JP2013136192A - Method of manufacturing multilayered film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a multilayered film which forms a urethane resin layer on a substrate film, and suppresses the generation of foreign matters or coating unevenness.SOLUTION: The method of manufacturing the multilayered film includes: a step of coating aqueous dispersion containing polyurethane on a substrate film; and a step of forming the urethane resin layer by curing the layer. In the polyurethane, a ratio V1/V2 of a percentage V1 (vol.%) of particles with a particle diameter of 0.2 μm or more and a percentage V2 (vol.%) of particles with a particle diameter of less than 0.2 μm is 0.11 or less.

Description

  The present invention relates to a method for producing a multilayer film formed by forming a layer containing polyurethane on a base film.

  For example, a film made of a thermoplastic resin is known as a film used in various image display devices such as a liquid crystal display device, an organic EL display device, and a plasma display. Since these films are excellent in optical properties, for example, electrode substrates of liquid crystal cells constituting liquid crystal display devices, polarizing plates, protective films for polarizing plates, retardation films, viewing angle widening films, brightness enhancement films, touch panels Development for optical applications such as a film with a transparent electrode, a light guide plate, and an optical disk is being made.

  Films used for optical applications such as those described above are bonded to members having various other functions such as polarizers, hard coat layers, antireflection layers, antistatic layers, antiglare layers, and antifouling layers. Often used. Therefore, it is desired that the film has high adhesive strength with the member to be bonded.

  However, some films having a layer made of a thermoplastic resin are inferior in adhesion to other members. Therefore, it has been conventionally performed to provide an easy adhesion layer on the surface of the film. The easy-adhesion layer is a layer that reinforces the adhesive force of the film and bonds it more firmly when the film is bonded to some member via an adhesive as necessary. About the easily bonding layer, what was formed with the urethane resin has been proposed conventionally (refer patent documents 1-3).

JP 2009-274390 A JP 2006-201736 A JP 2009-80177 A

  However, the film provided with the easy-adhesion layer sometimes causes foreign matter and uneven coating. When such a film having foreign matter or coating unevenness is used in an image display device, the display quality may deteriorate.

  The present invention was devised in view of the above problems, and is a method for producing a multilayer film comprising applying a water dispersion containing polyurethane on a base film and curing to form a urethane resin layer. Then, it aims at providing the manufacturing method of the multilayer film in which the production | generation of the foreign material and the coating nonuniformity was suppressed.

As a result of intensive studies to solve the above-mentioned problems, the present inventor has applied a water dispersion containing polyurethane on a base film and cured to form a urethane resin layer. In the method, the present inventors have found that the above-mentioned problems can be solved by using a polyurethane water dispersion having a specific particle size distribution as the polyurethane, and completed the present invention.
That is, the gist of the present invention is the following [1] to [4].

[1] A method for producing a multilayer film comprising applying a polyurethane-containing aqueous dispersion on a base film and curing to form a urethane resin layer,
In the polyurethane, a ratio V1 / V2 of a ratio V1 (volume%) of particles having a particle diameter of 0.2 μm or more and a ratio V2 (volume%) of particles having a particle diameter of less than 0.2 μm is 0.11 or less. A method for producing a multilayer film.

[2] The ratio V1 / V2 of the ratio V1 (volume%) of particles having a particle diameter of 0.2 μm or more and the ratio V2 (volume%) of particles having a particle diameter of less than 0.2 μm is 0.11 or less. Water dispersion
When the standard dust dispersion water is filtered at 10 L / min, it is filtered through a filter having a particle trapping performance represented by the maximum particle diameter of 99% or more and 5 μm to 20 μm, and then the particle trapping performance is 0.8 μm. After filtering with a filter of 5 μm or less,
The method according to [1], wherein the method is applied onto a base film.

[3] The production method according to [1] or [2], wherein the aqueous dispersion containing the polyurethane further contains a crosslinking agent.
[4] The production method according to any one of [1] to [3], wherein the aqueous dispersion containing polyurethane further contains fine particles.

  ADVANTAGE OF THE INVENTION According to this invention, the production method of the multilayer film which can suppress the production | generation of a foreign material and coating unevenness and can implement | achieve a high optical characteristic can be provided.

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

  In the production method of the present invention, an aqueous dispersion containing polyurethane (hereinafter sometimes referred to as “polyurethane aqueous dispersion”) is applied on a base film and cured to form a urethane resin layer. A method for producing a multilayer film comprising: a ratio of a ratio V1 (volume%) of particles having a particle diameter of 0.2 μm or more and a ratio V2 (volume%) of particles having a particle diameter of less than 0.2 μm. V1 / V2 is 0.11 or less.

  Here, the particle size of the polyurethane is a value measured based on a particle size distribution measured using a laser diffraction scattering method particle size distribution measuring apparatus. As the measuring device, it is preferable to use a device whose lower limit of the measurable particle size range is 0.05 μm or less. For example, you may measure by the laser diffraction scattering method particle size distribution measuring device LS-230 by a Coulter company.

  When V1 / V2 is 0.11 or less, the production of foreign matter and coating unevenness can be suppressed in the production of a multilayer film. This is because the proportion of polyurethane particles having a large particle size is small, and the particles can be prevented from agglomerating to become foreign matters, thereby preventing unevenness in circular coating resulting from loss of continuity of the coated surface by foreign matters. This is because it can be suppressed.

[Base film]
As the base film, a resin film is usually used. The resin forming the base film contains at least one polymer. Examples of the polymer contained in such a resin include olefin polymers such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyarylene sulfides such as polyphenylene sulfide; polyvinyl alcohol; polycarbonate; polyarylate; Polysulfone; Polysulfone; Polyallyl sulfone; Polyvinyl chloride; Alicyclic structure-containing polymer; Acrylic polymer; Styrenic polymer such as polystyrene; In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  As the resin to be used, a resin containing an alicyclic structure-containing polymer (hereinafter referred to as “alicyclic structure-containing polymer resin” as appropriate), a resin containing an acrylic polymer, and a resin containing a polycarbonate are preferable and transparent. In particular, an alicyclic structure-containing polymer resin is particularly preferable because of its excellent properties, low hygroscopicity, dimensional stability, lightness, and the like, and is suitable for an optical film. Further, in general, the alicyclic structure-containing polymer resin has low affinity with water, and it may be difficult to uniformly apply the polyurethane water dispersion. According to the production method of the present invention, the polyurethane water dispersion Can be applied uniformly, and it is possible to produce a multilayer film with less foreign matter and uneven coating.

  Further, the base film may be a single layer structure film having only one layer, or may be a multilayer structure film having two or more layers. When the base film includes two or more layers, it is preferable that the layer formed of an alicyclic structure-containing polymer resin, a resin containing an acrylic polymer, or a polycarbonate resin forms the outermost surface of the base film. .

[Alicyclic structure-containing polymer resin]
The alicyclic structure-containing polymer resin is a resin containing an alicyclic structure-containing polymer. The alicyclic structure-containing polymer is a polymer having an alicyclic structure in the repeating unit of the polymer, and has a polymer having an alicyclic structure in the main chain and an alicyclic structure in the side chain. Any of the polymers may be used. An alicyclic structure containing polymer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Among these, a polymer containing an alicyclic structure in the main chain is preferable from the viewpoint of mechanical strength, heat resistance, and the like.

  Examples of the alicyclic structure include a saturated alicyclic hydrocarbon (cycloalkane) structure and an unsaturated alicyclic hydrocarbon (cycloalkene) structure. From the viewpoint of mechanical strength and heat resistance, the cycloalkane structure is exemplified. Is preferred.

  The number of carbon atoms constituting the alicyclic structure is not particularly limited, but is usually 4 or more, preferably 5 or more, usually 30 or less, preferably 20 or less, more preferably 15 or less. , The mechanical strength, heat resistance, and moldability of the base material are highly balanced and suitable.

  The ratio of the repeating unit having an alicyclic structure in the polymer having an alicyclic structure is preferably 55% by weight or more, more preferably 70% by weight or more, particularly preferably 90% by weight or more, and usually 100% by weight. % Or less. It is preferable from a viewpoint of transparency and heat resistance that the ratio of the repeating unit which has an alicyclic structure in the polymer which has an alicyclic structure exists in the said range.

