JP7780655B2 - Polyester release film and method for producing the same - Google Patents

Description

The present invention relates to a polyester release film and a method for producing the same.

With the trend toward larger and thinner displays, there is a growing demand for thinner polarizing plates in image display devices.

One method for making polarizing plates thinner is to thin out typical polarizer protective materials such as polyethylene terephthalate (PET) and triacetyl cellulose (TAC). Another method for making polarizing plates thinner is to replace the polarizer protective material with a coating layer with barrier properties (hereinafter referred to as a "barrier coating layer").

The barrier coating layer is formed by uniformly applying the barrier coating layer-forming composition to any substrate, curing it, and then peeling it off.

To obtain a high-quality barrier coating layer, the barrier coating layer must be applied uniformly to the substrate, and the cured barrier coating layer must be easily peeled from the substrate.

When a silicone-based release film is used as the substrate, the barrier coating layer is difficult to form with a uniform thickness due to the low surface energy of the silicone-based release film, and static electricity problems may occur due to the silicone.

One object of the present invention is to provide a polyester release film that has excellent releasability, coating processability, and antistatic properties, and that has low frictional electrostatic voltage.

Another object of the present invention is to provide a polyester release film that can prevent static electricity from being generated during film running and winding, and significantly reduce the amount of air or foreign matter that is introduced due to static electricity.

Another object of the present invention is to provide a method for producing the polyester release film.

One embodiment of the present invention provides a polyester release film comprising a polyester substrate film, a release layer formed on one side of the substrate film, and an antistatic layer formed on the other side of the substrate film, wherein the release layer comprises a water-based coating composition including a polyester resin, an acrylic resin, and a polyolefin wax, and the antistatic layer comprises a water-dispersible antistatic composition including a conductive polymer.

According to another embodiment of the present invention, there is provided a method for manufacturing a polyester release film, comprising: a first step of preparing a polyester substrate film; a second step of applying a water-based coating composition containing a polyester resin, an acrylic resin, and a polyolefin wax to one side of the substrate film to form a release layer; a third step of applying a water-dispersible antistatic composition containing a conductive polymer to the other side of the substrate film to form an antistatic layer; and a fourth step of heat-treating a laminate comprising the substrate film, the release layer formed on the substrate film, and the antistatic layer while stretching it.

The polyester release film according to one embodiment of the present invention not only has excellent peelability and coating processability, but also has excellent antistatic properties, with a significantly low frictional electrostatic voltage of less than 50 V.

In addition, the polyester release film according to one embodiment of the present invention can prevent static electricity from being generated during film running and winding, significantly reducing the amount of air or foreign matter that is drawn in due to static electricity.

The polyester release film according to one embodiment of the present invention can solve problems such as reduced yield due to unreacted materials generated when forming a coating layer, and the adsorption of foreign matter due to static electricity.

The present invention is described in detail below.

However, the embodiments of the present invention can be modified in various different forms, and the scope of the present invention is not limited to the embodiments described below.

Furthermore, the embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the art.

Furthermore, as used in the specification and the appended claims, the singular forms "a," "an," and "the" may be intended to include the plural forms as well, unless the context clearly dictates otherwise.

Furthermore, throughout the specification, unless expressly stated to the contrary, reference to "comprising" an element means that it may further include other elements, rather than excluding other elements.

A polyester release film according to one embodiment of the invention includes a polyester base film, a release layer formed on one side of the base film, and an antistatic layer formed on the other side of the base film.

In one embodiment, the release layer may comprise a water-based coating composition including a polyester resin, an acrylic resin, and a polyolefin wax.

In one embodiment, the antistatic layer may include a water-dispersible antistatic composition containing a conductive polymer.

In one embodiment, the polyester release film may have a frictional electrostatic voltage of less than 50 V.

The inventors have conducted ongoing research into release films used as substrates in the production of optical films such as thin-film polarizing plates.

As a result, they discovered that if a water-based coating composition containing a polyester resin, an acrylic resin, and a polyolefin wax is applied to a substrate film using an in-line coating method to form a release layer, and then a water-dispersible antistatic composition containing a conductive polymer is applied to the other side of the substrate film where the release layer is not formed to form an antistatic layer, a polyester release film can be provided that not only has excellent coating processability and release properties, but also excellent antistatic properties and a low frictional electrostatic voltage, which led to the completion of the present invention.

The polyester release film not only exhibits excellent coating processability and peelability during post-processing (e.g., the process of forming a barrier coating layer on the release film), but also has a low frictional electrostatic voltage of less than 50 V, preventing contamination caused by static electricity.

The polyester release film includes a polyester base film, a release layer formed on one side of the base film, and an antistatic layer formed on the side of the base film where the release layer is not formed (hereinafter referred to as the other side).

The polyester substrate film is made of a polyester resin, and any polyester resin commonly used in the technical field to which the present invention pertains can be used without any particular restrictions. For example, the polyester substrate film may be made of polyethylene terephthalate, polyethylene naphthalate, etc.

As a non-limiting example, the substrate film may be made of polyethylene terephthalate with an intrinsic viscosity in the range of 0.6 to 0.8 dl/g, which may be advantageous in terms of ensuring throat resistance and hydrolysis resistance.

The release layer may comprise a water-based coating composition containing a polyester resin, an acrylic resin, and a polyolefin wax.

The polyester resin is a resin obtained by condensation polymerization of an acid component primarily composed of a dicarboxylic acid and a glycol component primarily composed of an alkylene glycol. The acid component can primarily be terephthalic acid or its alkyl ester or phenyl ester, with some of it being substituted with isophthalic acid, oxyethoxybenzoic acid, adipic acid, sebacic acid, 5-sodium sulfoisophthalic acid, sulfoterephthalic acid, etc. The glycol component can primarily be ethylene glycol, diethylene glycol, etc., with some of it being substituted with propylene glycol, trimethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,4-bisoxyethoxybenzene, bisphenol, polyoxyethylene glycol, etc.

As a non-limiting example, the polyester resin can be obtained by polycondensation of 50 mol% of a glycol component containing diethylene glycol and ethylene glycol in a molar ratio of 5:5, and 50 mol% of an acid component containing terephthalic acid and sulfoterephthalic acid in a molar ratio of 8.5:1.5.

