IL26513A - Polyamide filament yarn and process of manufacturing it - Google Patents

Description

PATENTS AND DESIGNS ORDINANCE SPECIF ICATIO We, IMPERIAL CHEMICAL INDUSTRIES LJMITED, v a British Company of Imperial Chemical House, Millbank, London, S. W.1.. England DO HEREBY DECLARE the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement : - This invention relates to filaments derived from polyamides i.e. condensation polymers wherein amide groups form an integral part of the polymer chain, and to a process for their manufacture.

Polyamide filaments are most rapidly and economically obtaanined on a large scale by the extrusion of a molten mass of the polyamide, and, melt-spinning, as it is commonly referred to, has attained pre-eminence as the commercial method of manufacturing polyamide filaments* In one typical melt-spinning method, the polyamide prepared by a conventional polymerisation prooess is cooled, broken into chips and dried. The chips are them melted and the molten fibre-forming material continuously pumped, by means of a metering pump, through a filter pack generally containing a finegrained particulate material, and then extruded through the orifices in a spinneret under the pressure exerted on it at the back of the spinneret by the action of the pump. The freshly extruded filaments, which on emergence from the spinneret orifices are in the form of a viscous molten liquid, cool and elongate as they move away from the spinneret, the cooling often being assisted by a transverse or co-current stream of air flowing in a quenching chamber, often referred to as the chimney. The cooled and solidified filaments may then, as in polyhexamethylene adipamide (6.6 nylon) spinning, pass through a steam conditioner tube prior to passing over finish application rolls. Finally the filaments are wound up on a suitable support. In order that the filaments should achieve their maximum. strength it is necessary that they be stretched by several, usually at least three, times their original length. This stretching normally referred to as drawing is carried out by passing the filaments between two sets of rotating rolls, the second set of rolls, drawrolls, rotating at a higher peripheral speed than the first, set, feed rolls, to impart the desired degree of stretch to the filaments which are then wound up on a bobbin or like support.

A snubbing pin may be positioned between the two sets of rolls to locate the point of drawo The point below the spinneret face at which the molten filaments solidify, hereinafter for convenience referred to as the solidification point, represents the point at which the mobility of the polyamide molecules has decreased, with the falling temperature, to such an extent that the viscosity of the material is sufficiently high to preclude, at least temporarily, for changes may subsequently occur as a concomitant to crystallisation, any further elongation of the filaments, thereby substantially stabilising the denier thereof. The temperature associated with the solidification point is below the normal melting point of and the bulk solid polymer, the spun filamentary material is therefore supercooled. Generally a high degree of supercooling of the spun filamentary material at the solidification point is oonsidered to be desirable in, for example, minimising the growth of large spherulites which are well-known to have adverse effects on filament processability. In order to obtain the required high degree of supercooling it is necessary to impose a limit on the speed maximum spinning/achievable in a particular spinning prooess, the actual value of this limit being dependant upon factors such as spun filament denier.

The elongation which the freshly extruded filaments undergo before solidification is generally referred to as the "draw down". As well as reducing the denier of the filaments draw down also causes the molecules in the filaments to become oriented to some degree and there is some increase in the degree of orientation even after solidification. This orientation causes well-known birefringence effects to become visible when the filament is viewed transversely through a polarising microscope. Birefringence in the as-spun filaments, that is filaments which have not been subjected to an additional drawing process, is called the "spun birefringence" and its value may be determined by known techniques using a polarising microscope and a Berek compensator.

That a filament exhibits a measurable birefringence indicates that the segments of the polymer molecules which possess an intrinsic optical aipLsotropy must have a preferred orientation relative to the filament axis. Other techniques have to be employed to obtain more precise information on the nature of the preferred orientation. As is well-known one such technique is by means of the wide-angle X-ray Laue pattern from the fibre.

The Laue pattern exhibited by the fibre comprises two major rings, an inner and an outer ring, which are reflections from the principal paratropic lattice planes of the crystalline structure. The intensities of these rings (M) at meridian, the meridian being a straight line on the X-ray film parallel to the fibre directio and passing through the position of the primary X-ray beam, and (E) at equator, the equator being a straight line on the X-ray film perpendicular to the fibre direction and passing through the position of the primary X-ray beam, M - E can be determined and orientation factors ■" -, calculated.

