JP7552040B2 - Release Film - Google Patents

Description

The present invention relates to a release film that has a release layer on at least one side of a polyester film.

Polyester films, such as polyethylene terephthalate and polyethylene naphthalate, have excellent mechanical strength, dimensional stability, flatness, heat resistance, chemical resistance, optical properties, etc., and are cost-effective, so they are used for a variety of purposes.

Examples of applications for polyester film include process films used in various processes, such as for electromagnetic wave shielding and transfer applications such as simultaneous transfer during molding, for the manufacture of flexible printed wiring boards, and as process paper for the manufacture of plastic sheets. When used for these applications, a method has been proposed in which a release coating is laminated onto the surface of the polyester film to provide release properties for various resins and adhesives.

In plasma displays (PDPs) and the like, an electromagnetic wave shielding film, i.e., a conductive film, is attached to the front of the display panel, and a conductive film made of polyester film with a mesh of thin metal wires is commonly used as this electromagnetic wave shielding film.

This type of electromagnetic wave shielding film is formed on a support film, and then the film is pressed at high temperature onto the surface of various devices to transfer the electromagnetic wave shielding film.
Conventionally, a flat polyester film has generally been used as the support film for such a transfer-type electromagnetic shielding film, but in order to give the product a matte appearance, it has been proposed to use a polyester film with a matte surface as the support film and transfer this matte surface to the product.

In simultaneous molding and transfer, a transfer foil is generally used, which is made by laminating transfer layers such as a hard coat layer, a pattern printed layer, and an adhesive layer in order on a release layer of a support film. This transfer foil is set in a mold for injection molding, and a transfer foil sheet is bonded integrally to the surface of a resin molded product while the resin molded product is being molded, and the design is transferred to the resin molded product to decorate it. This so-called in-mold transfer method is widely known.
Even in such an in-mold transfer method, a molded product having a low gloss may be required as one of the design features of the molded product. As a means for imparting a low gloss to a molded product, a method of using a polyester film with a matte surface as the support film and transferring this matte surface to the product can be given.

For example, Patent Document 1 discloses a release film having a release layer on at least one film surface, the release layer containing a release agent, a thermosetting compound, and a binder polymer, and the peel strength between the release layer and an acrylic adhesive tape around 100% elongation is within a specific range.

For example, Patent Document 2 discloses an adhesive release polyester film for in-mold transfer materials, which has an adhesive release layer on at least one side of a polyester film, the adhesive release layer containing a fluorine-based polymer having a glass transition temperature of -40°C to 20°C, a urethane-based polymer having a glass transition temperature of -60°C to 10°C, and a crosslinking agent, the peel strength of a hard coat layer from the adhesive release layer being 0.2 N/mm to 0.4 N/mm, and the surface hardness of the adhesive release layer being 0.5 GPa to 4.5 GPa as measured by a microhardness meter.

Patent document 3 discloses a biaxially oriented polyester film for release, which has a polyester A layer containing inorganic particles and/or organic particles in at least one outermost layer, the average surface roughness Ra of the outermost polyester A layer surface being 0.38 μm or more and 1.0 μm or less, the average length RSm of the roughness curve element of the polyester A layer surface being 10 μm or more and 80 μm or less, and the release layer is a composition containing a fluorine-based polymer.

JP 2010-247456 A JP 2012-11658 A JP 2016-175229 A

As described above, by providing a release layer on the surface of the polyester film, it is possible to maintain releasability from various resin layers, and use it as a polyester film for transfer. In addition, when the surface of the polyester film is roughened to give it a matte finish, the surface of the polyester film can be pressed against the surface of an object and then the polyester film can be peeled off to transfer the roughened surface state to the surface of the object, resulting in a matte appearance.

In the conventional transfer polyester films of this type, a large amount of release agent had to be added to the release layer to give it release properties. However, when such a release layer was used, there was a risk that the release component would be transferred to the transferred resin surface, changing the properties of the transferred resin layer surface, or that secondary processing such as providing a protective layer or adhesive layer on the resin layer surface would not be carried out properly.

The present invention relates to a polyester film used for transferring a resin layer or transferring the surface state of a polyester film, and aims to provide a new release film that has excellent releasability for various resin layers, has little transfer of release components to the surface of the transferred resin layer, and allows for good secondary processing of the surface of the transferred resin layer.

The present invention proposes a release film comprising a release layer formed from a release layer-forming composition on at least one side of a polyester film, the release layer-forming composition containing less than 15 mass% of a release agent as a proportion of all non-volatile components, and the release layer containing 3.4 mg/ ^m2 or more of the release agent.

The release film proposed by the present invention has a release agent content in the release layer of 3.4 mg/ ^m2 or more, which makes it possible to effectively peel off various resin layers. By making the release agent content less than 15 mass% of the total non-volatile components in the release layer-forming composition, it is possible to reduce the amount of the release component transferred to the resin layer surface, and secondary processing of the resin layer surface can be performed smoothly.

Next, the present invention will be described based on an embodiment example. However, the present invention is not limited to the embodiment described below.

＜＜Release film＞＞
A release film according to one embodiment of the present invention (referred to as "this release film") comprises a release layer (referred to as "this release layer") formed from a release layer-forming composition on at least one side of a polyester film (referred to as "this polyester film") as a substrate, in which the release agent accounts for less than 15 mass% of the total non-volatile components in the release layer-forming composition, and the content of the release agent in the release layer is 3.4 mg/m2 or ^more .
The laminated structure of the present release film may be a structure in which a release layer is formed on one side of the present polyester film and the surface of the polyester film substrate is left as is on the other side, or a structure in which another layer is formed on the other side. Also, a structure in which release layers are formed on both sides of the present polyester film may be used.
Furthermore, other layers may be provided between the polyester film and the release layer.
However, the release layer is preferably on at least one outermost surface of the polyester film.

<<This polyester film>>
The polyester film serves as the substrate for the release film.
The polyester film may be a non-stretched film (sheet) or a stretched film. Of these, a uniaxially or biaxially stretched film is preferred. Of these, a biaxially stretched film is preferred in terms of excellent balance of mechanical properties and flatness.

The polyester film may be a single layer or a multi-layer film of two or more layers, and is not particularly limited. When the purpose is to impart a low gloss feel to the surface of the transfer resin layer, the release film also preferably has a matte surface shape. One method for imparting a matte feel is to have a structure that includes a particle-containing layer that contains particles.

The polyester film may be configured to have only a layer that does not contain particles, to have only a particle-containing layer that contains particles, or to have a particle-containing layer on one or both sides of a base layer.
Specific examples of the configuration having a particle-containing layer on one or both sides may include a configuration having a particle-containing layer A on both sides of a base layer, a configuration having a particle-containing layer A on one side of the base layer and a particle-containing layer B different from the particle-containing layer A formed on the other side of the base layer, a configuration having a particle-containing layer A on one side of the base layer and no layer formed on the other side of the base layer, or a configuration having a particle-containing layer A on one side of the base layer and a layer not containing particles formed on the other side of the base layer.
The present polyester film is preferably configured to include a particle-containing layer A, and particularly preferably configured to include a particle-containing layer A on one side of a base layer and a particle-containing layer B different from the particle-containing layer A on the other side of the base layer, which will be described in detail later.

(Genuine polyester)
The layers constituting the present polyester film, for example, the above-mentioned base layer, particle-containing layer A, particle-containing layer B and other layers, are preferably layers containing polyester as a main component resin.
The polyester which is the main component resin of the present polyester film (also referred to as "the present polyester") may be either a homopolyester or a copolymer polyester.
When the surface of the present release film is roughened to have a matte finish, the present polyester is preferably a copolymer polyester containing a copolymer component, and among these, polyethylene terephthalate containing a copolymer component (referred to as "copolymerized polyethylene terephthalate") is more preferred.
Here, the term "main component resin" refers to the resin that is contained in the largest proportion among the resin components that constitute each layer.

