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
2000-06-26
2001-08-28
Woodward, Ana (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...
C525S067000, C525S09200D, C525S070000, C525S072000, C525S123000, C525S166000, C525S176000, C525S183000
Reexamination Certificate
active
06281287
ABSTRACT:
The invention relates to multiphase thermoplastic resin compositions and more particularly to compositions in the form of a matrix in which nodules are dispersed.
Many thermoplastics have to be modified by incorporating rubbers or other polymers, for example in order to modify the flexural modulus thereof or to improve the impact strength.
The Applicant has discovered that if, in a matrix (M) containing nodules (S) part of (S) is replaced by a polymer (K), the tensile strength could be improved while maintaining the flexural modulus. In addition, this also very often results in a reduction in the size of the nodules of the phase dispersed in (M).
This has many advantages, for example when the polymer of the matrix is transparent or even translucent, the reduction in the size of the nodules increases the transparency or makes the polymer more translucent for a constant level of dispersed phase. The impact strength is also improved.
U.S. Pat. No. 5,070,145 describes compositions consisting of 80 parts of nylon-6 (PA-6) or nylon-6,6 (PA-6,6) in which 20 parts of a mixture (i) of a copolymer of ethylene and of an ethyl or butyl acrylate and (ii) of a copolymer of ethylene, ethyl acrylate and maleic anhydride have been dispersed. These compositions have good impact strength.
EP 284,379 describes multiphase compositions consisting of a polyamide and of an ethylene copolymer in the form of a polyamide matrix in which nodules (1) of an ethylene-ethyl acrylate-maleic anhydride copolymer are dispersed, and dispersed in these nodules (1) are nodules of polyamides. These nodules (1) are firstly prepared by dispersing a polyamide in the ethylene copolymer, and then these nodules are crosslinked and then dispersed in a polyamide. These compositions are also presented as having a good impact strength.
Patent FR 2,719,849 describes thermoplastic compositions consisting of a matrix of a thermoplastic polymer in which nodules of a second thermoplastic polymer, partially or totally encapsulated by an ethylene copolymer, are dispersed. These compositions are prepared by firstly encapsulating the second polymer and then the other polymer forming the matrix is added under conditions such that the capsules are not destroyed. This preparation is carried out in two steps which are completely separate or with one step following the other in the same extruder. These compositions have both good flexibility and good impact strength. The examples show PA-6, PA-12 or PBT (polybutylene terephthalate) matrices in which are dispersed nodules of PA-6,6 encapsulated by an ethylene-ethyl acrylate-glycidyl methacrylate copolymer. A comparative example shows that in a PA-6 matrix the PA-6,6 nodules encapsulated by the ethylene copolymer are coarser than the nodules formed only from the ethylene copolymer.
The present invention is therefore a thermoplastic composition comprising at least one polymer (M) forming a matrix in which are dispersed at least one polymer (S) and at least one polymer (K) and such that its tensile strength is greater than that of a composition comprising only (M) and (S), the proportion by weight of (M) being the same.
In order to modify the impact properties or the flexural modulus of a polymer (M), it is necessary to add a plasticizer and/or a polymer (S) to it. The drawback of a plasticizer is that, above a certain amount, it exudes and therefore the properties are not preserved. If the amount of (S) is increased too much, there may be compatibility problems and another property may also be affected. For example, if the amount of (S) in (M) is increased, a decrease in the flexural modulus is indeed obtained, but there is a reduction in the tensile strength, which may also be expressed by a decrease in the burst strength of an extruded tube.
The Applicant has therefore discovered that, by adding a polymer (K) to a mixture of (S) in (M), the tensile strength was improved. More specifically, by replacing a part of (S) by (K), so as to maintain the flexural modulus, an improvement in the tensile strength was obtained. This strength may be measured by the stress at 50% elongation according to ISO R527. It may also be manifested by the burst stress of an extruded tube, measured at 23° C. according to NFR 12632.
These properties may also be expressed by the burst modulus/flexural modulus ratio.
The Applicant has observed that the mixture of (M)+(S)+(K) was in the form of a matrix (M) and a dispersed phase comprising nodules of (K), nodules of (K) entirely or partly encapsulated in (S), and nodules of (S).
By choosing polymers (K) which are very compatible with (S), a dispersed phase of (K) and (S) in (M) is obtained, this dispersed phase essentially consisting of nodules of (K) entirely or partly encapsulated in (S), and, in addition, by choosing (K) and (M) from the same family (for example, two polyamides or two polyesters) and to be preferably very similar, for example PA-11 and PA-12, these encapsulated nodules may be smaller than the nodules of (S) in (M).
This is all the more so for essentially equal amounts of dispersed phase.
Thus, these compositions are also very useful for the transparent polymers (M) which can be used, for example, to make packaging, pipes of which the contents must be visible, tanks in which the level must be visible, or protective films.
For a transparent polymer (M), the increase in the amount of (S) in order to decrease the flexural modulus may also, depending on the nature of (S), cause a decrease in the transparency.
According to the present invention, although nodules of (M) remain in the (M)+(S)+(K) mixtures, the number of these nodules is not sufficient to impair the transparency, most of the nodules being nodules of (K) encapsulated entirely or partly in (S) having a smaller size than the nodules of (S) in (M) [lacuna] the transparency of (M)+(S)+(K) is superior than the transparency of (M)+(S), at the very least for a constant proportion of (M).
The polymer (M) may be a mixture of several miscible polymers forming a homogeneous phase. The same applies to the polymer (K) and the polymer (S). The compositions of the invention may also comprise several types of encapsulated nodules, for example nodules of (K1) which are encapsulated in (S) and nodules of (K2) which are encapsulated in (S) or else nodules of (K1) which are encapsulated in (S1) and nodules of (K2) which are encapsulated in (S2).
Thus, for example, it has been discovered that the nodules of an ethylene/alkyl acrylate/maleic anhydride copolymer in a nylon-11 (PA-11) matrix have a size of 0.2 &mgr;m while, in the same matrix, the nodules of nylon-12 (PA-12) which are encapsulated in the same ethylene/alkyl acrylate/maleic anhydride copolymer have a size of 0.07 &mgr;m (this is the size Dv (volume diameter) of the nodule together with the capsule, i.e. approximately the external diameter of the capsule).
The compositions of the invention have many advantages:
they are more stable;
they are essentially as flexible as the compositions of (M) comprising nodules containing only (S) since the polymer (K) may be screened with a sufficient thickness of capsule (S). We will return to this point later in the text;
the finer morphologies also increase the strength of reweld lines;
they are very easy to manufacture, simply by mixing (M), (K) and (S), for example in a short or barely plasticating extruder (standard or bottom-of-the-range extruder) or even directly in an injection moulding machine, while in the prior art it is necessary to make them in 2 steps;
they have good impact strength;
(M) need only be, relatively, the major phase in order for it to be the matrix and to avoid phase inversion. For example, it would therefore be possible to have 35 parts of (M), 32.5 parts of (S) and 32.5 parts of (K); and
in addition to these compositions being particularly stable, they may be prepared and sold in the form of granules and used in conventional machines, and may also be recycled, for example if there is manufacturing scrap due to cutting operations.
The polymers (
Guibouin Chrystelle
Hert Marius
Montanari Thibaut
Perret Patrice
Roumilhac Didier
Atofina
Pennie & Edmonds LLP
Woodward Ana
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