JP2018062120A - Biaxially oriented polyester film for optical use - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film having high transparency and brightness, in particular when providing it as a prism sheet for a backlight for LCD, a polyester film with low cost, high transparency, high brightness and excellent optical properties.SOLUTION: A biaxially oriented polyester film for optical use is characterized in that the haze is 3.0% or less, the total light transmittance is 90% or more, and the MOR-C value measured by a microwave molecular orientation meter is 4.5 or more.SELECTED DRAWING: None

Description

  The present invention relates to an optical polyester film, and more specifically, a microlens sheet used as an optical sheet for a backlight used in a liquid crystal display (hereinafter abbreviated as LCD) and a polyester used as a base material for a prism sheet. The present invention relates to an optical polyester film excellent in optical performance capable of realizing high brightness.

  Conventionally, polyester films, especially biaxially stretched films of polyethylene terephthalate and polyethylene naphthalate, have excellent mechanical properties, heat resistance, and chemical resistance. Magnetic tape, ferromagnetic thin film tape, photographic film, packaging It is widely used as a material for films, films for electronic parts, electrical insulation films, metal laminate films, films to be attached to glass surfaces such as glass displays, and protective films for various members.

  In recent years, polyester films are frequently used in various optical films, and are used in various applications such as prism sheets, light diffusion sheets, and composite sheets for LCD members. (Patent Document 1) In these optical products, in order to obtain a bright and clear image, a base film used as an optical film needs to have good transparency because of its use form. Along with the refinement, there has been a demand for higher brightness as a backlight unit.

  In order to improve the brightness of LCD, there are a method of increasing the number of LEDs that are light sources and a method of increasing the element, but this leads to an increase in the cost of the display body and increases the power consumed by the backlight unit due to the increase in power consumption. , Leading to defects such as curl and deflection of the film. On the other hand, the brightness of the backlight unit can be expected to increase by increasing the number of prism sheets used, using a prism resin with a high refractive index, and increasing the thickness of the prism layer. However, both lead to an increase in cost, and there are still problems in terms of cost.

JP 2010-256481 A

  The present invention has been made in view of such circumstances, and is a biaxially stretched polyester film having high transparency and brightness. In particular, when used as a prism sheet for a backlight for an LCD, it is highly transparent at low cost. The object is to provide a polyester film having high luminance and excellent optical properties.

  As a result of intensive studies in view of the above problems, the present inventor has found that the above problems can be easily solved according to a specific polyester film, and has completed the present invention.

  That is, the gist of the present invention is that the film haze is 3.0% or less, the total light transmittance is 90% or more, and the MOR-C value measured by a microwave molecular orientation meter is 4.5 or more. It exists in the biaxially stretched polyester film for optics characterized by this.

  When the MOR-C value measured with a microwave molecular orientation meter is within a specific range, the biaxially stretched polyester film has high transparency and brightness, particularly when used as a prism sheet for a backlight for LCD. A polyester film having excellent optical properties at low cost can be provided.

  The polyester film constituting the optically biaxially stretched polyester film of the present invention may have a single layer structure or a laminated structure, and it may be 4 as long as the gist of the present invention is not exceeded other than the two-layer or three-layer structure. It may be a laminate of layers or more, and is not particularly limited.

  The polyester used in the present invention may be a homopolyester or a copolyester. In the case of a homopolyester, those obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol are preferred. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Typical polyester includes polyethylene terephthalate and the like. On the other hand, examples of the dicarboxylic acid component of the copolyester include one or more of isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and the like. 1 type (s) or 2 or more types, such as ethylene glycol, diethylene glycol, propylene glycol, butanediol, 4-cyclohexane dimethanol, neopentyl glycol, are mentioned.

  There is no restriction | limiting in particular as a polymerization catalyst of polyester, A conventionally well-known compound can be used, For example, a titanium compound, a germanium compound, an antimony compound, a manganese compound, an aluminum compound, a magnesium compound, a calcium compound etc. are mentioned. Among these, titanium compounds and germanium compounds are preferable because they have high catalytic activity, can be polymerized in a small amount, and the amount of metal remaining in the film is small, so that the brightness of the film is increased. Furthermore, since a germanium compound is expensive, it is more preferable to use a titanium compound.

  The polyester used in the present invention may be obtained by a melt polymerization reaction. However, if a raw material obtained by solid-phase polymerization of a polyester polyester after melt polymerization is used, an oligomer contained in the raw material is used. Since the amount can be reduced, it is preferably used. The intrinsic viscosity of the obtained polyester is preferably 0.40 dL / g or more, and preferably 0.40 to 0.90 dL / g.