M + E For convenience these orientation factors are designated O^ for the inner ring and 0Q for the outer ring, by which terms these factors will be referred to hereinafter. orientation factors and 0Q as defined above for the as-spun yarn are usually negative and often differ slightly in numerical value. The negative sign indicates that the 'ό' axis of the crystal lattice unit cell, i.e. the molecular tj chain axis, is becoming oriented towards the filament axis, i.e the structure nay be described as having a preferred 'c' axis orientation. The degree of orientation is generally low as indicated by the magnitude of the spun birefringence. In a fully drawn yarn of course the 'c' axis orientation is high 0 and 0. and 0 tend to the value of -1 .

IU 1 0 If the orientation process is simply a progressive alignment of the molecular chains more and more parallel to the filament axis then 0. » 0 for all degrees of orientation. 1 0 However this condition frequently does not exist and it is 5 considered that when (CL - pQ) differs from zero then the orientation process is more conplex and it is useful to consider the size and magnitude of (CL - 0Q). In normal as-spun yarn of 6.6 nylon, for example, 0q is often numerically slightly larger than CL and then (θ^ - 0Q) is small but positive, that 0 it has a value in the range 0 to 0.2.

Generally the magnitude and nature of ths spun orientation will control the degree of extrusion available in the drawing process to achieve the desired drawn yarn extension at break.

It is well-known that the draw ratio subsequently required to 5 applied to an as-spun yarn to produce a drawn yarn having the desired extension at break, decreases as the spinning speed is increased.

Surprisingly we have now found that polyamide filaments can be obtained by melt spinning which, in the as-spun state, 0 have values for (0. - 0 ) greater than 0.2 and that these filanents can be spun at higher speeds, i.e ra d up speeds, with consequent increase in productivity, than the previously known filaments having lower values for (CK - 0Q). Such filanents exhibit a lesser degree of supercooling at the solidification point in the spinning process under otherwise comparable conditions,which has obvious process advantages.

Furthermore we have found that as-spun polyamide filaments in which (Ch - 0 ) is greater than 0.2, and which have been spun at spinning speeds greater than about 1 , 500 ft. per minute, may be drawn at higher draw ratios than as-spun filaments in which (0. - 0 ) is less than 0,2 and which are spun at the same speed. Thus these filaments exhibit orientation characteristics which allow a further increase in spinning productivity to be obtained, When the magnitude of (O^ - 0q) is large, i.e. greater than 0.7, O^ has a positive value and 0Q a negative value.

This condition implies that the 'a' axis of the crystal lattice unit cell is becoming oriented towards the filament axis, i.e. the structure may he described as having a preferred 'a' axis orientation which contrasts with the preferred 'σ' axis orientation of the previously known as-spun polyamide filaments.

Accordingly therefore, from one aspect, the present invention provides a yarn comprising one or more undraw polyamide filaments having molecular orientations exhibiting X-ray reflection patterns in which (O^ - 0 ) is greater than 0.2.

Preferably (O^ - 0Q) is greater than 0.7 and even more preferably O^ is greater than zero, A feature of the present invention is that the change in spun orientation of the filaments enables a draw ratio for required extension at break in the drs-wn yarn to be achieved which is largely insensitive to spinning speed.

The values of 0. and 0 are determined in the following 1 0 manner.

The yarn sample is wound as a parallel bundle of fibres on a fibre sample holder, which is then mounted in an evacuatable X-ray camera using a flat plate film. The camera is evacuated for a minimum period of 5 minutes ( to a vacuum better than 0.2 n.m. of Eg.), and an exposure of 15 minutes at and 15 πιΔ.· is given to each sample, the cameras being continuously evacuated during the exposure. Ni filtered Cu. Ka radiation is used from a sealed X-ray tube operating in a Philips PW1008/30 generator.

