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
1999-09-24
2001-04-03
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...
C525S071000, C525S238000
Reexamination Certificate
active
06211298
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is related to rubber-modified monovinylidene aromatic polymer compositions.
It is well known in the art that interpolymers of monovinylidene aromatic monomers and ethylenically unsaturated nitrile monomers, such as styrene-acrylonitrile, can be made more impact resistant by the inclusion of elastomeric materials (rubbers) into the matrix or continuous phase of the composition. Typically, the rubber, such as polybutadiene, is in the form of discrete rubber particles having amounts of the matrix interpolymer graft-polymerized to the rubber particles.
It is also well known in the art that the physical properties of these types of compositions are greatly affected by the relative amounts of rubber particles having different sizes and particle structures or morphologies. Larger rubber particles having diameters greater than about 0.5 micron (&mgr;m) generally improve impact resistance, but tend to reduce the gloss. Smaller rubber particles tend to increase gloss but offer less impact resistance. In addition, there is gloss sensitivity to consider, wherein gloss is reduced due to inadequate molding pressure in molding operations.
Additionally, it is known that grafted rubber particles containing occlusions of matrix polymer, provide more impact resistance than the same amount of rubber present as grafted, solid rubber particles. Such grafted, occlusion-containing rubber particles are usually produced in a mass polymerization process. Occlusion-containing particles produced in such mass processes are hereafter referred to as “mass particles”.
Solid or non-occluded grafted rubber particles are typically produced by emulsion polymerization of a rubber in the form of an aqueous latex. The non-occluded type of rubber particles, produced via emulsion polymerization process, are hereinafter referred to as “emulsion-particles”. When these emulsion particles have been grafted with a different, relatively rigid polymer, but still have a high rubber concentration, i.e. at least about 30 weight percent, these compositions are very suitable for blending with additional amounts of polymer, which may also contain rubber, to achieve a desired rubber content in the resultant composition. Such blendable intermediates are often referred to as “grafted rubber concentrates or “GRC's” and can be used to produce a wide variety of rubber-modified polymer compositions.
Under most circumstances, emulsion polymerization techniques are generally economically feasible only for the production of polymerized rubber particles having volume average diameters of less than about 0.3 micron. Larger particles can be made from these smaller polymerized rubber particles using other specific techniques, such as agglomeration.
Past research has been concentrated on obtaining ABS compositions having optimized physical properties by tailoring the rubber particle distributions (i.e., the sizes and types of rubber particles and the amounts of different size and/or type rubber particles) in the ABS and ABS-type compositions. See, for example, representative U.S. Pat. Nos. 3,509,237; 3,576,910; 3,652,721; 3,663,656; 3,825,621; 3,903,199; 3,903,200; 3,928,494; 3,928,495; 3,931,356; 4,009,226; 4,009,227; 4,017,559; 4,221,883; 4,224,419; 4,233,409; 4,250,271 and 4,277,574; wherein various “bimodal” particle size distributions are disclosed. As used in the art and herein, a composition having a “bimodal” particle size distribution contains two distinct groups of rubber particles, each group having a different average particle size. More recently, there have been disclosed “trimodal” rubber particle size rubber-reinforced polymer compositions wherein the rubber reinforcing ingredient takes the form of three distinct types of rubber particles.
U.S. Pat. No. 4,430,478 to Schmitt et al. and U.S. Pat. No. 4,713,420 to Henton disclose compositions, wherein relatively small and large emulsion rubber particles are used in combination with large mass rubber particles. The resulting “trimodal” compositions are characterized as having good combinations of toughness and gloss. However, Schmitt and Henton use mass rubber particles having a relatively large average particle diameter of at least 0.5 micron. Large mass particles are known to negatively affect the gloss and gloss sensitivity of the final product.
Additionally, U.S. Pat. No. 5,041,498 by Hare et al. discloses a trimodal composition which utilizes relatively small mass particles, i.e. 0.15 to 0.95 &mgr;m. However, Hare's composition is limited to compositions containing less than 30 weight percent mass rubber based on the total weight of the rubber and a maximum of 14 percent rubber in the total composition. As is known in the art, emulsion polymers are more costly to produce than mass polymers, therefore large amounts of emulsion polymers render these compositions economically disadvantaged.
Therefore, there remains a need to develop a more economical ABS-type polymer composition having excellent balance of gloss, gloss sensitivity and impact properties, wherein a high percentage of small rubber particles are obtained from a mass process.
SUMMARY OF THE INVENTION
Accordingly, the present invention is an improved rubber-modified polymeric composition comprising: (a) a continuous matrix phase comprising an inter-polymer of a monovinylidene aromatic monomer and an ethylenically unsaturated nitrile monomer and (b) from 5 to 40 weight percent, based on the total weight of said polymeric composition, of a rubber in the form of discrete rubber particles dispersed in said matrix, wherein the dispersed rubber particles comprise:
(1) at least 33 weight percent based on the total rubber content, of a mass rubber particle component having a volume average particle diameter (Dv) of from 0.15 to 0.40 micron (&mgr;m),
(2) from 15 to 67 weight percent based on the total rubber content, of a small-particle emulsion rubber component having a volume average diameter of from 0.05 to 0.30 micron; and
(3) from 0 to 35 weight percent based on the total rubber content, of a large emulsion particle rubber component having a volume average diameter of greater than 0.30 to 2.0 microns;
wherein the rubber particles of the composition have an average light absorbance ratio (LAR) of less than 1.4.
We have found that a composition containing a greater amount of small mass particles can have exceptional gloss, impact properties and reduced gloss sensitivity when the mass particles are between 0.15 and 0.40 &mgr;m and the rubber particles of the composition have an average light absorbance ratio of less than 1.4. The composition of the present invention contains a high percentage of small mass rubber particles, allowing for a more economical composition, yet maintains excellent gloss and impact properties. This composition also has improved thermal and color stability when compared to similar compositions with similar gloss and gloss sensitivity properties.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The composition of the present invention comprises a monovinylidene aromatic/ethylenically unsaturated nitrile interpolymer in a matrix or continuous phase and rubber particles dispersed in the matrix, wherein the rubber particles comprise two or three rubber particle size components.
The matrix or continuous phase of the present invention is an interpolymer comprising polymerized therein a monovinylidene aromatic monomer and an ethylenically unsaturated nitrile monomer. These compositions are generically known as SAN-type or SAN since poly(styrene-acrylonitrile) is the most common example. In general, the matrix portion of the composition comprises at least 50 percent by weight, typically at least 55, preferably at least 60, preferably at least 65, more preferably at least 70, and most preferably at least 80 percent by weight of the interpolymer.
The weight average molecular weight (Mw) of all of the matrix (ungrafted) interpolymer is typically from 50,000, preferably from 100,000, and more preferably from 140,000 to 300,000, preferably to 200,000 and most prefe
Ceraso Joseph M.
Galobardes Mercedes R.
Jones Mary Ann
Maes Dominique
Vanspeybroeck Rony S.
Asinovsky Olga
Seidleck James J.
The Dow Chemical Company
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