CA1253019A

CA1253019A - Fastening device

Info

Publication number: CA1253019A
Application number: CA000487183A
Authority: CA
Inventors: Ralph R. Miano; Frank C. Jaarsma
Original assignee: Celanese Corp
Current assignee: Celanese Corp
Priority date: 1984-07-26
Filing date: 1985-07-22
Publication date: 1989-04-25
Also published as: DE3526728A1; GB2167513A; FR2583833B1; FR2583833A1; GB2167513B

Abstract

ABSTRACT OF THE INVENTION

This invention relates to fastening devices, e.g., rivets, bolts, etc. which are fabricated from a thermotropic liquid cry-stalline polymer and which contain up to about 50% by weight of a filler material. The fastening devices are characterized by a shear strength of at least about 15,000 psi (e.g., 15,000 to 75,000 psi and higher), a tensile strength of at least 20,000 psi (e.g., 20,000 to 150,000 psi and higher), a linear coefficient of thermal expansion which is compatible with the materials to be fastened and which ranges from about -3.0 to 3.0 X 10-5 (in/in°C).
The fastening devices of this invention exhibit extremely high chemical resistance to a variety of deleterious materials. The fastening devices also exhibit a highly oriented skin. The ther-motropic liquid crystalline polymer utilized has an inherent vis-cosity of between about 1.0 and about 15 dl./g. when dissolved in a concentration of 0.1 percent by weight of pentafluorophenol at 60°C and may be fabricated from a wholly aromatic polyester, an aromatic-aliphatic polyester, a wholly aromatic poly(ester-amide), an aromatic-aliphatic poly(ester-amide), an aromatic polyazometh-ine, an aromatic polyester carbonate, etc. and mixtures thereof.

Description

;3~9 This application is related to copending Canadian patent application No. 487,182 of Frank C. Jaarsma and Ralph R.
Miano entitled "Fastening Device".
This invention relates to fastenlng devices and, more specifically, novel rivets, screws, bolts, nails and the like.
This invention provides novel fastening devices of the kind mentioned, in which such devices are made of a thermotropic liquid crystalline polymer.
The fastening devices of this invention find utility and provide advantages in an impressive number of end uses. The noteworthy properties of devices fabricated in accordance with the invention overcome and offer solutions to many fastening problems. One particular problem is encountered in the aircraft industry .
A most troublesome and severe problem confronting the aircraft industry today is effective fastening of aircraft structural skin materials, especially high-strength aluminum alloy sheets, titanium sheets and graphite fiber reinforced composite sheets. The problems include corrosion and/or exfol-iation of the aircraft structural skin materials starting at thefastener-receiving holes. While not residing exclusively in it, most of the problems can be attributed to the rivet per se.
For example, when fastening aluminum sheets, titanium or titanium/columbium alloy rivets have been substituted for Monel in order to save weight, but the titanium or titanium alloys were found to increase the corrosion rate of aluminum especially in salt spray environments and accelerated galvanic corrosion of the aluminum takes place which is apt to cause looseness of the joint. Furthermore, titanium may adsorb hyd-rogen from the galvanic action and hydrides may form thus causing failure of the rivet.

;

12~ 3 ~ 1 ~
If t~tanlum sheets are to be fastenled, alum~num rivets cannot be used although they are easy to upset and are light in weight because they corrode too rap~dly ~n the more noble t~tan~um.
Monel rivets are used for h~gh-s~rength ~e~els of shear but, as mentioned, they are heavy cD~pared to the weight of the sheets and they are harder to upset and d~stort the thin sheets when util~zed. ~hen t~tanium rivets are util~zed, they also cause unacceptable sheet distortion with thin sheets and they are app-rec~ably d~fficult to upset, thus requ~ring heavier rivet guns and bucking bars ~hich result ~n greater operator fatigue (which ~s an ~mportant factor) and are d~fficult to upset in remote places where buck~ng bars of less than ideal shape have to be used.
Metal cladding of the rivets or pDinting of the exterior surfaces of the aircraft does not eliminate this difficulty. ~hen the holes for the fasteners are drilled or punched in the struct-ural members or plates to receive the fasteners, the cladding no longer provides the desired protection for the end-grain of the high-strength base metal alloy which is then exposed ~n the walls of the fastener-receiving holes. Moisture seeps or ~s drawn into the fayed surfaces or between the fasteners and the walls of the holes and countersunk openings where the end-grain of the struct-ural material or sheets was exposed by the drill1ng (or punch~ng), for the reception of the fasteners.
~ ith pa~nt coatings, when applied to the skin surfaces, mo~s-ture penetration may be retarded or postponed to some degree but once the coat~ng becomes aged it begins to crack or flake around the fastener heads. ~his allows the moisture direct access to the crit~cal end- grain areas ~n the wblls of the holes oround the f~steners. In either case, although paint~ng has been prevlously ., recommended, s~nce ~t afforded some degree of temporary protect-ion, moisture was found to eventually penetrate, and corrosion and exfoliat~on occ~rred.

