CA1246820A - Non-woven articles comprised of thermotropic liquid crystal polymer fibers and method of production thereof - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Non-woven articles comprised of thermotropic liquid crystal polymer fibers and a method of production thereof are disclosed. Such non-woven articles exhibit desirable thermal stability and chemical and solvent resistance. In addition, the articles exhibit desirable multi-dimensional tensile strength and modulus.

Description

~46~3~Q

This application is related -to United States Patent No. 4,395,307 and Canadian Patent Application Serial No. 453,672.
BACKGROUND OF THE INVE~TION
The present invention relates to non-woven articles comprised of thermotropic liquid crystal polymer fibers.
Various conventional non-woven articles comprised of polymeric materials have been employed for many purposes. For example, non-woven articles have been employed as filters, electrical insulation and reinforcement for resins. However, such non-woven articles have frequently been found to not be appropriate for use in a high temperature environment (e.g., in excess of about 200C) or in an environment where the structure will come into contact with solvents or corrosive chemicals. It is therefore desirable to provide non-woven articles comprised of a .
~, 2 polymeric material which is resistant to solvents or corrosive ehemicals and also suitable for use at high temperatures.
It is known to those skilled in the art that fibers comprised of lyotropic liquid crystal polymers have been employed in the production of non-woven scrim sheets in conjunction with polyester fibers which are not capable of forming an anisotropic melt phase wherein the polyester fibers are thermally bonded to the lyotropic liquid crystal polymer fibers.
It is also known to those sXilled in the art ~hat the heat treatment of shaped articles of l iquid crystal polymers increases the melting tempera~ure, molecular weight and mecha-nical properties of the polymer. See~ for example, U.5. Patent Nos, 3,975,487; 4~183,895; and 4,247,514.

OBJECTS AND SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide non-woven articles which are resistant to thermal degra-dation.
It is also an object of the present invention to pro-vide non-woven articles which are resistant to solvent and chemical degradation.
It is further an object of the present invention to provide non-woven articles which exhibit desirable multi-dimensional tensile strength and modulus.
In accordance with one aspect of the present invention, there is thus provided a non-woven article which exhibits desir-able thermal stability and chemical and solvent resistance comprised of fibers of a polymer which is capable of forming an ani~o~rop;.~ P~. s~;d fibers being bonded together to an extent ~ufficient to impart structural integrity to said article.

__ .

In accordance with another aspect of the present inven~
tion, there is thus provided 2 method for forming a non-woven article in the form of a web or sheet which exhibits desirable thermal stability and chemical and solvent resistance comprised of fibers of a polymer which is capable of forming an anisotropic melt phase, said method comprising spray spinning said polymer in the melt phase to form a multitude of discontinuous fibers and collecting said fibers in the form of a web or sheet.

DETAILED DESCRIPTION OF THE INVENTION
Thermotropic liquid crys~al polymers are polymers which are liquid crystalline (i.e., anisotropic) in the melt phase.
These polymers have been described by various terms, including ~liquid crystalline,n nliquid crystal" and ~anisotropic.~
Briefly, the polymers of this class are thought to involve a parall~l ordering of the molecular chains. The state wherein the molecules are so ordered is often referred to either as the liquid crystal state or the nematic phase of the liquid crystal-line material. These polymers are prepared from monomers which are generally long, flat and fairly rigid along the long axis of the molecule and commonly have chain-extending linkages that are either coaxial or parallel.
Such polymers readily form liquid crystals (i.e., exhi-bit anisotropic properties) in the melt phase. Such properties may be confirmed by conventional polarized light techniques whereby crossed polarizers are utilized. More specifically, the anisotropic melt phase may be confirmed by the use of a Leitz polarizing microscope at a magnification of 4~X with the sample on a Leitz hot stage and under nitrogen atmosphere. The polymer . ~

~' ~

~f~820 is optically anisotropic; i.e., it transmits light when examined between crossed polarizers. Polarized light is transmitted when the sample is optically anisotropic even in the static state.
Those ther~otropic liquid crystal polymers suitable for use in the present invention include but are not limited to wholly aromatic polyesters, aromatic-aliphatic polyesters, aroma-tic polyazomethines, wholly and non-wholly aromatic poly(ester amide)s and aromatic polyester-carbonates.
The wholly aromatic thermotropic liquid crystal polymers are comprised of moieties which contribute at least one aromatic ring to the polymer backbone and which enable the poly-mer to exhibit anisotropic properties in the melt phase. Such moieties include ~ut are not limited to aromatic diols, aromatic amines, aromatic diacids and aromatic hydroxy acidsu Moieties which may be present in the thermotropic liquid crystal polymers employed in the present invention (wholly aromatic or non-wholly aromatic) include but are not limited to the following:
.
_ ~ ~C~
~ 0~'' ~~
E ~ ~ CH2-~O_CH2_C~2-O~ ~ ' . _ ~2~6i320 NH~ NH ~ ~ t NH ~

Preferably, the thermotropic liquid crystal polymers which are employed comprise not less than about 10 mole percent of recurring units which include a naphthalene moiety.
Preferred naphthalene moieties include 6-oxy-2-naphthoyl, 2,6-dioxynaphthalene, and 2,6-dicarboxynaphthalene.
Specific examples of suitable aromatic-aliphatic polyesters are copolymers of polyethylene terephthalate and hydroxybenzoic acid as disclosed in Polyester X7G-A Self Reinforced Thermoplastic, by W.J. Jackson, Jr., H.F. Kuhfuss, and T.F. Gray, Jr., 30th Anniversary Technical Conference, 1975 Reinforced Plastics/Composites Institute, The Society of the Plastics Industry, Inc., Section 17-D, Pages 1-4. A further disclosure of such copolymers can be found in "Liquid Crystal Polymers: I. Preparation and Properties of p-Hydroxybenzoic Acid Copolymers," Journal of Polymer Science, Polymer Chemistry Edition, Vol. 14, pp.2043-58 (1976), by W.J. Jackson, Jr. and H.F. Kuhfuss.
Aromatic polyazomethines and processes of preparing the same are disclosed in the United States Patent Nos.
3,493,522; 3,493,524; 3,503,739; 3,516,970; 3,516,971;
3,526,611; 4,048,148; and 4,122,070. Specific examples of such polymers include poly(nitrilo-2-methyl-1,4-phenyl-enenitrilo-ethylidyne-1,4-phenyleneethylidyne); polytnitrilo-2-methyl-1,4-phenylenenitrilomethylidyne-1,4-phenylene-methylidyne); and poly(nitrilo-2-chloro-1,4-phenylenenitrilomethylidyne-1,4-

