White laminated polyester film

Abstract

To provide a white laminated polyester film. More specifically, the present invention provides a white laminated polyester film in which blocking at the time of water adhesion is reduced and which is suitable as an information recording material or a printing material having excellent ink adhesiveness.SOLUTION: In the white laminated polyester film having a coating layer on at least one surface of a polyester film base material, the coating layer is formed by curing a composition containing a urethane resin having a polycarbonate structure and a branched structure, a crosslinking agent and a polyester resin.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a white laminated polyester film, and more particularly to a white laminated polyester film that exhibits reduced blocking when water is applied and excellent ink adhesion, making it suitable for use as an information recording material or a printing material. [Background technology]

[0002] Biaxially oriented polyester films have excellent properties such as mechanical properties, electrical properties, and dimensional stability, and are therefore used as base films in many fields, including magnetic recording materials, packaging materials, electrical insulating materials, photosensitive materials, drafting materials, and photographic materials. However, when other materials are coated or laminated on the polyester film in these applications, the polyester film has the disadvantage of poor adhesion, depending on the material used.

[0003] Therefore, one known method for imparting adhesiveness to the surface of a polyester film is to coat the surface of the polyester film with various resins to provide a coating layer with adhesive properties.

[0004] In many conventional ink-adhesive polyester-based coated films, a coating layer made of a specific resin is provided on the surface of a base polyester film (see, for example, Patent Document 1). Examples of the resin constituting the coating layer include polyester-based resins, polyurethane-based resins, acrylic-based resins, etc., either alone or in mixtures of two or more types, as well as mixtures of the above resins with specific crosslinking agents (melamine, isocyanate, etc.).

[0005] However, with this conventional technology, especially during winter transport of film rolls between indoor and outdoor locations, such as factories, condensation water can form on the film roll due to the temperature difference between indoor and outdoor air, resulting in blocking problems in which the film surface and its coating layers stick together. This type of blocking differs from the typical blocking that occurs under pressure after exposure to water vapor-containing air; it only occurs through liquid water. In other words, achieving both ink adhesion and blocking resistance has been difficult. It has been particularly difficult to achieve both adhesion and blocking resistance for ultraviolet-curable inks (UV inks). Seasoning is an effective way to avoid this problem, but it cannot be completely avoided. The addition of a seasoning process slows down processing, leading to reduced productivity. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-229355 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in view of the problems of the prior art. That is, an object of the present invention is to provide a white laminated polyester film that has resistance to blocking when water is applied and has excellent adhesion to UV ink. [Means for solving the problem]

[0008] In the course of investigating the causes of the above problems in order to solve the above problems, the present inventors discovered that the problems of the present invention can be solved when a polyester film substrate has a coating layer on at least one side thereof, and the coating layer is formed by curing a composition containing a crosslinking agent, a polyester resin, and a urethane resin having a polycarbonate structure and a branched structure, and thus completed the present invention.

[0009] That is, the present invention comprises the following: 1. A white laminated polyester film having a coating layer on at least one side of a polyester film substrate, the coating layer being formed by curing a composition containing a urethane resin having a polycarbonate structure and a branched structure, a crosslinking agent, and a polyester resin. 2. The white laminated polyester film according to item 1 above, wherein the crosslinking agent is a compound having a tri- or higher functional blocked isocyanate group. 3. The white laminated polyester film according to item 1 or 2 above, wherein the urethane resin having a polycarbonate structure and a branched structure is obtained by synthesizing and polymerizing a polycarbonate polyol component and a polyisocyanate component, and the mass ratio of the polycarbonate polyol component to the polyisocyanate component (mass of the polycarbonate polyol component / mass of the polyisocyanate component) during the synthesis and polymerization is 0.5 to 3. [Effects of the Invention]

[0010] The white laminated polyester film of the present invention does not cause blocking even when condensed water adheres to it, and has excellent adhesion to UV ink, particularly in low-dose processing. DETAILED DESCRIPTION OF THE INVENTION

[0011] (Polyester film base) In the present invention, the polyester resin constituting the polyester film substrate is polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, polytrimethylene terephthalate, etc., as well as copolymerized polyester resins in which a portion of the diol component or dicarboxylic acid component of the above-mentioned polyester resins is replaced with a copolymerization component such as the following. For example, the copolymerization component may include diol components such as diethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, and polyalkylene glycol, and dicarboxylic acid components such as adipic acid, sebacic acid, phthalic acid, isophthalic acid, 5-sodium isophthalic acid, and 2,6-naphthalenedicarboxylic acid.

[0012] In the present invention, polyester resins suitable for use in the polyester film substrate are primarily selected from polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate. Among these polyester resins, polyethylene terephthalate is most preferred in terms of the balance between physical properties and cost. Furthermore, polyester film substrates made from these polyester resins are preferably biaxially oriented polyester films, which can improve chemical resistance, heat resistance, mechanical strength, and the like.

[0013] The catalyst for polycondensation used in producing the polyester resin is not particularly limited, but antimony trioxide is preferred because it is inexpensive and has excellent catalytic activity. It is also preferred to use a germanium compound or a titanium compound. More preferred polycondensation catalysts include catalysts containing aluminum and / or its compound and a phenolic compound, catalysts containing aluminum and / or its compound and a phosphorus compound, and catalysts containing an aluminum salt of a phosphorus compound.

[0014] The polyester film substrate in the present invention is particularly preferably a biaxially oriented film from the viewpoint of practical properties such as strength and stiffness.

[0015] The layer structure of the polyester film substrate may be a single layer structure or a laminate structure, but a preferred embodiment is a laminate structure of Layer A / Layer B / Layer A, in which Layer A contains inorganic particles and Layer B contains microvoids. By disposing a layer containing inorganic particles in Layer A, which is the surface layer, it is possible to improve the film's slipperiness, i.e., handleability and hiding power. By incorporating microvoids only in Layer B, which is the inner layer, it is possible to obtain a desirable white appearance and ensure the film's surface strength while exhibiting cushioning properties. While the method for forming the laminate structure is not particularly limited, coextrusion is preferred from the standpoint of manufacturing stability and processing costs.

[0016] The polyester film substrate of the present invention may have a single-layer structure or a multi-layer structure, and it is preferable that some or all of the layers are opaque. The optical density, which indicates the opacity of the white laminated polyester film, is preferably 0.3 or more, more preferably 0.3 to 4.0, and particularly preferably 0.5 to 3.0. An optical density of 0.3 or more is preferable because, when printing is performed on the coating layer surface of the white laminated polyester film, the printing effect becomes clear. Furthermore, an optical density of 4.0 or less is preferable because better printing effects can be expected.

[0017] The method for obtaining an optical density within the above range is not particularly limited, but can be achieved by incorporating inorganic particles or a thermoplastic resin incompatible with the polyester resin into the polyester resin. The content of these is not particularly limited, but in the case of inorganic particles, the content is preferably 5 to 35 mass% relative to the resulting polyester, and particularly preferably 8 to 25 mass%. On the other hand, when an incompatible thermoplastic resin is incorporated, the content is preferably 5 to 35 mass% relative to the polyester, and particularly preferably 8 to 28 mass%. Furthermore, when inorganic particles and a thermoplastic resin incompatible with the polyester resin are used in combination, it is preferable that the total amount be 40 mass% or less relative to the polyester film substrate, from the viewpoints of film strength, stiffness, and film formation stability.

[0018] The inorganic particles used are not particularly limited, but inorganic particles with an average particle size of 0.1 to 4.0 μm are preferred, and inorganic particles with an average particle size of 0.3 to 1.5 μm are particularly preferred. Specifically, white pigments such as titanium oxide, barium sulfate, calcium carbonate, and zinc sulfide are preferred, and these may be mixed. Furthermore, inorganic particles commonly contained in films, such as silica, alumina, talc, kaolin, clay, calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, calcium fluoride, and calcium sulfate, may also be used in combination.

[0019] Furthermore, the thermoplastic resin incompatible with the polyester resin is not particularly limited, but examples thereof include, when mixed with polyethylene terephthalate resin, polyolefin resins such as polystyrene resin, polyethylene resin, polypropylene resin, and polymethylpentene resin, acrylic resin, phenoxy resin, polyphenylene oxide resin, and polycarbonate resin. These thermoplastic resins may be mixed or modified. Naturally, they may also be used in combination with the inorganic particles. Needless to say, various whitening agents may be added as needed.

[0020] The average particle size of the particles was measured by observing the particles on the cross section of the film with a scanning electron microscope, observing 50 particles, and taking the average value as the average particle size.

[0021] The shape of the particles is not particularly limited as long as it satisfies the objectives of the present invention, and spherical particles and irregular, non-spherical particles can be used. The particle diameter of irregular particles can be calculated as the equivalent circle diameter. The equivalent circle diameter is the value obtained by dividing the observed particle area by π, calculating the square root, and then multiplying it by two.

[0022] Furthermore, the white laminated polyester film of the present invention has an apparent density of 0.3 to 1.3 g / cm 3 It is preferable that the polyester film is a microvoid-containing polyester film having the formula:

[0023] In addition, from the viewpoint of achieving both cushioning properties and surface peel strength, a white laminate polyester film having a void lamination density of 0.20 / μm or more, preferably 0.25 / μm or more, and more preferably 0.30 / μm or more is also preferred. As a result, the resulting white laminate polyester film has excellent print clarity and processing characteristics during printing. Here, the void lamination density (cavities / μm) is defined by the formula: number of cavities in the film thickness direction (cavities) / film thickness (μm). From the viewpoint of void development efficiency, the upper limit of the void lamination density is preferably 0.80 / μm, more preferably 0.55 / μm. Methods for adjusting the void density within the above range include, but are not limited to, adjusting the amount, type, viscosity, etc. of the incompatible thermoplastic resin added, changing the screw shape of the extruder, or installing a static mixer in the molten resin flow path.

[0024] These void-containing white laminated polyester films are particularly useful because the microvoids contained in the film cause light scattering at the interface with the polyester matrix, thereby further improving opacity and allowing the addition of the inorganic particles to be reduced. Furthermore, the inclusion of microvoids reduces the weight of the substrate film itself, making it easier to handle and providing significant economic benefits such as reduced raw material costs and transportation costs.

[0025] As a method for obtaining such a white laminated polyester film, a publicly known method can be used, such as a method in which a thermoplastic resin that is incompatible with the polyester resin as described above is kneaded into a thermoplastic polyester resin matrix, and the incompatible resin is dispersed in the form of fine particles in the polyester resin, and the resulting sheet is stretched in at least one direction to generate cavities around the incompatible resin fine particles.

