Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-09-02
2001-07-24
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S434000, C523S461000
Reexamination Certificate
active
06265469
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an epoxy resin adhesive composition. More specifically, it relates to an epoxy resin adhesive composition having excellent adhesion flexibility, heat resistance, and chemical resistance, suitable for use in the production of a flexible printed circuits.
2. Background of the Invention
Flexible printed circuits have enormous development potential for use in huge new product areas where extreme thinness, highest density and volume manufacturability are important. A typical flexible printed circuit consists of three layers of material: a dielectric layer, a conductor layer and a coverlayer. An adhesive is the bonding medium between layers for creating a laminate of flexible printed circuit. The adhesive chosen is normally carefully matched to achieve the best mix of desirable properties for the laminate. The adhesive must be able to meet the demands for the manufacturing of the lamination and the processing of the flexible printed circuit.
There are many requirements of adhesive to meet the different demands that can be placed on a flexible printed circuit, for instance, should have good thermal properties, chemical resistance, bonding strength and flexibility. In addition, the adhesive must be easily processing.
Epoxy resins have excellent characteristics in thermal properties electrical properties, mechanical strength, and chemical resistance, and good bonding to copper foil and to polyimide film. They are used as an adhesive materials for printed circuits or flexible printed circuits. However, epoxy resins have a drawback of being brittle, resulting from their excessively high density of crosslinking while the resins are cured with amines, acid anhydrides and phenol compounds. The epoxy resin used as an adhesive for the flexible printed circuits should be a flexible compound, because brittle adhesive may cause a deadly damage in any bending occurrence.
A conventional method of reducing the crosslinking density to improve toughness is by using either of the epoxy resin itself or by the curing agent being compounding in excess of one another. However, since the molecular chain is terminated by the epoxy resin or by the curing agent positioned at the molecular terminal in the curing reaction, the thermal properties and chemical properties of epoxy resin will be greatly deteriorated.
Another approach is by using a rubber modified epoxy resin composition which may give the epoxy resin toughness without reducing the crosslinking density and, furthermore, only modest reductions in thermal properties.
Compounding a rubber into the epoxy resin composition may obtain a satisfied toughness without degrading the chemical resistance and bonding properties, however, the thermal properties will be degraded. The rubber compounds may be easily oxidized and deteriorated under either a high temperature laminating process or a high temperature soldering process. Thus some antioxidant compounds can be employed into the rubber-compounding epoxy resin composition to overcome said oxidation problem. In the present invention, a hindered piperidinyloxy compound, formula I,
is served as anti-oxidation agent for both of epoxy resins and rubber compounds. The hindered amine compound may stabilize the epoxy resins and rubber compounds while they are under a high temperature processing. It was found in the present invention that employing small amount of the hindered amine compounds into the epoxy resin composition can dramatically improve the peel strength of laminate for flexible printed circuits.
SUMMARY OF THE INVENTION
This invention relates to epoxy resin adhesive formulations, which can improve the bonding strength of laminates without loss of flexibility. This invention also comprises one or more epoxy resins, rubber compounds, curing agents, a hindered piperidinyloxy compounds, and optionally one or more fillers.
The epoxy resin adhesive of this invention is prepared by admixing one or more brominated epoxy resins and butadiene rubber. In another embodiment the adhesive formulation will further contains a multifunctional epoxy resin, which serves to improve the heat resistance of the adhesive formulation while exposing to high temperature processing of lamination or soldering.
The epoxy resin adhesive of this invention comprising an antioxidant of hindered amine compound is served to prevent oxidation of the both of the epoxy resin compositions and the compounding butadiene rubber.
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to epoxy resin adhesive formulations comprising
(a) one or more epoxy resin;
(b) a curing agent;
(c) a rubber;
(d) optionally, an inorganic filler; and
(e) a hindered piperidinyloxy compound.
Examples of suitable epoxy resins include:
bisphenol A epoxy resin, bisphenol F epoxy resin, brominated bisphenol A epoxy resin, brominated bisphenol F epoxy resin, fluorinated bisphenol A epoxy resin, fluorinated bisphenol F epoxy resin, cresol novolac epoxy resin and phenol novolac epoxy resin. In the present invention epoxy resins may be used either alone or in combination.
To improve the flame retardance of adhesive, the preferred epoxy resin is selected from brominated epoxy resins. The preferred amount of brominated epoxy resin is comprising at least 55 parts by weight based on 100 parts by weight of epoxy resin. To improve the thermal properties or chemical resistance of the adhesive, the preferred epoxy resins further comprised multifunctional epoxy resins. The preferred amount of multifunctional epoxy resin is comprising 1 to 45 parts by weight based on 100 parts by weight of epoxy resin. Examples of multifunctional epoxy resin include cresol novolac epoxy resin, phenol novolac epoxy resin and epoxy resin consisted of a tetrakis-glycidyl-4-phenyloethane, formula II
Examples of suitable curing agents include:
3,3′-diaminodiphenyl sulfone(3,3′-DDS), 4,4′diaminodiphenyl sulfone(4,4′-DDS), methylene dianiline(DDM), 4,4′-oxydianiline(ODA), m-phenylene diamine(MPD), tetra-methyl-di(4-aminophenyl)-di-isopropyl benzene and dicyandiamide(DICY).
Examples of suitable curing catalysts include:
2-methyl-imidazole (2MI/2MZ), 2-ethyl-4-methyl-imidazole (2E4MI/2E4MZ), 2-phenyl-imidazole (2PI/2PZ), dimethylaminomethyl phenol, tris(dimethylaminomethyl) phenol, benzyldimethylamine(BDMA), diazabicycloundecene(DBU) and dicyandiamide(DICY). The preferred curing catalyst is an imidazole catalyst.
Examples of suitable rubber include:
carboxyl-terminated butadiene acrylonitrile (CTBN), styrene-butadiene rubber(SBR), amine terminated butadiene acrylonitrile (ATBN) and silicon rubber.
There are many types of elastomeric materials may be considered for the toughness modification of epoxy resins, the preferred rubber in the present invention is butadiene-acrylonitrile. Increasing the content of rubber in the epoxy resin composition results in an increase the fraction of elastomeric phase, however, too much rubber contained may deteriorate the mechanical properties of epoxy resin. The preferred amount of rubber is 10 to 200 parts by weight based on 100 parts by weight of epoxy resin.
Inorganic fillers allow the possibility to modify various characteristics of epoxy resin including thermal conductivity, thermal expansion coefficient and dimensional stability. The filler employed also influence the processing behavior of the epoxy resin. However, the type and amount of the filler in the present invention may depended on the processing and final application of the epoxy resin adhesive.
Examples of suitable inorganic fillers include:
silica, mica, aluminum oxide, aluminum hydroxide, titanium oxide talc, magnesium hydroxide, zinc carbonate and antimony trioxide.
The hindered piperidinyloxy compound, more preferable is a tetraalkyl piperidinyloxy, represent as formula I, was used in present invention in order to improve the heat resistance of epoxy resin composition. Wherein R
1
,R
2
,R
3
and R
4
, which may be the same or different are selected from hydrogen or a C
1-3
alkyl group, and
Chen Chien-Yu
Chiu Chien-Hwa
Sun Der-Jen
Tsai Ya-Fen
Aylward D.
Bacon & Thomas
Dawson Robert
Du Pont Wirex Ltd
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