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
2002-07-03
2004-03-16
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...
C525S207000, C525S210000, C525S221000, C525S222000, C525S232000, C525S238000, C525S240000, C525S241000
Reexamination Certificate
active
06706814
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to rubber-reinforced monovinylidene aromatic polymer compositions of the type commonly referred to as “high impact polystyrene” or “HIPS” and copolymers of Acrylonitrile-Styrene-Butadiene, “ABS”. More particularly, the invention relates to such compositions, in which the rubber-reinforcing particles are produced from a specific polybutadiene rubber, have a specific particle size distribution and a process for the production of such compositions.
Rubber-reinforced polymer compositions of the HIPS type are widely used in many applications because of their ease of molding, good gloss, and generally good mechanical properties. It has been known that the specific properties of the rubbers used has a strong influence on the properties of HIPS resins. The specific attributes of the rubbers such as micro structure, molecular weight, molecular weight distribution and branching are important parameters. Many examples exist in the art that combine one or more of these attributes to improve the properties of the final product.
It has been known for some time that improved combinations of gloss, flow and mechanical properties can be achieved in such rubber-reinforced polymers by providing a so-called “bimodal” distribution in the sizes of the rubber reinforcing particles, i.e. the particles show two distinct peaks in their size distribution. This can be achieved by combining two or more such resins or components, each having a group of rubber particles having a different average particle size. Various monovinylidene aromatic polymer compositions are known having at least two groups of rubber particles wherein the groups have different average particle sizes. For example such compositions are disclosed in U.S. Pat. Nos. 4,146,589; 4,214,056 and 4,334,039, incorporated herein by reference and European Patents 0 096 447, 0 158 258 and 0 152 752.
U.S. Pat. No. 4,493,922 also discloses rubber-reinforced polystyrene compositions having certain bimodal rubber particle size distributions. The average rubber particle sizes disclosed for the groups of particles range from 2 to 8 micrometers (especially from 5 to 6 micrometers) for the group of larger particles and from 0.2 to 2.0 micrometers for the group of smaller particles. A number of methods are proposed for achieving such a bimodal particle distribution. For example, U.S. Pat. 4,153,645 discloses a method for the preparation of a HIPS-type polymer in which two polymer compositions are prepared using standard production processes, the compositions having different average particle sizes. These two polymer compositions are then mixed by a subsequent mechanical blending process.
An alternative approach to producing HIPS polymers with a bimodal rubber distribution has been to introduce feed streams of monomer and rubber at two different points in the polymerization system. This results in a polymer product which generally has a relatively broad distribution of rubber particle sizes. Examples of this approach are described in EP 0 015 752, U.S. Pat. No. 4,334,039 and EP 0 096 447. A disadvantage of such methods is that the desired mechanical properties of the resulting product can be somewhat poor and difficult to control.
Yet a another approach to a bimodal rubber particle size distribution is disclosed in U.S. Pat. No. 4,146,589 and EP 0 048 389. In this method, two prepolymer compositions are prepared containing rubber particles with different particle sizes. The prepolymer compositions are then mixed and further polymerized to provide a polymer having a bimodal rubber particle size distribution.
Other relevant references include EP-418,042 wherein the rubber comprises a partially coupled radial or star rubber, having a cis content of less than or equal to about 70 percent, JP 02762722 wherein the rubber is a mixture of a high cis polybutadiene of high molecular weight and a low cis polybutadiene of low molecular weight, and JP 95005789 wherein the rubber is a mixture of a high molecular weight polybutadiene and a low molecular weight polybutadiene, both having a cis content of greater than 80 percent. However, a desirable balance of impact strength and tensile strength is still not attained for some specific end-use applications.
A lot of work has gone into designing specific rubber particle size distribution in the finished resin through modification of rubber that is being used, modification of process variables during the manufacture of the resin, blending of different resin compositions and the like. However, very little effort is gone into understanding how the rubber molecules in rubber particles function and how their performance can be improved further.
Therefore, it is still highly desirable to obtain a rubber modified monovinylidene aromatic polymer having an improved balance of gloss, flow, impact and tensile properties for select applications.
SUMMARY OF THE INVENTION
The present invention is a rubber modified monovinylidene aromatic polymer comprising:
a) a monovinylidene aromatic polymer matrix; and
b) rubber particles dispersed therein, characterized in that the rubber particles are produced from a diene rubber having substantially linear structure containing less than one long chain branch per 10,000 carbon atoms in the polymer backbone with a solution viscosity of 5 cPoise to 1,000 cPoise and a Mooney Viscosity of from 5 to 120.
A preferred embodiment of the present invention is a rubber modified monovinylidene aromatic polymer comprising:
a) a monovinylidene aromatic polymer matrix; and
b) rubber particles dispersed therein, in the form of cellular or core-shell particles, which particles are produced from a polybutadiene rubber of substantially linear structure containing less than one long chain branch per 10,000 carbon atoms in the polymer backbone.
Another aspect of the present invention is a process for preparing a rubber-modified monovinylidene aromatic polymer comprising the steps of: (a) continuously supplying a reaction mixture comprising monovinylidene aromatic monomer and a dissolved diene rubber to a reactor means, (b) continuously polymerizing the monovinylidene aromatic monomer in the presence of the dissolved diene rubber in the reactor means under conditions whereby phase inversion subsequently occurs, (c) continuously removing from the reactor means a diene rubber-reinforced monovinylidene aromatic polymer, which process is characterized in that: (d) the diene rubber which is dissolved in the reaction mixture comprises substantially linear polybutadiene containing less than one long chain branch per 10,000 carbon atoms in the polymer backbone.
In the preferred embodiment, the process further comprises (e) the use of appropriate amounts of grafting initiators and sufficient level of agitation of the reactors to achieve desired rubber particle size distribution.
In another preferred embodiment, the process further comprises (f) the use of a rubber blend comprising two different diene rubbers to achieve desired rubber particle size and particle size distribution.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Monovinylidene aromatic polymers suitable for the present invention are those produced by polymerizing a vinyl aromatic monomer. Vinyl aromatic monomers include, but are not limited to those described in U.S. Pat. Nos. 4,666,987, 4,572,819 and 4,585,825, which are herein incorporated by reference. Preferably, the monomer is of the formula:
wherein R′ is hydrogen or methyl, Ar is an aromatic ring structure having from 1 to 3 aromatic rings with or without alkyl, halo, or haloalkyl substitution, wherein any alkyl group contains 1 to 6 carbon atoms and haloalkyl refers to a halo substituted alkyl group. Preferably, Ar is phenyl or alkylphenyl, wherein alkylphenyl refers to an alkyl substituted phenyl group, with phenyl being most preferred. Typical vinyl aromatic monomers which can be used include: styrene, alpha-methylstyrene, all isomers of vinyl toluene, especially paravinyltoluene, all isomers of ethyl styrene, propyl styrene, vinyl biphen
Dow Global Technologies Inc.
Nutter Nathan M.
LandOfFree
Monovinylidene aromatic polymers based on highly linear high... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Monovinylidene aromatic polymers based on highly linear high..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Monovinylidene aromatic polymers based on highly linear high... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3261950