[0026] The thickness of the obtained white laminated polyester film is preferably 5 to 300 μm. In particular, the thickness of a white laminated polyester film having a void lamination density of 0.20 / μm or more is preferably 20 to 300 μm, and more preferably 40 to 250 μm.

[0027] The whiteness required for use in printing materials can be expressed in color values. In particular, the color L value is a measure of brightness, with a higher value indicating whiter. Furthermore, a higher color b value indicates a stronger yellow tint, while a lower value indicates a stronger blue tint. In other words, a high L value and a low b value indicate high whiteness, which means that the color appears white to the naked eye. This improves clarity when printed.

[0028] (coating layer) To improve adhesion to UV ink and blocking resistance when water is applied, the white laminated polyester film of the present invention preferably has a coating layer laminated on at least one side thereof, the coating layer being formed by curing a composition containing a urethane resin having a polycarbonate structure and a branched structure, a crosslinking agent, and a polyester resin. The coating layer is thought to be formed by curing a urethane resin or polyester resin having a polycarbonate structure and a branched structure, which is crosslinked by a crosslinking agent. However, since it is difficult to express the crosslinked chemical structure itself, the coating layer is expressed as being formed by curing a composition containing a urethane resin having a polycarbonate structure and a branched structure, a crosslinking agent, and a polyester resin. The coating layer may be formed on both sides of the polyester film substrate, or on only one side of the polyester film substrate, with a different resin coating layer formed on the other side.

[0029] The composition of each coating layer will be described in detail below. (Urethane resin having a polycarbonate structure and a branched structure) The urethane resin having a polycarbonate structure in the present invention preferably has a urethane bond portion derived from at least a polycarbonate polyol component and a polyisocyanate component, and a branched structure, and further contains a chain extender as needed. The branched structure referred to here is preferably introduced by forming a branched molecular chain structure after synthesis and polymerization due to the presence of three or more terminal functional groups in any of the raw material components constituting the molecular chain, as described above.

[0030] In the urethane resin having a polycarbonate structure and a branched structure of the present invention, the lower limit of the number of terminal functional groups in the molecular chain is preferably 3, more preferably 4, due to the branched structure. Three or more terminal functional groups is preferable because it can improve blocking resistance when water is attached. In the urethane resin having a polycarbonate structure of the present invention, the upper limit of the number of terminal functional groups in the molecular chain is preferably 6, due to the branched structure. Six or less terminal functional groups is preferable because it can stably disperse the resin in an aqueous solution.

[0031] The lower limit of the mass ratio of the polycarbonate polyol component to the polyisocyanate component (mass of the polycarbonate polyol component / mass of the polyisocyanate component) when synthesizing and polymerizing the urethane resin having a polycarbonate structure and a branched structure in the present invention is preferably 0.5, more preferably 0.6, even more preferably 0.7, particularly preferably 0.8, and most preferably 1.0. A ratio of 0.5 or more is preferable because adhesion to UV ink can be improved. The upper limit of the mass ratio of the polycarbonate polyol component to the polyisocyanate component when synthesizing and polymerizing the urethane resin having a polycarbonate structure in the present invention is preferably 3.0, more preferably 2.2, even more preferably 2.0, particularly preferably 1.7, and most preferably 1.5. A ratio of 3.0 or less is preferable because blocking resistance when water is attached can be improved.

[0032] The polycarbonate polyol component used for synthesizing and polymerizing the urethane resin having a polycarbonate structure and a branched structure in the present invention preferably contains an aliphatic polycarbonate polyol, which has excellent heat resistance and hydrolysis resistance. Examples of the aliphatic polycarbonate polyol include an aliphatic polycarbonate diol and an aliphatic polycarbonate triol, and the aliphatic polycarbonate diol is preferably used. Examples of the aliphatic polycarbonate diol used for synthesizing and polymerizing the urethane resin having a polycarbonate structure in the present invention include aliphatic polycarbonate diols obtained by reacting one or more diols such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, 1,8-nonanediol, neopentyl glycol, diethylene glycol, and dipropylene glycol with carbonates such as dimethyl carbonate, ethylene carbonate, and phosgene.

[0033] The number average molecular weight of the polycarbonate polyol in the present invention is preferably 1000 to 3000, more preferably 1200 to 2900, and most preferably 1500 to 2800. When it is 1000 or more, ink adhesion can be improved, which is preferable. When it is 3000 or less, blocking resistance when water is attached can be improved, which is preferable.

[0034] Examples of polyisocyanates used in the synthesis and polymerization of the urethane resin having a polycarbonate structure and a branched structure in the present invention include aromatic aliphatic diisocyanates such as xylylene diisocyanate, alicyclic diisocyanates such as isophorone diisocyanate, 4,4-dicyclohexylmethane diisocyanate, and 1,3-bis(isocyanatomethyl)cyclohexane, aliphatic diisocyanates such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate, and polyisocyanates obtained by pre-adding one or more of these compounds with trimethylolpropane or the like. The use of the aromatic aliphatic diisocyanates, alicyclic diisocyanates, or aliphatic diisocyanates described above is preferred because it does not cause yellowing problems. Furthermore, it is also preferred because it does not form an overly rigid coating film, can relieve stress due to thermal shrinkage of the polyester film substrate, and provides good adhesion.

[0035] Examples of chain extenders include glycols such as ethylene glycol, diethylene glycol, 1,4-butanediol, neopentyl glycol, and 1,6-hexanediol; polyhydric alcohols such as glycerin, trimethylolpropane, and pentaerythritol; diamines such as ethylenediamine, hexamethylenediamine, and piperazine; amino alcohols such as monoethanolamine and diethanolamine; thiodiglycols such as thiodiethylene glycol; and water.

[0036] To form a branched structure in the urethane resin, for example, a method can be preferably employed in which the polycarbonate polyol component, polyisocyanate, and chain extender are reacted at an appropriate temperature for an appropriate time, and then a compound having a tri- or higher functional hydroxyl group or isocyanate group is added, and the reaction is further allowed to proceed.

[0037] Specific examples of compounds having three or more functional hydroxyl groups include caprolactone triol, glycerol, trimethylolpropane, butanetriol, hexanetriol, 1,2,3-hexanetriol, 1,2,3-pentanetriol, 1,3,4-hexanetriol, 1,3,4-pentanetriol, 1,3,5-hexanetriol, 1,3,5-pentanetriol, polyethertriol, etc. Examples of the polyethertriol include compounds obtained by addition polymerization of one or more monomers such as ethylene oxide, propylene oxide, butylene oxide, amylene oxide, glycidyl ether, methyl glycidyl ether, t-butyl glycidyl ether, phenyl glycidyl ether, etc., using one or more compounds having three active hydrogens, such as alcohols such as glycerin and trimethylolpropane, and diethylenetriamine, as initiators.

[0038] A specific example of a compound having a tri- or higher functional isocyanate group is a polyisocyanate compound having at least three isocyanate (NCO) groups in one molecule. In the present invention, the tri- or higher functional isocyanate compound includes biuret compounds, nurate compounds, adduct compounds, and the like obtained by modifying isocyanate monomers having two isocyanate groups, such as aromatic diisocyanates, aliphatic diisocyanates, araliphatic diisocyanates, and alicyclic diisocyanates. Examples of aromatic diisocyanates include 1,3-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,4-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-toluidine diisocyanate, dianisidine diisocyanate, and 4,4'-diphenyl ether diisocyanate. Examples of aliphatic diisocyanates include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate. Examples of the aromatic aliphatic diisocyanate include xylylene diisocyanate, ω,ω'-diisocyanate-1,4-diethylbenzene, 1,4-tetramethylxylylene diisocyanate, and 1,3-tetramethylxylylene diisocyanate. Examples of alicyclic diisocyanates include 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (also known as IPDI, isophorone diisocyanate), 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), and 1,4-bis(isocyanatomethyl)cyclohexane. The biuret form is a self-condensation product having a biuret bond formed by the self-condensation of an isocyanate monomer, and examples thereof include the biuret form of hexamethylene diisocyanate. The nurate is a trimer of an isocyanate monomer, and examples thereof include a trimer of hexamethylene diisocyanate, a trimer of isophorone diisocyanate, and a trimer of tolylene diisocyanate. The adduct refers to a tri- or higher functional isocyanate compound obtained by reacting the above-mentioned isocyanate monomer with a tri- or higher functional low-molecular-weight active hydrogen-containing compound, and examples thereof include a compound obtained by reacting trimethylolpropane with hexamethylene diisocyanate, a compound obtained by reacting trimethylolpropane with tolylene diisocyanate, a compound obtained by reacting trimethylolpropane with xylylene diisocyanate, and a compound obtained by reacting trimethylolpropane with isophorone diisocyanate.

[0039] Examples of chain extenders having three or more functional groups include alcohols having three or more hydroxyl groups, such as trimethylolpropane and pentaerythritol, which are mentioned in the above description of chain extenders.

[0040] The coating layer in the present invention is preferably formed using an aqueous coating liquid by the in-line coating method described below. Therefore, the urethane resin of the present invention is preferably water-soluble or water-dispersible. The term "water-soluble or water-dispersible" means that the resin is dispersible in water or an aqueous solution containing less than 50% by mass of a water-soluble organic solvent.

[0041] To impart water dispersibility to urethane resins, sulfonic acid (salt) groups or carboxylic acid (salt) groups can be introduced (copolymerized) into the urethane molecular structure. To maintain moisture resistance, it is preferable to introduce weakly acidic carboxylic acid (salt) groups. Nonionic groups such as polyoxyalkylene groups can also be introduced.

[0042] To introduce carboxylic acid (salt) groups into a urethane resin, for example, a polyol compound having a carboxylic acid group, such as dimethylolpropanoic acid or dimethylolbutanoic acid, is introduced as a copolymerization component and neutralized with a salt-forming agent. Specific examples of salt-forming agents include ammonia, trialkylamines such as trimethylamine, triethylamine, triisopropylamine, tri-n-propylamine, and tri-n-butylamine, N-alkylmorpholines such as N-methylmorpholine and N-ethylmorpholine, and N-dialkylalkanolamines such as N-dimethylethanolamine and N-diethylethanolamine. These can be used alone or in combination of two or more.