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

  The norbornene-based polymer is a homopolymer of a monomer having a norbornene structure (hereinafter referred to as a norbornene-based monomer) or a copolymer of a norbornene-based monomer and another monomer. Specifically, a ring-opening polymer of a norbornene monomer, a ring-opening copolymer of a norbornene monomer and another monomer, or a hydride thereof; an addition polymer of a norbornene monomer Alternatively, an addition copolymer of a norbornene monomer and another monomer, or a hydride thereof can be used. Among these, a ring-opening (co) polymer hydride of a norbornene monomer is particularly preferably used from the viewpoints of transparency, moldability, heat resistance, low hygroscopicity, dimensional stability, lightness, and the like. Can do. “(Co) polymerization” means polymerization and copolymerization.

Examples of the norbornene-based monomer include bicyclo [2.2.1] hept-2-ene (common name: norbornene), tricyclo [4.3.0.1 ^2,5 ] deca-3,7-diene. (Common name: dicyclopentadiene), 7,8-benzotricyclo [4.3.0.1 ^2,5 ] dec-3-ene (common name: methanotetrahydrofluorene), tetracyclo [4.4.0. 1 ^2,5 . ^{17, 10} ] dodec-3-ene (common name: tetracyclododecene), and derivatives of these compounds (for example, those having a substituent in the ring). In addition, a norbornene-type monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  Here, as a substituent which the monomer which has a norbornene structure has, an alkyl group, an alkylene group, a polar group etc. can be mentioned, for example. These substituents may be of one type or two or more types. Further, the number of substituents substituted on one monomer may be one or two or more. Examples of the polar group include a hetero atom or an atomic group having a hetero atom. Examples of the hetero atom include an oxygen atom, a nitrogen atom, a sulfur atom, a silicon atom, and a halogen atom. Specific examples of the polar group include a carboxyl group, a carbonyloxycarbonyl group, an epoxy group, a hydroxyl group, an oxy group, an ester group, a silanol group, a silyl group, an amino group, a nitrile group, and a sulfone group. In order to obtain a multilayer film having a low moisture permeability, it is preferable that the amount of polar groups is small, and it is more preferable that polar groups are not present.

Other monomers capable of ring-opening copolymerization with norbornene monomers include, for example, monocyclic olefins such as cyclohexene, cycloheptene, and cyclooctene and derivatives thereof; cyclic conjugated dienes such as cyclohexadiene and cycloheptadiene; Derivatives thereof; and the like. In addition, these other monomers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
A ring-opening polymer of a norbornene-based monomer and a ring-opening copolymer with another monomer that can be copolymerized with the norbornene-based monomer include, for example, a known ring-opening polymerization catalyst. It can be obtained by (co) polymerization in the presence.

Examples of other monomers capable of addition copolymerization with norbornene monomers include, for example, α-olefins having 2 to 20 carbon atoms such as ethylene, propylene, 1-butene, and derivatives thereof; cyclobutene, cyclopentene, cyclohexene, and the like. And non-conjugated dienes such as 1,4-hexadiene, 4-methyl-1,4-hexadiene, and 5-methyl-1,4-hexadiene. Among these, α-olefin is preferable and ethylene is more preferable. In addition, these other monomers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
An addition polymer of a norbornene monomer and an addition copolymer with another monomer copolymerizable with the norbornene monomer, for example, the monomer in the presence of a known addition polymerization catalyst. It can be obtained by polymerization.

Among the norbornene polymers described above, as a repeating unit, X: bicyclo [3.3.0] octane-2,4-diyl-ethylene structure and Y: tricyclo [4.3.0.1 ^2,5 ] are used. Having a decane-7,9-diyl-ethylene structure, and the content of these repeating units X and Y is 90% by weight or more based on the entire repeating unit of the norbornene polymer, and the content of X The ratio of the ratio and the content ratio of Y is preferably 100: 0 to 40:60 by weight ratio of X: Y. By using such a polymer, it is possible to obtain a multilayer film having no dimensional change in the long term and excellent optical property stability.

  The polymer which has an alicyclic structure may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The molecular weight of a polymer having an alicyclic structure was measured by a gel permeation chromatography using cyclohexane as a solvent (however, toluene may be used when the polymer resin does not dissolve in cyclohexane). Isoprene or polystyrene-equivalent weight average molecular weight (Mw), usually 10,000 or more, preferably 15,000 or more, more preferably 20,000 or more, usually 100,000 or less, preferably 80,000 or less, more Preferably it is 50,000 or less. When the weight average molecular weight Mw is in such a range, the mechanical strength and molding processability of the multilayer film obtained in the present invention are highly balanced, which is preferable.

  Furthermore, the resin containing a polymer having an alicyclic structure may contain other components in addition to the polymer having an alicyclic structure, if necessary. For example, the polymer having an alicyclic structure may include a polymer having no alicyclic structure. However, the amount of the polymer having no alicyclic structure is preferably in a range that does not significantly impair the effects of the present invention. Specifically, with respect to 100 parts by weight of the polymer having an alicyclic structure, Usually 50 parts by weight or less, preferably 30 parts by weight or less.

  The alicyclic structure-containing polymer resin may contain other components in addition to the alicyclic structure-containing polymer as long as the effects of the present invention are not significantly impaired. Examples of other components include colorants such as pigments and dyes; plasticizers; fluorescent brighteners; dispersants; thermal stabilizers; light stabilizers; ultraviolet absorbers; antistatic agents; An additive such as a surfactant may be mentioned. These components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  However, it is preferable that the alicyclic structure-containing polymer resin does not substantially contain particles. Here, “substantially free of particles” means that, even when particles are included in the alicyclic structure-containing polymer resin, the increase in haze of the base film from a state in which no particles are included is 0.05% or less. This means that up to an amount in the range is acceptable. Since the alicyclic structure-containing polymer lacks affinity with many organic particles and inorganic particles, voids are generated when the alicyclic structure-containing polymer resin containing particles exceeding the above range is stretched. As a result, the haze may be significantly reduced.

  The layer made of the alicyclic structure-containing polymer resin is not particularly limited by the production method. The layer made of the alicyclic structure-containing polymer resin is obtained by molding the alicyclic structure-containing polymer resin by a known film forming method. Examples of the film forming method include a cast forming method, an extrusion forming method, and an inflation forming method. Among these, a melt extrusion method that does not use a solvent can reduce the amount of residual volatile components efficiently, and is preferable from the viewpoints of the global environment and work environment, and excellent manufacturing efficiency. Examples of the melt extrusion method include an inflation method using a die, and among them, a method using a T die is preferable in terms of excellent productivity and thickness accuracy.

[Resin containing acrylic polymer]
An acrylic polymer used for a resin containing an acrylic polymer means a polymer of acrylic acid or an acrylic acid derivative, for example, a polymer such as acrylic acid, acrylic ester, acrylamide, acrylonitrile, methacrylic acid, and methacrylic ester. And copolymers.

  As the acrylic polymer, a polymer containing a repeating unit derived from a (meth) acrylic acid ester is preferable. Here, “(meth) acrylic acid” means acrylic acid and methacrylic acid.

  Examples of (meth) acrylic acid esters include alkyl esters of (meth) acrylic acid. Especially, the thing derived from (meth) acrylic acid and a C1-C15 alkanol or cycloalkanol is preferable, and the thing derived from a C1-C8 alkanol is more preferable. By reducing the number of carbon atoms as described above, the elongation at break of the retardation film can be reduced.

  Specific examples of the acrylate ester include methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, sec-butyl acrylate, and t-acrylate. -Butyl, n-hexyl acrylate, cyclohexyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, n-decyl acrylate, n-dodecyl acrylate, and the like.

  Specific examples of the methacrylic acid ester include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, sec-butyl methacrylate, methacrylic acid. Examples thereof include t-butyl acid, n-hexyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, n-decyl methacrylate, and n-dodecyl methacrylate.

Furthermore, the (meth) acrylic acid ester may have a substituent such as a hydroxyl group or a halogen atom as long as the effects of the present invention are not significantly impaired. Examples of the (meth) acrylic acid ester having such a substituent include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, 2-methacrylic acid 2- Examples include hydroxypropyl, 4-hydroxybutyl methacrylate, 3-chloro-2-hydroxypropyl methacrylate, and glycidyl methacrylate.
In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  The acrylic polymer may be a polymer of acrylic acid or an acrylic acid derivative alone, but may be a copolymer of acrylic acid or an acrylic acid derivative and a monomer copolymerizable therewith. Examples of the copolymerizable monomer include α, β-ethylenically unsaturated carboxylic acid ester monomers other than the above-mentioned (meth) acrylic acid esters, and α, β-ethylenically unsaturated carboxylic acid monomers. Examples include a monomer, an alkenyl aromatic monomer, a conjugated diene monomer, a non-conjugated diene monomer, a carboxylic acid unsaturated alcohol ester, and an olefin monomer. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  Specific examples of α, β-ethylenically unsaturated carboxylic acid ester monomers other than (meth) acrylic acid esters include dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, and dimethyl itaconate. It is done.

