Laminated film

Abstract

To provide a laminated film useful as a film for various processes and excellent in releasability.SOLUTION: A laminated film having a release layer on at least one surface of a polyester film, wherein the release layer has a C7H11 + content at a sputtering time of 0 to 10 seconds of 5.6% or more with respect to the C7H11 + content of the entire release layer in the depth direction, as calculated from the C7H11 + fragment ion intensity in the depth direction of the release layer measured using a time-of-flight secondary ion mass spectrometer (TOF-SIMS).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a laminated film. [Background technology]

[0002] Polyester films, such as polyethylene terephthalate and polyethylene naphthalate, are used in a variety of applications because they have excellent mechanical strength, dimensional stability, flatness, heat resistance, chemical resistance, optical properties, and cost performance. One example is a release film, which is used as a process film in various manufacturing processes, such as for transfer during molding, for manufacturing flexible printed wiring boards, and as a process paper for manufacturing plastic sheets.

[0003] When a polyester film is used as a release film, a method of laminating a release coating film on the surface of the polyester film has been proposed in order to obtain releasability against various resins and adhesives. For example, Patent Document 1 discloses a release film having a coating layer formed on at least one surface of a polyester film from a coating liquid containing a release agent and an active methylene-blocked isocyanate compound.

[0004] Patent Document 2 also discloses a method for producing a surface protective film for a transparent conductive substrate, which comprises a coating step of coating, onto one surface of a substrate made of a polyester film, a pressure-sensitive adhesive composition containing a (meth)acrylic acid ester copolymer and a crosslinking agent, wherein the polymer having a molecular weight of 100,000 or less accounts for 5% by mass or less of the total, the unreacted monomer accounts for 0.5 to 10% by mass of the charged monomers, and the glass transition temperature is −30° C. or less; and a heat treatment step of removing the unreacted monomer. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-151481 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-193702 Summary of the Invention [Problem to be solved by the invention]

[0006] The release film disclosed in Patent Document 1 is said to be able to reduce deterioration of releasability due to heat during processing. However, there is still room for improvement in reducing changes in the releasability of the film when heat or pressure is applied.

[0007] The surface protective film disclosed in Patent Document 2 is described as having an adhesive layer that can suppress the transfer of oligomers from the base material of the protective film to the transparent conductive substrate even when the transparent conductive substrate to which the protective film is attached is subjected to heat treatment, but no consideration is given to improving the peelability of the protective film.

[0008] The problem to be solved by the present invention is to provide a laminated film having excellent releasability, which is useful as a film for various processes under the above circumstances. [Means for solving the problem]

[0009] After extensive research, the inventors discovered that by concentrating the long-chain alkyl group portion on the surface of the release layer, the release component can function effectively and excellent release properties can be achieved, thereby completing the present invention. That is, according to the present invention, the following [1] to [6] are provided.

[0010] [1] A laminated film having a release layer on at least one side of a polyester film, wherein the release layer has a C7H 11 + The C7H of the entire depth direction of the release layer calculated from the fragment ion intensity 11 + C7H content at sputtering times of 0 to 10 seconds11 + A laminated film having a content of 5.6% or more. [2] The laminated film according to [1] above, wherein the release layer is formed from a composition for forming a release layer, which contains a compound having a long-chain alkyl group having 9 or more carbon atoms. [3] The laminated film according to [2] above, wherein the compound having a long-chain alkyl group has, as a copolymerization component, a (meth)acrylic acid ester containing an alkyl group having 9 or more carbon atoms. [4] The laminated film according to the above [2] or [3], wherein the acid value of the compound having a long-chain alkyl group is 100 mgKOH / g or more. [5] The laminated film according to any one of the above [1] to [4], wherein the composition for forming a release layer further contains a crosslinking agent. [6] The laminated film according to any one of the above [1] to [5], wherein the peel strength of the release layer with respect to an adhesive tape (manufactured by Nitto Denko Corporation, "No. 31B") is 100 mN / cm or less. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a laminated film having excellent releasability, which is useful as a film for various processes. DETAILED DESCRIPTION OF THE INVENTION

[0012] <<Laminated film>> The laminated film of the present invention has a release layer on at least one side of the polyester film. The release layer has a C7H ion concentration in the depth direction of the release layer measured using a time-of-flight secondary ion mass spectrometer (TOF-SIMS). 11 + The C7H of the entire depth direction of the release layer calculated from the fragment ion intensity 11 + C7H content at sputtering times of 0 to 10 seconds 11 + The content is 5.6% or more.

[0013] Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is a method of irradiating a solid sample with an ion beam (primary ions) and mass-separating the ions (secondary ions) emitted from the surface by utilizing the difference in their flight times (flight time is proportional to the square root of weight). TOF-SIMS can obtain information on elements and molecular species present at a depth of 1 nm or less from the sample surface with high detection sensitivity. On the other hand, to detect information about elements and molecular species present at depths of more than 1 nm, measurements can be made by combining sputtering. The spectral information obtained by alternately repeating sputtering and TOF-SIMS measurements can detect information about elements and molecular species present at depths of more than 1 nm.

[0014] In addition, "C7H at sputtering times of 0 to 10 seconds" 11 + The "content" is the C7H detected during the sputtering time of 0 to 10 seconds. 11 + The sum of the fragment ion intensities is referred to as "C7H 11 + The "content" is the amount of CH detected between sputtering time 0 and the end of measurement. 11 + It refers to the sum of fragment ion intensities. Also, "at the end of measurement" refers to the time when C7H4O is detected as a secondary ion derived from the polyester film substrate. + This refers to the point at which the fragment ion intensity becomes constant.

[0015] In addition, C7H at sputtering times of 0 to 10 seconds 11 + The content can be measured and calculated by the method described in the examples below.

[0016] C7H 11 +The fragment ions are detected as secondary ions derived from the long-chain alkyl groups contained in the release agent in the release layer. Therefore, the higher the content, the more the long-chain alkyl group portion of the release agent is unevenly distributed on the surface of the release layer. On the other hand, the lower the content, the more the long-chain alkyl group portion of the release agent is dispersed throughout the release layer. 11 + By making the content of 5.6% or more, the long-chain alkyl group portion of the release agent is unevenly distributed on the surface of the release layer, and excellent releasability can be exhibited. C7H for sputtering times of 0 to 10 seconds 11 + The content is preferably 6.0% or more, more preferably 6.5% or more, even more preferably 7.0% or more, even more preferably 7.5% or more, even more preferably 8.0% or more, even more preferably 9.0% or more, and particularly preferably 10.0% or more.

[0017] The laminated structure of the laminated film of the present invention may be a structure in which a release layer is provided on one side of the polyester film and the surface of the polyester film is left as is on the other side, or a structure in which another layer is formed on the other side. The polyester film may have a release layer on both sides thereof. Furthermore, another layer may be provided between the polyester film and the release layer, and the release layer is preferably on at least one outermost surface of the polyester film. Preferably, the laminated film of the present invention has a laminated structure in which a release layer is provided adjacent to the polyester film on at least one side of the polyester film.

[0018] The polyester film and the release layer constituting the laminated film of the present invention will be described in detail below.

[0019] <Polyester film> The polyester film constituting the laminated film of the present invention may have a single layer structure or a multi-layer structure of two or more layers, and the number of layers is not particularly limited. The polyester film may be a non-stretched film (sheet) or a stretched film, preferably a uniaxially or biaxially stretched film, and more preferably a biaxially stretched film from the viewpoints of balance of mechanical properties, flatness, and thinning.

