Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
2000-10-20
2002-11-26
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C428S416000, C428S457000, C428S458000
Reexamination Certificate
active
06485833
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a resin-coated metal foil suitable for use particularly as a material for multi-layered printed wiring board. More particularly, the present invention relates to a copper foil coated with a resin which is superior in handleability and storage stability in a semi-cure state and, after complete cure, high in heat resistance and superior in dielectric properties.
2. Description of the Prior Art
Conventional resin-coated metal foils are obtained by coating, on a metal foil, an insulating resin varnish (a solution of an epoxy resin and a curing agent such as dicyandiamide or the like in a solvent) and semi-curing the insulating resin varnish into a B-stage by heating and drying. Thus obtained conventional resin-coated metal foils have been used in production of a multi-layered printed wiring board by laminating the resin-coated metal foils with a substrate for inner layer obtained by formation of a circuit pattern and subjecting the laminate to molding.
However, the resin-coated metal foils used in above production of the multi-layered printed wiring board have had, during the production (for example, when an external pressure is applied in winding by rolls), problems of generation of cracking or peeling in B-stage resin and scattering of powder in cutting of the resin-coated metal foil.
Conventional resin-coated metal foils have had another problem in that the resin after complete cure has low heat resistance. All of these problems have remained undissolved.
OBJECT AND SUMMERY OF THE INVENTION
In view of the above-mentioned problems of the prior art, the present invention aims at providing a resin-coated metal foil which is superior in handleability and storage stability in a semi-cure state and, after complete cure, high in heat resistance and superior in dielectric properties.
The present inventors thought of an idea that when a composition containing a polycarbodiimide resin of good film formability and an epoxy resin is coated and semi-cured on a metal foil, the resulting resin-coated metal foil may be superior in handleability and, when the semi-cured resin is completely cured, the resin may have high heat resistance owing to the reaction between carbodiimide group and epoxy group or the self-crosslinking reaction of carbodiimide group and moreover may have excellent dielectric properties owing to the polycarbodiimide resin. Based on the idea, the present inventors made a study and completed the present invention.
According to the present invention, there is provided a resin-coated metal foil comprising:
a metal foil, and
a resin layer formed on the metal foil by coating and semi-curing, on the metal foil, a composition containing a polycarbodiimide resin having a number-average molecular weight of 3,000 to 50,000, an epoxy resin and, as necessary, a curing agent for epoxy resin, the proportions of the polycarbodiimide resin and the epoxy resin being 100 parts by weight and 20 to 200 parts by weight, respectively.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
In the present invention, the composition used for forming a resin layer on a metal foil contains a polycarbodiimide resin and an epoxy resin, or contains a polycarbodiimide resin, an epoxy resin and a curing agent for epoxy resin. As the polycarbodiimide resin, there can be used those produced by various processes. There can be used an isocyanate-terminated polycarbodiimide produced basically by a conventional process for production of polycarbodiimide resin [U.S. Pat. No. 2,941,956; J. Org. Chem., 28, 2069-2075 (1963); Chemical Review 1981, Vol. 81, No. 4, pp. 619-621], and specifically by a condensation reaction of organic polyisocyanate, associated with carbon dioxide removal.
In the above process, as the organic polyisocyanate which is a raw material for synthesis of polycarbodiimide resin, there can be used, for example, aromatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates and mixtures thereof. Specific examples are 1,5-naphhtalene diisocyanate, 4,4′-diphenylmethane diisocyanate, 4,4′-diphenyldimethylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, a mixture of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, hexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, xylylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4-4′-diisocyanate, methylcyclohexane diisocyanate, tetramethylxylylene diisocyanate, 2,6-diisopropylphenyl diisocyanate and 1,3,5-triisopropylbenzene-2,4-diisocyanate.
As the polycarbodiimide resin used in the present invention, there is preferred a polycarbodiimide obtained from at least one kind of aromatic polyisocyanate. (Incidentally, the aromatic polyisocyanate refers to an isocyanate containing, in the molecule, at least two isocyanate groups directly bonding to the aromatic ring). The reason is that the polycarbodiimide obtained from at least one kind of aromatic polyisocyanate is thermosetting and has film formability
The above polycarbodiimide resin may have an appropriately controlled polymerization degree by using a compound reactive with the terminal isocyanate of carbodiimide compound, for example, a monoisocyanate.
As the monoisocyanate for terminal blocking of polycarbodiimide and control of the polymerization degree, there can be mentioned, for example, phenyl isocyanate, tolyl isocyanate, dimethylphenyl isocyanate, cyclohexyl isocyanate, butyl isocyanate and naphthyl isocyanate.
As the compound reactive with the terminal isocyanate of polycarbodiimide, there can also be used, for example, aliphatic, aromatic or alicyclic compounds having -OH group (e.g. methanol, ethanol, phenol, cyclohexanol, N-methylethanolamine, polyethylene glycol monomethyl ether and polypropylene glycol monomethyl ether), ═NH group (e.g. diethylamine and dicyclohexylamine), —NH
2
group (e.g. butylamine and cyclohexylamine), —COOH group (e.g. propionic acid, benzoic acid and cyclohexanecarboxylic acid), —SH group (e.g. ethylmercaptan, allylmercaptan and thiophenol), epoxy group or the like.
The decarboxylative condensation of organic polyisocyanate proceeds in the presence of a carbodiimidization catalyst. As the carbodiimidization catalyst, there can be used, for example, phosphorene oxides such as 1-phenyl-2-phosphorene-1-oxide, 3-methyl-1-phenyl-2-phosphorene-1-oxide, 1-ethyl-2-phosphorene-1-oxide, 3-methyl-2-phosphorene-1-oxide, 3-phosphorene isomers thereof and the like. Of these, 3-methyl-1-phenyl-2-phosphorene-1-oxide is preferred from the reactivity.
The polycarbodiimide resin used in the present invention has a number-average molecular weight of 3,000 to 50,000, preferably 10,000 to 30,000, more preferably 15,000 to 25,000 (in terms of polystyrene conversion) as measured by gel permeation chromatography (GPC), irrespective of the use of a terminal-blocking agent. When the number-average molecular weight is less than 3,000, no sufficient film formability or heat resistance is obtained. When the number-average molecular weight is more than 50,000, a long time is required for synthesis of polycarbodiimide, a varnish of the resulting polycarbodiimide resin has an extremely short pot life. Therefore, such molecular weights are not practical.
As the epoxy resin used in the composition in the present invention, there can be mentioned, for example, at least one kind of epoxy resin having at least two epoxy groups in the molecule or a mixture of such epoxy resins, all selected from glycidyl ether type epoxy resins (e.g. bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin and cresol novolac type epoxy resin), alicyclic epoxy resins, glycidyl ester type epoxy resins, heterocyclic epoxy resins, liquid rubber-modified epoxy resins, and so forth. Preferred are bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin and cresol novolac type epoxy resin
Imashiro Yasuo
Ito Takahiko
Nakamura Norimasa
Tomita Hideshi
Kiliman Leszek
Kubovcik & Kubovcik
Nisshinbo Industries Inc.
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