The polyester may be any polyester obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the other aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative polyesters include polyethylene terephthalate (PET) and polyethylene-2,6-naphthalenedicarboxylate (PEN), with polyethylene terephthalate being preferred.

Examples of the dicarboxylic acid component of the copolymerized polyester and copolymerized polyethylene terephthalate include one or more selected from isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acids (e.g., p-oxybenzoic acid), and examples of the other glycol component include one or more selected from ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, and neopentyl glycol.
Among these, the copolymerization components of the copolymerized polyethylene terephthalate are preferably copolymerization components that give the copolymerized polyethylene terephthalate a melting point of 240°C or less, more preferably copolymerization components that give the copolymerized polyethylene terephthalate a melting point of 235°C or less, and even more preferably copolymerization components that give the copolymerized polyethylene terephthalate a melting point of 230°C or less.
By making the melting point of the copolymerized polyethylene terephthalate 240°C or less, when a layer containing the copolymerized polyethylene terephthalate is stretched and heat-treated, protrusions having a relatively large height are likely to appear on the layer surface, and a film having sufficiently low gloss can be obtained, which is preferable.
In order to make the melting point 240° C. or less, the dicarboxylic acid component of the copolymerized polyethylene terephthalate preferably contains one or more selected from isophthalic acid, phthalic acid, sebacic acid, etc., and the glycol component preferably contains one or more selected from diethylene glycol, propylene glycol, butanediol, etc. In particular, from the viewpoint of being able to efficiently lower the melting point and facilitating synthesis of copolymerized polyethylene terephthalate, it is preferable for the dicarboxylic acid component of the copolymerized polyethylene terephthalate to contain isophthalic acid.

(Base layer)
The base layer of the polyester film is the thickest layer among all the layers constituting the polyester film, and may have any composition as long as it contains the above-mentioned polyester as the main resin component.

The substrate layer may include a layer containing particles, or may consist of only a layer containing particles. However, from the viewpoint of cost, it is preferable that the layer does not contain particles such as organic particles or inorganic particles, which will be described later.

From the viewpoint of preventing curling of the polyester film, the thickness of the base layer is preferably 60 to 100% of the thickness of the polyester film, more preferably 65% or more or 99% or less, and even more preferably 70% or more or 99% or less. By being in this range, the base layer itself has stiffness, making the polyester film less likely to curl.

(Particle-containing layer)
The polyester film preferably has a particle-containing layer that contains particles in order to impart low gloss and easy lubricity. In particular, a preferred configuration has a particle-containing layer A on one side of a base layer and a particle-containing layer B different from the particle-containing layer A on the other side of the base layer.
The preferred structures of the particle-containing layer A and the particle-containing layer B described below also apply to the preferred structures of the particle-containing layer in the present polyester film.

(particle)
The particles are not particularly limited as long as they can impart a matte finish. For example, they may be inorganic particles, organic particles, or crosslinked polymer particles. Inorganic particles are preferred because they may form voids in the film when stretched, and therefore do not require the addition of a white pigment to improve visibility, while organic particles are preferred because they are less likely to form voids, and therefore do not reduce the strength of the film.

Examples of inorganic particles include silica, calcium carbonate, kaolin, talc, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, lithium fluoride, calcium fluoride, lithium fluoride, zeolite, and molybdenum sulfide. The silica particles may contain, in addition to silicon dioxide (SiO ₂ ), for example, hydrous silicon dioxide.

Examples of organic particles include acrylic resin, styrene resin, urea resin, phenol resin, epoxy resin, and benzoguanamine resin. Among them, particles made of resins in which methyl methacrylate or styrene or both are copolymerized components are particularly preferred because they are compatible with PET films. Other organic particles that may be used include polytetrafluoroethylene, benzoguanamine resin, thermosetting epoxy resin, unsaturated polyester resin, thermosetting urea resin, and thermosetting phenol resin.

Examples of crosslinked polymer particles include copolymers of crosslinkable monomers such as divinylbenzene and polyacrylate with styrene, acrylic acid, methacrylic acid, derivatives of acrylic acid or methacrylic acid, and various other vinyl monomers.

The shape of the particles is arbitrary. For example, they may be spherical, blocky, rod-like, flat, etc. However, from the viewpoint of obtaining a uniform matte surface, spherical shape is preferable. There are no particular restrictions on the hardness, specific gravity, color, etc. of the particles, and two or more different types may be used in combination.

(Particle-containing layer A)
The particle-containing layer A is preferably a layer containing particles X having an average particle size of 2.0 μm to 10.0 μm, and is preferably a layer on the surface of which a release layer, which will be described later, is provided.

By containing particles X having an average particle size of 2.0 μm or more in the particle-containing layer A, the surface of the particle-containing layer A can be roughened and made matte. However, if the particles X are too large, the pressure rise in the filter in the polyester extrusion step during film production may increase, resulting in reduced productivity.
Therefore, the average particle size of the particles X is preferably 2.0 μm or more, and more preferably 10.0 μm or less, and even more preferably 3.0 μm or more or 9.0 μm or less, and even more preferably 4.0 μm or more or 8.0 μm or less.

When the particles are in the form of a powder, the average particle size of the particles can be determined by measuring the powder using a centrifugal sedimentation particle size distribution measuring device (e.g., Model SA-CP3 manufactured by Shimadzu Corporation) and determining the particle size at an integrated volume fraction of 50% (d50) in the equivalent sphericity distribution.
The average particle size of particles in a film, layer, or resin can be determined by observing 10 or more particles with a scanning electron microscope (SEM) to measure the diameters of the particles and calculating the average value. In this case, in the case of non-spherical particles, the average value of the longest diameter and the shortest diameter can be measured as the diameter of each particle. The same applies to particles described later.

Particles X are not particularly limited as long as they are particles that can impart a matte finish. For example, they may be the aforementioned inorganic particles, organic particles, or crosslinked polymer particles.

The particles X contained in the particle-containing layer A are preferably particles with a small true specific gravity. If the true specific gravity is small, the number of particles can be relatively increased. That is, the number of particles can be increased with the same size and the same content (mass%), and the number of protrusions on the surface of the particle-containing layer A, in other words, the density, can be increased, and the low gloss feeling can be further improved.
From this viewpoint, the true specific gravity of the particles X contained in the particle-containing layer A is preferably 2.0 or less, more preferably 1.5 or less, and even more preferably 1.3 or less. The lower limit is about 0.5.

From the viewpoint of roughening the surface of the particle-containing layer A to give it a matte finish, it is preferable that the true specific gravity of the particles X contained in the particle-containing layer A is 2.0 or less and the average particle size is in the range of 2.0 to 10.0 μm.

The content of particles X in particle-containing layer A is preferably 0.1 to 20% by mass in particle-containing layer A (100% by mass) from the viewpoint of being able to suitably roughen the surface of particle-containing layer A and preventing breakage or the like from occurring during film stretching, and is more preferably 1% by mass or more or 18% by mass or less, more preferably 2% by mass or more or 15% by mass or less, more preferably 3% by mass or more or 13% by mass or less, and even more preferably 5% by mass or more or 10% by mass or less.

The polyester A that constitutes the main component resin of the particle-containing layer A may be a homopolyester or a copolymer polyester that contains a copolymer component.

It is preferable that the copolymerization component is contained in an amount of 0.1 to 10 mol% based on the total amount of polyester constituting the particle-containing layer A. If the copolymerization component is contained in an amount of 0.1 mol% or more, the particle-containing layer A can be softened, and the height of the protrusions on the surface of the particle-containing layer A can be increased. On the other hand, if the copolymerization component is contained in an amount of 10 mol% or less, the film can be efficiently produced without breakage, which is preferable. In addition, when the present laminated polyester film is a stretched film, it is preferable that the proportion of the copolymerization component is within the above range, since stretch orientation and heat fixation are possible.
From this viewpoint, the copolymerization component is preferably contained in an amount of 0.1 to 10 mol % relative to the total amount of polyester constituting the particle-containing layer A, more preferably 1 mol % or more or 8 mol % or less, and even more preferably 3 mol % or more or 6 mol % or less.

