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
2000-10-19
2002-04-30
Seidleck, James J. (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...
C525S263000, C524S404000, C524S405000
Reexamination Certificate
active
06380320
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of anhydride-grafted polymers and in particular to a process for preparing anhydride-grafted polymers having improved colour using oxo-boron compounds.
BACKGROUND OF THE INVENTION
The use of polyolefins grafted with anhydrides, including maleic anhydride, as film laminates is well known in the prior art. In preparing such film laminates, it is important that a uniform product be made when grafting the anhydride onto the polymer. It is also important that the anhydride-grafted polymer have desired colour properties if it is to be used in association with colour-sensitive materials to produce products such as clear laminate films.
It is known in the prior art that the properties of polyolefins may be modified by the grafting of ethylenically unsaturated carboxylic acids and anhydrides onto hydrocarbon alpha-olefins. For example, European Patent Application No. 0 266 994 of P. C. Wong, published May 11, 1988, discloses a process for the melt grafting of an ethylenically unsaturated monomer onto a copolymer. In the process, an admixture of the copolymer, monomer, and an organic peroxide is mixed in an extruder at a temperature above the melting point of the copolymer for a period of time that is at least four times the half-life of the organic peroxide. The preferred monomers are maleic acid and maleic anhydride.
When polyolefins are treated with maleic anhydride to make a maleic anhydride grafted polymer, the colour of the resulting polymer tends to be yellow. For unknown reasons, some polyolefins form end-products that are a darker yellow than others. These dark yellow maleic anhydride-grafted polymers have proven to be commercially undesirable.
Several attempts have been made in the prior art to try to improve the colour stability of maleic anhydride.
For example, U.S. Pat. No. 3,939,183 to Gardner, entitled “Purification of Maleic Anhydride”, discloses a process for obtaining purified maleic anhydrides of desired colour stability by combining and contacting a metal halide and P
2
O
5
or a perborate with the crude maleic anhydride before final distillation of the crude maleic anhydride. Gardner does not, however, disclose using this process or suggesting another process for obtaining a maleic anhydride-grafted polymer with improved colour.
U.S. Pat. No. 3,975,408 to Boyer, entitled “Color Stabilization of Refined Dicarboxylic Acid Anhydrides” describes a process for retarding discolouration of maleic anhydride using treating agents such as halides, the transition elements, vanadium, chromium, manganese, mercury, silicon, phosphorus, bismuth, antimony, lead, cerium, and sulfur. Boyer does not, however, disclose a process for retarding discoloration of maleic anhydride-grafted polymers.
U.S. Pat. No. 4,358,600 to Kuhlmann, entitled, “Process for the Manufacture of Maleic Anhydride Having Improved Age Molten Colour” similarly provides a process for improving the colour of maleic anhydride, but not the colour of a maleic anhydride-grafted polymer. This process includes polymerizing crude maleic anhydride in the presence of metal chloride catalyst prior to fractionating the crude maleic anhydride and distilling off the purified maleic anhydride.
U.S. Pat. No. 5,026,876 to Sugawara et al, entitled, “Process for Producing Maleic Anhydride”, describes a process for producing maleic anydride with colour stability by adding n-propyl gallate, cuprous chloride, and zinc chloride or tridecyl phosphite to distilled maleic anhydride.
All of these prior art patents are directed to improving the colour of maleic anhydride. None of these patents discuss or suggest a process for improving the colour of a maleic anhydride-grafted polymer.
U.S. Pat. No. 5,106,916 to Mitchell, entitled “Process for the Preparation of Grafted Polymers of Improved Colour”, attempts to improve the colour of maleic anhydride-grafted polymers by providing a process for grafting maleic anhydride onto polar polymers in the presence of a phosphorus containing compound. The colour improvement of Mitchell's process is, however, limited to grafted polar polymers, it does not address the need to improve the colour of grafted non-polar polymers.
Thus, there still remains a need to provide a process for improving the colour of maleic anhydride-grafted non-polar polymers.
SUMMARY OF THE INVENTION
It is an object of one aspect of the present invention to provide a process for making a colour improved anhydride-grafted polymer.
According to one aspect of the present invention, there is provided a process for preparing an anhydride grafted polymer with improved colour comprising the steps of:
(a) admixing in an extruder a polyolefin, a free radical initiator, and an anhydride-providing monomer at a temperature above the melting point of the polyolefin;
(b) adding an effective amount of an oxo-boron compound to the admixture; and
(c) extruding the resultant anhydride grafted polymer into a shaped article.
Preferably, the oxo-boron compound is boric acid and the anhydride-providing monomer is maleic anhydride.
In a further aspect of the invention, a free-radical initiator is not added to the admixture. Accordingly, in this aspect of the invention, there is provided a process for preparing an anhydride-grafted polymer with improved colour comprising the steps of:
(a) admixing in an extruder a polyolefin and an anhydride-providing monomer at a temperature above the melting point of the polyolefin;
(b) adding an effective amount of an oxo-boron compound to the admixture; and
(c) extruding the resultant anhydride grafted polymer into a shaped article.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be described with reference to its preferred embodiments.
The present invention provides a process for obtaining an anhydride grafted polymer that has improved colour by introducing an oxo-boron containing compound into the grafting process.
The anhydride-grafted polymers may be used by themselves or blended with other polymers. They may be extruded into film or moulded into articles by using process well known in the art, such as blow moulding, rotational moulding or injection moulding.
Suitable polyolefins for use in the present invention include homopolymers and copolymers of unsaturated hydrocarbons having 2-20 carbon atoms. They can be made by processes well known in the art, including polymerization processes in which metallocene catalysts are used (single site catalysts). In particular, the polymers are homopolymers of ethylene or propylene or copolymers of ethylene with one or more alpha-olefin hydrocarbons having 3-10 carbon atoms, especially propylene, butene-1, hexene-1 and octene-1 and styrene. Suitable alpha-olefins also include dienes, that is, monomers with more than 1 site of unsaturation, especially 1,3 butadiene, 1,5 hexadiene, 5-ethylidene-2-norbornene and norbornadiene. In particularly preferred embodiments, the polyolefins are copolymers of ethylene with a hydrocarbon alpha-olefin having from 4-8 carbon atoms and having a density in the range of about 0.850 to about 0.970 grams per cubic centimetre (g/cm
3
) and especially in the range of 0.860 to 0.930 g/cm
3
. Preferably, the polymers have a melt index (MI) in the range of 0.05 to 120 g/10 min, especially 0.1 to 75 g/10 min and in particular 1 to 10 g/10 min (as measured per ASTM D-1238).
Other suitable polymers that may be used in the process of the present invention may be ethylene/alpha olefin copolymers such as copolymers of ethylene and a vinyl alkanoate, especially ethylene/vinyl acetate copolymers. The copolymers may have a relatively high ethylene content, and tend to be non-tacky copolymers, or lower ethylene contents, and tend to be relatively tacky copolymers. The latter include copolymers that in pellet form tend to agglomerate. In addition, the copolymers are available in a variety of molecular weights, which is usually expressed in terms of melt index. The nature of the copolymer, especially with respect to ethylene content and molecular weight, that is subjected to
Asinovsky Olga
Clarizio Dino P.
Dimock Stratton Clarizio LLP
DuPont Canada Inc.
Seidleck James J.
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