[0020] The polyester used as the raw material for the polyester film may be a homopolyester or a copolymer polyester. In the case of a homopolyester, it is preferably one obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. Examples of aromatic dicarboxylic acids include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of aliphatic glycols include ethylene glycol, diethylene glycol, 1,4-cyclohexanedimethanol, etc. A typical example of a homopolyester is polyethylene terephthalate. On the other hand, examples of the dicarboxylic acid component of the copolymer polyester 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 glycol component include one or more selected from ethylene glycol, diethylene glycol, propylene glycol, butanediol, 4-cyclohexanedimethanol, and neopentyl glycol.

[0021] As the polyester polymerization catalyst, a conventionally known compound known as a polyester polymerization catalyst can be used, and examples thereof include antimony compounds, titanium compounds, germanium compounds, manganese compounds, aluminum compounds, magnesium compounds, and calcium compounds.

[0022] In order to suppress the amount of oligomer components deposited on the film surface, the film may be produced using a polyester having a low content of oligomer components as the raw material. As a method for producing a polyester having a low content of oligomer components, various known methods can be used, such as a method of solid-phase polymerization after polyester production. The amount of oligomer component precipitation may be suppressed by using a polyester film having three or more layers and using a polyester raw material with a low content of oligomer components as the outermost layer of the polyester film. The polyester may also be obtained by carrying out the esterification or transesterification reaction, followed by melt polycondensation at a higher reaction temperature under reduced pressure.

[0023] The polyester film may contain an ultraviolet absorber to improve the weather resistance of the film and to prevent deterioration of the adherend or the like. The ultraviolet absorber may be an organic ultraviolet absorber or an inorganic ultraviolet absorber, with organic ultraviolet absorbers being preferred from the viewpoint of transparency of the polyester film. Examples of organic ultraviolet absorbers include cyclic iminoesters, benzotriazoles, and benzophenones. From the viewpoint of durability and heat resistance, for example, the ability to withstand heat applied in the polyester film manufacturing process, cyclic iminoesters and benzotriazoles are more preferred. These ultraviolet absorbents may be used alone or in combination of two or more.

[0024] Particles may be blended into the polyester film mainly for the purposes of imparting lubricity and preventing scratches during each step in the production of the polyester film. The type of particles to be blended is not particularly limited as long as they are particles that can impart lubricity, and examples thereof include inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, aluminum oxide, and titanium oxide; and organic particles such as acrylic resin, styrene resin, urea resin, phenolic resin, epoxy resin, and benzoguanamine resin. Furthermore, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester production process can also be used.

[0025] There is no particular limitation on the shape of the particles used, and any of spherical, blocky, rod-like, flat, etc. may be used. There are also no particular limitations on the hardness, specific gravity, color, etc. Two or more types of these particles may be used in combination as needed.

[0026] The average particle size of the particles is preferably 5 μm or less. When the average particle size is 5 μm or less, the surface roughness of the polyester film can be made appropriate, and for example, when the laminated film of the present invention is used as a transfer sheet, it is preferable because it does not affect the surface shape of the transfer molding surface. From the viewpoint of the surface roughness of the film and the aforementioned imparting of easy slippage, the particle size is more preferably in the range of 0.1 to 3 μm.

[0027] Furthermore, the content of particles in the polyester film is preferably 5% by mass or less. When the content of particles is 5% by mass or less, the transparency of the polyester film can be improved. From the viewpoints of the transparency of the polyester film and imparting the aforementioned easy slip property, the content of particles is more preferably in the range of 0.0003 to 3% by mass. When particles are contained, for example, it is preferable to form a multilayer polyester film having a surface layer and an intermediate layer, and to contain particles in the surface layer. In this case, it is more preferable to form a multilayer structure having a particle-containing surface layer, an intermediate layer, and another particle-containing surface layer in this order.

[0028] The method for adding particles to a polyester film is not particularly limited, and any conventionally known method can be used. For example, in the case of a multi-layer polyester film, the particles can be added at any stage in the production of the polyester constituting each layer, and it is preferable to add the particles after the completion of the esterification or transesterification reaction.

[0029] In addition to the above-mentioned particles, conventionally known antioxidants, antistatic agents, heat stabilizers, lubricants, dyes, pigments, etc. may be added to the polyester film as needed.

[0030] The thickness of the polyester film is not particularly limited as long as it is within a range that allows it to be formed into a film, but from the viewpoints of mechanical strength, handleability, productivity, etc., it is usually in the range of 5 to 350 μm, preferably 25 to 250 μm, and more preferably 38 to 125 μm.

[0031] An example of a method for producing a polyester film will be specifically described below, but the method is not limited to the following description. For example, when producing a biaxially stretched film, dried polyester pellets described above are extruded from a die using an extruder to form a molten sheet, and then rapidly cooled and solidified on a rotating cooling drum to a temperature below the glass transition temperature to obtain an unstretched sheet. In this case, in order to improve the flatness of the unstretched sheet, it is preferable to increase the adhesion between the molten sheet and the rotating cooling drum, and an electrostatic application adhesion method and / or a liquid application adhesion method are preferably used. The unstretched sheet is then stretched in one direction using a roll or tenter type stretching machine at a stretching temperature of usually 70 to 120°C, preferably 80 to 110°C, and at a stretching ratio of usually 2.5 to 7 times, preferably 3.0 to 6 times. Next, the film is stretched in a direction perpendicular to the first-stage stretching direction, usually at 70 to 170°C, and at a stretching ratio of usually 3.0 to 7 times, preferably 3.5 to 6 times. Then, the film is subsequently heat-treated at a temperature of 180 to 270° C. under tension or under relaxation of 30% or less to obtain a biaxially stretched film. In the above stretching, a method of stretching in one direction in two or more stages can be adopted, in which case it is preferable to perform the stretching so that the final stretching ratios in both directions are each within the above ranges.

[0032] In addition, simultaneous biaxial stretching may be employed when producing a biaxially stretched polyester film. The simultaneous biaxial stretching method is a method in which the unstretched sheet is simultaneously stretched in the machine direction and the width direction under temperature control, usually at 70 to 120°C, preferably 80 to 110°C, and the stretching ratio is 4 to 50 times, preferably 7 to 35 times, and more preferably 10 to 25 times in terms of area ratio. Subsequently, the film is heat-treated under tension or relaxation of 30% or less at a temperature of 170 to 270°C to obtain a biaxially stretched film. As for the simultaneous biaxial stretching device, a conventionally known stretching method such as a screw method, a pantograph method, or a linear drive method can be used.

[0033] <Release layer> The laminated film of the present invention has a release layer on at least one surface of the polyester film. The release layer is formed from a composition for forming a release layer containing a release agent, and the release agent is preferably a compound having a long-chain alkyl group, specifically a compound containing a long-chain alkyl group, or a wax as a main component. These release agents may be used alone or in combination. When the release agent contains a long-chain alkyl group, not only does it have good compatibility with the components other than the release agent in the composition for forming a release layer, but it can also exhibit good releasability even in a small amount. The term "main component" used herein means the component that is contained in the largest proportion in the release agent. In addition to the long-chain alkyl group-containing compound and wax, a conventionally known mold release agent, such as a fluorine compound or a silicone compound, may be used in combination.

[0034] As described above, the release layer of the laminated film of the present invention has a C7H 11 + C7H content at sputtering times of 0 to 10 seconds 11 + The content is 5.6% or more. 11 + By setting the content to 5.6% or more, excellent releasability can be obtained as described above.

[0035] C7H for sputtering times of 0 to 10 seconds 11 + Methods for increasing the content to 5.6% or more include a method of increasing the molecular weight of the compounds in the release layer-forming composition that forms the release layer, such as alkyl group-containing compounds having 9 or more carbon atoms as release agents, waxes, and binders described below, a method of crosslinking the compounds with a crosslinking agent, and a method of increasing the acid value of the release agent.

