Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-12-19
2002-12-10
Sellers, Robert E. L. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S064000, C525S065000, C525S066000, C525S068000, C525S069000, C525S074000, C525S077000, C525S09200D, C525S09200D, C525S09200D, C525S09200D, C525S09200D, C525S117000, C525S118000, C525S119000, C525S120000, C525S121000, C525S122000, C525S123000, C525S132000, C525S142000, C525S143000, C525S144000, C525S145000, C525S149000, C525S168000, C525S169000, C525S170000, C525S182000, C525S183000, C525S184000, C525S199000, C525S200000, C525S208000, C525S218000, C525S221000, C525S227000, C525S240000, C525S241000, C525S
Reexamination Certificate
active
06492462
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to polymeric materials which modify the rheological behavior of crosslinkable resin systems.
2. Introduction to the Invention
Crosslinkable resin systems are well known. It is known that in order to produce such a system which is relatively stable in storage, one of the active chemical moieties (e.g., a catalytic moiety or a reactive moiety) can be present in a “latent” form, which can be activated (by heating or otherwise) when rapid reaction is desired. Reference may be made for example to U.S. Pat. Nos. 4,349,651, 4,358,571, 4,420,605, 4,430,445, 4,659,779, 4,689,388, 4,701,378, 4,742,148 and 4,933,392 and European Patent Publication No. 362787A2. Copending, commonly assigned, U.S. application Ser. Nos. 08/726,739, 08/726,740 and 08/726,741 , all abandoned (each of which was filed Oct. 15, 1996 and claims priority from U.S. application Ser. No. 08/399,724 filed Mar. 7, 1995, now abandoned) and corresponding International Application No. PCT/US96/03023 (published Sep. 12, 1996, as International Publication No. WO-96/27641) disclose particularly valuable latent materials comprising an active chemical moiety which is bonded to a side chain crystalline (SCC) polymer moiety or to another crystalline polymeric moiety which melts over a narrow temperature range. These latent materials, which are referred to in the applications as polymeric modifying agents, are preferably in the form of particles having an average size of 0.1 to 50 microns. Copending, commonly assigned U.S. application Ser. No. 08/710,161 (Docket No. 10762-4 filed Sep. 12, 1996), abandoned, and corresponding International Application No. PCT/US 97/16019 (which was not published at the date of this application) disclose that even when there is no chemical bond between the active and polymeric moieties, a physical bond between the moieties can produce a lesser but still useful latent effect. Application Ser. Nos. 08/726,739, 08/726,740, 08/726,741 and 08/710,161 have all been abandoned in favor of a continuation-in-part application, Ser. No. 09/216,520, filed Dec. 16, 1998, U.S. Pat. No. 6,255,367. It is also known that curable resin systems tend to shrink when they cure, and that in some systems this tendency can be lessened or overcome by adding various polymeric additives; such additives are referred to as low profile additives (often abbreviated to “LPA”s). Reference may be made for example to pages 48 to 78 (Chapter 4 by Kenneth E. Atkins) in “Sheet Molding Compounds”, edited by Hamid Kia (1993), Plastics Compounding, July/August 1988, pages 35-45, and U.S. Pat. Nos. 3,674,893, 3,718,714, 3,721,642, 3,772,241, 3,842,142, 4,125,702, 4,160,759, 4,161,471, 4,245,068, 4,284,736, 4,288,571, 4,374,215, 4,491,642, 4,555,534, 4,673,706, 5,290,854, 5,428,105, 5,504,151, 5,552,478 and 5,589,538.
The disclosure of each of the U.S. patents and patent applications, International and European patent publications, and literature references referred to in the preceding paragraph is incorporated herein by reference for all purposes.
