Easy-to-adhere polyester film

Abstract

To provide an easily-adhesive polyester film that has excellent adhesion to a functional layer, such as a hard coat layer and an adhesive agent, and also provide a laminated polyester film provided with the functional layer.SOLUTION: The present invention pertains to an easily-adhesive polyester film having a polyester film substrate and a coating layer on at least one surface thereof. The coating layer is formed from a composition containing a polycarbonate polyurethane resin and a polyester resin. The polycarbonate polyurethane resin and the polyester resin each include a cyclohexane ring in a molecule, and have a structure in which at least one hydrogen atom on the cyclohexane ring is substituted with a hydrocarbon group. The easily-adhesive polyester film satisfies a formula (1): X-Y(%)≤5 (where X represents the adhesion (%) between the polyester film and the functional layer when the functional layer is formed on the coating layer of the easily-adhesive polyester film to prepare the laminated polyester film; Y represents the adhesion (%) between the polyester film and the functional layer when the easily-adhesive polyester film is kept at 80°C and 90% RH for 24 hours and then left at room temperature for 12 hours, and subsequently the functional layer is formed on the coating layer of the easily-adhesive polyester film to prepare the laminated polyester film; where, the adhesion is determined in accordance with a criteria of section 8.5.1 in JIS-K5400-1990.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an easily adherable polyester film with excellent adhesion to various functional layers, and a laminated polyester film having said functional layer. [Background technology]

[0002] A hard coat film, which consists of a transparent hard coat layer laminated onto the front surface of displays such as touch panels, computers, televisions, and liquid crystal displays, as well as decorative materials, is used. Panel components used in displays are formed by bonding a hard coat film to a polarizer or to other components, and an adhesive component is applied to the bonding process.

[0003] A transparent polyester film is commonly used as the base material, and in order to improve the adhesion between the polyester film base material, the hard coat layer, and the adhesive, an easily adhesive coating layer is often provided on the surface of the polyester film as an intermediate layer.

[0004] The aforementioned hard coat film is required to have durability against temperature, humidity, and light, as well as transparency, chemical resistance, scratch resistance, and stain resistance. Furthermore, since it is often used on the surface of displays and decorative materials, visibility and aesthetic appeal are required. For this reason, in order to suppress glare and iridescent colors caused by reflected light when viewed from any angle, it is common practice to provide a multilayer anti-reflective layer on top of the hard coat layer, which consists of layers of high refractive index and low refractive index stacked on top of each other.

[0005] In recent years, hard coat layers with various compositions have been developed, and the adhesion between the substrate and the hard coat layer is being discussed according to its composition. For example, when a film with a laminated hard coat layer is used as a display for a liquid crystal television, in order to ensure high reliability for long-term use, not only initial adhesion immediately after lamination but also properties such as resistance to humidity and heat, and adhesion retention over time are required.

[0006] The same applies to the aforementioned adhesives, which are required to have durability against temperature, humidity, and light, as well as transparency, chemical resistance, scratch resistance, and stain resistance. Furthermore, since they are often used on the surfaces of displays and decorative materials, visibility or aesthetic appeal is required. In recent years, adhesives with various compositions have been developed, and the adhesion between the substrate and the adhesive is being discussed according to its composition. For example, when components bonded with adhesive are used in the display of an LCD television, in order to ensure high reliability for long-term use, not only initial adhesion immediately after lamination but also resistance to humidity and heat, and adhesion retention over time are required.

[0007] In liquid crystal display devices, due to their image formation method, polarizing plates are arranged on both sides of the glass substrate that forms the surface of the liquid crystal panel. Generally, the polarizing plates have a structure in which a polarizer made of a polyvinyl alcohol-based film and a dichroic material such as iodine is bonded to both sides of the polarizer via a hydrophilic adhesive such as a polyvinyl alcohol-based resin. Conventionally, triacetylcellulose film has been used as the protective film for protecting the polarizer due to its optical properties and transparency.

[0008] However, triacetylcellulose does not have sufficient durability, and when polarizers using triacetylcellulose film as a polarizer protective film are used under high temperature or high humidity conditions, the performance of the polarizer, such as polarization degree and hue, may deteriorate. Furthermore, in recent years, there has been a demand for thinner polarizers to accommodate the thinning of displays, but there have been limitations to thinning triacetylcellulose film while maintaining moisture barrier properties. Therefore, the use of polyester film as a polarizer protective film with durability and moisture barrier properties has been proposed (see, for example, Patent Document 1).

[0009] Triacetylcellulose film, used as a protective film for polarizers, has its surface treated with alkali or other methods, giving it extremely high affinity for hydrophilic adhesives. Therefore, protective films made of triacetylcellulose film have extremely high adhesion to polarizers coated with hydrophilic adhesives. However, polyester films have insufficient adhesion to hydrophilic adhesives, and this tendency is even more pronounced in the case of polyester films that have orientation due to stretching treatment. Therefore, in order to improve the adhesion to polarizers or hydrophilic adhesives applied to polarizers, it has been reported that a coating layer is provided by coating the surface of a polyester film with a highly hydrophilic material (see, for example, Patent Document 1).

[0010] In the field of conventional easily adhering polyester films, it has been reported that laminated polyester films, in which a coating layer containing a polyester resin with a naphthalenedicarboxylic acid component is provided on at least one side of the polyester film, exhibit excellent adhesion to surface functional layers such as hard coat layers (see, for example, Patent Document 2).

[0011] Furthermore, it has been reported that an easily adhesive polyester film, in which a coating layer containing a polyurethane resin composed of aliphatic polycarbonate polyol, which has excellent flexibility and adhesion, is provided on at least one side of the polyester film, exhibits excellent adhesion to an optical functional layer under high temperature and high humidity conditions (see, for example, Patent Document 3). However, although adhesion was confirmed in all cases, no easily adhesive polyester film with excellent adhesion after long-term storage had been obtained. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] Japanese Patent Publication No. 2013-063610 [Patent Document 2] Japanese Patent Publication No. 2011-246663 [Patent Document 3] Japanese Patent Publication No. 2011-168053 [Overview of the project] [Problems that the invention aims to solve]

[0013] This invention was made against the backdrop of the problems of the prior art. Specifically, the object of this invention is to provide an easily adhesive polyester film with excellent adhesion to functional layers such as hard coat layers and adhesives. It is also to provide a laminated polyester film equipped with such functional layers.

[0014] The inventors of this invention have diligently studied and developed the present invention to achieve the above objective. Specifically, the present invention has the following configuration.

[0015] [1] An easily adherable polyester film having a polyester film substrate and a coating layer on at least one side thereof, wherein the coating layer is formed from a composition comprising a polycarbonate polyurethane resin and a polyester resin, and both the polycarbonate polyurethane resin and the polyester resin contain a cyclohexane ring in their respective molecules, and have a structure in which at least one hydrogen atom on the cyclohexane ring is substituted with a hydrocarbon group. [2] The easy-to-adhere polyester film according to [1], wherein both the polycarbonate polyurethane resin and the polyester resin have a structure represented by formula (1) in their respective molecules. [ka] (In the formula, * indicates a bonding site.) [3] The easily adhering polyester film according to [2], wherein the structure represented by formula (1) is the structure represented by formula (2). [ka] (In the formula, * is the same as above.) [4] The easily adherable polyester film according to [3], wherein the structure represented by the formula (2) is the structure represented by the formula (3).

Chemical formula

Advantages of the Invention

[0016] The easily adherable polyester film of the present invention is excellent in the adhesion between the functional layer and the polyester film (especially the adhesion after long - term storage, etc.), and has high adhesion reliability. Also, it has excellent blocking resistance and transparency. Therefore, it can be widely applied to optical applications and the like.

Embodiments for Carrying out the Invention

[0017] polyester film The polyester film used as a base material in the easily adhesive polyester film of the present invention is a film mainly composed of polyester resin. Here, "a film mainly composed of polyester resin" means a film formed from a resin composition containing 50% by mass or more of polyester resin. When blended with other polymers (e.g., polycarbonate resin, polyimide resin, etc.), it means that the polyester resin is contained at 50% by mass or more, and when copolymerized with other monomers, it means that the polyester structural units are contained at 50 mol% or more. Preferably, the polyester film contains 90% by mass or more of polyester resin, more preferably 95% by mass or more, and even more preferably 100% by mass.

[0018] The polyester resin material is not particularly limited, but copolymers formed by polycondensation of a dicarboxylic acid component and a diol component, or blended resins thereof, can be used. Examples of dicarboxylic acid components that make up polyester resins include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfoncarboxylic acid, anthracenedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, azelaic acid, dimeric acid, sebacic acid, suberic acid, and dodecadicarboxylic acid.

[0019] Examples of diol components that make up polyester resins include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexadiol, 2,2-bis(4-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)sulfone.

[0020] The dicarboxylic acid component and the diol component may be one or more of each. Other polycarboxylic acid components such as trimellitic acid and other polyol components such as trimethylolpropane may also be added as appropriate.

[0021] Examples of polyester resins include polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, among which polyethylene terephthalate is preferred due to its balance of physical properties and cost. Furthermore, it is preferable to include other copolymerization components or other polymers to control optical properties such as polarization. From the viewpoint of controlling the optical properties of the polyester film, preferred copolymerization components include diethylene glycol and copolymerization components having norbornene in their side chains.

[0022] The intrinsic viscosity of polyester resin (solvent:phenol / tetrachloroethane = 60:40) is, for example, 0.50 to 1.0 dl / g.

