IE43298B1 - Improvements in and relating to shaped articles from synthetic polymers - Google Patents

Abstract

A process for improving the tenacity of a filament having a tenacity of at least one gram per denier and formed from a synthetic linear condensation polymer, characterized in that the polymer is capable of forming an anisotropic melt and that the filament is subjected to heat treatment at a temperature below the flow temperature of the filament and in an inert below the flow temperature of the filament and in an inert a atmosphere and while the filament is in an essentially relaxed condition, the said treatment being conducted until the filament tenacity is improved by at least 50% and exceeds 10 grams per denier. [IN144854A1]

Description

This invention concerns improvements in and relating to shaped articles, especially synthetic filaments ,and films, and more particularly filaments that can be prepared by spinning melts of synthetic polymers. The invention is particularly directed to a treatment process whereby the properties, especially the strength, of such filaments, flows and other shaped articles, can be improved, and to the resulting new filaments, and other articles, The filaments'have useful properties, e.g. high strength, such as make them particularly interesting for use as industrial filaments, e.g. for reinforcement of tires, and for other uses as shaped articles. The invention will be more particularly described in relation to filamentary articles, it being understood that similar treatment Is possible for films and other articles shaped from appropriate polymers.

The basic principles of forming fully synthetic linear polymers were described by W. H. Carothers over 40 years ago, and the commercial preparation of nylon filaments by melt spinning followed. The preparation of poly(ethylene terephthalate) filaments was first disclosed by Whinfield & Dickson and the commercial preparation of polyesters by melt spinning has essentially followed these same disclosures. The most convenient and economical process for forming filaments from synthetic polymers has been melt extrusion, usually referred to as melt spinning, which is generally preferred over spinning from solution. Not only does the need for solvent add to the cost and complexity of the spinning process, but its use often has an adverse effect on the tensile properties of the resulting filaments, even after removal of the solvent.

For some purposes, it is advantageous to have filaments of extremely high strength. Strength is the property of greatest importance in most industrial yarns, e.g. for use as tire cord, although other properties also can be of importance. It has long been possible to Improve the tenacity of nylon and poly(ethylene terephthalate) filaments by drawing.

Manufacture of typical commercial polyesters suitable for use as tire cord is discussed by Riggert, Modern Textiles, November 1971, 21-24. An important feature of this manufacturing process discussed by Riggert is the need to use poly(ethylene terephthalate) of high molecular weight and to maintain preorientation of the freshly-spun poly(ethylene terephthalate) at a low level, i.e. until solidification and attenuation of the filament is complete. Thus, it is Important to delay subjecting the solidifying poly(ethylene terephthalate) filament to the drawing tension until after completion of this stage, and only then to stretch the solidified filament to induce orientation and Increase its strength. For this reason, if poly(ethylene terephthalate) filaments of high strength are required, poly(ethylene terephthalate) of high molecular weight is spun Into a heated zone to delay orientation. Further, to prevent degradation at the high temperatures necessary to lower the melt viscosity to permit extrusion, the polymer is heated first to a lower temperature and is then passed through a special filter - 3 43298 leading to the spinning orifices to raise the temperature (by converting mechanical energy into thermal energy) to that desirable for spinning through the orifices to form filaments.

This as can be imagined, takes a lot of time and in spite of all f this treatment, however, it has not been practical commercially to provide nylon or poly(ethylene terephthalate) industrial filaments of tenacity much over 10 grams/denier.

Comparatively recently, much stronger aramid filaments have been provided on a limited commercial scale; although such aramid filaments are extremely strong and useful, it has been necessary to prepare them by spinning from solution, so that it has still been desirable to provide strong filaments from synthetic polymers that can be melt spun. For this purpose, it qj is important that the melting point of the starting polymer not be so high as to make melt spinning impractical. It is also important that the flow temperature of the filament be sufficiently high to avoid loss of strength in operation and during processing, and 30 it would be desirable for such filaments to have a flow temperature of at least 200°C., preferably at least 250°C.j the term flow temperature, as used herein, is explained in greater detail hereinafter.

In our Patent .Specification No. we ?5· disclose and claim novel polyesters that have extremely interesting and useful properties in that they form anisotropic melts from which oriented filaments can be melt spun.

The notable structural characteristic of the polyesters of our above mentioned copending application. - 4 43298 ls that the molecular units in the polymeric chains are predominantly ring structures (aromatic or cycloaliphatic). Homopolyesters from unsubstituted wholly ring structures are too high melting to be generally useful, e.g. for melt spinning. We believe that it is important, in order to obtain useful anisotropic melts, to have the stiffness of a chain comprising predominantly aromatic or cycloaliphatic rings, while reducing In a controlled way the melting point to within the range desirable for useful purposes. We believe that one can achieve this desideratum of desirable melting point, without losing the stiffness characteristic of euch ring compound polyesters required for anisotropy in the melt, by modifying wholly ring structure homopolyesters as follows:(1) Limited substitution of the ring structures, such as with chlorine and bromine atoms and lower alkyl groups, this being preferred; and/or (2) Limited copolymerization, i.e., using more than one R-^ and/or more than one R2, this often being preferred; and/or (3) Introduction of limited flexibility between the rings, e.g., by ether linkages and/or aliphatic chains of limited length.

In contrast to conventional melt spun filaments of Industrial, i.e. high strength, polyesters, principally poly(ethylene terephthalate), which are spun into filaments in which the polymer molecules immediately become randomly arranged, i.e. unoriented, and which require drawing in order to induce the polyester molecules to become oriented, these new polyesters can be melt spun into - 5 43 2 9 8 oriented filaments provided that they are subjected to sufficient stretch as they emerge from the spinning orifice, a spin-stretch factor of 10 generally being sufficient. It is believed that this capability of melt spinning to oriented filaments results from the unique nature of the anisotropic melts from which the filaments are melt spun; It is believed that the anisotropic nature of the melt results from the fact that the polyester molecules are in extended chain form and are oriented in local domains of the melt, and that these local domains are oriented during extrusion, and that this orientation persists thereafter.

It has previously been suggested, e.g. by Rowland Hill, Fibres From Synthetic Polymers, Elsevier Publishing Company, 1953j that, although the higher the molecular weight of a polymer, the greater should theoretically be the tenacity of Its filament, in practice the properties of prior polyester filaments level out as the molecular weight increases.

It has not been practical to use polyesters of extremely high molecular weight for making filaments because of their high melt viscosity, as disclosed in U.S. 3,216,187, and the resulting processing difficulties, in conjunction with the tendency of such prior polyesters to degrade at high temperatures such as have been necessary to obtain an extrudable melt. Thus, there has always been, in practice, an optimum molecular weight beyond which it has not been practical to obtain polyester filaments of improved, tenacity. It has not previously been possible, after spinning commercial polyester filaments, e.g., poly (ethylene terephthalate), from a melt of suitable - 6 43298 melt viscosity and molecular weight, to Increase the tenacity significantly by Increasing the molecular weight of the polymer in filamentary form. Although it has been possible to increase the molecular weight of poly(ethylene terephthalate) filaments after spinning, the tenacity has not Increased significantly. Xt is believed that the effect of this heating has generally been to increase the folding of the molecular chains of poly(ethylene terephthalate) and to decrease the orientation, as mentioned by Wilson, Polymer, Vol. 15, 277-282, May 1974.

