Multilayer film

Abstract

The objective is to provide a multilayer film that achieves both excellent interlayer strength and excellent flexibility, and when used as a release film, exhibits excellent conformability and can suppress the leakage of the resin constituting the film. [Solution] A multilayer film having a first resin layer and a second resin layer, wherein the first resin layer is located on the outermost surface, the first resin layer contains a polyester resin (A) having a melting point of 180°C or higher, and the second resin layer contains a polyester resin (B) having a melting point of 25°C or higher and less than 180°C.

Description

Technical Field

[0001] The present invention relates to a multilayer film.

Background Art

[0002] Polyester films are used not only as a base material for adhesive tapes and a release film for protecting an adhesive layer, but also as a release film for protecting an object in a manufacturing process. Examples of the manufacturing process include an FPC process, a semiconductor molding process, a CFRP molding process, an MLCC molding, etc.

[0003] For example, Patent Document 1 discloses a release film in which a release layer is formed on at least one side of a polyester film, which does not cause silicone transfer to an electronic / electrical component material when used in the manufacture of electric / electronic components, has release characteristics comparable to those of a silicone release layer, is excellent in processing suitability, and has good release properties.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] These polyester films, such as PET films and PBT films, are often used as single-layer films. However, a multilayer film combining a polyester film and a polyolefin film may be used for the purpose of ensuring the flexibility of the film. By forming such a multilayer film, it is possible to obtain a film having functions such as tensile strength and heat resistance while exhibiting flexibility. However, such multilayer films sometimes suffered from insufficient interlaminar strength between the polyolefin film and the polyester film. On the other hand, polyester resin was sometimes mixed into the resin constituting the polyolefin film to increase interlaminar strength. In this case, although the interlaminar strength improved, the polyester resin present in the polyolefin film could not be sufficiently dispersed, making it impossible to form a polyolefin film of uniform thickness. When the polyolefin film is not of uniform thickness, not only is the original flexibility of the polyolefin film impaired, but the overall tensile strength of the multilayer film can also decrease.

[0006] The present invention aims to provide a multilayer film that achieves both excellent interlayer strength and excellent flexibility, exhibits excellent conformability when used as a release film, and can suppress the leakage of the resin constituting the film. [Means for solving the problem]

[0007] Disclosure 1 is a multilayer film having a first resin layer and a second resin layer, wherein the first resin layer is located on the outermost surface, the first resin layer contains a polyester resin (A) having a melting point of 180°C or higher, and the second resin layer contains a polyester resin (B) having a melting point of 25°C or higher and less than 180°C. Disclosure 2 is a multilayer film of Disclosure 1 having a third resin layer on the side of the second resin layer opposite to the first resin layer. Disclosure 3 is a multilayer film according to Disclosure 1 or 2, wherein the total thickness of the multilayer film is 100 μm or less. Disclosure 4 is a multilayer film of Disclosure 1, 2, or 3, wherein the thickness of the first resin layer is thinner than the thickness of the second resin layer. Disclosure 5 is a multilayer film according to Disclosure 1, 2, 3, or 4, wherein the ratio of the thickness of the first resin layer to the thickness of the second resin layer (thickness of the first resin layer / thickness of the second resin layer) is 0.01 or more and 1.0 or less. Disclosure 6 is a multilayer film of Disclosure 1, 2, 3, 4, or 5, wherein the thickness of the first resin layer is 3 μm or more and 25 μm or less. Disclosure 7 is a multilayer film of Disclosure 1, 2, 3, 4, 5, or 6, wherein the thickness of the second resin layer is 10 μm or more and 150 μm or less. Disclosure 8 is a multilayer film of Disclosure 1, 2, 3, 4, 5, 6, or 7 in which the polyester resin (A) contains an aromatic polyester resin. Disclosure 9 is a multilayer film of Disclosure 8 in which the aromatic polyester resin includes a resin having a polybutylene terephthalate skeleton. Disclosure 10 is a multilayer film of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, or 9, in which the polyester resin (A) comprises a resin having structural units derived from butanediol. Disclosure 11 is a multilayer film of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, in which the polyester resin (B) has a melting point of 120°C or less. Disclosure 12 is a multilayer film of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11, in which the polyester resin (B) comprises a resin having structural units derived from butanediol. Disclosure 13 further comprises a multilayer film of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, in which the second resin layer further includes the polyester resin (A). Disclosure 14 is a multilayer film of Disclosure 13, wherein the content of the polyester resin (A) in the resin constituting the second resin layer is less than 50% by mass. Disclosure 15 is a multilayer film of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 or 14 used as a release film. Disclosure 16 is a multilayer film of Disclosure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 used in the manufacture of flexible circuit boards. The present invention will be described in detail below.