  In order to suppress the precipitation amount after the heat treatment of the oligomer contained in the polyester raw material, it is mentioned that a film is produced using a polyester having a low oligomer content as a raw material. Various known methods can be used as a method for producing a polyester having a low oligomer content, and examples thereof include a method of solid-phase polymerization after polyester production. Moreover, the suppression effect of oligomer precipitation can be exhibited highly by making it the film which has the structure which carried out the coextrusion lamination so that polyester with little oligomer content may come to an outermost layer.

  The thickness of the layer containing polyester with a low oligomer content is usually 1 to 20 μm, preferably 3 to 15 μm. When the layer thickness is less than 1 μm, oligomers from adjacent layers pass through the layer having a low oligomer content and are deposited on the film surface, and the bright spots are detected as foreign matters, resulting in a decrease in luminance. There is a case. Moreover, when the layer thickness exceeds 20 μm, the film tends to curl, and the ratio of the amount of the polyester having a small oligomer content and the amount of the polyester containing particles increases, resulting in an increase in cost.

  The polyester film of the present invention may contain an ultraviolet absorber for improving the weather resistance of the film and preventing deterioration of the liquid crystal. The ultraviolet absorber is not particularly limited as long as it is a compound that absorbs ultraviolet rays and can withstand the heat applied in the production process of the polyester film.

  As the ultraviolet absorber, there are an organic ultraviolet absorber and an inorganic ultraviolet absorber, and an organic ultraviolet absorber is preferable from the viewpoint of transparency. Although it does not specifically limit as an organic type ultraviolet absorber, For example, a cyclic imino ester type, a benzotriazole type, a benzophenone type etc. are mentioned. From the viewpoint of durability, a cyclic imino ester type and a benzotriazole type are more preferable. It is also possible to use two or more ultraviolet absorbers in combination.

  In the polyester film of the present invention, particles may be blended mainly for the purpose of imparting slipperiness from the standpoint of preventing damage to the film and winding characteristics when slitting the product from the master roll. The kind of the particle to be blended is not particularly limited as long as it is a particle capable of imparting slipperiness. Specific examples thereof include silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, and phosphoric acid. Examples include inorganic particles such as magnesium, kaolin, aluminum oxide, and titanium oxide, and organic particles such as acrylic resin, styrene resin, urea resin, phenol resin, epoxy resin, and benzoguanamine resin. Furthermore, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the production process of the polyester can also be used. When the polyester film has a laminated structure, it is preferable to blend particles in the surface layer.

  On the other hand, the shape of the particles to be used is not particularly limited, and any of a spherical shape, a block shape, a rod shape, a flat shape, and the like may be used. Moreover, there is no restriction | limiting in particular also about the hardness, specific gravity, a color, etc. These series of particles may be used in combination of two or more as required.

  Moreover, the average particle diameter of the particle | grains to be used is 5 micrometers or less normally, Preferably it is the range of 0.01-3 micrometers. When the thickness exceeds 5 μm, the surface roughness of the film becomes too rough and irregularities are generated, so that the processing suitability may deteriorate in prism processing for the backlight unit.

  Furthermore, the content of particles in the polyester is usually 5% by weight or less, preferably in the range of 0.0003 to 3% by weight. When there are no or few particles, the transparency of the film will be high, but the slipperiness may be insufficient, so by putting particles in the coating layer, such as improving the slipperiness, etc. May be necessary. Further, when the particle content exceeds 5% by weight, the transparency of the film may be insufficient.

  The method for adding particles to the polyester is not particularly limited, and a conventionally known method can be adopted. For example, it can be added at any stage of producing the polyester, but it is preferably added after completion of the esterification or transesterification reaction.

  In addition to the above-described particles and UV absorber, conventionally known antioxidants, antistatic agents, heat stabilizers, lubricants, dyes, pigments, and the like are added to the polyester film of the present invention as necessary. be able to.

  The thickness of the polyester film of the present invention is not particularly limited as long as it can be formed into a film, but is usually 10 to 350 μm, preferably 25 to 250 μm.

  It is important that the haze of the polyester film of the present invention is 3% or less. Preferably it is 2% or less, More preferably, it is 0% or more or 1.5% or less. If the haze exceeds 3%, the transparency is lowered and the brightness is lowered, which is not suitable for optical use.

  It is important that the total light transmittance of the polyester film of the present invention is 90% or more. Preferably it is 91% or more, More preferably, it is 92% or more or 100% or less. If the total light transmittance is less than 90%, the luminance is reduced and it is not suitable for optical use.