[0043] When a polyol compound having a carboxylic acid (salt) group is used as a copolymerization component to impart water dispersibility, the molar ratio of the polyol compound having a carboxylic acid (salt) group in the urethane resin is preferably 3 to 60 mol%, and more preferably 5 to 40 mol%, when the total polyisocyanate components of the urethane resin are taken as 100 mol%. A molar ratio of 3 mol% or more is preferred because water dispersibility is obtained. Furthermore, a molar ratio of 60 mol% or less is preferred because water resistance is maintained and moist heat resistance is obtained.

[0044] The urethane resin in the present invention may have a blocked isocyanate structure at the end to improve hardness.

[0045] (Crosslinking agent) In the present invention, the crosslinking agent contained in the coating layer-forming composition is preferably a blocked isocyanate, more preferably a tri- or higher functional blocked isocyanate, and particularly preferably a tetra- or higher functional blocked isocyanate, which can improve blocking resistance when water is attached.

[0046] The lower limit of the NCO equivalent of the blocked isocyanate is preferably 100, more preferably 120, even more preferably 130, particularly preferably 140, and most preferably 150. An NCO equivalent of 100 or more is preferred because there is no risk of coating cracking. The upper limit of the NCO equivalent is preferably 500, more preferably 400, even more preferably 380, particularly preferably 350, and most preferably 300. An NCO equivalent of 500 or less is preferred because it improves blocking resistance when water is attached.

[0047] The lower limit of the boiling point of the blocking agent for the blocked isocyanate is preferably 150°C, more preferably 160°C, even more preferably 180°C, particularly preferably 200°C, and most preferably 210°C. The higher the boiling point of the blocking agent, the more suppressed is the volatilization of the blocking agent by heat addition during the drying process after application of the coating liquid or during the film formation process in the case of an in-line coating method, thereby suppressing the occurrence of minute unevenness on the coated surface and improving the transparency of the film. The upper limit of the boiling point of the blocking agent is not particularly limited, but from the viewpoint of productivity, it is thought that the upper limit is about 300°C. Since the boiling point is related to the molecular weight, in order to increase the boiling point of the blocking agent, it is preferable to use a blocking agent with a large molecular weight, and the molecular weight of the blocking agent is preferably 50 or more, more preferably 60 or more, and even more preferably 80 or more.

[0048] The upper limit of the dissociation temperature of the blocking agent is preferably 200°C, more preferably 180°C, even more preferably 160°C, particularly preferably 150°C, and most preferably 120°C. The blocking agent dissociates from the functional group by thermal addition during the drying process after application of the coating solution or during the film formation process in the case of an in-line coating method, generating a regenerated isocyanate group. This allows the crosslinking reaction with urethane resins and the like to proceed, improving adhesion. When the dissociation temperature of the blocked isocyanate is below the above temperature, the dissociation of the blocking agent proceeds sufficiently, resulting in good adhesion, particularly good moist heat resistance.

[0049] In the present invention, blocking agents used in the blocked isocyanate have a dissociation temperature of 120°C or lower and a boiling point of 150°C or higher, and include bisulfite compounds such as sodium bisulfite, pyrazole compounds such as 3,5-dimethylpyrazole, 3-methylpyrazole, 4-bromo-3,5-dimethylpyrazole, and 4-nitro-3,5-dimethylpyrazole, active methylene compounds such as malonic acid diesters (dimethyl malonate, diethyl malonate, di-n-butyl malonate, and di-2-ethylhexyl malonate), methyl ethyl ketone, and triazole compounds such as 1,2,4-triazole. Among these, pyrazole compounds are preferred from the viewpoints of wet heat resistance and yellowing.

[0050] In the present invention, the tri- or higher functional polyisocyanate, which is a precursor of the blocked isocyanate, can be suitably obtained by introducing an isocyanate monomer, such as a biuret, nurate, or adduct obtained by modifying an isocyanate monomer, such as an aromatic diisocyanate, aliphatic diisocyanate, araliphatic diisocyanate, or alicyclic diisocyanate, each having two isocyanate groups. The biuret form is a self-condensation product having a biuret bond formed by the self-condensation of an isocyanate monomer, and examples thereof include the biuret form of hexamethylene diisocyanate. The nurate is a trimer of an isocyanate monomer, and examples thereof include a trimer of hexamethylene diisocyanate, a trimer of isophorone diisocyanate, and a trimer of tolylene diisocyanate. The adduct refers to a tri- or higher functional isocyanate compound obtained by reacting an isocyanate monomer with a tri- or higher functional low-molecular-weight active hydrogen-containing compound, and examples thereof include a compound obtained by reacting trimethylolpropane with hexamethylene diisocyanate, a compound obtained by reacting trimethylolpropane with tolylene diisocyanate, a compound obtained by reacting trimethylolpropane with xylylene diisocyanate, and a compound obtained by reacting trimethylolpropane with isophorone diisocyanate.

[0051] Examples of the isocyanate monomer include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 1,5-naphthylene diisocyanate, 1,4-naphthylene diisocyanate, phenylene diisocyanate, tetramethylxylylene diisocyanate, 4,4'-diphenylether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, 3,3' Examples of suitable diisocyanates include aromatic diisocyanates such as 4,4'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, and 3,3'-dimethoxydiphenyl-4,4'-diisocyanate; aromatic aliphatic diisocyanates such as xylylene diisocyanate; alicyclic diisocyanates such as isophorone diisocyanate, 4,4-dicyclohexylmethane diisocyanate, and 1,3-bis(isocyanatomethyl)cyclohexane; and aliphatic diisocyanates such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate. From the viewpoints of transparency, adhesion, and wet heat resistance, aliphatic and alicyclic isocyanates and their modified products are preferred.

[0052] The blocked isocyanate of the present invention can introduce hydrophilic groups into the precursor polyisocyanate to impart water solubility or water dispersibility. Examples of hydrophilic groups include (1) quaternary ammonium salts of dialkylamino alcohols and quaternary ammonium salts of dialkylaminoalkylamines, (2) sulfonates, carboxylates, and phosphates, and (3) polyethylene glycols and polypropylene glycols capped at one end with an alkyl group. When a hydrophilic moiety is introduced, the resulting polymer will be (1) cationic, (2) anionic, or (3) nonionic. Since many other water-soluble resins are anionic, anionic or nonionic polymers are preferred because they are easily compatible with other resins. Furthermore, anionic polymers have excellent compatibility with other resins, and nonionic polymers lack ionic hydrophilic groups, which improves resistance to moist heat.

[0053] The anionic hydrophilic group preferably has a hydroxyl group for introduction into polyisocyanate and a carboxylic acid group for imparting hydrophilicity. Examples include glycolic acid, lactic acid, tartaric acid, citric acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxypivalic acid, dimethylolacetic acid, dimethylolpropanoic acid, dimethylolbutanoic acid, and polycaprolactone having a carboxylic acid group. To neutralize the carboxylic acid group, an organic amine compound is preferred. Examples include linear or branched primary, secondary, or tertiary amines having 1 to 20 carbon atoms, such as ammonia, methylamine, ethylamine, propylamine, isopropylamine, butylamine, 2-ethylhexylamine, cyclohexylamine, dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, trimethylamine, triethylamine, triisopropylamine, tributylamine, and ethylenediamine; cyclic amines, such as morpholine, N-alkylmorpholine, and pyridine; and hydroxyl group-containing amines, such as monoisopropanolamine, methylethanolamine, methylisopropanolamine, dimethylethanolamine, diisopropanolamine, diethanolamine, triethanolamine, diethylethanolamine, and triethanolamine.

[0054] The nonionic hydrophilic group preferably has 3 to 50 repeating units of ethylene oxide and / or propylene oxide in polyethylene glycol or polypropylene glycol capped at one end with an alkyl group, more preferably 5 to 30. Small repeating units result in poor compatibility with resins and increased haze, while large repeating units may result in reduced adhesion under high temperature and humidity conditions. To improve water dispersibility, the blocked isocyanate of the present invention can be supplemented with nonionic, anionic, cationic, or amphoteric surfactants. Examples of such surfactants include nonionic surfactants such as polyethylene glycol and polyhydric alcohol fatty acid esters, anionic surfactants such as fatty acid salts, alkyl sulfates, alkylbenzene sulfonates, sulfosuccinates, and alkyl phosphates, cationic surfactants such as alkylamine salts and alkylbetaines, and surfactants such as amine carboxylates, amine sulfonates, and sulfate ester salts.

[0055] In addition to water, a water-soluble organic solvent may also be contained. For example, the organic solvent used in the reaction may be removed, and another organic solvent may be added.

[0056] (polyester resin) The polyester resin used to form the coating layer in the present invention may be a linear one, but is more preferably a polyester resin containing a dicarboxylic acid and a diol having a branched structure as its constituent components. The dicarboxylic acid referred to here includes, as its main component, terephthalic acid, isophthalic acid, or 2,6-naphthalenedicarboxylic acid, as well as aliphatic dicarboxylic acids such as adipic acid and sebacic acid, and aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid. Furthermore, the branched glycol refers to a diol having a branched alkyl group, and examples thereof include 2,2-dimethyl-1,3-propanediol, 2-methyl-2-ethyl-1,3-propanediol, 2-methyl-2-butyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-methyl-2-isopropyl-1,3-propanediol, 2-methyl-2-n-hexyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-ethyl-2-n-butyl-1,3-propanediol, 2-ethyl-2-n-hexyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, 2-n-butyl-2-propyl-1,3-propanediol, and 2,2-di-n-hexyl-1,3-propanediol.

[0057] The polyester resin preferably contains the branched glycol component, which is a more preferred embodiment of the present invention, at a ratio of 10 mol % or more, and more preferably 20 mol % or more, of the total glycol components. If the ratio is 10 mol % or less, the crystallinity may be high, and the adhesiveness of the coating layer may decrease. The upper limit of the glycol component content of the total glycol components is preferably 80 mol % or less, and more preferably 70 mass %. If the ratio is 80 mol % or more, the concentration of oligomers, which are by-products, may increase, which may affect the transparency of the coating layer. Ethylene glycol is the most preferred glycol component other than the above compounds. Small amounts of diethylene glycol, propylene glycol, butanediol, hexanediol, 1,4-cyclohexanedimethanol, etc. may also be used.