2~

phenylene-methylidyne).
Aromatic polyester-car~onates are disclosed in United States Patent Mo. 4,107,143. Examples of such polymers include those consisting essentially o~ hydroxybenzoic acid units, hydroquinone units, carbonate units, and aromatic carboxylic acid units~
The liquid crystal polymers which are preferred ~or use in the present invention include thermotropic wholly aromatic polyesters~ Recent publications disclosing such poly-esters include (a) Belgian Patent Nos. 828,935 and 828,936, (b) Dutch Patent No. 7505551, (c) West German Patent Nos. 2,520,819, 2,520,820, and 2,722,120, (d) Japanese Patent Nos. 43-223, 2132-116, 3017-692, and 3021-293, (e) United States Patent Nos. 3,991,013; 3,991,014; 4,057,597; 4,066,620;
4,075,262; 4,118,372; 4,146,702; 4,153,77g, 4,156,070;
4,159,365; 4,169,933, 4,181,792; 4,188;476; 4,201,856;
4,226,970; 4,232,1~3; 4,232,144; 4,238,600; 4,245,08~;
4,267,304; 4,424,496; and 4,269,965; and (f) United Kingdom Application No. 2,002,404.
Wholly aromatic polymers which are preferred for use in the present invention include wholly aromatic polyesters and poly(ester-amide)s which are disclosed in commonly-assigned United States Patent Nos. 4,067,852; 4,083,829; 4,130,545;
4,161,470; 4,184,996; 4,219,461; 4,238,599; 4,256,624;
4,279,803; 4,337,191; 4,299,756 and 4,330,457. I'he wholly aromatic polymers disclosed therein typically are capable of forming an anisotropic melt phase at a temperature below approximately 400C, and preferably below approximately 350C.
The wholly aromatic polymers including wholly aromatic polyesters and poly(ester-amide)s which are suitable ~29~6B;2~3 for use in the present invention may be formed by a variety of ester-forming -techniques whereby organic monomer compounds possessing functional groups which, upon condensation, form the requisite recurring moieties are reacted. For instance, the functional groups of the organic monomer compounds may be carboxylic acid groups, hydroxylgroups,ester groups, acyloxy groups, acid halides, amine groups, etc. The organic monomer compounds may be reacted in the absence of a heat exchange fluid via a melt acidolysis procedure. They, accordingly, may be heated initially to form a melt solution of the reactants with the reaction continuing as the polymer particles are suspended therein. A vacuum may be applied to facilitate removal of volatiles formed during the final stage of the condensation (e.g., acetic acid or water).
Commonly-assigned United States Patent No. 4,083,829, entitled "Melt Processable Thermotropic Wholly Aromatic Polyester," describes a slurry polymerization process which may be employed to form the wholly aromatic polyesters which are preferred for use in the present invention. According to such a process, the solid product is suspended in a heat exchange medium.
When employing either the melt acidolysis procedure or the slurry procedure of United States Patent No. 4,083,829, the organic monomer reactants from which the wholly aromatic polyesters are derived may be initially provided in a modified form whereby the usual hydroxy groups of such monomers are esterified (i.e., they are provided as lower acyl esters~O The lower acyl groups pre-ferably have frc~ about two to about our carbon atoms. Pre-ferably, the aceta~e esters of organic ~onomer reactants are provided.
Representative catalysts which optionally may be employed in either th~ melt acidolysis procedure or in the slurry procedure of U.S. Patent No. 4,083,829 include dialkyl tin oxide (e.g., dibutyl tin oxide) ! diaryl tin oxide, titanium dioxide, antimony trioxide~ alkoxy titanium silicates, I itanium alkoxides, alkali and alkaline earth metal salts of carboxylic acids (e.g., zinc acetate3, the gaseous acid catalysts such as Lewis acids (e.y., BF3), hydrogen halides ~e.g., HCl), etc. The quantity of catalyst utilized typically is about O.OOl to l percent by weight based upon the total monomer weight, and most commonly about O.Ol to 0.2 percent by weight.
The wholly aromatic polymers suitable for use in the present invention 1:end to be substantially insoluble in common solvents and accordingly are not susceptible to solution proces-sing. As discussed previously, they can be readily processed by common melt processing techniques. Most suitable wholly aromatic polymers are soluble in pentafluorophenol to a limited degree.
The wholly aromatic polyesters which are preferred for use in the present invention commonly exhibit a weight average molecular weight of about 2jO00 to 200,000, and preferably about lO,000 to 50,000, and mo~t preferably about 20,000 to 25,000.
The wholly aromatic poly~ester-amide)s which are preferred com-monly exhibit a molecular weight of about 5000 to 50,000 and preferably about lO,000 to 30,000; e.g., 15,000 to l7,000. Such molecular weight may be dete~;n~d b gel pe~e~t ion ~h~m~

