WO2026079334A1 - Easy-adhesion polyester film - Google Patents

Abstract

The present invention addresses the problem of providing an easy-adhesion polyester film that has excellent antistatic properties on an easy-adhesion layer front surface, is such that an antistatic agent in an easy-adhesion layer is prevented from being transferred to the rear surface (back surface) of the easy-adhesion polyester film itself, and that also has excellent bonding properties to a functional layer such as a hard coat. The easy-adhesion polyester film has a polyester film substrate and an easy-adhesion layer on at least one surface of the polyester film substrate, the easy-adhesion layer containing a crosslinking agent, an antistatic agent, and a polyester resin having a polycyclic aromatic skeleton. The water contact angle of the easy-adhesion layer front surface, the sulfur atom ratio of the easy-adhesion layer front surface, and adhesion when a functional layer is provided on the easy-adhesion layer satisfy a specific relationship.

Description

Easy-to-adhere polyester film

This invention relates to an easily adhesive polyester film that exhibits excellent adhesion to various functional layers, blocking resistance, transparency, and antistatic properties. More specifically, it relates to an easily adhesive polyester film suitable for optical applications.

Hard-coat films, which consist of a laminated transparent hard-coat layer, are used on the front surfaces of displays such as touch panels, computers, televisions, and liquid crystal displays, as well as decorative materials. Furthermore, transparent polyester film is commonly used as the base material, and to improve the adhesion between the polyester film and the hard-coat layer, an easily adhesive layer is often provided on the surface of the polyester film as an intermediate layer.

The aforementioned hard coat film is required to have durability against temperature, humidity, and light, as well as transparency, chemical resistance, scratch resistance, and stain resistance. Furthermore, because it is often used on the surfaces of displays and decorative materials, visibility and aesthetic appeal are also required. Therefore, to suppress glare and iridescent coloration caused by reflected light when viewed from any angle, it is common practice to provide a multi-layer anti-reflective layer on top of the hard coat layer, consisting of alternating layers of high and low refractive index layers.

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

In the field of conventional easy-to-adhere polyester films, when a polyester resin containing naphthalenedicarboxylic acid is used in an easy-to-adhere layer, it exhibits excellent adhesion to the polyester film substrate and has been proposed as a suitable example (see, for example, Patent Document 1). Furthermore, a method has been proposed in which a polyurethane resin containing a polycarbonate component is used in the easy-to-adhere layer as a resin with excellent flexibility and high adhesion (see, for example, Patent Document 2).
However, although adhesion was confirmed in all cases, an easily adhesive polyester film that maintained antistatic properties had not been obtained.

Polyester films have high insulating properties, and static electricity during various processes often leads to problems in the functional layer application process, such as dust adhesion causing missed application of the hard coat layer coating solution, and poor handling due to film-to-film adhesion caused by triboelectric charging, resulting in reduced yield.

Japanese Patent Publication No. 2011-246663 Japanese Patent Publication No. 2011-168053

This invention was made against the backdrop of the problems of the prior art described above. Specifically, the object of this invention is to provide an easily adhesive polyester film that exhibits excellent antistatic properties on the surface of the easily adhesive layer, suppresses the migration of the antistatic agent in the easily adhesive layer to the back surface of the easily adhesive polyester film itself, and furthermore, exhibits excellent adhesion to functional layers such as hard coats.

The inventors of this invention have diligently studied and developed the present invention to achieve the above objective. Specifically, the present invention has the following configuration.
1. A polyester film substrate and having an easy-adhesion layer on at least one side thereof,
The easy-adhesion layer is formed from an easy-adhesion layer forming composition,
The aforementioned easy-adhesion layer-forming composition is formed from a composition comprising a polyester resin having a polycyclic aromatic skeleton, a crosslinking agent, and an antistatic agent.
The water contact angle on the surface of the easy-adhesion layer is 45° or more and 60° or less.
The sulfur atom ratio (As:at%) of the surface of the easy-adhesion layer, determined by X-ray photoelectron spectroscopy (ESCA), satisfies the following formula (1):
1.2 ≦ As ≦ 3.0 ... Formula (1)
An easy-to-adhere polyester film having an adhesion X (%) of 95% or more when a functional layer is provided on the easy-to-adhere layer.
2. The easy-to-adhere polyester film according to the first description above, wherein the surface resistivity of the easy-to-adhere layer surface is greater than 1.0 × ^10¹² Ω/sq and less than 1.0 × ^10¹⁴ Ω/sq.
3. The easy-to-adhere polyester film according to the first or second above, wherein the antistatic agent is a sulfate-type ionic antistatic agent.
4. The easy-to-adhere polyester film according to the first to third claims, wherein the polyester having a polycyclic aromatic skeleton is a polyester having a naphthalene skeleton.
5. A laminated polyester film having one or more functional layers selected from the group consisting of a hard coat layer, an anti-glare layer, an anti-glare anti-reflective layer, an anti-reflective layer, and a low-reflection layer, on the easy-adhesion layer of the easy-adhesion polyester film described in any of the first to fourth above.

The easily adhesive polyester film of the present invention exhibits excellent antistatic properties, suppresses the migration of antistatic agents to the back surface even under high temperature and high humidity conditions, and provides an easily adhesive polyester film that maintains antistatic performance while ensuring reliable adhesion to functional layers such as hard coat layers, thus enabling a wide range of applications, including optical applications.

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

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

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

The dicarboxylic acid and diol components constituting the polyester resin may be one or more of each. Furthermore, other polycarboxylic acid components such as trimellitic acid and other polyol components such as trimethylolpropane may be added as appropriate.

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

Specifically, examples of polyester resins include polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. Among these, polyethylene terephthalate is preferred due to its balance of physical properties and cost. Furthermore, it is preferable to include other copolymer components or other polymers to control optical properties such as polarization. From the viewpoint of controlling the optical properties of the polyester film, preferred copolymer components include diethylene glycol and copolymer components having norbornene in their side chains.

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

Furthermore, "substantially free of particles" means, for example, in the case of inorganic particles, that when elemental analysis of particles is performed quantitatively using X-ray fluorescence analysis, the content is 50 ppm or less, preferably 10 ppm or less, and most preferably below the detection limit. This is because even without actively adding particles to the base film, contamination components originating from foreign substances, or dirt adhering to the raw material resin or the film manufacturing process lines and equipment, can inevitably become mixed into the film through detachment.

Furthermore, when using a multilayer structure for polyester film, a two-layer, three-layer configuration is possible, where particles are substantially absent in the inner layers and present only in the outermost layers (the second layer). This allows for a balance between transparency and processability, which is preferable.

The polyester film used as the base material may be a single layer or a laminate of two or more layers. Furthermore, various additives can be incorporated into the film as needed, within the range that the effects of the present invention are achieved. Examples of additives include antioxidants, lightfastness agents, gelation inhibitors, organic wetting agents, antistatic agents, UV absorbers, and surfactants. If the film has a laminated structure, it is also preferable to incorporate additives according to the function of each layer as needed. For example, adding a UV absorber to the inner layer to prevent photodegradation of the polarizer is a preferred embodiment.