It may be advantageous for the polyester resin to have a weight-average molecular weight of 2,000 to 25,000 g/mol to ensure that the release layer has adequate solvent resistance. Preferably, the weight-average molecular weight of the polyester resin may be 2,000 to 25,000 g/mol, or 2,000 to 20,000 g/mol, or 3,000 to 20,000 g/mol, or 3,000 to 15,000 g/mol.

In this specification, the weight average molecular weight refers to the weight average molecular weight in terms of polystyrene measured by the GPC method. In the process of measuring the weight average molecular weight in terms of polystyrene measured by the GPC method, commonly known analytical equipment, detectors such as a refractive index detector, and analytical columns can be used, and commonly used temperature conditions, solvents, and flow rates can be applied.

The acrylic resin may contain a glycidyl group-containing radically polymerizable unsaturated monomer as a copolymerizable monomer in an amount of 20 to 80 mol % of the total monomer components. The glycidyl group-containing radically polymerizable unsaturated monomer is preferred because it can improve the strength of the release layer through a crosslinking reaction and prevent oligomer leakage. Examples of the glycidyl group-containing radically polymerizable unsaturated monomer include glycidyl acrylate, glycidyl methacrylate, and aryl glycidyl ether.

Radically polymerizable unsaturated monomers copolymerizable with the glycidyl group-containing radically polymerizable unsaturated monomer include vinyl esters, unsaturated carboxylic acid esters, unsaturated carboxylic acid amides, unsaturated nitriles, unsaturated carboxylic acids, allyl compounds, nitrogen-containing vinyl monomers, hydrocarbon vinyl monomers, and vinylsilane compounds. Examples of vinyl esters that can be used include vinyl propionate, vinyl stearate, and vinyl chloride. Examples of unsaturated carboxylic acid esters that can be used include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, ethyl methacrylate, butyl methacrylate, butyl maleate, octyl maleate, butyl fumarate, octyl fumarate, hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl methacrylate, and hydroxypropyl acrylate. Examples of unsaturated carboxylic acid amides that can be used include acrylamide, methacrylamide, methylolacrylamide, and butoxymethylolacrylamide. Examples of unsaturated nitriles that can be used include acrylonitrile. Examples of unsaturated carboxylic acids that can be used include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, maleic acid esters, fumaric acid esters, and itaconic acid esters. Examples of allyl compounds that can be used include allyl acetate, allyl methacrylate, allyl acrylate, allyl itaconate, and diallyl itaconate. Examples of nitrogen-containing vinyl monomers that can be used include vinylpyridine and vinylimidazole. Examples of hydrocarbon vinyl monomers that can be used include ethylene, propylene, hexene, octene, styrene, vinyltoluene, and butadiene. Examples of vinylsilane compounds that can be used include dimethylvinylmethoxysilane, dimethylvinylethoxysilane, methylvinyldimethoxysilane, methylvinyldiethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropyldimethoxysilane.

As a non-limiting example, the acrylic resin may be a copolymer of 40 to 60 mol % of glycidyl acrylate and 40 to 60 mol % of propionic acid.

The acrylic resin preferably has a weight-average molecular weight of 20,000 to 70,000 g/mol. More preferably, the weight-average molecular weight of the polyester resin may be 20,000 to 60,000 g/mol, or 30,000 to 60,000 g/mol, or 40,000 to 60,000 g/mol, or 45,000 to 55,000 g/mol.

In one embodiment, the weight ratio of the solids of the polyester resin to the acrylic resin may be 1:0.1 to 1:1.5, and more specifically, 1:0.2 to 1:1. When a release layer is produced from an aqueous coating composition that satisfies this range, the polyester release film not only has excellent releasability but also exhibits improved processability and coating properties.

The release layer may contain polyolefin wax, which may be dispersed on the polyester resin and acrylic resin.

The specific type of polyolefin wax is not particularly limited, but one or more types selected from the group consisting of polyethylene wax and polypropylene wax can be preferably used.

The polyolefin wax may be included in an amount of 20 to 50 parts by weight or 30 to 40 parts by weight per 100 parts by weight of the polyester resin. To ensure that the release layer exhibits appropriate peel strength, the polyolefin wax is preferably included in an amount of 20 parts by weight or more per 100 parts by weight of the polyester resin. However, if an excessive amount of the polyolefin wax is added to the release layer, backside transfer problems and reduced process coating properties may occur. Therefore, the polyolefin wax is preferably included in an amount of 50 parts by weight or less per 100 parts by weight of the polyester resin.

For example, the polyolefin wax may be included in an amount of 20 parts by weight or more, or 25 parts by weight or more, or 30 parts by weight or more, and 50 parts by weight or less, or 45 parts by weight or less, or 40 parts by weight or less, per 100 parts by weight of the polyester resin. Specifically, the polyolefin wax may be included in an amount of 20 to 50 parts by weight, or 25 to 50 parts by weight, or 25 to 45 parts by weight, or 30 to 45 parts by weight, or 30 to 40 parts by weight, per 100 parts by weight of the polyester resin.

The total content of the polyester resin, acrylic resin, and polyolefin wax contained in the water-based coating composition is preferably 1 to 10 wt%, 2 to 9 wt%, 4 to 8 wt%, or 5 to 6 wt% based on the solids content.

A polyester release film manufactured when the total content, based on solids, of the binder and polyolefin wax contained in the aqueous coating composition satisfies the above range not only has excellent transfer properties and peelability, but also exhibits a significantly reduced frictional electrostatic voltage of less than 50 V. Furthermore, a release film manufactured when the above range is satisfied can prevent the occurrence of fine pinholes, thereby improving processability and coating properties.

In one embodiment of the present invention, the aqueous coating composition applied to the release layer may further contain additives such as silicone-based wetting agents, fluorine-based wetting agents, curing agents, acid catalysts, slip agents, antifoaming agents, wetting agents, surfactants, thickeners, plasticizers, antioxidants, UV absorbers, preservatives, and crosslinking agents, as needed. The additives can be used selectively to the extent that they do not impair the physical properties of the release layer.

The antistatic layer may contain a water-dispersible antistatic composition containing a conductive polymer.