[0008] The inventors focused on the compatibility of the resins constituting each layer of a multilayer film and investigated how to improve the interlayer strength of a multilayer film by making the resins constituting each layer of the multilayer film highly compatible with one another. Furthermore, they discovered that by making the polyester resin used as the resin constituting each layer of such a multilayer film have a specific range of melting points for each layer, it is possible to obtain a multilayer film with excellent flexibility. As a result, they found that it is possible to obtain a multilayer film that achieves both excellent interlayer strength and excellent flexibility, and when used as a release film, exhibits excellent conformability and can suppress the seepage of the resin constituting the film, thus completing the present invention.

[0009] The multilayer film of the present invention comprises a first resin layer and a second resin layer. The first resin layer is positioned on the outermost surface of the multilayer film and imparts tensile strength, heat resistance, and release properties to the multilayer film of the present invention. The second resin layer imparts flexibility to the multilayer film of the present invention. The multilayer film of the present invention may have a two-layer structure in which the first resin layer is located on one side of the second resin layer, or it may have a three-layer structure in which the third resin layer is located on the side of the second resin layer opposite to the first resin layer. In particular, from the viewpoint of preventing fusion of the second resin layer, the multilayer film of the present invention is preferably a three-layer structure having the above-described structure. Furthermore, the above multilayer film may have a structure with more than three layers.

[0010] The first resin layer contains a polyester resin (A) having a melting point of 180°C or higher (hereinafter sometimes simply referred to as "polyester resin (A)"). The inclusion of polyester resin (A) in the first resin layer improves its tensile strength, resulting in the multilayer film of the present invention exhibiting superior interlayer strength. Therefore, for example, the multilayer film of the present invention becomes less prone to tearing when pressed on an object. Furthermore, the heat resistance of the multilayer film of the present invention is improved. Therefore, for example, the multilayer film of the present invention can be pressed on an object in a high-temperature environment.

[0011] The melting point of the polyester resin (A) is not particularly limited as long as it is 180°C or higher, but a preferred lower limit is 190°C. A melting point of 190°C or higher for the polyester resin (A) relatively improves the tensile strength of the first resin layer. Therefore, for example, it becomes less prone to tearing during pressing. Furthermore, the heat resistance of the multilayer film of the present invention is further improved, making it possible, for example, to layer the multilayer film of the present invention on an object to be pressed and press it in a higher temperature environment. A more preferred lower limit for the melting point of the polyester resin (A) is 200°C, and an even more preferred lower limit is 210°C. Furthermore, from the viewpoint of further improving the flexibility of the first resin layer and the multilayer film of the present invention, the preferred upper limit of the melting point of the polyester resin (A) is 350°C, and the more preferred upper limit is 300°C. In this specification, "melting point" refers to the temperature at which a crystal turns into a molten liquid, and can be determined using differential scanning calorimetry (DSC) in accordance with JIS K7121:1987.

[0012] The polyester resin (A) is not particularly limited, but it is preferable to include an aromatic polyester resin from the viewpoint of further improving the flexibility of the first resin layer. By including an aromatic polyester resin in the polyester resin (A), for example, when the multilayer film of the present invention is used as a release film, the release film will have superior conformability.

[0013] The above aromatic polyester resin is not particularly limited, but crystalline aromatic polyester resins are preferred. Specifically, examples include resins having a polyethylene terephthalate skeleton, resins having a polybutylene terephthalate skeleton, resins having a polyhexamethylene terephthalate skeleton, resins having a polyethylene naphthalate skeleton, resins having a polybutylene naphthalate skeleton, resins having a benzoic acid skeleton, and butanediol terephthalate polytetramethylene glycol copolymers. These aromatic polyester resins may be used individually or in combination of two or more. In particular, from the viewpoint of balancing heat resistance, release properties, and conformability, the above aromatic polyester resin preferably includes a resin having a polybutylene terephthalate skeleton. Furthermore, a mixed resin of a resin having a polybutylene terephthalate skeleton and a block copolymer of polybutylene terephthalate and an aliphatic polyether is also preferred. The aliphatic polyether is not particularly limited and examples include polyethylene glycol, polydiethylene glycol, polypropylene glycol, and polytetramethylene glycol.

