JP2022145807A - release film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a release film which enables molding of a resin sheet that suppresses occurrence of pin holes and scratches of a resin sheet and has high smoothness even when the resin sheet is molded on the release film and is wound up into a roll.

SOLUTION: A release film for molding a resin sheet has a base material film which does not substantially contain inorganic particles, has a release coating layer on one surface of the base material film, and a slippery coating layer containing particles on the other surface of the base material, wherein area surface average roughness (Sa) of the slippery coating layer is 1 nm or more and 25 nm or less and a maximum projection height (P) thereof is 60 nm or more and 500 nm or less, and an average length (RSm) of a roughness curve element is 10 μm or less, and the slippery coating layer contains particles having a particle diameter of 150 nm or more and 600 nm or less.

SELECTED DRAWING: None

COPYRIGHT: (C)2023,JPO&INPIT

Description

The present invention relates to a release film. More particularly, it relates to a release film for molding a resin sheet, which is used when a thin resin sheet is formed from a solution.

Release films based on polyester films have high heat resistance and mechanical properties, and have been used as process films for solution-casting resin sheets such as adhesive sheets, cover films, and polymer electrolyte membranes. In recent years, high smoothness and transparency are required for resin sheets used especially for electronic parts and optical applications, and therefore high smoothness has been required for the surface of release films used as process films. Therefore, techniques such as those described in Patent Documents 1 to 3 have been disclosed, and proposals have been made to reduce the surface roughness of the release layer surface.

However, according to the prior art, although the surface of the release layer of the release film has high smoothness, the smoothness of the opposite surface has been unsatisfactory. When molding a resin sheet on a release film, the resin sheet is molded on the release surface of the release film and then wound into a roll. will come into contact. Therefore, no matter how smooth the surface of the release film is, if the surface of the release film opposite to the surface on which the resin sheet is molded is not highly smooth, the unevenness is transferred to the resin sheet, resulting in poor smoothness of the resin sheet. There was a problem. Resin sheets to be molded in recent years have become thinner, and these problems have become more pronounced, and it has become important to provide both sides of the release film with high smoothness. On the other hand, if both surfaces of the release film have too high smoothness, the slipperiness is poor and the windability deteriorates.

JP 2012-144021 A JP 2014-154273 A JP 2015-182261 A

The present invention has been made against the background of such problems of the prior art. That is, the object of the present invention is to suppress the occurrence of pinholes and scratches in the resin sheet even when the resin sheet is molded on a release film and wound into a roll, and to mold a resin sheet having high smoothness. To provide a release film capable of

The present inventor has completed the present invention as a result of intensive studies to achieve this object. That is, the present invention consists of the following configurations.
1. The base film does not substantially contain inorganic particles, has a release coating layer on one surface of the base film, and contains particles on the other surface of the base film. Having a coating layer, the smooth coating layer has a region surface average roughness (Sa) of 1 nm or more and 25 nm or less, a maximum protrusion height (P) of 60 nm or more and 500 nm or less, and an average length (RSm) of roughness curve elements is 10 μm or less for molding a resin sheet.
2. 1. The release film for resin sheet molding as described in 1 above, wherein the release coating layer has an average area surface roughness (Sa) of 5 nm or less and a maximum projection height (P) of 200 nm or less.
3. 2. The release film for molding a resin sheet according to 1 or 2 above, wherein the release coating layer has a surface free energy of 15 mJ/m ² or more and 45 mJ/m ² or less.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a release film for resin sheet production that prevents pinholes, partial thickness variations, etc., and has high smoothness even in a resin sheet that requires a thin film with high smoothness.

The present invention will be described in detail below.
The release film of the present invention is a release film having a release coating layer on one side of a base film and a smooth coating layer containing particles on the other side.

In order to increase the density of protrusions on the slippery surface, the present inventors have adjusted the average length (RSm) of the roughness curve element of the slippery coated surface to within a specific range, making it possible to respond to the thinning of ceramic green sheets in recent years. proposed a release film (International Application No. PCT/JP2017/017354). The present inventors have newly discovered that such a technique can be applied to a release film for molding a resin sheet, which is required to be thin and have high smoothness, and have completed the present invention.

(Base film)
The film that is preferably used as a substrate in the present invention is not particularly limited, and films of polyethylene, polypropylene, polyester, etc. can be used, but polyester films are preferable from the viewpoint of mechanical strength and the like. A polyester film is a film composed of a polyester resin, and preferably a polyester film containing at least one selected from polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. Moreover, the film may be a film made of a polyester in which a third component monomer is copolymerized as part of the dicarboxylic acid component of the polyester or the diol component as described above. Among these polyester films, polyethylene terephthalate film is most preferable from the viewpoint of balance between physical properties and cost.

Moreover, the polyester film may be a single layer or a multilayer. In addition, each of these layers may contain various additives in the polyester resin, if necessary, as long as the effect of the present invention is achieved. Examples of additives include antioxidants, light stabilizers, anti-gelling agents, organic wetting agents, antistatic agents, and ultraviolet absorbers.

(Smooth coating layer)
The release film of the present invention has an easy-slip coating layer on one surface of the polyester base film as described above. It is preferable that at least a binder resin and particles are contained in the easy-slip coating layer.

(Binder resin in slippery coating layer)
The binder resin constituting the easy-smooth coating layer is not particularly limited, but specific examples of polymers include polyester resins, acrylic resins, urethane resins, polyolefin resins, polyvinyl resins (polyvinyl alcohol, etc.), polyalkylene glycol, poly Alkylene imine, methyl cellulose, hydroxy cellulose, starches and the like can be mentioned. Among these resins, polyester resins, acrylic resins, and urethane resins are preferably used from the viewpoint of particle retention and adhesion.

When a polyester resin is used as the binder resin, it is not particularly limited, but in order to achieve solubility in solvents, dispersibility, and adhesiveness to the substrate film and other layers, it is preferable to be a copolymerized polyester. preferable. Incidentally, the polyester resin may be modified with polyurethane.

When an acrylic resin is used as the binder resin, it is preferably an acrylic resin having a hydroxyl group and a carboxyl group in its molecule, although it is not particularly limited. It is more preferable that the structural unit having a hydroxyl group is contained in an amount of 20 to 90 mol % in 100 mol % of all structural units. It is preferable that the structural unit having a hydroxyl group is 20 mol % or more because the water solubility of the acrylic resin can be appropriately maintained. On the other hand, if it is 90 mol % or less, the hydroxyl groups of the acrylic resin and the particles contained in the easy-smooth coating layer do not cause excessive interaction, and the particles are uniformly dispersed, which is preferable.

In order to introduce a hydroxyl group into an acrylic resin, a monomer having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, or 2-hydroxyethyl ( A ring-opening adduct of γ-butyrolactone or ε-caprolactone to meth)acrylate may be used as a copolymerization component. Among them, 2-hydroxyethyl (meth)acrylate is preferable because it does not inhibit water solubility. In addition, you may use together 2 or more types of these.

The hydroxyl value of the acrylic resin is preferably 2 mgKOH/g or more, more preferably 5 mgKOH/g or more, still more preferably 10 mgKOH/g or more. If the hydroxyl value of the acrylic resin is 2 mgKOH/g or more, the water solubility of the acrylic resin is improved, which is preferable.

The hydroxyl value of the acrylic resin is preferably 250 mgKOH/g or less, more preferably 230 mgKOH/g or less, still more preferably 200 mgKOH/g or less. If the hydroxyl value of the acrylic resin is 250 mgKOH/g or less, the particles contained in the easy-slip coating layer do not interact excessively, which is preferable because the particles are uniformly dispersed.

The acrylic resin used in the present invention is preferably a resin having carboxyl groups in addition to hydroxyl groups. By having a carboxyl group, it becomes possible to form a crosslinked structure with a crosslinking agent and to easily impart water solubility. Examples include monomers containing a carboxy group such as (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid and fumaric acid, and monomers containing an acid anhydride group such as maleic anhydride and itaconic anhydride.

A monomer having a carboxyl group is preferably 4 mol % or more, more preferably 10 mol % or more, in 100 mol % of all structural units of the acrylic resin. When it is 4 mol % or more, it becomes easy to form a crosslinked structure in the slippery coating layer and to impart water solubility, which is preferable. The monomer having a carboxyl group is preferably 65 mol % or less, more preferably 50 mol % or less. When it is 65 mol % or less, the Tg of the resulting coating film does not become too high relative to the preferable range described later, and the film-forming properties and the stretching suitability in in-line coating are favorable, which is preferable.

In order to develop good water solubility, it is preferable to neutralize the carboxyl groups introduced into the acrylic resin by copolymerization of acrylic acid or methacrylic acid. Basic neutralizers include amine compounds such as ammonia, trimethylamine, triethylamine and dimethylaminoethanol, and inorganic basic substances such as potassium hydroxide and sodium hydroxide. It is preferable to use an amine compound as a neutralizing agent for ease of application and ease of formation of a crosslinked structure. The neutralization rate is preferably 30 mol % to 95 mol %, more preferably 40 mol % to 90 mol %. When the neutralization rate is 30 mol% or more, the acrylic resin has sufficient water solubility, the acrylic resin can be easily dissolved during preparation of the coating solution, and there is no risk of whitening of the coated film surface after drying. preferable. On the other hand, when the neutralization rate is 95 mol % or less, the water solubility is not too high, and alcohol or the like can be easily mixed in preparation of the coating liquid, which is preferable.