~2~.~i3~19 F~stener ~nstallation w~th a wet zinc chromate primer, or uncured fuel tank sealant has also been used but th~s did not pro-duce the des~red results~ part~cularly, ~t does not solve the problems of nonelectrical cont~nuity and te~perature var~at~ons.
Resistance to chem~cal sc1vents is of utmost i~portance for plaseic fas~eners. For example, methyleth~lketone (MEK) ~s used pr~or to paint1ng of aircraft and similar components and pa~nt str~ppers are even more of a concern due to their corrosive and solub~l~zlhg effect on convent~onal plastic fastening mater~als.
U.S. Patent Nos. 3,642.312 and 4,107.805 attempt to overcome the corrosion problem encountered when ut~li2ing alum~num r~vets by making a r~vet of h~gh-strength aluminum alloy and-then apply-~ng a soft eoat~ng of pure aluminum to the exter~or of the formed r~vet. The resulting r~vets, however, as well as the method of making them leave much to be desired ~n that the coating methods, in addit~on to being onerous, do not provide the desired ant1-corros~on character~st1cs.
Use of plastic fastening means per se as well as plastic clad metal fasteners have been contemplated by the art. For example, U.S. Patent 2,510,693 provldes for a re~nforced plastic fastening member wh~ch are fabr~cated from a plastlc mater~al hav~ng a fi-brous re~nforcing medlum there~n. The dev~ces therein are formed from stock wh~ch can be ~n the form of a sol1d or a hollow rod of a plastic mater~al wh~ch has re~nforc~ng cont~nuous fibers runn~ng substant1ally longitudinally there~n and which extend cont1nuously into the head of such fastening dev~ces.
U.S. Patent 3,076,373 d~scloses w~re-re~nforced plast~c fila-ment fasteners such as staples, etc. to overcome a corrosion pro-blem. ~hese compr~se steel or non-ferrous metal re~nforclng means contained wtth~n a plastic body. ~he plastic body ~s a ther~o-plast~c material w~th cold flow propert~es such as nylon and propylene wh~ch ~s co-extruded through suitable extrus~on dies to prov~de the desired cross-sect~onal shape and ~lso to molecularly orient the plastic ~n order to give ~ncreased tens~le strength in the linear dlrection of the f~lament as ~ell as to effect the firm bond w~th the reinforcing w~res.
U.S. Patent 3,2~2.569 dlscloses a thermoplastic coated na~l ~n wh~ch a thermoplastic mater~al such as nylon or an acryl~c res~n ~s bonded to core w~res by passage through su~table extru-slon dies ~n order to or~ent long cha~n-l~ke molecules of the thermoplast~c materidl and impart an orderly arrangement in para-llel relat~on to the extrus~on axis rather than the hapha2ard arrangement of the unoriented thermop1ast~c material.
Also well known ~n the fastener art is the problem of main-t~n~ng adequate compression or torque when assembling metal or non-metal parts to other assemblies having dissimilar coeffic~ents of thermal expansion. This problem has persisted ~n ~ndustry for many years and has previously den~ed the acceptance of mater~als in fields of appl~cat~on in wh~ch they would otherw~se f~nd great ut~lity. A part which is subjected to a compress~ve load due to the clamping action of a fastener will tend to deform over a period of t~me, as a result of a condit~on known as ~cold flow~, i.e., permanent deformat~on result~ng from prolonged application of a stress below the elastic limit of a material. This cond~t~on ts further aggravated when an assembly ~s thermally cycled and the part tends to undergo a greater expans~on than the metal fastener will perm~t due to the d~ssimilarit~es ~n thermal expans~on co-eff~c~ents. Thls is especlally true, for ~nstance, ~n the a~r-craft ~nd the automotive ~ndustr~es where assembl~es are frequen~-ly exposed to severe temperature cycles dur~ng wh~ch the mater~als are alternately subjected to thermal_expaniion and contract~on.

~3 E:3~9 In the past, various types of inserts have been employ-ed in plastic articles either by press-fitting the insert into a finished molding or by placing the insert in the cavity so that it becomes an integral part of the molding. By way of example, U.S. Patent 4,289,061 describes a fastener which is designed to collapse uniformly in an axial direction without exerting later-al forces on the part due to lateral motion of the external surface. In this manner, the insert described herein will pre-vent substantial deformation of the part while maintaining the specified compressive loading on the assembly.
It is therefore, an object of the present invention to minimize or obviate problems of the type discussed above.
A further object of the invention is to provide a fastening device which minimizes weight and bulk but provides advantageous physical and chemical properties.
Another subject is to provide a fastening device which are easily fabricated and yet exhibit desired physical and chemical properties.
FIGURE 1 depicts the shear failure mode, conducted by shear strength testing, of a fastening device.
FIGURE 2 depicts the cross-section of the shank of an extruded fastening device which presents the polymer structure of the extrudate in accordance with this invention FIGURE 3 depicts the cross-section of the shank of an injection molded fastening device which presents the polymer structure of the polymer molded in accordance with this invent-ion.
FIGURE 4 depicts a fastening device in accordance with the present invention having a second head positioned on the axial shank.

~?r5~19 71012-44 FIGURE 5 depicts a fastening device in accordance with the present invention having threads disposed on the ex-terior surface of the shank.
FIGURE 6 depicts a fastening device in accordance with the present invention wherein the head and shank are hollow along the linear axis of the fastening device.

