such feedback control, it is possible to precisely control the film thickness of each layer of the pre-stretched film, so that a retardation film having a desired retardation can be stably produced.

  Specifically, the film thickness adjustment by feedback control is performed by coextruding the resin A1, the resin B, and the resin A2 from the opening of the die having an opening whose size can be adjusted in the coextrusion step. A pre-stretch film is obtained, and the film thicknesses of the resin layer a1, the resin b, and the resin layer a2 of the pre-stretch film are measured with an infrared film thickness meter, and the measured film thickness of each layer And an opening adjusting step for adjusting the size of the opening of the die accordingly.

  FIG. 2 is a diagram schematically illustrating an outline of a retardation film manufacturing apparatus according to an embodiment of the method for manufacturing a multilayer film of the present invention. In the manufacturing apparatus 200 shown in FIG. 2, the film 300 before extending | stretching is manufactured as a multilayer film of this invention, The film 300 before extending | stretching is extended | stretched, and the phase difference film 400 is manufactured.

  As shown in FIG. 2, the manufacturing apparatus 200 includes a hopper 210, an extruder 220, a die 230, a cooling roll 240, a first stretching machine 250, a second stretching machine 260, an infrared film thickness meter 270, and a control device 280. Prepare.

  The hopper 210 is a device that can supply the resin A1, the resin B, and the resin A2 to the extruder 220. The extruder 220 is a device that can send out the molten resin A1, resin B, and resin A2 to the die 230 by, for example, a screw (not shown). Resin A1, resin B, and resin A2 supplied from the hopper 210 to the extruder 220 are sent from the extruder 220 to the die 230 by screws.

  The die 230 has a slit 231 as an opening through which the molten resin A1, resin B, and resin A2 can be coextruded. The shape of the slit 231 is set according to the width of the unstretched film 300 and the film thicknesses of the resin layer a1, the resin layer b, and the resin layer a2. Specifically, the slit length is set according to the width of the unstretched film 300, and the slit width is set according to the film thickness of each of the resin layer a1, the resin layer b, and the resin layer a2. A flow path (not shown) through which resin A1, resin B, and resin A2 circulate is formed inside the die 230, and the resin A1, resin B, and resin A2 sent from the extruder 220 are formed in the die 230. The resin A1 layer (resin layer a1), the resin B layer (resin layer b), and the resin A2 layer (resin layer a2) are coextruded from the slits in this order. It is like that.

  In addition, adjustment bolts 232 are provided at a plurality of positions in the longitudinal direction of the slit 231 in the slit 231 of the die 230. The adjusting bolt 232 is an adjusting unit that can adjust the size (specifically, the slit width) of the slit 231 and is loosened or tightened by an appropriate mechanism (not shown). Therefore, the slit width of the slit 231 can be adjusted by the adjustment bolt 232, and increases when the adjustment bolt 232 is loosened, and decreases when tightened.

  Further, the die 230 is provided with a heater 233 for independently heating the resin A1, the resin B, and the resin A2 flowing through the flow path. The temperature of the heater 233 can be adjusted, and by adjusting the temperature of the heater 233, the temperatures of the resin A1, the resin B, and the resin A2 flowing through the flow path can be controlled. Therefore, the heater 233 functions as an extrusion rate adjusting unit, and adjusts the viscosity of the resin A1, the resin B, and the resin A2 by controlling the temperature, and the extrusion rate of the resin A1, the resin B, and the resin A2 extruded from the slit 231. (That is, the speed at which the resin is extruded) can be adjusted independently.

  The cooling roll 240 is a roll that can cool the resin A1, the resin B, and the resin A2 that are coextruded in a film shape from the slit 231 of the die 230. The resin A1, the resin B, and the resin A2 that have been melted by being cooled by the cooling roll 240 are cured, and the unstretched film 300 is obtained. The obtained pre-stretching film 300 is sent to the first stretching machine 250 and then sent to the second stretching machine 260.

