Polyester film and its manufacturing method

Abstract

The present invention provides: an easy-adhesive polyester film that does not damage the opposite side of the coating layer or the functional layer during post-processing such as film formation and the application of functional layers; and a laminated polyester film having the functional layer. The present invention provides an easy-to-adhere 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 polycarbonate polyurethane resin (A), polyester resin (B), end-capped isocyanate crosslinking agent (C), and particles. In a particle shedding test, the amount of particles shed within the field of view is less than 30%.

Description

[Technical Field]

[0001] The present invention provides: an easy-to-adhere polyester film, which does not damage the opposite side of the coating layer or the functional layer formed on the opposite side during post-processing such as film formation and application of functional layers; and a laminated polyester film having the functional layer. [Previous Technology]

[0002] A hard coating film with a transparent hard coating layer is used on the front surface of displays such as touch panels, computers, televisions, and liquid crystal display devices, as well as decorative materials. Furthermore, the panel components used in displays are formed by bonding the hard coating film to a polarizing mirror or to other components, and the bonding is performed by applying an adhesive component.

[0003] As for the transparent plastic film of the substrate, a transparent polyester film is generally used. In order to improve the adhesion between the polyester film of the substrate and the hard coating and the adhesive, an easy-to-adhere coating layer is usually provided on the surface of the polyester film as an intermediate layer.

[0004] For the aforementioned hard-coated thin film, requirements include durability against temperature, humidity, and light, transparency, chemical resistance, scratch resistance, and stain resistance. Furthermore, since it is mostly used on the surface of displays or decorative materials, visual recognizability and design are also required. Therefore, in order to suppress glare and iridescent colors caused by reflected light when viewed from any angle, a multi-layered anti-reflective layer is generally provided, consisting of alternating layers of high-refractive-index and low-refractive-index layers on top of the hard coating.

[0005] In recent years, hard coatings with various compositions have been developed, and the adhesion between the substrate and the hard coating has been investigated based on their composition. For example, in the case of using a film with a hard coating for a display of an LCD TV, in order to ensure high reliability for long-term use, not only is initial adhesion required immediately after lamination, but also properties such as resistance to damp heat and retention of adhesion over time are required.

[0006] The same applies to the aforementioned adhesives, which require durability, transparency, chemical resistance, scratch resistance, and stain resistance under temperature, humidity, and light conditions. Furthermore, since they are mostly used on the surfaces of displays or decorative materials, visual recognizability and design appeal are also required. In recent years, adhesives with various compositions have been developed, and the adhesion between the substrate and the adhesive has been explored based on their composition. For example, in the case of using adhesive-bonded components in the display of an LCD TV, to ensure high reliability for long-term use, not only initial adhesion after lamination is required, but also resistance to damp heat and moisture, and retention of adhesion over time.

[0007] In liquid crystal display devices, due to their image formation method, polarizing plates are disposed on both sides of the glass substrate forming the surface of the liquid crystal panel. Generally, the polarizing plate has the following structure: a polarizing mirror protective film is bonded to both sides of a polarizing mirror made of a polyvinyl alcohol-based film and a dichroic material such as iodine through a hydrophilic adhesive such as a polyvinyl alcohol-based resin. Regarding the protective film used to protect the polarizing mirror, from the viewpoint of optical properties and transparency, triacetyl cellulose film has conventionally been used.

[0008] However, triacetyl cellulose has insufficient durability. When triacetyl cellulose film is used as a polarizing plate in a polarizing mirror protective film under high temperature or high humidity conditions, the performance of the polarizing plate, such as polarization and hue, will decrease. Furthermore, in recent years, in order to meet the trend of thinner displays, there is a need for thinner polarizing plates, but from the viewpoint of maintaining moisture barrier properties, the thinning of triacetyl cellulose film is limited. Therefore, there have been proposals to use polyester film as a polarizing mirror protective film with both durability and moisture barrier properties (for example, see Patent Document 1).

[0009] Triacetyl cellulose films used as protective films for polarizing lenses have undergone alkali treatment or similar processes on their surfaces and exhibit extremely high affinity for hydrophilic adhesives. Therefore, protective films made from triacetyl cellulose films have extremely high adhesion to polarizing lenses coated with hydrophilic adhesives. However, the adhesion between polyester films and hydrophilic adhesives is not sufficient, especially in the case of polyester films that have acquired orientation through stretching treatments. Therefore, in order to improve adhesion to polarizing lenses or hydrophilic adhesives coated on polarizing lenses, it has been reported in the literature to coat the surface of polyester films with highly hydrophilic materials to form a coating layer (for example, see Patent Document 1).

[0010] In the field of conventional easy-to-adhere polyester films, there are reports of laminated polyester films formed by providing a coating layer on at least one side of the polyester film, which have excellent adhesion to surface functional layers such as hard coatings, and the coating layer includes polyester resins containing naphthalic acid components (for example, see Patent Document 2).

[0011] Furthermore, existing literature reports on easily bondable polyester films having a coating layer of polyurethane resin composed of aliphatic polycarbonate polyols with excellent flexibility and high adhesion on at least one side of the polyester film, exhibiting excellent adhesion to optical functional layers under high temperature and humidity conditions (for example, see Patent Document 3). [Prior Art Documents] [Patent Documents]

[0012] [Patent Document 1] Japanese Patent Application Publication No. 2013-063610 [Patent Document 2] Japanese Patent Application Publication No. 2011-246663 [Patent Document 3] Japanese Patent Application Publication No. 2011-168053 [Summary of the Invention]

[0013] [Problem to be Solved by the Invention] In recent years, even when used as display components in areas near the surface, there is a need for high-quality films, especially those with high transparency or no scratches. Furthermore, to improve productivity, there is a tendency to increase the transport speed of film forming as a process condition, necessitating films that do not produce scratches even under more demanding conditions. Display applications generally involve multiple surface processing steps, but there is a problem where scratches can occur during post-processing, thus reducing productivity. In polyester films having a polyester film substrate and a coating layer, the inventors focused on the potential for scratches related to adhesion and slippage, and thus completed the present invention.

[0014] This invention was made against the backdrop of related prior art issues. Specifically, the object of this invention is to provide an easily bondable polyester film that, during post-processing such as film formation and functional layer application of a film having a coating layer, can suppress the formation of scratches on the opposite side of the coating layer contact, and also suppress the formation of scratches on the functional layer formed on the opposite side. Furthermore, this invention provides a laminated polyester film having this functional layer.

[0015] To achieve this objective, the inventors conducted in-depth research and discovered that by controlling the softness of the coating layer, the shedding of particles contained in the coating layer can be suppressed, making it less prone to scratches, thus completing the present invention. That is, the present invention comprises the following components. [Means for Solving the Problem]

[0016] [1] An easy-to-adhere polyester film having a polyester film substrate and a coating layer, the coating layer being formed of a composition containing polycarbonate polyurethane resin (A), polyester resin (B), end-capped isocyanate crosslinking agent (C), and particles, wherein in a particle shedding test, the amount of particles shed within the field of view is less than 30%. [2] The easy-to-adhere polyester film as described in [1], wherein the difference in film haze before and after the aforementioned particle shedding test is less than 0.55%. [3] The easy-to-adhere polyester film as described in [1] or [2] above, wherein the aforementioned polycarbonate polyurethane resin (A) has the structure shown in formula (1) in its molecule.

[0017] (In the formula, * represents the respective bonding location, and n represents an integer from 5 to 10.)

[0018] [4] The easy-adhesive polyester film described in any of [1] to [3], wherein the aforementioned polyester resin (B) is a polyester resin having the structure shown in formula (1) in its molecule.

[0019] (In the formula, * represents the respective bonding location, and n represents an integer from 5 to 10.)

[0020] [5] A method for manufacturing an easy-to-adhere polyester film, which is a method for manufacturing an easy-to-adhere polyester film as described in any one of [1] to [4], comprising the step of coating a coating layer forming composition onto at least one side of a polyester film substrate, wherein the coating layer forming composition comprises a polycarbonate polyurethane resin (A), a polyester resin (B), a capped isocyanate crosslinking agent (C), and particles, wherein the polycarbonate polyurethane resin (A) has the structure shown in formula (1) in its molecule.

[0021] (In the formula, * represents the respective bonding location, and n represents an integer from 5 to 10.)

[0022] The aforementioned polyester resin (B) has the structure shown in formula (1) in its molecule.

[0023] (In the formula, * represents the respective bonding location, and n represents an integer from 5 to 10.)

[0024] The aforementioned end-capped isocyanate-based crosslinking agent (C) has the structure shown in formula (1) in its molecule. (In the formula, * represents each bonding site, and n represents an integer from 5 to 10.) [6] A laminated polyester film having a functional layer further comprising a coating layer of an easy-to-adhere polyester film as described in any one of [1] to [4]. [7] A method for manufacturing a laminated polyester film, comprising a method for manufacturing a laminated polyester film as described in any one of [1] to [4], comprising the step of coating a functional layer forming composition onto a coating layer of an easy-to-adhere polyester film as described in any one of [1] to [4]. [Effects of the Invention]

[0025] The easy-adhesive polyester film of the present invention improves the flexibility of the coating layer and maintains high adhesion to the lubricant particles, thereby preventing particles from falling off the coating layer and preventing scratches on the contact surface caused by falling particles. Therefore, during post-processing such as film forming and functional layer application of the film having the coating layer, when winding it into a roll, it can suppress the formation of scratches on the opposite side of the coating layer contact, and also suppress the formation of scratches on the functional layer formed on the opposite side. Furthermore, since it also has excellent anti-adhesion and transparency, it can be widely used in optical applications, etc.

Implementation Method

[0026] [Forms of the Invention] Polyester Film Substrate The polyester film used as a substrate in the easy-to-adhere 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. In the case of blending with other polymers (e.g., polycarbonate resin, polyimide resin, etc.), it means containing 50% by mass or more of polyester resin; in the case of copolymerization with other monomers, it means containing 50% by mass or more of polyester building units. 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.

[0027] The material of the polyester resin is not particularly limited, but copolymers formed by polycondensation of dicarboxylic acid component and diol component, or blended resins thereof, can be used. Examples of dicarboxylic acid components that constitute polyester resins include: terephthalic acid, isophthalic acid, phthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, dibenzoic acid, diphenoxyethanedicarboxylic acid, dibenzoic 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-methyl adipic acid, trimethyl adipic acid, pimelic acid, azelaic acid, dimeric acid, sebacic acid, octanoic acid, dodecanoic acid, etc.

[0028] Examples of diols constituting polyester resins include: ethylene glycol, propylene glycol, hexanediol, neopentyl glycol, 1,2-cyclohexanediethanol, 1,4-cyclohexanediethanol, decanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-bis(4-hydroxyphenyl)propane, bis(4-hydroxyphenyl) benzoxene, etc.

