Laminate polyester film

Abstract

To provide a laminate polyester film which has peel force suitable for various sheet molding, and can be produced utilizing a composition that has adequate base material adhesion, is aqueous and has a high pot life.SOLUTION: A laminate polyester film has a release layer on at least one surface of the polyester film, wherein the release layer is formed of a coating composition for release, the coating composition contains an urethane resin containing a reactive functional group and a silicone structure, and a crosslinking agent, and a solvent of the coating composition is composed of an aqueous solvent. A method for producing a laminate polyester film includes forming a release layer by an in-line coating method of coating a coating composition for release in a step of producing a polyester film.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a laminated polyester film, and more particularly to a laminated polyester film having a peel strength suitable for use in various sheet moldings, tapes, adhesive separators, and the like. [Background technology]

[0002] Polyester films, such as polyethylene terephthalate and polyethylene naphthalate, are widely known to have excellent properties such as dimensional stability, heat resistance, and mechanical strength, and are used in a variety of fields.

[0003] Polyester films are also used as release films for various tapes, sheet moldings, adhesive separators, etc., but they often lack releasability, and studies have been conducted on the application of a separate coating film with releasability (for example, Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] : JP 2018-028049 A [Patent Document 2] : JP 2005-313601 A [Patent Document 3] :Special Publication No. 2000-500706 Summary of the Invention [Problem to be solved by the invention]

[0005] Generally, organic solvent-based silicone compounds are used for release coatings, but silicone compounds have problems such as being difficult to adhere to substrates and the silicone components easily migrate to the release layer and the adherend. In response to this, Patent Document 1 proposes a release film formed from hydroxyl-containing silicone, polyol, and isocyanate. Patent Document 2 proposes a release film formed from hydroxyl-containing silicone and isocyanate.

[0006] However, these coating methods mainly use organic solvents, and it is costly to make the drying equipment in the coating equipment explosion-proof. In addition, it is difficult to recover the volatile solvent, which poses a problem from the perspective of environmental impact.

[0007] Patent Document 3 proposes a release film using a water-based coating material composed of an addition-curing type silicone resin and a polyurethane resin.

[0008] However, addition-curing silicone resins generally require the use of platinum-based catalysts, which poses problems in terms of pot life.In addition, from the viewpoint of environmental friendliness, the recyclability of laminated polyester films is also an important issue, and addition-curing silicone resins have the disadvantage of being difficult to decompose and difficult to recycle.

[0009] The present invention has been made in consideration of the above-mentioned technical problems, and aims to provide an environmentally friendly laminated polyester film that has adhesion to polyester films and a peel strength suitable for various sheet molding applications, tapes, adhesive separators, etc. [Means for solving the problem]

[0010] As a result of intensive research, the inventors have found that the above-mentioned problems can be solved by a release layer formed using a release coating composition containing a urethane resin and a crosslinking agent according to the present invention. In addition, the solvent of the release coating composition in the present invention is composed of an aqueous solvent, so that the above-mentioned problems can be solved.

[0011] That is, the present invention comprises the following:

[0012] [1] A laminated polyester film having a polyester film as a substrate and a release layer in this order, The release layer is formed from a release coating composition, The release coating composition includes a urethane resin having a reactive functional group and a silicone structure, and a crosslinking agent, The solvent for the release coating composition is an aqueous solvent.

[0013] [2] The laminated polyester film according to [1], wherein the proportion of the silicone component contained in the urethane resin is 0.1% by mass or more and less than 50% by mass, relative to the total mass of the urethane resin (100% by mass).

[0014] [3] The laminated polyester film according to [1] or [2], wherein the release layer is formed by stretching in at least one direction.

[0015] [4] The laminated polyester film according to any one of [1] to [3], wherein the reactive functional group of the urethane resin containing a silicone structure contains a carboxy group.

[0016] [5] The laminated polyester film according to any one of [1] to [4], wherein the crosslinking agent contained in the coating composition has a carboxy group reactivity or a hydroxy group reactivity.

[0017] [6] A method for producing the laminated polyester film described herein, comprising the steps of: Forming a release layer by an in-line coating method in which a release coating composition is applied during the production process of a polyester film; or After producing a polyester film, a release layer is formed by an offline coating method in which a release coating composition is applied to the polyester film. A method for producing a laminated polyester film.

[0018] [7] A method for producing the laminated polyester film described herein, comprising the steps of: The release coating composition has a haze value of a composition when a urethane resin and a crosslinking agent are blended therein, and A method for producing a laminated polyester film, wherein the variation in haze value of the composition when the composition is heated at 60° C. for 4 hours is 2.5% or less. Effect of the Invention

[0019] The release coating composition of the present invention can be formed by containing the urethane resin containing the reactive functional group and silicone structure according to the present invention and a crosslinking agent, so that the solvent of the release coating composition can be composed of an aqueous solvent. As a result, unlike the release layer forming composition composed mainly of an organic solvent, the drying equipment in the coating device can be made explosion-proof, and the safety of the workers and the surrounding environment can be improved. In addition, the cost related to the explosion-proofing can be reduced. Furthermore, since the solvent of the release coating composition can be mainly composed of an aqueous solvent, the recovery of volatile solvent can be reduced or eliminated, which is also excellent from the viewpoint of environmental load. Furthermore, by containing a urethane resin containing a reactive functional group and a silicone structure according to the present invention, an excellent pot life can be exhibited, and further, compared to addition-curing silicone resins, the decomposition ability during recycling is also excellent. The laminated polyester film of the present invention having such characteristics is a laminated polyester film having a peel strength suitable for applications such as various sheet moldings, tapes, and adhesive separators, and has appropriate adhesion to substrates and can be produced using an aqueous composition with a long pot life.

[0020] Furthermore, the release layer of the present invention has high adhesion to the substrate and can inhibit the silicone component from migrating to the adherend to which the release layer is attached.

[0021] In addition, since the present invention does not use an addition curing type silicone resin as a main component, it is possible to obtain a coating composition with a long pot life. Since the present invention can use a water-based coating composition with a long pot life, it is possible to improve the coating suitability of the release layer and reduce the amount of waste of the composition.

[0022] Furthermore, from the viewpoint of environmental friendliness, the recyclability of the laminated polyester film is also an important issue, and the present invention does not use an addition-curing type silicone resin as the main component, but contains urethane bonds that are easily decomposed by heat, hydrolysis, or light, thereby improving decomposition and achieving improved recyclability. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, the embodiments of the present invention will be described in detail, but the present invention is not limited to these embodiments.

[0024] The present invention relates to a laminated polyester film having a polyester film as a substrate and a release layer in this order, and for example, the release layer can be provided on at least one side of the polyester film as a substrate. The release layer is formed from a release coating composition, which contains a urethane resin including a reactive functional group and a silicone structure, and a crosslinking agent, and the solvent of the release coating composition is composed of an aqueous solvent.