[0036] The thickness of the release layer is preferably 0.003 to 1 μm. If it is 0.003 μm or more, the function of the release layer can be fully exhibited, and if it is 1 μm or less, the appearance and transparency will be good. The thickness of the release layer is more preferably in the range of 0.005 to 0.5 μm, and even more preferably in the range of 0.01 to 0.2 μm.

[0037] (Compounds with long-chain alkyl groups) The compound having a long-chain alkyl group as a release agent refers to a compound having a linear or branched alkyl group having 4 or more carbon atoms. The alkyl group preferably has 9 or more carbon atoms, more preferably 12 or more carbon atoms, even more preferably 15 or more carbon atoms, and particularly preferably 18 or more carbon atoms. By making the number of carbon atoms in the alkyl group 4 or more, it is possible to impart releasability to the release layer of the laminated film of the present invention, and by making it 9 or more, the releasability becomes even better. There is no particular restriction on the upper limit of the number of carbon atoms in the alkyl group, but it is usually about 30, and 25 or less is preferred from the viewpoint of solubility in a solvent contained in a coating liquid, which is a preferred form of the composition for forming a release layer, which will be described later. Examples of linear or branched alkyl groups having 4 or more carbon atoms include n-butyl, isobutyl, sec-butyl, t-butyl, pentyl, neopentyl, isoamyl, hexyl, heptyl, 2-ethylhexyl, octyl, isooctyl, nonyl, isononyl, decyl, isodecyl, undecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, stearyl, isostearyl, and behenyl groups. Examples of compounds having a long-chain alkyl group include various long-chain alkyl group-containing polymer compounds, long-chain alkyl group-containing amine compounds, long-chain alkyl group-containing ether compounds, long-chain alkyl group-containing quaternary ammonium salts, etc. From the viewpoint of exhibiting good mold releasability, long-chain alkyl group-containing polymer compounds are preferred.

[0038] The long-chain alkyl group-containing polymer compound is preferably a polymer compound having a long-chain alkyl group on the side chain, and the method for producing the polymer compound is as follows: (1) A method of polymerizing a monomer having a long-chain alkyl group, or copolymerizing a monomer having a long-chain alkyl group with a monomer copolymerizable with said monomer; (2) A method of reacting a polymer having a reactive group with a compound having a long-chain alkyl group that can react with the reactive group. As the compound having a long-chain alkyl group, a long-chain alkyl group-containing polymer compound having a (meth)acrylic acid ester containing an alkyl group having 9 or more carbon atoms as a copolymerization component, which can be suitably produced by the method (1) above, is more preferred.

[0039] In the above method (1), the monomer having a long-chain alkyl group is preferably a (meth)acrylic monomer, for example, a (meth)acrylic acid ester having an alkyl group having 4 to 30 carbon atoms is preferred. More specifically, examples of such a (meth)acrylic acid ester include isobutyl (meth)acrylate, t-butyl (meth)acrylate, n-amyl (meth)acrylate, isoamyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-heptyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, lauryl (meth)acrylate, octadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, and behenyl (meth)acrylate. In this case, as in the above, the number of carbon atoms in the alkyl group is preferably 9 or more, more preferably 12 or more, even more preferably 15 or more, and particularly preferably 18 or more. The long-chain alkyl group-containing polymer compound obtained by the above method (1) is preferably a (meth)acrylic acid ester (co)polymer, and the content of the structural unit derived from the monomer having the long-chain alkyl group is preferably in the range of 10 to 100 mass%. From the viewpoint of compatibility with the solvent contained in the coating liquid, which is a preferred form of the release layer-forming composition described below, the content of the structural unit is preferably in the range of 10 to 80% by mass, and more preferably in the range of 10 to 60% by mass. If it is 10% by mass or more, sufficient release properties are obtained, and if it is 80% by mass or less, compatibility with the solvent is good. However, when an additive such as a surfactant is used to improve compatibility with the solvent, the content is not limited to the above range. Furthermore, from the viewpoint of releasability, the content of the structural unit is preferably in the range of 10 to 100% by mass, more preferably in the range of 20 to 100% by mass, even more preferably in the range of 30 to 100% by mass, and particularly preferably in the range of 35 to 100% by mass. That is, from the viewpoint of compatibility with the solvent and releasability, the content of this structural unit is more preferably in the range of 30 to 80% by mass, and even more preferably in the range of 35 to 60% by mass.

[0040] On the other hand, the monomer copolymerizable with the monomer having a long-chain alkyl group is not particularly limited, but (meth)acrylic monomers, vinyl group-containing monomers, and the like are preferred. Examples of the (meth)acrylic monomer include hydroxyl group-containing monomers such as hydroxyalkyl (meth)acrylates, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate; carboxy group-containing monomers such as (meth)acrylic acid, itaconic acid, carboxyethyl acrylate, mono(2-acryloyloxyethyl) succinate, ω-carboxy-dicarolactone monoacrylate, and monohydroxyethyl acrylate phthalate; and alkyl (meth)acrylates having less than 4 carbon atoms other than the compounds having the long-chain alkyl group, such as methyl (meth)acrylate, ethyl (meth)acrylate, and n-propyl (meth)acrylate. Examples of vinyl group-containing monomers include styrene, vinyl acetate, vinyl propionate, and divinylbenzene. Among these, the copolymerizable monomer preferably includes a monomer containing a functional group such as a hydroxyl group-containing monomer or a carboxy group-containing monomer, from the viewpoint of contributing to the reaction with the crosslinking agent described later, and more preferably includes a carboxy group-containing monomer such as (meth)acrylic acid. In the present specification, (meth)acrylic means acrylic or methacrylic.

[0041] In the above method (2), examples of the reactive group of the polymer having a reactive group include a hydroxyl group, an amino group, a carboxy group, an acid anhydride, etc. Specific examples of the polymer having a reactive group include polyvinyl alcohol, polyethyleneimine, polyethyleneamine, a polyester resin containing a reactive group, a poly(meth)acrylic resin containing a reactive group, etc. Among these, polyvinyl alcohol and a poly(meth)acrylic resin containing a reactive group are preferred from the viewpoints of releasability and ease of handling.

[0042] In order to exhibit good water solubility of the long-chain alkyl group-containing compound, it is preferable to neutralize the reactive group. Examples of basic stabilizers include inorganic basic compounds such as calcium hydroxide, magnesium hydroxide, lithium hydroxide, potassium hydroxide, and sodium hydroxide, and amine compounds such as ammonia, trimethylamine, triethylamine, diethylamine, and dimethylaminoethanol. Among them, in order to efficiently distribute the long-chain alkyl group moiety unevenly on the surface of the release layer, it is preferable to use an inorganic basic compound as the neutralizing agent, and considering the balance with reaction inhibition when adding a crosslinking agent, calcium hydroxide, magnesium hydroxide, and lithium hydroxide are preferred.

[0043] Examples of compounds having an alkyl group capable of reacting with the reactive group include long-chain alkyl group-containing isocyanates such as octyl isocyanate, decyl isocyanate, lauryl isocyanate, octadecyl isocyanate, stearyl isocyanate, and behenyl isocyanate; long-chain alkyl group-containing acid chlorides such as hexanoyl chloride, octanoyl chloride, decanoyl chloride, lauroyl chloride, octadecanoyl chloride, and behenoyl chloride; long-chain alkyl group-containing amines; and long-chain alkyl group-containing alcohols. Among these, from the viewpoints of mold releasability and ease of handling, long-chain alkyl group-containing isocyanates are preferred, and stearyl isocyanate is particularly preferred.