[0029] One or more dicarboxylic acid components and two diol components may each be used. In addition, other polycarboxylic acid components such as trimellitic acid and other polyol components such as trimethylolpropane may be added as appropriate.

[0030] Regarding polyester resins, specific examples include: polyethylene terephthalate, polyethylene terephthalate, polyethylene terephthalate, polyethylene terephthalate, and polyethylene naphthalate, among which polyethylene terephthalate is preferred from the perspective of balancing physical properties and cost. Furthermore, in order to control optical properties such as polarization, including other copolymer components or other polymers is also a preferred approach. From the viewpoint of controlling the optical properties of polyester films, preferred copolymer components include: diethylene glycol or copolymer components with noronene side chains, etc.

[0031] The inherent viscosity of the polyester resin (solvent: phenol / tetrachloroethane = 60:40) is, for example, 0.50 to 1.0 dl / g.

[0032] To improve the smoothness, winding properties, and other operability of the polyester film, the film may contain inert particles. Examples of inert particles include: inorganic particles such as silica, kaolin, 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 silane, magnesium carbonate, and magnesium hydroxide; and organic particles such as melamine, acrylic acid, styrene, and polysiloxane. This average particle size was measured using the method described in the examples (average particle size based on number obtained by SEM). To maintain high transparency, the content of inert particles in the film is preferably as low as possible. Therefore, it is preferable to make a multilayer structure in which particles are present only on the surface of the film, or to make the film substantially free of particles but contain microparticles only in the coating layer deposited on at least one side of the polyester film.

[0033] Furthermore, the term "substantially free of particles" refers to, for example, in the case of inorganic particles, a content of less than 50 ppm, preferably less than 10 ppm, and most preferably below the detection limit when quantitatively analyzing the elements derived from the particles using fluorescence X-ray analysis. This is because, even without actively adding particles to the substrate film, contaminants from foreign matter, raw material resins, or contaminants adhering to the production line or equipment during the film manufacturing process can inevitably be shed and mixed into the film.

[0034] Furthermore, when the polyester film is made into a multilayer structure, two three-layer structures can be made, in which the inner layer does not substantially contain inert particles but only the outermost layer (the second layer) contains inert particles. This allows for both transparency and processability, which is preferable.

[0035] The polyester film used as the substrate can be a single layer or a laminated film consisting of two or more layers. Furthermore, various additives can be included in the film as needed to achieve the effects of the present invention. Examples of additives include: antioxidants, lightfastness agents, antigelling agents, organic wetting agents, antistatic agents, ultraviolet absorbers, and surfactants. When the film has a laminated structure, it is preferable to include additives as needed according to the function of each layer. For example, adding an ultraviolet absorber to the inner layer to prevent light degradation of the polarizer is also a preferred approach.

[0036] The polyester film can be manufactured by conventional methods. For example, it can be obtained by melting and extruding a material containing the above-mentioned polyester resin into a film shape, and then cooling and solidifying it in a casting drum to form a film. As for the polyester film of the present invention, either a non-stretched film or a stretched film can be used, but from the viewpoint of mechanical strength and chemical resistance durability, a stretched film is preferred.

[0037] When the polyester film is a stretched film, the stretching method is not particularly limited, and longitudinal uniaxial stretching, transverse uniaxial stretching, longitudinal and transverse successive biaxial stretching, and simultaneous longitudinal and transverse biaxial stretching can be used. In the case of a stretched polyester film, stretching can be performed before or after the easily bondable coating layer described later in the laminated process. Alternatively, uniaxial stretching can be performed in the longitudinal or transverse direction before the easily bondable coating layer, and stretching can be performed in the other direction after the laminated coating layer.

[0038] Coating Layer The easily bondable polyester film of the present invention comprises a polyester film and a coating layer. For example, an easily bondable coating layer is laminated on at least one side of the polyester film serving as a substrate. The coating layer of the present invention is a layer formed from a composition comprising polycarbonate polyurethane resin (A), polyester resin (B), end-capped isocyanate crosslinking agent (C), and particles. The present invention can have the coating layer of the present invention on both sides of the polyester film substrate.

[0039] Hereinafter, the components of the coating layer will be described in detail. The adhesive resin constituting the coating layer is a resin with easy adhesion, which includes: an urethane resin having a polycarbonate structure, namely polycarbonate polyurethane resin (A), and a polyester resin (B), and the crosslinking agent includes a capped isocyanate-based crosslinking agent (C).

[0040] The polycarbonate polyurethane resin (A) has the following structure: it contains a cyclohexane ring structure in its molecule and at least one (especially one or two) hydrogen atoms on the cyclohexane ring are replaced by a hydrocarbon group (hereinafter, this structure is referred to as "cyclohexane ring structure"). In other words, it has the following structure: at least one hydrogen atom on the cyclohexane ring is bonded to a carbon atom of a hydrocarbon group (e.g., an alkyl group having 1 to 3 carbon atoms, an alkyl group having 1 to 3 carbon atoms, etc.).

[0041] The polycarbonate polyurethane resin (A) further has in its molecule a structure containing a methylene chain having 5 to 10 carbon atoms (hereinafter, this structure may be labeled as "C5 to C10 methylene chain structure"). The polycarbonate polyurethane resin (A) may be one type or a mixture of two or more types.

[0042] Considering the interaction with the polycarbonate polyurethane resin (A), the polyester resin (B) has a cyclohexane ring structure and / or a C5-C10 methylene chain structure in its molecule. That is, it has both or either a cyclohexane ring structure and a C5-C10 methylene chain structure in its molecule. The polyester resin (B) may be one type or a mixture of two or more types.

[0043] Considering the interaction with polycarbonate polyurethane resin (A) and polyester resin (B), the end-capped isocyanate crosslinking agent (C) has a cyclohexane ring structure and / or a C5-C10 methylene chain structure in its molecule. That is, it has both a cyclohexane ring structure and a C5-C10 methylene chain structure, or either one, in its molecule. The end-capped isocyanate crosslinking agent may be one type or a mixture of two or more types.

[0044] In one state, the polycarbonate polyurethane resin (A) has the structure shown in formula (1) in the molecule;

[0045] (In the formula, * represents the respective bonding location, and n represents an integer from 5 to 10.)

[0046] By having the above-described structure, the polycarbonate polyurethane resin (A) can improve the flexibility of the coating layer and maintain high adhesion to particles (e.g., lubricant particles). Furthermore, it can prevent particles in the coating layer from falling off and prevent scratches on the contact surface caused by falling particles.

[0047] In one state, the polyester resin (B) has the structure shown in formula (1) in the molecule.

[0048] (In the formula, * represents the respective bonding location, and n represents an integer from 5 to 10.)

[0049] By having the above-described structure, the polyester resin (B) improves the flexibility of the coating layer and maintains high adhesion to particles (e.g., lubricant particles). Furthermore, it prevents particles from detaching from the coating layer and prevents scratches on the contact surface caused by detached particles. Moreover, in this invention, good compatibility with polycarbonate polyurethane resin (A) is maintained, improving the adhesion between the substrate and the coating layer. Although not limited to a specific theory, it is speculated that a suitable interaction (stereostructure) is formed between the polycarbonate polyurethane resin (A) and the polyester resin (B), simultaneously satisfying particle retention and flexibility.

[0050] In one state sample, the end-capped isocyanate crosslinking agent (C) has the structure shown in formula (1) in the molecule;

[0051] (In the formula, * represents the respective bonding location, and n represents an integer from 5 to 10.)

[0052] By having the structure shown in formula (1) in its molecule, the end-capped isocyanate crosslinking agent (C) can maintain good compatibility with polycarbonate polyurethane resin (A) and polyester resin (B). It is speculated that due to the good compatibility, the end-capped isocyanate crosslinking agent (C) can exhibit the effect of uniform crosslinking in the resin and forming a stronger coating film.

[0053] Regarding the "cyclohexane ring structure" contained in the molecules of the above-mentioned polycarbonate polyurethane resin (A), polyester resin (B) and crosslinking agent that is a capped isocyanate crosslinking agent (C), for example, the structure shown in formula (1) can be listed.

[0054] (In the formula, * indicates the bonding location.)

[0055] The structure shown in Equation (1) is preferred to be the structure shown in Equation (1a).

[0056] (In the formula, * refers to the same as above.)

[0057] Furthermore, the structure shown in equation (1b) is preferred.

[0058] (In the formula, * refers to the same as above.)

[0059] The structure shown in formula (1b) above is preferably derived from cyclohexanediethanol (especially 1,4-cyclohexanediethanol). In this case, the two asterisks represent sites bonded to the oxygen atoms constituting the resin.

[0060] Furthermore, regarding the “C5-C10 methylene chain structure”, for example, the structure shown in formula (2) can be listed.

[0061] (In the formula, n represents an integer from 5 to 10, and * represents the bonding location.)

[0062] In formulas (1) and (2) above, * represents the site where the atom is bonded to the atom constituting the adhesive resin or crosslinking agent. The atom may be the same or different, and examples include: hydrogen atom, carbon atom, oxygen atom, nitrogen atom, etc. Preferably, at least one of the two * in each formula is a carbon atom, oxygen atom, nitrogen atom, etc. In formula (2) above, n is preferably 5 to 9, more preferably 5 to 6.

[0063] The "cyclohexane ring structure" and "C5-C10 methylene chain structure" contained in the polycarbonate polyurethane resin (A), polyester resin (B), and end-capped isocyanate crosslinking agent (C) may be the same or different.

[0064] By using a coating layer composed of an adhesive resin and a crosslinking agent having such a structure, the adhesion between the polyester film substrate and the functional layer is improved dramatically.

[0065] For this reason, the following can be cited: the coating layer has good compatibility with the composition of the functional layer described later. Furthermore, the functional layer can be obtained by UV curing through UV irradiation, and has a cross-linked mesh structure. The polycarbonate polyurethane resin (A), polyester resin (B), and end-capped isocyanate crosslinking agent (C) of the coating layer all have at least a cyclohexane ring structure or a C5-C10 methylene chain structure in their molecules, thus the resins interact with each other, and the resins are easily compatible and become easily entangled. Furthermore, it is believed that this entangled resin, through entanglement with the mesh structure of the functional layer formed thereon, results in a coating layer with superior adhesion than before. Moreover, it is believed that the coating layer contains polyester resin (B), thus the adhesion to the polyester film as the substrate is also good, resulting in a coating layer with superior adhesion.

[0066] (Polycarbonate polyurethane resin (A)) The polycarbonate polyurethane resin (A) has the following two structures in its molecule: a cyclohexane ring structure, that is, a structure in which the molecule contains a cyclohexane ring structure and at least one hydrogen atom on the cyclohexane ring has been replaced by a hydrocarbon group; and a C5 to C10 methylene chain structure, that is, a structure containing a methylene chain with 5 to 10 carbon atoms.

