JP2011126084A - Multilayer film, phase difference film and method for producing them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer film from which a phase difference film of high quality having suppressed phase difference unevenness can be produced, the phase difference film of high quality having suppressed phase difference unevenness and further a method for producing them. <P>SOLUTION: The multilayer film has a core layer and skin layers respectively arranged on both surfaces of the core layer and is molded by melting extrusion of a molten resin. The number of the linear rugged patterns having breadth of 300 to 1,000 μm and height of 10 to 1,000 nm at an interface between the core layer and the skin layer is two or below per 1,400 mm breadth of the multilayer film. Further, the phase difference film obtained by stretching the multilayer film and the method for producing them are provided. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a multilayer film and a retardation film formed by melt-extruding a molten resin, and methods for producing them.

  Liquid crystal display devices have features such as thinness, light weight, and low power consumption, and are widely used in televisions, personal computers, and the like. A liquid crystal display device generally includes a liquid crystal panel including a light incident side polarizing plate, a liquid crystal cell, and a light emitting side polarizing plate in this order, and a light source that emits light from the light incident side of the light incident side polarizing plate. Has been. At this time, the transmission axis of the light incident side polarizing plate and the transmission axis of the light output side polarizing plate are arranged so as to be orthogonal to each other. In such a liquid crystal display device, an image is displayed on the screen by changing the orientation of the liquid crystal molecules by applying a voltage to the liquid crystal cell and adjusting the amount of transmitted light.

  A liquid crystal display device is sometimes provided with a retardation film for the purpose of improving image quality, and optical compensation is sometimes performed. Such a retardation film is usually manufactured by melt-extruding a resin, which is a material of the retardation film, from a die to produce an original film, and stretching the original film.

  However, when a raw film is produced by melt-extruding a resin, linear irregularities (die lines) along the flow direction of the raw film may be formed on the surface of the raw film. When linear unevenness is formed on the original film, the linear unevenness is also formed on the surface of the retardation film obtained by stretching the original film, and the retardation film has uneven retardation due to the linear unevenness. May occur. For this reason, conventionally, the development of the technique which prevents the linear unevenness | corrugation of the surface was made | formed (refer patent documents 1-3).

JP 2002-156525 A JP 2007-98916 A JP 2009-73107 A

In recent years, retardation films having various layer structures have been developed for the purpose of improving optical characteristics of retardation films. As an example, there is a retardation film having a three-layer structure in which a core layer having a large retardation (retardation) is sandwiched between skin layers having a small retardation.
In this type of retardation film, even when the line unevenness is not formed on the surface, retardation unevenness caused by the line unevenness may occur. Similar retardation unevenness may occur even in a retardation film having a multilayer structure having four or more layers. However, the above-described phase difference unevenness may occur even when there is no linear unevenness on the surface, and thus cannot be solved by conventional techniques such as Patent Documents 1 to 3.

  The present invention has been invented in view of the above problems, a multilayer film capable of producing a high-quality retardation film with suppressed retardation unevenness, a high-quality retardation film with suppressed retardation unevenness, and the above It aims at providing the manufacturing method which can manufacture this multilayer film and retardation film.

In order to solve the above-described problems and achieve the object, the present inventors have intensively studied, and as a result, the above-described retardation unevenness that occurs even when the surface has no linear unevenness is caused by the core layer and the skin. The knowledge that it was caused by the linear unevenness of the core layer formed at the interface with the layer was obtained. Furthermore, it has been found that the retardation unevenness can be more effectively improved by preventing the linear unevenness at the interface between the core layer and the skin layer rather than the surface of the skin layer. The present invention has been completed based on such findings.
That is, according to the present invention, the following [1] to [7] are provided.

[1] A multilayer film comprising a core layer and skin layers respectively disposed on both sides of the core layer, and formed by melt extrusion of a molten resin,
The multilayer film in which the number of linear irregularities having a width of 300 μm to 1000 μm and a height of 10 nm to 1000 nm at the interface between the core layer and the skin layer is 2 or less per 1400 mm width of the multilayer film.
[2] A retardation film obtained by stretching the multilayer film according to [1].
[3] A method for producing a multilayer film according to [1],
Including melt coextrusion of a molten resin corresponding to the skin layer and the core layer from a die,
The molten resin corresponding to the core layer is supplied to the die after being filtered by a polymer filter,
The polymer filter is
A bottom portion having a flat inner bottom surface on which a delivery port is formed, a side wall portion having a cylindrical inner surface perpendicular to the inner bottom surface, and a flow channel provided on the opposite side of the side wall portion from the bottom portion. A housing including a lid portion formed with an inlet;
A strut portion that is erected on the inner bottom surface in the housing and in which a channel that communicates with the delivery port is formed;
A polymer filter comprising: a disk-shaped filter element mounted on the strut portion so as to stack a plurality of sheets, filtering the molten resin flowing from the inflow port and sending it to the flow path of the strut portion; ,
The casing is located on the center side of the casing with respect to the inner bottom surface and the inner side surface so as to straddle between the inner bottom surface and the inner side surface at a boundary portion between the inner bottom surface and the inner side surface. It has a convex part that is convex toward
0.3 ≦ d ₁ /d≦0.8 and 0.3 ≦ d ₂ /d≦0.8 (d represents the distance from the filter element to the inner surface. D ₁ is from the inner surface. The distance in the radial direction of the inner surface to the point where the inner bottom surface and the convex surface portion intersect, d ₂ from the inner bottom surface to the point where the inner surface and the convex surface portion intersect, The distance is expressed in a direction perpendicular to the inner bottom surface).
[4] A method for producing a multilayer film according to [1],
Including melt coextrusion of a molten resin corresponding to the skin layer and the core layer from a die,
The die has a plurality of resin inflow ports into which molten resin corresponding to the skin layer and the core layer flows, and the molten resin corresponding to the skin layer and the core layer from the resin inflow flows. A plurality of resin flow paths, a resin merge section where the plurality of resin flow paths merge, a merge resin flow path where the molten resin merged in the resin merge section flows, and the molten resin flowing through the merge resin flow path A resin discharge port for discharging the film into a film,
The method for producing a multilayer film, wherein an average circulation time of the molten resin from a junction of the molten resin in the resin junction to the resin discharge port is 2 seconds or more.
[5] A method for producing a multilayer film according to [3],
The die has a plurality of resin inflow ports into which molten resin corresponding to the skin layer and the core layer flows, and the molten resin corresponding to the skin layer and the core layer from the resin inflow flows. A plurality of resin flow paths, a resin merge section where the plurality of resin flow paths merge, a merge resin flow path where the molten resin merged in the resin merge section flows, and the molten resin flowing through the merge resin flow path A resin discharge port for discharging the film into a film,
The method for producing a multilayer film, wherein an average circulation time of the molten resin from a junction of the molten resin in the resin junction to the resin discharge port is 2 seconds or more.
[6] A method for producing a multilayer film according to any one of [3] to [5],
The manufacturing method of the multilayer film whose viscosity of the molten resin corresponding to the said core layer is 550 Pa.s or less in the said die | dye.
[7] A multilayer film comprising two or more skin layers and one or more core layers provided between the skin layers, the film being formed by melt-extruding a molten resin, A method for producing a retardation film, comprising stretching a multilayer film in which the number of linear irregularities having a width of 300 μm or more and 1000 μm or less and a height of 10 nm or more and 1000 nm or less is 2 or less per 1400 mm width of the multilayer film Because
The manufacturing method of retardation film including extending | stretching the multilayer film manufactured by the manufacturing method as described in any one of [3]-[6].

According to the multilayer film of the present invention, a high-quality retardation film with suppressed retardation unevenness can be produced.
According to the retardation film of the present invention, a high-quality retardation film in which occurrence of retardation unevenness is suppressed can be realized.
According to the method for producing a multilayer film of the present invention, a multilayer film capable of producing a high-quality retardation film with suppressed retardation unevenness can be produced.
According to the method for producing a retardation film of the present invention, it is possible to produce a high-quality retardation film in which the occurrence of retardation unevenness is suppressed.

FIG. 1 is a cross-sectional view schematically showing an example of a multilayer film. FIG. 2 is a cross-sectional view schematically showing another example of the multilayer film. FIG. 3 is a schematic diagram showing an outline of a multilayer film manufacturing apparatus according to an embodiment of the present invention. FIG. 4 is a cross-sectional view schematically showing a cross section of the polymer filter 201 schematically shown in FIG. 3 taken along a plane perpendicular to the inner bottom surface. FIG. 5 is a cross-sectional view schematically showing a part of a cross section of the polymer filter shown in FIG. FIG. 6 is a cross-sectional view schematically showing another example of the polymer filter. FIG. 7 is a cross-sectional view schematically showing a part of the cross section of the polymer filter shown in FIG. FIG. 8 is a cross-sectional view schematically showing a cross section of the die 301 schematically shown in FIG. 3 taken along a plane perpendicular to the width direction of the die 301. FIG. 9 is a cross-sectional view schematically showing an enlarged part of the cross section of the die 301 shown in FIG. FIG. 10 is a cross-sectional view for explaining the flow of the molten resin Rc when the polymer filter shown in FIG. 4 is used.

  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 their equivalents are described below. It can be implemented with any change in the range.

[1. Overview〕
The multilayer film of the present invention is a multilayer film comprising a core layer and skin layers disposed on both sides of the core layer, and formed by melt extrusion of a molten resin, the core layer and the skin layer The number of the linear unevenness | corrugation of the predetermined magnitude | size in the interface with is small, or it is a multilayer film which is zero. By stretching the multilayer film of the present invention, a high-quality retardation film with suppressed retardation unevenness can be produced. Hereinafter, the relationship between the linear unevenness and the phase difference unevenness will be described by way of example.

1 and 2 are both examples of the multilayer film of the present invention, and include a single core layer and two skin layers arranged on each side of the core layer. It is sectional drawing which shows typically the multilayer film shape | molded by melt extrusion.
A multilayer film 10 shown in FIG. 1 includes a core layer 12 and skin layers 11 and 13 provided in contact with the core layer 12 in the vertical direction in the figure. In the core layer 12, linear irregularities 14 are formed at the interface between the core layer 12 and the skin layer 13 by the depression of the core layer 12. Further, a linear unevenness 15 is formed on the upper surface of the skin layer 13 in the figure.

  According to the recognition of those skilled in the art, in the extruded multilayer film 10, if the linear irregularities 15 on the surface of the skin layer 13 are sufficiently small, that is, a multilayer film in which all layers are flat is obtained. It was thought that it was. Therefore, it is considered that retardation unevenness does not occur in the retardation film produced by stretching the multilayer film 10 having a sufficiently small linear unevenness 15 on the surface of the skin layer 13. Separately, there has been no investigation of defects at the interface between the core layer and the skin layer. However, when the retardation film is produced by stretching the multilayer film 10 and expressing a large in-plane retardation in the core layer 12 according to the study of the present inventors, the core layer 12 caused by the linear irregularities 14 It has been found that thickness unevenness is a major cause of in-plane retardation unevenness in a stretched film.

