Cross-linking agent for thermosetting resin and composition for hard substrate using cross-linking agent

Abstract

To provide a cross-linking agent for a thermosetting resin which has excellent electrical characteristics, excellent thermosetting properties and a high glass transition temperature of a cured product and can prepare a hard substrate having excellent electrical properties required for next-generation high frequency.SOLUTION: There is provided a cross-linking agent for a thermosetting resin used for a hard substrate material, which has 3 or more groups represented by the following formula (1) in the molecule. In the formula -O-R (1), R is a hydrocarbon group having at least one unsaturated bond and a cyclic structure, in which all hydrogens bonded to the cyclic structure are substituted with fluorine.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a crosslinking agent for thermosetting resins, and more specifically, to a crosslinking agent capable of crosslinking a crosslinkable compound to obtain a hard substrate having excellent electrical properties that can be suitably used for next-generation high-frequency substrates. [Background technology]

[0002] In recent years, development has been progressing towards next-generation radio frequency technologies that will enable high-speed, large-capacity transmission in the field of information and communications devices such as smartphones and tablet terminals. To accommodate this, the circuit board materials used are also being required to have low dielectric constants and low dielectric tangents that can reduce transmission losses. Conventionally, as resin materials for high-speed communication and transmission, fluororesins such as epoxy resins, polyphenylene ether resins (Patent Document 1), fluorinated poly(arylene ether)s and crosslinkable fluorinated poly(arylene ether)s (Patent Documents 2 and 3), or perfluororesins in which all hydrogen in the molecular chain is replaced with fluorine, have been used because they have excellent electrical properties.

[0003] However, in order to produce circuit boards that can handle next-generation high-frequency frequencies exceeding 5 GHz, the circuit board materials must also have superior electrical properties, a low coefficient of thermal expansion after heat curing that allows use over a wide temperature range, and a high glass transition temperature that allows use in high-temperature environments and soldering, as well as the ability to reliably mold the prepregs used to produce the circuit boards. From this perspective, the present applicant has proposed a fluororesin that has excellent electrical properties (low dielectric constant and low dielectric loss), excellent dimensional stability, high solvent solubility for facilitating thin film formation, and excellent crosslinking properties that enable film formation by heating at about 200°C, as well as excellent heat resistance, as a substrate material for high-speed communication and transmission (Patent Document 4). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-128718 A [Patent Document 2] U.S. Pat. No. 5,115,082 [Patent Document 3] U.S. Pat. No. 5,179,188 [Patent Document 4] Patent Publication No. 2022-89150 Summary of the Invention [Problem to be solved by the invention]

[0005] The above-mentioned resin materials are themselves crosslinkable, and therefore substrates can be formed without using a crosslinking agent. However, the use of a crosslinking agent improves performance by forming a stronger crosslinked structure, increasing the glass transition temperature, improving dimensional stability, and so on. For this reason, crosslinking agents made of polyfunctional monomers such as isocyanurate derivatives, divinylbenzene, bismaleimides, or bistriazenes, particularly triallyl isocyanate (TAIC), have been used in the past. However, in order to prepare substrates, particularly rigid substrates, that are compatible with next-generation high-frequency waves exceeding 5 GHz, a new crosslinking agent that can provide rigid substrates with more suitable electrical properties, a high glass transition temperature, and excellent heat resistance is desired.

[0006] Therefore, an object of the present invention is to provide a crosslinking agent capable of molding a hard substrate having excellent thermosetting properties, a high glass transition temperature of the cured product, excellent flame retardancy, and excellent electrical properties required for next-generation high-frequency devices. Another object of the present invention is to provide a composition for hard substrates comprising a crosslinkable compound (prepolymer) and the above-mentioned crosslinking agent, in particular a composition for hard substrates in which the crosslinkable compound is a specific fluorine-containing compound. [Means for solving the problem]

[0007] According to the present invention, there is provided a crosslinking agent for thermosetting resins used in hard substrate materials, characterized in that the crosslinking agent has three or more groups represented by the following formula (1) in the molecule. -OR- (1) In the formula, R is a hydrocarbon group having at least one unsaturated bond and a cyclic structure, in which a hydrogen bonded to the cyclic structure is substituted with a fluorine.

[0008] In the crosslinking agent of the present invention, the formula (1) is preferably a group represented by the following formula (2). [ka] In the formula, X is a bridging group containing an unsaturated bond.

[0009] The present invention also provides a composition for hard substrates, which comprises the above-mentioned crosslinking agent and a crosslinkable compound having a plurality of unsaturated bonds.

[0010] In the composition for hard substrates of the present invention, the composition ratio (molar ratio) of the crosslinking agent to the crosslinkable compound is preferably in the range of 1:99 to 60:40. Effect of the Invention

[0011] The crosslinking agent of the present invention has excellent solvent solubility and can therefore be suitably used for crosslinking crosslinkable compounds (prepolymers) used in molding rigid substrates. The resulting cured product has excellent electrical properties and a high glass transition temperature, and is also excellent in flame retardancy and dimensional stability. Such effects of the fluorine-containing compound of the present invention are also evident from the results of Experimental Examples 1 to 3 described below. That is, it is clear that the substrate molded from the composition for hard substrate materials of Experimental Example 1 using the crosslinking agent of the present invention has a higher glass transition temperature (Tg) and a significantly improved dielectric constant (Dk) at 28 GHz than a substrate molded from the same fluorine-containing compound as in Experimental Example 1 without using a crosslinking agent (Experimental Example 4) or a substrate molded from a composition for hard substrates containing the same amount of TAIC instead of the crosslinking agent of the present invention as the crosslinking agent (Experimental Example 5). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] (Crosslinking agent) An important feature of the crosslinking agent of the present invention is that it has three or more groups represented by the following formula (1) in the molecule. -OR- (1) In the formula, R is a hydrocarbon group having at least one unsaturated bond and a cyclic structure, in which a hydrogen bonded to the cyclic structure is substituted with a fluorine.