[0023] To improve the handling properties of polyester films, such as their slipperiness and windability, inert particles can be incorporated into the film. Examples of inert particles include inorganic particles such as silica, kaolinite, talc, light calcium carbonate, heavy calcium carbonate, zeolite, alumina, barium sulfate, carbon black, zinc oxide, zinc sulfate, zinc carbonate, titanium dioxide, satin white, aluminum silicate, diatomaceous earth, calcium silicate, aluminum hydroxide, hydrated halloysite, magnesium carbonate, and magnesium hydroxide. The average particle size of the inert particles can range from 200 to 5000 nm, and more specifically, from 250 to 4500 nm. This average particle size is measured using the method described in the examples (average particle size based on the number of particles measured by SEM). To maintain high transparency, it is preferable to keep the amount of inert particles in the film as low as possible. Therefore, it is preferable to have a multilayer structure in which particles are contained only on the surface layer of the film, or to contain fine particles only in a coating layer laminated on at least one side of the polyester film, without substantially containing particles in the film itself.

[0024] Furthermore, "substantially free of particles" means, for example, in the case of inorganic particles, that when elements derived from the particles are quantitatively analyzed by X-ray fluorescence analysis, the content is 50 ppm or less, preferably 10 ppm or less, and most preferably below the detection limit. This is because even without actively adding particles to the base film, contaminants from foreign substances or dirt adhering to the raw resin or film manufacturing process lines and equipment may inevitably detach and become mixed into the film.

[0025] Furthermore, when the polyester film has a multilayer structure, it is possible to have a two-type, three-layer structure in which the inner layers substantially do not contain inert particles, and inert particles are contained only in the outermost layers (the second layer). This makes it possible to achieve both transparency and processability, which is preferable.

[0026] The polyester film used as the base material may be a single layer or a laminate of two or more layers. Furthermore, various additives can be included in the film as needed, within the limits of achieving the effects of the present invention. Examples of additives include antioxidants, lightfastness agents, gelation inhibitors, organic wetting agents, antistatic agents, ultraviolet absorbers, and surfactants. If the film has a laminated structure, it is also preferable to include additives according to the function of each layer as needed. For example, it is a preferred embodiment to add an ultraviolet absorber or the like to the inner layer to prevent light degradation of the polarizer.

[0027] Polyester film can be manufactured according to conventional methods. For example, it can be obtained by melt-extruding a material containing the above-mentioned polyester resin into a film shape and then cooling and solidifying it in a casting drum. In the present invention, either an unstretched film or a stretched film can be used as the polyester film, but a stretched film is preferred in terms of durability such as mechanical strength and chemical resistance.

[0028] When the polyester film is a stretched film, the stretching method is not particularly limited, and methods such as longitudinal uniaxial stretching, transverse uniaxial stretching, longitudinal and transverse sequential biaxial stretching, and longitudinal and transverse simultaneous biaxial stretching can be employed. When stretching a polyester film, the stretching may be performed before laminating the easily adhesive coating layer described later, or after laminating the easily adhesive coating layer. It is also possible to uniaxially stretch in the longitudinal or transverse direction before laminating the easily adhesive coating layer, and then stretch in the other direction after laminating the coating layer.

[0029] Coating layer The easily adhering polyester film of the present invention has an easily adhering coating layer laminated on at least one surface of the polyester film substrate described above. The coating layer can be formed from a composition containing a binder resin and, if necessary, additives.

[0030] The composition of each layer of the coating layer is described in detail below. The binder resin constituting the coating layer is an easily adhesive resin and includes polycarbonate polyurethane resin, which is a urethane resin having a polycarbonate structure, and polyester resin. In both resins, the molecule contains a cyclohexane ring, and at least one hydrogen atom on the cyclohexane ring has a structure in which it is substituted with a hydrocarbon group. In other words, at least one hydrogen atom on the cyclohexane ring has a structure in which it is bonded to a carbon atom of a hydrocarbon group (for example, an alkyl group having 1 to 3 carbon atoms, an alkylene group having 1 to 3 carbon atoms, etc.). By adopting such a coating layer, the adhesion between the polyester film substrate and the functional layer is dramatically improved.

[0031] One reason for this is the good compatibility between the composition of the coating layer and the functional layer described later. The functional layer is obtained by UV curing with UV irradiation and has a crosslinked network structure. Since both the polycarbonate polyurethane resin and the polyester resin of the coating layer are resins that contain units with cyclohexane rings, interactions occur between the resins, making them more compatible and prone to entanglement. Furthermore, it is believed that these entangled resins become intertwined with the network structure of the functional layer formed on top of it, resulting in a coating layer with superior adhesion compared to conventional methods. In addition, because the coating layer contains polyester resin, the adhesion to the polyester film substrate is also improved, resulting in a coating layer with even better adhesion.

[0032] Polycarbonate polyurethane resins and polyester resins have a structure in which at least one hydrogen atom on the cyclohexane ring is substituted with a hydrocarbon group, and an example of such a structure is the structure represented by formula (1). [ka] (In the formula, * indicates a bonding site.) Here, * represents a site that bonds with an atom constituting the resin. Examples of such atoms, which may be the same or different, include hydrogen atoms, carbon atoms, oxygen atoms, nitrogen atoms, etc. It is preferable that at least one of the two *s is a carbon atom, oxygen atom, nitrogen atom, etc.

[0033] The structure represented by formula (2) is preferred over the structure represented by formula (1). [ka] (In the formula, * is the same as above.)

[0034] The structure represented by formula (3) is preferred over the structure represented by formula (2). [ka] (In the formula, * is the same as above.)

[0035] The structure represented by formula (3) above is more preferably derived from cyclohexanedimethanol (particularly 1,4-cyclohexanedimethanol). In this case, the two * symbols become sites that bond with oxygen atoms constituting the resin.

[0036] In polycarbonate polyurethane resins, it is necessary that the molecule contains a cyclohexane ring, and that at least one hydrogen atom on the cyclohexane ring is substituted with a hydrocarbon group.

[0037] The content of cyclohexane ring structures in polycarbonate polyurethane resin is typically 5% by mass or more and 55% by mass or less, preferably 10% by mass or more and 50% by mass or less, and more preferably 15% by mass or more and 45% by mass or less. If the content is 5% by mass or more, there are enough cyclohexane ring units for the resins to interact with each other, so the strength of the resin in the coating layer is maintained and adhesion under high temperature and high humidity conditions is likely to be good. If the content is 55% by mass or less, the flexibility of the resin in the coating layer is maintained and adhesion under room temperature and high temperature and high humidity conditions is likely to be good. The content of cyclohexane ring structures in polycarbonate polyurethane resin is the amount of cyclohexane ring structures (C6H) per 100g of total mass of polycarbonate polyurethane resin. 10 This is the calculation of the mass ratio of -CH2-). Specifically, it can be calculated from "the molecular weight and mole percent of each component constituting the polycarbonate polyurethane resin, such as the polycarbonate diol component and the diisocyanate component," "the mole percent of the component having a cyclohexane ring," and "the proportion of the molecular weight of the cyclohexane ring structure within the molecular weight of the component having a cyclohexane ring."

[0038] Polycarbonate polyurethane resin is formed by the addition reaction of a polycarbonate diol component, a diisocyanate component, and, if necessary, a diol component as a chain extender. At least one of these components contains a cyclohexane ring, and at least one hydrogen atom on the cyclohexane ring is substituted with a hydrocarbon group.

[0039] Examples of diol components necessary for preparing polycarbonate polyurethane resin include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediethanol, decamethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexadiol, 2,2-bis(4-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)sulfone. Among these, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, and 1,4-cyclohexanediethanol are particularly preferred because they have a structure in which at least one hydrogen atom on the cyclohexane ring is substituted with a hydrocarbon group. These diol components can be used individually or in combination of two or more. There are no particular limitations on the ratio when combining two or more, and the ratio can be adjusted to obtain a polycarbonate polyurethane with the desired properties.

[0040] Examples of diisocyanate components necessary for preparing polycarbonate polyurethane resin include toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylene diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, 4,4-methylenebiscyclohexyl diisocyanate, 1,2-bis(isocyanatomethyl)cyclohexane, and 1,4-bis(isocyanatomethyl)cyclohexane. Among these, isophorone diisocyanate, 4,4-methylenebiscyclohexyl diisocyanate, 1,2-bis(isocyanatomethyl)cyclohexane, and 1,4-bis(isocyanatomethyl)cyclohexane are particularly preferred because they have a structure in which at least one hydrogen on the cyclohexane ring is substituted with a hydrocarbon group. Furthermore, these isocyanate components can be used individually or in combination of two or more. There are no particular restrictions on the ratio when combining two or more materials; the ratio can be adjusted to obtain polycarbonate polyurethane with the desired properties.

[0041] The polyester resin used in combination with the polycarbonate polyurethane resin also contains a cyclohexane ring in its molecule, and has a structure in which at least one hydrogen atom on the cyclohexane ring is substituted with a hydrocarbon group.

