JP5898925B2 - Multilayer film - Google Patents

Description

  The present invention relates to a multilayer film excellent in mechanical properties and optical properties.

  Thermoplastic resins are generally widely used according to applications, such as films, sheets, pipes, fibers, etc., from the viewpoints of excellent processability and various practical performance and economy. In recent years, optical applications have attracted attention as applications of thermoplastic resin films.

  Conventionally, an optical film using a thermoplastic resin such as polyvinyl alcohol has been used for a protective film of a polarizing element. However, the required performance for optical films is high, and in addition to optical properties, mechanical properties and dimensional stability, as well as durability of various qualities when used over time are required. A film using the thermoplastic resin as described above does not sufficiently satisfy these requirements.

  Among the thermoplastic resins, a specific resin, for example, a polypropylene resin is a highly productive thermoplastic resin that is highly productive and inexpensive, and is extremely versatile as a film material. However, there is a problem that it is relatively soft in a use environment at room temperature or higher, and that dimensional change and material deformation are likely to occur due to external force load or heating. The polypropylene resin has crystallinity and can improve mechanical properties by accelerating crystallization. However, transparency is lowered by accelerating crystallization and is suitable for optical applications. is not.

  In order to improve the above problems, the polypropylene resin may be used as a composite material to which other resins or fillers are added. In such a composite material, mechanical properties such as rigidity are improved when the amount of filler added is increased. For example, Patent Document 1 proposes a polypropylene resin composition in which an olefin-based elastomer and an inorganic material are blended with a polypropylene resin having a specific stereoregular structure to improve bending rigidity and impact resistance. Moreover, in patent document 2, the resin composition which improved heat resistance, impact resistance, bending rigidity, and a flame retardance by adding a needle-shaped inorganic filler to this based on various impact-resistant resin, and its Molded bodies have been proposed. Further, in Patent Document 3, by using a propylene homopolymer, a specific propylene copolymer and a specific inorganic filler, it is excellent in scratch resistance and impact resistance, has low surface gloss and excellent surface smoothness. A polypropylene resin composition and a molded body using the resin composition as a skin material for a polypropylene base have been proposed. Further, Patent Document 4 describes a laminated film in which 5 to 3000 resin layers are laminated in the thickness direction, at least one layer is a crystalline resin layer, and at least one layer is an amorphous resin layer. Yes.

  However, since the polypropylene resin composition described in Patent Document 1 uses an olefin-based elastomer as a resin component, the problem is that the heat resistance is inferior to that of polypropylene alone, and the surface scratch resistance is particularly low. There is. Further, the resin composition and the molded body described in Patent Document 2 do not sufficiently improve the mechanical properties and the optical properties such as transparency and optical anisotropy are lowered depending on the type and shape of the inorganic filler. There is a problem of doing. In addition, the polypropylene resin composition and the molded body described in Patent Document 3 are not sufficiently studied for transparency, and a propylene copolymer is used as a resin component. There is a problem that the rigidity is insufficient. Furthermore, the laminated film described in Patent Document 4 does not describe the use of an inorganic filler, and has insufficient rigidity, toughness, and dimensional stability.

JP 7-33920 A JP 2006-169447 A JP 2004-91701 A Japanese Patent Laid-Open No. 2004-130761

  This invention is made | formed in view of said problem, and it aims at providing the multilayer film excellent in mechanical characteristics, transparency, and optical anisotropy.

  As a result of intensive studies to achieve the above object, the present inventors have obtained a multilayer film in which the first thermoplastic resin layer and the second thermoplastic resin layer are alternately laminated, 2 thermoplastic resin layer contains an inorganic filler, the total number of laminated layers of the first thermoplastic resin layer and the second thermoplastic resin layer is 10 or more, the inorganic filler is needle-like and It has been found that the above object can be achieved by a multilayer film having at least one shape selected from a plate shape and oriented substantially parallel to the plane direction of the multilayer film, and the present invention has been completed. It was.

That is, this invention relates to the following multilayer film.
1. A multilayer film in which a first thermoplastic resin layer and a second thermoplastic resin layer are alternately laminated,
The second thermoplastic resin layer contains an inorganic filler,
The total number of laminations of the first thermoplastic resin layer and the second thermoplastic resin layer is 10 or more;
The said inorganic filler is at least 1 sort (s) selected from needle shape and plate shape, and is orientating substantially parallel with respect to the surface direction of a multilayer film, The multilayer film characterized by the above-mentioned.
2. The multilayer film according to Item 1, wherein the inorganic filler has an aspect ratio of 10 or more.
3. Item 3. The multilayer film according to Item 1 or 2, wherein the first thermoplastic resin layer contains a polypropylene resin.
4). The multilayer film according to any one of Items 1 to 3, wherein the inorganic filler contains titanate.

  Hereinafter, the multilayer film of the present invention will be described in detail.

  In the multilayer film of the present invention, the first thermoplastic resin layer and the second thermoplastic resin layer are alternately laminated, and the second thermoplastic resin layer contains an inorganic filler, and the inorganic film The filler has at least one shape selected from a needle shape and a plate shape, and is oriented substantially parallel to the surface direction of the multilayer film, and the first thermoplastic resin layer and the second shape The total number of laminated thermoplastic resin layers is 10 or more.

  In the multilayer film of the present invention having the above characteristics, the second thermoplastic resin layer containing an inorganic filler having at least one shape selected from a needle shape and a plate shape is alternately formed with the first thermoplastic resin layer. The inorganic filler contained in the second thermoplastic resin is a specific layer by setting the total number of laminated layers of the first thermoplastic resin layer and the second thermoplastic resin layer to 10 or more. By being in the plane, orientation in the thickness direction is suppressed, and plane orientation is improved. For this reason, it is excellent in mechanical properties such as rigidity and surface hardness, film running stability is increased, and optical properties such as transparency and in-plane optical anisotropy are excellent. When such a multilayer film of the present invention is used in, for example, a liquid crystal display device, it becomes possible to stabilize the image display of the liquid crystal panel over a long period of time.

  Hereinafter, details of the multilayer film of the present invention will be described.

  FIG. 1 is a cross-sectional view showing an embodiment of the multilayer film of the present invention. A multilayer film 1 shown in FIG. 1 has first thermoplastic resin layers 21 to 26 and second thermoplastic resin layers 31 to 37. The first thermoplastic resin layers 21 to 26 and the second thermoplastic resin layers 31 to 37 are alternately laminated in the thickness direction of the multilayer film 1. Moreover, the sum total of the lamination | stacking number of the 1st thermoplastic resin layers 21-26 and the 2nd thermoplastic resin layers 31-37 is 10 or more.