  The α, β-ethylenically unsaturated carboxylic acid monomer may be any of a monocarboxylic acid, a polyvalent carboxylic acid, a partial ester of a polyvalent carboxylic acid, and a polyvalent carboxylic acid anhydride. Specific examples thereof include crotonic acid, maleic acid, fumaric acid, itaconic acid, monoethyl maleate, mono n-butyl fumarate, maleic anhydride, itaconic anhydride and the like.

  Specific examples of the alkenyl aromatic monomer include styrene, α-methylstyrene, methyl α-methylstyrene, vinyl toluene and divinylbenzene.

  Specific examples of the conjugated diene monomer include 1,3-butadiene, 2-methyl-1,3-butadiene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, and 2-chloro-1. , 3-butadiene, cyclopentadiene and the like.

  Specific examples of the non-conjugated diene monomer include 1,4-hexadiene, dicyclopentadiene, ethylidene norbornene and the like.

  Specific examples of the carboxylic acid unsaturated alcohol ester monomer include vinyl acetate.

  Specific examples of the olefin monomer include ethylene, propylene, butene, pentene and the like.

  When the acrylic polymer contains a copolymerizable monomer, the content of the repeating unit derived from the monomer copolymerizable with acrylic acid or an acrylic acid derivative in the acrylic polymer is preferably 50% by weight. Hereinafter, it is more preferably 15% by weight or less, particularly preferably 10% by weight or less.

  Of these acrylic polymers, polymethacrylate is preferred, and polymethyl methacrylate is more preferred.

  The resin containing an acrylic polymer preferably contains rubber particles in addition to the acrylic polymer. The rubber particle content is preferably 5 to 50 parts by weight with respect to 100 parts by weight of the acrylic polymer.

  Examples of the rubber particles include particles composed of acrylic ester polymer rubber, polymer rubber mainly composed of butadiene, ethylene-vinyl acetate copolymer rubber, and the like. Examples of the acrylic ester polymer rubber include those having butyl acrylate, 2-ethylhexyl acrylate, or the like as a main component of a monomer unit. Of these, acrylic acid ester polymer rubber mainly composed of butyl acrylate and polymer rubber mainly composed of butadiene are preferable.

  The rubber particles may be formed by laminating two kinds of polymers. Typical examples include a core made of a rubber elastic component obtained by grafting alkyl acrylate such as butyl acrylate and styrene, and a hard resin layer (shell) made of polymethyl methacrylate and / or a copolymer of methyl methacrylate and alkyl acrylate. ) And particles forming a layer with a core-shell structure.

  The rubber particles have a refractive index np (λ) at a wavelength of 380 nm to 780 nm and a refractive index nm (λ) at a wavelength of 380 nm to 780 nm of an acrylic polymer serving as a matrix, | np (λ) −nm (λ) It is preferable that the relationship | ≦ 0.05 is satisfied. In particular, it is more preferable that | np (λ) −nm (λ) | ≦ 0.045. Note that np (λ) and nm (λ) are average values of the main refractive index at the wavelength λ. When the value of | np (λ) −nm (λ) | exceeds the above value, transparency may be impaired due to interface reflection caused by a difference in refractive index at the interface.

  The resin containing the acrylic polymer may contain other components in addition to the acrylic polymer and the rubber particles as long as the effects of the present invention are not significantly impaired. If the example of another component is given, the example similar to the other component which alicyclic structure containing polymer resin may contain is given. In addition, the other component may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The layer made of a resin containing an acrylic polymer is not particularly limited by the manufacturing method. The layer made of a resin containing an acrylic polymer can be produced, for example, in the same manner as the layer made of the above-described alicyclic structure-containing polymer resin.

[Resin containing polycarbonate]
Any polycarbonate can be used as the polycarbonate used in the resin including the polycarbonate as long as it is a polymer having a repeating unit (hereinafter referred to as “carbonate component” as appropriate) by a carbonate bond (—O—C (═O) —O—). Can be used. Moreover, what consists of one type of repeating unit may be used for a polycarbonate, and what combined two or more types of repeating units in arbitrary ratios may be used. Further, the polycarbonate may be a copolymer having a repeating unit other than the carbonate component. When the polycarbonate is a copolymer, the polycarbonate may be a random copolymer, a block copolymer, or a graft copolymer. However, even when the polycarbonate has a repeating unit other than the carbonate component, the content of the carbonate component contained in the polycarbonate is preferably high. Specifically, the content is preferably 80% by weight or more, and more preferably 85% by weight or more.

  Examples of the polycarbonate include bisphenol A polycarbonate, branched bisphenol A polycarbonate, o, o, o ', o'-tetramethylbisphenol A polycarbonate, and the like.

  The resin containing the polycarbonate may contain other components in addition to the polycarbonate as long as the effects of the present invention are not significantly impaired. If the example of another component is given, the example similar to the other component which alicyclic structure containing polymer resin may contain is given. In addition, the other component may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The layer made of a resin containing polycarbonate is not particularly limited by the production method. The layer made of a resin containing polycarbonate can be produced, for example, by the same method as the layer made of the above-described alicyclic structure-containing polymer resin.

[Stretching of base film]
The base film may be a non-stretched unstretched film or a stretched stretched film.

  The stretching method of the base film is not particularly limited, and for example, either a uniaxial stretching method or a biaxial stretching method may be adopted. As an example of the stretching method, as an example of the uniaxial stretching method, a method of uniaxial stretching in the longitudinal direction using a difference in peripheral speed of a roll for film conveyance; a transverse direction (width direction, And a method of uniaxial stretching in the TD direction). In addition, as an example of the biaxial stretching method, the simultaneous biaxial stretching method in which the guide rail is extended in the transverse direction at the same time as the longitudinal stretching with a gap between the clips to be fixed; between the rolls for film conveyance Examples include a biaxial stretching method such as a sequential biaxial stretching method in which the both ends are stretched in the longitudinal direction using the difference in peripheral speeds of the two, and the two ends are stretched in the lateral direction using a tenter stretching machine. . Further, for example, using a tenter stretching machine that can add a feeding force, a pulling force, or a pulling force at different speeds in the horizontal or vertical direction, in a direction that forms an arbitrary angle θ with respect to the width direction of the film. An oblique stretching method that continuously obliquely stretches may be used.

Examples of the apparatus used for stretching include a longitudinal uniaxial stretching machine, a tenter stretching machine, a bubble stretching machine, and a roller stretching machine.
The temperature during stretching is preferably between (Tg-30 ° C) and (Tg + 60 ° C), more preferably (Tg-10), where Tg is the glass transition temperature of the material forming the unstretched substrate film. ° C) and (Tg + 50 ° C).
The draw ratio may be appropriately selected according to the optical properties of the base film to be used, and is usually 1.05 times or more, preferably 1.1 times or more, and usually 10.0 times or less, preferably 2.0. Is less than double.

[Surface modification treatment of base film]
If necessary, the surface of the base film may be subjected to surface modification treatment before providing the urethane resin layer. At this time, it is preferable to perform a surface modification treatment on the surface of the base film on which the urethane resin layer is provided.

  By performing the surface modification treatment, for example, a functional group such as a hydroxyl group, a carboxyl group, a carbonyl group, an amino group, or a sulfone group can be introduced on the surface of the base film. Accordingly, when the polyurethane water dispersion is applied, the water dispersion becomes compatible with the surface of the base film, so that uniform coating is possible and a urethane resin layer having a uniform thickness can be formed.

  Examples of the surface modification treatment include corona treatment, plasma treatment, ultraviolet irradiation treatment, and saponification treatment. From the viewpoint of processing efficiency, corona treatment and plasma treatment are preferred, and corona treatment is particularly preferred. Further, when the surface to be subjected to the surface modification treatment is formed of a resin containing an acrylic polymer, it is preferable to perform a saponification treatment as the surface modification treatment.

[Physical properties of base film]
The base film preferably has a total light transmittance of 80% or more in terms of 1 mm thickness. More preferably, the total light transmittance is 90% or more.
The base film preferably has a haze at a thickness of 1 mm of 0.3% or less. More preferably, the haze is 0.2% or less. If the haze exceeds 0.3%, the transparency of the base film may be lowered.

The average thickness of the base film is preferably 5 μm or more, more preferably 20 μm or more, preferably 500 μm or less, more preferably 300 μm or less.
The thickness variation width of the base film is preferably within ± 3% of the average thickness over the longitudinal direction and the width direction. By setting the thickness variation within the above range, variations in optical characteristics such as retardation of the base film can be reduced.