[0025] [Polyester film] The polyester constituting the polyester film used as the substrate film (hereinafter, sometimes referred to as substrate) in the present invention is not particularly limited, and a film formed from a polyester generally used as a substrate for a release film can be used. A crystalline linear saturated polyester consisting of an aromatic dibasic acid component and a diol component is preferable, and for example, polyethylene terephthalate, polyethylene isophthalate, polyethylene-2,6-naphthalate, polybutylene terephthalate, poly(1,4-cyclohexylene dimethylene terephthalate), polytrimethylene terephthalate, or a copolymer mainly composed of these resin components is more preferable. Among them, a polyester film formed from polyethylene terephthalate is particularly preferable. The polyethylene terephthalate preferably has a repeating unit of ethylene terephthalate of 90 mol % or more, more preferably 95 mol % or more, and may be copolymerized with a small amount of other dicarboxylic acid components and diol components. For example, from the viewpoint of cost, it is preferable to use one produced only from terephthalic acid and ethylene glycol.

[0026] In addition, known additives such as antioxidants, light stabilizers, ultraviolet absorbers, crystallizing agents, etc. may be added within a range that does not impair the effects of the release film of the present invention. The polyester film is preferably a biaxially oriented polyester film because of its high bidirectional elastic modulus.

[0027] The intrinsic viscosity of the polyester film is preferably 0.50 dl / g or more and 0.70 dl / g or less, more preferably 0.52 dl / g or more and 0.65 dl / g or less. When the intrinsic viscosity is 0.50 dl / g or more, breakage does not occur frequently during the stretching process, which is preferable. On the other hand, when the intrinsic viscosity is 0.70 dl / g or less, cuttability is good when cutting into a predetermined product width, and dimensional defects do not occur, which is preferable. In addition, it is preferable to thoroughly vacuum dry the raw material pellets.

[0028] In this specification, unless otherwise specified, the term "polyester film" refers to a polyester film having (laminate) a surface layer A and a surface B described below. The polyester film as the substrate may be a single-layer polyester film containing particles.

[0029] The method for producing the polyester film in the present invention is not particularly limited, and a method generally used in the past can be used. For example, the polyester is melted in an extruder, extruded into a film, and cooled on a rotating cooling drum to obtain an unstretched film, and the unstretched film is biaxially stretched to obtain the film. The biaxially stretched film can be obtained by a method in which a uniaxially stretched film in the longitudinal or transverse direction is biaxially stretched in the transverse or longitudinal direction successively, or a method in which an unstretched film is biaxially stretched in the longitudinal and transverse directions simultaneously.

[0030] In the present invention, the stretching temperature during stretching of the polyester film is preferably equal to or higher than the second-order transition point (Tg) of the polyester, and the stretching is preferably performed at a ratio of 1 to 8 times, particularly 2 to 6 times, in both the longitudinal and transverse directions.

[0031] The polyester film preferably has a thickness of 12 μm or more and 100 μm or less, more preferably 16 μm or more and 50 μm or less, and even more preferably 19 μm or more and 33 μm or less. If the thickness of the film is 12 μm or more, it is preferable because there is no risk of deformation due to heat during film production, processing, and molding. On the other hand, if the thickness of the film is 100 μm or less, even if it is discarded after use, the amount of film is not extremely large, which is preferable in terms of reducing the environmental load.

[0032] The polyester film substrate may be a single layer or a multi-layer structure of two or more layers. For example, the substrate film may be a polyester film having a surface layer A that is substantially free of particles having a particle size of 1.0 μm or more, and a surface layer B that contains particles. Preferably, the surface layer A is substantially free of inorganic particles having a particle size of 1.0 μm or more.

[0033] In this embodiment, particles having a particle size of less than 1.0 μm and 1 nm or more may be present in the surface layer A. By making the surface layer A substantially free of particles having a particle size of 1.0 μm or more, such as inorganic particles, it is possible to reduce defects caused by the transfer of the particle shape in the substrate to the resin sheet.

[0034] In one embodiment, the surface layer A does not contain any particles having a particle size of less than 1.0 μm, so that defects caused by the transfer of the particle shape in the base material to the object to be peeled can be more effectively prevented.

[0035] In one embodiment, the polyester film substrate is preferably a laminate film having a surface layer A substantially free of inorganic particles on at least one side thereof, which can more effectively prevent defects caused by the transfer of particle shapes in the substrate to the resin sheet.

[0036] For example, a preferred embodiment is one in which the surface layer A substantially does not contain particles having a particle size of less than 1.0 μm, and also substantially does not contain particles having a particle size of 1.0 μm or more.

[0037] Here, in the present invention, "substantially free of particles" means, for example, in the case of inorganic particles less than 1.0 μm, that the content is 50 ppm or less, preferably 10 ppm or less, and most preferably below the detection limit when the inorganic elements are quantified by fluorescent X-ray analysis. This is because even if particles are not actively added to the film, contaminants from foreign matter or dirt attached to the raw material resin or the line or equipment in the film manufacturing process may peel off and be mixed into the film. In addition, "substantially free of particles with a particle size of 1.0 μm or more" means that particles with a particle size of 1.0 μm or more are not actively included.

[0038] In the case of a laminated polyester film having a multi-layer structure of two or more layers, it is preferable that a surface layer B that can contain inorganic particles is provided on the surface opposite to a surface layer A that does not substantially contain inorganic particles.

[0039] As for the laminated structure, if the layer on the side to which the release layer is applied is called layer A, the layer on the opposite side is called layer B, and the other core layer is called layer C, the layer structure in the thickness direction can be a laminated structure such as release layer / A / B or release layer / A / C / B. Naturally, layer C can be a multi-layer structure. Also, surface layer B can be free of inorganic particles. In that case, it is preferable to provide a coating layer containing at least inorganic particles and a binder on surface layer B in order to impart slip properties for winding the film into a roll.

[0040] In the polyester film substrate of the present invention, the surface layer B forming the side opposite to the side to which the release layer is applied preferably contains inorganic particles, particularly silica particles and / or calcium carbonate particles, from the viewpoint of the slipperiness of the film and ease of air escape. The content of the inorganic particles contained in the surface layer B is preferably 5000 ppm or more and 15000 ppm or less in total.

[0041] In this case, the area surface average roughness (Sa) of the film of the surface layer B is preferably in the range of 1 nm to 40 nm. More preferably, it is in the range of 5 nm to 35 nm. When the total of the silica particles and / or calcium carbonate particles is 5000 ppm or more and Sa is 1 nm or more, air can be uniformly released when the film is wound into a roll, and the film has a good rolled shape and good flatness, which is suitable for sheet production, etc. In addition, when the total of the silica particles and / or calcium carbonate particles is 15000 ppm or less and Sa is 40 nm or less, the lubricant is less likely to aggregate and large protrusions are not formed, which is preferable because the quality is stable, especially during sheet production, etc.

[0042] As the particles contained in the above-mentioned B layer, in addition to silica and / or calcium carbonate, inactive inorganic particles and / or heat-resistant organic particles can be used, but from the viewpoint of transparency and cost, it is more preferable to use silica particles and / or calcium carbonate particles. Other inorganic particles that can be used include alumina-silica composite oxide particles and hydroxyapatite particles. Heat-resistant organic particles include crosslinked polyacrylic particles, crosslinked polystyrene particles, and benzoguanamine particles. When silica particles are used, porous colloidal silica is preferred, and when calcium carbonate particles are used, light calcium carbonate that has been surface-treated with a polyacrylic acid-based polymer compound is preferred from the viewpoint of preventing the lubricant from falling off.