[0058] The dicarboxylic acid constituting the polyester resin is most preferably terephthalic acid or isophthalic acid. In addition to the dicarboxylic acids, 5-sulfoisophthalic acid or the like is preferably copolymerized in a range of 1 to 10 mol % to impart water dispersibility to the copolymerized polyester resin. Examples include sulfoterephthalic acid, 5-sulfoisophthalic acid, and 5-sodium sulfoisophthalic acid. A polyester resin containing a dicarboxylic acid having a naphthalene skeleton may be used, but to prevent a decrease in adhesion to UV ink, the quantitative proportion of the dicarboxylic acid is preferably 5 mol % or less of the total carboxylic acid components, and it may not be used at all.

[0059] When the total solid content of the polyester resin, urethane resin having a polycarbonate structure, and crosslinking agent in the coating solution is taken as 100% by mass, the lower limit of the content of the crosslinking agent is preferably 5% by mass, more preferably 7% by mass, and even more preferably 10% by mass. A content of 5% by mass or more is preferred because it can improve blocking resistance when water is applied. The upper limit of the content of the crosslinking agent is preferably 50% by mass, more preferably 40% by mass, even more preferably 35% by mass, and most preferably 30% by mass. A content of 50% by mass or less is preferred because it improves adhesion to UV ink.

[0060] When the total solid content of the polyester resin, urethane resin having a polycarbonate structure, and crosslinking agent in the coating liquid is taken as 100% by mass, the lower limit of the content of the urethane resin having a polycarbonate structure is preferably 5% by mass. A content of 5% by mass or more is preferable because adhesion to UV ink can be improved. The upper limit of the content of the urethane resin having a polycarbonate structure is preferably 50% by mass, more preferably 40% by mass, even more preferably 30% by mass, and most preferably 20% by mass. A urethane resin content of 50% by mass or less is preferable because blocking resistance when water is attached can be improved.

[0061] When the total solid content of the polyester resin, urethane resin, and crosslinking agent in the coating solution is taken as 100% by mass, the lower limit of the polyester resin content is preferably 10% by mass, more preferably 20% by mass, even more preferably 30% by mass, particularly preferably 35% by mass, and most preferably 40% by mass. A polyester resin content of 10% by mass or more is preferred because it improves adhesion between the coating layer and the polyester film substrate. The upper limit of the polyester resin content is preferably 70% by mass, more preferably 67% by mass, even more preferably 65% ​​by mass, particularly preferably 62% by mass, and most preferably 60% by mass. A polyester resin content of 70% by mass or less is preferred because it improves moist heat resistance after UV ink processing.

[0062] (additives) The coating layer of the present invention may contain known additives, such as surfactants, antioxidants, heat stabilizers, weather stabilizers, ultraviolet absorbers, organic lubricants, pigments, dyes, organic or inorganic particles, antistatic agents, and nucleating agents, within the range that does not impair the effects of the present invention.

[0063] In the present invention, it is particularly preferred that the composition forming the coating layer further contains an antistatic agent, since this can prevent static electricity problems during various processes for labeling the resulting film, such as coating with an adhesive, printing, cutting, punching, etc. Antistatic agents that can be used include those commonly used as coating-type antistatic agents (e.g., quaternary ammonium salt-based antistatic agents), particulate carbon black, metal powders such as nickel and copper, metal oxides such as tin oxide and zinc oxide, metal-coated fibers such as fibrous brass, stainless steel, and aluminum, conductive fillers such as flake graphite, aluminum flakes, and copper flakes, and conductive polymers such as sulfonated polyaniline and polypyrrole, as long as they do not impair the effects of the present invention.

[0064] In order to reduce the glossiness of the coating layer surface, inert particles may be contained in the coating layer.

[0065] Examples of the inert particles include inorganic particles such as titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, and calcium fluoride, and organic polymer particles such as polystyrene-based, polyacrylic-based, melamine-based, benzoguanamine-based, and silicone resin-based particles. These may be used alone or in combination of two or more.

[0066] The average particle size of the inert particles is preferably 0.1 to 2.4 μm, more preferably 0.3 to 2.0 μm. If the average particle size of the inert particles is 0.04 μm or less, the glossiness of the film surface may increase. Conversely, if the average particle size exceeds 2.4 μm, the particles tend to fall off from the coating layer, causing powdering.

[0067] The method for measuring the average particle size is as described above. The particle shape is not particularly limited as long as it satisfies the objectives of the present invention, and spherical particles and irregular, non-spherical particles can be used. The particle size of irregular particles can be calculated as the circle-equivalent diameter.

[0068] When it is desired to increase the glossiness of the coating layer surface, it is also preferable not to include particles in the coating layer.

[0069] (Production of white laminated polyester film) The method for producing the white laminated polyester film of the present invention is arbitrary and is not particularly limited, but for example, a general method can be used in which a mixture consisting of the above-mentioned composition is melted and extruded into a sheet to form an unstretched film, and then this unstretched film is stretched.

[0070] In the white laminated polyester film of the present invention, a thermoplastic resin incompatible with the polyester resin is dispersed in the polyester resin during the process of melting and extruding the film raw material. In the examples of the present invention, the polyester resin and the thermoplastic resin incompatible with the polyester resin were supplied in pellet form, but the present invention is not limited to this.

[0071] The raw materials fed into the extruder for melt molding into a film are prepared by pelletizing these resins according to the desired composition. However, when polyester resin and polyolefin resin are used as the raw materials for the void-containing polyester film of the substrate of the present invention, the specific gravities of the resins are significantly different, so it is preferable to take measures to prevent segregation of the pellets once mixed during the process of feeding them to the extruder. A suitable method for preventing segregation is to combine some or all of the raw material resins in advance, knead them, and pelletize them to form masterbatch pellets. This method was used in the examples of the present invention, but is not particularly limited as long as it does not interfere with the effects of the present invention.

[0072] Furthermore, when these incompatible resins are mixed and finely dispersed in a molten state, they tend to re-aggregate due to the effect of reducing the interfacial energy of the resins, which causes the void-producing agent to become coarsely dispersed during extrusion molding of the unstretched film, hindering the desired physical properties.

[0073] To prevent this, when molding the film of the present invention, it is preferable to finely disperse the void-producing agent in advance using a twin-screw extruder, which has a higher mixing effect. If this is difficult, it is also preferable to supply the raw resin from the extruder to the feed block or die via a static mixer as an auxiliary means. Examples of static mixers that can be used here include static mixers and orifices. However, when using these methods, care must be taken to avoid the possibility of thermally degraded resin remaining in the melt line.

[0074] In addition, since the incompatible resin once dispersed in the polyester resin as fine particles tends to re-aggregate over time under low-shear molten conditions, a fundamental solution is to reduce the residence time in the melt line from the extruder to the die. In the present invention, the residence time in the melt line is preferably 30 minutes or less, and more preferably 15 minutes or less.

[0075] The conditions for stretching and orienting the unstretched film obtained as described above are closely related to the physical properties of the film. Below, the stretching and orientation conditions will be explained using the most common sequential biaxial stretching method, particularly the method of stretching an unstretched film in the longitudinal direction and then in the width direction, as an example.

[0076] In the longitudinal stretching step, the film is stretched 2.5 to 5.0 times in the machine direction using rolls heated to 80 to 120°C to obtain a uniaxially stretched film. The heating method may be a method using heated rolls or a non-contact heating method, or a combination of these. The uniaxially stretched film is then introduced into a tenter and stretched 2.5 to 5.0 times in the width direction at a temperature of (Tm-10°C) or less, where Tm is the melting point of the polyester.

[0077] The biaxially stretched film is also subjected to heat treatment as required, preferably in a tenter at a temperature in the range of (Tm-60°C) to Tm.

[0078] The coating layer can be provided after or during the film production process. From the viewpoint of productivity, it is particularly preferred to form the coating layer by applying a coating liquid to at least one surface of an unstretched or uniaxially stretched PET film at any stage of the film production process.

[0079] Any known method can be used to apply this coating solution to the PET film. Examples include reverse roll coating, gravure coating, kiss coating, die coating, roll brushing, spray coating, air knife coating, wire bar coating, pipe doctor coating, impregnation coating, and curtain coating. These methods can be used alone or in combination.

[0080] In the present invention, the thickness of the coating layer can be appropriately set within the range of 0.001 to 2.00 μm, but in order to achieve both processability and adhesiveness, it is preferably within the range of 0.01 to 1.00 μm, more preferably 0.02 to 0.80 μm, and even more preferably 0.05 to 0.50 μm. A coating layer thickness of 0.001 μm or more is preferable because it provides good adhesiveness. A coating layer thickness of 2.00 μm or less is preferable because it is less likely to cause blocking.

[0081] Among conventional polyester films having coating layers containing polyester resins, polyurethane resins, acrylic resins, etc., either alone or in combination, or mixtures of two or more of these resins with specific crosslinking agents (e.g., melamine, isocyanate), many have satisfactory blocking resistance when left in a normal water vapor environment. However, in winter, condensation can occur during transportation between indoors and outdoors, causing liquid water to adhere to the film surface or coating layer surface. In such cases, polyester films having coating layers containing polyester resins, polyurethane resins, acrylic resins, and crosslinking agents have the problem of blocking. However, the white laminated polyester film of the present invention not only exhibits blocking resistance when left in a normal water vapor environment, but also eliminates the risk of blocking even when a highly adhesive polyester film transported between indoors and outdoors in winter condenses due to changes in environmental temperature, causing liquid water to adhere to the film surface or coating layer surface. [Example]

[0082] Next, the present invention will be described in detail using examples and comparative examples, but the present invention is not limited to the following examples. First, the evaluation methods used in the present invention will be described below.

[0083] (1) Evaluation of blocking resistance when water is applied The highly adhesive polyester film produced in the examples described below was cut to a width of 10 cm and a length of 1.5 cm. A film measuring 1.5 cm in width and 1.5 cm in length was placed on the edge of the coated layer surface of the cut film. A 0.03 g drop of water was dropped onto the coated layer surface at the opposite edge. The coated layers of the films cut to a width of 10 cm and a length of 1.5 cm were then placed together, and rolled evenly to prevent air from entering the side where the water drop was dropped to the side where the film was placed. The sample was then placed in an oven (50°C) for 24 hours. The film was then peeled off, and the peeling condition was evaluated according to the following criteria. ◯: The coating layer was not transferred and could be easily peeled off. △: The coating layer is maintained, but the surface layer of the coating layer is partially transferred to the opposing surface. ×: The two films were stuck together and could not be separated, or even if they could be separated, the film substrate was cleaved.