  The content of residual volatile components in the base film is preferably 0.1% by weight or less, more preferably 0.05% by weight or less, and still more preferably 0.02% by weight or less. By making the content of the volatile component in the above range, the dimensional stability can be improved, and the temporal change of the in-plane retardation Re and the thickness direction retardation Rth of the base film can be reduced. Deterioration of a polarizing plate or a liquid crystal display device provided with the multilayer film obtained by the production method of the invention can be suppressed, and the display on the display can be kept stable and favorable over the long term. Volatile components are substances having a molecular weight of 200 or less, and examples thereof include residual monomers and solvents. The content of volatile components can be quantified by analyzing the total amount of substances having a molecular weight of 200 or less by gas chromatography.

  As the base film, a long film is usually used. Here, the long length means one having a length of at least about 5 times the width of the film, preferably 10 times or more, specifically in a roll shape. It has a length that can be wound and stored or transported.

[Urethane resin layer]
In the production method of the present invention, a polyurethane water dispersion is applied onto the substrate film and cured to form a urethane resin layer. At this time, the urethane resin layer may be formed on the surface of the base film via another layer such as an adhesive layer, but usually, directly on the surface of the base film without any other layer. It is formed. The urethane resin layer may be provided on one surface of the base film or on both surfaces.

Since the urethane resin has excellent affinity with the adhesive, the urethane resin layer reinforces the adhesion between the base film and the polarizer by the adhesive when the laminated film of the present invention is bonded to a member such as a polarizer. Thus, it functions as an easy-adhesion layer (also referred to as a primer layer) that adheres more firmly.
In addition, since the urethane resin has high adhesion to the base film, in the laminated film of the present invention, the base film and the urethane resin layer are firmly adhered and are difficult to peel off.

[Polyurethane]
In the formation of the urethane resin layer, an aqueous dispersion containing polyurethane is used. Such an aqueous dispersion is obtained by dispersing polyurethane and, if necessary, other components in water. Examples of the polyurethane production method include: (i) a method in which a component containing an average of two or more active hydrogens in one molecule and (ii) a polyvalent isocyanate component are reacted; or the above (i) component and ( ii) The component is urethanated in an organic solvent that is inert to the reaction and has a high affinity for water under the condition of excess isocyanate group to obtain polyurethane as an isocyanate group-containing prepolymer, and then the prepolymer is mixed with water. And the like. These polyurethanes may contain an acid component (acid residue).

  The chain extension method of the isocyanate group-containing prepolymer may be a known method. For example, water, a water-soluble polyamine, glycols, or the like is used as the chain extender, and the isocyanate group-containing prepolymer and the chain extender are used. May be reacted in the presence of a catalyst as necessary.

  The component (i) (that is, a component containing an average of 2 or more active hydrogens in one molecule) is not particularly limited, but preferably has a hydroxylic active hydrogen. Specific examples of such compounds include the following.

(1) Polyol compound As the polyol compound, for example, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 2,3-butylene glycol, 1,4-butylene glycol. 1,5-pentanediol, neopentyl glycol, 1,6-hexane glycol, 2,5-hexanediol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, tricyclodecane dimethanol 1,4-cyclohexanedimethanol and the like.

(2) Polyether polyol As the polyether polyol, for example, an alkylene oxide adduct of the aforementioned polyol compound; a ring-opening (co) polymer of alkylene oxide and a cyclic ether (for example, tetrahydrofuran); polyethylene glycol, polypropylene glycol, ethylene Glycol-propylene glycol copolymer; glycols such as glycol, polytetramethylene glycol, polyhexamethylene glycol, polyoctamethylene glycol; and the like.

(3) Polyester polyol Examples of the polyester polyol include dicarboxylic acids such as adipic acid, succinic acid, sebacic acid, glutaric acid, maleic acid, fumaric acid, and phthalic acid, and anhydrides thereof, and those mentioned in (1) above. Obtained by polycondensation with a polyol compound such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,8-octamethylenediol, neopentylglycol and the like under conditions of excess hydroxyl group. Etc. More specifically, for example, ethylene glycol-adipic acid condensate, butanediol-adipine condensate, hexamethylene glycol-adipic acid condensate, ethylene glycol-propylene glycol-adipic acid condensate, and lactone with glycol as an initiator. Examples thereof include polylactone diols obtained by ring-opening polymerization.

(4) Polyether ester polyol As the polyether ester polyol, for example, an ether group-containing polyol (for example, the polyether polyol or diethylene glycol of (2) above) or a mixture of this with another glycol is used as the above (3). And those obtained by reacting with an alkylene oxide mixed with a dicarboxylic acid or an anhydride thereof as exemplified above. More specifically, examples include polytetramethylene glycol-adipic acid condensate.

(5) Polycarbonate polyol As the polycarbonate polyol, for example, the general formula HO-R- (OC (O) -O-R) x-OH (wherein R is saturated with 1 to 12 carbon atoms) A fatty acid polyol residue, and x is the number of repeating units of the molecule, and is usually an integer of 5 to 50). These are a transesterification method in which a saturated aliphatic polyol and a substituted carbonate (for example, diethyl carbonate, diphenyl carbonate, etc.) are reacted under the condition that the hydroxyl group becomes excessive; the saturated aliphatic polyol and phosgene are reacted, or If necessary, it can be obtained by a method of further reacting a saturated aliphatic polyol thereafter.

  The compounds as exemplified in the above (1) to (5) may be used alone or in combination of two or more at any ratio. Among these, it is particularly preferable to use (3) polyester polyol.

  Examples of the component (ii) to be reacted with the component (i) (that is, the polyvalent isocyanate component) include, for example, an aliphatic, alicyclic or aromatic compound containing an average of two or more isocyanate groups in one molecule. Is mentioned.

  The aliphatic diisocyanate compound is preferably an aliphatic diisocyanate having 1 to 12 carbon atoms, and examples thereof include hexamethylene diisocyanate and 2,2,4-trimethylhexane diisocyanate. The alicyclic diisocyanate compound is preferably an alicyclic diisocyanate having 4 to 18 carbon atoms, and examples thereof include 1,4-cyclohexane diisocyanate and methylcyclohexylene diisocyanate. Examples of the aromatic isocyanate include tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, and the like.

  In addition, polyurethane containing an acid structure (hereinafter referred to as “acid structure-containing polyurethane” as appropriate) can be dispersed in water without using a surfactant or with a small amount of surfactant. Therefore, it is expected that the water resistance of the formed urethane resin layer is improved. In addition, an acid structure-containing polyurethane is preferable because it does not require or requires a small amount of a surfactant, and is excellent in adhesiveness with a base film and can maintain high transparency.

Examples of the acid structure include acid groups such as a carboxyl group (—COOH) and a sulfo group (—SO ₃ H). In addition, the acid structure may be present in the side chain or at the terminal in the polyurethane.

  The content of the acid structure is preferably 20 mgKOH / g or more, more preferably 25 mgKOH / g or more, preferably 250 mgKOH / g or less, more preferably 150 mgKOH / g or less as the acid value of the polyurethane. If the acid value is less than 20 mgKOH / g, water dispersibility tends to be insufficient, and if the acid value is greater than 250, the water resistance of the formed urethane resin layer tends to be poor.

  As a method for introducing an acid structure into polyurethane, a conventionally used method can be used without any particular limitation. Preferable examples include dimethylol alkanoic acid by replacing some or all of the glycol components described in (2) to (4) above with a polyether polyol, polyester polyol, polyether ester polyol, etc. The method of introduce | transducing group is mentioned. Examples of the dimethylol alkanoic acid used here include dimethylol acetic acid, dimethylol propionic acid, and dimethylol butyric acid. In addition, dimethylol alkanoic acid may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  Moreover, it is preferable to neutralize at least a part of the acid structure contained in the polyurethane. By providing a urethane resin layer formed of polyurethane obtained by neutralizing the acid structure (hereinafter referred to as “polyurethane after neutralization treatment” as appropriate), the multilayer film obtained in the present invention is Even if it has an exposed thermal history, it maintains its properties as an optical material, and when it is used by being laminated on another optical film (especially a polarizer), the multilayer film adheres to the other optical film. It is possible to maintain good properties. Moreover, even if the acid structure is neutralized, the polyurethane can be dispersed in water without using a surfactant or even if the amount of the surfactant is small.

