JP2012035445A - Method for production of oriented optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for high-efficiency production of an oriented optical film in which a geometric properties (for example, thickness) and an optical characteristic (for example, in-plane retardation, Re) are uniform in plane.SOLUTION: The method for production of an oriented optical film includes stretching a pre-stretching film simultaneously in both longitudinal and lateral directions by moving a long pre-stretching film gripping with a plurality of grippers. The total thickness of the pre-stretching film to be stretched or the thickness of at least one of layers composing the pre-stretching film has such a thickness gradient that the central portion of the pre-stretching film is thinner than the edge portion thereof.

Description

  The present invention relates to a method for producing a stretched optical film.

  In the liquid crystal display device, an optical film such as a retardation film is used to improve performance. As the optical film, stretched optical films imparted with anisotropy by stretching the film are widely used.

  In general, as one method for producing a stretched film, simultaneous biaxial stretching is known in which a pre-stretched film is stretched in two different directions parallel to the surface (for example, Patent Document 1). Simultaneous biaxial stretching has an advantage that a biaxially stretched film can be produced with higher efficiency than sequential biaxial stretching. However, in simultaneous biaxial stretching, it is difficult to make the geometric properties (for example, thickness) and optical properties (for example, retardation Re in the in-plane direction) of the stretched film uniform in the plane. This is a particular problem in the production of stretched optical films that require strict control of optical properties.

JP 2010-046879 A

  It is an object of the present invention to be highly efficient and to have a stretched film whose geometric properties (eg, thickness) and optical properties (eg, in-plane retardation Re) are uniform in the plane. It is providing the manufacturing method of an optical film.

In the process of studying to solve the above-mentioned problems, the present inventor made various conditions for simultaneous biaxial stretching more precisely than before (variation in film thickness before stretching, variation in stretching speed, variation in stretching ratio, etc.). The stretching system was adjusted so that it could be precisely controlled. As a result, the present inventors have found that in the simultaneous biaxial stretching, thickness and Re non-uniformity occurs with a specific tendency that is not seen in other stretching methods such as uniaxial stretching and sequential biaxial stretching. It was. This non-uniformity of this particular tendency is so slight that it cannot be found at all in the conventional simultaneous biaxial stretching applied to the production of products with low precision. However, in a method for producing a high-quality stretched optical film, which requires a more uniform uniformity of the optical properties of the stretched film, it is understood that such non-uniformity is a factor affecting the performance of the product. Found for the first time. Furthermore, the present inventor has also found that such non-uniformity can be solved by performing stretching using a pre-stretching film of a specific embodiment. The present invention has been completed based on these findings.
That is, according to the present invention, the following is provided:

[1] A method for producing a stretched optical film, comprising simultaneously stretching a film before stretching in the longitudinal direction and width direction by gripping and moving a long stretched film with a plurality of grippers. And
The total thickness of the unstretched film to be subjected to the stretching or the thickness of one or more layers among the layers constituting the unstretched film has a thickness gradient that is thinner in the center than in the width direction in the width direction. A process for producing a stretched optical film.
[2] A method for producing a stretched optical film according to [1],
The unstretched film is composed of a plurality of layers, and one or more layers of the plurality of layers are layers having a thickness gradient that is thinner at the center than at the end of the unstretched film in the width direction. Manufacturing method of optical film.
[3] A method for producing a stretched optical film according to [2],
The method for producing a stretched optical film, wherein the layer having a thinner thickness gradient at the center than the end of the unstretched film in the width direction is a layer to which optical anisotropy is imparted in the stretching.
[4] A method for producing a stretched optical film according to [3],
Among the plurality of layers, the thickness of one or more layers other than the layer to which optical anisotropy is imparted in the stretching is such that, in the width direction, a thickness gradient is thicker at the center than at the end of the film before stretching. A method for producing a stretched optical film.

  According to the production method of the present invention, in the simultaneous biaxial stretching with high production efficiency, a high-quality stretched optical film in which the optical characteristics in the width direction are more uniform than the stretched optical film obtained by the conventional simultaneous biaxial stretching. Can be manufactured.

