Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-04-14
2002-11-26
Toomer, Cephia D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S139000, C523S451000
Reexamination Certificate
active
06486242
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a resin composition having excellent flame retardancy without using any halogenous flame retarder, and prepregs and laminates using the resin composition.
Thermosetting resins, such as epoxy resins typically, are widely used for electric and electronic equipment parts because of their excellent properties, and in many cases such resins are provided with flame retardancy for securing safety against fire. Conventionally, halogen-containing compounds such as brominated epoxy resins have been generally used as flame-retardant resins. These halogen-containing compounds have a high degree of flame retardance, but aromatic bromine compounds not only release corrosive bromine and hydrogen bromide when pyrolized but also are liable to form highly toxic polybromodibenzofuran and polydibromobenzoxine when decomposed in the presence of oxygen. Further, superannuated waste material containing bromine is very difficult to dispose of. For these reasons, attention is now focused on phosphorus compounds for use as a flame retarder in place of the conventional bromine-containing compounds.
As mentioned above, flame retardation can be realized by use of phosphorus compounds. Their flame-retarding mechanism is as follows: decomposition and thermal condensation of a phosphorus compound generates polyphosphoric acid, and this polyphosphoric acid forms a coating film on the surface of an epoxy resin to produce heat-insulating effect and oxygen barrier effect, which serve for preventing combustion of the resin.
The phosphorus compounds, however, have disadvantages in that they are apt to absorb water, and that if they are added in large quantities in a thermosetting resin for providing the desired flame retarding effect, the innate properties of the resin would be greatly deteriorated.
OBJECT AND SUMMARY OF THE INVENTION
The present invention has been attained as a result of the studies pursued for solving the above problems, and it realizes the objective flame retardation without using any halogenous compound, by using a novolak epoxy resin and a novolak resin, both of which have high heat resistance, as an epoxy resin and a curing agent therefor, and further by incorporating therein a phosphorus compound. Because of use of a resin and a curing agent both having high heat resistance, the present invention can provide a resin composition having sufficient flame retardancy by addition of a small quantity of a phosphorus compound. The present invention is also designed to provide prepregs using the resin composition, and flame-retardant laminates made of the prepregs.
The present invention provides a flame-retardant resin composition comprising as essential constituents (A) a novolak epoxy resin, (B) a novolak resin and (C) a phosphorus compound reactable with said epoxy resin or novolak resin. The present invention also provides a prepreg comprising a fiber base impregnated with said flame-retardant resin composition, and further provides a flame-retardant laminate or copper-clad laminate produced by hot-pressing a sheet or a stack of two or more sheets of said prepreg.
DETAILED DESCRIPTION OF THE INVENTION
As mentioned above, use of a phosphorus compound can realize sufficient flame retardance without using a halogen compound. The phosphorus compound, however, has tendency to absorb moisture, so that use of the phosphorus compound in large quantities gives adverse effect to the innate properties such as moisture resistance of the cured product of a resin. But the novolak epoxy resin and the novolak resin used in the present invention have a high content of benzene rings and high heat resistance, so that their flame retardance is higher than that of other ordinary epoxy resins. It is therefore possible to obtain sufficient flame retardance even if the amount of the phosphorus compound blended is lessened as compared with the conventional formulations.
Thus, the flame-retardant resin composition according to the present invention is highlighted in that it can provide sufficient flame retardance without using any halogen compound, by using an epoxy resin and a curing agent therefor both having high heat resistance, and also using a phosphorus compound as a flame retarder.
The novolak epoxy resins usable as constituent (A) in the present invention include, for example, phenolic novolak epoxy resins, cresol novolak epoxy resins, bisphenol A novolak epoxy resins and the like, and are not limited thereto. Two or more types of these novolak epoxy resins may be used simultaneously. In view of heat resistance, it is preferable to use a phenolic novolak epoxy resin or a cresol novolak epoxy resin which has a higher content of benzene rings. The phenolic aralkyl epoxy resins represented by the following formula 1, the naphthalene aralkyl epoxy resins represented by the following formula 2 and the biphenyl-modified epoxy resins represented by the following formula 3 are also preferred as they can provide higher heat resistance and lower water absorption because of a high content of aromatic rings and a small proportion of polar groups:
wherein n is a natural number,
wherein n is a natural number,
wherein n is a natural number.
It is advisable for the improvement of heat resistance and flame retardance to use a novolak epoxy resin as mentioned above in an amount of 50% by weight or more in the whole epoxy resin.
As the novolak resin (B), usually phenolic novolak resins or phenolic aralkyl resins are used in the present invention. Use of a triazine-modified novolak resin represented by the following formula 4 is preferred as flame retardance is improved by the triazine rings which constitute the nitrogenous moiety. Since an epoxy resin having high heat resistance is used for improving flame retardance, a nitrogen content of higher than 2.5% is unnecessary considering that a phosphorus compound is contained. A nitrogen content exceeding 4.0% is undesirable as it elevates hygroscopicity of the composition.
In the above formula, R is NH
2
, alkyl group or phenyl group; and n and m are each a natural number.
The phenolic aralkyl resins represented by the following formula 5, the naphthalene aralkyl resins represented by the following formula 6, the biphenyl-modified novolak resins represented by the following formula 7 and the toluene-, xylene- or mesitylene-modified novolak resins represented by the following formula 8 are preferred as they are helpful for providing high heat resistance and low water absorption because of a high content of aromatic rings and a low proportion of polar groups:
wherein n is a natural number,
wherein n is a natural number,
wherein n is a natural number,
wherein m and n are each a natural number, and l is a number of 1, 2 or 3.
In the present invention, as the novolak resin (B), combined use of a triazine-modified novolak resin (a) of the formula 4 and at least one member (b) selected from the phenolic aralkyl resins of the formula 5, the naphthalene aralkyl resins of the formula 6, the biphenyl-modified novolak resins of the formula 7 and the toluene-, xylene- or mesitylene-modified novolak resins of the formula 8 is preferred as it gives high heat resistance and excellent flame retardance to the composition. The (a)/(b) ratio in this combination is preferably 60/40 to 20/80 in view of said properties.
The ratio of the novolak resin to the novolak epoxy resin in the composition is preferably 0.8 to 1.2 in terms of equivalent ratio (phenolic hydroxyl groups/epoxy groups) . If this ratio is above or below the above-defined range, there remain the free epoxy groups or phenolic hydroxyl groups to adversely affect heat resistance and/or water absorption properties of the composition.
Use of a bisphenol S compound represented by the following formula 9 with a novolak resin is also preferable as it provides a quick-curing composition:
wherein R
1
, R
2
, R
3
and R
4
are each hydrogen, alkyl group or aryl group.
In this case, the amount of the novolak resin blended is lessened by a portion equivalent to
Honjoya Tomoyoshi
Tobisawa Akihiko
Smith , Gambrell & Russell, LLP
Sumitomo Bakelite Company Limited
Toomer Cephia D.
LandOfFree
Flame-retardant resin composition and prepreg and laminate... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Flame-retardant resin composition and prepreg and laminate..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Flame-retardant resin composition and prepreg and laminate... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2956210