Easily bondable polyester film

Abstract

[Problem] To provide an easy-adhesion polyester film which is suitable for optical use and the like by suppressing a decrease in adhesion over time. [Solution] An easy-adhesion polyester film which is an easy-adhesion polyester film having a coating layer on at least one side of a polyester film, the coating layer being formed by curing a composition containing a polyester having a polycyclic aromatic skeleton and a crosslinking agent having a skeleton selected from at least one of aliphatic, alicyclic, and heterocyclic, when the surface of the aforementioned coating layer on the side not in contact with the polyester film is measured by Fourier transform infrared spectroscopy (FT-IR), the relative absorption intensity ratio (I ‑1 ) of the absorption intensity (I 1640 ) of the peak at 1640 cm ‑1 which is attributable to a urea group and the absorption intensity (I 1410 ) of the peak at 1410 cm 1640 which is attributable to CH stretching of the polyester satisfies a specific relationship. 1410 ​

Description

TECHNICAL FIELD

[0001] The present application relates to an easily-adhesive polyester film which can ensure elimination of the problem of rainbow when a hard coat layer or the like functional layer is laminated, has low interference, and has excellent adhesion to the aforementioned functional layer, anti-blocking property, and transparency. More specifically, the present application relates to an easily-adhesive polyester film which is also suitable for more transparent optical applications. BACKGROUND

[0002] A hard coat film in which a transparent hard coat layer is laminated is used on the front surface of a display, a decorative material, or the like, such as a touch panel, a computer, a television, a liquid crystal display device, and the like. In addition, as a transparent plastic film serving as a base material, a transparent polyester film is generally used, and in order to improve the adhesion of the polyester film serving as a base material to the hard coat layer, a coating layer having easy adhesion is often provided as an intermediate layer on the surface of the polyester film.

[0003] The aforementioned hard coat film is required to have durability against temperature, humidity, light, transparency, chemical resistance, abrasion resistance, stain resistance, and the like. In addition, since it is used on the surface of a display or a decorative material in many cases, visibility and designability are required. Therefore, in order to suppress glare, rainbow-like color, and the like caused by reflected light when viewed from any angle, a multilayer antireflection layer in which a high refractive index layer and a low refractive index layer are laminated is often provided on the upper layer of the hard coat layer.

[0004] In recent years, hard coat layers having various skeletons have been developed, and the adhesion of the base material to the hard coat layer has been discussed each time. Not only the initial adhesion immediately after lamination is required, but also the reliability for long-term use of the product, such as humidity and heat resistance, adhesion retention, and a small decrease in adhesion over time, is required, and a product having various evaluation resistances is required.

[0005] In the field of existing easily-adhesive polyester films, when a polyester resin using naphthalene dicarboxylic acid as a copolymer component is used for a coating layer having easy adhesion, the adhesion to the base material polyester film is also excellent, and is proposed as a suitable example (for example, see Patent Document 1). In addition, as a resin having excellent softness and high adhesion, a method of using a polyurethane resin having a polycarbonate component is proposed (for example, see Patent Document 2).

[0006] However, although the adhesion is confirmed, an easily-adhesive polyester film which guarantees the reliability for long-term use is not obtained.

[0007] PRIOR ART DOCUMENTS

[0008] PATENT DOCUMENTS

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 2011-246663

[0010] Patent Literature 2: Japanese Patent Application Laid-Open No. 2011-168053 SUMMARY

[0011] PROBLEMS TO BE SOLVED BY THE INVENTION

[0012] The present application has been made in view of the above-described problems of the prior art. That is, the object of the present application is to provide an easy-adhesion polyester film improved in reliability of adhesion, particularly an easy-adhesion polyester film which is suitable for optical use and the like by suppressing a decrease in adhesion over time.

[0013] The present inventors have conducted intensive studies in order to achieve the above-described object, and as a result, the present application has been conceived.

[0014] That is, the present application comprises the following configuration.

[0015] 1. An easy-adhesion polyester film which is an easy-adhesion polyester film having a coating layer on at least one side of a polyester film, the coating layer being formed by curing a composition comprising a polyester having a polycyclic aromatic skeleton and a crosslinking agent having a skeleton selected from at least one of aliphatic, alicyclic, and heterocyclic groups, wherein when the surface of the coating layer on the side not in contact with the polyester film is measured by Fourier transform infrared spectroscopy (FT-IR), the relative absorption intensity ratio (I -1 ) of the absorption intensity (I 1640 ) as a peak to the absorption intensity (I -1 ) as a peak of CH stretching of the polyester is defined, the following relationship is satisfied. 1410 1640 1410

[0016] The relative absorption intensity ratio (X) obtained by evaluating the easy-adhesion polyester film after film formation and the relative absorption intensity ratio (Y) obtained by evaluating the polyester film after being left in an environment of 80°C, 90% RH for 24 hours satisfy the following formula (1)

[0017] 110 ≤ (Y / X) x 100 ≤ 140... (1)

[0018] 2. The easy-adhesion polyester film according to the above-mentioned item 1, wherein the polyester having a polycyclic aromatic skeleton is a polyester having a naphthalene skeleton.

[0019] 3. The easy-adhesion polyester film according to the above-mentioned item 1 or 2, wherein the crosslinking agent having a skeleton selected from at least one of aliphatic, alicyclic, and heterocyclic groups is an isocyanate crosslinking agent having a skeleton selected from at least one of aliphatic, alicyclic, and heterocyclic groups.

[0020] ​​​4. The easily-adherable polyester film according to any one of the above items 1 to 3, wherein when a hard coat layer containing a resin having an aromatic skeleton is provided on the surface of the above-mentioned coating layer, the adhesion is 95% or more.

[0021] Effects of the Invention

[0022] According to the present application, an easily-adherable polyester film that ensures reliable adhesion for a long time can be provided, and can be widely used for optical applications and the like. DETAILED DESCRIPTION

[0023] (Polyester Film)

[0024] The polyester film used as the base material in the present application is a film composed mainly of a polyester resin. Here, the "film composed mainly of a polyester resin" refers to a film formed from a resin composition containing 50% by mass or more of a polyester resin. In the case of blending with other polymers, it refers to a film containing 50% by mass or more of a polyester resin, and in the case of copolymerization with other monomers, it refers to a film containing 50% by mole or more of a polyester structural unit. The polyester film preferably contains 90% by mass or more, more preferably 95% by mass or more, and further preferably 100% by mass of a polyester resin.

[0025] The material of the polyester resin is not particularly limited, and a copolymer formed by polycondensation of a dicarboxylic acid component and a diol component, or a blended resin thereof can be used. As the dicarboxylic acid component, for example, terephthalic acid, isophthalic acid, phthalic acid, 2,5-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 1,4-naphthalene dicarboxylic acid, 1,5-naphthalene dicarboxylic acid, diphenyl carboxylic acid, diphenyloxy ethane dicarboxylic acid, diphenyl sulfone carboxylic acid, anthracene dicarboxylic acid, 1,3-cyclopentane dicarboxylic acid, 1,3-cyclohexane dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethyl malonic acid, succinic acid, 3,3-diethyl succinic acid, glutaric acid, 2,2-dimethyl glutaric acid, adipic acid, 2-methyl adipic acid, trimethyl adipic acid, pimelic acid, azelaic acid, dimer acid, sebacic acid, suberic acid, dodecanedicarboxylic acid, and the like can be given.

[0026] As the diol component constituting the polyester resin, for example, ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexane dimethanol, 1,4-cyclohexane dimethanol, decamethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-bis(4-hydroxyphenyl)propane, bis(4-hydroxyphenyl) sulfone, and the like can be given.

[0027] The dicarboxylic acid component and the diol component constituting the polyester resin can be used individually or two or more kinds. In addition, other acid components such as trimellitic acid, other hydroxyl components such as trimethylolpropane can also be appropriately added.

[0028] As the polyester resin, specifically, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and the like can be given, among which, from the balance of the physical properties and the cost, polyethylene terephthalate is preferred. Further, in order to control the optical properties such as the polarizing properties, it is also preferred to contain other copolymer components, other polymers. From the viewpoint of controlling the optical properties of the polyester film, as the preferred copolymer components, diethylene glycol, copolymer components having norbornene in the side chain, and the like can be given.

[0029] In order to improve the slidability, the winding properties, and the like of the polyester film, sometimes, non-active particles are contained in the film, but in order to maintain high transparency, it is preferred that the content of the non-active particles in the film is as little as possible. Therefore, it is preferred that the film is made of a multi-layer structure in which the particles are contained only in the surface layer, or that the film is made substantially free of particles, and the particles are contained only in the cover layer laminated on at least one side of the polyester film.