The exposed film is processed as follows: -5 minutes in Ilford PQX-1 X-ray film developer (at 20°C), 1 nin. wash, mins, in M & B Perfix fixer (at 20°C), followed by a 30 min. or more wa.sh, to give a maximum optical density on the film of approximately 1.0.

Using a Joyce-Loebl double beam recording microdensitometer (Model E.12 Mk III), diametrical scans are made across the equator and meridian of the diffraction pattern, the fibre axis being along the meridian* The two records are produced superimposed on one chart. A common background is drawn in before measurements are made of the intensity (E and M respectively) at the equator and meridian for the two main reflections. The ratios and jjj are M"+" then determined.

M + E E Figure 1 of the drawings is a representation of an X-ray pattern obtained from an as-spun filament of 6.6 nylon of the present invention, indicating the reflections from the principal paratropic lattice planes of the crystalline structure which are used in the determination of the values of 0. and 0 . 1 o Figure 2 of the drawings is a representation of an X-ray pattern yarn obtained from a noraal as-spur¾of 6.6 nylon. Comparison of the figures su rs the nature of the orientation differences of the two filaments.

As examples of polyanides with regard to which the present invention is especially useful there nay be mentioned poly- hexamethylene adipamide (6.6 nylon) and polyhexamethylene suberami.de (6.8 nylon).

The desired orientation may be induced in the as-spun polyamide filaments by the incorporation of at least 0.05» preferably 0.5 to 1.5, per cent by weight of a finely divided nucleating agent in the polymer prior to spinning. The nucleating agent is preferably polymeric and should have an optical melting point greater than the melt holding temperature at spinning. Preferably the optical melting point of the polymeric nucleating agent is at least 10°C, or even more preferably at least 30°C, above the melt holding temperature at spinning.

The optical melting point of the polymeric nucleating agent is determined by observing under a microscope a sample of the material supported between glass slides that rest on an electrically heated stagei the melting point is taken as the temperature at which the optical birefringence of the sample disappears.

The melt holding temperature at spinning is defined as the temperature at the base of the melt pool above the booster pump in a conventional melt spinning unit such as is ucod in the manufacture of 6.6 nylon.

It is known to incorporate nucleating agent in polymers such as polyanides which are to be used in moulding and for xam i ov inter a ia th trans aranc of the resultant product. However it has not been known to deliberately incorporate nucleating agents in polymers which are to be melt spun into textile filaments.

According to another aspect, therefore, the present invention provides a process for the manufacture of a yarn consisting of undrawn polyajni.de filaments comprising incorporating a finely divided nucleating agent in a polyamide, forcing the molten polyamide containing the nucleating agent through a filtering medium, extruding the said polyamide through orifices contained in a spinneret plate and winding up the filaments.

Preferably the polymer contains at least 0.05$ by weight, and more preferably 0.5$ to 1. $ by weight of the nucleating agent.

Although it is preferred that the polymer should contain at least 0.05% of the nucleating agent, the actual lower limit for the concentration of the nucleating agent will depend upon the fineness of its state of division and may well be less than 0.01$ by weight.

The term nucleating agent is to be understood to refer to solid substances which, when present in a finely divided state i.e. having a particle size less than 0. ^ diameter in the as-spun polyamide filaments, induce the formation and growth of a crystalline texture which does not exhibit in the polarising microscope at the extinction position any discrete resolvable patterns characteristic of the well-known sphorulites, i.e. the so-called Maltese cross pattern. Spherulite growth, if present, must therefore be limited to sizes approximately equal to or below the wavelength of visible light that is below about 1.5,-i*. in diameter.

Pol amides havin o tical meltin oints reater than and preferably at least 10 C above the melt holding tenperature at spinning of the base polyner may usefully be employed as nucleating agents. Especially affective are polyamides or copolyanides containing an aryl group in the polyner chain.

