Laminated film and copper-clad laminate

Abstract

The present invention provides: a layered film that exhibits excellent heat resistance and dimensional stability in addition to low dielectric properties; and a copper-clad layered sheet in which a copper foil is layered on at least one primary surface of the layered film.　This layered film includes at least one crosslinked polyolefin layer and at least one polyimide resin layer. The crosslinked polyolefin layer comprises a crosslinked product of a graft-modified polyolefin composition containing a graft-modified polyolefin (A) and a crosslinking agent (B). A polar group is introduced into the graft-modified polyolefin (A) by graft modification.

Description

[Technical Field]

[0001] The present invention relates to a laminate film and a copper-clad laminate in which a copper foil is laminated on at least one main surface of the laminate film. [Background technology]

[0002] In recent years, there has been a demand for communication devices such as smartphones and electronic devices such as next-generation televisions to transmit and receive large volumes of data at high speeds. This has led to the trend toward higher frequencies for electrical signals. Specifically, in the field of wireless communications, the fifth-generation mobile communication system (5G) is expected to be introduced around 2020. The use of high-frequency bands above 10 GHz is being considered for the introduction of the fifth-generation mobile communication system.

[0003] However, as the frequency of the signals used increases, the quality of the output signal decreases, which can lead to erroneous recognition of information, i.e., transmission loss increases. This transmission loss consists of conductor loss caused by the conductor and dielectric loss caused by the insulating resin that makes up electrical and electronic components such as circuit boards in electronic and communication devices. Since conductor loss is proportional to the 0.5th power of the frequency used and dielectric loss is proportional to the first power of the frequency, the impact of dielectric loss becomes extremely large in high frequency bands, especially in the GHz band.

[0004] Therefore, in order to reduce transmission loss, there is a demand for low-dielectric materials that have low relative permittivity and dielectric loss tangent, which are factors related to dielectric loss. Under these circumstances, the use of compositions containing polyolefins, which have excellent electrical properties such as low dielectric loss and low dielectric loss tangent, as low-dielectric materials that can be used in high-frequency bands, has been studied (see Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-245305 Summary of the Invention [Problem to be solved by the invention]

[0006] A preferred application of a material having excellent low dielectric properties is flexible printed wiring boards, in which the material having low dielectric properties is usually used as a film or sheet.

[0007] Flexible printed wiring boards are usually copper-clad laminates (CCLs), but films and sheets made of polyolefin compositions such as those described in Patent Document 1 are required to have improved heat resistance and dimensional stability to the levels required for flexible printed wiring board applications.

[0008] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a laminated film that has excellent heat resistance and dimensional stability in addition to low dielectric properties, and a copper-clad laminate in which copper foil is laminated on at least one main surface of the laminated film. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to solve the above problems and have completed the present invention.

[0010] That is, the present invention provides the following (1) to (11). (1) At least one crosslinked polyolefin layer and at least one polyimide resin layer, the crosslinked polyolefin layer comprises a crosslinked product of a graft-modified polyolefin composition containing a graft-modified polyolefin (A) and a crosslinking agent (B); A laminated film, wherein the graft-modified polyolefin (A) is a polyolefin into which a polar group has been introduced by graft modification. (2) The laminate film according to (1), wherein the ratio of the total thickness of the crosslinked polyolefin layer and the polyimide resin layer to the thickness of the laminate film is 50% or more and 100% or less. (3) The laminated film according to (1) or (2), wherein the ratio of the thickness of the crosslinked polyolefin layer to the total thickness of the crosslinked polyolefin layer and the polyimide resin layer is 5% or more and 95% or less. (4) The laminated film according to any one of (1) to (3), wherein at least one of the main surfaces is made of a crosslinked polyolefin layer. (5) The laminated film according to any one of (1) to (4), wherein at least one crosslinked polyolefin layer and at least one polyimide resin layer are in contact with each other. (6) The crosslinking agent (B) is triallyl cyanurate or triallyl isocyanurate 、 The laminated film according to any one of (1) to (5), wherein the compound is at least one selected from the group consisting of trimethallyl isocyanurate and trimethylolpropane tri(meth)acrylate. (7) The laminated film according to any one of (1) to (6), wherein the content of the crosslinking agent (B) in the graft-modified polyolefin composition is 1 part by mass or more and 100 parts by mass or less per 100 parts by mass of the graft-modified polyolefin (A). (8) The laminate film according to any one of (1) to (7), wherein the crosslinked product has a crosslinked structure due to intermolecular crosslinking of the graft-modified polyolefin (A) and / or a crosslinked structure in which the molecules of the graft-modified polyolefin (A) are crosslinked via the crosslinking agent (B). (9) The laminated film according to any one of (1) to (8), wherein the graft-modified polyolefin (A) has an epoxy group as the polar group. (10) The laminated film according to any one of (1) to (9), wherein the graft-modified polyolefin (A) is graft-modified with glycidyl (meth)acrylate and styrene. (11) A copper-clad laminate in which a copper foil is laminated on at least one main surface of the laminate film according to any one of (1) to (10). [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a laminate film that has excellent heat resistance and dimensional stability in addition to low dielectric properties, and a copper-clad laminate in which copper foil is laminated on at least one main surface of the laminate film. DETAILED DESCRIPTION OF THE INVENTION

[0012] <Laminated film> The laminated film includes at least one crosslinked polyolefin layer and at least one polyimide resin layer. The crosslinked polyolefin layer is made of a crosslinked product of a graft-modified polyolefin composition containing a graft-modified polyolefin (A) and a crosslinking agent (B). The graft-modified polyolefin (A) is a polyolefin into which a polar group has been introduced by graft modification.

[0013] By employing a crosslinked polyolefin layer that satisfies the above requirements and a polyimide resin layer as layers that constitute a laminate film, it is possible to provide a laminate film that is excellent in low dielectric properties, heat resistance, and dimensional stability. Although polyolefin films have excellent low dielectric properties, they may have poor heat resistance and dimensional stability. However, by laminating a crosslinked polyolefin layer that satisfies the above-mentioned requirements with a polyimide resin layer, the heat resistance and dimensional stability of the laminated film can be imparted without significantly impairing the excellent low dielectric properties of the crosslinked polyolefin layer.

[0014] The ratio of the total thickness of the crosslinked polyolefin layer and the polyimide resin layer to the thickness of the laminated film is not particularly limited as long as it does not impair the object of the present invention. The ratio of the total thickness of the crosslinked polyolefin layer and the polyimide resin layer to the thickness of the laminated film is, for example, preferably 50% or more and 100% or less, more preferably 60% or more and 100% or less, even more preferably 70% or more and 100% or less, particularly preferably 80% or more and 100% or less, and most preferably 100%. That is, it is preferable that the laminated film is composed only of a crosslinked polyolefin layer and a polyimide resin layer, which makes it easier to obtain a laminated film that is particularly excellent in low dielectric properties, heat resistance, and dimensional stability.

[0015] In the laminated film, the ratio of the thickness of the crosslinked polyolefin layer to the total thickness of the crosslinked polyolefin layer and the polyimide resin layer is not particularly limited, and is preferably 5% to 95%, more preferably 30% to 95%, even more preferably 50% to 95%, particularly preferably 60% to 90%, and most preferably 70% to 90%. If the ratio of the thickness of the crosslinked polyolefin layer to the total thickness of the crosslinked polyolefin layer and the polyimide resin layer is too high, it may be difficult to obtain a laminated film having excellent heat resistance and dimensional stability. If the ratio of the thickness of the crosslinked polyolefin layer to the total thickness of the crosslinked polyolefin layer and the polyimide resin layer is too low, it may be difficult to obtain a laminated film that exhibits the desired level of low dielectric properties.

[0016] The thickness of the laminate film is not particularly limited as long as it does not impair the object of the present invention. The thickness of the laminate film is appropriately determined depending on the application. The thickness of the laminate film is typically preferably 10 μm or more and 300 μm or less, more preferably 15 μm or more and 200 μm or less, and even more preferably 25 μm or more and 100 μm or less.