The acid value of the acrylic resin is preferably 40 mgKOH/g or more, more preferably 50 mgKOH/g or more, still more preferably 60 mgKOH/g or more. If the acid value of the acrylic resin is 40 mgKOH/g or more, the number of cross-linking points with the oxazoline cross-linking agent or the carbodiimide cross-linking agent increases, so that a strong coating film with a higher cross-linking density can be obtained, which is preferable.

The acid value of the acrylic resin is preferably 400 mgKOH/g or less, more preferably 350 mgKOH/g or less, still more preferably 300 mgKOH/g or less. If the acid value of the acrylic resin is 400 mgKOH/g or less, the carboxyl groups of the acrylic resin and the particles contained in the easy-slip coating layer do not cause excessive interaction, and the particles are uniformly dispersed, which is preferable. Good dispersibility of the particles is preferable because coarse projections do not occur on the easy-to-smooth coating surface and pinholes in the resin sheet do not occur.

The glass transition temperature (Tg) of the acrylic resin is preferably 50°C or higher, more preferably 55°C or higher, and still more preferably 60°C or higher. When the glass transition temperature of the acrylic resin is 50° C. or higher, the hardness of the slippery coating layer is appropriately increased, which is preferable.

The glass transition temperature (Tg) of the acrylic resin is preferably 110°C or lower, more preferably 105°C or lower, and still more preferably 100°C or lower. When the glass transition temperature of the acrylic resin is 110° C. or lower, the coating film is uniformly stretched without causing cracks in the stretching step after the easy-slip coating layer is applied, which is preferable.

A (meth)acrylic monomer or a non-acrylic vinyl monomer can be used as the Tg-adjusting monomer that is copolymerized to adjust the Tg to the above range. Specific examples of (meth) acrylic monomers include methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, n-amyl (meth) acrylates, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, (meth)acrylic acid alkyl esters such as stearyl (meth)acrylate; nitrogen-containing acrylic monomers such as (meth)acrylamide, diacetoneacrylamide, n-methylolacrylamide, and (meth)acrylonitrile; and vinyl methacrylate. These can be used alone or in combination of two or more.

Examples of non-acrylic vinyl monomers include styrene, α-methylstyrene, vinyltoluene (a mixture of m-methylstyrene and p-methylstyrene), styrene-based monomers such as chlorostyrene; vinyl acetate, vinyl propionate, and vinyl butyrate. , vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl cyclohexanecarboxylate, vinyl pivalate, vinyl octylate, vinyl monochloroacetate, divinyl adipate, Vinyl esters such as vinyl crotonate, vinyl sorbate, vinyl benzoate and vinyl cinnamate; vinyl halide monomers such as vinyl chloride and vinylidene chloride;

The monomers for adjusting Tg are preferably used as the balance after determining appropriate amounts of the hydroxyl group-containing monomer and the carboxyl group-containing monomer. The Tg of the copolymer is determined by the following Fox formula.

Ｗ_n：各モノマーの質量分率（質量％）
Ｔｇ_n：各モノマーのホモポリマーのＴｇ（Ｋ）

W _n : mass fraction of each monomer (% by mass)
Tg _n : Tg (K) of homopolymer of each monomer

A component that lowers surface free energy such as a long-chain alkyl group may be introduced as a monomer to be copolymerized for adjusting Tg. As the acrylic resin into which a long-chain alkyl group has been introduced, one having an alkyl group having about 8 to 20 carbon atoms in the side chain of the acrylic resin is preferable. Further, a copolymer having a (meth)acrylic acid ester as a main repeating unit and containing a long-chain alkyl group having 8 to 20 carbon atoms in the transesterified portion can also be preferably used.

The monomer having a long-chain alkyl group among the monomers copolymerized for Tg adjustment is preferably 50 mol % or less, more preferably 40 mol % or less, in 100 mol % of all structural units of the acrylic resin. When it is 50 mol % or less, the Tg of the resulting coating film does not become too low relative to the preferred range, and the hardness of the coating film can be kept high, which is preferable. In the present invention, the monomer having a long-chain alkyl group may be 0 mol% as long as the Tg can be maintained within a suitable range. becomes clear and is preferable.

The acrylic resin used in the present invention can be obtained by known radical polymerization. Emulsion polymerization, suspension polymerization, solution polymerization, bulk polymerization, and the like can all be adopted. From the point of handleability, solution polymerization is preferred. Water-soluble organic solvents that can be used for solution polymerization include ethylene glycol n-butyl ether, isopropanol, ethanol, n-methylpyrrolidone, tetrahydrofuran, 1,4-dioxane, 1,3-oxolane, methyl solosolve, and ethyl solosolve. , ethyl carbitol, butyl carbitol, propylene glycol monopropyl ether, propylene glycol monobutyl ether and the like. These may be used by mixing with water.

The polymerization initiator may be any known compound that generates radicals, but water-soluble azo polymerization initiators such as 2,2-azobis-2-methyl-N-2-hydroxyethylpropionamide are preferred. The temperature, time, etc. of the polymerization are appropriately selected.

The weight average molecular weight (Mw) of the acrylic resin is preferably about 10,000 to 200,000. A more preferred range is from 20,000 to 150,000. When Mw is 10,000 or more, there is no risk of thermal decomposition in the tenter, which is preferable. When the Mw is 200,000 or less, the viscosity of the coating liquid does not significantly increase and the coatability is good, which is preferable.

(crosslinking agent)
In the present invention, the slippery coating layer may contain a cross-linking agent to form a crosslinked structure in the slippery coating layer. By containing a cross-linking agent, it becomes possible to further improve adhesion under high temperature and high humidity conditions. Specific cross-linking agents include urea-based, epoxy-based, melamine-based, isocyanate-based, oxazoline-based, carbodiimide-based, and the like. In addition, a catalyst or the like can be appropriately used as necessary in order to accelerate the cross-linking reaction.

(Particles in slippery coating layer)
The easy-slip coating layer preferably contains lubricant particles in order to impart slipperiness to the surface. The particles may be inorganic particles or organic particles, and are not particularly limited, and include (1) silica, kaolinite, talc, light calcium carbonate, heavy calcium carbonate, zeolite, alumina, Barium sulfate, carbon black, zinc oxide, zinc sulfate, zinc carbonate, zirconium oxide, titanium dioxide, satin white, aluminum silicate, diatomaceous earth, calcium silicate, aluminum hydroxide, hydrated halloysite, calcium carbonate, magnesium carbonate, calcium phosphate, hydroxide inorganic particles such as magnesium and barium sulfate; Examples include organic particles such as isoprene, methyl methacrylate/butyl methacrylate, melamine, polycarbonate, urea, epoxy, urethane, phenol, diallyl phthalate, and polyester. Silica is particularly preferably used to impart lubricity.

The average particle size of the particles is preferably 10 nm or more, more preferably 20 nm or more, and still more preferably 30 nm or more. When the average particle size of the particles is 10 nm or more, it is preferable because the particles are less likely to aggregate and the lubricity can be ensured.

The average particle size of the particles is preferably 1000 nm or less, more preferably 800 nm or less, and even more preferably 600 nm or less. When the average particle diameter of the particles is 1000 nm or less, the transparency is maintained and the particles do not fall off, which is preferable.

Further, for example, a mixture of particles having a small average particle size of about 10 to 270 nm and particles having a large average particle size of about 300 to 1000 nm can be used to achieve the area surface average roughness (Sa) and the maximum protrusion height ( It is preferable to reduce the average length (RSm) of the roughness curve element while keeping P) small, and to achieve both slipperiness and smoothness. It is to use together particles having a large diameter of 350 to 600 nm. When small particles and large particles are mixed, it is preferable that the mass content of small particles is larger than the mass content of large particles with respect to the total solid content of the coating layer.

The method of measuring the average particle size of the particles is to observe the particles in the cross section of the film after processing with a transmission electron microscope or scanning electron microscope, observe 100 particles that are not agglomerated, and use the average value as the average particle size. It was performed by the method of using the diameter.

The shape of the particles is not particularly limited as long as it satisfies the object of the present invention, and spherical particles and irregularly shaped non-spherical particles can be used. The particle diameter of amorphous particles can be calculated as a circle equivalent diameter. The circle-equivalent diameter is a value obtained by dividing the observed particle area by π, calculating the square root, and doubling the result.

The ratio of the particles to the total solid content of the smooth coating layer is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. If the ratio of the particles to the total solid content of the easy-smooth coating layer is 50% by mass or less, the transparency is maintained and the particles do not significantly drop off from the easy-smooth coating layer, which is preferable.

The ratio of the particles to the total solid content of the smooth coating layer is preferably 1% by mass or more, more preferably 1.5% by mass or more, and still more preferably 2% by mass or more. If the ratio of the particles to the total solid content of the easy-smooth coating layer is 1% by mass or more, the slipperiness can be ensured, which is preferable.