[0043] The average particle size of the inorganic particles added to the surface layer B is preferably 0.1 μm or more and 2.0 μm or less, particularly preferably 0.3 μm or more and 1.0 μm or less. If the average particle size of the inorganic particles is 0.1 μm or more, the slipperiness of the release film is good, which is preferable.

[0044] In order to improve the adhesion of a release layer or the like to be applied later, to prevent static electricity, or the like, a coating layer may be provided on the surface of the surface layer A and / or the surface layer B before stretching or after uniaxial stretching in the film-forming process, and corona treatment or the like may also be performed.

[0045] From the viewpoint of reducing pinholes, it is preferable not to use recycled raw materials for the surface layer A, which is the layer on which the release layer is to be formed, in order to prevent inclusion of inorganic particles such as lubricants.

[0046] The thickness ratio of the surface layer A, which is the layer on which the release layer is provided, is preferably 20% to 50% of the total thickness of the base film. If it is 20% or more, the film is less susceptible to the influence of particles contained in the surface layer B, etc. from the inside, and it is easy for the area surface average roughness Sa to satisfy the above range, which is preferable. If it is 50% or less of the total thickness of the base film, the proportion of recycled raw materials used in the surface layer B can be increased, which is preferable because it reduces the environmental load.

[0047] From the viewpoint of economic efficiency, recycled raw materials such as film scraps and PET bottles, each of which is 50% by mass to 90% by mass, can be used for the layers (surface layer B or the above-mentioned intermediate layer C) other than the surface layer A. Even in this case, it is preferable that the type and amount of the lubricant contained in layer B, the particle size, and the area surface average roughness (Sa) satisfy the above ranges.

[0048] In addition, in order to improve the adhesion of a release layer or the like to be applied later, or to prevent static electricity, a coating layer may be provided on the surface of surface layer A and / or surface layer B before stretching or after uniaxial stretching in the film-forming process, or a surface treatment may be applied.

[0049] In one embodiment, the release layer-forming surface to which the aqueous coating composition is applied can be surface-treated or provided with an easy-adhesion layer in order 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 the easy-adhesion layer include a layer containing the same resin as the base film and further containing an antistatic agent, a pigment, a surfactant, a lubricant, an antiblocking agent, etc. When an adhesion improver such as a coupling agent is added to the aqueous coating composition, the release layer can have sufficient adhesion to the base film even without providing an easy-adhesion layer, etc.

[0050] (Release layer) The release layer of the present invention is formed from a release coating composition, The coating composition includes a urethane resin containing a reactive functional group and a silicone structure, and a crosslinking agent, and the solvent of the coating composition is an aqueous solvent. Although not intended to be limited to a particular theory, the release coating composition contains a urethane resin containing a reactive functional group and a silicone structure according to the present invention, and a crosslinking agent, so that the solvent of the composition can be constituted by an aqueous solvent. In addition, since the composition contains a urethane resin containing reactive functional groups and silicone structures, a crosslinking agent, and an aqueous solvent, the recovery of volatile solvents can be reduced or eliminated, which is excellent from the viewpoint of environmental load. In addition, the composition exhibits an excellent pot life, and in addition, the composition has a superior decomposition ability during recycling, compared to addition-curing silicone resins.

[0051] (urethane resin) The urethane resin used in the coating composition is a urethane resin containing a reactive functional group and a silicone structure. The urethane resin according to the present invention has high adhesion to the substrate and can chemically bond the silicone component during the synthesis process. Compared with conventional thermal addition silicone, the low molecular weight silicone component generated during the coating film formation process can be reduced, so that the silicone component can be prevented from migrating to the adherend with the release layer.

[0052] In addition, since the present invention does not use an addition curing type silicone resin as a main component, it is possible to obtain a coating composition with a long pot life. Since the present invention can use a water-based coating composition with a long pot life, it is possible to improve the long-length processability of the release layer and reduce the amount of waste of the composition.

[0053] Additionally, from an environmental perspective, the recyclability of laminated polyester films is also an important issue, but by incorporating urethane bonds into the main chain, decomposition is improved compared to conventional thermal addition silicones, and improved recyclability can be achieved.

[0054] The urethane resin containing reactive functional groups and silicone structures has a carboxyl group, an amino group, As long as it has a reactive functional group such as a hydroxyl group or an epoxy group and can be made into a water-based system, it is not particularly limited, and any structure can be used. A water-soluble polymer may be used, or a dispersion in an aqueous solvent may be used. In the present invention, the release coating composition is composed of an aqueous solvent. "Composed of an aqueous solvent" means that the aqueous solvent occupies more than 50% by mass and 100% by mass or less of the total amount of the solvent contained in the release coating composition, more preferably 80% by mass or more and 100% by mass or less, for example 90% by mass or more and 100% by mass or less. The aqueous solvent may substantially occupy 100% by mass of the total amount of the solvent contained in the release coating composition.

[0055] Here, the aqueous solvent is a solvent containing 50% to 100% water, and may be a completely aqueous system, and may be used in combination with a water-soluble solvent such as alcohols as necessary. From the viewpoint of environmental load, the water ratio is preferably 70% to 100%, more preferably 80% to 100%, and even more preferably 90% to 100%. It is particularly preferable not to intentionally use a solvent other than water.

[0056] When preparing a dispersion in an aqueous solvent, either the self-emulsification method or the forced emulsification method can be used. A self-emulsification dispersion that is easy to control the particle size is preferable, and more preferably, a urethane resin that has a wide range of crosslinking agent types and contains a carboxyl group that can contribute to self-emulsification, and more preferably, a urethane resin that has been neutralized with amines or ammonia to improve dispersibility in an aqueous solvent. By making the urethane resin water-soluble or water-dispersible, the environmental load can be reduced, and the costs associated with explosion-proofing drying equipment and solvent recovery can be reduced.

[0057] The synthesis method of the urethane resin containing a silicone structure is not particularly limited, and the silicone structure may be included in the main chain of the urethane resin or in the side chain. The urethane resin may be modified with silicone during the synthesis process, or after the synthesis of the urethane resin. Particularly preferred is a side-chain silicone modified body in which the silicone component is easily localized on the surface and can be modified either before or after the synthesis of the urethane resin. Two or more types of urethane resin containing a silicone structure may be used in combination as necessary. The releasability can be controlled by incorporating any silicone structure into the urethane resin.

[0058] The following is an example of a method for producing a urethane resin containing a silicone structure. The urethane resin containing a silicone structure can be obtained by a conventional method. As long as it is finally made water-based, an organic solvent may be used in the synthesis process, and the production method and synthesis raw materials are not limited. For example, it can be synthesized by utilizing the reaction of polyols, reactive functional group-containing silicone, and polyisocyanate.

[0059] Examples of polyols include polyether polyols, polyester polyols, polycaprolactone polyols, polycarbonate polyols, and acrylic polyols. They may be used alone or in combination. By appropriately selecting the structure and molecular weight of the polyols, the coating strength, adhesion, water dispersibility, etc. can be controlled. Even if an organic solvent is used in the synthesis process, the solvent can be recovered at a lower cost and with minimal impact on the human body than if it were recovered in the coating film formation process.