  About the polyester film of this invention, it is important that the MOR-C value measured with the microwave type | system | group molecular orientation meter is 4.5 or more. More preferably, it is 5.0 or more. When the MOR-C value is less than 4.5, the film has a large thickness flutter and is not suitable for processing. Further, since the brightness is lowered, it is not suitable for optical use. On the other hand, the upper limit is not particularly limited, but is preferably 15 or less, and more preferably 10 or less.

Next, although the manufacturing method of the biaxially stretched polyester film of this invention is demonstrated concretely, as long as the summary of this invention is satisfied, this invention is not specifically limited to the following illustrations. First, a method in which a polyester chip dried by a known technique is supplied to a melt extrusion apparatus, extruded as a molten sheet from a die using an extruder, and cooled and solidified with a cooling roll to obtain an unstretched sheet is preferable. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum, and an electrostatic application adhesion method and / or a liquid application adhesion method is preferably employed.
Next, the obtained unstretched sheet is stretched in the biaxial direction. In that case, first, the unstretched sheet is stretched in one direction in a longitudinal direction (longitudinal direction (MD)) by a roll or a tenter type stretching machine. The stretching temperature is usually 70 to 120 ° C., preferably 80 to 110 ° C., and the stretching ratio is usually 2.0 to 7.0 times, preferably 2.5 to 5.0 times. Next, the film is stretched in a direction (transverse direction (TD)) perpendicular to the first stretching direction. In that case, the stretching temperature is usually 70 to 170 ° C., and the stretching ratio is usually 3.0 to 7.0. Times, preferably 3.5 to 6.0 times. Subsequently, heat treatment is performed at a temperature of 180 to 270 ° C. under tension or under relaxation within 30% to obtain a biaxially oriented film. In the above-described stretching, a method in which stretching in one direction is performed in two or more stages can be employed. In that case, it is preferable to carry out so that the draw ratios in the two directions finally fall within the above ranges.

  In order to obtain the film of the present invention, the ratio (MD / TD) between the stretching ratio in the longitudinal direction (longitudinal direction (MD)) of the film and the stretching ratio in the direction orthogonal to the longitudinal direction (transverse direction (TD)) Is preferably 0.25 to 0.70. More preferably, it is 0.30-0.65, More preferably, it is 0.35-0.60. When the MD / TD satisfies the above range, a sufficient MOR-C value can be satisfied, and the film becomes a preferable film for optical applications.

  Since the film of the present invention is used for prism and microlens sheets used as optical sheets for LCD backlights, it improves adhesion to solvent-free UV curable resins such as prism and microlens resins. For this purpose, it is preferable to provide a coating layer as an undercoat layer on the film surface. Also, it is preferable to provide a coating layer as an undercoat layer on the opposite film side in order to improve adhesion and improve the total light transmittance.

  Next, formation of the coating layer which comprises the laminated polyester film in this invention is demonstrated. Regarding the coating layer, it may be provided by in-line coating which treats the film surface during the process of forming a polyester film, or offline coating which is applied outside the system on a once produced film may be adopted. More preferably, it is formed by in-line coating.

  In-line coating is a method of coating within the process of manufacturing a polyester film, and specifically, a method of coating at any stage from melt extrusion of the polyester to heat setting after stretching and winding up. Usually, it is coated on any of an unstretched sheet obtained by melting and quenching, a stretched uniaxially stretched film, a biaxially stretched film before heat setting, and a film after heat setting and before winding. Although not limited to the following, for example, in sequential biaxial stretching, a method of stretching in the transverse direction after coating a uniaxially stretched film stretched in the longitudinal direction (longitudinal direction) is particularly excellent. According to such a method, there is a merit in manufacturing cost because film formation and coating layer formation can be performed at the same time, and in order to perform stretching after coating, the thickness of the coating layer can be changed by the stretching ratio, Thin film coating can be performed more easily than off-line coating films. Further, by providing the coating layer on the film before stretching, the coating layer can be stretched together with the base film, whereby the coating layer can be firmly adhered to the base film. Furthermore, in the production of biaxially stretched polyester film, the film can be constrained in the vertical and horizontal directions by stretching it while holding the film edge with a clip, etc. High temperature can be applied while maintaining flatness. Therefore, since the heat treatment performed after coating can be performed at a high temperature that cannot be achieved by other methods, the film forming property of the coating layer can be improved, and the coating layer and the base film can be more firmly adhered to each other. Furthermore, it can be set as a firm coating layer, and performances such as adhesion to various functional layers that can be formed on the coating layer and wet heat resistance can be improved.

