Release film for resin sheet molding

Abstract

Provided is a release film which has excellent release layer coating uniformity, release force velocity dependence, coating properties onto various resin sheets, and recyclability.　A release film for molding resin sheets which has a polyester film and a release layer obtained by reacting and solidifying an aqueous coating composition, wherein: the aqueous coating composition contains water, a silicone A having a Q unit represented by SiO4 / 2, a silicone B having an Si-H group, a cross-linking reaction inhibitor, a platinum catalyst and a coupling agent; and the content of Si atoms which constitute the Q unit in the silicone A is within the range of 5-60 mol%.

Description

[Technical Field]

[0001] The present invention relates to a release film for molding resin sheets, having a polyester film and a release layer. [Background technology]

[0002] Conventionally, release films based on polyester film have high heat resistance and mechanical properties, and are used as support films for solution-forming resin sheets such as adhesive sheets, cover films, and polymer electrolyte membranes. For this reason, technologies such as those described in Patent Documents 1 to 3 have been disclosed, and a release layer that forms the casting surface of the resin sheet has been proposed to be made from a special chemical substance.

[0003] However, in the technologies described in Patent Documents 1 to 3, special chemical substances are formed in the release layer, making it easier for foreign matter to be incorporated when the used release film is crushed, melted, and reused as a raw material for polyester film. For this reason, there is a method of recycling by removing the release layer, but since removal requires the use of chemicals or mechanical removal, the recycling process is increased, leading to higher costs and increased consumption of fossil fuels, which is not a desirable solution.

[0004] As silicone-based release films, those with a release layer made of an addition polymerization cured product or a condensation polymerization cured product of polydimethylsiloxane are known. These cured products have the advantages of being non-adhesive, having excellent release effect, and having excellent thermal stability. However, because the surface free energy of the release layer is small, the wettability of the coating material is poor, and coating defects due to poor wettability tend to occur in the resulting resin sheet. Therefore, there is a need for a release film with excellent wettability and release properties during resin sheet molding. In addition, due to the excellent release properties, the adhesion between the release layer and the base film and the uniformity of the coating and formation of the release layer tend to become problems.

[0005] To address these challenges, Patent Document 4 proposes a release film having a release layer obtained by reacting and solidifying an aqueous coating composition containing two types of trialkoxysilanes.

[0006] Furthermore, as a technique for controlling the reactivity of silicone, Patent Document 5 proposes a release film having a release layer formed by curing an aqueous coating composition containing an alkenyl group-containing silicone, a Si-H group-containing silicone, a crosslinking reaction inhibitor, and a platinum-based catalyst.

[0007] Furthermore, Patent Document 6 describes alkenyl groups and / or SiO 4 / 2 A release film has been proposed that has a release layer formed using an aqueous coating composition containing a silicone containing a Q unit represented by in a predetermined mol% range and a silicone having a Si-H group. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2020-131440 [Patent Document 2] Japanese Patent Publication No. 2012-171230 [Patent Document 3] Japanese Patent Publication No. 2003-246035 [Patent Document 4] Japanese Patent Publication No. 2019-55567 [Patent Document 5] Japanese Patent Publication No. 2014-83697 [Patent Document 6] Japanese Patent Publication No. 2021-11081 [Overview of the project] [Problems that the invention aims to solve]

[0009] On the one hand, according to the research of the present inventors, when using a silicone-based release film, depending on the composition of the release layer, the release force may become heavy due to an increase in the release speed, and it has been found that this has affected the production efficiency of various resin sheets. Further, according to the research of the present inventors, when recycling a silicone-based release film and using it as a raw material for a polyester film serving as a base material, depending on the composition of the release layer, a large number of foreign substances larger than a specific size occur, and it has been found that this causes unevenness on the release layer.

[0010] However, in the inventions of Patent Documents 4 to 6, these problems are not considered, and there is room for improvement in producing a release film with good coating uniformity of the release layer, speed dependence of the release force, coating properties of various resin sheets, and recyclability.

[0011] Therefore, an object of the present invention is to provide a release film having good coating uniformity of the release layer, speed dependence of the release force, coating properties of various resin sheets, and recyclability.

Means for Solving the Problems

[0012] As a result of intensive studies to achieve such problems, the present inventors have found that the above problems can be solved by forming a release layer with an aqueous coating composition containing silicone A having a predetermined amount of Q units, silicone B having a Si-H group, and a coupling agent, and have completed the present invention. That is, the present invention includes the following contents.

[0013] [1] A release film for resin sheet molding having a polyester film and a release layer formed by reacting and curing an aqueous coating composition, The aqueous coating composition contains water, silicone A having Q units represented by SiO 4 / 2 and includes silicone B having a Si-H group, a crosslinking reaction inhibitor, a platinum-based catalyst, and a coupling agent, A release film for resin sheet molding, wherein in the silicone A, the content of Si atoms constituting the Q units is in the range of 5 to 60 mol%.

[0014] [2] The release film for resin sheet molding according to [1], wherein the coupling agent is a silane coupling agent having a vinyl group, an epoxy group, an amino group, or a mercapto group.

[0015] [3] The aqueous coating composition contains 0.1 to 30 parts by mass of the coupling agent with respect to a total of 100 parts by mass of the silicone A and the silicone B, the release film for resin sheet molding according to [1] or [2].

[0016] [4] The silicone A is silicone A1 having an alkenyl group in addition to the Q unit in the molecule, or silicone A2 having the Q unit but not having an alkenyl group in the molecule, and the aqueous coating composition further comprises silicone C having an alkenyl group but not having the Q unit in the molecule. A release film for molding resin sheets according to any one of [1] to [3], wherein the content of Si atoms bonded to alkenyl groups relative to the total Si atoms in the silicone A1, or the total Si atoms in the silicone A2 and the silicone C, is in the range of 0.05 to 20 mol%.

[0017] [5] A release film for resin sheet molding according to any one of items [1] to [4], wherein the surface free energy of the release layer is 10 mN / m or more and 40 mN / m or less.

[0018] [6] The release film for resin sheet molding according to any one of [1] to [5], wherein the polyester film has a particle-free surface layer and the release layer is disposed on the surface layer.

