Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-01-31
2001-08-21
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
active
06277909
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
This invention relates generally to fiber reinforced resins, and to the use of thermotropic liquid crystalline polymers to improve such resins.
Shaped articles that are made from fiber reinforced thermoplastics typically are formed by a process involving one or more stages wherein the thermoplastic is melted and mechanical forces are applied. As one typical example, the thermoplastic is first melted and then conveyed along an extruder, wherein the fiber is added along with other additives such as processing aids, flame retardants, plasticizers and stabilizers. The fiber reinforced thermoplastic obtained from this first extrusion stage is then subjected to a second melt processing stage such as injection molding, wherein the polymer is melted and forced, under pressure, into a mold. A characteristic of such operations is that the fiber reinforced thermoplastic is subjected to shear forces through the conveying and mixing processes at temperatures near or above the melting point of the thermoplastic. These shear forces result in damage to the fiber, including reduction in fiber length, which reduces the mechanical properties of the article that is eventually obtained. It is generally desirable, therefore, to minimize this fiber damage, in order to provide optimum mechanical properties in the final article produced from the thermoplastic.
Various processing techniques, such as adding the glass fiber as late as possible to the process, are known in the art for reducing damage to the fibers. These techniques are not, however, always compatible with either the processing method being employed, or the equipment used to carry out the process.
This invention concerns the use of thermotropic liquid crystalline polymers (“TLCPs”) to minimize fiber damage during processing. The use of TLCPs to reduce the viscosity of thermoplastics is well known in the art. The rheology of thermoplastic/TLCP blends is complex, with numerous examples of significant negative deviations from linear mixing rules. Blends of thermoplastics and TLCP, for example, can have viscosities substantially lower than either component individually. TLCPs have even been used to reduce the viscosity of glass fiber reinforced thermoplastics. Cogswell et al. in U.S. Pat. Nos. 4,433,083 and 4,386,174, for example, reported a 5% viscosity reduction in a polysulfone resin when 10 wt. % of a miscible TLCP was added and sheared at 1000 s
−1
.
In the present invention TLCPs are added to fiber reinforced thermoplastics before the thermoplastics are processed in order to minimize the fiber damage that occurs during the processing. In contrast to Cogswell, a TLCP and thermoplastic are chosen that are at least partly immiscible. The addition of TLCP to the thermoplastic before processing minimizes the amount of fiber damage to the fiber reinforced thermoplastic during processing, when compared to the fiber damage that occurs when the fiber reinforced thermoplastic is processed without TLCP. In many instances, the addition of TLCP even increases the viscosity of the fiber reinforced thermoplastic, in further contrast to the teachings of Cogswell.
SUMMARY OF THE INVENTION
In accordance with the purpose(s) of this invention, as embodied and broadly described herein, this invention, in one aspect, relates to a melt processable, fiber reinforced polymer composition comprising: a first polymer, the first polymer being a thermoplastic polymer; a second polymer, the second polymer being a TLCP; and a reinforcing fiber; wherein: the first and second polymers have an overlapping melt processing range; and the second polymer is partly immiscible with or is immiscible with the first polymer when mixed with the first polymer within the overlapping melt processing range.
In another aspect the invention relates to a process for lessening shear-induced reduction of fiber length in a melt processable, fiber reinforced polymer composition comprising the steps of: admixing a first polymer, the first polymer being a thermoplastic polymer, with a second polymer being a TLCP, and a reinforcing fiber; and subjecting the composition to shear, wherein the first and second polymers have melt processing ranges that overlap over an overlapping melt processing range; and the second polymer is partly immiscible with or immiscible with the first polymer when mixed with the first polymer within the overlapping melt processing range.
In yet another embodiment the invention relates to a melt processable, fiber reinforced polymer composition comprising: a first polymer, the first polymer being a thermoplastic polymer; a second polymer, the second polymer being a TLCP, and a reinforcing fiber; wherein: the first and second polymers have an overlapping melt processing range; and wherein the second polymer and first polymer are present in the composition at a weight ratio of second polymer to first polymer of less than 1:10.
In still another aspect the invention relates to a process for lessening shear-induced reduction of fiber length in a melt processable, fiber reinforced polymer composition comprising the steps of: admixing a first polymer, the first polymer being a thermoplastic polymer, with a second polymer, the second polymer being a TLCP, and a reinforcing fiber; and subjecting the composition to shear, wherein: the first and second polymers have melt processing ranges that overlap over an overlapping melt processing range; and the composition is subjected to over 1000 s
−1
units of shear.
Additional aspects and advantages of the invention will be set forth in part in the description that follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
DESCRIPTION OF THE INVENTION
The present invention may be understood more readily by reference to the following detailed description of the invention and to the examples included herein. Before the present compounds, compositions and methods are disclosed and described, however, it is to be understood that this invention is not limited to specific methods, or to particular compositions or processing regimens, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.
It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “an aromatic compound” includes mixtures of aromatic compounds, reference to “a polyester” includes mixtures of two or more such polyesters, and the like.
References in the specification and concluding claims to parts by weight, of a particular element or component in a composition or article, denote the weight relationship between the element or component and any other elements or components in the composition or article for which a part by weight is expressed. Thus, in a compound containing 2 parts by weight of component X and 5 parts by weight component Y, X and Y are present at a weight ratio of 2:5, and are present in such ratio regardless of whether additional components are contained in the compound.
Ranges are often expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that a more preferred range is typically from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value is typically more preferred.
In this specification a
Cherry Cathy D.
Cherry Clinton
Wilson Bruce Edwin
Cain Edward J.
Cherry Cathy D.
Eastman Chemical Company
Gwinnell Harry J.
Tubach Cheryl J.
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