[0017] The layer structure of the laminate film is not particularly limited. The two main surfaces of the laminate film may each be composed of a crosslinked polyolefin layer, a polyimide resin layer, or a layer other than these layers. From the viewpoint of adhesion to the copper foil, the two main surfaces of the laminate film are preferably composed of a crosslinked polyolefin layer or a polyimide resin layer, and more preferably composed of a crosslinked polyolefin layer. Both the crosslinked polyolefin layer and the polyimide resin layer have polar groups, and therefore have good adhesion to the copper foil. For this reason, it is preferable that at least one main surface of the laminated film is made of a crosslinked polyolefin layer.

[0018] In addition, in order to obtain good interlayer adhesion, it is preferable that at least one crosslinked polyolefin layer and at least one polyimide resin layer are in contact with each other in the laminated film.

[0019] The layer structure of the laminated film is not particularly limited. The number of layers constituting the laminated film is typically preferably 2 or more and 5 or less, and more preferably 2 or 3. A preferred layer structure is, for example, Two-layer structure consisting of a cross-linked polyolefin layer and a polyimide resin layer; a three-layer structure in which a cross-linked polyolefin layer, a polyimide resin layer, and a cross-linked polyolefin layer are laminated in this order; a three-layer structure in which a polyimide resin layer, a cross-linked polyolefin layer, and a polyimide resin layer are laminated in this order; a four-layer structure in which a cross-linked polyolefin layer, a polyimide resin layer, a cross-linked polyolefin layer, and a polyimide resin layer are laminated in this order; a five-layer structure in which a crosslinked polyolefin layer, a polyimide resin layer, a crosslinked polyolefin layer, a polyimide resin layer, and a crosslinked polyolefin layer are laminated in this order; a five-layer structure in which a polyimide resin layer, a cross-linked polyolefin layer, a polyimide resin layer, a cross-linked polyolefin layer, and a polyimide resin layer are laminated in this order; etc.

[0020] The layers constituting the laminated film will be described below.

[0021] <Crosslinked polyolefin layer> The crosslinked polyolefin layer is made of a crosslinked product of a graft-modified polyolefin composition containing a graft-modified polyolefin (A) and a crosslinking agent (B) described below. The graft-modified polyolefin (A) is crosslinked by the action of the crosslinking agent (B), thereby imparting heat resistance to the crosslinked polyolefin layer without significantly impairing the excellent low dielectric properties of the graft-modified polyolefin (A).

[0022] The graft-modified polyolefin composition and its constituent components will be described below.

[0023] [Graft-modified polyolefin composition] The graft-modified polyolefin composition contains a graft-modified polyolefin (A) having a polar group and a crosslinking agent (B). Since the molded article made of the graft-modified polyolefin composition contains the crosslinking agent (B), it can be crosslinked by, for example, heating, electron beam irradiation, etc. The crosslinked molded article is endowed with desirable heat resistance and improved mechanical properties for flexible printed wiring board applications.

[0024] Essential and optional components that the graft-modified polyolefin composition may contain will be described below.

[0025] (Graft-modified polyolefin (A))

[0026] The graft-modified polyolefin (A) is not particularly limited as long as it is a resin in which a polyolefin has been graft-modified and has a polar group.

[0027] Here, the polar group refers to a polar atomic group, and when this group is present in an organic compound, the compound becomes polar. Specific examples of polar groups that can be introduced into polyolefins by grafting include carboxy groups derived from unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, tetrahydrophthalic acid, itaconic acid, citraconic acid, crotonic acid, and isocrotonic acid; acid anhydride groups, halocarbonyl groups, carboxylic acid amide groups, imide groups, and carboxylic acid ester groups derived from derivatives of the above-mentioned unsaturated carboxylic acids, such as acid anhydrides, acid halides, amides, imides, and esters; glycidyl methacrylate, glycidyl acrylate, maleic acid, and the like; Examples of the polar groups include monoglycidyl ester, diglycidyl maleate, monoglycidyl itaconate, diglycidyl itaconate, monoglycidyl allyl succinate, diglycidyl allyl succinate, glycidyl p-styrenecarboxylate, allyl glycidyl ether, methacrylic glycidyl ether, styrene-p-glycidyl ether, p-glycidylstyrene, 3,4-epoxy-1-butene, 3,4-epoxy-3-methyl-1-butene, and epoxy groups derived from epoxy group-containing vinyl monomers such as vinylcyclohexene monoxide. Among these polar groups, epoxy groups are preferred because they provide good adhesion between the graft-modified polyolefin composition or its crosslinked product and a polyimide resin layer or copper foil, and good crosslinking reactivity between the graft-modified polyolefin (A) and the crosslinking agent (B).

[0028] Typically, the graft-modified polyolefin (A) is a resin in which a polyolefin is graft-modified with a vinyl monomer having a polar group in the presence of a radical polymerization initiator.

[0029] The graft-modified polyolefin (A) is preferably a polyolefin graft-modified with a vinyl monomer having a polar group and an aromatic vinyl monomer, and more preferably a polyolefin graft-modified with glycidyl (meth)acrylate and styrene.

[0030] Examples of polyolefins include linear polyolefins such as polyethylene, polypropylene, poly-1-butene, polyisobutylene, polymethylpentene, propylene-ethylene copolymers, ethylene-propylene-diene copolymers, ethylene / butene-1 copolymers, and ethylene / octene copolymers; and cyclic polyolefins such as copolymers of cyclopentadiene with ethylene and / or propylene.

[0031] Among these polyolefins, polymethylpentene, polyethylene, polypropylene, and propylene-ethylene copolymers are preferred because they are easily modified, and polymethylpentene is more preferred in terms of heat resistance and low dielectric properties. In terms of heat resistance, the polyolefin is preferably a polyolefin that does not contain a structural unit derived from ethylene. Examples of polyolefins that do not contain a structural unit derived from ethylene include polypropylene, poly-1-butene, polyisobutylene, polymethylpentene, and a copolymer of cyclopentadiene and propylene, more preferably polypropylene and polymethylpentene, and particularly preferably polymethylpentene.

[0032] It is generally believed that when polymeric materials are irradiated with radiation, molecular chain scission and cross-linking between molecular chains occur. From this point of view, polymers in which cross-linking occurs primarily upon radiation exposure are classified as cross-linked polymers, and polymers in which molecular chain scission occurs primarily upon radiation exposure are classified as degraded polymers. Here, polyethylene and polypropylene are classified as crosslinked polymers. In a resin composition containing a crosslinked polymer in combination with a crosslinking agent (B) such as triallyl isocyanurate (TAIC) described later, when the resin composition is formed into a film and then the obtained film is crosslinked by electron beam crosslinking, the crosslinked film may become brittle due to an excessively high crosslink density. On the other hand, polyisobutylene and polymethylpentene are classified as degradable polymers. In a resin composition containing a degradable polymer in combination with a crosslinking agent (B) such as triallyl isocyanurate (TAIC) described below, when the resin composition is formed into a film and the resulting film is subjected to electron beam crosslinking, crosslinking between molecular chains proceeds while some molecular chain scission occurs, so the crosslinked film is unlikely to be in an over-crosslinked state. Therefore, electron beam crosslinking can be used to obtain a film that maintains the desired mechanical strength while improving heat resistance.

[0033] Examples of radical polymerization initiators that can be used when graft-modifying polyolefins include ketone peroxides such as methyl ethyl ketone peroxide and methyl acetoacetate peroxide; peroxyketals such as 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, n-butyl-4,4-bis(tert-butylperoxy)valerate, and 2,2-bis(tert-butylperoxy)butane; hydroperoxides such as permethane hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, diisopropylbenzene hydroperoxide, and cumene hydroperoxide; dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, α,α'-bis(tert-butylperoxy-m-isopropyl)benzene, te Examples of the peroxyester include dialkyl peroxides such as rt-butylcumyl peroxide, di-tert-butyl peroxide, and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3; diacyl peroxides such as benzoyl peroxide; peroxydicarbonates such as di(3-methyl-3-methoxybutyl)peroxydicarbonate and di-2-methoxybutylperoxydicarbonate; and peroxyesters such as tert-butylperoxyoctate, tert-butylperoxyisobutyrate, tert-butylperoxylaurate, tert-butylperoxy-3,5,5-trimethylhexanoate, tert-butylperoxyisopropylcarbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, tert-butylperoxyacetate, tert-butylperoxybenzoate, and di-tert-butylperoxyisophthalate. The above radical polymerization initiators can be used alone or in combination of two or more.

