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
2002-02-08
2004-02-24
Nutter, Nathan M. (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...
C525S216000, C525S221000, C525S222000
Reexamination Certificate
active
06696524
ABSTRACT:
FIELD OF INVENTION
This invention relates to blends comprising an ethylene based polymer having a specific glass transition temperature and a cycloolefin polymer, and to their applications in molded articles and films.
BACKGROUND OF THE INVENTION
Cycloolefin polymers have long been used in the preparation of molded articles. But these materials are stiff and brittle. As a consequence, improvement of impact strength, or toughness, of cycloolefin polymers has long been of interest. Resistance to shattering or brittle breaking on impact of molded articles is a desirable feature of any molded article.
Tendency to break on impact in a brittle fashion is a significant limitation on the usefulness of such articles. By “ductile” is meant that sharp cracks in the molded polymer are not initiated, or if initiated do not tend to propagate, from the area of impact. Breaks are characterized more by tearing with a large volume of adjacent material yielding at the edge of the crack or tear rather than a sharp, clean break with little molecular displacement. A polymer having good ductility is one that is resistant to crack propagation caused by impact.
It would therefore be useful to provide a cycloolefin polymer based composition flexible enough to be more resistant to impact when under the form of molded articles or under the form of extruded films.
SUMMARY OF THE INVENTION
Now, it has been surprisingly found that the incorporation of an ethylene based polymer having a specific glass transition temperature into a composition comprising a cycloolefin polymer increases the impact resistance of molded articles made from said composition.
A first aspect of the invention is a blend comprising at least an ethylene based polymer having a glass transition temperature lower than or equal to 20° C. and at least a cycloolefin polymer.
Another aspect of the invention is an article, in particular a molded article, comprising the above blend.
Another aspect of the invention is a film comprising the above blend.
The blend of the invention allows one to obtain improved mechanical properties of molded article.
DETAILED DESCRIPTION OF THE INVENTION
The first essential component of the invention is a cycloolefin polymer. Suitable cycloolefin polymers for the invention have a mean molecular weight Mw (weight average) in the range from 200 to 100,000. They are substantially amorphous, i.e. have a crystallinity of less than 5% by weight. They preferably show a glass transition temperature Tg, which is generally in the range from 0 to 300° C. The polydispersity Mw/Mn of the cycloolefin polymers is preferably from 1 to 5.
Cycloolefin polymers (COPs) are homopolymers built up from only one type of cycloolefins or copolymers built up from cycloolefins and comonomers (COCs), where the comonomer content is at most 20% by weight, based on the weight of the cycloolefin polymer. Cycloolefins are mono or polyunsaturated polycyclic ring systems, such as cycloalkenes, bicycloalkenes, tricycloalkenes or tetracycloalkenes. The ring systems can be monosubstituted or polysubstituted. Preference is given to the cycloolefins which are built up from monoalkylated or unsubstituted cycloolefins. Particularly preferred cycloolefin homopolymers are polynorbornene, polydimethyloctahydronaphthalene, polycyclopentene and poly(5-methyl)norbornene. The cycloolefin polymers can also be branched. Products of this type can have comb or star structures.
If desired, the above-described cycloolefins can also be copolymerized with comonomers. In a preferred embodiment of the invention, these cycloolefin copolymers (COCs) contain up to 20% by weight, preferably about 1-15% by weight, in particular about 1-8% by weight, based on the weight of the COC, of comonomer. Preferred comonomers are olefins having 2 to 6 carbon atoms, in particular ethylene and butylene.
Preferred cycloolefin polymers of the invention are ethylene-norbornene copolymers.
The cycloolefin polymers can be prepared with the aid of transition-metal catalysts. Preparation processes are described, for example, in DD-A-109 225, EP-A-0 407 870, EP-A-0 485 893 and U.S. Pat. Nos. 5,869,586, U.S. 6,068,936 and WO98/27126 which are incorporated herein by way of reference. Molecular weight regulation during the preparation can advantageously be effected using hydrogen. Suitable molecular weights can also be established through targeted selection of the catalyst and reaction conditions. Details in this respect are given in the above mentioned specifications.
Suitable cycloolefin for the invention are the products sold under the trademark Topas® by Ticona.
The cycloolefin polymer is usually present in the blend of the invention in an amount from 50 weight % to about 99.9%, relative to the weight of the blend.
The second essential component of the composition of the invention is an ethylene based polymer having a glass transition temperature or Tg lower than or equal to 20° C., more preferably lower than or equal to 0° C. Tg is measured through thermomechanical analysis according to ASTM D 3418. This ethylene based polymer is preferably a copolymer or a terpolymer. The ethylene based polymer of the invention preferably comprises ethylene and a comonomer selected from the group of carboxylic acids, alkyl acrylates and alpha-olefins.
Preferred alpha-olefins are selected from the ones having 3-20 carbon atoms, more preferably from the group of 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-butene and 1-octene such as described in U.S. Pat. Nos. 5,272,236, 5,278,272 and in WO 94/06817. Most preferably, alpha-olefins have 4-8 carbon atoms. Most preferred alpha-olefins are selected from the group of 1-butene, 1-hexen and 1-octene.
In a preferred embodiment of the invention, the ethylene based polymer is polar, that is to say that it is an ethylene based polymer where part of the hydrogen atoms in the hydrocarbon chain of polyethylene is substituted by at least one atom chosen from oxygen or nitrogen. The ethylene monomer is preferably present in an amount of at least 60 weight %, relative to the weight of the polymer.
In a preferred embodiment of the invention, the ethylene based polymer is of ethylene, &agr;,&bgr;-ethylenically unsaturated C
3
-C
8
carboxylic acid, and optionally one or more softening comonomers copolymerizable with ethylene. The &agr;,&bgr;-ethylenically unsaturated C
3
-C
8
carboxylic acid is preferably present in an amount of 5-15 weight %, relative to the weight of the polymer. The softening monomer is preferably present in an amount of less than 25 weight %, relative to the weight of the polymer. Acrylic and methacrylic acids are preferred acid comonomers. The softening comonomer can be an alkyl acrylate selected from the group consisting of methyl acrylate, n-propyl-, iso-butyl-, n-butyl-, n-octyl-, 2-ethylhexyl-. and 2-methoxyethyl-acrylates. The preferred alkyl acrylates are iso-butyl-, n-butyl-, 2-ethylhexyl-, and 2-methoxyethyl-acrylates. The softening comonomer can also be an alkyl vinyl ether selected from the -group consisting of n-butyl-, n-hexyl-, 2-ethylhexyl-, and 2-methoxyethyl-vinyl ether. The preferred alkyl vinyl ethers are n-butyl vinyl ether and n-hexyl vinyl ether.
The polymer is optionally about 0.01 to 99.5% neutralized with metal ions selected from groups Ia, Ib, IIa, IIIa, IVa, VIb, and VIII of the Periodic Table of Elements such as sodium, potassium, zinc, calcium, magnesium, lithium, aluminum, nickel, and chromium. Such neutralized ethylene acid copolymers are known in the art as ‘ionomers’. Typically, neutralization will be from 10-70%. Preferably the copolymer has from about 35 to about 70% of the carboxylic acid groups ionized by neutralization with metal ions selected from the group consisting of sodium, potassium, zinc, calcium, and magnesium. Ionomers and their methods of manufacture are described in U.S. Pat. No. 3,264,272.
Suitable polymers for use in the present invention are the ionomers commercially available under the trademark Surlyn® from E. I. du Pont de Nemours and Company and the ethylene acid copolymers
E. I. du Pont de Nemours and Company
Nutter Nathan M.
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