[0019] [7] The release film for resin sheet molding according to any one of [4] to [6], wherein the molar ratio of the content of Si atoms bonded to the alkenyl group to the content of Si atoms constituting the Q unit (content of Si atoms bonded to the alkenyl group / content of Si atoms contained in the Q unit) is 0.1 or more and 1.0 or less. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide a release film that exhibits excellent uniformity of release layer application, speed dependence of peeling force, coating properties for various resin sheets, and recyclability.

[0021] Although the exact reasons for these effects are unclear, it is thought that by keeping the Si atom content constituting the Q units, which can form a three-dimensional structure, below a predetermined value, foreign matter is less likely to be generated during recycling, and non-uniformity is less likely to occur when applying the aqueous coating composition. Furthermore, by keeping the Si atom content constituting the Q units above a predetermined value, sufficient coating hardness can be achieved, improving the rate dependence of peeling force and the coatability of various resin sheets. In this case, it is thought that the coupling agent also contributes to the formation of the three-dimensional structure and affects the coating hardness, particularly improving the coatability of various resin sheets. Silicone B, which has Si-H groups, is also thought to contribute to this curing reaction. [Modes for carrying out the invention]

[0022] The present invention will be described in detail below.

[0023] [Release film] The release film of the present invention comprises a polyester film as a base film and a release layer formed by reacting and solidifying an aqueous coating composition. As will be described in detail later, the aqueous coating composition contains silicone A, silicone B, and a coupling agent that can react with each other, so identifying the structure of the resulting polymer and specifying claims based thereon is not easy and impractical. For this reason, the release film of the present invention is specified in the form of a product-by-process claim.

[0024] Furthermore, depending on the embodiment, the present invention may include at least one of the reaction formulas shown in (1) to (5) below. In the following reaction formulas, the -Si-OH group is a chemical structure that can also be produced by the hydrolysis of an alkoxy group bonded to a Si atom, and can contribute to the formation of the Q unit described later.

[0025] [ka]

[0026] [Release layer] The release layer in this invention is obtained by reacting and solidifying an aqueous coating composition. The aqueous coating composition is water, SiO2. 4 / 2 The material is characterized by containing a silicone A having a Q unit represented by , a silicone B having a Si-H group, a crosslinking reaction inhibitor, a platinum-based catalyst, and a coupling agent. Furthermore, the content of Si atoms constituting the Q unit in the silicone A is in the range of 5 to 60 mol%. The constituent components will be described in detail below.

[0027] (SiO 4 / 2 Silicone A) having Q units represented by SiO 4 / 2 Examples of silicone A containing Q units represented by (hereinafter simply referred to as Q units) include organopolysiloxanes having the following general formula (I).

[0028] R1 a R2 b SiO (4-a-b) / 2 ...(I) (In formula (I), R1 is an alkenyl group having 2 to 8 carbon atoms, R2 is a monovalent saturated hydrocarbon group having 1 to 16 carbon atoms selected from alkyl or aryl groups, a is an integer between 0 and 3, and b is an integer between 0 and 3 such that a + b ≤ 3.) Examples of the alkenyl group having 2 to 8 carbon atoms represented by R1 include a vinyl group, an allyl group, a butenyl group, a pentenyl group, a hexenyl group, etc., and among these, a vinyl group is particularly preferable. Examples of the alkyl group represented by R2 include a methyl group, an ethyl group, a propyl group, a butyl group, etc., and examples of the aryl group include a phenyl group, a tolyl group, etc. Among these, it is preferable in terms of easy peeling that 50 mol% or more of the substituents of R2 are methyl groups.

[0029] When the silicone A having a Q unit is contained in the release layer, the coating film hardness of the silicone-based release layer increases due to the dense network structure, and the viscous loss when peeling the resin sheet can be suppressed, leading to easy peeling. Further, when the release layer contains the silicone A containing a Q unit, the wettability is improved, so that pinhole defects during resin sheet coating can be suppressed.

[0030] In formula (I), when a = b = 0, it becomes a constitutional unit which is a Q unit represented by SiO 4 / 2 Further, in formula (I), when a is 1 to 2 and b is 0 to 1, it becomes a constitutional unit (D' unit) composed of Si atoms bonded to an alkenyl group. Further, in formula (I), when a is 0 and b is 2, it becomes a constitutional unit (D unit) composed of Si atoms bonded to two alkyl groups or aryl groups. In formula (I), when a + b is 1, it becomes a T unit.

[0031] The silicone A having a Q unit only needs to have at least a Q unit, and may further contain each of the above constitutional units. For example, it may be silicone A1 having a constitutional unit (D' unit) having an alkenyl group in the molecule in addition to the Q unit, or may be silicone A2 having a constitutional unit (D unit) composed of Si atoms bonded to two alkyl groups or aryl groups and a Q unit and not having an alkenyl group in the molecule. Silicone A1 may be a silicone containing a D unit in the molecule in addition to the Q unit and the D' unit. Further, it is also possible to use silicone A1 and silicone A2 in combination.

[0032] The aqueous coating composition may contain silicone A1, and may further contain silicone C, which has an alkenyl group and does not contain the aforementioned Q unit in its molecule. In other words, if multiple types of silicone are included, it is sufficient if any one of them contains the Q unit.

[0033] The Si atom content in the Q unit is 5 to 60 mol%, preferably 10 to 55 mol%, and more preferably 20 to 50 mol%, relative to the total Si atoms in the silicone A contained in the aqueous coating composition. If the Si atom content in the Q unit is less than 5 mol%, sufficient coating hardness cannot be achieved, and mild peeling does not occur. If it exceeds 60 mol%, excessive wettability is imparted, resulting in strong adhesion and ultimately causing severe peeling.

[0034] The aqueous coating composition preferably contains a silicone having a Si atom (D' unit) bonded to an alkenyl group, and examples include a case where silicone A is silicone A1 having an alkenyl group in addition to a Q unit in the molecule, and / or a case where silicone A is silicone A2 having a Q unit but no alkenyl group in the molecule, and the aqueous coating composition further contains silicone C having an alkenyl group but no Q unit in the molecule.