  In the coating layer of the film of the present invention, it is preferable to use a binder resin for the purpose of improving the adhesion to the prism sheet and the microlens sheet. Specific examples of the binder resin include acrylic resin, polyurethane resin, polyester resin, polyvinyl (polyvinyl alcohol, polyvinyl chloride, vinyl chloride vinyl acetate copolymer, etc.), polyalkylene glycol, polyalkylene imine, methyl cellulose, hydroxy cellulose, starch And the like. These may be used alone or in combination.

  Among these binder resins, it is preferable to use an acrylic resin or a polyurethane resin from the viewpoint of further improving the adhesion.

  The acrylic resin that can be used for forming the coating layer in the film of the present invention is a polymer composed of a polymerizable monomer including an acrylic or methacrylic monomer. These may be either homopolymers or copolymers, and copolymers with polymerizable monomers other than acrylic and methacrylic monomers. Moreover, the copolymer of these polymers and other polymers (for example, polyester, polyurethane, etc.) is also included. For example, a block copolymer or a graft copolymer. Alternatively, a polymer (possibly a mixture of polymers) obtained by polymerizing a polymerizable monomer in a polyester solution or a polyester dispersion is also included. Similarly, a polymer obtained by polymerizing a polymerizable monomer in a polyurethane solution or a polyurethane dispersion (sometimes a mixture of polymers) is also included. Similarly, a polymer (in some cases, a polymer mixture) obtained by polymerizing a polymerizable monomer in another polymer solution or dispersion is also included. Moreover, in order to improve adhesiveness more, it is also possible to contain a hydroxyl group and an amino group.

The polymerizable monomer is not particularly limited, but particularly representative compounds include, for example, various carboxyl groups such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, and citraconic acid. Monomers, and salts thereof; such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, monobutyl hydroxyl fumarate, monobutyl hydroxy itaconate Various hydroxyl group-containing monomers; various (meth) acrylic acid esters such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, lauryl (meth) acrylate; (Meth) acrylamide, Various nitrogen-containing compounds such as acetone acrylamide, N-methylol acrylamide or (meth) acrylonitrile; various styrene derivatives such as styrene, α-methylstyrene, divinylbenzene, vinyltoluene, and various vinyls such as vinyl propionate Esters; various silicon-containing polymerizable monomers such as γ-methacryloxypropyltrimethoxysilane, vinyltrimethoxysilane, etc .; phosphorus-containing vinyl monomers; various vinyl halides such as vinyl chloride and biridene chloride Various conjugated dienes such as butadiene.
Among these, from the viewpoint of improving adhesion, an acrylic resin having a glass transition temperature of preferably 50 ° C. or lower, more preferably 40 ° C. or lower is preferable. Moreover, from a viewpoint of deterioration of blocking, the minimum with a preferable glass transition temperature is -30 degreeC or more.

  The polyurethane resin that can be used for forming the coating layer in the film of the present invention is a polymer compound having a urethane bond in the molecule, and is usually prepared by the reaction of a polyol and an isocyanate. Examples of the polyol include polycarbonate polyols, polyester polyols, polyether polyols, polyolefin polyols, and acrylic polyols. These compounds may be used alone or in combination. From the viewpoint of improving adhesion, polycarbonate polyols or polyester polyols are preferable, and polycarbonate polyols are more preferable.

  Polycarbonate polyols are obtained from a polyhydric alcohol and a carbonate compound by a dealcoholization reaction. Polyhydric alcohols include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, trimethylolpropane, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, , 5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, , 10-decanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 3,3-dimethylol heptane and the like. Examples of the carbonate compound include dimethyl carbonate, diethyl carbonate, diphenyl carbonate, and ethylene carbonate. Examples of polycarbonate polyols obtained from these reactions include poly (1,6-hexylene) carbonate, poly (3- And methyl-1,5-pentylene) carbonate.

  Polyester polyols include polycarboxylic acids (malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, fumaric acid, maleic acid, terephthalic acid, isophthalic acid, etc.) or their acid anhydrides. Product and polyhydric alcohol (ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol 2-methyl-2-propyl-1 3-propanediol, 1,8-octanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2,5-dimethyl-2,5-hexanediol 1,9-nonanediol, 2-methyl-1,8-octanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-butyl-2-hexyl-1,3-propanediol, cyclohexane Diol, bishydroxymethylcyclohexane, dimethanolbenzene, bishydroxyethoxybenzene, alkyl dialkanolamine, lactone diol, etc.) and those having derivative units of lactone compounds such as polycaprolactone.

  Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polyethylene propylene glycol, polytetramethylene ether glycol, polyhexamethylene ether glycol, and the like.