[0013] Examples of the cyclic structure of R in the above formula (1) include a benzene ring, cyclopentenyl, biphenyl, etc., and a benzene ring is particularly preferable. When the cyclic structure is a benzene ring, the electrical properties (dielectric properties) are improved, and the glass transition temperature and decomposition temperature are increased, thereby imparting excellent heat resistance to the cured product. In addition, by replacing the hydrogen bonded to the cyclic structure with fluorine, it is possible to obtain a cured product that has the excellent electrical properties and flame retardancy that fluorine possesses, as well as an improved decomposition temperature (heat resistance).

[0014] Specific examples of the above formula (1) include the following formulas (2) and (3).

[0015] [ka] In the formula, X is a bridging group containing an unsaturated bond.

[0016] [ka]

[0017] In the above formula (2), the bridging group X containing an unsaturated bond is preferably located at the para-position of the oxygen atom. When the bridging group X is located at the para-position, there is less steric hindrance and the crosslinking reaction occurs more easily. In addition, the molecular structure is more symmetrical than when the bridging group X is located at the ortho- or meta-position, resulting in better electrical properties. The above formula (1) in the crosslinking agent of the present invention is preferably the following formulas (4) and (5), and particularly preferably the following formula (4).

[0018] [ka]

[0019] [ka]

[0020] In the crosslinking agent of the present invention, the basic skeleton into which the group represented by the above formula (1) is introduced is preferably a trivalent or tetravalent organic group. A trivalent or tetravalent organic group is a residue obtained by removing three or four hydrogen atoms from an organic compound that serves as the base. Examples of the organic compound that serves as the base include aliphatic compounds such as 2,2-dimethylpropane; cyclic aliphatic compounds such as cyclohexane; aromatic compounds such as benzene, triphenylmethane, and triphenylethane; and heterocyclic compounds such as triazine and isocyanurate. Specific examples of the crosslinking agent of the present invention include those represented by the following formulae (6) to (9), with those represented by the following formulae (6) and (7) being particularly preferred, and with those represented by the following formula (6) being most preferred.

[0021] [ka]

[0022] [ka]

[0023] [ka]

[0024] [ka]

[0025] The crosslinking agent of the present invention is preferably soluble in a solvent, which means that 1 g or more, preferably 10 g or more of the crosslinking agent is dissolved in 100 g of a solution obtained from a given solvent. The crosslinking agent of the present invention is preferably soluble in hydrocarbons such as benzene, toluene, xylene, heptane, cyclohexane, methylcyclohexane, mineral spirits, etc., and from the viewpoint of cost, is particularly preferably soluble in toluene.

[0026] (Composition for hard substrates) The crosslinking agent of the present invention can be used as a crosslinking agent for thermosetting resins used in molding rigid substrates used in prepregs, copper-clad laminates, printed circuit boards and the like. Examples of such thermosetting resins include thermosetting resins that have been used in the molding of conventional hard substrates, such as polyphenylene ether resins, fluorine-containing resins, polymaleimide resins, and epoxy resins, with fluorine-containing resins being particularly preferred.

[0027] The composition for hard substrates containing the crosslinking agent of the present invention is a precursor of the above-mentioned thermosetting resin and can be combined with a crosslinkable compound (prepolymer) having a plurality of unsaturated bonds, such as modified phenylene ether, maleimide, or citraconimide. Among these, the following fluorine-containing compounds having excellent electrical properties and flame retardancy can be preferably used. That is, it is preferable that the crosslinkable compound is a fluorine-containing compound comprising: a structural unit A having a structure in which the main skeleton contains a 3- to 12-membered cyclic structure in which 50% or more of the hydrogen atoms in the cyclic structure are substituted with fluorine atoms; a structural unit B having a structure in which the main skeleton contains a benzene ring in which fluorine atoms account for 30% or less of the number of atoms in the structural unit; and a structural unit C having an olefinic carbon-carbon double bond or carbon-carbon triple bond, and the structural units A to C are bonded to each other via the structural unit C as an end.

[0028] The fluorine-containing compound has excellent electrical properties (low dielectric constant and low dielectric loss) and flame retardancy possessed by the structural unit A, and excellent solvent solubility and high glass transition temperature possessed by the structural unit B. In addition, since the structural unit C is located at the end of the compound, the excellent reactivity of the structural unit C enables the compound to have excellent thermosetting properties that enable a cured product with a high gel fraction to be molded.

[0029] This fluorine-containing compound is characterized in that the structural units A to C are CB-(AB) n -C···(i) or CA-(BA) n -C···(ii) The bond is in the order of n, the value of n being in the range of 1 to 4, and it is particularly preferable that the compound has a low molecular weight where n is 1. This increases the proportion of crosslinking points in the compound, making it possible to obtain a cured product with a high gel fraction (crosslinking density). In the above formula (i) or (ii), n represents the average degree of polymerization. The average degree of polymerization can be predicted from the stoichiometric ratio of the monomers, and can also be measured by a conventionally known method such as nuclear magnetic resonance spectroscopy. In the present invention, "n is 1" means that the average degree of polymerization of the compound is 0.5 to 1.4. In the present invention, n may be expressed as an integer, but similarly includes those with a distribution.

[0030] [Structural unit A] The structural unit A has a structure in which the main skeleton contains a 3- to 12-membered cyclic structure, and 50% or more of the hydrogen atoms in the cyclic structure are substituted with fluorine atoms. By substituting 50% or more, preferably 100%, of the hydrogen atoms in the cyclic structure of the structural unit A with fluorine atoms, it becomes possible to impart the excellent electrical properties and flame retardancy that fluorine possesses to the fluorine-containing compound. In the structural unit A, the main skeleton may have three or more 3- to 12-membered ring structures, but preferably has one or two ring structures in the main skeleton, and preferably has one to three ring structures including side chains. The elements constituting the ring structure are not particularly limited, and examples thereof include carbon atoms, nitrogen atoms, oxygen atoms, sulfur atoms, and silicon atoms.