[0035] In this case, the content of Si atoms (in D' units) bonded to alkenyl groups relative to the total Si atoms in silicone A1, or the total Si atoms in silicone A2 and silicone C, in the aqueous coating composition is preferably in the range of 0.05 to 20 mol%, more preferably 0.1 to 17 mol%, and even more preferably 0.2 to 15 mol%. If the content of Si atoms bonded to alkenyl groups is above the lower limit, the curing rate of the composition becomes sufficient, making it easier to efficiently form a cured silicone coating during film formation as described later. Also, if the proportion of Si atoms bonded to alkenyl groups is below the upper limit, excessive wettability is not imparted, making it less likely to cause severe peeling.

[0036] Furthermore, it is preferable that the Si atom content in the Q unit is greater than the Si atom content bonded to the alkenyl group. A preferred range is a ratio of 0.10 or more to 1.0 or less for the ratio of Si atoms bonded to the alkenyl group to the Si atom content in the Q unit. When this ratio is 0.10 or more, the coating film cohesiveness of the silicone containing the Q unit improves, resulting in a strong coating film. When this ratio is 1.0 or less, the amount of silicone containing alkenyl groups increases relative to the silicone containing the Q unit, which increases the surface free energy and improves the castability of the resin sheet raw material, thus which is preferable. A more preferred range is a ratio of 0.15 or more to 0.7 or less for the ratio of Si atoms bonded to the alkenyl group to the Si atom content in the Q unit.

[0037] The silicone containing Q units in the present invention can be produced by known methods. For example, it can be produced by copolymerizing an alkoxysilane with four alkoxy groups bonded to it, or by crosslinking or increasing the molecular weight of a silicone oligomer having a structural unit composed of Si atoms with two alkoxy groups bonded to its side chain. Furthermore, it is preferable that the silicone containing Q units in the present invention be included in the composition in the form of an aqueous dispersion.

[0038] Since silicone A is the main component of the silicone contained in the release layer, the content of silicone A is preferably 65 to 99% by mass, and more preferably 80 to 98% by mass, of the total amount of silicone contained in the aqueous coating composition.

[0039] (Silicone B having Si-H groups) Silicone B having a Si-H group is a silicone (hereinafter sometimes referred to as Silicone B) having hydrogen atoms directly bonded to Si atoms represented by a Si-H group. Examples of Silicone B include organohydrogenpolysiloxane having a structural unit represented by the following general formula (II). In addition to this structural unit, it is preferable to have a structural unit in the following general formula (II) where d is 0 and c is 2.

[0040] R3 c H d SiO (4-c-d) / 2 ...(II) (In formula (II), R3 is a monovalent saturated hydrocarbon group having 1 to 16 carbon atoms, selected from alkyl or aryl groups, where c is between 0 and 2, and d is between 1 and 3, satisfying the condition c + d ≤ 3.) Silicone B having a Si-H group may have either a linear or branched structure. Examples of alkyl groups represented by R3 include methyl, ethyl, propyl, and butyl groups, and examples of aryl groups include phenyl and tolyl groups. In particular, it is preferable that 50 mol% or more of the substituents of R3 are methyl groups in terms of easy peelability.

[0041] From the viewpoint of curing properties, silicone B having Si-H groups preferably has at least three, preferably five or more, hydrogen atoms bonded to Si atoms in one molecule of silicone B. Si-H group-containing silicone can be manufactured by known methods. Furthermore, it is preferable that silicone B having Si-H groups be included in an aqueous coating composition in the form of an aqueous dispersion.

[0042] Furthermore, the content of silicone B having Si-H groups is preferably 1 to 60 parts by mass, more preferably 2 to 50 parts by mass, and even more preferably 3 to 40 parts by mass, when the total content of silicone A having Q units (which may also have alkenyl groups) and silicone B containing Si-H groups is 100 parts by mass. When the content is 1 part by mass or more, the curing reaction proceeds easily, making it easier to obtain sufficient coating hardness. When the content is 60 parts by mass or less, Si-H is less likely to precipitate excessively on the surface, making it less likely to cause severe delamination of the resin sheet.

[0043] (Surfactants) In aqueous coating compositions for providing a release layer, it is preferable to add a surfactant to promote wetting of the substrate film. Examples of such surfactants include anionic surfactants, cationic surfactants, and nonionic surfactants, and it is possible to use one or more of these. However, as a result of diligent research by the inventors, it was found that it is preferable to use a nonionic surfactant as an emulsifier in order to prevent aggregation of the respective aqueous dispersions and not affect the curing reaction of the silicone.

[0044] As for nonionic surfactants, an HLB value in the range of 6 to 18 is preferred, and examples include at least one selected from alkylene oxide adducts of higher alcohols or higher fatty acids, esters of alkylene oxide adducts of higher fatty acids and alcohols, alkylene oxide adducts of alkanolamides, alkylene oxide adducts of sorbitan esters, and alkylene oxide adducts of higher fatty acid glycerides. Here, the HLB value is a value calculated by Griffin's formula.

[0045] Examples of alkylene oxides include ethylene oxide, propylene oxide, and butylene oxide, and one or more of these may be used. When multiple are used, the addition method can be block or random, but the HLB value is preferably in the range of 8 to 18, and more preferably in the range of 10 to 15. Among these nonionic surfactants, polyoxyethylene lauryl ether and polyoxyethylene tridecyl ether are particularly preferred. If necessary, two or more nonionic surfactants may be mixed. If a nonionic surfactant with an HLB value outside the applicable range is used as an emulsifier for a silicone aqueous dispersion, the emulsifying and dispersing power and the stability of the aqueous dispersion may decrease. The nonionic surfactant is preferably used in a range of 0.1 to 20% by mass relative to the total solid content, more preferably in the range of 0.2 to 15% by mass, and even more preferably in the range of 0.5 to 10% by mass. If it is above the lower limit of this range, the emulsification state will be good, and if it is below the upper limit of this range, it will be less likely to cause severe delamination.

[0046] (Aqueous solvent) The aqueous solvent used in the aqueous coating composition is one that contains water. By using an aqueous solvent, a silicone release layer can be formed during the film manufacturing process without the need for explosion-proof and recovery equipment required for organic solvents. If necessary, organic solvents or a mixture of water and organic solvents can also be used.

[0047] (Platinum catalyst) For example, a platinum-based catalyst can be used in the aqueous coating composition to promote the addition reaction between one or more silicones containing alkenyl groups and / or Q units and a Si-H group-containing silicone.