[0042] The content of cyclohexane ring structures in the polyester resin is usually 5% by mass or more and more preferably 20% by mass or less, and more preferably 10% by mass or more and more than 15% by mass or less. A content of 20% by mass or less makes it easier to ensure the mobility and flexibility of the resin, while a content of 5% by mass or more ensures a sufficient number of cyclohexane ring structure units that interact with the polycarbonate polyurethane resin, thereby ensuring the strength of the resin in the coating layer and making it easier to maintain adhesion under high temperature and high humidity conditions. The content of cyclohexane ring structures in the polyester resin is the amount of cyclohexane ring structures (C6H) per 100g of total mass of the polyester resin. 10This is the calculation of the mass ratio of -CH2-). Specifically, it can be calculated from "the mole percent and molecular weight of each monomer component constituting the polyester resin", "the mole percent of monomer components having a cyclohexane ring among all monomer components", and "the proportion of the molecular weight of the cyclohexane ring structure among the molecular weight of monomer components having a cyclohexane ring".

[0043] Polyester resin is a copolymer polyester formed by the polycondensation of a dicarboxylic acid component and a diol component. One or more dicarboxylic acid and diol components may be used. In the present invention, at least one of the dicarboxylic acid and diol components contains a cyclohexane ring, and at least one hydrogen atom on the cyclohexane ring is substituted with a hydrocarbon group.

[0044] Examples of dicarboxylic acid components include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfoncarboxylic acid, anthracenedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, cyclohexylmethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, cyclohexylmethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, azelaic acid, dimeric acid, sebacic acid, suberic acid, dodecadicarboxylic acid, and 1,1-cyclohexanediacetic acid. Among these, cyclohexylmethylmalonic acid, cyclohexylmethylsuccinic acid, and 1,1-cyclohexanediacetic acid are particularly preferred because they have a structure in which at least one hydrogen atom on the cyclohexane ring is substituted with a hydrocarbon group.

[0045] If used in small quantities, monocarboxylic acids such as cyclohexylacetic acid may also be used as needed.

[0046] Examples of diol components include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediethanol, decamethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexadiol, 2,2-bis(4-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)sulfone. Among these, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, and 1,4-cyclohexanediethanol are particularly preferred because they have a structure in which at least one hydrogen atom on the cyclohexane ring is substituted with a hydrocarbon group.

[0047] If used in small quantities, monools such as cyclohexanemethanol may also be used as needed.

[0048] The ratio of the dicarboxylic acid component and the diol component when combining them as described above is not particularly limited and can be adjusted to obtain a polyester with the desired properties.

[0049] The polycarbonate polyurethane resin and polyester resin used in the coating layer both contain a cyclohexane ring, and the effects of the present invention are effectively realized when the structure contains at least one hydrogen atom on the cyclohexane ring substituted with a hydrocarbon group. Although the exact mechanism by which the effects of the present invention are realized is not clear, the coating layer of the present invention can maintain the rigidity of the resin while also improving the flexibility of the resin, thus functioning as the best coating layer. In other words, it not only has excellent adhesion to the substrate polyester film, functional layer, and other adherends, but its adhesion over time is also greatly improved. This makes it possible to obtain a film that maintains its quality for a long period of time.

[0050] (Crosslinking agent) In the present invention, the composition used to form the coating layer may contain a crosslinking agent in order to form a crosslinked structure between resins in the coating layer. By including a crosslinking agent, it is possible to further improve adhesion under high temperature and high humidity conditions. Specific examples of crosslinking agents include urea-based, epoxy-based, melamine-based, isocyanate-based, oxazoline-based, and carbodiimide-based crosslinking agents. Among these, isocyanate-based crosslinking agents are preferred from the viewpoint of the long-term stability of the coating solution and the effect of improving adhesion under high temperature and high humidity treatment. Furthermore, catalysts and the like can be used as appropriate as needed to promote the crosslinking reaction.

[0051] When the coating layer-forming composition contains a binder resin and a crosslinking agent, from the viewpoint of adhesion, when the total mass of the binder resin and crosslinking agent is 100% by mass, the binder resin content is preferably 50 to 95% by mass, more preferably 55 to 90% by mass, even more preferably 60 to 90% by mass, and most preferably 80 to 90% by mass. If it is 95% by mass or less, the strength of the coating film of the coating layer is maintained and adhesion under high temperature and high humidity is good, and if it is 50% by mass or more, the flexibility of the coating layer is maintained and adhesion under room temperature and high temperature and high humidity is good, which is preferable. Furthermore, when the total mass of the binder resin and crosslinking agent is 100% by mass, the crosslinking agent content is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, even more preferably 10 to 40% by mass, and most preferably 10 to 20% by mass.

[0052] In this invention, it is important that the binder resin contains polycarbonate polyurethane resin and polyester resin. The ratio of the two is not particularly limited as long as the physical properties of the resulting coating layer are ensured. When the total amount of binder resin is 100% by mass, the polycarbonate polyurethane resin is preferably 40% to 85% by mass, more preferably 45% to 80% by mass, and even more preferably 50% to 75% by mass. Having 40% or more of polycarbonate polyurethane resin ensures a balance between the flexibility and hardness of the urethane resin and ensures adhesion over time. Furthermore, by setting it to 85% or less by mass, a balance between the hardness and softness of the coating layer can be maintained and flexibility can be improved, thus functioning as the coating layer best.

[0053] When using isocyanate-based crosslinking agents, it is preferable to use blocking agents to control the reactivity of the isocyanates. Examples of blocking agents 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; phenols such as phenol and cresol; aliphatic alcohols such as methanol and ethanol; active methylene compounds such as dimethyl malonate and acetylacetone; mercaptans such as butyl mercaptan and dodecyl mercaptan; acid amides such as acetanilide and acetic acid amide; lactams such as ε-caprolactam and δ-valerolactam; acid imides such as succinimide and maleimide; oxime compounds such as acetaldehyde oxime, acetone oxime, and methyl ethyl ketoxime; and amines such as diphenylaniline, aniline, and ethyleneimine. From a reactivity standpoint, a blocking agent having a pyrazole skeleton is preferred for this system.

[0054] In block isocyanate-based crosslinking agents, it is preferable to introduce hydrophilic groups from the viewpoint of imparting water dispersibility in aqueous solvents. Furthermore, preferred hydrophilic groups are anionic groups such as carboxyl groups or sulfonic acid groups, and nonionic groups such as oxyalkyl groups. These hydrophilic crosslinking agents can be prepared by pre-reacting a polyisocyanate, which serves as the base for the block isocyanate, with a compound having hydrophilic groups and reactive groups such as hydroxyl groups.

[0055] (Additives) In the coating layer of the present invention, known additives such as surfactants, antioxidants, heat stabilizers, weather stabilizers, ultraviolet absorbers, organic lubricants, pigments, dyes, organic or inorganic particles, antistatic agents, nucleating agents, etc., may be added, to the extent that they do not impair the effects of the present invention. However, it is preferable not to use substances that are undesirable in the environment or for other reasons.

[0056] To further improve the blocking resistance of the coating layer, it is also preferable to add inert particles to the coating layer. Examples of particles to be included in the coating layer include inorganic particles and organic polymer particles. Examples of inorganic particles include titanium dioxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, or mixtures thereof, and they can also be used in combination with other general inorganic particles, such as calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, calcium fluoride, and others. Examples of organic polymer particles include styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based polymer particles.

[0057] The average particle size of the inert particles in the coating layer (average particle size based on the number of particles measured by SEM; the same applies hereinafter) is preferably 0.04 to 2.0 μm, and more preferably 0.1 to 1.0 μm. When the average particle size of the inert particles is 0.04 μm or more, it is easier to form irregularities on the surface of the coating layer, which improves the handling properties such as the slipperiness and winding properties of the easily adhesive polyester film, and is preferable because it provides good processability during lamination. On the other hand, when the average particle size of the inert particles is 2.0 μm or less, particle detachment is less likely to occur, which is preferable. The particle concentration in the coating layer is preferably 1 to 20% by mass relative to the resin content.

[0058] (Formation of the coated layer) The coating layer-forming composition (hereinafter also referred to as "coating liquid") for forming a coating layer may further contain surfactants for the purpose of improving leveling properties during application and defoaming the coating liquid. Examples of surfactants include cationic, anionic, and nonionic surfactants, with silicone-based, acetylene glycol-based, or fluorine-based surfactants being preferred. These surfactants are preferably included in the coating layer-forming composition to an extent that does not impair the effect of suppressing iridescent coloration or adhesion under a three-wavelength LED light source.

[0059] As for the method of applying the coating solution onto the polyester film, both the so-called in-line coating method, in which the coating is applied simultaneously with the formation of the polyester film, and the so-called off-line coating method, in which the coating is applied separately with a coater after the polyester substrate film has been formed, can be applied. However, the in-line coating method is more efficient and therefore preferable.

[0060] As for the coating method, any known method can be used to apply the coating solution to the polyethylene terephthalate (hereinafter abbreviated as PET) film. Examples include the reverse roll coating method, gravure coating method, kiss coating method, die coater method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method, impregnation coating method, curtain coating method, etc. These methods can be used individually or in combination.

[0061] In the present invention, a method for providing a coating layer on a polyester film is to apply a coating solution containing a solvent, particles, and a resin to the polyester film and then dry it. As the solvent, water or a mixture of water and an organic solvent is used, but preferably, from the viewpoint of environmental issues, water alone or a mixture of water and a water-soluble organic solvent is preferred. For example, examples of water-soluble organic solvents include alcohol-based solvents such as isopropyl alcohol and ethanol; ketone-based solvents such as methyl ethyl ketone; ether-based solvents such as butyl cellosolve; amine-based solvents such as triethanolamine; and amide-based organic solvents such as N-methylpyrrolidone.