[0034] The amount of the radical polymerization initiator used is not particularly limited as long as the graft modification reaction proceeds well, and is preferably 0.01 to 10 parts by mass, more preferably 0.2 to 5 parts by mass, per 100 parts by mass of the polyolefin.

[0035] Examples of vinyl monomers having a polar group that can be used for graft modification include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, tetrahydrophthalic acid, itaconic acid, citraconic acid, crotonic acid, and isocrotonic acid; derivatives of these unsaturated carboxylic acids such as acid anhydrides, acid halides, amides, imides, and esters; and epoxy group-containing vinyl monomers such as glycidyl methacrylate, glycidyl acrylate, monoglycidyl maleate, diglycidyl maleate, monoglycidyl itaconate, diglycidyl itaconate, monoglycidyl allyl succinate, diglycidyl allyl succinate, glycidyl p-styrenecarboxylate, allyl glycidyl ether, methacrylic glycidyl ether, styrene-p-glycidyl ether, p-glycidylstyrene, 3,4-epoxy-1-butene, 3,4-epoxy-3-methyl-1-butene, and vinylcyclohexene monoxide.

[0036] Among these, epoxy group-containing vinyl monomers are preferred, glycidyl methacrylate and glycidyl acrylate are more preferred, and glycidyl methacrylate is particularly preferred.

[0037] The above vinyl monomers having a polar group can be used alone or in combination of two or more.

[0038] The amount of the vinyl monomer having a polar group used for graft-modifying the polyolefin to be added is preferably 0.1 to 12 parts by mass, more preferably 0.5 to 10 parts by mass, and particularly preferably 1 to 8 parts by mass, per 100 parts by mass of the polyolefin.

[0039] By using a polyolefin modified with a vinyl monomer having a polar group in an amount within this range, it is easy to obtain a graft-modified polyolefin (A) that provides a crosslinked polyolefin layer that adheres well to a polyimide resin layer or copper foil.

[0040] As mentioned above, the graft-modified polyolefin (A) is preferably a polyolefin graft-modified with a vinyl monomer having a polar group and an aromatic vinyl monomer.

[0041] By using a vinyl monomer having a polar group in combination with an aromatic vinyl monomer, the grafting reaction is stabilized, making it easier to graft a desired amount of the vinyl monomer having a polar group.

[0042] Specific examples of aromatic vinyl monomers include styrene; alkylstyrenes such as o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, β-methylstyrene, dimethylstyrene, and trimethylstyrene; chlorostyrenes such as o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, α-chlorostyrene, β-chlorostyrene, dichlorostyrene, and trichlorostyrene; bromostyrenes such as o-bromostyrene, m-bromostyrene, p-bromostyrene, dibromostyrene, and tribromostyrene; o-fluorostyrene, m-fluorostyrene, p-fluorostyrene, fluorostyrenes such as o-nitrostyrene, m-nitrostyrene, p-nitrostyrene, dinitrostyrene, and trinitrostyrene; nitrostyrenes such as o-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, dihydroxystyrene, and trihydroxystyrene; hydroxystyrenes such as o-divinylbenzene, m-divinylbenzene, p-divinylbenzene, o-diisopropenylbenzene, m-diisopropenylbenzene, and p-diisopropenylbenzene; and dialkenylbenzenes such as o-divinylbenzene, m-divinylbenzene, p-divinylbenzene, o-diisopropenylbenzene, m-diisopropenylbenzene, and p-diisopropenylbenzene.

[0043] Among these aromatic vinyl monomers, styrene, α-methylstyrene, p-methylstyrene, o-divinylbenzene, m-divinylbenzene, p-divinylbenzene, or a mixture of divinylbenzene isomers is preferred from the viewpoint of low cost, and styrene is particularly preferred.

[0044] The aromatic vinyl monomers can be used alone or in combination of two or more.

[0045] The amount of aromatic vinyl monomer having a polar group used for graft-modifying the polyolefin is preferably 0.1 to 12 parts by mass, more preferably 0.5 to 10 parts by mass, and particularly preferably 1 to 8 parts by mass, per 100 parts by mass of the polyolefin.

[0046] The melting point of the graft-modified polyolefin (A) is not particularly limited and is preferably 80°C or higher, more preferably 100°C or higher, and even more preferably 120°C or higher and 240°C or lower. From the viewpoint of heat resistance of the molded article, the melting point of the graft-modified polyolefin (A) is preferably 200° C. or higher. When the melting point of the graft-modified polyolefin (A) is within the above range, good heat resistance can be imparted to the crosslinked polyolefin layer formed using the graft-modified polyolefin composition. Furthermore, when the melting point of the graft-modified polyolefin (A) is 240°C or lower, decomposition and sublimation of the crosslinking agent (B) can be easily suppressed during preparation and use of the graft-modified polyolefin composition.

[0047] (Crosslinking agent (B)) The graft-modified polyolefin composition contains a crosslinking agent (B). The crosslinking agent (B) crosslinks the graft-modified polyolefin (A), thereby contributing to improving the heat resistance and mechanical properties of the laminate film including the crosslinked polyolefin layer formed using the graft-modified polyolefin composition.

[0048] The crosslinking agent (B) crosslinks the graft-modified polyolefins (A) together by a crosslinking treatment such as heating or electron beam irradiation, which is selected depending on the type of reactive functional group contained in the crosslinking agent (B) (described later).

[0049] The crosslinking agent (B) is a compound having two or more reactive functional groups in the same molecule. In a molded article made from the graft-modified polyolefin composition, molecular crosslinking by the crosslinking agent (B) makes it easy to obtain a molded article having particularly excellent heat resistance.

[0050] Examples of reactive functional groups possessed by the crosslinking agent (B) include carbon-carbon double bond-containing groups, halogen atoms, dicarboxylic anhydride groups, carboxy groups, amino groups, cyano groups, and hydroxyl groups. Multiple reactive functional groups possessed within the same molecule of the crosslinking agent may be the same or different. Among the reactive functional groups mentioned above, a carbon-carbon double bond-containing group is preferred because it has excellent crosslinking reactivity and the stability of the crosslinked structure after crosslinking. Examples of the carbon-carbon double bond-containing group include alkenyl groups such as vinyl, allyl, and methallyl groups, unsaturated acyl groups such as acryloyl and methacryloyl groups, and maleimide groups. Preferred carbon-carbon double bond-containing groups are alkenyl groups having 2 to 4 carbon atoms, with allyl groups being particularly preferred.

[0051] Specific preferred examples of the crosslinking agent (B) include triallyl cyanurate, triallyl isocyanurate, trimethallyl isocyanurate, trimethylolpropane tri(meth)acrylate, 1,3,5-triacryloylhexahydro-1,3,5-triazine, triallyl trimellitate, m-phenylenediamine bismaleimide, p-quinonedioxime, p,p'-dibenzoylquinonedioxime, dipropargyl terephthalate, diallyl phthalate, N,N',N'',N'''-tetraallyl terephthalamide, and vinyl group-containing polysiloxanes such as polymethylvinylsiloxane and polymethylphenylvinylsiloxane. Note that "(meth)acrylate" refers to both acrylate and methacrylate.

[0052] Among these, one or more selected from the group consisting of triallyl cyanurate, triallyl isocyanurate, trimethallyl isocyanurate, and trimethylolpropane tri(meth)acrylate are more preferred. In particular, from the viewpoint of crosslinking reactivity, it is preferred that the crosslinking agent (B) contains triallyl isocyanurate (TAIC) and / or trimethylolpropane tri(meth)acrylate (TMPTMA), and it is particularly preferred that the crosslinking agent (B) is TAIC.