As examples of this class of nucleants there may be mentioned polyamides comprising poly(nethylene) terephthalanide where x is an integer between 2 and 12 such as poly hexanethylene terephthalanide (6.T nylon), poly octenetliylene terephthalanide (8.T nylon), poly decanethylene terephthalanide (10.T nylon) and poly dodecanethylene terephthalanide (12.T nylon). Copolyanides of the terephthalamides with other polyamides, e.g. poly hexanethylene adipamide/poly hexanethylene terephthalanide (6.6 : 6.T) copolyner, polyhexanethylene adipanide/poly octanethylene terephthalanide (6.6 ; 8.T) copolymer, poly hexanethylene adipanide/poly decanethylene terephthalanide (6.6 s 10T) copolymer, poly epsilon caprolactam/ poly hexanethylene terephthalanide (6 % 6.T) copolyner and poly hexanethylene suberanide/poly hexanethylene terephthalanide (6.8 s 6.T) copolyner are particularly the 6.6 : 6,T copolyner being the preferred nucleating agent for 6.6 nylon.

The proportions of the aliphatic to aryl containing polyanides in the copolyanides to give the aost effective nucleating agent for any given polyanide have to be determined by experiment, for the effective nucleation of 6.6. nylon by 6.6 : 6.T copolymer it is thought that the copolyner should contain at least 30o by weight, and preferably at least ΰ/α by weight of polyhexane hylene terephthalanide. Also effective as nucleating agents are poly p-xylyene adipanide and its copolyners with 6.6 nylon, and poly hexanethylene hexahydroterephthalarri.de and its copolyners with 6.6. nylon. present invention nay also contain the usual range of additives such as delustering agents, pignents, antioxidants, stabilisers against the effects of heat and light, and so an and up to about 5¾ by weight of another polyanide.

It has been observed that the filanents of this invention have a higher tenperature at the solidification point in the spinning chimney i.e. show a lesser degree of supercooling, than previously known filaments. This effect can be readily verified while the filanents are being produced by chopping samples fron the filanont in either nolten or solid forn using known nethods. After determination of the solidification point by this nethod the tenperature associated with this point can be measured utilising a thermocouple or infra red pyrometer.

This increase in the tenperature at the solidification point of the filanents in the chinney can be assessed more conveniently by the use of differential thermal analysis (D.T.A.) since, at a defined rate of cooling, the freezing point of a nucleated polymer is higher than the freezing point of the base polymer. This increase is usually of the order of at least °C and nay be as nuch as 10°C. D.T.A. freezing point can therefore be used to give an indication of whether or not a polyanide has been nucleated in a nanner which will, when the polymer is nelt spun, yield an undrawn yarn having the defined parameters. For exanple polyhexamethylene adipamide has a D.T.A. freezing point of about 223°Cj the inclusion of 1 of a (50 s 50)6.6 : 6.T copolymer nay raise the said freezing point to 234°C.

D.T.A. freezing point is determined using a differential scanning calorimeter DSC-1 available from the Perkin-Elmer Corporation, N rwalk, Connecticut, U.S.A. in combination with a recorder, the instrument sold as Model ¥ by Leeds and Northup Co. being perfectly satisfactory. Differential power (i.e. the difference between the power supplied to test and control samples to maintain them at the same temperature and with the same rate of increase or decrease of temperature) which is equivalent to temperature, since the temperature increase or decrease is linear with time, is automatically plotted against time on the recorder. The temperature scale is automatically marked out on the side of the chart paper. In most instances it is conventient to determine on the same sample both its melting point, at a 2°C per minute linear rate increase of temperature, and the solidification point, i.e. the freezing point of the molten material, using a 64°C per minute rate offall in temperature, although for the purposes of this specification, the latter point, which can be determined more accurately than the former, is generally the more significant.

The detailed method employed in conducting the D.T.A. test using the above rates of heating and cooling is as followss- A sample of 5-15 nig. in weight is cut from polymer chip with a razor blade and sealed in an aluminium sample pan (as supplied by Perkin-Elmer) and placed in the DSC-1 pan holder.

With dry nitrogen at room temperature flowing through apparatus at 2 cc/min. the sample temperature is raised using manual control fairly rapidly (taking about 10 sees, for 200°C) to 232°C. It is left at this temperature for 2 mins. for the whole sample to reach equilibrium, then the scanning speed of the instrument is set at 2°c/min., and the temperature of the sample automatically raised. The machine is left to run until the temperature melt transition has been passed when the curve which is being traced out by the recorder pen straightens out.