[0067] The content of the cyclohexane ring structure in the polycarbonate polyurethane resin (A) is typically 5% by mass to 55% by mass, preferably 10% by mass to 50% by mass, and even more preferably 15% by mass to 45% by mass. If the content is 5% by mass or more, the resin strength in the coating layer is maintained due to the sufficient number of cyclohexane ring structure units that allow the resins to interact with each other, and the particle shedding property in the coating layer is also easily improved. If the content is 55% by mass or less, the resin flexibility of the coating layer is maintained, and the particle holding force is strengthened, and the particle shedding property is improved. The content of the cyclohexane ring structure in the polycarbonate polyurethane resin (A) is calculated as the ratio of the mass of the cyclohexane ring structure (-C6H10-CH2-) to 100g of the total mass of the polycarbonate polyurethane resin (A). Specifically, it can be calculated from "the molecular weight and mole% of each component, such as polycarbonate diol and diisocyanate, that constitute polycarbonate polyurethane resin (A)", "the mole% of the component with a cyclohexane ring", and "the proportion of the molecular weight of the component with a cyclohexane ring in the molecular weight".

[0068] The content of C5-C10 methylene chain structures in the polycarbonate polyurethane resin (A) is typically 5% to 55% by mass, preferably 10% to 50% by mass, and even more preferably 15% to 45% by mass. If the content is 5% by mass or more, the sufficient number of units of the C5-C10 methylene chain structures that allow the resins to interact with each other results in increased resin entanglement in the coating layer, maintaining strength and improving adhesion under high temperature and humidity. If the content is 55% by mass or less, the resin flexibility of the coating layer is maintained, and particle shedding is also improved.

[0069] The content of C5-C10 methylene chain structures in polycarbonate polyurethane resin (A) is calculated by the ratio of the mass of C5-C10 methylene chain structures (-(CH2)n-, where n is as described above) to 100g of the total mass of polycarbonate polyurethane resin (A). Specifically, it can be calculated from "the molecular weight and mole % of each component constituting polycarbonate polyurethane resin (A), such as polycarbonate diol and diisocyanate", "the mole % of the component having methylene chains with 5 to 10 carbon atoms", and "the proportion of the molecular weight of the component having methylene chains with 5 to 10 carbon atoms".

[0070] The polycarbonate polyurethane resin (A) is formed by adding a polycarbonate diol component, a diisocyanate component, and a diol component as a chain extender as needed, wherein at least one component contains a cyclohexane ring structure and / or a C5-C10 methylene chain structure, and the polycarbonate polyurethane resin (A) as a whole contains both a cyclohexane ring structure and a C5-C10 methylene chain structure.

[0071] The polycarbonate diol component required for preparing polycarbonate polyurethane resin (A) can be manufactured by reacting the diol component with the carbonate component. Examples of diol components include: ethylene glycol, propylene glycol, hexanediol, neopentyl glycol, 1,2-cyclohexanediethanol, 1,4-cyclohexanediethanol, 1,4-cyclohexanediethanol, decanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-bis(4-hydroxyphenyl)propane, bis(4-hydroxyphenyl)benzene, etc. Among these, 1,2-cyclohexanediethanol, 1,4-cyclohexanediethanol, and 1,4-cyclohexanediethanol, which have the aforementioned cyclohexane ring structure, are particularly preferred. Furthermore, hexanediol, decanediol, 1,5-pentanediol, and 1,6-hexanediol, which possess the aforementioned C5-C10 methylene chain structure, are particularly preferred. Moreover, these diol components can be used alone or in combination of two or more. The ratio when combining two or more is not particularly limited and can be adjusted to obtain polycarbonate or polyurethane with the necessary properties. Examples of carbonate components include dimethyl carbonate, ethyl carbonate, and phosgene.

[0072] Examples of diisocyanate components required for preparing polycarbonate polyurethane resin (A) include: toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylene diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, 4,4-methylene dicyclohexyl diisocyanate, 1,2-bis(isocyanomethyl)cyclohexane, and 1,4-bis(isocyanomethyl)cyclohexane. Among these, isophorone diisocyanate, 4,4-methylene dicyclohexyl diisocyanate, 1,2-bis(isocyanomethyl)cyclohexane, and 1,4-bis(isocyanomethyl)cyclohexane, having the aforementioned cyclohexane ring structure, are particularly preferred. Furthermore, these isocyanate components can be used alone or in combination of two or more. When combining two or more types, the ratio is not particularly limited and can be adjusted in a way that yields polycarbonate or polyurethane with the necessary properties.

[0073] (Polyester Resin (B)) Regarding the polyester resin (B) used in combination with polycarbonate polyurethane resin (A), it has a cyclohexane ring structure and / or a C5-C10 methylene chain structure in its molecule.

[0074] The content of the cyclohexane ring structure in the polyester resin (B) is generally preferably 5% by mass or more and 20% by mass or less, and more preferably 10% by mass or more and 15% by mass or less. By setting the content to 20% by mass or less, it becomes easier to ensure the flowability and flexibility of the resin. By setting it to 5% by mass or more, the number of units of the cyclohexane ring structure that interact with the polycarbonate polyurethane resin (A) can be ensured, thus ensuring the strength of the resin in the coating layer and making it easier to remove particles.

[0075] The content of the cyclohexane ring structure in the polyester resin (B) is calculated as the ratio of the mass of the cyclohexane ring structure (-C6H10-CH2-) to 100g of the total mass of the polyester resin (B). Specifically, it can be calculated from "the mole % and molecular weight of each monomer component constituting the polyester resin (B)," "the mole % of the monomer component having the cyclohexane ring among all monomer components," and "the proportion of the molecular weight of the monomer component having the cyclohexane ring in the molecular weight of the monomer component having the cyclohexane ring."

[0076] The content of C5-C10 methylene chain structures in the polyester resin (B) is generally preferably 5% to 20% by mass, and more preferably 10% to 15% by mass. By setting the content to 20% by mass or less, it becomes easier to ensure the flowability and flexibility of the resin. By setting it to 5% by mass or more, the number of units of the C5-C10 methylene chain structures that interact with the polycarbonate polyurethane resin (A) can be ensured, thus ensuring the strength of the resin in the coating layer and making it easier to remove particles. The content of C5-C10 methylene chain structures in the polyester resin (B) is calculated as the ratio of the mass of the C5-C10 methylene chain structures (-(CH2)n-, where n is as described above) to 100g of the total mass of the polyester resin (B). Specifically, it can be calculated from "the mole % and molecular weight of each monomer component constituting the polyester resin (B)," "the mole % of the monomer components having methylene chains with 5 to 10 carbon atoms in all monomer components," and "the proportion of the molecular weight of the monomer components having methylene chains with 5 to 10 carbon atoms in the molecular weight of the monomer components having methylene chains with 5 to 10 carbon atoms."

[0077] The polyester resin (B) is formed by polycondensation of a dicarboxylic acid component and a diol component, and is a copolymer polyester composed of a dicarboxylic acid component and a diol component. One or more dicarboxylic acid components and diol components may be used. In this invention, at least one of the dicarboxylic acid component and diol component has a cyclohexane ring structure and / or a C5-C10 methylene chain structure.

[0078] Regarding dicarboxylic acid components, examples include: terephthalic acid, isophthalic acid, phthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, dibenzoic acid, diphenoxyethanedicarboxylic acid, dibenzoic 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-methyl adipic acid, trimethyl adipic acid, pimelic acid, azelaic acid, dimeric acid, sebacic acid, octanoic acid, dodecanoic acid, 1,1-cyclohexanediacetic acid, etc. Among these, cyclohexylmethylmalonic acid, cyclohexylmethylsuccinic acid, and 1,1-cyclohexanediacetic acid, which possess the aforementioned cyclohexane ring structure, are particularly preferred.

[0079] Water dispersibility can be imparted to the polyester resin (B). In this case, for example, the dicarboxylic acid component mentioned above, as well as dicarboxylic acid components having hydrophilic groups (such as sulfonyl groups), can be copolymerized. Examples of dicarboxylic acid components having hydrophilic groups include 5-sulfoterephthalic acid, 5-sulfoisophthalic acid, and their salts. The dicarboxylic acid component having this hydrophilic group can be copolymerized in the range of 1 to 10 mol% of the total dicarboxylic acid components.

[0080] If the quantity is small, cyclohexylacetic acid, a monocarboxylic acid, may be used as needed.

[0081] Regarding the diol component, examples include: ethylene glycol, propylene glycol, neopentyl glycol, 1,2-cyclohexanediethanol, 1,4-cyclohexanediethanol, 1,4-cyclohexanediethanol, decanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-bis(4-hydroxyphenyl)propane, bis(4-hydroxyphenyl)benzene, etc. Among these, 1,2-cyclohexanediethanol, 1,4-cyclohexanediethanol, and 1,4-cyclohexanediethanol, which have the aforementioned cyclohexane ring structure, are particularly preferred. Furthermore, hexanediol, decanediol, 1,5-pentanediol, and 1,6-hexanediol, which have the aforementioned C5-C10 methylene chain structure, are particularly preferred.

[0082] The ratio of the above-mentioned dicarboxylic acid component and diol component is not particularly limited, and can be adjusted in a way that yields a polyester with the necessary properties.

[0083] In this invention, the adhesive resin includes polycarbonate polyurethane resin (A) and polyester resin (B). The ratio of the two is not particularly limited to ensure the physical properties of the resulting coating layer. When the total amount of the adhesive resin is set to 100% by mass, the polycarbonate polyurethane resin (A) is generally preferably 35% by mass or more and 85% by mass or less, more preferably 40% by mass or more and 80% by mass or less, and even more preferably 45% by mass or more and 75% by mass or less. By having the polycarbonate polyurethane resin (A) at 35% by mass or more, a balance between the softness and hardness of the polyurethane resin can be ensured, guaranteeing adhesion over time. Furthermore, by having it at 85% by mass or less, a balance between the hardness and softness of the coating layer can be maintained, and softness can also be improved, thus allowing the coating layer to perform its optimal function.

[0084] (Crosslinking Agent) In this invention, a crosslinking agent is included in the composition used in forming the coating layer to form a crosslinked structure between the resins. The inclusion of a crosslinking agent improves adhesion under high temperature and humidity. Furthermore, it is believed that by including a crosslinking agent together with the polycarbonate polyurethane resin (A) and the polyester resin (B), it becomes easier to appropriately adjust the flexibility of the coating layer, thus improving particle shedding resistance. Specifically, from the viewpoint of the long-term stability of the coating solution and the retention of the flexibility of the coating layer, isocyanate-based crosslinking agents (especially the end-capped isocyanate-based crosslinking agent (C) described later) can be cited as examples of crosslinking agents. Additionally, catalysts or the like can be used as needed to promote the crosslinking reaction.

[0085] This isocyanate-based crosslinking agent is preferably a polyisocyanate-based crosslinking agent with two or more functions (or even three or more functions). Examples of such crosslinking agents include: urethane esters, biuret esters, adducts, diketone esters, isotrimeric isocyanates, and other polyisocyanate-based crosslinking agents of polyisocyanate (especially diisocyanate) compounds. Examples of polyisocyanate compounds include: hexamethylene diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, pentamethylene diisocyanate, isoflavone diisocyanate, bis(isocyanomethyl)cyclohexane, and other diisocyanate compounds.