[0053] The amount of the crosslinking agent (B) used is not particularly limited as long as it does not impair the object of the present invention. The amount of the crosslinking agent (B) used in the graft-modified polyolefin composition is, for example, preferably 1 part by mass or more and 100 parts by mass or less, more preferably 3 parts by mass or more and 50 parts by mass or less, and even more preferably 5 parts by mass or more and 30 parts by mass or less, per 100 parts by mass of the graft-modified polyolefin.

[0054] (Various initiators) The graft-modified polyolefin composition may contain various initiators according to the crosslinking method described below. For example, when crosslinking is performed by heating, the above-mentioned radical initiators can be used. When crosslinking is performed by light irradiation, a photoacid generator can be added depending on the type of reactive functional group possessed by the crosslinking agent (B). Examples of photoacid generators include nitrobenzyl compounds, onium salts, sulfonates, and carboxylates. When crosslinking is performed by electron beam irradiation, various initiators are not required, and it is preferable that the composition is substantially free of them. However, a small amount of the initiator used in the production of the graft-modified polyolefin (A) may remain. Specifically, the content of the initiator per 100 parts by weight of the total solid content of the graft-modified polyolefin composition is preferably less than 0.05 parts by weight, more preferably less than 0.01 parts by weight, and even more preferably less than 0.001 parts by weight.

[0055] (Other resins) The graft-modified polyolefin composition may contain other resins besides the graft-modified polyolefin (A) within the scope of not impairing the object of the present invention. The mass ratio of the graft-modified polyolefin (A) to the total mass of the resin components contained in the graft-modified polyolefin composition is typically preferably 80 mass%, more preferably 90 mass% or more, even more preferably 95 mass% or more, and particularly preferably 100 mass%.

[0056] Examples of other resins include non-graft-modified polyolefins, graft-modified polyolefins other than graft-modified polyolefins, non-liquid crystal polyesters such as polyethylene terephthalate and polybutylene terephthalate, liquid crystal polyesters, polyamides, polyesteramides, polyimides, polyamideimides, polycarbonates, polyacetals, polyphenylene sulfides, polyphenylene ethers, polysulfones, polyethersulfones, polyetherimides, silicone resins, and fluororesins.

[0057] (inorganic filler) The graft-modified polyolefin composition may contain an inorganic filler as needed. Examples of inorganic fillers include calcium carbonate, talc, clay, silica, magnesium carbonate, barium sulfate, titanium oxide, alumina, montmorillonite, gypsum, glass flakes, glass fiber, milled glass fiber, carbon fiber, alumina fiber, silica-alumina fiber, aluminum borate whisker, and potassium titanate fiber. The inorganic fillers may be used alone or in combination of two or more.

[0058] The amount of these inorganic fillers used is determined appropriately depending on the application of the graft-modified polyolefin composition, so long as the low dielectric properties of the graft-modified polyolefin composition are not impaired. For example, when the graft-modified polyolefin composition is used to form a film, the upper limit of the amount of inorganic fillers used is determined so long as the mechanical strength of the film is not significantly impaired.

[0059] (additives) The graft-modified polyolefin composition may further contain various additives, such as organic fillers, antioxidants, heat stabilizers, light stabilizers, flame retardants, lubricants, antistatic agents, colorants, rust inhibitors, foaming agents, fluorescent agents, surface smoothing agents, surface gloss improvers, and mold release improvers, as needed.

[0060] These additives may be used alone or in combination of two or more.

[0061] The form of the graft-modified polyolefin composition is not particularly limited. The graft-modified polyolefin composition may be, for example, a composition in which a crosslinking agent (B) is dispersed in a solid graft-modified polyolefin (A), or a powdery composition in which a powdery graft-modified polyolefin (A) and a powdery crosslinking agent (B) are mixed. As the graft-modified polyolefin composition, a composition in which a crosslinking agent (B) is dispersed in a solid graft-modified polyolefin (A) is preferred.

[0062] The dielectric loss tangent at 10 GHz of the graft-modified polyolefin composition is preferably 0.0025 or less. The relative dielectric constant of the graft-modified polyolefin composition at a frequency of 10 GHz is preferably 2.8 or less.

[0063] There are no particular limitations on the method for producing the graft-modified polyolefin composition. The graft-modified polyolefin composition can be produced by mixing the graft-modified polyolefin (A) with the crosslinking agent (B). The method for mixing the graft-modified polyolefin (A) and the crosslinking agent (B) is not particularly limited, but a preferred mixing method is a method using a melt kneading device such as a single-screw extruder or a twin-screw extruder.

[0064] The mixing conditions are not particularly limited as long as the graft-modified polyolefin (A) and the crosslinking agent (B) can be uniformly mixed and the components are not excessively thermally decomposed or sublimated. When a melt-kneading device is used, the melt-kneading is carried out at a temperature that is preferably 5°C or higher and 100°C or lower, more preferably 10°C or higher and 50°C or lower, higher than the melting point of the graft-modified polyolefin (A).

[0065] After forming a film from the graft-modified polyolefin composition, the resulting film is subjected to a crosslinking treatment with a crosslinking agent (B) to form a crosslinked polyolefin layer. The crosslinking treatment may be carried out either before or after laminating the uncrosslinked film with a polyimide resin layer or other layers. By carrying out the crosslinking treatment, a crosslinked structure is formed in the crosslinked product of the graft-modified polyolefin composition by crosslinking between molecules of the graft-modified polyolefin (A) and / or by crosslinking molecules of the graft-modified polyolefin (A) via the crosslinking agent (B), and as a result, the crosslinked product is endowed with heat resistance superior to that of an uncrosslinked graft-modified polyolefin. The method of crosslinking treatment is not particularly limited and may be appropriately selected depending on the type of reactive functional group possessed by the crosslinking agent (B). Examples of the crosslinking treatment method include electron beam irradiation, heating, and light irradiation. Electron beam irradiation is preferred because it allows for the formation of a crosslinked structure after film formation. When electron beam irradiation is performed, the dose of electron beams is preferably 100 kGy or more and 1200 kGy or less, and more preferably 200 kGy or more and 800 kGy or less. In the method of crosslinking by heating, if the crosslinking temperature is excessively high, the film made of the graft-modified polyolefin composition may be thermally deteriorated or deformed during crosslinking. Conversely, if the crosslinking temperature is excessively low, the graft-modified polyolefin composition may crosslink in the extruder. In this case, the viscosity of the graft-modified polyolefin composition increases in the extruder, which tends to result in poor appearance of the molded product, making it difficult to apply melt molding as a molding method for the graft-modified polyolefin composition. In the method of photoirradiation, except in special cases, an initiator such as a photoacid generator must be added to the graft-modified polyolefin composition. However, such initiators are prone to decomposition in the high-temperature extruder. Considering the above points, electron beam irradiation is preferred because it can easily form a crosslinked structure in the film without causing various problems. That is, the crosslinked polyolefin layer crosslinked with the crosslinking agent (B) can be produced by the following method: forming the graft-modified polyolefin composition into a film; A method including irradiating the obtained film with an electron beam to crosslink the film with the crosslinking agent (B) is preferred.

[0066] <Polyimide resin layer> The polyimide resin layer is not particularly limited. Typically, a polyimide resin film is laminated with a crosslinked polyolefin layer or a film constituting another layer, thereby forming a polyimide resin layer in a laminate film.

[0067] Polyimide films are produced using polyamic acid as a precursor. Any known method can be used to produce polyamic acid. The acid dianhydride component and diamine component used in the production of polyamic acid are not limited, but aromatic tetracarboxylic dianhydrides and aromatic diamines are preferred.

[0068] A typical method for producing polyamic acid is described below. First, an aromatic tetracarboxylic dianhydride and an aromatic diamine in an amount substantially equimolar to the aromatic tetracarboxylic dianhydride are dissolved in an organic solvent. The resulting solution is stirred under controlled temperature conditions until polymerization is complete, producing polyamic acid. The concentration of the polyamic acid solution is typically 5% by mass or more and 35% by mass or less, and preferably 10% by mass or more and 30% by mass or less. A concentration within this range will achieve an appropriate molecular weight and solution viscosity.