(First thermoplastic resin layer)
The thermoplastic resin that forms the first thermoplastic resin layer is not particularly limited, and a conventionally known thermoplastic resin can be used. It is preferable to include a polypropylene resin in that it can exhibit properties required for optical applications such as high transparency, low intrinsic birefringence, and a small photoelastic coefficient, and exhibit high mechanical properties. . In addition to the above-mentioned properties, the polypropylene resin is further obtained by radical addition polymerization, so that it is difficult to generate a cross-linked product or a deteriorated product that may cause appearance defects, and has moderate hydrophobicity. It is difficult to damage the characteristics, and can be easily manufactured and obtained at low cost.

  The melt flow rate of the polypropylene resin (hereinafter appropriately referred to as “MFR”) is preferably 5 to 30 g / 10 minutes, and more preferably 10 to 20 g / 10 minutes. By using a polypropylene resin exhibiting such MFR, the quality of the first thermoplastic resin layer as a multilayer film such as moldability and stretchability can be improved.

  The MFR is a value measured according to JISK7120 using a plastometer used in JISK6760.

  It is preferable that content of the said polypropylene resin is 60 to 95 weight% in 100 weight% of resin compositions used for formation of the said 1st thermoplastic resin layer. When there is too little content of the said polypropylene resin, there exists a possibility that the transparency and mechanical toughness of a film may fall.

  The polypropylene resin preferably contains a homopolypropylene resin as a main component. Homopolypropylene resins have higher stereoregularity than block polypropylene copolymers and random polypropylene copolymers. A material with high stereoregularity has high crystallinity and affinity between the same molecules, can obtain mechanical properties, and further exhibits a certain thermoplasticity, so that high rigidity can be imparted to the multilayer film. . The homopolypropylene resin is more preferably an isotactic homopolypropylene resin in terms of higher stereoregularity and easier crystallization.

  The homopolypropylene resin preferably has a heptane-insoluble content of 90% or more, and more preferably 99% or more. By using such a homopolypropylene resin, a thermoplastic resin layer having high thermoplasticity and dense molecular orientation after stretching can be obtained.

  In addition, the said heptane insoluble content is a parameter | index of the stereoregularity of a homo polypropylene resin, and it shows that stereoregularity is so high that heptane insoluble content is large. Specifically, the heptane-insoluble content is the ratio of the heptane-insoluble content in the homopolypropylene resin that is not dissolved by heptane. The above-mentioned heptane-insoluble matter also serves as an index of the content of isotactic polypropylene resin that is not dissolved by heptane. The heptane-insoluble matter can be measured, for example, according to the method described in JP-A-10-330706.

  The isotactic homopolypropylene resin preferably has a mesopentad fraction (mmmm) of 95% or more, and more preferably 98% or more. By using such an isotactic homopolypropylene resin, a thermoplastic resin layer having high thermoplasticity and dense molecular orientation after stretching can be obtained.

  The mesopentad fraction is an index of the stereoregularity of the polypropylene resin, and indicates a ratio in which five methyl groups contained in the propylene monomer unit in the polypropylene resin are continuous in the same direction. The higher the mesopentad fraction, the higher the stereoregularity. The mesopentad fraction can be measured, for example, according to the method described in JP-A-3-14851.

  The thermoplastic resin forming the first thermoplastic resin layer may contain other components as necessary within the range not impairing the object of the present invention. Examples of the other components include 2,6-di-t-butyl-4-methylphenol, 2- (1-methylcyclohexyl) -4,6-dimethylphenol, 2,2-methylene-bis- (4-ethyl). Antioxidants such as -6-tert-butylphenol) and tris (di-nonylphenyl phosphite); pt-butylphenyl salicylate, 2,2'-dihydroxy-4-methoxy-benzophenone, and 2- (2 UV absorbers such as' -dihydroxy-4'-m-octoxyphenyl) benzotriazole; cross-linking agents such as trimethylolpropane; lubricants such as paraffin phenos and hydrogenated oils; stearoadipropylpropyl-β-hydroxyethylammonium And antistatic agents such as traits.

  The first thermoplastic resin layer preferably has a thickness of 2 to 800 μm, and more preferably 10 to 150 μm. By setting the thickness of the first thermoplastic resin layer in the above range, a multilayer film excellent in mechanical properties, optical properties, film-forming properties, film appearance, and film running stability can be obtained.

(Second thermoplastic resin layer)
The multilayer film of the present invention is formed by alternately laminating first thermoplastic resin layers and second thermoplastic resin layers.

  The thermoplastic resin that forms the second thermoplastic resin layer may be the same as the thermoplastic resin that forms the first thermoplastic resin layer.

  The second thermoplastic resin layer has at least one shape selected from a needle shape and a plate shape, and contains an inorganic filler oriented substantially parallel to the plane direction of the multilayer film. When the second thermoplastic resin layer contains the inorganic filler, the mechanical properties, optical properties, and heat resistance of the multilayer film are improved.

  It is preferable to use titanate as the inorganic filler. The titanate can be obtained, for example, by mixing and baking a titanium compound or a compound containing an alkali metal salt or an alkaline earth metal salt.

  The titanium compound is not particularly limited as long as it generates titanium oxide by heating, and includes titanium dioxide, orthotitanic acid, metatitanate, orthotitanate, titanium chloride, titanium sulfate, titanium hydroxide, and the like. be able to. The said titanium compound may be used independently and may use 2 or more types together.

  The compound containing an alkali metal salt or an alkaline earth metal salt is not particularly limited as long as it generates an alkali metal oxide or an alkaline earth metal oxide by heating. For example, an alkali metal or an alkali Examples include earth metal oxides, hydroxides, carbonates, nitrates, bicarbonates, and oxalates. Among these, potassium compounds that are alkali metals are preferable. The compound containing an alkali metal salt or an alkaline earth salt may be used alone or in combination of two or more.

  The inorganic filler may be a single crystal, a polycrystal, or an amorphous body.

  The inorganic filler preferably has an aspect ratio of 10 or more. If the aspect ratio is less than 10, the mechanical properties may be inferior. The aspect ratio is more preferably 10-100. If the aspect ratio is too large, the optical properties, film formability, and film appearance may be inferior.

  The average diameter of the inorganic filler is preferably 0.1 to 20 μm. Moreover, it is preferable that the average length of the said inorganic filler is 1 micrometer-15 mm.