FIG. 1 is a top view schematically showing a stretching mechanism by a link device in a pantograph simultaneous biaxial stretching machine capable of implementing the manufacturing method of the present invention. FIG. 2 is a cross-sectional view schematically showing a cross section of the pre-stretched film used in the production method of the present invention taken along a plane perpendicular to the longitudinal direction. FIG. 3 shows a cross section of a stretched optical film obtained by stretching the pre-stretching film 2 shown in FIG. 2 by simultaneous biaxial stretching, cut along a plane parallel to the width direction and perpendicular to the film surface. Width distribution graph (upper graph), inner layer thickness distribution graph (middle graph) and Re width distribution graph (lower graph) It is a schematic diagram. FIG. 4 is a cross-sectional view schematically showing a cross section of a pre-stretched film for comparison with the present invention, taken along a plane perpendicular to the longitudinal direction. FIG. 5 shows a cross section of a stretched optical film obtained by stretching the pre-stretching film 4 shown in FIG. 4 by simultaneous biaxial stretching, taken along a plane parallel to the width direction and perpendicular to the film surface. Width distribution graph (upper graph), inner layer thickness distribution graph (middle graph) and Re width distribution graph (lower graph) It is a schematic diagram. 6 is a graph showing the measurement results of the total thickness of the film before stretching in Example 1. FIG. FIG. 7 is a graph showing the measurement results of the inner layer thickness of the pre-stretch film in Example 1. 8 is a graph showing the measurement results of the total thickness of the two outer layers of the film before stretching in Example 1. FIG. FIG. 9 is a graph showing the measurement results of the Re profile in the width direction of the stretched optical film in Example 1 and Comparative Example 1. FIG. 10 is a graph showing the measurement results of the total thickness of the unstretched film in Comparative Example 1. FIG. 11 is a graph showing measurement results of the inner layer thickness of the pre-stretch film in Comparative Example 1. 12 is a graph showing the measurement results of the total thickness of two outer layers of the film before stretching in Comparative Example 1. FIG.

  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 the claims of the present invention and equivalents thereof. Any change can be made without departing from the above range.

[Stretching]
In the method for producing a stretched optical film of the present invention, the film before stretching is simultaneously stretched in the longitudinal direction and the width direction by gripping and moving the ends of the long stretched film with a plurality of grippers. including. Such a stretching method in which stretching in the longitudinal direction and the width direction (that is, the short direction) of the film is simultaneously performed is a stretching method generally called simultaneous biaxial stretching.
“Long” means a material having a length of at least 5 times the width, preferably 10 times or more, and specifically wound in a roll shape. It has a length that can be stored or transported. In the processing of a long film, since the film is usually conveyed along the longitudinal direction, the longitudinal direction of the film usually coincides with the flow direction (conveying direction) of the film.
In all the steps of stretching, stretching in the longitudinal direction and stretching in the width direction are usually performed simultaneously from the start to the end thereof, but only a part thereof may be performed simultaneously. For example, it may be a step in which stretching in the longitudinal direction and stretching in the width direction are started at the same time, and then stretching in the width direction is terminated, while stretching in the longitudinal direction is continued, and then stretching in the longitudinal direction is terminated.

  In the production method of the present invention, the draw ratio can be appropriately adjusted according to desired conditions. For example, the draw ratio in the longitudinal direction is usually 1.2 times or more, preferably 1.4 times or more, more preferably 1.6 times or more, usually 3.5 times or less, preferably 3 times or less, more Preferably it is 2.5 times or less. On the other hand, the draw ratio in the width direction is usually 1.1 times or more, preferably 1.15 times or more, more preferably 1.2 times or more, usually 3 times or less, preferably 2.5 times or less, more preferably Is less than twice.

  In the production method of the present invention, the stretching temperature can be appropriately adjusted so as to match the desired conditions, particularly the glass transition temperature of the material constituting the film before stretching, for example, glass in a layer that imparts optical anisotropy. With reference to the transition temperature Tg (a), the temperature can be in the range of Tg (a) −5 ° C. to Tg (a) + 15 ° C.

  A specific example of simultaneous biaxial stretching in the present invention and a specific example of an apparatus for performing such simultaneous biaxial stretching will be described with reference to FIG. FIG. 1 is a top view schematically showing a stretching mechanism by a link device in a pantograph simultaneous biaxial stretching machine capable of implementing the manufacturing method of the present invention.

  In FIG. 1, the pre-stretch film is continuously supplied from the upstream (left side in FIG. 1) along the direction of arrow A5 and passes through the stretcher. The link device 101 is mainly composed of a plurality of link plates connected in a zigzag shape. The link device 101 is a ring-shaped device in which a plurality of link plates including the link plate 102a are connected in a ring shape, but a part of the link device 101 is omitted in FIG. Also, a pair of link devices 101 are usually provided on both the left and right sides in the film flow direction, but one end side is omitted in FIG. The link device 101 circulates in the direction indicated by the arrow A1 when the bearing rollers 103a and 103b pass through the grooves formed by the guide rails 104a to 104c and are driven by the outlet sprockets 106L and 106R and the inlet sprocket 106b. .

  A gripper 110 is provided at the end of the link plate 102a. By any suitable mechanism (not shown), the gripper 110 grips the pre-stretch film 105a in the region D1. Further, as the width of the guide rail 104 is increased or decreased, the link device 101 is completely contracted in the region D1, and the link pitch at the time of contraction, that is, the pitch when gripping the film before stretching is the length indicated by P1 in FIG. Become.