  The first stretching machine 250 is a device that can perform a uniaxial stretching process in one direction on the pre-stretching film 300 at either the temperature T1 or T2. Further, the second stretching machine 260 performs the first stretching in the direction orthogonal to the direction in which the uniaxial stretching process is performed on the pre-stretching film 300 stretched by the first stretching machine 250. This is an apparatus that can perform the uniaxial stretching process at a temperature T2 or T1 different from the uniaxial stretching process in the machine 250. Therefore, when the uniaxial stretching process is performed by the first stretching machine 250 and the second stretching machine 260, a desired retardation is developed in the unstretched film 300, and the retardation film 400 is obtained. ing.

  The infrared film thickness meter 270 is a measuring instrument that can measure the film thickness of each of the resin layer a1 made of the resin A1, the resin layer b made of the resin B, and the resin layer a2 made of the resin A2 of the unstretched film 300. The infrared film thickness meter 270 irradiates infrared rays to the unstretched film 300 being conveyed, detects the absorption thereof, and measures the film thickness of each of the resin layer a1, the resin layer b, and the resin layer a2. As the resin A1, the resin B, and the resin A2, those having different infrared absorption bands are used. The measured value is sent to the control device 280 as indicated by an arrow A1.

  The control device 280 includes an opening control unit 281 that can adjust the slit width of the slit 231 of the die 230. The opening controller 281 can adjust the slit width of the slit 231 to a desired size at a desired position by performing control to loosen or tighten the adjustment bolt 232 as indicated by an arrow A2. . At this time, the opening control unit 281 varies the film thickness in the TD direction of the unstretched film 300 according to the respective film thicknesses of the resin layer a1, the resin layer b, and the resin layer a2 sent from the infrared film thickness meter 270. The slit width of the slit 231 is adjusted so that the variation in the total film thickness in the MD direction of the unstretched film 300 is reduced.

  In addition, the control device 280 includes an extrusion speed control unit 282 that controls the heating temperature of the heater 233 to adjust the extrusion speeds of the resin A1, the resin B, and the resin A2. The extrusion speed control unit 282 adjusts the viscosity of each of the resin A1, the resin B, and the resin A2 by controlling the temperature of the heater 233 provided in the die 230, as indicated by an arrow A3, and the slit 231 of the die 230. The extrusion speed of each of the resin A1, the resin B, and the resin A2 extruded from can be adjusted. At this time, the extrusion speed control unit 282 performs the resin layer a1, the resin layer b, and the resin layer a2 according to the thickness of each of the resin layer a1, the resin layer b, and the resin layer a2 sent from the infrared film thickness meter 270. The extrusion speeds of the resin A1, the resin B, and the resin A2 are adjusted so that the variation in the film thickness in each MD direction is reduced.

  The hardware configuration of the control device 280 is not limited, but is usually configured by a computer including a processor such as a CPU, a memory such as a RAM and a ROM, an interface such as an input / output terminal. Then, control is performed according to the control content recorded in advance in a memory or the like.

  Since the manufacturing apparatus 200 of the present embodiment is configured as described above, when the retardation film 400 is manufactured, the resin A1, the resin B, and the resin A2 are supplied to the hopper 210 as indicated by an arrow A4. The supplied resin A1, resin B, and resin A2 are sent to the die 230 by the extruder 220. The resin A1, the resin B, and the resin A2 sent to the die 230 are coextruded as a film-like molten resin from the slit 231 and cooled by the cooling roll 240 to become the pre-stretching film 300 (coextrusion step).

  The unstretched film 300 is sent to the first stretching machine 250 and subjected to a uniaxial stretching process (first stretching step). Thereafter, the unstretched film 300 that has been subjected to the uniaxial stretching process by the first stretching machine 250 is sent to the second stretching machine 260, and the uniaxial stretching process is performed at a temperature and direction different from those of the first stretching machine 250. (Second stretching step). Thereby, since a desired retardation is developed in the pre-stretched film 300, the retardation film 400 is obtained. The obtained retardation film 400 is wound up in the MD direction and collected as a roll 410.