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

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

(Easy adhesive layer)
The easy-to-adhere polyester film of the present invention has an easy-to-adhere layer laminated on a polyester base film as described above. The easy-to-adhere layer can be formed from an easy-to-adhere layer forming composition. The easy-to-adhere layer forming composition comprises at least a binder resin, a crosslinking agent, and an antistatic agent, and may also contain other additives.

The following provides a detailed explanation of the composition of each component of the easy-adhesion layer-forming composition.

(Binder resin)
The binder resin constituting the easy-adhesion layer-forming composition is a resin with easy adhesion properties. From the viewpoint of particle retention and adhesion, polyester is suitable, and in the present invention, polyester having a polycyclic aromatic skeleton is optimal. This is partly due to its compatibility with the composition of the hard coat layer described later, but it is also suitable from the viewpoint of conjugated interactions when the composition of the hard coat layer has an aromatic skeleton.

Specific examples of polyesters having a polycyclic aromatic skeleton include polyesters with a naphthalene skeleton, polyesters with a fluorene skeleton, polyesters with an anthracene skeleton, and polyesters with a phenanthrene skeleton.

Polyester resin is a copolymer polyester formed by the polycondensation of a dicarboxylic acid component and a diol component. One or more dicarboxylic acid and diol components may be used. In this invention, at least one of the dicarboxylic acid and diol components has a polycyclic aromatic skeleton structure.

Examples of dicarboxylic acid components include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfoncarboxylic acid, 9,9-dimethyl-9H-fluorene-2,7-dicarboxylic acid, anthracenedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, and 1,3-cyclohexanedicarboxylic acid. Examples include ammonium compounds, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, cyclohexylmethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, cyclohexylmethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, azelaic acid, dimeric acid, sebacic acid, suberic acid, dodecadicarboxylic acid, and 1,1-cyclohexanediacetic acid. Among these, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonic acid, 9,9-dimethyl-9H-fluorene-2,7-dicarboxylic acid, and anthracenedicarboxylic acid are particularly preferred because they possess the aforementioned polycyclic aromatic skeleton.

Examples of diol components include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediethanol, decamethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexadiol, 1,2-naphthalenediol, 1,3-naphthalenediol, 1,4-naphthalenediol, 2,6-naphthalenediol, 2,7-naphthalenediol, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, 2,2-bis(4-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)sulfone. Among these, 1,2-naphthalenediol, 1,3-naphthalenediol, 1,4-naphthalenediol, 2,6-naphthalenediol, 2,7-naphthalenediol, and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene are particularly preferred because they possess the aforementioned polycyclic aromatic skeleton.

The ratio of the dicarboxylic acid and diol components when combining them is not particularly limited and can be adjusted to obtain a polyester with the desired properties.

As the binder resin, a polyester having a polycyclic aromatic skeleton may be used alone and included in the easy-adhesion layer-forming composition, but other types of resins may also be used in combination to form the easy-adhesion layer. In that case, considering the adhesion to the substrate, polyester resins and polyurethane resins are preferred.

The polyester is preferably present in an amount of 10% to 90% by mass relative to the total solid content of the resin and crosslinking agent contained in the easy-adhesion layer-forming composition. More preferably, it is present in an amount of 15% to 85% by mass. When the polyester resin content is 90% by mass or less, adhesion to functional layers such as hard coat layers under high temperature and high humidity conditions is preferred. Conversely, when the content is 10% by mass or more, adhesion to polyester substrate films is more easily maintained at room temperature and under high temperature and high humidity conditions, which is preferred.

(Crosslinking agent)
In the present invention, it is preferable that the composition used for forming the easily adhesive layer contains a crosslinking agent in order to form a crosslinked structure between resins within the easily adhesive layer. By including a crosslinking agent, it becomes possible to further improve adhesion under high temperature and high humidity conditions.
For example, in the easily adhesive layer according to the present invention, if a crosslinking agent is not included, the water contact angle tends to fall outside the range of the present invention. When a crosslinking agent is not included and the water contact angle falls outside the range of the present invention, although the detailed mechanism has not been analyzed, the surface resistivity and adhesion after moist heat treatment decrease. Therefore, the present invention can improve both the surface resistivity and adhesion after moist heat treatment by including a crosslinking agent.
Specific crosslinking agents include, for example, urea-based, epoxy-based, melamine-based, isocyanate-based, oxazoline-based, and carbodiimide-based crosslinking agents. Among these, isocyanate-based crosslinking agents are preferred from the viewpoint of the long-term stability of the coating solution and the effect of improving adhesion under high temperature and high humidity treatment. Furthermore, catalysts and the like can be used as appropriate to promote the crosslinking reaction.

When the easy-adhesion layer-forming composition contains a binder resin and a crosslinking agent, the binder resin content is preferably 50 to 95% by mass, more preferably 55 to 90% by mass, and even more preferably 60 to 90% by mass, when the total mass of the binder resin and crosslinking agent is 100% by mass. A content of 95% by mass or less maintains the strength of the easy-adhesion layer coating film and provides good adhesion under high temperature and high humidity conditions. A content of 50% by mass or more maintains the flexibility of the easy-adhesion layer and provides good adhesion under normal temperature and high temperature and high humidity conditions, which is preferable. Furthermore, when the total mass of the binder resin and crosslinking agent is 100% by mass, the crosslinking agent content is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, even more preferably 10 to 40% by mass, and most preferably 10 to 20% by mass.

When using isocyanate-based crosslinking agents, it is preferable to use blocking agents to control the reactivity of the isocyanates. Examples of blocking agents include bisulfite compounds such as sodium bisulfite; pyrazole compounds such as 3,5-dimethylpyrazole, 3-methylpyrazole, 4-bromo-3,5-dimethylpyrazole, and 4-nitro-3,5-dimethylpyrazole; phenols such as phenol and cresol; aliphatic alcohols such as methanol and ethanol; active methylene compounds such as dimethyl malonate and acetylacetone; mercaptans such as butyl mercaptan and dodecyl mercaptan; acid amides such as acetanilide and acetic acid amide; lactams such as ε-caprolactam and δ-valerolactam; acid imides such as succinimide and maleimide; oxime compounds such as acetaldehyde oxime, acetone oxime, and methyl ethyl ketone oxime; and amines such as diphenylaniline, aniline, and ethyleneimine. From a reactivity standpoint, pyrazole compounds having a pyrazole skeleton are suitable as blocking agents.

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

The crosslinking agent is preferably contained in an amount of 5% to 50% by mass of the total resin and crosslinking agent solid content in the easy-adhesion layer forming composition. More preferably, it is 10% to 45% by mass. Even more preferably, it is 10% to 30% by mass, and most preferably, 10% to 20% by mass. A concentration of 5% by mass or more is preferable because it maintains the strength of the resin in the easy-adhesion layer and provides good adhesion under high temperature and high humidity conditions. A concentration of 50% by mass or less is preferable because it maintains the flexibility of the resin in the easy-adhesion layer and provides good adhesion at room temperature and under high temperature and high humidity conditions.