When polyester is produced (polycondensed) using ethylene glycol as one of the raw materials, a portion of the ethylene glycol is modified to become diethylene glycol, which is then introduced into the polyester skeleton. This diethylene glycol is called by-product diethylene glycol, and the amount of by-product varies depending on the type of polycondensation (ester exchange method, direct polycondensation), but is approximately 1 to 5 mol% of the ethylene glycol. In the present invention, diethylene glycol produced as a by-product from ethylene glycol is not considered to be a copolymerization component.

A preferred embodiment of the particle-containing layer A, which allows the release film to have an even better low gloss surface while maintaining the productivity of the release film, is one in which the true specific gravity of the particles X in the particle-containing layer A is 2.0 or less, the average particle size of the particles X is 2.0 to 10.0 μm, and the copolymer component is contained in an amount of 0.1 to 10 mol % relative to the total amount of polyester constituting the particle-containing layer A.

The thickness of the particle-containing layer A is preferably 1.0 to 20 μm, more preferably 2.0 μm or more or 20 μm or less, even more preferably 3.0 μm or more or 20 μm or less, and even more preferably 4.0 μm or more or 15 μm or less.
By making the thickness of the particle-containing layer A 1.0 μm or more, a matte finish can be effectively imparted. Even if the thickness of the particle-containing layer A exceeds 20 μm, the effect of improving the matte finish remains almost the same.

(Particle-containing layer B)
As described above, a particle-containing layer A can be provided on one side of the base layer, and a particle-containing layer B different from the particle-containing layer A can be formed on the other side of the base layer as a layer that does not have a release layer, which will be described later.

In this case, it is preferable that the particle-containing layer B also contains particles X having an average particle size of 2.0 to 10.0 μm, in order to prevent curling of the entire polyester film.
However, since the surface of the particle-containing layer B only needs to be roughened to an extent that makes it easy to handle, it does not need to be as rough as the surface of the particle-containing layer A. Therefore, the content of particles X having an average particle size of 2.0 to 10.0 μm may be less than that of the particle-containing layer A.
Specifically, the content of the particles X contained in the particle-containing layer B is preferably 0.1 to 100% by mass of the content of the particles X contained in the particle-containing layer A, and more preferably 1% by mass or more or 95% by mass or less, and even more preferably 5% by mass or more or 90% by mass or less.

The particle-containing layer B may contain particles Y having an average particle size of less than 2.0 μm in order to whiten the polyester film.
In this case, the particle-containing layer B may contain particles Y without containing particles X, or may contain particles Y together with particles X.
When particles Y are contained together with particles X, the mass ratio of particles X to particles Y is preferably 1:99 to 99:1, more preferably 10:90 to 90:10, and even more preferably 15:85 to 85:15.

The shape of the particles Y is arbitrary. For example, it may be any of spherical, blocky, rod-like, flat, etc. However, from the viewpoint of preventing the formation of coarse protrusions due to aggregation, the particles Y are preferably spherical.
There are no particular limitations on the hardness, specific gravity, color, etc. of the particles Y, and two or more different types may be used in combination.

From the viewpoint of imparting white opacity through a light scattering effect, the average particle size of the Y particles is preferably 0.05 μm to 0.50 μm, more preferably 0.10 μm or more or 0.45 μm or less, even more preferably 0.20 μm or more or 0.40 μm or less, and even more preferably 0.25 μm or more.

The particles Y are preferably metal compound particles from the viewpoint of imparting white opacity through a light scattering effect.
Examples of metal compound particles include titanium oxide, calcium carbonate, barium sulfate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, aluminum oxide, and zirconium oxide, and among these, metal compound particles such as titanium oxide, calcium carbonate, and barium sulfate can be mentioned.

The polyester constituting the main component resin of the particle-containing layer B may be the same as or different from the polyester constituting the main component resin of the particle-containing layer A. That is, it may be a copolymerized polyester containing a copolymer component, or a homopolyester containing no copolymer component.
In particular, when the polyester constituting the particle-containing layer B contains the same copolymerization component as the polyester constituting the particle-containing layer A, it is preferable that the content of the copolymerization component of the polyester constituting the particle-containing layer B is lower than the content of the copolymerization component of the polyester constituting the particle-containing layer A. In other words, it is preferable that the content of the copolymerization component of the polyester constituting the particle-containing layer A is higher than the content of the copolymerization component of the polyester constituting the particle-containing layer B. This is because, in the case of a configuration in which a release layer is provided on the surface of the particle-containing layer A, the surface on the particle-containing layer B side does not need to be as rough as the surface on the particle-containing layer A side.
In this case, the difference between the content ratio of the copolymerization component relative to the total amount of polyester constituting the particle-containing layer A and the content ratio of the copolymerization component relative to the total amount of polyester constituting the particle-containing layer B is preferably 5 mol % or less, more preferably 4 mol % or less, and even more preferably 3 mol % or less.
When the content ratio of the copolymerization component satisfies the above range, not only curling can be suppressed, but also adhesion between the particle-containing layer B and other layers, such as a hard coat layer, can be improved when the other layers are further laminated thereon.

From the viewpoint of preventing curling of the polyester film, the thickness of the particle-containing layer B is preferably the same as that of the particle-containing layer A. From this viewpoint, the thickness of the particle-containing layer B is also preferably 1.0 to 20 μm, and more preferably 2.0 μm or more or 20 μm or less, more preferably 3.0 μm or more or 20 μm or less, and even more preferably 4.0 μm or more or 15 μm or less.

(Other ingredients)
Each layer constituting the polyester film base may contain, as necessary, a conventionally known weathering agent, light resistance agent, light shielding agent, antioxidant, heat stabilizer, lubricant, antistatic agent, fluorescent brightener, dye, pigment, etc. Depending on the application, an ultraviolet absorbing agent, particularly a benzoxazinone ultraviolet absorbing agent, may be contained.

<Thickness of this polyester film>
The thickness of the polyester film is not particularly limited as long as it is within a range that allows film formation. In particular, from the viewpoints of mechanical strength, handling properties, productivity, etc., it is preferably 1 μm to 300 μm, more preferably 5 μm or more or 125 μm or less, more preferably 8 μm or more or 100 μm or less, and even more preferably 12 μm or more or 75 μm or less.

<Release layer>
The present release film has a release layer formed from a release layer-forming composition on at least one side of the present polyester film, in which the release agent accounts for less than 15 mass% of the total non-volatile components in the release layer-forming composition, and the content of the release agent in the release layer is 3.4 mg/ ^m2 or more.

(Formation of the Release Layer)
The release layer is preferably provided on at least one surface of the polyester film, particularly on the surface of the particle-containing layer A, i.e., the roughened surface, and is therefore preferably formed by employing a coating and stretching method (in-line coating), although the method is not limited to this.

As a coating and stretching method (in-line coating), for example, in sequential biaxial stretching, it is preferable to coat the "release layer forming composition" after the first stage of stretching is completed and before the second stage of stretching. In this way, coating is possible simultaneously with stretching, and the thickness of the release layer can be made thinner according to the stretching ratio, making it possible to produce a film suitable as a polyester film.

Methods for applying the coating solution consisting of the release layer-forming composition include, for example, air doctor coating, blade coating, rod coating, bar coating, knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss roll coating, cast coating, spray coating, curtain coating, calendar coating, and extrusion coating, and other conventionally known coating methods can be used.

More specifically, for example, in the case of sequential biaxial stretching, a method in which a coating liquid consisting of a release layer-forming composition is coated on a uniaxially stretched film that has been particularly stretched in the longitudinal direction (machine direction), and then the film is stretched in the transverse direction to form a polyester film is particularly advantageous. This method has the advantage of being able to simultaneously form the polyester film and the release layer, and is advantageous in terms of production costs. In addition, because stretching is performed after coating, the thickness of the release layer can be changed by changing the stretch ratio, and thin film coating can be performed more easily than offline coating.