  Furthermore, in this embodiment, before the uniaxial stretching process is performed by the first stretching machine 250, the film thicknesses of the resin layer a1, the resin layer b, and the resin layer a2 of the unstretched film 300 are each measured by an infrared film thickness meter 270. Measure (measurement process). The measured film thickness data is sent to the controller 280.

  In the control device 280, the slit width of the slit 231 is adjusted by controlling the opening control unit 281 to loosen or tighten the adjustment bolt 232 (opening adjustment process). At this time, according to the film thickness measured by the infrared film thickness meter 270, the opening control unit 281 has a slit 231 at a position where the total film thickness of the film 300 before stretching is thicker than the target value in the TD direction of the film 300 before stretching. Control is performed so that the slit width of the slit 231 is increased at a position where the total film thickness is thinner than the target value. Thereby, since the dispersion | variation in the total film thickness in the TD direction of the film 300 before extending | stretching can be made small, it becomes possible to control the thickness of the film 300 before extending | stretching and the retardation film 400 in the TD direction precisely, and also the phase difference film 400 by extension. It is possible to precisely control the retardation of the film.

  In addition, the opening control unit 281 determines the slit of the slit 231 when the total film thickness of the unstretched film 300 becomes larger than the target value in the MD direction of the unstretched film 300 according to the film thickness measured by the infrared film thickness meter 270. When the width is reduced and the total film thickness becomes thinner than the target value, control is performed to increase the slit width of the slit 231. Thereby, since the dispersion | variation in the total film thickness in MD direction of the film 300 before extending | stretching can be made small, it becomes possible to control the thickness of MD direction in the film 300 before extending | stretching and the phase difference film 400 precisely, and by extension, phase difference film 400 It is possible to precisely control the retardation of the film.

  Further, in the control device 280, the extrusion speed control unit 282 controls the temperature of the heater 233 to adjust the respective viscosities of the resin A1, the resin B, and the resin A2, whereby the resin A1, the resin B, and the resin A2 from the slit 231 are adjusted. Each extrusion speed is adjusted (speed adjustment process). At this time, the extrusion speed control unit 282 reduces the extrusion speed when the film thickness of each layer becomes larger than the target value in the MD direction of the unstretched film 300 according to the film thickness measured by the infrared film thickness meter 270. Control is performed such that the thickness is adjusted to be thin, and when the film thickness of each layer becomes thinner than the target value, the extrusion speed is increased to adjust the film thickness to be thick. Thereby, since the dispersion | variation in the film thickness in the MD direction of each layer of the film 300 before extending | stretching can be made small, it becomes possible to control the thickness of the MD direction in each layer of the film 300 before extending | stretching and the phase difference film 400 precisely, and by extension. The retardation of the retardation film 400 can be precisely controlled. For temperature adjustment of the resin A1, the resin B, and the resin A2 by the heater 233, for example, Japanese Patent Application Laid-Open No. 2006-188018 may be referred to.

As mentioned above, although one Embodiment of the manufacturing method of the retardation film using the feedback control based on a film thickness was described, the said embodiment may be changed further and may be implemented.
For example, the infrared film thickness meter 270 is provided between the first stretching machine 250 and the second stretching machine 260, and after the uniaxial stretching process by the first stretching machine 250 and uniaxial by the second stretching machine 260. You may make it measure the film thickness of the film 300 before extending | stretching before extending | stretching. Further, for example, the infrared film thickness meter 270 is also provided downstream of the second stretching machine 260 and measures the film thickness of the retardation film 400 after uniaxial stretching by the second stretching machine 260. Good. Here, from the viewpoint that the film thickness can be measured with high accuracy, it is preferable that the film thickness of each layer when measuring the film thickness is large. Specifically, each film thickness of the resin layer a1, the resin layer b, and the resin layer a2 is preferably 3 μm or more, and more preferably 5 μm or more. The upper limit of the film thickness is preferably 300 μm or less, and more preferably 250 μm or less. Furthermore, it is preferable that the thickness of each layer is different. Specifically, the difference in film thickness of each layer is preferably 3 μm or more, more preferably 5 μm or more, and preferably 300 μm or less, more preferably 250 μm or less.