In contrast, however, we have now found that it is possible, according to the present invention, to spin the novel polymers, according to our above mentioned Irish Patent Specification, from anisotropic melts of suitable melt viscosity into filaments and, thereafter, to increase their tenacity by heating. The increase in tenacity has been accompanied by an increase ln molecular weight, and often an increase in orientation.

It is believed that, with the correct combination of flexibility and stiffness in the molecular chain such that the polymer forms an anisotropic melt, the heating of the as-spun fibers increases the molecular weight of the molecules while maintaining or increasing the overall order and orientation, instead of permitting folding of the molecular chains as apparently occurs in poly(ethylene terephthalate). It is important that the polyester have a flow temperature high enough to permit such heat treatment. It is also important to perform the heat treatment while further polymerization is still possible, because end-capping of the molecules (e.g., by oxidation), seems to affect adversely the possibility of such heat treatment. We prefer to heat treat the filaments at as high a temperature as possible, i.e., as close to the flow temperature as possible, and in practice within about 20°C. below the flow temperature.

If such a heat treatment were to be applied to poly(ethylene terephthalate), the tenacity would decrease rapidly, as shown by Wilson (loc. cit.). Commercial heat treating temperatures for many of the preferred polyester starting materials are expected to be above the melting point of poly(ethylene terephthalate), e.g., In the range of 280-320°C.

The improvement in the properties of the novel polyesters under the oonditions of heat treat15 ment is quite different from a heat setting, or annealing, treatment which has been conventional for previous melt spun filaments, such as nylon or poly(ethylene terephthalate), for the purpose of removing stresses in the filaments. Indeed, it was extremely surprising that such heat treatment could cause such a significant improvement in these desirable properties of the filaments spun from such anisotropic melts.

Since the making of this discovery, it has subsequently been found that some synthetic polymers other than these novel polyesters are also capable of forming anisotropic melts from which filaments can be melt spun, and also share this characteristic, namely that we have been able to Improve the properties by heat treatment of the filaments subsequent to their extrusion. Furthermore, it is believed that this is a property that Is - 8 4 3 2 9 8 characteristic of the polymer itself in the form of a shaped article, rather than the fact that it has been melt spun.

There is provided, therefore, according to this invention, a process for improving the tenacity of a shaped article in the form of a filament or fibre formed from a synthetic linear polymer that is capable of forming an anisotropic melt, wherein the filament or fibre is subjected to heat treatment such that its tenacity is improved by at least 50%· There is also provided a process for improving the tensile strength of a shaped article in the form of a film formed from a synthetic linear polymer that is capable of forming an anisotropic melt, wherein the film is subjected to heat treatment such that its tensile strength is improved by at loast 50%.

Furthermore, there is provided a process for improving the impact strength of a shaped article other than a filament, fibre or film formed from a synthetic linear polymer that is capable of forming an anisotropic melt wherein the shaped article is subjected to heat treatment such that its impact strength is Improved by at least 50%· Preferably such polymers have flow temperatures above 200°C., especially above 250°C., such flow temperatures being measured as described hereinafter for the starting polymers subjected to the heat treatment, it being recognized that tho treated filament, film or other shaped article may have a flow temperature as much as 50°C, higher than the starting polymer.

For the avoidance of any doubt, it should be emphasized that our process is different from any disclosed in U.S. 3,778,410 and 3,804,805, which disclose, respectively, a process for preparing a final copolyester by reacting a starting polyester with an acyloxy· aromatic carboxylic acid, and copolyesters prepared from poly(ethylene terephthalate) and an acyloxy benzoic acid, and also disclose conventional melt spinning of fibers from such copolyesters and subsequently drafting, heat setting and further processing according to techniques that were said to be well known in the art (column 7, penultimate paragraph of U.S. 3,778,410). It seems clear, e.g. from Examples 1 and 2, therein, that the effect of the heat setting treatment was not such as to cause any significant increase in the fiber tenacity. - 9 Furthermore although we have been able to prepare anisotropic melts from such copolyesters, e.g., derived from 60 mol % of residues of p-acetoxybenzoic acid and 40 mol % of residues of polyfethylene terephthalate) as disclosed in Example 1 therein, and in certain other proportions, e.g. 67 mol % of the p-acetoxybenzoic acid residues, and we have spun oriented filaments from such anisotropic melts, we have not succeeded in effecting a significant increase in tenacity by subjecting such filaments to heat treatment ln contrast to filaments such as are shown in our Examples, hereinafter. It is not dear why these prior art filaments are not suitable materials for heat treatment according to the present invention, but It Is believed that one reason may be the significantly large amount of poly(ethylene terephthalate) residues containing significant amounts Of ethylene linkages present in a repeat unit of formula; - |c-o-ch2-ch2-o-c<^ Q It will be noted that this repeat unit contains a chain of 6 non-ring atoms, and is not. predominantly comprised of rings, and so may be expected to have sufficient flexibility to exhibit the chain-folding that Is typical of poly(ethylene terephthalate) and has been reported by Wilson (loc. cit.) in contrast to the repeat units of the starting polyesters shown in the Examples, herein, e.g. - 10 43298 •Cl, % 7B HO Q)o-c<0)occ-o H “ It will be noted that the longest chain between rings in these structures contains 4 non-ring chain atoms, and this is present in 4A ln a copolymer, i.e., not every repeat unit contains this long flexible linkage. Preferred starting polyesters for heat treatment according to the present Invention contain no more than 4 non-ring chain atoms. It will be recognized that some non-ring radicals provide less flexibility than others, and that the maximum number of chain atoms can he expected to vary depending on the overall combination of flexibility and chain stiffness of the molecules. It will also be noted that the repeat units are predominantly comprised of ring structures. It is also important that the starting polymers be capable of further polymerization below their flow temperatures, whereas polymers that have been prepared by the 2-stage fragraentation/building up process from poly(ethylene terephthalate) and an acyloxyaromatic carboxylic acid do not appear to be capable of such desirable further polymerization under such conditions. Preferred polymer starting materials are prepared by polycondensation of dihydric phenols with aromatic and/or cycloaliphatic diearboxylic acids, and then subjected to the heat treatment before end-capping occurs, e.g. by oxidation. If desired, as shown in Example 10 herein, an acyloxy aromatic carboxylic acid may be polycondensed with the dihydric phenol(s) and aromatic ^nd/or cycloaliphatic diearboxylic acid(s) to give a copolyester .5 that is formed into a shaped article that is similarly capable of heat treatment to improve its tenacity according to the present invention. It will also be noted that the specific process used to make the prior art polymers may be connected with the inability of their filaments to strengthen under the heat treating conditions we use according to the present invention, e.g. the fact that the process appears to produce polymers having units of poly(ethylene terephthalate) In their chains, or the fact that the process produces aliphatic hydroxy end groups.