The temperature is then raised manually to the holding temperature, which, for any particular polymer, is the melt pool temperature of a spinning unit, e.g. 285°C in the case of 6.6 nylon. The sample is held at this temperature for 2 mins.

Then the scanning speedis set to 64°c/min., and the temperature automatically lowered at the required rate. When the transition is finished the temperature is lowered manually down to room temperature.

To take readings from the recorder chart so obtained, a ruler is placed along the portion of the trace immediately prior to the transition to establish the best straight base-line that the slightly uneven curve will fit onto, and the transition (solidification and/or melting) temperature is taken to be that point at which the curve first moves away from the base-line* This can be determined to better than 1°C accuracy.

The test is also used to determine the freezing point of undrawn i.e. as-spun filaments.

Various methods, some of which will now be described in more detail, may be employed for introducing the nucleating agent into the polyamide.

For instance, in one method, herein for convenience referred to as the solution blending method, solutions of the polymer and nucleating agentin miscible solvents, are mixed together and the solute co-precipitated therefrom by the additon of a liquid in which it is insoluble. In employing this method it is often necessary, generally for the purpose of adjusting the proportion of nucleating agent in the polyamide to the desired level, to subject the co-precipitate, which may be regarded as a "master-batch" of the nucleating agent in the polymer, in a suitable further blending may be achieved by chip blending, i.e. by •addition of ohips of the master baton to the required amount of polyamide chips, or by chip coating, that is forming a paste of the master batch and using this paste to coat polyamide chip.

The nucleating agent can also be incorporated into the polyamide in the correct proportions by a melt-dispersion process, for example, by passing the mixed components through a heated screw extruder optionally combined with a metering pump, for instance a Duplex pump. This method may be used to form a master batch of the nucleating agent in the polyamide which may then be further blended with ±he required amount of additional polyamide by chip blending or chip coating.

The nucleating agent could be incorporated into the polyamide by introducing it into the autoclave during the polymerisation of the polyamide forming salt, or into the polymerisation coil in a continuous polymerisation process.

In processes involving the melt-dispersion of a nucleating agent in a polyamide it is most important that the temperature does not exceed a limit which is dependant upon the optical melting point of the nucleating agent as otherwise the effectiveness of the nucleating agent is lost. We have found that the melt-dispersion temperature should not exceed 1.08, and preferably 1.04, times the optical melting point of the nucleating agent.

Any other convenient method of mixing, such as by the use of a Banbury mill, may be employed. It is most important, however, that the nucleating agent be well dispersed in the polyamide since poor dispersion will result in an inadequately nucleated polymer and the novel filaments of the present invention will not be obtained therefrom.

Nucleated polymer may be extruded into filaments using any conventional spinning method involving filtering the polymer through a conventional filter pack prior to extrusion through spinneret orifices at normal temperatures, e.g. of the order of 290°C as is normally employed in spinning nylon 6.6.

The following examples are illustrative of the ways in which the novel filaments of the present invention may be prepared and of the various compositions of the said filaments.

It is to be understood that the examples are not intended to in any way limit the scope of the invention.

EXAMPLE 1 Preparation of a (50 i 50) 6.6 s 6T copolymer nucleating agent.

Equivalent molecular proportions of hexamethylene diammonium adipate and hexamethylene diammonium terephthalate and a small amount of water (used to maintain homogeneity) , were mixed together and heated, with continuous agitation, in an autoclave at a temperature of 230°C and under a pressure of 350 p.s.i. for a period of 3 hours. The low molecular weight polymer was then further polymerised in the solid state by heating at 290°C in a steam for a period of 5s" hours. The copolymer so obtained had an optical melting point of 330°C.

Incorporation of the copolymer nucleating agent into 6.6 nylon.

