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
1999-11-19
2001-03-27
Short, Patricia A. (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...
C525S09200D, C525S125000, C525S131000
Reexamination Certificate
active
06207752
ABSTRACT:
FIELD OF INVENTION
The present invention relates to thermoplastic vulcanizates (TPVs) containing thermoplastic polyurethane and small particles of cured nitrile rubber dispersed therein. The present invention further contains addition type curing aids, which enhance processability and will not affect or breakdown the thermoplastic phase.
BACKGROUND OF THE INVENTION
Heretofore, many types of thermoplastic vulcanizates were known. More specifically, U.S. Pat. No. 4,226,953 to Coran and Patel relates to thermoplastic compositions comprising blends of styrene-acrylonitrile (SAN) resin and nitrile rubber of high gel content.
U.S. Pat. No. 4,141,863 to Coran et al. relates to a thermoplastic composition comprising blends of cross-linked rubber and thermoplastic linear crystalline polyester using thermoplastic polyesters having a softening point above 50° C. Rubbers include natural or synthetic diene rubber polyurethane rubber and nitrile rubber. The blends may also contain plasticizers.
U.S. Pat. No. 4,666,972 relates to polyalkylene terephthalates which contain a fluorinated polyolefin in addition to a polymer having a glass transition temperature of less than −30° C.
U.S. Pat. No. 5,397,839 relates to elastomeric compositions having improved heat aging properties provided by blends of thermoplastic polyester resin and hydrogenated nitrile rubber. The rubber component of the composition is at least partially cured.
U.S. Pat. No. 5,550,190 to Hasegawa et al. relates to a thermoplastic elastomer composition obtained by dynamically crosslinking (A) 51-95% by weight of a thermoplastic polyester-ether elastomer and (B) 49-5% by weight of a rubber during kneading.
U.S. Pat. No. 5,637,407 to Hert et al. relates to a composite including a rubber/thermoplastic blend adherent by itself to a thermoplastic material; the blend is in the form of a thermoplastic matrix containing rubber nodules functionalized and vulcanized during the mixing with the thermoplastic. Composite articles are obtained by overmoulding the vulcanized rubber/thermoplastic blend onto the thermoplastic.
U.S. Pat. No. 5,376,723 to Vogt et al. relates to a thermoplastic polymer blend of polyurethane and nitrile rubber having a Shore A hardness of about 55 to 70. The thermoplastic polyurethane component includes at least about 50 weight percent (wt. %) polyisocyanate; the nitrile rubber component includes about 34 mole percent (mol %) acrylonitrile; and, the ratio between the thermoplastic polyurethane component and the nitrile rubber component is about 30:70 to 40:60 volume percentage (vol. %). A peroxide crosslinking agent for the nitrile rubber may be mixed into the TPU
itrile rubber blend.
SUMMARY OF INVENTION
The thermoplastic vulcanizate compositions (TPV) of the present invention provide advantages over the currently available TPVs by offering improved melt processability by providing product melt phase degassing, improved processability due to the decreased tendency of the product melt to adhere to metal, improved physical properties using the curatives of this invention, and increased upper service temperatures. Generally, the TPVs of the present invention have a continuous phase of a thermoplastic polyurethane having a molecular weight sufficient to be considered an engineering plastic and a carboxylated nitrile rubber phase generally in the form of particles made from acrylonitrile and a major amount of one or more conjugated diene monomers with butadiene or isoprene being preferred. The nitrile rubber phase is cured via the bound acid functionality present, using addition type curing agents such as oxazoline, which avoids the generation of undesirable volatiles which can breakdown the TPU (thermoplastic polyurethane) continuous plastic phase and cause processing problems due to entrapment of gases in the viscous polymer melt. As a result of inertness towards the molten TPU, the unique curatives of this invention allow the preparation of TPVs with enhanced properties over the corresponding simple rubber and plastic blends, which are not attainable by the use of conventional nitrile rubber cure systems, such as peroxides or resole type phenolic resins. Practice of this invention allows the preparation of TPU containing products with improved processability over conventional TPUs due to the ready degassability of the molten material of this invention, and also due to the greatly reduced stickiness of the molten TPV to metal. Stickiness to metal of the molten products of this invention can be further reduced by the addition of maleated hydrocarbon polymers to the desired TPV composition (TPU/carboxylated NBR) either prior to or subsequent to dynamic vulcanization. The TPVs of the present invention offer increased upper service temperature over comparable thermoplastic polyurethanes. The various components are dynamically vulcanized at a temperature above the melting point of the thermoplastic or the thermoplastic elastomer.
DETAILED DESCRIPTION
The thermoplastic polymers are desirably polar, crystalline, and have high melting points. The melting point of the thermoplastic polymers is desirably at least 170° C., desirably at least 200° C. and preferably at least 220° C. Excessively high melt temperatures are avoided inasmuch as during melt mixing of the thermoplastic with the carboxylated nitrile rubber, the high melt temperature will degrade the nitrile rubber. Accordingly, the thermoplastic generally has a high melting point below 260° C., and more desirably below 240° C. Suitable thermoplastic polymers include polyesters, polycarbonates, block copolymers of polyester, and the like.
Polyesters are condensation polymers. The various polyesters can be either aromatic or aliphatic or combinations thereof and are generally directly or indirectly derived from the reactions of diols such as glycols having a total of from 2 to 6 carbon atoms and desirably from about 2 to about 4 carbon atoms with aliphatic acids having a total of from about 2 to about 20 carbon atoms and desirably from about 3 to about 15 carbon atoms or aromatic acids having a total of from about 8 to about 15 carbon atoms. Generally, aromatic polyesters are preferred such as polyethyleneterephthalate (PET), polytrimethyleneterephthalate (PTT), polybutyleneterephthalate (PBT), polyethyleneisophthalate, and polybutylenenapthalate.
Various polycarbonates can also be utilized and the same are esters of carbonic acid. A suitable polycarbonate is that based on bisphenol A, e.g., poly(carbonyldioxy-1,4-phenyleneisopropylidene-1,4-phenylene).
Suitable polyester block copolymers include segmented polyester-polyether and the like. These block copolymers contain at least one block of a polyester and at least one rubbery block such as a polyether derived from glycols having from 2 to 6 carbon atoms, e.g., polyethylene glycol, or from alkylene oxides having from 2 to 6 carbon atoms. A preferred block polyester-polyether polymer is polybuty-leneterephthalate-b-polytetramethylene glycol which is available as Hytrel from DuPont.
The molecular weight of the various thermoplastic resins is such that it is a suitable engineering plastic. Accordingly, the weight averages molecular weight of the various polyesters generally range from about 40,000 to above 110,000 with from about 50,000 to about 100,000 being preferred.
The rubber phase of the thermoplastic vulcanizate composition of the present invention comprises carboxylated nitrile rubber. Such rubber desirably has a small particle size below 50 microns and preferably from about 1 to 10 microns to yield good physical properties and processing characteristics. Nitrile rubbers are generally derived from conjugated dienes having from 4 to 8 carbon atoms with isoprene being desired and butadiene being preferred, and from acrylonitrile. The amount of the conjugated diene content within the copolymer is generally a majority, that is, from about 50 to about 80 percent by weight, and desirably from about 60 to about 75 percent by weight. The acrylonitrile content of the copolymer is thus the corresponding minority amount,
Abdou-Sabet Sabet
Abraham Tonson
Barber Norman
Ouhadi Trazollah
Advanced Elastomer Systems LP
Hudak Daniel J.
Short Patricia A.
Skinner William A.
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