The precise conditions of heat treatment will vary with the species of polymer that is being treated, and will be exemplified particularly by reference to polyester filaments spun from anisotropic melts and as !0 shown in the Examples, hereinafter. - 12 43298 The heat treatment generally proceeds more expeditiously as the temperature increases within the desired range, it being usually desired not to operate at a temperature so high that it ls impractical to rewind the yarn because of fusion between the filaments. Problems may arise at slightly lower temperatures because of sticking of the filaments, but it is possible to operate at such temperatures if the filaments are precoated with a thin layer of an inert substance, e.g. finely divided talc, graphite or alumina, and useful results have been obtained by operating in this way, ae was done in Examples 4D and 4G.

Continuous purging with nitrogen is extremely important. The exhaust stream of nitrogen has been found to contain polymerization by-products, such as acetic acid from a 1,4-phenylene-type diacetate starting material.

Thus, it Is believed that the heat-treatment causes continued polymerization of the polymer molecules without affecting the shape of the treated article, because the temperature is below the flow temperature. It is important that these polymerization by-products be removed from the polymer to permit continued polymerization to occur during the heat treating. Other gases that are inert to the polymer under the heat treating conditions could be used instead of the nitrogen, or the heating may be under reduced pressure to remove the by-products. A convenient way of determining when heat treatment should be discontinued is to monitor the exhaust gas stream for carbon dioxide, or other decomposition products, and to discontinue the heat treatment appropriately. The filaments do not essentially - 13 13298 change in length during the heat treatment, in contrast to prior polyesters, which tend to shrink significantly when heated below their flow temperature under similar conditions.

The filaments are preferably heat treated in an essentially relaxed condition, i.e. the filaments should preferably not be treated under significant tension.

In practice, it may be desirable to heat treat the filaments on a bobbin, e.g. as in some of the Examples herein, -1-0 where the filaments are held taut under slight tension, but are free to expand or contract slightly during the heat treatment, because of the yielding surface of the bobbin. We have found that the filaments break If heat treated under significant tension under preferred conditions, namely at a relatively high temperature below the flow temperature, and generally within 20°C. below the flow temperature. We have found, however, that it Is practical to heat treat under very slight tensions, the maximum operable tension being limited by the strength of the >0 filaments under the conditions of heat treatment, e.g. the temperature and/or time. Although yarns can be strengthened by heat treatment under some slight tensions (usually well below 1 g./denier) no significant advantage In the tenacity enhancement is obtained.

The filaments will generally be oriented before heat treatment, i.e. have an X-ray orientation angle less than about 65°C. It Is generally preferred to heat treat filaments that already have a tenacity of at least 1 gpd.

An Important feature of the present invention is that it is now possible to melt spin polymer filaments and then heat treat them to provide tenacities greater than 10 grams/denier. The resulting filaments are preferred products of the present invention, especially those filaments that have significantly higher tenacities, e.g. at least 15 grams/denier and those that have at least 20 grams/denier.

It will be noted that the heat treatment often increases the modulus, as well as the tenacity of the filaments. Preferred products of the present invention are those filaments that have a modulus of at least 100 grams/denier, and especially those that have a modulus of at least 300 grams/denier, which Is comparable with that of glass.

The process of the present invention will be further described with particular reference to the following Examples, which, for simplicity and convenience, are presented in tabular form. Most of the polymers that are heat treated in these Examples are novel polyesters that appear also In the Examples of our above-mentioned Irish Patent Specification, to which reference may be made for further details. Additional polymers heat treated in the following Examples are: Example IF - a homopolymer prepared from chloro-substituted, 1,4-phenylene diacetate and ethylenedioxy-bis(2,6-dimethyl-4-benzoic acid), Examples 7B and 7C - copolyestere comprising residues of mono- and di-chloro-substituted 1,4-phenylene diols and of p-carboxyphenoxyacetic acid (7B) and of methylenedioxy-4,4’-dihenzoic acid (7C). Note that 7B shows good results from polyesters from a diearboxylic acid with one aromatic carboxy group and one aliphatic carboxy group separated from a ring by a short chain (-OCHg-) i.e. the longest chain between the rings in this polymer is (-OCH2~$-O) of which a large proportion is an ester group.

Example 8D - a thiol/oxygen ester comprising residues derived from p-mercaptophenol, oxy-bis(4-benzoic acid) and terephthalic acid.

Example 10 shows a copolymer containing 82 mol % residues of p-oxybenzoyl and 18 mol ί residues of oxy-bis (1,4 phenyleneoxy) and of terephthaloyl, being an instance of a copolyester that Is derived by reacting an acyloxyaromatic carboxylic acid with a combination selected from the dihydric phenol derivatives and aromatic and/or cycloaliphatic diearboxylic acids referred to above. The polymerization conditions are conventional, as indicated in such applications, and the importance of the Invention lies In the surprising properties of the shaped articles, especially oriented filaments, that can be obtained from the melts of such polymers, these melts having the common characteristics of being anisotropic, and melting In a range that is useful commercially. The melt spinning conditions are conventional, except that, in all the Examples herein, oriented fibers were spun by subjecting the emerging filaments to a spin-stretch factor of over 10. The testing methods are described hereinafter.

The R^ groups in Example 1 are chloro-substltuted (A & B), bromo-substituted (C) and methyl-substituted (D & E) - 16 43298 1,4-phenylene rings and are derived by reacting, respectively, the corresponding chloro-, bromo- and methyl-substituted 1,4-phenylene diaeetate in equimolar proportions with the appropriate dicarboxylic acid which provides the Rg groups.

The reactants are reacted conventionally, e.g., in a polymer melt tube with a sidearra, a bleed tube for nitrogen or inert gas, micro-adapter, stirrer and distillate collection tube. The polymerization conditions are as indicated, e.g., for Example IA the reactor and contents are heated with stirring first at 283°C. for 1 hour (60 minutes) in the presence of anhydrous sodium acetate (catalyst), the acetic acid by-product being distilled off, and then at 283°C. for 10 minutes under a (reduced) pressure of 0.2 mm. Hg and finally at 305°C. for 25 minutes under the same pressure of 0.2 mm. Hg, following which the resulting anisotropic melt ls cooled and the polymer is isolated and Is found to have an inherent viscosity of 3·1! (using solvent 2). The reactants are generally agitated by the mechanical stirrer, especially in the first stage, and/or by passing nitrogen or inert gas therethrough and/or by the passage of by-product which Is formed and distils therefrom, especially under reduced pressure. A catalyst is not generally necessary, and was also used only in Examples 5D (antimony trioxide) and 8d and 10A (sodium acetate) hereinafter.