  After the link device 101 reaches the stretching start portion 655, the link device 101 progresses toward the end in the direction A5 of the film in the oven while stretching, and when it reaches the stretching end portion 652, the link device 101 is stretched. The length is indicated by P2. Due to the progress of the end spread, the pre-stretched film is stretched in the width direction at a stretch ratio of (B2 / B1) times and stretched in the longitudinal direction at a stretch ratio of (P2 / P1) times to become a stretched optical film. . The value of (B2 / B1) and the value of (P2 / P1) can be adjusted by adjusting the positions of the guide rail holding portions 130a and 130b supported by the drive shaft 120. The gripper 110 releases the stretched optical film 105b by any suitable mechanism before the link plate 102a exits the region D2, and then the link plate 102a is returned toward the region D1. The stretched optical film 105b is sent downstream along the flow direction.

[Film before stretching]
In the production method of the present invention, the pre-stretch film is a film subjected to stretching in the production method of the present invention. The unstretched film is usually an unstretched film, but may be a film that has already been subjected to preliminary stretching.

[Film before stretching: thickness gradient]
In the pre-stretch film used in the present invention, the total thickness or the thickness of one or more layers among the layers constituting the pre-stretch film is thinner in the center than in the width direction in the width direction. It has a thickness gradient (hereinafter, this thickness gradient may be referred to as a “concave thickness gradient”).
The presence or absence of such a thickness gradient can be determined based on a simple moving average (20 sections moving average with a width of 5 mm as one section). Further, the degree of the concave thickness gradient can be appropriately adjusted so that desired physical properties of the stretched optical film (such as a uniform Re value in the width direction) can be obtained. For example, (the thickness of the film end before stretching) -As the value of (thickness of film center before stretching) / (average thickness of film before stretching), the upper limit is preferably 0.11 or less, more preferably 0.08 or less, and the lower limit is preferably 0.01 or more. More preferably, it is 0.02 or more.

In a preferred embodiment, the pre-stretch film comprises a plurality of layers, and one or more of the plurality of layers are layers having a concave thickness gradient in the width direction.
In a more preferred embodiment, the layer having a concave thickness gradient in the width direction is a layer to which optical anisotropy is imparted in the stretching.
In an even more preferred embodiment, the thickness of one or more layers other than the layer to which optical anisotropy is imparted in the stretching among the plurality of layers is more central than the end of the film before stretching in the width direction. It has a thicker thickness gradient (this thickness gradient is sometimes referred to as a “convex thickness gradient” hereinafter).

  The specific method for imparting optical anisotropy to some of the plurality of layers constituting the pre-stretch film is not particularly limited, but such selection can be made by appropriately selecting the material constituting each layer and the stretching conditions. The optical anisotropy can be imparted. For example, when stretching a pre-stretch film composed of an inner layer and an outer layer outside thereof, the stretching temperature is lower than the glass transition temperature of the inner layer and close to the glass transition temperature of the outer layer or higher than the glass transition temperature of the outer layer. By doing so, optical anisotropy can be selectively imparted only to the inner layer. In this case, even if the thickness of the outer layer is not uniform, the stretched optical film can be useful as a stretched optical film as long as the properties such as mechanical strength and total light transmittance of the stretched optical film are within an allowable range.

Advantages and specific examples of these aspects will be described with reference to FIGS.
FIG. 2 is a cross-sectional view schematically showing a cross section of the pre-stretched film used in the production method of the present invention taken along a plane perpendicular to the longitudinal direction.
The unstretched film 2 shown in FIG. 2 is a long multilayer film, and has three layers of an inner layer 21 and outer layers 22a and 22b provided on upper and lower surfaces of the inner layer 21, respectively. In the unstretched film 2, the thickness in the width direction of the inner layer 21 has a concave thickness gradient, that is, a thickness gradient that is thinner in the central portion C than in the end portion E. On the other hand, the outer layers 22a and 22b of the unstretched film 2 have a convex thickness gradient, that is, a thicker thickness gradient in the central portion C than in the end portion E. The total film thickness of the unstretched film 2 has a uniform thickness with no thickness gradient.

FIG. 3 shows a cross section of a stretched optical film obtained by stretching the pre-stretching film 2 shown in FIG. 2 by simultaneous biaxial stretching, cut along a plane parallel to the width direction and perpendicular to the film surface. Width distribution graph (upper graph), inner layer thickness distribution graph (middle graph) and Re width distribution graph (lower graph) It is a schematic diagram.
When stretching the film 2 before stretching, the material of the inner layer 21 and the outer layers 22a and 22b and stretching conditions (stretching temperature, etc.) are appropriately selected to stretch the film 2 before stretching, so that the inner layer 21 is preferentially compared to the outer layer. The outer layers 22a and 22b can be generally isotropic layers for imparting strength to the stretched film. The stretched optical film 3 shown in FIG. 3 is obtained by stretching under such conditions, and has an inner layer 31 and outer layers 32a and 32b respectively derived from the inner layer 21 and the outer layers 22a and 22b of the film 2 before stretching. is doing. Therefore, in the stretched optical film 3, only the inner layer 31 has optical anisotropy, and the outer layers 32a and 32b are optically isotropic layers. Therefore, Δn and Re of the stretched optical film 3 are hardly influenced by the outer layers 32 a and 32 b and are mainly expressed based on the thickness and optical anisotropy of the inner layer 31.