  The multilayer film 20 shown in FIG. 2 includes a core layer 22 and skin layers 21 and 23 provided in contact with the upper and lower sides of the core layer 22 in the figure, but the interface between the core layer 22 and the skin layers 21 and 23. The occurrence of linear unevenness at is suppressed, and there is no linear unevenness at the interface. For this reason, the retardation film produced by stretching the multilayer film 20 does not cause retardation unevenness caused by linear irregularities at least at the interface between the core layer and the skin layer. In addition, even if the linear unevenness 24 is formed on the skin layer 23 as shown in FIG. 2, when the linear unevenness 24 is sufficiently small or when the multilayer film 10 is stretched, the skin layer 23. In the case where the in-plane retardation expressed in (2) is sufficiently small, it is possible to prevent the retardation unevenness from occurring in the retardation film produced by stretching the multilayer film 20. In the multilayer film 20, it is preferable that the number of linear irregularities is small or zero not only on the interface between the core layer and the skin layer but also on the surfaces of the skin layers 21 and 22.

[2. (Structure of multilayer film)
The multilayer film of the present invention is a multilayer film that includes a core layer and skin layers disposed on both sides of the core layer, and is formed by melt extrusion of a molten resin. Therefore, the multilayer film of the present invention includes a skin layer, a core layer, and a skin layer in this order. Further, both the skin layer and the core layer are layers formed of a resin. Furthermore, the multilayer film of the present invention may include layers other than the skin layer and the core layer.

  The multilayer film of the present invention includes a single core layer and two skin layers disposed on both sides of the single core layer, and the two skin layers are melted in the same manner. It is formed by melt extrusion of a resin, that is, it has a so-called two-type, three-layer structure, ease of manufacturing, and the resulting multilayer film and the curl of the retardation film obtained from the film It is preferable from the viewpoint of reduction. However, the multilayer film of the present invention is not limited to this, and may be a film having two or more core layers. For example, the multilayer film of the present invention may have a layer structure of two types and five layers such as skin layer-core layer-skin layer-core layer-skin layer. In addition, a plurality of layers having different materials may exist inside the core layer. For example, in the multilayer film of the present invention, the core layer may be composed of a plurality of layers C1 and C2, and may have a layer structure of skin layer-C1 layer-C2 layer-skin layer.

[2-1. (Core layer of multilayer film)
In the multilayer film of the present invention, the number of linear irregularities having a width of 300 μm or more and 1000 μm or less and a height of 10 nm or more and 1000 nm or less at the interface between the core layer and the skin layer is 2 or less per 1400 mm width of the multilayer film. Preferably, it is 1 or less, more preferably 0. By reducing the number of linear irregularities of the above-mentioned size at the interface between the core layer and the skin layer, linear shapes that may cause retardation unevenness in the core layer of the retardation film obtained by stretching the multilayer film of the present invention Since the number of irregularities can be reduced or the size of the linear irregularities can be reduced, it is possible to suppress phase difference unevenness. Here, the “width” of the linear irregularities is the width in the direction perpendicular to the melt extrusion direction in the plane of the film, and the “height” of the linear irregularities is the height in the thickness direction of the film. is there.

  The linear irregularities may be formed in a concave shape on the core layer (that is, formed in a groove shape on the core layer), or may be formed in a convex shape on the core layer (that is, the core layer). In some cases, it is formed in a mountain range above. In the case of a concave shape, the depth from the flat part of the reference core layer to the deepest part of the concave shape corresponds to the “height” of the linear unevenness, and in the case of a convex shape, the reference core layer The height from the flat part to the highest part of the convex shape corresponds to the “height” of the linear unevenness.

  The number of linear irregularities in the multilayer film can be counted by observing the cross section of the multilayer film with a microscope. Here, for example, it is not practical to perform microscopic observation over the entire width of a multilayer film having a wide width of 1400 mm, for example, so that the multilayer film is irradiated with light and the transmitted light is projected onto a screen, resulting in defects. The method of observing the part of the multilayer film corresponding to the part which has produced the defect after specifying the location is preferable.

  Specifically, the number of linear irregularities at the interface between the core layer and the skin layer of the multilayer film defined in the present invention can be counted as follows. That is, the multilayer film is irradiated with light, the transmitted light is projected onto the screen, and the brightness of the transmitted light projected on the screen is observed over the entire width along the direction corresponding to the width direction of the multilayer film. A linear portion that is brighter or darker than the surroundings is specified. A portion of the multilayer film corresponding to the linear portion on the screen is cut out to a size of about 3 cm square, and the surfaces of both sides of the film are observed using a microscope, on the interface between the core layer and the skin layer. The depth and height of the linear unevenness and the width thereof are measured. As a microscope for observation, for example, a three-dimensional surface structure analysis microscope (manufactured by Zygo) can be used.

  According to the counting method, in general, all linear irregularities having a width of 300 μm or more and 1000 μm or less and a height of 10 nm or more and 1000 nm or less at the interface between the core layer and the skin layer can be detected. On the other hand, as for the linear unevenness on the surface of the skin layer, the linear unevenness having a width of 300 μm to 1000 μm and a height of 10 nm to 1000 nm may not be detected. However, according to the study by the present inventor, the linear unevenness on the surface of the skin layer that is not detected by the counting method is unlikely to cause uneven retardation when the multilayer film is stretched to obtain a retardation film. Therefore, the above-described counting method can accurately detect the linear unevenness that causes the retardation unevenness of the retardation film.

  The core layer of the multilayer film exhibits a retardation when the multilayer film is stretched. Since the core layer is designed to express a retardation when stretched in this way, if the core layer has a linear unevenness of a predetermined size, the retardation unevenness is caused by the linear unevenness. The problem of occurring has arisen. In the multilayer film of the present invention, since the number of linear irregularities of a predetermined size of the core layer is not more than a predetermined value, the development of retardation unevenness after stretching is suppressed.

  How much retardation is developed in the core layer when the multilayer film of the present invention is stretched depends on the optical properties required for the retardation film produced by stretching the multilayer film of the present invention. It is not uniform. However, from the viewpoint of remarkably exhibiting the effects of the present invention, it is preferable that a large retardation is developed in the core layer by stretching. Specifically, when the stretching temperature is appropriately selected according to the glass transition temperature of the resin forming the core layer, and the multilayer film of the present invention is stretched in the width direction at a stretching ratio of 3 times, for example, The absolute value of the in-plane retardation that can be developed in the core layer is preferably 10 nm or more, more preferably 20 nm or more, and particularly preferably 30 nm or more. In addition, although there is no restriction | limiting in particular in an upper limit, Usually, it is 550 nm or less, Preferably it is 500 nm or less, More preferably, it is 450 nm or less.

  Further, when paying attention to the relationship between the core layer and the skin layer when the multilayer film is stretched, the absolute value of the in-plane retardation expressed in the core layer when the multilayer film of the present invention is stretched is the skin layer. It is preferably larger than the absolute value of the in-plane retardation that develops. This is to prevent the uneven retardation after stretching by stably preventing the formation of the linear irregularities in the core layer. Furthermore, from the viewpoint of more effectively suppressing retardation unevenness after stretching, the absolute value of the in-plane retardation developed in the core layer and the in-plane retardation developed in the skin layer when the multilayer film is stretched. It is preferable that the difference from the absolute value is large. Specifically, when the multilayer film of the present invention is stretched in the width direction at a stretching ratio of 3 times at the stretching temperature set in conformity with the glass transition temperature of the resin forming the core layer described above, the core The difference between the absolute value of the in-plane retardation expressed in the layer and the absolute value of the in-plane retardation expressed in the skin layer is preferably 10 nm or more, more preferably 20 nm or more, and particularly preferably 30 nm or more. In addition, although there is no restriction | limiting in particular in an upper limit, Usually, it is 550 nm or less, Preferably it is 500 nm or less, More preferably, it is 450 nm or less.

  The in-plane retardation of each layer is | nx−ny | × d (where nx represents a refractive index in a direction perpendicular to the thickness direction (in-plane direction) and giving the maximum refractive index, and ny represents It is a value expressed by a refractive index in a direction perpendicular to the thickness direction (in-plane direction) and orthogonal to the nx direction, and d indicates the film thickness of each layer. The retardation in the thickness direction of each layer is {| nx + ny | / 2−nz} × d (where nx is a direction perpendicular to the thickness direction (in-plane direction) and gives the maximum refractive index). Ny represents the refractive index in the direction perpendicular to the thickness direction (in-plane direction) and orthogonal to the nx direction, nz represents the refractive index in the thickness direction, and d represents the film thickness. )). The retardation is evaluated for light having a wavelength of 550 nm. Each retardation can be measured using a commercially available automatic birefringence meter. A. It can be measured with a spectroscopic ellipsometer M-2000U manufactured by Woollam. Unless otherwise specified, the retardation measurement wavelength is 550 nm.

As the resin for forming the core layer, a thermoplastic resin containing at least one polymer (polymer) and other components as required is usually used.
Examples of the polymer contained in the resin forming the core layer are: polystyrene polymer; olefin polymer such as polyethylene and polypropylene; polyester polymer such as polyethylene terephthalate and polybutylene terephthalate; polyarylene sulfide heavy such as polyphenylene sulfide Polymer; Polyvinyl alcohol polymer; Polycarbonate polymer; Polyarylate polymer; Cellulose ester polymer; Polyether sulfone polymer; Polysulfone polymer; Polyallyl sulfone polymer; Polyvinyl chloride polymer; Norbornene polymer; Polymers: Polyarylene ether polymers such as polyphenylene ether polymers. In addition, the polymer contained in resin which forms a core layer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  Among the above examples, a polystyrene polymer is preferable from the viewpoint of retardation development. The polystyrene polymer is a polymer having a structure derived from an aromatic vinyl monomer in a part or all of repeating units. Specific examples include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-chlorostyrene, p-nitrostyrene, p-aminostyrene, p-carboxystyrene, p- Homopolymers of aromatic vinyl monomers such as phenylstyrene, p-methoxystyrene, pt-butoxystyrene; aromatic vinyl monomers and ethylene, propylene, butene, butadiene, isoprene, methacrylonitrile, acrylonitrile , Α-chloroacrylonitrile, methyl methacrylate, methyl acrylate, ethyl methacrylate, ethyl acrylate, methacrylic acid, acrylic acid, maleic anhydride, maleimide, phenylmaleimide, vinyl acetate, vinyl chloride and other aromatic vinyl monomers Copolymerization with other ethylenically unsaturated monomers Examples include coalescence. Of these, styrene homopolymers and copolymers of styrene and maleic anhydride are preferred. In the present specification, the term “monomer” includes not only a single monomer but also a state in which a plurality of monomers are mixed, that is, a so-called monomer mixture. To do.