Under the heading Polymerization are given temperature (or range of temperatures) and time(s) of heating, e.g., first at 283°C, for 60 minutes for Example IA, whereas the pressure (mm Hg) is given only if it differs from atmospheric pressure. The inherent viscosity - 17 3 29 8 (' ( inh) is measured on the resulting polymer, unless it is indicated by (F) that the measurement was on the filament; the method and solvent are ae indicated hereinafter; ”Insol indicates that the inherent viscosity j could not be measured because the polymer did not dissolve in the solvent(s) tried, although solution in other solvent(s) might prove possible.

The heat treatment is carried out using the following techniques, indicated by the appropriate letter: (a) A skein of yarn is suspended in an oven swept with a continuous stream of nitrogen. The oven and sample are heated through the temperature/time cycle indicated; - (b) The yarn is wound onto a perforated bobbin, that has first been covered with ceramic insulating batting to provide a soft heat resistant surface that yields under low stresses, and is placed in an oven and treated as in (a); (0) Yarn is loosely piled into a perforated metal basket, which is placed in an oven and treated as in (a), or into a glass tube which Is heated through the temperature/time cycle with continuous passage of nitrogen over the filaments. 2'5 The temperature/time cycle is indicated in the Tables, e.g., in Example IA the oven and sample are heated In nitrogen at 170°C. for 1 hour, then at 230°C. for 1 hour, then at 260°C. for 2 hours and finally at 290°C. for 3/4 of an hour. Generally, the temperature is changed so rapidly that the oVen and sample is at the recorded - 18 43298 temperature for substantially the entire period Indicated, but less rapid changes of temperature are Indicated as follows: an arrow, as in Example IB (25->310/0.7), indicates that the temperature changes less quickly, whereas the word to, as in Example 50» (150 to 160/1.5) indicates that the temperature was within the stated temperature range trending upward, and whereas a dash, as in Example 5A, (235-265/1.5) indicates that the temperature was changed gradually over the initial 10 to 30 minutes, and then remained at the higher temperature for the rest of the indicated period. 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CM t o cu cn rd #» CM CM rd 1 ' co m kO ·» ·» - -> cn m ·» ·» 1 CM cn rd -cnrf •x o • cn in in •v O rd X « · xo . · X * o rd • b- in co CM ι Ο O • o p • co in X CM O rd • CM •i *«-> Gl\\ o W o ♦ • p x—’». X X ο I - CM X5 X o o o X O o -=± x· o o in X o rd X o co cn OSO ox X CM «X-✓ co tn in O X X in kO CM CM xo cu cn o in cn O in CM rd · X CO X A CM . . cu . . cn η • o ·» • ί . o CM ·» rd CM rd t t 1 .ft . cn rd cn 1 rd X 1 rd CM 1 X ί t I X X X O 0 I kO Jri·1 o o1 o o1 in o in in o o in x cm o m.=t cn Jd- vo CO inxo s- in o CM cn cn o cn CM rd CM O CM CM CM rd CM CM 0J cu cu cm cn cn CM CM cn o 00 cn IS rf ^b •zf- in • • V • • « ω • • w co co 00 s- o kO G) o> cn ο rd rd rd H CM rd rd rd rd H «χ—x S_^Z x—* *x^X *»—»* Pi N-* Pl cn cn ao rd rd in g in s rd 1 rd rd 1 CM 1 rd 1 cn ti w 1 z—·. . W I CM to 1 Ph Pn pH >H Ph 1 PH Ph | 1 1 I 1 1 -H- 1 l •=fr CM cn 00 X -d- co in O o m cn cn rd ^f· O rd CM cn X CM cn •sh in in in xt- x-x -d- ±j· *—* X X X X X 'S - X rd in CO co rd kO 43 kO 00 43 • • • • • • ϋ • • o rd CM o rd rd rd G rd O G X X X X X X Ή X X-H vo s- cn vo X cn in • • • • • • o • • o m cn kO -it- rd tn m rd (Ώ Ω W fc 43298· in EXAMPLE •P . ti O ti 0 0) ti ti •rl Pt w ω • H CO H P. ti ti Ch o · r-l p, fo ti ,d ti •rl fo I rrt ti o •rt p ti 11 X •rt c ti 'rt |\ S o rrt O 0 fo CU o in . tn o trt o 00 co CO co cu Ch σν cu CU rrt CO in o co O in OJ •d ti ti <-v z“X ti rrt CO cu rl ti X—Z x_«* ο CO vo cu •ti* rrt * • • • >> 04 co rrt CU C ti Λ fo t •if •4 rl o § o * o\ o o OJ · · ·.< ? o o co οι h · O' UAX OS rrt O cu co co I I \ ο o tn vo cn h cu OJ co cu § rrt X CO o X co CO cu ao cn CO rrt CU · cv · CU c p O X •»X *x o in oo o ch cu vo w X rrt CO LTA χ-χ. cn in ϊη^η co o oo o Lnco cu co « cn CM CM fo 0 = 0 tn in in o 1 o o o rrt O • • 1 rl o o 6 6 I o rrt • Λ ti ti ti •rt ti Ό rl 1 >5 CO ti ·» ti CU Λ fo 1 0 it rrt 0 O ti ti 0 O rrt Λ CU ti w •rt •ti ti I Ό in ti •4 rrt CU ti fi (p •rl 0 w fo fo El CO ! Ph O ϋ k0 0—0 β 2 H 00 P a ti til «Ρ H ra - 28 3298 fe P fi I cu ,C. fi •rl fi co o X co rH rH rH H rH I—1 1 1 ft >-» ft ft 1 1 ro 1 rH 1 -fi* § o Ch KO rH Jd· cu OJ X X X o co .fi· cu • • • jj· ro oo -fi· X X X o in 00 • OJ rH rH c- I I I OJ Ch P fi (U β ω EXAMPLE 5 CONT'D P fi P o fi o Q) ·» in n X r'—s in · fi • o •*^x o x cu H O X in X X X—' in oo OJ o o w co cu X in •»00 X cu I o cu in cu in ι in KO • j in O KO «*-> CM *1 o o cu ro cu .o in in\ s 0J »—* ·» • • O 0J •V e> in rH rH rH in /H ηΐηρ X — rH P X w · · O fi o o fi CU X ft o oo^> KO cu θ _ CU o\\ cu in rH cu Ρ Ό cu co in in X a) CU Ό o n · o o «a P *» . cu oo t 1 1 r-l O P P a) fi rH XX rH Φ X1 in in o o o o Ο Λ cu in coco x ch in o O 0 o cu cu cu H CU rH cu O fi cu P it V P« O fi ft ft ω t ca ClJ o U fi fi ft I •rl P Pl X ts cd X IS X H > rH rH CO rH 0J rH rH H ( t ft ft ft I I ι CO KO Ch O 00 in CU cu H X X X rH •fi* 00 CJ OJ cu \ X X sf co KO KO co «fi CQ ϋ Ch co* rd rH ι ft I OJ Ch •χ oo oo ro 4339 8 ν •ρ · d) υ β ο 0) β · β ρ, •rt β Ρι ω w Η tn σ> w «< 0.10 283/16, 305/20/0.2 1.8(1) 263 290 ο +5 Η Ο Γ) . «5 ο rn a> Cl* o •rl srt 1 p. Pl o X Ci Pi i>f 1 Ό •rJ •P (U X GJ M Cl X. C-« ir' •P £ (1) te, 1 CO r—I in Η fe & CJ X in x cn fe I rd O rd on r-l •P £ £ •rl cn QJ ♦rl ♦P C I Φ fi. fj P rri I ro Φ « tn P Ci d 3 OJ o Cl .£ 0« X al 0) te o p Jd ai ♦rl < fe E-« F· nj P id Q Ο Ο O in οι X on rd ci cu . lilt q in o * rd tn O r-ι cj cj in nJ R nOO cy tn cy • I ·» ·» o o in ιηχ x • · o ci XX h -p Ο O H cti vo cj o rd Cl -Ρ Ό Ο Ο O .£ tn ο ο ω rd Cl O fc z-s o rd *00 CJ rd ·*->· -=f IS ι ι fe fe I 1 X rd cO b- rd rd X X •zf- in CJ cj X X cn Cl on - 31 tf « ** Jl •p · ri 0 r< 0 ri ρ P, ’rl β Ρι ri W Ed ο Ο 0 ιη ιη 0 cn CM cn Ό ri 0) •P (0 M3 s- rd Η ϋ· X cn σι CM rd xi β • OS M3 CM rd ω fi •d ' § δ § co •ri ri β ri rd L X β fe Ο CM w ο ο W fe 0=0 β o •rd •P ri Ν X •rl β k -rd rd 0 0 fe •rl * OS τ5 ο X •Η co rd *» pri cn 0 Ο β ιη · tn 03 Ο X 1 tn 1 0 feri SO Η os β · r-3 CM · Λ CM « I = 0 J o I rd K ι o X s CM O *. Ό X tn β o σι ω 0 co σι ι M3 X in t> 00 xso * CM CM CM rd 1 1 · I 0 in tn in 0 X so so O CM CM cu so 0 0 tn o »1 I o ίκ o rd •rd •d co •rd β β •Η Ό β ri «id Γ Ο α> k d +5 X »d is β β Γ Η Ί ι ww ο ο co •rl β β •Η CO ri •Ρ ο * •43298 As-Spun Properties Heat Treated Properties -P ti ti $ ti ti o ti £ -p o ti o ti W •rl χ Til X fe rl X ·< cu in I I in cv tA Cv cv cv „ cu CU it Ch • Ch rl CO rl x_> rl vo xz in cu in ro 1 vo 1 fo 1 fo I fo 1 cu 1 X in X Ch ro X X X o co ro ch r| TO X X X X o IT. it ti* H ESI P H| .43298 ΓΧ I ο P . o rl o 0) c • fi fa •ri fi fa o w O o CM cn CM CM H CM cn cn cn CM Μ CJ H fa P, fi Q) (H vo o cn tn O cn -=t o cn it o cn ' J o = u I fa0, I = 0 I o I r~ fa I l 2 to fa g co g fa o o .C fi •H p* , fi o •H P d M •rl Q) •g t—I o 0 fa N| rt P Hl cq H CJ X co ό ό •s CM CM ϊ O vo X X cn n ri CO X CM o ·* ri cu X I cn X CM J o tn X CM CM X H tn cnvo cn ι ι cn CM o ο χ * (MO o o CM XX cn cm χνο 1 cn XX CM t CM x o tn o tn ri CM X . O CM X cn cn cm H CO VO l 1 X X. XX cn CM CM ooo OA ri H O CM CM cm cn cn cn cn on CM x O vo CM o in ! it vo H cn cn tn § o cn d o ·» •P o CM ω V) β \ o •Η σ) 1 co in CM r 1 ·» o cn ^n tnco CM CM Ί 3298 Ο fj ti ti ο U) ti o •rt 1 il Q) fo fo O X ti ίχ fo I d ti •rt |0 ti K ti w ti X E' Eh |0 ti j ti fo r β •r ' Γ Ο CU rl rl I I ίΗ t* I I in cu co if rl rl X X in Ch if tn X X o in rl rl I I CJ * w ll) •rt •P i-i fl) ti fo d P. w I ω cu e X rl X X I rl vo X cu CU x_z if cu CJ cu o rl I ΪΗ vo o rl if X co in I •P a ti u ro •p ti ti '1 ti b ti E X •P Ό ti 0 fl) fo ζ-χ 0J X in XI o r- •4 X-Z 0 X « tn CO •P cu • X \ΰ p o 'd o«— X X φ in OH in cu rl cu w X m o o CJ •V o o * b- in O +0 in cu »4 cu t- in o » η TJ ♦ ·» • X-Z rl rl ti pH O if X X rl XX in O 0 o o’ cu co in in o vo cu co cu cu o rl CJ CU CJ H vo • co r—x cu o z—s Ch 0J H H Ch X-z x^Z X*.Z rl if if in X_Z rl CO if in 1 1 in !x fo 1 1 1 1 in O O § O O I CO cu H rl if X X X X in H H X CJ CO X in X X X X rl in Ch if CO cu CU H E: ω -P fo fo 1X1 q.3 . 0) Ο Ρ Ο α) r* Ρ Ρ, •Η C Pj ο ω £μ, o KO co •=J- xt iH cn cn cn rd Pi fo fi KO Cb Cb co cn Cb OJ cn OJ S >» § H I ι r-P (X I --1 · Λ2 P •H tr Ol OI Ol • X-* H rd rd O 0 0 CO β g CO β •rd »fd •rf co H P o •fd d-3 tf Μ X •H β P -rd R fo o-o I pT 0-0 I o I r— rt I o > OJ cn ι co rd rd cn · -X o o rd KO rd OJ cn cn ι I o co Cb rd oj cn § s o cn in *X in o cn cn o tsjf co K n co e fo a o xi o o o Kw o o φ“ O rd o cn rd rd ·“**o in -13 2 9 8 As-Spun Properties Heat Treated Properties O fi fi o < O ( I •H X.