As a method for measuring the content of particles contained in the easy-smooth coating layer, for example, when the easy-smooth coating layer contains a resin as an organic component and inorganic particles, the following method can be used. First, the easy-slip coating layer provided on the processed film is extracted from the processed film using a solvent or the like, and dried to obtain the easy-slip coating layer. Next, heat is applied to the easy-smooth coating layer so that the organic components contained in the easy-smooth coating layer are burned and distilled off by the heat, whereby only the inorganic component can be obtained. By measuring the weight of the obtained inorganic component and the slippery coating layer before combustion and distillation, the mass % of the particles contained in the slippery coating layer can be measured. At this time, a commercially available differential thermal/thermogravimetric simultaneous measurement device can be used for accurate measurement. In addition, the ratio of the particles in the total solid content of the easy-smooth coating layer means the ratio of the total amount of the plural kinds of particles when plural kinds of particles are present.

(Additive in slippery coating layer)
In order to impart other functionality to the easy-slip coating layer, various additives may be added within a range that does not impair the coating appearance. Examples of the additives include fluorescent dyes, fluorescent whitening agents, plasticizers, ultraviolet absorbers, pigment dispersants, foam inhibitors, antifoaming agents, preservatives, and the like.

The smooth coating layer may contain a surfactant for the purpose of improving leveling properties during coating and defoaming the coating solution. The surfactant may be cationic, anionic, or nonionic, but silicone, acetylene glycol, or fluorine-based surfactants are preferred. These surfactants are preferably contained in the coating layer within a range in which abnormalities in coating appearance do not occur due to excessive addition.

The surface free energy of the slippery coating layer of the present invention is preferably 65 mJ/m ² or less. More preferably, it is 50 mJ/m ² or less. 40 mJ/m ² or less is more preferable. When it is 65 mJ/m ² or less, the slipperiness is good, and even if the smoothness of the easy-slip coating layer is high, the windability and film runnability are good, which is preferable. Although the lower limit of the surface free energy is not particularly limited, it is preferably 15 mJ/m ² or more.

As the coating method, both the so-called in-line coating method in which the coating is applied at the same time as the formation of the polyester base film and the so-called off-line coating method in which the polyester base film is coated separately with a coater after the formation of the polyester base film can be applied. is efficient and preferred.

As a coating method, any known method can be used to apply the coating liquid to a polyethylene terephthalate (hereinafter sometimes abbreviated as PET) film. For example, reverse roll coating method, gravure coating method, kiss coating method, die coater method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method, impregnation coating method, curtain coating method, etc. mentioned. These methods are applied singly or in combination.

In the present invention, as a method of providing a smooth coating layer on a polyester film, a method of coating a polyester film with a coating liquid containing a solvent, particles and a resin and drying the coating liquid can be mentioned. Examples of the solvent include an organic solvent such as toluene, water, or a mixed system of water and a water-soluble organic solvent. From the standpoint of environmental problems, water alone or a mixture of water and a water-soluble organic solvent is preferred. is preferred.

The solid content concentration of the slippery coating liquid depends on the type of binder resin and the type of solvent, but is preferably 0.5% by mass or more, more preferably 1% by mass or more. The solid content concentration of the coating liquid is preferably 35% by mass or less, more preferably 20% by mass or less.

The drying temperature after coating also depends on the type of binder resin, the type of solvent, the presence or absence of a cross-linking agent, the solid content concentration, etc., but is preferably 70° C. or higher and preferably 250° C. or lower.

(Manufacturing of polyester film)
In the present invention, the polyester film that serves as the base film can be produced according to a general method for producing a polyester film. For example, a polyester resin is melted and a non-oriented polyester extruded into a sheet is stretched in the longitudinal direction using the speed difference between rolls at a temperature equal to or higher than the glass transition temperature, and then stretched in the transverse direction with a tenter, A method of applying a heat treatment can be mentioned. Moreover, the method of biaxially stretching simultaneously longitudinally and transversely in a tenter is also mentioned.

In the present invention, the polyester film that serves as the base film may be a uniaxially stretched film or a biaxially stretched film, but is preferably a biaxially stretched film.

The thickness of the polyester film substrate is preferably 5 µm or more, more preferably 10 µm or more, and still more preferably 15 µm or more. When the thickness is 5 μm or more, the film is less likely to wrinkle during transportation, which is preferable.

The thickness of the polyester film substrate is preferably 50 µm or less, more preferably 45 µm or less, and still more preferably 40 µm or less. A thickness of 40 μm or less is preferable because the cost per unit area is reduced.

In the case of in-line coating, it may be applied to an unstretched film before stretching in the longitudinal direction, or may be applied to a uniaxially stretched film after stretching in the longitudinal direction and before stretching in the transverse direction. In the case of coating before stretching in the machine direction, it is preferable to provide a drying step before roll stretching. When the uniaxially stretched film is coated before being stretched in the transverse direction, the film heating process in the tenter can also serve as the drying process, so a separate drying process is not necessarily required. The same applies to simultaneous biaxial stretching.

The film thickness of the lubricous coating layer is preferably 0.001 μm or more, more preferably 0.01 μm or more, still more preferably 0.02 μm or more, and particularly preferably 0.03 μm or more. It is preferable that the film thickness of the coating layer is 0.001 μm or more because the film forming property of the coating film is maintained and a uniform coating film is obtained.

The film thickness of the lubricous coating layer is preferably 2 µm or less, more preferably 1 µm or less, still more preferably 0.8 µm or less, and particularly preferably 0.5 µm or less. When the film thickness of the coating layer is 2 μm or less, blocking is not likely to occur, which is preferable.

The resin sheet to be coated and molded on the release coating layer described below is wound into a roll together with the release film after coating and molding. At this time, the surface of the resin sheet is wound with the easy-slip coating layer of the release film in contact with the surface of the resin sheet. In order not to cause defects on the surface of the resin sheet, the outer surface of the easy-slip coating layer (the surface of the easy-slip coating layer of the entire coating film that is not in contact with the polyester film) must be moderately flat. It is preferable that the average roughness (Sa) is 1 nm or more and 25 nm or less and the maximum protrusion height (P) is 60 nm or more and 500 nm or less.

If the surface average roughness (Sa) of the outer surface of the lubricating coating layer is 1 nm or more and the maximum projection height (P) is 60 nm or more, the lubricating coating surface does not become too smooth and moderate lubricity is maintained. Therefore, the windability becomes good, which is preferable. It is preferable that the area surface average roughness (Sa) is 25 nm or less and the maximum projection height (P) is 500 nm or less, since the easily coated surface is not too rough and defects of the resin sheet due to projections do not occur.

In the present invention, in addition to setting the region surface average roughness (Sa) and the maximum protrusion height (P) within the above ranges, the average length (RSm) of the roughness curve element is preferably 10 μm or less. By controlling the average length (RSm) of the roughness curve element to 10 μm or less, the number of protrusions per unit area increases. As the number of protrusions increases, the pressure applied to each protrusion is dispersed and reduced, which is preferable because the occurrence of pinholes can be effectively suppressed. The average length (RSm) of the roughness curve element is more preferably 5 μm or less, still more preferably 3 μm or less. However, if the average length (RSm) of the roughness curve element is too small, it is associated with an excessive content of particles in the easy-smooth coating layer, etc., and the area surface average roughness (Sa) increases. Also, the maximum projection height (P) is related to an increase.

In the present invention, the average particle size of the particles contained in the easy-smooth coating layer is preferably 1000 nm or less in order to keep the average length (RSm) of the roughness curve element within a predetermined range. It is more preferably 800 nm or less, still more preferably 600 nm or less. When the particle diameter is 1000 nm or less, the distance between particles does not become too large, and RSm is preferably adjusted within a predetermined range.

(Release coating layer)
The resin constituting the release coating layer in the present invention is not particularly limited, and silicone resins, fluororesins, alkyd resins, various waxes, aliphatic olefins, etc. can be used, and each resin can be used alone or in combination of two or more. You can also

As the release coating layer of the present invention, for example, a silicone resin is a resin having a silicone structure in the molecule, and includes curable silicones, silicone graft resins, and modified silicone resins such as alkyl-modified silicone resins. It is preferable to use a reactive curable silicone resin from the viewpoint of properties. Examples of reactive curable silicone resins that can be used include those of addition reaction type, those of condensation reaction type, those of ultraviolet ray or electron beam curable type, and the like. More preferably, a low-temperature curing addition reaction system that can be processed at a low temperature and an ultraviolet or electron beam curing system are preferable. By using these materials, the polyester film can be processed at a low temperature during the coating process. Therefore, the polyester film is less thermally damaged during processing, a polyester film with high flatness can be obtained, and defects such as pinholes can be reduced even when producing a thin resin sheet.

Examples of the addition-reactive silicone resin include those obtained by reacting polydimethylsiloxane having vinyl groups at its terminals or side chains and hydrogen siloxane with a platinum catalyst to cure the resin. At this time, it is more preferable to use a resin that can be cured at 120° C. within 30 seconds because processing can be performed at a low temperature. Examples include low temperature addition curable types manufactured by Dow Corning Toray (LTC1006L, LTC1056L, LTC300B, LTC303E, LTC310, LTC314, LTC350G, LTC450A, LTC371G, LTC750A, LTC755, LTC760A, etc.) and thermal UV curable types (LTC245 -510, BY24-561, BY24-562, etc.), solvent addition + UV curing type manufactured by Shin-Etsu Chemical Co., Ltd. (X62-5040, X62-5065, X62-5072T, KS5508, etc.), dual cure curing type (X62-2835, X62 -2834, X62-1980, etc.).

As a condensation reaction type silicone resin, for example, polydimethylsiloxane having an OH group at the terminal and polydimethylsiloxane having an H group at the terminal are subjected to a condensation reaction using an organic tin catalyst to form a three-dimensional crosslinked structure. mentioned.