.~ _ ~Zf~ 320 graphy as well as by standard techniques not involving the solutioning of the polymer, e.g., by end group determination via infrared spectroscopy on compression molded films.
A]ternatively, light scattering techniques in a pentafluoro-phenol solution may be employed to determine the molecular weight.
The wholly aromatic polyesters and poly(ester-amide)s additionally commonly exhibit an inherent viscosity (i.e., I.V.) of at least approximately 2.0 dl./g., e.g., approximately 2.0 to 10.0 dl./g., when dissolved in a concentration of 0.1 percent by weight in pentafluorophenol at 60C.
Especially preferred wholly aromatic polymers are those which are disclosed in above-noted United States Patent Nos. 4,161,470, 4,184,996, 4,219,461, 4,238,599, 4,256,624 and 4,330,457.
For the purposes of the present invention, the aromatic rings which are included in the polymer backbones of the polymer components employed in the present invention may include substitution of at least some of the hydrogen atoms present upon an aromatic ring. Such substituents include alkyl groups of up to four carbon atoms; alkoxy groups having up to four carbon atoms; halogens; and additional aromatic rings, such as phenyl or substituted phenyl. Preferred halogens include fluorine, chlorine, and bromine. Although bromine atoms tend to be released from organic compounds at high temperatures, bromine is more stable on aromatic rings than on aliphatic chains, and therefore is suitable for inclusion as a possible substituent on the aromatic rings.
The wholly aromatic polyester which is disclosed in United States Patent No. 4,161,470 is a melt processable wholly aromatic dr~

polyester capable of forming an anisotropic melt phase at a tem-perature below approximately 350C. The polyester consists essentially of the recurring moieties I and II wherein:

I is ~ and II is ~ ~ c~ .

The polyester comprises approximately 10 to 90 mole percent of moiety I, and approximately 10 to 90 mole percent of moiety II.
In one embodiment, moiety II is present in a concentration of approximately 65 to 85 mole percent, and preferably in a con-centration of approximately 70 to 80 mole percent, e.g~, approxi-mately 75 mole percent. In another embodiment, moiety II is present in a lesser proportion of approximately 15 to 3~ mole percent, and preferably in a concentration of approximately 20 to 30 mole percent. In addition, at least some of the hydrogen atoms present upon the rings optionally may be replaced by sub-stitution selected fra~ the group consisting of an alkyl group of 1 to 4 carbon atoms, an alkoxy group of 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl, and mixtures thereof.
The wh~lly aromatic polyester which is disclosed in UOS~ Patent ND. 4,184,996 is a melt processable wholly aromatic polyester capable of forming an anisotropic melt phase at a tem-perature below approximately 325C. The polyester consists essentially of the recurring moieties I, II, and III wherein;

l~s ~-'?~~

s~

~LZ4~GB20 II is ~ I ~ , and III is The polyester comprises approximately 30 to 70 mole percent of moiety I. The polyester preferably comprises approximately 40 to 60 mole percent of moiety I, approximately 20 to 30 mole percent of moiety II~ and approximately 20 to 30 mole percent of moiety III. In addition, at least some of the hydrogen atoms present upon the rings optionally may be replaced b~ substitution selected from the group consisting of an alkyl group of 1 to 4 carbon atoms, an alkoxy group of 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl, and mixtures thereof.
The wholly aromatic polyester which is disclosed in U.S. Patent No. 4,238,599 is a melt processable polyester capable of forming an anisotropic melt phrase at a temperature no higher than approximately 320C. consisting essentially of the recurring moieties I, II, III and IV wherein:

Iis `E'~'l~ , II is ~H~ H H ~ ~0~

III is ~ and --~Z4~21~

E~
IV is ~ , where R is methyl, chloro, bromo, or mixtures thereof, and is substituted for a hydrogen atom present upon the aro-matic ring, and wherein said polyester ~omprises approximately 20 to 60 mole percent of moiety I, approximately 5 to 18 mole percent of moiety II, approximately 5 to 35 mole percent of moiety III, and approximately 20 to 40 mole percent of moiety IY. The polyester preferably comprises approximately 35 to 45 mole percent of moiety I, approximately 10 to 15 mole percent of moiety II, approximately 15 to 25 mole percent of moiety III, and approxi mately 25 to 35 mole percent of moiety IV, with the proviso that the total molar concentration of moieties II and III is substan-tially identical to that of moiety IV. In addition, at least some of th~ hydrogen atoms present upon the rings optionally may be replaced by substitution selected from the group consisting of an alkyl group of 1 to 4 carbon atoms, an alkoxy group of 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl, and mixtures thereof. This wholly aromatic polyester commonly exhibits an inherent viscosity of at least 2.0 dl./g., e.g., 2.0 to 10.0 dl./g., when dissolved in a concentration of 0.1 weight/volume percent in pentafluorphenol at 60C.
The polyester disclosed in U.S. Patent No. 4,219,461 is a melt processable wholly aromatic polyester which is capable of forming an anisotropic melt phase at a temperature below approxi-mately 320C. The polyester consists essentially of the recurring moieties I, II, III, and IV wherein:

~ 6820 I is II i~ ~ c III is a dioxy aryl moiety of the formula ~O-Ar-O~
wherein Ar is a divalent radical comprising at least, one aromatic ring, and o IV is a dicarboxy aryl moiety of the formula ~C-Ar'-C~
where Ar' is a divalent radical comprising at least one aromatic ring, and wherein the polyester ~omprises approximately 20 to 40 mole per-cen~ of moiety I, in excess of 10 up to about 50 mole percent of moiety II, in excess of 5 up to about 30 mole percent of moiety III, and in excess of 5 up to about 30 mole percent of moiety IV. The polyester preferably comprises approximately 20 to 30 (e.g., approx~mately 25) mole percent of moiety I, approximately 25 to 40 (e.g., approximately 35) mole percent of moiety II, approximately 15 to 25 (e.g. approximately 20) mole percent of moiety III, and approximately 15 to 25 (e.g., approximately 20) mole percent of moiety IV. In addition, at least some of the hydrogen ato~.s present upon the rings optionally may be replaced by substitution selected from the group consisting of an alkyl group of 1 to 4 carbon atoms, an alkoxy group of 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl, and mixtures thereof.
Moieties III and IV are preferably symmetrical in the sense that the divalent bonds which join these moieties to other ,~_ ~ I ~

2~

moieties in the main polymer chain are symmetrically disposed on one or more aromatic rings ~e.g., are para to each other or diagonally disposed when present on a naphthalene ring)~ How-ever~ non-symmetrical moieties, such as those derived from resorcinol and isophthalic acid, may also be used.
Preferred moieties II I and IV are se$ forth in above-no~ed U~S. Patent No. 4,219,461. The preferred dioxy aryl moiety III is:

_ ~~

and the preferred dicarboxy aryl moiety IV is:

~T{~~ .