[0031] Specific examples of the structural unit A include cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, cyclopropene, cyclobutene, cyclopentene, cyclohexene, cycloheptene, cyclooctene, cyclononene, cyclodecene, cyclobutadiene, cyclopentadiene, cyclohexadiene, cycloheptadiene, cyclooctadiene, cyclononadiene, cyclodecadiene, cycloheptatriene, cyclooctatriene, cyclododecatriene, benzene, biphenyl, terphenyl, pentalene, indene, naphthalene, azulene, heptalene, indane, acenaphthylene, fluorene, spirofluorene, benzofluorene, dibenzofluorene, phenalene, phenanthrene, anthracene, fluoranthene, triphenylene, pyrene, chrysene, naphthal ... Futacene, picene, perylene, pentaphene, hexacene, pentacene, rubicene, coronene, ovalene, pyrrole, thiophene, furan, imidazole, pyrazole, thiazole, isothiazole, oxazole, isoxazole, pyridine, pyrazine, pyrimidine, pyridazine, isoindoline, indoline, indazoline, purine, quinoline, isoquinoline, benzoquinoline, phthalazine, naphthyridine, quinoxaline, quinazoline, cinnoline, galbazole, phenanthridine, acridine, phenanthroline, phenazine, benzimidazole, benzofuran, benzothiophene, isobenzothiazole, benzoxazole, isobenzoxazole, triazole, tetrazole, oxadiazole, triazine, dibenzofuran, dibenzothiophene, benzocarbazole, dibenzocarbazole, thiadiazole, imidazopyridine, and the like. When the structural unit A contains a plurality of 3- to 12-membered cyclic structures, they may be the same structure or different structures.

[0032] Examples of the substituent include any of the following substituents. fluorine, chlorine, bromine, iodine, hydroxyl group, cyano group, nitro group, amino group, amidino group, hydrazine group, hydrazone group, carboxylic acid group or a salt thereof, sulfonic acid group or a salt thereof, phosphoric acid group or a salt thereof, C1 to C60 alkyl group, C2 to C60 alkenyl group, C2 to C60 alkynyl group, and C1 to C60 alkoxy group; Fluorine, chlorine, bromine, iodine, hydroxyl group, cyano group, nitro group, amino group, amidino group, hydrazine group, hydrazone group, carboxylic acid group or a salt thereof, sulfonic acid group or a salt thereof, phosphoric acid group or a salt thereof, cyclopentyl group, cyclohexyl group, cycloheptyl group, cyclopentenyl group, cyclohexenyl group, phenyl group, biphenyl group, terphenyl group, pentalenyl group, indenyl group, naphthyl group, azulenyl group, heptalenyl group, indanyl group, acenaphthyl group, fluorenyl group, sulfuric acid group, fluor ... Pyrofluorenyl, benzofluorenyl, dibenzofluorenyl, phenalenyl, phenanthrenyl, anthracenyl, fluoranthenyl, triphenylenyl, pyrenyl, chrysenyl, naphthacenyl, picenyl, perylenyl, pentaphenyl, hexacenyl, pentacenyl, rubicenyl, coronenyl, ovalenyl, pyrrolyl, thiophenyl, furanyl, imidazolyl, pyrazolyl, thiazolyl, isothiazolyl, oxazolyl, iso xazolyl group, pyridinyl group, pyrazinyl group, pyrimidinyl group, pyridazinyl group, isoindolyl group, indolyl group, indazolyl group, purinyl group, quinolinyl group, isoquinolinyl group, benzoquinolinyl group, phthalazinyl group, naphthyridinyl group, quinoxalinyl group, quinazolinyl group, cinnolinyl group, carbazolyl group, phenanthridinyl group, acridinyl group, phenanthrolinyl group, phenazinyl group, benzimidazolyl group, benzofuranyl group, benzothiophenyl group, isobenzothiazolyl group a C1-C60 alkyl group, a C2-C60 alkenyl group, a C2-C60 alkynyl group, and a C1-C60 alkoxy group, each of which is substituted with at least one selected from the group consisting of a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, a thiadiazolyl group, an imidazopyridinyl group, and an imidazopyrimidinyl group;

[0033] Cyclopentyl, cyclohexyl, cycloheptyl, cyclopentenyl, cyclohexenyl, phenyl, biphenyl, terphenyl, pentalenyl, indenyl, naphthyl, azulenyl, heptalenyl, indanyl, acenaphthyl, fluorenyl, spiro-fluorenyl, benzofluorenyl, dibenzofluorenyl, phenalenyl, phenanthrenyl, nyl group, anthracenyl group, fluoranthenyl group, triphenylenyl group, pyrenyl group, chrysenyl group, naphthacenyl group, picenyl group, perylenyl group, pentaphenyl group, hexacenyl group, pentacenyl group, rubicenyl group, coronenyl group, ovalenyl group, pyrrolyl group, thiophenyl group, furanyl group, imidazolyl group, pyrazolyl group, thiazolyl group, isothiazolyl group, oxazolyl group, isoxazolyl group groups, pyridinyl groups, pyrazinyl groups, pyrimidinyl groups, pyridazinyl groups, isoindolyl groups, indolyl groups, indazolyl groups, purinyl groups, quinolinyl groups, isoquinolinyl groups, benzoquinolinyl groups, phthalazinyl groups, naphthyridinyl groups, quinoxalinyl groups, quinazolinyl groups, cinnolinyl groups, carbazolyl groups, phenanthridinyl groups, acridinyl groups, phenanthrolinyl groups, phenazinyl groups, benzimidazolyl groups, benzofuranyl groups, benzothiophenyl groups, isobenzothiazolyl groups, benzoxazolyl groups, isobenzoxazolyl groups, triazolyl groups, tetrazolyl groups, oxadiazolyl groups, triazinyl groups, dibenzofuranyl groups, dibenzothiophenyl groups, benzocarbazolyl groups, dibenzocarbazolyl groups, thiadiazolyl groups, imidazopyridinyl groups and imidazopyrimidinyl groups;