Examples of UV-curing silicone resins include, for example, the most basic types of resins that use the same radical reaction as in normal silicone rubber cross-linking, those that introduce unsaturated groups and undergo photo-curing, and those that decompose onium salts with ultraviolet rays. For example, a strong acid is generated to cleave the epoxy group to cause cross-linking, or a thiol addition reaction to vinylsiloxane causes cross-linking. Also, an electron beam can be used instead of the ultraviolet rays. Electron beams have stronger energy than ultraviolet rays, and can perform a cross-linking reaction by radicals without using an initiator as in the case of ultraviolet curing. Examples of resins used include Shin-Etsu Chemical UV curable silicone (X62-7028A/B, X62-7052, X62-7205, X62-7622, X62-7629, X62-7660, etc.), Momentive Performance Materials UV curable silicones (TPR6502, TPR6501, TPR6500, UV9300, UV9315, XS56-A2982, UV9430, etc.), Arakawa Chemical UV curable silicones (Silicolase UV POLY200, POLY215, POLY201, KF-UV265AM, etc.) ).

Acrylate-modified or glycidoxy-modified polydimethylsiloxane can also be used as the ultraviolet curable silicone resin. Good release performance can also be obtained by mixing these modified polydimethylsiloxanes with polyfunctional acrylate resins, epoxy resins, or the like and using them in the presence of an initiator.

Examples of other resins that can be used include stearyl-modified or lauryl-modified alkyd resins or acrylic resins, or alkyd resins obtained by reaction of methylated melamine, acrylic resins, and olefin resins. When molding a resin sheet used for electronic parts and the like, a mold release agent that does not contain silicone is also preferable.

Examples of aminoalkyd resins obtained by reaction of methylated melamine include Tesfine 303, Tesfine 305 and Tesfine 314 manufactured by Hitachi Chemical Co., Ltd. Examples of aminoacrylic resins obtained by reaction of methylated melamine include Tesfine 322 manufactured by Hitachi Chemical Co., Ltd.

When the above resins are used in the release coating layer of the present invention, one type may be used, or two or more types may be mixed and used. Also, in order to adjust the release force, it is possible to mix additives such as a light release additive and a heavy release additive.

The release coating layer of the present invention may contain particles having a particle size of 1 μm or less, but from the viewpoint of generating pinholes, it is preferable not to substantially contain particles that form protrusions.

Additives such as an adhesion improver and an antistatic agent may be added to the release coating layer of the present invention. In order to improve adhesion to the substrate, it is also preferable to subject the surface of the polyester film to pretreatment such as anchor coating, corona treatment, plasma treatment, atmospheric pressure plasma treatment, etc. before providing the release coating layer.

In the present invention, the thickness of the release coating layer may be set according to the purpose of use, and is not particularly limited. Preferably, the thickness of the release coating layer after curing is 0.005 to 2.0 μm. Good range. It is preferable that the thickness of the release coating layer is 0.005 μm or more because the release performance is maintained. Further, when the thickness of the release coating layer is 2.0 μm or less, the curing time is not excessively long, and there is no risk of unevenness in the thickness of the resin sheet due to deterioration of the flatness of the release film, which is preferable. Moreover, since the curing time does not become too long, there is no risk of aggregation of the resin constituting the release coating layer, and there is no risk of formation of protrusions.

The outer surface of the film on which the release coating layer is formed (the release coating layer surface of the entire coating film that is not in contact with the polyester film) is flat so as not to cause defects in the resin sheet coated and molded thereon. It is preferable that the region surface average roughness (Sa) is 5 nm or less and the maximum protrusion height (P) is 200 nm or less. More preferably, the average surface roughness of the region is 5 nm or less and the maximum projection height is 100 nm or less, and more preferably 5 nm or less and the maximum projection height is 30 nm or less. When the region surface roughness is 5 nm or less and the maximum projection height is 200 nm or less, defects such as pinholes do not occur when the resin sheet is formed, and the yield is good, which is preferable. It can be said that the smaller the region surface average roughness (Sa) is, the more preferable it is, but it may be 0.1 nm or more, or 0.3 nm or more. It can be said that the smaller the maximum protrusion height (P) is, the more preferable it is, but it may be 1 nm or more, or 3 nm or more.

The lower limit of the surface free energy of the release coating layer provided on the release film of the present invention is preferably 15 mJ/m ² or more. More preferably, it is 18 mJ/m ² or more, and more preferably 20 mJ/m ² or more. If it is 15 mJ/m ² or more, cissing or the like is less likely to occur when the solution of the resin sheet is applied, which is preferable.

The upper limit of the surface free energy of the release coating layer provided on the release film of the present invention is preferably 45 mJ/m ² or less. More preferably, it is 40 mJ/m ² or less, and even more preferably 35 mJ/m ² or less. When it is 45 mJ/m ² or less, it is preferable because the peelability of the molded resin sheet is good.

In the present invention, the PET film preferably contains substantially no inorganic particles in order to adjust the surface roughness of the film on which the release coating layer is formed within a predetermined range. The term "substantially free of inorganic particles" in the present invention means that, for both the base film and the release coating layer, when the elements derived from the particles are quantitatively analyzed by fluorescent X-ray analysis, the content is 50 ppm or less. defined as being, preferably less than or equal to 10 ppm, most preferably less than or equal to the limit of detection. This is because even if particles are not actively added to the base film, contaminants derived from foreign substances and dirt adhering to the lines and equipment in the raw material resin or film manufacturing process will peel off and enter the film. This is because there are cases where

In the present invention, the method for forming the release coating layer is not particularly limited. After removing such as by drying, a method of heat drying, heat curing or ultraviolet curing is used. At this time, the drying temperature during solvent drying and heat curing is preferably 180° C. or less, more preferably 150° C. or less, and most preferably 120° C. or less. The heating time is preferably 30 seconds or less, more preferably 20 seconds or less. When the temperature is 180° C. or lower, the flatness of the film is maintained, and the possibility of causing unevenness in the thickness of the resin sheet is small, which is preferable. When the temperature is 120° C. or lower, the film can be processed without impairing the flatness of the film, and the possibility of causing unevenness in the thickness of the resin sheet is further reduced, which is particularly preferable.

In the present invention, the surface tension of the coating liquid when applying the release coating layer is not particularly limited, but is preferably 30 mN/m or less. By adjusting the surface tension as described above, the wettability after coating can be improved, and the unevenness of the coating film surface after drying can be reduced.

In the present invention, the coating liquid for coating the release coating layer is not particularly limited, but it is preferable to add a solvent having a boiling point of 90° C. or higher. By adding a solvent having a boiling point of 90° C. or higher, bumping during drying can be prevented, the coating film can be leveled, and the smoothness of the coating film surface after drying can be improved. As for the amount to be added, it is preferable to add about 10 to 80% by mass based on the entire coating liquid.

As a method for applying the coating liquid, any known coating method can be applied, for example, a roll coating method such as a gravure coating method or a reverse coating method, a bar coating method such as a wire bar method, a die coating method, a spray coating method, and an air knife. A conventionally known method such as a coating method can be used.

The resin sheet molded into the release film of the present invention is one in which 30% by mass or more of the components constituting the resin sheet is composed of organic components, and 70% by mass or more of inorganic substances such as ceramic green sheets are included. things do not apply. Although the organic component is not particularly limited, resins such as epoxy-based resins, polyester-based resins, urethane-based resins, fluorine-based resins, acrylic-based resins, and cross-linked structures containing cross-linking agents such as isocyanate and melamine. I do not care. In addition to the organic component, any component such as inorganic particles and additives may be included as long as the above range is satisfied.

The use of the release film of the present invention is not particularly limited, and it can be used as long as it is used for molding a resin sheet. Examples of resin sheets include urethane sheets, polymer electrolyte membranes, adhesive sheets, and cycloolefin films.

The molding method of the resin sheet to be molded into the release film of the present invention is not particularly limited, but it is preferable to mold the release film of the present invention by dissolving or dispersing the raw material in a solvent by an existing coating method.

EXAMPLES Next, the present invention will be described in detail using examples and comparative examples, but the present invention is of course not limited to the following examples. Moreover, the evaluation methods used in the present invention are as follows.

(Surface properties of release film)
These are values measured under the following conditions using a non-contact surface profile measurement system (VertScan R550H-M100). For the area surface average roughness (Sa) and the average length of the roughness curve element (RSm), the average value of five measurements was adopted, and for the maximum protrusion height (P), the maximum value of the five measurements was adopted.
(Measurement condition)
・Measurement mode: WAVE mode ・Objective lens: 50x ・0.5×Tube lens ・Measurement area: 187×139 μm (Sa, P measurement)
・Measurement length (Lr: reference length): 187 μm (RSm measurement)

(Particle dispersibility evaluation of slippery coating layer)
The value of the maximum protrusion height (P) measured above was judged according to the following criteria.
○: maximum projection height (P) is 0.2 μm or less ○△: maximum projection height (P) is greater than 0.2 μm and less than 0.3 μm △: maximum projection height (P) is 0.2 μm 3 μm or more

(Surface free energy)
Water (drop volume 1.8 μL) on the release surface of the release film using a contact angle meter (manufactured by Kyowa Interface Science Co., Ltd.: fully automatic contact angle meter DM-701) at 25 ° C. and 50% RH. , diiodomethane (appropriate amount 0.9 μL), and 1-bromonaphthalene (appropriate amount 0.9 μL) were prepared and their contact angles were measured. As the contact angle, the contact angle 10 seconds after dropping each liquid onto the release film was adopted. The contact angle data of water, diiodomethane, and ethylene glycol obtained by the above method are calculated from the "Kitazaki-Hata" theory to obtain the dispersion component γsd, the polar component γsp, and the hydrogen bond component γsh of the surface free energy of the release film, The sum of each component was taken as the surface free energy γs. This calculation was performed using the calculation software in this contact angle meter software (FAMAS).