[0069] As the polymerization method, any known method or a combination thereof can be used. The polymerization method is characterized by the order of addition of the monomers. By controlling the order of addition of the monomers when producing polyamic acid, it is possible to control the various physical properties of the resulting polyimide resin. Representative polymerization methods include, for example, the following methods 1) to 4). 1) A method in which an aromatic diamine is dissolved in an organic polar solvent, and an aromatic tetracarboxylic dianhydride is polymerized with the aromatic diamine in an amount substantially equal to the number of moles of the aromatic diamine. 2) A method in which an aromatic tetracarboxylic dianhydride is reacted with an aromatic diamine compound in a molar amount less than the molar amount of the aromatic tetracarboxylic dianhydride in an organic polar solvent to obtain a prepolymer having acid anhydride groups at both ends, and the prepolymer is then further polymerized with an aromatic diamine compound so that the molar amount of the aromatic tetracarboxylic dianhydride and the molar amount of the aromatic diamine compound finally used are substantially equal. 3) A method in which an aromatic tetracarboxylic dianhydride is reacted with an aromatic diamine compound in a molar amount greater than the number of moles of the aromatic tetracarboxylic dianhydride in an organic polar solvent to obtain a prepolymer having amino groups at both ends, and then the prepolymer is further polymerized with an aromatic tetracarboxylic dianhydride so that the number of moles of the aromatic tetracarboxylic dianhydride and the number of moles of the aromatic diamine compound finally used are substantially equal. 4) A method in which an aromatic tetracarboxylic dianhydride is dissolved and / or dispersed in an organic polar solvent, and then an aromatic diamine compound is added to the organic polar solvent in an amount substantially equal in moles to the aromatic tetracarboxylic dianhydride, thereby polymerizing the resulting product. 5) A method of polymerizing a mixture of substantially equimolar amounts of an aromatic tetracarboxylic dianhydride and an aromatic diamine in an organic polar solvent. These methods may be used alone or in partial combination.

[0070] It is also preferable to use a polymerization method in which a prepolymer is obtained using a diamine component having a rigid structure, such as paraphenylenediamine or substituted benzidine. This method facilitates the production of polyimide films with a high tensile / storage modulus and a low coefficient of moisture expansion. In this method, the molar ratio of the aromatic diamine having a rigid structure to the aromatic tetracarboxylic dianhydride used in preparing the prepolymer is preferably 100:70 to 100:99, more preferably 100:75 to 100:90. Furthermore, the molar ratio is preferably 70:100 to 99:100, more preferably 75:100 to 90:100. When a prepolymer is produced using an aromatic diamine and an aromatic tetracarboxylic dianhydride in such a molar ratio, the desired improvement effects in the tensile / storage modulus and the moisture absorption coefficient of expansion are easily obtained, and adverse effects such as an excessively small linear expansion coefficient and an excessively small tensile elongation are unlikely to occur.

[0071] The materials used in the production of polyamic acid will be described below.

[0072] Examples of aromatic tetracarboxylic dianhydrides include pyromellitic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-oxyphthalic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)propane dianhydride, ) propane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)ethane dianhydride, oxydiphthalic dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, p-phenylene bis(trimellitic acid monoester anhydride), ethylene bis(trimellitic acid monoester anhydride), bisphenol A bis(trimellitic acid monoester anhydride), and the like. These can be preferably used alone or as a mixture in any ratio.

[0073] When pyromellitic dianhydride is used, the amount of pyromellitic dianhydride used is preferably 40 mol% to 100 mol%, more preferably 45 mol% to 100 mol%, and even more preferably 50 mol% to 100 mol%, relative to the number of moles of aromatic tetracarboxylic dianhydride. By using pyromellitic dianhydride in this range, the glass transition temperature and the storage modulus at heat can be easily maintained within ranges suitable for use or film formation.

[0074] Examples of aromatic diamines include 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenylmethane, benzidine, 3,3'-dichlorobenzidine, 3,3'-dimethylbenzidine, 2,2'-dimethylbenzidine, 3,3'-dimethoxybenzidine, 2,2'-dimethoxybenzidine, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 4,4'-oxydianiline, 3,3'-oxydianiline, 3,4'-oxydianiline, 1,5-diaminonaphthalene, 4,4'-diaminodiphenyldiethylsilane, 4,4'-diaminodiphenylsilane, 4,4'-diaminodiphenylethylphosphine oxide, 4,4'-diaminodiphenyl N- Examples of the aminobenzophenone include methylamine, 4,4'-diaminodiphenyl N-phenylamine, 1,4-diaminobenzene (p-phenylenediamine), 1,3-diaminobenzene, 1,2-diaminobenzene, bis{4-(4-aminophenoxy)phenyl}sulfone, bis{4-(3-aminophenoxy)phenyl}sulfone, 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-bis(3-aminophenoxy)biphenyl, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, and the like.

[0075] The polyimide film can be obtained by appropriately determining the types and compounding ratios of the aromatic tetracarboxylic dianhydride and aromatic diamine so as to obtain a film having the desired properties.

[0076] The solvent for synthesizing polyamic acid can be any solvent that dissolves polyamic acid. Preferred solvents include amide solvents. Specific examples of suitable amide solvents include N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone, with N,N-dimethylformamide and N,N-dimethylacetamide being particularly preferred.

[0077] To improve the properties of the film, a filler can be added to the polyamic acid or polyimide resin. Any filler can be used. For example, the fillers described above for the graft-modified polyolefin composition can be blended with the polyamic acid or polyimide resin. Preferred examples of fillers to be blended with the polyamic acid or polyimide resin include silica, titanium oxide, alumina, silicon nitride, boron nitride, calcium hydrogen phosphate, calcium phosphate, and mica.

[0078] The particle size of the filler is not particularly limited. In general, the average particle size of the filler is preferably 0.05 μm or more and 100 μm or less, more preferably 0.1 μm or more and 75 μm or less, even more preferably 0.1 μm or more and 50 μm or less, and particularly preferably 0.1 μm or more and 25 μm or less. When the average particle size of the filler is within the above range, the desired modifying effect can be easily obtained without using the filler, and a laminated film having desirable surface properties and mechanical properties can be easily obtained. The number of parts of filler added is not particularly limited, as it is determined by the film properties to be modified, the particle size of the filler, etc. Generally, the amount of filler added is preferably 0.01 to 100 parts by mass, more preferably 0.01 to 90 parts by mass, and even more preferably 0.02 to 80 parts by mass, per 100 parts by mass of polyamic acid or polyimide resin. When the amount of filler added is within the above range, it is easy to obtain the desired modifying effect of the filler and to obtain a laminated film with desirable mechanical properties. Specific examples of how fillers can be added include: 1. A method of adding a filler to the polymerization reaction solution before or during polymerization when producing polyamic acid. 2. After polymerization is complete, a filler is mixed into the polyamic acid using a three-roll mill or similar. 3. Method of mixing a dispersion containing a filler into a polyamic acid organic solvent solution etc. Among these methods, the method of mixing a filler-containing dispersion into a polyamic acid solution is preferred, and the method of mixing the filler into the polyamic acid solution immediately before film formation is particularly preferred because it minimizes contamination of the production line by the filler. When preparing a filler-containing dispersion, it is preferable to use the same solvent as the polymerization solvent for the polyamic acid as the dispersion medium in the dispersion. Furthermore, in order to disperse the filler well and stabilize the dispersion state, dispersants, thickeners, etc. can also be used within the range that does not affect the physical properties of the film.

[0079] A polyimide film can be produced from a polyamic acid solution by a conventionally known method, including a thermal imidization method and a chemical imidization method, either of which can be used to produce the film.