The polyester release film according to one embodiment of the present invention includes the release layer and antistatic layer made of a non-silicone material, which not only provides excellent coating processability and peelability, but also excellent antistatic properties, with a significantly low frictional electrostatic voltage of less than 50 V.

The conductive polymer may be a nano-sized structure that is electrically conductive and polar. The conductive polymer may include, for example, one or more conductive polymers selected from polythiophene-based, polypyrrole-based, and polyaniline-based conductive polymers.

In one embodiment, the category of conductive polymers can also include resin compositions containing conductive polymers. The resins may be, for example, water-based resins or resins containing ionic polymers.

The ionic polymer may be a polymer having a group containing a cationic or anionic group, such as polystyrene sulfonate or polystyrene ammonium salt, but is not limited thereto. When using the ionic polymer, its content is not limited as long as the objective of the present invention is achieved, but it may be used in a weight ratio of 0.01 to 2 with respect to the conductive polymer, for example.

In one embodiment, the conductive polymer may be a polythiophene-based conductive polymer or polyethylenedioxythiophene:polystyrenesulfonate (PEDOT:PSS). When PEDOT:PSS is used as the conductive polymer, it has excellent water dispersibility and is suitable for use in an in-line coating process, and is more preferred because it does not lose transparency even after a stretching process after the in-line coating process and can exhibit a surface resistance of 10 ¹⁰ Ω/□ or less.

The water-dispersible antistatic composition may further contain a water-based polyurethane resin. By mixing the water-based polyurethane resin with a conductive polymer, an antistatic layer can be formed that has excellent miscibility, improved surface resistance, and excellent adhesion to a polyester base film, and exhibits minimal change in physical properties and little yellowing under high-temperature, high-humidity conditions. The water-based polyurethane resin uses a polyurethane binder obtained by reacting a polycarbonate-based polyol with a diisocyanate, achieving physical properties with excellent heat resistance and a low rate of change in surface resistance. More preferably, the diisocyanate used is hexamethylene diisocyanate, which is preferred from the perspective of improving heat resistance and forming a coating film with minimal yellowing, but is not limited thereto.

In one embodiment, the water-dispersible antistatic composition may contain 1 to 30 wt% of conductive polymer and 70 to 99 wt% of water-based polyurethane resin, based on a 100 wt% solids content. More specifically, the water-dispersible antistatic composition may contain 5 to 25 wt% of conductive polymer and 75 to 95 wt% of polyurethane binder. Even more specifically, the water-dispersible antistatic composition may contain 5 to 20 wt% of conductive polymer and 80 to 95 wt% of polyurethane binder.

More specifically, the antistatic layer may be formed by applying a water-dispersible antistatic composition containing a conductive polymer solution, a water-based polyurethane resin solution, an organic solvent, and water.

More specifically, for example, the water-dispersible antistatic composition may contain 40 to 90 wt% of a conductive polymer solution with a solids content of 1 to 3 wt%, 5 to 50 wt% of a water-based polyurethane resin solution with a solids content of 30 to 40 wt%, 3 to 50 wt% of an organic solvent, and the balance being water.

The conductive polymer may be used as a conductive polymer solution in a solvent to achieve optimal dispersibility. Specifically, for example, when PEDOT:PSS is used, it may be mixed with water, alcohol, or a solvent with a high dielectric constant.

The content of the conductive polymer solution in the antistatic composition may be 40 to 90 wt%, more preferably 50 to 70 wt%, as long as it is a content sufficient to achieve the objectives of the invention, but is not limited to this amount.

The water-based polyurethane resin may also be dispersed in a solvent. The solvent is not limited, but may be any one or a mixture of two or more solvents selected from the group consisting of amide-based organic solvents and aprotic highly dipolar (AHD) organic solvents.

The content of the water-based polyurethane resin in the water-dispersible antistatic composition may be 5 to 50 wt %, more preferably 10 to 30 wt %, but is of course not limited to this.

The organic solvent is not particularly limited, but may be any one or a mixture of two or more solvents selected from the group consisting of alcohol-based organic solvents and aprotic highly polar organic solvents, and is not limited thereto.

The content of the organic solvent in the water-dispersible antistatic composition may be 50 wt% or less, 40 wt% or less, 30 wt% or less, 20 wt% or less, or 10 wt% or less, with the lower limit being 1 wt% or 2 wt% or more. This range is a content suitable for improving the dispersibility of the conductive polymer and water-based polyurethane resin, but is not limited thereto.

The alcohol-based organic solvent is not limited, but specific examples include methanol, ethanol, propanol, isopropanol, butanol, and 2-amino-2-methyl-1-propanol, and can be used alone or in combination of two or more.

The aprotic highly polar organic solvent is not limited, but specific examples include dimethyl sulfoxide and propylene carbonate, which can be used alone or in combination. The use of aprotic highly polar organic solvents can further improve the conductivity of the conductive polymer.

As the water-dispersible antistatic composition contains each substance in the above content range, the polyester release film according to one embodiment of the present invention has excellent antistatic properties with a significantly low frictional electrostatic voltage of less than 50 V. This prevents static electricity from being generated during film running and winding, and significantly reduces the amount of air or foreign matter that is drawn in due to static electricity.

In addition, because the water-dispersible antistatic composition satisfies the above content range, the polyester release film according to one embodiment of the present invention can solve problems such as reduced yield due to unreacted materials generated when forming a coating layer using the composition, and adhesion of foreign matter due to static electricity.

In one embodiment of the present invention, the surface resistance of the antistatic layer may be 10 ¹⁰ Ω/□ or less, more specifically, 10 ⁹ Ω/□ or less.

In one embodiment of the present invention, the water-dispersible antistatic composition may further contain, as needed, a silicone-based wetting agent, a fluorine-based wetting agent, a slip agent, an antifoaming agent, a moistening agent, a surfactant, a thickener, a plasticizer, an antioxidant, an ultraviolet absorber, a preservative, a crosslinking agent, and the like.

The thicknesses of the base film, release layer, and antistatic layer are not particularly limited and can be adjusted depending on the specific application of the polyester release film.

For example, the substrate film may have a thickness of 10 to 300 μm, and the release layer and antistatic layer may have a thickness of 10 to 200 nm, but these are not necessarily limited to these.