(pinhole evaluation)
Using the following method, three types of resin sheets were prepared and evaluated.
(resin sheet (1))
A resin solution (1) was prepared by dissolving 0.5 parts by mass of a cyclic olefin resin (ARTON® G7810/manufactured by JSR, solid content 100% by mass) in 80 parts by mass of toluene and 20 parts by mass of tetrahydrofuran. An applicator is used on the release surface of the release film sample so that the resin sheet after drying has a thickness of 0.5 μm. After applying a load of 1 kg/cm ² for 10 minutes, the release film was peeled off to obtain a resin sheet (1).
(resin sheet (2))
10 parts by mass of ion exchange resin (20% Nafion (registered trademark) 20Dispersion Solution DE2021 CS type, manufactured by Wako Pure Chemical Industries, Ltd., solid content 20% by mass), 10 parts by mass of water, and 20 parts by mass of isopropyl alcohol are mixed to form a resin. Solution (2) was made. An applicator is used on the release surface of the release film sample so that the resin sheet after drying has a thickness of 0.5 μm. After applying a load of 1 kg/cm ² for 10 minutes, the release film was peeled off to obtain a resin sheet (2).
(resin sheet (3))
UV curable resin (urethane acrylate, product name: 8UX-015A, manufactured by Taisei Fine Chemical Co., Ltd., solid content 100% by mass) 20 parts by mass, methyl ethyl ketone 40 parts by mass, isopropyl alcohol 39 parts by mass, photoradical initiator (Irgacure (registered trademark) ) 907, manufactured by BASF) was mixed to prepare a resin solution (3). An applicator is used on the release surface of the release film sample so that the resin sheet after drying has a thickness of 1.0 ^μm . The surface of the resin sheet was superimposed on the surface of the easy-slip coating layer, and after applying a load of 1 kg/cm ² for 10 minutes, the release film was peeled off to obtain a resin sheet (3).

All three types of resin sheets obtained were evaluated by the following methods.
In the central region of the obtained resin sheet in the film width direction, an area of 25 cm ² was irradiated with light from the opposite side of the resin slurry-applied surface, and the state of occurrence of pinholes visible through light transmission was observed, and visually observed according to the following criteria. Judged.
◯: No pinholes, no particular problem with thickness variation Δ: No pinholes, but slight dents were observed. There is no particular problem with thickness variations.
×: Slightly generated pinholes and/or slightly conspicuous thickness variations XX: Slightly generated pinholes and slightly conspicuous thickness variations XXX: Many pinholes generated , and the thickness variation is large and conspicuous

(Preparation of polyethylene terephthalate pellets (PET (I)))
As the esterification reactor, a continuous esterification reactor comprising a three-stage complete mixing tank having a stirrer, a partial condenser, a raw material inlet and a product outlet was used. TPA (terephthalic acid) was adjusted to 2 tons/hour, EG (ethylene glycol) was adjusted to 2 mol per 1 mol of TPA, and antimony trioxide was adjusted to give an amount of Sb atoms of 160 ppm relative to the produced PET. It was continuously supplied to the first esterification reactor of the reaction apparatus and reacted at 255° C. for an average residence time of 4 hours under normal pressure. Next, the reaction product in the first esterification reaction can is continuously taken out of the system and supplied to the second esterification reaction can, and distilled from the first esterification reaction can into the second esterification reaction can. 8 mass % of EG is supplied to the produced PET, and further, an EG solution containing magnesium acetate tetrahydrate in an amount such that the Mg atom is 65 ppm relative to the produced PET, and an EG solution containing 40 ppm of P atom relative to the produced PET. An EG solution containing TMPA (trimethyl phosphate) in an amount corresponding to the above was added and reacted at 260° C. under normal pressure for an average residence time of 1 hour. Next, the reaction product in the second esterification reactor was continuously taken out of the system, supplied to the third esterification reactor, and subjected to 39 MPa (400 kg/cm ² ) using a high-pressure disperser (manufactured by Nippon Seiki Co., Ltd.). 0.2% by mass of porous colloidal silica having an average particle size of 0.9 μm, which has been subjected to dispersion treatment for an average of 5 passes at a pressure of , and 1% by mass of ammonium salt of polyacrylic acid per calcium carbonate. While adding 0.4% by mass of synthetic calcium carbonate with a diameter of 0.6 μm as a 10% EG slurry, the mixture was reacted at normal pressure at 260° C. for an average residence time of 0.5 hours. The esterification reaction product produced in the third esterification reaction vessel was continuously supplied to a three-stage continuous polycondensation reactor to carry out polycondensation, thereby sintering stainless steel fibers having a 95% cut diameter of 20 μm. After filtration with a filter, ultrafiltration was performed, the product was extruded into water, and after cooling, it was cut into chips to obtain PET chips having an intrinsic viscosity of 0.60 dl/g (hereinafter abbreviated as PET (I)). . The lubricant content in the PET chip was 0.6% by mass.

(Preparation of polyethylene terephthalate pellets (PET (II)))
On the other hand, in the production of the PET chips, PET chips having an intrinsic viscosity of 0.62 dl/g and containing no particles such as calcium carbonate and silica were obtained (hereinafter abbreviated as PET (II)).

(Production of laminated film Z)
After drying these PET chips, they were melted at 285° C. and melted at 290° C. by a separate melt extruder extruder to filter sintered stainless steel fibers with a 95% cut diameter of 15 μm and Two-stage filtration of sintered 15 μm stainless steel particles is performed and combined in the feed block to form PET (I) as the anti-release side layer and PET (II) as the release side layer. , extruded (casting) into a sheet at a speed of 45 m/min, electrostatically adhered on a casting drum at 30 ° C. by an electrostatic adhesion method, cooled, and unstretched with an intrinsic viscosity of 0.59 dl / g A polyethylene terephthalate sheet was obtained. The layer ratio was adjusted so that PET (I)/(II)=60%/40% by calculation of the discharge amount of each extruder. Then, the unstretched sheet was heated with an infrared heater and then stretched 3.5 times in the machine direction at a roll temperature of 80° C. due to the speed difference between the rolls. After that, it was led to a tenter and stretched 4.2 times in the transverse direction at 140°C. It was then heat treated at 210° C. in a heat setting zone. After that, a 2.3% relaxation treatment was applied in the transverse direction at 170° C. to obtain a biaxially oriented polyethylene terephthalate film Z with a thickness of 31 μm. Sa of the release surface side layer of the obtained film Z was 2 nm, and Sa of the anti-release surface side layer was 28 nm.

(Production of acrylic polyol A-1)
77 parts by mass of methyl methacrylate (MMA), 100 parts by mass of hydroxyethyl methacrylate (HEMA), and 33 parts by mass of methacrylic acid (MAA) were added to a four-necked flask equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen blowing tube. and 490 parts by mass of isopropyl alcohol (IPA) were charged, and the temperature inside the flask was raised to 80° C. while stirring. Stirring was performed for 3 hours while maintaining the inside of the flask at 80° C., and then 0.5 parts by mass of 2,2-azobis-2-methyl-N-2-hydroxyethylpropionamide was added to the flask. After purging with nitrogen while raising the temperature in the flask to 120° C., the mixture was stirred at 120° C. for 2 hours.
Subsequently, a pressure reduction operation of 1.5 kPa was performed at 120° C. to remove unreacted raw materials and solvent to obtain an acrylic polyol. The inside of the flask was returned to atmospheric pressure and cooled to room temperature, and 840 parts by mass of an IPA aqueous solution (water content: 50% by mass) was added and mixed. After that, using a dropping funnel while stirring, triethylamine is added, the acrylic polyol is neutralized until the pH of the solution is in the range of 5.5 to 7.5, and the solid content concentration is 20% by mass. (A-1) was obtained. Table 1 also shows the composition ratio, Tg, stretching suitability, and acid value of the acrylic polyol (A-1) measured by NMR.

(Production of acrylic polyols (A-2) to (A-12))
As shown in Table 1, the solid content concentration was 20 in the same manner as in the production of acrylic polyol 1 except that the amounts of MMA, St, SMA, HEMA, MAA, AA, IPA during preparation, and IPA aqueous solution during dilution were changed. % by mass of acrylic polyols (A-2) to (A-12) were obtained. Table 1 also shows the composition ratio, Tg, stretching suitability, and acid value of the acrylic polyols (A-2) to (A-12) measured by NMR. The composition ratios are MMA, St (styrene), and SMA (stearyl methacrylate), respectively, l-1, l-2, and l-3 (units), HEMA, m (units), MAA, and AA (acrylic acid). was expressed as n (unit).