In addition, by providing a release layer on the polyester film before stretching, the release layer can be stretched together with the polyester film, and the release layer can be firmly attached to the polyester film. Furthermore, in the production of biaxially stretched polyester films, the film can be restrained in the longitudinal and lateral directions by stretching while holding the film ends with clips or the like, and high temperatures can be applied in the heat setting step while maintaining the flatness without wrinkles or the like.
Therefore, the heat treatment performed after coating can be performed at a high temperature that cannot be achieved by other methods, which improves the film-forming properties of the release layer and enables the release layer and polyester film to adhere more firmly to each other, thereby resulting in a stronger release layer.

Regardless of whether the release layer is formed by offline coating or in-line coating, a heat treatment and irradiation with active energy rays such as ultraviolet light may be used in combination as necessary. In order to improve the coatability and adhesion of the coating solution that forms the release layer to the polyester film, the polyester film may be subjected to a surface treatment such as a chemical treatment, corona discharge treatment, plasma treatment, ozone treatment, chemical treatment, or solvent treatment before coating.

The release layer-forming composition, i.e., the coating liquid, can be a resin composition containing a release agent, a crosslinking agent, and various polymers.

The "release agent" to be incorporated in the release layer-forming composition is not particularly limited, and any conventionally known release agent can be used. Examples of the release agent include wax, a compound containing a long-chain alkyl group, a fluorine compound, and a silicone compound.
Among these, wax and compounds containing long-chain alkyl groups are preferred from the viewpoint of low possibility of contamination when applied to optical applications, and wax is preferred from the viewpoint of low reduction in surface free energy and excellent wettability with respect to the processed layer.

The wax may include natural wax, synthetic wax, and modified wax.
Natural waxes include vegetable waxes, animal waxes, mineral waxes and petroleum waxes.
Examples of vegetable waxes include candelilla wax, carnauba wax, rice wax, wood wax, and jojoba oil.
Examples of animal waxes include beeswax, lanolin, and spermaceti, etc. Examples of mineral waxes include montan wax, ozokerite, and ceresin, etc.
Petroleum waxes include paraffin wax, microcrystalline wax, and petrolatum.
Synthetic waxes include synthetic hydrocarbons, modified waxes, hydrogenated waxes, fatty acids, acid amides, amines, imides, ester waxes and ketones.

Examples of synthetic waxes include Fischer-Tropsch wax (also known as Sasol wax) and polyethylene wax. Other examples include the following low molecular weight polymers (specifically, polymers with a number average molecular weight of 500 to 20,000): polypropylene, ethylene-acrylic acid copolymer, polyethylene glycol, polypropylene glycol, and block or graft bond of polyethylene glycol and polypropylene glycol.

Examples of modified waxes include montan wax derivatives, paraffin wax derivatives, and microcrystalline wax derivatives. The derivatives referred to here are compounds obtained by any of the following processes, or a combination of these: refining, oxidation, esterification, and saponification. Hydrogenated waxes include hydrogenated castor oil and hydrogenated castor oil derivatives.

Among these, from the viewpoint of excellent release performance, the release agent in the release layer is preferably a synthetic wax, more preferably a polyethylene wax, and even more preferably an oxidized polyethylene wax.
The number average molecular weight of the synthetic wax is usually 500 to 30,000, preferably 1,000 to 15,000, and more preferably 2,000 to 8,000, from the viewpoints of suppressing transfer of the release component and of ease of handling.

In addition, when the release layer is formed, taking into consideration the fact that heating is performed for crosslinking or the like, among the above waxes, those having a melting point or softening point of 80° C. or higher, particularly 110° C. or higher are preferred. From the viewpoint of controlling the release performance after heat treatment, the wax is preferably 200° C. or lower, particularly 170° C. or lower, particularly 150° C. or lower.
The melting point of the wax can be measured by differential scanning calorimetry (DSC).

The release agent is preferably less than 15% by mass as a proportion of all non-volatile components in the release layer forming composition. By making the release agent less than 15% by mass as a proportion of all non-volatile components in the release layer forming composition, transfer of the release components can be suppressed. The proportion of the release agent is preferably less than 15% by mass, and more preferably 1% by mass or more or 13% by mass or less, more preferably 3% by mass or more or 11% by mass or less, and even more preferably 5% by mass or more or 9% by mass or less. There is no particular lower limit for the content, but it is usually about 0.05% by mass.

The proportion of the release agent in the release layer can be calculated, for example, by the following thermogravimetric analysis (using data on thermal weight loss).
When calculated by the following method, the ratio of the release agent in the release layer is preferably less than 15% by mass, more preferably 1% by mass or more or 14% by mass or less, even more preferably 3% by mass or more or 12% by mass or less, even more preferably 5% by mass or more or 10% by mass or less. The lower limit of the content is not particularly limited, but is usually about 0.05% by mass.
Thermogravimetric analysis method:
The weight loss rate of each material constituting the release layer is measured by thermogravimetric analysis at a heat treatment temperature in the production of the film, for example, 230 to 250° C. The content of each component in the release layer-forming composition is multiplied by the weight loss rate obtained to determine the content of each component in the release layer, and the content ratio of the release agent is determined from the content of each component obtained.

The proportion of the release agent in the above-mentioned release layer can be regarded as synonymous with the proportion of the release agent in all non-volatile components in the above-mentioned release layer-forming composition, and therefore this release film can also be regarded as a release film which has a release layer on at least one side of a polyester film, in which the proportion of the release agent in the release layer is less than 15 mass%, and the content of the release agent in the release layer is 3.4 mg/ ^m2 or more.
Furthermore, a release film having a release layer on at least one side of a polyester film, in which the release agent accounts for less than 15 mass% of the release layer and the content of the release agent in the release layer is 3.4 mg/ ^m2 or more, is included in one of the embodiments of the present invention.

The content of the release agent in the release layer is preferably 3.4 mg/m ² or more. By having the content of the release agent in the release layer be 3.4 mg/m ² or more, it is possible to maintain good release performance, including the balance of characteristics before and after heat treatment. Therefore, the content of the release agent in the release layer is preferably 3.4 mg/m ² or more, more preferably 4.0 mg/m ² or more, even more preferably 4.5 mg/m ² or more, and even more preferably 5.0 mg/m ² or more.
There is no particular upper limit, but it is usually 1000 mg/m2 ^or less.
The content of the release agent in the release layer can be calculated, for example, by using the above-mentioned thermogravimetric analysis method.
In addition, the content of the release agent in the release layer can be adjusted, for example, by adjusting the content ratio of the release agent in the release layer-forming composition or the coating amount of the release layer-forming composition.

The proportion of the release agent in the release layer and the content of the release agent in the release layer can be determined, for example, by subjecting the surface of the release film to X-ray photoelectron spectroscopy (ESCA), Fourier transform infrared spectroscopy (FT-IR) ATR method, and time-of-flight secondary ion mass spectrometry (TOF-SIMS), or by dissolving and extracting the release layer in a solvent, separating it by chromatography, and then analyzing the structure using proton nuclear magnetic resonance spectroscopy (1H-NMR), carbon nuclear magnetic resonance spectroscopy (13C-NMR), and Fourier transform infrared spectroscopy (FT-IR), and then performing pyrolysis gas chromatography mass spectrometry (GC-MS).

From the viewpoint of increasing the strength of the release layer to make the layer less susceptible to transfer of the release component, it is preferable to contain a crosslinking agent in the release layer-forming composition. When the release layer is formed by crosslinking the crosslinking agent, the formed release layer will have compounds derived from the crosslinking agent as described above.