G •ri ¢7 P G 0 β M •P fi fi d 0 0 fi ft HX •P o fi o Q) w s I •rl tl F (I) X pt ft Ph ft ί ft l Ol co OJ KO co m Ch CO o cu co co jfi m fi- X X X X X 04 X 00 OJ KO CO CO co in in X X X X \ Ch rH X co co rH rH H rH I I I cu rH ·» X in in · X rH Η X I in χ in cu Η ι o r-> * CU ft in oi • in ·» Ο n * + H X CM O X ιηχχ ο o moo >co xa H OJ CO O cu *—* . CU OJ ft A H t ι ι fi Τ X 1 rn.fi- ’ o m χ x w o co CU H CU «fi X CU fi co X o o co in o co OJ fitn in · ts H H'S I --t in S m cu H J, O h CU X m cu . in * o > · + h \wo \ in W OO'moo > oo x h cu co o cu . CU CU X . H til (ί f \ 1 ΙΠ4 O tnss w o co cu H CU < ts CU m -fi- CO Ch O co H OJ rH <-*· in •fi· Ch rH rH rH I I I fe fe fe I I I X co co m Ch co co co fi- X X X cu a) m cu o cu X X X m co X in cu X cu j-j £ £ •H Oi W 0) £ 0) Ci CD o · rd P, fe £ QJ C-d 0=0 I COPOLYESTERS WITH REPEAT UNITS l-O-R -O-l -C-R O cn cn vo H cn rd £ o § i Ν X -H £ di $ r-l 0 0 fe HI Ci co 3 298 EXAMPLE 10 CONT'D -P 1 β ti) £ in •P 5-t ri o fl) 0 β xi Η X •P o ri o ϋ) W fe X X Os rd VD GJ I fe I in X X OS so > OS I ri ri O rd OS OS rd x-z SO GJ I fe J £ rd X GJ x ITS - 39 43398 As indicated, above, certain of the polyesters used in the process according to the invention are described and. claimed in our Patent Specification Ho. filed on even date herewith. These polyesters may be broadly represented as 5 containing units of formulaίΟ 0 II It fo-R^O-C-Kj-C] 1 wherein -0-R^-0- is a divalent residue of a dihydric phenol and 10 0 0 It 11 -c-R2-cis a divalent residue of an aromatic or cycloaliphatic dicarboxylic acid. As shown above, a variation in these polymers 1-5 is the replacement of at least one of the ester oxygen atoms by sulphur, e.g. by using a p-mercaptophenol as a monomer component to produce a polythiol ester. Other suitable polyesters are those of our British Application No. 19707/75 and which comprise residues of one or more phenolic carboxylic acids such as p'0 hydroxy-benzoic acid. Such polyesters may be for example copolyesters also containing residues of one or more dihydric phenols and/or one or more aromatic and/or cycloaliphatic dicarboxylic acids.