[0034] Fluorine, chlorine, bromine, iodine, hydroxyl group, cyano group, nitro group, amino group, amidino group, hydrazine group, hydrazone group, carboxylic acid group or a salt thereof, sulfonic acid group or a salt thereof, phosphoric acid group or a salt thereof, C1 to C60 alkyl group, C2 to C60 alkenyl group, C2 to C60 alkynyl group, C1 to C60 alkoxy group, cyclopentyl group, cyclohexyl group, cycloheptyl group, cyclopentenyl group, cyclohexenyl group, phenyl group, biphenyl group, terphenyl group, pentalenyl group, indenyl group, naphthyl group, azulenyl group, heptaphenyl group, nyl, indanyl, acenaphthyl, fluorenyl, spiro-fluorenyl, benzofluorenyl, dibenzofluorenyl, phenalenyl, phenanthrenyl, anthracenyl, fluoranthenyl, triphenylenyl, pyrenyl, chrysenyl, naphthacenyl, picenyl, perylenyl, pentaphenyl, hexacenyl, pentacenyl, rubicenyl, coronenyl, ovalenyl, pyrrolyl, thiophenyl, furanyl, imidazolyl, pyrazolyl, thiazolyl, isothiazolyl, oxazolyl, isothiazolyl, isothiophene, ... a soxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a biphenyl group, a terphenyl group, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, or an indanyl group, each of which is substituted with at least one group selected from the group consisting of a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, a thiadiazolyl group, an imidazopyridinyl group, and an imidazopyrimidinyl group;Acenaphthyl, fluorenyl, spiro-fluorenyl, benzofluorenyl, dibenzofluorenyl, phenalenyl, phenanthrenyl, anthracenyl, fluoranthenyl, triphenylenyl, pyrenyl, chrysenyl, naphthacenyl, picenyl, perylenyl, pentaphenyl, hexacenyl, pentacenyl, rubicenyl, coronenyl, ovalenyl, pyrrolyl, thiophenyl, furanyl, imidazolyl, pyrazolyl, thiazolyl, isothiazolyl, oxazolyl, isoxazolyl, pyridinyl, pyrazinyl, pyrimidinyl, pyridazinyl, isoindolyl, indolyl, indazolyl, linyl group, quinolinyl group, isoquinolinyl group, benzoquinolinyl group, phthalazinyl group, naphthyridinyl group, quinoxalinyl group, quinazolinyl group, cinnolinyl group, carbazolyl group, phenanthridinyl group, acridinyl group, phenanthrolinyl group, phenazinyl group, benzimidazolyl group, benzofuranyl group, benzothiophenyl group, isobenzothiazolyl group, benzoxazolyl group, isobenzoxazolyl group, triazolyl group, tetrazolyl group, oxadiazolyl group, triazinyl group, dibenzofuranyl group, dibenzothiophenyl group, benzocarbazolyl group, dibenzocarbazolyl group, thiadiazolyl group, imidazopyridinyl group and imidazopyrimidinyl group; etc. A group may have a plurality of substituents, and in this case, the substituents may be the same or different.

[0035] The structural unit A preferably contains a benzene ring or cyclopentenyl. More preferably, it may be benzene which may have a substituent; cyclopentenyl which may have a substituent; a compound in which a benzene ring such as biphenyl or terphenyl which may have a substituent is bonded to another aromatic ring; or a compound in which a benzene ring such as naphthalene which may have a substituent is condensed to another aromatic ring. Particularly preferred are compounds represented by the following structural formulas (A-1) to (A-5).

[0036] [ka] (In the formula, each m independently represents an integer of 0 to 6.)

[0037] In the above structural formula, each R is independently the substituent described above. As described above, the structural unit A more preferably has a structure in which 100% of the hydrogen atoms in the cyclic structure of the main skeleton are substituted with fluorine atoms.

[0038] Examples of compounds capable of forming the structural unit A include structural units derived from monomers having a benzene ring, such as hexafluorobenzene, perfluorobiphenyl, perfluoronaphthalene, 4,4-difluorobenzophenone, 1,1'-(1,1,2,2,3,3,4,4,5,5,6,6 dodecafluoro-1,6-hexanediyl)bis-4-fluorobenzene, and structural units derived from monomers having a cyclopentenyl, such as octafluorocyclopentene. Among these, those derived from hexafluorobenzene, perfluorobiphenyl, perfluoronaphthalene, and octafluorocyclopentene, as represented by the above formulas (A-1) to (A-5), are preferred.

[0039] [Structural unit B] The structural unit B constituting the fluorine-containing compound of the present invention has a structure containing a benzene ring in the main skeleton, and fluorine atoms account for 30% or less of the number of atoms in the structural unit. It is preferable that the structural unit B does not contain fluorine atoms, and even if it does contain fluorine atoms, it is important that the number of atoms in the structural unit B is 30% or less. This provides excellent solvent solubility in the fluorine-containing compound and ensures the synthesis of the fluorine-containing compound. The structural unit B may have four or more benzene rings in the main skeleton, but preferably has two or three benzene rings in the main skeleton, and more preferably has a ring structure of 1 to 4 rings including the side chains.

[0040] Examples of the structural unit B include benzene, biphenyl, terphenyl, indene, naphthalene, indane, acenaphthylene, fluorene, spirofluorene, benzofluorene, dibenzofluorene, phenalene, phenanthrene, anthracene, fluoranthene, triphenylene, pyrene, chrysene, naphthacene, picene, perylene, pentaphene, hexacene, pentacene, rubicene, coronene, ovalene, isoindoline, indoline, indazoline, quinoline, isoquinoline, benzoquinoline, phthalazine, quinoxaline, quinazoline, cinnoline, galbazole, phenanthridine, acridine, phenanthroline, phenazine, benzimidazole, benzofuran, benzothiophene, isobenzothiazole, benzoxazole, isobenzoxazole, dibenzofuran, dibenzothiophene, benzocarbazole, and dibenzocarbazole, which may have a substituent. Examples of the substituent include those exemplified for the structural unit A.

[0041] Such a structural unit B is preferably a structural unit derived from a bisphenol represented by the following formula (B).

