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
2001-11-08
2003-07-29
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...
C525S199000, C525S233000, C525S239000, C525S240000
Reexamination Certificate
active
06599982
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to extrusion of non-fluorinated melt-processable polymers which contain two or more unimodal fluoroelastomer processing aids of different Mooney viscosities.
BACKGROUND OF THE INVENTION
The melt extrusion of high molecular weight polymers, for example, hydrocarbon polymers and polyamides, into shaped structures such as tubing, pipe, wire coating or film is accomplished by well-known procedures wherein a rotating screw pushes a viscous polymer melt through an extruder barrel into a die in which the polymer is shaped to the desired form and is then subsequently cooled and solidified into a product having the general shape of the die.
In order to achieve low production costs, it is desirable to extrude the polymer at rapid rates. Higher extrusion rates may be readily obtained by increasing the rate of revolution of the extruder screw. However, this technique is subject to limitations imposed by the viscoelastic properties of the polymer substrate. Thus, at very high extrusion rates an unacceptable amount of thermal decomposition of the polymer can result. Further, extrudates having a rough surface are often obtained which can lead to formation of an undesirable pattern on the surface of the extrudate. Extrusion at elevated temperatures obviates this problem but adds to processing costs. Also, cooling of the extrudate becomes problematic. In addition, if polyolefins are extruded at temperatures near their decomposition points, polymer degradation occurs.
It is desirable, therefore, to find highly efficient means of increasing the extrusion rate without raising the melt temperature, while producing articles having smooth surfaces. Changes in extruder and die configuration can improve polymer melt flow, but these modifications are not always practical or economically feasible. Another approach involves the addition of conventional wax-type process aids which reduce bulk viscosity and in some cases improve processing properties. However, the efficiency is marginal and the high levels of additive required often adversely affect other properties.
In Blatz, U.S. Pat. No. 3,125,547, it is disclosed that the use of 0.01-2.0 wt. % of a fluorocarbon polymer that is in a fluid state at the process temperature, such as a fluoroelastomer, will reduce die pressure in extrusions of non-fluorinated polymers such as high and low density polyethylenes and other polyolefins. Further, use of this additive allows significant increase in extrusion rates without melt fracture.
More recently, improved fluoropolymer process aid compositions have been disclosed in for example, U.S. Patent Nos. 4,855,360; 5,587,429 and 5,707,569. In these fluoropolymer process aid compositions, a second additive, such as a poly(oxyalkylene) or an ionomer resin, is introduced in order to improve extrusion processability of the non-fluorinated polymer.
Various processing aids that are blends of two or more elastomeric or thermoplastic fluoropolymers have been described in the prior art. U.S. Pat. No. 4,904,735 discloses blends of a tetrafluoroethylene homo- or copolymer (which is a solid at the extrusion temperature) with either a fluoroelastomer having a Tg less than the extrusion temperature, or a crystalline fluoropolymer having a melting point below the extrusion temperature. U.S. Pat. No. 5,106,911 discloses blends of a fluoroelastomer and a crystalline vinylidene fluoride homo- or copolymer wherein the latter has a melting point less than the extrusion temperature.
U.S. Pat. No. 6,242,548 B1 discloses process aids which are multimodal fluoroplastic terpolymers having a low, high and (optionally) an ultra-high molecular weight component. U.S. Pat. No. 6,277,919 B1 discloses process aids which are multimodal amorphous or semi-crystalline fluoropolymers having at least a low molecular weight component and a high molecular weight component. The latter process aids may optionally contain a poly(oxyalkylene) polymer. The multimodal fluoropolymers may be manufactured by a variety of means. For example, a step change may be made in reaction conditions part way through a polymerization (e.g. by addition of a chain transfer agent or by changing the reactor temperature). Another method for making multimodal polymers is by intimately mixing either latexes or powder products of the separate high and low molecular weight fluoropolymer components.
SUMMARY OF THE INVENTION
It has been surprisingly discovered that process aids which are unimodal blends of a high molecular weight fluoroelastomer and a low molecular weight fluoroelastomer are more efficient process aids than the prior art fluoropolymer process aids. By “more efficient” is meant that less conditioning time is required for an extruded article to be free of melt fracture when a unimodal fluoroelastomer blend process aid of this invention is included in the extrudable composition, rather than a bimodal fluoropolymer process aid.
Accordingly, one aspect of the present invention is an extrudable unimodal fluoroelastomer composition comprising:
A) 0.001 to 10 weight percent, based on total weight of the extrudable composition, of a first unimodal fluoroelastomer having a first Mooney viscosity ML(1+10) at 121° C.;
B) 0.001 to 10 weight percent, based on total weight of the extrudable composition, of a second unimodal fluoroelastomer having a second Mooney ML(1+10) at 121° C., said second Mooney viscosity being less than said first Mooney viscosity; and
C) a non-fluorinated melt processable polymer, wherein the difference between said first and second Mooney viscosities is at least 15.
Another aspect of the invention is an extrudable composition made by a process comprising mixing together simultaneously i) 0.001 to 10 weight percent, based on total weight of the extrudable composition, of a first fluoroelastomer having a first Mooney viscosity ML(1+10) at 121° C., ii) 0.001 to 10 weight percent, based on total weight of the extrudable composition, of a second fluoroelastomer having a second Mooney ML(1+10) at 121° C., and iii) a non-fluorinated melt processable polymer, wherein the difference between said first and second Mooney viscosities is at least 15.
Another aspect of the invention is an extrudable composition made by a process comprising:
A) mixing 0.001 to 10 weight percent, based on total weight of the extrudable composition, of a first fluoroelastomer with a non-fluorinated melt processable polymer to form a pre-composition, wherein said first fluoroelastomer has a first Mooney viscosity ML(1+10) at 121° C.;
B) mixing 0.001 to 10 weight percent, based on total weight of the extrudable composition, of a second fluoroelastomer into said pre-composition to form an extrudable composition, wherein said second fluoroelastomer has a second Mooney viscosity ML(1+10) at 121° C., and wherein the difference between said first and second Mooney viscosities is at least 15.
Another aspect of the invention is an extrudable composition made by a process comprising mixing A) a first pre-composition comprising i) a first fluoroelastomer having a first Mooney viscosity ML(1+10) at 121° C. and ii) a non-fluorinated melt processable polymer, with B) a second pre-composition comprising i) a second fluoroelastomer having a second Mooney viscosity ML(1+10) at 121° C. and ii) a non-fluorinated melt processable polymer to form an extrudable composition comprising 0.001 to 10 weight percent, based on total weight of the extrudable composition, of said first fluoroelastomer and 0.001 to 10 weight percent, based on total weight of the extrudable composition, of said second fluoroelastomer, and wherein the difference between said first and second Mooney viscosities is at least 15.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to means for improving the extrusion processability of non-fluorinated melt processable polymer compositions. The term “extrusion processability” as used herein refers to the conditioning time (i.e. the elapsed time between extruder start up when extruded art
DuPont Dow Elastomers L.L.C.
Nutter Nathan M.
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