Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
1999-06-30
2001-05-22
Lovering, Richard D. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C502S164000, C523S445000, C568S002000
Reexamination Certificate
active
06235865
ABSTRACT:
This invention relates to novel phosphonium borate compounds useful as a curing catalyst in epoxy and other resin compositions, and a method for preparing the same. It also relates to a curing catalyst and an epoxy resin composition comprising the same.
BACKGROUND OF THE INVENTION
The current mainstream in the semiconductor industry resides in diodes, transistors, ICs, LSIs and VLSIs of the resin encapsulation type. Epoxy resin compositions comprising an epoxy resin, curing agent and additives have superior moldability, adhesion, electrical properties, mechanical properties, and moisture resistance to other thermosetting resins. It is thus a common practice to encapsulate semiconductor devices with epoxy resin compositions. Recently, the semiconductor devices are increasing their degree of integration and accordingly becomes larger in chip size. By contrast, the outer configuration of packages is reduced in size or thickness in order to meet the demand for size and weight reduction of electronic equipment. As to the method of mounting semiconductor parts on circuit boards, the surface mounting of semiconductor parts becomes predominant since the parts on boards are increased in density.
For the surface mounting of semiconductor devices, a method of dipping entire semiconductor devices in a solder bath and a method of passing them through a hot zone where solder is melted are commonly employed. These methods bring about thermal shocks, by which the encapsulating resin layer can be cracked or separation occur at the interface between the lead frame or chip and the encapsulating resin. Such cracks or separation becomes more outstanding if the encapsulating resin layer on semiconductor devices has picked up moisture prior to the thermal shocks during surface mounting. In actual working processes, it is impossible to avoid the moisture absorption of the encapsulating resin layer. As a consequence, the semiconductor devices encapsulated with epoxy resins often suffer from a serious loss of reliability after surface mounting. One common countermeasure against such a popcorn phenomenon is to load epoxy resins with large amounts of filler for reducing moisture absorption. Also one approach for improving the molding of thin packages is to reduce the viscosity of epoxy resin compositions. Further, fast curing catalysts have also been studied to shorten the molding cycle for increasing productivity.
Prior art curing catalysts, for example, imidazole derivatives, tertiary amine compounds, tertiary phosphine compounds and derivatives thereof are less stable during shelf storage. When resins are milled therewith, these curing catalysts give rise to such problems as an increased viscosity upon milling and poor flow upon molding.
JP-B 56-45491 discloses an epoxy resin composition comprising an epoxy resin and a curing agent. The curing agent is obtained by heat treating a mixture of a novolac type phenolic resin and tetraphenylphosphonium tetraphenylborate (abbreviated as TPP-K, hereinafter) at a temperature above the softening point of the novolac type phenolic resin until the resin system is colored to be yellowish brown or brown. Allegedly this epoxy resin composition is shelf stable and produces cured products having improved moisture resistance. However, because of a low activity and poor fast-curing ability, this curing catalyst must be used in large amounts, rather detracting from the shelf stability of the epoxy resin composition.
TPP-K itself is a useful curing catalyst. Although it has good latency in that reaction starts above a certain temperature, it lacks fast-curing ability. JP-A 9-328535 discloses a thermosetting resin composition using as a catalyst a modified compound of TPP-K with only the boron atom being substituted. However, this modified compound of TPP-K with only the boron atom being substituted has a catalytic activity which cannot fully comply with the recent demand for fast curing. Thus phosphorus catalysts having higher activity are desired. Triphenylphosphine which is generally used from the past has a superior fast-curing ability, but is poor in shelf stability.
The prior art curing catalysts are thus difficult to produce epoxy resin compositions which are improved in shelf stability and flow and have excellent properties including fast curing, latency and moisture resistance.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a novel and improved phosphonium borate compound, a method for preparing the same, a curing catalyst comprising the same, and an epoxy resin composition, the phosphonium borate compound being improved in that when it is blended in an epoxy resin composition, the composition has good flow, fast-curing ability and latency and cures into a product having improved moisture resistance etc.
Making efforts to solve the above-mentioned problems of an epoxy resin composition comprising an epoxy resin, a phenolic resin curing agent, and an inorganic filler, we have found that a phosphonium borate salt of the following general formula (1) is obtained by reacting a phosphonium borate compound of the following general formula (2) with one or more compounds of the following general formula (3) at a temperature of 120 to 250° C. The phosphonium borate salt of formula (1) is an effective curing catalyst for the epoxy resin and phenolic resin curing agent. The phosphonium borate salt of formula (1) is a good latent catalyst in that reaction starts above a certain temperature, as compared with the prior art triphenyl phosphine catalyst, and has high activity and reactivity as compared with TPP-K. Additionally, this salt is fully compatible with resins. Accordingly, an epoxy resin composition having the phosphonium borate salt of formula (1) blended as a curing catalyst has good flow, fast-curing ability, latency and shelf stability and cures into a product having improved moisture resistance.
In a first aspect, the invention provides a phosphonium borate compound of the following general formula (1):
wherein R
1
, R
2
, R
3
and R
4
, which may be the same or different, each are a monovalent organic group having an aromatic or heterocyclic ring or a monovalent aliphatic group, at least one of R
1
, R
2
, R
3
and R
4
which are bonded to phosphorus atom and at least one of R
1
, R
2
, R
3
and R
4
which are bonded to boron atom are each an organic group derived by releasing a proton from a proton donor selected from the group consisting of an aromatic carboxylic acid having at least one carboxyl group in a molecule, an aromatic carboxylic acid having at least one acid anhydride group and at least one carboxyl group in a molecule, a phenol compound having at least one phenolic hydroxyl group in a molecule, an aromatic compound having at least one carboxyl group and at least one phenolic hydroxyl group in a molecule, and an aliphatic carboxylic acid having at least one carboxyl group in a molecule.
In a second aspect, the invention provides a method for preparing a phosphonium borate compound of formula (1), comprising the step of reacting at a temperature of 120 to 250° C. a phosphonium borate compound of the following general formula (2) with at least one compound of the following general formula (3):
[(R
5
)
4
P]
+
[(R
5
)
4
B]
−
(2)
HO—(R
6
) (3)
wherein R
5
is a monovalent organic group having an aromatic ring, and R
6
is a monovalent organic group having an aromatic or heterocyclic ring or a monovalent aliphatic group. The compound of formula (3) is a proton donor selected from the group consisting of an aromatic carboxylic acid having at least one carboxyl group in a molecule, an aromatic carboxylic acid having at least one acid anhydride group and at least one carboxyl group in a molecule, a phenol compound having at least one phenolic hydroxyl group in a molecule, an aromatic compound having at least one carboxyl group and at least one phenolic hydroxyl group in a molecule, and an aliphatic carboxylic acid having at least one carboxyl group in a molecule.
In a third aspec
Shimizu Hisashi
Shiobara Toshio
Takei Minoru
Lovering Richard D.
Shin-Etsu Chemical Co. , Ltd.
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