In the easily adhesive polyester film of the present invention, the easily adhesive layer is preferably formed by curing a composition containing a polyester having a polycyclic aromatic skeleton and a crosslinking agent having at least one skeleton selected from aliphatic, alicyclic, and heterocyclic groups. The expression "formed by curing this composition" is used because it is difficult to appropriately describe the chemical composition after reaction curing with the crosslinking agent.

(Antistatic agent)
In an easy-adhesion layer forming composition, it is essential to use an antistatic agent with polar groups in order to impart an antistatic function. The antistatic agent is not particularly limited as long as it does not impair the invention, but an ionic antistatic agent is preferred. Due to their high polarity, ionic antistatic agents are known to have the effect of lowering the surface resistivity, and cationic antistatic agents, anionic antistatic agents, and amphoteric antistatic agents are known.

The antistatic agent is not particularly limited as long as it does not impair the invention, and nonionic antistatic agents with functional groups such as sorbitan type, ether type, ester type, sorbitol type, and glucose type can also be used, but an ionic antistatic agent is preferred. Examples of ionic antistatic agents include cationic types such as quaternary ammonium salt type, quaternary ammonium resin type, imidazoline type, Arcover type, and Solomin A type, anionic types such as alkyl sulfate type, alkyl phosphate type, phosphate ester salt type, and sulfate ester salt type, and amphoteric surfactant types or polymer types such as betaine type, amino acid type, and aminosulfate ester type. Among these, anionic antistatic agents are more preferred in terms of coating stability, and sulfate-type ionic antistatic agents are particularly preferred in terms of surface resistivity stability, ink adhesion, and suppression of migration of the antistatic agent to other articles or the back surface.
For example, sulfate-type antistatic agents have a sulfate structure ( _-SO₃Na ). Sulfate-type antistatic agents usually have an ionic structure, and are sometimes described as sulfate-type ionic antistatic agents.

The concentration of the antistatic agent in the easily adhesive layer is preferably more than 0.5% by mass and 10% by mass or less relative to the resin content (where resin content refers to the sum of the solid content masses of the resin and the crosslinking agent). More preferably, it is 0.8% by mass or more and 7% by mass or less. For example, it may be 1.0% by mass or more and 6% by mass or less. In the composition of the easily adhesive layer according to the present invention, if the concentration of the antistatic agent exceeds 0.5% by mass, the antistatic effect is sufficiently exhibited. If it is 10% by mass or less, due to the high polarity of the antistatic agent, gelation due to ion adsorption interaction is suppressed when mixed with the polyester resin or polyurethane resin, making it preferable as a coating liquid.

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

In this invention, it is also preferable to add particles (preferably inert particles) to the easy-adhesion layer in order to further improve its blocking resistance. Examples of particles to be contained in the easy-adhesion layer in this invention include titanium dioxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, or mixtures thereof. Other examples of such particles include other general inorganic particles, such as calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, calcium fluoride, and other inorganic particles, as well as organic polymer particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based particles.

The average particle size of the particles in the easy-adhesion layer (average particle size based on the number of particles measured by SEM; the same applies hereinafter) is preferably 0.04 to 2.0 μm, and more preferably 0.1 to 1.0 μm. An average particle size of 0.04 μm or more is preferable because it facilitates the formation of irregularities on the film surface, improving handling properties such as film slipperiness and winding ability, and resulting in good processability during lamination. On the other hand, an average particle size of 2.0 μm or less is preferable because it reduces the likelihood of particle detachment. The particle concentration in the easy-adhesion layer is preferably 1 to 20% by mass relative to the resin content.

In this invention, it is preferable that the water contact angle on the surface of the easy-adhesion layer is in the range of 45° to 60°. This is preferable because it is believed that the concentration (segregation) of the antistatic agent over time can be suppressed, allowing the antistatic performance to be maintained for a long period. Preferably, the water contact angle on the surface of the easy-adhesion layer is 47° to 60°.

In this invention, the antistatic performance is achieved by the antistatic agent present on the surface of the easily adhesive layer. In other words, the amount of antistatic agent present on the surface of the easily adhesive layer is crucial for the development of antistatic performance.

The amount of antistatic agent present on the surface of the easy-adhesion layer was confirmed by measuring the surface elemental distribution using X-ray photoelectron spectroscopy (ESCA). It is preferable that the sulfur atom ratio (As: at%) on the surface of the easy-adhesion layer, as determined by X-ray photoelectron spectroscopy (ESCA), is within the range of the following formula (1).
1.2≦As≦3.0...Formula (1)
Since sulfate-type ionic antistatic agents are preferably used as the antistatic agent, the sulfur atoms shown here represent part of the antistatic agent. In other words, a larger value (As) indicates a greater amount of antistatic agent on the surface of the easily adhering layer, which leads to the development of antistatic performance. However, as mentioned above, sulfur atoms are only a part of the antistatic agent and do not mean that all sulfur atoms are antistatic agents, so it is preferable to add an amount of antistatic agent that falls within the range of formula (1).
The value of As is more preferably 2.6 or less, and even more preferably 2.3 or less. When it is 3.0 or less, a film is obtained that not only ensures the antistatic properties described above, but also ensures reliable adhesion, which is preferable. Therefore, the sulfur atom ratio (As:at%) on the surface of the easy-adhesion layer is preferably 1.2 or more and 2.6 or less, and even more preferably 1.2 or more and 2.3 or less. In this specification, the sulfur atom ratio (As:at%) on the surface of the easy-adhesion layer may be indicated as (AsX).

In the present invention, it is preferable that the surface resistivity of the surface of the easily adhering layer of the easily adhering polyester film is greater than 1.0 × ^10¹² Ω/sq and less than 1.0 × ^10¹⁴ Ω/sq.
A surface resistivity of less than 1.0 × ^10¹⁴ Ω/sq on the easily adhering layer surface prevents dust adhesion due to static electricity generated during friction or peeling, reduces coating defects when a functional layer is applied, and makes it possible to obtain a high-quality laminated polyester film. Furthermore, electrostatic attraction between films is preferable because it prevents phenomena such as poor handling during transport and double feeding of films.
Furthermore, by making the surface resistivity greater than 1.0 × ^10¹² Ω/sq, the adhesion reliability when a functional layer is applied is improved, making it possible to obtain a laminated polyester film with high adhesion reliability. It is preferable that the surface resistivity is greater than 5.0 × ^10¹² Ω/sq, and more preferably greater than 1.0 × ^10¹³ Ω/sq. The surface resistivity may be greater than 5.0 × ^10¹² Ω/sq and less than 1.0 × ^10¹⁴ Ω/sq, and may be greater than 1.0 × ^10¹³ Ω/sq and less than 1.0 × ^10¹⁴ Ω/sq.
It has been confirmed that there is a trade-off between lowering the surface resistivity to improve antistatic performance and increasing adhesion reliability. In the easily adhesive polyester film of the present invention, both can be achieved by achieving a surface resistivity within the aforementioned range.

The present invention can exhibit a good surface resistivity even when subjected to moist heat treatment under conditions of 60°C for 96 hours, and can achieve effects such as preventing a decrease in antistatic performance even under high temperature and high humidity conditions.