[0062] The solid content concentration of the coating solution depends on the type of binder resin and solvent, but it is preferably 2% by mass or more, and more preferably 4% by mass or more, relative to the total mass of the coating solution. The solid content concentration of the coating solution is preferably 35% by mass or less, and more preferably 15% by mass or less.

[0063] The drying temperature after coating also depends on the type of binder resin, the type of solvent, the presence or absence of a crosslinking agent, the solid content concentration, etc., but it is preferably 80°C or higher and preferably 250°C or lower.

[0064] The amount of coating solution applied depends on the amount of solids on the polyester film after drying, for example, 0.03 to 0.24 g / m². 2 Furthermore, 0.06~0.18 g / m 2 The product can be adjusted to achieve the above-mentioned result. If a film stretching step is included after coating and drying, the product can be adjusted so that the amount of solids on the stretched polyester film falls within the above range.

[0065] The stretching process may employ either uniaxial stretching or biaxial stretching. The stretched polyester film can be heat-treated (for example, 70-250°C, preferably 80-245°C) while fixed in a tenter, and then relaxed at 120-250°C.

[0066] As described above, the easily adhesive polyester film of the present invention is manufactured through the processes of coating, drying, stretching, and heat treatment.

[0067] The thickness of the coating layer is 30 nm to 200 nm. A thickness within this range is preferable because it easily balances processability and adhesion. More preferably, it is 50 nm to 150 nm, and even more preferably, 70 nm to 100 nm. A coating layer thickness of 30 nm or more is preferable because it provides good adhesion. A coating layer thickness of 200 nm or less is preferable because it is less likely to cause blocking.

[0068] The thickness of the coating layer was determined by observing the cross-section of a cut film using a transmission electron microscope (TEM), and taking the average of 10 randomly measured points of the coating layer thickness.

[0069] Laminated polyester film The present invention also provides a laminated polyester film in which a functional layer having various properties is provided on a coated layer of an easily adhering polyester film. The functional layer refers to a layer having functionality for purposes such as preventing reflections, suppressing glare, suppressing rainbow unevenness, and suppressing scratches, such as a hard coat layer, anti-glare layer, anti-glare anti-reflective layer, anti-reflective layer, low-reflection layer, and antistatic layer. Various types of functional layers known in the art can be used, and there are no particular limitations on their type.

[0070] For example, when forming a hard coat layer on a coated layer, the hard coat layer material can be any known material and is not particularly limited. As the material, a resin compound (especially a curable resin) that polymerizes and / or reacts by drying, heat, chemical reaction, or irradiation with electron beams, radiation, or ultraviolet light can be used. Examples of such curable resins include melamine-based, acrylic-based, silicone-based, and polyvinyl alcohol-based curable resins, but photocurable acrylic-based curable resins are preferred in terms of obtaining high surface hardness or optical design. As such acrylic-based curable resins, polyfunctional (meth)acrylate monomers and acrylate-based oligomers can be used, and examples of acrylate-based oligomers include polyester acrylate, epoxy acrylate, urethane acrylate, polyether acrylate, polybutadiene acrylate, and silicone acrylate. By mixing these acrylic-based curable resins with a reaction diluent, a photopolymerization initiator, a sensitizer, etc., a coating composition for forming the optical functional layer can be obtained.

[0071] The hard coat layer described above may have an anti-glare function that scatters ambient light. The anti-glare function is obtained by forming irregularities on the surface of the hard coat layer. In this case, the haze of the film is ideally preferably 0-50%, more preferably 0-40%, and particularly preferably 0-30%. Of course, 0% is ideal, and it may be 0.2% or more, or 0.5% or more.

[0072] Furthermore, by providing layers with different refractive indices as functional layers and changing the light transmission characteristics, a low-reflection treatment (anti-reflection treatment) can be applied to suppress light reflection. Ideally, the refractive index of functional layers such as the hard coat layer should be adjusted to have a reflectivity of 0 to 1.0%, more preferably 0 to 0.8%, and particularly preferably 0 to 0.5%. Of course, 0% is ideal, and it may be 0.05% or higher, or 0.1% or higher.

[0073] The easily adhering polyester film of the present invention can be used as a polarizer protective film. Generally, a polarizer plate is formed by placing polarizer protective films on both sides of a polarizer, but it is preferable that the polarizer protective film on at least one side of the polarizer is the easily adhering polyester film of the present invention. The polarizer protective film on the other side may be the easily adhering polyester film of the present invention, or it may be a non-birefringent film such as a triacetylcellulose film, acrylic film, or norbornene-based film.

[0074] Examples of polarizers include those made of polyvinyl alcohol containing a dichroic material such as iodine. The polarizer protective film is bonded to the polarizer directly or via an adhesive layer, but bonding via an adhesive is preferable from the viewpoint of improving adhesion. In this case, it is preferable to place the coating layer of the easily bondable polyester film of the present invention on the polarizer surface or the adhesive layer surface. Examples of polarizers to which the polyester film of the present invention is bonded include those obtained by dyeing and adsorbing iodine or a dichroic material onto a polyvinyl alcohol-based film, uniaxially stretching it in a boric acid aqueous solution, and then washing and drying it while maintaining the stretched state. The stretching ratio for uniaxial stretching is usually about 4 to 8 times. Polyvinyl alcohol is suitable as the polyvinyl alcohol-based film, and commercially available products such as "Kuraray Vinylon" [(manufactured by Kuraray Co., Ltd.)], "Tosero Vinylon" [manufactured by Tosero Co., Ltd.], and "Nihon Synthetic Chemical Co., Ltd." can be used. Examples of dichroic materials include iodine, disazo compounds, and polymethine dyes.

[0075] When applying an adhesive to a polarizer, if the adhesive layer is thin, a water-based adhesive is preferred, i.e., an adhesive in which the adhesive components are dissolved in water or dispersed in water. For example, a composition can be used in which a polyvinyl alcohol-based resin, urethane resin, etc., is used as the main component, and isocyanate compounds, epoxy compounds, etc., are added as needed to improve adhesion. The thickness of the adhesive layer is preferably 5 μm or less, more preferably 3 μm or less, and even more preferably 1 μm or less.

[0076] When using a polyvinyl alcohol-based resin as the main component of the adhesive, in addition to partially saponified polyvinyl alcohol and fully saponified polyvinyl alcohol, modified polyvinyl alcohol-based resins such as carboxyl group-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, methylol group-modified polyvinyl alcohol, and amino group-modified polyvinyl alcohol may also be used. The concentration of the polyvinyl alcohol-based resin in the adhesive is preferably 1 to 10% by mass, and more preferably 2 to 7% by mass.

[0077] To further increase productivity when using an adhesive applied to a polarizer, it is preferable to use a photocurable adhesive. The thickness of the adhesive layer after curing can be arbitrarily set by the design of the polarizer's characteristics, and a smaller thickness is preferable from the viewpoint of reducing adhesive material costs. Generally, it is 0.01 to 20 μm, preferably 0.1 to 10 μm, and more preferably 0.5 to 5 μm. An adhesive layer thickness of 0.01 μm or more is preferable because it makes it difficult for air bubbles to be incorporated into the adhesive layer, resulting in good adhesion and durability. An adhesive layer thickness of 20 μm or less is preferable because the reaction rate of the adhesive is sufficient, resulting in good moisture and heat resistance of the polarizer.

[0078] The photocurable adhesive preferably has an epoxy compound that does not contain aromatic rings as its main component and contains a photocationic curable component (I) and a photocationic polymerization initiator (II).

[0079] The photocationic curable component (I) is preferably mainly composed of an epoxy compound that does not contain an aromatic ring. An epoxy compound that does not contain an aromatic ring is an epoxy compound other than an aromatic epoxy compound, and is hereinafter referred to as an aliphatic epoxy compound. An "epoxy compound" is a compound that has at least one epoxy group in its molecule. The main component aliphatic epoxy compound may contain two or more epoxy compounds. "Main component" means that the content of the aliphatic epoxy compound is 50% by mass or more of 100% by mass of the photocurable adhesive. The content of the aliphatic epoxy compound is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and still more preferably 90% by mass or more.

[0080] Aliphatic epoxy compounds may be epoxy compounds having an alicyclic ring, or they may be epoxy compounds that do not contain an alicyclic ring and consist only of a linear hydrocarbon structure and / or a branched hydrocarbon structure. Furthermore, aliphatic epoxy compounds may contain unsaturated bonds such as double bonds, and may further contain heteroatoms other than the oxygen atom contained in the epoxy group (oxygen atoms, nitrogen atoms, sulfur atoms, halogen atoms, etc.).

[0081] The photocationic polymerization initiator (II) can initiate cationic polymerization by irradiation with active energy rays, thereby curing the photocationically curable component (I) and forming an adhesive layer. The photocationic polymerization initiator (II) generates cationic species or Lewis acids by irradiation with active energy rays such as visible light, ultraviolet rays, X-rays, and electron beams, and initiates the polymerization reaction of the photocationically curable component. Because the photocationic polymerization initiator (II) acts catalytically with light, it exhibits excellent storage stability and workability even when mixed with the photocationically curable component.

[0082] Examples of photocationic polymerization initiators (II) include aromatic diazonium salts; onium salts such as aromatic iodonium salts and aromatic sulfonium salts; and iron-arene complexes.

[0083] Examples of aromatic diazonium salts include benzenediazonium hexafluoroantimonate, benzenediazonium hexafluorophosphate, and benzenediazonium hexafluoroborate.