- 5a -S UM~IARY O F TEI E I NVENT I ON
The present invention provides a one-piece fastening device formed by melt-processing of thermotropic liquid crystalline polymer containing up to about 50% by weight of a reinforcing agent whercin said therrnotropic liquid crystalline polymer is caused to f]ow comprising a head and a relatively rigid axial shank adapted to be inserted in the aperture of a workpiece characterized by a shear strength of at least about 15,000 psi and a tensile strength of at least 20,000 psi, wherein said fastening device possesses a highly oriented skin of polymer molecules which was imparted to the same during said melt-processing of said thermotropic liquid crystalline polymer to form said fasteniny device.
The present invention further provides a one-piece shapable fastening device comprising a composition of a melt-processed thermotropic liquid crystalline polymer and up to about 50% by weight of a reinforcing agent, said fastening device being in the form of a head and a relatively rigid axial shank adapted to be inserted in an aperture of a workpiece, said fastening device having a shear strength of at least about 15,000 psi and a tensile strength of at least about 20,000 psi, and possessing a highly oriented skin of polymer molecules formed during melt process shaping of said thermotropic liquid crystalline polymer to form said fastening device.
It has been found that a fastening device, e.g., a rivet, bolt, etc. can be fabricated from a thermotropic liquid crystalline polymer which contains up to about 50% by weight of a filler material. The resulting article is characterized by a shear strength of at least about 15,000 psi (e.g., 15,000 to 75,000 psi and higher), a tensile strength of at least 20,000 psi (e.g., 20,000 to 150,000 psi and higher), a linear ~2.~3~9 coefficient of thermal expansion which advantageously is compatible with the materials to be fastened and which ranges from about -3.0 to 3.0 X 10 5 (in/inC). The fastening devices of this invention also exhibit extremely high chemical resistance to a variety of deleterious materials.
Advantageously, the fastening device exhibits a highly oriented skin from which the advantages accrue. The thermotropic liquid crystalline polymer utilized has an inherent viscosity of between about 1.0 and about 15 dl./g. when dissolved in a concentration of 0.1 percent by weight of pentafluorophenol at 60C and may be fabricated from a wholly aromatic polyester, an aromatic-aliphatic polyester, a wholly aromatic poly(ester-amide), an aromatic-aliphatic poly(ester-amide), an aromatic polyazomethine, an aromatic polyester carbonate, etc. and mixtures thereof. Preferably, the liquid crystalline polymer is a wholly aromatic polyester, a wholly aromatic poly(ester-amide), or an aromatic~aliphatic poly(ester-amide), or mixtures thereof.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The polymer from which the fastening devices of the present invention is formed must be a thermotropic liquid crystalline polymer which is of the requisite molecular weight to be capable of being shaped by injection molding or melt extrusion or the like. Such thermotropic liquid crystalline polymers have been known in the art but have not prior to the present invention been recognized to be suitable for forming the presently claimed fastening devices which evidence the surprising physical and chemical properties discussed hereinlater.

6a

2~3~19 As is known in polymer technology a thermotropic liquid crystalline polymer exhbits optical anisotropy in the melt. The anisotropic character of the polymer melt may be confirmed by conventional polarized light techniques whereby cross polarizers are utilized. More specifically, the anisotropic nature of the melt phase may conveniently be confirmed by the use of a Leitz polarizing microscope at a magnification of 40X with the sample on a Leitz hot stage and under a nitrogen atmosphere. The amount of light transmitted changes when the sample is forced to flow; how-~ver, the sample is optically anisotropic even in the static state. On the contrary typical melt processable polymers do not transmit li~ht to any substantial degree when examined under iden-tical conditions.
Representative classes of polymers from which the thermo-tropic liquid crystalline polymer sutiable for use in the present invention may be selected include wholly aromatic polyesters, aromatic-aliphatic polyesters, wholly aromatic poly(ester-amides), aromatic-aliphatic poly(ester-amides), aromatic polyazomethines, aromatic polyester-carbonates, and mixtures of the same. In preferred embodiments the thermotropic liquid crystalline polymer is a wholly aromatic polyester, a wholly aromatic polyester-amide), or an aromatic-aliphatic poly(ester-amide). In such wholly aromatic polyester and wholly aromatic poly(ester-amide) each moiety present within the polymer chain contributes at least one aromatic ring. Also, it is preferred that naphthalene moieties be included in the thermotropic liquid crystalline poly-mer, e.g., 6-oxy-2-naphthoyl moiety, 2,6-dioxynaphthalene moiety, or 2,6-dicarboxynaphthalene moiety, in a concentration of not less than about 10 mole percent. The particularly preferred naphtha-lene moiety for inclusion in the thermotropic liquid crystalline ... ... .
polymer is the 6-oxy-2-naphthoyl moiety in a concentration of not less than about 10 mole percent.

~3~l9 Representative wholly aromatic polyesters which exhib-it thermotropic liquid crystalline properties include those dis-closed in the following United States Patents: 3,991,013;

3,991,014; 4,066,620; 4,067,852; ~,075,262; 4,083,829; 4,093,595;

4,118,372; 4,130,545; 4,146,702; 4,153,779; 4,156,070; 4,159,365;
4,161,470; 4,169,933; 4,181,792; 4,183,895; 4,184,996; 4,188,476;
4,201,856; 4,219,461; 4,224,433; 4,226,970; 4,230,817; 4,232,143;
4,232,144; 4,238,598; 4,238,599; 4,238,600; 4,242,496; 4,245,082;
4,245,084; 4,247,514; 4,256,624; 4,265,802; 4,267,304; 4,269,965 4,279,803; 4,299,756; 4,294,955; 4,318,841; 4,337,190; 4,337,191;
and 4,355,134. As discussed hereinafter the wholly aromatic poly-ester of U.S. Patent 4,161,470 is particularly preferred for use in the present invention.
Representative aromatic-aliphatic polyesters which exhibit thermotropic liquid crystalline properties are copolymers of polyethylene terephthalate and hydroxybenzoic acid as disclos-ed in Polyester X-7G-A Self Reinforced Thermoplastic, by W.J.
Jackson, Jr., H.F. Kuhfuss, and T.F. Gray, Jr., 30th Anniversary Technical Conference, 1975 Reinforced Plastic/Composites Instit-ute, 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, Poly-mer Chemistry Edition, Vol. 14, pages 2043 to 2058 (1976), by W.J.
Jackson, Jr. and H.F. Kuhfuss. See also commonly assigned United States Patent Nos. 4,318,842 and 4,355,133.