[0044] The number-average molecular weight (Mn) of the long-chain alkyl group-containing polymer compound obtained by the above methods (1) and (2) is preferably 1,000 to 100,000, more preferably 2,000 to 100,000. When these number-average molecular weights are equal to or greater than the lower limit, the low-molecular-weight components in the release layer can be reduced, allowing the long-chain alkyl group moiety to be efficiently localized on the surface of the release layer, thereby achieving sufficient releasability. On the other hand, when the number-average molecular weight is equal to or less than the upper limit, the composition is easily dissolved in a solvent contained in a coating liquid, which is a preferred form of the release layer-forming composition described below, and is easily applied to a polyester film. The dispersity (Mw / Mn) is preferably 1.1 to 10. A dispersity of 1.1 or more is preferred from the viewpoint of versatility in terms of condition control in a general polymerization process, and a dispersity of 10 or less stabilizes the peel force. In the case of the above method (1), the average molecular weight can be controlled by the polymerization conditions such as the polymerization time. In the above method (2), the average molecular weight can be controlled by adjusting the average molecular weight of the polymer having a reactive group and the average molecular weight of the compound having an alkyl group capable of reacting with the reactive group.

[0045] As the method (1) above, conventionally known polymerization methods such as solution polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization can be applied, and among these, solution polymerization is preferred. The solution polymerization is carried out by polymerizing a monomer having a long-chain alkyl group and other copolymerizable monomers in an organic solvent in the presence of a polymerization initiator. The polymerization temperature can be set appropriately, for example, at 60 to 100°C, preferably 70 to 90°C, and the polymerization time can be set appropriately, for example, at 30 minutes to 10 hours, preferably 3 to 8 hours. As the polymerization initiator, a conventional radical polymerization initiator can be used, and specific examples include azo-based polymerization initiators such as azobisisobutyronitrile and azobisdimethylvaleronitrile. The amount of polymerization initiator used depends on the target number average molecular weight, but is usually preferably 0.1 to 5 parts by mass, and more preferably 0.5 to 3 parts by mass, per 100 parts by mass of monomer. If the amount is 0.1 part by mass or more, polymerization proceeds sufficiently, and if the amount is 5 parts by mass or less, it is advantageous in terms of cost.

[0046] The acid value of the long-chain alkyl group-containing compound is preferably 100 mgKOH / g or more, more preferably 105 mgKOH / g or more, even more preferably 110 mgKOH / g or more, and particularly preferably 115 mgKOH / g or more. If the acidity is 100 mgKOH / g or more, the difference in compatibility between the acid component and the long-chain alkyl group moiety allows the long-chain alkyl group moiety to be efficiently concentrated on the surface of the release layer, thereby achieving excellent release properties. The upper limit is usually preferably 300 mgKOH / g from the viewpoint of the coatability of the release agent and the suppression of low molecular weight components during polymerization of the release agent.

[0047] The melting point of the long-chain alkyl group-containing compound is preferably 0°C or higher and 100°C or lower, more preferably 10°C or higher and 100°C or lower, and even more preferably 20°C or higher and 90°C or lower. A temperature of 0° C. or higher is desirable from the viewpoint of ease of handling in the synthesis and purification process of the long-chain alkyl group-containing compound. If the temperature is 100° C. or lower, the appearance of the release layer is less likely to deteriorate and the haze is less likely to increase during the process of applying a coating liquid, which is a preferred form of the composition for forming the release layer, to the polyester film, as described below.

[0048] (wax) Examples of waxes include natural waxes, synthetic waxes, and waxes made by combining these.

[0049] Natural waxes include vegetable waxes, animal waxes, mineral waxes, and petroleum waxes. Examples of vegetable waxes include candelilla wax, carnauba wax, rice wax, Japan wax, and jojoba oil. Examples of animal waxes include beeswax, lanolin, and spermaceti. Examples of mineral waxes include montan wax, ozokerite, and ceresin. Examples of petroleum waxes include paraffin wax, microcrystalline wax, and petrolatum.

[0050] Examples of synthetic waxes include synthetic hydrocarbons, modified waxes, hydrogenated waxes, fatty acids, fatty acid amides, amines, imides, ester waxes, and ketones. Synthetic hydrocarbons include Fischer-Tropsch wax (Sazol wax), polyethylene wax, oxidized polyethylene wax, oxidized polypropylene wax, etc. Also included are low molecular weight polymers (number average molecular weight 500-20,000), such as polypropylene, ethylene-acrylic acid copolymer, polyethylene glycol, polypropylene glycol, and block or graft conjugates of polyethylene glycol and polypropylene glycol. Examples of modified waxes include montan wax derivatives, paraffin wax derivatives, and microcrystalline wax derivatives. The derivatives herein refer to compounds obtained by any of the following treatments: purification, oxidation, esterification, and saponification, or a combination thereof. Hydrogenated waxes include hydrogenated castor oil and hydrogenated castor oil derivatives.

[0051] Among these waxes, synthetic waxes are preferred from the viewpoint of excellent release properties and easy availability, synthetic hydrocarbons are more preferred, and oxidized polyethylene wax and oxidized polypropylene wax are even more preferred. In addition, from the viewpoint of efficiently distributing the long-chain alkyl group portion on the surface of the release layer by reducing the low molecular weight components in the release layer, the number average molecular weight (Mn) of the wax is preferably in the range of 1,000 to 100,000, and the weight average molecular weight (Mw) is preferably in the range of 2,000 to 100,000.

[0052] The acid value of the wax is preferably 0.5 mgKOH / g or more, more preferably 1 mgKOH / g or more, even more preferably 4 mgKOH / g or more, and particularly preferably 7 mgKOH / g or more. If the acidity is 1 mgKOH / g or more, the difference in compatibility between the acid component and the long-chain alkyl group moiety allows the long-chain alkyl group moiety to be efficiently localized on the surface of the release layer, thereby achieving excellent release properties. The upper limit is usually preferably 50 mgKOH / g from the viewpoint of the coatability of the release agent.

[0053] Furthermore, the melting point or softening point of the wax is preferably 80°C or higher, more preferably 110°C or higher, taking into consideration durability against heat treatment during use, and is preferably 200°C or lower, more preferably 170°C or lower, and even more preferably 150°C or lower, from the viewpoint of controlling release performance after heat treatment. The melting point of the wax can be measured by a differential scanning calorimeter (DSC).

[0054] (Fluorine compounds) The fluorine compound may be any polymeric compound containing a fluorine atom in the molecule, such as a perfluoroalkyl group-containing polymeric compound, a polymer of an olefin compound containing a fluorine atom, etc. From the viewpoint of being able to exhibit releasability with a small content, a perfluoroalkyl group-containing polymeric compound is preferred. As the monomer for forming the perfluoroalkyl group-containing polymer compound, a perfluoroalkyl group-containing (meth)acrylate, a perfluoroalkyl group-containing vinyl ether, or the like is preferred.

[0055] Examples of perfluoroalkyl group-containing (meth)acrylates include perfluoroalkyl (meth)acrylate, perfluoroalkylmethyl (meth)acrylate, 2-perfluoroalkylethyl (meth)acrylate, 3-perfluoroalkylpropyl (meth)acrylate, 3-perfluoroalkyl-1-methylpropyl (meth)acrylate, and 3-perfluoroalkyl-2-propenyl (meth)acrylate. Examples of perfluoroalkyl group-containing vinyl ethers include perfluoroalkylmethyl vinyl ether, 2-perfluoroalkylethyl vinyl ether, 3-perfluoropropyl vinyl ether, 3-perfluoroalkyl-1-methylpropyl vinyl ether, and 3-perfluoroalkyl-2-propenyl vinyl ether. These may be polymerized singly or in combination of two or more. From the viewpoint of exhibiting releasability with a small content, the perfluoroalkyl group preferably has 3 to 11 carbon atoms. In addition, from the viewpoint of efficiently distributing the long-chain alkyl group portion on the surface of the release layer by reducing the low molecular weight components in the release layer, the number average molecular weight (Mn) of the fluorine compound (polymer compound) is preferably in the range of 1,000 to 100,000, and the weight average molecular weight (Mw) is preferably in the range of 2,000 to 100,000.