Of the acid structure contained in the polyurethane, the proportion of the acid structure to be neutralized is preferably 20% or more, and particularly preferably 50% or more. 20% or more of the acid structure is neutralized, so that even if the multilayer film obtained in the present invention has a heat history exposed to a high temperature, while maintaining the characteristics as an optical material, When it is used by being laminated on the optical film, the adhesion with the optical film can be further maintained.
In addition, as for the polyurethane after neutralization process, all of the acid structures which acid structure containing water-based urethane contains may be neutralized.

[Nonvolatile base]
As the neutralizing agent for neutralizing the acid structure, a nonvolatile base is usually used. Examples of the non-volatile base include a base that is substantially non-volatile under the processing conditions when the polyurethane water dispersion is applied to the surface of the base film and then dried (for example, when left at 80 ° C. for 1 hour). Is mentioned. Here, being substantially non-volatile means that a decrease in non-volatile base is usually 80% or less.

  As the non-volatile base, those which are soluble in water or can be emulsified by dispersing in water are preferable. As a result, when an uncured polyurethane resin is used as the aqueous dispersion, it is possible to easily form the urethane resin layer by improving the applicability.

Examples of the non-volatile base include inorganic bases such as sodium hydroxide and potassium hydroxide;
2-amino-2-methyl-1-propanol (AMP), monoethanolamine, 2-amino-2-methyl-1,3-propanediol (AMPD), 2-amino-2-hydroxymethyl-1,3- Propane potassium hydroxide, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β (aminoethyl) -γ-aminopropyltrimethoxysilane, N-β (aminoethyl) -γ-aminopropyltrimethyl Dimethoxysilane, 3-ureidopropyltrimethoxysilane, 3-aminopropyl-tris (2-methoxy-ethoxy-ethoxy) silane, cyclohexylamine, hexamethylenediamine, ethylenediamine, diethylenetriamine, tetraethylenepentamine, pentaethylenepentamine, Amino Eth Ethanolamine, 1,2-propanediamine, isophoronediamine, 4,4'-dicyclohexylmethanediamine, 3,3'-dimethyl-dicyclohexylmethanediamine, 1,2-cyclohexanediamine, 1,4-cyclohexanediamine, aminoethylethanol Amine, aminopropylethanolamine, aminohexylethanolamine, aminoethylpropanolamine, aminopropylpropanolamine, aminohexylpropanolamine, 5-aminopyrazole, 1-methyl-5-aminopyrazole, 1-isopropyl-5-aminopyrazole, 1-benzyl-5-aminopyrazole, 1,3-dimethyl-5-aminopyrazole, 1-isopropyl-3-methyl-5-aminopyrazole, 1-benzyl-3-methyl-5 -Aminopyrazole, 1-methyl-4-chloro-5-aminopyrazole, 1-methyl-4-asino-5-aminopyrazole, 1-isopropyl-4-chloro-5-aminopyrazole, 3-methyl-4-chloro Primary amines such as -5-aminopyrazole, 1-benzyl-4-chloro-5-aminopyrazole;

Secondary amines such as diethanolamine, morpholine, piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, N-phenyl-γ-aminopropyltrimethoxysilane;
N-methyl-3-aminopropyltrimethoxycarboxylic acid dihydrazide, carbodihydrazide, oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, adipic acid dihydrazide, sebacic acid dihydrazide, dodecanedioic acid dihydrazide, isophthalic acid dihydrazide, terephthalic acid dihydrazide Hydrazide compounds such as glycolic acid dihydrazide and polyacrylic acid dihydrazide;
Triethanolamine, triisopropanolamine, tri [(2-hydroxy) -1-propyl] amine, N, N-diethylmethanolamine, N, N-dimethylethanolamine, N, N, N ′, N′-tetramethyl Three such as ethylenediamine, N, N-dimethylbenzylamine, diethylaminopropylamine, N- (2-aminoethyl) piperazine, 2,4,6-tris (dimethylaminomethyl) phenol, N, N-bis (trimethylsilyl) urea Secondary amines;

Imidazole, 2-methylimidazole, 1- (2-aminoethyl) -2-methylimidazole, 1- (2-aminoethyl) -2-ethylimidazole, 2-aminoimidazole sulfate, 2- (2-aminoethyl)- Imidazole compounds such as benzimidazole;
Imidazoline compounds such as imidazoline and 2-methyl-2-imidazoline; and the like.

Among them, a compound having a hydrazino group (—NHNH ₂ group) such as a hydrazide compound has high reactivity, and therefore can appropriately improve the mechanical strength of the urethane resin layer, and has a relatively high boiling point. Since the heat resistance of a layer can be made high, it is especially preferable. Moreover, a non-volatile base may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

[Production of water dispersion]
In the present invention, the above polyurethane is used as an aqueous dispersion. The method of using polyurethane as an aqueous dispersion is not limited, but in the method for producing polyurethane, (i) a component containing an average of two or more active hydrogens in one molecule and (ii) a polyvalent isocyanate component are combined with an isocyanate group. Under excess conditions, polyurethane is obtained as an isocyanate group-containing prepolymer by urethanation in an organic solvent that is inert to the reaction and has a high affinity for water, and then water is added to the prepolymer to obtain an aqueous dispersion. It is preferable to use the method. According to this method, a polyurethane having a desired particle size distribution and V1 / V2 of 0.11 or less can be easily obtained as an aqueous dispersion.

  The number average molecular weight of the polyurethane used in the present invention is preferably 1,000 or more, more preferably 20,000 or more, preferably 1,000,000 or less, more preferably 200,000 or less. The smaller the number average molecular weight of the polyurethane, the smaller the particle size when the aqueous dispersion is made. Therefore, the value of V1 / V2 can be adjusted by adjusting the number average molecular weight of the polyurethane.

  When polyurethane is obtained as a prepolymer in an organic solvent and water is added to the prepolymer to form an aqueous dispersion, a solution or dispersion in which the prepolymer is dissolved or dispersed in an organic solvent is added to the water and dispersed. It is preferable to make it. The concentration of the prepolymer in the organic solvent is preferably 10 to 60% by weight, more preferably 20 to 50% by weight. The lower the concentration of the prepolymer in the organic solvent, the smaller the particle size when the aqueous dispersion is obtained. Therefore, the value of V1 / V2 can be adjusted by adjusting the concentration of the prepolymer in the organic solvent.

  The amount of water when the solution or dispersion is added to water is such that the solid content concentration when polyurethane is used as an aqueous dispersion is preferably 5 to 35% by weight, more preferably 10 to 30% by weight. It is. The lower the solid content concentration is, the smaller the particle size of the aqueous dispersion can be made. Therefore, the value of V1 / V2 can be adjusted by adjusting the amount of water used for dispersion.

  When adding and dispersing the solution or dispersion in water, it is preferable to stir the water at a high speed to mix and disperse the water and the solution or dispersion. The stirring method is not particularly limited. The rotation speed of stirring is preferably 2,000 rpm to 10,000 rpm, and more preferably 4,000 rpm to 8,000 rpm.

  As described above, a polyurethane water dispersion having V1 / V2 of 0.11 or less can be obtained.

  As another method for obtaining a polyurethane water dispersion having a V1 / V2 of 0.11 or less, a polyurethane water dispersion having a V1 / V2 of greater than 0.11 is produced and filtered to increase the particle size. A method of removing particles and obtaining a polyurethane water dispersion in which V1 / V2 is 0.11 or less is also included. However, this method may not sufficiently remove particles having a large particle size. This is presumably because the shape of polyurethane particles is not constant in water, and even if a filter finer than the particle size of the particles to be removed during filtration is used, the particles pass through the filter and remain in the filtrate. The On the other hand, if filtration is performed using an excessively fine filter, particles with a small particle size are also removed, and the amount of particles contained in the filtrate is reduced. Further, the filter is clogged and productivity is reduced. There is. Therefore, a method of forming an aqueous dispersion in which V1 / V2 is 0.11 or less in the step of dispersing polyurethane in water by the above method is preferable.

  The polyurethane water dispersion may contain a water-soluble solvent. Examples of the water-soluble solvent include methanol, ethanol, isopropyl alcohol, acetone, methyl ethyl ketone, tetrahydrofuran, N-methylpyrrolidone, dimethyl sulfoxide, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, and the like. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  The polyurethane water dispersion was filtered for 120 seconds when the pressure of 0.2 MPa was applied to a filter having a diameter of 25 mm and an average pore diameter of 1 μm when the solid content concentration of polyurethane in the water dispersion was 10% by weight. The amount is preferably 7 g or more, and more preferably the amount of filtration for 120 seconds when it is similarly filtered except that a filter having an average pore size of 0.5 μm is used is 7 g or more.

[Other ingredients]
The polyurethane water dispersion may contain components other than those described above as long as the effects of the present invention are not significantly impaired.