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

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

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

In this invention, a method for providing an easily adhesive layer on a polyester film involves applying a coating solution containing a solvent, particles, and a resin to the polyester film and then drying it. As the solvent, water or a mixture of water and an organic solvent is used. Preferably, from an environmental standpoint, water alone or a mixture of water and a water-soluble organic solvent is preferred. For example, examples of water-soluble organic solvents include alcohol-based solvents such as isopropyl alcohol and ethanol; ketone-based solvents such as methyl ethyl ketone; ether-based solvents such as butyl cellosolve; amine-based solvents such as triethanolamine; and amide-based organic solvents such as N-methylpyrrolidone.

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

The drying temperature after coating is also preferable to be 80°C or higher, and preferably 250°C or lower, although this depends on the type of binder resin, the type of solvent, the presence or absence of a crosslinking agent, and the solid content concentration.

The amount of coating solution applied can be adjusted so that the amount of solids on the polyester film after drying is, for example, 0.03 to 0.24 g/ ^m² , and more specifically, 0.06 to 0.18 g/ ^m² . If a film stretching step is included after coating and drying, the amount of solids on the polyester film after stretching can be adjusted so that it falls within the above range.

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

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

The thickness of the easy-adhesion layer may be between 30 nm and 200 nm. A thickness within this range is preferable because it easily balances processability and adhesion. More preferably, it is between 50 nm and 150 nm, and even more preferably between 70 nm and 100 nm. A thickness of 30 nm or more is preferable because it provides good adhesion. A thickness of 200 nm or less is preferable because it reduces the likelihood of blocking.

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

(Manufacturing of easily adhesive polyester film)
The polyester film that serves as the base material for the easily adhesive polyester film of the present invention can be manufactured according to a general method for manufacturing polyester films. For example, one method involves melting polyester resin, extruding the unoriented polyester into a sheet, stretching it longitudinally using the speed difference of rolls at a temperature above the glass transition temperature, then stretching it transversely with a tenter, and finally heat-treating it.

The polyester film used in this invention may be either uniaxially oriented or biaxially oriented. However, when a biaxially oriented film is used as a protective film on the front surface of a liquid crystal panel, while iridescent color spots may not be visible when viewed from directly above the film surface, they may be visible when viewed from an oblique angle. Therefore, caution is necessary.

This phenomenon occurs because a biaxially oriented film is composed of refractive index ellipsoids with different refractive indices in the running direction, width direction, and thickness direction. Due to the direction of light transmission within the film, there is a direction in which retardation becomes zero (the refractive index ellipsoid appears as a perfect circle). Therefore, when observing a liquid crystal display screen from a specific oblique direction, a point where retardation is zero may occur, resulting in concentric rainbow-like color patches centered around that point. If we define θ as the angle from directly above the film surface (normal direction) to the position where the rainbow-like color patches are visible, this angle θ increases as the birefringence within the film surface increases, making the rainbow-like color patches less visible. Since biaxially oriented films tend to have a smaller angle θ, uniaxially oriented films are preferable because the rainbow-like color patches are less visible.

However, a perfectly uniaxial (uniaxially symmetrical) film is undesirable because its mechanical strength in the direction perpendicular to the orientation direction is significantly reduced. The present invention preferably exhibits biaxiality (biaxial symmetry) within a range where rainbow-like color fringing does not occur substantially, or within the viewing angle range required for liquid crystal display screens.

(Laminated polyester film)
The easily adhesive polyester film of the present invention can be preferably used mainly for optical applications as a laminated polyester film in which a functional layer such as a hard coat layer is laminated on the easily adhesive layer. A hard coat layer or the like made of an electron beam or ultraviolet curable acrylic resin or a siloxane-based thermosetting resin can be provided on the easily adhesive layer.

The present invention also provides a laminated polyester film in which a functional layer having various properties is provided on an easy-adhesion layer of an easy-adhesion polyester film. A functional layer refers to a layer having functionality such as a hard coat layer, anti-glare layer, anti-glare anti-reflective layer, anti-reflective layer, or low-reflection layer, for purposes such as preventing reflections, suppressing glare, suppressing rainbow unevenness, and suppressing scratches. The present invention may have one or more functional layers selected from the group consisting of these layers. Various types of functional layers known in the art can be used, and their type is not particularly limited.

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

The hard coat layer described above may have an anti-glare function that scatters ambient light. This anti-glare function is achieved by forming irregularities on the surface of the hard coat layer. Ideally, the film's haze is preferably 0-50%, more preferably 0-40%, and particularly preferably 0-30%. Of course, 0% is ideal; it may be 0.2% or more, or 0.5% or more. The haze can be 0.2-50%, 0.2-40%, 0.2-30%, 0.5-50%, 0.5-40%, 0.5-30%, etc.

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

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

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

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

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

(Manufacturing of laminated polyester film)
The laminated polyester film of the present invention can be manufactured by providing a functional layer on an easily adhesive layer of an easily adhesive polyester film. Specific embodiments are described below, but are not limited to these embodiments.

A functional layer-forming composition (functional layer-forming coating liquid) is applied to the easily adhesive layer surface of the aforementioned easily adhesive polyester film. Examples of the functional layer-forming composition include the aforementioned electron beam or UV-curable acrylic resin (including its oligomers, monomers, etc.) or siloxane-based thermosetting resin. If the easily adhesive layer is provided on both sides of the easily adhesive polyester film, the composition can be applied to at least one of the easily adhesive layer surfaces. While the functional layer-forming coating liquid does not necessarily need to be diluted, it can be diluted with an organic solvent as needed to control viscosity, wettability, film thickness, etc., without any particular problem. After applying the functional layer-forming coating liquid to the film, the coated film can be dried as needed, and then cured by electron beam or UV irradiation and heating according to the curing conditions to form a functional layer.

More typically, a coating solution for forming a functional layer with the above composition is applied to the easily adhesive layer of an easily adhesive polyester film using a wire bar or the like as appropriate, and the solvent can be removed by drying at 60 to 100°C for 0.5 to 10 minutes. Then, the film coated with the functional layer is irradiated with ultraviolet light at 300 mJ/ ^cm² using, for example, a high-pressure mercury lamp to obtain a laminated polyester film having a functional layer.

In this invention, the thickness of the functional layer is preferably 1 to 15 μm. A thickness of 1 μm or more is preferable because it efficiently exhibits the effects of the functional layer on chemical resistance, scratch resistance, and stain resistance. On the other hand, a thickness of 15 μm or less is preferable because it maintains the flexibility of the functional layer and prevents cracking.

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

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

Thus, the easily adhering polyester film of the present invention has high adhesion reliability with the functional layer, and exhibits high adhesion not only after film formation but also after exposure to high temperature and high humidity environments (even after long-term storage). In other words, it has the characteristic of having sufficiently high adhesion X after film formation and high adhesion Y after long-term storage. That is, if the above-mentioned X (%) and Y (%) satisfy the following formula (2), the adhesion reliability can be evaluated as high.
X - Y (%) ≤ 5 ... Equation (2)

The value of equation (2) is typically 5% or less, even 3% or less, and especially 0%. A value of 5% or less indicates no significant difference between the adhesion after film formation and the adhesion after moist heat treatment, suggesting sufficient adhesion in both cases. Therefore, even after prolonged storage, no decrease in the adhesion of the functional layer is observed, ensuring reliable adhesion.