[0060] Examples of polyether polyols include those obtained by polymerizing alkylene oxides such as ethylene oxide and propylene oxide with low molecular weight polyols such as ethylene glycol and glycerin as an initiator. Commercially available products include the "DK Polyol Series" manufactured by Daiichi Kogyo Seiyaku Co., Ltd., the "Adeka Polyether Series" manufactured by ADEKA Corporation, and the "EXCENOL Series" manufactured by AGC Corporation.

[0061] Examples of polyester polyols include those obtained by polycondensation of dibasic acids such as terephthalic acid, adipic acid, and succinic acid with polyols such as ethylene glycol, polyoxyethylene glycol, and 1,6-hexanediol. Commercially available products include the "ADEKA NEW ACE series" manufactured by ADEKA CORPORATION, the "POLYLITE series" manufactured by DIC CORPORATION, and the "NIPPOLAN series" manufactured by Tosoh Corporation.

[0062] Examples of polycaprolactone polyols include those obtained by ring-opening polymerization of caprolactones such as ε-caprolactone using polyols as initiators. Commercially available products include the "Capromer series" manufactured by BASF, the "Capa series" manufactured by Ingevity, and the "Placcel series" manufactured by Daicel Corporation.

[0063] Examples of polycarbonate polyols include those obtained by reacting glycols such as ethylene glycol, 1,6-hexanediol, and bisphenol A with carbonates such as ethylene carbonate and diphenyl carbonate. Commercially available products include the "ETERNACOLL series" manufactured by UBE Corporation, the "DURANOL series" manufactured by Asahi Kasei Corporation, and the "BENEBiOL series" manufactured by Mitsubishi Chemical Corporation.

[0064] Examples of acrylic polyols include acrylic acid derivatives containing hydroxyl groups, such as hydroxyethyl acrylate, hydroxyethyl methacrylate, and hydroxybutyl acrylate. Examples of such products include those obtained by copolymerizing with acrylic acid, methacrylic acid, acrylic acid esters, etc. Commercially available products include the "#6000 series" manufactured by Taisei Fine Chemical Co., Ltd., the "ACRYDIC series" manufactured by DIC Corporation, and the "ARUFON series" manufactured by Toagosei Co., Ltd.

[0065] The urethane resin used in the present invention has a reactive functional group. It is particularly preferable that the reactive functional group contains a carboxyl group which acts as a crosslinking reaction point and improves dispersibility in an aqueous solvent. By using a crosslinking reaction, it is possible to control the release property and develop solvent resistance. If the above polyol does not contain a carboxyl group, a carboxyl group can be introduced by reacting an acid anhydride such as phthalic anhydride, trimellitic anhydride, or pyromellitic anhydride with the polyol. More preferably, a carboxyl group-containing diol such as 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, or 2,2-dimethylolbutyric acid is used in combination as a polyol or a urethane synthesis raw material. By adjusting the amount of carboxyl group introduced according to the required release property, it is possible to control the crosslinking property and to lead the release layer to an appropriate coating hardness. In addition, it is also possible to impart resistance to organic solvents used during sheet molding, etc., as necessary.

[0066] The isocyanates used in the synthesis of the urethane resin can be any isocyanates having two or more isocyanate groups in one molecule. They may be used alone or in combination. For example, hexamethylene diisocyanate, trimethylene diisocyanate, 1,4-cyclohexane diisocyanate, bis(4-isocyanatophenyl)methane, toluene-2,4-diisocyanate, 4,4'-toluene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 4,4'-diphenyl isocyanate, and the like can be mentioned. In addition to the above monomers, polymers such as dimers, biurets, and isocyanurates derived from polyisocyanate monomers, as well as adducts obtained by adding monomeric isocyanates to low molecular weight polyols such as trimethylolpropane, can also be used. Particularly preferred are those having two isocyanate groups in the molecule because of the ease of reaction control. By appropriately selecting the isocyanate, it is possible to control the water dispersibility, particle size control, coating strength, adhesion, and / or solvent resistance of the release layer.

[0067] The silicone for modifying the urethane resin may be any silicone containing a reactive functional group. It is also preferable that the silicone contains a hydrophilic functional group to improve water dispersibility. The silicone may be modified during or after the synthesis of the urethane resin. Examples of amino-modified silicones include "DOWSIL BY 16-205" and "DOWSIL FZ-3760" manufactured by Dow-Toray Industries, Inc., and "X-22-161A" and "PAM-E" manufactured by Shin-Etsu Chemical Co., Ltd.; examples of epoxy-modified silicones include "DOWSIL BY 16-839 Fluid" and "DOWSIL SF 8421 Fluid" manufactured by Dow-Toray Industries, Inc., and "X-22-163" and "KF-105" manufactured by Shin-Etsu Chemical Co., Ltd.; examples of hydroxyl- or carbinol-modified silicones include "DOWSIL BY 16-201" and "DOWSIL SF 8427 Fluid" manufactured by Dow-Toray Industries, Inc., "X-22-176DX" and "X-22-176F" manufactured by Shin-Etsu Chemical Co., Ltd., and "Silaplane FM-DA26" manufactured by JNC Corporation. Silicone-modified polyurethane can be obtained by reacting with reactive functional groups such as hydroxyl groups and carboxyl groups contained in polyol or isocyanate. Any amount of silicone modification can be used, but it is preferable that the silicone component is 0.1% to 50% by mass relative to the total mass of the urethane resin (100% by mass). It is 0.1% to less than 50% by mass, more preferably 0.1% to 30% by mass, more preferably 0.5% to 20% by mass, and particularly preferably 0.5% to 15% by mass relative to the total mass (100% by mass). By adjusting the amount of silicone to an appropriate range, it is possible to achieve both releasability and dispersibility in aqueous solvents, leading to a release layer coating composition with excellent adhesion to polyester films. The molecular chain length and modification amount of silicone, functional group modification, etc. can lead to the development of appropriate releasability of the laminated polyester film.

[0068] A known catalyst may be used in the production of the urethane resin, such as an organometallic compound or a tertiary amine compound.

[0069] Examples of the organometallic compound include dibutyltin dichloride, dibutyltin diacetate, triethyltin ethoxide, dibutyltin dilaurate, tetrabutyl titanate, butoxytitanium trichloride, and zinc naphthenate.

[0070] Examples of the tertiary amine compound include triethylamine, triethylenediamine, N,N-dimethylbenzylamine, etc. When a catalyst is used, it may be used alone or in combination of two or more kinds.

[0071] A known technique can be used to make the urethane resin aqueous. A water-soluble urethane resin may be used, or it may be dispersed in an aqueous solvent. The urethane resin composition of the present invention is a silicone modified body, and therefore is difficult to dissolve in water, and is preferably dispersed in an aqueous solvent. A dispersion of a urethane resin in an aqueous solvent can be obtained by a forced emulsification method or a self-emulsification method. In the forced emulsification method, a urethane resin is solution-polymerized, then dispersed in an aqueous solvent to which an emulsifier has been added, and the solvent is removed. A water dispersion by the self-emulsification method can be obtained by synthesizing a urethane resin having a hydrophilic functional group such as a carboxy group in a low-boiling point solvent such as acetone or methyl ethyl ketone, neutralizing it with amines, ammonia, alkali metals, etc. to give it dispersibility in an aqueous solvent, and removing the solvent. Ammonia and trimethylamine are preferred as neutralizing agents from the viewpoint of stabilizing dispersion in an aqueous solvent. The neutralization step may be carried out in one step, or may be divided into two or more steps. The neutralizing agent is preferably 1 equivalent or more relative to the object to be neutralized (e.g., a carboxy group), more preferably about 2.0 equivalents, and even more preferably about 1.5 equivalents. If the amount of neutralizer is equivalent to the amount of the neutralizing agent to be neutralized, unneutralized components will remain, and if the amount of neutralizer is too much, the neutralizing agent will remain in the coating solution, so it is preferable to use a neutralizing agent in an appropriate range. By making the urethane resin water-based, the burden on the environment can be reduced.