The above phenolic carboxylic acids employed may generally be selected for example from such acids having the ring structures inter-ring linkages, substituents etc. described below in relation to dihydric phenols and dicarboxylic acids.

As described above, it is necessary to choose particular groups R^ and Rg in the above formula in order to obtain the ) desired combination of flexibility and stiffness in the molecular chain such that the polymer is capable of forming an anisotropic melt and can be heat treated after shaping to improve its tenacity. The examples given hereinbefore illustrate how a suitable choice of R^ and Rg can be made to obtain polymers having the desired properties. Bearing these considerations in mind, it is possible to choose R^ and Rg from a wide variety of organic groups.

Thus, either or both of the groups R^ and Rg in formula 1 above may be, for example, a divalent aromatic group containing for example, one or more benzene rings which may be fused or linked either directly by a carben-carbon bond or indirectly by an oxygen atom (ether linkage) or by a divalent aliphatic group, e.g. a - C(CH2)20 - or a - 40 4 3 2 9 8 -ΟΙ ho CH3 group. In Rg the -CO- groups may he linked directly to one or more rings or at least one - CO - group may be linked to a ring via a short aliphatic chain such as - 0 - CHg -, in the latter case the - CO - group being attached to the carbon atom of the CHg group. Examples of such groups include phenylene groups such as the 1,3- phenylene group or more preferably the 1,4-phenylene group; biphenylene groups such as the 4,4 - biphenylene group; oxy- and thio- 1,4-diphenylene group ; and naphthylene groups such as the 2,6-naphthylene group.

These groups, may, if desired be substituted, especially in the case of R^, examples of suitable substituents including halogen atoms, e.g. fluorine or bromine atoms or more preferably chlorine atoms; and lower alkyl or alkoxy groups, e.g. ethyl, methoxy or more preferably methyl groups. Such substituents are preforably present in the o-position (in the case of mono-substituteon) and in the 2,6-positions (in the case of di-substitution). In the case of the group Rg this can be a cyclohexylene group, preferably a 1,4-cyclohexylene group.

Particularly preferred polyesters of the type disclosed in our Patent Specification No. include the following:I. about 95 mol fa or more of the R^ radical being chlorosubstituted 1,4-phenylene and about 95 mol fa or more of the Rg radicals being trans-1,4-cyclohexylene, e.g., poly(chloro-1,4phenylenetrans-1,4-cyclohexane dicarboxylate).

II. Ro being bis(4-carboxyphenyl)ether, and being selected from chloro-and methyl-substituted 1,4-phenylene, or less preferably bromo-1,4-phenylene, e.g., up to 20%, and up to mol fa of the total of the Rj and Rg units being replaced, i.e., up to 20 mol far, of 1?! being replaced by 1,4-phenylene, dichloro-1,4phenylene, 4,4'-biphenylene, oxy-1,4-diphenylene, thio-1,4diphenylene or 3,3 ,5,5 -tetramenthyl-4,4'-biphenylene,and/or up to 20 mol% ofRgbeing replaced by 1,4-phenylene, 1,4cyclohexylene, 2,6-naphthylene, 4,4'-biphenylene or ethylene dioxy di-1,4-phenylene, or less preferably 1,3-phenylene, ehloroand/or bromo-substituted 1,4-phenylene; III. R9 being 20-80 mol fa bis(4-phenyleneoxy)ethylene and 80-20 mol fan selected from 1,4-phenylene, 1,4-cyclohexylene and 4,4 -biphenylene, and being 20-100 mol % selected from methyland chloro-substituted 1,4-phenylene, and up to 80 mol fan 1,4phenylene ; IV - being the range of copolymers shown in Examples 2 and 3, - 41 3298 R^ being 85-60 mol %, preferably 70 mole S, chloroor methyl-substituted 1,4-phenylene and 15-40 mol %, preferably 30 mol J, oxy-bis(l,4-phenylene) ether and Rg being 1,4-phenylene; and V - R2 being 20-80 mol ί of 1,4-phenylene and 80-20 mol % 4,4’-biphenylene and/or 2,6-naphthylene and/or 1,4’-cyclohexylene and/or oxy-bis(l,4-phenylene), and R^ being chloroor methyl-substituted 1,4-phenylene, or lese preferably bromo1,4-phenylene.

It is evident from the large number of polymers exemplified that many further variations are possible, and that polymers other than polyesters, e.g. thlolesters, may be treated according to the invention. Although commercial considerations will probably dictate a preference > for using comparatively simple and/or inexpensive reactants In relatively simple combinations, it should be recognized that the present invention is based on a fundamental discovery, and it is predictable that particular combinations that have not been.disclosed precisely herein can also be heat treated to improve their properties.