[0030] Note that, by "substantially free of particles", for example in the case of inorganic particles, it means that the content of the elements derived from the particles is 50 ppm or less, preferably 10 ppm or less, and most preferably below the detection limit, when quantitatively analyzed by fluorescent X-ray analysis. This is because, even if the particles are not actively added in the base film, there are cases where contaminant components derived from foreign substances, contaminants attached to the pipelines and devices in the manufacturing process of the raw material resin or the film, and the like are inevitably mixed into the film.

[0031] Further, when the polyester film is made of a multi-layer structure, a two-layer structure in which the inner layer is substantially free of non-active particles, and the non-active particles are contained only in the outermost layer is preferred, in which the transparency and the processability are balanced.

[0032] The polyester film serving as the base material can be a single layer, or can be a laminate of two or more layers. Further, various additives can be contained in the film as needed, as long as it is within the range to exert the effects of the present application. As the additives, for example, antioxidants, light-resistant agents, anti-gelling agents, organic wetting agents, antistatic agents, ultraviolet absorbers, surfactants, and the like can be given. In the case where the film has a laminate structure, it is also preferred that the additives are contained in each layer as needed according to the function of each layer. For example, in order to prevent the optical degradation of the polarizing plate, it is also preferred to add ultraviolet absorbers and the like in the inner layer.

[0033] The polyester film can be produced according to a conventional method. For example, it is obtained by melt-extruding the polyester resin described above into a film shape, and allowing it to cool and solidify on a casting drum to form a film. As the polyester film in the present application, either a non-stretched film or a stretched film can be used, but from the viewpoint of mechanical strength, chemical resistance, and durability, a stretched film is preferable. In the case where the polyester film is a stretched film, the stretching method is not particularly limited, and a longitudinal monoaxial stretching method, a transverse monoaxial stretching method, a longitudinal-transverse sequential biaxial stretching method, a longitudinal-transverse simultaneous biaxial stretching method, or the like can be employed. In the case where the polyester film is stretched, the stretching can be performed before the lamination of the easily-adherable layer described below, or after the lamination of the easily-adherable layer. It is also possible to perform monoaxial stretching in the longitudinal direction or the transverse direction before the lamination of the easily-adherable layer, and to perform stretching in the other direction after the lamination of the cover layer.

[0034] (coating layer)

[0035] The easily-adherable polyester film of the present application is obtained by laminating an easily-adherable coating layer on the substrate film made of polyester described above. The coating layer contains a binder resin and an additive.

[0036] Hereinafter, each component of the coating layer will be described in detail.

[0037] As the binder resin constituting the coating layer, a resin having easy adhesion is used, and from the viewpoint of particle retention and adhesion, polyester is the most preferable, and further in the present application, a polyester having a polycyclic aromatic skeleton is the most preferable. It also has compatibility with the composition of the hard coat layer described below, but when the composition of the hard coat layer has an aromatic skeleton, it is also suitable from the viewpoint of conjugate interaction.

[0038] As a specific example of the polyester having a polycyclic aromatic skeleton, a polyester having a naphthalene skeleton, a polyester having a fluorene skeleton, a polyester having an anthracene skeleton, a polyester having a phenanthrene skeleton, and the like can be given.

[0039] In the present application, as the binder resin constituting the coating layer, it is preferable not to contain a polyurethane resin. From the viewpoint of the elasticity of the coating film and easy moldability, a polyurethane resin is used, but it is obvious that urea compounds are mixed as impurities due to the polyurethane resin, and if the amount of urea compounds present in the coating layer becomes excessive, it sometimes becomes difficult to satisfy the characteristics related to the relative absorption intensity ratio described below, and from the viewpoint of maintaining the stability of adhesion over time, it is preferable not to contain a polyurethane resin.

[0040] The aforementioned polyester is preferably contained at 10 mass% or more and 90 mass% or less, more preferably 15 mass% or more and 85 mass% or less, in terms of the mass of the solid content of the polyester resin relative to the sum of the mass of the solid content of the resin and the crosslinking agent, in the coating layer. The content of the polyester resin is preferably 90 mass% or less in order to maintain adhesion to the hard coat layer under high temperature and high humidity. Conversely, if the content is 10 mass% or more, adhesion to the polyester film under normal temperature and high temperature and high humidity is easily maintained.

[0041] In the present application, in order to form a crosslinked structure in the coating layer, a crosslinking agent is preferably contained. A crosslinking agent that can generate a urea group through a side reaction of crosslinking is suitable, and as a specific crosslinking agent, isocyanate-based crosslinking agents and carbodiimide-based crosslinking agents can be given. Among these, isocyanate crosslinking agents are suitable in terms of the stability of the coating liquid over time and the adhesion improvement effect under high temperature and high humidity treatment. Furthermore, in the present application, isocyanates having at least one skeleton selected from the group consisting of aliphatic, alicyclic, and heterocyclic are optimal. In addition, in order to promote the crosslinking reaction, a catalyst or the like can be appropriately used as needed in the composition for forming a coating layer.

[0042] As specific examples of aliphatic isocyanates, 1,4-diisocyanatobutane, 1,5-pentamethylene diisocyanate, 2-methyl-1,5-pentamethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,12-dodecane diisocyanate, 2,2,4-trimethyl-1,6-hexamethylene diisocyanate, 2,4,4-trimethyl-1,6-hexamethylene diisocyanate, 3,5,5-trimethyl-1,6-hexamethylene diisocyanate, and the like can be given.

[0043] As specific examples of alicyclic isocyanates, cyclohexane diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, 1,4-bis(isocyanatomethyl)cyclohexane, cyclohexyl 1,4-diisocyanate, 1,1-bis(isocyanatomethyl)cyclohexane, 2,4-hexahydroxylylene diisocyanate, 2,6-hexahydroxylylene diisocyanate, and the like can be given.

[0044] As specific examples of the heterocyclic isocyanate, 2,5-diisocyanatothiophene, 2,5-bis(isocyanatomethyl)thiophene, 2,5-diisocyanatotetrahydrothiophene, 2,5-bis(isocyanatomethyl)tetrahydrothiophene, 3,4-bis(isocyanatomethyl)tetrahydrothiophene, 2,5-diisocyanato-1,4-dithiane, 2,5-bis(isocyanatomethyl)-1,4-dithiane, 4,5-diisocyanato-1,3-dithiolane, 4,5-bis(isocyanatomethyl)-1,3-dithiolane, 4,5-bis(isocyanatomethyl)-2-methyl-1,3-dithiolane, 2,6-bis(isocyanatomethyl)furan, 5,5'-methylenebisfurfuryl isocyanate, 5,5'-isopropylidenebisfurfuryl isocyanate, or a trimer of diisocyanate, 2,4,6-trioxohexahydro-1,3,5-triazine-1,3,5-triazinyl tri(6,1-hexanediyl)triisocyanate, 1,3,5-tris[(5-isocyanato-1,3,3-trimethylcyclohexyl)methyl]-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, and the like can be given.

[0045] In the present application, the isocyanate having an aromatic skeleton is easily reacted with moisture in the air due to its high reactivity, and the generation of urea compounds is promoted more than necessary, and thus it is preferable not to be contained in the coating layer-forming composition. Further, from the viewpoint of weather resistance, it is also preferable that the isocyanate have at least one skeleton selected from the group consisting of an aliphatic skeleton, an alicyclic skeleton, and a heterocyclic skeleton.

[0046] The content of the solid component of the crosslinking agent in the coating layer-forming composition is preferably 5% by mass or more and 50% by mass or less, in terms of the percentage of the mass of the solid component of the crosslinking agent with respect to the sum of the masses of the resin and the solid component of the crosslinking agent. More preferably, it is 10% by mass or more and 45% by mass or less. Further preferably, it is 10% by mass or more and 30% by mass or less, and most preferably, it is 10% by mass or more and 20% by mass or less. If it is 5% by mass or more, the strength of the resin of the coating layer is maintained, and the adhesion under high temperature and high humidity is good, and if it is 50% by mass or less, the softness of the resin of the coating layer is maintained, and the adhesion under normal temperature, high temperature and high humidity is maintained, and thus it is preferable.

[0047] The coating layer in the easily-adherable polyester film of the present application is preferably formed by curing a composition containing a polyester having a polycyclic aromatic skeleton and a crosslinking agent having at least one skeleton selected from the group consisting of an aliphatic skeleton, an alicyclic skeleton, and a heterocyclic skeleton. The chemical composition after the curing of the composition is not properly exhibited due to the difficulty in properly exhibiting the reaction after the curing of the crosslinking agent, and thus this is described as such.

[0048] (Additives)

[0049] In the coating layer in the present application, a publicly known additive such as a surfactant, an antioxidant, a heat-resistant stabilizer, a weather-resistant stabilizer, an ultraviolet absorber, an organic slip agent, a pigment, a dye, an organic or inorganic particle, an antistatic agent, a nucleating agent, and the like can be added within a range not impairing the effects of the present application. However, it is preferable that a substance not friendly to the environment or the like is not used.