[0014] The content of the aromatic polyester resin in the resin constituting the first resin layer is not particularly limited, but a preferred lower limit is 70% by mass. If the content of the aromatic polyester resin is 70% by mass or more, the release properties of the multilayer film are improved. A more preferred lower limit for the content of the aromatic polyester resin in the resin constituting the first resin layer is 75% by mass. Furthermore, the upper limit of the content of the aromatic polyester resin in the resin constituting the first resin layer is 100% by mass, meaning that the first resin layer may be composed solely of the aromatic polyester resin.

[0015] The above polyester resin (A) is not particularly limited, but from the viewpoint of further improving the flexibility of the first resin layer, it preferably contains a resin having a structural unit derived from butanediol. By the above polyester resin (A) containing a resin having a structural unit derived from butanediol, when the multilayer film of the present invention is used as a release film, the release film will be excellent in followability.

[0016] Examples of the resin having a structural unit derived from butanediol include resins containing a polybutylene terephthalate skeleton, resins containing a polybutylene succinate skeleton, resins containing a polybutylene adipate terephthalate skeleton, and the like. Among them, from the viewpoint of balance such as heat resistance, releasability, and followability, a resin containing a polybutylene terephthalate skeleton is preferred.

[0017] The content ratio of the resin having a structural unit derived from butanediol in the resin constituting the first resin layer is not particularly limited, but the preferred lower limit is 70% by mass. If the content ratio of the resin having a structural unit derived from butanediol is 70% by mass or more, the releasability of the multilayer film of the present invention will be further improved. A more preferred lower limit of the content ratio of the resin having a structural unit derived from butanediol in the resin constituting the first resin layer is 75% by mass. Also, the upper limit of the content ratio of the resin having a structural unit derived from butanediol in the resin constituting the first resin layer is 100% by mass, that is, the first resin layer may be composed only of the resin having a structural unit derived from butanediol.

[0018] The content ratio of the resin having a polybutylene terephthalate skeleton in the resin constituting the first resin layer is not particularly limited, but the preferred lower limit is 70% by mass. If the content ratio of the resin having a polybutylene terephthalate skeleton is 70% by mass or more, the releasability of the multilayer film of the present invention will be improved. A more preferred lower limit of the content ratio of the polybutylene terephthalate resin in the resin constituting the first resin layer is 75% by mass. In addition, the upper limit of the content ratio of the resin having a polybutylene terephthalate skeleton in the resin constituting the first resin layer is 100% by mass. That is, the first resin layer may be composed only of the resin having a polybutylene terephthalate skeleton.

[0019] Among the above polyester resins (A), commercially available ones include, for example, "Perprene P70-B" (manufactured by Toyobo Co., Ltd., melting point 200 ° C), "Novaduran 5020" (manufactured by Mitsubishi Chemical Corporation, melting point 220 ° C), "TRN-RTJC" (manufactured by Teijin Limited, melting point 260 ° C), "Solona" (manufactured by Huafeng Group Co., Ltd., melting point 228 ° C), and the like.

[0020] The first resin layer may contain a rubber component. When the first resin layer contains a rubber component, the followability of the multilayer film of the present invention is further improved. The rubber component is not particularly limited, and examples thereof include natural rubber, styrene-butadiene copolymer, polybutadiene, polyisoprene, acrylonitrile-butadiene copolymer, ethylene-propylene copolymer (EPM, EPDM), polychloroprene, butyl rubber, acrylic rubber, silicone rubber, urethane rubber, and the like. Further, examples of the rubber component include olefin-based thermoplastic elastomer, styrene-based thermoplastic elastomer, vinyl chloride-based thermoplastic elastomer, ester-based thermoplastic elastomer, amide-based thermoplastic elastomer, and the like.

[0021] The first resin layer may contain a stabilizer. The stabilizer is not particularly limited, and examples thereof include hindered phenol-based antioxidants, heat stabilizers, and the like. The above-mentioned hindered phenol antioxidants are not particularly limited, and examples include 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene and 3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)-propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5,5]undecane. The above-mentioned heat stabilizers are not particularly limited, and examples include tris(2,4-di-t-butylphenyl) phosphite, trilauryl phosphite, 2-t-butyl-α-(3-t-butyl-4-hydroxyphenyl)-p-cumenylbis(p-nonylphenyl) phosphite, dimyristyl 3,3'-thiodipropionate, distearyl 3,3'-thiodipropionate, pentaerythryltetrakis(3-laurylthiopropionate), ditridecyl 3,3'-thiodipropionate, and the like.

[0022] The first resin layer described above may further contain conventionally known additives such as fibers, inorganic fillers, flame retardants, ultraviolet absorbers, antistatic agents, inorganic substances, and higher fatty acid salts.