[0084] Examples of aromatic iodonium salts include diphenyliodonium tetrakis(pentafluorophenyl)borate, diphenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate, and di(4-nonylphenyl)iodonium hexafluorophosphate.

[0085] Examples of aromatic sulfonium salts include triphenylsulfonium hexafluorophosphate, triphenylsulfonium tetrakis(pentafluorophenyl)borate, 4,4-bis[diphenylsulfonio]diphenyl sulfide bishexafluorophosphate, 4,4-bis[di(β-hydroxyethoxy)phenylsulfonio]diphenyl sulfide bishexafluoroantimonate, 4,4-bis[di(β-hydroxyethoxy)phenylsulfonio]diphenyl sulfide bishexafluorophosphate, 7-[di(p-toluyl)sulfonio]-2-isopropylthioxanthone hexafluoroantimonate, 7-[di(p-toluyl)sulfonio]-2-isopropylthioxanthone tetrakis(pentafluorophenyl)borate, and 4-phenylcarbonyl-4-diphenylsulfonio-diphenyl sulfide. Examples include hexafluorophosphate, 4-(p-tert-butylphenylcarbonyl)-4-diphenylsulfonio-diphenyl sulfide; hexafluoroantimonate, 4-(p-tert-butylphenylcarbonyl)-4-di(p-toluyl)sulfonio-diphenyl sulfide; and tetrakis(pentafluorophenyl)borate.

[0086] Examples of iron-arene complexes include xylene-cyclopentadienyl iron(II) hexafluoroantimonate, cumene-cyclopentadienyl iron(II) hexafluorophosphate, and xylene-cyclopentadienyl iron(II) tris(trifluoromethylsulfonyl) methanide.

[0087] The photocationic polymerization initiator (II) may be used alone or in combination of two or more types. Among the above, aromatic sulfonium salts are particularly preferred because they have ultraviolet absorption properties even in the wavelength region around 300 nm, resulting in excellent curability and providing an adhesive layer with good mechanical and adhesive strength.

[0088] The content of the photocationic polymerization initiator (II) is preferably 1 to 10 parts by mass, and more preferably 2 to 6 parts by mass, per 100 parts by mass of the total photocationic curable component (I). By including 1 part by mass or more of the photocationic polymerization initiator (II), the photocationic curable component (I) can be sufficiently cured, and the resulting polarizing plate can be given high mechanical strength and adhesive strength. On the other hand, if the content is too high, the amount of ionic substances in the cured product increases, which increases the hygroscopicity of the cured product and may reduce the durability of the polarizing plate. Therefore, it is preferable that the content of the photocationic polymerization initiator (II) is 10 parts by mass or less per 100 parts by mass of the photocationic curable component (I).

[0089] The applications of the laminated polyester film of the present invention are mainly in the field of optical films, including base films for optical components such as LCDs, flat-screen TVs, and CRTs, such as prism lens sheets, AR (anti-reflection) films, hard coat films, diffusers, and shatterproof films; near-infrared absorption filters used as front panels for plasma displays; and transparent conductive films for touch panels and electroluminescence. It can be suitably used in any of these applications.

[0090] Examples of acrylic resins that harden by electron beam or ultraviolet light for forming the functional layer mentioned above include compositions containing a reactive oligomer, which is a (meth)acrylate oligomer, and a reactive monomer (reactive diluent), which is a (meth)acrylate-based monomer. Examples of (meth)acrylate oligomers include compounds in which a reactive (meth)acrylic group is bonded to a (meth)acrylic resin skeleton, polyester acrylate, epoxy acrylate, polyurethane acrylate, silicone acrylate, melamine acrylate, and polyether acrylate. Examples of (meth)acrylate monomers include monofunctional monomers such as ethyl (meth)acrylate and ethylhexyl (meth)acrylate; and polyfunctional monomers such as trimethylolpropane tri(meth)acrylate, hexanediol (meth)acrylate, tripropylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and neopentyl glycol di(meth)acrylate. If necessary, a third component can be added as appropriate. For example, it may contain relatively low molecular weight polyester resins, polyether resins, acrylic resins, epoxy resins, urethane resins, alkyd resins, spiroacetal resins, polybutadiene resins, polythiol polyene resins, polyhydric alcohols, etc.

[0091] In the case of electron beam or UV-curable acrylic resins, for example, acetophenones, benzophenones, Michler-benzoylbenzoate, α-amyloxime esters, tetramethylthiraum monosulfide, and thioxanthones can be used as photopolymerization initiators in the aforementioned resin. Alternatively, a mixture of the photopolymerization initiator and a photosensitizer such as n-butylamine, triethylamine, or tri-n-butylphosphine can be used.

[0092] Silicone-based (siloxane-based) thermosetting resins can be produced by hydrolysis and condensation reactions of organosilane compounds, either individually or in combination of two or more, under an acid or base catalyst. In particular, for low-reflectance applications, mixing one or more fluorosilane compounds and proceeding with the hydrolysis and condensation reactions is even better in terms of improving low refractive index, stain resistance, and other properties.

[0093] Manufacturing of laminated polyester film The laminated polyester film of the present invention can be manufactured by providing a functional layer on a coated layer of an easily adhering polyester film. Specific embodiments are described below, but are not limited thereto.

[0094] A functional layer-forming composition (functional layer-forming coating liquid) is applied to the coated layer surface of the aforementioned easy-to-adhere polyester film. Examples of the functional layer-forming composition include the aforementioned electron beam or ultraviolet curable acrylic resin (including its oligomers, monomers, etc.) or siloxane-based thermosetting resin. If the coated layer is provided on both sides of the easy-to-adhere polyester film, it can be applied to at least one of the coated layer surfaces. The functional layer-forming coating liquid does not need to be diluted, but it is acceptable to dilute it with an organic solvent as needed to control its viscosity, wettability, film thickness, etc. After applying the functional layer-forming coating liquid to the film, the coated film can be dried as needed, and then cured by electron beam or ultraviolet irradiation and heating according to the curing conditions to form a functional layer.

[0095] More typically, a functional layer-forming coating solution with the above composition is applied to a coated layer of an easily adhering polyester film using a wire bar or the like as appropriate, and the solvent can be removed by drying at 60-100°C for 0.5-10 minutes. Then, the film coated with the functional layer is exposed to a 250-600 mJ / cm² lamp, for example, using a high-pressure mercury lamp. 2 By irradiating with ultraviolet light, a laminated polyester film having a functional layer can be obtained.

[0096] In the present invention, the thickness of the functional layer is preferably 1 to 15 μm. A thickness of 1 μm or more is preferable because it efficiently exhibits the effects of the functional layer on chemical resistance, scratch resistance, stain resistance, etc. On the other hand, a thickness of 15 μm or less is preferable because it maintains the flexibility of the functional layer and there is no risk of cracking or the like occurring.

[0097] The easily adhering polyester film and laminated polyester film of the present invention are suitable for use mainly in optical applications, and therefore, high transparency is preferable. The lower limit of haze is ideally 0%, and the closer to 0%, the better. The upper limit of haze is preferably 2%. A haze of 2% or less is preferable because it provides good light transmittance and allows for the acquisition of clear images in liquid crystal display devices. The haze can be measured, for example, according to the method described in the examples below.

[0098] (Evaluation of adhesion) The adhesion between the polyester film and the functional layer in a laminated polyester film can be evaluated by the method described in the examples. Specifically, a laminated polyester film was prepared by forming a functional layer on a coated layer of an easily adhesive polyester film, and its adhesion X (%) was evaluated. Separately, after storing the easily adhesive polyester film for a long period of time, a laminated polyester film was prepared by forming a functional layer on its coated layer, and its adhesion Y (%) was evaluated. Ideally, long-term storage conditions should be measured after being left in a normal room temperature environment for several weeks to several months. However, since leaving samples at room temperature takes an extremely long time, this specification uses an accelerated measurement method: the samples are left for 24 hours in a high-temperature, high-humidity environment of 80°C and 90%RH, followed by 12 hours at room temperature (10-30°C). As is clear from Table 3 of the examples, the adhesion X is usually 95% or higher, moreover 98% or higher, and especially 100%. When the adhesion X is 95% or higher, it can be said that sufficient adhesion is maintained between the coated layer and the functional layer. Furthermore, the adhesion Y after long-term storage is usually 95% or higher, even higher than 98%, and especially 100%. When the adhesion Y is 95% or higher, it can be said that sufficient adhesion between the coated layer and the functional layer is maintained even after long-term storage. In the easily adhering polyester film of the present invention, both adhesion X and adhesion Y are high, and adhesion Y is equivalent to or almost unchanged from adhesion X.

[0099] Thus, the easily adhering polyester film of the present invention has high reliability in adhesion with the functional layer, and exhibits high adhesion not only after film formation but also after exposure to high temperature and high humidity environments (even after long-term storage). In other words, it has the characteristic of having sufficiently high adhesion X after film formation and high adhesion Y after long-term storage. That is, the above-mentioned X(%) and Y(%) satisfy the following formula (1). XY(%) ≦ 5...Equation (1)

[0100] The value of equation (1) is usually 5% or less, even 3% or less, and especially 0%. When it is 5% or less, it can be judged that there is no significant difference between the adhesion after film formation and the adhesion after moist heat treatment, and that both are sufficiently adhered. Therefore, it can be judged that the adhesion of the functional layer does not deteriorate even after long-term storage, and adhesion reliability can be ensured.