  In addition, the measuring method of the average diameter of the inorganic filler in this invention, average length, and aspect ratio is as follows. That is, the number average minor axis diameter and the number average major axis diameter are measured by a flow type particle image analyzer (manufactured by Malvern Industries, model number “FPIA-3000”). Let the average major axis diameter be the average length. Further, the value obtained by dividing the average length by the average diameter is defined as the aspect ratio. The number average minor axis diameter and the number average major axis diameter are defined as the average value of the number of fillers to be observed with the short side length of the smallest rectangle (circumscribed rectangle) when the inorganic filler is surrounded by a rectangle. The average minor axis diameter is used, and the average value of the long side length is also used as the number average major axis diameter.

  The inorganic filler is oriented substantially parallel to the plane direction of the multilayer film. By aligning the inorganic filler almost parallel to the plane direction of the multilayer film, the multilayer film has excellent mechanical properties such as rigidity and surface hardness, and hardly causes appearance defects such as elongation, scratches and dents during processing. Become.

  The inorganic filler is preferably substantially parallel to the plane direction of the multilayer film and oriented in the longitudinal direction. As described later, the multilayer film in which the inorganic filler is oriented in such a direction can be easily produced by adjusting the draw ratio in the production process, and the orientation effect of the filler and the resin molecule is expressed. Mechanical properties, haze, front retardation value, etc. can be improved.

  The surface of the inorganic filler is preferably treated with a chemical such as an acid, alkali, coupling agent, or surfactant. By processing with the said chemical | medical agent, the compatibility with the thermoplastic resin which forms an inorganic filler and a 2nd thermoplastic resin layer can be improved. The surface of the inorganic filler is preferably covered with a metal layer formed of antimony, indium, niobium or the like. By covering with the metal layer, conductivity can be imparted to the inorganic filler.

  The content of the inorganic filler in the second thermoplastic resin layer is appropriately determined depending on the type, shape, specific gravity and the like of the inorganic filler to be used, but the thermoplastic resin composition used for forming the second thermoplastic resin layer It is preferable that it is 1 to 50 weight% with respect to 100 weight% of a thing. If the content of the inorganic filler is less than 1% by weight, mechanical properties and optical properties may be insufficient. When the content of the inorganic filler exceeds 50% by weight, it may be difficult to uniformly disperse the inorganic filler in the thermoplastic resin composition, and the film forming property is lowered, and the transparency of the multilayer film is reduced. May decrease and become brittle.

  The second thermoplastic resin layer preferably has a thickness of 2 to 800 μm, and more preferably 10 to 150 μm. By setting the thickness of the second thermoplastic resin layer in the above range, a multilayer film excellent in mechanical properties, optical properties, film-forming properties, film appearance, and film running stability can be obtained.

(Multilayer film)
The multilayer film of the present invention is formed by alternately laminating the first thermoplastic resin layer and the second thermoplastic resin layer. In addition, the total number of the first thermoplastic resin layer and the second thermoplastic resin layer is 10 or more. If the total number of laminated layers is less than 10, the multilayer film cannot sufficiently exhibit mechanical properties.

  In addition, the total number of stacked layers is preferably 2000 or less, and more preferably 1000 or less. If the total number of layers is too large, the transparency and optical anisotropy of the multilayer film may be inferior.

  The average thickness of the multilayer film is not particularly limited, but is preferably 5 to 1000 μm, and more preferably 20 to 200 μm. If the average thickness of the multilayer film is too thin, mechanical strength may be insufficient, durability may be insufficient, and problems such as warping may occur over time. If the average thickness of the multilayer film is too thick, the transparency may be insufficient or the adhesiveness may be reduced. When the average thickness of the multilayer film is within the above range, the birefringence expression is not impaired, the mechanical strength is constant, and further, weight reduction of a member important when being laminated on a liquid crystal display device is achieved. be able to. The average thickness of each layer of the multilayer film is appropriately set according to the number of laminated layers.

  In addition, the measuring method of the average thickness of the multilayer film in this invention is as follows. That is, the film width direction is taken as a reference axis, and a strip-like film piece is collected with the longitudinal direction being 50 mm and the width direction being full width with respect to the reference axis. The thickness of the strip film piece was measured at an interval of 10 mm in parallel with the longitudinal direction of the collected strip film piece using a film thickness measuring instrument (trade name “Millitron 1240” manufactured by Seiko EM Co., Ltd.), and the average of the measured values Is calculated as the average thickness (μm) of the multilayer film.

  The tensile elastic modulus of the multilayer film is preferably 1000 MPa or more, and more preferably 1500 to 3000 MPa. When the tensile elastic modulus of the multilayer film is within the above range, the rigidity is excellent, and therefore, the deformation resistance against external force is high, and the workability such as coating, surface treatment, and lamination is stabilized. In addition, when laminated with other members and used as a composite material, the composite material is hardly deformed such as warpage and excellent in dimensional stability.

  The multilayer film preferably has a haze of 10% or less. It is more preferably 5% or less, and further preferably 3% or less. If the haze is too high, it may cause a decrease in light transmission, particularly when used for applications such as optical films.

The front retardation R0 (nm) of the multilayer film is preferably 20 to 300 nm, and more preferably 80 to 280 nm. When the front retardation R0 is within the above range, stable and high-quality image display can be obtained when the multilayer film is laminated on the liquid crystal panel. If the value of the retardation R0 is outside the above range, birefringence when passing through the liquid crystal may not be fully compensated, and in particular, the commercial value as an optical film may be reduced. R0 is a value calculated by the following formula (1).
R0 (nm) = (nx−ny) × d (1)
(Where nx: maximum refractive index in the film plane, ny: refractive index in the direction perpendicular to the nx direction in the film plane, d: average thickness of the retardation compensation film (nm))

  In the multilayer film, the molecular main chain orientation angle (°) with respect to the width direction of the film is preferably within 1.0 °, and more preferably within 0.5. By setting the molecular main chain orientation angle within the above range, the molecular main chain is uniformly aligned and the optical axis is stabilized. Therefore, when it is laminated on a liquid crystal panel, there is no display unevenness and stable image display can be obtained.

  The multilayer film preferably has a surface hardness indicated by pencil hardness of HB or higher. It is more preferably H or more, and further preferably 2H or more. When the pencil hardness is lower than HB, the surface of the multilayer film may be damaged when the film is processed or stored during processing, and the appearance quality may be impaired. There is a risk that stable and high-quality image display cannot be obtained due to inferiority or scratches.

  The multilayer film preferably has a static friction coefficient of 0.2 to 0.5. Generation | occurrence | production of the film blocking inside a scroll can be suppressed even if it does not use a surface protection film as the static friction coefficient of a multilayer film exists in the said range. If the static friction coefficient exceeds 0.5, a single film that does not use a surface protective film may cause film blocking in a roll state, and the commercial value as a multilayer film may be significantly impaired. If the friction coefficient is less than 0.2, the film meandering becomes more noticeable as the film surface slippage becomes excessive, so that a so-called telescope or bamboo shoot phenomenon that the shape of the scroll collapses may occur and the commercial value may be impaired. .