(Polymerization of polyester resin B0-1)
In a stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser, 194.2 parts by weight dimethyl terephthalate, 184.5 parts by weight dimethyl isophthalate, 14.8 parts by weight dimethyl-5-sodium sulfoisophthalate, 185.1 parts by mass of ethylene glycol, 185.1 parts by mass of neopentyl glycol, and 0.2 parts by mass of tetra-n-butyl titanate were charged, and the transesterification reaction was carried out at a temperature of 160° C. to 220° C. over 4 hours. . Then, the temperature was raised to 255° C., the pressure of the reaction system was gradually reduced, and the reaction was allowed to proceed under a reduced pressure of 30 Pa for 1 hour and 30 minutes to obtain a copolymer polyester resin (B0-1). The obtained copolymer polyester resin (B0-1) was pale yellow and transparent. When the reduced viscosity of the copolymer polyester resin (B0-1) was measured, it was 0.60 dl/g. The glass transition temperature by DSC was 65°C.

(Production of polyester water dispersion B-1)
30 parts by mass of polyester resin (B0-1) and 15 parts by mass of ethylene glycol-n-butyl ether were placed in a reactor equipped with a stirrer, a thermometer and a reflux device, heated at 110° C. and stirred to dissolve the resin. After the resin was completely dissolved, 55 parts by mass of water was gradually added to the polyester solution with stirring. After the addition, the liquid was cooled to room temperature while stirring to prepare a milky white polyester water dispersion (B-1) having a solid content of 30% by mass.

(Polymerization of polyester resin B0-2)
In a stainless steel autoclave equipped with an agitator, thermometer, and partial reflux condenser, 163 parts by weight dimethyl terephthalate, 163 parts by weight dimethyl isophthalate, 169 parts by weight 1,4 butanediol, 324 parts by weight ethylene glycol, and 0.5 parts by mass of tetra-n-butyl titanate was charged, and the transesterification reaction was carried out from 160° C. to 220° C. over 4 hours.
Then, 14 parts by mass of fumaric acid and 203 parts by mass of sebacic acid were added, and the temperature was raised from 200° C. to 220° C. over 1 hour to carry out an esterification reaction. Next, the temperature was raised to 255° C., the pressure of the reaction system was gradually reduced, and the reaction was allowed to proceed under a reduced pressure of 29 Pa for 1 hour and 30 minutes to obtain a hydrophobic copolyester resin (B0-2). The resulting hydrophobic copolyester resin (B0-2) was pale yellow and transparent.

(Production of polyester water dispersion B-2)
Then, 60 parts by mass of this copolymer polyester resin (B0-2), 45 parts by mass of methyl ethyl ketone and 15 parts by mass of isopropyl alcohol were added to a reactor equipped with a stirrer, a thermometer, a reflux device, and a metered dropping device for producing a graft resin. The resin was dissolved by heating and stirring at 65°C. After the resin was completely dissolved, 24 parts by weight of maleic anhydride was added to the polyester solution.
Then, a solution obtained by dissolving 16 parts by mass of styrene and 1.5 parts by mass of azobisdimethylvaleronitrile in 19 parts by mass of methyl ethyl ketone was added dropwise to the polyester solution at 0.1 ml/min, and stirring was continued for 2 hours. After sampling for analysis from the reaction solution, 8 parts by mass of methanol was added. Then, 300 parts by mass of water and 24 parts by mass of triethylamine were added to the reaction solution and stirred for 1 hour.
Thereafter, the internal temperature of the reactor is raised to 100° C., and methyl ethyl ketone, isopropyl alcohol, and excess triethylamine are distilled off to obtain a pale yellow, transparent polyester-based resin having a solid content of 25% by mass and uniform water dispersibility. A polyester graft copolymer dispersion (B-2) was prepared. The glass transition temperature of the resulting polyester-based graft copolymer was 68°C.

(Production of Polyurethane Water Dispersion C-1)
43.75 parts by mass of 4,4-dicyclohexylmethane diisocyanate, 12.85 parts by mass of dimethylolbutanoic acid, 153.41 parts by mass of polyhexamethylene carbonate diol having a number average molecular weight of 2000, 0.03 parts by mass of dibutyltin dilaurate, and 84.00 parts by mass of acetone as a solvent were added, and the mixture was stirred for 3 hours at 75°C under a nitrogen atmosphere to react. It was confirmed that the liquid reached the predetermined amine equivalent weight. Next, after the temperature of this reaction liquid was lowered to 40° C., 8.77 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. Next, 450 g of water was added to a reaction vessel equipped with a homodisper capable of high-speed stirring, adjusted to 25° C., and while stirring and mixing at 2000 min ⁻¹ , the polyurethane prepolymer solution was added and dispersed in water. . After that, acetone and part of the water were removed under reduced pressure to prepare a water-soluble polyurethane resin solution C-1 having a solid content of 37% by mass. The glass transition temperature of the obtained polyurethane resin was -30°C.

(Production of oxazoline-based cross-linking agent D-1)
A flask equipped with a stirrer, a reflux condenser, a nitrogen inlet tube and a thermometer was charged with 460.6 parts of isopropyl alcohol and heated to 80° C. while nitrogen gas was slowly passed through. A previously prepared monomer mixture consisting of 126 parts of methyl methacrylate, 210 parts of 2-isopropenyl-2-oxazoline and 84 parts of methoxypolyethylene glycol acrylate, and 2,2'-azobis as a polymerization initiator were added thereto. (2-Methylbutyronitrile) ("ABN-E" manufactured by Nippon Hydrazine Kogyo Co., Ltd.) 21 parts of an initiator solution and 189 parts of isopropyl alcohol are added dropwise from a dropping funnel over 2 hours to react, and dropwise. After completion, the reaction was continued for 5 hours. Nitrogen gas was continuously flowed during the reaction to keep the temperature in the flask at 80±1°C. Thereafter, the reaction solution was cooled to obtain an oxazoline group-containing resin (D-1) having a solid concentration of 25%. The resulting resin (D-1) having oxazoline groups had an oxazoline group content of 4.3 mmol/g and a number average molecular weight of 20,000 as measured by GPC (gel permeation chromatography).

(Production of oxazoline-based cross-linking agent D-2)
Resin (D-2) having a solid content of 10% and having a different composition (oxazoline group weight and molecular weight) was obtained in the same manner as the synthesis of resin (D-1) having oxazoline groups. The resulting oxazoline group-containing resin (D-2) had an oxazoline group weight of 7.7 mmol/g and a number average molecular weight of 40,000 measured by GPC.

(Production of carbodiimide cross-linking agent E-1)
A flask equipped with a stirrer, a thermometer and a reflux condenser was charged with 168 parts by mass of hexamethylene diisocyanate and 220 parts by mass of polyethylene glycol monomethyl ether (M400, average molecular weight: 400), stirred at 120°C for 1 hour, and then stirred for 4 hours. 26 parts by mass of 4′-dicyclohexylmethane diisocyanate and 3.8 parts by mass of 3-methyl-1-phenyl-2-phosphorene-1-oxide as a carbodiimidation catalyst (2% by mass relative to the total isocyanate) were added, and the mixture was stirred under a nitrogen stream at 185°C. °C for an additional 5 hours. The infrared spectrum of the reaction solution was measured, and it was confirmed that absorption at wavelengths of 2200 to 2300 cm ^-1 had disappeared. After allowing to cool to 60° C., 567 parts by mass of ion-exchanged water was added to obtain a carbodiimide water-soluble resin (E-1) having a solid content of 40% by mass.

(Silica particles G-1)
Colloidal silica (manufactured by Nissan Chemical Industries, trade name MP2040, average particle size 200 nm, solid content concentration 40% by mass)

(Silica particles G-2)
Colloidal silica (manufactured by Nissan Chemical Industries, trade name Snowtex XL, average particle size 40 nm, solid content concentration 40% by mass)

(Silica particles G-3)
Colloidal silica (manufactured by Nissan Chemical Industries, trade name Snowtex ZL, average particle size 100 nm, solid content concentration 40% by mass)

(Silica particles G-4)
Colloidal silica (manufactured by Nissan Chemical Industries, trade name MP4540M, average particle size 450 nm, solid content concentration 40% by mass)

(Acrylic particles G-5)
Acrylic particle water dispersion (manufactured by Nippon Shokubai, trade name MX100W, average particle size 150
nm, solid content concentration 10% by mass)

(Release agent solution X-1)
100 parts by mass of UV curable silicone resin (UV9300 manufactured by Momentive, solid content concentration 100% by mass) and 1 part by mass of curing catalyst bis(alkylphenyl)iodonium hexafluoroantimonate were added to toluene/methyl ethyl ketone/heptane (=3:5: 2) Dilute with the solution to prepare a release agent solution having a solid content of 2% by mass.

(Release agent solution X-2)
Thermosetting aminoalkyd resin (Tesfine 314, manufactured by Hitachi Chemical Co., Ltd., solid content 60% by mass) 100 parts by mass and p-toluenesulfonic acid as a curing catalyst (Dryer 900, manufactured by Hitachi Chemical Co., Ltd., solid content 50% by mass)1. Two parts by mass of the solution were diluted with a toluene/methyl ethyl ketone/heptane (=3:5:2) solution to prepare a release agent solution with a solid content of 2% by mass.