[0056] (silicone compounds) The silicone compound is a compound having a siloxane bond (—Si—O—) in the molecule, and examples thereof include silicone emulsion, acrylic-grafted silicone, silicone-grafted acrylic, amino-modified silicone, perfluoroalkyl-modified silicone, alkyl-modified silicone, etc. From the viewpoints of releasability, heat resistance, etc., curable silicone resins are preferred. The types of curable silicone resins include addition type, condensation type, ultraviolet curable type, and electron beam curable type, and any of the curable types can be used. In addition, from the viewpoint of efficiently distributing the long-chain alkyl group portion on the surface of the release layer by reducing the low molecular weight components in the release layer, the number average molecular weight (Mn) of the silicone compound is preferably in the range of 100 to 100,000, and the weight average molecular weight (Mw) is preferably in the range of 200 to 100,000.

[0057] The composition for forming the release layer may further contain particles, a binder, a crosslinking agent, and additives in addition to the release agent. The particles are added to improve blocking properties and slip properties, and the type, shape, average particle size, and content thereof are the same as those of the particles that may be incorporated into the polyester film described above.

[0058] (binder) The composition for forming a release layer may contain a binder. The binder serves to disperse the release agent, particles, additives, etc. in the coating liquid, which is a preferred form of the composition for forming a release layer, as described below. Examples of binders include polyester resins, acrylic resins, and polyurethane resins.

[0059] The polyester resin used as the binder may contain, as its main constituents, for example, the following acid components and polyhydroxy compounds. Examples of the acid component that can be used include dicarboxylic acids such as 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, and succinic acid; tricarboxylic acids such as trimellitic acid and trimesic acid; tetracarboxylic acids such as pyromellitic acid; acid anhydrides such as trimellitic anhydride and phthalic anhydride; p-hydroxybenzoic acid; trimellitic acid monopotassium salt; and ester-forming derivatives thereof. Examples of polyhydric 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. Polyester resins can be obtained by selecting one or more of these compounds as appropriate and subjecting them to a conventional polycondensation reaction.

[0060] Also, a product obtained by copolymerizing sulfoisophthalic acid as part of the acid component, introducing sulfonic acid groups into the polyester skeleton, and neutralizing the resulting polyester to be hydrophilized is preferably used. The amount copolymerized is usually 1 to 10 mol %, preferably 2 to 8 mol %, based on the total amount of the acid component. By introducing an appropriate amount of sulfonic acid groups, it is possible to further improve the dispersion stability of a coating liquid, particularly an aqueous coating liquid, which is a preferred form of the release layer-forming composition described below.

[0061] The acrylic resin used as a binder is a polymer having structural units derived from polymerizable monomers including (meth)acrylic monomers. These may be homopolymers or copolymers, or copolymers with polymerizable monomers other than (meth)acrylic monomers. Furthermore, the polymer may be a block copolymer or a graft copolymer of such a polymer with another polymer (such as polyester or polyurethane), such as an acrylic-modified polyester resin or an acrylic-modified polyurethane resin. Also included are polymers (and in some cases mixtures of polymers) obtained by polymerizing (meth)acrylic monomers in a solution or dispersion of polyester, polyurethane or other polymer. In order to further improve the adhesion of the release layer to the polyester film, the acrylic resin may contain a hydroxyl group or an amino group.

[0062] Examples of the (meth)acrylic monomer include carboxyl group-containing monomers such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, and citraconic acid, and their salts; hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, monobutylhydroxyfumarate, and monobutylhydroxyitaconate; (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, and lauryl (meth)acrylate; nitrogen-containing compounds such as (meth)acrylamide, diacetone acrylamide, and (meth)acrylonitrile; hydroxyl group-containing nitrogen-containing compounds such as N-methylol (meth)acrylamide; and silicon-containing monomers such as γ-methacryloxypropyltrimethoxysilane. Among these, (meth)acrylic acid alkyl esters are preferred. These (meth)acrylic monomers may be copolymerized with various styrene derivatives such as styrene, α-methylstyrene, divinylbenzene, and vinyltoluene; various vinyl esters such as vinyl propionate; various silicon-containing polymerizable monomers such as vinyltrimethoxysilane; phosphorus-containing vinyl monomers; various vinyl halides such as vinyl chloride and vinylidene chloride; and various conjugated dienes such as butadiene.

[0063] Furthermore, from the viewpoint of facilitating dissolving or dispersing the binder in a coating liquid, particularly an aqueous coating liquid, which is a preferred form of the release layer-forming composition described below, the acrylic resin preferably has a hydrophilic group such as a hydroxyl group or a carboxyl group. Therefore, as the acrylic resin, a polymer obtained by polymerizing a polymerizable monomer including a (meth)acrylic acid alkyl ester and a hydrophilic group-containing monomer such as a hydroxyl group-containing monomer or a carboxyl group-containing monomer is also preferred. The acrylic resin may also be an emulsion polymer obtained by polymerizing a polymerizable monomer in the presence of a surfactant.

[0064] The polyurethane resin used as a binder is a polymer compound having a urethane bond in the molecule, and is preferably water-dispersible or water-soluble. One type of polyurethane resin may be used alone, or two or more types may be used in combination.

[0065] In order to impart water dispersibility or water solubility, it is common and preferable to introduce hydrophilic groups such as hydroxyl groups, carboxyl groups, sulfonic acid groups, sulfonyl groups, phosphate groups, ether groups, etc. Among these hydrophilic groups, carboxyl groups and sulfonic acid groups are particularly preferred from the viewpoint of improving adhesiveness.

[0066] One method for producing such polyurethane resins involves the reaction of a hydroxyl group-containing compound with an isocyanate. Polyols are preferably used as the hydroxyl group-containing compound, including, for example, polyether polyols, polyester polyols, polycarbonate polyols, polyolefin polyols, and acrylic polyols. These may be used alone or in combination of two or more.

[0067] Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polyethylene propylene glycol, polytetramethylene ether glycol, and polyhexamethylene ether glycol.

[0068] Examples of polyester polyols include polycarboxylic acids (malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, fumaric acid, maleic acid, terephthalic acid, isophthalic acid, etc.) or their acid anhydrides and polyhydric alcohols (ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 2-methyl-1,5-pentanediol, 2- methyl-2,4-pentanediol, 2-methyl-2-propyl-1,3-propanediol, 1,8-octanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2,5-dimethyl-2,5-hexanediol, 1,9-nonanediol, 2-methyl-1,8-octanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-butyl-2-hexyl-1,3-propanediol, cyclohexanediol, bishydroxymethylcyclohexane, dimethanolbenzene, bishydroxyethoxybenzene, alkyldialkanolamine, lactonediol, etc.

[0069] Examples of polycarbonate polyols include polycarbonate diols obtained by dealcoholization reaction of polyhydric alcohols with dimethyl carbonate, diethyl carbonate, diphenyl carbonate, ethylene carbonate, etc., such as poly(1,6-hexylene) carbonate and poly(3-methyl-1,5-pentylene) carbonate.

[0070] Of these, polyester polyols are preferred.

[0071] Examples of isocyanates used to obtain polyurethane resins include aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, and tolidine diisocyanate; aliphatic diisocyanates having an aromatic ring such as α,α,α',α'-tetramethylxylylene diisocyanate; aliphatic diisocyanates such as methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, and hexamethylene diisocyanate; and alicyclic diisocyanates such as cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, and isopropylidenedicyclohexyl diisocyanate. These may be used alone or in combination of two or more.