[0023] The thickness of the first resin layer is not particularly limited. The thinner the first resin layer, the greater the flexibility of the multilayer film of the present invention. The thicker the first resin layer, the greater the strength of the multilayer film of the present invention. For example, when the multilayer film of the present invention is used as a release film, it is advantageous in that it is less likely to tear during pressing, and it is also advantageous in that it ensures the release properties of the multilayer film and improves dimensional stability before and after the hot pressing process by reducing thermal shrinkage. The thickness of the first resin layer described above has a preferred lower limit of 3 μm, a preferred upper limit of 25 μm, a more preferred lower limit of 5 μm, and a more preferred upper limit of 20 μm.

[0024] Furthermore, it is preferable that the multilayer film of the present invention has a first resin layer thickness ratio of 15% or more to the total thickness. By ensuring a rigid first resin layer thickness ratio, the tensile strength is relatively increased, making it less likely to tear during pressing.

[0025] The multilayer film of the present invention has a second resin layer. By having the second resin layer, the flexibility of the multilayer film of the present invention is improved, and its conformability can be enhanced. As a result, the multilayer film of the present invention can be made into a multilayer film that is excellent in both release properties and conformability. For example, when performing a heat press with the multilayer film placed between a coverlay film and a heat press plate, excellent release properties are required for the first resin layer that is in direct contact with the coverlay film and the heat press plate. Therefore, it can be suitably used in the manufacturing process of flexible circuit boards and the like in flexible printed circuit boards, where there are certain constraints on improving conformability.

[0026] The second resin layer contains a polyester resin (B) (hereinafter sometimes simply referred to as "polyester resin (B)") having a melting point of 25°C or higher and less than 180°C. Since polyester resin (B) is a polyester resin, it has good compatibility with polyester resin (A) which constitutes the first resin layer. As a result, the adhesion between the first resin layer and the second resin layer is improved, and the multilayer film of the present invention has excellent interlayer strength. Furthermore, since the melting point of polyester resin (B) is relatively low, the second resin layer has appropriate flexibility, and therefore the multilayer film of the present invention has excellent flexibility. As a result, when used as a release film, the multilayer film of the present invention has excellent conformability. In addition, since polyester resin (B) is not too soft, it is possible to suppress the seepage of the resin constituting the film.

[0027] The melting point of the polyester resin (B) is not particularly limited as long as it is between 25°C and 180°C, but a preferred upper limit is 120°C. Because the melting point of the polyester resin (B) is 120°C or lower, the second resin layer has more appropriate flexibility, and the multilayer film of the present invention has better conformability. A more preferred upper limit for the melting point of the polyester resin (B) is 110°C, and an even more preferred upper limit is 100°C. Furthermore, the preferred lower limit of the melting point of the polyester resin (B) is 50°C. A melting point of 50°C or higher for the polyester resin (B) further suppresses the leakage of resin from the second resin layer. A more preferred lower limit for the melting point of the polyester resin (B) is 70°C, and an even more preferred lower limit is 80°C.

[0028] The polyester resin (B) is not particularly limited, but from the viewpoint of improving compatibility with the polyester resin (A) constituting the first resin layer, it is preferable that it contains a resin having structural units derived from butanediol. By including a resin having structural units derived from butanediol in the polyester resin (B), the adhesion between the first resin layer and the second resin layer is improved, and the multilayer film of the present invention has superior interlayer strength.

[0029] Examples of resins having structural units derived from the above-mentioned butanediol include resins containing a polybutylene terephthalate skeleton, resins containing a polybutylene succinate skeleton, and resins containing a polybutylene adipate terephthalate skeleton.

[0030] The content of the resin having the butanediol-derived structural units in the resin constituting the second resin layer is not particularly limited, but a preferred lower limit is 70% by mass. If the proportion of the resin having the butanediol-derived structural units is 70% by mass or more, the compatibility with the polyester resin (A) constituting the first resin layer becomes better, and the release properties of the multilayer film of the present invention are improved. A more preferred lower limit for the content of the resin having the butanediol-derived structural units in the resin constituting the second resin layer is 75% by mass. Furthermore, the upper limit of the content of the resin having the constituent units derived from butanediol in the resin constituting the second resin layer is 100% by mass, that is, the second resin layer may be composed solely of the resin having the constituent units derived from butanediol.