[0086] One or more polyisocyanate crosslinking agents selected from the group consisting of urea esters, biuret esters and adducts of the above-mentioned polyisocyanate crosslinking agents are preferred because they have low steric hindrance as polymers and become more readily interact with the structures shown in formulas (1) and (2) derived from polycarbonate diols constituting polycarbonate polyurethane.

[0087] The so-called urethane ester refers to a compound obtained by reacting a polyisocyanate with an alcohol to form an aminocarbamate and then reacting it with another polyisocyanate. Examples include compounds obtained by reacting a monohydric alcohol (1-butanol, etc.) with dicyclohexylmethane-4,4'-diisocyanate.

[0088] The so-called addition substance refers to an isocyanate with three or more functions obtained by reacting a polyisocyanate with a low molecular weight compound containing active hydrogen. Examples include compounds obtained by reacting trimethylolpropane with hexamethylene diisocyanate and compounds obtained by reacting trimethylolpropane with dicyclohexylmethane-4,4'-diisocyanate.

[0089] By including such urea ester, biuret or adduct in the composition of the coating layer, the reactivity is improved, making it easier to carry out the crosslinking reaction, thereby increasing the crosslinking density of the resulting coating layer and improving the compactness of the resulting coating layer.

[0090] To control the reactivity of isocyanates, the isocyanate-based crosslinking agent should preferably be a capped isocyanate-based crosslinking agent (C) that introduces the capping agent. Examples of capping 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; phenolic compounds such as phenol and cresol; aliphatic alcohols such as methanol and ethanol; and active compounds such as dimethyl malonate and acetone. End-capping agents include methylene-based agents; thiol-based agents such as butyl mercaptan and dodecyl mercaptan; acid-amine-based agents such as acetoaniline and acetate-amine; lactone-amine-based agents such as ε-caprolactam and δ-pentanolide; acetylimine-based agents such as succinylimine and maleimine; oxime-based agents such as acetaldehyde oxime, acetone oxime, and methyl ethyl ketone oxime; and amine-based agents such as diphenylaniline, aniline, and ethyleneimine. From a reactivity point of view, end-capping agents with a pyrazole-based backbone are more suitable for this system.

[0091] Furthermore, from the perspective of improving the interaction with the resin used in combination, the above-mentioned end-capped isocyanate crosslinking agent (C) has a cyclohexane ring structure and / or a C5-C10 methylene chain structure in its molecule.

[0092] The content of the cyclohexane ring structure in the end-capped isocyanate crosslinking agent (C) is generally preferably 10% by mass or more and 40% by mass or less, and more preferably 15% by mass or more and 35% by mass or less. By setting the content to 40% by mass or less, it becomes easier to ensure the mobility and flexibility of the crosslinking agent. By setting it to 10% by mass or more, the number of units of the cyclohexane ring structure that interact with the resin can be ensured, thus ensuring the strength of the resin in the coating layer and expecting an improvement in the particle retention force in the coating layer. The content of the cyclohexane ring structure in the end-capped isocyanate crosslinking agent (C) is calculated as the ratio of the mass of the cyclohexane ring structure (-C6H10-CH2-) to 100g of the total mass of the end-capped isocyanate crosslinking agent (C). Specifically, it can be calculated from "the mole % and molecular weight of each component constituting the end-capped isocyanate crosslinking agent (C)," "the mole % of the components containing the cyclohexane ring in all components," and "the proportion of the molecular weight of the components containing the cyclohexane ring in the molecular weight of the components containing the cyclohexane ring."

[0093] The content of C5-C10 methylene chain structures in the end-capped isocyanate crosslinking agent (C) is generally preferably 10% by mass or more and 40% by mass or less, and more preferably 15% by mass or more and 35% by mass or less. By setting the content to 40% by mass or less, it becomes easier to ensure the flowability and flexibility of the resin. By setting it to 10% by mass or more, the number of units of the C5-C10 methylene chain structures that interact with the resin can be ensured, thus ensuring the strength of the resin in the coating layer and expecting an improvement in the particle retention force in the coating layer. The content of C5-C10 methylene chain structures in the end-capped isocyanate crosslinking agent (C) is calculated as the ratio of the mass of the C5-C10 methylene chain structures (-(CH2)n-, where n is as described above) to 100g of the total mass of the end-capped isocyanate crosslinking agent (C). Specifically, it can be calculated from "the mole % and molecular weight of each component constituting the end-capped isocyanate crosslinking agent (C)," "the mole % of the components having methylene chains with 5 to 10 carbon atoms in all components," and "the proportion of the molecular weight of the components having methylene chains with 5 to 10 carbon atoms in the molecular weight of the components having methylene chains with 5 to 10 carbon atoms."

[0094] The isocyanate-based crosslinking agent (C) has a cyclohexane ring structure and / or a C5-C10 methylene chain structure in its molecule. Examples of diisocyanate components that can be used to prepare this isocyanate-based crosslinking agent (C) include: pentamethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, 4,4-methylene dicyclohexyl diisocyanate, 1,2-bis(isocyanomethyl)cyclohexane, and 1,4-bis(isocyanomethyl)cyclohexane. Among these, isophorone diisocyanate, 4,4-methylene dicyclohexyl diisocyanate, 1,2-bis(isocyanomethyl)cyclohexane, and 1,4-bis(isocyanomethyl)cyclohexane are particularly preferred, as they have a structure in which at least one hydrogen atom on the cyclohexane ring is replaced by a hydrocarbon group. Furthermore, hexamethylene diisocyanate and the like, having a C5-C10 methylene chain structure, are particularly preferred. Also, these isocyanate components can be used alone or in combination of two or more. The ratio when combining two or more is not particularly limited and can be adjusted to obtain an isocyanate-based crosslinking agent that achieves the necessary properties.

[0095] From the viewpoint of imparting water dispersibility to aqueous solvents, the isocyanate-based crosslinking agent (C) preferably incorporates hydrophilic groups. Furthermore, in terms of hydrophilicity, anionic groups such as carboxyl or sulfonic acid groups, and nonionic groups such as oxyalkyl groups, are preferred. Such crosslinking agents with hydrophilic groups can be prepared by reacting a polyisocyanate, which forms the matrix of the isocyanate-based crosslinking agent (C), with compounds possessing reactive groups such as hydrophilic groups and hydroxyl groups.

[0096] Therefore, the isocyanate-based crosslinking agent (C) is a 2-functional or more (or even 3-functional or more) isocyanate-based crosslinking agent, preferably a urethane, biuret or adduct of a polyisocyanate compound.

[0097] When the total mass of the adhesive resin (especially polycarbonate polyurethane resin (A) and polyester resin (B)) and the end-capped isocyanate crosslinking agent (C) is set to 100% by mass, from the viewpoint of adhesion, the content of the adhesive resin is preferably 45-95% by mass, more preferably 55-90% by mass, further preferably 60-90% by mass, and most preferably 80-90% by mass. If it is 95% by mass or less, the coating strength of the coating layer is maintained, and the adhesion under high temperature and high humidity is good. If it is 50% by mass or more, the flexibility of the coating layer is maintained, and the adhesion under normal temperature, high temperature and high humidity is maintained, which is preferred. Furthermore, when the total mass of the adhesive resin and the crosslinking agent is set to 100% by mass, the content of the end-capped isocyanate crosslinking agent (C) is preferably 5-50% by mass, more preferably 10-45% by mass, further preferably 10-40% by mass, and most preferably 10-20% by mass.

[0098] In this invention, the characteristic is that the polycarbonate polyurethane resin (A) used in the coating layer contains a cyclohexane ring structure and a C5-C10 methylene chain structure within its molecule; the polyester resin (B) and the end-capped isocyanate crosslinking agent (C) each contain a cyclohexane ring structure and / or a C5-C10 methylene chain structure, thereby effectively exerting the effects of this invention. The exact mechanism is not yet clear, but the coating layer of this invention, while maintaining the rigidity of the resin, also improves the resin's flexibility, thus performing its optimal function as a coating layer. That is, it not only exhibits excellent adhesion to the substrate, such as the polyester film and functional layer, but also significantly improves adhesion over time. This results in a film that maintains its quality over a long period.

[0099] (Additives) In the coating layer of the present invention, known additives may be added to a extent that does not impair the effects of the present invention, such as surfactants, antioxidants, heat stabilizers, weather stabilizers, ultraviolet absorbers, organic slip agents, pigments, dyes, organic or inorganic particles, antistatic agents, nucleating agents, etc. However, it is preferable not to use substances that are undesirable in the environment, etc.

[0100] To further improve the adhesion resistance of the coating layer, it is preferable to add particles (especially inert particles) to the coating layer. Examples of particles contained in the coating layer include: inorganic particles and organic polymer particles. Examples of inorganic particles include: titanium dioxide, barium sulfate, calcium carbonate, calcium sulfate, silicon dioxide, alumina, talc, kaolin, clay, or mixtures thereof. Furthermore, they can be used in combination with other common inorganic particles, such as calcium phosphate, mica, lithium bentonite, zirconium oxide, tungsten oxide, lithium fluoride, and calcium fluoride. Examples of organic polymer particles include: styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and polysiloxane-based polymer particles.

[0101] The average particle size (average particle size based on the number of particles obtained using SEM; the same applies below) of the inert particles in the coating layer is preferably 0.04 to 2.0 μm, more preferably 0.05 to 1.0 μm. If the average particle size of the inert particles is 0.04 μm or more, the surface of the coating layer is more prone to unevenness, thus improving the smoothness, rollability, and other operability of the easily bondable polyester film, resulting in good processability during lamination, which is preferable. On the other hand, if the average particle size of the inert particles is 3.0 μm or less, the particles are less likely to detach, which is preferable. The particle concentration in the coating layer is preferably 1 to 20% by mass relative to the resin composition.

[0102] (Formation of the coating layer) The coating layer forming composition (hereinafter also referred to as "coating liquid") used to form the coating layer may further contain surfactants to improve leveling properties during coating and to defoam the coating liquid. Examples of surfactants include cationic, anionic, and nonionic surfactants, preferably polysiloxane, acetylene glycol, or fluorine surfactants. These surfactants are preferably contained in the coating layer forming composition to a degree that does not impair the suppression effect or adhesion of iridescent colors under 3-wavelength LED light sources.

[0103] Regarding the method of applying coating liquid to polyester film, it can be applied to either the so-called online coating method, which is applied simultaneously during the polyester film making process, or the so-called offline coating method, which is applied to the polyester substrate film separately by a coating machine after film making. However, the online coating method is more efficient and better.