The release layer and antistatic layer may have the same or different thicknesses. Specifically, the thickness of the substrate film may be 10 to 200 μm, 10 to 100 μm, or 10 to 50 μm. The thickness of the release layer may be 10 to 100 nm, more specifically 50 to 100 nm. The thickness of the antistatic layer may be 10 to 100 nm, more specifically 20 to 80 nm.

In the polyester release film, the base film may be, but is not limited to, uniaxially stretched in the machine direction (MD) or transverse direction (TD), or biaxially stretched in the machine direction (MD) and transverse direction (TD). The release layer and antistatic layer may be uniaxially or biaxially stretched, but are preferably uniaxially stretched in the transverse direction (TD) because this can better impart the properties of the present invention.

By satisfying the above-mentioned properties, the polyester release film not only has excellent releasability but also has low frictional electrostatic voltage, making it excellent in antistatic properties.

For example, the polyester release film may have a peel strength of 350 to 700 gf/inch, or 400 to 650 gf/inch, or 400 to 600 gf/inch. Polyester release films with a peel strength within this range may exhibit excellent coating processability and peelability during post-processing (e.g., a process of forming a barrier coating layer on the release film).

In this specification, the peel strength is measured according to the standard test method of ASTM D 3330. Specifically, the peel strength can be measured by laminating an acrylate adhesive tape (NITTO #31B tape, manufactured by Nitto Denko, width: 25 mm) cut to a size of 5 mm x 180 mm on the release layer of the polyester release film, applying a load of 70 g/ ^cm² to the tape, leaving it at room temperature for 30 minutes, and then peeling the tape 180° at a peel rate of 300 mm/min using a peel tester.

Furthermore, the polyester release film may have a significantly low frictional electrostatic voltage of less than 50 V, or less than 40 V, or less than 30 V, or less than 20 V, or less than 10 V. The lower limit of the frictional electrostatic voltage is not particularly limited, but may be, for example, 1 V or more, 3 V or 5 V or more.

In this specification, the frictional electrostatic voltage is measured according to the standard test method of KS K 0555. Specifically, the frictional electrostatic voltage can be measured by measuring the frictional static electricity on the polyester release film using a conventional rotary static tester. Here, the amount of static electricity generated is measured by rubbing side A (the release layer side of the polyester release film) and side B (the antistatic layer side of the polyester release film) at a rotational speed of 300 rpm for 180 seconds.

Furthermore, the polyester release film exhibits excellent processing and coating properties while maintaining a low haze value.

For example, the polyester release film may have a haze of 3.90% or less. Preferably, the polyester release film may have a haze of 3.50 to 3.90%, 3.60 to 3.90%, or 3.70 to 3.86%.

Furthermore, the polyester release film can have excellent process-coating properties that satisfy the following formula 1.

[Formula 1]
N _H =0

In the above formula 1, N _H is the number of pinholes generated per unit area (m ² ) when a UV resin is applied to a thickness of 10 μm on the release layer of the polyester release film and cured.

In other words, when a resin layer is formed on the release layer in any manufacturing process using the polyester release film as a substrate, pinholes are substantially not formed on the release layer, demonstrating excellent processing and coating properties.

In addition, the polyester release film can exhibit a total light transmittance of 90% to 95%, a water contact angle of 85° to 90°, a diiodomethane contact angle of 50° to 60°, and a surface energy of 30 to 35 mN/m.

In addition, the polyester release film according to one embodiment of the present invention may be a polyester release film for thin-film polarizers, but is not limited thereto and can be applied to a variety of fields requiring anti-static properties, coating processability, and releasability. For example, in addition to thin-film polarizer applications, the film can be used as a cover tape for MLCC (Multi-Layer Ceramic Capacitor) carriers, for FPCB (Flexible Printed Circuits Board) process protection, for OCA (Opticaly Clear Adhesive) and OCA protection, and for protecting the surfaces of optical components for displays (various display surfaces).

In the polyester release film, the release layer and antistatic layer may be formed on the polyester substrate film by in-line coating. The release layer may be formed by applying an aqueous coating composition containing the polyester resin, acrylic resin, and polyolefin wax to one side of the polyester substrate film by in-line coating.

The antistatic layer can be formed by applying a water-dispersible antistatic composition containing the conductive polymer to the other side of the substrate film using an in-line coating method.

The release layer and antistatic layer are formed using an in-line coating method, which allows for a thin coating thickness while still providing excellent adhesion to the polyester substrate film and excellent resistance to moisture and solvents.

The polyester release film has excellent coating processability, releasability, and low frictional charging voltage, making it suitable for use as a release substrate film when manufacturing thin-film polarizing plates.

As a non-limiting example, when manufacturing the thin film polarizer, a laminate can be formed by sequentially laminating a barrier coating layer, a polyvinyl alcohol resin layer, an adhesive layer, and a resin layer such as polyethylene terephthalate (PET), triacetyl cellulose (TAC), or polymethyl methacrylate (PMMA) on the substrate film of the polyester release film.

The polyester release film can also be removed from the laminate.

The manufacturing method for polyester release film is explained in detail below.

A method for producing a polyester release film according to one embodiment of the present invention may include: a first step of preparing a polyester substrate film; a second step of applying a water-based coating composition containing a polyester resin, an acrylic resin, and a polyolefin wax to one side of the substrate film to form a release layer; a third step of applying a water-dispersible antistatic composition containing a conductive polymer to the other side of the substrate film to form an antistatic layer; and a fourth step of heat-treating a laminate including the substrate film, the release layer formed on the substrate film, and the antistatic layer while stretching the laminate.

The first step is to prepare a polyester substrate film, which is made of polyester resin.

The polyester substrate film may be any polyester commonly used in the technical field to which the present invention pertains, without any particular limitations. The polyester substrate film may be prepared as one stretched in the machine direction (MD, or length direction), although this is not necessarily limited thereto. Preferably, the polyester substrate film may be stretched 2 to 5 times in the machine direction (MD). The polyester substrate film preferably has a thickness of 10 to 300 μm, but is of course not limited thereto as long as the objectives of the present invention are achieved.

The second step is to form a release layer by applying an aqueous coating composition containing a polyester resin, an acrylic resin, and a polyolefin wax to one side of the substrate film, and the aqueous coating composition is used to form the release layer on the polyester substrate film.