[0072] (Crosslinking agent component) The crosslinking agent used in the coating composition is not particularly limited as long as it can be made aqueous and can react with the urethane resin, and conventionally known crosslinking agents can be used. For example, compounds having various reactive functional groups such as oxazoline, melamine, isocyanate, carbodiimide, and epoxy can be used arbitrarily. They may be used alone or in combination of two or more. Preferred are oxazoline-based and carbodiimide-based crosslinking agents that are reactive to carboxy groups and have excellent coating liquid stability. In addition, in cases where unreacted hydroxyl groups remain in the synthesis of the urethane resin, or where hydroxyl groups are generated in the process of crosslinking reactions such as self-crosslinking reactive groups and epoxy, it is also preferable to use or use in combination a crosslinking agent having hydroxyl group reactivity such as isocyanate. The crosslinking agent can be added arbitrarily within a range that does not impair film-forming properties. The crosslinking agent is preferably 1 to 90% by mass, more preferably 1 to 70% by mass, and particularly preferably 1 to 50% by mass as the composition of the entire coating liquid, and is preferably adjusted to a range in which the desired release properties are expressed without impairing film-forming properties. In addition, a catalyst suitable for the crosslinking reaction can be used in combination as necessary. When the urethane resin containing a silicone structure contains a functional group that reacts with active energy rays, such as an acryloyl group, a photopolymerization initiator or a thermal polymerization initiator can be used in combination. By adjusting the appropriate crosslinking agent type / amount depending on the urethane resin containing a silicone structure, the coating hardness and releasability can be controlled.

[0073] Examples of oxazoline crosslinking agents include compounds that have an oxazoline group in the molecule, and any can be used as long as it is compatible with water-based paints. It is particularly preferable to use them in the form of a polymer. They can be produced by polymerizing oxazolines containing alkenyl groups, such as 2-vinyl-2-oxazoline and 2-isopropenyl-2-oxazoline, alone or with other monomers. Examples of commercially available products include the "Epocross Series" manufactured by Nippon Shokubai Co., Ltd.

[0074] Examples of melamine-based crosslinking agents include alkylolated melamine derivatives and ether-modified alkylolated melamine derivatives that have a melamine skeleton in the molecule, and any crosslinking agent that can be used is suitable for use in water-based paints. Commercially available products include "MW-22," "MS-21," "MX-730," and "MX-45" manufactured by Nippon Carbide Industries Co., Ltd.

[0075] For aqueous applications, it is preferable to use an isocyanate-based crosslinking agent that is a blocked isocyanate derivative of isocyanate, as exemplified in the synthesis of urethane resin. Any blocking agent can be used, and examples of such blocking agents include phenol, cresol, acetylacetone, ε-caprolactam, ethyleneimine, and methyl ethyl ketone oxime. Commercially available products include the "Meikanate Series" manufactured by Meisei Chemical Industry Co., Ltd. and the "Trixene Series" manufactured by GSI Creos Co., Ltd.

[0076] As the carbodiimide crosslinking agent, any compound having two or more carbodiimide structures in the molecule can be used as long as it is compatible with aqueous systems. It can be synthesized by conventionally known techniques and obtained by decarbonating isocyanate using a catalyst. Commercially available products include "V-02", "SV-02", "E-02", and "E-05" manufactured by Nisshinbo Chemical Inc.

[0077] As the epoxy crosslinking agent, any epoxy crosslinking agent that has two or more epoxy groups in the molecule and can be made into a water-based agent can be used. It can be synthesized by a conventionally known method, for example, by reacting polyfunctional phenols such as bisphenol A and ethylene glycol or alcohols with epichlorohydrin. Commercially available products include "JER W2801" manufactured by Mitsubishi Chemical Corporation, "MODEPIX 303" manufactured by Arakawa Chemical Industries Co., Ltd., and "ADEKA RESIN Series" manufactured by ADEKA Corporation.

[0078] (Other ingredients) The release coating composition of the present invention may further contain an adhesion promoter, a colorant, an ultraviolet absorber, particles, etc., within the scope of the present invention. In addition, a surface conditioner may be used from the viewpoint of improving wettability to the polyester film, and various binder components may be blended. By incorporating various components as necessary, various properties can be controlled to produce the desired laminated polyester film.

[0079] [Method of forming release layer] In the present invention, a release layer is laminated on at least one side of a polyester film using the release coating composition of the present invention. The method of forming the release layer constituting the laminated polyester film is not particularly limited, and may be offline coating in which a coating process of the release coating composition is performed after the polyester film is produced, or an in-line coating method in which the release coating composition is applied during the polyester film production process. More preferably, the release layer is formed by the in-line coating method, and even more preferably, the release coating composition is applied to the polyester film before the crystal orientation is completed.

[0080] Here, the polyester film before the crystal orientation is completed includes an unstretched film, a uniaxially oriented film obtained by aligning an unstretched film in either the longitudinal direction (hereinafter, the direction of continuous film production, the longitudinal direction, or the MD direction) or the transverse direction (hereinafter, the direction perpendicular to the longitudinal direction, the width direction, or the TD direction), and further a film oriented by low-magnification stretching in both the longitudinal and transverse directions (a biaxially oriented film before finally re-stretching in the longitudinal or transverse direction to complete the orientation crystallization). Among them, so-called in-line coating is preferred, in which an aqueous coating solution of the above composition is applied to an unstretched film or a uniaxially oriented film, and then the film is stretched longitudinally and / or transversely and heat-set. The coating layer may be dried by a stretching process or a heat-setting process after coating, and a drying process may be added as necessary. The film may be cured by a stretching process or a heat-setting process, and a curing process may be added as necessary.

[0081] In the present invention, after the polyester film is produced, a release layer may be formed by an off-line coating method in which a release coating composition is applied to the polyester film.

[0082] That is, it is also preferable to produce the film by using offline coating, in which a release coating composition (e.g., an aqueous coating liquid) is applied to a roll of film while the roll is being transported again in a coating facility, and the film is then dried and cured. If necessary, a curing step may be added after the offline coating.

[0083] When applying a release coating composition (e.g., an aqueous coating liquid) to a polyester film, it is preferable to subject the film surface to a physical treatment such as corona surface treatment, flame treatment, plasma treatment, etc. as a preliminary treatment to improve the coatability, or to use a wetting agent together with the composition.

[0084] The coating method may be any known coating method, such as roll coating, gravure coating, roll brushing, spray coating, air knife coating, impregnation, curtain coating, or the like, which may be used alone or in combination.

[0085] The release coating composition has a variation of 2.5% or less between the haze value of the composition when the urethane resin and the crosslinking agent are blended and the haze value of the composition when the composition is heated at 60°C for 4 hours.