[0104] Regarding the coating method, any known method may be used for coating the coating liquid onto a polyethylene terephthalate (PET) film. Examples include: reverse roll coating, gravure coating, kiss coating, die coating, roller brush coating, spray coating, air knife coating, rod coating, tube coating, impregnation coating, curtain coating, etc. These methods may be used alone or in combination.

[0105] In this invention, regarding the method of forming a coating layer on a polyester film, an example is a method of coating a polyester film with a coating liquid containing a solvent, particles, and resin and then drying it. Regarding the solvent, examples include water, or a mixture of water and an organic solvent; preferably, from an environmental perspective, it is water alone or a mixture of water and a water-soluble organic solvent. Examples of water-soluble organic solvents include: alcohols such as isopropanol and ethanol; ketones such as methyl ethyl ketone; ethers such as butyl celestine; amines such as triethanolamine; and amides such as N-methylpyrrolidone.

[0106] The concentration of solid components in the coating liquid depends on the type of adhesive resin or solvent, but is preferably 2% by mass or more, and more preferably 4% by mass or more, relative to the total mass of the coating liquid. The concentration of solid components in the coating liquid is preferably 35% by mass or less, and more preferably 15% by mass or less.

[0107] As for the drying temperature after coating, it also depends on the type of adhesive resin, the type of solvent, the presence or absence of crosslinking agent, the concentration of solid components, etc., but it is preferably above 80°C and preferably below 250°C.

[0108] The coating amount of the coating liquid can be adjusted so that the solid content on the dried polyester film is, for example, 0.03 to 0.24 g / m2, or even 0.06 to 0.18 g / m2. If a film stretching step is included after coating and drying, the solid content on the stretched polyester film can be prepared in the above range.

[0109] The stretching step can be performed using either uniaxial stretching or biaxial stretching. The stretched polyester film can be heat-treated (e.g., 70–250°C, preferably 80–245°C) while fixed in a tenter frame, and further relaxed at 120–250°C.

[0110] As described above, the easy-to-adhere polyester film of the present invention can be manufactured through coating, drying, stretching and heat treatment steps.

[0111] The thickness of the coating layer is 30 nm to 200 nm. If the coating is prepared within this range, it is preferable to have both processability and adhesion. More preferably, it is 50 nm to 150 nm, and even more preferably, it is 70 nm to 110 nm. If the coating layer thickness is 30 nm or more, the adhesion is good, which is preferable. If the coating layer thickness is 200 nm or less, adhesion is less likely to occur, which is preferable.

[0112] The thickness of the coating layer is determined by observing the cut film cross-section with a transmission electron microscope (TEM) and taking the average value of the coating layer thickness obtained by randomly measuring 10 points as the coating layer thickness.

[0113] Laminated Polyester Film The present invention also provides a laminated polyester film, which comprises a functional layer having various properties disposed on a coating layer of an easily bondable polyester film. The so-called functional layer refers to a layer with functions such as preventing reflection, suppressing glare, suppressing iris, and suppressing scratches, for example, a hard coating layer, an anti-glare layer, an anti-glare anti-reflective layer, an anti-reflective layer, a low-reflection layer, and an antistatic layer. Various types of functional layers known in the art can be used, and their types are not particularly limited.

[0114] For example, in the case of forming a hard coating layer on the coating layer, the material used for the hard coating layer can be any known material and is not particularly limited. As such a material, resin compounds (especially curing resins) that are polymerized and / or reacted by drying, heat, chemical reaction, or irradiation with an electron beam, radiation, or ultraviolet light can be used. Examples of such curing resins include melamine-based, acrylic-based, polysiloxane-based, and polyvinyl alcohol-based curing resins, but from the viewpoint of obtaining high surface hardness or optical design, photocurable acrylic-based curing resins are preferred. For such acrylic-based curing resins, polyfunctional (meth)acrylate monomers or acrylate oligomers can be used. Examples of acrylate oligomers include polyester acrylates, epoxy acrylates, urethane acrylates, polyether acrylates, polybutadiene acrylates, and polysiloxane acrylates. By mixing reactive diluents, photopolymerization initiators, sensitizers, etc., into these acrylic curable resins, a coating composition for forming the aforementioned optical functional layer can be obtained.

[0115] The aforementioned hard coating can have an anti-glare function that scatters external light. The anti-glare function is obtained by forming an uneven surface on the hard coating. In this case, the haze of the film is ideally 0-50%, more preferably 0-40%, and particularly preferably 0-30%. Of course, 0% is ideal, so it can be 0.2% or more, or 0.5% or more.

[0116] Furthermore, by setting layers with different refractive indices as functional layers and changing the light transmission characteristics, low-reflection processing (anti-reflection processing) that suppresses light reflection can be implemented. Ideally, the refractive index of functional layers such as hard coatings should be adjusted to a reflectance of 0 to 1.0%, more preferably 0 to 0.8%, and especially preferably 0 to 0.5%. Of course, 0% is ideal, but it can also be 0.05% or higher, or 0.1% or higher.

[0117] The easily bondable polyester film of the present invention can be used as a protective film for polarizing mirrors. Generally, a polarizing plate is formed by placing a protective film on both sides of a polarizing mirror, and preferably, the protective film on at least one side of the polarizing mirror is the easily bondable polyester film of the present invention. The protective film on the other side can be the easily bondable polyester film of the present invention, or it can be a non-birefringent film represented by triacetin cellulose film, acrylic film, or norbornene-based film.

[0118] Regarding polarizing mirrors, examples include polyvinyl alcohol-based films containing dichroic materials such as iodine. The protective film for the polarizing mirror is bonded to the polarizing mirror directly or through an adhesive layer, but from the viewpoint of improving adhesion, bonding through an adhesive is preferred. In this case, the coating layer of the easily bondable polyester film of the present invention is preferably disposed on the polarizing mirror surface or the adhesive layer. For preferred polarizing mirrors used to bond the polyester film of the present invention, examples include polarizing mirrors obtained by dyeing and adsorbing iodine or a dichroic material onto a polyvinyl alcohol-based film, performing uniaxial stretching in a boric acid aqueous solution, and washing and drying while maintaining the stretched state. The uniaxial stretching ratio is typically about 4 to 8 times. For polyvinyl alcohol (PVA) based films, PVA is more suitable, and commercially available products such as "Kuraray Vinylon" [Kuraray Co., Ltd.], "Tocello Vinylon" [Tocello Co., Ltd.], and "Nippon Vinylon" [Nippon Synthetic Chemicals Co., Ltd.] can be used. For dichroic materials, examples include iodine, diazo compounds, and polyacetylenic dyes.

[0119] When the adhesive layer is thinned, the adhesive applied to the polarizing mirror is preferably water-based, that is, the adhesive component is dissolved in water or dispersed in water. For example, polyvinyl alcohol resin, urethane resin, etc. can be used as the main component, and to improve adhesion, a composition containing isocyanate compounds, epoxy compounds, etc., can be used as needed. 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.

[0120] When using polyvinyl alcohol-based resins as the main component of an adhesive, in addition to partially saponified polyvinyl alcohol and fully saponified polyvinyl alcohol, modified polyvinyl alcohol-based resins such as carboxyl-modified polyvinyl alcohol, acetyl-modified polyvinyl alcohol, hydroxymethyl-modified polyvinyl alcohol, and amino-modified polyvinyl alcohol can also be used. The concentration of the polyvinyl alcohol-based resin in the adhesive is preferably 1 to 10% by mass, more preferably 2 to 7% by mass.

[0121] As an adhesive applied to the polarizer, a photocurable adhesive is preferred to further improve productivity. The thickness of the cured adhesive layer can be arbitrarily set according to the characteristics of the polarizer, and a smaller thickness is preferred 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. If the thickness of the adhesive layer is 0.01 μm or more, air bubbles are less likely to be mixed into the adhesive layer, resulting in good adhesion and durability. If the thickness of the adhesive layer is 20 μm or less, the reaction rate of the adhesive is sufficient, and the resistance of the polarizer to damp heat is good.

[0122] The photocurable adhesive is preferably composed of an epoxy compound that does not contain an aromatic ring as the main component, and contains a photocationic curable component (I) and a photocationic polymerization initiator (II).

[0123] The photo-cryogenic curing component (I) is preferably a main component of an epoxy compound that does not contain an aromatic ring. The epoxy compound that does not contain an aromatic ring is an epoxy compound other than aromatic epoxy compounds, hereinafter referred to as an aliphatic epoxy compound. An "epoxy compound" is a compound having at least one epoxy group in its molecule. The aliphatic epoxy compound serving as the main component may contain two or more epoxy compounds. The term "main component" refers to an aliphatic epoxy compound content of 50% by mass or more in 100% by mass of the photo-curing adhesive. The aliphatic epoxy compound content is preferably 60% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0124] Aliphatic epoxy compounds may be epoxy compounds having alicyclic rings, or they may be epoxy compounds that do not have alicyclic rings but are composed only of straight-chain hydrocarbon structures and / or branched-chain hydrocarbon structures. 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 atom, nitrogen atom, sulfur atom, halogen atom, etc.).

[0125] The photocationic polymerization initiator (II) can initiate cationic polymerization by irradiation with an active energy line, and harden the photocationic curing component (I) to form an adhesive layer. The photocationic polymerization initiator (II) generates cationic species or Lewis acids by irradiation with an active energy line such as visible light, ultraviolet light, X-rays, or electron beams, thereby initiating the polymerization reaction of the photocationic curing component. Because the photocationic polymerization initiator (II) acts as a catalyst under light, it maintains excellent stability and workability even when mixed with the photocationic curing component.

[0126] Examples of photocationic polymerization initiators (II) include: aromatic diazonium salts; aromatic iodonium salts or aromatic sulfonium salts; iron-aromatic complexes, etc.

[0127] Examples of aromatic diazonium salts include: benzodiazepine hexafluoroantimonate, benzodiazepine hexafluorophosphate, and benzodiazepine hexafluoroborate.

[0128] Examples of aromatic iodonium salts include: diphenyliodonium tetra(pentafluorophenyl)borate, diphenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate, and di(4-nonylphenyl)iodonium hexafluorophosphate.

[0129] Among aromatic sulfides, examples include: triphenylsulfide hexafluorophosphate, triphenylsulfide tetra(pentafluorophenyl)borate, 4,4-bis[diphenyldihydrosulfo]diphenylsulfide hexafluorophosphate, 4,4-bis[bis(β-hydroxyethoxy)phenyldihydrosulfo]diphenylsulfide hexafluoroantimonate, 4,4-bis[bis(β-hydroxyethoxy)phenyldihydrosulfo]diphenylsulfide hexafluorophosphate, 7-[bis(p-toluenemethyl)] [7-[di(p-toluenemethyl)dihydrosulfo]-2-isopropyl9-oxosulfur hexafluoroantimonate, 7-[di(p-toluenemethyl)dihydrosulfo]-2-isopropyl9-oxosulfur tetra(pentafluorophenyl)borate, 4-phenylcarbonyl-4-diphenyldihydrosulfo-diphenyl sulfide hexafluorophosphate, 4-(p-tert-butylphenylcarbonyl)-4-diphenyldihydrosulfo-diphenyl sulfide hexafluoroantimonate, 4-(p-tert-butylphenylcarbonyl)-4-di(p-toluenemethyl)dihydrosulfo-diphenyl sulfide tetra(pentafluorophenyl)borate.