[0050] In the present application, it is also preferable to add a particle to the coating layer in order to further improve the blocking resistance of the coating layer. As the particle contained in the coating layer in the present application, for example, titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, or a mixture thereof can be given, and further, inorganic particles such as calcium phosphate, mica, hectorite, zirconium oxide, tungsten oxide, lithium fluoride, calcium fluoride, and the like, organic polymer particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, silicone-based, and the like, and the like can be used in combination with other conventional inorganic particles.

[0051] The average particle diameter of the non-active particle in the coating layer (average particle diameter on the basis of the number based on SEM. The same applies hereinafter) is preferably 0.04 to 2.0 μm, and further preferably 0.1 to 1.0 μm. If the average particle diameter of the non-active particle is 0.04 μm or more, it is easy to form unevenness on the surface of the film, and thus the operability such as the sliding property, the winding property, and the like of the film is improved, and the processability at the time of lamination is good, and thus it is preferable. On the other hand, if the average particle diameter of the non-active particle is 2.0 μm or less, it is not easy to cause the particle to fall off, and thus it is preferable. The particle concentration in the coating layer is preferably 1 to 20 mass% in the solid content.

[0052] The thickness of the coating layer in the present application can be appropriately set within a range of 0.001 to 2.00 μm, and in order to balance the processability and the adhesiveness, it is preferable that the range is 0.01 to 1.00 μm, more preferably 0.02 to 0.80 μm, and further preferably 0.05 to 0.50 μm. If the thickness of the coating layer is 0.001 μm or more, the adhesiveness is good, and thus it is preferable. If the thickness of the coating layer is 2.00 μm or less, it is not easy to cause blocking, and thus it is preferable.

[0053] The present application focuses on the change in the amount of the urea compound, which is a crosslinking agent component present in the composition for forming a coating layer, deformed due to the reaction with moisture or the like in the air.

[0054] When the surface of the coating layer of the easily-adhesive polyester film of the present application is measured by Fourier transform infrared spectroscopy (FT-IR), the peak attributed to the urea group at 1640 cm -1 The absorption intensity (I 1640 ) of the peak is compared with the absorption intensity of the peak attributed to the CH stretching of the polyester at 1410 cm -1 The absorption intensity (I1410 The relative absorption intensity ratio (I) 1640 / I 1410 When defined, a higher relative absorption intensity ratio indicates the formation of more urea compounds in the coating layer. The 1640 cm⁻¹ portion is attributed to urea compounds. -1 The peak may not necessarily appear exactly at 1640cm. -1 It exists at 1640±5cm -1 The range is approximately 1000 to 1000 cm. Additionally, 1410 cm belongs to polyester resins with a polycyclic aromatic backbone. -1 The peak may not necessarily appear exactly at 1410cm. -1 It exists at 1410±5cm -1 The range of motion, left and right.

[0055] Preferably, the relative absorption strength ratio (X) obtained by evaluating the easy-to-adhere polyester film after film preparation and the relative absorption strength ratio (Y) obtained by evaluating the easy-to-adhere polyester film after being kept at 80°C and 90%RH for 24 hours satisfy the following relationship (1).

[0056] 110≤(Y / X)×100≤140···(1)

[0057] In this invention, "after film formation" refers to a sample placed under a specific environment for no more than 240 hours after film fabrication. Specifically, this specific environment refers to a temperature range of 5°C to 40°C and a humidity range of 30% RH to 60% RH. Samples maintained within these ranges are preferred as they are in their initial state, as no changes over time are observed.

[0058] For the easily bondable polyester film of the present invention, the aforementioned (Y / X)×100 of the coating layer present on the film surface is preferably 140 or less, and more preferably 130 or less. If it is 140 or less, the proportion of urea in the coating layer is not too high, which can prevent the urea compound with polar groups from adsorbing more moisture from the air, thus reducing the long-term stability and reliability of the seal, which is preferred. If the aforementioned (Y / X)×100 is 110 or more, the content of the original crosslinking agent is not insufficient, and crosslinking and other reactions can be carried out appropriately to obtain good seal and reliable seal, which is also preferred.

[0059] Ideally, the adhesive properties of polyester films could be evaluated by the ratio of their relative absorption strength before and after being placed at room temperature for several weeks to several months. However, since it is difficult to perform such a placement test, an accelerated evaluation was conducted by placing the films at 80°C and 90% RH for 24 hours as a substitute.

[0060] To satisfy the relational expression (1) of the relative absorption intensity ratio, it is preferable to control the ratio of the resin to the crosslinking agent in the coating layer. By increasing the resin component in the composition for forming a coating layer, the values of X and Y gradually increase, and when the total of the solid components of the resin component and the crosslinking agent component is taken as 100 mass%, the solid component of the resin component is preferably 70 mass% or more. More preferably, it is 75 mass% or more, and further preferably, it is 80 mass% or more. If it is 70 mass% or more, the ratio of the crosslinking agent is not excessively large, the proportion of the excess urea compound can be reduced, and it becomes easy to satisfy the relational expression (1). However, these means are only examples, and other means of implementation are not excluded. When the total of the solid components of the resin component and the crosslinking agent component is taken as 100 mass%, the solid component of the crosslinking agent component is preferably 30 mass% or less, more preferably 25 mass% or less, and further preferably 20 mass% or less.

[0061] In this case, the value of X is preferably 1.78 or less. More preferably, it is 1.60 or less, and further preferably, it is 1.41 or less. By increasing the resin component and reducing the crosslinking agent component, the proportion of the excess urea compound can be reduced, the hard coat adhesion becomes good, and this is preferable. On the other hand, the value of X is preferably 1.10 or more, the addition ratio as a crosslinking reaction with the resin can be satisfied, the adhesion to the hard coat layer under high temperature and high humidity becomes easy to satisfy, and this is preferable. The value of X is more preferably 1.15 or more, and further preferably, it is 1.20 or more.

[0062] In addition, the value of Y is preferably 2.70 or less. More preferably, it is 2.30 or less, and further preferably, it is 1.85 or less. By reducing the crosslinking agent component, the proportion of the excess urea compound can be reduced over time, the hard coat adhesion becomes good, and this is preferable. On the other hand, if the value of Y is 0.90 or more, the addition ratio as a crosslinking reaction with the resin can be satisfied, the adhesion to the hard coat layer under high temperature and high humidity becomes easy to satisfy, and this is preferable. The value of Y is more preferably 1.20 or more, and further preferably, it is 1.40 or more.

[0063] The composition for forming a coating layer can also contain a surfactant for the purpose of improving the leveling property at the time of coating, and defoaming of the coating liquid. The surfactant can be cationic, anionic, nonionic, or the like, and any of these can be used, but an organic silicon-based, acetylene glycol-based, or fluorine-based surfactant is preferable. These surfactants are preferably contained in the composition for forming a coating layer within a range that does not destroy the inhibitory effect on the iridescent color under a fluorescent lamp, and the degree of adhesion.

[0064] As the coating method, either the so-called online coating method in which coating is performed at the same time as the film formation of the polyester base film, or the so-called offline coating method in which coating is performed separately using a coater after the film formation of the polyester base film can be applied, but the online coating method is effective, and this is more preferable.

[0065] As a coating method, any known method can be used to coat the coating liquid onto a polyethylene terephthalate (PET) film. Examples include reverse roller coating, gravure coating, coincidence coating, die coating, roller brush coating, spray coating, air knife coating, wire rod coating, tube blade coating, dip coating, curtain coating, etc. These methods can be used individually or in combination.

[0066] In this invention, a method for forming a coating layer on a polyester film can be described as applying a coating liquid containing a solvent, particles, and resin onto the polyester film and then drying it. As a solvent, water or a mixture of water and an organic solvent can be used; preferably, from an environmental perspective, water alone or in a mixture of water and a water-soluble organic solvent is preferred.

[0067] Examples of water-soluble organic solvents include isopropanol, ethanol and other alcohols, methyl ethyl ketone and other ketones, butyl cellosolve and other ethers, triethanolamine and other amines, and N-methylpyrrolidone and other amides.

[0068] The concentration of solid components in the coating liquid also depends on the type of binder resin, the type of solvent, etc., and is preferably 2% by mass or more, more preferably 4% by mass. The concentration of solid components in the coating liquid is preferably 35% by mass or less, more preferably 15% by mass or less.

[0069] The drying temperature after coating also depends on the type of adhesive resin, the type of solvent, the presence or absence of crosslinking agent, and the concentration of solid components, etc. It is preferably above 80°C and preferably below 250°C.