[0080] The manufacturing process for polyimide film is as follows: a) a step of reacting an aromatic diamine with an aromatic tetracarboxylic dianhydride in an organic solvent to obtain a polyamic acid solution; b) casting a membrane-forming dope containing a polyamic acid solution onto a support; c) heating the film-forming dope cast on the support, and then peeling the gel film from the support; d) further heating the gel film to dry the gel film while imidizing the polyamic acid remaining in the gel film; It is preferred that the compound contains:

[0081] In the above step, a curing agent containing a dehydrating agent typified by an acid anhydride such as acetic anhydride and an imidization catalyst typified by a tertiary amine such as isoquinoline, β-picoline, or pyridine may be used.

[0082] The following describes the steps for producing a polyimide film, taking the chemical imidization method, which is a preferred method for producing a polyimide resin film, as an example. However, the method for producing a polyimide resin film is not limited to the following example. The film formation conditions and heating conditions may vary depending on the type of polyamic acid, the film thickness, etc.

[0083] A dehydrating agent and an imidization catalyst are mixed into a polyamic acid solution at low temperature to obtain a membrane dope. The membrane dope is then cast into a film on a support such as a glass plate, aluminum foil, an endless stainless steel belt, or a stainless steel drum. The cast membrane dope is heated on the support at a temperature range of 80°C to 200°C, preferably 100°C to 180°C, to activate the dehydrating agent and the imidization catalyst. After partially curing and / or drying the cast membrane dope, the polyamic acid film (hereinafter referred to as a gel film) is peeled off from the support. The gel film is in an intermediate stage of curing from polyamic acid to polyimide and is self-supporting. For the gel film, the volatile content calculated by the following formula (1) is preferably 5% by mass or more and 500% by mass or less, more preferably 5% by mass or more and 200% by mass or less, and even more preferably 5% by mass or more and 150% by mass or less. (AB) × 100 / B····(1) (In equation (1), A is the mass of the gel film, and B is the mass of the gel film after heating at 450°C for 20 minutes.) When the volatile content is within the above range, problems such as film breakage during the baking process, uneven color tone of the film due to uneven drying, and variations in properties are unlikely to occur.

[0084] The amount of the dehydrating agent is preferably 0.5 to 5 mol, more preferably 1.0 to 4 mol, per mol of amide acid unit in the polyamide acid. The amount of the imidization catalyst is preferably 0.05 to 3 mol, more preferably 0.2 to 2 mol, per mol of amide acid unit in the polyamide acid. The amide acid unit is a structure consisting of an amide bond, (-CO-NH-), and a carboxy group adjacent to the amide bond.

[0085] When the amounts of the dehydrating agent and the imidization catalyst are within the above ranges, chemical imidization can be sufficiently carried out, and the polyimide resin film is less likely to break during baking or to lose its mechanical strength. Furthermore, when the amounts of the dehydrating agent and the imidization catalyst are within the above ranges, imidization can be carried out at an appropriate rate, and the film-forming dope can be easily cast into a film.

[0086] The gel film is dried while fixing the edges to prevent shrinkage during curing, to remove water, residual solvent, remaining dehydrating agent, and imidization catalyst, and the remaining amic acid is completely imidized to obtain a polyimide film.

[0087] When the gel film is dried and imidized, it is preferable to finally heat it at a temperature of 400° C. to 650° C. for a time period of 5 to 400 seconds. By heating the gel film under such temperature conditions for the time period within the aforementioned range, it is possible to sufficiently promote imidization while suppressing thermal degradation of the formed polyimide resin film.

[0088] Furthermore, in order to relieve internal stress remaining in the polyimide resin film, the polyimide resin film can be heat-treated under the minimum tension necessary for transporting the film. This heat treatment can be carried out during the film production process, or a separate process can be added. The heating conditions are determined appropriately depending on the properties of the polyimide resin film and the equipment used. Generally, the heating conditions are preferably 200°C to 500°C, more preferably 250°C to 500°C, and particularly preferably 300°C to 450°C, and are preferably 1 second to 300 seconds, more preferably 2 seconds to 250 seconds, and particularly preferably 5 seconds to 200 seconds. Heat treatment under these conditions can relieve internal stress.

[0089] The properties of the polyimide resin film can be appropriately controlled by the type of monomer used, the order of adding the monomers during polymerization, the imidization method selected, etc. It is preferable to molecularly design the polyimide resin film so that it generally has the following properties. 1. The tensile modulus is preferably 4.0 GPa or more, more preferably 4.5 GPa or more, and particularly preferably 5.0 GPa or more. 2. The moisture absorption expansion coefficient is preferably 20 ppm or less, more preferably 16 ppm or less. 3. The linear expansion coefficient is preferably 1 ppm or more and 20 ppm or less, and more preferably 5 to 18 ppm or less.

[0090] When the polyimide resin layer is the outermost layer in the laminate film, it is preferable that the temperature at which the storage modulus of the polyimide resin film starts to decrease is 250°C or higher, and that the storage modulus of the polyimide resin film at the copper foil lamination temperature is 0.01 GPa or higher and 1.0 GPa or lower. This makes it possible to obtain a copper-clad laminate using the laminate film that has excellent dimensional stability after copper foil removal and after heating at 250°C for 30 minutes.

[0091] Specifically, by having a storage modulus decrease starting temperature of 250°C or higher and a storage modulus at the copper foil lamination temperature in the range of 0.01 GPa to 1.0 GPa, the MD / TD residual strain that occurs particularly significantly in lamination methods can be alleviated, and dimensional changes after copper foil removal and heating can be suppressed. The storage modulus decrease starting temperature here refers to the storage modulus inflection point when measuring the storage modulus of the polyimide resin film. The storage modulus inflection point can be determined by dynamic mechanical analysis (DMA). Furthermore, by having a storage modulus decrease starting temperature of 250°C or higher, dimensional changes after heating, particularly after high-temperature heating at 250°C for 30 minutes, can be suppressed.

[0092] When the polyimide resin layer is the outermost layer in the laminate film, by appropriately controlling both the temperature at which the storage modulus of the polyimide resin film starts to decrease and the storage modulus at the copper foil lamination temperature as described above, it is possible to suppress the occurrence of defects due to dimensional changes in the wiring pattern formation process by etching the copper foil layer, and in the solder reflow process and solder dipping process.

[0093] <Other layers> The laminated film may include layers other than the crosslinked polyolefin layer and the polyimide resin layer. The material of the other layers is not particularly limited as long as it does not impair the object of the present invention. Examples of the material of the other layers include a liquid crystal polymer layer, a PTFE layer, a PFA layer, an epoxy resin layer, and a PPE layer.

[0094] <Laminated film manufacturing method> The method for producing the laminated film is not particularly limited. Typically, the laminated film is produced by a lamination method in which a crosslinked polyolefin film obtained by crosslinking a film made of the above-mentioned graft-modified polyolefin composition, a polyimide resin film, and optionally other films constituting other layers are pressure-bonded or thermocompression-bonded. The pressure-bonding conditions and thermocompression-bonding conditions are appropriately determined taking into account the types and thermal properties of the graft-modified polyolefin and polyimide resin.

[0095] Furthermore, as long as the object of the present invention is not impaired, the crosslinked polyolefin film and the polyimide resin film may be laminated together using an adhesive that is used in the production of laminated films.

[0096] The method for producing a laminated film using a crosslinked polyolefin film has been described above. However, after producing a laminated film by the above method using an uncrosslinked polyolefin film made of the above-mentioned graft-modified polyolefin composition, the obtained laminated film can also be subjected to a crosslinking treatment.

[0097] Furthermore, a solution obtained by dissolving the above-mentioned graft-modified polyolefin composition in an organic solvent can be used as a coating liquid to produce a laminated film. The solvent for dissolving the graft-modified polyolefin composition is preferably a hydrocarbon solvent, more preferably an aromatic hydrocarbon solvent such as toluene or xylene. The solvent for dissolving the graft-modified polyolefin composition may be heated as necessary.

[0098] Specifically, a coating solution containing a graft-modified polyolefin composition is first applied to a polyimide resin film, a film constituting another layer, or a copper foil. The formed coating film is then dried to form an uncrosslinked polyolefin film on the polyimide resin film, a film constituting another layer, or the copper foil. Thereafter, the uncrosslinked polyolefin film is subjected to a crosslinking treatment to form a crosslinked polyolefin film on the polyimide resin film, a film constituting another layer, or the copper foil. A laminated film can be produced by repeating such an operation including coating or by combining it with the above-mentioned lamination method.