[0130] For example, iron-aromatic complexes include xylene-cyclopentadienyl iron(II) hexafluoroantimonate, cumene-cyclopentadienyl iron(II) hexafluorophosphate, and xylene-cyclopentadienyl iron(II) trifluoromethylsulfonyl methane.

[0131] Photocationic polymerization initiator (II) can be used alone or in combination with two or more. Among the above, aromatic sulfides are particularly preferred because they have ultraviolet absorption characteristics even in the wavelength region around 300 nm, thus imparting an adhesive layer with excellent curability, good mechanical strength, and good adhesion strength.

[0132] The content of photocationic polymerization initiator (II) is preferably 1 to 10 parts by mass, more preferably 2 to 6 parts by mass, relative to 100 parts by mass of the photocationic curing component (I). By containing more than 1 part by mass of photocationic polymerization initiator (II), the photocationic curing component (I) can be sufficiently cured, and the resulting polarizing plate can be endowed with high mechanical strength and adhesion strength. On the other hand, if its content increases, the hygroscopicity of the cured material will increase due to the increase of ionic substances, which may reduce the durability of the polarizing plate. Therefore, the content of photocationic polymerization initiator (II) is preferably 10 parts by mass or less relative to 100 parts by mass of the photocationic curing component (I).

[0133] The applications of the laminated polyester film of the present invention mainly cover all optical films, including: base films for optical components such as prisms, AR (Anti-Reflection) films, hard-coated films, diffuser plates, and shatterproof films in LCDs, flat-panel TVs, CRTs, etc.; near-infrared absorbing filters used as components in the front panels of plasma displays; and transparent conductive films for touch panels or electroluminescent displays. It can be appropriately used for any application.

[0134] Examples of acrylic resins that are cured by electron beam or ultraviolet light to form the above-mentioned functional layers include oligomers of (meth)acrylates as reactive oligomers and compositions of (meth)acrylate monomers as reactive monomers (reactive diluents). Examples of (meth)acrylate oligomers include compounds with reactive (meth)acrylate groups bonded to the backbone of the (meth)acrylate resin, polyester acrylates, epoxy acrylates, polyurethane acrylates, silicone acrylates, melamine acrylates, and polyether acrylates. Regarding (meth)acrylate monomers, examples 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, neopentyltetrol tri(meth)acrylate, dinepentyltetrol hexa(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and neopentyl glycol di(meth)acrylate. A third component may be added as needed, such as low molecular weight polyester resins, polyether resins, acrylic resins, epoxy resins, urethane resins, alkyd resins, spiroacetal resins, polybutadiene resins, polythiol polyene resins, and polyols.

[0135] In the case of electron beam or ultraviolet light curable acrylic resins, the aforementioned resins may use, for example, acetophenones, benzophenones, milcheryl benzoate, α-pentoxime ester, tetramethylthiuram monosulfide, and 9-oxosulfur derivatives as photopolymerization initiators. Furthermore, the photopolymerization initiator may be mixed with, for example, n-butylamine, triethylamine, or tri-n-butylphosphine as photosensitizers.

[0136] Polysiloxane thermosetting resins can be manufactured by hydrolyzing and condensing organosilane compounds, either alone or in combination, under acid or alkali catalysts. Especially for applications requiring low reflectivity, mixing one or more fluorosilane compounds for hydrolysis and condensation further improves low refractive index and stain resistance.

[0137] The laminated polyester film can be manufactured by providing a functional layer on the coating layer of the easy-to-adhere polyester film of the present invention. Specific examples are described below, but are not limited thereto. For example, the present invention can provide the following examples. A method for manufacturing an easy-to-adhere polyester film includes the step of coating a coating layer forming composition onto at least one side of a polyester film substrate, the coating layer forming composition comprising a polycarbonate polyurethane resin (A), a polyester resin (B), and a capped isocyanate-based crosslinking agent (C), and further comprising particles. The components are as described in this specification.

[0138] In one embodiment, the present invention provides a laminated polyester film having a functional layer further present on a coating layer of an easily bondable polyester film. A composition for forming a functional layer (a coating liquid for forming a functional layer) is coated on the coating layer of the aforementioned easily bondable polyester film. Examples of such a composition for forming a functional layer include, for example, the aforementioned electron beam or ultraviolet curable acrylic resin (including its oligomers, monomers, etc.) or silicone thermosetting resin. When the coating layer is provided on both sides of the easily bondable polyester film, the coating can be performed on at least one coating layer. There is no particular need for dilution of the coating liquid for forming a functional layer, but it is not a particular problem to dilute it with an organic solvent according to the requirements of its viscosity, wettability, coating thickness, etc. After the aforementioned coating liquid for forming a functional layer is applied to the film, the coating film can be dried as needed, and then cured by electron beam or ultraviolet irradiation and heating according to its curing conditions, thereby forming a functional layer.

[0139] More typically, a coating liquid for forming a functional layer, as described above, is applied to a coating layer of an easily bondable polyester film using a suitable wire-wound rod or the like, and dried, for example, at 60–100°C for 0.5–10 minutes to remove the solvent. Then, the film coated with the functional layer is irradiated with ultraviolet light of 300 mJ / cm² using, for example, a high-pressure mercury lamp, to obtain a laminated polyester film with a functional layer.

[0140] In this invention, the thickness of the functional layer is preferably 1 to 15 μm. If the thickness of the functional layer is 1 μm or more, it can effectively exert the effects of the functional layer on chemical resistance, scratch resistance, and stain resistance, and is therefore preferred. On the other hand, if the thickness is 15 μm or less, the flexibility of the functional layer is maintained, and there is no risk of cracking, etc., which is also preferred.

[0141] The laminated polyester film with a functional layer disposed on the coating layer of the easy-to-adhere polyester film of the present invention is preferably highly transparent, as it is mainly suitable for optical applications. Ideally, the lower limit of haze is 0%, and the closer to 0%, the better. The upper limit of haze is preferably 2%. If it is below 2%, the light transmittance is good, and a clear image can be obtained in the liquid crystal display device, which is therefore preferred. Haze can be measured, for example, according to the method described in the embodiments below.

[0142] (Evaluation of Particle Shedding Performance) In the particle shedding performance test, the easy-to-adhere polyester film of the present invention exhibits a particle shedding rate of less than 30% within the field of view. Because the particle shedding rate is less than 30%, the easy-to-adhere polyester film of the present invention maintains high adhesion between the particles and resin within the coating layer, preventing particle shedding from the coating layer and preventing damage to the contact surface caused by shed particles. For example, the particle shedding rate is 0.1% to 28%, for example, 0.5% to 27%, or 1.0% to 26%. With the particle shedding rate within such a range, damage to the contact surface caused by shed particles can be prevented, and good smoothness can also be maintained. Here, the particle shedding performance test of the present invention can be performed by the method described later. By means of this method, during post-processing such as film formation and functional layer application of a film with a coating layer, such as when it is wound into a roll, it is possible to evaluate the particle shedding properties of the surface in contact with the coating layer, taking into account friction and pressure.

[0143] The scratch resistance of the opposite side of the polyester film was evaluated using the method described in the examples. Specifically, an easy-to-adhere polyester film was mounted on a friction tester (made by Daiei Scientific Instruments Co., Ltd., RT-200) with the easy-to-adhere layer facing upwards. A film with a low-reflection surface treatment was used at the contact point between the load head (2cm × 2cm, 200g) and the test film, and the film was moved back and forth 10 times at a speed of 2 seconds per round trip at a distance of 10cm. The evaluation of the present invention here assumes that friction occurs under a certain load, and for example, the effect when winding the film roll. After the friction test, the resulting film was observed using a scanning electron microscope (magnification: 3000x), the number of particles X (particles) in the field of view was calculated, and the amount of detachment (%) was calculated from the number of particles Y (particles) in the same field of view before the evaluation using Equation (1). X / Y × 100 (%)... Equation (1)

[0144] For example, the difference in film haze before and after the particle shedding test is less than 0.55%. Preferably, the difference in film haze is 0.10% to 0.50% (or 0.15% to 0.45%), for example, preferably 0.20% to 0.40%. By keeping the film haze difference within this range, scratches on the contact surface caused by shed particles can be prevented, thereby maintaining smoothness and anti-adhesion properties. [Example]

[0145] 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 method for measuring the measured values ​​used in the present invention is as follows.

[0146] (1) Average particle size [Measurement method using scanning electron microscope] The average particle size of the particles present in the coating layer of the present invention can be measured by the following method. The particles are photographed with a scanning electron microscope (SEM), and the maximum diameter (distance between two furthest points) of 300 to 500 particles is measured at a magnification of 2 to 5 mm with the size of the smallest particle. The arithmetic mean of these values ​​is taken as the average particle size.

[0147] [Dynamic Light Scattering Method] The average particle size can also be obtained during the manufacture of particles or thin films using the dynamic scattering method. The sol is diluted with a dispersion medium, and the parameters of the dispersion medium are measured using a submicron particle analyzer N4PLUS (manufactured by Beckman Coulter). The average particle size is calculated using the cumulative method. In the dynamic light scattering method, the average particle size of the particles in the sol is observed; when particles aggregate, the average particle size of those aggregated particles is observed.

[0148] (2) Haze of easy-to-adhere polyester film for optical use The haze of easy-to-adhere polyester film was measured using a turbidimeter (Nippon Denshoku Corporation, NDH2000) in accordance with JIS K 7136:2000.

[0149] (3) The difference in haze (ΔHAZE) between the polyester film before and after the particle shedding test and before the scratch resistance evaluation is calculated using the following formula (2). ΔHAZE=A(%)-B(%)…(2) A(%): Haze of the film before the particle shedding test B(%): Haze of the film after the particle shedding test

[0150] (Evaluation of particle shedding properties) An easy-to-adhere polyester film was mounted onto a friction tester (Daei Scientific Instruments Co., Ltd., RT-200) with the easy-to-adhere layer facing upwards. A film with a low-reflection surface treatment was used at the contact point between the load head (2cm × 2cm, 200g) and the test film. The film was subjected to 10 round trips at a distance of 10cm, each round trip lasting 2 seconds. After the friction test, the resulting film was observed using a scanning electron microscope (magnification: 3000x). The number of particles X (particles) within the field of view was calculated, and the shedding amount (%) was calculated from the number of particles Y (particles) within the same field of view before evaluation using Equation (1). X / Y × 100 (%)… Equation (1)

[0151] (Evaluation of scratch resistance) The thin film with low-reflection surface processing obtained during the above-mentioned particle shedding test was observed and evaluated using an optical microscope (50x), and the scratch resistance was judged according to the following: ◎: The number of scratches after the particle shedding test is less than 2. ○: The number of scratches after the particle shedding test is 2 or more but less than 5. △: The number of scratches after the particle shedding test is 5 or more but less than 8. ×: The number of scratches after the particle shedding test is 8 or more. Here, the number of scratches refers to the number of scratches with a length of 10 mm or more in the reciprocating direction of the load-bearing head.