  Examples of the polyisocyanates constituting the polyurethane resin include aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, and tolidine diisocyanate, α, α, α ′, α′-tetra. Aliphatic diisocyanates having an aromatic ring such as methylxylylene diisocyanate, methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, aliphatic diisocyanates such as trimethylhexamethylene diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, methylene bis (4 -Cyclohexyl Isocyanate), dicyclohexylmethane diisocyanate, alicyclic diisocyanates such as isopropylidene dicyclohexyl diisocyanates. These may be used alone or in combination of two or more. These polyisocyanate compounds may be a dimer, a trimer represented by an isocyanuric ring, or a polymer higher than that. Among the above isocyanates, aliphatic isocyanates or alicyclic isocyanates are more preferable than aromatic isocyanates from the viewpoint of improving adhesion to the active energy ray-curable coating material and preventing yellowing due to ultraviolet rays.

  A chain extender may be used when synthesizing the polyurethane resin, and the chain extender is not particularly limited as long as it has two or more active groups that react with an isocyanate group. Alternatively, a chain extender having two or more amino groups can be mainly used.

  Examples of the chain extender having two or more hydroxyl groups include aliphatic glycols such as ethylene glycol, propylene glycol, butanediol and pentanediol, aromatic glycols such as xylylene glycol and bishydroxyethoxybenzene, neopentyl glycol, neo Mention may be made of glycols such as ester glycols such as pentyl glycol hydroxypivalate. Examples of the chain extender having two or more amino groups include aromatic diamines such as tolylenediamine, xylylenediamine, diphenylmethanediamine, ethylenediamine, propylenediamine, hexanediamine, and 2,2-dimethyl-1,3. -Propanediamine, 2-methyl-1,5-pentanediamine, trimethylhexanediamine, 2-butyl-2-ethyl-1,5-pentanediamine, 1,8-octanediamine, 1,9-nonanediamine, 1,10 -Aliphatic diamines such as decanediamine, 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, dicyclohexylmethanediamine, isopropylidine cyclohexyl-4,4'-diamine, 1,4-diaminocyclohexane, 1,3-bisaminomethylcyclohex Emissions, alicyclic diamine such as isophorone diamine.

The polyurethane resin that can be used for forming the coating layer in the film of the present invention may be one using an organic solvent as a medium, but is preferably one using water as a medium. In order to disperse or dissolve the polyurethane resin in water, there are a forced emulsification type using an emulsifier, a self-emulsification type in which a hydrophilic group is introduced into the polyurethane resin, and a water-soluble type. In particular, a self-emulsification type in which an ionic group is introduced into a skeleton of a polyurethane resin to form an ionomer is preferable because of excellent storage stability of the liquid and water resistance, transparency and adhesion of the resulting coating layer.
Examples of the ionic group to be introduced include various groups such as a carboxyl group, sulfonic acid, phosphoric acid, phosphonic acid, quaternary ammonium salt, and the like, and a carboxyl group is preferable. As a method for introducing a carboxyl group into a polyurethane resin, various methods can be taken in each stage of the polymerization reaction. For example, there are a method of using a carboxyl group-containing resin as a copolymer component during prepolymer synthesis, and a method of using a component having a carboxyl group as one component such as polyol, polyisocyanate, and chain extender. In particular, a method in which a desired amount of carboxyl groups is introduced using a carboxyl group-containing diol depending on the amount of this component charged is preferred. For example, dimethylolpropionic acid, dimethylolbutanoic acid, bis- (2-hydroxyethyl) propionic acid, bis- (2-hydroxyethyl) butanoic acid, etc. are copolymerized with a diol used for polymerization of polyurethane resin. Can do. The carboxyl group is preferably in the form of a salt neutralized with ammonia, amine, alkali metal, inorganic alkali or the like. Particularly preferred are ammonia, trimethylamine and triethylamine. In such a polyurethane resin, the carboxyl group from which the neutralizing agent is removed in the drying step of the coating solution can be used as a crosslinking reaction point by another crosslinking agent. Thereby, it is possible to further improve the durability, water resistance, blocking resistance, and the like of the obtained coating layer as well as excellent stability in a liquid state before coating.

  The coating layer in the film of the present invention may be used in combination with a crosslinking agent in order to improve the adhesion between the coating layer, the prism layer, and the microlens layer, and to strengthen the coating film. As the crosslinking agent, it is preferable to use an oxazoline compound, an isocyanate compound, an epoxy compound, a melamine compound, or a carbodiimide compound. Among these, it is more preferable to use at least one of an oxazoline compound or an isocyanate compound from the viewpoint of improving adhesion.