[0084] (2) Adhesion to UV ink The coated layer of the laminated polyester film was printed using a UV ink (manufactured by T&K TOKA Corporation, product name "BEST CURE UV161 Indigo S") with a printing machine (manufactured by Akira Manufacturing Co., Ltd., product name "RI Tester"), and then the film coated with the ink layer was irradiated with 40 mJ / cm using a high-pressure mercury lamp. 2 The ink was irradiated with ultraviolet light to cure the UV-curable ink. Next, a 24 mm wide, 50 mm long piece of Nichiban cellophane adhesive tape (CT405AP-24) was cut out and completely adhered to the surface of the ink layer with a handy rubber roller, taking care not to trap air. The cellophane adhesive tape was then peeled off vertically, and the remaining area of ​​the printed layer was observed in a 24 mm x 50 mm area and evaluated according to the following criteria. ○: The remaining area of ​​the printed layer is 99% or more of the total. △: The remaining area of ​​the printed layer is 90% or more but less than 99% of the total. ×: Less than 90% of the printed layer remains

[0085] (3) Method for measuring number average molecular weight of polycarbonate polyol When urethane resins with polycarbonate structures are measured by proton nuclear magnetic resonance spectroscopy (H-NMR), a peak derived from the methylene group adjacent to the OCOO bond is observed at around 4.1 ppm. Additionally, a peak derived from the methylene group adjacent to the urethane bond formed by the reaction of polyisocyanate with polycarbonate polyol is observed approximately 0.2 ppm higher than this peak. The number-average molecular weight of the polycarbonate polyol was calculated from the integral values ​​of these two peaks and the molecular weight of the monomers that make up the polycarbonate polyol.

[0086] (4) Apparent density The film was cut into four 5.00 cm square pieces to be used as samples. Then, measure the thickness at 10 points with a micrometer to four significant figures, and calculate the average value of the overlap thickness. This average value was divided by 4, rounded to the fourth decimal place, and the average frame rate per sheet was calculated. The film thickness (t: μm) was calculated to the third decimal place. The mass (w: g) of the four samples was also calculated. The apparent density was calculated using the following formula: , apparent density was rounded to three significant figures. Apparent density (g / cm 3 )=w×10 4 / (5.00×5.00×t×4)

[0087] (5) Optical density The opacity of polyester films was measured using a Macbeth TR-927 densitometer to measure the light transmittance through a G filter. The optical density was calculated from the obtained light transmittance and used as an index of opacity. The optical density is expressed as the logarithm (Log10) of the reciprocal of the light transmittance (range: 0-100%). The higher the optical density value, the higher the opacity.

[0088] (6) L value, b value The reflected color L value and color b value were measured using a color difference meter (ZE6000, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS-8722.

[0089] (Polymerization of urethane resin A-1 having a polycarbonate structure) 27.5 parts by mass of hydrogenated m-xylylene diisocyanate, 6.5 parts by mass of dimethylolpropanoic acid, 60 parts by mass of polyhexamethylene carbonate diol with a number average molecular weight of 1800, 6 parts by mass of neopentyl glycol, and 84.00 parts by mass of acetone as a solvent were added to a four-neck flask equipped with a stirrer, Dimroth condenser, nitrogen inlet tube, silica gel drying tube, and thermometer. The mixture was stirred under a nitrogen atmosphere at 75°C for 3 hours, and it was confirmed that the reaction solution had reached the specified amine equivalent. Next, 5 parts by mass of trimethylolpropane was added, and the mixture was stirred under a nitrogen atmosphere at 75°C for 1 hour, and it was confirmed that the reaction solution had reached the specified amine equivalent. After cooling the reaction solution to 40°C, 5.17 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisper capable of high-speed stirring, and the temperature was adjusted to 25°C. The mixture was stirred for 2000 min. -1 The polyurethane prepolymer solution was added and dispersed in water while stirring and mixing at 50°C. Then, the acetone and a portion of the water were removed under reduced pressure to prepare a water-dispersible urethane resin solution (A-1) with a solids content of 34% by mass.

[0090] (Polymerization of urethane resin A-2 having a polycarbonate structure) A four-neck flask equipped with a stirrer, Dimroth condenser, nitrogen inlet tube, silica gel drying tube, and thermometer was charged with 25 parts by weight of 4,4-dicyclohexylmethane diisocyanate, 5 parts by weight of dimethylolpropanoic acid, 52 parts by weight of polyhexamethylene carbonate diol with a number average molecular weight of 2600, 6 parts by weight of neopentyl glycol, and 84.00 parts by weight of acetone as a solvent. The mixture was stirred under a nitrogen atmosphere at 75°C for 3 hours, and the reaction mixture was confirmed to have reached the required amine equivalent. Next, 18 parts by weight of a polyisocyanate compound having an isocyanurate structure (Asahi Kasei Chemicals, Duranate TPA, trifunctional) made from hexamethylene diisocyanate was added, and the mixture was stirred under a nitrogen atmosphere at 75°C for 1 hour, and the reaction mixture was confirmed to have reached the required amine equivalent. The reaction mixture temperature was then lowered to 50°C, and 8 parts by weight of methyl ethyl ketoxime was added dropwise. After the reaction solution was cooled to 40°C, 5.17 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisper capable of high speed stirring, and the temperature was adjusted to 25°C and stirred for 2000 min. -1 The polyurethane prepolymer solution was added and dispersed in water while stirring and mixing at 50°C. Then, the acetone and a portion of the water were removed under reduced pressure to prepare a water-dispersible urethane resin solution (A-2) with a solids content of 35% by mass.

[0091] (Polymerization of urethane resin A-3 having a polycarbonate structure) A four-neck flask equipped with a stirrer, Dimroth condenser, nitrogen inlet tube, silica gel drying tube, and thermometer was charged with 22 parts by weight of 4,4-dicyclohexylmethane diisocyanate, 20 parts by weight of polyethylene glycol monomethyl ether with a number average molecular weight of 700, 53 parts by weight of polyhexamethylene carbonate diol with a number average molecular weight of 2100, 5 parts by weight of neopentyl glycol, and 84.00 parts by weight of acetone as a solvent. The mixture was stirred under a nitrogen atmosphere at 75°C for 3 hours, and the reaction mixture was confirmed to have reached the required amine equivalent. Next, 16 parts by weight of a polyisocyanate compound having an isocyanurate structure (Asahi Kasei Chemicals, Duranate TPA, trifunctional) made from hexamethylene diisocyanate was added, and the mixture was stirred under a nitrogen atmosphere at 75°C for 1 hour, and the reaction mixture was confirmed to have reached the required amine equivalent. The reaction mixture temperature was then lowered to 50°C, and 7 parts by weight of methyl ethyl ketoxime was added dropwise. After the reaction solution was cooled to 40°C, a polyurethane prepolymer solution was obtained. Next, 450 g of water was added to a reaction vessel equipped with a homodisper capable of high speed stirring, and the temperature was adjusted to 25°C. The mixture was stirred for 2000 min. -1 The polyurethane prepolymer solution was added and dispersed in water while stirring and mixing at 50°C. Then, the acetone and a portion of the water were removed under reduced pressure to prepare a water-dispersible urethane resin solution (A-3) with a solids content of 35% by mass.

[0092] (Polymerization of urethane resin A-4 having a polycarbonate structure) 22 parts by mass of 4,4-dicyclohexylmethane diisocyanate, 3 parts by mass of dimethylol butanoic acid, 73 parts by mass of polyhexamethylene carbonate diol with a number average molecular weight of 2000, 2 parts by mass of neopentyl glycol, and 84.00 parts by mass of acetone as a solvent were added to a four-neck flask equipped with a stirrer, Dimroth condenser, nitrogen inlet tube, silica gel drying tube, and thermometer. The mixture was stirred under a nitrogen atmosphere at 75°C for 3 hours, and it was confirmed that the reaction solution had reached the specified amine equivalent. Next, 4 parts by mass of trimethylolpropane was added, and the mixture was stirred under a nitrogen atmosphere at 75°C for 1 hour, and it was confirmed that the reaction solution had reached the specified amine equivalent. Next, the reaction solution was cooled to 40°C, and 8.77 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisperser capable of high-speed stirring, and the temperature was adjusted to 25°C. The mixture was stirred for 2000 min. -1 The polyurethane prepolymer solution was added and dispersed in water while stirring and mixing at 50°C. Then, the acetone and a portion of the water were removed under reduced pressure to prepare a water-dispersible urethane resin solution (A-4) with a solids content of 34% by mass.

[0093] (Polymerization of urethane resin A-5 having a polycarbonate structure) A four-neck flask equipped with a stirrer, Dimroth condenser, nitrogen inlet tube, silica gel drying tube, and thermometer was charged with 47 parts by mass of 4,4-dicyclohexylmethane diisocyanate, 21 parts by mass of polyethylene glycol monomethyl ether having a number-average molecular weight of 700, 20 parts by mass of polyhexamethylene carbonate diol having a number-average molecular weight of 1200, 12 parts by mass of neopentyl glycol, and 84.00 parts by mass of acetone as a solvent. The mixture was stirred under a nitrogen atmosphere at 75°C for 3 hours, and it was confirmed that the reaction solution had reached the specified amine equivalent. Next, 4 parts by mass of trimethylolpropane was added, and the mixture was stirred under a nitrogen atmosphere at 75°C for 1 hour, and it was confirmed that the reaction solution had reached the specified amine equivalent. Next, the reaction solution was cooled to 40°C, and 8.77 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisperser capable of high-speed stirring, and the mixture was stirred at 25°C for 2000 min.-1 The polyurethane prepolymer solution was added and dispersed in water while stirring and mixing at 50°C. Then, the acetone and a portion of the water were removed under reduced pressure to prepare a water-dispersible urethane resin solution (A-5) with a solids content of 34% by mass.

[0094] (Polymerization of urethane resin A-6 having a polycarbonate structure) 23.5 parts by mass of 4.4-dicyclohexylmethane diisocyanate, 4.5 parts by mass of dimethylol butanoic acid, 70 parts by mass of polyhexamethylene carbonate diol with a number average molecular weight of 2000, 2 parts by mass of neopentyl glycol, and 84.00 parts by mass of acetone as a solvent were added to a four-neck flask equipped with a stirrer, Dimroth condenser, nitrogen inlet tube, silica gel drying tube, and thermometer. The mixture was stirred at 75°C for 3 hours under a nitrogen atmosphere, and it was confirmed that the reaction solution had reached the required amine equivalent. Next, the reaction solution was cooled to 40°C, and 8.77 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisper capable of high-speed stirring, and the temperature was adjusted to 25°C. The mixture was stirred for 2000 min. -1 The polyurethane prepolymer solution was added and dispersed in water while stirring and mixing at 50°C. Then, the acetone and a portion of the water were removed under reduced pressure to prepare a water-dispersible urethane resin solution (A-6) with a solids content of 34% by mass.