  The multilayer film is particularly preferably used as a component of a liquid crystal display device. The multilayer film may be used alone, or may be laminated and integrated with a polarizing plate and used as a composite polarizing plate. Further, as an alternative to the protective film, a multilayer film may be laminated and integrated on the liquid crystal cell side of the polarizing plate via an adhesive layer and used as a polarizing plate. As a polarizing plate, a multilayer film is laminated and integrated with an adhesive layer on the liquid crystal cell side of the polarizing plate as an alternative to a protective film in that the liquid crystal display device can be thinned and the production efficiency can be improved. It is preferable to be used.

  When the multilayer film is used by being joined to another member, it is preferable to perform a surface modification treatment. As a method for surface modification treatment, a normal method can be used. As a chemical treatment method, a surface grafting method for attaching a monomer or polymer having a functional group capable of reacting with an adhesive molecule to the surface, Other polymer or monomer coating methods, coupling agent treatment, treatment with highly oxidizing chemicals, chemical treatment to remove the surface layer, CASING treatment to strengthen the surface layer, chemical treatment as a surface roughening method, etc. It is done. Examples of physical treatment methods include ultraviolet irradiation treatment, glow discharge treatment, corona discharge treatment, plasma treatment, and sputtering treatment as a surface roughening method. Furthermore, various performances can be added to the surface of the multilayer film by applying various functional coatings, laminating, etc. by coating or vapor deposition, and the utility value can be improved.

(Method for producing multilayer film)
The manufacturing method of the multilayer film of this invention is not specifically limited, A conventionally well-known method can be used. For example, the raw material resin is supplied to an extruder, melted and kneaded, extruded from a mold attached to the tip of the extruder into a film, and then applied by an electrostatic charge cast method, a touch roll method, or an air knife cast method. Then, after cooling and solidifying on a cooling roll and forming a film on a long film, or after casting a solution obtained by dissolving the thermoplastic resin in an organic solvent onto a drum or an endless belt, A molding method such as a solution casting method in which an organic solvent is evaporated to form a long film can be used. It is preferable to use the melt extrusion method in terms of easy production and low production cost.

  As a method for producing the multilayer film, for example, a first thermoplastic resin layer and a second thermoplastic resin layer are alternately laminated, and the second thermoplastic resin layer contains an inorganic filler. The total number of laminated layers of the first thermoplastic resin layer and the second thermoplastic resin layer is 10 or more, and the inorganic filler is at least one selected from a needle shape and a plate shape. And a method for producing a multilayer film oriented substantially parallel to the plane direction of the multilayer film, wherein a thermoplastic resin composition and an inorganic filler-containing thermoplastic resin composition are obtained by a melt extrusion method. Laminating and forming into a film to obtain a resin laminate (1), laminating the resin laminate and discharging from a die lip opening to obtain a multilayer resin laminate (2), and the multilayer resin Laminate is cooled by cooling roll A step (3) for obtaining a multilayer film by cooling, and an opening area (s1) of the die lip used in the step (2), and a cross-sectional area (s2) of the multilayer film obtained in the step (3) The manufacturing method whose draw ratio ((s1) / (s2)) represented by these is 3.0-30.0 is mentioned.

  According to the said manufacturing method, the said multilayer film can be manufactured easily. Moreover, the multilayer film in which the inorganic filler is oriented substantially parallel to the plane direction of the multilayer film and is oriented in the longitudinal direction of the multilayer film can be easily produced.

  The step (1) is a step of obtaining a resin laminate by laminating a thermoplastic resin composition and an inorganic filler-containing thermoplastic resin composition by a melt extrusion method to form a film.

  The said thermoplastic resin composition can use the thermoplastic resin composition containing the thermoplastic resin which forms the 1st thermoplastic resin layer mentioned above. Moreover, as said inorganic filler containing thermoplastic resin composition, the inorganic filler containing thermoplastic resin composition containing the thermoplastic resin and inorganic filler which form the 2nd thermoplastic resin layer mentioned above can be used.

  As the melt extrusion method, in order to form a film, it is necessary to make the die lip opening into an elongated shape. Therefore, a flat die (T-die) forming method is preferably used. In the T-die molding method, the T-die is provided with a resin inflow portion and a manifold. The manifold is longer in the width direction than the resin inflow portion, and has a structure connected to the resin inflow portion. The resin supplied from the resin inflow portion flows so as to expand in the width direction within the manifold, and is then discharged from the die lip opening.

  Examples of the melt extrusion method include a coextrusion method as a melt extrusion method in which a plurality of thermoplastic resin compositions are formed into a film and laminated to form a resin laminate. The co-extrusion method is a method in which a plurality of thermoplastic resin compositions are extruded in a molten state from individual molding machines, introduced into a mold, and laminated in a molten state inside and outside the mold. The co-extrusion is roughly classified into several types such as a feed block method and a multi-manifold method depending on the timing of laminating the extruded thermoplastic resin composition.

  In the above feed block method, two or more types of thermoplastic resin compositions are supplied to the manifold in a laminated state at the resin inflow portion, and the width direction is expanded while maintaining the laminated state in the manifold, and the laminated state is obtained from the die lip opening. This is a method of discharging. The above feed block method does not require a manifold for each thermoplastic resin composition to be laminated, so it is possible to simplify the structure of the flat die as compared to other methods, and therefore operability and maintainability. Excellent.

  The multi-manifold system is a system in which a resin inflow portion and a manifold are provided for each thermoplastic resin composition, and each thermoplastic resin composition is laminated in front of a die lip opening in a state where the thermoplastic resin composition spreads in the width direction. In the multi-manifold system, before the thermoplastic resin composition forming each layer is joined and laminated, the inside of the manifold individually flows in the width direction and is laminated after being widened. The occurrence of the wraparound phenomenon can be suppressed, the thickness distribution can be set to a desired distribution, and the influence of the flow characteristics of the thermoplastic resin composition can be suppressed.

  When carrying out the above-mentioned coextrusion molding, considering the desired layer thickness and film width, molding environment and operability, etc., the type and composition of the resin contained in the thermoplastic resin composition, the equipment specifications as appropriate , Methods and conditions can be selected.