  The oxazoline compound is a compound having an oxazoline group in the molecule, and a polymer containing an oxazoline group is particularly preferable, and can be prepared by polymerization of an addition polymerizable oxazoline group-containing monomer alone or with another monomer. Addition polymerizable oxazoline group-containing monomers include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, and the like can be mentioned, and one or a mixture of two or more thereof can be used. Among these, 2-isopropenyl-2-oxazoline is preferred because it is easily available industrially. The other monomer is not limited as long as it is a monomer copolymerizable with an addition polymerizable oxazoline group-containing monomer. For example, alkyl (meth) acrylate (the alkyl group includes a methyl group, an ethyl group, an n-propyl group, an isopropyl group, (Meth) acrylic acid esters such as n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, cyclohexyl group); acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrene Unsaturated carboxylic acids such as sulfonic acid and its salts (sodium salt, potassium salt, ammonium salt, tertiary amine salt, etc.); Unsaturated nitriles such as acrylonitrile, methacrylonitrile; (meth) acrylamide, N-alkyl ( (Meth) acrylamide, N, N-dialkyl (meth) acrylamide, ( As alkyl groups, unsaturated amides such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, cyclohexyl, etc.); vinyl acetate Vinyl esters such as vinyl propionate; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; α-olefins such as ethylene and propylene; halogen-containing α, β-unsaturated monomers such as vinyl chloride and vinylidene chloride; styrene, An α, β-unsaturated aromatic monomer such as α-methylstyrene can be used, and one or more of these monomers can be used. From the viewpoint of improving adhesion, the amount of the oxazoline group of the oxazoline compound is preferably 0.5 to 10 mmol / g, more preferably 1 to 9 mmol / g, still more preferably 3 to 8 mmol / g, and particularly preferably 4 to 6 mmol / g. The range of g.

  The epoxy compound is a compound having an epoxy group in the molecule, and examples thereof include condensates of epichlorohydrin with ethylene glycol, polyethylene glycol, glycerin, polyglycerin, bisphenol A and the like hydroxyl groups and amino groups, There are polyepoxy compounds, diepoxy compounds, monoepoxy compounds, glycidylamine compounds, and the like. Examples of the polyepoxy compound include sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, triglycidyl tris (2-hydroxyethyl) isocyanate, glycerol polyglycidyl ether, trimethylolpropane. Examples of the polyglycidyl ether and diepoxy compound include neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, resorcin diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and propylene glycol diglycidyl ether. , Polypropylene glycol diglycidyl ether, poly Examples of tetramethylene glycol diglycidyl ether and monoepoxy compounds include allyl glycidyl ether, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, and glycidyl amine compounds such as N, N, N ′, N′-tetraglycidyl-m-xylyl. Examples include range amine and 1,3-bis (N, N-diglycidylamino) cyclohexane. From the viewpoint of improving adhesion, a polyether-based epoxy compound is preferable. Further, the amount of the epoxy group is preferably a polyepoxy compound having a polyfunctionality of 3 or more rather than a bifunctional.

  The melamine compound is a compound having a melamine skeleton in the compound. For example, an alkylolized melamine derivative, a compound partially or completely etherified by reacting an alcohol with an alkylolated melamine derivative, and these Mixtures can be used. As alcohol used for etherification, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, isobutanol and the like are preferably used. Moreover, as a melamine compound, either a monomer or a multimer more than a dimer may be sufficient, or a mixture thereof may be used. Further, a product obtained by co-condensing urea or the like with a part of melamine can be used, and a catalyst can be used to increase the reactivity of the melamine compound.

  Further, in order to improve the water solubility and water dispersibility of the polycarbodiimide compound as long as the effects of the present invention are not lost, a surfactant is added, a polyalkylene oxide, a quaternary ammonium salt of a dialkylamino alcohol, a hydroxy A hydrophilic monomer such as an alkyl sulfonate may be added and used.

  When such a crosslinking component is contained, a component for accelerating crosslinking, for example, a crosslinking catalyst can be used in combination.

  The cross-linking agent used for the coating layer in the film of the present invention is used in a design that improves the performance of the coating layer by reacting in the drying process or the film forming process. It can be inferred that unreacted products of these crosslinking agents, compounds after the reaction, or mixtures thereof exist in the finished coating layer.

  In the coating layer in the film of the present invention, particles can be used in combination as a constituent component of the coating layer in order to improve slipperiness and blocking.

  When the particles are used in combination, the average particle size is preferably in the range of 1.0 μm or less, more preferably 0.5 μm or less, and particularly preferably 0.2 μm or less from the viewpoint of the transparency of the film. Specific examples of the particles include silica, alumina, kaolin, calcium carbonate, and organic particles.

  Furthermore, as long as it does not impair the gist of the present invention, the coating layer may include an antifoaming agent, a coating property improver, a thickener, an organic lubricant, an ultraviolet absorber, an antioxidant, a foaming agent, a dye, A pigment or the like may be contained. These additives may be used alone or in combination of two or more as required.