[0031] Examples of commercially available polyester resins (B) include "BioPBS FZ91PB" (manufactured by Mitsubishi Chemical Corporation, melting point 115℃), "Luminy LX575" (manufactured by Total Corbion, melting point 165℃), "ecoflex C1200" (manufactured by BASF, melting point 115℃), "Green Planet X331N" (manufactured by Kaneka Corporation, melting point 100℃), "VYLON GM-350" (manufactured by Toyobo Co., Ltd., melting point 98℃), and "Bellprene P-30B" (manufactured by Toyobo Co., Ltd., melting point 149℃).

[0032] Preferably, the second resin layer further contains the polyester resin (A). Because the second resin layer contains the polyester resin (A), the compatibility between the resin constituting the first resin layer and the resin constituting the second resin layer is further improved, and the adhesion between the first resin layer and the second resin layer is improved, resulting in a multilayer film of the present invention having excellent interlayer strength.

[0033] In conventional multilayer films, when polyester resin is mixed with the resin constituting the polyolefin film used to impart flexibility in order to improve interlayer strength, the polyester resin present in the polyolefin film cannot be sufficiently dispersed, resulting in the problem that the polyolefin film cannot be made into a thin film of uniform thickness. On the other hand, in the multilayer film of the present invention, since the second resin layer that imparts flexibility is composed of a resin containing the polyester resin (B), even if another polyester resin, the polyester resin (A), is mixed into the second resin layer to improve the interlayer strength of the multilayer film, each polyester resin contained in the constituent resin has excellent compatibility with each other and disperses well, so that the second resin layer can be made into a film of uniform thickness. Furthermore, in order for a multilayer film to exhibit sufficient flexibility, it was usually necessary to adjust the ratio of the thicknesses constituting the multilayer film. Therefore, in conventional multilayer films, it was difficult to make the polyolefin film into a thin film of uniform thickness for the reasons mentioned above, making it difficult to make the multilayer film into a thin film. On the other hand, from the above viewpoint, the second resin layer can be made into a thin film of uniform thickness, and the multilayer film of the present invention can be made into a thin film. Accordingly, the multilayer film of the present invention is also useful in this respect. By making the multilayer film of the present invention thinner, the flexural modulus of the entire film decreases, resulting in a more flexible film.

[0034] The content ratio of the polyester resin (A) in the resin constituting the second resin layer is not particularly limited, but it is preferably less than 50% by mass. Because the content ratio of the polyester resin (A) is less than 50% by mass, the second resin layer has appropriate flexibility, and therefore the multilayer film of the present invention has excellent flexibility. As a result, when the multilayer film of the present invention is used as a release film, it has excellent conformability and can prevent the resin constituting the film from seeping out. A more preferable upper limit for the content ratio of the polyester resin (A) is 30% by mass, and an even more preferable upper limit is 25% by mass. Furthermore, the lower limit of the polyester resin (A) content in the second resin layer may be 0% by mass (i.e., the second resin layer may not contain polyester resin (A)). However, from the viewpoint of improving the adhesion between the first resin layer and the second resin layer and ensuring that the multilayer film of the present invention has superior interlayer strength, a more preferable lower limit for the polyester resin (A) content is 5% by mass, and an even more preferable lower limit is 10% by mass.

[0035] The above-mentioned second resin layer may further contain additives such as fibers, inorganic fillers, flame retardants, ultraviolet absorbers, antistatic agents, inorganic substances, and higher fatty acid salts.

[0036] The second resin layer described above may be a single-layer structure consisting of one layer, or it may be a multilayer structure consisting of a laminate of multiple layers. If the second resin layer is a multilayer structure, the multiple layers may be laminated and integrated via an adhesive layer.

[0037] The thickness of the second resin layer is not particularly limited, but a preferred lower limit is 10 μm and a preferred upper limit is 150 μm. If the thickness of the second resin layer is 10 μm or more, the flexibility of the multilayer film of the present invention is further improved. If the thickness of the second resin layer is 150 μm or less, the leakage of resin from the second resin layer can be further suppressed. A more preferred lower limit for the thickness of the second resin layer is 20 μm, a more preferred upper limit is 100 μm, an even more preferred lower limit is 30 μm, and an even more preferred upper limit is 80 μm.

[0038] Furthermore, it is preferable that the multilayer film of the present invention has a ratio of the thickness of the second resin layer to the total thickness of 50% or more. By ensuring a ratio of the thickness of the flexible second resin layer, the multilayer film of the present invention becomes more flexible and its conformability is further improved.

[0039] In the multilayer film of the present invention, it is preferable that the thickness of the first resin layer is thinner than the thickness of the second resin layer. By making the thickness of the first resin layer thinner than the thickness of the second resin layer, the multilayer film of the present invention has superior flexibility.