The polyester disclosed in U.S. Patent No. 4,256,624 is a melt processable wholly aromatic polyester which is capable of forming an anisotropic melt phase at a temperature below approxi-mately 400C. The polyester consists essentially of the recurring moieties I, II, and III wherein:

I is ~ ~ ~ , II is a dioxy aryl moi^'y of the f~rmul~ Ar~ Yh~.-e ~' ~

Ar is a divalent radical comprising at least one aromatic ring, and III is a dicarboxy aryl moiety of the formula ~C-Ar'-C~
where Ar' is a divalent radical comprising at least one aromatic ring, and wherein the polyester comprises approximately 10 to 90 mole per-cent of moiety I, approximately 5 to 4~ mole percent of moiety II, and approximately 5 to 45 mole percent of moiety III. The polyester preferably cQmprises approximat~ly 20 to 80 mole percent of moiety I, approximately 10 to 40 mole percent of moiety II, and approximately 10 to 40 mole percent of moiety III. The polyester more preferably comprises approximately 60 to 80 mole percent of moiety I, approximately 10 to 20 mole percent of moiety II, and approximate~y 10 to 20 mole percent of moiety III. In addition, at least some of the hydrogen atoms present upon the rings opt:ionally may be replaced by substitution selected from the group consisting of an alkyl group of 1 to 4 carbon atoms, an alkoxy group of 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl, and mixtures thereof.
As with moieties III and IV of the polyester disclosed in U.S. Patent No. 4,219,461, moieties II and III of the poly-ester described immediately above may be symmetrical or nonsym-metrical, but are preferably symmetrical.
Preferred moieties ~I and III are set forth in above-noted U.S. Patent No. 4j256,624. The preferred dioxy aryl moiety II is:

~ o _~o~ , and the preferred dicarboxy aryl moiety III is:

~:~ t United States Patent No. 4,330,457 discloses a melt processable poly(ester-amide) which is capable of forming an anisotropic melt phase at a temperature below approximately 400C. The poly(ester-amide) consists essentially of the recurring moieties I, II, III and optionally IV wherein:

I is ¦ ~ C ~

II is ~C-A-C~, where A is a divalent radical comprising at least one aromatic ring or a divalent transcyclohexane radical;
III is ~Y-Ar-Z~, where Ar is a divalent radical com-prising at least one aromatic ring, Y is O, NH, or NR, and Z
is NH or NR, where R is an alkyl group of 1 to 6 carbon atoms or an aryl group; and IV is ~O-Ar'-O~, where Ar' is a divalent radical com-prising at least one aromatic ring;

~2~6~

and wherein said poly(ester-amide) comprises approximately 10 to 90 mole percent of moiety I, approximately 5 to 4S mole percent of moiety II, approximately 5 to 45 mole percent of moiety III, and approximately O to 40 mole percent of moie-ty IV. In addition, at least some of the hydrogen atoms present upon the rings optionally may be replaced by subs-titution selected from the group consisting of an alkyl group of 1 to 4 carbon atoms~ an alkoxy group of 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl, and mixtures thereof.
lQ Preferred moieties II, III and IV are set forth in above-noted United States Patent No. 4,330,457. The preferred dicarboxy aryl moiety II is:

O O
_ ~ _ , the preferred moeity III is:

t ~1 ~ O ~ or t N~

and the preferred dioxy aryl moiety IV is:

;. - 18 --- :~ - o The non-woven articles o the present invention are comprised of fibers o thermotropic liquid crystal polymers and may be prod~ced in a variety of ways. For example, a thermotro-pic liquid cxystal polymer may be spray spun onto a web or screen to provide a random ~rray of polymeric fibers. In the alterna-tive, melt spun fibers of a thermotropic liquid crystal polymer cut to appr~priately short lengths can be slurried with a liquid which is a non-solvent for the polymer (e~g., water) and subse-quently filtered (or wet-laid) onto a web ox screen to provide a random (i~e., multi-dimensional ) array of fibers.
The thus-produced random array may then be subjected to a suitable thermal bonding or heat pressing step at a suitable t~mperature to ~ond the fibers together and impart the desired structural integrity thereto. That is, the article at a minimum will support its own weight and preferahly can be pulled apart only with difficulty. In such a process the fibers are heated and pressed together for a period of time and at a pressure suf-ficient to at least bond the fibers together at the cross-over points. Such fusion bonding does not result in any significant loss of orientation (and accordingly, loss of strength) since the polymer of which the fibers is ~omprised forms an anisotropic melt phase. Such a characteristic is in direct contrast to con-ventional thermoplastic polymers which do not form an anisotropic melt phase and which readily lose their orientation upon being _~ g_ ~L~f~