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

(1) Average particle size [Measurement method using scanning electron microscope]
The average particle size of particles present in the easily adhesive 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 the two furthest points) of 300 to 500 particles is measured at a magnification such that the size of the smallest single particle is 2 to 5 mm. The arithmetic mean of these measurements is taken as the average particle size.

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

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

(3) Polyester resin composition The polyester resin was dissolved in deuterated chloroform, and ^1H -NMR analysis was performed using a Varian Gemini-200 nuclear magnetic resonance analyzer (NMR), and the molar percentage ratio of each component was determined from the integral ratio.

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

(5) Number average molecular weight
0.03 g of resin was dissolved in 10 ml of tetrahydrofuran, and the number-average molecular weight was measured using a GPC-LALLS low-angle light scattering photometer LS-8000 (manufactured by Tosoh Corporation, tetrahydrofuran solvent, reference: polystyrene) at a column temperature of 30°C, a flow rate of 1 ml/min, and a column (Showa Denko Corporation's Shodex KF-802, 804, 806).

(6) Haze of easy-to-adhere polyester film The haze of the easy-to-adhere polyester film was measured in accordance with JIS K 7136:2000 using a turbidimeter (Nippon Denshoku, NDH2000).

(7) Adhesion of the functional layer A hard coat layer was formed on an easily adhesive layer of the polyester film. The adhesion between the hard coat layer and the base film of the easily adhesive polyester film with the hard coat layer formed was determined in accordance with the description in JIS K5400-1990 8.5.1.

The coating solution used for forming the hard coat layer was prepared as follows.
(Preparation of coating solution L for hard coat layer formation)
Isopropanol 21.00% by mass
Toluene 49.00% by mass
Pentaerythritol triacrylate 21.38% by mass
(Shin Nakamura Chemical A-DPH)
Urethane acrylate 7.12% by mass
(Mitsubishi Chemical Corporation's Shiko UV-7600B)
Photopolymerization initiator 1.50% by mass
(Omnirad184 manufactured by IGM Resins B.V.)

(Preparation of coating solution M for hard coat layer formation)
Methyl ethyl ketone 64.40% by mass
Dipentaerythritol hexaacrylate 27.20% by mass
(Shin Nakamura Chemical A-DPH)
Polyethylene glycol diacrylate 3.40% by mass
(Light Acrylate 9EG-A manufactured by Kyoeisha Chemical Co., Ltd.)
Bisphenol A diacrylate 4.00% by mass
(Light Acrylate BP-4PA manufactured by Kyoeisha Chemical Co., Ltd.)
Photopolymerization initiator 1.00% by mass
(Omnirad184 manufactured by IGM Resins B.V.)

(Formation of the hard coat layer)
An easily adhesive polyester film was stored at a temperature and humidity of 20°C and 65% RH. Twelve hours after film formation, a hard coat layer forming solution (L or M) of the above composition was applied to the easily adhesive layer using a #14 wire bar, dried at 70°C for 1 minute, and the solvent was removed. Next, the film with the hard coat layer was irradiated with ultraviolet light at 300 mJ/ ^cm² using a high-pressure mercury lamp to obtain a hard coat film (laminated polyester film) having a hard coat layer with a thickness of 7 μm.

The specific method for measuring adhesion is as follows: Using a cutter guide with a gap of 2 mm, 100 grid-like cuts were made on the hard coat layer surface, penetrating the hard coat layer and reaching the base film. Next, cellophane adhesive tape (Nichiban, No. 405; 24 mm wide) was applied to the grid-like cut surfaces and rubbed with an eraser to ensure complete adhesion. After that, the cellophane adhesive tape was peeled vertically from the hard coat layer surface of the easy-adhesion polyester film on which the hard coat layer had been formed. The number of grid squares that peeled off the hard coat layer surface was visually counted, and the adhesion between the hard coat layer and the base film was determined using the following formula. Note that grid squares that were partially peeled off were also counted as peeled squares.
Adhesion (%) = {1 - (Number of peeled squares / 100)} × 100 ... Equation (3)

(8) Humid and heat resistance (adhesion after being left at 80°C and 90% RH)
The obtained easily adhering polyester film was left in a high-temperature, high-humidity chamber at 80°C and 90% RH for 24 hours, and then left at room temperature (20°C, 65% RH) for 12 hours. After that, a hard coat layer was formed using the same method as described above, and the adhesion (Y) to the base film was determined.
Next, to evaluate the adhesion reliability, when applied to equation (2) above,
Items that satisfy equation (2) ・・〇 Items that do not satisfy equation (2) ・・×
That's what I decided.

(9) Cross-sectional observation using a transmission electron microscope The obtained easy-to-adhere polyester film was cut into 1 mm × 10 mm sections and embedded in epoxy resin. Then, thin cross-sectional sections parallel to the short side of the embedded sample were prepared using an ultramicrotome. Next, these thin sections were stained with ruthenium tetroxide, and areas without significant damage were observed using a transmission electron microscope (JEOL JEM2100) at an acceleration voltage of 200 kV and magnification of 20,000. From the observed images of the easy-to-adhere layer, the thickness of the easy-to-adhere layer was measured at 10 points at each level, and the average value was taken as the thickness of the easy-to-adhere layer.

In the present invention, the thickness (d: nm) of the easily adhering layer is preferably given by the following formula (6).
30≦d≦200...Formula (6)
Products prepared within this range are preferable because they easily achieve both processability and adhesion.
The thickness of the easy-adhesion layer is more preferably 50 nm to 150 nm, and even more preferably 70 nm to 100 nm. A thickness of 30 nm or more of the easy-adhesion layer is preferable as it provides good adhesion. A thickness of 200 nm or less of the easy-adhesion layer is preferable as it makes blocking less likely to occur.

(10) Water Contact Angle Under conditions of 25°C and 50% RH, a contact angle meter (Kyowa Interface Science Co., Ltd.: Fully Automatic Contact Angle Meter DM-701) was used to prepare droplets of water (appropriate amount of liquid, 1.8 μL) on the easily adhesive layer surface of the obtained easily adhesive polyester film, and the contact angle was measured. The contact angle was taken from the contact angle 10 seconds after dropping each droplet onto the easily adhesive polyester film.

(11) Evaluation of the sulfur element ratio on the surface of the easily adhering layer The ratio of the amount of sulfur atoms to the total amount of all elements in the surface region (sulfur atom ratio ( _As : at%)) was evaluated by X-ray photoelectron spectroscopy (ESCA) (K-Alpha ⁺ , Thermo Fisher Scientific). The measurement conditions are shown below. Background removal was performed using the Shirley method during the analysis. Furthermore, _As was calculated as the average of the measurement results from three locations.
Measurement conditions: Excitation X-ray: Monochromatized Al Kα-ray; X-ray output: 12 kV, 6 mA
Photoelectron escape angle: 90°
Spot size: 400 μmφ
Pass energy: 50 eV
Step: 0.1 eV

Based on the data evaluated in this way, it is a necessary requirement for the present invention that the sulfur atom ratio (As:at%) on the surface of the easily adhering layer falls within the range of formula (1) above.