  According to the finding of the present inventor, when the film is stretched by simultaneous biaxial stretching to be an anisotropic stretched film, the thickness d of the stretched film obtained has a thinner gradient at the center than at the end. On the other hand, the Δn value (Δn = nx−ny; where nx and ny are the refractive indices at the slow axis and the fast axis in the in-plane direction of the stretched film) has a gradient that is larger at the center than at the end. Arise. Such a gradient of Δn value is not observed in a stretched film obtained by uniaxial stretching and sequential biaxial stretching. And, the Re value (Re = Δn × d) of the stretched film is close to evenly with these gradients canceling out, but the tendency of the gradient due to Δn appears relatively strongly, and as a result, Re is more in the central portion than the end portion. This produces a gradient that becomes larger.

  Like the example shown in FIG.2 and FIG.3, one or more layers of the plurality of layers of the pre-stretch film have a concave thickness gradient in the width direction. The distribution can be made uniform, and as a result, a stretched optical film having a uniform Re distribution in the width direction can be obtained.

  Furthermore, while the layer having a concave thickness gradient in the width direction is a layer to which optical anisotropy is imparted in stretching, while obtaining desired optical performance such as uniform Re distribution in the width direction, and The strength of the stretched optical film can also be ensured. That is, although the layer imparted with optical anisotropy in the stretched optical film has a relatively high degree of concave thickness gradient in the width direction, no optical anisotropy is imparted in stretching, ie, stretching. The isotropic film can ensure the strength in the entire width direction even after passing through, and a stretched optical film having both high optical performance and high strength can be obtained. In particular, as in the example shown in FIGS. 2 and 3, the thickness of one or more layers other than the layer to which optical anisotropy is imparted in stretching has a convex thickness gradient in the width direction. The strength of the central portion of the optical film can be made particularly good, and the thickness gradient in the width direction of the entire stretched optical film can be reduced.

For comparison with the examples shown in FIGS. 2 and 3, examples of the manufacturing method using the unstretched film that does not satisfy the requirements for use in the manufacturing method of the present invention are shown in FIGS. 4 and 5.
FIG. 4 is a cross-sectional view schematically showing a cross section of the pre-stretched film for comparison with the pre-stretched film 2 shown in FIG. 2 taken along a plane perpendicular to the longitudinal direction. The film before stretching shown in FIG. 4 has an inner layer 41, an outer layer 42a, and an outer layer 42b, which correspond to the inner layer 21, outer layer 22a, and outer layer 22b of the film before stretching 2 shown in FIG. 2, respectively. The inner layer 41, the outer layer 42a, and the outer layer 42b are the same layers as the inner layer 21, the outer layer 22a, and the outer layer 22b of the unstretched film 2 except that there is no thickness gradient in the width direction.

FIG. 5 shows a cross section of a stretched optical film obtained by stretching the pre-stretching film 4 shown in FIG. 4 by simultaneous biaxial stretching, taken along a plane parallel to the width direction and perpendicular to the film surface. Width distribution graph (upper graph), inner layer thickness distribution graph (middle graph) and Re width distribution graph (lower graph) It is a schematic diagram.
The conditions for stretching the pre-stretching film 4 are the same as the conditions for stretching the pre-stretching film 2 described above, whereby the inner layer 41 preferentially exhibits optical anisotropy, while the outer layers 42a and 42b. Is a generally isotropic layer for imparting strength to the stretched film. The stretched optical film 5 shown in FIG. 5 is obtained by stretching under such conditions, and has an inner layer 51 and outer layers 52a and 52b derived from the inner layer 41 and the outer layers 42a and 42b of the unstretched film 4 respectively. is doing. Therefore, in the stretched optical film 5, the inner layer 51 mainly has optical anisotropy, and the outer layers 52a and 52b are optically isotropic layers.

