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
2001-05-09
2002-09-03
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...
C525S316000
Reexamination Certificate
active
06444752
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”. 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 for some time that improved combinations of gloss 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. See for example U.S. Pat. Nos. 4,146,589, 4,214,056 and 4,334,039 and European Patents 0 096 447, 0 158 258 and 0 152 752 which disclose such compositions.
U.S. Pat. No. 4,493,922 also discloses rubber-reinforced polystyrene compositions having bimodal rubber particle size distributions. The average rubber particle sizes disclosed for the groups of particles are 2 to 8 micrometers (especially from 5 to 6 micrometers) for the group of larger particles and 0.2 to 2.0 micrometers for the group of smaller particles.
As mentioned, a number of methods are proposed for achieving such a bimodal particle distribution. For example, U.S. Pat. No. 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 fairly broad spread of rubber particle sizes. Examples of this 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 mechanical properties of the resulting product can be somewhat poor and difficult to control.
Yet a further approach 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 particle size distribution.
Other references in this area 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 structure of greater than 80%. However, a desirable balance of impact strength and tensile strength is still not attained for some specific applications.
Therefore, it is still desirable to obtain a rubber modified monovinylidene aromatic polymer having an improved balance of 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,
b) rubber particles dispersed therein, characterized in that the rubber particles are produced from a dine rubber having I) from 20 to 80 percent, based on the total weight of said rubber particles, of a high solution viscosity component having a viscosity value ranging from 110 to 500 centipoise and II) from 80 to 20 percent, based on the total weight of said rubber particles, of a low solution viscosity component having a viscosity value ranging from 1 to 100 centipoise, further characterized in that the ratio of solution viscosity of high solution viscosity component to the solution viscosity of low solution viscosity ranges from 1.1 to 500, wherein both components I and II have a 1,4 cis content of greater than 30 percent, and III) the rubber is grafted with monovinylidene aromatic polymer to the extent that there is at least 30 percent monovinylidene aromatic polymer present as grafts on the rubber.
In a preferred embodiment the present invention is a rubber modified monovinylidene aromatic polymer comprising:
a) a monovinylidene aromatic polymer matrix,
b) rubber particles dispersed therein in the form of small and large particles, wherein the volume average particle diameter of the small particles is from about 0.1 to about 2 micrometers and the volume average particle diameter of the large particles is from about 2 to about 6 micrometers, characterized in that the rubber particles are produced from a diene rubber having I) from 20 to 80 percent, based on the total weight of said rubber particles, of a high solution viscosity component having a viscosity value ranging from 110 to 500 centipoise and II) from 80 to 20 percent, based on the total weight of said rubber particles, of a low solution viscosity component having a viscosity value ranging from 1 to 100 centipoise, further characterized in that the ratio of solution viscosity of high solution viscosity component to the solution viscosity of low solution viscosity ranges from 1.1 to 500, wherein both components I and II have a 1,4 cis content of greater than 30 percent, and III) the rubber is grafted with monovinylidene aromatic polymer to the extent that there is at least 30 percent monovinylidene aromatic polymer present as grafts on the rubber, wherein the amount of rubber in the polymer represents about 2 to 20 percent based on the total weight of the polymer.
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 has I) from 20 to 80 percent, based on the total weight of said diene rubber, of a high solution viscosity component having a viscosity value ranging from 120 to 500 centipoise and II) from 80 to 20 percent, based on the total weight of said diene rubber, of a low solution viscosity component having a viscosity value ranging from 1 to 100 centipoise, further characterized in that the ratio of solution viscosity of high solution viscosity component to the solution viscosity of low solution viscosity ranges from 1.2 to 500, wherein both components I and II have a 1,4 cis content of greater than 30.
In a preferred embodiment, the process further comprises (e) wherein the process conditions prior to phase inversion are adjusted to produce different groups of diene rubber particles from the high and low molecular weight components of the diene rubber, each group having a different average rubber particle size.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Monovinylidene aromatic polymers suitable for the present i
Demirors Mehmet
Maughon Dianne J. M.
Rego Jose M.
Schrader David
Asinovsky Olga
Seidleck James J.
The Dow Chemical Company
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