[0048] Known platinum-based catalysts can be used, such as platinum chloride and chloroplatinic acid. Considering dispersibility in silicone, a 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum(0) complex (Karstedt catalyst) may also be used as the platinum-based catalyst, and uniform dispersion can be ensured by dispersing it simultaneously when emulsifying the silicone.

[0049] The amount of platinum-based catalyst is preferably such that the mass of platinum is in the range of 10 to 800 ppm relative to the total mass of silicone (including silicone A, silicone B, etc.) contained in the aqueous coating composition. This range allows for sufficient curing of the silicone, suppresses the formation of silicone aggregates, and enables the creation of a release film with excellent surface properties. If the mass ratio of platinum exceeds the upper limit, the addition reaction between alkenyl groups and Si-H groups is accelerated, tending to generate silicone aggregates. From this viewpoint, the amount of platinum-based catalyst is more preferably 600 ppm or less, even more preferably 500 ppm or less, particularly preferably 200 ppm or less, very preferably 120 ppm or less, and most preferably 100 ppm or less. Furthermore, if the mass ratio of platinum is above the lower limit, the addition reaction proceeds sufficiently, making it less likely to cause poor silicone curing. From this viewpoint, the amount of platinum catalyst is more preferably 15 ppm or more, even more preferably 20 ppm or more, particularly preferably 25 ppm or more, and most preferably 80 ppm or more.

[0050] (Crosslinking reaction inhibitor) To suppress the activity of platinum-based catalysts at room temperature, it is preferable that the aqueous coating composition contains a crosslinking reaction inhibitor. Such a crosslinking reaction inhibitor is preferably one having an alkynyl group. The crosslinking reaction inhibitor having an alkynyl group is not particularly limited as long as it has an alkynyl group, but specific examples include 1-ethynyl-1-cyclohexanol, 4-ethyl-1-octin-3-ol, 3-methyl-1-dodecine-3-ol, 3,7,11-trimethyl-1-dodecine-3-ol, 1,1-diphenyl-2-propyne-3-ol, 3-ethyl-6-ethyl-1-nonin-3-ol, 3-methyl-1-pentadecin-3-ol, 2,5-dimethyl-3-hexyn-2,5-diol, and 3-phenyl-1-butyne-3-ol. Since the present invention employs an aqueous emulsion coating composition, it is preferable to use a crosslinking reaction inhibitor having an exemplified alkynyl group and a hydroxyl group, considering the balance between affinity for water and coordination ability to platinum, as well as the boiling point.

[0051] The crosslinking reaction inhibitor content is preferably 5 to 1000 ppm, more preferably 10 to 700 ppm, and even more preferably 20 to 500 ppm, relative to the mass of the aqueous coating composition used to form the release layer. When the crosslinking reaction inhibitor content is above the lower limit, the pot life is extended, the addition curing reaction of the silicone is less likely to proceed at room temperature, and silicone aggregates tend to be less likely to form. Furthermore, when the crosslinking reaction inhibitor content is below the upper limit, the silicone is less likely to migrate to the mating material after the mating material is peeled off, and the amount of reaction inhibitor that volatilizes during heat treatment is reduced, thus reducing contamination inside the oven.

[0052] (Coupling agent) The coupling agent in the present invention is, for example, a compound represented by the general formula YRSiX3, and a silane coupling agent can be given as an example. Here, Y is an organic functional group such as a vinyl group, epoxy group, amino group, or mercapto group, and it is particularly preferable that Y is an epoxy group or a vinyl group.

[0053] R is an alkylene group such as a methylene, ethylene, or propylene group, or a single bond. X is a hydrolyzable group such as a methoxy group, ethoxy group, or acetoxy, or an alkyl group, and at least one of the three Xs is a hydrolyzable group, preferably all three Xs are hydrolyzable groups. A methoxy group is preferred as the hydrolyzable group.

[0054] Preferred silane coupling agents include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, vinyltrimethoxysilane, vinyltris(2-methoxyethoxy)silane, vinylmethyldimethoxysilane, and the like.

[0055] Other examples of coupling agents include organometallic compounds containing metals such as zirconium, titanium, and aluminum, with preferred organometallic compounds being classified as alkoxides, chelates, or acylates. Specific examples include, but are not limited to, zirconium tetraacetylacetonate, zirconium acetate, titanium acetylacetonate, triethanolamine titanate, and titanium lactate.

[0056] Furthermore, it is possible to use two or more coupling agents, such as using a silane coupling agent in which Y is an epoxy group and a silane coupling agent in which Y is a vinyl group in combination.

[0057] Adding a coupling agent improves the durable adhesion between the silicone, the main component of the release layer, and the polyester film. For example, when casting resin sheets using a solution casting method with organic solvents, organic solvent components may penetrate the release layer, potentially causing erosion. However, adding a coupling agent can suppress this erosion. When casting resin sheets using a melt casting method at high temperatures, the release layer is exposed to high temperatures, potentially leading to thermal degradation. However, adding a coupling agent can suppress thermal degradation and maintain the release layer.

[0058] From the above viewpoint, the coupling agent content is preferably 0.1 to 30 parts by mass, and more preferably 1 to 20 parts by mass, based on 100 parts by mass of the total of silicone A and silicone B contained in the aqueous coating composition.

[0059] (Other ingredients) Other additives such as antistatic agents, ultraviolet absorbers, pigments, colorants, organic or inorganic particles, lubricants, and antiblocking agents may be mixed into the aqueous coating composition, provided that they do not impair the effects of the present invention.

[0060] (Preparation of silicone aqueous dispersion) In preparing the silicone aqueous dispersions that serve as raw materials for aqueous coating compositions, one method involves emulsifying them using the silicone components, aqueous solvents, and surfactants mentioned above. Known methods can be used to emulsify these components; for example, a method can be used in which pre-prepared silicone and surfactant, along with other components as needed, are mechanically emulsified in an aqueous medium using a stirring device such as a homogenizer, an adiohomomicker, or an ultraplanetary mixer.

[0061] Furthermore, the particle size of the aqueous dispersion can be adjusted by adjusting the size of the stirring blade, the stirring speed, and the stirring time. The average particle size of the dispersed particles in each silicone aqueous dispersion is preferably 200 nm or less, and more preferably 100 to 200 nm.