[0070] (Manufacturing of easy-to-adhere polyester film)

[0071] The polyester film that serves as the substrate for the easily adhesive polyester film of the present invention can be manufactured according to a general polyester film manufacturing method. For example, the following method can be used: melting polyester resin, extruding and molding it into a sheet to obtain a non-oriented polyester, stretching the obtained non-oriented polyester longitudinally at a temperature above the glass transition temperature using the speed difference of the rollers, and then stretching it transversely using a tenter frame and performing heat treatment.

[0072] The polyester film in this invention can be a uniaxially stretched film or a biaxially stretched film. When a biaxially stretched film is used as a protective film in front of the liquid crystal panel, no rainbow-like color spots are seen even when viewed from directly above the film surface. However, rainbow-like color spots are sometimes observed when viewed from an oblique direction. Therefore, this should be noted.

[0073] This phenomenon is due to the fact that biaxially stretched films are composed of refractive ellipsoids having different refractive indices in the traveling direction, the width direction, and the thickness direction, and there are directions in which the retardation becomes zero (the refractive ellipsoids are seen as a perfect circle) depending on the transmission direction of light inside the film. Therefore, if the liquid crystal display screen is observed from a specific direction inclined from the normal direction, sometimes a point at which the retardation becomes zero is generated, and a rainbow-like color stain is generated in concentric circles centered on this point. Moreover, if the angle at which the position of the rainbow-like color stain is observed from directly above the film surface (the normal direction) is set as θ, the larger the birefringence in the film surface, the larger the angle θ, and it becomes more difficult to observe the rainbow-like color stain. In biaxially stretched films, there is a tendency for the angle θ to decrease, and therefore, in the case of uniaxially stretched films, it becomes easier to observe the rainbow-like color stain, which is preferable.

[0074] However, in a completely uniaxial (uniaxially symmetric) film, the mechanical strength in the direction perpendicular to the orientation direction is significantly reduced, and therefore, it is not preferable. The present application preferably has biaxiality (biaxial symmetry) in a range in which rainbow-like color stains are not generated substantially, or in a range in which rainbow-like color stains are not generated within the required viewing angle range of a liquid crystal display screen.

[0075] (Laminated polyester film)

[0076] In the present application, a laminated polyester film for optical use is obtained by providing a hard coat layer or the like formed of an electron beam or ultraviolet-curable acrylic resin or a siloxane-based thermosetting resin or the like on the coating layer of the easily adhesive polyester film of the present application.

[0077] It is also a preferable method to provide a functional layer on the coating layer of the easily adhesive polyester film of the present application. The functional layer refers to a layer having functionality such as an antiglare layer, an antiglare and antireflection layer, an antireflection layer, a low reflection layer, and an antistatic layer, in addition to the aforementioned hard coat layer, for the purpose of preventing light reflection, suppressing glare, suppressing rainbow unevenness, suppressing scratches, and the like. The functional layer can use various substances known in the technical field, and the type is not particularly limited. Hereinafter, each functional layer is described.

[0078] For example, in the formation of the hard coat layer, a publicly known hard coat layer can be used, and there is no particular limitation, and a resin compound that is polymerized and / or reacted by drying, heat, chemical reaction, or irradiation of any of an electron beam, a radiation line, or ultraviolet rays can be used. As such a curable resin, a melamine-based, an acrylic-based, a silicone-based, or a polyvinyl alcohol-based curable resin can be given, and in terms of obtaining a high surface hardness or optical design, an acrylic-based curable resin of a photocurable type is preferable. As such an acrylic-based curable resin, a multifunctional (meth) acrylate-based monomer, an acrylate-based oligomer can be used, and as examples of the acrylate-based oligomer, a polyester acrylate-based, an epoxy acrylate-based, a urethane acrylate-based, a polyether acrylate-based, a polybutadiene acrylate-based, a silicone acrylate-based, or the like can be given. By mixing a reaction diluent, a photopolymerization initiator, a sensitizer, or the like in these acrylic-based curable resins, a coating composition for forming the aforementioned optical functional layer can be obtained.

[0079] The aforementioned hard coat layer can have an anti-glare function (anti-glare function) that scatters external light. The anti-glare function (anti-glare function) can be obtained by forming a concave-convex on the surface of the hard coat layer. At this time, the haze of the film is desirably preferably 0 to 50%, more preferably 0 to 40%, particularly preferably 0 to 30%. Of course, 0% is ideal, and can be 0.2% or more, or 0.5% or more.

[0080] In addition, in order to implement low reflection processing (anti-reflection processing) that suppresses the reflection of light by imparting a layer having a different refractive index and changing the light transmittance, it is preferable to adjust the refractive index of the hard coat layer and the functional layer and desirably achieve a reflectance of 0 to 1.0%, more preferably 0 to 0.8%, particularly preferably 0 to 0.5%. Of course, 0% is ideal, and can be 0.05% or more, or 0.1% or more.

[0081] In particular, as the hard coat composition used in the present application, in order to adjust the refractive index, a resin that contains an aromatic component at a ratio of 5 mol% or more and 20 mol% or less with respect to the total number of moles of the monomers and oligomers that constitute the resin is generally used.

[0082] The easily adhesive polyester film of the present application and the laminated polyester film in which a functional layer is laminated on the coating layer thereof are mainly used for optical films in general, and are particularly suitable for use as a base film for optical members such as a prism lens sheet, an AR (anti-reflection) film, a hard coat film, a diffusion plate, a shatterproof film, and the like for LCDs, flat panel TVs, CRTs, and the like, a near-infrared absorbing filter as a member of a front panel for a plasma display, a transparent conductive film for a touch panel, electroluminescence, and the like.

[0083] As the acryl resin cured by electron beam or ultraviolet rays for forming the hard coat layer described above, in detail, those having acrylate-based functional groups, for example, the following can be used: a lower molecular weight polyester resin, a polyether resin, an acryl resin, an epoxy resin, a polyurethane resin, an alkyd resin, a spiroacetal resin, a polybutadiene resin, a polysulfide polyene resin; an oligomer or a prepolymer of a (meth)acrylate or the like containing a polyfunctional compound such as a polyol and the like, and a monofunctional monomer such as ethyl (meth)acrylate, ethylhexyl (meth)acrylate, styrene, methylstyrene, N-vinylpyrrolidone, and the like, and a polyfunctional monomer such as trimethylolpropane tri(meth)acrylate, hexanediol (meth)acrylate, tripropyleneglycol di(meth)acrylate, diethylene glycol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, and the like.

[0084] Further, in the case of the electron beam or ultraviolet ray curable resin, the aforementioned resins can be used by mixing a phenone-based compound, a benzophenone-based compound, a Michler's benzoyl benzoic acid ester, an α-amyloxim ester, a tetramethylthiuram monosulfide, a thioxanthone-based compound as a photopolymerization initiator, or by mixing n-butylamine, triethylamine, tri-n-butylphosphine, or the like as a photosensitizer.

[0085] In addition, the silicone-based (siloxane-based) thermosetting resin can be produced by hydrolysis and condensation reaction of a single or two or more kinds of organosilane compounds in the presence of an acid or base catalyst. In particular, in the case of low reflection, further good improvements in low refractive index, stain resistance, and the like are achieved when one or more kinds of fluorosilane compounds are mixed and subjected to hydrolysis and condensation reaction.

[0086] (Manufacture of laminated polyester film)

[0087] The manufacture method of the laminated polyester film using the easily-adherable polyester film of the present application will be described, but is not limited to the specific examples described.

[0088] On the coated layer surface of the aforementioned easily-adherable polyester film, the aforementioned electron beam or ultraviolet ray curable acryl resin, oligomer, monomer, or silicone-based thermosetting resin is coated. In the case where the coated layer is provided on both surfaces, it is coated on at least one coated layer surface. The coating liquid does not need to be particularly diluted, but there is no particular problem even if it is diluted with an organic solvent according to the viscosity, wettability, coating film thickness, and the like of the coating liquid as needed. For the coated layer, after the aforementioned coating liquid is coated on the aforementioned film, it is dried as needed, and the coated layer is cured by electron beam or ultraviolet ray irradiation and heating in accordance with the curing conditions of the coating liquid, thereby forming a hard coat layer.

[0089] In the present application, the thickness of the hard coat layer is preferably 1 to 15 μm. If the thickness of the hard coat layer is 1 μm or more, the effects of the hard coat layer on chemical resistance, scratch resistance, stain resistance, and the like are effectively exhibited, and are thus preferred. On the other hand, if the thickness is 15 μm or less, the flexibility of the hard coat layer can be maintained, and there is no concern of cracking or the like, and thus is preferred.

[0090] As the scratch resistance, when the coated surface is abraded with black paper, it is preferred that the scratch is not apparent to the naked eye. If the scratch is not apparent in the aforementioned evaluation, the surface is not easily scratched when passing through a guide roll, and is thus preferred in terms of workability and the like.