[0072] A chain extender may be used when producing the polyurethane resin. The chain extender is not particularly limited as long as it has two or more active groups that react with an isocyanate group, and generally, a chain extender having two hydroxyl groups or two amino groups can be mainly used.

[0073] Examples of chain extenders having two hydroxyl groups include glycols such as aliphatic glycols such as ethylene glycol, propylene glycol, and butanediol; aromatic glycols such as xylylene glycol and bishydroxyethoxybenzene; and ester glycols such as neopentyl glycol hydroxypivalate.

[0074] Examples of chain extenders having two amino groups include aromatic diamines such as tolylenediamine, xylylenediamine, and diphenylmethanediamine; aliphatic diamines such as ethylenediamine, propylenediamine, hexanediamine, 2,2-dimethyl-1,3-propanediamine, 2-methyl-1,5-pentanediamine, trimethylhexanediamine, 2-butyl-2-ethyl-1,5-pentanediamine, 1,8-octanediamine, 1,9-nonanediamine, and 1,10-decanediamine; and alicyclic diamines such as 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, dicyclohexylmethanediamine, 1,4-diaminocyclohexane, and 1,3-bisaminomethylcyclohexane.

[0075] In addition, in order to impart water dispersibility or water solubility to a polyurethane resin, a method is also preferably used in which a carboxy group is introduced into the urethane skeleton using dimethylolpropionic acid, dimethylolbutanoic acid, or the like, and then the urethane is hydrophilized by neutralizing the resulting urethane with a basic compound.

[0076] As the binder, a polyester resin is preferred from the viewpoint of adhesion of the release layer to the polyester film. The binder may be used alone or in combination of two or more.

[0077] (Crosslinking agent) The composition for forming a release layer may further contain a crosslinking agent. The crosslinking agent can be added to the composition for forming a release layer, preferably to the coating liquid, and examples thereof include melamine compounds, oxazoline compounds, epoxy compounds, isocyanate compounds, carbodiimide compounds, and silane coupling agents. Among these crosslinking agents, it is preferable to use a melamine compound because of its high crosslink density and elastic modulus. The crosslinking agent is reacted with the release layer-forming composition, preferably the coating liquid, on the surface of the polyester film during the drying process after application, or during the film-forming process such as stretching, to improve the performance of the release layer. In the present invention, the crosslinking agent can effectively cause the release agent to be unevenly distributed on the surface of the release layer, which may make it easier to achieve the effects of the present invention. The crosslinking agent is believed to be present in the release layer in the form of either an unreacted substance or a reacted compound.

[0078] The melamine compound is a compound having a melamine skeleton in the molecule, and examples thereof include trimethoxymethylmelamine, hexamethoxymethylmelamine, hexaethoxymethylmelamine, hexapropoxymethylmelamine, and hexabutoxymethylmelamine.

[0079] The oxazoline compound is a compound having an oxazoline group in the molecule, and a polymer containing an oxazoline group is particularly preferred. Examples of the oxazoline group-containing monomer include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline.

[0080] The epoxy compound is a compound having an epoxy group in the molecule, and examples thereof include condensation products of epichlorohydrin with a hydroxyl group or an amino group of ethylene glycol, polyethylene glycol, glycerin, polyglycerin, bisphenol A, etc., polyepoxy compounds, diepoxy compounds, monoepoxy compounds, glycidylamine compounds, etc.

[0081] Examples of isocyanate compounds include tolylene diisocyanate compounds such as 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate; xylylene diisocyanate compounds such as 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate and tetramethylxylylene diisocyanate; aromatic isocyanate compounds such as 1,5-naphthalene diisocyanate and triphenylmethane triisocyanate; hexamethylene diisocyanate, isophorone diisocyanate, and adducts of these isocyanate compounds with polyol compounds such as trimethylolpropane; and biuret compounds and isocyanurates of these polyisocyanate compounds.

[0082] Examples of carbodiimide compounds include monocarbodiimide compounds such as dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, t-butylisopropylcarbodiimide, diphenylcarbodiimide, di-t-butylcarbodiimide, and di-β-naphthylcarbodiimide; and isocyanate-terminated polycarbodiimides obtained by condensation reaction of diisocyanate accompanied by decarbonation.

[0083] Examples of the silane coupling agent include γ-mercaptopropyltrimethoxysilane, γ-isocyanatepropyltriethoxysilane, γ-isocyanatepropyltrimethoxysilane, and N-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propanamine. When the release layer-forming composition, preferably the coating liquid, contains a crosslinking agent, the content of the crosslinking agent can be 10 to 100 parts by mass per 100 parts by mass of the release agent. If the content is 10 parts by mass or more, the function of the crosslinking agent is fully exerted, and the long-chain alkyl group moiety can be effectively localized on the surface of the release layer. On the other hand, if the content is 100 parts by mass or less, it is advantageous in terms of the performance of the release agent. From the above viewpoints, the content of the crosslinking agent is more preferably in the range of 15 to 80 parts by mass, and even more preferably in the range of 20 to 70 parts by mass.

[0084] (additives) Various additives may be added to the release layer-forming composition as needed. Specifically, antistatic agents, ultraviolet absorbers, antioxidants, antifoaming agents, lubricants, foaming agents, dyes, pigments, etc. may be added.

[0085] (Release layer forming composition) The release layer in the laminated film of the present invention is formed on at least one side of the polyester film using a composition for forming a release layer, and the composition for forming a release layer contains a release agent such as the compound having a long-chain alkyl group, a wax, a fluorine compound, or a silicone compound, and may further contain a binder, a crosslinking agent, particles, other additives, and a solvent. In particular, the composition is preferably in the form of a coating liquid containing a solvent. When the composition is used as a coating solution, the solids concentration of the composition is preferably 0.1 to 50% by mass. If the solids concentration is 0.1% by mass or more, a release layer of the desired thickness can be efficiently formed, and if the solids concentration is 50% by mass or less, the composition is easily dissolved in a solvent and can be easily applied. From these viewpoints, the solids concentration is more preferably 0.5 to 40% by mass, and even more preferably 1 to 30% by mass. The content of the release agent in the solid content is preferably in the range of 10 to 100% by mass, more preferably in the range of 20 to 100% by mass, and even more preferably in the range of 30 to 99% by mass.

[0086] (solvent) The composition for forming a release layer contains a solvent to form a liquid coating liquid, which can be applied to the surface of the polyester film, and dried and cured as necessary to form a release layer. In addition, each component of the coating liquid that forms the release layer may be dissolved in a solvent or may be dispersed in a solvent. The solvent can be either water or an organic solvent. Examples of organic solvents include aromatic hydrocarbons such as toluene; aliphatic hydrocarbons such as hexane, heptane, and isooctane; esters such as ethyl acetate and butyl acetate; ketones such as ethyl methyl ketone and isobutyl methyl ketone; alcohols such as ethanol and 2-propanol; and ethers such as diisopropyl ether and dibutyl ether. These solvents may be used alone or in combination, taking into account solubility, coatability, boiling point, and the like. From the viewpoint of reducing the environmental impact, when the release layer-forming composition is used as a coating liquid, it is preferable to use an aqueous coating liquid containing water as the main solvent (50% by mass or more of the solvent constituting the coating liquid). The water content is preferably 60% by mass or more, more preferably 70% by mass or more. The aqueous coating liquid may contain a small amount of organic solvent. The amount of organic solvent is, for example, less than 30% by mass, preferably less than 20% by mass, more preferably less than 10% by mass of the solvent, based on mass. Examples of organic solvents that may be contained in the aqueous coating liquid 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 dimethylethanolamine. These can be used alone or in combination. By appropriately selecting and adding these organic solvents to the aqueous coating liquid as needed, the stability and coatability of the coating liquid may be improved.