The weight average molecular weight of the polymer contained in the resin forming the core layer is usually 10,000 or more, preferably 15,000 or more, and usually 300,000 or less, preferably 250,000 or less.
The weight average molecular weight can be measured as a value in terms of standard polyisoprene by, for example, gel permeation chromatography using cyclohexane as a solvent.

The resin forming the core layer may contain an additive as necessary. Examples of additives include lubricants; layered crystal compounds; inorganic fine particles; stabilizers such as antioxidants, heat stabilizers, light stabilizers, weathering stabilizers, ultraviolet absorbers, near infrared absorbers, infrared absorbers; Plasticizers: coloring agents such as dyes and pigments; antistatic agents; In addition, 1 type may be used for an additive and 2 or more types may be used for them in arbitrary ratios.
The amount of the additive can be appropriately determined within a range that does not significantly impair the effects of the present invention, and is, for example, a range in which the total light transmittance of the retardation film can be maintained at 85% or more.

  The glass transition temperature of the resin forming the core layer is preferably 110 ° C. or higher, preferably 200 ° C. or lower, more preferably 150 ° C. or lower.

  The thickness of the core layer of the multilayer film is usually 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and usually 300 μm or less, preferably 200 μm or less, more preferably 100 μm or less. When the multilayer film of the present invention has a plurality of core layers, the preferred thickness range is a preferred thickness for each layer.

[2-2. (Skin layer of multilayer film)
As the resin for forming the skin layer, a thermoplastic resin containing at least one type of polymer (polymer) and other components as required can be usually used.
Resin for forming a skin layer in order to improve the strength and durability of the multilayer film and retardation film of the present invention, and from the viewpoint of keeping the retardation expressed in the skin layer in the multilayer film within the above preferred range. Preferably contains a methacrylic acid ester polymer as a polymer, and more preferably contains a methacrylic acid ester polymer (I) described later.

The methacrylic acid ester polymer (I) is a polymer having a methacrylic acid ester (M1) as a main component. Examples of the methacrylic acid ester polymer (A) include a homopolymer of methacrylic acid ester and a copolymer of methacrylic acid ester and other monomers.
As the methacrylic acid ester (M1), alkyl methacrylate is usually used. Examples of other monomers that are copolymerized with a methacrylic acid ester when used as a copolymer include acrylic acid esters, aromatic vinyl compounds, and vinylcyan compounds.

  The methacrylic acid ester polymer (I) is an alkyl methacrylate having an alkyl group having 1 to 4 carbon atoms, an acrylate ester (M2), and a compound having a vinyl group copolymerizable therewith (if necessary) ( A polymer obtained by polymerization of a monomer containing M3) is preferred.

Examples of the alkyl methacrylate include methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate and the like, and methyl methacrylate is particularly preferably used.
As the acrylic ester (M2), an alkyl acrylate is usually used, and the alkyl group may have about 1 to 8 carbon atoms. Examples include methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, and the like.
As the compound (M3) having a vinyl group that can be copolymerized with an alkyl methacrylate (M1) and / or an acrylic ester (M2), various monomers conventionally used in the field of methacrylic resins are used. Examples thereof include aromatic vinyl compounds such as styrene and vinylcyan compounds such as acrylonitrile.
Each of these monomers may be used alone or in combination of two or more at any ratio.

The methacrylic acid ester polymer (I) is 50% by weight to 100% by weight, more preferably 50% by weight to 99.9% by weight, still more preferably 50% by weight to 99.5% by weight. And 0% to 50% by weight of the acrylate ester (M2), more preferably 0.1% to 50% by weight, and still more preferably 0.5% to 50% by weight. A compound obtained by polymerizing a monomer composed of 0% by weight to 49% by weight of the compound (M3) having a vinyl group is preferable.
In addition, a methacrylic acid ester polymer (I) may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The weight average molecular weight of the methacrylic acid ester polymer (a) is usually 10,000 or more, preferably 15000 or more, more preferably 20000 or more, and usually 300000 or less, preferably 250,000 or less, more preferably 200000 or less.

  The polymerization method of the methacrylic acid ester polymer (a) is not particularly limited, and can be synthesized by a general polymerization method such as suspension polymerization, emulsion polymerization, bulk polymerization and the like. Moreover, in order to obtain a suitable glass transition temperature or to obtain a viscosity showing a moldability to a suitable multilayer film, it is preferable to use a chain transfer agent during polymerization. What is necessary is just to determine the quantity of a chain transfer agent suitably according to the kind and composition of a monomer.

  The resin forming the skin layer may contain particles for the purpose of improving the handling properties of the multilayer film and the retardation film of the present invention. For example, when the resin forming the skin layer contains a methacrylic acid ester polymer (a), it is preferable that the resin further contains particles (b) having an outer layer made of a methacrylic polymer and an inner layer made of rubber having a crosslinked structure. The phrase “having” the particle (b) includes an outer layer and an inner layer does not mean that the particle (b) is composed of only the outer layer and the inner layer, and may further include other layers. For example, as described later, an inner core layer can be further provided inside the inner layer.

The methacrylic polymer constituting the outer layer of the particles (b) is a polymer having a methacrylic acid or methacrylic ester structure as a repeating unit, preferably the polymer constituting the methacrylic ester polymer (a) The same thing is mentioned, More preferably, the said methacrylic acid ester (M1) 50 weight%-100 weight%, the said acrylic acid ester (M2) 0 weight%-50 weight%, and the compound which has the said vinyl group ( M3) What is obtained by polymerizing a monomer composition (ii) composed of 0 to 49% by weight is mentioned.
In addition, the methacryl polymer which comprises the outer layer of particle | grains (b) may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  As the rubber having a crosslinked structure constituting the inner layer of the particles (b), rubbers made of various elastic copolymers can be used. Moreover, the rubber | gum which comprises the inner layer of particle | grain (b) may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Especially, as rubber | gum which comprises the inner layer of particle | grain (b), Preferably, the alkyl acrylate monomer (m1) is 50 weight%-99.9 weight%, and a carbon-carbon double bond is 1 per molecule. Monofunctional monomer (m2) having 0 to 49.9 wt%, and polyfunctional monomer (m3) having at least two carbon-carbon double bonds in one molecule A copolymer (i-1) with 10 weight% is mentioned.

  As said alkyl acrylate (m1), the C1-C8 thing of an alkyl group is mentioned, for example. Of these, alkyl groups having 4 to 8 carbon atoms such as butyl acrylate and 2-ethylhexyl acrylate are preferable. In addition, alkyl acrylate (m1) may be used individually by 1 type, and may be used combining 2 or more types by arbitrary ratios.

  Examples of the monofunctional compound (m2) having one carbon-carbon double bond in one molecule used as necessary include, for example, methacrylic acid esters such as methyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, Preferred examples include aromatic vinyl compounds such as styrene and vinylcyan compounds such as acrylonitrile. In addition, a monofunctional compound (m2) may be used individually by 1 type, and may be used combining 2 or more types by arbitrary ratios.

  Examples of the polyfunctional compound (m3) having at least two carbon-carbon double bonds in one molecule include unsaturated carboxylic acid diesters of glycols such as ethylene glycol dimethacrylate and butanediol dimethacrylate, and allyl acrylate. , Alkenyl esters of unsaturated carboxylic acids such as allyl methacrylate and allyl cinnamate, polyalkenyl esters of polybasic acids such as diallyl phthalate, diallyl maleate, triallyl cyanurate and triallyl isocyanurate, trimethylolpropane tri Examples thereof include unsaturated carboxylic acid esters of polyhydric alcohols such as acrylate, divinylbenzene, and the like. Of these, alkenyl esters of unsaturated carboxylic acids and polyalkenyl esters of polybasic acids are preferred. In addition, a polyfunctional compound (m3) may be used individually by 1 type, and may be used combining 2 or more types by arbitrary ratios. Moreover, it is preferable that a polyfunctional compound (m3) has crosslinkability.

  The particles (b) preferably contain 10 to 400 parts by weight of the monomer composition (ii) in the presence of 100 parts by weight of the core particles (b-1) having at least a surface layer of rubber containing the crosslinked structure. It can be prepared by polymerization. The core particles (B-1) may all be formed from rubber containing the crosslinked structure. Specifically, in the presence of 100 parts by weight of the core particles (B-1), the monomer composition (ii) is usually 10 to 400 parts by weight, preferably 20 to 400 parts by weight, more preferably 20 to 200 parts by weight. By polymerizing parts by weight, at least one layer of the polymer layer of the monomer composition (ii) can be bonded to the surface of the core particle (B-1). When the amount of the monomer composition (ii) is within the above range, the core particles (B-1) are hardly aggregated, and the transparency when a retardation film is obtained is improved. If the amount of the monomer composition (ii) is out of the above range, the fluidity of the entire composition of the methacrylic ester polymer in which the particles (b) are dispersed is lowered, and it is difficult to form a skin layer. There is a risk. In this polymerization, the reaction conditions can be adjusted so that the average particle diameter of the inner layer of the particles (b) is 0.05 μm or more and 0.3 μm or less.

  For example, the particles (b) may be obtained by polymerizing the monomer components (m1) to (m3) constituting the copolymer (i-1) by at least one-stage reaction by an emulsion polymerization method or the like. A core particle (B-1) having at least the coalescence (I-1) on its surface layer is obtained, and the monomer composition (ii) is obtained by emulsion polymerization in the presence of the core particle (B-1). It can be produced by polymerizing in at least one stage reaction. By such a multi-stage polymerization, the monomer composition (ii) is graft-copolymerized to the core particle (b-1) to produce particles (b) that are cross-linked elastic copolymers having graft chains. be able to. That is, the particles (b) become a graft copolymer having a multilayer structure containing alkyl acrylate as a main component of rubber.

  The particles (b) further have an inner core layer inside the inner layer, and the inner core layer contains 70% to 100% by weight of a methacrylic acid ester (M4) and 0% by weight of a compound (M5) having a vinyl group. More preferably, it is composed of 30% by weight of (co) polymer (i-2). This is because when the particle (b) has a structure of three or more layers, the elastic modulus, surface smoothness, surface hardness and the like of the retardation film are improved. The particles (b) having a structure of three or more layers are prepared by, for example, firstly polymerizing the monomer constituting the (co) polymer (i-2), and then in the presence of the resulting polymer. It is obtained by polymerizing the monomer constituting the copolymer (i-1) and polymerizing the monomer composition (ii) in the presence of the obtained core particle (B-1). be able to.