The copolymer additive was then incorporated into 6.6 nylon by a solution blending method as follows:- 72 gms of the copolymer additive were dissolved in 648 gms of 0 per cent aqueous phenol (10 per cent weight by weight solution) by refluxing and stirring under an atmosphere of nitrogen. Another solution containing 1 ,368 gms of polyhexamethylene adipamide having a relative viscosity of 40» was made by dissolving the polyamide in 12, 312 gms of 90 per cent aqueous phenol (10 per cent weight by weight solution).

The two solutions were mixed, "by stirring together, at a temperature of around 40°C, in amounts such that the final ratio of solutes was one part of weight of the copolymer nucleating agent to |9 parts of 6.6 nylon. The homogenous phenol solution was poured into methanol, and the precipitate filtered off and washed with methanol, and then boiled with uatex for several days to steam distil off the residual phenol. The precipitate, after drying was in the form of a fairly fine powder (master batch powder) . 940 gms of the master batch powder was homogenised with 2 litres water using an "Ultra Turrax" high speed mixer to form a paste. 280 gms pigmentary nylon base (20$¾ pigmentary nylon -a very finely divided low molecular weight 6.6 nylon + QOfo water) was also added and mixed in with the master batch powder. This was necessary to ensure satisfactory adherence of the pov/der to the polymer chip in the final chip coating operation, particularly at the relatively high level required.

The paste prepared as described above was chip coated onto standard production 6.6 nylon chip (relative viscosity 0 , 0.3% TiO^ content) in a Gardner mixer using Q lb. polyamide chip so that the ratio of master batch powder to the 6.6 nylon chip was 1;]Tgiving a final level of 1 per cent of the copolymer nucleating agent of the coated chip for spinning.

The resultant polymer had a D.T.A. freezing point of 234°C while a control polymer without nucleant had a D.T.A. freezing point of 223°C.

The polymer was melted in a gravity melter and the melt extruded through a 10 hole spinneret (each hole being 0.013 inches in diameter) into filaments at a rate of approximately 0.054 lbs. total polymer per minute at a spinning temperature of 289 C.

The filaments were spun into a quenching chamber wherein they were cooled by a transverse stream of air and in which they became solid. The 10 filament yarn so obtained, in which the filaments were each 9 denier, was collected at ambient temperature and relative humidity at a speed of 3930 feet per minute in the form of a yarn package. To provide the comparative information a control yarn, derived from polyhexamethylene adipamide chips having a relative viscosity of 40 and containing 0.3 per cent Ti02 as a delustrant but no copolymer nucleating agent,was spun and collected under identical conditions. The yarn containing the filaments of the present invention had a birefringence calue of 0.01.01 and the control yarn a value of 0.0 85· Both yarns were drawn using a production type drawtwister operating at a drawing speed of 1520 feet per minute. The draw ratios were adjusted for each yarn to give drawn yarn of 30 denier with 0.5Z turns per inch twist and with a nominal extension at break of approximately 30 per cent.

The yarn containing the filaments of this invention had to be drawn at a draw ratio of 4·40 to produce a yarn with an extension at break of approximately 30 per cent while the same extension at break could be obtained in the control yarn by drawing it at a draw ratio of only 3.12. The increase in spinning productivity, arising from the opportunity which was afforded of using larger throughputs of the polymer, was therefore of the order of 40 per cent.

Without lim ting the invention to any particular theory it is believed that the incorporation of a nucleating agent such as that described in Example 1 in a polyamide influences the development of crystallinity in filaments spun from the molten polymer to the end that the filaments solidify nearer the spinneret plate than unnucleated filaments, with a reduced degree of supercooling at the solidification point. The nucleant also causes the formatiom The filaments were spun into a quenching chamber wherein they were cooled by a transverse stream of air and in which they became solid. The 10 filament yarn so obtained, in the filaments were each 9 denier, was collected at ambient temperature and relative humidity at a speed of 3930 feet per minute in the form of a yarn package. To provide the comparative information a control yarn, derived from polyhexamethylene adipamide chips having a relative viscosity of 40 and containing 0.3 per cent iO^ as a delustrant but no copolymer nucleating agent, was spun and collected under identical conditions. The yarn containing the filaments of the present invention had a birefringence calue of 0.0101 and the control yarn a value of 0.0185. Both yarns were drawn using a production type drawtwister operating at a drawing speed of 1520 feet per minute. The draw ratios were adjusted for each yarn to give drawn yarn of 30 denier with 0,52 turns per inch twist and with a nominal extension at break of approximately 30 per cent.