As the crosslinking agent, a conventionally known material can be used. Examples include melamine compounds, oxazoline compounds, isocyanate compounds, epoxy compounds, carbodiimide compounds, silane coupling compounds, hydrazide compounds, and aziridine compounds. Among these, melamine compounds, oxazoline compounds, isocyanate compounds, epoxy compounds, and carbodiimide compounds are preferred. From the viewpoint of further strengthening the strength of the release layer and improving adhesion to the substrate film, melamine compounds are particularly preferred.

The melamine compound is a compound having a melamine skeleton in the compound. For example, alkylolated melamine derivatives, compounds partially or completely etherified by reacting an alkylolated melamine derivative with an alcohol, and mixtures thereof can be used. Examples of alkylolation include methylolation, ethylolation, isopropylolation, n-butyrolation, and isobutyrolation, and from the viewpoint of reactivity, methylolation is preferred. As alcohols used for etherification, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, isobutanol, etc. are preferably used. From the viewpoint of improving the coating strength and facilitating the formation of a fine protrusion structure, a partially etherified alkylolated melamine derivative is preferred, and an alkylol etherified with methyl alcohol is more preferred. The melamine compound may be either a monomer or a polymer of dimer or more, or a mixture of these may be used. Furthermore, a compound in which urea or the like is co-condensed with a part of melamine can also be used.

Specific examples of polymers include polyester resins, acrylic resins, urethane resins, polyvinyls (polyvinyl alcohol, vinyl chloride-vinyl acetate copolymers, etc.), polyalkylene glycols, polyalkyleneimines, methyl cellulose, hydroxycellulose, and starches. Among these, polyester resins and urethane resins are preferred because they allow easy control of release properties, and polyester resins are more preferred because they enhance adhesion to the polyester film, suppress transfer of the release component, and allow control of the balance of release properties before and after heat treatment.

Polyester resins are mainly composed of polyvalent carboxylic acids and polyvalent hydroxy compounds, such as those listed below. That is, examples of polyvalent carboxylic acids that can be used include terephthalic acid, isophthalic acid, orthophthalic acid, phthalic acid, 4,4'-diphenyldicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2-potassium sulfoterephthalic acid, 5-sodium sulfoisophthalic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, glutaric acid, succinic acid, trimellitic acid, trimesic acid, pyromellitic acid, trimellitic anhydride, phthalic anhydride, p-hydroxybenzoic acid, trimellitic acid monopotassium salt, and ester-forming derivatives thereof. Examples of polyvalent hydroxy compounds that can be used include: Ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 2-methyl-1,5-pentanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, p-xylylene glycol, bisphenol A-ethylene glycol adduct, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polytetramethylene oxide glycol, dimethylolpropionic acid, glycerin, trimethylolpropane, sodium dimethylolethylsulfonate, and potassium dimethylolpropionate can be used. One or more of these compounds can be appropriately selected and a polyester resin can be synthesized by a conventional polycondensation reaction.

When a crosslinking agent is blended in the release layer-forming composition, the content of the crosslinking agent in the release layer-forming composition is preferably 5 to 98% by mass, and more preferably 15% by mass or more or 90% by mass or less, more preferably 30% by mass or more or 70% by mass or less, and even more preferably 38% by mass or more or 50% by mass or less. If the content of the crosslinking agent is 5% by mass or more, the strength of the coating film can be increased, and if the content of the crosslinking agent is 98% by mass or less, there is a possibility that sufficient releasability of the release layer and adhesion to the polyester film can be ensured.

When a polymer is blended into the release layer-forming composition, the content of the polymer in the release layer-forming composition is preferably 1 to 80% by mass, more preferably 5% by mass or more or 70% by mass or less, and even more preferably 20% by mass or more or 60% by mass or less.

The coating liquid of the release layer-forming composition may be an aqueous coating liquid using water as a solvent, and in this case, may contain a small amount of an organic solvent.
In this case, examples of the organic solvent include alcohols such as ethanol, isopropanol, ethylene glycol, and glycerin, ethers such as ethyl cellosolve, t-butyl cellosolve, propylene glycol monomethyl ether, and tetrahydrofuran, ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate, and amines such as methylethanolamine. These can be used alone or in combination. By appropriately selecting and adding these organic solvents to the aqueous coating liquid as necessary, the stability and coatability of the coating liquid can be improved.

The release layer-forming composition may contain particles to prevent blocking or improve slippage, if necessary. In addition, it may contain defoamers, coatability improvers, thickeners, organic lubricants, UV absorbers, antioxidants, foaming agents, etc.

<Physical properties of this release film>

(Film surface roughness)
When used for the purpose of imparting a low gloss feel, the roughness of the release layer surface of the present release film, i.e., if a release layer is formed on one side of the polyester film, the surface, in other words, the surface on one side of the present polyester film, or if release layers are formed on both sides of the polyester film, both surfaces, in other words, the average surface roughness (Ra) of both sides of the present polyester film, is preferably 0.1 μm to 2.0 μm.
When the average surface roughness (Ra) of the surface of the present polyester film is within the above range, a matte feel can be expressed, and by pressing this surface against an object and releasing it, the matte feel can be imparted to the surface of the object.
From this viewpoint, the average surface roughness (Ra) of at least the release layer side surface of the polyester film is preferably 0.1 to 2.0 μm, more preferably 0.2 to 1.0 μm, and even more preferably 0.3 to 0.9 μm.
The average surface roughness (Ra) of the film surface can be measured by the measuring method described in the Examples below.
In addition, methods for adjusting the average surface roughness (Ra) of the release layer side surface to the above range include using a polyester film having a particle-containing layer, and in particular using a copolymer polyester or particles having a particle size or true specific gravity in the above-mentioned range as the material for the particle-containing layer, and adjusting the thickness of the particle-containing layer, the stretching conditions of the polyester film, and the heat treatment conditions.

In order to further improve the low gloss feel, it is preferable that the release layer surface has many relatively high protrusions, in other words, a surface formed with high density. However, when looking at the average surface roughness (Ra) value of the release layer surface, it is important to note that the characteristics of the release layer surface, i.e., the characteristics of a surface formed with many relatively high protrusions, are not very apparent in the Ra value.

If one surface of the polyester film is matte-finished, the other surface needs only to be roughened to an extent that does not interfere with handling, and from the viewpoint of improving adhesion when laminating with other layers, it is preferable that the average surface roughness (Ra) of the other surface is smaller than that of the release layer side surface. From this viewpoint, the average surface roughness (Ra) of the other surface is preferably 0.01 μm to 1.0 μm, and more preferably 0.03 μm or more or 0.8 μm or less, more preferably 0.05 μm or more or 0.5 μm or less, and even more preferably 0.1 μm or more or 0.3 μm or less.

(Glossiness)
In the present polyester film, it is preferable that the gloss of at least the surface on the release layer side is 30% or less.
If the gloss of the film surface is 30% or less, a high-quality matte finish can be obtained, with the lower limit being approximately 0.1%.
From this viewpoint, in the present polyester film, the gloss of at least the surface on the release layer side is preferably 30% or less, more preferably 0.1% or more or 30% or less, even more preferably 25% or less, and even more preferably 20% or less.

(Surface Free Energy of Release Layer Surface)
In the present polyester film, the surface free energy of the release layer side surface is preferably 27 mN/m or more.
If the surface free energy of the release layer surface is 27 mN/m or more, the wettability is not inferior, and it is possible to process a resin layer to be transferred onto the surface of the release layer, and even if the release component is transferred, it is possible to reduce adverse effects on the surface of the counterpart material. Also, if the surface free energy is 60 mN/m or less, it is possible to obtain releasability with respect to the resin layer to be transferred.
From this viewpoint, in the present polyester film, the surface free energy of the release layer surface is preferably 27 mN/m or more or 60 mN/m or less, more preferably 30 mN/m or more or 50 mN/m or less, and even more preferably 33 mN/m or more or 45 mN/m or less.
Methods for adjusting the surface free energy include selection of a release agent, selection of a crosslinking agent or polymer used in combination, and adjustment of the content or content ratio of the release agent in the release layer.