  As said methacrylic acid ester (M4), alkyl methacrylate, especially methyl methacrylate is advantageous. Examples of the compound (M5) having a vinyl group used as necessary include acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate and cyclohexyl acrylate; aromatic vinyl compounds such as styrene; acrylonitrile and the like. And vinyl cyanide compounds. The vinyl group-containing compound (M5) is preferably a copolymerizable cross-linkable substance. As such a substance, the same compound as the polyfunctional compound (m3) which is a component constituting the copolymer (i-1) can be used. In addition, as for the methacrylic acid ester (M4) and the compound (M5) having a vinyl group, one type may be used, or two or more types may be used in combination at an arbitrary ratio.

The particles having the three-layer structure as described above are disclosed in, for example, Japanese Patent Publication No. 55-27576 (US Pat. No. 3,793,402). In particular, the one described in Example 3 of the publication is one of the preferred compositions.
In addition, when the particles (b) are particles having a multilayer structure composed of at least three layers as described above, the monomer composition (ii) to be grafted as the outer layer includes the copolymer (i-1) and the (( It is preferable to use 10 to 400 parts by weight with respect to 100 parts by weight of the total of (co) polymer (i-2).

  The average particle size of the inner layer of the particles (b) is usually 0.05 μm or more, usually 0.3 μm or less, preferably 0.2 μm or less. When the average particle size of the inner layer of the particles (b) is within this range, the film-forming property of the skin layer is stabilized, and the flexibility and handleability of the multilayer film and the retardation film itself are excellent. When the average particle size of the inner layer of the particles (b) is too small, the flexibility of the multilayer film and the retardation film is impaired, and the handleability tends to decrease. On the other hand, when the average particle size of the inner layer of the particles (b) is too large, the surface smoothness is lowered, and the transparency of the retardation film may be impaired. The average particle diameter of the particles (b) including the outer layer made of a methacrylic polymer is preferably 0.07 μm or more, preferably 0.1 μm or more, and usually 0.5 μm or less, preferably 0.45 μm or less. It is.

  The average particle diameter of the inner layer of the particles (b) can be set to an appropriate value by adjusting the addition amount of the emulsifier and the charged amount of the monomer in the emulsion polymerization. The average particle size of the inner layer of the particles (b) is obtained by mixing the particles (b) with a methacrylic polymer to form a film, staining the cross section with ruthenium oxide, and observing the diameter of the stained particles with an electron microscope. Can be obtained. That is, the particles (b) are not dyed by mixing the methacrylic polymer of the outer layer with the methacrylic polymer to be mixed, and only the inner layer made of rubber having a crosslinked structure is dyed. Thus, the particle diameter of the inner layer of the particles (b) can be obtained.

  When the resin forming the skin layer contains the methacrylic acid ester polymer (ii) and the particles (b), and the total amount of the resin forming the skin layer is 100% by weight, the amount of the particles (b) is It is usually 1% by weight or more, preferably 5% by weight or more, more preferably 10% by weight or more, and usually 80% by weight or less, preferably 35% by weight or less, more preferably 25% by weight or less. When the amount of the particles (b) is in such a range, the retardation film will not become brittle, and the film-forming property of the skin layer can be improved or the multilayer film can be stretched without breaking. it can. If the amount of particles (b) is too small, it may be difficult to form a film, and if the amount is too large, the transparency and surface hardness of the retardation film may be lost. Further, the proportion of the methacrylic acid ester polymer (I) is usually 20 to 99% by weight, but when it contains other additives other than the methacrylic acid ester polymer (I) and particles (B), the proportion Can be adjusted as appropriate.

  The resin forming the skin layer may contain an additive. Examples of the additive include an ultraviolet absorber, an organic dye, a pigment, an inorganic dye, an antioxidant, an antistatic agent, and a surfactant. In addition, 1 type may be used for an additive and it may use it combining 2 or more types by arbitrary ratios. Among these, an ultraviolet absorber is preferably used in terms of giving better weather resistance.

Examples of the UV absorber include commonly used benzotriazole UV absorbers, 2-hydroxybenzophenone UV absorbers, and salicylic acid phenyl ester UV absorbers. Specific examples of the benzotriazole ultraviolet absorber include 2,2′-methylenebis [4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol]. 2- (5-methyl-2-hydroxyphenyl) -2H-benzotriazole, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2- ( 3,5-di-tert-butyl-2-hydroxyphenyl) -2H-benzotriazole, 2- (3-tert-butyl-5-methyl-2-hydroxyphenyl) -5-chloro-2H-benzotriazole, 2 -(3,5-di-tert-butyl-2-hydroxyphenyl) -5-chloro-2H-benzotriazole, 2- (3,5-di-tert-a Mil-2-hydroxyphenyl) -2H-benzotriazole, 2- (2′-hydroxy-5′-tert-octylphenyl) -2H-benzotriazole, and the like. Specific examples of the 2-hydroxybenzophenone ultraviolet absorber include 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octyloxybenzophenone, 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxy. -4'-chlorobenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone and the like. Furthermore, specific examples of salicylic acid phenyl ester ultraviolet absorbers include p-tert-butylphenyl salicylic acid ester and p-octylphenyl salicylic acid ester.
In addition, a ultraviolet absorber may use one type and may use it combining two or more types by arbitrary ratios.
When an ultraviolet absorber is blended, the amount is usually 0.1 parts by weight or more, preferably 0, based on, for example, 100 parts by weight of the total of the methacrylic acid ester polymer (a) and the particles (b). .3 parts by weight or more, and preferably 2 parts by weight or less.

  The glass transition temperature of the resin forming the skin layer is preferably 40 ° C. or higher, and more preferably 60 ° C. or higher. When the glass transition temperature of the resin forming the skin layer is less than 40 ° C., the heat resistance of the multilayer film and the retardation film of the present invention may be lowered. The glass transition temperature of the resin forming the skin layer is, for example, when a composition containing the methacrylic acid ester polymer (A) is used as the resin forming the skin layer, the other amount copolymerized with the methacrylic acid ester. It can be set as appropriate by changing the type and amount of the body. In addition, since the glass transition temperature of the homopolymer of methyl methacrylate is about 106 ° C., when methyl methacrylate is used as the methacrylic ester, the glass transition temperature of the methacrylic ester polymer (I) is usually 106 ° C. or lower. It becomes.

  Furthermore, when the glass transition temperature of the resin forming the core layer is Tg (c) and the glass transition temperature of the resin forming the skin layer is Tg (s), Tg (s) is lower than Tg (c). It is preferable that the relationship of Tg (c)> Tg (s) + 5 ° C. is satisfied. On the other hand, the upper limit of the difference between Tg (c) and Tg (s) is usually less than 40 ° C. and preferably less than 30 ° C. That is, it is usually preferable that Tg (c) <Tg (s) + 40 ° C. and Tg (c) <Tg (s) + 30 ° C. By satisfying such a relationship, when the multilayer film is stretched, the core layer is effectively provided with optical anisotropy, and a good retardation film can be obtained. In addition, although resin which forms a skin layer may show two or more glass transition temperatures, the value of the higher glass transition temperature is set to said Tg (s) in that case.

The melt viscosity of the resin forming the skin layer measured at a temperature of 250 ° C. and a shear rate of 150 sec ⁻¹ is preferably 400 Pa · s or more, more preferably 450 Pa · s or more, preferably 1000 Pa · s or less, more preferably 900 or less. By having such a melt viscosity, breakage during stretching is less likely to occur, and the strength during stretching and use of the product can be further improved.

  The thickness of the skin layer of the multilayer film is usually 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and usually 400 μm or less, preferably 200 μm or less, more preferably 100 μm or less. The multilayer film of the present invention has a plurality of skin layers, and the preferred thickness range is a preferred thickness for each layer.

The multilayer film of the present invention comprises two or more skin layers, but the composition and dimensions of the two or more skin layers may be the same or different.
Two or more skin layers are provided in the multilayer film, and preferably two skin layers are provided in contact with the front and back of one core layer. The skin layer is usually provided on the outermost layer on the front and back of the multilayer film, but is not necessarily limited thereto. For example, the multilayer film may have another layer on the outer layer of the skin layer. Moreover, when there are two or more core layers, a skin layer may further exist between them.

  In the multilayer film of the present invention, the number of linear irregularities in the skin layer is preferably small. As described above, the multilayer film of the present invention is capable of reducing the retardation unevenness in the retardation film after stretching because the occurrence of linear irregularities in the core layer is suppressed. This is for further reduction. Specifically, the number of linear irregularities having a width in the skin layer of the multilayer film of the present invention of usually 300 μm or more and 1000 μm or less and a height of 10 nm or more and 1000 nm or less is preferably 2 or less, more preferably 1 The number is particularly preferably 0.

[2-3. Other layers of multilayer film]
The multilayer film of the present invention may include other arbitrary layers in addition to the core layer and the skin layer as long as the effects of the present invention are not significantly impaired. Examples of such an optional layer include a hard coat layer, an antireflection layer, and a diffusion layer.

[3. (Method for producing multilayer film)
The multilayer film of the present invention is manufactured by forming into a film shape by melt-extruding a molten resin corresponding to each layer constituting the multilayer film. Therefore, for example, when manufacturing a multilayer film including a skin layer, a core layer, and a skin layer in this order, the resin that forms the skin layer, the core layer, and the skin layer is melted, and the molten resins are laminated in the order described above. In this way, a multilayer film having a three-layer structure can be produced by coextrusion. Usually, a die is used for co-extrusion of the molten resin, and a multilayer film is produced by melt-coextrusion of the molten resin corresponding to the skin layer and the core layer from the die.

  In the production of the multilayer film of the present invention, the following means (1) and / or (2) can be taken in order to reduce the linear unevenness at the interface between the core layer and the skin layer to a predetermined number or less. In addition to the means (1) and / or (2), it is preferable to take one or more of the following means (3) to (5).

(1) The molten resin corresponding to the core layer is supplied to the die after being filtered by a polymer filter with reduced residence in the casing.
One of the causes of the occurrence of linear irregularities in the core layer is considered to be that foreign substances present in the molten resin adhere to the inner surface of the die. Therefore, by making it difficult for the molten resin corresponding to the core layer to stay in the polymer filter, it is possible to prevent the molten resin from agglomerating and generating foreign matters during the retention, and to form linear irregularities in the core layer. To prevent.

(2) The average flow time for flowing through the merged resin flow path until the molten resin merged at the resin merge portion in the die is discharged from the resin discharge port is increased.
It is considered that the foreign matter in the molten resin, which is one of the causes of the linear unevenness in the core layer, adheres to the upstream side of the resin joining portion where the molten resin corresponding to the skin layer and the core layer joins in the die. Therefore, it is considered that the linear unevenness in the core layer is formed upstream of the resin joining portion in the die. Therefore, by extending the time for flowing through the merged resin flow path downstream from the resin merged portion, the molten resin corresponding to the core layer is sandwiched at a high pressure for a long time by the molten resin corresponding to the skin layer. As a result, the linear irregularities formed upstream from the merging channel are flattened by the pressure applied from the surroundings for a long time in the downstream merging channel, so that the linear irregularities are formed in the core layer. Can be prevented.