[0152] (Evaluation of adhesion resistance) Two pairs of samples were cut into 10cm × 5cm squares and stacked with the evaluation surfaces overlapping. A load of 1kg / cm² was applied to the center while the samples were placed in an oven at 50°C for 24 hours. The following evaluation criteria were then used to determine the appearance of the two samples upon peeling. Each sample was tested 5 times. ◎: No sound or peeling residue upon peeling. ○: Slight sound upon peeling but no residue. △: Sound upon peeling and residue remaining on part or all of the surface. ×: No peeling.

[0153] (4) Reduced viscosity ηsp / c (unit: dl / g) 0.10g of polyester resin was dissolved in 25ml of a mixed solvent of phenol / tetrachloroethane (mass ratio 6 / 4) and measured at 30°C using an Ubbelohde viscometer.

[0154] (5) Cross-sectional observation using a transmission electron microscope: After cutting the obtained easy-to-adhere polyester film into 1mm×10mm pieces and embedding them in epoxy resin, a thin section parallel to the short side of the embedded sample was prepared using an ultramicrotome. Next, the sectioned film was stained with ruthenium tetroxide, and areas without obvious damage were observed using a transmission electron microscope (JEM2100, Nippon Electron) at an accelerating voltage of 200kV and magnification of 20000. From the observed image of the coating layer, the thickness of the coating layer was measured at 10 points at each level, and the average value was taken as the thickness of the coating layer.

[0155] (6) The resin composition of polyester was dissolved in deuterated chloroform and analyzed by 1H-NMR using a Varian Gemini-200 nuclear magnetic resonance analyzer (NMR). The molar percentage of each component was determined by the integral ratio.

[0156] (7) The viscosity of the polyester resin dispersion was measured by filling a 140cc glass bottle with an aqueous polyester resin dispersion and using a viscometer model BL (TOKIMEC INC.) No.1 or No.2 rotor at a rotation speed of 60 rpm for 1 minute in a constant temperature bath at 25°C.

[0157] [Polyurethane Resin] Synthesis of polyurethane resin (PCPU-1): In a four-necked flask equipped with a stirrer, a Demrod condenser, a nitrogen inlet tube, a silicone drying tube, and a thermometer, 28.0 parts by mass of 4,4'-diphenylmethane diisocyanate, 63.6 parts by mass of polycarbonate diol with a melting point of 33°C and 1,4-butanediol / 1,6-hexanediol (=75 / 25 (MoR ratio)) as the main raw materials with a number average molecular weight of 1000, 7 parts by mass of dimethylolpropionic acid, and 200 parts by mass of ethyl methyl ketone as a solvent were added. The mixture was stirred at 75°C for 3 hours under nitrogen atmosphere. The infrared spectrum of the reaction solution was measured, confirming that the isocyanate groups in the reaction solution disappeared. Next, after cooling the solution to room temperature, 8.2 parts by mass of triethylamine were added to obtain a polyurethane resin (PCPU-1) solution with a solid content of 50.0% by mass. The polycarbonate polyurethane (PCPU-1) has a total cyclohexane ring structure content of 0.0% by mass and a methylene chain structure with 5 to 10 carbon atoms content of 11.3% by mass.

[0158] Preparation of an aqueous dispersion of polyurethane resin (PCPU-1) (PCPU-1WD): In a reaction vessel equipped with a homogenizer capable of high-speed stirring, a predetermined amount of water was added, the temperature was adjusted to 25°C, and the aforementioned polyurethane resin (PCPU-1) solution was gradually added and dispersed in water while stirring at 2000 min⁻¹. Subsequently, ethyl methyl ketone, used as a solvent, was removed under reduced pressure. The concentration was adjusted by water to prepare an aqueous dispersion (PCPU-1WD) of polycarbonate polyurethane resin (PCPU-1) with a solid content of 35.0% by mass.

[0159] Synthesis of polyurethane resin (PCPU-2) and preparation of aqueous dispersion (PCPU-2WD): Except that the main raw material of polycarbonate diol was changed from 1,4-butanediol / 1,6-hexanediol (=75 / 25 (molar ratio)) to 1,4-cyclohexanediol / 1,6-hexanediol (=75 / 25 (molar ratio)), (PCPU-2) was prepared in the same manner as the synthesis of (PCPU-1) described above, and the aqueous dispersion (PCPU-2WD) was obtained in the same manner as the preparation of (PCPU-1WD). The overall proportion (content) of the cyclohexane ring structure of this polycarbonate polyurethane (PCPU-1) is 29.1% by mass, and the proportion (content) of the methylene chain structure with 5 to 10 carbon atoms is 8.5% by mass.

[0160] [Polyester Resin] Manufacturing of Polyester Resin (PEs-1): Polyester resin (PEs-1) was polymerized according to a known polymerization method. The composition of the resulting polymer was analyzed by 1H-NMR, and the molar percentage of each component was determined by its integral ratio. The results are recorded in Table 1. The reduced viscosity of the resulting polyester resin was 0.583 dl / g. Hereinafter, the abbreviations recorded in Table 1 are described. TPA: Terephthalic acid IPA: Isophthalic acid CHMM: Cyclohexylmethylmalonic acid DSS: Sodium dimethyl isophthalate-5-sulfonate EG: Ethylene glycol HD: 1,6-hexanediol DEG: Diethylene glycol NPG: Neopentyl glycol CHDM: 1,4-cyclohexanediol Here, the proportion (content) of the cyclohexane ring structure of this polyester (PEs-1) is 12.6% by mass, and the proportion (content) of the methylene chain structure with 5 to 10 carbon atoms is 0.0% by mass.

[0161] Preparation of polyester aqueous dispersion (PEs-1WD): In a reactor equipped with a stirrer, thermometer, and reflux device, 30 parts by weight of copolymerized polyester resin (PEs-1) and 15 parts by weight of ethylene glycol-n-butyl ether were added. The mixture was heated and stirred at 110°C to dissolve the resin. After the resin was completely dissolved, 55 parts by weight 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 polyester resin (PEs-1) aqueous dispersion (PEs-1WD) with a solid content of 25.1% by weight. The viscosity of the resulting aqueous dispersion was 84 mPa·s.

[0162] Manufacturing of polyester resin (PEs-2) and preparation of polyester aqueous dispersion (PEs-2WD): Similar to the polymerization of the aforementioned polyester resin (PEs-1), polyester resin (PEs-2) was manufactured according to a known polymerization method. The composition ratio was determined in the same manner as for PEs-1, and the reduced viscosity of the resulting resin was evaluated. The respective results are recorded in Table 1. Here, the overall cyclohexane ring structure of this polyester (PEs-2) was 12.8% by mass, and the proportion (content) of methylene chain structures with 5 to 10 carbon atoms was 0.0% by mass. Similar to the preparation of the aforementioned polyester aqueous dispersion (PEs-1WD), polyester aqueous dispersion (PEs-2WD) was prepared. The solid component concentration and liquid viscosity were evaluated in the same manner as for PEs-1WD. The respective results are recorded in Table 2.

[0163] [Table 1] Composition ratio (from) 1 H-NMR) Reduced viscosity TPA IPA CHMM GCM EG HD DEG CHDM [dl / g] PEs-1 34 34 28 4 80 0 20 0 0.583 PEs-2 46 47 7 twenty two 45 2 31 0.493

[0164] [Table 2] NV ηB % mPa・s PEs-1WD 25.1 84 PEs-2WD 24.9 46

[0165] [Polyisocyanate Compounds] Polyisocyanate compound (PI-1): Referring to Japanese Patent Application Publication No. 8-225511, a polyisocyanate compound (PI-1) having a biuret structure was prepared using dicyclohexylmethane-4,4'-diisocyanate. The NCO concentration of this polyisocyanate compound was 16.0 wt%. Furthermore, the proportion (content) of the cyclohexane ring structure was 37.0 wt%, and the proportion (content) of the methylene chain structure with 5 to 10 carbon atoms was 0.0 wt%.

[0166] Polyisocyanate compound (PI-2): A polyisocyanate compound (PI-2) having a biuret structure was prepared in the same manner as polyisocyanate compound (PI-1) by replacing dicyclohexylmethane-4,4'-diisocyanate with cyclohexane-1,2-dimethylbis(methylene)diisocyanate. The NCO concentration of this polyisocyanate compound was 21.6 wt%. Furthermore, the proportion (content) of the cyclohexane ring structure was 50.0% by mass, and the proportion (content) of the methylene chain structure with 5 to 10 carbon atoms was 0.0% by mass.

[0167] [Crosslinking Agent] Preparation of an aqueous dispersion (C-1WD) of a capped isocyanate-based crosslinking agent (C-1): 140.1 parts by weight of a polyisocyanate compound (PI-1) with a biuret structure, based on dicyclohexylmethane-4,4'-diisocyanate, 50.0 parts by weight of dipropylene glycol dimethyl ether, and 53.9 parts by weight of 3,5-dimethylpyrazole were added to a flask equipped with a stirrer, thermometer, and reflux condenser. The mixture was stirred at 70°C for 2 hours under nitrogen atmosphere. Subsequently, the infrared spectrum of the reaction solution was measured to confirm the disappearance of isocyanate group absorption. Next, after cooling to room temperature, 6 parts by weight of polyethylene glycol (n=12) monolaurate were added, and water was added while stirring at 2000 min⁻¹. The concentration was adjusted with water to prepare an aqueous dispersion (C-1WD) of capped isocyanate-based crosslinking agent (C-1) with a solid content of 30.0% by weight. Here, the proportion (content) of the cyclohexane ring structure in the solid component of this end-capped isocyanate crosslinking agent (C-1) is 26.7% by mass, and the proportion (content) of the methylene chain structure with 5 to 10 carbon atoms is 0 by mass.

[0168] Preparation of an aqueous dispersion (C-2WD) of a capped isocyanate crosslinking agent (C-2): In the same manner as the preparation of the aqueous dispersion (C-1WD), an aqueous dispersion (C-2WD) of a capped isocyanate crosslinking agent (C-2) was prepared using a polyisocyanate compound (PI-2) and an adduct of the polyisocyanate (PI-4).

[0169] The proportion (content) of cyclohexane ring structure in the solid component of the end-capped isocyanate crosslinking agent (C-2) is 32.9% by mass, and the proportion (content) of methylene chain structure with 5 to 10 carbon atoms is 0% by mass.