  In the step (1), the temperature at which the thermoplastic resin composition is melt-kneaded is (Tm) to (Tm + 200) ° C., where the melting point is Tm (° C.) when the thermoplastic resin is a crystalline resin. Is preferred. In the case of an amorphous resin, the glass transition temperature is preferably (Tg + 50) to (Tg + 200) ° C., where Tg is the glass transition temperature. By melt-kneading at the above temperature, it is possible to obtain a film having excellent resin fluidity during film extrusion molding and excellent dimensional accuracy such as thickness and length. ⇒ “The temperature at which the thermoplastic resin composition is melt-kneaded is preferably (Tm) to (Tm + 200) ° C., where the melting point is Tm (° C.) when the thermoplastic resin is a crystalline resin. In the case of a crystalline resin, the glass transition temperature is Tg, and is preferably (Tg + 50) to (Tg + 200) ° C. By melt-kneading at the above temperature, the resin fluidity at the time of film extrusion molding is excellent, A film excellent in dimensional accuracy such as length can be obtained.

  The resin laminate is formed by the step (1) described above.

  The step (2) is a step in which the resin laminate is laminated and discharged from the die lip opening to obtain a multilayer resin laminate. The method for laminating the resin laminate is not particularly limited as long as the resin laminate can be laminated in the thickness direction, but a method using a multilayer block can be mentioned. As the multilayer block, the resin laminate is divided in a direction perpendicular to the surface of the resin laminate and parallel to the flow direction of the resin laminate at the time of manufacture, and the divided resin laminate is laminated. A multilayer block that obtains a multilayer resin laminate by discharging from a die lip opening can be used.

  By the step (2) described above, a multilayer resin laminate is formed.

  The step (3) is a step of obtaining a multilayer film by cooling the multilayer resin laminate with a cooling roll. Although it does not specifically limit as a method to cool with the said cooling roll, The electrostatic printing cast method, the touch roll method, or the air knife cast method is mentioned. In the step (3), the resin laminate is cooled and solidified on a cooling roll and formed into a long multilayer film.

  In the said process (3), a multilayer film is shape | molded by quenching a resin laminated body, and the crystal phase and molecular orientation of a multilayer film are fixed. When the thermoplastic resin is a crystalline resin, the surface temperature of the cooling roll is preferably (Tm-100) to (Tm-50) ° C. with the melting point being Tm (° C.). In the case of an amorphous resin, the glass transition temperature is preferably (Tg−150) to (Tg) ° C., where Tg is the glass transition temperature.

  In the manufacturing method, the draw ratio ((s1)) represented by the opening area (s1) of the die lip used in the step (2) and the cross-sectional area (s2) of the multilayer film obtained in the step (3). / (S2)) is preferably 3.0 to 30.0, and more preferably 5.0 to 25.0. If the draw ratio ((s1) / (s2)) is too small, mechanical properties such as elastic modulus, breaking strength and surface hardness are lowered, haze increases and the quality of the multilayer film from which transparency is obtained is insufficient. There is a risk of becoming.

  The draw ratio will be described with reference to FIG. FIG. 2 is a schematic diagram showing a process between a die lip and a cooling roll in the method for producing a multilayer film. In FIG. 2, the resin laminate 4 and the multilayer film 7 are discharged from the top to the bottom, and the cooling rolls 6 are each rotated in the direction of the arrow. The thermoplastic resin composition and the inorganic filler-containing thermoplastic resin composition are discharged from the opening 51 of the die lip 5 and formed into a film to form the resin laminate 4. A multilayer film 7 is obtained by cooling the resin laminate 4 with a cooling roll 6. In the draw ratio ((s1) / (s2)), s1 is the opening area of the opening 51 of the die lip 5, and s2 is the cross-sectional area of the multilayer film 7.

Specifically, the draw ratio ((s1) / (s2)) is a value calculated by the following equation (2).
η = (s1) / (s2) = (W1 × d1) / (W2 × d2) (2)
η: draw ratio s1: opening area s2 of the die lip used in the step (2): cross-sectional area W1 of multilayer film obtained in the step (3) 1: longitudinal width (mm) of the die lip opening
d1: Width in the direction perpendicular to the longitudinal direction of the die lip opening (mm)
W2: Film width of the multilayer film after cooling (mm)
d2: Average thickness (mm) in the width direction of the multilayer film after cooling

  It is preferable that the manufacturing method further includes a step (4a) of heat-treating the multilayer film uniaxially in the longitudinal direction or the width direction of the film after the step (3). When the step (4a) is included, the multilayer film can be heated and stretched in one direction to obtain the retardation necessary for the optical compensation member, and the mechanical properties can be further improved.

  The step (4a) is a step of stretching the multilayer film in the longitudinal direction or the width direction while heating the multilayer film, thereby improving the molecular orientation in the specific direction of the multilayer film constituent molecules. Can do. The mechanical orientation and adhesiveness as a multilayer film can be further improved by the molecular orientation.

  A conventionally known method can be adopted as a longitudinal uniaxial stretching method in the longitudinal direction. Examples of the longitudinal uniaxial stretching method include an inter-roll stretching method and a clip tenter method. From the viewpoint of improving the operability and reducing the equipment cost, the inter-roll stretching method is more preferable. The above-mentioned inter-roll stretching method is such that a plurality of rolls rotated at different rotational speeds are arranged at arbitrary intervals in the longitudinal direction, with the upstream side installed roll being a low speed and the downstream side installed roll being a high speed. This is a method of stretching the multilayer film according to the roll speed difference by running the multilayer film while heating. If the stretching distance, which is the roll arrangement distance, is shorter than the width of the multilayer film, the molecular orientation in the longitudinal direction may be insufficient. If the stretching distance is too long, the multilayer film may be broken, the wrinkles of the multilayer film, contact scratches on the heating furnace parts, etc. may easily occur. The stretching distance can be appropriately set according to the running property of the multilayer film. The roll preferably includes a nip mechanism in order to enhance the holding force of the film to the roll, improve the grip, and not to affect the influence of stress in the heating and stretching process on the preceding and following processes.

  Any conventionally known tenter stretching method can be employed as the lateral uniaxial stretching method in the width direction. Examples of the horizontal uniaxial stretching method include a method in which both end portions in the width direction of the non-oriented film are gripped with a tenter clip, the width in the width direction of the tenter clip is gradually separated, the film is widened in the width direction, and stretched. It is done.

  It is preferable that the manufacturing method further includes a step (4b) of heat-treating the multilayer film biaxially in the longitudinal direction and the width direction of the film after the step (3). In the case of having the step (4b), the multilayer film can be heated and stretched in two directions, whereby the retardation necessary for the optical compensation member can be obtained, and the mechanical properties are further improved.