[Crosslinking agent]
For the purpose of improving the mechanical strength of the resulting urethane resin layer, the polyurethane water dispersion preferably contains a crosslinking agent. As the crosslinking agent, any compound having a functional group that reacts with a reactive group of polyurethane can be used without particular limitation. Examples of preferred crosslinking agents include water-based epoxy compounds, water-based amino compounds, water-based isocyanate compounds, water-based carbodiimide compounds and the like from the viewpoint of versatility of materials. Especially, it is preferable from an adhesive viewpoint to use a water-based epoxy compound or a water-based amino compound.

  The water-based epoxy compound may be any compound that is soluble in water or has two or more epoxy groups emulsified. Examples of water-based epoxy compounds include glycols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, 1,6-hexane glycol, and neopentyl glycol 1 Diepoxy compound obtained by etherification of 1 mol of mol and 2 mol of epichlorohydrin; obtained by etherification of 1 mol of polyhydric alcohols such as glycerin, polyglycerin, trimethylolpropane, pentaerythritol, sorbitol and 2 mol or more of epichlorohydrin Polyepoxy compound: Diepoxy obtained by esterification of 1 mol of dicarboxylic acid such as phthalic acid, terephthalic acid, oxalic acid, adipic acid and 2 mol of epichlorohydrin Epoxy compounds such as shea compounds; and the like.

  The aqueous amino compound may be any compound that is soluble in water or has two or more amino groups emulsified. Examples of water-based amino compounds are carbodihydrazide, oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, adipic acid dihydrazide, sebacic acid dihydrazide, dodecanedioic acid dihydrazide, isophthalic acid dihydrazide, terephthalic acid dihydrazide, glycolic acid Examples include hydrazide compounds such as polyacrylic acid dihydrazide, melamine resins, urea resins, and guanamine resins.

  The water-based isocyanate compound may be any compound that is soluble in water or has two or more non-blocked isocyanate groups or block-type isocyanate groups emulsified. Examples of the non-blocking isocyanate compound include compounds obtained by reacting a polyfunctional isocyanate compound with a monovalent or polyvalent nonionic polyalkylene ether alcohol. Examples of the block type isocyanate compound include 2,4-tolylene diisocyanate (2,4-TDI), 2,6-tolylene diisocyanate (2,6-TDI), 4,4′-diphenylmethane diisocyanate (MDI), Xylylene diisocyanate (XDI), isophorone diisocyanate (IPDI), methylcyclohexyl diisocyanate (H6TDI), 4,4′-dicyclohexylmethane diisocyanate (H12MDI), 1,3-bis (isocyanatomethyl) cyclohexane (H6XDI), tetramethylxylylene Range isocyanate (TMXDI), 2,2,4-trimethylhexamethylene diisocyanate (TMHDI), hexamethylene diisocyanate (HDI), norbornene diisocyanate (NBD) ), 2,4,6-triisopropylphenyl diisocyanate (TIDI), 1,12-diisocyanatododecane (DDI), 2,4, -bis- (8-isocyanatooctyl) -1,3-dioctylcyclobutane (OCDI), n-Pentane-1,4-diisocyanate and their isocyanurate-modified products, adduct-modified products, burette-modified products, allophanate-modified products, and polymers having one or more isocyanate groups are polyoxyalkylenes Examples thereof include compounds obtained by modification with a group, a carboxyl group, etc., making it water-soluble and / or water-dispersible, and masking an isocyanate group with a blocking agent (phenol, ε-caprolactam, etc.).

  The water-based carbodiimide compound may be a compound that is soluble in water or has two or more carbodiimide bonds (—N═C═N—) emulsified. A compound having two or more carbodiimide bonds can be obtained, for example, by a method of forming a carbodiimide bond by decarboxylation of two isocyanate groups using two or more molecules of polyisocyanate and a carbodiimidization catalyst. . The polyisocyanate and the carbodiimidization catalyst used when producing a compound having two or more carbodiimide bonds are not particularly limited, and conventionally known ones can be used.

  A crosslinking agent may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The amount of the cross-linking agent is usually 1 part by weight or more, preferably 5 parts by weight or more, and usually 30 parts by weight or less, preferably 15 parts by weight or less, based on 100 parts by weight of polyurethane (solid content). is there. Thereby, both the strength of the urethane resin layer and the stability of the aqueous dispersion can be achieved.

[Fine particles]
The polyurethane water dispersion preferably further contains fine particles. When an aqueous dispersion containing fine particles is used, the resulting urethane resin layer contains fine particles, and irregularities can be formed on the surface of the urethane resin layer. As a result, the area where the urethane resin layer comes into contact with other layers during winding is reduced, and the sliding property of the surface of the urethane resin layer is improved by that much, and when the multilayer film of the present invention is wound. The generation of wrinkles can be suppressed.

  The average particle size of the fine particles is usually 1 nm or more, preferably 5 nm or more, more preferably 10 nm or more, and usually 500 nm or less, preferably 300 nm or less, more preferably 200 nm or less. By making the average particle diameter equal to or greater than the lower limit value of the range, the slipperiness of the urethane resin layer can be effectively increased, and by making the average particle diameter equal to or less than the upper limit value of the range, haze can be suppressed low. In addition, as an average particle diameter of microparticles | fine-particles, a particle size distribution is measured by the laser diffraction method, and the particle size from which the cumulative volume calculated from the small diameter side in the measured particle size distribution becomes 50% (50% volume cumulative diameter D50) Is adopted.

As the fine particles, either inorganic fine particles or organic fine particles may be used, but it is preferable to use water-dispersible fine particles. Examples of inorganic fine particles include inorganic oxides such as silica, titania, alumina, zirconia; calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate, calcium phosphate Etc. Examples of the organic fine particle material include silicone resin, fluororesin, and acrylic resin. Among these, silica is preferable. This is because the fine particles of silica are excellent in the ability to suppress the generation of wrinkles and transparency, hardly cause haze, and are not colored, and thus have less influence on the optical properties of the multilayer film of the present invention. Further, silica is good in dispersibility and dispersion stability in urethane resin. Among the silica fine particles, amorphous colloidal silica particles are particularly preferable.
In addition, fine particle may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  The amount of fine particles used is usually 0.5 parts by weight or more, preferably 5 parts by weight or more, more preferably 8 parts by weight or more, and usually 20 parts by weight or less, preferably 18 parts by weight or less, relative to 100 parts by weight of polyurethane. More preferably, it is 15 parts by weight or less. By setting the amount of fine particles to be equal to or more than the lower limit of the above range, it is possible to suppress the occurrence of wrinkles when the multilayer film obtained in the present invention is wound. Moreover, the external appearance without the cloudiness of the multilayer film obtained by this invention can be maintained by making the quantity of fine particles below the upper limit of the said range.

  The fine particles may be used in the form of a composition (for example, sol) in which fine particles are dispersed in a solvent. In this case, it is not always necessary to take out the fine particles from the sol, and the sol may be mixed with the polyurethane water dispersion.

  Further, in the polyurethane water dispersion, for example, a heat resistance stabilizer, a weather resistance stabilizer, a leveling agent, an antistatic agent, a slip agent, an antiblocking agent, an antifogging agent, a lubricant, and a dye may be used unless the effects of the present invention are significantly impaired. , Pigments, natural oils, synthetic oils, waxes, crosslinkers and the like may be included. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

[Formation of urethane resin layer]
In the production method of the present invention, an aqueous dispersion containing polyurethane is applied on a substrate film and cured to form a urethane resin layer. In the polyurethane water dispersion, the ratio V1 / V2 of the ratio V1 (volume%) of particles having a particle diameter of 0.2 μm or more and the ratio V2 (volume%) of particles having a particle diameter of less than 0.2 μm is 0. .11 or less, for example, it may be in the form of an emulsion or a colloidal dispersion.

  The solid content concentration of polyurethane in the polyurethane water dispersion is preferably 0.5% by weight or more, more preferably 1% by weight or more, preferably 15% by weight or less, more preferably 10% by weight or less. This is because the polyurethane water dispersion is excellent in handleability and easy to apply.

[Filtration of aqueous dispersion]
The polyurethane water dispersion having V1 / V2 of 0.11 or less is preferably used after filtration. By performing the filtration, a urethane resin layer with few foreign substances can be formed. This does not necessarily remove large particles by filtration as described above, but when the aqueous dispersion passes through the filter, the individual particles are uniformly dispersed to suppress secondary aggregation of the particles. This is thought to be possible.

