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
2001-08-16
2003-09-02
Short, Patricia A. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S437000, C525S509000, C525S519000
Reexamination Certificate
active
06613847
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates to improved melt-flow liquid crystalline polymer compositions (LCPs) with unusually high toughness.
2. Background of the Invention
Liquid crystalline polymer compositions are known in the art by various terms, including “liquid crystal” and “anisotropic melts.” LCPs are known to have exceptionally high tensile strength and modulus compared to analogous polymers not having a liquid crystalline character. LCPs are useful in many applications, including molding resins for a variety of electrical parts, and for other uses such as films. While LCPs are known for their ability to flow under difficult molding conditions, in some instances such as for encapsulating electronic components, the melt viscosities of normal molding grade LCPs are too high.
Generally speaking, the melt viscosity of any given LCP is most affected by the polymer molecular weight, the lower the molecular weight the lower the melt viscosity. While low molecular weight LCPs can be synthesized directly by condensation polymerization, this method may have some drawbacks. The polymer produced may have a tendency to increase in molecular weight (MW) during melt processing by continuation of the melt condensation process. At extremely low viscosity levels of 50 Pa*s or less, these LCPs are very brittle. Additionally, the handling of such low molecular weight polymers in processes designed to produce molding grade polymers can be problematical.
European Patent Application 376,615 describes a method of preparing a LCP with a relatively low melt viscosity by mixing 100 parts of a high molecular weight LCP with 1-100 parts, preferably 10-40 parts, of a low molecular weight LCP with MW about 1000 to 7000, preferably between 1000-4000. This method requires production of an unusual low molecular weight LCP using special equipment, since the low molecular weight LCP material is not readily commercially available at a MW range of 1000 to 7000.
U.S. Pat. No. 4,434,262 describes an improved melt processable blend of a major amount of polyester or polyolefin with a low MW liquid crystalline compound preferably below 1000 molecular weight. The liquid crystalline compound does not chemically react with the polyolefin or the polyester component in the melt blend. Melt viscosity reductions of 25% to 75% were obtained by adding 10 parts by weight of the liquid crystalline compound to 90 parts by weight of polyolefin or polyester.
Accordingly, it is an object of this invention to provide a method for improving the melt viscosity or fluidity of an LCP, as well as an LCP resin composition having improved melt-viscosity, or fluidity, that can be efficiently fabricated into an article having a small thickness or an intricate shape at lower processing temperatures, while still maintaining the original strength, rigidity, and elongation characteristics of the parent LCP.
SUMMARY OF THE INVENTION
A composition having improved fluidity and excellent toughness characteristics, comprising: a thermotropic liquid crystalline polymer and about 5 to about 250 milli equivalents of the liquid crystalline polymer, of a functional compound per kilogram whose functionality is selected from the group consisting of hydroxyl, carboxyl, carboxylate, ester, and primary or secondary amine.
The invention also relates to a practical method for the production of a lower melt-viscosity thermotropic liquid crystalline polymer by combining under reaction conditions, the liquid crystalline polymer with a functional compound, at a ratio of about 5 to about 250 milli equivalents of functional compound per kilogram of the liquid crystalline polymer. The functional compound is selected from the group consisting of hydroxyl, carboxyl, carboxylate, ester, and primary or secondary amine.
The present invention further relates to a method for improving the fluidity of a liquid crystalline polymer by combining the liquid crystalline polymer with about 5 to about 200 milli equivalents per kilogram of said liquid crystalline polymer of a functional compound, whose functionality is selected from the group consisting of hydroxyl, carboxyl, carboxylate, ester, and primary or secondary amine, at a temperature sufficient to cause reaction of said functional compound with said liquid crystalline polymer, and for a period of time sufficient to cause at least a 10% lowering of a melt viscosity of said liquid crystalline polymer when measured at a shear rate of 1000 sec
−1
.
DETAILS OF THE INVENTION
LCP Component
Thermotropic liquid crystalline polymers are known in the art by various terms, including “liquid crystal” and “anisotropic melts.” Liquid crystalline polymers are prepared from monomers which are generally long, flat, and fairly rigid along the axis of the molecule and have chain extending linkages that are either coaxial or parallel. Whether or not a polymer is in a liquid crystal state can be determined by known procedures for determining optical anisotropy. A polymer is optically anisotropic if, in the melt phase, it transmits light when examined between crossed polarizers utilizing a polarizing microscope. A thermotropic liquid crystalline polymer herein is given its conventional meaning, is an LCP by the TOT test described in U.S. Pat. No. 4,075,262, which is hereby included by reference. The LCP polymers useful herein include polyesters, poly(ester-amides), poly(ester-imide), poly(ester-amide-imide), polyazomethines, or mixtures thereof. Any thermotropic LCP may be used in these compositions and processes.
Preferred thermotropic LCPs are polyesters or poly(ester-amides), and it is especially preferred that the polyester or poly(ester-amide) is partly or fully aromatic. By aromatic polyesters is meant that the carbon atom and oxygen atom, —C(O)O— (bolded in this formula), of the ester linkages, are bonded to carbon atoms which are part of aromatic rings.
Functional Compounds
The functional compounds used herein may be mono-, di-, trifunctional, etc. The functionality for any particular functional compound should preferably be the same functional group if more than one functional group is present. It is also preferred that the functional group is bound directly to a carbon atom of an aromatic ring. More than one functional compound may be used, so long as the total amount of functional compound added is within the range of about 5 to about 250 milli equivalents per kilogram (meq/kg) of LCP. The functional compound may contain other substitutents, so long as these substitutents do not interfere with the process of reducing the LCP viscosity.
Useful functional compounds include hydroquinone, 1-naphthol, bisphenol-A, 1,6-hexanediaminecarbamate, terephthalic acid, trimesic acid, 2,6-naphthalene dicarboxylic acid, 1-napthoic acid, sodium benzoate, dimethyl terephthalate, hudroquinone diacetate, 6-hydroxy-2-napthoic acid, 4-aminophenol, hexamethylenediammonium adipate, 1,4-cyclohexanedicarboxylic acid, cyclohexanoic acid, 1,12-dodecanedicarboxylic acid, 4,4′-biphenol, 1,6-hexanediamine, 4-sulfoisophthalic acid, and isophthalic acid. The preferred functional groups are hydroxyl and amine, with hydroxyl and carboxyl being particularly preferred because they are surprisingly more effective at reducing viscosity on an equivalent basis. The preferred functional compounds are mono-functional or di-functional with di-functional being more preferred. However, if it is desired to also introduce branching or crosslinking into the LCP while lowering its viscosity, tri- or higher functional compounds are used. Preferably, the functional compound has a molecular weight of about 100 to about 300 grams per mole.
Besides the useful functional compounds listed above, compounds that readily generate the appropriate functional groups in the list for reducing the LCP viscosity are also included within the definition of useful groups. For instance, amine carbamates generally readily decompose thermally to their respective amines, and are therefore considered herein as amines.
An important factor in the choice of the funct
E. I. du Pont de Nemours
Short Patricia A.
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