[0101] In this invention, "after film formation" means the period after a coating layer has been formed on the polyester film, and refers to the period after the film has been stored in a temperature environment of 40°C or lower for a period of up to 6 months. Within that period, the performance of the coating layer of the easily adhering polyester film remains virtually unchanged.

[0102] Separately, the easily adhesive polyester film after film formation was wound into a roll as an actual product, and left for 6 months in an environment with a temperature of 0°C to 30°C and a humidity of 10%RH to 80%RH. After that, a sample was taken from the roll, a functional layer was formed on the coated layer, and the adhesion Z(%) was evaluated. As is clear from Table 3 of the examples, the adhesion Z is usually 90% or higher, even more so 95% or higher, and especially 100%. An adhesion Z of 90% or higher means that the adhesion Z of the easily adhering polyester film is maintained even after being wound into a roll and left for a long period of time, and that it has high adhesion reliability. [Examples]

[0103] Next, the present invention will be described in detail using examples, comparative examples, and reference examples, but the present invention is not limited to the following examples. Furthermore, the measurement methods used in the present invention are as follows.

[0104] (1) Average particle size [Measurement method using a scanning electron microscope] The average particle size of particles present in the coating layer of the present invention can be measured by the following method. A scanning electron microscope (SEM) is used to take a photograph of the particles, and the maximum diameter (distance between the two furthest points) of 300 to 500 particles is measured at a magnification such that the size of the smallest single particle is 2 to 5 mm. The arithmetic mean of these measurements is then taken as the average particle size.

[0105] [Dynamic light scattering method] The average particle size can also be determined by dynamic scattering during the manufacturing of particles and films. The sol was diluted with a dispersion medium, and the average particle diameter was obtained by measuring it using a submicron particle analyzer N4 PLUS (Beckman Coulter) with the parameters of the dispersion medium, and then calculating it using the cumulant method. Dynamic light scattering observes the average particle diameter of particles in the sol, and if there is aggregation of particles, the average particle diameter of those aggregated particles is observed.

[0106] (2) Refractive index of particles The refractive index of the particles can be measured by the following method. After drying inorganic particles at 150°C, they were ground in a mortar and pestle. The fine particles were then immersed in solvent 1 (with a lower refractive index than the particles), and solvent 2 (with a higher refractive index than the particles) was added in small amounts until the fine particles became almost transparent. The refractive index of this solution was measured using an Abbe refractometer (Abbe refractometer manufactured by Atago Co., Ltd.). The measurement was performed at 23°C and in the D line (wavelength 589 nm). Solvents 1 and 2 were selected to be miscible with each other, and depending on the refractive index, examples of solvents include 1,1,1,3,3,3-hexafluoro-2-propanol, 2-propanol, chloroform, carbon tetrachloride, toluene, and glycerin.

[0107] (3) Haze of easily adhering polyester film for optical use The haze of the easy-to-adhere polyester film was measured using a turbidimeter (NDH2000, manufactured by Nippon Denshoku) in accordance with JIS K 7136:2000.

[0108] (4) Adhesion of the functional layer (1) A hard coat layer was formed on the easily adhering coating layer of the polyester film obtained in the example. The adhesion between the hard coat layer and the base film of the easily adhering polyester film with the hard coat layer formed was determined in accordance with the description in JIS-K5400-1990 8.5.1.

[0109] The coating solution used for forming the hard coat layer was prepared as follows. (Preparation of coating solution L for hard coat layer formation) Methyl ethyl ketone 36.00% by mass Toluene 18.00% by mass Cyclohexanone 6.00% by mass Urethane acrylate 40.00% by mass (Arakawa Chemical Co., Ltd. BS577) Surfactant 0.10% by mass Photopolymerization initiator 2.00% by mass (IGM Resins BV Omnirad 184)

[0110] (Preparation of coating solution M for hard coat layer formation) Methyl ethyl ketone 64.40% by mass Dipentaerythritol hexaacrylate 27.20% by mass (Shin Nakamura Chemical A-DPH) Polyethylene glycol diacrylate 3.40% by mass (Light Acrylate 9EG-A manufactured by Kyoeisha Chemical Co., Ltd.) Bisphenol A diacrylate 4.00% by mass (Light Acrylate BP-4PA manufactured by Kyoeisha Chemical Co., Ltd.) Photopolymerization initiator 1.00% by mass (IGM Resins BV Omnirad 184)

[0111] (Formation of the hard coat layer) The easily adhering polyester film produced in the example was stored at a temperature and humidity of 20°C and 65%RH. Twelve hours after film formation, the hard coat layer forming solution (L or M) of the above composition was applied to the easily adhering coating layer using a #14 wire bar, dried at 70°C for 1 minute, and the solvent was removed. Next, the film with the hard coat layer was subjected to a pressure of 300 mJ / cm² using a high-pressure mercury lamp. 2 By irradiating with ultraviolet light, a hard coat film having a hard coat layer with a thickness of 7 μm was obtained.

[0112] The specific method for measuring adhesion is as follows: Using a cutter guide with a 2mm gap spacing, 100 grid-like cuts were made on the hard coat layer surface, penetrating the hard coat layer and reaching the base film. Next, cellophane adhesive tape (Nichiban, No. 405; 24mm wide) was applied to the grid-like cut surfaces and rubbed with an eraser to ensure complete adhesion. Then, the cellophane adhesive tape was peeled vertically from the hard coat layer surface of the easy-adhesion polyester film on which the hard coat layer had been formed. The number of grid squares that peeled off the hard coat layer surface was visually counted, and the adhesion between the hard coat layer and the base film was determined using the following formula. Note that grid squares that were partially peeled off were also counted as peeled squares. Adhesion (%) = {1 - (Number of peeled squares / 100)} × 100

[0113] (5) Adhesion of the functional layer (2) A photocurable adhesive layer was formed on the easily adhering coating layer of the polyester film obtained in the examples. The adhesion between the photocurable adhesive layer and the substrate film of the easily adhering polyester film with the photocurable adhesive layer formed was determined in accordance with the description in JIS-K5400-1990, 8.5.1.

[0114] The coating solution used for forming the photocurable adhesive layer was prepared as follows. (Preparation of coating solution N for forming a photocurable adhesive layer) 3,4-Epoxycyclohexylmethyl-3,4'-Epoxycyclohexanecarboxylate 23.81% by mass (Celloxide2021P manufactured by Daicel Corporation) 1,4-Cyclohexanedimethanol diglycidyl ether 23.81% by mass (Nagase ChemteX EX-216L) 3-Ethyl-3-[(3-ethyloxetane-3-yl)methoxymethyl]oxetane 47.62% by mass (Aron oxetane DOX221 manufactured by Toagosei) Cation initiator 4.76% by mass (Sanapro CPI-100P) The aromatic component in the total resin of the prepared photocurable adhesive layer-forming coating solution N was 13.3% by molar ratio.

[0115] (Formation of a photocurable adhesive layer) The easily adhering polyester film produced in the example described later was stored at a temperature and humidity of 20°C and 65%RH. Twelve hours after film formation, the photocurable adhesive layer forming coating solution N with the above composition was applied to the easily adhering coating layer using a #3 wire bar. Next, the film coated with the photocurable adhesive layer was subjected to a high-pressure mercury lamp at a rate of 500 mJ / cm². 2 By irradiating with ultraviolet light, a polarizer protective film having a 5 μm thick photocurable adhesive layer was obtained.

[0116] The specific method for measuring adhesion is as follows: Using a cutter guide with a gap of 2 mm, 100 grid-like cuts were made on the surface of the photocurable adhesive layer, penetrating the layer and reaching the base film. Next, cellophane adhesive tape (Nichiban, No. 405; 24 mm wide) was applied to the grid-like cut surfaces and rubbed with an eraser to ensure complete adhesion. Then, the cellophane adhesive tape was peeled vertically from the surface of the photocurable adhesive layer of the easy-to-adhere polyester film, and the number of grids that peeled off the surface of the photocurable adhesive layer was visually counted. The adhesion between the photocurable adhesive layer and the base film was then calculated using the following formula. Note that grids that were partially peeled off were also counted as peeled grids. Adhesion (%) = {1 - (Number of peeled squares / 100)} × 100

[0117] (6) Humid heat resistance (adhesion after being left at 80°C and 90% RH) The obtained easily adhering polyester film was left in a high-temperature, high-humidity chamber at 80°C and 90%RH for 24 hours, and then left at room temperature (20°C, 65%RH) for 12 hours. After that, a functional layer was formed using the same method as described above, and the adhesion to the base film was determined.

[0118] (7) Reduced viscosity ηsp / c (unit: dl / g) 0.10 g of polyester resin was dissolved in 25 ml of a phenol / tetrachloroethane mixed solvent (mass ratio 6 / 4), and measured at 30°C using an Ubbelohde viscous tube.

[0119] (8) Cross-sectional observation using a transmission electron microscope The obtained easily adhering polyester film was cut into 1 mm × 10 mm sections and embedded in epoxy resin. Then, thin sections parallel to the short side of the embedded sample were prepared using an ultramicrotome. Next, these section thin films were stained with ruthenium tetroxide, and areas that were not significantly damaged were observed using a transmission electron microscope (JEOL JEM2100) at an acceleration voltage of 200 kV and magnification of 20,000. From the observed images of the coated layer, the thickness of the coated layer was measured at 10 points at each level, and the average value was taken as the thickness of the coated layer.