heated to temperatures in excess of their melting temperature.
This is also in contrast to lyotropic liquid crystal polymers which cannot be fusion bondedO
It should be noted ~hat if the spray spun fibers are not allowed to cool sufficiently prior to being deposited on the web, the fibers will beco~e bonded together as they collect upon the web or ficreen and a formal hea~ pressing step will not he required. Polymers which are capable of forming an anisotropic melt phase are particularly suited for use in such a method since the pvlymer retains its orientation upon being spun and collected in the form of a web or sheet. The spray-spun fibers can thus be thermally bonded together to form a non-woven article having the desired degree of structural integrity withQut exhibiting a significant loss of orientation (and strength) as a result of being bonded together in the melt phase.
The above-described spray spinning and slurry filtering production processes are conventional processes for the produc-tion of non-woven articles and are well within the knowledge of one skilled in the art.
The fibers may also be bonded together by means of adhesives such as hermoplastic or thermosetting resins, epoxies, water soluble adhesives such as casine, guar gum, or polyacrylic acid, solvent-based adhesives, and emulsion or latex based adhe-sives such as styrene/butyl/acrylic copolymer systems~ The adhesives may be coated onto the web or array of thermotropic liquid crystal fibers by use of kiss rolls. In the alternative, the adhesives may be sprayed upon or deposited upon the web by known emulsion techniques (for use with wet laid paper). The use of adhesives in such methods is known and will not be discussed ~ ` ~

in greater detail herein~
The non-woven articles of the present invention possess many advantageous characteristics due to the presence of thermo-tropic liquid crystal polymers therein. That is, ~ince liquid crystal polymers are fully drawn and highly oriented as spun, the fibers which comprise the non-woven articles of the presen~
invention possess relatively high tensile strength and modulus.
Accordingly, non-woven articles comprised of such fibers simi-larly exhibit relatively high tenacity and modulus.
In addition, ~he article exhibits such tensile s~rength and modulus in a multi-dimensicnal manner due to the multi-dimensional orientation of the fibers within the structure.
The non-woven articles also benefit from other physical characteristics of thermotropic liquid crystal polymers such as resistance to chemical corrosion or solvation and high tempera-ture stability due to the high melting temperatures of the fibers. For instance, the melting temperature of the polymer is preferably in excess of 200C. and most preferably in excess of 400C. Such articles thus are well suited for use as filters in high temperature and~or otherwise destructive environments which would tend to degrade conventional filters such as treatment of stack gases from electrical generating plants. The articles can also be used to filter a variety of liquids without dissolving or being subject to corrosion or other degradative chemical pro-cesses.
A particularly interesting use for such non-woven articles i5 as the matrix material in ballistics pro~ection wear-ing apparrel. Due to the high tenacity and modulus exhibited by the liquid crystal polymers which comprise the non-w~ven ~ ,~

p~ ! ~

~2~

articles, such articles are readily adaptable to such a use~ In order to take full advanta~e of the properties of the fibers of thermotropic liquid crystal polymers, it is preferred that the non-woven article cvmprise at least a major portion ~e.q., at least about 50 percent by weight) of the fibers and preferably consists essentially of such fibers. In a most preferred embodi-ment the article consists entirely of fibers of liquid crystal polymers.
The mechanical properties of the non-woven articles produced in accordance with the present invention can be improved by subjecting the articles to a heat treatment following forma-tion thereof. me heat treatment improves the properties of the article by increasing the molecular weight of the liquid crystal-line polymer which comprises the fibers present within the article and increasing the degree of crystallinity thereof while also increasing the melting temperature of the polymer. Such heat treatment can also serve to bond the fibers together.
The articles may be thermally treated in an inert atmosphere (e.g., nitrogen, carbon dioxide, argon, helium) or alternatively, in a flowing oxygen-containing atmosphere (e.g., air). The use of a non-oxidizing substantially moisture-free atmosphere is preferred to avoid the possibility of thermal degradation. For instance, the article may be brought to a tem-perature approximately 10 to 30 centigrade degrees below the melting temperature of the liquid crystal polymer, at which tem-perature the fibers remain a solid object. It is preferable for the temperature of the heat treatment to be as high as possible without e~ualing or exceeding the melting temperature of the polymer. It is most preferable to gradually increase the tem-pera~ure o~ heat treatment in accordance with the increase of the melting temperature of the polymer during heat treatment.
The duration of the heat treatment will commonly range frcm a few minutes to a number of days~ e.g , from 0.5 to 200 hours, or more. Prefera~ly, the hea~ treatment is conducted for a time of 1 to 48 hours and typically from about ~ to 30 hours.
Generally, ~he duration of heat treatment varies -~
depending upon the heat treatment temperature; that is, a shorter treatment time is required as a higher treatment temperature is used. Thus, the duration of the heat treatment can be shortened for higher melting polymers, since higher heat treatment tempera-tures can be applied withou~ melting the polymer.
Preferably, the heat treatment i5 conducted under con-ditions sufficient to increase the melting temperature of the polymer at least 10 centigrade degrees. Most preferably, the melting temperature of the liquid crystal polymer is increased from between about 20 to about 50 centigrade degrees as a resul~
of the heat treatment. The amount of increase which is obtained is dependent upon the temperature used in the heat treatment, with higher heat treatment temperatures giving greater increases.
Similar advantages can also be obtained by heat treat~
ment of the fibers prior to their incorporation into the non-woven structure. It is, however, preferable to heat treat the structure subsequent to its formation since ~he thermal bonding and heat treatment steps can then be combined.
It should be noted at this time that reference herein to a temperature below which a specific polymer may exhibit aniso~ropic properties in the melt phase is intended to refer to the ~emperature below which the polymer exhibit~ su~h pr~perties ~ a "~
prior to any heat treatment thereof.
The chemical resistance of the polymer also increases with heat treatmen~ and the solubility into pent fluorophenol, one of the rare ~ol~ents for thermotropic liquid crystal poly-mers, continuously decreases with increasing heat reatment time and eventually the material will not dissolve even minimally ~such as in amounts of Ool pexcent by weight). Accordingly, reference herein to solution characteristics of specific polymers is intended to refer to such characteristics prior to any heat treatment of the polymer~
The invention is additionally illustrated in connection with the following Example~ which are to be considered as illus-trative of the present inventionr It should be understood, however, that the invention is not limited to the ~pecific details of the Examples.