  The step (4b) is a step of stretching the multilayer film in the longitudinal direction and the width direction while heating the multilayer film, whereby the molecular orientation in the specific direction of the multilayer film constituent molecules can be improved. . The mechanical orientation and adhesiveness as a multilayer film can be further improved by the molecular orientation.

  Examples of the method of stretching in the longitudinal direction and the width direction include a biaxial stretching method. As the above biaxial stretching method, the multilayer film is stretched in the longitudinal direction or the width direction and then stretched in a direction perpendicular to the stretching direction in the previous stage, or simultaneously stretched in the longitudinal direction and the width direction simultaneously. An axial stretching method is mentioned. The biaxial stretching method can be appropriately selected in consideration of optical compensation performance and productivity. The sequential biaxial stretching method is preferable from the viewpoint of reducing the equipment cost and improving the operability and the optical compensation performance, and the simultaneous biaxial stretching method is preferable from the viewpoint of increasing the isotropic property of the in-plane properties of the multilayer film.

  Any conventionally known tenter stretching method can be employed as the biaxial stretching method. For example, as the above simultaneous biaxial stretching method, the both ends of the non-oriented multilayer film in the width direction are gripped with a tenter clip, the interval in the width direction of the tenter clip is gradually separated, and the multilayer film is widened in the width direction, The method of extending | stretching is mentioned. Further, in addition to the above-described width direction stretching method, a method of stretching a multilayer film in the longitudinal direction by gradually separating the clips adjacent to each other in the longitudinal direction using a clip link mechanism by a pantograph structure, a screw structure or a linear motor system. Can be mentioned.

  In the above steps (4a) and (4b), it is preferable that a preheating step and a heat stretching step of stretching the multilayer film while heating are performed when the multilayer film is stretched. Moreover, in the said process (4a) and (4b), it is preferable that the heat processing process which heat-processes the stretched multilayer film is performed. Examples of the heating method for the multilayer film in each step include a hot roll contact heating method and an air convection heating method using an air floating heating method. These heating methods may be used in combination. The heating method for the multilayer film is appropriately selected according to the stretched form.

  The preheating step is a step of heating the multilayer film to a film temperature at which the multi-layer film can be stretched, thereby reducing a curved pattern (so-called bowing) of molecular orientation that occurs in a tenter clip-type stretch form, and aligning the orientation. it can.

  In the preheating step, the non-oriented multilayer film is heated to around the temperature at which it can be stretched. The preheating temperature of the multilayer film in the preheating step is (Tm-50) to (Tm) ° C, where Tm (° C) is the melting point of the thermoplastic resin contained in the thermoplastic resin layer forming the multilayer film. Is preferred. If the preheating temperature is too low, the stretching stress becomes too large in the stretching process, and the multilayer film may be easily cut. If the preheating temperature is too high, the stretching stress of the multilayer film may be insufficient, and the stretching effect may not be sufficiently obtained, and the crystallization may cause stretching and cutting.

  The stretching ratio in the longitudinal direction and the width direction in the heating and stretching step is preferably 1.10 to 15.00 times, and more preferably 1.50 to 10.00 times. If the draw ratio is too low, the desired molecular orientation effect may not be obtained. In addition, if the stretching ratio is too high, the multilayer film may be cut during stretching due to excessive stretching stress, and when using a tenter-type stretching machine, the tenter clip may come off. There is a risk of impairing running stability. The draw ratio affects the degree of molecular orientation and controls the draw effect quantitatively, and can be appropriately determined to obtain the optical properties, toughness and adhesiveness of the multilayer film.

  The strain rate during stretching in the heating and stretching step is preferably 50 to 2000% / min, and more preferably 100 to 2000% / min. If the strain rate is too slow, orientation relaxation occurs following the molecular orientation by stretching, and a sufficient molecular orientation effect may not be obtained. If the strain rate is too high, the multilayer film may be cut or the tenter clip may come off. In addition, by stretching at a high strain rate, particularly in the stretching by the tenter clip method, the clip rail opening angle can be increased and the furnace length of the stretching zone can be shortened as much as possible.

  The heating temperature Ts in the heating and stretching step is preferably (Tm-30) to (Tm) ° C., where T m (° C.) is the melting point of the thermoplastic resin contained in the thermoplastic resin layer forming the multilayer film. . By heating and stretching in the above temperature range, the deformation of the multilayer film can be suppressed from proceeding selectively at the minimum thickness portion of the non-oriented film, and thus is not easily affected by the thickness failure of the original fabric. Become.

  If the heating temperature Ts is too high, the stretching stress is insufficient, the molecular orientation effect due to stretching cannot be sufficiently obtained, and the orientation relaxation is prioritized and the desired mechanical properties and adhesiveness may not be obtained. . If the heating and stretching temperature Ts is too low, a non-uniform deformation due to uneven stretching results in a multilayer film with a poor thickness, which may reduce the commercial value of the optical film. Moreover, there exists a possibility that the image display quality of a liquid crystal panel may fall, For this reason, there exists a possibility that the commercial value as a multilayer film may fall.

  The stretching time in the heating and stretching step is preferably 10 to 100 seconds, and more preferably 20 to 60 seconds. When the said extending | stretching time is too long, there exists a possibility that the molecular orientation effect by extending | stretching cannot be acquired by the orientation relaxation by heating. If the stretching time is too short, the molecular orientation becomes non-uniform due to remarkable bowing, and there is a risk that dimensional stability such as heat shrinkage rate and anisotropy of tensile properties such as breaking strength and elongation may be exhibited. When used as a film, the accuracy of the optical axis may deteriorate. In addition, the multilayer film may be cut during stretching or the tenter clip may be detached due to excessive stretching stress, which may impair film running stability.

  The heat treatment step is a step for removing or reducing residual strain of the stretched multilayer film and annealing. By the heat treatment step, bowing of the stretched multilayer film can be reduced and the orientation can be made uniform. Accordingly, the anisotropy of mechanical properties can be reduced, dimensional stability characteristics can be imparted, and the thickness can be made uniform.

  The heating temperature in the heat treatment step is preferably (Tm-100) to (Tm-10) ° C, where Tm (° C) is the melting point of the thermoplastic resin contained in the thermoplastic resin layer forming the multilayer film. . By setting the heating temperature within the above range, bowing can be controlled and the molecular alignment accuracy can be increased, and further, the rigidity of the multilayer film can be improved by increasing the thermoplasticity. If the heating temperature is too high, the molecular orientation obtained by stretching may be relaxed and the mechanical strength may be reduced.