[0120] (9) Polyester resin composition The polyester resin was dissolved in deuterated chloroform, and a Varian Gemini-200 nuclear magnetic resonance analyzer (NMR) was used to analyze it. 1 1H-NMR analysis was performed, and the molar percentage ratio of each component was determined from the integrated ratio.

[0121] (10) Viscosity of polyester resin dispersion A 140cc glass bottle was filled with an aqueous dispersion of polyester resin, and the viscosity of the aqueous dispersion was measured using a viscometer model BL (TOKIMEC INC.) with rotor No. 1 or No. 2 in a 25°C constant temperature bath. The measurement was performed for 1 minute at a rotation speed of 60 rpm.

[0122] [Polyurethane resin] Synthesis of polyurethane resin (PCPU-1): Into a four-necked flask equipped with a stirrer, Dimroth condenser, nitrogen inlet tube, silica gel drying tube, and thermometer, 29.4 parts by mass of dicyclohexylmethane-4,4'-diisocyanate, 63.6 parts by mass of a polycarbonate diol having a melting point of 33 °C with 1,4-butanediol / 1,6-hexanediol (= 80 / 20 (molar ratio)) with a number average molecular weight of 1000 as the main raw material, 7 parts by mass of dimethylolpropionic acid, and 200 parts by mass of ethyl methyl ketone as a solvent were charged, and stirred at 75 °C for 3 hours under a nitrogen atmosphere. The infrared spectrum of the reaction solution was measured to confirm the disappearance of isocyanate groups in the reaction solution. Next, after cooling the solution to room temperature, 8.2 parts by mass of triethylamine was added to obtain a polyurethane resin (PCPU-1) solution with a solid content of 50.0% by mass. The proportion (content) of the cyclohexane ring structure in the whole of this polycarbonate polyurethane (PCPU-1) was 10.7% by mass.

[0123] Preparation of an aqueous dispersion (PCPU-1WD) of the polyurethane resin (PCPU-1): A predetermined amount of water was added to a reaction vessel equipped with a homodisper capable of high-speed stirring, adjusted to 25 °C, and while stirring and mixing at 2000 min -1 the above-mentioned polyurethane resin (PCPU-1) solution was gradually added and dispersed in water. Then, under reduced pressure, ethyl methyl ketone as a solvent was removed. By adjusting the concentration with water, an aqueous dispersion (PCPU-1WD) of a polycarbonate polyurethane resin (PCPU-1) with a solid content of 35.0% by mass was prepared.

[0124] Synthesis of the polyurethane resin (PCPU-2) and preparation of the aqueous dispersion (PCPU-2WD): The polyurethane resin (PCPU-2) was prepared in the same manner as the synthesis of the above (PCPU-1), except that the main raw material of the polycarbonate diol was changed to 1,4-cyclohexanedimethanol / 1,6-hexanediol (= 75 / 25 (molar ratio)), and an aqueous dispersion (PCPU-2WD) was obtained in the same manner as the preparation of (PCPU-1WD). The proportion (content) of the cyclohexane ring structure in the whole of this polycarbonate polyurethane (PCPU-2) was 39.4% by mass.

[0125] Synthesis of polyurethane resin (PCPU-3) and preparation of aqueous dispersion (PCPU-3WD): PCPU-3 was prepared in the same manner as the synthesis of PCPU-1, except that dicyclohexylmethane-4,4'-diisocyanate was replaced with cyclohexane-1,2-diirbis(methylene)diisocyanate and the number of moles was adjusted. An aqueous dispersion (PCPU-3WD) was obtained in the same manner as the preparation of PCPU-1WD. The proportion (content) of the cyclohexane ring structure in the entire polycarbonate polyurethane (PCPU-3) was 11.5% by mass.

[0126] Synthesis of polyurethane resin (PCPU-4) and preparation of aqueous dispersion (PCPU-4WD): Except for changing the main raw material of the polycarbonate diol to 1,4-cyclohexanedimethanol / 1,6-hexanediol (=75 / 25 (molar ratio)), (PCPU-4) was prepared in the same manner as the synthesis of (PCPU-3) above, and an aqueous dispersion (PCPU-4WD) was obtained in the same manner as the preparation of (PCPU-3WD). The proportion (content) of the cyclohexane ring structure in the entire polycarbonate polyurethane (PCPU-4) was 42.7% by mass.

[0127] Synthesis of polyurethane resin (PCPU-5) and preparation of aqueous dispersion (PCPU-5WD): PCPU-5 was prepared in the same manner as the synthesis of PCPU-2, except that dicyclohexylmethane-4,4'-diisocyanate was replaced with 4,4'-diphenylmethane diisocyanate and the number of moles was adjusted. An aqueous dispersion (PCPU-5WD) was obtained in the same manner as the preparation of PCPU-2WD. The proportion (content) of the cyclohexane ring structure in the entire polycarbonate polyurethane (PCPU-5) was 29.1% by mass.

[0128] Synthesis of polyurethane resin (PCPU-6) and preparation of aqueous dispersion (PCPU-6WD): Except for substituting 4,4'-diphenylmethane diisocyanate for dicyclohexylmethane-4,4'-diisocyanate and adjusting the molar ratio, (PCPU-6) was prepared in the same manner as the synthesis of (PCPU-1) above, and an aqueous dispersion (PCPU-6WD) was obtained in the same manner as the preparation of (PCPU-1WD). The proportion (content) of the cyclohexane ring structure in the entire polycarbonate polyurethane (PCPU-6) was 0.0% by mass.

[0129] Synthesis of polyurethane resin (PCPU-7) and preparation of aqueous dispersion (PCPU-7WD): PCPU-7 was prepared in the same manner as the synthesis of PCPU-6, except that xylene diisocyanate was substituted for 4,4'-diphenylmethane diisocyanate and the number of moles was adjusted. An aqueous dispersion (PCPU-7WD) was obtained in the same manner as the preparation of PCPU-6WD. The proportion (content) of the cyclohexane ring structure in the entire polycarbonate polyurethane (PCPU-7) was 0.0% by mass.

[0130] [Polyester resin] Manufacturing of polyester resin (PEs-1): Following known polymerization methods, polyester resin (PEs-1) was polymerized. The composition of the resulting polymer was: 1 ¹H-NMR analysis was performed, and the molar percentage ratio of each component was determined from the integral ratio. The results are shown in Table 1. The reduced viscosity of the obtained polyester resin was 0.583 dl / g. The abbreviations listed in Table 1 are shown below. TPA: Terephthalic acid IPA: Isophthalic Acid CHMM: Cyclohexylmethylmalonic acid DSS: Dimethyl-5-sodium sulfisophthalate EG: Ethylene glycol HD: Hexanediol DEG: Diethylene glycol CHDM: 1,4-Cyclohexanedimethanol

[0131] Preparation of polyester aqueous dispersion (PEs-1WD): In a reactor equipped with a stirrer, thermometer, and reflux device, 30 parts by mass of copolymerized polyester resin (PEs-1) and 15 parts by mass of ethylene glycol-n-butyl ether were added and heated at 110°C, stirring to dissolve the resin. After the resin was completely dissolved, 55 parts by mass of water were gradually added to the polyester solution while stirring. After the addition, the liquid was cooled to room temperature while stirring to prepare a milky white aqueous dispersion of polyester resin (PEs-1) (PEs-1WD) with a solid content of 25.1% by mass. The viscosity of the obtained aqueous dispersion was 84 mPa·s.

[0132] Manufacturing of polyester resins (PEs-2 to PEs-4): Similar to the polymerization of the polyester resin (PEs-1) described above, polyester resins (PEs-2), (PEs-3), and (PEs-4) were manufactured following known polymerization methods. As with PEs-1, the composition ratios were determined, and the reduced viscosity of the obtained resins was evaluated. The results are shown in Table 1.

[0133] Preparation of polyester aqueous dispersions (PEs-2WD to PEs-4WD): Polyester aqueous dispersions (PEs-2WD), (PEs-3WD), and (PEs-4WD) were prepared in the same manner as the preparation of the polyester aqueous dispersion (PEs-1WD) described above. Similar to PEs-1WD, the solid content concentration and liquid viscosity were evaluated. The results for each are shown in Table 2.

[0134] [Table 1]

[0135] [Table 2]

[0136] [Crosslinking agent] Preparation of an aqueous dispersion (C-1WD) of a blocked isocyanate crosslinking agent (C-1): In a flask equipped with a stirrer, thermometer, and reflux condenser, 125.2 parts by mass of a polyisocyanate compound having a biuret structure (manufactured by Asahi Kasei Chemicals, Duranate 24A-100, NCO concentration 23.1%) derived from hexamethylene diisocyanate, 50.0 parts by mass of dipropylene glycol dimethyl ether, and 68.8 parts by mass of 3,5-dimethylpyrazole were added and the mixture was held at 70°C with stirring under a nitrogen atmosphere for 2 hours. The infrared spectrum of the reaction solution was then measured to confirm the disappearance of the isocyanate group absorption. Next, after cooling to room temperature, 6 parts by mass of polyethylene glycol (n=12) monolaurate were added, and the mixture was stirred for 2000 min. -1 Water was added while stirring and mixing. By adjusting the concentration with water, an aqueous dispersion (C-1WD) of a blocked isocyanate crosslinking agent (C-1) with a solid content of 30.0% by mass was prepared.