[0062] [Polyester film] As the polyester film used as the base film for the release film, known polyester films can be used, including known polyesters such as polyethylene terephthalate, polyethylene isophthalate, polybutylene terephthalate, poly(1,4-cyclohexylenedimethylene terephthalate), and polyethylene naphthalene dicarboxylate. Among these, polyethylene terephthalate is particularly preferred because it has a good balance of mechanical properties and moldability.

[0063] Each of the polyesters exemplified above may be a homopolymer, a copolymer with one of these polyesters as the main component, or a blend. Here, "main component" refers to a percentage of 80 mol% or more based on the number of moles of the repeating structural units of the polyester. The percentage of the main component is preferably 85 mol% or more, and more preferably 90 mol% or more. The copolymer or blended component is 20 mol% or less, preferably 15 mol% or less, and more preferably 10 mol% or less, based on the number of moles of the repeating structural units of the polyester.

[0064] The polyester film may contain lubricant particles, colorants, antistatic agents, and antioxidants, to the extent that it does not impair the objectives of the present invention. When surface flatness is required, it is preferable that the lubricant particles are substantially omitted.

[0065] Known methods are used to produce polyester, including a method in which a low degree of polymerization polyester is obtained by an esterification reaction or transesterification reaction, and then the degree of polymerization is increased using a polymerization catalyst.

[0066] Furthermore, polyester films can also be obtained by known methods, and either sequential stretching or simultaneous biaxial stretching may be used. For example, a polyester film can be produced by a process of extruding molten polyester from an extruder die into a sheet, cooling and solidifying the resulting sheet to obtain an unstretched polyester film, and then stretching the obtained unstretched polyester film in the film-forming direction and the width direction. If the polyester film has a laminated structure, for example, polyester for layer A and polyester for layer B can be prepared, laminated in a molten state and co-extruded from a die into a sheet, and then a film can be formed according to the method described above.

[0067] As for the polyester film, a film without lubricants is preferred in terms of surface flatness, but a film containing lubricants, such as inorganic fine particles such as calcium carbonate, kaolin, silica, titanium dioxide, and / or precipitated fine particles of catalyst residue, may also be used to control surface roughness. Preferably, a base film can be used that has a smooth layer without lubricants on the surface on which the release layer is provided, and a rough layer containing lubricants on the back side to control surface roughness.

[0068] This configuration makes it possible to achieve both surface smoothness and slipperiness. In this invention, "free of particles" specifically means that the particle content is 0.5% by mass or less, preferably 0.1% by mass or less, more preferably 0.05% by mass or less, even more preferably 0.01% by mass or less, and particularly preferably 0.005% by mass or less, based on the mass of the polyester film. If at least one surface layer of the laminated polyester film is configured to be particle-free, then the particle content is 0.5% by mass or less, preferably 0.1% by mass or less, more preferably 0.05% by mass or less, even more preferably 0.01% by mass or less, and particularly preferably 0.005% by mass or less, based on the mass of that layer. If the polyester film contains particles, surface protrusions of the polyester film formed by the particles may be transferred to the resin sheet in a concave manner or cause penetration of the resin sheet.

[0069] There are no particular restrictions on the thickness of the polyester film, but from the viewpoint of transportability, strength, and cost as a carrier film, a thickness of 10 to 250 μm is preferred, 15 to 100 μm is preferred, and 20 to 50 μm is more preferred.

[0070] Furthermore, the surface to which the water-based coating composition is applied to form the release layer can be surface-treated or an easy-adhesion layer can be provided to enhance adhesion with the release layer. Examples of surface treatments include plasma treatment, corona discharge treatment, ultraviolet treatment, flame treatment, and electron beam / radiation treatment. Examples of easy-adhesion layers include layers containing the same resin as the base film, and further containing antistatic agents, pigments, surfactants, lubricants, antiblocking agents, etc. However, in the present invention, since the water-based coating composition used for the release layer contains a coupling agent, the release layer can have sufficient adhesion to the base film even without providing an easy-adhesion layer or the like.

[0071] [Formation of release layer] In the present invention, a release layer is formed on at least one surface of a substrate film using an aqueous coating composition. The release layer is formed by applying the aqueous coating composition onto the substrate film, followed by heating and drying, which causes the aqueous coating composition to react and solidify. It is preferable that the release layer is formed during the film manufacturing process.

[0072] The thickness of the release layer after drying is preferably 5 to 100 nm. If the thickness of the release layer is above the lower limit, sufficient release properties are easily obtained, and if it is below the upper limit, the peel strength tends not to increase easily, and it tends to be easier to apply as it eliminates the need to increase the concentration of the aqueous coating composition or the amount of coating applied. Therefore, the thickness of the release layer is more preferably 10 to 80 nm, and even more preferably 15 to 70 nm.

[0073] When applying an aqueous coating composition onto a substrate film, the solid content concentration is preferably 20% by mass or less, and more preferably 1 to 10% by mass, based on the mass of the aqueous coating composition. When the solid content concentration in the aqueous coating composition is above the lower limit, the film-forming properties tend to be good. Also, when the solid content concentration is below the upper limit, the stability of the coating solution and the appearance of the release layer tend to be good. Water is preferably used as the aqueous solvent to adjust the solid content concentration.

[0074] The aqueous coating composition can be applied to the substrate film at any stage, but it is preferable to apply it during the polyester film manufacturing process, and more preferably to the polyester film before orientation crystallization is complete.

[0075] Here, polyester films before crystal orientation is complete include unstretched films, uniaxially oriented films in which the unstretched film is oriented in either the longitudinal direction (hereinafter sometimes referred to as the continuous film formation direction, longitudinal direction, or MD direction) or the transverse direction (hereinafter sometimes referred to as the direction perpendicular to the longitudinal direction, width direction, or TD direction), and films that have been low-magnification stretched and oriented in both the longitudinal and transverse directions (biaxially oriented films before they are finally re-stretched in the longitudinal or transverse direction to complete the orientation crystallization).

[0076] In particular, so-called in-line coating is preferred, in which an aqueous coating composition is applied to an unstretched film or a uniaxially oriented film, and then longitudinally and / or transversely stretched and heat-set. The release layer may be dried by the stretching or heat-setting process after application, and a drying process may be added as needed. Furthermore, when curing the composition using a catalyst to obtain a cured film, curing can be achieved by the stretching or heat-setting process, and a curing process may be added as needed.