The water-based coating composition may contain the polyester resin, the acrylic resin, and the polyolefin wax, and the specific details regarding the resin and wax are as described above.

The water-based coating composition can be prepared by uniformly mixing the above-mentioned components with water. The solids content of the water-based coating composition is preferably 20 to 60 wt % to ensure the efficiency of the coating process.

The release layer can be formed on one side of the polyester substrate film by an in-line coating method using the aqueous coating composition. By forming the release layer by the in-line coating method, the coating thickness is thin, but the layer has excellent adhesion to the polyester substrate film and exhibits excellent resistance to moisture and solvents.

The in-line coating method can be carried out using conventional equipment.

When performing the in-line coating, the aqueous coating composition can be applied so that the thickness of the release layer is 20 to 200 nm after final stretching and drying. Specific details regarding the thickness and other properties of the release layer can be found above.

The release layer can be formed by applying the water-based coating composition to the polyester substrate film, removing the water from the water-based coating composition, and then curing the composition.

The third step is to form an antistatic layer by applying a water-dispersible antistatic composition containing a conductive polymer to the other side of the substrate film. The water-dispersible antistatic composition may further contain a water-based polyurethane resin. Specific details regarding the conductive polymer, water-based polyurethane resin, etc., can be found above.

The water-dispersible antistatic composition can be prepared by uniformly mixing the above-mentioned components with water. It may be preferable for the solids content of the antistatic composition to be 5 to 50 wt % to ensure the efficiency of the coating process.

The water-dispersible antistatic composition may further contain an organic solvent, and the details regarding this are as described above.

The antistatic layer can be formed on the other side of the polyester substrate film by an in-line coating method using the water-dispersible antistatic composition. Specific details regarding the in-line coating method can be applied as described above for the release layer.

The fourth step is a step of heat-treating the laminate including the base film and the release layer and antistatic layer formed on the base film while stretching it in the machine direction (MD) or transverse direction (TD).

In one embodiment, although not necessarily limited thereto, the laminate is preferably stretched 2 to 5 times in the transverse direction (TD) since this is suitable for achieving the desired physical properties in one embodiment of the present invention.

For example, the release layer and antistatic layer can be formed on the polyester substrate film, which has been uniaxially stretched in the machine direction (MD), and then stretched in the transverse direction (TD). Through this stretching process, the polyester substrate film is biaxially stretched in the machine direction and the transverse direction, and the release layer and antistatic layer are uniaxially stretched in the transverse direction.

The fourth step can be carried out using a conventional heat treatment device such as a tenter. In the fourth step, the laminate can be passed continuously through the tenter.

The laminate is preheated while passing through the front section of the tenter, stretched, for example, in the transverse direction (TD) while passing through the middle section of the tenter, and heat-treated while passing through the rear section of the tenter. The heat treatment may involve heating the laminate while maintaining the tension applied to it during the transverse stretching.

Preferably, the fourth step can be performed by passing the laminate through a heat treatment device in which the total heat amount of the air supplied to the passage section is 222,000 kcal/min to 229,000 kcal/min. The laminate passing through the heat treatment device is stretched and heat-treated while being exposed to the total heat amount range.

Specifically, the fourth step can be performed by passing the laminate through a heat treatment device in which the total heat capacity of the air supplied to the entire passage section is 222,000 kcal/min to 229,000 kcal/min, or 225,000 kcal/min to 229,000 kcal/min, or 226,000 kcal/min to 229,000 kcal/min, or 226,000 kcal/min to 228,000 kcal/min, or 226,000 kcal/min to 227,000 kcal/min.

In the fourth step, the total heat quantity (kcal) of the air supplied to the entire section through which the laminate passes can be calculated from data such as the temperature (°C) of the section, the mass (kg/min) of the air supplied to the heat treatment device, and the specific heat of the air (kcal/kg°C). The mass (kg/min) of the air can be obtained from the volumetric flow rate ( ^Nm3 /min) of the air and the density (kg/ ^Nm3 ).

For example, in the heat treatment device, when the density of air supplied to a given zone is 1.286 kg/ ^Nm3 , the specific heat of the air is 0.24 kcal/kg°C, the volumetric flow rate of the air is 380 ^Nm3 /min, the initial temperature of the air is 20°C, and the set temperature of the zone is 220°C, the total heat (kcal) of the air supplied to the zone can be calculated as 23,456.64 kcal/min using the following calculation formulas 1 and 2.

[Formula 1]
Mass of air (kg/min) = Volumetric flow rate of air (Nm ³ /min) × Air density (kg/Nm ³ )

[Formula 2]
Heat content of air (kcal/min) = mass of air (kg/min) x specific heat of air (kcal/kg °C) x temperature change (°C)

When the passage length of the section is 3 m and the laminate passes through the section at a speed of 100 m/min, the amount of heat exposed to the laminate in the section can be calculated as 7,037 kcal/zone using the following equation 3.

[Formula 3]
Amount of heat to which the laminate is exposed (kcal/zone) = Amount of heat of air (kcal/min) × Passage length of section (m/zone) × Speed of laminate (m/min)

According to one embodiment of the invention, the process can include the steps of preheating the laminate by passing it through a section where a heat amount of 44,000 kcal/min to 46,000 kcal/min is supplied; stretching the preheated laminate in the machine direction (MD) or transverse direction (TD) while passing it through a section where a heat amount of 62,000 kcal/min to 64,000 kcal/min is supplied; and heat-treating the stretched laminate while passing it through a section where a heat amount of 114,000 kcal/min to 120,000 kcal/min is supplied.

Preferably, the preheating step can be carried out while the laminate is passed through a section where a heat quantity of 45,000 kcal/min to 46,000 kcal/min is supplied.

Preferably, the stretching step can be carried out while the preheated laminate is passed through a section where a heat quantity of 63,000 kcal/min to 64,000 kcal/min is supplied.

Preferably, the heat treatment step can be carried out by passing the stretched laminate through a section to which a heat amount of 115,000 kcal/min to 120,000 kcal/min, or 115,000 kcal/min to 119,000 kcal/min, or 116,000 kcal/min to 119,000 kcal/min, or 117,000 kcal/min to 118,500 kcal/min, or 118,000 kcal/min to 118,500 kcal/min is supplied.