(3) The viscosity of the molten resin corresponding to the core layer that circulates the die is lowered.
If the viscosity is low, the linear irregularities once formed are also easily flattened in the merging channel portion, and the linear irregularities can be prevented from being formed in the core layer. The viscosity of the molten resin can be lowered, for example, by increasing the temperature in the die or increasing the shear rate of the molten resin in the die.

(4) The surface of the resin flow channel upstream of the resin joining portion where the molten resin corresponding to the core layer flows is formed of the same material, and the surface roughness of the resin flow channel is reduced.
As one of the causes of the linear unevenness in the core layer, it is conceivable that the molten resin stays in the resin flow channel upstream of the resin joining portion in the die. When the molten resin stays, foreign matter is generated as described above. Therefore, by making the material of the surface of the resin flow channel upstream of the resin joining portion the same and reducing the surface roughness, the molten resin is prevented from staying, and linear irregularities are formed in the core layer. Can be prevented.

(5) To reduce the scratches at the downstream tip portion of the resin flow path where the molten resin corresponding to the core layer flows into the resin joining portion, and to reduce the number of scratches.
Since the scratch is considered to be one of the causes of the linear unevenness in the core layer, by reducing the size or reducing the number thereof, it is difficult to form the linear unevenness, the core layer It prevents the formation of linear irregularities on the surface.

  Hereinafter, a method for producing a multilayer film as an embodiment of the present invention will be described by taking as an example a multilayer film having a skin layer, a core layer and a skin layer in this order and having a laminated structure of two types and three layers. In the following description of the embodiment, when referring to “parallel” or “vertical”, an error is usually within ± 10 °, preferably within ± 5 °, more preferably within ± 3 °, unless otherwise specified. May be included.

  FIG. 3 is a schematic diagram showing an outline of a multilayer film manufacturing apparatus according to an embodiment of the present invention. As shown in FIG. 3, the manufacturing apparatus 1 of this embodiment includes an extruder 101 that is a resin supply device, a polymer filter 201, a die 301, and a die heater 401 as a temperature adjusting unit that controls the temperature of the die 301. With. In the manufacturing apparatus 1, the resin (Rc) corresponding to the core layer is sent from the extruder 101 as a molten resin Rc and supplied to the polymer filter 201 through the pipe X1. The molten resin Rc is filtered by the polymer filter 201 and supplied to the die 301 through the pipe X2. On the other hand, from another extruder (not shown), molten resins Rs1 and Rs2 corresponding to the skin layers are supplied to the die 301 via the pipes X3 and X4, respectively. The molten resins Rc, Rs1, and Rs2 are melt-coextruded from the die 301 as a film-like resin molded product F. The resin molded product F is subjected to an arbitrary operation such as cooling as necessary, and then a desired multilayer film is produced.

The extruder 101 is a device that supplies the molten resin Rc in a pressurized state to the inlet 254 of the polymer filter 201.
In the present embodiment, the flow rate of the molten resin Rc can be controlled by adjusting the pressure at which the extruder 101 pressurizes the molten resin Rc. From the viewpoint of preventing the formation of linear irregularities in the core layer of the multilayer film, the pressure at which the extruder 101 pressurizes the molten resin Rc is the same as that of the molten resin Rs1 and the molten resin Rs2 at the resin junction 340 in the die 301. The average flow time for flowing through the merged resin flow path 350 until the merged molten resin Rc is discharged from the resin discharge port 360 can be set to a desired time (see the description of FIG. 8 described later).

  FIG. 4 is a cross-sectional view schematically showing a cross section of the polymer filter 201 schematically shown in FIG. 3 taken along a plane perpendicular to the inner bottom surface. In the present embodiment, as illustrated in FIG. 4, a vertical state in which the bottom cover 204 is installed on a horizontal base will be described as an example. However, the polymer filter 201 may be installed horizontally or obliquely. It may be in the opposite direction (that is, the direction in which the lid portion is vertically downward and the bottom portion is vertically upward).

  As schematically shown in FIG. 4, the polymer filter 201 used in the present embodiment is a device that circulates the molten resin Rc and filters the molten resin Rc, and as a housing having a hollow portion 202 formed therein. Housing 203, a center pole 206 as a supporting column housed in the hollow portion 202 of the housing 203, and a plurality of filter elements 207 housed in the hollow portion 202 of the housing 203. The housing 203 includes a bottom cover 204 as a bottom portion and a case 205 having a lid portion 251 and a side wall portion 252. The hollow portion 202 in the housing 203 accommodates a center pole 206 as a support portion and a plurality of filter elements 207, and the molten resin Rc flowing through the hollow portion 202 is filtered by the filter element 207. .

  The bottom cover 204 is a flat plate-like member that is located in the lower part (downstream side) of the housing 203 and has a delivery port 241 that penetrates the front and back at the center. An upper surface (upstream side) 204A of the bottom cover 204 is formed in a flat shape. Therefore, a portion of the upper surface 204 </ b> A of the bottom cover 204 that is not covered by the case 205 and exposed to the hollow portion 202 constitutes the inner bottom surface 203 </ b> A of the housing 203.

  The center pole 206 is provided at the central portion of the bottom cover 204 so as to stand vertically to the inner bottom surface 203A. In the present embodiment, the center pole 206 is described as being formed integrally with the bottom cover 204, but the center pole 206 and the bottom cover 204 may be detachably provided. The center pole 206 has a portion (except the top portion) 261 where the filter element 207 is mounted formed in a polygonal column shape (for example, a hexagonal column shape). A hollow portion 262 that penetrates from the top portion to the bottom portion of the center pole 206 and communicates with the delivery port 241 is formed in the axial center portion of the center pole 206. Further, the portion 261 of the center pole 206 is formed with a discharge port 263 that connects the outside and the inside hollow portion 262 of the center pole 206. Therefore, in the present embodiment, the gap 264, the discharge port 263, and the hollow portion 262 formed between the center pole 206 and the filter element 207 function as a flow path through which the molten resin Rc flows, and are sent out from the filter element 7. The filtered molten resin Rc flows through the flow path including the gap 264, the discharge port 263, and the hollow portion 262, and is sent out of the polymer filter 201 from the outlet 241.

The filter element 207 is a disk-shaped filtering member, and a central hole 271 for mounting the filter element 207 to the center pole 206 is formed at the center thereof. Any filter element 207 can be used as long as it has a disk shape. In this embodiment, for example, a filter medium (not shown) is provided on both the front and back surfaces, and the molten resin Rc filtered by the filter medium is used. A leaf disk type filter element that feeds to the inner central hole 271 (that is, to the gap 264) through a flow path (not shown) in the filter element 207 is used.
Normally, the filter element 207 is attached to the center pole 6 so that a plurality of filter elements 207 are laminated. In this embodiment, the filter element 207 is attached to the center pole 206 using a seal member such as packing that seals between the filter elements 207 stacked at the inner edge 272 of the filter element 207. Specifically, the seal members (not shown) and the filter elements 207 are alternately assembled, and a desired number of filter elements 207 are mounted on the center pole 206, and a pressing disk 208 is assembled on the upper side thereof, and pressed from above. It is assumed that the two-speed 209 that also functions as a holding bolt is bolted to the top of the center pole 206 and assembled.

  The case 205 is a container in which a hollow portion 202 having a size capable of accommodating the center pole 206, the filter element 207, the pressing disk 208, and the two-speed 209 is formed, and includes the lid portion 251 and the side wall portion 252 as described above. In the present embodiment, the lid 251 and the side wall 252 are described as being integrally formed. However, the lid 251 and the side wall 252 may be detachably provided.

  The lid portion 251 is located on the upper portion (upstream side) of the housing 203, and is a portion located on the upper side (that is, opposite to the bottom cover 204) of the side wall portion 252 in the case 205. The shape and dimensions of the inner surface 251A of the lid 251 are such that the center pole 206, the filter element 207, the pressing disk 208, and the two-speed 209 accommodated in the hollow section 202 do not contact the inner surface 251A, and the pressing disk 208 and the two-speed 209 A gap 253 is formed between the inner surface 2051A and the inner surface 2051A. In addition, an inflow port 254 for supplying the molten resin Rc to the hollow portion 202 is formed in the central portion of the lid portion 251, and the molten resin Rc flowing from the inflow port 254 flows through the gap 253. Yes.

  The side wall portion 252 is located on the side of the housing 203 and is located between the lid portion 251 and the bottom cover 204. The shape and dimensions of the inner surface 252A of the side wall portion 252 are such that the center pole 206, the filter element 207, the pressing disk 208 and the two-speed 209 accommodated in the hollow portion 202 are not in contact with the inner surface 252A. A gap 255 is formed between 208 and the inner surface 252A. Therefore, the molten resin Rc flowing from the inlet 254 and flowing through the gap 253 flows through the gap 255 and is filtered by each filter element 207.

  The inner surface 252A is a cylindrical surface perpendicular to the inner bottom surface 203A except for the convex surface portion 252B formed at the lower end thereof. Therefore, a portion of the cylindrical surface perpendicular to the inner bottom surface 203 </ b> A of the inner surface 252 </ b> A of the side wall portion 252 constitutes the inner side surface 203 </ b> B of the housing 203. Of the inner surface 252A of the side wall portion 252, the convex surface portion 252B formed at the lower end thereof is located at the boundary between the inner bottom surface 203A and the inner side surface 203B of the housing 203, and is formed between the inner bottom surface 203A and the inner side surface 203B. The surface portion is formed so as to straddle the gap.

  The convex surface portion 252B has a convex shape toward the center side of the housing 203 with respect to the inner bottom surface 203A and the inner side surface 203B. In other words, the convex surface portion 252 </ b> B is a substantially surface-shaped portion that protrudes to the inside of the hollow portion 202. That is, the convex surface portion 252B is positioned above the inner bottom surface 203A (that is, the side closer to the lid portion 251) in the direction perpendicular to the inner bottom surface 203A, and in the cylindrical radial direction formed by the inner side surface 203B. It is located inside the inner side surface 203B (that is, the side closer to the center pole 206). By providing the convex surface portion 252B having such a shape, a corner portion (entrance corner portion) formed by the inner bottom surface 203A and the inner side surface 203B is filled, so to speak, the flow provided at the corner portion is filled. The road is chamfered. In other words, the flow path is formed in a tapered structure narrowed radially inward of the inner side surface 203B (center pole 206 side / X direction described later).

