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
2002-05-09
2004-04-20
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...
C525S240000, C521S134000, C521S920000, C523S201000, C523S202000
Reexamination Certificate
active
06723792
ABSTRACT:
The present invention concerns dispersions and concentrates of additives, which can be used in processing polymers, particularly olefin polymers. It is known that in order to obtain better dispersion of additives in the finished polymeric products, and optimize the properties imparted to said finished products, it is preferable, and sometime necessary, to add the additives to the polymer in form of suitably prepared dispersions or concentrates.
Said dispersions or concentrates are generally obtained by dispersing from relatively low to high concentrations of the additives in materials which are compatible with the polymer materials constituting the finished products. In order to obtain the best usage economy, the concentrates should contain the highest possible quantity of additive while allowing an effective dispersion of the additive to be reached when said concentrates are diluted in polymer materials to obtain the finished products. For this purpose, the solution most commonly used in the art consists of coextruding the additive with a polymer compatible with the polymer materials which constitute the finished product, thus obtaining a concentrate in the form of pellets.
Said pellets are prepared in such a way that they can be used directly in the polymer processing plants.
On the other hand, in the field of olefin polymerization are taking hold, at the present time, some processes by which one can produce polymer particles in regular form, particularly spheroidal ones, and with a controlled particle size distribution.
Said polymer particles, because of their high flowability and absence of fines, can be used directly in the polymer processing plants and represent an economical alternative to the use of pellets. Further, single screw extruders are not designed to handle liquid or low melting additives. Above a concentration of 5-7 weight % of an additive a screw slipping occurs, which leads to a variable quality and a low yield in extruder production.
Moreover, one must remember that extrusion often leads to degradation, and therefore loss, of some of the additive used in preparing concentrates. Therefore, the need for additive dispersions and concentrates obtained directly from the above mentioned polymer particles, thus eliminating the extrusion stage, is strongly felt.
Said dispersions and concentrates should satisfy the typical requirements established in the relevant art, in particular:
1) high additive content in the case of concentrates;
2) ability of producing good dispersion of the additives when the concentrates are diluted in the polymer to be processed;
3) possibility of being used directly in the polymer transformation plants;
4) good storage stability and resistance to damage during transport and processing.
Useful solutions to this problem have been already disclosed in published European patent applications EP 290 149 and EP 459 208 and in U.S. Pat. Nos. 5,231,119 and 5,326,962. All these solutions have in common the fact of using polymer particles substantially consisting of a single polymer phase, selected from homopolymers and copolymers. Moreover, the said homopolymers and copolymers are characterized by a relatively high degree of crystallinity, and consequently, relatively high levels of melting temperature and heat of fusion, which limit their ability of producing good dispersions by mixing the concentrates with other polymers in the molten state. This problem can become dramatical when the said concentrates of the prior art are added to polymers with different crystalline structures or low degrees of crystallinity, as the compatibility between the two kinds of polymers (i.e. the polymer present in the concentrate and the polymer mixed with the concentrate) can become even very low.
Obviously, another limit of the said solutions is that generally the crystalline polymers are rigid and lack softness, so that they would adversely affect the mechanical properties of the polymers mixed with the concentrate, when flexibility and softness are desired.
Therefore it would be useful and desirable to obtain dispersions and concentrates from polymer particles containing two or more different polymeric phases, in order to optimize their compatibility with a large range of polymers, both in terms of miscibility and mechanical properties. This effect could be achieved to the maximum level by using the so called “polymer alloys” wherein the polymer phases are very finely and homogeneously dispersed, thus generating a polymer material which behaves, from many respects, as a single-phase polymer having intermediate properties between its components.
However in the prior art there is no appreciation of the possibility of preparing nonextruded dispersions and concentrates by using these kinds of polymer materials. In fact such polymer materials are generally prepared by sequential polymerization processes, wherein the various polymer phases are caused to grow and accumulate on the polymer particles produced in the preceding polymerization step(s), so that it is common belief that the subsequently added polymer phases tend to cover the surface and fill the voids of the growing polymer particle, thereby reducing drastically the presence of pores and cracks. Actually, the so obtained polymer particles show a relatively smooth surface.
However it has now been found that when such polymer materials are prepared by using certain kinds of polymerization catalysts, preferably carrying out one or more polymerization steps in gas phase, the resulting particles, even if having a rather smooth surface, result to be permeable to liquid additives due to the presence of through-going channels, making it possible for said liquid additives to penetrate inside the particles and fill, partially or totally, the internal voids that are present in such particles as another effect caused by the use of the said polmerization catalyst.
The only document known to the applicant wherein nonextruded polymer particles with an internal cavity are disclosed, is U.S. Pat. No. 4,724,225. However such document, even if suggesting the use of such particles for dispersing liquid additives, does not disclose or suggest how to produce dispersions or concentrates on polyolefin particles containing two or more different polymeric phases.
The distinction between dispersion and concentrate is purely based on the amount of dispersed additive. While the term “dispersion” is used here to define materials wherein the dispersed additive content is comprised in a wide range, indicatively from 0.5% up to 25% by weight, the term “concentrate” is used to define dispersions preferably containing at least 5% by weight of dispersed additive.
The object of the present invention, therefore, is to obtain a dispersion of one or more additives, in particular liquid or low melting additives, to be used in the processing of olefin polymers or copolymers, said dispersion comprising nonextruded particles of olefin polymers containing at least two immiscible polyolefinic phases and having internal voids partially or totally filled by the said additive or additives, wherein the amount of additive or additives present in the said internal voids is from 0.5 to 25% by weight, preferably from 0.5 to 20% by weight, with respect to the total weight of the dispersion.
A more specific object of the present invention is to obtain such dispersion in form of a concentrate of one or more additives, in particular liquid or low melting additives, to be used in the processing of olefin polymers or copolymers, said concentrate comprising nonextruded particles of olefin polymers containing at least two immiscible polyolefinic phases and having internal voids partially or totally filled by the said additive or additives, wherein the amount of additive or additives present in the said internal voids is from 5 to 25% by weight, preferably from 10 to 20% by weight, with respect to the total weight of the concentrate.
Nonextruded particles as used herein means as-polymerized particles not subjected to processing or treatments after polymerization. They c
Basell Poliolefine Italia S.p.A.
Nutter Nathan M.
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