(Release agent solution X-3)
Thermosetting aminoalkyd resin (Tesfine 305, manufactured by Hitachi Chemical Co., Ltd., solid content 50% by mass) 100 parts by mass and p-toluenesulfonic acid as a curing catalyst (Dryer 900, manufactured by Hitachi Chemical Co., Ltd., solid content 50% by mass)1. 0 part by mass was diluted with a toluene/methyl ethyl ketone/heptane (=3:5:2) solution to prepare a release agent solution with a solid content of 2% by mass.

(Release agent solution X-4)
A liquid obtained by thermally dissolving 10 parts by mass of a cycloolefin copolymer (TOPAS6017S manufactured by Polyplastics Co., Ltd., solid content 100% by mass) in 90 parts by mass of toluene was diluted with a toluene/tetrahydrofuran (= 8:2) solution to obtain a solid content of 2. A mass percent release agent solution was prepared.

(Back surface smoothing coating liquid Y)
94 parts by mass of dipentaerythritol hexaacrylate [solid content 100% by mass] as an active energy ray compound, and polydimethylsiloxane having a polyether-modified acryloyl group as polyorganosiloxane [manufactured by Big Chemie Japan Co., Ltd., trade name] "BYK-3500", solid content 100% by mass] 1 part by mass, and an α-aminoalkylphenone-based photopolymerization initiator [manufactured by BASF, trade name "IRGACURE907", 2-methyl-1 as a photopolymerization initiator [4-(Methylthio)phenyl]-2-morpholinopropan-1-one, solid content 100% by mass] 5 parts by mass, isopropyl alcohol / methyl ethyl ketone mixed solvent (mass ratio 3/1) to dilute the solid content A 20% by weight back-smoothing coat layer-forming material was obtained.

(Example 1)
(Adjustment of slippery coating liquid 1)
A smooth coating liquid 1 having the following composition was prepared.
(Smooth coating liquid 1)
Water 48.33 parts by mass Isopropyl alcohol 35.00 parts by mass Polyester water dispersion B-1 (solid content concentration 30% by mass) 15.78 parts by mass Silica particles G-1 0.59 parts by mass (average particle size 200 nm, solid concentration 40% by mass)
Surfactant (fluorine-based, solid content concentration 10% by mass) 0.30 parts by mass

(Manufacturing of polyester film)
As a film raw material polymer, PET resin pellets (PET (II)) having an intrinsic viscosity (solvent: phenol/tetrachloroethane = 60/40) of 0.62 dl / g and containing substantially no particles (PET (II)) It was dried at 135° C. for 6 hours under reduced pressure. After that, it was supplied to an extruder, melt-extruded into a sheet at about 280° C., and rapidly cooled and solidified on a rotating cooling metal roll whose surface temperature was maintained at 20° C. to obtain an unstretched PET sheet.

This unstretched PET sheet was heated to 100° C. by a heated roll group and an infrared heater, and then stretched 3.5 times in the longitudinal direction by a roll group with a peripheral speed difference to obtain a uniaxially stretched PET film.

Next, after applying the smooth coating liquid to one side of the PET film with a bar coater, it was dried at 80° C. for 15 seconds. The coating amount after the final stretching and drying was adjusted to 0.1 μm. Subsequently, the film was stretched 4.0 times in the width direction at 150°C with a tenter, heated at 230°C for 0.5 seconds while fixing the length of the film in the width direction, and further heated at 230°C for 10 seconds 3. % in the width direction to obtain an in-line coated polyester film with a thickness of 31 μm.

(Formation of release coating layer)
On the surface of the in-line coated polyester film obtained above, opposite to the easy-slip coating layer laminated surface, the release agent solution X-1 was applied with a reverse gravure coater so that the thickness after drying was 0.1 μm, Next, after drying with hot air at 90° C. for 30 seconds, the resin sheet was immediately irradiated with ultraviolet rays (300 mJ/cm ² ) using an electrodeless lamp (H bulb manufactured by Fusion Co., Ltd.) to form a release coating layer and release for resin sheet production. A mold film was obtained. It should be noted that there were no particular problems with regard to winding properties, process passability, and handling properties, and the results were excellent.

(Example 2)
A polyester film was obtained in the same manner as in Example 1, except that the easy-slipping coating liquid 1 was changed to the following easy-slipping coating liquid 2.
(Smooth coating liquid 2)
Water 45.18 parts by mass Isopropyl alcohol 35.00 parts by mass Polyester water dispersion B-2 (solid content concentration 25% by mass) 18.93 parts by mass Silica particles G-1 0.59 parts by mass (average particle size 200 nm, solid concentration 40% by mass)
Surfactant (fluorine-based, solid content concentration 10% by mass) 0.30 parts by mass

(Example 3)
A polyester film was obtained in the same manner as in Example 1, except that the easy-slipping coating liquid 1 was changed to the following easy-slipping coating liquid 3.
(Smooth coating liquid 3)
Water 51.32 parts by mass Isopropyl alcohol 35.00 parts by mass Polyurethane resin aqueous dispersion C-1 (solid content concentration 37% by mass) 12.79 parts by mass Silica particles G-1 0.59 parts by mass (average particle diameter 200 nm, Solid content concentration 40% by mass)
Surfactant (fluorine-based, solid content concentration 10% by mass) 0.30 parts by mass

(Example 4)
A polyester film was obtained in the same manner as in Example 1, except that the slippery coating liquid 1 was changed to the slippery coating liquid 4 below.
(Smooth coating liquid 4)
Water 41.86 parts by mass Isopropyl alcohol 35.00 parts by mass Acrylic polyol resin A-1 (solid content concentration 20 mass%) 16.57 parts by mass Oxazoline-based cross-linking agent D-1 (solid content concentration 25 mass%) 5.68 Parts by mass Silica particles G-1 0.59 parts by mass (average particle size 200 nm, solid content concentration 40% by mass)
Surfactant H-1 (fluorine-based, solid content concentration 10% by mass) 0.30 parts by mass

(Example 5)
The same as in Example 4 except that the easy-slipping coating liquid 5 in which the cross-linking agent in the easy-slipping coating liquid 4 used in Example 4 was changed to carbodiimide-based cross-linking agent E-1 (solid content concentration 40% by mass) was used. to obtain a polyester film.
(Smooth coating liquid 5)
Water 43.99 parts by mass Isopropyl alcohol 35.00 parts by mass Acrylic polyol resin A-1 (solid content concentration 20 mass%) 16.57 parts by mass Carbodiimide-based cross-linking agent E-1 (solid content concentration 40 mass%) 3.55 Parts by mass Silica particles G-1 0.59 parts by mass (average particle size 200 nm, solid content concentration 40% by mass)
Surfactant H-1 (fluorine-based, solid content concentration 10% by mass) 0.30 parts by mass

(Example 6)
The same as in Example 4 except that the easy-slipping coating liquid 6 in which the cross-linking agent in the easy-slipping coating liquid 4 used in Example 4 was changed to oxazoline-based cross-linking agent D-2 (solid content concentration 10% by mass) was used. to obtain a polyester film.
(Smooth coating liquid 6)
Water 33.34 parts by mass Isopropyl alcohol 35.00 parts by mass Acrylic polyol resin A-1 (solid content concentration 20 mass%) 16.57 parts by mass Oxazoline-based cross-linking agent D-2 (solid content concentration 10 mass%) 14.20 Parts by mass Silica particles G-1 0.59 parts by mass (average particle size 200 nm, solid content concentration 40% by mass)
Surfactant H-1 (fluorine-based, solid content concentration 10% by mass) 0.30 parts by mass

(Example 7)
A polyester film was obtained in the same manner as in Example 4, except that the easy-slipping coating liquid 4 was changed to the following easy-slipping coating liquid 7.
(Smooth coating liquid 7)
Water 43.28 parts by mass Isopropyl alcohol 35.00 parts by mass Acrylic polyol resin A-1 (solid content concentration 20 mass%) 9.47 parts by mass Oxazoline-based cross-linking agent D-1 (solid content concentration 25 mass%) 11.36 Parts by mass Silica particles G-1 0.59 parts by mass (average particle size 200 nm, solid content concentration 40% by mass)
Surfactant H-1 (fluorine-based, solid content concentration 10% by mass) 0.30 parts by mass

(Example 8)
A polyester film was obtained in the same manner as in Example 4, except that the easy-slipping coating liquid 4 was changed to the following easy-slipping coating liquid 8.
(Smooth coating liquid 8)
Water 41.15 parts by mass Isopropyl alcohol 35.00 parts by mass Acrylic polyol resin A-1 (solid content concentration 20 mass%) 20.12 parts by mass Oxazoline-based cross-linking agent D-1 (solid content concentration 25 mass%) 2.84 Parts by mass Silica particles G-1 0.59 parts by mass (average particle size 200 nm, solid content concentration 40% by mass)
Surfactant H-1 (fluorine-based, solid content concentration 10% by mass) 0.30 parts by mass

(Example 9)
Example 4 except that the acrylic polyol A-1 (solid content concentration 20% by mass) in the slippery coating liquid 4 used in Example 4 was changed to acrylic polyol A-2 (solid content concentration 20% by mass). A polyester film was obtained in the same manner.

(Example 10)
Example 4 except that the acrylic polyol A-1 (solid content concentration 20% by mass) in the slippery coating liquid 4 used in Example 4 was changed to acrylic polyol A-3 (solid content concentration 20% by mass). A polyester film was obtained in the same manner.