[0087] (Method for forming release layer) When forming a release layer, the method for applying the release layer-forming composition, preferably the coating liquid, to a polyester film is not particularly limited, and any conventionally known coating method can be used, such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, or curtain coating. Methods for forming the release layer include in-line coating and off-line coating. Drying and curing conditions are not particularly limited, and when the release layer is formed by off-line coating, the heat treatment is usually carried out at 80 to 200°C for 3 to 40 seconds, preferably at 100 to 180°C for 3 to 40 seconds. On the other hand, when the release layer is formed by in-line coating, the heat treatment is usually carried out at 70 to 280°C for 3 to 200 seconds.

[0088] The laminated film of the present invention is preferably formed by in-line coating, which treats the film surface during the polyester film production process. In-line coating is a method of coating a polyester film with the coating solution and heat-treating it during the polyester film production process. Specifically, coating is performed at any stage between melt-extrusion of the polyester, stretching, heat setting, and winding up. Typically, the coating liquid is applied to any of the following: an unstretched sheet obtained by melting and quenching, a stretched uniaxially stretched film, a biaxially stretched film before heat setting, or a film after heat setting but before winding up, and then heat-treated to form the coating. Although not limited to the following, for example, in the case of sequential biaxial stretching, a method is preferred in which the coating liquid is applied to a uniaxially stretched film that has been particularly stretched in the longitudinal direction (machine direction), and then the film is heat-treated and stretched in the transverse direction after coating. This method has the advantage of being able to simultaneously produce a polyester film and form a 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 adjusting the stretch ratio, and coating a thin release layer can be performed more easily than offline coating. Furthermore, by providing a release layer on the film before stretching, the release layer can be stretched together with the polyester film, thereby allowing the release layer to adhere firmly to the polyester film. Furthermore, in the production of biaxially stretched polyester films, the film can be stretched while holding the edges with clips or the like, thereby restraining the film in both the longitudinal and transverse directions, and in the heat setting process, high temperatures can be applied while maintaining flatness and preventing wrinkles. Therefore, the heat treatment carried out after application of the coating liquid can be carried out at a high temperature that cannot be achieved by other methods, resulting in good coatability of the release layer and allowing the release layer to adhere more firmly to the polyester film.

[0089] In addition, regardless of whether off-line coating or in-line coating is used, when forming the release layer, heat treatment and irradiation with active energy rays such as ultraviolet radiation may be used in combination, if necessary. The polyester film constituting the laminated film of the present invention may be previously subjected to a surface treatment such as a corona treatment or a plasma treatment.

[0090] (Release layer peel strength) When an adhesive layer (double-sided adhesive tape (manufactured by Nitto Denko Corporation, "No. 31B") is attached to the release layer of the laminated film, the peel strength of the release layer to the adhesive tape, measured according to the method described in the examples below, is preferably 100 mN / cm or less, more preferably 95 mN / cm or less, and even more preferably 90 mN / cm or less.

[0091] The laminated film of the present invention has excellent release properties, and therefore can be suitably used as a release film for various processes, such as for transfer such as simultaneous transfer during molding, for the production of flexible printed wiring boards, and as a process paper for the production of plastic sheets. [Example]

[0092] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.

[0093] <Evaluation method> (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.

[0094] (2) Average particle size The laminated films of the examples and comparative examples were observed using a transmission electron microscope (TEM) (Hitachi High-Tech Corporation, "H-7650", acceleration voltage 100 kV), and the average particle size of 10 particles was taken as the average particle size.

[0095] (3) Release layer thickness The surface of the release layer of the laminated film of each of the examples and comparative examples was stained with RuO4 and embedded in epoxy resin. Then, sections prepared by ultrathin sectioning were stained with RuO4, and the cross section of the release layer was measured using a transmission electron microscope (TEM) (Hitachi High-Technologies Corporation, "H-7650", accelerating voltage 100 kV).

[0096] (4) C7H with sputtering time of 0 to 10 seconds 11 + Content The distribution of the long-chain alkyl groups of the release agent in the depth direction from the surface of the release layer of the laminated film was evaluated from the depth profile using TOF-SIMS (manufactured by ION TOF, "TOF-SIMS IV" and "IONPTIKA GCIB-10S"). The distribution of long-chain alkyl groups in the release agent was measured using the secondary ions CH 11 + Calculation was performed using fragment ion intensities.

[0097] (Measurement conditions and calculation method) Bi3 as the primary ion 2+ The acceleration voltage was set to 25 kV. To evaluate the distribution of long-chain alkyl groups per unit area in the depth direction, Ar 3000 + Ion sputtering (accelerating voltage: 10 kV, area: 3 mm square) was carried out. The CH detected between sputtering time 0 and the end of measurement 11 + The sum of the fragment ion intensities was calculated as C7H 11 + Content, C7H detected during sputtering time 0-10 seconds 11 + The sum of fragment ion intensities was calculated for C7H at sputtering times of 0 to 10 seconds. 11 + The content is C7H throughout the depth direction of the release layer. 11 + C7H content at sputtering times of 0 to 10 seconds 11 + The content was calculated.

[0098] The end point of the sputtering time measurement was the C7H4O detected as a secondary ion derived from the polyester film substrate. + This was the point at which the fragment ion intensity became constant. Furthermore, the sputtering time of 0 to 10 seconds refers to the vicinity of the surface of the release layer, and the compound distribution in the vicinity of the surface of the release layer can be estimated from the fragment ions detected during the sputtering time of 0 to 10 seconds.

[0099] The TOF-SIMS measurement conditions are as follows: Secondary ion polarity: positive Raster size: 200 μm Charge neutralization: Yes Primary ion: Bi3 2+ Primary ion acceleration voltage: 25 kV Sputter ions: Ar 3000 + Sputter ion acceleration voltage: 10 kV

[0100] (5) Peel strength of laminated film A 5cm-wide piece of double-sided adhesive tape (Nitto Denko Corporation, "No. 31B") was pressed back and forth with a 2kg rubber roller onto one side of the release layer of the sample film, and the film was left at room temperature for 1 hour before measuring the peel strength. The peel strength was measured using a small tabletop tester "EZ Graph" (Shimadzu Corporation), with a 180° peel angle at a tensile speed of 300mm / min. The peeling force is preferably 100 mN / cm or less, more preferably 95 mN / cm or less, and even more preferably 90 mN / cm or less.

[0101] (6) Acid value of release agent The acid value of the release agent was determined by neutralization titration. The release agent was dissolved in a 50 / 50 (v / v) mixed solution of toluene and ethanol to prepare a 1% by mass solution, which was used as a measurement sample. Using an automatic titrator (manufactured by DKK-TOA Corporation), the solution was titrated with a 0.5N KOH ethanol solution, and the acid value was calculated from the pH inflection point.

[0102] (7) Number average molecular weight (Mn) and dispersity (Mw / Mn) of the release agent The number average molecular weight and dispersity of the release layer were determined using values ​​calculated in terms of polystyrene measured by gel permeation chromatography. Measurement samples were prepared by dissolving bone-dried release agents in tetrahydrofuran (THF). The measuring device and measuring conditions are as follows. Measuring device: Tosoh Corporation "EcoSEC 8320" Column: 4 "TSKgel GMHXL" manufactured by Tosoh Corporation Measurement solvent: THF Measurement temperature: 40℃

[0103] <Materials used> (a) Polyester (A): Polyethylene terephthalate homopolymer with an intrinsic viscosity of 0.63 dL / g (b) Polyester (B): Polyethylene terephthalate homopolymer containing 0.2% by mass of silica particles with an average particle size of 2 μm and having an intrinsic viscosity of 0.65 dL / g (c) Crosslinking agent: hexamethoxymethylmelamine

[0104] (Preparation of coating solution for forming laminated film) Solutions 1 to 3 containing long-chain alkyl group-containing polyacrylate were prepared based on the descriptions of the following Preparation Examples or Comparative Preparation Examples. Table 1 shows the solution compositions and reaction conditions. Next, the crosslinking agent was added to these solutions as needed to prepare coating solutions for forming laminated films. Table 2 shows the coating solutions used in each of the Examples and Comparative Examples.