In addition, for example, only one of the control by the opening control unit 281 and the control by the extrusion speed control unit 282 may be performed.
Further, instead of automatically controlling by the control unit 280, the user controls based on the respective film thicknesses of the resin layer a1, the resin layer b, and the resin layer a2 measured by the infrared film thickness meter 270. You may make it perform.
Furthermore, the manufacturing apparatus 200 for the retardation film 400 may include components other than those described above.

(Liquid crystal display device)
According to the production method of the present invention, a retardation film having a precisely controlled retardation can be realized, so that a high degree of birefringence compensation is possible. For this reason, for example, the retardation film obtained in the present invention can be used alone or in combination with other members to provide a liquid crystal display device, an organic electroluminescence display device, a plasma display device, an FED (field emission) display device, an SED ( (Surface electric field) The present invention may be applied to a display device such as a display device.

  A liquid crystal display device generally includes a pair of polarizers (light incident side polarizing plate and light emitting side polarizing plate) whose absorption axes are substantially orthogonal to each other, and a liquid crystal cell provided between the pair of polarizers. . When the retardation film obtained by the present invention is applied to a liquid crystal display device, for example, the retardation film obtained by the present invention may be provided between the pair of polarizers. In this case, the retardation film may be provided on the light incident side of the liquid crystal cell, or may be provided on the light emission side of the liquid crystal cell.

  Usually, the pair of polarizers, the retardation film and the liquid crystal cell are combined to form a single member called a liquid crystal panel, and the liquid crystal panel is irradiated with light from a light source and displayed on the light emitting side of the liquid crystal panel. An image is displayed on the screen. In this case, since the retardation film is precisely controlled, the retardation film exhibits an excellent polarizing plate compensation function and can reduce light leakage when the display surface of the liquid crystal display device is viewed from an oblique direction. . In addition, since the retardation film obtained in the present invention usually has an excellent optical function in addition to the polarizing plate compensation function, it is possible to further improve the visibility of the liquid crystal display device.

  Liquid crystal cell driving methods include, for example, in-plane switching (IPS) method, vertical alignment (VA) method, multi-domain vertical alignment (MVA) method, continuous spin wheel alignment (CPA) method, hybrid alignment nematic (HAN) Examples thereof include a twisted nematic (TN) method, a super twisted nematic (STN) method, and an optically compensated bend (OCB) method. Of these, the in-plane switching method and the vertical alignment method are preferable, and the in-plane switching method is particularly preferable. Although the in-plane switching type liquid crystal cell has a wide viewing angle, the viewing angle can be further expanded by applying the retardation film obtained in the present invention.

The retardation film may be bonded to a liquid crystal cell or a polarizing plate. For example, the retardation film may be bonded to both sides of the polarizing plate, or may be bonded only to one side. A known adhesive can be used for bonding.
Moreover, the retardation film obtained by this invention may be used individually by 1 sheet, and may be used in combination of 2 or more sheet.
Furthermore, when providing the retardation film obtained by this invention in a display apparatus, you may use it in combination with another retardation film. For example, when the retardation film obtained in the present invention is provided as a retardation film in a liquid crystal display device having a vertical alignment type liquid crystal cell, a viewing angle is added between a pair of polarizers in addition to the retardation film obtained in the present invention. You may provide another retardation film for improving a characteristic.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples, and may be arbitrarily changed without departing from the gist of the present invention and its equivalent scope. May be implemented. In the following description, “%” and “parts” representing amounts are based on weight unless otherwise specified.