~ 71012-44 Representative wholly aromatic and aromatic-aliphatic poly-(ester-amides) which exhibit thermotropic liquid crystall-ine properties are disclosed in United States Patent No. 4,272, 625 and in commonly assigned United States Patent Nos. 4,330,457;
4,351,917; 4,351,918; 4,341,688; 4,355,132; and 4,339,375. As discussed hereafter the poly(ester-amide) of United States Patent No. 4,330,457 is particularly preferred for use in the present invention.
Representative aromatic polyazomethines which exhibit thermotropic liquid crystalline properties are disclosed in 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-phenylenenitriloethylidyne-1,4-phenyleneethylidyne); poly-(nitrolo-2-methyl-1,4-phenylenenitrilomethylidyne-1,4-phenylene-methylidyne); and poly(nitrilo-2-chloro-1,4-phenylenenitrilo-methylidyne-1,4-phenylenemethylidyne).
Representative aromatic polyester-carbonates which exhibit thermotropic liquid crystalline properties are disclosed in United States Patent Nos. 4,107,143 and 4,284,757, and in commonly assigned United States Patent No. 4,371,660. Examples of such polymers include those consisting essentially of p-oxy-benzoyl units, p-dioxyphenyl units, dioxycarbonyl units, and terephthoyl units.
A thermotropic liquid crystalline polymer commonly is selected for use in the formation of the fastening device of the present invention which possesses a melting temperature within the range that is amenable to melt extrusion while employ-ing commerically available equipment. For instance, thermotropic liquid crystal-line polymers commonly are selected which exhibit a melting temp-erature somewhere within the range of approximately 250 to 400C.
The thermotropic liquid crystalline polymer selected prefer-ably also 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 60C. ~e.g., an inherent viscosity of appro-ximately 1.0 to 15.D dl./g.).
The particularly preferred wholly aromatic polyester for use in the present invention is that disclosed in United States Patent No. 4,161,470 which is capable of forming an anisotropic melt phase at a temperature below approximately 350C. This polyester consists essentially of the recurring moieties I and II wherein:

_ 0 ~ , and II is --O ~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 73 mole percent. In another embodiment, moiety II is in a lesser proportion of approximately 15 to 35 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 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. Such polymer preferably has an inherent viscosity of approximately 3.5 to 10 dl./g. when dissolved in a concentration of 0.1 percent by weight in pentafluorophenol at 60C.
The particularly preferred wholly aromatic poly(ester-amide) or aromatic-aliphatic poly(ester-amide) for use in the.present invention is disclosed in commonly assigned United States Patent No. 4,330,457 which is capable of forming an anisotropic melt phase at a temperature below approximately 400C. The poly(ester-amide)s there disclosed consist essentially of recurring moieties I, II, lII, and, optionally, IV wherein:

O O
II is ~ ~ - A ~ ~ , where A is a divalent radical comprising at least one aromatic ring or a divalent trans-1,4-cyclohexylene radical;

" 11 ;3~19 III iS ~Y - Ar - Z ~ , where Ar is a div31ent radical comprising at least one aromatic ring, Y is 0, 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 ~0 - Ar' - O ~ , where Ar' is a divalent radical comprising at least one aromatic ring;

wherein at least some of the hydrogen atoms present upon the rings optionally may be replaced by substitution selected from tbe 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, and wherein said poly(ester-amide) comprises approximately 10 to 90 mole percent of moiety I, approximately 5 to 45 mole percent of moiety III, and approximately O to 40 mole percent of moiety IV. The preferred dicarboxy aryl moiety II is:

1l /~\ 1l C ~--C--and the preferred moiety III is:

NH ~ O or . NH ~ NH-and the preferred dioxy aryl moiety IV is:

0~0-- .

., ~2~;3~9 Such polymer preferably has an inherent viscosity of approximately 1.0 to 15 dl./g. when dissolved in a concentration of O.l percent by weight in pentafluorophenol at 60C.
When forming the articles of the present invention by inject-ion molding, conventional injection apparatus can be used. Suit-able injection apparatus include the Stubbe automatic injection molding machine model SKM 50/45.
The temperature and pressure conditions selected for inject-ion molding, the molten thermotropic liquid crystalline polymer will be influenced by the melting temperature of the polymer and its viscosity as will be apparent to those skilled in the art.
Typically, injection molding temperatures approximately 5C. to 50C. above the polymer melting temperature and pressures of approximately 2000 to 20,000 psi are selected. The term "Melting Temperature" as used herein is meant that at which the polymer has sufficiently low viscosity for adequate flow in the molding pro-cess.
In the injection molding of liquid crystalline polymer, melt flows into the cavity in laminar fashion, with each strata in the melt flowing at a uniform rate without substantial inter-strata mixing. When this flow strikes the downstream dead-end of the cavity and rebounds therefrom, laminar flow at this end ceases due to interference from the rebound molecular wave patterns. Since the mechanical properties of molded liquid crystalline polymer are directly related to the degree of ordered arrangement of molecules in each strata, this reverse flow may cause points of structural weakness in the molded article, detracting from its mechanical properties.

~2,;~3~9 lf desired, an outlet may be placed at the downstream end of the cavity which allows molten material to flow out of the cavity, thus preventing undesired rebound molecular wave motion ti.e., patterns) with~n t~e tavity~ In a preferred embodiment, a passage communicates with the downstream outlet so as to receive the molten material. This technique is disclosed in commonly assigned Canadian Patent Application No. 455,411.