  The thickness of the coating layer in the film of the present invention is usually 0.002 to 1.0 μm, preferably 0.005 to 0.5 μm, more preferably 0.01 to 0.2 μm, and particularly preferably 0.01 to 0.00. The range is 1 μm. When the thickness is less than the above range, the adhesion may be insufficient. When the thickness is more than the above range, there is a concern that adverse effects such as deterioration of blocking and increase of haze may occur.

  In the film of the present invention, as a method for providing the coating layer, a conventionally known coating method such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, curtain coating or the like can be used.

  In the film of the present invention, the drying and curing conditions for forming the coating layer on the polyester film are not particularly limited. For example, when the coating layer is provided by off-line coating, it is usually 3 at 80 to 200 ° C. The heat treatment should be performed for ˜40 seconds, preferably 100 to 180 ° C. for 3 to 40 seconds.

  On the other hand, when the coating layer is provided by in-line coating, it is usually preferable to perform heat treatment at 70 to 280 ° C. for 3 to 200 seconds as a guide.

  Further, irrespective of off-line coating or in-line coating, heat treatment and active energy ray irradiation such as ultraviolet irradiation may be used in combination as required. The polyester film constituting the laminated polyester film in the present invention may be subjected to surface treatment such as corona treatment or plasma treatment in advance.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. The measurement method and evaluation method used in the present invention are as follows.

(1) Determination of intrinsic viscosity (dL / g) of polyester 1 g of polyester from which other polymer components and pigments incompatible with polyester have been removed are precisely weighed and mixed with phenol / tetrachloroethane = 50/50 (weight ratio) 100 ml of solvent was added and dissolved, and measurement was performed at 30 ° C.

(2) Measurement of haze and total light transmittance of film Total light transmittance is JIS K7361, haze is based on JIS K7136 by Nippon Denshoku Industries Co., Ltd. integrating sphere turbidimeter “NDH2000”, total light transmittance, Haze was measured.

(3) Measurement of MOR-C value by microwave molecular orientation meter The MOR-C value was measured using a microwave molecular orientation meter manufactured by Oji Scientific Instruments.

(4) Luminance evaluation of polyester film Optical characteristics when used as a prism sheet were evaluated.
That is, a prism layer was formed on the coating layer A surface side of the film in the following manner to obtain a prism sheet. Use the backlight unit mounted in the backlight unit (Matsushita Electric Industrial Co., Ltd. LCD TV VIERA TH-LX80 (32 inches)) so that the center of the prism sheet overlaps the diagonal center of the backlight. : (Configuration) Reflector / CCFL / diffusion plate / light diffusion sheet) and the luminance was measured. For luminance measurement, CS-200 manufactured by Konica Minolta Sensing Co., Ltd. was used, and the luminance value (cd / m ² ) was measured with a measurement angle of 1 °, the distance between the sample and the luminance meter being 500 mm, and compared with the reference sample.
As a reference sample, a prism sheet in which a prism layer similar to the following was formed on the film of Comparative Example 1 was used. The luminance value of the reference sample was set to 100.0%, and the luminance values of the examples and comparative examples were calculated as relative values.
<Manufacture of prism sheets>
A UV curable resin (Microsharp, MCL555, refractive index = 1.58) is applied on the surface of the coating layer A1 of the sample film, a template having a prism sheet shape is superimposed on the coating surface, and a metal halide lamp is applied. Using this, UV irradiation of 400 mJ / cm ^{2 in} terms of integrated light quantity was performed to obtain a prism sheet having the following shape.
・ Cross-sectional shape: isosceles triangle with apex angle of 90 ° and base angle of 45 ° ・ Height: 25μm
-Interval between apex angle and apex angle: 50 μm

The content of the polyester raw material used below will be described.
<Method for producing polyester (a)>
Using 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol as starting materials, 0.09 parts by weight of magnesium acetate tetrahydrate as a catalyst is placed in the reactor, the reaction start temperature is set to 150 ° C., and the methanol is distilled off gradually. The reaction temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. After adding 0.04 part by weight of ethyl acid phosphate to this reaction mixture, 0.03 part by weight of antimony trioxide was added, and a polycondensation reaction was carried out for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time when the intrinsic viscosity was 0.68 dL / g due to a change in stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure. The intrinsic viscosity of the obtained polyester (a) was 0.63 dL / g.