As already explained, according to the finding of the present inventors, when the film is stretched by simultaneous biaxial stretching to have anisotropy, the thickness d of the stretched film obtained is from the end to the center. However, the Δn value has a gradient that is greater at the center than at the end. Then, the Re value of the stretched film becomes close to uniform even when these gradients cancel each other, but the tendency of the gradient due to Δn appears relatively strongly, and as a result, Re has a gradient that is larger in the central portion than in the end portion.
The unstretched film 4 has an inner layer 41 that does not have a concave thickness gradient. Therefore, in the stretched optical film 5 obtained by stretching it, the gradient of Δn appears larger than that of the stretched optical film 3 of FIG. On the other hand, in the stretched optical film 5, the thickness gradient of the inner layer 51 appears smaller than that of the stretched optical film 3. And since the tendency of the gradient due to Δn appears relatively strongly, as a result, Re of the stretched optical film 5 has a gradient in which the central portion is larger than the end portion.
Since the distribution in the width direction of the entire thickness of the film 4 before stretching was the same as that of the film 2 before stretching, the distribution in the width direction of the entire thickness of the stretched optical film 5 was almost the same as that of the stretched optical film 3. It becomes the same. However, since the thicknesses of the outer layers 52a and 52b, which are layers related to securing the strength of the stretched optical film, are relatively thin in the central portion, the strength of the stretched optical film 5 may be insufficient in the vicinity of the central portion.

[Film before stretching: material]
A thermoplastic resin can be used as the material of the pre-stretch film used in the method for producing a stretched optical film of the present invention. As the thermoplastic resin, a resin suitable for a stretched optical film can be appropriately selected.

  When a multilayer film composed of a layer to which optical anisotropy is imparted in stretching and other layers is used as the pre-stretch film, examples of such multilayer films include resins that are advantageous for imparting optical anisotropy. And a layer made of a resin advantageous for securing strength (hereinafter sometimes referred to as “B layer”). Can be mentioned.

  Examples of the resin of the material of the A layer include a resin having a negative intrinsic birefringence value (hereinafter sometimes referred to as “resin A” as appropriate). On the other hand, as a resin of the material of the B layer, a transparent resin (hereinafter, also referred to as “resin B” as appropriate) may be mentioned.

Examples of the polymer contained in the resin A include a styrene polymer, a polyacrylonitrile polymer, a polymethyl methacrylate polymer, or a multi-component copolymer thereof. The styrenic polymer is a polymer having a styrene unit structure as a part or all of repeating units, such as polystyrene; styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, p-chloro. Styrene monomers such as styrene, p-nitrostyrene, p-aminostyrene, p-carboxystyrene, p-phenylstyrene, ethylene, propylene, butadiene, isoprene, acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, N -Copolymers with other monomers such as phenylmaleimide, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, acrylic acid, methacrylic acid, maleic anhydride, vinyl acetate and the like. Among these, styrene-based polymers are preferable from the viewpoint of high retardation development, and among them, polystyrene, a copolymer of styrene and N-phenylmaleimide, or a copolymer of styrene and maleic anhydride is particularly preferable.
These polymers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The molecular weight of the polymer contained in the resin A is appropriately selected depending on the purpose of use, but using gel as a solvent (however, toluene may be used when the polymer does not dissolve in cyclohexane). The weight average molecular weight (Mw) in terms of polyisoprene measured by ablation chromatography (in terms of polystyrene when the solvent is toluene) is usually 10,000 or more, preferably 15,000 or more, more preferably 20,000 or more. It is usually 100,000 or less, preferably 80,000 or less, more preferably 50,000 or less. It is preferable that the weight average molecular weight is in such a range because the mechanical strength and molding processability of the obtained stretched optical film are highly balanced.

  For the resin A, for example, an antioxidant, a heat stabilizer, a light stabilizer, an ultraviolet absorber, an antistatic agent, a dispersant, a chlorine scavenger, a flame retardant, a crystallization nucleating agent, a reinforcing agent, and a blocking agent as necessary. Anti-fogging agents, anti-fogging agents, release agents, pigments, organic or inorganic fillers, neutralizing agents, lubricants, decomposing agents, metal deactivators, antifouling agents, and antibacterial agents, and other resins, thermoplastics You may include well-known additives, such as an elastomer, in the range which does not impair the effect of this invention. The amount of these additives is usually 0 to 50 parts by weight, preferably 0 to 30 parts by weight with respect to 100 parts by weight of the polymer contained in the resin A.

  Resin B is a resin having transparency with a total light transmittance of 70% or more, preferably 80% or more, more preferably 90% or more, measured by forming a test piece having a thickness of 1 mm. preferable.

  Examples of the polymer contained in the resin B include acrylic polymer, methacrylic polymer, polycarbonate polymer, polyester polymer, polyethersulfone polymer, polyarylate polymer, polyimide polymer, chain polyolefin polymer, Examples thereof include polyethylene terephthalate polymer, polysulfone polymer, polyvinyl chloride polymer, diacetyl cellulose polymer, triacetyl cellulose polymer, and alicyclic olefin polymer. Of these, alicyclic olefin polymers and methacrylic polymers are preferred.