In the polymer filter 201 used in the present embodiment, the retention of the molten resin Rc can be suppressed by appropriately setting the dimensions of the convex surface portion 252B (see means (1)). The setting of the dimensions will be described with reference to FIG. FIG. 5 is a cross-sectional view schematically showing a part of a cross section of the polymer filter 201 shown in FIG. 4 cut along a plane perpendicular to the inner bottom surface 203A. The vicinity of the convex surface portion 252B in FIG. 4 is enlarged. FIG. In FIG. 5, the radial direction of the cylindrical shape formed by the inner side surface 203B is shown as the X direction, and the direction perpendicular to the inner bottom surface 203A is shown as the Y direction.
As shown in FIG. 5, d represents the distance (shortest distance) from the filter element 207 to the inner surface 203 </ b> B of the housing 203. D ₁ represents the distance in the radial direction X of the inner side surface 203B from the inner side surface 203B of the housing 203 to the point P where the inner bottom surface 203A of the housing 203 and the convex surface portion 252B intersect. D ₂ represents the distance in the direction Y perpendicular to the inner bottom surface 203A from the inner bottom surface 203A of the housing 203 to the point Q where the inner surface 203B of the housing 203 and the convex surface portion 252B intersect. When the distances d, d ₁ and d ₂ are defined in this way, d ₁ / d is 0.3 or more, preferably 0.4 or more, more preferably 0.6 or more, and 0.8 or less. The dimension of the convex portion 252B is set so that Furthermore, the dimension of the convex portion 252B is set so that d ₂ / d is 0.3 or more, preferably 0.4 or more, more preferably 0.6 or more, and 0.8 or less. Here, the units of distances d, d ₁ and d ₂ are unified, and the units of d ₁ / d and d ₂ / d are dimensionless. By setting the dimension of the convex surface part 252B as described above, the retention of the molten resin Rc can be suppressed.

Hereinafter, the point that the retention of the molten resin Rc can be suppressed by forming the convex surface portion 252B will be described in detail in comparison with a polymer filter without the convex surface portion 252B. FIG. 6 is a cross-sectional view schematically showing a cross section of a polymer filter having no convex surface portion cut along a plane perpendicular to the inner bottom surface. FIG. 7 is a cross-sectional view schematically showing a part of a cross section of a polymer filter in which a convex surface portion is not formed, taken along a plane perpendicular to the inner bottom surface, and the connection between the bottom cover and the case in FIG. It is a figure which expands and shows the vicinity of a part. 6 and 7, the same parts as those in FIGS. 4 and 5 are denoted by the same reference numerals as those in FIGS.
A polymer filter 901 shown in FIGS. 6 and 7 is configured in the same manner as the polymer filter 201 according to the above-described embodiment except that the convex surface portion 252B is not formed. As shown in FIG. 203B extends continuously to the inner bottom surface 203A. Therefore, as shown in FIG. 7, in the hollow portion 202 in the polymer filter 901, there is a cross section near the boundary between the inner bottom surface 203 </ b> A and the inner side surface 203 </ b> B of the housing 203 (that is, the corner on the bottom side of the hollow portion 202). A region 202E having a substantially right triangle shape is formed. The applicant of the present application conducted an experiment of filtering the molten resin Rc in which black carbon is dispersed by the polymer filter 901, and confirmed by visual observation that the colored resin tends to remain in the vicinity of the inner bottom surface 203A of the housing 203. Furthermore, it has been found by simulation that the cause of the remaining colored resin in the vicinity of the inner bottom surface 203A is that the molten resin Rc stays in the region 202E having a substantially right-angled cross section. Then, as a result of studying the flow path shape so as not to cause the molten resin Rc to stay, as shown in FIG. 5, the inner bottom surface according to the distance d between the filter element 207 and the inner surface 203B of the housing 3 is obtained. It was found that by narrowing the flow path in the vicinity of the boundary between 203A and the inner side surface 203B, the retention of the molten resin Rc can be suppressed and the residual of the molten resin Rc in the vicinity of the inner bottom surface 203A can be prevented. . Specifically, by setting d ₁ / d and d ₂ / d to be equal to or greater than the lower limit of the above range, the molten resin Rc is in the region 202E where the cross section where the molten resin Rc is likely to stay is substantially a right triangle. It is possible to prevent the entry and prevent the stay. Moreover, it can be inferred that by making d ₁ / d and d ₂ / d equal to or less than the upper limit value of the above range, it is possible to prevent an unexpected problem from occurring due to an excessively narrow flow path in the vicinity of the convex surface portion 252B.

Regarding the shape of the convex surface portion 252B shown in FIG. 5, d ₁ / d ₂ is preferably 0.5 or more, more preferably 1.0 or more, and preferably 2.0 or less, more preferably 1.0 or less. By setting d ₁ / d ₂ to a value within the above range, it is possible to prevent the molten resin Rc from entering the region 202E and to suppress the occurrence of stagnation.

The convex surface portion 252B may be formed by a single surface that is smoothly continuous, or may be formed by a plurality of surfaces that are divided into two or more regions. Furthermore, the convex surface portion 252B may be formed by a flat surface, a curved surface, or a combination of a flat surface and a curved surface. However, when the convex surface portion 252B is formed in a curved surface shape in which the cross section of the convex surface portion 252B cut by a plane perpendicular to the inner bottom surface 203A is a curved shape, a value obtained by dividing the curvature radius R of the curved surface of the cross section by d. Is preferably 0.5 or more, more preferably 1.0 or more. By setting the value obtained by dividing R by d within the preferable range, it is possible to prevent the molten resin Rc from entering the region 202E and to suppress the occurrence of stagnation.
In this embodiment, as shown in FIGS. 4 and 5, the convex surface portion 252B has a shape in which a cross section cut by a plane perpendicular to the inner bottom surface 203A is a linear shape, and an inner shape that is a cylindrical shape. It is assumed that the curved surface is smoothly curved in the circumferential direction of the side surface 203B. According to such a configuration, the retention of the molten resin Rc can be further suppressed.

FIG. 8 shows a plane perpendicular to the width direction of the die 301 (that is, the direction parallel to the width direction of the film-like resin molded product F extruded from the discharge port 360) of the die 301 schematically shown in FIG. It is sectional drawing which shows the cut cross section typically.
As schematically shown in FIG. 8, the die 301 of the present embodiment includes a plurality of resin inlets 311, 321, 331 into which molten resins Rc, Rs 1, Rs 2 corresponding to the core layer and the skin layer respectively flow, A plurality of resin flow paths 310, 320, 330 through which the molten resins Rc, Rs 1, Rs 2 flowing in from the inflow ports 311, 321, 331 flow, and a resin junction 340 where the plurality of resin flow paths 310, 320, 330 merge together, The molten resin Rc, Rs1, Rs2 merged at the resin merge point 340 flows in parallel, and the molten resin Rc, Rs1, Rs2 flowing in the merged resin flow channel 350 is discharged into a film. And an outlet 360.

  The resin inlet 311 is connected to the outlet 241 of the polymer filter 201 via a pipe X2 (FIG. 3), and the molten resin Rc is supplied to the resin inlet 311 at a predetermined pressure. . In addition, the resin flow path 310 includes a manifold 312, an upstream resin flow path 313 that communicates from the resin inlet 311 to the manifold 312, and a downstream resin flow path 314 that communicates from the manifold 312 to the resin junction 340. ing. Further, the manifold 312 and the downstream resin flow path 314 are formed to extend in the width direction of the die 301. As a result, the molten resin Rc that has flowed into the upstream resin flow path 313 from the resin inlet 311 is spread in the width direction of the die 301 by the manifold 312 and flows downstream in that state.

  Similarly, the resin inlets 321 and 331 are connected to extruders (not shown) corresponding to the molten resins Rs1 and Rs2 via pipes X3 and X4 (FIG. 3), respectively. Molten resin Rs1, Rs2 is supplied to 331 at a predetermined pressure. Further, the resin flow paths 320 and 330 are connected to the manifolds 322 and 332, the upstream resin flow paths 323 and 333 communicating from the resin inlets 321 and 331 to the manifolds 322 and 332, and the manifolds 322 and 332 to the resin junction 340, respectively. And downstream resin flow paths 324 and 334 communicating with each other. Further, the manifolds 322 and 332 and the downstream resin flow paths 324 and 334 are formed to extend in the width direction of the die 301. As a result, the molten resins Rs1 and Rs2 flowing into the upstream resin flow paths 323 and 333 from the resin inlets 321 and 331 are spread in the width direction of the die 301 by the manifolds 322 and 332 and flow downstream in that state.

FIG. 9 is a cross-sectional view schematically showing an enlarged part of the cross section of the die 301 shown in FIG. 8, and in the vicinity of the resin joining point 340, the joining resin flow path 350 and the resin discharge port 360 in FIG. 8. It is a figure which expands and shows.
As shown in FIG. 9, the downstream end portions of the downstream resin flow paths 314, 324, and 334 are all connected to the resin junction 340. Further, the merged resin flow path 350 has an upstream end connected to the resin merge point 340 and a downstream end connected to the resin discharge port 360.

  Both the resin joining point 340 and the joining resin flow path 350 are formed to extend in the width direction of the die 301. Further, the resin discharge port 360 is a slit-like opening extending in the width direction of the die 301. Accordingly, the molten resins Rc, Rs1, and Rs2 that have circulated in the width direction from the downstream resin flow paths 314, 324, and 334 merge at the resin junction 340 while maintaining the width direction. Then, while maintaining the state expanded in the width direction, the layers are formed and circulated through the merged resin flow path 350 and discharged from the resin discharge port 360 into a film shape.

  Furthermore, in the present embodiment, the molten resin Rc, Rs1, Rs2 merged at the resin merge point 340 is increased in flow time through the merged resin flow path 350 until it is discharged from the resin discharge port 360. The length L of the path 350 is increased. Specifically, the length L is set so that the average flow time for the molten resin Rc, Rs1, Rs2 to flow through the merged resin flow path 350 is usually 2 seconds or longer, preferably 2.5 seconds or longer. . The upper limit of the average circulation time is usually 10 seconds or less (refer to means (2)). As a result, the core layer can be flattened by the long-time pressure in the merging channel portion 350. The length L of the merged resin flow path 350 is preferably 90 mm or more.

  In the present embodiment, the surface 310A of the resin flow path 310 (that is, the manifold 312, the upstream resin flow path 313, and the downstream resin flow path 314) through which the molten resin Rc flows is formed of the same material, and the resin flow The surface roughness of the path 310 is reduced (see means (4)). The specific degree of surface roughness is usually 1 μm or less in terms of arithmetic average roughness Ra. The arithmetic average roughness Ra is defined in JIS B0601-1994. Thereby, the retention of the molten resin Rc in the resin flow path 310 can be prevented.