(12) Measurement of surface resistivity The surface resistivity of the easily adhesive polyester film was measured using a surface resistance meter (Nitto Seiko Analyc Highresta MCP-HT800).
The easily adhering layer surface of the easily adhering polyester film was measured using a method compliant with JIS K6911 under an applied voltage of 500V and a 23°C/65% RH environment.

(13) Evaluation of the concentration of the antistatic agent on the surface of the easy-to-adhere layer and its migration to other surfaces under a humid, hot, and pressurized environment The concentration of the antistatic agent on the surface of the easy-to-adhere layer and the degree of migration to other surfaces were evaluated using the following method.
A 5 cm square of easily adhesive polyester film was cut and used as a sample. The surface of the easily adhesive layer of the sample was superimposed on polyester film E5001 (thickness 50 μm) manufactured by Toyobo Co., Ltd., and held for 3 days under high temperature and high humidity conditions of 60°C and 90% RH, and a pressure of 1 kg/ ^cm² using a constant temperature and humidity chamber (IG401 manufactured by Yamato Scientific Co., Ltd.) (high temperature and high humidity treatment).
If the surface resistivity of the easily adhesive layer of the sample before treatment (R _x0 ) and the surface resistivity of E5001 before treatment (R _y0 ) are related to the surface resistivity of the easily adhesive layer of the sample after treatment (R _x1 ) and the surface resistivity of E5001 before treatment (R _y1 ) as shown in equations (4) and (5) below, then it was determined that there was no migration of the antistatic agent to the other side before and after treatment.
｜Log ₁₀ (R _x1 )－Log ₁₀ (R _x0 )｜<1...(4)
｜Log ₁₀ (R _y1 )－Log ₁₀ (R _y0 )｜＜0.1...(5)

Under pressurized conditions in a humid and hot environment, the degree of concentration (segregation) of the antistatic agent on the surface of the easy-to-adhere layer differs. As surface concentration (segregation) increases, the amount of concentration (segregation) increases. This not only increases the surface resistivity of the easy-to-adhere layer surface, but also increases the migration of the antistatic agent to the other superimposed surface, which is thought to increase the surface resistivity of the E5001 surface.
By satisfying equations (4) and (5), it is possible to form a coating film with controlled segregation, suppressing concentration (segregation) over time even on film rolls that have been stored for a long period, and maintaining antistatic performance for an extended period.

The surface resistivity of the easily adhering layer surface of the sample was determined as follows.
○: Satisfies equation (4).
△: Some samples do not satisfy equation (4).
×: Does not satisfy equation (4).
Furthermore, the surface resistivity of the other surfaces was determined as follows.
○: Satisfies equation (5).
×: Does not satisfy equation (5).

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

[Polyester resin]
Manufacturing of polyester resin (PEs-1):
Polyester resin (PEs-1) was polymerized following a known polymerization method. The composition of the obtained polymer was determined by ^1H -NMR analysis, and the molar percentage ratio of each component was determined from the integral ratio. The results are shown in Table 1. The reduced viscosity of the obtained polyester resin was 0.493 dl/g.
The abbreviations listed in Table 1 are shown below.
TPA: Terephthalic acid IPA: Isophthalic acid NDC: Naphthalenedicarboxylic acid SA: Sebacic acid Na: Azelaic acid DSS: Dimethyl-5-sodium sulfisophthalate EG: Ethylene glycol PD: Pentanediol HD: Hexanediol FD: Fluoroadiol DEG: Diethylene glycol NPG: Neopentyl glycol

Preparation of polyester aqueous dispersion (PEs-1WD):
In a reactor equipped with a stirrer, thermometer, and reflux device, 30 parts by mass of copolymerized polyester resin (PEs-1) and 15 parts by mass of ethylene glycol-n-butyl ether were added and heated at 110°C, stirring to dissolve the resin. After the resin was completely dissolved, 55 parts by mass of water were gradually added to the polyester solution while stirring. After the addition, the liquid was cooled to room temperature while stirring to prepare a milky white aqueous dispersion of polyester resin (PEs-1WD) with a solid content of 24.9% by mass. The viscosity of the obtained aqueous dispersion was 32 mPa·s.

Manufacturing of polyester resin (PEs-2):
Similar to the polymerization of the polyester resin (PEs-1) described above, polyester resin (PEs-2) was manufactured following a known polymerization method. As with PEs-1, the composition ratio was determined, and the reduced viscosity of the obtained resin was evaluated. The results are shown in Table 1.

Preparation of polyester aqueous dispersion (PEs-2WD):
A polyester aqueous dispersion (PEs-2WD) was prepared by substituting PEs-2 for PEs-1, in the same manner as the preparation of the polyester aqueous dispersion (PEs-1WD) described above. Similar to PEs-1WD, the solid content concentration (mass%) and liquid viscosity (mPa·s) were evaluated. The results are shown in Table 2.

Manufacturing of polyester resin (PEs-3):
Similar to the polymerization of the polyester resin (PEs-1) described above, polyester resin (PEs-3) was manufactured following a known polymerization method. As with PEs-1, the composition ratio was determined, and the reduced viscosity of the obtained resin was evaluated. The results are shown in Table 1.

Preparation of polyester aqueous dispersion (PEs-3WD):
A polyester aqueous dispersion (PEs-3WD) was prepared by substituting PEs-3 for PEs-1, in the same manner as the preparation of the polyester aqueous dispersion (PEs-1WD) described above. Similar to PEs-1WD, the solid content concentration (mass%) and liquid viscosity (mPa·s) were evaluated. The results are shown in Table 2.

[Polyurethane resin]
Synthesis of polyurethane resin (PCPU-1):
In a four-necked flask equipped with a stirrer, a Liebig condenser, a nitrogen inlet tube, a silica gel drying tube, and a thermometer, 29.4 parts by mass of dicyclohexylmethane-4,4'-diisocyanate, 63.6 parts by mass of polycarbonate diol with a melting point of 33°C, mainly composed of 1,4-butanediol/2,2-dimethyl-1,3-propanediol (=75/25 molar ratio) 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 a nitrogen atmosphere. The infrared spectrum of the reaction solution was measured to confirm the disappearance of isocyanate groups in the reaction solution. Next, after the solution was cooled to room temperature, 8.2 parts by mass of triethylamine was added to obtain a polyurethane resin (PCPU-1) solution with a solid content of 50.0% by mass.