If the total heat quantity of the air supplied to the passage section in the fourth stage (particularly the heat treatment zone after stretching) is too low, the releasability and transferability of the polyester release film may deteriorate and the frictional charging voltage may increase. Furthermore, if the total heat quantity of the air supplied to the passage section in the fourth stage (particularly the heat treatment zone after transverse stretching) is too high, the surface energy of the polyester release film may decrease, resulting in poor process coatability.

Furthermore, in the fourth step, it is preferable that the laminate passes through the heat treatment device at a speed of 80 m/min to 120 m/min, or 90 m/min to 110 m/min, or 90 m/min to 100 m/min.

When performing the fourth step, it is preferable that the laminate passes through the heat treatment device within the above speed range so that the laminate is exposed to an appropriate amount of heat in each section and the transverse stretching and heat treatment are sufficiently carried out.

The fourth step can be carried out at a temperature of 120°C to 245°C. For example, the fourth step can be carried out by preheating the laminate at a temperature of 120°C to 150°C; stretching the preheated laminate in the transverse direction at a temperature of 130°C to 150°C; and heat-treating the stretched laminate at a temperature of 215°C to 245°C.

In particular, the heat treatment of the stretched laminate can be carried out at 215°C or higher, 220°C or higher, 225°C or higher, or 230°C or higher; and 245°C or lower, or 240°C or lower. Specifically, the heat treatment of the stretched laminate can be carried out at 215-245°C, 220-245°C, 220-240°C, 225-240°C, or 230-240°C.

When the temperature in the heat treatment process of the stretched laminate satisfies the above range, not only will the polyester release film have excellent releasability, but the frictional charging voltage will also be reduced, and fine pinholes will not occur during the production of the polyester release film, improving processing and coating properties.

After the fourth step, a process of relaxing the fabric by 2 to 10% in both the machine and cross directions can be carried out at 150 to 200°C.

The final thickness of the polyester release film obtained through this process may be 20 to 100 μm, or 30 to 80 μm, or 30 to 50 μm.

The following describes the present invention by providing specific examples of manufacturing, working examples, and experimental examples. However, the examples and experimental examples described below only partially illustrate the present invention, and the present invention is not limited thereto.

<Preparation Example 1> Preparation of first aqueous coating composition (1) Preparation of first resin composition A first polyester resin (weight average molecular weight 10,000 g/mol) was obtained by condensation polymerization of 50 mol% of a glycol component containing diethylene glycol and ethylene glycol in a molar ratio of 5:5, and 50 mol% of an acid component containing terephthalic acid and sulfoterephthalic acid in a molar ratio of 8.5:1.5.

100 parts by weight of the first polyester resin and 25 parts by weight of polyethylene wax (Wax No. 1, manufactured by Takamatsu Co., Ltd., Japan) were added to distilled water and stirred for 30 minutes to produce a first resin composition (solids content 20 wt%).

(2) Production of Second Resin Composition A second polyester resin (weight average molecular weight: 3,000 g/mol) was obtained by condensation polymerization of 50 mol% of a glycol component containing diethylene glycol and ethylene glycol in a molar ratio of 5:5, and 50 mol% of an acid component containing terephthalic acid and sulfoterephthalic acid in a molar ratio of 8.5:1.5.

An acrylic resin was obtained by copolymerizing 60 mol% glycidyl acrylate and 40 mol% vinyl propionate (weight average molecular weight: 50,000 g/mol).

50 parts by weight of the second polyester resin, 50 parts by weight of the acrylic resin, and 25 parts by weight of polyethylene wax were added to distilled water and stirred for 30 minutes to produce a second resin composition (solids content 20 wt%).

(3) Preparation of Water-Based Coating Composition A first water-based coating composition was prepared by mixing 14.3 wt % (solid content 20 wt %) of the first resin composition, 14.3 wt % (solid content 20 wt %) of the second resin composition, 0.2 wt % of a silicone-based wetting agent (Dow Corning, Q2-5212, solid content 90 wt %), 0.2 wt % of a fluorine-based wetting agent (DuPont, FS-31, solid content 25 wt %), and the remaining amount of water.

Preparation Example 2: Preparation of second aqueous coating composition A second aqueous coating composition was prepared in the same manner as Preparation Example 1, except that the first resin composition prepared in Preparation Example 1 was not used and the second resin composition was added in the same amount. That is, the second aqueous coating composition according to Preparation Example 2 contained only 28.6 wt % of the second resin composition.

Preparation Example 3 Preparation of First Antistatic Coating Composition 60 wt% of a conductive polymer aqueous dispersion (Heraeus, Clevios P, solids content 1.3 wt%), 6 wt% water, and 5 wt% isopropyl alcohol (IPA) were placed in a mixing vessel and stirred for 1 hour. 2 wt% of 2-amino-2-methyl-1-propanol (Alfa Aesar, 95%) was then added to the mixing vessel and stirred for another hour. 20 wt% of a water-based polyurethane resin (Neo Resins, Neorez R-960, solids content 31 wt%) was then added and stirred again for 30 minutes. 5 wt% of dimethyl sulfoxide and 2 wt% of a silicone-based wetting agent (BYK 348) were then added to the mixing vessel and stirred for an additional hour to prepare a first water-dispersible antistatic composition (solids content 6.98 wt%). The first water-dispersible antistatic composition was then subjected to a second dilution. In this case, 30 wt % of the first water-dispersible antistatic composition, 69.6 wt % of water, 0.2 wt % of a silicone-based wetting agent (Dow Corning, Q2-5212, solid content 90 wt %), and 0.2 wt % of a fluorine-based wetting agent (DuPont, FS-31, solid content 25 wt %) were mixed to prepare a first antistatic coating composition.

Comparative Preparation Example 1 Preparation of third aqueous coating composition A third aqueous coating composition was prepared by mixing 20 wt % of a silicone release base (Wacker 400E, solids content 55 wt %), 1.1 wt % of a curing agent (Wacker V-72, solids content 40 wt %), 0.18 wt % of a silicone wetting agent (Dow Corning Q2-5212, solids content 90 wt %), 5 wt % of isopropyl alcohol (IPA), and the remaining amount of water.