[0099] Furthermore, a laminated film can be produced using a varnish containing polyamic acid or a varnish containing a solvent-soluble polyimide resin as a coating liquid. The lamination method using a varnish containing polyamic acid or a varnish containing polyimide resin is similar to the method using a coating liquid containing a graft-modified polyolefin composition, except that no crosslinking treatment is performed. However, when a varnish containing polyamic acid is used, the coating film is dried to form a film mainly composed of polyamic acid, and then the film is heated at any time to imidize the polyamic acid.

[0100] For example, after forming a polyimide resin layer on copper foil by the above-mentioned coating method, copper foils each having a polyimide resin layer can be laminated together using a cross-linked polyolefin film as an intermediate layer to obtain a copper-clad laminate having copper foil on two main surfaces, the laminate consisting of copper foil / polyimide resin layer / cross-linked polyolefin layer / polyimide resin layer / copper foil. Such a copper-clad laminate includes a laminate film having a three-layer structure consisting of a polyimide resin layer / a cross-linked polyolefin layer / a polyimide resin layer.

[0101] <Copper-clad laminate> The laminated film has excellent low dielectric properties in the high frequency band of 10 GHz or more, and is also excellent in heat resistance and dimensional stability. Therefore, by laminating a copper foil on at least one main surface of the laminated film, a copper-clad laminate that can be suitably used in a high frequency band of 10 GHz or more can be obtained. The copper foil may be laminated on only one of the main surfaces or on both of the main surfaces. The copper foil is attached to the laminate film in the same manner as in the general method for manufacturing a copper-clad laminate. The thickness of the copper foil is also appropriately selected taking into consideration the application and required performance of the copper-clad laminate. [Example]

[0102] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0103] [Production Example 1] (Production of modified α-olefin copolymers (graft-modified polyolefins)) 100 parts by mass of (a1) an α-olefin copolymer having a polymethylpentene structure (Absortomer EP1013 manufactured by Mitsui Chemicals) and 0.15 parts by mass of (b1) 1,3-di(tert-butylperoxyisopropyl)benzene (Perbutyl P manufactured by NOF Corp.) were fed from the hopper port into a twin-screw extruder (46 mmφ, L / D=63, manufactured by Kobe Steel Ltd.) set at a cylinder temperature of 180°C and a screw rotation speed of 150 rpm, and melt-kneaded. 1 part by mass of (c1) styrene and 1 part by mass of (d1) glycidyl methacrylate were then added midway through the cylinder. Graft-modified polyolefin (e1) pellets were then obtained by vacuum devolatilization through a vent port.

[0104] The obtained resin pellets were dissolved in xylene at 130°C, and then cooled to room temperature again to precipitate a recrystallized resin. The amount of glycidyl methacrylate modification was measured using an automatic potentiometric titrator (AT700 manufactured by Kyoto Electronics Manufacturing Co., Ltd.) in accordance with JIS K 7236. The amount of glycidyl methacrylate modification of the modified α-olefin copolymer (e1) was 0.23 mass%.

[0105] [Production Examples 2 and 3] Pellets of graft-modified polyolefins (e2) to (e3) were obtained in the same manner as in Production Example 1, except that the types and parts of the materials used were changed according to Table 1. In Production Examples 2 and 3, the cylinder temperature was changed to 230°C. In Table 1, a2 is (a2) polymethylpentene (TPX grade MX002 manufactured by Mitsui Chemicals), and a3 is (a3) ​​polypropylene (polypropylene grade J106G manufactured by Prime Polymer). The amount of glycidyl methacrylate modification in the resulting graft-modified polyolefin (e2) was 0.35% by mass, and the amount of glycidyl methacrylate modification in (e3) was 0.23% by mass.

[0106] [Table 1]

[0107] [Production Example 4] 100 parts by mass of the modified α-olefin copolymer (e1) obtained in Production Example 1 and 3 parts by weight of triallyl isocyanurate (TAIC) were fed from the hopper mouth into a twin-screw extruder (25 mmφ, L / D=40, Technovel) set at a cylinder temperature of 180°C and a screw rotation speed of 150 rpm, and melt-kneaded to obtain a composition containing the modified α-olefin copolymer and a crosslinking agent. The composition obtained as described above was melted at 230°C, and the molten composition was extruded through a 140 mm wide T-die to obtain a film. The obtained film was irradiated with an electron beam at an acceleration voltage of 200 kV and an absorbed dose of 400 kGy to crosslink the film with the crosslinking agent, thereby obtaining a crosslinked modified α-olefin copolymer film (f1).

[0108] [Production Examples 5 to 12] Crosslinked polyolefin films (f2) to (f9) were obtained in the same manner as in Production Example 4, except that the types and parts of the materials used were changed according to Table 2. In Production Examples 5 to 12, the cylinder temperature was changed to 230°C. In Table 2, TPATMA is trimethylolpropane tri(meth)acrylate.

[0109] [Table 2]

[0110] [Production Example 13] (Production of polyimide film) In a 500 mL glass flask, 164.2 g of N,N-dimethylformamide (DMF), 3.0 g of 1,3-bis(4-aminophenoxy)benzene (TPE-R), and 6.4 g of p-phenylenediamine (p-PDA) were dissolved. To the resulting solution, 12.2 g of s-biphenyltetracarboxylic dianhydride (s-BPDA) and 7.9 g of 4,4'-oxyphthalic dianhydride (ODPA) were added, and the solution was stirred for 30 minutes to dissolve the components. A separately prepared DMF solution of pyromellitic dianhydride (PMDA) (0.5 g PMDA / 5.8 g DMF) was carefully added to the resulting solution, and the addition was stopped when the viscosity reached approximately 1500 poise. The solution in the flask was then stirred for 1 hour to yield a polyamic acid solution with a solids concentration of approximately 15 wt% and a rotational viscosity of 1500-2000 poise at 23°C. To 55 g of this polyamic acid solution, 27.5 g of a curing agent consisting of acetic anhydride / isoquinoline / DMF (weight ratio 42:21:37) was added, followed by stirring and degassing at a temperature below 0°C. The degassed solution was cast onto aluminum foil using a comma coater. After drying the resin film on the aluminum foil at 110°C for 180 seconds, the gel film was peeled off the foil and fixed to a metal frame, taking care not to shrink the gel film. The gel film fixed to the metal frame was heated in a preheated hot air circulating oven at 300°C for 56 seconds and in a far-infrared (IR) oven at 380°C for 49 seconds, and then separated from the frame to obtain a polyimide film.

[0111] Example 1 The cross-linked modified α-olefin copolymer film (f1) obtained in Production Example 4, a polyimide resin film (Apical NPI, manufactured by Kaneka Corporation), and copper foil were laminated in the order of copper foil, cross-linked modified α-olefin copolymer film, polyimide resin film, cross-linked modified α-olefin copolymer film, and copper foil, and a copper-clad laminate 1 was obtained by a hot press set at 180°C. The two cross-linked modified α-olefin copolymer films used for lamination had the same thickness. The thickness of the copper-clad laminate 1 minus the thickness of the copper foil, i.e., the total thickness of the crosslinked polyolefin layer and the polyimide resin layer, was 100 μm. The ratio of the thickness of the crosslinked polyolefin layer to the total thickness of the crosslinked polyolefin layer and the polyimide resin layer was 75%, and the ratio of the polyimide resin layer was 25%.

[0112] Example 2 A copper-clad laminate was obtained in the same manner as in Example 1, with the thickness of the crosslinked modified α-olefin copolymer film and the thickness of the polyimide resin film being adjusted. The thickness of the copper-clad laminate 2 minus the thickness of the copper foil, i.e., the total thickness of the crosslinked polyolefin layer and the polyimide resin layer, was 100 μm. The ratio of the thickness of the crosslinked polyolefin layer to the total thickness of the crosslinked polyolefin layer and the polyimide resin layer was 87.5%, and the ratio of the polyimide resin layer to the total thickness of the crosslinked polyolefin layer and the polyimide resin layer was 12.5%.