.,--~

~Z~ Q

As-spun fibers comprised of a thermotropic liquid crystal polymer consisting of 40 molc percent of a p-oxybenzoyl moiety and 60 mole percen~ of a 6-oxy-2-naphthoyl moiety are provided having a denier per filament ranging from about 7 to 10. The fibers are chopped into microfibers ranging in length from about 1/4 to 3~8 inch in length and admixed with water to form a slurry. The slurry is well stirred to achieve a uniform dispersal of the chopped fibers in the slurry.
The slurry admixture is poured into a tall Buchner filter funnel containing a disk of filter paper. The water is drained off with the aid of a vacuum leaving a random mat of chopped fibers upon the filter paper. The web is carefully removed from contact with the fiiter paper and dried. The dried web of fibers demonstrates weak structural integrity ~i.e., it barely supports its own weigh~ and is easily pulled apart).
The fibers are bound together by pressing the web between two heated plates whereupon the web is heated to approxi-mately 275C. The web is sandwiched between Kapton release films to prevent the web from sticking to the plates. The web subsequent to hot pressing exhibits substantial structural integrity and is pulled apart only with difficulty while also exhibiting textile-like draping characteristics.

Pellets ccmprised of a thermotropic liquid crystal polymer consisting of 40 mole percent of a p-oxybenzoyl moietY

and 60 mole percent of a 6-oxy-2-naphthoyl m~iety are dried for 24 hours in a warm vacuwn oven~ The pellets are then introduced into the hopper of a spray spinning unit with the temperature of the polymer subsequently being raised to 360C wi~hin ~he extruder section o the unit to provide a polymer melt. The melt is then spun from a 0.16 mill jet into an air attenuation section of the spray spinning unit where the melt is exposed to the air drag of three impinging unheated air jets and reduced to a f iber of about 50 denier per filament. The spun fiber is collected as a non-bonded mat upon a wire screen located approximately 30 inches from the jet.
Air heated to between about 200-500C. is also employed to attenuate ~he melt which results in the production of a mat of fibers which are bonded together at their cross-over points.
This bonded mat is formed by collecting the fibers on a screen located approximately 12 to 16 inches from the jet.
The princ:iples, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. The invention which is intended to be protected herein, however, is not to be construed as limited to the particular forms disclosed, since these are to be regarded as illustrative rather than restrictive. Variations and changes may be made by those skilled in the art without departing from the spirit of the invention.

-2~-_

Claims (62)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A non-woven article which exhibits desirable thermal stability and chemical and solvent resistance comprised of fib-ers of a polymer which is capable of forming an anisotropic melt phase, said fibers being bonded together to an extent suffi-cient to impart structural integrity to said article.

2. The article of claim 1 wherein said polymer is a wholly aromatic polymer.

3. The article of claim 1 wherein said polymer is a wholly aromatic polyester.

4. The article of claim 1 wherein said polymer exhibits an inherent viscosity of at least 2.0 dl./g. when dissolved in a concentration of 0.1 percent by weight in pentafluorophenol at 60°C.

5. The article of claim 1 wherein said polymer comprises not less than about 10 mole percent of recurring units which include a naphthalene moiety.

6. The article of claim 5 wherein said naphthalene moiety of said wholly aromatic polymer is selected from the group con-sisting of a 6-oxy-2-naphthoyl moiety, a 2,6-dioxynaphthalene moiety, and a 2,6-dicarboxynaphthalene moiety.

7. The article of claim 1 wherein said polymer is capable of forming an anisotropic melt phase at a temperature below approximately 400°C.

8. The article of claim 1 wherein said polymer comprises a melt processable wholly aromatic polyester which is capable of forming an anisotropic melt phase and consists essentially of the recurring moieties I, II, and III wherein:
I is , II is , and III is , and wherein said polyester comprises approximately 30 to 70 mole percent of moiety I and wherein at least some of the hydrogen atoms present upon the rings optionally may be replaced by substitution selected from the group consisting of an alkyl group of 1 to 4 carbon atoms, an alkoxy group of 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl, and mixtures there-of.

9. The article of claim 8 wherein said polyester com-prises approximately 40 to 60 mole percent of moiety I, approxi-mately 20 to 30 mole percent of moiety II, and approximately 20 to 30 mole percent of moiety II.

10. The article of claim 1 wherein said polymer comprises a melt processable wholly aromatic polyester which is capable of forming an anisotropic melt phase and consists essentially of the recurring moieties I and II wherein:

and I is , and II is , wherein said polyester comprises approximately 10 to 90 mole, percent of moiety I, and approximately 10 to 90 mole percent of moiety II and wherein at least some of the hydrogen atoms present upon the rings optionally may be replaced by substitu-tion selected from the group consisting of an alkyl group of 1 to 4 carbon atoms, an alkoxy group of 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl, and mixtures thereof.

11. The article of claim 10 wherein said polyester com-prises approximately 65 to 85 mole percent of moiety II.

12. The article of claim 10 wherein said polyester com-prises approximately 15 to 35 mole percent of moiety II.

13. The article of claim 1 wherein said polymer comprises a melt processable wholly aromatic polyester which is capable of forming an anisotropic melt phase and consists essentially of the recurring moieties I, II, and III wherein:

I is II is a dioxy aryl moiety of the formula ?O-Ar-O?
where Ar is a divalent radical comprising at least one aromatic ring, and III is a dicarboxy aryl moiety of the formula ??-Ar'-??
where Ar' is a divalent radical comprising at least one aromatic ring, and wherein said polyester comprises approximately 10 to 90 mole percent of moiety I, approximately 5 to 45 mole percent of moiety II, and approximately 5 to 45 mole percent of moiety III and wherein at least some of the hydrogen atoms present upon the rings optionally may be replaced by substitution selected from the group consisting of an alkyl group of 1 to 4 carbon atoms, an alkoxy group of 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl, and mixtures thereof.