The methacrylic polymer is a polymer containing a methacrylic acid alkyl ester unit as a main monomer unit. As a methacrylic polymer, a homopolymer of a methacrylic acid alkyl ester having an alkyl group having 1 to 4 carbon atoms such as methyl methacrylate and ethyl methacrylate; the hydrogen of the alkyl group is OH group, COOH group or NH ₂ group A homopolymer of a methacrylic acid alkyl ester having a C 1-4 alkyl group substituted by a functional group; or a methacrylic acid alkyl ester and styrene, vinyl acetate, α, β-monoethylenically unsaturated carboxylic acid, vinyl Examples thereof include copolymers with ethylenically unsaturated monomers other than alkyl methacrylate such as toluene, α-methylstyrene, acrylonitrile, and alkyl acrylate. Of these, acrylic acid alkyl esters are suitable for copolymerization with methacrylic acid alkyl esters. In a suitable methacrylic polymer, the methacrylic acid alkyl ester unit having an alkyl group having 1 to 4 carbon atoms which may be substituted with a functional group is preferably 50 to 100% by weight, more preferably 50 to 99.9% by weight. %, More preferably 50 to 99.5% by weight, and the alkyl ester unit is preferably 0 to 50% by weight, more preferably 0.1 to 50% by weight, and still more preferably 0.5 to 50% by weight. contains.

  The alicyclic olefin polymer is an amorphous thermoplastic polymer having an alicyclic structure in the main chain and / or side chain. Examples of the alicyclic structure in the alicyclic olefin polymer include a saturated alicyclic hydrocarbon (cycloalkane) structure and an unsaturated alicyclic hydrocarbon (cycloalkene) structure. Of these, a cycloalkane structure is preferable from the viewpoint of mechanical strength, heat resistance, and the like. The number of carbon atoms constituting the alicyclic structure is not particularly limited, but is usually 4 or more, preferably 5 or more, usually 30 or less, preferably 20 or less, more preferably 15 or less. In some cases, mechanical strength, heat resistance, and film formability are highly balanced and suitable.

  The ratio of the repeating unit having an alicyclic structure constituting the alicyclic olefin polymer is preferably 55% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight or more. It is preferable from a transparency and heat resistant viewpoint that the ratio of the repeating unit which has an alicyclic structure in an alicyclic olefin polymer exists in this range.

  Examples of the alicyclic olefin polymer include a norbornene polymer, a monocyclic olefin polymer, a cyclic conjugated diene polymer, a vinyl alicyclic hydrocarbon polymer, and a hydride thereof. Among these, norbornene polymers can be suitably used because of their good transparency and moldability.

Examples of the norbornene polymer include a ring-opening polymer of a monomer having a norbornene structure, a ring-opening copolymer of a monomer having a norbornene structure and another monomer, or a hydride thereof; norbornene structure Or an addition copolymer of a monomer having a norbornene structure with another monomer, or a hydride thereof. Among these, a ring-opening (co) polymer hydride of a monomer having a norbornene structure is particularly suitable from the viewpoints of transparency, moldability, heat resistance, low hygroscopicity, dimensional stability, lightness, and the like. Can be used.
In addition, these polymers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The molecular weight of the polymer contained in the resin B is appropriately selected according to the purpose of use, but using gel as a solvent (however, if the polymer does not dissolve in cyclohexane, toluene may be used) The weight average molecular weight (Mw) in terms of polyisoprene measured by ablation chromatography (in terms of polystyrene when the solvent is toluene) is usually 10,000 or more, preferably 15,000 or more, more preferably 20,000 or more. It is usually 100,000 or less, preferably 80,000 or less, more preferably 50,000 or less. It is preferable that the weight average molecular weight is in such a range because the mechanical strength and molding processability of the obtained stretched optical film are highly balanced.

  If necessary, the resin B may contain a known additive as in the case of the resin A as long as the effects of the present invention are not impaired. The amount of these additives is usually 0 to 50 parts by weight, preferably 0 to 30 parts by weight with respect to 100 parts by weight of the polymer contained in the resin B.

  When the glass transition temperature of the resin A is Tg (a) (° C.) and the glass transition temperature of the resin B is Tg (b) (° C.), it is preferable that Tg (a)> Tg (b) + 8 ° C. Tg (a)> Tg (b) + 20 ° C. is more preferable, and Tg (a)> Tg (b) + 24 ° C. is more preferable. In general, Tg (a) <Tg (b) + 50 ° C.

  The glass transition temperature Tg (b) of the resin B is preferably 40 ° C. or higher, more preferably 60 ° C. or higher. Further, the upper limit value of the glass transition temperature Tg (b) of the resin B is usually 140 ° C. or lower.

[Film before stretching: other geometric properties]
In the case where the pre-stretch film is a multilayer film composed of an A layer and a B layer, the average thickness of the A layer is the total thickness of the A layer and the B layer (that is, the total thickness of the A layer and the B layer). The ratio to the average is usually 20% or more, preferably 30% or more, more preferably 40% or more. Thus, by increasing the thickness of the A layer, suitable optical characteristics can be exhibited.
Moreover, the upper limit of the ratio of the average thickness of A layer to the average of the total thickness of A layer and B layer is usually less than 80%. By making the thickness of the A layer less than 80%, the obtained stretched optical film can be prevented from becoming brittle and the handling property can be kept good.