[0077] When applying an aqueous coating composition to a polyester film, it is preferable to perform a physical treatment on the film surface, such as corona surface treatment, flame treatment, or plasma treatment, as a preliminary treatment to improve the coating properties, or to use the aforementioned emulsifier as a wetting agent together with the composition.

[0078] Any known coating method can be applied. For example, roll coating, gravure coating, roll brushing, spray coating, air knife coating, impregnation, curtain coating, etc., can be used individually or in combination.

[0079] [Characteristics of release film] In the present invention, the surface free energy of the release layer in the test method described later is preferably in the range of 10 mN / m to 40 mN / m, more preferably 12 mN / m to 38 mN / m, even more preferably 14 mN / m to 36 mN / m, and particularly preferably 15 mN / m to 35 mN / m. If the surface free energy of the release layer is below the upper limit, the adhesion force is reduced and severe peeling becomes less likely. If it is above the lower limit, defects due to repulsion during resin sheet coating are less likely to occur, and pinhole defects are also less likely to occur.

[0080] [Application] The release film of the present invention is used as a release film used as a carrier film for resin sheet molding during the manufacture of resin sheets. When used in this application, even if a thin resin sheet with a dried thickness of 1 μm or less is produced on the release film, the wettability is good, so pinholes in the resin sheet are reduced, and for example, when used as a release film for the manufacture of green sheets, the defect rate of thin-walled multilayer ceramic capacitors can be reduced. [Examples]

[0081] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. The evaluation methods for physical properties, etc., in the following examples are as follows.

[0082] (1) Surface free energy of the release layer For samples that had been conditioned for 24 hours under conditions of 23°C and 50% RH, the static contact angle was measured using a contact angle meter (DMo-501, manufactured by Kyowa Interface Chemical Co., Ltd.) after adding water and allowing it to stand for 30 seconds. Similarly, the static contact angles of ethylene glycol and methylene iodide were measured, and the following simultaneous equations relating to the surface tension components of the release layer were constructed using the surface tension components of each liquid listed below (the measured solutions for water, ethylene glycol, and methylene iodide are designated as 1, 2, and 3 respectively; γLD is the dispersion force component of the liquid, γLP is the polar force component of the liquid, γLH is the hydrogen bonding component of the liquid, γL is the sum of the surface tension components in the liquid, γSD is the dispersion force component of the release layer, γSP is the polar force component of the release layer, and γSH is the hydrogen bonding component of the release layer. Also, θ represents the contact angle). (γSD·γLD1) 1 / 2 +(γSP·γLP1) 1 / 2 +(γSH·γLH1) 1 / 2 =γL1(1+cosθ1) / 2 (γSD·γLD2) 1 / 2 +(γSP·γLP2) 1 / 2 +(γSH·γLH2) 1 / 2 =γL2(1+cosθ2) / 2 (γSD·γLD3) 1 / 2 +(γSP·γLP3) 1 / 2 +(γSH·γLH3) 1 / 2 =γL3(1+cosθ3) / 2 The γLD, γLP, γLH, and γL values ​​for water, ethylene glycol, and methylene iodide are shown in Table 1.

[0083] [Table 1]

[0084] Next, the surface free energy γS of the release layer surface was calculated using the following formula based on the values ​​of γSD, γSP, and γSH obtained above. γS = γSD + γSP + γSH

[0085] (2) Uniformity of the release layer application The release film was cut to A4 size, and the number of aggregated coating defects was compared when the release layer surface was visually observed using fluorescent and halogen lights, and evaluated according to the following criteria. ◎: No application defects ○: 1-2 coating defects △: 3-5 application defects ×: Six or more coating defects

[0086] (3) Velocity dependence of peeling force A polyester adhesive tape (Nitto Denko, No. 31B) was applied to the release layer surface of the release film using a rubber roller, and then pressed down with a 5kg pressure roller for one pass. It was left in this state for one day at a temperature of 23°C and a humidity of 55±5%RH. Using a high-speed peel tester (Tester Industries Co., Ltd., TE-701), the bonded tape was pulled at peel speeds of 10m / min, 30m / min, 50m / min, 70m / min, and 90m / min at a peel angle of 180°, and the peel force (mN / 50mm) was used to evaluate the relationship between peel speed and peel force. ○: The peeling force is reduced as the peeling speed increases. △: The peeling force hardly changes even when the peeling speed increases. ×: The peeling force increases as the peeling speed increases.

[0087] (4) Pin pole evaluation (coating properties of resin sheets) Three types of resin sheets were fabricated and evaluated using the following method. (4-1) Resin sheet (A) A resin solution (A) was prepared by dissolving 0.5 parts by mass of cyclic olefin resin (ARTON G7810, manufactured by JSR, 100% solids by mass) in 80 parts by mass of toluene and 20 parts by mass of tetrahydrofuran. The resin solution was applied to the release surface of a release film sample using an applicator so that the dried resin sheet would be 0.5 μm thick. After drying at 100°C for 1 minute, the A layer surface of another release film sample was placed on top of the resin sheet surface and dried for 10 minutes at a rate of 1 kg / cm². 2 After applying the load, the release film was peeled off to obtain a resin sheet (A). (4-2) Resin sheet (B) A resin solution (B) was prepared by mixing 10 parts by mass of ion exchange resin (20% Nafion dispersion solution, DE2021CS type, manufactured by Fujifilm Wako Chemical Co., Ltd., solids content 20% by mass), 10 parts by mass of water, and 20 parts by mass of isopropyl alcohol. The resin was applied to the release surface of a release film sample using an applicator so that the dried resin sheet would be 0.5 μm thick. After drying at 100°C for 1 minute, the A layer surface of another release film sample was placed on top of the resin sheet surface and dried for 10 minutes at a rate of 1 kg / cm². 2 After applying the load, the release film was peeled off to obtain the resin sheet (B). (4-3) Resin sheet (C) A resin solution (C) was prepared by mixing 20 parts by mass of UV-curable resin (urethane acrylate, product name: 8UX-015A, manufactured by Taisei Fine Chemical Co., Ltd., solids content 100% by mass), 40 parts by mass of methyl ethyl ketone, 39 parts by mass of isopropyl alcohol, and 1 part by mass of photoradical initiator (Irgacure® 907, manufactured by BASF). The solution was applied to the release surface of a release film sample using an applicator so that the dried resin sheet would be 1.0 μm thick, dried at 90°C for 15 seconds, and then subjected to a pressure of 300 mJ / cm² using a high-pressure mercury lamp. 2 The resin sheet surface is irradiated with ultraviolet light, and the A-layer surface of another release film sample is placed on top of it for 10 minutes at a rate of 1 kg / cm². 2 After applying the load, the release film was peeled off to obtain a resin sheet (C).