[0042] [ka]

[0043] In the formula, L is a structure represented by the following formula (b-1) or (b-2):

[0044] [ka]

[0045] R in the above formulas (b-1) and (b-2) 1 and R 2 are each independently a hydrogen atom, C1 to C 10 Alkyl groups, C1-C 10 Haloalkyl groups, C6-C 10 or R1 and R 2 are groups which together form a ring structure which may have a substituent. C1~C 10 Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a 2-methylpropyl group (isobutyl group), a butyl group, and a pentyl group. 10 Examples of haloalkyl groups include trifluoromethyl, pentafluoroethyl, and perfluoropropyl groups. 10 Examples of the aryl group include a phenyl group and a naphthyl group (including 1-isomers and 2-isomers).

[0046] Alternatively, R 1 and R 2 may be a group that, together with each other, forms a ring structure that may have a substituent. Examples of the group that forms a ring structure include a tetramethylene group (forming a cyclopentane ring), a pentamethylene group (forming a cyclohexane ring), an undecamethylene group (forming a cyclododecane ring), a 2-methyl-pentamethylene group (forming a methylcyclohexane ring), a 2,2,4-trimethyl-pentamethylene group (forming a trimethylcyclohexane ring), and a biphenyl-2,2'-diyl group (forming a fluorene ring).

[0047] In the above formula (B), R 3 and R 4 each independently represents a hydrogen atom, a fluorine atom, or a C1-C6 in which some or all of the hydrogen atoms may be substituted with halogen 10 or a C6-C saturated or unsaturated hydrocarbon group in which some or all of the hydrogen may be substituted with halogen. 10 An aryl group having a structure of C1 to C6 in which some or all of the hydrogen atoms may be substituted with halogen. 10Examples of the saturated or unsaturated hydrocarbon group include a methyl group, an ethyl group, a propyl group, a 2-methylpropyl group (isobutyl group), a butyl group, a pentyl group, a trifluoromethyl group, a pentafluoroethyl group, a perfluoropropyl group, a vinyl group, an allyl group, a 1-methylvinyl group, a 2-butenyl group, a 3-butenyl group, and the like. 10 Examples of aryl groups include phenyl groups, naphthyl groups (including 1-isomers and 2-isomers), perfluorophenyl groups, and the like.

[0048] Suitable examples of the structural unit B include structural units derived from bisphenol AF (2,2-bis(4-hydroxyphenyl)hexafluoropropane), bisphenol F (bis(4-hydroxyphenyl)methane), bisphenol Z (1,1-bis(hydroxyphenyl)cyclohexane), bisphenol A (2,2'-bis(4-hydroxyphenyl)propane), bisphenol C (2,2-bis(3-methyl-4-hydroxyphenyl)propane), 4-hydroxyphenylbutane, 4,4'-(1,3-dimethylbutylidene)diphenol, bisphenol P (1,4-bis(2-(4-hydroxyphenyl)-2-propyl)benzene), 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane, 1,1-bis4-hydroxy-3-methylphenyl)cyclohexane, 4,6-di-tert-butylresorcinol, and 1,7-dihydroxynaphthalene. Among these, structural units derived from bisphenol AF and bisphenol Z are preferred.

[0049] [Structural unit C] The structural unit C constituting the fluorine-containing compound of the present invention has a structure derived from a reactive compound having an olefinic carbon-carbon double bond or a carbon-carbon triple bond, which makes it possible to impart excellent thermosetting (crosslinking) properties that allow the molding of a cured product with a high gel fraction even without using a crosslinking agent. In addition, the structural unit C preferably contains at least one fluorine atom, and more preferably contains fluorine atoms that account for 50% or less of the number of atoms in the structural unit. This, in combination with the fluorine atoms of the structural unit A, can impart excellent electrical properties and flame retardancy. Furthermore, it is preferable that the structural unit C has a benzene ring. Suitable structural units C include the following structures (C-1) to (C-10).

[0050] [ka]

[0051] In the formula, p is an integer from 0 to 4, and in some embodiments, p is 4. In other embodiments, p is 0. R is a C1-C 10 Alkyl groups of C6 to C 10 R' represents a hydrogen atom or a C1-C 10 represents an alkyl group represented by the formula:

[0052] The structural unit C particularly preferably has the following structures (C-11) to (C-15).

[0053] [ka]

[0054] [others] The above-mentioned fluorine-containing compound does not exclude the inclusion of a small amount of other structural units than the structural units A to C, so long as the various functions provided by the structural units A to C described above are not impaired. For example, in order to improve electrical properties, a constituent unit derived from an aliphatic diol compound that does not contain a benzene ring or a fluorine atom, or an alicyclic diol compound that does not contain a benzene ring or a fluorine atom, may be contained in an amount of 20 mol % or less of all constituent units constituting the fluorine-containing compound.

[0055] Examples of such aliphatic diol compounds that do not contain a benzene ring or a fluorine atom include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,5-hexanediol, 2,5-hexanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-dodecanediol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, Panediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2,4-diethyl-1,5-pentanediol, 1,2-hexane glycol, 1,2-octyl glycol, 2-ethyl-1,3-hexanediol, 2-ethyl-1,6-hexanediol, 2,3-diisobutyl-1,3-propanediol, 2,2-diisoamyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-methyl-1,8-octanediol, and the like.

[0056] Examples of alicyclic diol compounds not containing a benzene ring or a fluorine atom include cyclohexanediols such as 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, and 2-methyl-1,4-cyclohexanediol; cyclohexanedimethanols such as 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol; norbornanedimethanols such as 2,3-norbornanedimethanol and 2,5-norbornanedimethanol; tricyclodecane dimethanol, pentacyclopentadecanedimethanol, 1,3-adamantanediol, and the like. 2,2-adamantanediol, decalin dimethanol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, isosorbide, 3,9-bis(2-hydroxyethyl)-2,4,8,10-tetraoxaspiro(5.5)undecane, 3,9-bis(2-hydroxy-1,1-dimethylethyl)-2,4,8,10-tetraoxaspiro(5.5)undecane, 3,9-bis(2-hydroxy-1,1-diethylethyl)-2,4,8,10-tetraoxaspiro(5.5)undecane, 3,9-bis(2-hydroxy-1,1-dipropylethyl)-2,4,8,10-tetraoxaspiro(5.5)undecane, and the like.