The following articles other than filaments have also been heat treated according to the invention:A - A strong film having an edge orientation angle of about 20° was prepared from an anisotropic melt of poly(chloro-l,4-phenylene trans-l,4-cyclohexane-dicarboxylate) by melt extrusion at 303-310°C. in a Sterling extruder through a slot of dimensions 3 Ins x 3 mils (8cm. x 0.08 mm.) onto a casting drum, quenched in water and wound up. After heat treatment in a stream of nitrogen at 170°C./3 hours, 230°C./ * 16 hours, 260eC./22 hours, 285°C,/7 hours and 260°/64 hours, the cooled film was of thickness 0.04 mm. and had tensile strength/elongation/modulus of 110,000 psi/3.5%/2,950,000 psi (7,700 Kg/sq.cm./3.5%/2O7,000 Kg/sq.cm) B - Bars molded from the novel polyesters have shown good properties of stiffness, as measured by flexural modulus (FM), and toughness, as measured by notched Izod impact strength (ni), e.g. bars of poly(chloro-1,4-phenylene 1,4-cyclohexane-dicarboxylate) have shown a FM of 580,000 psi (41,000 kg./sq.cm) and a ni of 2.2 ft.-lb./in. (12Kg.~ cm./cm.) of notch.

We believe that these bars can be heat treated provided that provision is made for removal of polymerization by-products, which is more of a problem for massive articles than for filaments or films, which are relatively thin. We expect that internal heating, e.g. by dielectric means, may be preferred for some purposes to avoid first polymerizing the surface of the article and creating a seal which could impede or prevent removal of by-products. We have heat treated bars of poly(chloro-1,4-phenylene terephthalate/2, 6-naphthalate, (70/30) to increase the notched Izod impact strength by about 250% and in general the increase of notched Izod impact strength after heat treatment of bars and other telectively thick articles will be at least 50%.

The characteristics referred to herein were measured as follows:Optical Anisotropy - TOT (Thermo-optical test) It is well known that translucent optically anisotropic materials cause polarized light to be transmitted in optical systems equipped with crossed polarizers, whereas transmission of light should theoretically be zero for isotropic materials under the same conditions. The following thermo-optical test (TOT) uses this feature to identify polymers that show anisotropy with an apparatus that is essentially similar to that described by I. Kirshenbaum,, R. B. Isaacson, and W. C. Feist, Polymer Letters, 2 897-901 (1964), but uses apparatus units that are available to us. This procedure was designed particularly for testing polyesters, and may require modification for other polymers.

The thermo-optical test (TOT) requires a polarizing microscope which should have strain-free optics and suffl.0 ciently high extinction with crossed (90°) polarizers to be capable of giving a background transmission specified below.

A Leitz Dialux-Pol microscope was used for the determination reported herein. It was equipped with Polaroid (Registered Trade Mark) polarizers, binocular eyepieces, and a heating stage. A photodetector 5 was attached at the top of the microscope barrel. The microscope had a 32X, long working distance objective, and a Red I plate (used only when making visual observations with crossed polarizers; inserted at an angle of 45° to each polarizer).

Light from a light source is directed through the polarizer, through the sample on the heating stage and through the analyzer to either the photodetector or the eyepieces. A slide permits transferring the image from eyepieces to photodetector. The heating stage used Is one capable of being heated to 500°C. A Unitron model MHS vacuum heating stage ' (Unitron Instrument Co., 66 Needham St., Newton Highlands, Massachusetts 02161) was used. The photodetector signal Is amplified and fed to the Y-axls of an X-Y recorder. The system response to light intensity should be linear and the error of measurement within + 1 mm on the chart paper. The heating stage is provided with two attached thermocouples.

One is connected to the X-axis of the X-Y recorder to record stage temperature, the other to a programmed temperature controller. The microscope is focused visually (with crossed polarizers) on a polymer sample prepared and mounted as described below. The sample, but not the cover slip, is removed from the optical path. The Polaroid analyzer of the microscope is removed from the optical path, the slide is shifted to transfer the image to the photodetector and the system is adjusted so that full-scale deflection (18 cm on the chart paper used) on the Y-axis of the X-Y recorder corresponds to 36% of the photometer signal. The background transmission value is recorded with crossed (90°) polarizers and with the cover slip, but not the sample, in the optical path. The background transmission in the system used should be independent of temperature and should be less than about 0.5 cm on the chart paper.

The sample is preferably a 5μ section mlcrotomed with a diamond knife from a solid well-coalesced chip of pure polymer (e.g., as prepared ln the Examples), mounted in epoxy resin. A less preferred method, but one especially useful for low molecular weight materials that shatter when mlcrotomed, is to heat on a hot plate a sample of finely divided polymer on a cover slip resting on a microscope slide. The hot plate temperature (initially about 10°C. above the polymer flow temperature) is increased until the polymer just coalesces to a thin film essentially equivalent in thickness to the mlcrotomed sections, i.e., about 5u.

The sample section is pressed flat between cover slips. One cover slip is removed and the sample on the remaining cover slip is placed (glass down) on the heating stage. The background transmission is measured, and the sample is positioned so that essentially all the light intercepted by the photodetector will pass through the sample.

With the sample between crossed (90°) polarizers and under 5 nitrogen, the light intensity and temperature are recorded on the X-Y recorder as the temperature is raised at a programmed rate of about l4°C/min from 25° to 450°C, The sample temperature is obtained from the recorded temperature by use of a suitable calibration curve. 0 The use of the TOT test will be further described with reference to the accompanying drawing In which are shown traces of light intensity plotted against temperature for poly(ethylene terephthalate) which forms an isotropic . melt (Curve A) in contrast to a polyester that can be 5 heat treated according to the invention, poly(chloro-l,4-phenylene trans-1,4-cyclohexanedicarboxylate) which forms an anisotropic melt (Curve B).

The intensity of light transmitted through the analyzer when isotropic melts (the sample should be com0 pletely melted) are placed between crossed (90°) polarizers is essentially that of the background transmission (that obtained when the sample but not the cover slip is outside the field of view with 90° crossed polarizers). As the melt forms, the Intensity of the light transmission (1) is either , already essentially that of the background transmission or (2) decreases to such values from a higher value as in Curve A of the Figure, which illustrates an intensity trace of poly(ethylene terephthalate), which forms an isotropio melt.

The polymers that can be heat treated according to the present invention are considered to form anisotropic - 46 43298 melt3 if, as a eample is heated between crossed (90°) polarizers to temperatures above its flow temperature, the intensity of the light transmitted through the resulting anisotropic melt gives a trace on the recorder chart whose height Is at least twice the height of the background transmission trace and Is at least 0.5 cm greater than the background transmission trace. As these melts form, the value (height) of the light transmission trace (1) is at least 0.5 cm greater than that of the background transmission, and Is at least twice that of the background, or (2) increases at least thereto. Curve B of the Figure is of type (2) and illustrates the type of intensity trace usually obtained for systems forming anisotropic melts according to our experience hitherto.