The yarn containing the filaments of this invention had to be drawn at a draw ratio of 4«40 to produce a yarn with an extension at break of approximately 30 per cent while the same extension at break could be obtained in the control yarn by drawing it at a draw ratio of only 3.12. The increase in spinning productivity, arising from the opportunity which was afforded of using larger throughputs of the polymer, was therefore of the order of 40 per cent.

Without limiting the invention to any particular theory it is believed that the incorporation of a nucleating agent such as that described in Example 1 in a polyamide influences the development of crystallinity in filaments spun from the molten polymer to the end that the filaments solidify nearer the spinneret plate than unnucleated filaments, with a reduced degree of supercooling at the solidification point. The nucleant also causes the formatiom of a large number of small optically birefringent regions uniformly distributed throughout the filament to the exclusion of large spherulites, which regions, when viewed in polarised light, do not exhibit any resolvable pattern of preferred orientation such as the well-known extinction patterns normally associated with sphorulitic structures and are usually less than 1 micron across.

The influence of the nucleating agent employed in Example 1, i.e. a (50 s 50) 6.6 i 6T copolymer, at varying concentrations, on the D.T.A. freezing point of 6.6 nylon is shown graphically in Figure 3, in which freezing point is plotted against rate of cooling. The curves in Figure 3 are identified as follows: Curve A - polyhexamethylene adipamidc with no copolymer nucleating agent Curve B with O.05 per cent nucleating agent Curve C with 0.1 " " " " Curve D - with 0.3 " " " " Curve E - with 1 " " " Curve F - with 3,5 & 10 per cent " The Figure shows that the freezing point of the polymer increases with increase in concentration of the nucleating agent up to between 1 and 3 levels, there being little detectable change as the concentration is increased from 3 to 10 (curve F) .

Figures 4 and 5 show graphically on linear and ljjg scales respectively, the variation in D.T.A. freezing point of 6.6 nylon containing different amounts of the copolymer nucleating agent.

The freezing points being determined at a fixed rate of cooling, i.e. 64°c/min. Little change in freezing point is seen until the concentration of the nucleating agent reaches at least the about the 2$¾ level after which there is little or no increase.

A copolymer nucleating agent concentration in the range 0.5 to would appear to be a satisfactory working range.

Although the above-mentioned graphs were constructed from results obtained from bulk polymers, the conclusions are equally applicable to filaments spun from the polymer which would normally be cooled at a rate exceeding 64°C/min.

In the further examples described hereinafter the increase in productivity is indicated by the productivity ratio (P.R.) which is defined as:- Draw ratio to yield 30 extension at break for a filament „ containing nucleating agent Jr.xi. -a ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Draw ratio to yield 30% extension at break for a filament without nucleating agent The as-spun yarns are also characterised by reference to the draw ratio at a nominal stress of 0.5 g/d. This parameter is determined by measuring the drawing tension of the yarn when drawn at a draw roll speed of 800 f.p.m. at draw ratios of 1.25, 1 .50 , 1 .75, etc. until the yarn breaks. The values of drawing tension are converted to nominal stress by the relationships - . , drawing tension nominal stress = " ■ ■■ spun denier, where spun denier is the denier of the undrawn yarn. Nominal stress is then plotted against draw ratio and the draw ratio at a nominal drawing stress of 0.5 g Comparison of the draw ratios at a nominal stress of 0.5 g d of as-spun filaments containing a nucleating agent with as-spun filament without a nucleating agent, clearly shows that higher draw ratios can be achieved with the former.

In order to obtain the filaments of the present invention it is essential that the nucleating agent remain as discrete particles in the polymer during spinning and also during melt dispersion when this method is used to incorporate the nucleating agent in the polymer. It is also important under these circumstances that the holding time of the polymer containing the nucleating agent in the molten state during melt-dis^roLrig find spinning be kept as short as practicable to limit the degree of amide interchange taking place between the polymer and the whioh would nucleating agent / effectively destroy the latter.

