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
2001-12-14
2004-05-25
Woodward, Ana L. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S063000, C525S064000, C525S065000, C525S067000, C525S09200D, C525S166000, C525S179000
Reexamination Certificate
active
06740708
ABSTRACT:
The invention relates to a process for the preparation of an impact-resistant polymer composition containing 0.5-75 parts by weight of a rubber composition (per 100 parts by weight of the matrix polymer).
Such compositions are known from, inter alia, U.S. Pat. No. 4,174,358 and this patent publication discloses various processes for the preparation of these compositions. These processes all essentially comprise a rubber functionalization step followed by incorporation of the functionality rubber in the desired concentration into the matrix polymer.
These state-of-the-art polymer compositions in general exhibit a good impact resistance, which is determined, inter alia, to an important degree by the rubber content of the composition. However, the presence of the rubber composition causes the stiffness to decrease and the creep to increase.
For applications in which no or only minimal creep is allowed while a good impact resistance is required, for instance in plastic hammer heads, it is therefore necessary to have a polymer composition that possesses this combination of conflicting properties. Another application in which this combination of properties is required is that of plastic profiles that serve as heat bridge in metal window and door profiles and screw plugs, where toughness is required for assembly purposes while no creep may occur when the materials are subsequently subjected to a permanent load. Compositions obtained by the state-of-the-art process, however, cannot fully meet this requirement.
The aim of the invention therefore is a process for the preparation of an impact-resistant polymer composition that has an excellent impact resistance at no or only minimal creep.
This aim is achieved by melt mixing of a matrix polymer A with a composition comprising a dispersed rubber composition in a matrix polymer B, the dispersed rubber composition in matrix polymer B having been obtained by melt mixing of matrix polymer B with a rubber composition that contains at least one non-functionality rubber and one functionality rubber, in such amounts that the desired rubber concentration in the impact-resistant polymer composition is reached.
Also part of the invention are the composition obtainable by the process according to the invention and the products obtained from the composition according to the invention as well as the (granule) mixture of matrix polymer A and the dispersed rubber composition in matrix polymer B as needed for the process of the invention.
Matrix polymer A can in principle be chosen freely, but the process according to the invention offers advantages if polymer A is chosen from the group consisting of polyamides, polyesters, polyacetals and polycarbonates. The invention is effective in particular if polymer A is a polyamide or a polyester.
For matrix polymer B in principle any polymer can be chosen that can suitably be mixed with polymer A and in which the rubber composition can suitably be dispersed. Preferably, polymer B is chosen from the group consisting of polyamides, polyesters, polyacetals and polycarbonates. Even more preferably, polymers A and B are of the same type of polymer, for instance A and B are both polyamides, for instance an aliphatic and a semi-aromatic polyamide. Most preferably, A and B are identical.
The rubber composition dispersed in polymer B comprises at least one non-functionality rubber and at least one functionality rubber. Rubber is here understood to mean a polymeric compound with a glass transition temperature lower than 0° C., preferably lower than −20° C., most preferably lower than −40° C.
A rubber is called functionality when it contains groups that can react with matrix polymer B and/or A.
Examples of polymers covered by the definition of rubber are copolymers of ethylene and &agr;-olefins, for instance ethylene-propylene rubbers. Very suitable for use in the process according to the invention are the so-called plastomers based on ethylene and C4-C12 olefins, for instance octene, and produced using a metallocene catalyst.
Other rubbers that can suitably be used in the process according to the invention are styrene-butadiene based block copolymers.
Functional groups can be introduced into the rubber in many ways. A great many preparation methods and examples of these functionality rubbers are described, for instance, in the above-mentioned U.S. patent publication U.S. Pat. No. 4,174,358. Several of these functionality rubbers are commercially available under different names. Very suitable are rubbers that are chemically modified by reaction with maleic anhydride or by graft polymerization of the rubber with an unsaturated dicarboxylic anhydride or an unsaturated dicarboxylic acid or an ester thereof, for instance maleic anhydride, itaconic acid and itaconic anhydride, fumaric acid and maleic acid or a glycidyl acrylate, for instance glycidyl methacrylate, and vinyl alkoxysilane. The functional groups are highly reactive relative to, inter alia, amino end groups in polyamides, hydroxyl end groups in polyesters and acid end groups in both polyamides and polyesters.
The content of compounds supplying functional groups in the functionality rubber may vary within wide limits, for instance between 0.01 and 5 wt. %. The best results are generally achieved with a content between 0.3 and 3 wt. %.
The weight ratio of non-functionality to functionality rubber may vary within wide limits and is determined in part by the functional groups content of the rubber and the available reactive groups in the matrix polymer. One skilled in the art can determine this by means of simple experiments. In general, this ratio will be between 10 and 0.1, preferably between 5 and 0.1.
The rubber composition content of the composition with matrix polymer B may vary within wide limits, for instance between 20 and 70 wt. %, calculated on the total weight of rubber composition + polymer B, preferably the rubber composition content is chosen as high as possible, for instance higher than 30 wt. %, more preferably higher than 40 wt. %. Very good results are achieved with contents of at least 50 wt. % or higher.
The non-functionality rubber and the rubber that is functionality may be identical or different. Combinations are for instance possible of an ethylene-&agr;-olefin copolymer and the same ethylene-&agr;-olefin copolymer modified with, for instance, maleic anhydride. The same ethylene-&agr;-olefin copolymer may also be combined with, for instance, an acid-modified styrene-butadiene tri block copolymer.
Particularly good results are achieved with the process according to the invention when the rubber composition in matrix polymer B is present in finely dispersed particles. Preferably, the dispersed particles of the rubber composition are then built up of a core of non-functionality rubber and a shell of functionality rubber.
The composition of matrix polymer B with the rubber composition can be obtained by melt mixing of the constituent components. In doing so, use is preferably made of high shear forces and the conditions are chosen so that the viscosity in the melt of the rubber phase is higher than that of the polymer matrix. During the melt mixing process crosslinking of the rubber phase may optionally take place. However, a non-crosslinked rubber is preferred. Non-crosslinked rubber is here understood to be a rubber that is substantially not crosslinked. In practice, however, some degree of crosslinking can hardly be avoided during melt mixing at the high temperatures then prevailing. The resulting gel content will be lower than 50 wt. %, preferably lower than 30 wt. %, even more preferably lower than 10 wt. %. The gel content is here defined as the rubber fraction that is insoluble in the solvent that is suitable for the rubber in question. For ethylene-propylene copolymer rubbers, for instance, this solvent is xylene. When reference is made to crosslinking of the rubber composition, this is understood to mean the melt mixing process carried out in the presence of a vulcanization agent, for instance a peroxide.
Optionally, the r
Bruls Wilhelmus G. M.
De Kroon Jan
Repin Johannes F.
DSM IP Assets B.V.
Pillsbury & Winthrop LLP
Woodward Ana L.
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