[Evaluation method]
[Film thickness measurement by infrared film thickness meter]
It measured using the in-line infrared film thickness meter (the Kurabo Industries make, brand name RX-200). The measurement interval is 5 mm in the width direction, and the line speed is 5 m / min. The absorption at wavelengths 2.37 μm and 2.47 μm is recorded as the absorption corresponding to the resin layer containing polycarbonate and the resin layer containing polystyrene, respectively. In addition, the absorption at a wavelength of 1.58 μm is recorded as the absorption of the layer containing the infrared absorber. For each layer, five standard products with a thickness of 30 to 200 μm are prepared, the absorption at each wavelength is measured to obtain a calibration curve, and the film thickness of each layer is calculated based on this. Regarding the concentration of the infrared absorbent, the film thickness is calculated in accordance with the Lambert-Beer rule, assuming that the amount of infrared absorption is proportional to the product of the concentration and the film thickness.

[Thickness measurement by microscope]
After embedding the film before stretching in an epoxy resin, it is sliced using a microtome (“RUB-2100” manufactured by Yamato Kogyo Co., Ltd.), and the cross section is observed using a scanning electron microscope, and the resin layer A1 of the film before stretching, The film thickness of resin layer B1, resin layer A2, and the whole film was measured.

(Plane orientation coefficient)
The PC layer of the formed film was measured for nx, ny, and nz from the critical angle of the prism and the PC layer at a measurement wavelength of 532 nm using a refractive index film thickness measuring device (“Prism coupler” manufactured by Metricon).

[Film transportability]
The film that has been subjected to the stretching process is transported to 10 metal rolls having a diameter of 100 mm for 500 m at a line speed of 10 m / min. A sample that did not break once was A, a sample that was broken once or twice, and B was broken three times or more until C was completed.

[Measurement of retardation]
The stretched film was measured for retardation Re at an incident angle of 0 ° and retardation R40 at an incident angle of 40 ° using an automatic birefringence meter (“KOBRA-21ADH” manufactured by Oji Scientific Instruments) at a measurement wavelength of 590 nm. did.

[Production Example 1]
[Preparation of film before stretching]
A film forming apparatus for coextrusion molding of three types and three layers (type of forming a film composed of three layers with three types of resins) was prepared.
Pellets of polycarbonate resin (“Wanderlite PC-115” manufactured by Asahi Kasei Co., Ltd., glass transition temperature 145 ° C.) were charged into a first single screw extruder equipped with a double flight type screw and melted. This polycarbonate resin corresponds to the resin A1 containing polycarbonate.

  Also, a pellet of styrene-maleic anhydride copolymer resin (“Dylark D332” manufactured by Nova Chemicals, maleic anhydride unit content 17% by weight, glass transition temperature 129 ° C.) was added to the second equipped with a double flight type screw. It was put into a single screw extruder and melted. This styrene-maleic anhydride copolymer resin corresponds to the resin B having a negative intrinsic birefringence value.

  100 parts of a pellet of polycarbonate resin ("Wonderlite PC-115" manufactured by Asahi Kasei Co., Ltd., glass transition temperature of 145 ° C) and 1.5 parts of an infrared absorber ("NIR-AM1" manufactured by Nagase ChemteX Corporation) were added at a temperature of 270. The mixture was kneaded at 0 ° C. to obtain resin pellets. This resin pellet was put into a third single-screw extruder and melted. This resin corresponds to the resin A2 containing polycarbonate.

  The melted resin A1 at 260 ° C. was fed to the first manifold of a multi-manifold die (die slip surface roughness Ra = 0.1 μm) through a leaf disk-shaped polymer filter having an opening of 10 μm. Further, the melted resin B at 260 ° C. was supplied to the second manifold through a leaf disk-shaped polymer filter having an opening of 10 μm. Further, the melted resin A2 at 260 ° C. was supplied to the third manifold through a leaf disk-shaped polymer filter having an opening of 10 μm.