(Example 11)
Example 4 except that the acrylic polyol A-1 (solid content concentration 20% by mass) in the slippery coating liquid 4 used in Example 4 was changed to acrylic polyol A-4 (solid content concentration 20% by mass). A polyester film was obtained in the same manner.

(Example 12)
Example 4 except that the acrylic polyol A-1 (solid content concentration 20% by mass) in the slippery coating liquid 4 used in Example 4 was changed to acrylic polyol A-5 (solid content concentration 20% by mass). A polyester film was obtained in the same manner.

(Example 13)
Example 4 except that the acrylic polyol A-1 (solid content concentration 20% by mass) in the slippery coating liquid 4 used in Example 4 was changed to acrylic polyol A-6 (solid content concentration 20% by mass). A polyester film was obtained in the same manner.

(Example 14)
Example 4 except that the acrylic polyol A-1 (solid content concentration 20% by mass) in the slippery coating liquid 4 used in Example 4 was changed to acrylic polyol A-7 (solid content concentration 20% by mass). A polyester film was obtained in the same manner.

(Example 15)
Example 4 except that the acrylic polyol A-1 (solid content concentration 20% by mass) in the slippery coating liquid 4 used in Example 4 was changed to acrylic polyol A-8 (solid content concentration 20% by mass). A polyester film was obtained in the same manner.

(Example 16)
Example 4 except that the acrylic polyol A-1 (solid content concentration 20% by mass) in the slippery coating liquid 4 used in Example 4 was changed to acrylic polyol A-9 (solid content concentration 20% by mass). A polyester film was obtained in the same manner.

(Example 17)
Example 4 except that the acrylic polyol A-1 (solid content concentration 20% by mass) in the slippery coating liquid 4 used in Example 4 was changed to acrylic polyol A-10 (solid content concentration 20% by mass). A polyester film was obtained in the same manner.

(Example 18)
Example 4 except that the acrylic polyol A-1 (solid content concentration 20% by mass) in the slippery coating liquid 4 used in Example 4 was changed to acrylic polyol A-11 (solid content concentration 20% by mass). A polyester film was obtained in the same manner.

(Example 19)
Example 4 except that the acrylic polyol A-1 (solid content concentration 20% by mass) in the slippery coating liquid 4 used in Example 4 was changed to acrylic polyol A-12 (solid content concentration 20% by mass). A polyester film was obtained in the same manner.

(Example 20)
A polyester film was obtained in the same manner as in Example 1, except that the slippery coating liquid 4 was changed to the slippery coating liquid 20 below.
(Smooth coating liquid 20)
Water 41.74 parts by mass Isopropyl alcohol 35.00 parts by mass Acrylic polyol resin A-10 (solid content concentration 20 mass%) 16.57 parts by mass Oxazoline-based cross-linking agent D-1 (solid content concentration 25 mass%) 5.68 Parts by mass Silica particles G-1 0.59 parts by mass (average particle size 200 nm, solid content concentration 40% by mass)
Silica particles G-4 0.12 parts by mass (average particle size 450 nm, solid content concentration 40% by mass)
Surfactant H-1 (fluorine-based, solid content concentration 10% by mass) 0.30 parts by mass

(Example 21)
A polyester film was obtained in the same manner as in Example 4, except that the slippery coating liquid 4 was changed to the slippery coating liquid 21 below.
(Smooth coating liquid 21)
Water 41.15 parts by mass Isopropyl alcohol 35.00 parts by mass Acrylic polyol resin A-10 (solid content concentration 20 mass%) 16.57 parts by mass Oxazoline-based cross-linking agent D-1 (solid content concentration 25 mass%) 5.68 Parts by mass Silica particles G-2 1.18 parts by mass (average particle size 40 nm, solid content concentration 40% by mass)
Silica particles G-4 0.12 parts by mass (average particle size 450 nm, solid content concentration 40% by mass)
Surfactant H-1 (fluorine-based, solid content concentration 10% by mass) 0.30 parts by mass

(Example 22)
A polyester film was obtained in the same manner as in Example 4, except that easy-slipping coating liquid 4 was changed to easy-slipping coating liquid 22 below.
(Smooth coating liquid 22)
Water 41.27 parts by mass Isopropyl alcohol 35.00 parts by mass Acrylic polyol resin A-10 (solid content concentration 20% by mass) 16.57 parts by mass Oxazoline-based cross-linking agent D-1 (solid content concentration 25% by mass) 5.68 Parts by mass Silica particles G-3 1.18 parts by mass (average particle size 100 nm, solid content concentration 40% by mass)
Surfactant H-1 (fluorine-based, solid content concentration 10% by mass) 0.30 parts by mass

(Example 23)
A polyester film was obtained in the same manner as in Example 4, except that easy-slipping coating liquid 4 was changed to easy-slipping coating liquid 23 below.
(Smooth coating liquid 23)
Water 40.09 parts by mass Isopropyl alcohol 35.00 parts by mass Acrylic polyol resin A-10 (solid content concentration 20 mass%) 16.57 parts by mass Oxazoline-based cross-linking agent D-1 (solid content concentration 25 mass%) 5.68 Part by mass Acrylic particles G-5 2.37 parts by mass (average particle size 150 nm, solid content concentration 10% by mass)
Surfactant H-1 (fluorine-based, solid content concentration 10% by mass) 0.30 parts by mass

(Example 24)
A polyester film was obtained in the same manner as in Example 17, except that the release coating layer was formed as follows.
(Formation of release coating layer)
Release agent solution X-2 was applied to the inline-coated polyester film obtained above on the surface opposite to the easy-slip coating layer laminated surface with a reverse gravure coater so that the thickness after drying was 0.1 μm, and then. , and dried with hot air at 130°C for 30 seconds to form a release coating layer to obtain a polyester film.

(Example 25)
A polyester film was obtained in the same manner as in Example 24, except that the release coating layer was changed to X-3.

(Example 26)
A polyester film was obtained in the same manner as in Example 24, except that the release coating layer was changed to X-4.

(Comparative example 1)
As the film forming the release coating layer, instead of the in-line coating film having an easy-slip coating layer on one surface prepared in Example 1, E5000-25 μm (manufactured by Toyobo) was used. A polyester film was obtained in the same manner as in Example 1. E5000 contained particles inside the film, and Sa on both surfaces was 0.031 μm.

(Comparative example 2)
A polyester film was obtained in the same manner as in Comparative Example 1, except that the coating thickness of the release layer was changed to 1.0 μm.

(Comparative Example 3)
As the film forming the release coating layer, the same as in Example 1 except that the laminated film Z was used instead of the in-line coating film having a slippery coating layer on one surface prepared in Example 1. A polyester film was obtained by the method of A release coating layer was provided on the surface of the laminate film Z on which the PET (II) pellets were ejected (the layer containing no particles).

(Comparative Example 4)
The surface of the polyester film obtained in Comparative Example 3 opposite to the surface on which the release coating layer was formed was coated with the back smoothing coating liquid Y with a reverse gravure coater so that the thickness after drying was 0.5 μm, Next, after drying with hot air at 90° C. for 30 seconds, it was immediately irradiated with ultraviolet rays (300 mJ/cm ² ) with an electrodeless lamp (H bulb manufactured by Fusion Co., Ltd.) to form a back smoothing layer and obtain a polyester film. rice field.

(Comparative Example 5)
A polyester film was obtained in the same manner as in Comparative Example 4, except that the back surface smoothing layer was coated so as to have a thickness of 0.7 μm.

(Comparative Example 6)
A polyester film was obtained in the same manner as in Comparative Example 4, except that the back surface smoothing layer was coated so as to have a thickness of 1.0 μm.

Table 2 shows the evaluation results of each example and comparative example.

In Examples 1 to 26, all the parameters of Sa, P, and RSm on the surface of the slippery coating layer were within appropriate ranges, so that resin sheets without pinholes could be obtained. In Comparative Examples 1 to 3, since all the parameters of Sa, P and RSm of the slippery surface are large, pinholes were observed. In Comparative Examples 4 to 6, by filling the unevenness of the slippery surface with a smoothing layer, Sa and P can be kept within appropriate ranges, but since RSm is large, it is not possible to suppress the occurrence of pinholes. was enough. A large RSm means that the distance between projections is wide and the number of projections per unit area is small, and it is considered that the pressure applied to each projection increased and the pinhole occurred.

According to the present invention, when producing a resin sheet that is thin and requires high smoothness, it is possible to provide a release film for resin sheet production that has high smoothness by preventing pinholes and partial thickness variations. It becomes possible.

Claims (3)

The base film does not substantially contain inorganic particles, and has a release coating layer on one surface of the base film,
Having a smooth coating layer containing particles on the other surface of the base film,
The area surface average roughness (Sa) of the easy-smooth coating layer is 1 nm or more and 25 nm or less,
The maximum protrusion height (P) is 60 nm or more and 500 nm or less, and the average length (RSm) of the roughness curve element is 10 μm or less,
The smooth coating layer contains particles with a particle diameter of 150 nm or more and 600 nm or less.
Release film for resin sheet molding. 2. The release film for resin sheet molding according to claim 1, wherein the release coating layer has an average area surface roughness (Sa) of 5 nm or less and a maximum protrusion height (P) of 200 nm or less. The release film for resin sheet molding according to claim 1, wherein the release coating layer has a surface free energy of 15 mJ/ ^m2 or more and 45 mJ/ ^m2 or less.