<Method for producing polyester (b)>
Polyester (a) is used as a starting material, and is continuously fed into a stirred crystallizer maintained at about 160 ° C. in a nitrogen atmosphere so that the residence time is about 60 minutes. Polyester is continuously supplied to a solid-phase polycondensation apparatus, and is subjected to solid-phase polycondensation by adjusting the residence time so that the intrinsic viscosity of the obtained polyethylene terephthalate resin is 0.82 dL / g at 215 ° C. in a nitrogen atmosphere (B) was obtained. The intrinsic viscosity of the obtained polyester (b) was 0.82 dL / g.

<Method for producing polyester (c)>
The polyester (a) was produced in the same manner as in the production method of the polyester (a) except that silica particles having an average particle diameter of 2.1 μm were added so that the content with respect to the polyester was 0.3% by weight to obtain a polyester (c). . The intrinsic viscosity of the obtained polyester (c) was 0.63 dL / g.

-Coating layer (A1) composition The example of a compound which comprises a coating layer (A1) is as follows.
The following compounds (I), (II), (III), and (IV) are mixed at a weight ratio of 60/18/18/4, respectively.
(I): formed from polycarbonate polyol / methylenebis (4-cyclohexylisocyanate) / dimethylolpropanoic acid = 45/50/5 (mol%) having a number average molecular weight of 2000 consisting of 1,6-hexanediol and diethyl carbonate Aqueous dispersion of polycarbonate polyurethane resin (II): acrylic polymer having oxazoline group and polyalkylene oxide chain ("Epocross", manufactured by Nippon Shokubai Co., Ltd., amount of oxazoline group = 4.5 mmol / g)
(III): Water-soluble polyglycerol polyglycidyl ether (IV): Silica sol having an average particle size of 0.07 μm

-Coating layer (B1) composition The example of a compound which comprises a coating layer (B1) is as follows.
Each of the following compounds (V), (VI), and (VII) is mixed at a weight ratio of 80/16/4.
(V): Emulsion polymerization acrylic resin of ethyl acrylate / n-butyl acrylate / methyl methacrylate / N-methylol acrylamide / acrylic acid = 65/21/10/2/2 (% by weight) (glass transition point 40 ° C., emulsifier: Anionic surfactant)
(VI): water-soluble hexamethoxymethylolated melamine (VII): silica sol having an average particle size of 0.07 μm

Example 1
Mixing raw materials in which polyesters (b) and (c) are mixed at a ratio of 90% by weight and 10% by weight are used as surface layer materials, and 100% by weight of polyester (a) is used as intermediate layer materials in two extruders. Each was supplied, melted at 285 ° C., and then co-extruded on a cooling roll set at 40 ° C. in a layer configuration of two types and three layers (surface layer A / intermediate layer / surface layer B = 1/8/1). Thereafter, it was cooled and solidified to obtain an unstretched sheet. Next, the film is stretched in the machine direction at a film temperature of 85 ° C. using the difference in peripheral speed of the roll, and then the coating liquid A1 is applied to the surface A side of the longitudinally stretched film, and the coating liquid B1 is applied to the surface B side. After that, the film was guided to a tenter, stretched at 110 ° C. in the transverse direction, heat treated at 230 ° C., and then relaxed by 2% in the transverse direction, and the thicknesses of the coating layers on the surface layers A and B (after drying) were 0. A polyester film having a thickness of 0.03 μm and a thickness of 75 μm was obtained.

(Examples 2-4, Comparative Examples 1-2)
A polyester film was obtained in the same manner as in Example 1 except that the stretching ratios in the machine direction and the transverse direction of the film in Example 1 were as shown in Table 1.

(Comparative Example 3)
A polyester film was obtained in the same manner as in Example 1 except that 100% by weight of polyester (c) was used as a raw material for the surface layer and 100% by weight of polyester (a) was used as a raw material for the intermediate layer. .

(Comparative Example 4)
In Example 1, it manufactured similarly to Example 1 except not apply | coating coating liquid B1 to the surface B surface side of a film, and obtained the polyester film.

  The characteristics of each film obtained in the above Examples and Comparative Examples are shown in Table 1 below.

  The present invention relates to an optical polyester film, and more specifically, is a high-brightness type film having excellent optical characteristics, and can be suitably used for prism sheets and microlens sheets of LCD components, and its industrial Value is high.

Claims (3)

  Optical biaxial, characterized in that haze is 3.0% or less, total light transmittance is 90% or more, and MOR-C value measured by microwave molecular orientation meter is 4.5 or more Stretched polyester film.   The biaxially stretched polyester film for optics according to claim 1, wherein a coating layer is provided on both sides of the film.   The film is stretched by setting a ratio (MD / TD) between a stretching ratio in a longitudinal direction of the film and a stretching ratio in a direction orthogonal to the longitudinal direction to 0.25 to 0.70. Of producing a biaxially stretched polyester film for optical use.