14. The article of claim 13 wherein said polyester comprises approximately 20 to 80 mole percent of moiety I, approximately 10 to 40 mole percent of moiety II, and approxi-mately 10 to 40 mole percent of moiety III.

15. The article of claim 1 wherein said polymer com-prises a melt processable wholly aromatic polyester which is capable of forming an anisotropic melt phase and consists essen-tially of the recurring moieties I, II, III and IV wherein:

I is , II is , III is a dioxy aryl moiety of the formula ?O-Ar-O?
wherein Ar is a divalent radical comprising at least one aromatic ring, and IV is a dicarboxy aryl moiety of the formula ??-Ar'-??
where Ar' is a divalent radical comprising at least one aromatic ring, and wherein the polyester comprises approximately 20 to 40 mole percent of moiety I, in excess of 10 up to about 50 mole percent of moiety II, in excess of 5 up to about 30 mole percent of moiety III, and in excess of 5 up to about 30 mole percent of moiety IV and wherein at least some of the hydrogen atoms present upon the rings optionally may be replaced by substitution selected from the group consisting of an alkyl group of 1 to 4 carbon atoms, an alkoxy group of 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl, and mixtures thereof.

16. The article of claim 15 wherein said polyester comprises approximately 20 to 30 mole percent of moiety I, approximately 25 to 40 mole percent of moiety II, approximately 15 to 25 mole percent of moiety III and approximately 15 to 25 mole percent of moiety IV.

17. The article of claim 1 wherein said polymer comprises a melt processable poly(ester-amide) which is capable of forming an anisotropic melt phase and consists essentially of the recurring moieties I, II, III and optionally IV wherein:

I is , II is ??-Ar'-?? where A is a divalent radical comprising at least one aromatic ring or a divalent trans-cyclohexane radical;

III is ?Y-Ar-Z?, where Ar is a divalent radical comprising at least one aromatic ring, Y is O, NH, or NR, and Z is NH or NR, where R is an alkyl group of 1 to 6 carbon atoms or an aryl group; and IV is ?O-Ar'-O?, where Ar' is a divalent radical comprising at least one aromatic ring;
and wherein said poly(ester-amide) comprises approximately 10 to 90 mole percent of moiety I, approximately 5 to 45 mole percent of moiety II, approximately 5 to 45 mole percent of moiety III, and approximately 0 to 40 mole percent of moiety IV and wherein at least some of the hydrogen atoms present upon the rings optionally may be replaced by substitution selected from the group consisting of an alkyl group of 1 to 4 carbon atoms, an alkoxy group of 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl, and mixtures thereof.

18. The article of claim 1 wherein said polymer has been subjected to a heat treatment for a period of time and at a temperature sufficient to increase the melting temperature of the polymer between about 20 to 50 centigrade degrees.

19. The article of claim 18 wherein said polymer has been subjected to a heat treatment after formation of said article.

20. The article of claim 18 wherein said heat treat-ment temperature ranges from about 10 to about 30 centigrade degrees below the melting temperature of the polymer.

21. The article of claim 20 wherein said period of time ranges from about 0.5 to about 200 hours.

22. The article of claim 21 wherein said period of time ranges from about 1 to about 48 hours.

23. The article of claim 22 wherein said period of time ranges from about 5 to about 30 hours.

24. The article of claim 18 wherein said heat treat-ment occurs in a non-oxidizing atmosphere.

25. The article of claim 24 wherein said atmosphere is substantially moisture-free.

26. The article of claim 24 wherein said heat treat-ment occurs in a nitrogen atmosphere.

27. The article of claim 1 which is in the form of a sheet.

28. The article of claim 1 which consists essentially of fibers of a polymer which is capable of forming an anisotropic melt phase.

29. The article of claim 1 wherein said polymer has a melting temperature in excess of about 200°C.

30. The article of claim 29 wherein said polymer has a melting temperature in excess of about 400°C.

31. The article of claim 1 wherein said fibers are thermally bonded together.

32. The article of claim 1 wherein said fibers are bond-ed together by means of an adhesive.

33. A method for forming a non-woven article in the form of a web or sheet which exhibits desirable thermal stabil-ity and chemical and solvent resistance comprised of fibers of a polymer which is capable of forming an anisotropic melt phase, said method comprising spray spinning said polymer in the melt phase to form a multitude of discontinuous fibers and collecting said fibers in the form of a web or sheet the fibres being bonded together to an extend sufficient to impart structural integrity to said article.

34. The method of claim 33 wherein said fibers are collected on a screen.

35. The method of claim 33 wherein said fibers become thermally bonded together as they are collected.

36. The method of claim 33 wherein said fibers are ad-hesively bonded together subsequent to being collected.

37. The method of claim 33 wherein said polymer is a wholly aromatic polymer.

38. The method of claim 33 wherein said polymer is a wholly aromatic polyester.

39. The method of claim 33 wherein said polymer exhi-bits an inherent viscosity of at least 2.0 dl./g. when dissolved in a concentration of 0.1 percent by weight in pentafluorophenol at 60°C.

40. The method of claim 33 wherein said polymer com-prises not less than about 10 mole percent of recurring units which include a naphthalene moiety.

41. The method of claim 40 wherein said naphthalene moiety of said wholly aromatic polymer is selected from the group consisting of a 6-oxy-2-naphthoyl moiety, a 2,6-dioxynaphthalene moiety, and a 2,6-dicarboxynaphthalene moiety.

42. The method of claim 33 wherein said polymer is capable of forming an anisotropic melt phase at a temperature below approximately 400°C.