[0057] [Preferred embodiment] Suitable fluorine-containing compounds for use in the composition for hard substrates of the present invention include, but are not limited to, compounds having the following structure: (wherein n is a value of 1 to 4, and (*) indicates the bonding position).

[0058] [ka]

[0059] [ka]

[0060] The fluorine-containing compound is preferably soluble in a solvent. The term "soluble in a solvent" means that 1 g or more, preferably 10 g or more of the fluorine-containing compound is dissolved in 100 g of a solution obtained from a given solvent. The fluorine-containing compound is preferably soluble in a hydrocarbon, which will be described later. In addition, the fluorine-containing compound is particularly preferably soluble in toluene from the viewpoint of cost. The fluorine-containing compound is not limited as long as it satisfies the fluorine atom content defined in each of the above-mentioned structural units A to C, but it is preferable that the fluorine content is 20 to 40 mass% based on the total mass of the fluorine-containing compound, which provides excellent electrical properties as well as excellent solvent solubility and flame retardancy. The fluorine-containing compound preferably has a number average molecular weight in the range of 500 to 4000, particularly 1000 to 2000. When the number average molecular weight is in the above range, the solvent solubility is improved, and the crosslinking property is also improved, making it possible to increase the gel fraction of the cured product described below.

[0061] In the composition for hard substrates of the present invention, the composition ratio (molar ratio) of the crosslinking agent to the crosslinkable compound is preferably in the range of 1:99 to 60:40, more preferably 5:95 to 50:50, and even more preferably 10:90 to 40:60. This makes it possible to obtain a cured product that has a high glass transition temperature and decomposition temperature, excellent heat resistance, and excellent electrical properties, and also makes it possible to impart sufficient hardness to the cured product. The composition for hard substrates of the present invention may further include a solvent, a reaction initiator, a filler, and any additives known in the art, such as a defoamer, a heat stabilizer, an antistatic agent, an ultraviolet absorber, a colorant (dye or pigment), a flame retardant, a lubricant, and a dispersant.

[0062] The composition for hard substrates may be a varnish-like composition containing a solvent, and various solvents can be used. From the viewpoint of solvent solubility, it is preferable to use an aprotic solvent in the present invention. Such aprotic solvents include: hydrocarbons such as benzene, toluene, xylene, heptane, cyclohexane, methylcyclohexane, mineral spirits, etc.; ketones such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), diisobutyl ketone (DIBK), etc.; cyclic ketones such as cyclohexanone, cycloheptanone, cyclooctanone, etc.; esters such as ethyl acetate, butyl acetate, γ-butyrolactone, etc.; cyclic ethers such as tetrahydrofuran (THF), 1,3-dioxolane, etc.; amides such as N,N-dimethylformamide (DMF), diethylformamide (DEF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), N-cyclohexylpyrrolidone, etc.; sulfones such as sulfolane, dimethylsulfone, etc.; and sulfoxides such as dimethylsulfoxide (DMSO). In the present invention, preferred solvents are hydrocarbons, and aromatic hydrocarbons are particularly preferred.

[0063] The composition for hard substrates of the present invention may also contain a reaction initiator. This allows for more efficient crosslinking and curing under milder conditions. Examples of reaction initiators that can be used include benzoyl peroxide, di-t-butyl peroxide, t-butyl hydroperoxide, dicumyl peroxide, cumyl hydroperoxide, α,α'-di(t-butylperoxy)-diisopropylbenzene (Perbutyl (registered trademark) P, manufactured by NOF Corp.), bis(1-methyl-1-phenylethyl)peroxide (Percumyl (registered trademark) D, manufactured by NOF Corp.), t-butyl α,α-dimethylbenzyl peroxide (Perbutyl (registered trademark) C, manufactured by NOF Corp.), 2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne, 3,3',5,5'-tetramethyl-1,4-diphenoquinone, chloranil, 2,4,6-tri-t-butylphenoxyl, t-butylperoxyisopropyl monocarbonate, azobisisobutyronitrile, and the like.

[0064] The composition for hard substrates may further include one or more fillers. The filler may be an organic filler or an inorganic filler. Usable organic fillers include engineering plastics such as polyphenylene sulfide, polyether ether ketone (PEEK), polyamide, polyimide, and polyamideimide; and solvent-insoluble fluororesins such as polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane (PFA), and copolymers of tetrafluoroethylene and hexafluoropropylene (FEP). Usable inorganic fillers include metals; metal oxides such as aluminum oxide, zinc oxide, tin oxide, and titanium oxide; metal hydroxides; metal titanates; zinc borate; zinc stannate; boehmite; silica; glass; silicon oxide; silicon carbide; boron nitride; calcium fluoride; carbon black; mica; talc; barium sulfate; and molybdenum disulfide. Solvent-insoluble fluororesins are preferred in terms of improving the electrical properties (dielectric constant, dielectric loss, etc.) of the cured product of the fluorine-containing composition. Silica is also preferred in that it can reduce the thermal expansion coefficient without impairing the electrical properties (dielectric constant, dielectric loss, etc.) of the cured product of the fluorine-containing composition.

[0065] The composition for hard substrates can be formed by mixing the crosslinking agent of the present invention, the crosslinkable compound, and optional components. Heating may be performed during mixing. Mixing can be performed using any mixing device known in the art, such as various stirrers, ball mills, bead mills, planetary mixers, roll mills, etc.