(Transfer rate of release component)
The present release film preferably has a transfer rate of the release component measured by the method described below of 40% or less, more preferably 35% or less, even more preferably 33% or less, and even more preferably 30% or less.
If the transfer rate of the release component is 40% or less, the effect on the surface of the object is small, and it is possible to suppress adverse effects on secondary processing.

(Initial peel strength of hard coat layer)
The release film preferably has an initial peel strength against the hard coat layer measured by the method described later, which is greater than the peel strength of the hard coat layer after the press treatment described later, and in particular, the initial peel strength of the hard coat layer is preferably 1.1 times or more, more preferably 1.3 times or more, and particularly preferably 1.5 times or more, than the peel strength of the hard coat layer after the press treatment. If the initial peel strength of the hard coat layer is greater than the peel strength of the hard coat layer after the press treatment, it is possible to prevent the release film from peeling off before use in the transfer treatment.

(Peeling Force of Hard Coat Layer After Pressing)
The release film preferably has a peel strength against the hard coat layer after pressing for 30 minutes under conditions of 170°C x 3 MPa, as measured by the method described below, of 100 mN/cm, more preferably 80 mN/cm or less, even more preferably 60 mN/cm or less, and even more preferably 50 mN/cm or less. If it is 100 mN/cm or less, the stress required for peeling the hard coat layer is small, making it possible to prevent defects due to poor peeling.

<Method of manufacturing the present polyester film>
An example of the method for producing the present polyester film will be described below, although the method for producing the present polyester film is not limited to the method described below.

First, the raw materials for each layer, i.e., the base layer, the particle-containing layer A, the particle-containing layer B, and other layers, are prepared by a known method, and each is fed to a melt extrusion device, heated to a temperature equal to or higher than the melting point of each polymer, and melt-kneaded. Then, the molten polymer of each layer is usually introduced to a die via a multi-manifold or a feed block and laminated.
Next, the molten sheet extruded from the die is quenched and solidified on a rotating cooling drum to a temperature below the glass transition temperature to obtain a substantially amorphous unoriented sheet. In this case, in order to improve the flatness of the sheet, it is preferable to increase the adhesion between the sheet and the rotating cooling drum, and an electrostatic application adhesion method and/or a liquid application adhesion method are preferably adopted.

Next, the unstretched sheet is stretched in one direction using a roll or tenter type stretching machine. The stretching temperature is usually 70 to 150°C, preferably 80 to 140°C, and the stretching ratio is usually 2.5 to 7 times, preferably 3.0 to 6 times. Next, the sheet is stretched in a direction perpendicular to the first stretching direction, usually at 70 to 170°C, and the stretching ratio is usually 2.5 to 7 times, preferably 3.0 to 6 times. This is followed by heat treatment at a temperature of 180 to 270°C under tension or relaxation of 30% or less to obtain a biaxially oriented film. In the above stretching, a method of stretching in one direction in two or more stages can also be adopted. In that case, it is preferable to perform the stretching so that the final stretching ratios in both directions are each within the above range.

The above heat treatment, and the heat treatment after stretching in the transverse direction, is performed at a temperature higher than the melting point of the polyester containing the copolymer component. For example, if the polyester contains an isophthalic acid component, the heat treatment temperature is preferably 220°C or higher, and more preferably 230 to 250°C. If polyester A, which is the main component resin of particle-containing layer A, is a copolymer polyester, it becomes softened by such heat treatment, and the particles rise to the surface, making it possible to increase the height of the protrusions.

After the heat treatment step, it is preferable to relax the film by 2 to 20% in the longitudinal and/or transverse directions in the highest temperature zone of the heat treatment and/or in the cooling zone at the heat treatment exit. It is also possible to add re-longitudinal and/or re-transverse stretching as necessary.

In the above manufacturing method, it is preferable to coat the release layer with the "release layer forming composition" between the longitudinal stretching and the transverse stretching, as described above. In this way, coating can be performed simultaneously with stretching, and the thickness of the release layer can be reduced according to the stretching ratio, making it possible to produce a film suitable as a polyester film.

<How to use this release film>
This release film can be used for simultaneous molding transfer, in which a resin layer such as a hard coat layer is provided on the release layer surface to form a transfer foil, which is then set in a mold for injection molding, and the transfer foil is integrated and bonded at the same time as the resin molded product is formed, thereby transferring the foil to the resin molded product.
Furthermore, the release layer can be pressed against the surface of an object such as a hard coat layer and then the release film can be peeled off, thereby transferring the surface shape of the release layer to the surface of the object.
In addition, by designing the release layer side of the polyester film to have a low gloss, the roughened surface shape of the release layer surface can be transferred, and the low gloss of the release layer surface can be imparted to the product surface. In this case, the product surface can be, for example, an electromagnetic wave shielding film or a transfer foil for simultaneous molding transfer, particularly the hard coat layer surface thereof. However, it is not limited to these.
Therefore, the present release film can be suitably used for applications such as transferring a transfer foil consisting of a resin layer such as a hard coat layer onto a resin molded product, i.e., as a transfer release film for simultaneous molding transfer and simultaneous molding decoration.
In addition, the release film can also be suitably used for the purpose of imparting a low gloss feeling to the surface of various members, such as electromagnetic wave shielding members, by transferring the shape of the release layer side surface of the release film to the surface of the member, i.e., as a release film for transferring surface shapes.

<Explanation of terms>
In this specification, when expressed as "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, it includes the meaning of "X or more and Y or less", as well as "preferably larger than X" or "preferably smaller than Y".
In addition, when it is expressed as "X or more" (X is any number) or "Y or less" (Y is any number), it also includes the intention that "it is preferably greater than X" or "it is preferably less than Y".

The present invention will now be described in further detail with reference to the following examples and comparative examples.
First, methods for measuring and evaluating various physical properties in the following Examples and Comparative Examples will be described.
In the examples and comparative examples, "parts" refers to "parts by mass." The measurement methods used in the present invention are as follows.

(1) Intrinsic Viscosity of Polyester 1 g of polyester from which components incompatible with the polyester had been removed was precisely weighed, dissolved in 100 ml of a mixed solvent of phenol/tetrachloroethane = 50/50 (mass ratio), and measured at 30°C.

(2) Average particle size of particles The average particle size of particles was determined by measuring the diameters of 10 or more particles by scanning electron microscope (SEM) and averaging the diameters. In the case of non-spherical particles, the average of the longest and shortest diameters was measured as the diameter of each particle.

(3) Average surface roughness (Ra)
The surface roughness was measured using a surface roughness measuring instrument (SE-3500) manufactured by Kosaka Laboratory Co., Ltd., as follows. That is, a portion of reference length L (2.5 mm) was cut out from the film cross-sectional curve in the direction of the average line, and the average line of this cut out portion was expressed as the x-axis and the direction of longitudinal magnification as the y-axis, as a roughness curve y=f(x). The value given by the following formula is expressed in nm. Ten roughness curves were obtained from the surface of the sample film, and the arithmetic mean roughness was expressed as the average value of the arithmetic mean roughness of the cut out portions obtained from these roughness curves. The tip radius of the stylus was 2 μm, the load was 30 mg, and the cutoff value was 0.08 mm.
Ra=(1/L)∫ ^L ₀ |f(x)|dx

(4) Glossiness of Film Surface The 60 degree glossiness was measured according to the method of JIS Z-8741 using a glossmeter (VG-107 type) manufactured by Nippon Denshoku Co., Ltd. The reflectance of the sample was determined based on the reflectance of a black standard plate at an incident angle and a reflection angle of 60 degrees, and this was taken as the glossiness.

(5) Content of release agent in release layer The content of the release agent in the release layer was calculated by the following method. Each material constituting the release layer was heated in an air atmosphere at a temperature increase rate of 50°C/min using a differential thermal/thermogravimetric analyzer (Shimadzu Corporation DTG-60A), and the weight loss rate after holding at 240°C for 3 minutes was measured. The content of each component in the release layer-forming composition was multiplied by the obtained weight loss rate to obtain the content of each component in the release layer. The content of the release agent in the obtained content of each component was obtained.