[0091] The easily-adhesive polyester film and the laminated polyester film of the present application are mainly used for optical applications, and thus preferably have high transparency. The lower limit of the haze is desirably 0%, and is more preferably closer to 0%. The upper limit of the haze is preferably 2%, and if it is 2% or less, the light transmittance is good, and a clear image can be obtained in a liquid crystal display device, and thus is preferred. The haze of the polyester film can be measured, for example, according to the method described later.

[0092] The adhesion of the easily-adhesive layer to the hard coat layer is preferably 95% or more, based on the evaluation according to the measurement method described later. It is more preferably 98% or more, and is further preferably 100%. If it is 95% or more, it can be said that the adhesion of the easily-adhesive layer to the hard coat layer is sufficiently maintained.

[0093] The adhesion of the easily-adhesive layer to the hard coat layer under high-temperature high-humidity conditions of 80°C and 95% RH, evaluated according to the method described later, is also preferably 95% or more, as described above. It is more preferably 98% or more, and is further preferably 100%. If it is 95% or more, the adhesion of the easily-adhesive layer to the hard coat layer under high-temperature high-humidity conditions can be satisfied at one time, and the passability in the post-processing step can be satisfied at one time.

[0094] Originally, if the easily-adhesive polyester film could be evaluated in terms of the adhesion after being left in a room temperature environment for several weeks to several months, it would be ideal, but since it is difficult to perform the leaving measurement, as a substitute measurement, it is evaluated by being left in a high-temperature high-humidity environment of 80°C and 90% RH for 24 hours.

[0095] The easily-adhesive polyester film of the present application can be used for various purposes, preferably for the manufacturing process of a polarizing plate used in a liquid crystal display device, and particularly preferably as a protective film for a polarizing sheet constituting a polarizing plate. Generally, the polarizing sheet is mostly made of polyvinyl alcohol, and the easily-adhesive polyester film of the present application is adhered to the polarizing sheet as needed with an adhesive made of polyvinyl alcohol, a cross-linking agent, or the like added thereto. At this time, the coated layer of the easily-adhesive polyester film of the present application is more preferably used toward the opposite side of the surface to be adhered to the polarizing sheet. On the surface of the easily-adhesive polyester film of the present application to be adhered to the polarizing sheet, an easily-adhesive layer containing a polyester-based resin, a polyvinyl alcohol-based resin, and a cross-linking agent, which is described in International Publication No. 2012 / 105607, for example, is preferably laminated.

[0096] Examples

[0097] Next, the present application will be described in detail using examples, comparative examples, and reference examples, but the present application is of course not limited to the following examples. In addition, the evaluation methods used in the present application are described below.

[0098] (1) Average particle diameter

[0099] 〔Measurement method based on scanning electron microscope〕

[0100] The average particle diameter of the above-mentioned particles can be measured by the following method. For the particles, a photograph is taken with a scanning electron microscope (SEM) at a magnification of 2 to 5 mm for the size of one particle at the smallest, and the maximum particle diameters (the distance between the two points farthest apart) of 300 to 500 particles are measured, and the average value thereof is taken as the average particle diameter. The average particle diameter of the particles present in the coated layer in the present application can be measured by this measurement method.

[0101] 〔Dynamic light scattering method〕

[0102] The average particle diameter of the particles can also be found by the dynamic scattering method at the time of manufacturing the particles and the film. The sol is diluted with a dispersion medium, and using the parameters of the dispersion medium, the measurement is performed with a submicron particle analyzer N4 PLUS (manufactured by Beckman Coulter), and the average particle diameter is found by calculation in the cumulative method. In the dynamic light scattering method, the average particle diameter of the particles in the sol is observed, and when the particles aggregate with each other, the average particle diameter of these aggregated particles is observed.

[0103] (2) Refractive index of particles

[0104] The refractive index of the particles can be measured by the following method. The inorganic particles are dried at 150°C, then pulverized with a mortar to obtain a powder, the obtained powder is immersed in solvent 1 (of lower refractive index than the particles), and solvent 2 (of higher refractive index than the particles) is added little by little until the microparticles become substantially transparent. The refractive index of the solution is measured with an Abbe refractometer (manufactured by ATAGO CO., LTD.). The measurement is performed at 23°C under D-rays (wavelength 589 nm). Solvents 1 and 2 are selected so as to be miscible with each other, and examples of the solvents according to the refractive index include 1,1,1,3,3,3-hexafluoro-2-propanol, 2-propanol, chloroform, carbon tetrachloride, toluene, glycerol, and the like.

[0105] (3) Haze of the easily-adherable polyester film for optical use

[0106] The haze of the easily-adherable polyester film is measured with a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., NDH2000) according to JIS K 7136:2000.

[0107] (4) Adhesion

[0108] The easily-adherable polyester film obtained in the Examples is provided with a hard coat layer described in the item of the formation of the aforementioned hard coat layer. The adhesion of the hard coat layer to the base film is measured according to the description of 8.5.1 of JIS-K5400-1990 for the easily-adherable polyester film provided with the hard coat layer.

[0109] Specifically, a hard coat layer is provided with 100 grid-like scratches reaching the base film using a cutter guide with a gap of 2 mm. Next, a glass tape (manufactured by Nichiban, No. 405; 24 mm wide) is adhered to the grid-like scratch surface, and is wiped with an eraser so as to be completely attached. Thereafter, the glass tape is peeled vertically from the hard coat layer surface of the polarizing plate protective film, the number of grids peeled from the hard coat layer surface of the polarizing plate protective film is counted visually, and the adhesion of the hard coat layer to the base film is calculated from the following equation. Note that a grid partially peeled is also counted as a peeled grid.

[0110] Adhesion (%) = {1 - (number of peeled grids / 100)} x 100

[0111] (5) Moisture resistance (adhesion after storage at 80°C, 90% RH)

[0112] The obtained easily-adherable polyester film is stored in a high-temperature high-humidity tank at 80°C, 90% RH for 24 hours, and then stored at room temperature (20°C, 65% RH) for 12 hours. Thereafter, a hard coat layer is formed in the same manner as described above, and the adhesion to the base film is measured.

[0113] (6) Number average molecular weight

[0114] The number average molecular weight was measured by dissolving 0.03 g of the resin in 10 ml of tetrahydrofuran, using a GPC-LALLS apparatus, low-angle light scattering photometer LS-8000 (manufactured by Tosoh Corporation, tetrahydrofuran solvent, polystyrene reference), at a column temperature of 30°C and a flow rate of 1 ml / min, using a column (shodex KF-802, 804, 806, manufactured by Showa Denko K.K.), and measuring the number average molecular weight.

[0115] (7) Absorbance measurement based on infrared spectroscopy

[0116] FT-IR ATR measurement was performed on the obtained optical easily-adhesive polyester film under the following conditions.

[0117] Apparatus: Cary670 FTIR (manufactured by Agilent)

[0118] Accessories: SPECTRA-Tech Foundation Thunder Dome Ge 45° single reflection detector: TGS

[0119] Resolution: 4 cm -1

[0120] Number of accumulations: 128 times

[0121] Peak intensity at 1640 cm -1 was measured by drawing a baseline from the valley at about 1540 cm -1 , and measuring the height of the peak top from the baseline (I 1640 ).

[0122] Peak intensity at 1410 cm -1 was measured by taking a line connecting the valley at about 1420 cm -1 and the valley at about 1390 cm -1 as a baseline, and measuring the height of the peak top from the baseline (I 1410 ).

[0123] The relative absorbance intensity ratio was calculated as the ratio of I 1640 to I 1410 (I 1640 / I 1410 ).

[0124] For the measurement, the data "I 1640 / I 1410 calculated immediately after film formation was obtained.(X)", and data "I calculated from the measurement of the sample, after film formation, by placing in a high temperature and high humidity tank at 80°C, 90% RH for 24 hours, and then at room temperature (20°C, 65% RH) for 12 hours, (Y / X) x 100" 1640 / I 1410 (Y)", and calculating "(Y / X) x 100".

[0125] (Polymerization of the copolyester resin (A) for the coating layer)

[0126] In a stainless steel autoclave equipped with a stirrer, a thermometer, and a partial reflux condenser, dimethyl 2,6-naphthalene dicarboxylate 342.0 parts by mass, dimethyl terephthalate 35.0 parts by mass, dimethyl isophthalate-5-sodium sulfonate 35.5 parts by mass, ethylene glycol 198.6 parts by mass, 1,6-hexanediol 118.2 parts by mass, and tetra-n-butyl titanate 0.4 part by mass were charged, and an ester exchange reaction was performed at a temperature of 160°C to 220°C for 4 hours. Further, sebacic acid 60.7 parts by mass was added, and an esterification reaction was performed. Subsequently, the temperature was raised to 255°C, the reaction system was slowly depressurized, and a copolyester resin (A) was obtained by reaction at a reduced pressure of 30 Pa for 1 hour and 30 minutes. The obtained copolyester resin (A) was pale yellow and transparent. The specific viscosity of the copolyester resin (A) was measured, and the result was 0.72 dl / g. The glass transition temperature based on DSC was 40°C, and the number average molecular weight was 20000.