[0086] In this specification, the haze value of a composition when a urethane resin and a crosslinking agent are blended is referred to as the post-mix haze (%), and the haze value of a composition when the composition is heated at 60°C for 4 hours is also referred to as the post-heating haze (%).

[0087] The variation in haze value may also be referred to as Δ haze (%).

[0088] Here, Δhaze (%) is the difference between the haze after heating (%) and the haze after preparation (%). ΔHaze (%) = (Haze after heating (%) - Haze after preparation (%)) This can be shown as:

[0089] The haze after preparation can be, for example, 0.1% to 21.0%, 0.15% to 20.5%, or 0.2% to 19.5%. If the haze after preparation is 21.0% or less, a release coating composition with few coarse particles can be obtained. In addition, a homogeneous coating film with few foreign matters such as aggregates caused by coarse particles can be obtained.

[0090] The haze after heating can be, for example, 0.1% to 23.0%, 0.15% to 20.0%, or 0.2% to 19.5%. If the haze after heating is 23.0% or less, a release coating composition that suppresses the generation of coarse particles due to heating can be obtained. In addition, a homogeneous coating film with less foreign matter such as aggregates caused by coarse particles generated by heating can be obtained.

[0091] For example, such haze values ​​can be achieved using the release coating compositions described herein.

[0092] The haze fluctuation value (Δ haze) is, for example, −2.5% or more and 2.5% or less, may be −1.2% or more and 2.2% or less, may be −1.2% or more and 2.0% or less, or can be −1.1% or more and 1.9% or less.

[0093] Since the variation in haze is within a predetermined range, the release coating composition of the present invention can maintain a long pot life. In addition, since the variation in haze value is small even in a heated state, the effect of air temperature can be reduced when the release coating composition is prepared and then transported from the preparation site to the coating site. In addition, preparation, coating, and transportation can be performed in areas with high outside air temperatures, the transport distance of the release film can be reduced, and further, the amount of CO2 emissions associated with transportation can be reduced. In addition, the effect of the coating environment and the effect of heat leaking during coating and / or from the drying oven can be reduced.

[0094] Furthermore, the extended pot life can lead to a reduction in the amount of waste coating liquid, which can lead to a reduction in the environmental load. The release coating composition used in the present invention is characterized by having an excellent pot life. The urethane resin used in the present invention can be produced in the form of a resin, and therefore has excellent dispersion stability after dilution with an aqueous solvent compared to addition-curing silicones, which are often produced as O / W emulsions, and can suppress aggregation and coalescence of the release composition. In addition, the crosslinking agent component used in the present invention is known as a crosslinking agent having high reaction suppression ability in a room temperature environment as a conventionally known technology, and therefore makes it possible to easily provide a release coating composition having an excellent pot life. In addition, it makes it possible to provide a release coating liquid that has excellent environmental resistance and suppresses aggregation, sedimentation, and creaming even when the release coating composition is exposed to temperatures above room temperature for a certain period of time.

[0095] The release coating composition used in the present invention is preferably used within 1 week after preparation, more preferably within 72 hours after preparation, even more preferably within 48 hours after preparation, and particularly preferably within 24 hours after preparation. The use of a release coating composition having a long pot life can lead to a reduction in the amount of waste of the coating solution, which can lead to a reduction in the environmental load.

[0096] In the laminated polyester film of the present invention, the peelability using a polyester adhesive tape is 500 mN / 50 mm or more and 11000 mN / 50 mm or less, for example, 1000 mN / 50 mm or more and 11000 mN / 50 mm or less, 2500 mN / 50 mm or more and 10000 mN / 50 mm or less, or 3000 mN / 50 mm or more and 10000 mN / 50 mm or less. By having the peeling force within the above range, when peeling an ultra-thin ceramic green sheet or resin sheet, breakage of the peeling target can be prevented, and further, the presence of residue of the peeling target on the release layer after peeling can be greatly reduced.

[0097] As a result, the recycling efficiency of the laminated polyester film and the yield of the recycled raw material can be increased.

[0098] In one aspect, the present invention provides a release film for producing a resin sheet, an adhesive separator, or a multilayer ceramic capacitor.

[0099] (Resin sheet) The resin sheet in the present invention is not particularly limited as long as it is a sheet molded on the surface of the release layer opposite to the substrate, and examples thereof include a resin sheet formed by curing a resin sheet-forming composition containing a resin component and a crosslinking agent, and a resin sheet molded by melt film-forming or solution film-forming an organic component having film-forming properties. In one embodiment, the release film of the present invention is a release film for molding a resin sheet containing an inorganic compound. Examples of inorganic compounds include metal particles, metal oxides, and minerals, and examples of such compounds include calcium carbonate, silica particles, aluminum particles, and barium titanate particles. Since the present invention has a release layer with high smoothness, even in an embodiment in which the resin sheet contains these inorganic compounds, defects that may be caused by inorganic compounds, such as damage to the resin sheet and problems in which it is difficult to peel the resin sheet from the release layer, can be suppressed.

[0100] The resin component forming the resin sheet can be appropriately selected depending on the application. In one embodiment, the resin sheet containing an inorganic compound is a ceramic green sheet. For example, the ceramic green sheet can contain barium titanate as an inorganic compound. In addition, the resin component can contain, for example, a polyvinyl butyral resin.

[0101] (Ceramic green sheets and ceramic capacitors) Generally, a multilayer ceramic capacitor has a rectangular parallelepiped ceramic body. Inside the ceramic body, first internal electrodes and second internal electrodes are alternately provided along the thickness direction. The first internal electrodes are exposed on a first end face of the ceramic body. A first external electrode is provided on the first end face. The first internal electrode is electrically connected to the first external electrode at the first end face. The second internal electrode is exposed on a second end face of the ceramic body. A second external electrode is provided on the second end face. The second internal electrode is electrically connected to the second external electrode at the second end face.

[0102] In one embodiment, the release film of the present invention is a release film for producing a ceramic green sheet and is used for producing such a multilayer ceramic capacitor.

[0103] For example, when the release film for producing ceramic green sheets of the present invention is used, a ceramic green sheet is produced, for example, as follows. First, the release film of the present invention is used as a carrier film, and a ceramic slurry for forming a ceramic body is applied and dried. A conductive layer for forming a first or second internal electrode is printed on the applied and dried ceramic green sheet. A mother laminate is obtained by appropriately stacking and pressing a ceramic green sheet, a ceramic green sheet on which a conductive layer for forming a first internal electrode is printed, and a ceramic green sheet on which a conductive layer for forming a second internal electrode is printed. The mother laminate is divided into a plurality of pieces to produce a raw ceramic body. The raw ceramic body is fired to obtain a ceramic body. Then, a first and second external electrodes are formed to complete a multilayer ceramic capacitor.

[0104] (Adhesive separator) In another embodiment, the release film of the present invention can be applied to an adhesive separator. For example, an adhesive layer can be formed on the surface of the release layer opposite to the substrate.

[0105] The adhesive separator in the present invention is used on the surface of the release layer opposite to the substrate. There are no particular limitations on the type of adhesive as long as it is a suitable adhesive.