(6) Release agent content in the release layer The content of each component in the release layer was determined by the same method as in (5). The weight loss rate of the entire release layer-forming composition was calculated from the sum of these, and the amount of the release layer was calculated by multiplying it by the amount of the release layer applied. The release agent content in the release layer was calculated from the amount of the release layer obtained and the content ratio of the release agent in the release layer.

(7) Surface Free Energy of Release Layer Surface The contact angle of the release layer surface of a film sample that had been conditioned for 24 hours or more under an environment of 23°C and 50% RH was measured using an automatic contact angle meter (Data Physics, model OCA20) to measure the static contact angle of water and methylene iodide. Using the obtained contact angle and the surface tension component values of each solvent (Table 1), the surface free energy of the release layer surface was calculated according to the Owens-Wendt theoretical formula.

(8) Transfer rate of release component The release layer side surface of the film sample and the untreated surface of a test polyester film (T100, thickness 50 μm, manufactured by Mitsubishi Chemical Corporation) were stacked together so that they were in contact with each other, and the films were heat pressed for 30 minutes under conditions of 170° C.×1 MPa, and then humidified in an environment of 23° C.×50% RH. The film sample was then removed, and the tape peeling force (F1) was measured for the surface of the test polyester film that had been in contact with the release layer.
The polyester films obtained in Comparative Examples 1 and 2 were subjected to the same test, and the tape peel strengths (F01) and (F02) of the test polyester film surfaces were measured.
For the polyester film obtained in Comparative Example 2, the two films were superimposed so that the surface of the particle-containing layer A was in contact with the untreated surface of the test polyester film, and then hot-pressed.
In Examples 1 and 2, the transfer rate was calculated from the formula: transfer rate (%)=(F01-F1)/F01×100.
For Examples 3 to 22 and Comparative Examples 3 to 6, the transfer rate was calculated from the formula: transfer rate (%)=(F02-F1)/F02×100.
In Comparative Examples 1 and 2, the transfer rate was set to zero.
The tape peeling force was measured by attaching an acrylic adhesive tape (manufactured by Nitto Denko Corporation, "No. 31B") to this release layer, leaving it at room temperature for 1 hour, and then peeling it in a 180° direction at a tensile speed of 0.3 m/min.

(9) Peel strength of hard coat layer (initial)
A hard coat composition obtained by mixing 15-functional urethane acrylate (U-15HA manufactured by Shin-Nakamura Chemical Co., Ltd.), pentaerythritol triacrylate mixture (PET-3 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and photopolymerization initiator (Omnirad184 manufactured by IGM Resins B.V.) in a ratio of 70:30:5 was dissolved in methyl ethyl ketone (MEK), applied to the release layer so that the dry thickness was 5 μm, and then dried, followed by curing at 300 mJ/cm ² under a high-pressure mercury lamp to form a hard coat layer on the release film. Thereafter, a 24 mm wide cellophane tape (registered trademark) (LP-24 manufactured by Nichiban Co., Ltd.) was attached to the hard coat surface, and the stress was measured when the release film was peeled off in the 180° direction at a tensile speed of 1000 mm/min.

(10) Peel strength of hard coat layer (after press treatment)
The release film with the hard coat layer prepared in (9) was subjected to a press treatment for 30 minutes under conditions of 170° C. and 3 MPa. Thereafter, the stress when this release film was peeled off was measured in the same manner as in the initial peeling force.
If the hard coat layer could not be peeled off from the release film, it is recorded as "unpeelable", and if the resin was repelled during the formation of the hard coat layer and the hard coat layer could not be formed, it is recorded as "unprocessable".

The polyesters used in the examples and comparative examples were prepared as follows:

<Polyester (A)>
A polyethylene terephthalate homopolymer having an intrinsic viscosity of 0.63 dl/g.

<Polyester (B)>
A polyethylene terephthalate homopolymer having an intrinsic viscosity of 0.65 dl/g and containing 0.2% by mass of silica particles having an average particle size of 2 μm.

<Polyester (C)>
A polyethylene terephthalate homopolymer having an intrinsic viscosity of 0.61 dl/g and containing 10% by mass of alkyl methacrylate-styrene copolymer particles (true specific gravity: 1.1) having an average particle size of 4.5 μm.

<Polyester (D)>
A copolymerized polyethylene terephthalate polymer containing 22 mol % isophthalic acid, having an intrinsic viscosity of 0.70 dl/g and a melting point of 198°C.

The compounds used to form the release layer are as follows:

<Release Agent (IA)>
A water dispersion of oxidized polyethylene wax (melting point 125°C).

<Release Agent (IB)>
A water dispersion of modified polypropylene wax (melting point 156°C).

<Release Agent (IC)>
A long-chain alkyl group-containing compound obtained by adding octadecyl isocyanate to polyvinyl alcohol having an average polymerization degree of 500 and a saponification degree of 88 mol %.

<Polyester resin (II)>
An aqueous dispersion of a polyester resin copolymerized in the following ratios: (acid components) terephthalic acid/isophthalic acid/5-sodium sulfoisophthalic acid; (diol components) ethylene glycol/1,4-butanediol/diethylene glycol=56/40/4; and (70/20/10) (mol %).

<Melamine compound (III)>
Partially etherified melamine having a methylol group, a methoxy group and an imino group.

Example 1
A mixed raw material (particle content 0.02% by mass) obtained by mixing polyesters (A) and (B) in a ratio of 90% by mass and 10% by mass, respectively, was used as the raw material for the outermost layer (surface layer), and only polyester (A) was used as the raw material for the intermediate layer. Each of these was supplied to two extruders and melted at 285°C. After that, the materials were co-extruded onto a cooling roll set at 40°C in a layer structure of two types and three layers (extrusion amount of surface layer/intermediate layer/surface layer = 1:8:1), and then cooled and solidified to obtain an unstretched sheet. Next, the film was stretched 3.4 times in the longitudinal direction at a film temperature of 85°C by utilizing the difference in roll peripheral speed, and then a release layer forming composition having the composition shown in Table 2 below was diluted with water and coated on one side of this longitudinally stretched film as coating liquid 1. The film was then introduced into a tenter, stretched 4.3 times in the transverse direction at 110°C, and heat-treated at 235°C. After that, the film was relaxed by 2% in the transverse direction, and a release film (sample) having a thickness of 50 μm and a release layer with a coating amount (after drying) of 150 mg/ ^m2 was obtained.
The properties of this release film (sample) are shown in Table 3 below.

Example 2
In Example 1, the composition of the release layer forming composition was changed to the composition shown in Table 2, and the coating amount (after drying) was changed to 200 mg/ ^m2. Except for this, the same production as in Example 1 was carried out to obtain a polyester film (sample).
The properties of the obtained release film (sample) are shown in Table 3.
The release films (samples) of all the Examples had a low transfer rate of the release component and excellent releasability.

Example 3
A mixture of polyesters (A), (C), and (D) blended at ratios of 20 mass%, 60 mass%, and 20 mass%, respectively (particle content 6 mass%, copolymerization component amount 4.4 mol%) was melted in an extruder and supplied to the surface layer (particle-containing layer A) of a laminated die, while polyester (A) was supplied to the base layer of the laminated die, and a mixture of polyesters (A), (C), and (D) blended at ratios of 80 mass%, 10 mass%, and 10 mass%, respectively (particle content 1 mass%, copolymerization component amount 2.2 mol%) was supplied to the other surface layer (particle-containing layer B) of the laminated die, and a three-layer laminated polyester resin consisting of a three-kind, three-layer structure (particle-containing layer A/base layer/particle-containing layer B = 1:8:1 ratio) was extruded into a film, and cooled and solidified on a cooling roll at 35 ° C. to prepare an unstretched sheet. Next, after preheating with a heating roll at 80°C, the film was stretched 3.2 times in the longitudinal direction between rolls at 95°C using an infrared heater and a heating roll in combination, and then a release layer forming composition having the composition shown in Table 2 below diluted with water was applied to one side of this longitudinally stretched film as coating liquid 1. Next, the film end was held with a clip and introduced into a tenter, and the film was stretched 4.2 times in the transverse direction while being heated at a temperature of 110°C, and was subjected to heat treatment at 240°C for 10 seconds while simultaneously being relaxed by 10% in the width direction, thereby obtaining a release film (sample) having a thickness of 50 μm ⁽ particle-containing layer A/base layer/particle-containing layer B=5 μm/40 μm/5 μm) and having a release layer with a coating amount (after drying) of 150 mg/m2.