[0066] (Hard board) The gel fraction (crosslink density) of the cured product obtained by curing the composition for hard substrates of the present invention under conditions of 200°C for 120 minutes is preferably 80% or more, more preferably 90% or more, and most preferably 100%. A high gel fraction (crosslink density) is considered to have the effect of suppressing the decrease in durability due to the presence of unreacted crosslinked sites, and decreasing the thermal expansion coefficient due to an increase in crosslink density. The method for measuring the gel fraction will be described later. In addition, the glass transition temperature of this cured material is high at over 200°C, which reduces the coefficient of thermal expansion under normal usage conditions and improves durability when used as an electronic substrate. In addition, the small coefficient of thermal expansion at high temperatures offers the advantage of being usable in high-temperature environments and facilitating soldering. Furthermore, the thermal expansion coefficient in a temperature environment exceeding the glass transition temperature is preferably smaller than 200 ppm / ° C., more preferably smaller than 180 ppm / ° C., and even more preferably smaller than 150 ppm / ° C. The method for measuring the glass transition temperature will be described later. The cured product of the fluorine-containing compound of the present invention has excellent electrical properties, thermosetting properties, and flame retardancy, and can therefore be suitably used in prepregs, copper-clad laminates, and printed circuits.

[0067] [Prepreg] The composition for rigid substrates of the present invention can be suitably used for a prepreg comprising a semi-cured product of this composition and a fibrous base material. The fibrous substrates that can be used for the prepreg include glass woven fabric, aramid woven fabric, polyester woven fabric, carbon fiber woven fabric, glass nonwoven fabric, aramid nonwoven fabric, polyester nonwoven fabric, carbon fiber nonwoven fabric, pulp paper, linter paper, etc. A preferred fibrous substrate is glass woven fabric, which can achieve excellent mechanical strength. The fibrous substrate desirably has a thickness of 0.01 mm to 0.3 mm. In particular, since the composition for hard substrates of the present invention has excellent flame retardancy, it is possible to reduce or eliminate the amount of flame retardant added to conventional prepregs, thereby reducing or eliminating the effect of the incorporation of the flame retardant on electrical properties.

[0068] The prepreg can be formed by impregnating a fibrous substrate with a composition for hard substrates and drying it. The composition for hard substrates to be impregnated is preferably in a varnish state containing a solvent. The solvent can be any of those described above as solvents that can be used in compositions for hard substrates. As a result of the drying process, the solvent in the varnish is at least partially removed, and the composition for hard substrates is in a semi-cured state (so-called "B stage"). The impregnation process can be carried out by any method known in the art, such as immersion or coating. The content of the composition for hard substrates in the prepreg can be adjusted by carrying out the impregnation with the composition for hard substrates multiple times. The conditions (temperature and time) of the drying process depend on the type of reaction initiator and / or solvent. For example, the drying process can be carried out by heating to a temperature of 80°C to 170°C for 1 to 60 minutes.

[0069] [Copper-clad laminate] The cured product of the prepreg can be suitably used for a copper-clad laminate. A copper-clad laminate can be formed by laminating one or more prepregs, laminating copper foil on one or both surfaces of the prepregs, and integrating the resulting laminate by heating and pressing. The composition for hard boards in the copper-clad laminate is preferably in a state where curing is completed (so-called "C stage"). The conditions for the heating and pressing can be appropriately set based on the thickness of the copper-clad laminate to be produced, the composition of the composition for hard boards in the prepregs, and the like. For example, a copper-clad laminate can be produced by heating to a temperature of 170°C to 220°C for 60 to 150 minutes and applying a pressure of 1.0 MPa to 10 MPa.

[0070] [Printed circuit board] The cured prepreg can be suitably used for printed circuit boards. The printed circuit board can be manufactured by etching the copper layer of the above-mentioned copper-clad laminate to form a conductor pattern. Alternatively, the printed circuit board can be manufactured by laminating one or more prepregs and heating and pressing them to form a laminate, and then laminating a conductive material in a pattern on the surface of the laminate to form a conductor pattern. EXAMPLES

[0071] (Example 1) Synthesis of the crosslinking agent of the above formula (6) A glass reaction vessel was charged with 0.126 g (1.0 mmol) of phloroglucinol (anhydrous) and 0.160 g (4.0 mmol) of sodium hydroxide. The inside of the glass reaction vessel was evacuated to vacuum, and then replaced with nitrogen. Then, 5 mL of DMAc and 0.582 g (3.0 mmol) of 2,3,4,5,6-pentafluorostyrene were added to the glass reaction vessel. The reaction mixture was shielded from light, heated to 40° C. with stirring, and stirred for 24 hours. After heating, the reaction mixture was cooled to room temperature. Then, the reaction mixture was poured into 0.3 L of pure water. The reaction mixture was filtered by suction, and the obtained solid was washed with pure water and methanol. The washed solid was dried under reduced pressure to obtain 0.63 g of the crosslinking agent of the above formula (6).

[0072] (Example 2) Synthesis of the crosslinking agent of the above formula (7) The procedure of Example 1 was repeated, except that phloroglucinol (anhydrous) was replaced with 0.136 g (1.0 mmol) of pentaerythritol, sodium hydroxide was replaced with 0.281 g (5.0 mmol) of potassium hydroxide, and 2,3,4,5,6-pentafluorostyrene was used in an amount of 0.776 g (4.0 mmol), to obtain 0.74 g of the crosslinker of formula (7) above.

[0073] (Synthesis of fluorine-containing compounds) A glass reaction vessel was charged with 0.805 g (3.0 mmol) of 1,1-bis(4-hydroxyphenyl)cyclohexane (bisphenol Z), 0.501 g (1.5 mmol) of decafluorobiphenyl, and 0.912 g (6.6 mmol) of potassium carbonate. The inside of the glass reaction vessel was evacuated to vacuum, and then substituted with nitrogen. Then, 10 mL of DMAc and 0.582 g (3.0 mmol) of 2,3,4,5,6-pentafluorostyrene were added to the glass reaction vessel. The reaction mixture was shielded from light, heated to 80° C. with stirring, and stirred for 15 hours. After the heating, the reaction mixture was cooled to room temperature. Then, the reaction mixture was poured into 0.5 L of pure water. The reaction mixture was suction filtered, and the obtained solid was washed with pure water and methanol. The washed solid was dried under reduced pressure to obtain 1.54 g of a fluorine-containing compound. The resulting fluorine-containing compound has the structural formula of formula (10) above (wherein n is 1).