43. The method of claim 33 wherein said polymer com-prises a melt processable wholly aromatic polyester which is capable of forming an anisotropic melt phase and consists essen-tially of the recurring moieties I, II, and III wherein:
I is , II is , and III is , and wherein said polyester comprises approximately 30 to 70 mol percent of moiety I and wherein at least some of the hydrogen atoms present upon the rings optionally may be replaced by substitution selected from the group consisting of an alkyl group of 1 to 4 carbon atoms, an alkoxy group of 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl, and mixtures thereof.

44. The method of claim 43 wherein said polyester comprises approximately 40 to 60 mole percent of moiety I, approximately 20 to 30 mole percent of moiety II, and approxi-mately 20 to 30 mole percent of moiety III.

45. The method of claim 33 wherein said polymer comprises a melt processable wholly aromatic polyester which is capable of forming an anisotropic melt phase and consists essen-tially of the recurring moieties I and II wherein:
I is , and II is , wherein said polyester comprises approximately 10 to 90 mole percent of moiety I, and approximately 10 to 90 mole percent of moiety II and wherein at least some of the hydrogen atoms present upon the rings optionally may be replaced by substitution selected from the group consisting of an alkyl group of 1 to 4 carbon atoms, an alkoxy group of 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl, and mixtures thereof.

46. The method of claim 45 wherein said polyester com-prises approximately 65 to 85 mole percent of moiety II.

47. The method of claim 45 wherein said polyester com-prises approximately 15 to 35 mole percent of moiety II.

48. The method of claim 33 wherein said polymer comprises a melt processable wholly aromatic polyester which is capable of forming an anisotropic melt phase and consists essentially of the recurring moieties I, II, and III wherein:
I is , II is a dioxy aryl moiety of the formula ?O-Ar-O?
where Ar is a divalent radical comprising at least one aro-matic ring, and III is a dicarboxy aryl moiety of the formula ??-Ar'-?? where Ar' is a divalent radical comprising at least one aromatic ring, and wherein said polyester comprises approximately 10 to 90 mole percent of moiety I, approximately 5 to 45 mole percent of moiety II, and approximately 5 to 45 mole percent of moiety III and wherein at least some of the hydrogen atoms present upon the rings optionally may be replaced by substitution selected from the group consisting of an alkyl group of 1 to 4 carbon atoms, an alkoxy group of 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl, and mixtures thereof.

49. The method of claim 48 wherein said polyester com-prises approximately 20 to 80 mole percent of moiety I, approxi-mately 10 to 40 mole percent of moiety II, and approximately 10 to 40 mole percent of moiety III.

50. The method of claim 33 wherein said polymer comprises a melt processable wholly aromatic polyester which is capable of forming an anisotropic melt phase and consists essentially of the recurring moieties I, II, III and IV wherein:
I is , II is , III is a dioxy axyl moiety of the formula ?O-Ar-O?
wherein Ar is a divalent radical comprising at least one aro-matic ring, and IV is a dicarboxy aryl moiety of the formula ??-Ar'-?? where Ar' is a divalent radical comprising at least one aromatic ring, and wherein the polyester comprises approximately 20 to 40 mole per-cent of moiety I, in excess of 10 up to about 50 mole percent of moiety II, in excess of 5 up to about 30 mole percent of moiety III, and in excess of 5 up to about 30 mole percent of moiety IV and wherein at least some of the hydrogen atoms pre-sent upon the rings optionally may be replaced by substitution selected from the group consisting of an alkyl group of 1 to 4 carbon atoms, an alkoxy group of 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl, and mixtures thereof.

51. The method of claim 50 wherein said polyester com-prises approximately 20 to 30 mole percent of moiety I, approximately 25 to 40 mole percent of moiety II, approximately 15 to 25 mole percent of moiety III and approximately 15 to 25 mole percent of moiety IV.

52. The method of claim 33 wherein said polymer comprises a melt processable poly(ester-amide) which is capable of forming an anisotropic melt phase and consists essentially of the recurring moieties I, II, III and optionally IV wherein:
I is , II is ??-A-?? where A is a divalent radical compris-ing at least one aromatic ring or a divalent transcyclohexane radical;
III is ?Y-Ar-Z?, where Ar is a divalent radical comprising at least one aromatic ring, Y is O, NH, or NR, and Z is NH or NR, where R is an alkyl group of 1 to 6 carbon atoms or an aryl group; and IV is ?O-Ar'-O?, where Ar' is a divalent radical comprising at least one aromatic ring;
and wherein said poly(ester-amide) comprises approximately 10 to 90 mole percent of moiety I, approximately 5 to 45 mole percent of moiety II, approximately 5 to 45 mole percent of moiety III, and approximately 0 to 40 mole percent of moiety IV and wherein at least some of the hydrogen atoms present upon the rings optionally may be replaced by substitution selected from the group consisting of an alkyl group of 1 to 4 carbon atoms, an alkoxy group of 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl, and mixtures thereof.

53. The method of claim 33 wherein said polymer is subjected to a heat treatment for a period of time and at a temperature sufficient to increase the melting temperature of the polymer between about 20 to 50 centigrade degrees subsequent to formation of said article.

54. The method of claim 53 wherein said heat treatment temperature ranges from about 10 to about 30 centigrade degrees below the melting temperature of the polymer.

55. The method of claim 54 wherein said period of time ranges from about 0.5 to about 200 hours.

56. The method of claim 55 wherein said period of time ranges from about 1 to about 48 hours.

57. The method of claim 56 wherein said period of time ranges from about 5 to about 30 hours.

58. The method of claim 53 wherein said heat treatment occurs in a non-oxidizing atmosphere.

59. The method of claim 58 wherein said atmosphere is substantially moisture-free.

60. The method of claim 58 wherein said heat treatment occurs in a nitrogen atmosphere.

61. The method of claim 33 wherein said polymer has a melting temperature in excess of about 200°C.

62. The method of claim 61 wherein said polymer has a melting temperature in excess of about 400°C.