Once the molded article is removed from the mold, the stub of material that solidifies in the passage may be shorn from the article. It is preferred to remove more than the stub of material and remove at least some material from the shank per se. Articles molded and trimmed in accordance with this latter embodiment ex-hibit mechanical properties superior to those of articles molded and the stub removed conventionally.
The fastening devices of the present invention can also be formed by melt extruding an elongated member, chopping same to a desired length and subsequently forming a head on the shank. The shank may also be extruded as a tubular elongated member. When forming the melt extruded elongated member, from which the shank is cut, conventional melt extrusion apparatus can be used wherein an extrusion die is selected having a size and shape which corres-ponds to the cross-sectional configuration of the elongated member to be formed with the exception that the orifice dimensions will be larger than the dimensions of the resulting elongated member in view of drawdown of the molten polymer which occurs immediately following extrusion. Polymers other than thermotropic liquid crystalline polymers are recognized to be incapable of melt ex-trusion to form articles of the cross-sectional area herein dis-cusse~ wherein the profile will accurately correspond to the die shape. Accordingly, the thermotropic liquid crystalline polymers do not exhibit any substantial elastic recoil upon exiting from the extrusion die as do conventional polymers which are melt ex-- 14 _ ~. G~

truded. Suitable extrusion apparatus are described, for example, in the "Plastics Engineering Handbook" of the Society of the Plastics Industry, Pages 156 to 203, 4th Edition, edited by ~oel Frados, Van Nostrand Reinho1d Company, 1976. The elongated members of the present invention optionally may be formed in accordance with the teachings of commonly assigned United States Patent No. 4,332,759 of Yoshiaki Ide, entitled "Process for Extruding Liquid Crystal Polymer".
The t~mperature and pressure conditions selected for ex-truding the molten thermotropic liquid crystalline polymer will be influenced by the melting temperature of the polymer and its vis-cosity as will be apparent to those skilled in the art, Typi-cally, extrusion temperatures approximately 0 to 30C. above the polymer melting temperature and pressures of approximately 100 to

5,000 psi are selected. In order to induce relatively high mol-ecular orientation coextensive with the length of the elongated member, the extrudate is drawn while in the melt phase immediately adjacent the extrusion orifice and prior to complete solidifi-cation. The extent of such drawdown is influenced by the takeup speed under which the elongated member is wound or otherwise collected on an appropriate support or collection device. The resulting draw ratio is defined as the ratio of the die cross-sectional area to that of the cross-sectional area of the fully solidified extrudate. Such draw ratios commonly range between 4 and 100, and preferably between approximately 10 and 50 while utilizing the equipment described in the Examples~
In addition to the drawdown, appropriate cooling must be applied to the extrudate of thermotropic liquid crystalline poly-mer intermediate the extrusion orifice and the point of collect-ion. Appropriate fluid media, e.g., a gas or a liquid, may be -- ~

to impart the desired cooling. For instance, the extrudate may be simply contacted by a stream of air or other gas or preferably immersed in a circulating hath of w~ter or other liquid which is maintained at an appropriate temperature to impart the cooling required for solidification.
The resulting cross-sectional configuration is substantiallY
uniform and can be monitored by use of a laser or other appro-priate sensing device to insure the quality control demanded by the optical.fiber cable industry. The elongated members suitable for use as shanks possess a diameter or cross-section of at ~east about 1/16 inch up to 1/2 inch or more, if desired with about 1/8 inch to about 1/4 inch being the range diameters utilized most often.
When the cross-sections of the molded or extruded fasteners, which have the desired properties in accordance with this invent-ion, are closely examined, a highly oriented skin and a relatively less oriented core are usually observed. This can be detected with either cross-polarized or scanning electron micrographs or other microscopy means. It is found that the desirable properties of the fasteners are directly correlated to the thickness of the skin.
Referring to the drawings, FIGURE 1 locates a shear failure mode on a shank 2 of a rivet 3 to which this oriented skin phen-omena pertains most particularly. FIGURES 2 and 3 show in a cross-sectional view of the shank 2, the outer "true" skin 11, the innerskin layers 12 and an unoriented core 13. The innerskin layers 12 are comprised of macro fibrils 14 of about 5 micrometer, fibrils 15 of about 0.5 micrometer and micro fibers 16 of about 0.05 micrometer.
As used herein, the term "skin" means the actual surface skin and the inner oriented areas as well. The structural model for the inner oriented areas is a hierarchical fibrillar texture ranging from about 5 micrometer down to about 5 nanometer. The finest substructural unit observed, on the molecular level, are micro fibrils on the order of about 50 nanometer by 5 nanometer for the polymers used herein. This microfibrillar texture is associated into fibrillar units (fibrils) that are an order of magni~cude larger in size; that is, about 0.5 micrometer across.
Macro units (macro fibrils), about 5 micrometer in size, are also observed. Accordingly, this hierarchy of textures characterizes the fibrillar, fiber-like, elongated and highly oriented struct-ure of the skin which affords the desired physical and chemical properties.
Several mechanisms are believed responsible for this skincore fonnation. These are: (a) yield stress of the melt;
(b) radial distribution of the total shear strain; and (c) elong-ational strain after the exit of the die. The thickness of theskin based on the above mechanisms should be at least 5 percent of the cross-section of a suitable fastener and preferably at least 10 percent of the cross-section. Thus, a fastener having a 1/4 inch shank will have an oriented skin of at least 0.0125 inch (12.5 mil) and preferably about 0.025 inch (25 mil) to be suitable for use. Accordingly, orientation can be increased by drawing the extruded fastener stock; by manipulating molding conditions, e.g., using a "mild" set of conditions, such as relatively low melt and mold temperatures and injection pressures and speeds as found in a molding profile. Considering the estim-ate of skin thickness and also the sensitivity of orientation to elongational strains, the mechanism (c) caused by velocity re-arrangement seems most responsible for the skin-core morphology.
The head of the fastening device is formed by conven-tional techniques using sonic or ultrasonic energy with, in some instances, the application of heat. Figure 4 shows a fastening device in which a second head has been formed on the axial shank.
If the fastening device is in the configuration of a bolt, screw, nails and the like, threads, serrations, and other ~ ~3~19 modifications to the shape can be accomplished using techniques conventional with the shaping of plastic articles. Figure 5 shows a bolt wherein threads are present on the exterior of the shank. Figure 6 shows a fastening device wherein the head and shank are hollow along the linear axis.
If desired, physical properties such as shear strength, tensile strength, and elongation, of the solidified previously formed fastening devices of thermotropic liquid crystalline polymer may - 17a -optionally be enhanced by heat treatment at a temperature below the melting temperature of the thermotropic liquid crystalline polymer for a time sufficient to increase the melting temperature of the polymer by at least 10C. For instance, the elongated member may be heated belo~ the melting temperature while present in a nitrogen or other atmosphere for up to 24 hours at an ele-vated temperature within 50C. of the polymer melting temperature.
In accordance with the present invention, if the fastening devices are. rlvets, conventional means may be used to form the desired heads. For example, the forming of flush rivet heads may be accomplished by high pressure welding where the material is only softened by the application of ultrasonic energy~would not actually melt it. Protruding rivet heids may be formed by staking or by stake welding where the head is added as a separate piece.
It is also possible to expand the rivet in the hole by directing ultrasonic energy beyond the surface of the protruding rivet or boss and softening the body of the rivet.
Conventional ultrasonic equipment can be used, for example, twenty KHz or forty KHz can be used advantageously. The desired construction of fixtures and apparatus utilized, e.g., ultrasonic horns are known in the art.
In practice, the rivet head may be formed by providing a projection of the rivet or boss through the the workpieces to be secured introduce sonic or ultrasonic energy onto the projection or the boss. The energy, when suitably introduced, will change the shape of the projection or boss and, therefore, secure the workpieces.
More specifically, the projection or boss should have a height above the base workpiece so as to provide sufficient mat-., erial to form a head of the desired configuration. The ultrasonicenergy is introduced into the projection or boss by placing a coupler member adjacent a tip of the projection and, thereafter, ultrasonically vibrating the coupler member at a high frequency to beat it downwardly against the tip of the projection. Ultrasonic energy is thus coupled into the projection or boss to heat it and 93~9 render it flowable so that its tip is peened over by the beating of the coupler member.
The physical properties of the thermotropic liquid crystal-line polymer fastening device are considered to be unique and to be totally unattainable with other polymers which are capable of undergoing the shaping operation, i.e., injection molding or melt extrusion described herein.
The shear strength of the fastening devices of thermotropic liquid crystalline polymer is extremely high and is at least 10,000 psi (e.g., 10,000 to 75,000 psi). Such shear strength can be conveniently determined in accordance with the stanJard pro-cedure of ASTM D565-76. Accordingly, the fastening devices of the present invention~exhibit a remarkable tendency to withstand shear strain of the magnitude which would severely damage fastening devices formed from conventional thermoplastic materials.
The tensile strength of the fastening devices of thermotropic liquid crystalline polymer is also high and is at least 20,000 psi (e.g., 20,000 to 150,000 psi). Such tensile strength can be con-veniently determined in accordance with the standard procedure of ASTM D 638 with strain gauge at about 23C.
The chemical resistance of the fastening devices of thermo-tropic liquid crystalline polymer of the present invention is exemplified by the data set forth in the following Tables IA and IB. The resin from which the fastening devices are fabricated was exposed for 30 days to hydrochloric, chromic, nitric and sulfuric acids; sodium hydroxic and a plating solution at various temper-atures.