[0095] (Polymerization of urethane resin A-7 having a polycarbonate structure) 27.5 parts by mass of hydrogenated m-xylylene diisocyanate, 6.5 parts by mass of dimethylolpropanoic acid, 60 parts by mass of polyhexamethylene carbonate diol having a number average molecular weight of 1800, 6 parts by mass of neopentyl glycol, and 84.00 parts by mass of acetone as a solvent were added to a four-neck flask equipped with a stirrer, a Dimroth condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer. The mixture was stirred at 75°C for 3 hours under a nitrogen atmosphere, and it was confirmed that the reaction solution had reached the required amine equivalent. After cooling the reaction solution to 40°C, 5.17 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisper capable of high-speed stirring, the temperature was adjusted to 25°C, and the mixture was stirred for 2000 min. -1 The polyurethane prepolymer solution was added and dispersed in water while stirring and mixing at 50°C. Then, the acetone and a portion of the water were removed under reduced pressure to prepare a water-dispersible urethane resin solution (A-7) with a solids content of 34% by mass.

[0096] (Polymerization of urethane resin A-8 having a polycarbonate structure) A four-neck flask equipped with a stirrer, Dimroth condenser, nitrogen inlet tube, silica gel drying tube, and thermometer was charged with 400 parts by weight of a polycarbonate polyol composed of 1,6-hexanediol and diethyl carbonate and having a number average molecular weight of 2000, 10.4 parts by weight of neopentyl glycol, 58.4 parts by weight of isophorone diisocyanate, 74.3 parts by weight of dimethylol butanoic acid, and 320 parts by weight of acetone as a solvent. The mixture was stirred at 75°C under a nitrogen atmosphere for 3 hours, and it was confirmed that the reaction solution had reached the required amine equivalent. After cooling the reaction solution to 40°C, isophorone diamine was added to obtain a polyurethane prepolymer solution. Next, 1200 g of water was added to a reaction vessel equipped with a homodisper capable of high-speed stirring, the temperature was adjusted to 25°C, and the mixture was stirred for 2000 min. -1 The polyurethane prepolymer solution was added and dispersed in water while stirring and mixing at 50°C. Then, the acetone and part of the water were removed under reduced pressure to prepare a water-dispersible urethane resin solution (A-8) with a solids content of 34% by mass.

[0097] (Polymerization of urethane resin A-9 having a polycarbonate structure) A four-neck flask equipped with a stirrer, Dimroth condenser, nitrogen inlet tube, silica gel drying tube, and thermometer was charged with 50 parts by mass of 4,4-dicyclohexylmethane diisocyanate, 21 parts by mass of polyethylene glycol monomethyl ether having a number-average molecular weight of 700, 35 parts by mass of polyhexamethylene carbonate diol having a number-average molecular weight of 1200, 13 parts by mass of neopentyl glycol, and 84.00 parts by mass of acetone as a solvent. The mixture was stirred under a nitrogen atmosphere at 75°C for 3 hours, and it was confirmed that the reaction solution had reached the specified amine equivalent. Next, 1.2 parts by mass of trimethylolpropane was added, and the mixture was stirred under a nitrogen atmosphere at 75°C for 1 hour. It was confirmed that the reaction solution had reached the specified amine equivalent. Next, the reaction solution was cooled to 40°C, and 8.77 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisper capable of high-speed stirring, and the mixture was stirred at 25°C for 2000 min. -1 The polyurethane prepolymer solution was added and dispersed in water while stirring and mixing at 50°C. Then, the acetone and a portion of the water were removed under reduced pressure to prepare a water-dispersible urethane resin solution (A-9) with a solids content of 34% by mass.

[0098] (Polymerization of urethane resin A-10 not containing polycarbonate polyol component) 75 parts by weight of a 5000 molecular weight polyester polyol composed of terephthalic acid, isophthalic acid, ethylene glycol, and neopentyl glycol, 30 parts by weight of hydrogenated m-xylylene diisocyanate, 7 parts by weight of ethylene glycol, 6 parts by weight of dimethylolpropionic acid, and 84.00 parts by weight of acetone as a solvent were added and stirred under a nitrogen atmosphere at 75°C for 3 hours, and it was confirmed that the reaction solution had reached the required amine equivalent. After cooling the reaction solution to 40°C, 5.17 parts by weight of triethylamine was added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisperser capable of high-speed stirring, the temperature was adjusted to 25°C, and the mixture was stirred for 2000 min. -1The polyurethane prepolymer solution was added and dispersed in water while stirring and mixing at 50°C. Then, the acetone and a portion of the water were removed under reduced pressure to prepare a water-dispersible urethane resin solution (A-10) with a solids content of 34% by mass.

[0099] (Polymerization of urethane resin A-11 not containing polycarbonate polyol component) A four-neck flask equipped with a stirrer, Dimroth condenser, nitrogen inlet tube, silica gel drying tube, and thermometer was charged with 54 parts of 4,4-dicyclohexylmethane diisocyanate, 38 parts by mass of a polyester polyol having a number average molecular weight of 1500 and composed of ethylene glycol and adipic acid, 0.8 parts by mass of trimethylolpropane, and 84.00 parts by mass of acetone as a solvent. The mixture was stirred under a nitrogen atmosphere at 75°C for 3 hours, and it was confirmed that the reaction solution had reached the specified amine equivalent. Next, 4 parts by mass of sodium hydrogen sulfate was added, and the mixture was stirred under a nitrogen atmosphere at 75°C for 1 hour, and it was confirmed that the reaction solution had reached the specified amine equivalent. Next, the reaction solution was cooled to 40°C, and 8.77 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisper capable of high-speed stirring, and the temperature was adjusted to 25°C. The mixture was stirred for 2000 min. -1 The polyurethane prepolymer solution was added and dispersed in water while stirring and mixing at 50°C. Then, the acetone and a portion of the water were removed under reduced pressure to prepare a water-dispersible urethane resin solution (A-11) with a solids content of 34% by mass.

[0100] (Polymerization of blocked isocyanate crosslinking agent B-1) A flask equipped with a stirrer, thermometer, and reflux condenser was charged with 66.04 parts by weight of a polyisocyanate compound (Duranate TPA, manufactured by Asahi Kasei Chemicals) having an isocyanurate structure derived from hexamethylene diisocyanate, 17.50 parts by weight of N-methylpyrrolidone, and 95 parts by weight of 3,5-dimethylpyrazole (dissociation temperature: 120°C, boiling point: 218°C). The mixture was then maintained at 70°C for 1 hour under a nitrogen atmosphere. Subsequently, 30 parts by weight of dimethylolpropanoic acid was added dropwise. After measuring the infrared spectrum of the reaction solution and confirming that the absorption of the isocyanate groups had disappeared, 5.59 parts by weight of N,N-dimethylethanolamine and 132.5 parts by weight of water were added to obtain a blocked polyisocyanate aqueous dispersion (B-1) with a solids content of 40% by weight. The blocked isocyanate crosslinker had a functionality of 4 and an NCO equivalent of 280.

[0101] (Polymerization of blocked isocyanate crosslinking agent B-2) A flask equipped with a stirrer, thermometer, and reflux condenser was charged with 100 parts by weight of a polyisocyanate compound (Duranate TPA, manufactured by Asahi Kasei Chemicals) having an isocyanurate structure derived from hexamethylene diisocyanate, 55 parts by weight of propylene glycol monomethyl ether acetate, and 30 parts by weight of polyethylene glycol monomethyl ether (average molecular weight 750). The mixture was then maintained at 70°C for 4 hours under a nitrogen atmosphere. The reaction mixture was then cooled to 50°C, and 47 parts by weight of methyl ethyl ketoxime was added dropwise. The infrared spectrum of the reaction mixture was measured to confirm that the absorption of the isocyanate group had disappeared. Then, 210 parts by weight of water was added to obtain an oxime-blocked isocyanate crosslinking agent (B-2) with a solids content of 40% by weight. The blocked isocyanate crosslinking agent had 3 functional groups and an NCO equivalent of 170.

[0102] (Polymerization of carbodiimide B-3) A flask equipped with a stirrer, thermometer, and reflux condenser was charged with 168 parts by weight of hexamethylene diisocyanate and 220 parts by weight of polyethylene glycol monomethyl ether (M400, average molecular weight 400). The mixture was stirred at 120°C for 1 hour. 26 parts by weight of 4,4'-dicyclohexylmethane diisocyanate and 3.8 parts by weight of 3-methyl-1-phenyl-2-phospholene-1-oxide (2% by weight based on the total isocyanate) were then added as a carbodiimide catalyst. The mixture was stirred at 185°C for an additional 5 hours under a nitrogen stream. Infrared spectroscopy of the reaction solution confirmed the disappearance of absorption between 220 and 2300 cm-1. The mixture was allowed to cool to 60°C, and 567 parts by weight of ion-exchanged water was added to obtain a carbodiimide aqueous resin solution (B-3) with a solids content of 40% by weight.

[0103] (Polymerization of blocked isocyanate crosslinking agent B-4) 33.6 parts by weight of hexamethylene diisocyanate was added to 200 parts by weight of a polyester (molecular weight 2000) of ethylene oxide 2 mole adduct of bisphenol A and maleic acid, and the reaction was carried out at 100°C for 2 hours. The temperature of the system was then temporarily lowered to 50°C, and 73 parts by weight of a 30% aqueous solution of sodium bisulfite was added. After stirring at 45°C for 60 minutes, the mixture was diluted with 718 parts by weight of water to obtain a blocked polyisocyanate aqueous dispersion (B-1) with a solids content of 20% by weight. The blocked isocyanate crosslinker had 2 functional groups and an NCO equivalent of 1300.

[0104] (Polymerization of Polyester Resin C-1) A stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser was charged with 194.2 parts by mass of dimethyl terephthalate, 184.5 parts by mass of dimethyl isophthalate, 14.8 parts by mass of dimethyl-5-sodium sulfoisophthalate, 233.5 parts by mass of diethylene glycol, 136.6 parts by mass of ethylene glycol, and 0.2 parts by mass of tetra-n-butyl titanate, and the transesterification reaction was carried out at a temperature of 160 to 220°C for 4 hours. The temperature was then raised to 255°C, and the reaction system was gradually reduced in pressure. The reaction was then continued for 1 hour and 30 minutes under a reduced pressure of 30 Pa to obtain copolymer polyester resin (C-1). The resulting copolymer polyester resin (C-1) was pale yellow and transparent. The reduced viscosity of copolymer polyester resin (C-1) was measured and found to be 0.70 dL / g. The glass transition temperature measured by DSC was 40°C.