SUMMARY OF THE INVENTION
We have discovered, in accordance with the present invention, that the rheological properties of a crosslinkable resin system can be substantially improved by the presence of an SCC polymer (or a similar crystalline polymer which melts over a narrow temperature range). The polymer must be one which (a) at least partially dissolves in the curable system at temperatures above the melting point of the crystalline polymer (T
p
) and (b) when the curable composition is (i) heated to a temperature above T
p
under conditions such that the resin does not cure and (ii) is then cooled to a temperature below T
p
, at least partially forms a separate phase in the curable system. At temperatures below T
p
, the presence of this separate phase substantially increases the viscosity of the curable system (i.e. makes it thicker than the same system without the crystalline polymer). This is particularly valuable for sheet molding composites (SMCs), in which the increase in viscosity makes the composites less tacky and, therefore, (a) easier to handle cleanly, and (b) more likely to yield a cured product having a surface free from flaws. Above T
p
, the curable system containing the dissolved crystalline polymer has a viscosity which is substantially less than its viscosity below T
p
.
The crystalline polymer can be, but need not be, chemically or physically bound to an active chemical moiety which will take part in the reaction which forms the cured polymer. We believe, therefore, that under appropriate circumstances, some latent materials of the kind described in the copending, commonly assigned U.S. patent applications referred to above will function as RHMs. However, that possibility is not disclosed in those U.S. patent applications or the corresponding PCT applications. Under these circumstances, the extent to which our discovery can be the subject of patent protection may vary from country to country. Accordingly, and since this specification will serve not only as the specification for this U.S. patent application, but also as the priority document for corresponding applications elsewhere, the present invention is broadly defined as any product or process which embodies our discovery and which can properly be the subject of patent protection.
In a first preferred aspect, this invention provides a polymeric composition which comprises
1. a matrix material which
(a) provides a continuous phase, and
(b) comprises precursors which will react together to form a crosslinked polymer;
and
2. a rheological modifier (RHM) which
(a) comprises a crystalline polymer having an onset of melting temperature T
o
and a peak melting temperature T
p
which is (i) from 20° C. to 200° C., and (ii) such that T
p
−T
o
is less than T
p
0.7
,
(b) is uniformly distributed in the matrix material,
(c) is at least partially soluble in the matrix material when the composition is subjected to a treatment which consists of maintaining the composition at a temperature above T
p
under conditions such that the precursors do not react together to form a crosslinked resin, and
(d) becomes at least partially insoluble in the matrix material when the composition is subjected to said treatment at a temperature above T
p
and is then cooled to a temperature below T
o
,
the composition
(A) having a viscosity above T
p
which is less than its viscosity below T
o
; and
(B) having a viscosity at a temperature below T
o
which is substantially greater than the viscosity at the same temperature of a composition which is identical except that it does not contain the rheological modifier.
Preferably, the matrix material and the RHM and the relative amounts thereof are such that (a) the composition, or (b) if the composition contains solid fillers, a composition which is identical except that it does not contain the solid fillers, (A) has a viscosity at (T
p
−10)° C. which is at least twice, preferably at least 5 times, its viscosity at (T
p
+10)° C.; and/or (B) has a viscosity at 20° C. which is at least twice, preferably at least 5 times, the viscosity of a composition which is identical except that it does not contain the RHM.
The composition may also have at least one of the following characteristics, each of which provides an alternative or additional distinction over the disclosure of the commonly assigned U.S. applications and their PCT equivalents referred to above.
(1) At least 10%, at least 20% or at least 30% of the crystalline polymer is present in the form of particles or other discrete volumes which do not contain any material which takes part in the reaction which forms the crosslinked polymer.
(2) The composition, when maintained at 40° C., doubles in viscosity in less than 240 hours, e.g. in less than 24 hours.
(3) The RHM is not present in the form of discrete particles.
(4) The RHM is added to the matrix material in the form of particles having an average size of at least 75 microns, or as a solution in a solvent.
(5) W
Bitler Steven P.
Stewart Ray F.
Taft David D.
Landec Corporation
Sellers Robert E. L.
Sheldon Jeffrey G.
Sheldon & Mak
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