  The heating time in the heat treatment step can be appropriately set according to the film running speed determined based on continuous productivity. The heating time is preferably 5 to 60 seconds, and more preferably 10 to 30 seconds. By setting the heating time in the above range, bowing can be suppressed and molecular alignment accuracy can be improved. If the heating time is too short, a sufficient annealing effect cannot be obtained, and as a result, the orientation protrudes to the downstream side of the multilayer film flow, which may promote reverse bowing. If the heating time is too long, the orientation may protrude to the upstream side of the film flow, which may promote positive bowing. For this reason, the dimensional stability of a multilayer film is impaired, the image display quality of a liquid crystal panel falls, and there exists a possibility that the commercial value as a multilayer film may fall.

  In the multilayer film of the present invention, the second thermoplastic resin layer containing the inorganic filler is alternately laminated with the first thermoplastic resin layer, and the first thermoplastic resin layer and the second thermoplastic resin are laminated. The total number of layers is 10 or more, and the inorganic filler has at least one shape selected from needle-like and plate-like shapes, and is oriented substantially parallel to the plane direction of the multilayer film. Therefore, it has excellent mechanical properties, hardly causes appearance defects such as elongation during processing, scratches and dents, and is excellent in transparency and optical anisotropy.

It is sectional drawing of the optical film which concerns on one Embodiment of this invention. It is a schematic diagram which shows the process between the die lip and the cooling roll in the manufacturing method of a multilayer film.

(Example)
Examples of the present invention will be described below. The present invention is not limited to the following examples.

(Production Example 1)
95 parts by weight of polypropylene resin (manufactured by Prime Polymer Co., Ltd., trade name: S136, melting point 165 ° C., density 0.90 g / cm ³ , MFR 20 g / 10 min (measuring conditions: temperature 230 ° C., load 20 N)), and 6 potassium titanate In a twin screw extruder in which 5 parts by weight of a needle-like inorganic filler (made by Otsuka Chemical Co., Ltd., trade name: Tismo (registered trademark) D, aspect ratio: 33) is mixed and the cylinder temperature is set to 210 ° C. The supplied strand was filled and the extruded strand was cut with a pelletizer to produce pellets of the inorganic filler-containing polypropylene resin (1).

(Production Example 2)
Production Example 1 except that the acicular inorganic filler was changed to acicular inorganic filler mainly composed of 8 potassium titanate (manufactured by Otsuka Chemical Co., Ltd., trade name: Tismo (registered trademark) N, aspect ratio: 33). In the same manner, an inorganic filler-containing polypropylene resin (2) pellet was obtained.

(Production Example 3)
Manufacture example 1 except having changed the said acicular inorganic filler into the plate-shaped inorganic filler (made by Otsuka Chemical Co., Ltd., brand name: Terrases (trademark) PS, aspect ratio: 3) which has potassium 6 titanate as a main component. In the same manner as above, pellets of the inorganic filler-containing polypropylene resin (3) were obtained.

(Production Example 4)
A pellet of inorganic filler-containing polypropylene resin (4) was obtained in the same manner as in Production Example 1, except that the blending ratio of the polypropylene resin was 90 parts by weight and the blending ratio of the acicular inorganic filler was 10 parts by weight.

(Production Example 5)
Polypropylene resin (5) pellets were obtained in the same manner as in Production Example 1 except that the blending ratio of the polypropylene resin was 100 parts by weight and no acicular inorganic filler was blended.

(Example 1)
100 parts by weight of polypropylene resin (manufactured by Prime Polymer Co., Ltd., trade name: S136, melting point 165 ° C., density 0.90 g / cm ³ , MFR 20 g / 10 min (measuring conditions: temperature 230 ° C., load 20 N)) with a cylinder diameter of 90 mm It supplied to the single screw extruder I (full flight type screw, L / D = 28, compression ratio 2.5), and it melt-kneaded on the conditions of the cylinder temperature of 230 degreeC, and obtained the thermoplastic resin composition.

  At the same time, 100 parts by weight of the inorganic filler-containing polypropylene resin (1) pellets were transferred to a single-screw extruder II (full-flight screw, L / D = 35, compression ratio 2. 3) and melt-kneaded under the condition of a cylinder temperature of 220 ° C. to obtain an inorganic filler-containing thermoplastic resin composition.

  The thermoplastic resin composition and the inorganic filler-containing thermoplastic resin composition are made to have the same molten resin amount, and each is fixed to a fixed vane type feed block (hereinafter referred to as “FB” as appropriate) through a feed pipe. It was transported to. The film-like inorganic filler-containing thermoplastic resin composition melt-extruded from the single-screw extruder II is laminated on both surfaces of the film-like thermoplastic resin composition melt-extruded from the single-screw extruder I. Then, these were merged in the FB to obtain a resin laminate. Furthermore, 4 sets of multi-layer blocks that can be divided and stacked are attached to the downstream part of the FB, and the total number of stacked layers is set to 48 by stacking 16 of the above-mentioned 3 layers of resin laminates and introduced into the T-die. Widened and discharged from the die lip opening to obtain a multilayer resin laminate. The T die was provided with a straight type manifold, the die lip opening was rectangular, the longitudinal width was 1000 mm, and the width in the direction perpendicular to the longitudinal direction was 2.5 mm. A multilayer resin laminate is melt-extruded from a die lip opening of a T die onto a chrome-plated cooling roll at a take-up speed of 10 m / min, solidified by cooling, and continuously formed into a sheet, having a width of 700 mm and a width direction. A multilayer film having an average thickness of 500 μm was produced. The draw ratio ((s1) / (s2)) represented by the opening area (s1) of the die lip of the T die and the cross-sectional area (s2) of the obtained multilayer film was 7.2.

  The multilayer film was supplied to a roll type stretching machine having a preheating zone, a stretching zone, a heat treatment zone, and a cooling zone. The conveyance speed of the multilayer film was 10 m / min at the preheating zone entrance. The multilayer film was heated to 115 ° C. in the preheating zone. An upstream nip roll and a downstream nip roll are provided on the upstream side and the downstream side in the drawing direction of the multilayer film, and the rotational speed ratio of the downstream nip roll speed (va) to the upstream nip roll speed (vb) (Va) / (vb) was set to 3.0. The strain rate was 300% / min. In the stretching zone, the film was heated and stretched at 115 ° C. in the longitudinal direction, and then immediately cooled to 80 ° C. in the cooling zone and fixed in orientation to obtain a multilayer film uniaxially stretched in the longitudinal direction.