[0106] For example, the types of adhesives include adhesives with acrylic resin, urethane resin, silicone resin, polyester resin, polyether resin, fluororesin, natural rubber, synthetic rubber, etc. as a base polymer. The adhesive may be one type alone, or two or more types may be used in combination. In addition, colorants, tackifiers, various particles, crosslinking agents, antistatic agents, etc. can be used in combination as necessary. For example, the adhesive separator can be suitably used as a separator for OCA (optical transparent adhesive), various tapes, polarizing film, various protective film, etc. The adhesive separator in the present invention can control the peeling force from light peeling to heavy peeling, and can also be imparted with solvent resistance as necessary, making it possible to provide a laminated polyester film that is widely suitable for adhesive separators that require various properties depending on the application.

[0107] (Transfer foil separator) In another embodiment, the release film of the present invention can be applied to a separator for a transfer foil. For example, a transfer material (transfer material layer) can be formed on the surface of the release layer opposite to the substrate.

[0108] The type, material, and number of layers of the transfer foil in the present invention are not particularly limited as long as the transfer foil is a transfer material used on the surface of the release layer opposite to the substrate. For example, it can be used as a transfer separator in which a functional layer such as a hard coat layer, a metal layer, or a colored layer is laminated with various adhesive layers. It may be used alone or in combination of multiple types.

[0109] For example, the hard coat layer may be made of a resin compound that contains a polyfunctional (meth)acrylic group, epoxy group, hydroxyl group, etc. and that polymerizes and / or reacts by drying, heat, chemical reaction, and / or by irradiation with active energy rays such as electron beams, radiation, ultraviolet rays, etc. If necessary, it is also preferable to use a photopolymerization initiator, a thermal polymerization initiator, a crosslinking agent, a sensitizer, a colorant, an antibacterial agent, an organic particle, an inorganic particle, a radical scavenger, an ultraviolet absorber, a surface conditioner, a dispersant, etc. in combination.

[0110] The type and formation method of the metal layer used in the transfer foil of the present invention are not particularly limited, but particularly preferred are materials suitable for vacuum deposition and sputtering, such as aluminum, gold, silver, copper, tin, indium, chromium, nickel, etc., which may be used alone or in combination, and alloys may also be used. It is also preferable to provide a protective layer between the release layer and the metal layer for the purpose of protecting the metal deposition layer, and a colored layer, etc. may be provided as necessary.

[0111] The transfer foil in the present invention may be laminated with various adhesive layers as necessary. The type of material is not limited and an adhesive suitable for the application can be used, but it is particularly preferable to provide a heat seal layer for ease of handling. Examples of resins used in the heat seal layer include acrylic resin, polyester resin, polyolefin resin, polyurethane resin, etc. In addition, when the interlayer adhesion between the adhesive layer and the functional layer is insufficient, it is also preferable to use various primer layers in combination.

[0112] In one embodiment, the transfer foil of the present invention makes it possible to provide a laminated polyester film that reduces the migration of silicone components and achieves both good functional layer coatability and good peelability.

[0113] The present invention will be described below with reference to examples. Various physical properties were evaluated by the following methods.

[0114] (Applicability) The laminated polyester film was cut into A4 size sheets, and the coating layer surface was visually observed using fluorescent and halogen lights to compare the state of coating film formation and evaluate it according to the following criteria: Good: A uniform coating is formed without any appearance abnormalities such as cracks in the coating. Fair: Some paint cracks and other appearance abnormalities are observed. Defective: Cracks and other defects occur and the coating cannot be formed. (Adhesion to substrate) The coating layer surface of the laminated polyester film was pressed firmly with a finger and reciprocated 10 times, and the appearance of the coating was visually confirmed under a three-wavelength fluorescent lamp to confirm that the coating had not fallen off or otherwise occurred. 〇: No dropout 〇△(slightly missing) △(partially fallen off) × (Completely dropped out)

[0115] (Adhesive tape peelability) The peelability was evaluated by laminating a polyester adhesive tape (Nitto Denko Corporation, No. 31B) to the surface of the coating layer of the laminated polyester film, and then measuring the peel strength when peeled at 90° at a peel speed of 0.3 m / min using Shimadzu Corporation's Autograph AG-X.

[0116] (Film recyclability) The laminated polyester film was cut into strips, 50 g of which were placed in a flask and then cooled in a nitrogen atmosphere. The polymer was melted under stirring at 300°C for 1 hour under reduced pressure. After degassing, the molten polymer was attached to the tip of a glass tube and air was blown into it to mold the polymer into a balloon. The appearance of the molded polymer was visually checked, and it was evaluated as recoverable if it contained no foreign matter, and as unrecoverable if many foreign matter were found.

[0117] (Pot Life) The prepared coating solution was left at rest for a specified time at 25°C, and then a laminated polyester film was produced. The effect of the coating properties on the coating properties was evaluated.

[0118] (Hayes) The prepared coating solution was diluted with water to a solid content of 0.05% immediately after mixing, and after being left to stand at 60°C for 4 hours, and then placed in a glass cell for solution samples. Next, using a "Spectroscopic Haze Meter SH7000" manufactured by Nippon Denshoku Industries Co., Ltd., evaluation was performed according to the measurement standards JIS K 7361 (total light transmittance) and JIS K 7136 (haze), and the difference between the haze after heating and the haze before heating was calculated.

[0119] [Production Example] <Water dispersion of silicone modified urethane resin> As Production Example 1, 0.5 parts of one-terminal hydroxyl group-modified silicone ("X-22-176DX" manufactured by Shin-Etsu Chemical Co., Ltd.), 20 parts of polycarbonate diol (molecular weight 2000), 0.02 parts of dibutyltin dilaurate, and 100 parts of methyl ethyl ketone were charged in a flask and mixed and stirred under a nitrogen atmosphere. After heating to 80°C, 5.53 parts of isophorone diisocyanate were added dropwise at appropriate times and reacted for 5 hours, and cooled to room temperature to obtain a silicone-modified urethane prepolymer. Next, 2.28 parts of 2,2-dimethylolpropionic acid were added under a nitrogen atmosphere, heated to 80°C, and reacted for 5 hours to obtain a silicone-modified urethane resin containing a carboxy group.

[0120] Further, 50 parts of methyl ethyl ketone and 2.58 parts of triethylamine were added to carry out a neutralization reaction. Next, 300 parts of water were added while vigorously stirring using an emulsifier capable of stirring the entire contents of the container at room temperature (manufactured by NP Labs, device name "Ultra Planetary Mixer"), and after stirring for another hour, the pressure was reduced and the solvent was removed to prepare aqueous dispersion A of side-chain silicone-modified urethane resin.

[0121] In Production Example 2, the hydroxyl group-modified silicone in Production Example 1 was changed to a both-end-modified silicone ("Silaplane FM-4421" manufactured by JNC Corporation), and an aqueous dispersion B of a main chain silicone-modified urethane resin was prepared.

[0122] In Production Example 3, the amount of X22-176DX was changed to 2.5 parts, the amount of polycarbonate polyol was changed to 13.6 parts, and the 300 parts of water was changed to a mixed solvent of 150 parts of water and 150 parts of isopropyl alcohol to increase the silicone content, thereby preparing an aqueous dispersion C.