[0170] [Example 1] (Preparation of coating liquid) A coating liquid with the following composition was prepared. water 43.47 parts by weight Isopropanol 30.57 parts by weight Silica sol A-1 4.15 parts by weight (Silica sol with an average particle size of 100 nm and a solid content concentration of 4.0% by mass) PCPU-1WD 5.42 parts by weight (Solid component concentration 35.0% by mass) PEs-1WD 7.58 parts by weight (Solid component concentration 25.1% by mass) C-1WD 8.43 parts by weight (Solid component concentration 30.0% by mass) surfactants 0.05 parts by weight (Silicone-based, solid content 10.0% by mass) high boiling point solvent 0.34 parts by weight

[0171] (Manufacturing of Easy-to-Adhere Polyester Film) PET resin granules 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 granules were fed to an extruder and melt-extruded into sheets at approximately 280°C, and then rapidly cooled and solidified on rotating cooling metal rollers with a surface temperature maintained at 20°C. This yielded an unstretched PET sheet.

[0172] Next, the above coating liquid is applied to one side of the PET film by roller coating and dried at 80°C. The coating weight after final stretching and drying is adjusted to 0.12 g / m2. The film is then stretched 4.0 times its original width at 150°C using a tenter frame. With the width length of the film fixed, it is heated at 230°C and then relaxed in the width direction at 230°C to obtain an easy-to-adhere polyester film with a thickness of 50 μm.

[0173] The thickness of the coating layer of the obtained easy-to-adhere polyester film is 102 nm, and the haze of the film is 0.66%.

[0174] The particle shedding property of the obtained easy-to-adhere polyester film was evaluated, and the result X was 12%.

[0175] [Examples 2-3, 5-7] Except that the polycarbonate polyurethane resin, polyester resin, crosslinking agent and particles used were changed to the combination described in Table 3, an easy-to-adhere polyester film was made in the same manner as in Example 1.

[0176] The resulting easy-to-adhere polyester film was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 3.

[0177] [Examples 4, 9, 10, 14, 15] Except that the polycarbonate polyurethane resin, polyester resin, and crosslinking agent used were changed to the combinations listed in Table 3, and the particles were made in the same manner as in Example 1, except that in addition to silica sol A-1, silica sol A-2 (average particle size 80 nm, solid content concentration 40.0% by mass) or silica sol A-3 (average particle size 50 nm, solid content concentration 40.0% by mass) were also used.

[0178] 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 various evaluation results are recorded in Table 3.

[0179] [Examples 8, 11-12] Except that the polycarbonate polyurethane resin, polyester resin, and crosslinking agent used were changed to the combinations listed in Table 3, and the particles were changed to silica sol A-4 (average particle size 450 nm, solid content concentration 4.0 wt%) or silica sol B-1 (average particle size 50 nm, solid content concentration 3.5 wt%) or particle C (average particle size 300 nm, solid content concentration 20 wt%) instead of silica sol A-1, an easy-to-adhere polyester film was prepared in the same manner as in Example 1.

[0180] 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 various evaluation results are recorded in Table 3.

[0181] [Example 13] Except that the polycarbonate polyurethane resin, polyester resin, and crosslinking agent used were changed to the combination listed in Table 3, and particles D (average particle size 45 nm, solid content concentration 13% by mass) were used in addition to silica sol A-1, an easy-to-adhere polyester film was made in the same manner as in Example 1.

[0182] 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 various evaluation results are recorded in Table 3.

[0183] [Comparative Example 1] (Preparation of Coating Solution) A coating solution with the following composition was prepared, and an easy-to-adhere polyester film was made in the same manner as in Example 1. water 47.63 parts by weight Isopropanol 33.28 parts by weight Silica sol A-1 4.52 parts by weight (Silica sol with an average particle size of 100 nm and a solid content concentration of 4.0% by mass) PCPU-2WD 5.90 parts by weight (Solid component concentration 35.0% by mass) PEs-1WD 8.25 parts by weight (Solid component concentration 25.1% by mass) surfactants 0.05 parts by weight (Silicone-based, solid content 10.0% by mass) high boiling point solvent 0.37 parts by weight

[0184] 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 various evaluation results are recorded in Table 3.

[0185] [Comparative Example 2] Except that the polycarbonate polyurethane resin, crosslinking agent, and particles used were changed to the combination described in Table 3, and an equal amount of polyvinyl alcohol (manufactured by Kuraray Co., Ltd.) was used to replace the polyester resin, an easy-to-adhere polyester film was prepared in the same manner as in Example 1.

[0186] 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 various evaluation results are recorded in Table 3.

[0187] [Comparative Examples 3 and 4] Except for removing the polycarbonate polyurethane resin listed in Table 3, the easy-to-adhere polyester film was prepared in the same manner as in Example 1.

[0188] The resulting 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 various evaluation results are recorded in Table 3.

[0189] [Table 3] PU Pes Crosslinking agent Particle types ① Particle types ② Coating thickness Scratch evaluation The amount of particles shed before and after learning ΔHAZE Anti-adhesion nm ×~◎ % % ×~〇 Example 1 PCPU-1WD PEs-1WD C-1WD Silicon dioxide A-1 — 102 〇 12 0.34 〇 Example 2 PCPU-1WD PEs-1WD C-2WD Silicon dioxide A-1 — 105 〇 11 0.32 〇 Example 3 PCPU-2WD PEs-1WD C-1WD Silicon dioxide A-1 — 90 〇 15 0.38 〇 Example 4 PCPU-2WD PEs-1WD C-1WD Silicon dioxide A-1 Silicon dioxide A-2 98 〇 18 0.40 ◎ Example 5 PCPU-2WD PEs-2WD C-1WD Silicon dioxide A-1 — 96 ◎ 9 0.30 〇 Example 6 PCPU-2WD PEs-2WD C-1WD Silicon dioxide A-3 — 90 ◎ 7 0.27 〇 Example 7 PCPU-2WD PEs-2WD C-2WD Silicon dioxide A-1 — 90 ◎ 8 0.27 〇 Example 8 PCPU-2WD PEs-2WD C-2WD Silicon dioxide A-4 — 105 〇 19 0.44 ◎ Example 9 PCPU-2WD PEs-2WD C-2WD Silicon dioxide A-1 Silicon dioxide A-2 98 ◎ 8 0.32 〇 Example 10 PCPU-2WD PEs-2WD C-2WD Silicon dioxide A-4 Silicon dioxide A-3 97 △ 26 0.54 ◎ Example 11 PCPU-2WD PEs-2WD C-2WD Silicon dioxide B-1 — 92 ◎ 5 0.20 〇 Example 12 PCPU-2WD PEs-2WD C-2WD Particle C — 95 〇 18 0.39 ◎ Example 13 PCPU-2WD PEs-2WD C-2WD Silicon dioxide A-1 Particle D 95 ◎ 8 0.35 ◎ Example 14 PCPU-2WD PEs-2WD C-2WD Silicon dioxide A-1 Silicon dioxide A-2 155 ◎ 6 0.18 ◎ Example 15 PCPU-2WD PEs-2WD C-2WD Silicon dioxide A-1 Silicon dioxide A-2 46 〇 15 0.35 ◎ Comparative Example 1 PCPU-2WD PEs-2WD — Silicon dioxide A-1 — 102 × 35 0.55 〇 Comparative Example 2 PCPU-1WD None (PVA) C-1WD Silicon dioxide A-4 Silicon dioxide A-3 98 × 50 0.64 〇 Comparative Example 3 — PEs-2WD C-2WD Silicon dioxide A-1 — 99 × 34 0.55 〇 Comparative Example 4 — PEs-2WD — Silicon dioxide A-1 — 95 × 42 0.59 〇

[0190] The easy-adhesive polyester film of the present invention improves the flexibility of the coating layer and maintains high adhesion to the lubricant particles, thereby preventing particles from falling off the coating layer and preventing scratches on the contact surface caused by falling particles. Therefore, during post-processing such as film forming and functional layer application of the film having the coating layer, when winding it into a roll, it can suppress the formation of scratches on the opposite side of the coating layer contact, and also suppress the formation of scratches on the functional layer formed on the opposite side. Furthermore, since it also has excellent anti-adhesion and transparency, it can be widely used in optical applications, etc.

[0191] On the other hand, Comparative Example 1, lacking the end-capped isocyanate-based crosslinking agent (C), suffers scratches on the opposite side of the coating layer and also on the functional layer formed on the opposite side. Comparative Example 2, lacking the polyester resin (B) of the present invention, suffers scratches on the opposite side of the coating layer and also on the functional layer formed on the opposite side. Comparative Examples 3 and 4, lacking the polycarbonate-polyurethane resin (A), suffer scratches on the opposite side of the coating layer and also on the functional layer formed on the opposite side. [Industrial Applicability]

[0192] The easy-to-adhere polyester film of the present invention exhibits excellent adhesion between the functional layer and the polyester film (especially after long-term storage), resulting in high adhesion reliability. Furthermore, it also possesses excellent resistance to adhesion and transparency. Therefore, it can be widely used in optical applications, etc.

Claims

1. An easy-to-adhere polyester film having a polyester film substrate and a coating layer, wherein the coating layer is formed of a composition containing polycarbonate polyurethane resin (A), polyester resin (B), a capped isocyanate crosslinking agent (C), and particles, wherein in a particle shedding test, the amount of particles shed within the field of view is less than 30%, wherein the aforementioned capped isocyanate crosslinking agent (C) has the structure shown in formula (1) in its molecule (where * represents the respective bonding sites).

2. The easy-to-adhere polyester film as requested in claim 1, wherein the difference in film haze before and after the aforementioned particle shedding test is less than 0.55%.

3. The easy-bonding polyester film of claim 1, wherein the aforementioned polycarbonate polyurethane resin (A) has the structure shown in formula (1) in the molecule (where * denotes the respective bonding sites).

4. The easy-bonding polyester film of claim 1, wherein the aforementioned polyester resin (B) is a polyester resin having the structure shown in formula (1) in its molecule (where * denotes the respective bonding sites).

5. A method for manufacturing an easy-to-adhere polyester film, comprising the step of coating a coating layer forming composition onto at least one side of a polyester film substrate, the coating layer forming composition comprising a polycarbonate polyurethane resin (A), a polyester resin (B), and a capped isocyanate crosslinking agent (C), wherein the polycarbonate polyurethane resin (A) has the structure shown in formula (1) in its molecule (where * denotes the respective bonding sites), the aforementioned polyester resin (B) has the structure shown in formula (1) in its molecule (where * denotes the respective bonding sites), and the aforementioned capped isocyanate crosslinking agent (C) has the structure shown in formula (1) in its molecule (where * denotes the respective bonding sites).

6. A laminated polyester film having a functional layer on a coating layer of an easy-to-adhere polyester film as claimed in claim 1.

7. A method for manufacturing a laminated polyester film, comprising the step of coating a functional layer forming composition onto a coating layer of an easy-to-adhere polyester film as claimed in claim 1.