[0127] (Polymerization of the copolyester resin (B) for the coating layer)

[0128] In a stainless steel autoclave equipped with a stirrer, a thermometer, and a partial reflux condenser, dimethyl 2,6-naphthalene dicarboxylate 342.0 parts by mass, dimethyl terephthalate 35.0 parts by mass, dimethyl isophthalate-5-sodium sulfonate 35.5 parts by mass, ethylene glycol 198.6 parts by mass, 1,6-hexanediol 118.2 parts by mass, and tetra-n-butyl titanate 0.4 part by mass were charged, and an ester exchange reaction was performed at a temperature of 160°C to 220°C for 4 hours. Further, sebacic acid 60.7 parts by mass was added, and an esterification reaction was performed. Subsequently, the temperature was raised to 255°C, the reaction system was slowly depressurized, and a copolyester resin (A) was obtained by reaction at a reduced pressure of 30 Pa for 1 hour and 30 minutes. The obtained copolyester resin (A) was pale yellow and transparent. The specific viscosity of the copolyester resin (A) was measured, and the result was 0.72 dl / g. The glass transition temperature based on DSC was 40°C, and the number average molecular weight was 20000.

[0129] (Polymerization of the copolyester resin (C) for the coating layer)

[0130] In a stainless steel autoclave equipped with a stirrer, a thermometer, and a partial reflux condenser, dimethyl terephthalate 145.6 parts by mass, dimethyl isophthalate-5-sodium sulfonate 14.8 parts by mass, dimethyl azelate 43.3 parts by mass, ethylene glycol 80.7 parts by mass, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene 131.6 parts by mass, 3-methyl-l,5-pentanediol 70.9 parts by mass, and tetra-n-butyl titanate 0.4 part by mass were put in, and transesterification was carried out at a temperature of 160°C to 220°C for 4 hours. Subsequently, the temperature was raised to 255°C, and the reaction system was slowly depressurized, and then the reaction was carried out at a reduced pressure of 30 Pa for 1 hour and 30 minutes, to obtain a copolyester resin (C). The obtained copolyester resin (C) was pale yellow and transparent. The specific viscosity of the copolyester resin (C) was measured, and the result was 0.65 dl / g. The glass transition temperature based on DSC was 40°C, and the number average molecular weight was 19000.

[0131] (Polymerization of copolyester resin (D) for coating layer)

[0132] Dimethyl terephthalate was 194.2 parts by mass, dimethyl isophthalate was 184.5 parts by mass, dimethyl isophthalate-5-sodium sulfonate was 14.8 parts by mass, diethylene glycol was 233.5 parts by mass, ethylene glycol was 136.6 parts by mass, and tetra-n-butyl titanate was 0.2 part by mass, and in addition thereto, a copolyester resin (D) was obtained in the same manner as the polymerization of the resin (A). The specific viscosity of the obtained copolyester resin (D) was measured, and the result was 0.70 dl / g. The glass transition temperature based on DSC was 40°C.

[0133] (Preparation of polyester aqueous dispersions (Aw), (Bw), (Cw), (Dw))

[0134] In a reactor equipped with a stirrer, a thermometer, and a reflux device, 30 parts by mass of the copolyester resin (A) and 15 parts by mass of ethylene glycol n-butyl ether were put in, heated at 110°C, and stirred to dissolve the resin. After the resin was completely dissolved, 55 parts by mass of water was slowly added to the polyester solution while stirring. After the addition, the solution was stirred while being cooled to room temperature, to produce a milky white polyester resin (A) aqueous dispersion (resin A solution) (Aw) having a solid content of 25.0 mass%.

[0135] In the same manner, a polyester resin (B) aqueous dispersion (resin B solution) (Bw) in which the copolyester resin (B) was dissolved was produced.

[0136] In the same manner, a polyester resin (C) aqueous dispersion (resin C solution) (Cw) in which the copolyester resin (C) was dissolved was produced.

[0137] In the same manner, a water dispersion of a copolymer polyester resin (D) (resin D solution) (Dw) in which the copolymer polyester resin (D) was dissolved was prepared.

[0138] (Production of the polyurethane water dispersion (E))

[0139] [Polymerization of the water-dispersible polyurethane resin using an aliphatic polycarbonate polyol as a constituent component]

[0140] In a four-necked flask equipped with a stirrer, a condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 43.75 parts by mass of 4,4'-diphenylmethane diisocyanate, 12.85 parts by mass of dimethylolbutanoic acid, 153.41 parts by mass of polyhexamethylene carbonate diol having a number average molecular weight of 2000, 0.03 parts by mass of dibutyltin dilaurate, and 84.00 parts by mass of acetone as a solvent were charged, and the mixture was stirred at 75°C for 3 hours under a nitrogen atmosphere. The reaction solution was confirmed to have a predetermined amine equivalent. Subsequently, the reaction solution was cooled to 40°C, and 8.77 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Subsequently, in a reaction vessel equipped with a homogenizer capable of high-speed stirring, 450 g of water was added, and the temperature was adjusted to 25°C. While the mixture was stirred at 2000 rpm, the polyurethane prepolymer solution was added dropwise over 30 minutes. After the addition, the mixture was further stirred for 30 minutes. Subsequently, a portion of the acetone and water was removed under reduced pressure to prepare a water-soluble polyurethane resin solution (resin E solution) having a solid content of 37% by mass. The glass transition temperature of the obtained polyurethane resin was -30°C. -1 The polyurethane prepolymer solution was added dropwise while stirring and mixing. Subsequently, a portion of the acetone and water was removed under reduced pressure to prepare a water-soluble polyurethane resin solution (resin E solution) having a solid content of 37% by mass. The glass transition temperature of the obtained polyurethane resin was -30°C.

[0141] (Synthesis of the crosslinking agent P)

[0142] In a flask equipped with a stirrer, a thermometer, and a reflux condenser, 100 parts by mass of a polyisocyanate compound (NCO concentration: 23.1%) having an isocyanurate structure prepared from 1,6-hexamethylene diisocyanate according to a conventional method and 17.5 parts by mass of N-methylpyrrolidone were charged, and 35.00 parts by mass of 3,5-dimethylpyrazole was added dropwise under a nitrogen atmosphere at 70°C for 1 hour. Subsequently, 12.50 parts by mass of dimethylolpropionic acid was added dropwise. After the disappearance of the absorption of the isocyanate group was confirmed by measuring the infrared spectrum of the reaction solution, 8.72 parts by mass of N,N-dimethylethanolamine was added. After stirring for 1 hour in this state, an appropriate amount of water was added to obtain a blocked isocyanate water dispersion (crosslinking agent P solution) having a solid content of 40% by mass.

[0143] (Synthesis of the crosslinking agent Q)

[0144] In a flask equipped with a stirrer, a thermometer, and a reflux condenser, 100 parts by mass of a polyisocyanate compound having an isocyanurate structure (NCO concentration: 23.3%) prepared from hexamethylene diisocyanate according to a conventional method, 17.5 parts by mass of N-methylpyrrolidone, and 35.00 parts by mass of 3,5-dimethylpyrazole were added, and the mixture was stirred at 70°C for 1 hour under a nitrogen atmosphere.

[0145] After that, 12.50 parts by mass of dimethylolpropionic acid was added dropwise. After confirming disappearance of absorption of isocyanate groups by measuring infrared spectrum of the reaction solution, 8.72 parts by mass of N,N-dimethylethanolamine was added. After stirring for 1 hour in this state, an appropriate amount of water was added to obtain a blocked isocyanate water dispersion liquid (crosslinking agent Q solution) having a solid content of 40% by mass.

[0146] (Synthesis of Crosslinking Agent R)

[0147] In a flask equipped with a stirrer, a thermometer, and a reflux condenser, 100 parts by mass of a polyisocyanate compound having an isocyanurate structure (NCO concentration: 23.1%) prepared from 2,5-diisocyanatothiophene according to a conventional method, 17.5 parts by mass of N-methylpyrrolidone, and 35.00 parts by mass of 3,5-dimethylpyrazole were added, and the mixture was stirred at 70°C for 1 hour under a nitrogen atmosphere.

[0148] After that, 12.50 parts by mass of dimethylolpropionic acid was added dropwise. After confirming disappearance of absorption of isocyanate groups by measuring infrared spectrum of the reaction solution, 8.72 parts by mass of N,N-dimethylethanolamine was added. After stirring for 1 hour in this state, an appropriate amount of water was added to obtain a blocked isocyanate water dispersion liquid (crosslinking agent R solution) having a solid content of 40% by mass.