Here, the number of layers A and B included in the pre-stretch film may be one or two or more, respectively. When two or more A layers and B layers are provided, the ratio of the thickness of the A layer to the total thickness of the A layer and the B layer is calculated based on the total thickness of the A layer and the B layer.
In addition, after embedding a film in an epoxy resin, the thickness of each layer is sliced to 0.05 micrometer thickness using a microtome (for example, Daiwa Kogyo Co., Ltd., RUB-2100), and a transmission electron microscope is used. It can be obtained by observing and measuring the cross section.

  The average total thickness of the A layer and the B layer is not particularly limited and can be appropriately set according to the draw ratio and the like. The thickness of the desired stretched optical film (the upper limit is usually 180 μm or less, 120 μm or less, The lower limit can be appropriately set according to 25 μm or more, preferably 30 μm or more, and more preferably 35 μm or more.

  Although the width | variety of the film before extending | stretching is not specifically limited, 450-2000 mm, Preferably it can be 1000-1600 mm.

[Film before stretching: preparation method]
Examples of a method for preparing a pre-stretch film used in the production method of the present invention include a coextrusion molding method such as a coextrusion T-die method, a coextrusion inflation method, and a coextrusion lamination method; a film lamination molding method such as dry lamination; A known method such as a coating molding method for coating the base resin film with a resin solution can be appropriately performed. Among these, a molding method by coextrusion is preferable from the viewpoints of production efficiency and that volatile components such as a solvent do not remain in the film. The extrusion temperature can be appropriately selected according to the type of resin (resin A, resin B, etc.) constituting the film.
As a method of providing a concave or convex thickness gradient in the width direction of each layer constituting the pre-stretch film, for example, when using a T-die, there is a method of appropriately adjusting the shape of the die opening. it can.
[Properties of stretched optical film, etc.]
The film stretched by the stretching can be used as a stretched optical film as a product through an arbitrary operation such as an operation of cutting off a portion gripped by the gripper as it is, or an operation of cutting out into a desired shape. .
The properties of the stretched optical film obtained by the production method of the present invention are not particularly limited depending on the properties of the pre-stretched film and the stretching conditions. For example, the distribution variation in the width direction of Re is 0.6 nm to 2 nm. It can be in a very small range. The variation in the distribution of Re in the width direction is represented by the difference between the maximum value and the minimum value of the front retardation Re.

[Use of product]
The stretched optical film obtained by the production method of the present invention can be used alone or in combination with other members as a retardation plate or a viewing angle compensation film, such as a liquid crystal display device, an organic EL display device, a plasma display device, an FED (electric field). The present invention can be widely applied to (emission) display devices, SED (surface electric field) display devices, and the like.

[Others]
The above disclosure has described the present invention with reference to preferred embodiments for illustrative purposes. However, the present invention is intended to be limited only by the scope of the present application and its equivalent scope. Various modifications and changes can be further made in the above embodiment.
For example, the unstretched film described above with reference to FIG. 2 has a total thickness that is uniform in the width direction, and the resulting stretched optical film has a total thickness that has a concave gradient in the width direction. However, the distribution of the total thickness of the film before stretching can be changed to a distribution having a convex gradient in the width direction. By setting it as such distribution, it is also possible to make uniform the total thickness distribution of a stretched optical film.
Moreover, in order to obtain a stretched optical film having a more uniform thickness, the thickness and optical properties of the stretched optical film carried out through the stretching process are measured, and the die opening is controlled according to the measurement results. A feedback operation can also be performed.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited only to the following Examples.

<Example 1>
(1-1: stretching machine)
As a stretching machine for carrying out biaxial stretching, a pantograph system simultaneous biaxial stretching machine schematically shown in FIG. 1 was prepared. The stretching machine is installed in an oven that maintains a constant working environment temperature including a stretching region (a region from a stretching start unit 655 to a stretching end unit 652), and includes a pair of loop-shaped link devices 101. The film before stretching was gripped by a number of grips 110 provided at the end of the link plate 102a constituting the link device 101, stretched in the stretching region while being transported in the direction of arrow A5, and simultaneous biaxial stretching was performed. .