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

[Crosslinking agent]
Preparation of an aqueous dispersion (C-1WD) of a blocked isocyanate crosslinking agent (C-1):
In a flask equipped with a stirrer, thermometer, and reflux condenser, 64.5 parts by mass of a polyisocyanate compound having an isocyanurate structure derived from hexamethylene diisocyanate (Asahi Kasei Chemicals, Duranate TPA-100, NCO concentration 23.1%), 50.0 parts by mass of dipropylene glycol dimethyl ether, and 20.8 parts by mass of methyl ethyl ketone oxime were added, and the mixture was held at 70°C with stirring under a nitrogen atmosphere for 1 hour. Subsequently, 8.7 parts by mass of dimethylolpropionic acid were added. The reaction was continued at 70°C with stirring, and the infrared spectrum of the reaction solution was measured until the absorption of the isocyanate group disappeared. After cooling to room temperature, 6.0 parts by mass of dimethylethanolamine were added, and water was added while stirring at 2000 ^min⁻¹ . By adjusting the concentration with water, an aqueous dispersion (C-1WD) of a blocked isocyanate-based crosslinking agent (C-1) with a solid content of 30.0% by mass was prepared.

Preparation of an aqueous dispersion (C-2WD) of a carbodiimide crosslinking agent (C-2):
In a flask equipped with a stirrer, thermometer, and reflux condenser, 168 parts by mass of hexamethylene diisocyanate and 220 parts by mass of polyethylene glycol monomethyl ether (average molecular weight 400) were charged and stirred at 120°C for 1 hour. Then, 26 parts by mass of 4,4'-dicyclohexylmethane diisocyanate and 3.8 parts by mass of 3-methyl-1-phenyl-2-phosphoren-1-oxide (2% by mass relative to the total isocyanate) were added as a carbodiimide catalyst, and the mixture was stirred for a further 5 hours at 185°C under a nitrogen stream. The infrared spectrum of the reaction solution was measured to confirm that the absorption of the isocyanate group had disappeared. After cooling to 60°C, 567 parts by mass of deionized water were added to prepare an aqueous dispersion (C-2WD) of a carbodiimide-based crosslinking agent (C-2) with a solid content of 40% by mass.

[Antistatic agent]
(Antistatic agent P)
Sodium dodecylbenzenesulfonate (TB702, manufactured by Matsumoto Oil & Fat Pharmaceutical Co., Ltd.) was used.

(Antistatic agent Q)
A lithium salt electrolyte (Ionel LF-101, manufactured by Nippon Shokubai Co., Ltd.) was used.

(Example 1)
(Preparation of the coating solution)
A readily adhesive layer-forming composition 1 with the following composition was prepared.
Water 45.91 parts by mass, Isopropyl alcohol 27.84 parts by mass, Silica sol 1.21 parts by mass (Silica sol with an average particle size of 40 nm, solid content concentration 40% by mass)
Silica sol 1.11 parts by mass (Silica sol with average particle size of 450 nm, solid content concentration of 4% by mass)
PEs-1WD 16.30 parts by mass (solid content concentration 25% by mass)
C-1WD 5.49 parts by mass (solid content concentration 40% by mass)
Surfactant 0.30 parts by mass (silicone-based, solid content concentration 10% by mass)
High boiling point solvent 0.34 parts by mass Antistatic agent P
(Solid content concentration 5% by mass) 1.50 parts by mass

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

Next, the above-mentioned easy-adhesion layer-forming composition 1 was applied to one side of a PET film by a roll-coating method, dried at 80°C, and adjusted so that the amount of coating after drying following the final stretching was 0.07 g/ ^m² . Subsequently, the film was stretched 4.0 times in the width direction at 150°C using a tenter, and with the length in the width direction of the film fixed, it was heated at 200°C, and then a relaxation treatment in the width direction was performed at 200°C to obtain an easy-adhesion polyester film with a thickness of 50 μm.

The thickness of the easily adhering layer of the obtained easily adhering polyester film was 80 nm, and the film haze was 0.68%.

The water contact angle on the surface of this easily adhering layer was measured to be 58.3°.

The surface composition of the obtained film was measured using ESCA from the easily adhering layer side, and the sulfur element ratio was evaluated to be 1.4 at%.

When the surface resistivity of this easily adhering layer was measured, it was found to be Rx0 = 1.3 × ^10¹³ .

Polyester film E5001 (R _y0 = 1.0 × ^10¹⁴ ) manufactured by Toyobo Co., Ltd. and the surface of an easy-adhesion layer were superimposed and held for 3 days under high temperature and high humidity conditions of 60°C and 90% RH, and under a pressure of 1 kg/ ^cm² . After that, the surface resistivity of the superimposed surface was measured, and the following was found:
R _x1 = 9.6 × ^10¹² _, R _y1 = 1.0 × ^10¹⁴ ,
|Log ₁₀ (R _x1 ) - Log ₁₀ (R _x0 )| = 0.13 and |Log ₁₀ (R _y1 ) - Log ₁₀ (R _y0 )| = 0.
These results confirmed that the degree of increase in concentration (segregation) on the resin surface after constant temperature and humidity treatment was low, and that transfer to other films was minimal.

A laminated polyester film having a functional layer was obtained by applying a functional layer-forming coating solution (the hard coat layer-forming coating solution L described above) to the easily adhesive layer of the obtained easily adhesive polyester film, according to the formation method described above.

When the adhesion of the functional layer of the resulting laminated polyester film was evaluated, the adhesion strength X was found to be 100%.

On the other hand, the above-mentioned easily adhesive polyester film was left in a high-temperature, high-humidity chamber at 80°C and 90% RH for 24 hours, and then left at room temperature for 12 hours. Afterward, a functional layer was formed on the easily adhesive layer of the treated easily adhesive polyester film using the functional layer-forming coating solution (the hard coat layer-forming coating solution L mentioned above), thereby obtaining a laminated polyester film.

When the adhesion of the functional layer of this laminated polyester film was evaluated, the adhesion strength Y was found to be 100%.

From this result, X - Y = 0 (%).

Based on the above results, we were able to obtain an easily adhesive polyester film that achieves both antistatic properties and adhesion, while maintaining reliability in both antistatic and adhesion.

The above results are summarized in Table 3.

(Examples 2-3)
A film was obtained in the same manner as in Example 1, except that the resin/crosslinking agent composition ratio of the easy-adhesion layer forming composition 1 was adjusted to the composition ratio shown in Table 3. The physical properties of the obtained film are as shown in Table 3.

(Example 4)
A film was obtained in the same manner as in Example 1, except that the addition ratio of the antistatic agent P to the easily adhering layer-forming composition 1 was adjusted to the addition ratio shown in Table 3. The physical properties of the obtained film are as shown in Table 3.

(Examples 5-6)
A film was obtained in the same manner as in Example 1, except that the thickness of the easy-adhesion layer of the easy-adhesion layer forming composition 1 was adjusted to the thickness shown in Table 3. The physical properties of the obtained film are as shown in Table 3.