[0040] In the multilayer film of the present invention, the ratio of the thickness of the first resin layer to the thickness of the second resin layer (thickness of the first resin layer / thickness of the second resin layer) has a preferred lower limit of 0.01 and a preferred upper limit of 1.0. When the ratio of the thickness of the first resin layer to the thickness of the second resin layer is 0.01 or higher, the multilayer film of the present invention has superior tensile strength, heat resistance, and release properties. When the ratio of the thickness of the first resin layer to the thickness of the second resin layer is 1.0 or lower, the multilayer film of the present invention has superior flexibility. A more preferred lower limit for the ratio of the thickness of the first resin layer to the thickness of the second resin layer is 0.05, a more preferred upper limit is 0.7, an even more preferred lower limit is 0.1, and an even more preferred upper limit is 0.5.

[0041] When the multilayer film of the present invention has the above-described structure of three or more layers, the resin and thickness constituting the third resin layer are not particularly limited as long as they do not impair the effects of the present invention. However, from the viewpoint of improving adhesion with the second resin layer and enabling the multilayer film of the present invention to have superior interlayer strength, it is preferable that the third resin layer be made of the same resin as the first resin layer described above.

[0042] The total thickness of the multilayer film of the present invention is not particularly limited. A thinner total thickness of the multilayer film is advantageous in suppressing the leakage of resin from the second resin layer. A thicker total thickness of the multilayer film improves the flexibility of the multilayer film of the present invention, which is advantageous, for example, in conforming to large steps on the substrate surface during hot press molding. The total thickness of the multilayer film of the present invention has a preferred upper limit of 100 μm, a more preferred upper limit of 75 μm, and an even more preferred upper limit of 50 μm. Furthermore, the total thickness of the multilayer film of the present invention has a preferred lower limit of 5 μm, a more preferred lower limit of 10 μm, and an even more preferred lower limit of 20 μm.

[0043] The size of the multilayer film of the present invention is not particularly limited, but it is preferable that it be larger than the object to be pressed in order to prevent tearing when the multilayer film of the present invention is used as a release film and pressed on top of the object to be pressed. Specifically, the length in the width direction is preferably 75 mm or more, more preferably 100 mm or more, and from the viewpoint of film formation, it is preferable to be 3000 mm or less. In addition, the length in the longitudinal direction is preferably 75 mm or more, and from the viewpoint of transportation, it is preferable to be 2000 m or less.

[0044] The method for producing the multilayer film of the present invention is not particularly limited, and examples include a method of forming a film by co-extrusion T-die, a water-cooled or air-cooled co-extrusion inflation method, a solvent casting method, a hot press molding method, etc. Among these, the method of forming a film by co-extrusion T-die is preferred because it offers excellent control over the thickness of each layer.

[0045] The multilayer film of the present invention has no particular limitations on its applications. However, by achieving both excellent interlayer strength and excellent flexibility, it exhibits flexibility while also fully demonstrating functions such as tensile strength and heat resistance, thus providing excellent release properties. For this reason, it is preferable to use the multilayer film of the present invention as a release film. When used as a release film, the multilayer film of the present invention exhibits excellent conformability due to its excellent flexibility. On the other hand, the resin contained in the layer that provides flexibility to the multilayer film of the present invention is not too soft, suppressing the seepage of resin constituting the film and maintaining excellent release properties, heat resistance, chemical resistance, etc., on the film surface. The multilayer film of the present invention, when used as a release film, is particularly suitable for use in the manufacturing process of printed circuit boards such as flexible printed circuit boards (FPCs), printed wiring boards, and multilayer printed wiring boards, and is especially suitable for use in the manufacturing of flexible circuit boards in flexible printed circuit boards (FPCs) and in the manufacturing of printed circuit boards for automotive applications. Specifically, for example, in the manufacturing process of an FPC, the multilayer film of the present invention can be used when a coverlay film is heat-pressed onto a flexible circuit board body with copper circuits formed on it via a thermosetting adhesive or thermosetting adhesive sheet. The multilayer film of the present invention can also be suitably used in the production of FPCs using the RtoR method, where high release properties are required.