(1-2: Preparation of film before stretching)
Polystyrene resin as the inner layer resin (Nova Chemical, trade name “DAILARK D332”, maleic anhydride copolymer, glass transition temperature 130 ° C.) and methacrylic resin as the outer layer resin (manufactured by Sumitomo Chemical Co., Ltd., product name “SUMIPEX HT55Z”) And a glass transition temperature of 105 ° C.) are extruded in a molten state from a T-die into a sheet shape and cooled to stretch a multilayer film of two types and three layers with a width of 1450 mm and an inner layer resin sandwiched between outer layer resins. Prepared continuously as a prefilm. The total thickness of the obtained film before stretching, the total thickness of the inner layer and the outer layer 2 layers, using an in-line multilayer film thickness measuring device (product name: StraDex, manufactured by ISIS), the in-line measurement interval is 5 mm in the width direction. The line speed was 5 m / min, and measurement values were obtained over the entire width direction by measuring 290 times in the film width direction. The results of performing this measurement 30 times and obtaining the average value are shown in FIG. 6 (total thickness), FIG. 7 (inner layer thickness), and FIG. 8 (outer layer two layer total thickness). In the graphs of FIGS. 6 to 8 and FIGS. 10 to 12, the horizontal axis represents a value obtained by measuring the distance from the left end of the film to the measurement point in the width direction of the film when observing from the upstream to the downstream in the flow direction. The vertical axis indicates the thickness (μm) at the corresponding measurement point. As shown in FIG. 6, the total thickness of the film before stretching was approximately uniform at around 80 μm, but the inner layer thickness had a concave thickness gradient. Further, the total thickness of the two outer layers had a convex thickness gradient.

(1-3: Production of stretched optical film)
The pre-stretching film prepared in (1-2) was supplied to the stretching machine described in (1-1), and simultaneous biaxial stretching with the stretching machine was started. The gripping by the gripper was performed so that at least a region of 20 to 1430 mm in the width direction of the film before stretching was included in the stretching region. The draw ratio was 1.8 times in the longitudinal direction (longitudinal direction and MD direction), 1.2 times in the transverse direction (width direction and TD direction), and the drawing temperature was 130 ° C. After the completion of stretching, the ears on both sides were cut off except for a region corresponding to a region of 163 to 1288 mm in the width direction of the film before stretching to obtain a stretched optical film having a width of 1350 mm. In-plane retardation Re of the obtained stretched optical film was measured using an inline phase difference meter (manufactured by Oji Scientific Instruments: KOBRA-WIST / 2RT). The results are shown in FIG.

  As is clear from the results of FIG. 9, according to the method for producing a stretched optical film of the present invention, a film with little variation in Re in the width direction of the film can be obtained by stretching by simultaneous biaxial stretching.

<Comparative Example 1>
In the step (1-2), the shape of the opening of the T-die was changed, and the film before stretching, in which neither the inner layer nor the outer layer had a thickness gradient extruded, was operated in the same manner as in Example 1, and the film before stretching Was stretched to obtain a stretched optical film. The total thickness, inner layer thickness, and outer layer total thickness of the film before stretching were measured in the same manner as in Example 1. The measurement results are shown in FIGS. Further, Re of the stretched optical film was also measured in the same manner as in Example 1. The measurement results are shown in FIG.

  As is clear from the results of FIG. 9, in this comparative example in which a thickness gradient in the width direction of the inner layer of the film before stretching was not provided, the variation in Re in the width direction of the obtained stretched optical film was larger than that in Example 1. A stretched optical film which appeared large and whose center portion Re was undesirably larger than the end portion Re was obtained.

DESCRIPTION OF SYMBOLS 101 Link apparatus 102a Link plate 103a, 103b Bearing roller 104a-104c Guide rail 106L, 106R Outlet sprocket 106b Inlet sprocket 110 Gripper 105a Pre-stretch film 655 Stretch start part 652 Stretch end part 105b Stretch optical film 120 Drive shaft 130a, 130b Guide Rail holding part 2, 4 Film before stretching 21, 41 Film inner layer before stretching 22a, 22b, 42a, 42b Film outer layer before stretching E End part C Central part 3, 5 Stretched optical film 31, 51 Stretched optical film inner layer 32a, 32b, 52a, 52b Stretched optical film outer layer

Claims (4)

A method for producing a stretched optical film, comprising simultaneously stretching the pre-stretch film in the longitudinal direction and the width direction by gripping and moving the long pre-stretch film with a plurality of grippers,
The total thickness of the unstretched film to be subjected to the stretching or the thickness of one or more layers among the layers constituting the unstretched film has a thickness gradient that is thinner in the center than in the width direction in the width direction. A process for producing a stretched optical film. A method for producing a stretched optical film according to claim 1,
The unstretched film is composed of a plurality of layers, and one or more layers of the plurality of layers are layers having a thickness gradient that is thinner at the center than at the end of the unstretched film in the width direction. Manufacturing method of optical film. A method for producing a stretched optical film according to claim 2,
The method for producing a stretched optical film, wherein the layer having a thinner thickness gradient at the center than the end of the unstretched film in the width direction is a layer to which optical anisotropy is imparted in the stretching. A method for producing a stretched optical film according to claim 3,
Among the plurality of layers, the thickness of one or more layers other than the layer to which optical anisotropy is imparted in the stretching is such that, in the width direction, a thickness gradient is thicker at the center than at the end of the film before stretching. A method for producing a stretched optical film.

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