[0105] Preparation Example 1 (Solution 1) A four-neck flask equipped with a nitrogen gas inlet tube, stirrer, thermometer, and condenser was charged with 500 parts by weight of ethanol, 70 parts by weight of stearyl acrylate, and 30 parts by weight of glutaconic acid, and the system was purged with nitrogen gas. The temperature was raised and the mixture reached reflux, after which 1 part by weight of azobisisobutyronitrile (AIBN) was added to initiate the reaction, which was then allowed to react at 85°C for 4 hours. After completion of the reaction, the solvent was removed and the mixture was dissolved in water to prepare a solution containing long-chain alkyl group-containing polyacrylate. The long-chain alkyl group-containing polyacrylate had a number-average molecular weight of 5600 and a polydispersity of 1.8. Hereinafter, this solution will be referred to as Solution 1.

[0106] Preparation Example 2 (Solution 2) A solution containing a long-chain alkyl group-containing polyacrylate was prepared in the same manner as in Preparation Example 1, except that the monomers used in Preparation Example 1 were 55 parts by mass of stearyl acrylate and 45 parts by mass of acrylic acid. The long-chain alkyl group-containing polyacrylate had a number average molecular weight of 10,000 and a dispersity of 2.6. Hereinafter, this solution will be referred to as Solution 2.

[0107] Comparative Preparation Example 1 (Solution 3) A solution containing a long-chain alkyl group-containing polyacrylate was prepared in the same manner as in Preparation Example 1, except that the monomers used in Preparation Example 1 were 60 parts by mass of stearyl acrylate, 30 parts by mass of acrylic acid, and 10 parts by mass of carboxyethyl acrylate. The long-chain alkyl group-containing polyacrylate had a number average molecular weight of 10,000 and a dispersity of 2.4. Hereinafter, this solution will be referred to as Solution 3.

[0108] [Table 1]

[0109] [Table 2]

[0110] [Examples 1 to 3 and Comparative Example 1] (Laminated film manufacturing) A mixed raw material consisting of polyesters (A) and (B) mixed at a ratio of 90% by mass and 10% by mass, respectively, was used as the raw material for the outermost layer (surface layer), and polyester (A) alone was used as the raw material for the middle layer. These were fed into two extruders, melted at a temperature of 285°C, and then co-extruded onto a cooling roll set at a temperature of 40°C in a layer structure of two types and three layers (surface layer / middle layer / surface layer = discharge amount 1:8:1), cooled and solidified to obtain an unstretched sheet. Next, the film was stretched 3.4 times in the machine direction at a film temperature of 85°C using the difference in roll peripheral speed, and then one side of this machine-stretched film was coated with coating solutions 1 to 4 having the compositions shown in Table 2 above, introduced into a tenter, stretched 4.3 times in the transverse direction at a temperature of 110°C, heat-treated at a temperature of 235°C, and then relaxed 2% in the transverse direction to obtain a 50µm-thick laminate film having a release layer with a film thickness (after drying) of 0.02 to 0.04µm. The evaluation results for each of the obtained laminate films are shown in Table 3.

[0111] [Table 3]

[0112] As shown in Table 3, the C7H of the entire depth direction of the release layer measured using a time-of-flight secondary ion mass spectrometer (TOF-SIMS) in the release layer 11 + C7H content at sputtering times of 0 to 10 seconds 11 +By increasing the content, the peeling force of the release layer against the adhesive tape can be reduced. This is thought to be because the long-chain alkyl group moiety of the release agent in the release layer is unevenly distributed on the surface of the release layer, allowing the release agent to effectively exert its function and develop excellent releasability.

Claims

1. A laminated film having a release layer on at least one side of a polyester film, The release layer has a C in the depth direction of the release layer measured using a time-of-flight secondary ion mass spectrometer (TOF-SIMS). ７ H １１ ＋ C of the entire depth direction of the release layer calculated from the fragment ion intensity ７ H １１ ＋ Sputtered ions Ar content ３０００ ＋ , sputtering ion acceleration voltage 10 kV, sputtering area 3 mm square, sputtering time 0 to 10 seconds C ７ H １１ ＋ The content is 5.6% or more, the release layer is formed from a composition for forming a release layer, which contains a compound having a long-chain alkyl group having 9 or more carbon atoms; the compound having a long-chain alkyl group having 9 or more carbon atoms contains, as a copolymerization component, a (meth)acrylic acid ester having an alkyl group having 9 or more carbon atoms, The compound having a long-chain alkyl group having 9 or more carbon atoms has an acid value of 100 mgKOH / g or more. (However, this does not include release films used in the production of ceramic green sheets.)

2. A laminated film having a release layer on at least one side of a polyester film, The release layer has a C in the depth direction of the release layer measured using a time-of-flight secondary ion mass spectrometer (TOF-SIMS). ７ H １１ ＋ C of the entire depth direction of the release layer calculated from the fragment ion intensity ７ H １１ ＋ Sputtered ions Ar content ３０００ ＋ , sputtering ion acceleration voltage 10 kV, sputtering area 3 mm square, sputtering time 0 to 10 seconds C ７ H １１ ＋ The content is 5.6% or more, the release layer is formed from a composition for forming a release layer, which contains a compound having a long-chain alkyl group having 9 or more carbon atoms; the compound having a long-chain alkyl group having 9 or more carbon atoms contains, as a copolymerization component, a (meth)acrylic acid ester having an alkyl group having 9 or more carbon atoms, the acid value of the compound having a long-chain alkyl group having 9 or more carbon atoms is 100 mgKOH / g or more; The laminated film is used in such a way that a resin layer is laminated on the release layer and is peeled off from the resin layer after use.

3. 3. The laminate film according to claim 1, wherein the compound having a long-chain alkyl group having 9 or more carbon atoms is a polymer compound having a long-chain alkyl group on a side chain.

4. The laminate film according to any one of claims 1 to 3, wherein the compound having a long-chain alkyl group having 9 or more carbon atoms has a (meth)acrylic acid ester containing an alkyl group having 12 or more carbon atoms as a copolymerization component.

5. The laminate film according to any one of claims 1 to 4, wherein the compound having a long-chain alkyl group having 9 or more carbon atoms has a number average molecular weight (Mn) of 1,000 or more.

6. The laminate film according to any one of claims 1 to 5, wherein the amount of a (meth)acrylic acid ester containing an alkyl group having 9 or more carbon atoms contained as a copolymerization component in the compound having a long-chain alkyl group having 9 or more carbon atoms is 20% by mass or more.

7. The laminate film according to any one of claims 1 to 6, wherein the composition for forming a release layer further contains a crosslinking agent.

8. 8. The laminated film according to claim 1, wherein one side of the polyester film has a release layer, and the other side has no layer and the surface of the polyester film is left as is.

9. The laminate film according to any one of claims 1 to 8, wherein the release layer does not contain particles.

10. The laminated film according to any one of claims 1 to 9, wherein the polyester film contains particles.

11. The laminate film according to any one of claims 1 to 10, which is used as a process film for transfer, for producing flexible printed wiring boards, and for producing plastic sheets.

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