[0137] Preparation of an aqueous dispersion (C-2WD) of a blocked isocyanate crosslinking agent (C-2): In a flask equipped with a stirrer, thermometer, and reflux condenser, 100 parts by mass of a polyisocyanate compound having an isocyanurate structure prepared from 1,6-hexamethylene diisocyanate by an existing method (Asahi Kasei Chemicals, Duranate TPA-100, NCO concentration 23.1%) and 17.5 parts by mass of N-methylpyrrolidone were added dropwise to 35.00 parts by mass of 3,5-dimethylpyrazole, and the mixture was held at 70°C for 1 hour under a nitrogen atmosphere. Subsequently, 12.50 parts by mass of dimethylolpropionic acid were added dropwise. After measuring the infrared spectrum of the reaction solution and confirming that the absorption of the isocyanate group had disappeared, 8.72 parts by mass of N,N-dimethylethanolamine was added. After stirring for 1 hour, an appropriate amount of water was added to prepare an aqueous dispersion (C-2WD) of a blocked isocyanate crosslinking agent (C-2) with a solid content of 30.0% by mass.

[0138] [Example 1] (Preparation of the coating solution) A coating solution with the following composition was prepared. Water 43.47 parts by mass Isopropyl alcohol 30.57 parts by mass Silica sol 4.15 parts by mass (Silica sol with average particle size of 100 nm, solid content concentration of 10.5% by mass) PCPU-1WD 5.42 parts by mass (Solid content concentration 25.0% by mass) PEs-1WD 7.58 parts by mass (Solid content concentration 25.1% by mass) C-1WD 8.43 parts by mass (Solid content concentration 30.0% by mass) Surfactant 0.05 parts by mass (Silicone-based, solid content concentration 10.0% by mass) High-boiling point solvent 0.34 parts by mass

[0139] (Manufacturing of easily adhesive polyester film) As a film raw material polymer, PET resin pellets with an intrinsic viscosity (solvent: phenol / tetrachloroethane = 60 / 40) of 0.62 dl / g and substantially free of particles were dried at 135°C for 6 hours under reduced pressure of 133 Pa. Subsequently, the pellets were fed into an extruder and melt-extruded into a sheet at approximately 280°C. They were then rapidly cooled and solidified on a rotating, cooled metal roll maintained at a surface temperature of 20°C to obtain an unstretched PET sheet.

[0140] Next, the above coating solution was applied to one side of the PET film using the roll-coating method, dried at 80°C, and the coating amount after final stretching and drying was 0.12 g / m². 2 The film was then adjusted to achieve the following: It was subsequently stretched to 4.0 times its original width in the width direction at 150°C using a tenter, and with the width direction length of the film fixed, it was heated at 230°C, followed by a width direction relaxation treatment at 230°C to obtain an easily adhesive polyester film with a thickness of 50 μm.

[0141] The thickness of the easily adhering coating layer of the obtained easily adhering polyester film was 79 nm, and the film haze was 0.54%.

[0142] Next, a laminated polyester film having a functional layer was obtained by applying a functional layer forming solution (hard coat layer forming solution L and M from (4) above, and photocurable adhesive layer forming solution N from (5) above) to the easily adhesive coated layer of the easily adhesive polyester film, according to the formation method described above.

[0143] When the adhesion of the functional layer of the resulting laminated polyester film was evaluated, the adhesion strength X was found to be 96%.

[0144] On the other hand, the above-mentioned easy-to-adhere polyester film was left in a high-temperature, high-humidity chamber at 80°C and 90RH for 24 hours, and then left at room temperature for 12 hours. Subsequently, a functional layer was formed on the easy-to-adhere coating layer of the treated easy-to-adhere polyester film using a functional layer forming coating solution (same as above), thereby obtaining a laminated polyester film.

[0145] When the adhesion of the functional layer of this laminated polyester film was evaluated, the adhesion strength Y was found to be 95%.

[0146] From these results, XY = 1 (%). These results are shown in Table 3.

[0147] The above-mentioned easy-to-adhere polyester film, which had not undergone high-temperature and high-humidity treatment, was rolled up and left for 6 months in an environment with a temperature of 0°C to 30°C and a humidity of 10%RH to 80%RH. After this period, samples of the easy-to-adhere polyester film were taken from the rolls and their adhesion was evaluated in the same manner as described above.

[0148] Table 3 shows the results of the adhesion evaluation (Adhesion Z) of the sample from the roll. Based on these results, adhesion reliability was evaluated as follows: "A" for adhesion of 100% or more, "B" for adhesion of 95% or more but less than 100%, "C" for adhesion of 90% or more but less than 95%, and "D" for adhesion of less than 90%. The results of the adhesion reliability evaluation are recorded in the Adhesion Reliability column of Table 3. For samples with a Z of 90% or more, adhesion reliability can be confirmed.

[0149] The evaluation results showed an adhesion score of 92%, resulting in an adhesion reliability rating of "C". Therefore, it was determined that adhesion reliability was ensured.

[0150] [Examples 2 and 3] An easily adhesive polyester film was obtained in the same manner as in Example 1, except that the thickness of the coating solution was changed to the thickness shown in Table 3.

[0151] The obtained easy-to-adhere polyester film was evaluated in the same manner as in Example 1, and then a laminated polyester film with a functional layer was obtained in the same manner as in Example 1. The results of the various evaluations are shown in Table 3.

[0152] [Examples 4-17] An easily adhesive polyester film was obtained in the same manner as in Example 1, except that the combination of polycarbonate polyurethane resin and polyester resin used was changed to that shown in Table 3.

[0153] The obtained easy-to-adhere polyester film was evaluated in the same manner as in Example 1, and then a laminated polyester film with a functional layer was obtained in the same manner as in Example 1. The results of the various evaluations are shown in Table 3.

[0154] [Example 18] An easily adhesive polyester film was obtained in the same manner as in Example 1, except that the crosslinking agent used was changed to C-2WD.

[0155] The obtained easy-to-adhere polyester film was evaluated in the same manner as in Example 1, and then a laminated polyester film with a functional layer was obtained in the same manner as in Example 1. The results of the various evaluations are shown in Table 3.

[0156] [Examples 19-20] The evaluation was carried out in the same manner as in Example 1, except that the easily adhering polyester film prepared in the same manner as in Example 1 was given the functional layer described in Table 3. The results of each evaluation are shown in Table 3.

[0157] [Comparative Examples 1-10] An easily adhesive polyester film was obtained in the same manner as in Example 1, except that the combination of polycarbonate polyurethane resin and polyester resin used was changed to that shown in Table 3.

[0158] The obtained easy-to-adhere polyester film was evaluated in the same manner as in Example 1, and then a laminated polyester film with a functional layer was obtained in the same manner as in Example 1. The results of the various evaluations are shown in Table 3.

[0159] [Table 3] [Industrial applicability]

[0160] The easily adhering polyester film of the present invention exhibits excellent adhesion between the functional layer and the polyester film (particularly adhesion after long-term storage), and has high adhesion reliability. It also boasts excellent blocking resistance and transparency. Therefore, it can be widely applied to optical applications and other uses.

Claims

1. An easily adhering polyester film having a polyester film substrate and a coating layer on at least one side thereof, The coating layer is formed from a composition comprising a polycarbonate polyurethane resin and a polyester resin, wherein both the polycarbonate polyurethane resin and the polyester resin contain a cyclohexane ring in their respective molecules, and have a structure in which at least one hydrogen atom on the cyclohexane ring is substituted with a hydrocarbon group. An easily adhering polyester film that satisfies the following formula (1). X - Y (%) ≤ 5 ... Equation (1) (In the formula, X represents the adhesion (%) between the polyester film and the functional layer when a laminated polyester film is prepared by forming a functional layer on a coated layer of an easily adhesive polyester film. Y represents the adhesion (%) between the polyester film and the functional layer when an easily adhesive polyester film is left for 24 hours in an environment of 80°C and 90 RH, then left for 12 hours at room temperature, and then a functional layer is formed on the coated layer of the easily adhesive polyester film to prepare a laminated polyester film. Here, adhesion is determined in accordance with the description in JIS-K5400-1990, 8.5.

1. The functional layer is either a hard coat layer formed from a composition containing an acrylic curable resin, or a photocurable adhesive layer formed from a composition containing a photocationic curable component mainly composed of an epoxy compound that does not contain an aromatic ring.

2. The easy-to-adhere polyester film according to claim 1, wherein both the polycarbonate polyurethane resin and the polyester resin have a structure represented by formula (1) in their respective molecules. 【Chemistry 1】 (In the formula, * indicates a bonding site.)

3. The easily adhering polyester film according to claim 2, wherein the structure represented by formula (1) is the structure represented by formula (2). 【Chemistry 2】 (In the formula, * is the same as above.)

4. The easily adhering polyester film according to claim 3, wherein the structure represented by formula (2) is the structure represented by formula (3). 【Transformation 3】 (In the formula, * is the same as above.)

5. The easily adhering polyester film according to claim 4, wherein the structure represented by formula (3) is a structure derived from 1,4-cyclohexanedimethanol.

6. The easy-to-adhere polyester film according to claim 1, wherein the content of cyclohexane ring structures in the polycarbonate polyurethane resin is 5 to 55% by mass, and the content of cyclohexane ring structures in the polyester resin is 5 to 20% by mass.

7. A laminated polyester film comprising a functional layer on a coating layer of an easily adhering polyester film according to any one of claims 1 to 6, wherein the functional layer is a hard coat layer formed from a composition containing an acrylic curable resin, or a photocurable adhesive layer formed from a composition containing a photocationic curable component mainly composed of an epoxy compound that does not contain an aromatic ring.

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