The polymers that can be heat treated according to this invention often exhibit optical anisotropy throughout the temperature range tested, i.e., from the flow temperature to the decomposition temperature of the polymer or the maximum test temperature (450°C.). However, for some polymers, portions of the melt may become isotropic when the melt begins to decompose thermally. For still other species, the character of the melt may change completely from anisotropic to isotropic with increasing temperature. lnh (Inherent viscosity) - was determined as in U.S. Patent 3,827,998 but with these solvent systems (proportions by volume)ίί 1) 60% trifluoroacetic acid/40% methylene chloride (IB) 30% trifluoroacetic acid/70% methylene chloride (2) l,3-dichloro-l,l,3,3-tetrafluoroacetone hydrate (3) 50% solvent (2)/50% perehloroethylene (4) p-chlorophenol (5) 15? trifluoroacetic acid/35% methylene chloride/ ? solvent (2)/25? perehloroethylene 5 (6) 50% solvent (5)/50% solvent (4) The range of suitable inherent viscosities will depend greatly on the flexibility of the polymer molecules, and inherent viscosities are only pertinent to soluble polymers. Polymers of inherent viscosity as low as 0.3 LO could be useful, e.g. as coatings. For soluble polymers, inherent viscosities should generally be lower than 4.0, for ease of processability. As is well known, excessively high melt viscosities gives processing problems, e.g. in melt spinning filaments. Insoluble filaments that flow within •5 the indicated ranges of flow temperature could prove useful commercially.

Flow Temperature - This is the temperature at which the polymer flows. As the melt viscosity increases, this is manifest by the sharp edges of a tiny chip of -θ polymer or of a cut fiber becoming rounded. The flow temperature is determined by visual observation of the sample on a cover slip placed between crossed (90°) polarizers on the heating stage assembly described herein for the TOT procedure. A suitable heating rate is usually l4°C./min, but, in a few cases, where rapid further polymerization occurs, a faster rate, about 50°C./min., is used.

The flow temperature of any particular sample will depend on Its history. For example, shaped articles 3° sometimes have flow temperatures different from the polymer from which the article has been shaped; stepwise heating ordinarily raises the flow temperature, and permits progressively raising the temperature of heat treating to above the initial flow temperature, as shown In some of the Examples.

For processability, the polymers should flow at temperatures below those at which rapid decomposition occurs, otherwise plasticizers, solvents or other techniques would be necessary to provide the desired shaped articles. Although it may be practical to process some polymers with flow 10 temperatures as high as 45O°C,, for example, the flow temperature should preferably be less than 400°C., e.g. In the range of 200-370°C., especially from 250-350°C.

The spin-stretch factor is the ratio of the velocity of the extruded yarn (measured at wind-up) to the velocity of the melt through the spinneret, the latter being the volume of melt extruded per minute divided by (the crosssectional area of each hole x the number of holes).

Filament Properties - These are given for both as-spun filaments and heat-treated filaments. The tensile properties were measured as in U.S. 3,827,998, and the Y or F Indicates whether the properties of a multifilament yarn or a filament were measured. 0A°(arc°) indicate the orientation angle and (20 specific arc) as in U.S. 3,671,542, and were measured by method (2) therein.

Claims (33)

CLAIMS:

1. A process for improving the tenacity of a shaped article in the form of a filament or fibre formed from a synthetic linear polymer that is capable of forming an anisotrpic melt, wherein the filament or fibre is subjected to heat treatment such that its tenacity is improved by at least 50%.

2. A process for improving the tensile strength of a shaped article in the form of a film formed from a synthetic linear polymer that is capable of forming an anisotropic melt, wherein the film is subjected to heat treatment such that its tensile strength is improved by at least 5°%.

3. A process for improving the impact strength of a shaped article other than a filament, fibre or film formed from a synthetic linear polymer that is capable of forming an anisotropic melt wherein the shaped article is subjected to heat treatment such that its impact strength is improved by at least 50%.

4. A process as claimed in any of claims 1-3, wherein the polymer is formed hy polycondensation of the appropriate starting materials, and is formed into a shaped article and subjected to heat treatment before significant end-capping of the polymer molecules has occurred by other means,

5. A process as claimed in claim 1 or claim 4, wherein the shaped article is a filament, and the heat treatment is continued until the tenacity is over lOg./denier.

6. A process as claimed in any of claims 1-5, wherein the heat treatment is carried out at a temperature within 20°C. below the flow temperature of the shaped article.

7. A process as claimed in any of claims 1-6, wherein the heat treatment Is carried out at a temperature that is raised progressively as the flow temperature of the shaped article increases.

8. A process as claimed in any of claims 1 to 7, wherein the shaped article, before heat treatment, has a flow temperature of at least 200°C. - 50

9. A process as claimed in any of the preceding claims, wherein the shaped article is subjected to heat treatment while in an essentially relaxed condition.

10. A process as claimed in claim 9, wherein the filament is spun from an anisotropic melt and then subjected to the heat treatment.

11. A process as claimed in any of claims 1 and 3-10 wherein the shaped article is a filament and the heat treatment is carried out at a temperature that is not so high that it is impractical to rewind the yarn because of fusion between the filaments.

12. A process as claimed in any of the preceding claims wherein by-products formed in the heat treatment are continuously removed.

13. A process as claimed in claim 12 wherein the by-products are continuously removed by passing a stream of inert gas in contact with the article during the heat treatment.

14. A process as claimed in any of the preceding claims wherein the polymer is a polyester.

15. A process as claimed in claim l4 wherein the polyester comprises residues of one or more dihydric phenols and of one or more aromatic and/or cycloaliphatic dicarboxylic acids.

16. A process as claimed in claim l4 or claim 15 wherein the polyester comprises residues of one or more phenolic carboxylic acids.

17. A process as claimed in claim l6 wherein the polyester comprises residues of p-hydroxybenzoio acid.

18. A process as claimed in any of claims 15 to 17 wherein the polyester comprises ring structures linked only by ester groups, wherein some of the rings are substituted with chlorine and/or bromine atoms and/or lower alkyl groups.

19. A process as claimed in claim 18 wherein the said substitution is on an aromatic ring. •at ν ** «ζ ο

20. A process as claimed in claim 19 wherein the said substitution is on the residue of a dihydric phenol.

21. A process as claimed in any of claims 15 to 20 wherein the polyester comprises predominantly ring structures 5 with ether linkages between the rings.

22. A process as claimed in any of claims 15 to 21 wherein the polyester comprises predominantly ring structures, but containing chains containing aliphatic groups between the rings. .0

23. A process as claimed in any of claims 15 to 22 wherein the polyester contains ring structures substituted with chlorine.

24. A process as claimed in any of claims 15 to 22 wherein the polyester contains ring structures substituted with lower 5 alkyl groups.

25. A process as claimed in claim 24 wherein the polyester contains ring structures substituted with methyl groups.

26. A process as claimed in any of claims 15 to 22 wherein the polyester contains ring structures substituted with bromine. •

27. A process as claimed in any of claims l4 to 26 wherein the polyester is a copolyester.

28. A modification of the process as claimed in any of claims l4 to 27 wherein the said polyester is a polythiol ester.

29. A process for heat treating shaped articles prepared from polyesters substantially as herein described.

30. A process for heat treating shaped articles prepared from polyesters substantially as herein described with roforonce to any of the Examples.

31. Shaped articles whenever treated by a process as claimed in any of the preceding claims. - 52

32. Shaped articles as claimed in claim 31 in the form of filaments.

33. · Shaped articles as claimed in claim 32 in the form of filaments having such a molecular weight that the filaments do 5 - not melt.