[0149] (Synthesis of Crosslinking Agent S)

[0150] In a flask equipped with a stirrer, a thermometer, and a reflux condenser, 168 parts by mass of hexamethylene diisocyanate and 220 parts by mass of polyethylene glycol monomethyl ether (average molecular weight: 400) were added, and the mixture was stirred at 120°C for 1 hour. Further, 26 parts by mass of 4,4'-dicyclohexylmethane diisocyanate and 3.8 parts by mass of 3-methyl-1-phenyl-2-phospho-1-oxide as a carbodiimide catalyst (2% by mass relative to the total isocyanate) were added, and the mixture was further stirred at 185°C for 5 hours under a nitrogen stream. After confirming disappearance of absorption of isocyanate groups by measuring infrared spectrum of the reaction solution, the mixture was naturally cooled to 60°C. Further, 567 parts by mass of ion exchange water was added to obtain a carbodiimide crosslinking agent (crosslinking agent S solution) having a solid content of 40% by mass.

[0151] (Synthesis of Crosslinking Agent T)

[0152] In a flask equipped with a stirrer, a thermometer, and a reflux condenser, 100 parts by mass of a polyisocyanate compound having an isocyanurate structure (NCO concentration: 22.3%) prepared from 2,4-tolylene diisocyanate according to a conventional method, 17.5 parts by mass of N-methylpyrrolidone, and 35.00 parts by mass of 3,5-dimethylpyrazole were added dropwise. The mixture was stirred at 70°C for 1 hour under a nitrogen atmosphere.

[0153] After that, 12.50 parts by mass of dimethylolpropionic acid was added dropwise. After confirming that the absorption of isocyanate groups disappeared by measuring the infrared spectrum of the reaction solution, 8.72 parts by mass of N,N-dimethylethanolamine was added. After stirring the mixture for 1 hour, an appropriate amount of water was added to obtain a blocked isocyanate water dispersion (crosslinking agent T solution) having a solid content of 40% by mass.

[0154] (Zirconia particles)

[0155] In a 3-liter glass container, 2283.6 g of pure water and 403.4 g of oxalic acid dihydrate were put, and the mixture was heated to 40°C to prepare a 10.72% by mass oxalic acid aqueous solution. While the aqueous solution was stirred, 495.8 g of zirconium carbonate powder (ZrOCO3, manufactured by AMR International Corp., containing 39.76% by mass in terms of ZrO2) was slowly added, and the mixture was stirred for 30 minutes and then heated at 90°C for 30 minutes. Then, 1747.2 g of 25.0% by mass tetramethylammonium hydroxide aqueous solution (manufactured by Tomy Chemical Industry Co., Ltd.) was slowly added over 1 hour. At this time, the mixture was in a slurry state and contained 4.0% by mass in terms of ZrO2. The slurry was transferred to a stainless autoclave container, and subjected to hydrothermal treatment at 145°C for 5 hours. The product after the hydrothermal treatment was completely sol-gelized without ungelatinized matter. The obtained sol contained 4.0% by mass in terms of ZrO2, had a pH of 6.8, and had an average particle diameter of 19 nm based on the dynamic light scattering method. In addition, the transmittance of the sol adjusted to a ZrO2 concentration of 2.0% by mass with pure water was 88%. The particles were observed by transmission electron microscopy, and the result showed that the particles were mainly aggregated particles of ZrO2 primary particles of about 7 nm. For 4000 g of the zirconia sol having a ZrO2 concentration of 4.0% obtained by the above hydrothermal treatment, an ultrafiltration device was used to perform washing and concentration while slowly adding pure water, and 953 g of a zirconia sol having a ZrO2 concentration of 13.1% by mass, a pH of 4.9, and a transmittance of 76% at a ZrO2 concentration of 13.1% by mass was obtained. The refractive index of the obtained zirconia-based fine particles was 1.75.

[0156] (Zirconia sol)

[0157] To 300 g of the zirconia sol having a ZrO2 concentration of 13.1 mass% obtained by the above-described washing and concentration, 3.93 g of a 20 mass% aqueous citric acid solution and 11.0 g of a 25 mass% aqueous tetramethylammonium hydroxide solution were added, and then concentration was further performed using an ultrafiltration device, and as a result, 129 g of a high-concentration zirconia sol having a ZrO2 concentration of 30.5 mass% was obtained. The obtained high-concentration zirconia sol had a pH of 9.3 and an average particle diameter of 19 nm based on a dynamic light scattering method. In addition, the zirconia sol had no precipitate and was stable for one month or more at 50°C.

[0158] (titanium oxide sol)

[0159] An aqueous titanium tetrachloride solution containing 7.75 mass% of titanium tetrachloride (manufactured by Osaka Titanium Technologies Co., Ltd.) in terms of TiO2 basis, 12.09 kg, was mixed with ammonia water (manufactured by Ube Industries, Ltd.) containing 15 mass% of ammonia, 4.69 kg, to prepare a white slurry solution having a pH of 9.5. Next, the slurry was filtered and washed with pure water to obtain a wet titanium oxide filter cake having a solid content of 10 mass%, 9.87 kg. Next, to the filter cake, an aqueous hydrogen peroxide solution (manufactured by Mitsubishi Gas Chemical Company, Inc.) containing 35 mass% of hydrogen peroxide, 11.28 kg, and pure water, 20.00 kg, were added, and then the mixture was heated at 80°C for 1 hour under stirring, and further, pure water, 57.52 kg, was added to obtain an aqueous peroxotitanic acid solution containing 1 mass% of peroxotitanic acid in terms of TiO2 basis, 98.67 kg. The aqueous peroxotitanic acid solution was transparent yellowish brown and had a pH of 8.5.

[0160] Next, cation exchange resin (manufactured by Mitsubishi Chemical Corporation), 4.70 kg, was mixed in the above-described aqueous peroxotitanic acid solution, 98.67 kg, and to the mixture, an aqueous potassium stannate solution containing 1 mass% of potassium stannate (manufactured by Showa Chemical Industry Co., Ltd.) in terms of SnO2 basis, 12.33 kg, was slowly added under stirring. Next, the cation exchange resin incorporating potassium ions and the like was separated, and then the mixture was put in an autoclave (manufactured by Nitto Kogyo Industries Co., Ltd., 120 L) and heated at 165°C for 18 hours.

[0161] (titanium oxide sol)

[0162] Next, the obtained mixed aqueous solution was cooled to room temperature, and then concentrated with an ultrafiltration device (manufactured by Asahi Chemical Industry Co., Ltd., ACV-3010) to obtain a water dispersion sol 9.90 kg containing titanium-based fine particles (hereinafter, referred to as "P-1") having a solid content of 10 mass%. The solid content in the sol thus obtained was measured by the above-described method, and as a result, titanium-based fine particles (primary particles) having a crystal structure of rutile type and formed of a composite oxide containing titanium and tin were contained. Further, the content of the metal components contained in the titanium-based fine particles was measured, and as a result, the metal components were as follows on a basis of oxide conversion: TiO2 87.2 mass%, SnO2 11.0 mass%, and K2O 1.8 mass%. In addition, the pH of the mixed aqueous solution was 10.0. Further, the water dispersion sol containing the aforementioned titanium-based fine particles was transparent and milky white, the average particle diameter of the aforementioned titanium-based fine particles contained in the water dispersion sol was 35 nm, and the distribution frequency of coarse particles having a particle diameter of 100 nm or more was 0%. Further, the refractive index of the titanium-based fine particles thus obtained was 2.42.

[0163] (Zirconium oxide / titanium oxide mixed sol)

[0164] The zirconium oxide particles and the titanium oxide particles obtained in the above were mixed at respective ratios to prepare a zirconium oxide / titanium oxide mixed sol having a solid content concentration of 13 mass%.

[0165] (Formation of hard coat layer)

[0166] On the surface opposite to the surface to which a polarizing plate was bonded in the polyester film manufactured in the Examples described later, a hard coat layer-forming coating solution of the following composition was applied with a #14 wire bar, and dried at 70°C for 1 minute to remove the solvent. Next, the film on which the hard coat layer was applied was irradiated with 300 mJ / cm2of ultraviolet rays from a high-pressure mercury lamp to obtain a polarizing plate protective film having a hard coat layer with a thickness of 7 μm. 2

[0167] The coating solution used in the formation of the hard coat layer was prepared as follows.

[0168] (Preparation of hard coat layer-forming coating solution L)

[0169]

[0170]

[0171] The aromatic component in the entire resin in the prepared hard coat layer-forming coating solution L was 13.3% on a molar basis.