[0088] All three types of resin sheets obtained were evaluated using the following method: 25 cm in the central region in the film width direction of the obtained resin sheet. 2 Within the specified range, light was shone from the opposite side of the coated surface of the resin slurry, and the occurrence of pinholes visible through the transmitted light was observed and visually judged according to the following criteria. ○: No pinholes were found, and there were no particular issues with thickness variation. △: No pinholes were found, but slight indentations were observed. Thickness variations were not a particular problem. ×: There are slight pinholes and / or noticeable variations in thickness. ××: There are some pinholes, and some noticeable variations in thickness. ×××: Numerous pinholes were present, and the thickness variation was significant and noticeable.

[0089] (5) Recyclability assessment Recyclability was assessed by using a universal projector to magnify the size and number of foreign particles contained in the film 20 times under projection irradiation, and counting the number of foreign particles with a maximum diameter of 50 μm or more. The measurement area was 0.05 m². 2 That's what I decided. ◎: Number of foreign objects: 10 / 0.05m 2 Less than this does not pose a problem in terms of usage. ○: Number of foreign objects: 10 / 0.05m 2 Based on the above, 30 pieces / 0.05m 2 It slightly affects the flatness of the resin sheet, but this does not pose a problem in use. △: Number of foreign objects: 30 / 0.05 m 2 Based on the above, 100 pieces / 0.05m 2 Below a certain level, the resin sheet can be used with limited applications. ×: Number of foreign objects: 100 / 0.05m 2 In summary, the deformation of the cast surface of the resin sheet is significant and noticeable, making it unusable.

[0090] (6) Number average molecular weight Gel permeation chromatography (GPC) was measured, and the value was calculated as a polystyrene equivalent.

[0091] (7) Thickness of the release layer After cutting the release film into triangular pieces, a 2 nm thick Pt (platinum) layer was formed on the surface of the release layer by coating. The obtained samples were fixed in a multiaxial embedding capsule and embedded using epoxy resin. Using a microtome ULTRACUT-S, the film was sliced ​​perpendicular to the plane direction to obtain ultrathin samples with a thickness of 50 nm. Next, the obtained ultrathin samples were placed on a grid and vapor-stained with 2% osmium acid at 60°C for 2 hours. Using the ultrathin samples after vapor staining, the film cross-section was observed with a transmission electron microscope LEM-2000 under an acceleration voltage of 100 kV, and the thickness of the release layer was measured. Measurements were performed at 10 arbitrary points, and the average value was taken as the thickness of the release layer (unit: nm).

[0092] [Example 1] A layer of polyethylene terephthalate containing 0.06% by mass of calcium carbonate particles with an average particle size of 0.9 μm ([η]=0.63 dl / g, Tg=78°C) was used as layer A, and a particle-free polyethylene terephthalate layer ([η]=0.63 dl / g, Tg=78°C) was used as layer B. These two layers were laminated in a molten state and extruded through an extruder die. The film was then cooled in a cooling drum by a conventional method to obtain an unstretched film. Next, it was stretched 3.6 times in the longitudinal direction at 80°C, and then the coating solution (aqueous coating composition) obtained in Production Example 1 was uniformly applied to the surface of layer B of the film using a roll coater to a product thickness of 30 nm. The coating solution used was prepared within 24 hours.

[0093] Next, the coated film was dried at 115°C, stretched 4.0 times in the transverse direction at 145°C, and then heat-set at 230°C for approximately 10 seconds to obtain a release film (total thickness 12 μm, A layer thickness 9 μm, B layer thickness 3 μm) having a release layer formed by reacting and solidifying the coating liquid. The film was then evaluated. The evaluation results are shown in Table 3.

[0094] In addition, for the A layer, the release film portions that did not become products when collecting the product roll and the release films that did not become products due to defects or the like were pulverized for each example and comparative example until the long diameter of the film pieces became about 5 mm or less, melted, and 50% by mass of the recycled raw material was used.

[0095] Production Example 1 <Aqueous dispersion of silicone A1 containing an alkenyl group and Q unit> Using an emulsifying device capable of stirring the entire inside of the container (manufactured by N.P. Lab Co., Ltd., device name "Ultra Planetary Mixer"), 97% by mass of silicone A1 and 3% by mass of polyoxyethylene tridecyl ether (manufactured by Takemoto Yushi Co., Ltd., trade name "New Calgen D-1208") as a surfactant were mechanically emulsified in an aqueous medium to obtain an aqueous dispersion of silicone A1 with a solid content of 20% by mass. Also, the emulsion particle size was adjusted to an average particle size of 200 nm by adjusting the stirring speed and stirring time during emulsification.

[0096] In addition, the composition of silicone A1 is, in formula (I), R1 is a vinyl group, R2 is a methyl group, and for the silicon to which the vinyl group is directly bonded, there is 6.00 mol% of a structural unit in which only one vinyl group is bonded, 60.00 mol% of a structural unit composed of Q units where a = b = 0 in formula (I), and 34.00 mol% of a structural unit where R2 is a methyl group, a = 0, and b = 2 (both ends are a = 0, b = 3) in formula (I), and the number average molecular weight was adjusted to 250,000.

[0097] <Aqueous dispersion of silicone B having a Si-H group> Using an emulsifying device capable of stirring the entire inside of the container (manufactured by N.P. Lab Co., Ltd., device name "Ultra Planetary Mixer"), 97% by mass of a Si-H group-containing silicone and 3% by mass of polyoxyethylene tridecyl ether (manufactured by Takemoto Yushi Co., Ltd., trade name "New Calgen D-1208") as a surfactant were mechanically emulsified in an aqueous medium to obtain an aqueous dispersion of a Si-H group-containing silicone B with a solid content of 10% by mass. Also, the emulsion particle size was adjusted to an average particle size of 160 nm by adjusting the stirring speed and stirring time during emulsification.