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::~ E o ~ 9 In accordance with the present invention, the fastening de-vices of thermotropic liquid crystalline polymer have been found to exhibit a hig~ly satisfactory coefficient of linear thermal expansion property unlike the metallic devices presently utilized as well as all other plastic devices which are unsuitable for use because of this failing.
In the preferred embodiment, the coefficient of linear therm-al expansion of the fastening devices of the present invention are modified by.incorporating a reinforcing agent or a filler which exhibits the same reinforcing utility therein. Various fillers and/or reinforcing agents may be inc~uded in a total concentration of ahout 0~ to about 50X and over by weight and preferably about lOg to about 40X and over by weight of the resulting molded compound. Representative fibers which may serve as reinforcing agents therein include glass fibers, asbestos, graphitic carbon fibers, amorphous carbon fibers, synthetic polymeric fibers, aluminum fibers, aluminum silicate fibers, oxide of aluminum fibers, titanium fibers, boron fibers, magnesium fibers, rock wool fibers, steel fibers, tungsten fibers, cotton wool, and wood cellulose fibers~ etc. If desired, the fibrous reinforcement may be preliminarily treated to improved adhesion ability to the liquid crystalline polymer which ultimately serves as a continuous matrix phase. Representative filler materials include calcium silicate, silica, clays, talc, mica, polytetrafluoroethylene, graphite, aluminum trihydrate, sodium aluminum carbonate, barium ferrite, etc.
While some beneficial results will be seen from the use of any amount of glass fibers, it is preferred that the loading be controlled so as to modify the coefficient of thermal expansion.

Accordingly, the extent of the expansion and contraction .. .. ...
tendency of the shank of the fastening devices of thermotropic liquid crystalline polymer tends to beneficially coincide with the expansion and contraction of other material being fastened. The coefficient of linear therma1 expansion can be conveniently de-termined with a duPont thermomechanical analyzer while examining the elongated member at temperatures below 100C.