<Examples 4 to 22>
In Example 3, the composition of the release layer forming composition was changed to the composition shown in Table 2, and the coating amount (after drying) was changed to the composition shown in Table 3. Except for this, the same production process as in Example 3 was carried out to obtain a release film (sample).
The properties of the obtained release film (sample) are shown in Table 3.
The release films (samples) of all the Examples had good average surface roughness (Ra) and gloss, appropriate surface free energy, a low transfer rate of the release component, and good releasability.

<Comparative Example 1>
A polyester film (sample) was obtained in the same manner as in Example 1, except that no release layer was provided.
The properties of the obtained polyester film (sample) are shown in Table 3.
As shown in Table 3, the hard coat layer could not be peeled off.

<Comparative Example 2>
A polyester film (sample) was obtained in the same manner as in Example 3, except that no release layer was provided.
The properties of the obtained polyester film (sample) are shown in Table 3.
As shown in Table 3, the hard coat layer could not be peeled off.

<Comparative Examples 3 to 6>
In Example 3, the composition of the release layer forming composition was changed to the composition shown in Table 2, and the coating amount (after drying) was changed to the composition shown in Table 3. Except for this, the same production process as in Example 3 was carried out to obtain a release film (sample).
The properties of the obtained release film (sample) are shown in Table 3.
As shown in Table 3, in some cases a large amount of the release component was transferred, and in other cases the hard coat layer was impossible to peel off.

From the results of the above examples and the results of tests conducted by the inventors thus far, it has been found that when the release agent accounts for less than 15 mass% of all non-volatile components in the release layer-forming composition and the content of the release agent in the release layer is 3.4 mg/ ^m2 or more, the release properties are excellent and the amount of transfer of the release component can be reduced.

This release film has an appropriate release agent content ratio and amount, so it has excellent release performance and excellent secondary processability for the transfer target object, making it particularly suitable for use as a transfer release film for surface shape transfer to electromagnetic wave shielding materials, etc., and for simultaneous molding transfer applications.

Claims (14)

A release film comprising a release layer formed from a release layer-forming composition on at least one side of a polyester film, the release agent being 9 mass% or less as a proportion of all non-volatile components in the release layer-forming composition , and the content of the release agent in the release layer being 3.4 mg/m2 ^or more and less than 11.5 mg/ ^m2 , wherein the transfer rate of the release component is 40% or less as measured by the measurement method described below , and the initial peel force from the hard coat layer is greater than the peel force from the hard coat layer after press treatment for 30 minutes under conditions of 170°C x 3 MPa .
<Method for measuring transfer rate of release component>
The release layer side surface of the release film sample and the surface of a polyester film for measurement test (T100, thickness 50 μm, manufactured by Mitsubishi Chemical Corporation) that has not been surface-treated are stacked together, and the two films are heat-pressed for 30 minutes under conditions of 170° C. and 1 MPa, and then humidified under an environment of 23° C. and 50% RH. The release film sample is then removed, and the tape peeling force (F1) is measured for the surface of the polyester film for measurement test that was in contact with the release layer.
The same measurement as above is carried out on the release film sample not provided with a release layer, and the tape peeling force (F0) is measured.
The tape peeling force is the stress when an acrylic adhesive tape (manufactured by Nitto Denko Corporation, "No. 31B") is attached to the release layer, left at room temperature for 1 hour, and then peeled in a 180° direction at a tensile speed of 0.3 m/min.
The transfer rate (%) is calculated from the tape peeling forces (F1) and (F0) according to the following formula.
Transfer rate (%) = {(F0-F1)/F0}×100 A release film comprising a release layer on at least one side of a polyester film, the release layer containing a release agent in an amount of 10 mass% or less and a content of the release agent in the release layer of 3.4 mg/ ^m2 or more and less than 11.5 mg/m2 ^, wherein the transfer rate of the release component is 40% or less as measured by the following measurement method, and the initial peel strength from the hard coat layer is greater than the peel strength from the hard coat layer after press treatment for 30 minutes under conditions of 170°C x 3 MPa .
<Method for measuring transfer rate of release component>
The release layer side surface of the release film sample and the surface of a polyester film for measurement test (T100, thickness 50 μm, manufactured by Mitsubishi Chemical Corporation) that has not been surface-treated are stacked together, and the two films are heat-pressed under conditions of 170° C.×1 MPa for 30 minutes, and then humidified under an environment of 23° C.×50% RH. Thereafter, the release film sample is removed, and the tape peeling force (F1) is measured for the surface of the polyester film for measurement test that was in contact with the release layer.
The same measurement as above is carried out on the release film sample not provided with a release layer, and the tape peeling force (F0) is measured.
The tape peeling force is the stress when an acrylic adhesive tape (manufactured by Nitto Denko Corporation, "No. 31B") is attached to the release layer, left at room temperature for 1 hour, and then peeled in a 180° direction at a tensile speed of 0.3 m/min.
The transfer rate (%) is calculated from the tape peeling forces (F1) and (F0) according to the following formula.
Transfer rate (%) = {(F0-F1)/F0}×100 A release film comprising a release layer formed from a release layer-forming composition on at least one side of a polyester film, a release agent being 9 mass% or less as a proportion of all non-volatile components in the release layer-forming composition, and a content of the release agent in the release layer being 3.4 mg/m2 ^or more and less than 11.5 mg/ ^m2, wherein the polyester film comprises a particle-containing layer containing particles, the particles having an average particle size of 2.0 to 10.0 μm, and the initial peel strength from the hard coat layer is greater than the peel strength from the hard coat layer after press treatment for 30 minutes under conditions of 170°C x 3 MPa . A release film comprising a release layer on at least one side of a polyester film, the release layer containing a release agent in an amount of 10 mass % or less , and the release agent content in the release layer being 3.4 mg/ ^m2 or more and less than 11.5 mg/ ^m2 , wherein the polyester film comprises a particle-containing layer containing particles, the particles having an average particle size of 2.0 to 10.0 μm, and the initial peel strength from the hard coat layer is greater than the peel strength from the hard coat layer after a press treatment for 30 minutes under conditions of 170°C x 3 MPa . The release film according to any one of claims 1 to 4, wherein the surface free energy of the release layer side surface is 27 mN/m or more. The release film according to any one of claims 1 to 5, wherein the release agent is a wax. The release film according to any one of claims 1 to 6, wherein the release layer contains a compound derived from a crosslinking agent. The release film according to any one of claims 1 to 7, wherein the average surface roughness (Ra) of the release layer side surface is 0.1 μm to 2.0 μm. The release film according to any one of claims 1 to 8, wherein the gloss of the surface on the release layer side is 30% or less. The release film according to claim 1 or 2, wherein the polyester film has a particle-containing layer that contains particles. The release film according to claim 10, wherein the average particle size of the particles is 2.0 to 10.0 μm. The release film according to any one of claims 3, 4, and 10 to 11, wherein the particles have a true specific gravity of 2.0 or less. The release film according to any one of claims 3, 4, and 10 to 12, wherein the copolymer component is contained in an amount of 0.1 to 10 mol % relative to the polyester constituting the particle-containing layer. A transfer release film made using the release film according to any one of claims 1 to 13.