[0105] (Preparation of Polyester Water Dispersion Cw-1) A reactor equipped with a stirrer, thermometer, and reflux device was charged with 25 parts by mass of polyester resin (C-1) and 10 parts by mass of ethylene glycol n-butyl ether, and the mixture was heated to 110°C and stirred to dissolve the resin. After the resin was completely dissolved, 65 parts by mass of water was gradually added to the polyester solution while stirring. After the addition, the liquid was cooled to room temperature while stirring to produce a milky white polyester water dispersion (Cw-1) with a solids content of 25% by mass.

[0106] (Polyester Resin Polymerization C-2) A stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser was charged with 342.0 parts by weight of dimethyl 2,6-naphthalenedicarboxylate, 35.0 parts by weight of dimethyl terephthalate, 35.5 parts by weight of dimethyl-5-sodium sulfoisophthalate, 198.6 parts by weight of ethylene glycol, 118.2 parts by weight of 1,6-hexanediol, and 0.4 parts by weight of tetra-n-butyl titanate, and the mixture was subjected to a transesterification reaction at a temperature ranging from 160°C to 220°C for 4 hours. Further, 60.7 parts by weight of sebacic acid was added to carry out an esterification reaction. The temperature was then raised to 255°C, and the reaction system was gradually depressurized. The reaction was continued for 1 hour and 30 minutes under a reduced pressure of 30 Pa, yielding copolymer polyester resin (C-2). The resulting copolymer polyester resin was pale yellow and transparent.

[0107] (Preparation of Polyester Water Dispersion Cw-2) A reactor equipped with a stirrer, thermometer, and reflux device was charged with 25 parts by mass of copolymerized polyester resin (C-2) and 15 parts by mass of ethylene glycol-n-butyl ether, and the mixture was heated to 110°C and stirred to dissolve the resin. After the resin was completely dissolved, 55 parts by mass of water was gradually added to the polyester solution while stirring. After the addition, the liquid was cooled to room temperature while stirring to produce a milky white polyester water dispersion (Cw-2) with a solids content of 25% by mass.

[0108] (Polyester Resin Polymerization C-3) A stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser was charged with 194.2 parts by mass of dimethyl terephthalate, 184.5 parts by mass of dimethyl isophthalate, 14.8 parts by mass of dimethyl-5-sodium sulfoisophthalate, 185 parts by mass of neopentyl glycol, 188 parts by mass of ethylene glycol, and 0.2 parts by mass of tetra-n-butyl titanate, and a transesterification reaction was carried out at a temperature of 160 to 220°C for 4 hours. The temperature was then raised to 255°C, and the reaction system was gradually reduced in pressure. The reaction was then continued for 1 hour and 30 minutes under a reduced pressure of 30 Pa to obtain copolymer polyester resin (C-3). The resulting copolymer polyester resin (C-3) was pale yellow and transparent. The reduced viscosity of copolymer polyester resin (C-3) was measured and found to be 0.40 dL / g. The glass transition temperature measured by DSC was 65°C.

[0109] (Preparation of Polyester Water Dispersion Cw-3) A reactor equipped with a stirrer, thermometer, and reflux device was charged with 25 parts by mass of polyester resin (C-3) and 10 parts by mass of ethylene glycol n-butyl ether, and the mixture was heated to 110°C and stirred to dissolve the resin. After the resin was completely dissolved, 65 parts by mass of water was gradually added to the polyester solution while stirring. After the addition, the liquid was cooled to room temperature while stirring to produce a milky white polyester water dispersion (Cw-3) with a solids content of 25% by mass.

[0110] Example 1 (1) Preparation of coating solution The following coating agent was mixed with a mixed solvent of water and isopropanol to prepare a coating solution with a solids mass ratio of urethane resin solution (A-1) / crosslinking agent (B-1) / polyester water dispersion (Cw-1) of 25 / 26 / 49. Urethane resin solution (A-1) 6.30 parts by mass Crosslinking agent (B-1) 5.50 parts by mass Polyester water dispersion (Cw-1) 17.00 parts by mass Particles 23.00 parts by mass (Silica particles with an average particle size of 0.45 μm, solid content concentration of 40.00% by mass) Surfactant 0.15 parts by mass (Silicone-based, solid content 10% by mass)

[0111] (2) Manufacturing of white laminated polyester film (Preparation of Master Pellet) A pellet mixture of 60% by mass of polymethylpentene resin (DX820, manufactured by Mitsui Chemicals, Inc.) with a melt viscosity (ηO) of 1,300 poise, 20% by mass of polystyrene resin (G797N, manufactured by Nippon Polystyrene Co., Ltd.) with a melt viscosity (ηS) of 3,900 poise, and 20% by mass of polypropylene resin (J104WC, manufactured by Grand Polymer Co., Ltd.) with a melt viscosity of 2,000 poise was fed into a vented twin-screw extruder controlled at 285°C and pre-mixed. This molten resin was continuously fed into a vented single-screw kneader, kneaded, and extruded, and the resulting strand was cooled and cut to prepare void-producing agent master pellets (M1).

[0112] In addition, 50% by mass of polyethylene terephthalate resin with an intrinsic viscosity of 0.62 dl / g, produced by a known method, was mixed with 50% by mass of anatase-type titanium dioxide particles (TA-300, manufactured by Fuji Titanium Co., Ltd.) with an average particle size of 0.3 μm, and the mixture was fed into a vented twin-screw extruder and pre-kneaded. This molten resin was continuously fed into a vented single-screw kneader, kneaded, and extruded. The resulting strand was cooled and cut to prepare titanium dioxide-containing master pellets (M2).

[0113] (Preparation of film raw materials) 81% by mass of the polyethylene terephthalate resin having an intrinsic viscosity of 0.62 dl / g, which had been vacuum dried at 140°C for 8 hours, 9% by mass of the master pellets (M1), which had been vacuum dried at 90°C for 4 hours, and 10% by mass of the master pellets (M2), were mixed together to prepare a film raw material (C1).

[0114] (Preparation of unstretched film) The film raw material (C1) was mixed with 70% by mass of the same polyethylene terephthalate resin used in the film raw material (C1) and 30% by mass of the master pellets (M2) and fed separately to an extruder for layer A, the temperature of which was adjusted to 290° C. The molten resin discharged from the extruder for layer B was introduced into a feedbook via an orifice, and the resin discharged from the extruder for layer A was introduced into a feedbook via a static mixer, and a layer (B layer) made of film raw material (C1) and a layer (A layer) made of polyethylene terephthalate resin and master pellets (M2) were laminated in the order of A layer / B layer / A layer.

[0115] The molten resin was co-extruded through a T-die onto a cooling roll adjusted to 25°C in the form of a sheet, and then solidified by electrostatic application to produce an unstretched film with a thickness of 510 μm. The discharge rate of each extruder was adjusted so that the thickness ratio of each layer was 1:8:1. The molten resin remained in the melt line for approximately 12 minutes, and the shear rate it received from the T-die was approximately 150 / s.

[0116] (Preparation of biaxially stretched film) The resulting unstretched film was uniformly heated to 65°C using a heating roll and longitudinally stretched 3.4 times between two pairs of nip rolls (low-speed roll: 2 m / min, high-speed roll: 6.8 m / min) with different peripheral speeds. At this time, infrared heaters (rated output: 20 W / cm) equipped with gold reflective films were installed 1 cm from the film surface, facing both sides of the film, as auxiliary film heating devices. The above-mentioned coating solution was applied to one side of the resulting uniaxially stretched film using the reverse kiss coating method so that the resin solid thickness before stretching was 0.9 μm. After coating, the film was introduced into a tenter, heated to 150°C while drying, and transversely stretched 3.7 times. The width was fixed and heat-treated at 220°C for 5 seconds, and then further relaxed 4% in the width direction at 200°C to obtain a 50 μm-thick white laminated polyester film. The apparent density of this film was 1.10 g / cm. 3 The optical density was 0.8. The evaluation results are shown in Table 1.

[0117] Example 2 A white laminated polyester film was obtained in the same manner as in Example 1, except that the urethane resin in the coating liquid was changed to (A-2) and the polyester water dispersion was changed to (Cw-3).

[0118] Example 3 (1) Preparation of coating solution A coating liquid was prepared in the same manner as in Example 1, except that the urethane resin was changed to (A-3).

[0119] (2) Manufacturing of white laminated polyester film (Preparation of Master Pellet) A mixture of 50% by mass of polyethylene terephthalate resin with an intrinsic viscosity of 0.62 and 50% by mass of anatase-type titanium dioxide with an average particle size of 0.3 μm (by electron microscopy) was fed into a vented twin-screw extruder and kneaded to produce titanium oxide-containing master pellets (M3).

[0120] (Preparation of unstretched film) 85% by weight of polyethylene terephthalate resin with an intrinsic viscosity of 0.62, 10% by weight of polypropylene resin with an MFR of 2.5, Mw of 320,000, Mw / Mn of 4.0, and a deflection temperature under load of 92°C, and 5% by weight of the titanium oxide-containing master pellets (M3) were mixed and vacuum-dried to form the raw material for the void-containing polyester layer B. Meanwhile, 30% by weight of the titanium oxide-containing master pellets (M3) and 70% by weight of polyethylene terephthalate resin with an intrinsic viscosity of 0.62 were pellet-mixed and vacuum-dried to form the raw material for the inorganic particle-containing polyester layer A. These raw materials were fed into separate extruders, melted at 285°C, and laminated in the order A / B / A, with the void-containing polyester layer B and the inorganic particle-containing polyester layer A. The laminate was then joined by a feed block to a thickness ratio of 10 / 80 / 10, and extruded through a T-die onto a cooling drum adjusted to 30°C to produce an unstretched film with a two-type, three-layer structure.