Comparative Preparation Example 2: Preparation of fourth aqueous coating composition A fourth aqueous coating composition was prepared in the same manner as Preparation Example 1, except that the second resin composition prepared in Preparation Example 1 was not used and the first resin composition was added in the same amount. That is, the fourth aqueous coating composition according to Comparative Preparation Example 1 contained only 28.6 wt % of the first resin composition.

Comparative Preparation Example 3 Preparation of Second Antistatic Coating Composition A second antistatic coating composition was prepared by mixing 5.1 wt % of an acrylic aqueous dispersion (ATX-014, manufactured by Takamatsu Corporation of Japan, solid content 40 wt %), 9 wt % of an anionic polymer antistatic agent (ICP-323, manufactured by JINBO Corporation, molecular weight 100,000 g/mol or more, solid content 25.5 wt %), 2 wt % of a silicone wetting agent (BYK 384), and the remaining amount of water.

Example 1
(1) PET chips, the moisture content of which had been reduced to 100 ppm or less, were injected into a melt extruder, melted, and extruded through a T-die, and then rapidly cooled and solidified on a casting drum at a surface temperature of 20°C to produce a PET sheet. The produced PET sheet was stretched 3.5 times in the machine direction at 110°C and then cooled to room temperature to obtain the PET substrate film.

(2) Using a gravure coater, the first aqueous coating composition of Preparation Example 1 was applied to one side of the PET substrate film to a thickness of 70 nm after final drying to form a release layer, and the first antistatic coating composition of Preparation Example 3 was applied to the other side of the PET substrate film to a thickness of 50 nm after final drying to form an antistatic layer.

(3) Next, the laminate with the release layer and antistatic layer formed thereon was heat-treated while being stretched four times in the transverse direction (TD) in a tenter divided into a preheating zone, a stretching zone, and a heat-treatment zone.

The heat treatment step was carried out while the laminate (initial width 5.12 m, initial thickness 152 μm) was passing through the tenter, which had a total length of 33 m and included a preheating zone, stretching zone, and heat treatment zone in that order, at a moving speed of 100 m/min.

The heat treatment step was performed by passing the laminate through the tenter, in which the total heat capacity of the air supplied to the passage section was 226,400 kcal/min.

The density of the air supplied to the tenter was confirmed to be 1.286 kg/nm ³ , the specific heat of the air was confirmed to be 0.24 kcal/kg° C., and the volumetric flow rate of the air was adjusted within the range of 270 to 680 nm ³ /min.

Specifically, the laminate passed through the preheating zone (7.5 m in length), where a heat rate of 45,000 kcal/min was supplied at a temperature of approximately 120°C to 130°C. The preheated laminate then passed through the stretching zone (10.5 m in length), where a heat rate of 63,200 kcal/min was supplied at a temperature of approximately 130°C to 140°C, and was stretched four times in the transverse direction. The stretched laminate then passed through the heat treatment zone (15 m in length), where a heat rate of 118,200 kcal/min was supplied at a temperature of 230°C to 235°C, and was heat-treated.

(4) After the heat treatment step, the film was heat-set at 200°C, relaxing by 10% in both the machine direction and the transverse direction, to produce a polyester release film with a total thickness of 38 μm.

Example 2
In Example 2, a polyester release film having a total thickness of 38 μm was prepared in the same manner as in Example 1, except that the release layer of Example 1 was formed by coating the second aqueous coating composition of Preparation Example 2.

<Comparative Example 1>
In Comparative Example 1, a polyester release film having a total thickness of 38 μm was prepared in the same manner as in Example 1, except that the antistatic layer was not formed.

<Comparative Example 2>
In Comparative Example 2, a polyester release film having a total thickness of 38 μm was prepared in the same manner as in Example 1, except that the release layer was formed by coating the third aqueous coating composition of Comparative Preparation Example 1.

<Comparative Example 3>
In Comparative Example 3, a polyester release film having a total thickness of 38 μm was prepared in the same manner as in Comparative Example 2, except that the antistatic layer was not formed.

<Comparative Example 4>
In Comparative Example 4, a polyester release film having a total thickness of 38 μm was prepared in the same manner as in Example 1, except that the antistatic layer of Example 1 was formed by coating the second antistatic coating composition of Comparative Preparation Example 3.

Comparative Example 5
In Comparative Example 5, a polyester release film having a total thickness of 38 μm was prepared in the same manner as in Example 1, except that the release layer of Example 1 was formed by coating the fourth aqueous coating composition of Comparative Preparation Example 2.

<Evaluation items>
The following properties of the examples and comparative examples were measured and the values are shown in Table 1 below.

1. Optical Properties Haze and total light transmittance (TT) of the films of the following Examples and Comparative Examples were measured using a haze meter (Nippon Denshoku, NDH 5000).

2. Transfer test
An untreated PET substrate film was laminated on the release layer of the polyester release film, and a load of 50 gf/inch was applied, and the film was left in an oven at 45°C for 24 hours. If the difference in water contact angle was △2° or more, the transfer was recorded as "Yes", and if there was no difference in water contact angle, the transfer was recorded as "No".

The same transfer test was also performed on the antistatic layer of the polyester release film, and the presence or absence of transfer was noted.

3. Water Contact Angle The water contact angle of the release layer of the film was measured using a contact angle meter (KRUSS, DSA 100). 3 μl of pure water (S1, Volume mode) was dropped onto the film specimen, and the average water contact angle was measured for 15 seconds. A total of five measurements were taken, and the average value is shown.

4. Diiodomethane Contact Angle The contact angle of diiodomethane on the release layer of the film was measured using a contact angle meter (KRUSS, DSA 100). 1 μl of diiodomethane (S1, Volume mode) was dropped onto the film specimen, and the average diiodomethane contact angle was measured for 15 seconds. A total of five measurements were taken, and the average value is shown.

5. Surface Energy The surface energy of the release layer of the film was calculated from the measurement results of the water contact angle and diiodomethane contact angle using the Owens-Wendt method.

6. Coating Properties: A sample was prepared by applying a UV resin (Miwon Specialty Chemical Co., MIRAMER M1130) to a thickness of 10 μm on the release layer of the film and curing it with UV light. The coating properties of the sample were evaluated according to the following criteria.