  Specifically, it is preferable to perform filtration with a filter having a particle capturing performance of 5 μm or more and 20 μm or less, and then performing filtration with a filter having a particle capturing performance of 0.8 μm or more and 5 μm or less. Here, the particle trapping performance is a value represented by the maximum particle diameter that traps 99% or more when standard dust dispersion water is filtered at 10 L / min.

The flow rate during filtration is preferably 8 × 10 ⁻⁷ L / min / mm ² or more and 2 × 10 ⁻³ L / min / mm ² or less, more preferably 3 × 10 ⁻⁶ L / min / mm ² or more and 7 ×. 10 ⁻⁴ L / min / mm ² or less, more preferably 5 × 10 ⁻⁶ L / min / mm ² or more and 3 × 10 ⁻⁴ L / min / mm ² . If the flow rate is too small, the dispersion of the particles in the aqueous dispersion may be insufficient, and foreign matter in the urethane resin layer obtained by aggregation of the particles may increase. On the other hand, if the flow rate is too high, the pressure applied to the filter increases, and the filter may be broken or the service life may be shortened.

  When the polyurethane water dispersion is used after filtration, the previous components other than polyurethane and water may be added to the water dispersion before filtration, or may be added to the water dispersion after filtration.

[Application of polyurethane water dispersion]
The viscosity when the polyurethane water dispersion is applied on the base film is preferably 15 mPa · s or less, and particularly preferably 10 mPa · s or less. When the viscosity of the polyurethane water dispersion is within the above range, the polyurethane water dispersion can be applied thinly and uniformly on the surface of the base film. The viscosity is a value measured under a condition of 25 ° C. with a tuning fork type vibration viscometer. For example, the amount of polyurethane contained in the polyurethane water dispersion and the particle size of the polyurethane are adjusted. Can be controlled.

  The method for applying the polyurethane water dispersion on the base film is not particularly limited, and a known application method may be employed. Specific coating methods include, for example, a wire bar coating method, a dip method, a spray method, a spin coating method, a roll coating method, a gravure coating method, an air knife coating method, a curtain coating method, a slide coating method, and an extrusion coating method. Etc.

  The amount of the polyurethane water dispersion applied is the thickness of the urethane resin layer formed after curing, preferably 0.01 μm or more, more preferably 0.02 μm or more, particularly preferably 0.03 μm or more, preferably The amount is 5 μm or less, more preferably 4 μm or less, and particularly preferably 3 μm or less. What is necessary is just to adjust the solid content concentration and application quantity of a polyurethane water dispersion so that the thickness of the urethane resin layer after hardening may be in the said range. When the thickness of the urethane resin layer is within the above range, sufficient adhesive strength between the base film and the urethane resin layer can be obtained, and defects such as warpage of the multilayer film obtained in the present invention can be eliminated. it can.

[Curing]
After the polyurethane aqueous dispersion is applied to the base film, the polyurethane is cured to form a urethane resin layer to obtain a multilayer film.
Since the urethane resin contains water, the water is removed by drying when it is cured. The drying method is arbitrary, and for example, the drying may be performed by any method such as reduced pressure drying or heat drying. Among these, it is preferable to cure the polyurethane by heat drying from the viewpoint of promptly proceeding with a reaction such as a crosslinking reaction.

  When the polyurethane is cured by heating, the heating temperature is appropriately set within a range in which the solvent can be dried to cure the uncured polyurethane. However, when a stretched film is used as the base film and it is not desired to change the retardation developed in the base film, the heating temperature may be set to a temperature at which no orientation relaxation occurs in the base film. preferable. Specifically, when the glass transition temperature of the material forming the base film is Tg, it is preferably (Tg-30) ° C or higher, more preferably (Tg-10) ° C or higher, preferably (Tg + 60). ) ° C. or lower, more preferably (Tg + 50) ° C. or lower.

[Other layers]
The multilayer film obtained by the production method of the present invention may have other layers on the surface of the base film on which the urethane resin layer is not formed unless departing from the gist of the present invention. Examples thereof include an antireflection layer, a hard coat layer, an antistatic layer, an antiglare layer, an antifouling layer, a separator film and the like. These layers may be formed on the base film before the urethane resin layer is formed, or may be formed on the multilayer film after the urethane resin layer is formed.

[Use of multilayer film]
The multilayer film obtained by the production method of the present invention is usually used as an optical film. When the example of the optical film used as a multilayer film is given, a protective film, retardation film, an optical compensation film, etc. will be mentioned. The multilayer film may be used as a stretched film. That is, a stretched film may be used as a base film, and a urethane resin layer may be formed thereon, or a urethane resin layer may be formed and laminated on a base film (which may be a stretched film or an unstretched film). You may extend | stretch and use after manufacturing a film. Especially, since the multilayer film obtained with the manufacturing method of this invention is excellent in durability, it is preferable to use as a protective film. Specific examples include optical films such as a polarizer, a film with an antireflection film, a retardation film, a viewing angle widening film, and a brightness enhancement film in combination with the multilayer film obtained in the present invention. The durability of the optical film combined with the layer film can be improved. In addition, the film obtained in the present invention is excellent in adhesion with, for example, a UV curable resin, or excellent in adhesion with a film, sheet or substrate on which irregularities such as a prism shape are formed. Such an optical film can be easily attached.

  Among the applications described above, the multilayer film obtained by the production method of the present invention is suitable for a polarizing plate protective film. When using a multilayer film as a polarizing plate protective film, the polarizing plate protective film should just be equipped with the multilayer film obtained by this invention, for example, this multilayer film may be used alone as a polarizing plate protective film. The multilayer film and another film may be used in combination as a polarizing plate protective film.

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

[Ratio V1 / V2 of the ratio V1 (volume%) of particles having a particle diameter of 0.2 μm or more and the ratio V2 (volume%) of particles having a particle diameter of less than 0.2 μm]
50 g of a 0.5% by weight aqueous solution of sodium dodecyl diphenyl ether disulfonate was diluted with 2 g of an aqueous dispersion of an aqueous urethane resin and diluted, and the particle size distribution was measured with a laser diffraction scattering particle size distribution measuring device (LS-230, manufactured by Coulter). Calculated from the results.

[Filtration volume]
Pure water was added to the aqueous urethane resin water dispersion for dilution to prepare a test solution having a solid content concentration of 10%. The test solution was sucked up with a 5 mL syringe, a three-way cock, a pressure gauge, and a membrane filter with a pore size of 1.0 μm were attached, and held at a pressure of 0.2 MPa for 120 seconds, and the weight of the filtered test solution was measured.

[Filter particle capture performance]
When the standard dust dispersion water was filtered at 10 L / min, the minimum particle diameter at which 99% or more was trapped was defined as the particle trapping performance.

[Foreign matter]
A test piece of 400 mm × 2,500 mm was cut out from the multilayer films obtained in Examples and Comparative Examples, and the number of foreign matters was measured by visual observation and observation with a microscope. The case where the number of foreign matters of 100 μm or more was less than 2 was evaluated as A, the case of 2 or more and less than 5 was evaluated as B, and the case of 5 or more was evaluated as C.

[Uneven coating]
A test piece of 400 mm × 2,500 mm was cut out from the multilayer films obtained in Examples and Comparative Examples, and this was placed at 45 ° between polarizing plates arranged in crossed Nicols and visually observed. Less than A, 5 or more and less than 10 B, and 10 or more C.

[Production Example 1: Production of coating liquid A]
A reactor equipped with a thermometer, a stirrer, a nitrogen introduction tube and a cooling tube was charged with 317.2 parts of 3-methyl-1,5-pentanediol, 174 parts of terephthalic acid and 146 parts of adipic acid, and nitrogen gas was added under normal pressure. Then, an esterification reaction was carried out at a reaction temperature of 200 ° C. while distilling off the produced water to the outside of the reaction system. When the acid value of the polyester reached 1.0 mgKOH / g, the vacuum was gradually increased using a vacuum pump to complete the reaction. The obtained polyester polyol had a hydroxyl value of 56.1 mgKOH / g, an acid value of 0.2 mgKOH / g, and a number average molecular weight calculated from the hydroxyl value of 2,000.

  In a reactor equipped with a thermometer, a stirrer, a nitrogen introducing tube and a cooling tube, 840 parts of the polyester polyol obtained above, 119 parts of tolylene diisocyanate, and 900 parts of methyl ethyl ketone were added, and 75 ° C. while introducing nitrogen. The reaction was carried out for 1 hour. After completion of the reaction, the mixture is cooled to 60 ° C., 41 parts of dimethylolpropionic acid and 25 parts of triethylamine are added and reacted at 75 ° C. to obtain a prepolymer solution having a terminal isocyanate group with 0.5% NCO. It was. Next, this prepolymer solution was cooled to 40 ° C., 4,000 parts of water was added, and emulsification was performed by stirring at high speed with a homomixer. Methyl ethyl ketone was distilled off from the emulsion under heating and reduced pressure to obtain an aqueous dispersion of an aqueous urethane resin having a solid content of 20%. Table 1 shows the results of measuring the filtration weight of V1 / V2 and the urethane resin aqueous dispersion test solution for this aqueous dispersion.

