Foamed crystalline ionomer polyolefins

Details Foamed crystalline ionomer polyolefins Foamed crystalline ionomer polyolefins

1999-10-04

2001-07-24

Gorr, Rachel (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

C521S143000

Reexamination Certificate

active

06265455

ABSTRACT:

This invention concerns foamed ionomer graft copolymers. In particular, it concerns foamed thermoplastic olefin polymers. Moreover, this invention concerns articles manufactured from the above mentioned foamed polymers, and the process for the preparation of said polymers and articles. The embodiments of the present invention, i.e., the foamed ionomer polyolefins and the articles obtainable from them, have a variety of applications; thanks to the rigidity of said foamed polymers they are used to produce, for example, automotive parts and insulating structures for refrigerators.
Foamed polymers produced from cross-linked crystalline thermoplastic polyolefins are already known, however, said olefin polymers are not ionomeric. Examples of said foamed polymers are described in European patent application EP-A-450342 filed on behalf of Ausimont. Said patent application describes a foamed isotactic polypropylene cross-linked with peroxides and furfuraldiazine derivatives as the cross-linking coagents.
Crystalline or semicrystalline ionomer polyolefins and the process to produce them are already known; they are described, for example, in European patent application EP-A-370 736 filed on behalf of Du Pont.
Now unexpectedly it has been found that said ionomer polyolefins can also be used to produce foamed polymers.
Therefore, object of the present invention is a foamed ionomer polymer comprising metal ions pertaining to the IA, IIA or IIB Group of the Periodic Table, and a crystalline or semicrystalline graft copolymer where the backbone polymer chain of the graft copolymer is a polymer of an olefin selected from ethylene and C
3
-C
10
&agr;-olefins, and the grafted chains comprise monomers containing at least one functional group selected from carboxylic groups and their derivatives. In addition to ionic bonds, one can also find in said polymer interactions between the functional groups present in the grafted chains and the metal.
For the purpose of the present invention the terms crystalline and semicrystalline refer to those polymers that are less than 40% soluble in xylene at ambient temperature (i.e., about 25° C.).
The olefin polymers used to produce the graft copolymers of the present invention are preferably selected from homopolymers and random copolymers. The homopolymers and copolymers can be used alone or mixed together.
The olefin polymers for the production of the graft copolymers used in the present invention are preferably selected from a propylene homopolymer, and copolymer of propylene with ethylene or C
4
-C
10
&agr;-olefins, or mixtures thereof. The preferred comonomers are: ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene.
The quantity of comonomers in the above mentioned copolymers is less than 20% by weight with respect to the weight of the copolymer.
As mentioned above, the foamed polymers of the present invention are graft copolymers. The preparation takes place by grafting unsaturated monomers on the above mentioned olefin polymers, said monomers containing at least one functional group selected from the carboxylic groups and their derivatives, such as esters and anhydrides. Said monomers can contain one or more, such as two for example, carboxylic groups or their derivatives. Examples of the above mentioned monomers with functional groups are the vinyl monomer acids, among which the acrylic and methacrylic acids are the preferred ones. Other examples are the methacrylic, itaconic and citraconic, maleic, and fumaric acids, and the corresponding anhydrides and esters.
In the mixture of the present invention the above mentioned functionalized monomers are present preferably in a quantity ranging from 0.1 to 25%, more preferably from 0.6 to 10% by weight with respect to the weight of the polymer mass.
The metal present in the foamed polymer of this invention is a metal pertaining to the IA, IIA or IIB Group of the Periodic Table. Examples of said metals are sodium, lithium, potassium, zinc, magnesium, and calcium; the last three listed are the preferred ones.
The quantity of metal ions depend on the desired degree of cross-linking, and the quantity of functional groups grafted on the polymer. The polymer to be foamed is partially cross-linked. The definition of “partially cross-linked” refers to the degree of cross-linking, i.e., when the gel content with respect to the weight of the polymer soluble in hot xylene (135° C.) after cross-linking is preferably less than 20%, more preferably less than 15%. The gel corresponds to the fraction of polymer that is insoluble due to cross-linking.
In addition to the above mentioned components the foamed polymer of this invention can contain other ingredients that are generally added to thermoplastic polymers. Said additives are, for example, reinforcing fillers (such as silica, talc, cellulose, and carbon black), pigments and dies, antioxidants, thermal and optical stabilizers, and antistatic agents.
The graft copolymers used in this invention can be prepared according to known methods.
As a way of example, one can mix together the olefin polymer, the functionalized unsaturated monomers, and optional additives under conditions that cause the grafting of said monomers on the polymers.
The above mentioned grafting reaction is carried out by using known techniques. For example, one method consists of grafting the above mentioned functionalized monomers on the polymers in the presence of radical initiators. By properly selecting the quantity of the above mentioned monomers with functionalized groups that are added to the polymer to be modified, one obtains a polymer modified with functionalized monomers having the composition previously described. Said modification occurs by using the proper quantity of free radical initiators (for example peroxides such as the dicumyl peroxide, and the 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane), operating preferably in inert atmosphere, such as nitrogen for example. For said process one can use the same mixing and extrusion equipment described below.
An alternative method for the preparation of the graft copolymer consists of preparing in advance a concentrate comprising a polymer matrix, monomers with a functional group, and free radical initiators. Subsequently, said concentrate is mixed with the olefin polymer, and other additives if used, operating under conditions that will cause the grafting reaction to occur.
The above mentioned polymer matrix of the concentrate can have, for example, the same composition of the olefin polymer to be grafted, or it can be an other olefin polymer. As an alternative one can use a polymer different from the ones mentioned, but compatible with them.
The above mentioned mixing operations are carried out in apparatus commonly used for such purpose. For example said mixing can be done using internal mixers (such as a Banbury for example), or single screw extruders (such as a Buss for example), or twin-screw extruders equipped with mixing components (such as a Werner for example).
The mixing temperature generally ranges from 170° to 250° C.
The ionomer polymers used in this invention are known, and known methods are used for their preparation.
As a way of example, one of the preparation methods consists of mixing the graft copolymer previously obtained to a metal compound, such as, for example, an oxide, an hydroxide, or a salt, such as carbonate, or mixtures of said compounds. The mixing can occur under the same operating conditions and with the same equipment used for the preparation of the grafted polymer.
As an alternative, the ionomer polymer can be prepared by contacting the graft copolymer with an aqueous solution, or a fine dispersion in water of an alkaline compound of the above mentioned metals. The alkaline compound is preferably a hydroxide, a carbonate, or a bicarbonate of the aforesaid metals. Said method is described, for example, in the above mentioned patent application EP-A-370736.
The cross-linked polymers thus obtained are subsequently foamed in order to obtain the foamed polymers and articles of the present invention, whic

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