[0046] When the multilayer film of the present invention is used as a release film, it is preferable to use it in a hot pressing process, and in particular, it is preferable to use it in a hot pressing process in the manufacture of printed circuit boards, from the viewpoint of having excellent heat resistance. The conditions for the hot pressing process in which the multilayer film of the present invention is used are, for example, a temperature of 100 to 220°C and a pressure of 0.5 to 100 MPa. [Effects of the Invention]

[0047] According to the present invention, it is possible to provide a multilayer film that achieves both excellent interlayer strength and excellent flexibility, and when used as a release film, exhibits excellent conformability and can suppress the leakage of the resin constituting the film. [Modes for carrying out the invention]

[0048] The embodiments of the present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0049] (Example 1) 100 parts by mass of polybutylene terephthalate (PBT, Novaduran 5020 (manufactured by Mitsubishi Chemical Corporation)) was used as the resin for the first and third resin layers. 100 parts by mass of polybutylene succinate (PBS, BioPBS FZ91PB (manufactured by Mitsubishi Chemical Corporation)) was used as the resin for the second resin layer.

[0050] The resin for the first resin layer, the resin for the second resin layer, and the resin for the third resin layer were co-extruded in three layers using an extruder (GM30-28, manufactured by GM Engineering Co., Ltd. (screw diameter 30 mm, L / D 28)) at a molding temperature of 250°C and a T-die width of 400 mm. The extruded molten resin was cooled with a cooling roll (temperature 90°C, arithmetic mean surface roughness Ra 0.1 μm). This resulted in a multilayer film with a width of 1700 mm, having a three-layer structure with the first and third resin layers on either side of the second resin layer. The thickness of the first and third resin layers was 25 μm each, the thickness of the second resin layer was 50 μm, and the total thickness of the multilayer film was 100 μm.

[0051] The extruder described above is equipped with heat bolts and thickness gauges arranged along the entire width of the film at intervals of approximately 20 to 30 mm. The measurement results from the thickness gauges are fed back to the extruder, and the tightness of the heat bolts is adjusted by temperature control, thereby adjusting the gap of the T-die and adjusting the thickness of the multilayer film. During cooling, the contact time between the molten resin and the cooling roll was set to 1.0 second, and the tensile stress when the molten resin is cooled by the cooling roll was set to 450 kPa.

[0052] (Examples 2-23, Comparative Examples 1-9) A three-layer multilayer film was obtained in the same manner as in Example 1, except that the compositions of the resin for the first resin layer, the resin for the second resin layer, and the resin for the third resin layer, as well as the thicknesses of the first, second, and third resin layers, were as shown in Tables 1 to 3.

[0053] The types of resins used for the first resin layer, the second resin layer, and the third resin layer in Tables 1-3 are as follows: PBT: Polybutylene terephthalate PET: Polyethylene terephthalate PTT: Polytrimethylene terephthalate TPEE: Polyester-based elastomer PLA: Polylactic acid SPS: Syndiotactic Polystyrene PBS: Polybutylene succinate PBAT: Polybutylene adipate terephthalate PHBH: Poly-3-hydroxybutyrate-co-hydroxyhexanoate PE: Polyethylene PP: Polypropylene

[0054] The multilayer films obtained in the examples and comparative examples were evaluated using the following method. The results are shown in Tables 1 to 3.

[0055] <Interlayer strength> The obtained multilayer film was cut to a size of 25 mm in width and 100 mm in length. The third resin layer of the cut multilayer film was attached to a 2 mm thick polycarbonate plate using double-sided tape (Sekisui Chemical Co., Ltd., "#5782", 25 mm in width, 100 mm in length, 130 μm in thickness). Then, single-sided tape (Nitto Denko Corporation, "No.31B#25", 25 mm in width, 200 mm in length, 50 μm in thickness) was layered and attached onto the first resin layer of the multilayer film fixed to the polycarbonate plate. Finally, the layers were pressed together by moving a 2 kg rubber roller back and forth at a speed of 300 mm / min once, and the layers were left to stand for 10 minutes in an environment of 23°C and 50% RH to prepare a test sample. For the prepared test samples, a tensile testing machine (A&D Company, Limited, "Tensilon") was used. Under conditions of 23°C and a tensile speed of 500 mm / min, the single-sided tape was chucked to the top and pulled until the first resin layer peeled off. Three tensile tests were performed, and the average of the obtained values ​​(gf / cm) was defined as the interlayer strength.

[0056] The obtained interlaminar strengths were evaluated according to the following criteria. ◎: The first resin layer did not peel off, or the interlayer strength was 300 gf / cm or higher. ○: The interlaminar strength was between 100 gf / cm and less than 300 gf / cm. ×: The interlaminar strength was less than 100 gf / cm.