(Example 7)
A readily adhesive layer-forming composition 2 with the following composition was prepared.
Water 40.00 parts by mass, Isopropyl alcohol 30.21 parts by mass, Silica sol 1.33 parts by mass (Silica sol with average particle size of 40 nm, solid content concentration 40% by mass)
Silica sol 1.23 parts by mass (Silica sol with average particle size of 450 nm, solid content concentration of 4% by mass)
PEs-1WD 10.27 parts by mass (solid content concentration 25% by mass)
PEs-2WD 7.75 parts by mass (solid content concentration 25% by mass)
C-1WD 6.06 parts by mass (solid content concentration 40% by mass)
Surfactant 0.30 parts by mass (silicone-based, solid content concentration 10% by mass)
High boiling point solvent 0.34 parts by mass Antistatic agent P
(Solid content concentration 5% by mass) 1.50 parts by mass

A polyester film was obtained in the same manner as in Example 1, except that composition 2 was used to form the easy-adhesion layer instead of composition 1. The physical properties of the obtained film are as shown in Table 3.

(Example 8)
A readily adhesive layer-forming composition 3 with the following composition was prepared.
Water 41.53 parts by mass, Isopropyl alcohol 30.19 parts by mass, Silica sol 1.33 parts by mass (Silica sol with average particle size of 40 nm, solid content concentration 40% by mass)
Silica sol 1.23 parts by mass (Silica sol with average particle size of 450 nm, solid content concentration of 4% by mass)
PEs-1WD 10.27 parts by mass (solid content concentration 25% by mass)
PCPU-1WD 5.23 parts by mass (solid content concentration 37% by mass)
C-1WD 6.06 parts by mass (solid content concentration 40% by mass)
Surfactant 0.30 parts by mass (silicone-based, solid content concentration 10% by mass)
High boiling point solvent 0.34 parts by mass Antistatic agent P
(Solid content concentration 5% by mass) 3.50 parts by mass

A film was obtained in the same manner as in Example 1, except that easy-adhesion layer-forming composition 3 was used to form the easy-adhesion layer instead of easy-adhesion layer-forming composition 1. The physical properties of the obtained film are as shown in Table 3.

(Example 9)
A film was obtained in the same manner as in Example 1, except that the addition ratio of the antistatic agent P used in the easy-adhesion layer forming composition 3 was adjusted to the addition ratio shown in Table 3.

(Example 10)
A film was obtained in the same manner as in Example 1, except that PEs-1WD in the easy-adhesion layer forming composition 1 was changed to PEs-3WD. The physical properties of the obtained film are as shown in Table 3.

(Example 11)
A film was obtained in the same manner as in Example 1, except that C-1WD in the easy-adhesion layer forming composition 1 was changed to C-2WD. The physical properties of the obtained film are as shown in Table 3.

(Example 12)
A film was obtained in the same manner as in Example 1, except that the antistatic agent P in the easily adhering layer-forming composition 1 was replaced with the antistatic agent Q. The physical properties of the obtained film are as shown in Table 3.

(Example 13)
A film was obtained in the same manner as in Example 1, except that the type of hard coat applied to the easy-adhesion layer was changed from hard coat layer forming solution L to hard coat layer forming solution M. The physical properties of the obtained film are as shown in Table 3.

(Comparative Example 1)
A film was obtained in the same manner as in Example 1, except that PEs-1WD in the easy-adhesion layer forming composition 1 was changed to PEs-2WD. The physical properties of the obtained film are as shown in Table 3.

(Comparative Example 2)
A film was obtained in the same manner as in Example 1, except that PEs-1WD in the easy-adhesion layer forming composition 1 was replaced with PCPU-1WD. The physical properties of the obtained film are as shown in Table 3.

(Comparative Example 3)
A film was obtained in the same manner as in Example 1, except that C-1WD in the easy-adhesion layer forming composition 1 was not used. The physical properties of the obtained film are as shown in Table 3.

(Comparative Example 4)
A film was obtained in the same manner as in Example 1, except that the antistatic agent P in the easily adhering layer-forming composition 1 was not used. The physical properties of the obtained film are as shown in Table 3.

(Comparative Example 5)
A film was obtained in the same manner as in Example 1, except that the antistatic agent P in the easily adhering layer-forming composition 3 was not used. The physical properties of the obtained film are as shown in Table 3.

(Comparative Example 6)
A film was obtained in the same manner as in Example 1, except that the composition obtained by changing the addition ratio of the antistatic agent P in the easy-adhesion layer forming composition 3 to the addition ratio shown in Table 3 was used in place of the easy-adhesion layer forming composition 1. The physical properties of the obtained film are as shown in Table 3.

The present invention provides an easily adhesive polyester film that exhibits excellent antistatic properties on the surface of the easily adhesive layer, suppresses the migration of the antistatic agent in the easily adhesive layer to the back surface of the easily adhesive polyester film itself, and also provides excellent adhesion to functional layers such as hard coats.
On the other hand, Comparative Examples 1 and 2 do not contain the polyester resin having a polycyclic aromatic skeleton according to the present invention, and therefore cannot exhibit sufficient antistatic properties and adhesion, for example, under high temperature and high humidity conditions.
Comparative Example 3 did not contain the crosslinking agent according to the present invention, so the water contact angle and the sulfur atom ratio on the surface of the easily adhering layer, as determined by X-ray photoelectron spectroscopy (ESCA), were outside the range of the present invention. For example, the surface resistivity after moist heat treatment was poor, and the adhesion was also insufficient.
Comparative Examples 4 and 5 did not contain the antistatic agent according to the present invention, and therefore exhibited insufficient antistatic properties.
Comparative Example 6 had a water contact angle outside the range of the present invention, and also exhibited insufficient antistatic properties.

This invention provides an easily adhesive polyester film with excellent antistatic properties on the surface of the easily adhesive layer, suppression of migration of the antistatic agent in the easily adhesive layer to the back surface of the easily adhesive polyester film itself, and excellent adhesion to functional layers such as hard coats, thereby enabling the provision of a highly reliable film.

Claims (5)

A polyester film substrate and having an easy-adhesion layer on at least one side thereof,
The easy-adhesion layer is formed from an easy-adhesion layer forming composition,
The aforementioned easy-adhesion layer-forming composition is formed from a composition comprising a polyester resin having a polycyclic aromatic skeleton, a crosslinking agent, and an antistatic agent.
The water contact angle on the surface of the easy-adhesion layer is 45° or more and 60° or less.
The sulfur atom ratio (As:at%) of the surface of the easy-adhesion layer, determined by X-ray photoelectron spectroscopy (ESCA), satisfies the following formula (1):
1.2 ≦ As ≦ 3.0 ... Formula (1)
An easy-to-adhere polyester film having an adhesion X (%) of 95% or more when a functional layer is provided on the easy-to-adhere layer. The easy-to-adhere polyester film according to claim 1, wherein the surface resistivity of the easy-to-adhere layer surface is greater than 1.0 × ^10¹² Ω/sq and less than 1.0 × ^10¹⁴ Ω/sq. The easy-to-adhere polyester film according to claim 1, wherein the antistatic agent is a sulfate-type ionic antistatic agent. The easily adhering polyester film according to claim 1, wherein the polyester having a polycyclic aromatic skeleton is a polyester having a naphthalene skeleton. A laminated polyester film having one or more functional layers selected from the group consisting of a hard coat layer, an anti-glare layer, an anti-glare anti-reflective layer, an anti-reflective layer, and a low-reflection layer, on the easy-adhesion layer of an easy-adhesion polyester film according to any one of claims 1 to 4.