  Resin A1, resin B, and resin A2 are simultaneously extruded from the multi-manifold die at 260 ° C., and are provided on one surface of the resin layer a1 containing the resin A1 and the resin B containing the resin B. The film was formed in a three-layer configuration including a layer b and a surface of the resin layer b opposite to the resin layer a1, and a resin layer a2 containing the resin A2. The molten resin coextruded into a film in this way is cast onto a cooling roll adjusted to a surface temperature of 115 ° C., and then passed between two cooling rolls adjusted to a surface temperature of 120 ° C. A film before stretching having a three-layer structure provided with a resin layer b and a resin layer a2 in this order was obtained (coextrusion step). The width of the obtained film before stretching was 600 mm.

  About the obtained film before extending | stretching, the film thickness measurement with the infrared-type film thickness meter and the microscope was performed. It was found that the measurement with the infrared film thickness meter and the measurement with the microscope coincided, and the film thickness can be measured with high accuracy using the infrared film thickness meter. The results are shown in Table 1.

Further, this pre-stretched film was uniaxially stretched at a stretching temperature of 150 ° C. and a stretching ratio of 3.3 times using a tenter stretching machine. The stretched film is incident perpendicular to the film surface when the uniaxial stretching direction is the X axis, the direction perpendicular to the uniaxial stretching direction in the film plane is the Y axis, and the film thickness direction is the Z axis. The retardation Re of the linearly polarized light having the vibration plane of the electric vector in the XZ plane and incident perpendicularly to the film surface and having the vibration plane of the electric vector in the YZ plane was measured to be 108 nm and the phase was I found it late.
In addition, except that the stretching temperature of the pre-stretched film is set to 128 ° C., the linearly polarized light is incident perpendicularly to the stretched film surface and the vibration plane of the electric vector is in the XZ plane, and perpendicular to the film surface. The retardation Re for linearly polarized light that was incident and the plane of vibration of the electric vector was in the YZ plane was measured and found to be -960 nm, indicating that the phase was advanced.

[Example 1]
The film before stretching was supplied to a tenter transverse uniaxial stretching machine and stretched in the transverse direction at a stretching temperature of 153 ° C. and a stretching ratio of 3.30 (first stretching step). Subsequently, the stretched film is supplied to a longitudinal uniaxial stretching machine that uniaxially stretches using a difference in peripheral speed between rolls, and stretched in the longitudinal direction at a stretching temperature of 130 ° C. and a stretching ratio of 1.25 to obtain a resin layer. A three-layer retardation film provided with A1, resin layer B, and resin layer A2 in this order was obtained (second stretching step). In the obtained retardation film, the slow axis of the resin layer A1, the slow axis of the resin layer B, and the slow axis of the resin layer A2 were substantially parallel to each other. The plane orientation coefficient and retardation of the obtained stretched film were measured. The results are shown in Table 2.

[Example 2]
A retardation film was prepared and evaluated in the same manner as in Example 1 except that the stretching temperature in the second stretching step was 126 ° C. and the stretching ratio was 1.20. The results are shown in Table 2.

[Example 3]
A retardation film was prepared and evaluated in the same manner as in Example 1 except that the draw ratio in the second drawing step was 1.20. The results are shown in Table 2.

[Example 4]
A retardation film was prepared and evaluated in the same manner as in Example 1 except that the stretching temperature in the second stretching step was 122 ° C. and the stretching ratio was 1.10. The results are shown in Table 2.

[Example 5]
A retardation film is produced in the same manner as in Example 1 except that the stretching ratio in the first stretching step is 3.00, the stretching temperature in the second stretching step is 128 ° C., and the stretching ratio is 1.20. And evaluated. The results are shown in Table 2.

[Comparative Example 1]
A retardation film was prepared and evaluated in the same manner as in Example 1 except that the draw ratio in the second drawing step was 1.10. The results are shown in Table 2.

[Comparative Example 2]
A retardation film was prepared and evaluated in the same manner as in Example 1 except that the stretching temperature in the second stretching step was 140 ° C. and the stretching ratio was 1.20. The results are shown in Table 2.

