Prepreg and laminated board

Details Prepreg and laminated board Prepreg and laminated board

2000-03-13

2002-03-26

Dawson, Robert (Department: 1712)

Stock material or miscellaneous articles

Composite

Of epoxy ether

C428S414000, C428S297400, C428S901000

Reexamination Certificate

active

06361866

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a halogen-free prepreg formed of a resin composition having excellent flame retardancy and having good electric characteristics and heat resistance, for an insulating material, and a laminated board formed of the prepreg. The resin composition used in the present invention gives a cured product having good flame retardancy and electric characteristics and having excellent moisture absorption resistance and heat resistance and is therefore suitable for use in insulating materials. A laminated board formed of the above resin composition is halogen-free and phosphorus-free, satisfies the V-0 level of the UL standard generates neither dioxin nor phosphine during its combustion, and is therefore environmentally friendly.
PRIOR ART OF THE INVENTION
Laminated boards formed of epoxy resins as a main component are widely used as printed wiring materials for electronic machines and equipment. For flame-retarding epoxy resins, there is employed a method of using brominated epoxy resins as basic components. In recent years, it has been found that intensely toxic brominated dibenzodioxin or dibenzofuran is generated during the combustion of bromine-containing flame retardants, and regulations to be imposed on the bromine-containing flame retardants are discussed in various ways from the aspect of so-called environmental problems. As a result, in the field of thermoplastic resins, phosphorus-containing flame retardants have come to be used in place of the bromine-containing flame retardants. In the field of printed wiring materials using epoxy resins as a base material, various flame retardants to be incorporated are studied and various proposals have been made for excluding brominated epoxy resins. Methods of using phosphorus-containing flame retardants constitute the main stream in proposals presently found. However, the phosphorus-containing flame retardants not only degrade printed wiring materials to a great extent in mechanical, chemical and electrical properties, but also inevitably generate toxic gases during the combustion thereof. Under the present circumstances, there is a considerable doubt about the use of the phosphorus-containing flame retardants. It is therefore strongly desired to develop a material having excellent flame retardancy without using any one of a bromine-containing flame retardant and a phosphorus-containing flame retardant.
Flame-retardant epoxy resin laminated materials that are now available are generally fabricated by incorporating an amine-containing curing agent to a brominated epoxy resin as a base resin to obtain a varnish, impregnating a glass substrate with the varnish, semi-curing the resin under heat to obtain a prepreg and forming the prepreg into a laminate. Few flame-retardant laminated materials overcome the above environmental problems.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a halogen-free and phosphorus-free prepreg having good flame retardancy and having excellent electric characteristics and heat resistance.
According to the present invention, there is provided a prepreg formed of a resin composition comprising, as essential components, a phenol compound (I) having a structural unit of the formula (1),
wherein R
1
is hydrogen or phenol, R
2
is a hydrogen or methyl and n is an integer of 0 to 10, an epoxy resin (II) prepared by epoxidizing the same phenol compound as said phenol compound, a metal hydrate (III) and a molybdenum compound (IV), and a substrate which is impregnated with said resin composition or to which said resin composition is applied.
According to the present invention, there is also provided a laminated board formed of the above prepreg, for an insulating material.
DETAILED DESCRIPTION OF THE INVENTION
For achieving the above object, the present inventors have made diligent studies and have found that a laminated material obtained from an epoxy resin composition containing an epoxy resin obtained from a specific phenol compound and a specific epoxy resin as a curing agent and further containing a metal hydrate and a molybdenum compound in combination has excellent flame retardancy and good electric characteristics and heat resistance. The present invention is accordingly achieved.
That is, the present invention is concerned with a prepreg formed of a resin composition comprising, as essential components, a phenol compound (I) having a structural unit of the formula (1),
wherein R
1
is hydrogen or phenol, R
2
is a hydrogen or methyl and n is an integer of 0 to 10, an epoxy resin (II) prepared by epoxidizing said phenol compound, a metal hydrate (III) and a molybdenum compound (IV), and a substrate which is impregnated with said resin composition or to which said resin composition is applied. Further, the present invention is also concerned with a laminated board formed of the above prepreg, for an insulating material.
The phenol compound (I) used in the present invention is not specially limited so long as it is a compound having the structural unit of the formula (1). Typical examples of the phenol compound (I) include bisphenol F, phenol novolak, cresol novolak, tris(hydroxyphenyl)methane and an oligomer of tris(hydroxypheny)methane. These compounds may be used alone or in combination. Preferred are phenol novolak and an oligomer of tris(hydroxypheny)methane.
The amount of the phenol compound (I) is adjusted such that the molar ratio of phenolic hydroxyl groups to epoxy groups of the epoxy resin (II) is in the range of from 0.5 to 1.5, preferably from 0.8 to 1.2. When the above molar ratio is smaller than the above lower limit, undesirably in view of the object of the present invention, the resin composition shows very low heat resistance. When it exceeds the above upper limit, undesirably, the resin composition shows a very low humidity durability.
The epoxy resin (II) used in the present invention is not specially limited so long as it is a compound prepared by epoxidizing the same phenol compound as the phenol compound (I) having the structural unit of the formula (1). Typical examples of the epoxy resin (II) include glycidyl ethers of bisphenol F, phenol novolak, cresol novolak and tris(hydroxyphenyl)methane or derivatives of these compounds. These epoxy resins may be used alone or in combination. Preferred are glycidyl ethers of bisphenol F, phenol novolak and tris(hydroxyphenyl)methane or derivatives of these compounds.
The resin composition forming the prepreg in the present invention may contain other epoxy resin so long as the intended properties of the resin composition are not impaired. The above “other epoxy resin” can be selected from generally used epoxy resins without any special limitation. Typical examples of the other epoxy resin include glycidyl ethers of bisphenol A, bisphenol A novolak, biphenyl, polyfunctional phenol, naphthalene, alicyclic compounds, glycidyl amine resin, and glycidyl ester resins.
In the present invention, a known epoxy resin curing agent may be used in combination with the above phenol compound (I) so long as the intended properties are not impaired. The above epoxy resin curing agent can be selected from generally used epoxy resin curing agents without any special limitation. Typical examples of the epoxy resin curing agent include amine-containing compounds such as dicyandiamide, tetraethyldiaminodiphenylmethane and diaminodiphenylmethane, novolak compounds such as bisphenol A novolak, and acid anhydride compounds such as hexahydrophthalic acid anhydride. In the present invention, a curing promoter may be incorporated for adjusting the curing rate of the above resin composition as required. The curing promoter can be selected from curing promoters generally used for epoxy resins, without any special limitation. Typical examples of the curing promoter include imidazoles, derivatives thereof and tertiary amines.
The metal hydrate (III) used in the present invention is not specially limited so long as it is selected from hydrous compounds of alkali metals or alkaline earth metals. Exa

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