  The uniaxially stretched multilayer film was supplied to a transverse uniaxial tenter stretching machine having a preheating zone, a stretching zone, a heat treatment zone, and a cooling zone. The end of the uniaxially stretched multilayer film is gripped with a tenter clip, and the multilayer film is heated to 140 ° C. in the preheating zone and then transported to the subsequent stretching zone. The stretching ratio is 4.5 times, and the strain rate is 300% / In minutes, the film was heat-drawn at 155 ° C. in the width direction and immediately annealed at 130 ° C. in the subsequent heat treatment zone. Further, after cooling to 80 ° C. in the cooling zone and fixing the orientation, the end of the multilayer film was released from gripping the clip at the exit of the stretching machine. Next, the end of the multilayer film where the clip grip marks remained in the slitting process was removed by slitting with a shear blade installed symmetrically from the center of the multilayer film. The film was wound into a roll on a vinyl chloride resin core with a winding tension of 100 N / m width.

  The acicular inorganic filler of the obtained multilayer film was oriented substantially parallel to the plane direction of the multilayer film and was oriented in the longitudinal direction of the multilayer film. Moreover, the width | variety of the obtained multilayer film was 1500 mm except the both ends containing a tenter clip grip trace, and the average thickness of the width direction was about 60 micrometers. The obtained multilayer film was evaluated for tensile modulus, haze, front retardation value R0, surface hardness, and tear strength.

(Examples 2 to 4)
A multilayer film was produced in the same manner as in Example 1 except that the inorganic filler-containing polypropylene resin was changed to the resin shown in Table 1.

(Examples 5 and 6)
A multilayer film was produced in the same manner as in Example 1 except that the number of multilayer blocks was changed and the total number of multilayer films was changed as shown in Table 1.

(Comparative Example 1)
A multilayer film was produced in the same manner as in Example 1 except that the inorganic filler-containing polypropylene resin was changed to the resin described in Table 1.

(Comparative Example 2)
A multilayer film was produced in the same manner as in Example 1 except that the multilayer block was not used and the total number of multilayer films was changed as shown in Table 1.

(Comparative Example 3)
A multilayer film was produced in the same manner as in Example 1 except that the number of multilayer blocks was changed and the total number of multilayer films was changed as shown in Table 1.

(Evaluation)
The total number of laminates of the multilayer films produced in Examples 1 to 6 and Comparative Examples 1 to 3, tensile modulus, haze, front retardation value R0, surface hardness, and static friction coefficient were evaluated by the following evaluation methods.

(1) Total number of laminated layers The central portion in the width direction of the multilayer film was cut in parallel with the longitudinal direction with a sharp leather blade. The cross section was visually observed with a digital microscope (manufactured by Keyence Corporation, model number “VHX-200”), and the total number of laminated layers in the thickness direction was counted.

(2) Tensile modulus Measured according to the tensile test method described in JISK-7127 and JISK-7161. The measurement was performed in the longitudinal direction and the width direction of the multilayer film, and the average value was taken as the tensile modulus. The measurement atmosphere was a temperature of 23 ° C. and a relative humidity of 50% RH.

(3) Haze The measurement was performed in accordance with the plastic optical property test method described in JISK -7105. Using a haze meter (manufactured by Tokyo Denshoku Co., Ltd., model number “TC-H3DPK”), measurements were made at 50 mm intervals in the width direction of the multilayer film, and an average value was calculated to obtain the haze of the multilayer film.

(4) Front retardation value R0
It measured using the automatic birefringence measuring apparatus (Oji Scientific Instruments company make, model number "KOBRA-WR"). The wavelength of the measuring light is set to 550 nm, the axis perpendicular to the longitudinal direction of the multilayer film is used as a reference axis, the total average value is calculated by measuring the multilayer film in the width direction at intervals of 50 mm, and the front retardation value R0 of the multilayer film is calculated. It was.

(5) Surface hardness It measured based on the pencil scratch test method of JISK-5400. The surface hardness of the multilayer film was defined as the lowest pencil hardness at which a scratch with a pencil enters the multilayer film surface at a load of 0.98N.

(6) Tear strength Measured according to the tear strength test method (trouser method) described in JISK-7128-1. The measurement was performed along the longitudinal direction of the multilayer film. The measurement was performed under environmental conditions of a temperature of 23 ° C. and a relative humidity of 50% RH.

  The results are shown in Table 1 below.

(Discussion)
From the results in Table 1, the multilayer films of Examples 1 to 6 are formed by alternately laminating the first thermoplastic resin layer and the second thermoplastic resin layer, and the second thermoplastic resin layer is It contains an acicular inorganic filler, the total number of laminations of the first thermoplastic resin layer and the second thermoplastic resin layer is 10 or more, and the acicular inorganic filler is substantially parallel to the plane direction of the multilayer film. Since they are oriented, they have high tensile elastic modulus, pencil hardness, and tear strength, and are excellent in mechanical properties. Moreover, since the haze was low and the value of the front retardation R0 was appropriate, the optical properties were excellent.

  The multilayer film of Comparative Example 1 had inferior mechanical properties because the second thermoplastic resin layer did not contain an inorganic filler, and had low tensile elastic modulus, pencil hardness, and tear strength. Moreover, the value of the front retardation R0 was high and the optical characteristics were inferior.

  The multilayer films of Comparative Examples 2 and 3 had poor mechanical properties due to a small number of laminated layers, and had low tensile elastic modulus, pencil hardness, and tear strength. Moreover, the value of the front retardation R0 was high and the optical characteristics were inferior.

DESCRIPTION OF SYMBOLS 1 ... Multilayer film 21,22,23,24,25,26 ... 1st thermoplastic resin layer 31,32,33,34,35,36,37 ... 2nd thermoplastic resin layer 4 ... Resin laminated body 5 ... Die lip 51 ... Die lip opening 6 ... Cooling roll 7 ... Multilayer film

Claims (3)

A multilayer film in which a first thermoplastic resin layer and a second thermoplastic resin layer are alternately laminated,
The second thermoplastic resin layer contains a polypropylene resin and an inorganic filler,
The content of the polypropylene resin in the second thermoplastic resin layer is 90% by weight or more with respect to 100% by weight of the thermoplastic resin composition forming the second thermoplastic resin layer,
The content of the inorganic filler in the second thermoplastic resin layer is 10% by weight or less based on 100% by weight of the thermoplastic resin composition forming the second thermoplastic resin layer,
The total number of laminations of the first thermoplastic resin layer and the second thermoplastic resin layer is 10 or more;
The inorganic filler contains titanate, has at least one shape selected from a needle shape and a plate shape, and is oriented substantially parallel to the plane direction of the multilayer film. the film.   The multilayer film according to claim 1, wherein the inorganic filler has an aspect ratio of 10 or more.   The multilayer film according to claim 1 or 2, wherein the first thermoplastic resin layer includes a polypropylene resin.

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