  Further, in the present embodiment, the damage at the downstream tip portion 315 of the resin flow path 310 where the molten resin Rc flows into the resin junction 340 is reduced and the number of scratches is reduced (see means (5)). . Thereby, it is possible to make it difficult to form linear irregularities in the core layer.

  The die heater 401 is a heater provided to control the temperature of the die 301. The die heater 401 can adjust the viscosity of the molten resins Rc, Rs1, and Rs2 flowing through the inside by controlling the temperature of the die 301. Specifically, the die heater 401 controls the temperature of the die 301 to a temperature at which the viscosity of the molten resin Rc in the die can be normally 550 Pa · s or less, preferably 520 Pa · s or less, more preferably 490 Pa · s or less. It is like that. Thereby, the linear unevenness | corrugation once formed in the core layer can be easily planarized in the confluence | merging flow path part 350 (refer means (3)). In addition to setting the viscosity of the molten resin Rc corresponding to the core layer within the above range, the viscosity of the molten resin Rc corresponding to the core layer is preferably lower than the viscosity of the molten resin corresponding to the skin layer.

  In the production of a multilayer film by the multilayer film production apparatus of this embodiment, first, the molten resin Rc is supplied to the polymer filter 201 with a predetermined flow pressure by the extruder 101, and the polymer filter 201 filters the molten resin Rc. To remove foreign matter in the molten resin Rc.

FIG. 10 is a cross-sectional view for explaining the state of distribution of the molten resin Rc when the polymer filter shown in FIG. 4 is used. 10, the same parts as those in FIG. 4 are denoted by the same reference numerals as those in FIG. 4.
As shown in FIG. 5, when the molten resin Rc is supplied to the inlet 254 at a predetermined flow pressure, the molten resin Rc flows into the hollow portion 202 in the housing 203 (arrow A ₁ ). The molten resin Rc that has flowed in from the inlet 254 flows through the gap 253 between the pressing disk 208 and the toe speed 209 and the inner surface 251A of the lid 251 (arrow A ₂ ), and the filter element 207 and the pressing disk 208 and the side wall portion. The air gap 255 between the inner surface 252A of the 252 passes through the filter medium (not shown) of each filter element 207 and is filtered (arrow A ₃ ). The molten resin Rc filtered by the filter element 207 passes through a flow path (not shown) in the filter element 207 and passes through a gap 264 and a discharge port 263 between the center pole 206 and the filter element 207, thereby forming a hollow portion 262. (Arrow A ₄ ) and is sent out of the polymer filter 201 from the outlet 241 communicating with the hollow portion 262 (arrow A ₅ ). At this time, since the convex portion 252B is formed at the boundary portion between the inner bottom surface 203A and the inner side surface 203B of the housing 203, the stay of the molten resin Rc can be suppressed in the vicinity of the boundary portion. For this reason, it is possible to prevent foreign substances from being mixed into the molten resin Rc delivered from the delivery port 241 due to deterioration of the resin, and to prevent the formation of linear irregularities in the core layer.

  The molten resin Rc delivered from the polymer filter 201 flows into the resin inlet 311 of the die 301. Moreover, molten resin Rs1, Rs2 corresponding to the skin layer flows into the resin inlets 321 and 331 of the die 301. These molten resins Rc, Rs1, and Rs2 flow through the resin flow paths 310, 320, and 330, merge at the resin merge point 340, and flow through the merged resin flow path 350 in a layered state. The film is discharged from the resin discharge port 360 to obtain a multilayer film.

  At this time, by adjusting the pressure at which the extruder 101 pressurizes the molten resin Rc, the flow rate of the molten resin Rc is controlled, and the molten resin Rc merged with the molten resin Rs1 and the molten resin Rs2 at the resin merge point 340 is obtained. The average flow time for flowing through the merged resin flow path 350 before being discharged from the resin discharge port 360 is adjusted. As a result, the linear irregularities formed upstream from the resin junction 340 are flattened by the pressure applied from the surroundings for a long time in the downstream junction channel portion 350, so that the linear irregularities are formed in the core layer. Can be prevented.

  Further, the die heater 401 controls the temperature of the die 301 to lower the viscosity of the molten resin Rc. Thereby, the linear unevenness once formed in the core layer can be easily flattened in the merging flow path portion 350, and the linear unevenness can be prevented from being formed in the core layer.

  Further, the surface 310A of the resin flow path 310 through which the molten resin Rc flows is formed of the same material, and the surface roughness of the resin flow path 310 is reduced, so that the molten resin Rc stays in the resin flow path 310. It can prevent that a linear unevenness | corrugation is formed in a core layer.

  Furthermore, since the scratches on the downstream tip portion 315 of the resin flow path 310 where the molten resin Rc flows into the resin junction 340 are reduced and the number of scratches is reduced, it is difficult to form linear irregularities in the core layer. It is.

  Usually, a roll for cooling the film-shaped resin molded product F taken out from the discharge port 360 is provided in the vicinity of the discharge port 360 of the die 301 (not shown). By extruding the resin molded product F onto this roll and cooling, the resin is cured and a multilayer film is obtained.

[4. Retardation film)
The retardation film of the present invention is formed by stretching the multilayer film of the present invention. Therefore, the layer structure of the retardation film of the present invention is the same as that of the multilayer film of the present invention, and includes a core layer and skin layers respectively disposed on both sides of the core layer.

  The stretching temperature in such stretching can be 120 ° C to 140 ° C, and preferably 125 ° C to 135 ° C.

  The mode of stretching may be any mode that can be used for stretching of an optical film, for example, longitudinal stretching in the flow direction of the film, transverse stretching in the width direction of the film, and biaxial sequential in the longitudinal and lateral directions. Stretching, simultaneous biaxial stretching in the longitudinal and lateral directions, oblique stretching, and combinations thereof can be used.

  The draw ratio can be any ratio that can express a desired phase difference, but it is preferably 1.1 times or more and 5 times or less, and more preferably 1.3 times or more and 3 times or less. . In the case of biaxial stretching, stretching can be preferably performed at the above magnification in each of two directions.

  The thickness of the core layer in the retardation film of the present invention is preferably 5 μm or more, more preferably 10 μm or more, preferably 100 μm or less, more preferably 50 μm or less. On the other hand, the thickness of the skin layer is preferably 5 μm or more, more preferably 10 μm or more, preferably 100 μm or less, more preferably 50 μm or less. When the retardation film of the present invention includes a plurality of core layers and / or skin layers, the preferable thickness range is a preferable thickness for each layer.

  Although the in-plane retardation of the retardation film of the present invention and the in-plane retardation of each of the core layer and the skin layer are not uniform depending on the use of the retardation film, the viewpoint of remarkably exhibiting the effect of the present invention It is preferred that the core layer has a large retardation while the skin layer has a small retardation.

Specifically, the absolute value of the in-plane retardation expressed in the core layer of the retardation film (the value expressed as the total when there are multiple core layers) is preferably 10 nm or more, more preferably 30 nm or more. Especially preferably, it is 40 nm or more. In addition, although there is no restriction | limiting in particular in an upper limit, Usually, it is 550 nm or less, Preferably it is 500 nm or less, More preferably, it is 450 nm or less.
The absolute value of in-plane retardation expressed in the skin layer of the retardation film (value expressed as the sum of the plurality of skin layers) is preferably 2 nm or more, more preferably 5 nm or more. In addition, although there is no restriction | limiting in particular in an upper limit, Usually, it is 550 nm or less, Preferably it is 500 nm or less, More preferably, it is 450 nm or less.
The difference between the absolute value of the in-plane retardation expressed in the core layer and the absolute value of the in-plane retardation expressed in the skin layer is preferably 10 nm or more, more preferably 20 nm or more, and particularly preferably 30 nm or more. In addition, although there is no restriction | limiting in particular in an upper limit, Usually, it is 550 nm or less, Preferably it is 500 nm or less, More preferably, it is 450 nm or less.

  The in-plane retardation of the entire retardation film of the present invention is, for example, preferably 20 nm or more, more preferably 30 nm or more, and preferably 600 nm or less when the retardation film of the present invention is used as an optical compensation film. More preferably, it is 400 nm or less. The retardation in the thickness direction of the retardation film of the present invention is preferably −600 nm or more, more preferably −400 nm or more, preferably −20 nm when the retardation film of the present invention is used as an optical compensation film. Hereinafter, it is more preferably −30 nm or less.

  The retardation film of the present invention preferably has a total light transmittance of 92% or more and a haze of 5% or less. By having such a high total light transmittance and a low haze, it can be advantageously used as a retardation film.

  The retardation film of the present invention can be a film having little linear retardation unevenness. Such phase difference unevenness can be evaluated by the following method. In other words, it is sandwiched between two polarizing plates arranged in crossed Nicols, placed on the light emitting surface of the backlight device and observed, and linear unevenness that is visually judged to be darker or brighter than the surroundings is phase difference By counting as unevenness, the degree of unevenness in phase difference can be evaluated. The position of such observation can be the full width in the width direction of the retardation film, but in the multilayer film, at the location where linear irregularities exist on the skin layer surface and on the interface between the core layer and the skin layer. More efficient evaluation can be performed by observing the corresponding location on the retardation film.

[5. Use of retardation film)
The use of the retardation film of the present invention is not particularly limited. For example, in a display device such as a liquid crystal display device, it can be used as a brightness enhancement film in combination with a circularly polarized light separating element. Such a brightness enhancement film can be provided between a backlight device and a liquid crystal display device having a liquid crystal cell, for example. The retardation film converts predetermined circularly polarized light transmitted from the circularly polarized light separating element into linearly polarized light, and can efficiently supply predetermined linearly polarized light necessary for display of the liquid crystal cell to the liquid crystal cell.

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

<Example 1>
Using the apparatus schematically shown in FIG. 3, a multilayer film having a layer configuration of two types and three layers of a skin layer, a core layer, and a skin layer, and a retardation film formed by stretching the multilayer film were produced.

  As the molten resins Rs1 and Rs2 constituting the skin layer, a polymethyl methacrylate resin (glass transition temperature 105 ° C., 250 ° C., viscosity at 100 (/ s) of 880 Pa · s) containing rubber particles is used as a double flight type single resin. The resin was put into a shaft extruder and extruded. The extruded resin was passed through a polymer filter through a pipe, and further passed through a die 301 through pipes X3 and X4.

  On the other hand, as the molten resin Rc constituting the core layer, a polystyrene resin (glass transition temperature 130 ° C., trade name “DAILARK D332”, manufactured by Nova Chemical Co., 250 ° C., viscosity at 100 (/ s) is 485 Pa · s). Then, it was put into a double flight type single screw extruder 101 to extrude the resin. The extruded resin was passed through the polymer filter 201 via the pipe X1 and further passed through the die 301 via the pipe X2.