[0113] Examples 3 to 14 Copper-clad laminates were obtained in the same manner as in Example 1, except that the crosslinked modified polyolefin film and polyimide film used were changed according to Table 3. The thickness ratios of each layer were as shown in Table 3.

[0114] Comparative Examples 1 to 6 A copper clad laminate was obtained in the same manner as in Example 1, except that a film prepared using the type of olefin shown in Table 3 was used.

[0115] The copper-clad laminates obtained in each Example and Comparative Example were evaluated for relative permittivity, dielectric loss tangent, dimensional stability, peel strength, solder heat resistance, and storage modulus according to the following methods. The evaluation results are shown in Table 3.

[0116] [Dielectric constant / dielectric loss tangent] The dielectric constant and dielectric loss tangent were measured using a laminate film without copper foil as the sample, rather than a copper-clad laminate. A laminated film was obtained in the same manner as in each of the Examples and Comparative Examples, except that no copper foil was laminated, and the obtained laminated film was used as a test piece. The dielectric constant and dielectric loss tangent of the obtained laminated film were measured at the following frequencies using a cavity resonator perturbation method complex dielectric constant evaluation device. Measurement frequency: 10GHz Measurement conditions: temperature 22℃~24℃, humidity 45%~55% Measurement sample: A sample that had been left to stand for 24 hours under the above measurement conditions was used.

[0117] [Dimensional stability (dimensional change rate)] According to JIS C6481, four holes were drilled in a copper-clad laminate, and the distance between each hole was measured. Next, an etching process was performed to remove the metal foil from the copper-clad laminate, and the laminate was then left in a thermostatic chamber at 23°C / 55%RH for 24 hours. Thereafter, the distance between each of the four holes was measured in the same manner as before the etching process. The measured value of the distance between each hole before removing the metal foil was designated D1, and the measured value of the distance between each hole after removing the metal foil was designated D2, and the dimensional change rate before and after etching was calculated using the following formula (I): Dimensional change rate (%) = {(D2 - D1) / D1} × 100 Formula (I) The dimensional change rate was measured in both the MD and TD directions.

[0118] [Peel Strength] Measurement was performed in accordance with "6.5 Peel Strength" of JIS C6471. Specifically, a 1 mm wide metal foil portion was peeled off at a peel angle of 90 degrees at a rate of 100 mm / min, and the load applied when peeling off the metal foil was measured as the peel strength. If the copper foil and the laminated film were not in close contact and a test specimen could not be prepared, or if a test specimen could be prepared but the peel strength was less than 1 N / cm, the test was evaluated as "×", and if the peel strength was 1 N / cm or more, the test was evaluated as "Good".

[0119] [Solder heat resistance (heat resistance)] The copper-clad laminate samples were passed through a high-temperature reflow furnace (Antom, UNI6116S) under conditions simulating the operating temperature of lead-free solder, and the copper-clad laminate samples were observed after passing through the high-temperature reflow furnace. The conditions for passing through the high-temperature reflow furnace were a peak temperature of 288±3°C, a passing time of 60 seconds, and three passing cycles. Based on the observation results, cases where there was no change in the appearance of the laminate before and after reflow, such as dents or bulges, were marked as ◯, cases where there was a change were marked as ×, and cases where the copper foil and the laminate film were not adhered to each other and it was impossible to prepare a test piece were marked as XX.

[0120] [Storage modulus] A dynamic viscoelasticity measuring device was used as the measuring device to measure the storage modulus at 288°C of the graft-modified polyolefin (e3) film and the cross-linked modified polyolefin films (f3) to (f8). The storage modulus of the graft-modified polyolefin (e3) film was less than 0.01 MPa. The measurement results of the storage modulus of the cross-linked modified polyolefin films (f3) to (f8) are shown in the storage modulus column for Examples 8 to 13 in Table 3. The measurements were carried out under the following conditions. Sample measurement range: 25℃~310℃ Heating rate: 5°C / min Distortion amplitude: 0.1% Measurement frequency: 1Hz Minimum tension / compression force: 0.1g Initial force amplitude: 100g

[0121] [Table 3]

[0122] The laminate films obtained in Examples 1, 2, and 3 maintained low dielectric properties and were excellent in heat resistance and dimensional stability compared to the laminate films obtained in Comparative Examples 3 and 4. Furthermore, the copper foil of the copper-clad laminates obtained in Examples 1, 2, and 3 was less likely to peel than that of the copper-clad laminate obtained in Comparative Example 1. In Examples 8 to 14, the obtained laminated films were excellent in dielectric properties, heat resistance and dimensional stability, regardless of the degree of modification of the crosslinked modified polyolefin film or the type and amount of the crosslinking agent. Furthermore, when Example 1 is compared with Examples 3, 4, and 8 to 14, which have similar thickness ratios between the polyimide layer and the polyolefin layer, it is found that all of the Examples have good low dielectric properties, heat resistance, and dimensional stability. In other words, according to the present invention, good effects can be obtained in terms of low dielectric properties, heat resistance, and dimensional stability, regardless of the type of polyimide resin that constitutes the polyimide layer.

Claims

1. At least one crosslinked polyolefin layer and at least one polyimide resin layer are included, the crosslinked polyolefin layer is made of a crosslinked product of a graft-modified polyolefin composition containing a graft-modified polyolefin (A) and a crosslinking agent (B); the graft-modified polyolefin (A) is a polyolefin into which a polar group has been introduced by graft modification, the graft-modified polyolefin (A) has an epoxy group as the polar group, the crosslinking agent (B) is at least one selected from the group consisting of triallyl cyanurate, triallyl isocyanurate, trimethallyl isocyanurate, and trimethylolpropane tri(meth)acrylate; a laminated film, wherein the content of the crosslinking agent (B) in the graft-modified polyolefin composition is 1 part by mass or more and 30 parts by mass or less per 100 parts by mass of the graft-modified polyolefin (A).

2. A film comprising at least one crosslinked polyolefin layer and at least one polyimide resin layer, the crosslinked polyolefin layer is made of a crosslinked product of a graft-modified polyolefin composition containing a graft-modified polyolefin (A) and a crosslinking agent (B); the graft-modified polyolefin (A) is a polyolefin into which a polar group has been introduced by graft modification, the polyolefin is polymethylpentene, the crosslinking agent (B) is at least one selected from the group consisting of triallyl cyanurate, triallyl isocyanurate, trimethallyl isocyanurate, and trimethylolpropane tri(meth)acrylate; a laminated film, wherein the content of the crosslinking agent (B) in the graft-modified polyolefin composition is 1 part by mass or more and 30 parts by mass or less per 100 parts by mass of the graft-modified polyolefin (A).

3. 3. The laminate film according to claim 1, wherein a ratio of the total thickness of the crosslinked polyolefin layer and the polyimide resin layer to the thickness of the laminate film is 50% or more and 100% or less.

4. The ratio of the thickness of the crosslinked polyolefin layer to the total thickness of the crosslinked polyolefin layer and the polyimide resin layer is 5% or more and 95% or less. The laminate film according to any one of claims 1 to 3.

5. The laminate film according to any one of claims 1 to 4, wherein at least one main surface comprises the crosslinked polyolefin layer.

6. The laminate film according to any one of claims 1 to 5, wherein at least one of the crosslinked polyolefin layers and at least one of the polyimide resin layers are in contact with each other.

7. The laminate film according to any one of claims 1 to 6, wherein the crosslinked product has a crosslinked structure due to intermolecular crosslinking of the graft-modified polyolefin (A) and / or a crosslinked structure in which molecules of the graft-modified polyolefin (A) are crosslinked via the crosslinking agent (B).

8. 8. The laminated film according to claim 1, wherein the graft-modified polyolefin (A) is graft-modified with glycidyl (meth)acrylate and styrene.

9. A copper-clad laminate comprising the laminate film according to any one of claims 1 to 8, and a copper foil laminated on at least one main surface of the laminate film.

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