While not essential, it is preferred that the glass fibers be treated with a silane-type sizing agent. Typical sizing agents which have been used successfully are gamma-glycidoxy-propyl-trimethoxysilane and gamma-a~iropropyltriethoxysilane, although other coupling agents ma~ give similarly beneficial results.
Glass fiber already treated with coupling agents or other surface treatments can be purchased from commercia7 suppliers.
The present invention prefers a thermotropic liquid crystall-ine polyme~ matrix having glass fibers incorporated therein for reinforcement to prepare the molding compound utilized in the fastening devi ces .
As they appear in products of the present invention, the glass fibers have a number average length of about 0.1 to 1.0mm, more preferably about 0.2 to 0.5mm, and most preferably about 0.3 to .4mm. Suitable glass fibers are available commercially from various sources. Particularly useful commercial glass fibers have an average original length of about 1/8 inch to 1/4 inch.
Commercial glass fibers usually have an average diameter of about 10-13 micrometers.
Accordingly, the fastening devices of the present invention have been found to exhibit a highly satisfactory linear co-efficient of thermal expansion property unlike the metallic and other plastic fastening devices presently utilized. Advantage-ously, the materials herein exhibit a linear coefficient of thermal expansion which is compatible with the materials to be fastened and which ranges from about -3.0 to 3.0 X 10 5 (in/inC).
Preferred values for the reinforced polymers from which the fast-eners of this invention range from about -2.0 to about 2.0 X 10 5 (in/inC). Illustrative values are set forth below in comparison with competing materials where "C" represents the coefficient of linear thermal expansion.

C X 10~5~in!inC) Liquid Crystalline Polymer (of Example 1) +30X glass -.3 to -.07 Liquid Crystalline Polymer (of Example 1) +40X wollastonite .77 to 1.1 Aluminum 2.4 Titanium/Columbium 0.8 Nylon 7.2 Rynite*530 PET resin 2.4 - 3.6 Ultem*2300 polyetherimide resin 2.9 Ryton*polyphenylene sulfide resin 1.9 The following examples are presented as specific illustrations of the claimed invention. It should be understood, however, that the invention is not limited to the specific details set forth in the examples.

* Trade Mark A wholly aromatic polyester which exhibits thermotropic liquid crystalline properties was selected for use in the form-ation of melt extruded ~iniec~ion molded) fastening devices in accordance with the present invention. The wholly aromatic poly-ester was formed in accordance with the teachings of United States Patent No. 4,161,470 and consisted of 7~ mole percent of recurring p-oxybenzoyl units and 27 mole percent of recurring 6-oxy-2-naph-thoyl units. The wholly aromatic polyester exhibited an inherent viscosity of 8.4 dl./g. when dissolved in a concentration of 0.1 percent by weight in pentafluorophenol at 60C., and a different-ial scanning calorimetry melting temperature peak of 289C.

Example 1 was substantially repeated with the exception that a wholly aromatic poly~ester-amide) which exhibits thermotropic liquid crystalline properties was substituted for wholly aromatic polyester of Example 1 and different extrusion conditions were em-ployed. More specifically, the wholly aromatic poly(ester-amide) was formed in accordance with the teachings of commonly assigned United States Patent 4,330,457, issued May 18, 1982, and was derived from 60 mole percent of 6-hydroxy-2-naphthoic acid, 20 mole percent of terephthalic acid, and 20 mole percent of p-amino-phenol. The wholly aromatic poly(ester-amide) exhibited an ln-herent viscosity of 4.41 dl./g. when dissolved in a concentration of 0.1 percent by weight in pentafluorophenol at 60C., and a differential scanning calorimetry melting temperature peak of This example presents a comparison of tensile and shear prop-erties of typical filled liquid crystalline polymers with metals used for fasteners in the aircra`ft''~indust'ry. The'fill'ed materials ~ ~3~9 of Examples 1 and 2 are compared with aluminum and titanium/colum-bium alloys as follows. The specific gravities of the material are also included, as well as the strength to weight ratios.
When these are considered with the other properties, the liquid crystal polymer variants compare favorably. When chemical resistance and resistance to galvanic corrosion are considered, the liquid crystal polymers can be deemed superior for many uses.

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l -~ 9 EXA~PLE 4 Injection molded 1/4 inch diameter rods of four competitive materia1s were double shear tested. The results indicate a clear advantage for the li~uid crystal polymer materials of the present invention. The competitive materials evaluated included Nylon - a polyamide resin (33X glass fiber and nylon), Rynite 530 (30g glass fiber) - a polyethylene terephthalate resin manufactured by E.I.
duPont de Nemours and Company, Ultem 2300 (30% glass fiber) - a polyetherimide resin manufactured by General Electric Corporation, and Ryton R-4 (40% glass fiber) - a polyphenylene sulfide resin manufactured by Phillips Petroleum Corporation. The results are shown below with the liquid crystal polymer of Example 1 for comparison. It should also be remembered that in addition to the indicated shear strength advantage, liquid crystal polymer offers a chemical resistance advantage over all but the Ryton and a tensile strength advantage over each material.

Material Shear Strength (PSI) Nylon 14,200 Rynite 530 PET resin 9,890 Ultem 2300 polyetherimide resin13,210 Ryton R-4 polyphenylenesulfide resin 12,070 Liquid Crystalline Polymer (Example 1)+ 30~
Glass 20,070 Coefficients of thermal expansion were determined on rivets molded from the liquid crystalline polymer varients of Examples 1 and 2. The molding was conducted on an Arburg with a rivet mold which provided 1/4 inch shank diameter rivets. The molding runs .... . ..
employed melt temperatures between 260C and 280C, mold temper-atures between 40C and 80C, the i~jection pressure between 100 9~ ge psi and 500 psi ~ e readings and injection speeds of between 100 and 150 Set Point. The experiments were conducted by attaching a 1 inch extensometer to the shaft of the resulting rivets and o~g~
placing the ~H}~ in an oven. The oven temperature was raised from room temperature to 150C in steps of approximately 25C with ~, , the oven rising at about 2C per minute between steps.
From the temperature data collected during the thermal ex-periments, the following thermal expansion coefficients were cal-culated.