[0057] <Followability> A coverlay film (10cm x 10cm, polyimide thickness 25μm, epoxy adhesive layer thickness 35μm) with φ=1mm holes was laminated onto the copper foil surface of a copper-clad laminate (CCL) (12.5cm x 12.5cm, polyimide thickness 25μm, copper foil thickness 35μm), with the epoxy adhesive layer in contact with the copper foil surface. Furthermore, the resulting multilayer film (15cm x 15cm) was laminated with the first resin layer in contact with the coverlay film, aligning the centers of the coverlay film and the multilayer film. This laminate was heated at 180°C and 30kgf / cm². 2 The material was heat-pressed for 2 minutes under the specified conditions. After removing the release film, the epoxy adhesive that had flowed onto the copper-clad laminate (CCL) was observed using an optical microscope (100x magnification), and the width of the epoxy adhesive seepage was measured at 12 points, and the average value was calculated.

[0058] The average value of the width of the epoxy adhesive seepage was used for evaluation according to the following criteria. ◎: The average width of the epoxy adhesive leakage was 25 μm or less. ○: The average width of the epoxy adhesive leakage was greater than 25 μm and less than 50 μm. ×: The average width of the epoxy adhesive leakage was 50 μm or more. In the case of Comparative Example 8, it was not possible to perform measurements because the material could not be cleanly peeled off after hot pressing.

[0059] <Staining> The obtained multilayer film was cut into 10 cm squares, and the cut multilayer film was subjected to pressure bonding for 3 minutes at 180°C and 3 MPa by applying force in the thickness direction from the first resin layer side. The width of the second resin layer that seeped out from the cut surface of the bonded multilayer film was measured with calipers.

[0060] The width of the second resin layer that had seeped out was used for evaluation according to the following criteria. ◎: The width of the leakage from the second resin layer was 1.0 mm or less. ○: The width of the leaked second resin layer was greater than 1.0 mm and less than 5.0 mm. ×: The width of the leaked second resin layer was 5.0 mm or more. In the case of Comparative Example 8, it was not possible to perform measurements because the material could not be cleanly peeled off after hot pressing.

[0061] [Table 1]

[0062] [Table 2]

[0063] [Table 3] [Industrial applicability]

[0064] According to the present invention, it is possible to provide a multilayer film that achieves both excellent interlayer strength and excellent flexibility, and when used as a release film, exhibits excellent conformability and can suppress the leakage of the resin constituting the film.

Claims

1. It has a first resin layer and a second resin layer, The first resin layer is placed on the outermost surface, The first resin layer contains a polyester resin (A) having a melting point of 180°C or higher. The second resin layer contains a polyester resin (B) having a melting point of 25°C or higher and less than 180°C. A multilayer film characterized by the following features.

2. The multilayer film according to claim 1, wherein the second resin layer has a third resin layer on the side opposite to the first resin layer.

3. The multilayer film according to claim 1 or 2, wherein the total thickness of the multilayer film is 100 μm or less.

4. The multilayer film according to claim 1 or 2, wherein the thickness of the first resin layer is thinner than the thickness of the second resin layer.

5. The multilayer film according to claim 1 or 2, wherein the ratio of the thickness of the first resin layer to the thickness of the second resin layer (thickness of the first resin layer / thickness of the second resin layer) is 0.01 or more and 1.0 or less.

6. The multilayer film according to claim 1 or 2, wherein the thickness of the first resin layer is 3 μm or more and 25 μm or less.

7. The multilayer film according to claim 1 or 2, wherein the thickness of the second resin layer is 10 μm or more and 150 μm or less.

8. The multilayer film according to claim 1 or 2, wherein the polyester resin (A) comprises an aromatic polyester resin.

9. The multilayer film according to claim 8, wherein the aromatic polyester resin comprises a resin having a polybutylene terephthalate skeleton.

10. The multilayer film according to claim 1 or 2, wherein the polyester resin (A) comprises a resin having structural units derived from butanediol.

11. The multilayer film according to claim 1 or 2, wherein the polyester resin (B) comprises a resin having a melting point of 120°C or less.

12. The multilayer film according to claim 1 or 2, wherein the polyester resin (B) comprises a resin having structural units derived from butanediol.

13. The multilayer film according to claim 1 or 2, wherein the second resin layer further comprises the polyester resin (A).

14. The multilayer film according to claim 13, wherein the content of the polyester resin (A) in the resin constituting the second resin layer is less than 50% by mass.

15. A multilayer film according to claim 1 or 2, used as a release film.

16. A multilayer film according to claim 15, used in the manufacture of a flexible circuit board.

Images