[0123] [Examples 1 to 3] Molten polyethylene terephthalate ([η] = 0.64 dl / g, Tg = 78°C) containing 0.1 mass% calcium carbonate particles with an average particle size of 0.7 µm was extruded through a die and cooled on a cooling drum in the usual manner to form an unstretched film. The film was then stretched 3.6 times in the machine direction, and an aqueous coating liquid (aqueous dispersion with a solid content concentration of 3 mass%) prepared by mixing each component so as to obtain the solid content ratio shown in Table 1 was uniformly applied to the surface of the film with a roll coater.

[0124] The coated film was then dried at 115°C for about 5 seconds and stretched 4.5 times in the transverse direction at 145°C, and then heat-set at 230°C for about 5 seconds to obtain a 25 μm biaxially oriented polyester film having the coating layer shown in Table 1.

[0125] Thus, the laminated polyester film of the present invention can provide a laminated polyester film having suitable releasability, adhesion to a substrate, and recyclability.

[0126] In addition, it is possible to produce an environmentally friendly laminated polyester film by utilizing a coating composition that is water-based and has a long pot life, which allows good coatability to be maintained even 24 hours after formulation.

[0127] [Comparative Example 1] As Comparative Example I, an aqueous dispersion D of a urethane resin was prepared in the same manner as in Production Example 1, except that no silicone was added.

[0128] As an aqueous coating composition, the water dispersion and a commercially available crosslinker (oxazoline-containing acrylic polymer, "Epocross WS-500" manufactured by Nippon Shokubai Co., Ltd.) were mixed so that the solid content ratio of the resin component / crosslinker component was 70 / 30, and then the solid content concentration of the coating solution was diluted with water in which 0.5 wt% of "Sanonic SS-90" manufactured by Sanyo Chemical Industries, Ltd. was expanded so that the dry coating thickness was 0.5 μm, to prepare coating solutions A1, B1, and C1. In addition, the water was changed to a water / isopropyl alcohol 1:1 solution in the same manner to prepare coating solution D1.

[0129] [Comparative Example 2] <Water dispersion of addition-curing silicone> Using an emulsifying device capable of stirring the entire container (NP Labs, device name "Ultra Planetary Mixer"), silicone d containing alkenyl groups and silicone e containing Si-H groups were mechanically emulsified in an aqueous medium mixed with polyoxyethylene tridecyl ether (Takemoto Oil & Fat Co., Ltd., "New Calgen D-1208") to obtain an aqueous dispersion, and the solids ratio of the aqueous dispersion of silicone d to the aqueous dispersion of silicone e was adjusted to 65 / 35. 80 ppm of a platinum catalyst (Shin-Etsu Chemical Co., Ltd., "CAT-PM-10A") and 200 ppm of a crosslinking reaction inhibitor (1-ethynylcyclohexanol) were added relative to the coating mass, and the solids concentration of the coating solution was diluted with water so that the dry coating thickness was 40 nm, to prepare coating solution E.

[0130] [Comparative Example 3] A sample was prepared that did not include a release layer containing a release coating composition.

[0131] [Comparative Example 4] The same method as in Production Example 1 was used to synthesize the resin, but with 13 parts of X-22-176-DX, 0.2 parts of polycarbonate polyol, 4.9 parts of isophorone diisocyanate, 0.2 parts of 2,2-dimethylolpropionic acid, and 0.23 parts of triethylamine. However, when water was added, aggregates were generated, and a uniform dispersion in the aqueous solvent could not be obtained.

[0132] [Examples 4 to 7, Comparative Example 5] The coating solutions A1, B1, C1, D1, and E were adjusted to NV 5.0% in the same manner as in Examples 1 to 3 and Comparative Example 2. Table 1 shows various conditions and measurement results for the examples and comparative examples.

[0133] Table 2 shows the results of the heating test for the examples and comparative examples.

[0134] [Table 1]

[0135] [Table 2] The laminated polyester films of the present invention according to Examples 1 to 3 are laminated polyester films having a peel strength suitable for applications such as various sheet moldings, tapes, and adhesive separators, and have appropriate adhesion to substrates, and can be produced using a water-based composition with a long pot life.

[0136] Furthermore, the release layer of the present invention has high adhesion to the substrate and can inhibit the silicone component from migrating to the adherend to which the release layer is attached.

[0137] In addition, the solvent used in the coating composition of the present invention contains water as a main component, which makes it possible to omit explosion-proofing of the drying equipment in the coating device. Moreover, since recovery of the volatile solvent can be omitted, the environmental load can be reduced.

[0138] In addition, since the present invention does not use an addition curing type silicone resin as a main component, it is possible to obtain a coating composition with a long pot life. Since the present invention can use a water-based coating composition with a long pot life, it is possible to improve the coating suitability of the release layer and reduce the amount of waste of the composition.

[0139] From the viewpoint of environmental friendliness, the recyclability of laminated polyester films is also an important issue, and since the present invention does not contain an addition-curing type silicone resin as a main component, it is possible to improve degradability and thus achieve improved recyclability.

[0140] On the other hand, in Comparative Example 1, a urethane resin not having a silicone structure was used, and therefore the peel strength was insufficient.

[0141] In Comparative Example 2, the release layer was formed using an aqueous dispersion containing an addition curing type silicone as a main component, and therefore the results were inferior to those of the present invention in terms of coatability, substrate adhesion, and recoverability.

[0142] Comparative Example 3 did not have a release layer, and therefore the peel strength and the like were insufficient.

[0143] In Comparative Example 4, the silicone component was excessive, so that sedimentation occurred during the manufacturing process of the urethane resin containing a silicone structure. A dispersion could not be manufactured, and a release layer could not be formed.

[0144] The release coating liquids used for the laminated polyester film of the present invention according to Examples 4 to 7 have high thermal stability and are excellent in the effect of suppressing aggregation, sedimentation, and creaming. The use of the release coating liquid having excellent thermal stability makes it possible to produce a laminated polyester film.

[0145] On the other hand, in Comparative Example 5, a conventional O / W type emulsion was used, and a release layer was not formed using the release coating composition of the present invention, so the thermal stability was inferior to that of the present invention. [Industrial Applicability]

[0146] The laminated polyester film of the present invention is a laminated polyester film having a peel strength suitable for applications such as various sheet moldings, tapes, and adhesive separators, and has appropriate adhesion to substrates, and can be produced using an aqueous composition with a long pot life.

Claims

1. A laminated polyester film having a polyester film as a base material and a release layer in this order, The aforementioned release layer is formed from a release coating composition, The aforementioned release coating composition comprises a urethane resin containing reactive functional groups and a silicone structure, The proportion of silicone components contained in the urethane resin is 0.1% by mass or more and less than 50% by mass, relative to 100% by mass of the total mass of the urethane resin. The reactive functional group in the urethane resin containing the silicone structure includes a carboxyl group. The solvent of the aforementioned release coating composition is a laminated polyester film composed of an aqueous solvent.

2. A release coating composition, The composition comprises a urethane resin containing a reactive functional group and a silicone structure, The proportion of silicone components contained in the urethane resin is 0.1% by mass or more and less than 50% by mass, relative to 100% by mass of the total mass of the urethane resin. The reactive functional group contained in the urethane resin is a carboxyl group, The aforementioned composition does not primarily consist of an addition-curing type silicone resin, The solvent of the above composition is an aqueous solvent. The aforementioned composition is coated onto a polyester film as a substrate within 48 hours immediately after preparation. Release coating composition.