  As the polymer filter, a filter having a conventional casing schematically shown in FIGS. 6 and 7 provided with a leaf disk-shaped filter element having an opening of 5 μm was used. The extrusion amount of each resin to the flow paths X2, X3, and X4 was 1: 1: 1 (volume ratio). The temperature of the resin in the die 301 was 240 ° C. for all the resins.

  A die 301 having a structure schematically shown in FIG. 8 was used. In the die 301, the inner surface of the flow path 310 of the molten resin Rc was formed of the same material, and the surface roughness was Ra = 0.5μ. The length L of the merging resin flow path 350 from the resin merging point 340 to the resin discharge port 360 was 100 mm. The extrusion amount was determined so that the average time until the resin reached the discharge port 360 from the resin junction 340 was 2.5 s.

Under the above conditions, the resin was extruded from the die 301 into a long film. This was cast on a cooling roll whose temperature was adjusted to 100 ° C. to obtain a multilayer film having a three-layer structure of (skin layer)-(core layer)-(skin layer) and a width of 1400 mm. . The thickness of each layer determined by the interference film thickness meter was 45 μm, and the total thickness was 135 μm.
The obtained multilayer film was simultaneously biaxially stretched at a stretching temperature of 134 ° C., a stretching speed of 10 m / min, an MD (film flow direction) stretch ratio of 2.0 times, and a TD (film width direction) stretch ratio of 1.5 times. Thus, a retardation film was obtained.

  About the obtained multilayer film and retardation film, the number of linear unevenness | corrugation was evaluated as follows. The results are shown in Table 1.

(Evaluation of multilayer film)
The multilayer film is irradiated with light, the transmitted light is projected onto the screen, and the brightness of the transmitted light projected on the screen is observed over the entire width along the direction corresponding to the width direction of the multilayer film. Also, the brightened linear part or darkened linear part was identified. The multi-layer film portion corresponding to the linear portion on the screen is cut out to a size of about 3 cm square, and the surfaces of both sides of the film are observed using a three-dimensional surface structure analysis microscope (manufactured by Zygo). The depth and height of the linear irregularities present on the skin layer surface and on the interface between the core layer and the skin layer, and the width thereof were measured. At this time, a linear concave or convex portion having a width of 300 μm or more and a depth or height of 10 nm or more was counted as linear irregularities.
Table 1 shows the total number of linear irregularities observed by this counting method, and the number of linear irregularities present on the interface between the core layer and the skin layer.

(Evaluation of retardation film)
In the multilayer film, the part on the retardation film corresponding to the part where the linear irregularities existed on the surface of the skin layer and on the interface between the core layer and the skin layer was observed. The part to be observed is sandwiched between two polarizing plates arranged in crossed Nicols, placed on the planar light emitting surface of the backlight device and observed, and is linearly judged to be darker or brighter than the surroundings. Unevenness was counted as retardation unevenness. The results are shown in Table 1.
Usually, if the core layer has concave linear irregularities, it is visually determined that the area is darker, and if the core layer has convex linear irregularities, it is visually determined that the area is brighter.

<Example 2>
A multilayer film and a retardation film were produced and evaluated in the same manner as in Example 1 except that the temperature of the resin in the die 301 was 250 ° C. The results are shown in Table 1.

<Example 3>
A multilayer film and a retardation film are produced in the same manner as in Example 1, except that the shape of the polymer filter housing through which the molten resins Rs1, Rs2, and Rsc pass is changed and the shape of the die is changed. And evaluated. The results are shown in Table 1.
As the case of the polymer filter used in the present example, the one having a shape with a reduced retention inside as shown schematically in FIGS. 4 and 5 was used. Housing of dimension d shown in FIG. 5, the dimension of _{d 1} and _{d 2} were used 10 mm, what is 8mm and 8mm, respectively.
The dice used in this example have the same shape as that used in Examples 1 and 2 except that the length L of the joining resin flow path 350 from the resin joining point 340 to the resin discharge port 360 is 70 mm. Things were used.

<Example 4>
The same as in Example 1, except that the temperature of the resin in the die 301 was 250 ° C., and the same polymer filter used in Example 3 was used as the polymer filter through which the molten resins Rs1, Rs2, and Rsc passed. A multilayer film and a retardation film were manufactured and evaluated. The results are shown in Table 1.

<Comparative Example 1>
A multilayer film and a retardation film are manufactured in the same manner as in Example 1 except that the same die as used in Example 3 and having a length L of the confluence resin flow path 350 of 70 mm is used. And evaluated. The results are shown in Table 1.

<Comparative Example 2>
As the die, the same as that used in Example 3, except that the length L of the merged resin flow path 350 is 70 mm, and the temperature of the resin in the die is 250 ° C. In the same manner as in Example 1, a multilayer film and a retardation film were produced and evaluated. The results are shown in Table 1.

  In both the above Examples and Comparative Examples, the observed widths of the linear irregularities were all within 1000 μm, and the heights were both within 1000 nm. Moreover, when the whole obtained retardation film was observed visually, the nonuniformity which may be observed as retardation nonuniformity by the said "evaluation of retardation film" was not observed.

  In the description of the thickness of the skin layer in the table, a set of two values indicates that each of the two values is a thickness of the skin layer having two layers. For example, 45/45 indicates that each of the two skin layers has a thickness of 45 μm.

As shown in Table 1, the number of retardation unevenness appearing in the retardation film was almost equal to the number of linear irregularities generated at the interface between the core layer and the skin layer in the original multilayer film.
Moreover, in actual observation, the position where the retardation unevenness appeared in the retardation film corresponds to one of the places where linear irregularities existed at the interface between the core layer and the skin layer in the original multilayer film. It was. In the original multi-layer film, there was no spot where the retardation unevenness occurred in the retardation film at a position corresponding to the place where the linear unevenness was present only on the skin layer surface.

  From the above results, the retardation film of the present invention formed by stretching the multilayer film of the present invention having few linear irregularities at the interface between the core layer and the skin layer can be a film with little retardation unevenness. Recognize. Moreover, it turns out that the multilayer film of this invention with few linear unevenness | corrugations of the interface of a core layer and a skin layer is obtained by the predetermined manufacturing method of this invention.

1: Production apparatus 10, 20: Multilayer film 11, 13, 21, 23: Skin layer 12, 22: Core layer 14, 15, 24: Linear unevenness 101: Extruder 201, 901: Polymer filter 202: Hollow part 203: Housing 203A: Inner bottom surface 203B: Inner side surface 204: Bottom cover 205: Case 206: Center pole 207: Filter element 241: Outlet 251: Cover part 252: Side wall part 252B: Convex part 254: Inlet 301: Die 310 320, 330: Resin channel 310A: Resin channel surface 311, 321, 331: Resin inlet 340: Resin junction 350: Merged resin channel 360: Resin outlet 401: Die heater F: Resin molded product Rc , Rs1, Rs2: Molten resin

Claims (7)

A multilayer film formed by melting and extruding a molten resin, comprising a core layer and skin layers respectively disposed on both sides of the core layer;
The multilayer film in which the number of linear irregularities having a width of 300 μm to 1000 μm and a height of 10 nm to 1000 nm at the interface between the core layer and the skin layer is 2 or less per 1400 mm width of the multilayer film.   A retardation film obtained by stretching the multilayer film according to claim 1. It is a manufacturing method of the multilayer film of Claim 1, Comprising:
Including melt coextrusion of a molten resin corresponding to the skin layer and the core layer from a die,
The molten resin corresponding to the core layer is supplied to the die after being filtered by a polymer filter,
The polymer filter is
A bottom portion having a flat inner bottom surface on which a delivery port is formed, a side wall portion having a cylindrical inner surface perpendicular to the inner bottom surface, and a flow channel provided on the opposite side of the side wall portion from the bottom portion. A housing including a lid portion formed with an inlet;
A strut portion that is erected on the inner bottom surface in the housing and in which a channel that communicates with the delivery port is formed;
A polymer filter comprising: a disk-shaped filter element mounted on the strut portion so as to stack a plurality of sheets, filtering the molten resin flowing from the inflow port and sending it to the flow path of the strut portion; ,
The casing is located on the center side of the casing with respect to the inner bottom surface and the inner side surface so as to straddle between the inner bottom surface and the inner side surface at a boundary portion between the inner bottom surface and the inner side surface. It has a convex part that is convex toward
0.3 ≦ d ₁ /d≦0.8 and 0.3 ≦ d ₂ /d≦0.8 (d represents the distance from the filter element to the inner surface. D ₁ is from the inner surface. The distance in the radial direction of the inner surface to the point where the inner bottom surface and the convex surface portion intersect, d ₂ from the inner bottom surface to the point where the inner surface and the convex surface portion intersect, The distance is expressed in a direction perpendicular to the inner bottom surface). It is a manufacturing method of the multilayer film of Claim 1, Comprising:
Including melt coextrusion of a molten resin corresponding to the skin layer and the core layer from a die,
The die has a plurality of resin inflow ports into which molten resin corresponding to the skin layer and the core layer flows, and the molten resin corresponding to the skin layer and the core layer from the resin inflow flows. A plurality of resin flow paths, a resin merge section where the plurality of resin flow paths merge, a merge resin flow path where the molten resin merged in the resin merge section flows, and the molten resin flowing through the merge resin flow path A resin discharge port for discharging the film into a film,
The method for producing a multilayer film, wherein an average circulation time of the molten resin from a junction of the molten resin in the resin junction to the resin discharge port is 2 seconds or more. It is a manufacturing method of the multilayer film of Claim 3, Comprising:
The die has a plurality of resin inflow ports into which molten resin corresponding to the skin layer and the core layer flows, and the molten resin corresponding to the skin layer and the core layer from the resin inflow flows. A plurality of resin flow paths, a resin merge section where the plurality of resin flow paths merge, a merge resin flow path where the molten resin merged in the resin merge section flows, and the molten resin flowing through the merge resin flow path A resin discharge port for discharging the film into a film,
The method for producing a multilayer film, wherein an average circulation time of the molten resin from a junction of the molten resin in the resin junction to the resin discharge port is 2 seconds or more. It is a manufacturing method of the multilayer film as described in any one of Claims 3-5,
The manufacturing method of the multilayer film whose viscosity of the molten resin corresponding to the said core layer is 550 Pa.s or less in the said die | dye. A multilayer film comprising two or more skin layers and one or more core layers provided between the skin layers, and formed by melt extrusion of a molten resin, the width of the core layer A method for producing a retardation film, wherein a multilayer film having a number of linear irregularities of 300 μm or more and 1000 μm or less and a height of 10 nm or more and 1000 nm or less is 2 or less per 1400 mm width of the multilayer film. ,
The manufacturing method of retardation film including extending | stretching the multilayer film manufactured with the manufacturing method as described in any one of Claims 3-6.

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