  To 10 parts of the aqueous urethane resin aqueous dispersion obtained above, 1 part of Snowtex 20L (manufactured by Nissan Chemical Industries, Ltd.) and 33 parts of water, which is an aqueous dispersion of silica particles, are added and diluted to a solid content of 5%. The coating liquid A which is an aqueous dispersion containing polyurethane was obtained.

[Production Example 2: Production of coating liquid B]
A prepolymer solution was obtained in the same manner as in Production Example 1. Subsequently, this prepolymer solution was cooled to 40 ° C., 3,000 parts of water was added, and emulsification was performed by stirring at high speed with a homomixer. Methyl ethyl ketone was distilled off from the emulsion under heating and reduced pressure to obtain an aqueous dispersion of an aqueous urethane resin having a solid content of 25%. Table 1 shows the results of measuring the filtration weight of V1 / V2 and the urethane resin aqueous dispersion test solution for this aqueous dispersion.

  In 16 parts of the aqueous dispersion of the aqueous urethane resin obtained above, 0.2 part of carbodilite V-02 (Nisshinbo Co., Ltd.), which is an aqueous carbodiimide compound, 1 part of Snowtex 20L (Nissan Chemical Industries) and water By adding 123 parts and stirring, a coating liquid B which is an aqueous dispersion containing polyurethane having a solid content of 3% was obtained.

[Production Example 3: Production of coating liquid C]
A prepolymer solution was obtained in the same manner as in Production Example 1. Next, this prepolymer solution was cooled to 40 ° C., 1,500 parts of water was added, and emulsification was performed by stirring at high speed with a homomixer. Methyl ethyl ketone was distilled off from the emulsion under heating and reduced pressure to obtain an aqueous dispersion of an aqueous urethane resin having a solid content of 40%. Table 1 shows the results of measuring the filtration weight of V1 / V2 and the urethane resin aqueous dispersion test solution for this aqueous dispersion.

  An aqueous dispersion containing polyurethane by adding 1 part of Snowtex 20L (manufactured by Nissan Chemical Industries, Ltd.) and 73 parts of water to 10 parts of the aqueous dispersion of the aqueous urethane resin obtained above, and diluting to 5% solids. A coating liquid C was obtained.

[Production Example 4: Production of base film]
Pellets of alicyclic structure-containing polymer resin (ZEONOR 1430, manufactured by Nippon Zeon Co., Ltd .; glass transition temperature 135 ° C.) were dried at 70 ° C. for 2 hours using a hot air dryer in which air was circulated. Then, using a T-die type film melt extrusion molding machine having a resin melt kneader equipped with a 65 mm diameter screw, under a molding condition of a molten resin temperature of 270 ° C. and a T die width of 500 mm, a thickness of 100 μm and a length of 1000 m An unstretched film was produced. This unstretched film is continuously stretched uniaxially at a stretching temperature of 140 ° C. and a stretch ratio of 1.1 times using a roll-type longitudinal stretching machine, thereby forming a base film as a stretched film in which the orientation axis coincides with the length direction. A material film was obtained. This base film is a base film made of an alicyclic structure-containing polymer resin.

[Example 1]
Using a corona treatment device (Kasuga Denki Co., Ltd.), the surface of the base film obtained in Production Example 4 was subjected to a discharge treatment under the conditions of an output of 200 W, an electrode length of 240 mm, a workpiece electrode of 1.0 mm, and a conveying speed of 15 m / min. Was given. As the electrode, a wire electrode made of stainless steel and having a diameter of 1.2 mm was used. The average water contact angle of the base film after the corona treatment was 55 °.

The coating liquid A obtained in Production Example 1 was filtered at a flow rate of 4 × 10 ⁻⁵ L / min / mm ² and a first filter having a particle trapping performance of 10 μm (Advantech depth cartridge filter; TCPD-3-S1FE) And filtered. Subsequently, it filtered using the 2nd filter (Advantech depth cartridge filter; TCPD-01-S1FE) with a particle | grain capture | acquisition performance of 1 micrometer by filtration flow volume 4 * 10 < ^-5 > L / min / mm < ² >. The coating liquid A after filtration is applied to the surface of the base film subjected to corona treatment using a roll coater so that the dry film thickness becomes 200 nm, and dried at 130 ° C. for 1 minute to obtain a urethane resin. Was cured to obtain a multilayer film 1. Table 1 shows the results of measuring film defects and coating unevenness of this multilayer film 1.

[Example 2]
A coating liquid B was used instead of the coating liquid A as an aqueous dispersion containing polyurethane, and a second filter having a particle capture performance of 5 μm (depth cartridge filter manufactured by Advantech Co., Ltd .; TCPD-1-S1FE) was used. Others were carried out similarly to Example 1, and obtained the multilayer film 2. Table 1 shows the results of measuring film defects and coating unevenness of this multilayer film 2.

[Example 3]
A multilayer film 3 was obtained in the same manner as in Example 1, except that the first filter had a particle capturing performance of 20 μm (depth cartridge filter manufactured by Advantech Co., Ltd .; TCPD-7-S1FE). Table 1 shows the results of measuring film defects and coating unevenness of this multilayer film 3.

[Example 4]
A multilayer film 4 was obtained in the same manner as in Example 1 except that a particle filter having a particle capturing performance of 40 μm (depth cartridge filter manufactured by Advantech; TCPD-10-S1FE) was used as the first filter. Table 1 shows the results of measuring film defects and coating unevenness of this multilayer film 4.

[Example 5]
A first filter having a particle capture performance of 5 μm (Advantech depth cartridge filter; TCPD-1-S1FE) is used, and a second filter having a particle capture performance of 10 μm (Advantech depth cartridge filter; TCPD-3 A multilayer film 5 was obtained in the same manner as in Example 1 except that -S1FE) was used. Table 1 shows the results of measuring film defects and coating unevenness of this multilayer film 5.

[Comparative Example 1]
A multilayer film 6 was obtained in the same manner as in Example 1 except that the coating liquid C was used instead of the coating liquid A as an aqueous dispersion containing polyurethane. Table 1 shows the results of measuring film defects and coating unevenness of this multilayer film 6.

[Comparative Example 2]
A multilayer film 7 was obtained in the same manner as in Comparative Example 1 except that a first filter having a particle capturing performance of 5 μm (a depth cartridge filter manufactured by Advantech; TCPD-1-S1FE) was used. Table 1 shows the results of measuring film defects and coating unevenness of this multilayer film 7.

[Comparative Example 3]
A multilayer film 8 was obtained in the same manner as in Comparative Example 1 except that the filtration with the first filter and the second filter was not performed. Table 1 shows the results of measuring film defects and coating unevenness of this multilayer film 8.

  From the above, it can be seen that according to the method for producing a multilayer film of the present invention, a multilayer film having a uniform urethane resin layer with little foreign matter and coating unevenness can be obtained.

Claims (4)

A method for producing a multilayer film comprising applying a water dispersion containing polyurethane on a base film and curing to form a urethane resin layer,
In the polyurethane, a ratio V1 / V2 of a ratio V1 (volume%) of particles having a particle diameter of 0.2 μm or more and a ratio V2 (volume%) of particles having a particle diameter of less than 0.2 μm is 0.11 or less. A method for producing a multilayer film. A polyurethane aqueous dispersion in which a ratio V1 / V2 of a ratio V1 (volume%) of particles having a particle diameter of 0.2 μm or more and a ratio V2 (volume%) of particles having a particle diameter of less than 0.2 μm is 0.11 or less. The
When the standard dust dispersion water is filtered at 10 L / min, it is filtered through a filter having a particle capturing performance represented by the maximum particle diameter of 99% or more and 5 μm or more and 20 μm or less, and then the particle capturing performance is 0.8 μm. After filtering with a filter of 5 μm or less,
The manufacturing method according to claim 1, wherein the coating is performed on a base film. The manufacturing method of Claim 1 or 2 with which the aqueous dispersion containing the said polyurethane further contains a crosslinking agent. The manufacturing method in any one of Claims 1-3 in which the aqueous dispersion containing the said polyurethane further contains microparticles | fine-particles.