[Comparative Example 3]
A retardation film was prepared and evaluated in the same manner as in Comparative Example 2 except that the draw ratio in the first drawing step was 3.00. The results are shown in Table 2.

From the above examples and comparative examples, according to the production method of the present invention, breakage at the time of conveyance after winding and winding onto a roll is suppressed, and retardation Re at an incident angle of 0 ° and an incident angle of 40 It can be seen that a retardation film satisfying the relationship of 0.92 ≦ R ₄₀ /Re≦1.08 with retardation R ₄₀ at 0 can be stably and continuously produced.

200 Production equipment for retardation film 210 Hopper 220 Extruder 230 Die 231 Slit (opening)
232 Adjustment bolt 233 Heater 240 Cooling roll 250 First stretching machine 260 Second stretching machine 270 Interference film thickness meter 280 Controller 281 Opening control unit 282 Extrusion speed control unit 300 Film before stretching 400 Phase difference film 410 Phase difference film Roll of

Claims (4)

A resin layer A1 containing a polycarbonate-containing resin A1, a resin layer B containing a resin B provided on one surface of the resin layer A1 and having a negative intrinsic birefringence, and the resin in the resin layer B A resin layer A2 containing a resin A2 containing polycarbonate, provided on the surface opposite to the layer A1,
A retardation Re at an incident angle of 0 °, the retardation _{R 40} at an incident angle of 40 ° is a method for producing a retardation film which satisfies a relation of 0.92 ≦ _R 40 /Re≦1.08,
A resin layer a1 containing a polycarbonate-containing resin A1, a resin layer b containing a resin B provided on one surface of the resin layer a1 and having a negative intrinsic birefringence, and the resin in the resin layer b A resin layer a2 containing a resin A2 containing polycarbonate, provided on the surface opposite to the layer a1;
When the uniaxial stretching direction is the X axis, the direction perpendicular to the uniaxial stretching direction in the film plane is the Y axis, and the film thickness direction is the Z axis, the plane of incidence is perpendicular to the film plane and The phase of linearly polarized light in the XZ plane that is perpendicularly incident on the film surface and the plane of vibration of the electric vector in the YZ plane is delayed when uniaxially stretched in the X-axis direction at the temperature T1 and is different from the temperature T1. A film before stretching, which proceeds when uniaxially stretched in the X-axis direction at a temperature T2,
A first stretching step in which a uniaxial stretching process is performed in one direction at a temperature T1 or T2, and
By a stretching process having a second stretching process in which a uniaxial stretching process is performed at a temperature T2 or T1 different from the above in a direction orthogonal to the direction in which the uniaxial stretching process is performed in the first stretching process,
The plane orientation coefficient represented by (nx + ny) / 2-nz of the resin layer A1 formed by stretching the resin layer a1 and the resin layer A2 formed by stretching the resin layer a2 is 0.017. Including the steps described above,
A method for producing a retardation film.
(However, nx and ny represent the refractive index in the main axis direction in the plane of the retardation film, and nz represents the refractive index in the thickness direction of the retardation film.)   The production according to claim 1, further comprising a co-extrusion step of co-extruding the resin A1 containing polycarbonate, the resin B having a negative intrinsic birefringence value, and the resin A2 containing polycarbonate as the step of obtaining the film before stretching. Method.   The manufacturing method of Claim 1 or 2 with which the said resin A1 or resin A2 contains an infrared absorber. The resin A1, the resin A2, and the resin B have different infrared absorption bands,
In the co-extrusion step, the film before stretching is obtained by co-extruding the resin A1, the resin B, and the resin A2 from the opening of the die having an opening whose size can be adjusted.
A measuring step of measuring the film thickness of each of the resin layer a1, the resin b, and the resin layer a2 of the pre-stretch film with an infrared film thickness meter;
The manufacturing method of Claim 2 or 3 which has an opening adjustment process which adjusts the magnitude | size of the opening of die | dye according to the measured film thickness of each layer.

Images