[0121] (Preparation of biaxially stretched film) The resulting unstretched film was uniformly heated to 70°C using a heating roll and longitudinally stretched 3.4 times between two pairs of nip rolls with different peripheral speeds. At this time, infrared heaters (rated at 20 W / cm) equipped with gold reflective films were installed in the middle of the nip rolls as auxiliary film heating devices, facing both sides of the film (at a distance of 1 cm from the film surface). The above coating solution was applied to one side of the resulting uniaxially stretched film using the reverse kiss coating method so that the resin solid thickness before stretching was 0.9 μm. After coating, the film was introduced into a tenter, heated to 140°C while drying, and transversely stretched 4.0 times. The width was fixed, heat-treated at 235°C, and further relaxed 3% in the width direction at 210°C to obtain a 50 μm-thick white laminated polyester film. The apparent density of this film was 1.09 g / cm. 3 The optical density was 0.6, the L value was 94.4, and the b value was 1.6.

[0122] Example 4 A white laminated polyester film was obtained in the same manner as in Example 1, except that the crosslinking agent in the coating liquid was changed to (B-2).

[0123] Example 5 A white laminated polyester film was obtained in the same manner as in Example 1, except that the urethane resin in the coating liquid was changed to (A-2) and the crosslinking agent was changed to (B-2).

[0124] Example 6 A white laminated polyester film was obtained in the same manner as in Example 1, except that the urethane resin in the coating liquid was changed to (A-3) and the crosslinking agent was changed to (B-2).

[0125] Example 7 In the coating solution, the following coating agent was mixed with a mixed solvent of water and isopropanol, and the solid mass ratio of the urethane resin solution (A-2) / total of crosslinking agents (B-1, B-2) / polyester water dispersion (Cw-1) was changed to 25 / 26 / 49. A white laminated polyester film was obtained in the same manner as in Example 1. Urethane resin solution (A-2) 6.30 parts by mass Crosslinking agent (B-1) 3.73 parts by mass Crosslinking agent (B-2) 1.77 parts by mass Polyester water dispersion (Cw-1) 17.00 parts by mass Particles 23.00 parts by mass (Silica particles with an average particle size of 0.45 μm, solid content concentration of 40.00% by mass) Surfactant 0.15 parts by mass (Silicone-based, solid content 10% by mass)

[0126] Example 8 A white laminated polyester film was obtained in the same manner as in Example 7, except that the urethane resin in the coating liquid was changed to (A-3) and the polyester water dispersion was changed to (Cw-3).

[0127] Example 9 In the coating solution, the following coating agent was mixed with a mixed solvent of water and isopropanol, and the solid mass ratio of urethane resin solution (A-3) / crosslinking agent (B-2) / polyester water dispersion (Cw-1) was changed to 27 / 14 / 59. A white laminated polyester film was obtained in the same manner as in Example 1. Urethane resin solution (A-3) 7.00 parts by mass Crosslinking agent (B-2) 3.00 parts by mass Polyester water dispersion (Cw-1) 21.00 parts by mass Particles 23.00 parts by mass (Silica particles with an average particle size of 0.45 μm, solid content concentration of 40.00% by mass) Surfactant 0.15 parts by mass (Silicone-based, solid content 10% by mass) Antistatic agent 2.00 parts by mass (Quaternary ammonium salt-based antistatic agent, solid content concentration 17.50% by mass)

[0128] Example 10 In the coating solution, the following coating agent was mixed with a mixed solvent of water and isopropanol, and the solid mass ratio of urethane resin solution (A-3) / crosslinking agent (B-2) / polyester water dispersion (Cw-1) was changed to 28 / 11 / 61. A white laminated polyester film was obtained in the same manner as in Example 1. Urethane resin solution (A-3) 12.00 parts by mass Crosslinking agent (B-2) 4.00 parts by mass Polyester water dispersion (Cw-1) 35.00 parts by mass Particles 27.00 parts by mass (benzoguanamine formaldehyde condensate particles with an average particle size of 2 μm, Solid content concentration 40.00% by mass) MB6 Surfactant 0.15 parts by mass (Silicone-based, solid content 10% by mass) Antistatic agent 2.00 parts by mass (Quaternary ammonium salt-based antistatic agent, solid content concentration 17.50% by mass)

[0129] Example 11 In the coating solution, the following coating agent was mixed with a mixed solvent of water and isopropanol, and the solid mass ratio of urethane resin solution (A-1) / crosslinking agent (B-1) / polyester water dispersion (Cw-1) was changed to 22 / 10 / 68. A laminated polyester film was obtained in the same manner as in Example 1. Urethane resin solution (A-1) 5.80 parts by mass Crosslinking agent (B-1) 2.20 parts by mass Polyester water dispersion (Cw-1) 24.00 parts by mass Particles 23.00 parts by mass (Silica particles with an average particle size of 0.45 μm, solid content concentration of 40.00% by mass) Surfactant 0.15 parts by mass (Silicone-based, solid content 10% by mass)

[0130] Example 12 A laminated polyester film was obtained in the same manner as in Example 11, except that the urethane resin in the coating liquid was changed to (A-2).

[0131] Example 13 A laminated polyester film was obtained in the same manner as in Example 11, except that the urethane resin in the coating liquid was changed to (A-3).

[0132] Example 14 A laminated polyester film was obtained in the same manner as in Example 11, except that the crosslinking agent in the coating liquid was changed to (B-3) and the polyester water dispersion was changed to (Cw-3).

[0133] Example 15 A laminated polyester film was obtained in the same manner as in Example 11, except that the urethane resin in the coating liquid was changed to (A-4).

[0134] Example 16 A laminated polyester film was obtained in the same manner as in Example 11, except that the urethane resin in the coating liquid was changed to (A-5).

[0135] Example 17 A laminated polyester film was obtained in the same manner as in Example 11, except that the urethane resin in the coating liquid was changed to (A-3) and the crosslinking agent was changed to (B-2).

[0136] Example 18 A laminated polyester film was obtained in the same manner as in Example 11, except that the urethane resin in the coating liquid was changed to (A-3) and the particles were changed to calcium carbonate particles with an average particle size of 1 μm (solid content concentration 40.00 mass %).

[0137] Example 19 A laminated polyester film was obtained in the same manner as in Example 11, except that the urethane resin in the coating liquid was changed to (A-9).

[0138] (Comparative Example 1) A laminated polyester film was obtained in the same manner as in Example 1, except that the urethane resin in the coating liquid was changed to (A-6).

[0139] (Comparative Example 2) A laminated polyester film was obtained in the same manner as in Example 1, except that the urethane resin in the coating liquid was changed to (A-7).

[0140] (Comparative Example 3) A laminated polyester film was obtained in the same manner as in Example 11, except that the urethane resin in the coating liquid was changed to (A-6).

[0141] Comparative Example 4 A laminated polyester film was obtained in the same manner as in Example 11, except that the urethane resin in the coating liquid was changed to (A-7).

[0142] (Comparative Example 5) A laminated polyester film was obtained in the same manner as in Example 1, except that the solid mass ratio of the urethane resin solution (A-6) / crosslinking agent (B-1) / polyester water dispersion (Cw-2) in the coating liquid was changed to 38 / 7 / 55.

[0143] (Comparative Example 6) A laminated polyester film was obtained in the same manner as in Example 1, except that the solid mass ratio of the urethane resin solution (A-8) / crosslinking agent (B-4) / polyester aqueous dispersion (Cw-2) in the coating liquid was changed to 22 / 12 / 66.

[0144] As shown in Table 1, each Example achieved satisfactory results in terms of blocking resistance when water was applied and adhesion to UV ink. On the other hand, in Comparative Examples 1 to 6, the coating layer formed on at least one surface of the polyester film substrate did not contain a urethane resin having a branched structure, and therefore the blocking resistance when water was applied was not satisfactory.

[0145] (Comparative Example 7) A laminated polyester film was obtained in the same manner as in Example 1, except that the coating solution was changed so that the solids ratio of the urethane resin solution (A-1) / crosslinking agent (B-1) was 70 / 30, by mixing the following coating agent with a mixed solvent of water and isopropanol. Urethane resin solution (A-1) 15.00 parts by mass Crosslinking agent (B-1) 5.50 parts by mass Particles 23.00 parts by mass (Silica particles with an average particle size of 0.45 μm, solid content concentration of 40.00% by mass) Surfactant 0.15 parts by mass (Silicone-based, solid content 10% by mass)

[0146] (Comparative Example 8) A laminated polyester film was obtained in the same manner as in Example 1, except that the coating solution was changed so that the solids ratio of the urethane resin solution (A-1) / crosslinking agent (B-1) was 20 / 80, by mixing the following coating agent with a mixed solvent of water and isopropanol. Urethane resin solution (A-1) 4.70 parts by mass Crosslinking agent (B-1) 16.00 parts by mass Particles 23.00 parts by mass (Silica particles with an average particle size of 0.45 μm, solid content concentration of 40.00% by mass) Surfactant 0.15 parts by mass (Silicone-based, solid content 10% by mass)

[0147] As shown in Table 1, in Comparative Examples 7 and 8, the coating layer formed on at least one side of the polyester film substrate did not contain polyester resin, resulting in poor adhesion between the coating layer and the substrate and unsatisfactory adhesion to UV ink.

[0148] (Comparative Example 9) A laminated polyester film was obtained in the same manner as in Example 1, except that the urethane resin was changed to (A-10).

[0149] (Comparative Example 10) A laminated polyester film was obtained in the same manner as in Example 11, except that the urethane resin was changed to (A-11).

[0150] As shown in Table 1, in Comparative Examples 9 and 10, the coating layer formed on at least one side of the polyester film substrate did not contain a urethane resin having a polycarbonate structure, and therefore the adhesion to UV ink was not satisfactory.

[0151] Table 1 summarizes the evaluation results for each example and comparative example.

[0152] [Table 1] [Industrial Applicability]

[0153] According to the present invention, it is possible to provide a white laminated polyester film that can be suitably used in fields such as label applications.

Claims

1. A white laminated polyester film having a coating layer on at least one surface of a polyester film substrate, the coating layer is formed by curing a composition containing a urethane resin having a polycarbonate structure and a branched structure, a crosslinking agent, and a polyester resin, the optical density of the white laminated polyester film is 0.3 or more and 4.0 or less; White laminated polyester film.

2. The composition forming the coating layer further contains an antistatic agent. The white laminated polyester film according to claim 1 .

3. 2. The laminated polyester film according to claim 1, wherein the urethane resin having a polycarbonate structure and a branched structure is obtained by synthesizing and polymerizing a polycarbonate polyol component and a polyisocyanate component, and the mass ratio of the polycarbonate polyol component to the polyisocyanate component (mass of the polycarbonate polyol component / mass of the polyisocyanate component) during the synthesis and polymerization is 0.5 to 3.

4. A label comprising the white laminated polyester film of claim 1.

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