[0172] (Preparation of hard coat layer-forming coating solution M)

[0173] ​

[0174] The aromatic component in the prepared coating solution M for hard coat layer formation was 5.4% by mole ratio in the total resin.

[0175] (Preparation of coating solution N for hard coat layer formation)

[0176]

[0177]

[0178] The aromatic component in the prepared coating solution N for hard coat layer formation was 19.3% by mole ratio in the total resin.

[0179] (Example 1)

[0180] (Adjustment of coating solution)

[0181] A coating solution having the following composition was adjusted.

[0182]

[0183] (Production of easy-adhesion polyester film)

[0184] A PET resin pellet having an intrinsic viscosity (solvent: phenol / tetrachloroethane = 60 / 40) of 0.62 dl / g and substantially no particles was dried at 135°C for 6 hours under a reduced pressure of 133 Pa, and then supplied to an extruder to be melt-extruded into a sheet at about 280°C. The sheet was rapidly cooled and solidified on a rotating cooling metal roll maintained at a surface temperature of 20°C to obtain an unstretched PET sheet.

[0185] The unstretched PET sheet was heated to 100°C using a heated roll set and an infrared heater, and then stretched 3.5 times in the length direction using a roll set having a difference in peripheral speed to obtain a uniaxially stretched PET film.

[0186] Then, the above coating solution was applied to one side of the PET film by roll coating, and dried at 80°C to adjust the dried coating amount after final stretching to 0.12 g / m 2 Then, the film was stretched to 4.0 times in the width direction at 150°C in a tenter, heated at 230°C while the length in the width direction of the film was fixed, and further subjected to width direction relaxation treatment at 230°C to obtain an easy-adhesion polyester film having a thickness of 38 μm.

[0187] The absorbance of the easy-adhesion layer of the obtained easy-adhesion polyester film was measured by infrared spectroscopy, and the absorption intensity (I -1 of the peak attributable to the urea compound was calculated. 1640) and 1410 cm -1 The relative absorption intensity ratio "(I 1410 ) of the absorption intensity (I 1640 / I 1410 ) of the peak of the polyester resin was 1.375.

[0188] Next, using the aforementioned coating liquid A for forming a hard coat layer, a laminated polyester film was obtained in which a hard coat layer was formed on the easy-adhesion layer of the obtained easy-adhesion polyester film according to the aforementioned forming method.

[0189] The adhesion of the hard coat layer of the obtained laminated polyester film was evaluated, and the adhesion force was 100%.

[0190] Further, the obtained easy-adhesion polyester film was left in an 80°C, 90% RH environment for 24 hours in a high-temperature high-humidity tank, and then left at room temperature for 12 hours. Thereafter, the absorbance was measured by infrared spectroscopy on the easy-adhesion layer of the treated easy-adhesion polyester film, and the relative absorption intensity ratio "(I 1640 / I 1410 ) (Y)" was calculated, and the result was 1.750.

[0191] According to this result, when (Y / X) x 100 was calculated, it was 127.

[0192] Next, a hard coat layer was formed on the easy-adhesion layer of the treated easy-adhesion polyester film using a coating liquid L for forming a hard coat layer, and a laminated polyester film was obtained.

[0193] The adhesion of the hard coat layer of the obtained laminated polyester film was evaluated, and the adhesion force was 100%. In addition, the adhesion (hot and humid resistance) after the easy-adhesion polyester film was left in an 80°C, 90% RH environment was evaluated, and the result was 100%.

[0194] (Example 2)

[0195] A coating liquid having the following composition was adjusted, and otherwise, an easy-adhesion polyester film was obtained in the same manner as in Example 1.

[0196]

[0197] Evaluation of the obtained easy-adhesion polyester film was performed in the same manner as in Example 1, and the results are described in Table 1.

[0198] (Example 3)

[0199] A coating liquid having the following composition was adjusted, and otherwise, an easy-adhesion polyester film was obtained in the same manner as in Example 1.

[0200]

[0201]

[0202] The obtained easily-adherable polyester film was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0203] (Example 4)

[0204] The obtained easily-adherable polyester film was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0205] (Example 5)

[0206] The obtained easily-adherable polyester film was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0207] (Example 6)

[0208] The obtained easily-adherable polyester film was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0209] (Example 7)

[0210] The obtained easily-adherable polyester film was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0211] (Example 8)

[0212] The obtained easily-adherable polyester film was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0213] (Example 9)

[0214] The obtained easily-adherable polyester film was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0215]

[0216] The obtained easily-adherable polyester film was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0217] (Example 10)

[0218] A coating solution having the following composition was adjusted, and otherwise, an easily-adherable polyester film was obtained in the same manner as in Example 1.

[0219]

[0220]

[0221] Evaluation of the obtained easily-adherable polyester film was performed in the same manner as in Example 1, and the results are described in Table 1.

[0222] (Example 11)

[0223] A coating solution having the following composition was adjusted, and otherwise, an easily-adherable polyester film was obtained in the same manner as in Example 1.

[0224]

[0225] Evaluation of the obtained easily-adherable polyester film was performed in the same manner as in Example 1, and the results are described in Table 1.

[0226] (Examples 12-13)

[0227] The type of hard coating liquid applied to the obtained easily-adherable polyester film was changed as described in Table 1, and otherwise, an easily-adherable polyester film was obtained in the same manner as in Example 1. Evaluation of the obtained easily-adherable polyester film was performed in the same manner as in Example 1, and the results are described in Table 1.

[0228] (Comparative Example 1)

[0229] A coating solution having the following composition was adjusted, and otherwise, an easily-adherable polyester film was obtained in the same manner as in Example 1.

[0230]

[0231] Evaluation of the obtained easily-adherable polyester film was performed in the same manner as in Example 1, and the results are described in Table 1.

[0232] (Comparative Example 2)

[0233] A coating solution having the following composition was adjusted, and otherwise, an easily-adherable polyester film was obtained in the same manner as in Example 1.

[0234]

[0235]

[0236] Evaluation of the obtained easily-adherable polyester film was performed in the same manner as in Example 1, and the results are described in Table 1.

[0237] (Comparative Example 3)

[0238] The coating solution was adjusted using the resin D solution, and otherwise, the easily-adherable polyester film was obtained in the same manner as in Example 1. Evaluation of the obtained easily-adherable polyester film was performed in the same manner as in Example 1, and the results are described in Table 1.

[0239] (Comparative Example 4)

[0240] The coating solution was adjusted using the resin D solution, and otherwise, the easily-adherable polyester film was obtained in the same manner as in Example 1. Evaluation of the obtained easily-adherable polyester film was performed in the same manner as in Example 1, and the results are described in Table 1.

[0241]

[0242]

[0243] Evaluation of the obtained easily-adherable polyester film was performed in the same manner as in Example 1, and the results are described in Table 1.

[0244] (Comparative Example 5)

[0245] The coating solution was adjusted using the resin D solution, and otherwise, the easily-adherable polyester film was obtained in the same manner as in Example 1. Evaluation of the obtained easily-adherable polyester film was performed in the same manner as in Example 1, and the results are described in Table 1.

[0246] [Table 1]

[0247]

[0248] Industrial Applicability

[0249] According to the present application, an easily-adherable polyester film that ensures reliable adhesion after long-term storage in a high-temperature high-humidity environment can be provided, and application to optical uses and the like becomes easier.

Claims

1. An easily adhesive polyester film, comprising an easily adhesive polyester film having a coating layer on at least one side of the polyester film, said coating layer being formed by curing a composition comprising a polyester having a polycyclic aromatic backbone and an isocyanate crosslinking agent having at least one backbone selected from aliphatic, alicyclic, and heterocyclic groups, said composition not containing isocyanate having an aromatic backbone, wherein when the surface of the coating layer on the side not in contact with the polyester film is measured by Fourier transform infrared spectroscopy (FT-IR), the 1640 cm⁻¹ of the coating layer is attributed to urea groups. -1 The absorption intensity of the peak (I) 1640 ) and the CH stretching of which will be attributed to polyester 1410cm -1 The absorption intensity of the peak (I) 1410 The relative absorption intensity ratio (I) 1640 / I 1410 When subject to constraints, the following relationship must be satisfied: The relative absorbance intensity ratio (X) of the easily-adhesive polyester film after film formation satisfies the following relation with the relative absorbance intensity ratio (Y) of the polyester film after being left in an environment of 80°C, 90% RH for 24 hours, 110 ≤ (Y / X) x 100 ≤ 140 (1).

2. The easily-adhesive polyester film according to claim 1, wherein The polyester having a polycyclic aromatic skeleton is a polyester having a naphthalene skeleton.

3. The easily-adhesive polyester film according to claim 1 or 2, wherein When the hard coating layer containing the resin having an aromatic skeleton is provided on the surface of the coating layer, the adhesion is 95% or more.

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