* Grade 1 - no pinholes per unit area (m ² ) * Grade 2 - 2 or less pinholes per unit area (m ² ) * Grade 3 - 5 or less pinholes per unit area (m ² ) * Grade 4 - 10 or less pinholes per unit area (m ² ) * Grade 5 - more than 10 pinholes per unit area (m ² )

7. Peel Strength The peel strength was measured by a method including the steps of: preparing a first sample by adhering an acrylate adhesive tape (NITTO #31B, tape width: 25 mm, manufactured by Nitto Denko) on the release layer of the polyester release film; cutting the first sample into a size of 5 mm x 180 mm to prepare a second sample; and applying a load of 70 g/ ^cm2 to the second sample, leaving it at room temperature for 30 minutes, and then peeling the tape at a 180° angle at a peel rate of 300 mm/min using a peel tester.

8. Frictional Charging Voltage The frictional static electricity of the polyester release film was measured using a rotary static tester (Daiei Kagaku Seiki MFG, RST-300a). At this time, the amount of static electricity generated by rubbing the A side (the release layer side of the polyester release film) and the B side (the antistatic layer side of the release film) at a rotation speed of 300 rpm for 180 seconds was measured.

The surface resistance of the antistatic layer of the films prepared in the examples and comparative examples was evaluated. The surface resistance was measured using a Mitsubishi Chemical Corp. Hiresta-Up MCP-HP450 device under the conditions of 25°C, 50% RH, 10 V, and 10 seconds.

Referring to Table 1 above, it can be seen that the polyester release films according to the examples not only have superior transfer properties, peelability, and coating processability compared to the release films according to the comparative examples, but also have excellent antistatic properties, with a significantly low frictional electrification voltage of less than 50 V.

Therefore, the polyester release film of the present invention comprises a release layer containing an aqueous coating composition including a polyester resin, an acrylic resin, and a polyolefin wax, and an antistatic layer containing a water-dispersible antistatic composition including a conductive polymer. This not only provides excellent peelability and coating processability, but also excellent antistatic properties, with a significantly low frictional charging voltage of less than 50 V. This prevents static electricity from being generated during film running and winding, and significantly reduces the amount of air or foreign matter that is drawn in due to static electricity.

In addition, the polyester release film of the present invention can solve problems that arise when forming a coating layer using the release film, such as reduced yield due to unreacted materials and adhesion of foreign matter due to static electricity, and is suitable for use as a substrate when manufacturing optical films such as thin-film polarizing plates.

Claims (16)

The present invention relates to a polyester substrate film, a release layer formed on one surface of the substrate film, and an antistatic layer formed on the other surface of the substrate film,
the release layer comprises a water-based coating composition including a polyester resin, an acrylic resin, and a polyolefin wax;
The antistatic layer comprises a water-dispersible antistatic composition containing a conductive polymer ,
The polyester release film has a frictional electrification voltage of less than 50V . The polyester release film according to claim 1, wherein the weight ratio of the solid content of the polyester resin to the solid content of the acrylic resin is 1:0.1 to 1:1.5. The polyester release film according to claim 1, wherein the release layer contains 20 to 50 parts by weight of polyolefin wax per 100 parts by weight of polyester resin. The polyester release film according to claim 1, wherein the polyolefin wax is one or more waxes selected from the group consisting of polyethylene wax and polypropylene wax. The polyester release film according to claim 1, wherein the conductive polymer includes one or more selected from polythiophenes, polypyrroles, and polyanilines. The polyester release film according to claim 1, wherein the water-dispersible antistatic composition further contains a water-based polyurethane resin. 7. The polyester release film according to claim 6 , wherein the solid content of the water-dispersible antistatic composition comprises 1 to 30 wt % of a conductive polymer and 70 to 99 wt % of a water-based polyurethane resin. 2. The polyester release film according to claim 1, wherein the surface resistance of the antistatic layer is 10 ¹⁰ Ω/□ or less. 3. The polyester release film according to claim 1, having a haze of 90% or less and a processing coatability that satisfies the following formula 1:
[Formula 1]
N _H =0
In the above formula 1, N _H is the number of pinholes generated per unit area (m ² ) when a UV resin is applied to a thickness of 10 μm on the release layer of the polyester release film and cured. the release layer is formed by in-line coating of the aqueous coating composition,
2. The polyester release film according to claim 1, wherein the antistatic layer is formed by in-line coating of the water-dispersible antistatic composition. The polyester release film according to claim 1, wherein the base film is biaxially stretched, and the release layer and antistatic layer are uniaxially stretched in the transverse direction (TD). The polyester release film according to claim 1, wherein the thickness of the base film is 10 to 300 μm, and the thicknesses of the release layer and antistatic layer are 10 to 200 nm. The polyester release film according to claim 1, wherein the polyester release film is for protecting a polarizing plate. A first step of preparing a polyester substrate film;
a second step of applying a water-based coating composition containing a polyester resin, an acrylic resin, and a polyolefin wax to one surface of the substrate film to form a release layer;
A method for producing a polyester release film, comprising: a third step of applying a water-dispersible antistatic composition containing a conductive polymer to another surface of the substrate film to form an antistatic layer; and a fourth step of heat-treating a laminate including the substrate film, the release layer formed on the substrate film, and the antistatic layer while stretching the laminate,
The polyester release film has a frictional electrification voltage of less than 50 V. 15. The method for producing a polyester release film according to claim 14 , wherein the fourth step comprises passing the laminate through a heat treatment device in which a total heat amount of air supplied to a passing section is 222,000 kcal/min to 229,000 kcal/min, thereby performing stretching and heat treatment. The fourth step is a step of preheating the laminate by passing it through a section where a heat amount of 44,000 kcal/min to 46,000 kcal/min is supplied;
stretching the preheated laminate in a transverse direction (TD) while passing through a section to which a heat amount of 62,000 kcal/min to 64,000 kcal/min is supplied; and
The method for producing a polyester release film according to claim 14 , comprising the step of: subjecting the stretched laminate to the heat treatment while passing through a section in which a heat amount of 114,000 kcal/min to 120,000 kcal/min is supplied.