> Sample Thermal Expansion C X 10 5 (inchlinch/C) Liquid Crystalline Polymer (Example 1) 2130+30X glass 1/4" Round Head -1.4 Liquid Crystalline Polymer (Example 1) 2130+30X glass 1/4" Flat Head -1.2 Liquid Crystalline Polymer (Example 2) 4160+30X glass 3/16" Flat Head -1.6 Liquid Crystalline Polymer (Example 2) 4160+30X glass 1/4" Flat Head -1.9 All liquid crystalline polymer varients tested had negative thermal expansion coefficients in the thermal range evaluated.

Claims

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

1. A one-piece fastening device formed by melt-processing of thermotropic liquid crystalline polymer containing up to about 50% by weight of a reinforcing agent wherein said thermotropic liquid crystalline polymer is caused to flow comprising a head and a relatively rigid axial shank adapted to be inserted in the aperture of a workpiece characterized by a shear strength of at least about 15,000 psi and a tensile strength of at least 20,000 psi, wherein said fastening device possesses a highly oriented skin of polymer molecules which was imparted to the same during said melt-processing of said thermotropic liquid crystalline polymer to form said fastening device.

2. The fastening device of claim 1 wherein a second head is positioned on said axial shank.

3. The fastening device of claim 1 wherein threads are disposed on the exterior surface of said shank.

4. The fastening device as set forth in claim 1 wherein said head and shank are hollow along the linear axis of said fastening device.

5. The fastening device of claim 1 wherein the thermo-tropic liquid crystalline polymer has an inherent viscosity of between about 1.0 and about 15 dl./g. when dissolved in a con-centration of 0.1 percent by weight of pentafluorophenol at 60°C.

6. The fastening device of claim 1 wherein the thermo-tropic liquid crystalline polymer is selected from the group consisting of a wholly aromatic polyester, an aromatic-aliphatic polyester, a wholly aromatic poly(ester-amide), an aromatic-aliphatic poly(ester-amide), an aromatic polyazomethine, an aromatic polyester-carbonate, and mixtures thereof.

7. The fastening device of claim 1 wherein the thermotropic liquid crystalline polymer is selected from the group consisting of a wholly aromatic polyester, a wholly aromatic poly(ester-amide), an aromatic-aliphatic poly(ester-amide), and mixtures thereof.

30a

8. The fastening device of claim 1 wherein the thermotropic liquid crystalline polymer is melt processable poly(ester-amide) capable of forming an anisotropic melt phase at a temperature be-low approximately 400°C. consisting essentially of recurring moieties I, II, III, and, optionally, IV wherein:

I is II is where A is a divalent radical comprising at least one aromatic ring or a divalent trans-1,4-cyclohexylene radical;

III is , 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 , where Ar' is a divalent radical comprising at least one aromatic ring;

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, and mixtures there-of, and wherein said poly(ester-amide) comprises approximately 10 to 90 mole percent of moiety I, approximately 5 to 45 mole percent of moiety 11, approximately 5 to 45 mole percent of moiety III, and approximately 0 to 40 mole percent of moiety IV.

9. The fastening device of claim 1 wherein the thermotropic liquid crystalline polymer is a melt processable wholly aromatic polyester capable of forming an anisotropic melt phase at a temp-erature below approximately 400°C. consisting essentially of the recurring moieties I, II. and III which may include substitution of at least some of the hydrogen atoms present upon an aromatic ring 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 where Ar' is a divalent radical comprising at least one aromatic ring, with said optional substitution if present being selected from the group consisting of an alkyl group of 1 to 4 carbon atoms, an al-koxy group of 1 to 4 carbon atoms, halogen, a phenyl group and mixtures of the foregoing, and wherein said polyester comprises approximately 10 to 90 mole percent of moiety I, approximately S
to 45 mole percent of moiety II, and approximately 5 to 45 mole percent of moiety III.

10. The fastening device of claim 1 wherein the thermotropic liquid crystalline polymer is a melt processable wholly aromatic polyester capable of forming a thermotropic melt phase at a temp-erature below approximately 350°C. consisting essentially of the recurring moieties I and II which may include substitution of at least some of the hydrogen atoms present upon an aromatic ring wherein:

I is , and II is with said optional substitution if present being selected from the group consisting of an alkyl group of 1 to 4 carbon atoms, an al-koxy group of 1 to 4 carbon atoms, halogen, phenyl, and mixtures of the foregoing, and wherein said polyester comprises approxi-mately 10 to 90 mole percent of moiety I, and approximately 10 to 90 percent of moiety II.

11. The fastening device of claim 1 wherein the reinforcing agent is included in an amount of from about 10% to about 40% by weight.

12. The fastening device of claim 1 wherein the reinforcing agent comprises glass fibers which have a number average length of about 0.1 to 1.0mm.

13. The fastening device of claim 1 wherein the reinforcing agent comprises glass fibers which are treated with a silane sizing agent prior to being blended with the thermotropic liquid crystalline polymer to produce the fastening device.

14. The fastening device of claim 1 characterized by a linear coefficient of thermal expansion of from about -3.0 to 3.0 x 10-5 (in/in°C).

15. The fastening device of claim 1 wherein the reinforcing agent comprises glass fibers which have a number average length of about 0.3 to 0.4 mm.

16. The fastening device of claim 1, characterized by a linear coefficient of thermal expansion of from about -2.0 to 2.0 x 10-5 (in/in°C).

17. A one-piece shapable fastening device comprising a composition of a melt-processed thermotropic liquid crystalline polymer and up to about 50% by weight of a reinforcing agent, said fastening device being in the form of a head and a relatively rigid axial shank adapted to be inserted in an aperture of a workpiece, said fastening device having a shear strength of at least about 15,000 psi and a tensile strength of at least about 20,000 psi, and possessing a highly oriented skin of polymer molecules formed during melt process shaping of said thermotropic liquid crystalline polymer to form said fastening device.