[0098] Furthermore, the Si-H group-containing silicone composition is such that in formula (II), R3 is a methyl group, c=d=1, meaning that only one hydrogen group is bonded to the silicon atom to which a hydrogen group is directly bonded, and the hydrogen atom is not bonded to the terminal silicon atom. The composition consists of 30 repeating units of constituent units that have silicon atoms to which hydrogen groups are directly bonded, and dimethylsiloxane constituent units (with methyl groups at both ends). The number of repeating units of the latter constituent units was adjusted so that the number-average molecular weight is 4000.

[0099] <Coating liquid> As an aqueous coating composition, a silicone aqueous dispersion was prepared by mixing 90 parts by mass of silicone A1 containing alkenyl groups and Q units and 5 parts by mass of silicone B having Si-H groups. To this, 5 parts by mass of the coupling agent C-1 described below, 100 ppm of the platinum-based catalyst described below relative to the total mass of silicones A1 and B, and 200 ppm of the crosslinking reaction inhibitor described below relative to the mass of the coating solution were mixed. The solid content concentration of the coating solution was then diluted with water to achieve the target release layer thickness, and the coating solution was prepared. • Coupling agent C-1:3-glycidoxypropyltriethoxysilane (manufactured by Shin-Etsu Silicone Co., Ltd., product name "KBM-403") • Platinum-based catalyst: Platinum-based catalyst emulsion (manufactured by Shin-Etsu Chemical Co., Ltd., product name "CAT-PM-10A") • Crosslinking reaction inhibitor: 1-ethinylcyclohexanol (manufactured by Alfa Lancaster)

[0100] [Examples 2-11] In Example 1, a release film was prepared under exactly the same conditions as in Example 1, except that the composition of the aqueous coating composition was changed to that shown in Table 3 using silicones A-1 to A-11 shown in Table 2, and the aforementioned evaluation was performed. The results are shown in Table 3.

[0101] Furthermore, the coupling agent C-2 was vinyltriethoxysilane (manufactured by Shin-Etsu Silicone Co., Ltd., trade name "KBM-1003"), which was used without purification. In addition, silicone A-11 was adjusted to have a number average molecular weight of 2000.

[0102] [Comparative Examples 1-3] In Example 1, a release film was prepared under exactly the same conditions as in Example 1, except that the composition of the aqueous coating composition was changed to that shown in Table 4 using silicones A-9, A-10, or A-11 shown in Table 2, and the aforementioned evaluation was performed. The results are shown in Table 4.

[0103] [Comparative Example 4] In Example 1, a release film was prepared under exactly the same conditions as in Example 1, except that the coating solution was changed as described below, and the evaluation described above was performed. The results are shown in Table 4.

[0104] Specifically, the coating solution consisted of 48 parts by mass of melamine resin Nikalac MX-035 (manufactured by Sanwa Chemical Co., Ltd.), 50 parts by mass of silicone-modified acrylic resin Cymac US-480 (manufactured by Toagosei Co., Ltd.), and 2 parts by mass of silicone-based surfactant DOWSIL 500W Additive (manufactured by Dow-Toray Industries, Inc.). The solid content of the coating solution was diluted with water to achieve the target release layer thickness.

[0105] [Comparative Example 5] In Example 1, a release film was prepared under exactly the same conditions as in Example 1, except that a coupling agent was not used, and the evaluation described above was performed. The results are shown in Table 4.

[0106] [Table 2]

[0107] [Table 3]

[0108] [Table 4]

[0109] As shown in Table 3, in Examples 1 to 11, the uniformity of the release layer coating, the speed dependence of the peeling force, the coatability of various resin sheets, and the recyclability were all good.

[0110] In contrast, as shown in Table 4, Comparative Examples 1 and 3, which used silicone A-9 or A-11 with a Si atom content below the specified range for the Q unit, showed inferior speed dependence of peeling force and inferior coating properties for various resin sheets. Conversely, in Comparative Example 2, which used silicone A-10 with a Si atom content above the specified range for the Q unit, the increased resin component resulted in inferior coating uniformity and recyclability of the release layer.

[0111] Furthermore, in Comparative Example 4, where the release layer contained melamine resin or the like, the recyclability was inferior due to an increase in crosslinking components. [Industrial applicability]

[0112] The release film of the present invention exhibits excellent uniformity of release layer application, speed dependence of peeling force, coating properties for various resin sheets, and recyclability, making it suitable for a wide range of applications and giving it extremely high industrial value.

Claims

1. A release film for molding resin sheets, comprising a polyester film and a release layer formed by reacting and solidifying an aqueous coating composition, The aqueous coating composition comprises water, SiO ４／２ The mixture comprises a silicone A having Q units represented by, a silicone B having Si-H groups, a crosslinking reaction inhibitor, a platinum-based catalyst, and a silane coupling agent. The silicone A is silicone A1 having alkenyl groups in addition to the Q units in the molecule, and the aqueous coating composition further contains silicone C having alkenyl groups but not the Q units in the molecule. The content of silicone A is 65 to 99% by mass of the total amount of silicone contained in the aqueous coating composition. The silane coupling agent is contained in 1 to 30 parts by mass with respect to a total of 100 parts by mass of silicone A and silicone B. A release film for resin sheet molding, wherein the content of Si atoms constituting the Q unit in the silicone A is in the range of 5 to 60 mol%.

2. The release film for resin sheet molding according to claim 1, wherein the coupling agent is a silane coupling agent having a vinyl group, an epoxy group, an amino group, or a mercapto group.

3. The aqueous coating composition contains 1 to 20 parts by mass of the coupling agent with respect to a total of 100 parts by mass of the silicone A and the silicone B, as described in claim 1 or 2, for the release film for molding resin sheets.

4. The release film for molding resin sheets according to any one of claims 1 to 3, wherein the surface free energy of the release layer is 10 mN / m or more and 40 mN / m or less.

5. The release film for molding resin sheets according to any one of claims 1 to 4, wherein the polyester film has a surface layer that does not contain particles, and the release layer is disposed on the surface layer.

6. The release film for resin sheet molding according to claim 1, wherein the molar ratio of the content of Si atoms bonded to the alkenyl group to the content of Si atoms constituting the Q unit (content of Si atoms bonded to the alkenyl group / content of Si atoms contained in the Q unit) is 0.1 or more and 1.0 or less.

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