[0074] (Rating 1: Solvent soluble) 0.5 g of each of the crosslinking agents obtained in Examples 1 and 2 was weighed out, toluene was added, and the mixture was heated to 80° C. and mixed. If a 50% by mass toluene solution was obtained, it was determined to be soluble. As a result of the evaluation, all of Examples 1 and 2 were soluble.

[0075] (Evaluation 2: Evaluation of thermosetting properties (gel fraction)) 0.5 g of a mixture of the fluorine-containing compound of the above formula (10) and the crosslinking agent or triallyl isocyanurate (TAIC) obtained in Examples 1 and 2 in a ratio (mol %) shown in Table 1 relative to the fluorine-containing compound was added to toluene and heated and mixed at 80°C to obtain a 50 mass % solution (varnish-like composition). To the obtained solution (varnish-like composition), 0.005 g of Perbutyl (registered trademark) P (manufactured by NOF Corporation) was added as a reaction initiator, and the whole was placed in an aluminum cup and dried by heating at 200 ° C for 2 hours using a thermostatic oven (SPHH-102 manufactured by ESPEC Corporation) to obtain a cured product. The cured product was taken out of the aluminum cup and its weight was measured. 5 g of methyl ethyl ketone (MEK) and the cured product were placed in a 9 mL sample tube, and the cured product was immersed in MEK for 24 hours. Thereafter, the solvent was volatilized, and the cured product was washed with MEK, and then dried at 90 ° C for 3 hours using a hot plate. The mass after drying was measured and used as the mass of the dried cured product after immersion in MEK. The gel fraction was calculated as follows: (mass of the dried and cured product after immersion in MEK) / (mass of the cured product before immersion in MEK)×100 (%). The results are shown in Table 1.

[0076] (Evaluation 3: Electrical characteristics) [Preparation of prepreg] To each varnish-like composition obtained in the same manner as in the evaluation of thermosetting property (gel fraction), 0.005 g of Perbutyl (registered trademark) P (manufactured by NOF Corp.) was added as a reaction initiator, and the mixture was dropped onto a 8 cm x 7 cm piece of glass cloth (L2-1078, manufactured by Asahi Kasei Corp.) to uniformly impregnate the cloth. The impregnated material was then dried at 110°C for 10 minutes to obtain a prepreg. [Preparation of copper-clad laminate] The prepreg obtained by the above method was cut to 6 cm x 6 cm, and together with electrolytic copper foil (thickness 18 μm) (Furukawa Electric Co., Ltd., HVLP) was used in a vacuum hot press machine (Imoto Machinery Works, Ltd., Manual Hydraulic Vacuum Heating Press IMC-4900) to heat the material to 240°C while reducing the pressure, and then pressed at 240°C for 120 minutes at 4 MPa to bond the prepreg and the copper foil. The copper foil was removed from the copper-clad laminate, and the specimen was cut to 4 cm x 4 cm (thickness: about 0.1 mm). The dielectric constant of the specimen was measured using a vector network analyzer (KEYSIGHT 5247B) under the split cylinder method at 28 GHz and 25°C. The results are shown in Table 1.

[0077] (Evaluation 4: Measurement of glass transition temperature (Tg)) The copper-clad laminate prepared in the above electrical property evaluation was cut into test pieces having a length of 25 mm and a width of 5 mm at an angle of 45 degrees to the mesh of the glass cloth. A test piece was set in a dynamic viscoelasticity measuring device (DMA ARES-G2, manufactured by TA Instruments) using a film jig with a chuck distance of 10 mm. The measurement was performed in torsion mode with a frequency of 1.0 Hz and a strain of 0.1%, with the following temperature profile. (1) Hold at 25°C for 60 seconds and heat from 25°C to 360°C at a rate of 5°C / min. (2) The temperature is maintained at 360° C. for 60 seconds, and then the measurement is terminated. The temperature at the peak position of the obtained tan δ (ratio of storage elastic modulus to loss elastic modulus) curve was taken as the glass transition temperature (Tg). The results are shown in Table 1.

[0078] [Table 1]

[0079] As is clear from the results in Table 1, the hard substrate samples (Experimental Examples 1 to 3) using the crosslinking agent of the present invention have a lower dielectric constant and superior electrical properties than the hard substrate sample (Experimental Example 4) made of a fluorine-containing compound without a crosslinking agent and the hard substrate sample (Experimental Example 5) using general-purpose TAIC as a crosslinking agent for hard substrates. In addition, the glass transition temperatures of Experimental Examples 1 and 2 using a trifunctional crosslinking agent are higher than those of Experimental Examples 4 and 5. The glass transition temperature of Experimental Example 3 using a tetrafunctional crosslinking agent is lower than those of Experimental Examples 4 and 5, but is still at a sufficient level for practical use. [Industrial Applicability]

[0080] The crosslinking agent of the present invention has excellent thermosetting properties (crosslinkability) and solvent solubility, and can impart excellent electrical properties (low dielectric constant) and flame retardancy to the cured product. Therefore, the crosslinking agent can be suitably used for hard substrate materials used in electrical devices, electronic devices, and communication devices, and can be suitably used as a crosslinking agent for hard (rigid) substrate materials for next-generation high-frequency signals capable of high-speed and large-capacity transmission.

Claims

1. A crosslinking agent for thermosetting resins used in hard substrate materials, characterized in that the crosslinking agent has three or more groups represented by the following formula (1) in the molecule: -O-R (1) In the formula, R is a hydrocarbon group having at least one unsaturated bond and a cyclic structure, in which all hydrogen atoms bonded to the cyclic structure are substituted with fluorine atoms.

2. The crosslinking agent according to claim 1, wherein the formula (1) is a group represented by the following formula (2): 【Chemistry 1】 In the formula, X is a bridging group having an unsaturated bond.

3. A composition for hard substrates, comprising the crosslinking agent according to claim 1 and a crosslinkable compound having a plurality of unsaturated bonds.

4. 4. The composition for hard substrates according to claim 3, wherein the composition ratio (molar ratio) of said crosslinking agent to said crosslinkable compound is in the range of 1:99 to 60:40.

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