For the above reasons it is clear that a polymeric nucleating agent should have an optical melting point at least above the melt holding temperature at spinning. Preferably the optical melting point of the nucleating agent is at least 10°C or even more preferably at least 30°C above the melt holding temperature at spinning.

A polymeric nucleant which has an optical melting point which is considered to be too low to be wholly effective in a particular polyamide system, may have its melting point raised by a heat treatment. Thus it has been established that the optical melting point of a (50 : 50)6.6 s 6T copolymer can be raised from 325°C to 344°C by heating at 325°C for 1 hour under steam at atmospheric pressure.

EXAMPLES 2. 3 and 4 In thece examples the base polyamide was 6.6 nylon (40.R.V. containing 0.3 Ti02) and the nucleating agent a (50 s 50) 6.6 : 6T copolymer.

The spinning speed, in these and all subsequent examples, was 3930 f.p.m. unless stated to be otherwise.

The nucleating agent was prepared by mixing together in the presence of a small amount of water, equivalent molar preparations of hexamethylene di ammonium adipate and hexamethylene diammonium terephthalate. The mixing was carried out in an autoclave with continuous agitation at a t emperature of 250°C and a pressure of 510 p.s.i. for 2 hours. The low molecular weight polymer was further polymerised in the solid state by heating at 290°C in steam for a period of 5¾- hours. The optical melting point of the copolymer was 330°C.

Dispersion of the nucleating agent in 6.6 nylon was carried out using the general procedure described in Example 1 with various ratios of base polymer to nucleant employed in the preparation of the master batch. Details of the dispersion of the copolymer nucleating agent in 6,6 nylon base polymer are given in Table 1 below: TABLE T Example Master batch ratio (Uucleant.base polymer) 1 : 19 1 : 1 : 2 Solvent 90fcaq.pb.cnol 05&i . phenol 90 aq.phenol Precipitant Benzene Methanol Methanol Vols : Vol solvent 10 : 1 10 : 1 10 : 1 Chip coating ratio (Master batch: base polymer) 1 : 4 1 : 9 1 s 32.3 Concentration of nucleating agent 1 D.T.A. freezing point of 0 nucleated polymer 233 c 233°C 233°C The polymers were spun into 10 filament yarns at a spinning speed of 3930 ft/min. at a spinning temperature of 290°C and subsequently drawn at 1500 Details of spun yarn properties and draw ratios in table 2 .

EXAMPLES 5 , 6 and 7 The present examples illustrate a method of incorporating a nucleating agent in a base polymer by "melt-dispersion". The base polymer and a (50 s 50) 6. 6 s 6T polymeric nucleating agent were initially blended together at various nucleant to base polymer ratios by mixing the polymer and nucleant together in the dry state and then melt-dispersing the nucleant by passing it through a screw extruder. The molten polymer containing the disposed nucleating agent was cooled, chipped and blended with the base polymer chip to give the correct nucleant concentration. The screw extruder used had a screw diameter of -finch and ran at a speed of 25 r.p.m. The maximum temperature of the barrel of the extruder was 325°C and the throughput 30 ml/min. giving a polymer transit time in the extruder of approximately 1 minute. used in the previous experiments . Details of the processes and yarn properties are given in table 3.

TABLE 3 Example Melt dispersing Ratio nucleating agent to base polymer in master batch 1 s 1 s Temperature, C 315 325 325 Chip blending Ratio melt mix to base polymer 1 : Concentration of nucleating agent, °/o D.T.A. freezing point of nucleated polymer, °C j 231 229 231 Spun yarn properties Denier/f ilament ! 13.0 13.7 13.6 Birefringence j 0.0128 0.0113 0. x j 0.24 0.08 0.26 j -0.60 -0.53 -0.68 0. - 0 l o I 0.84 0.61 0.94 D.T.A. freezing point, ; 231 229 231 Draw ratio for 3 fo extension at break 4.20 4-40 Draw ratio at nominal stress of 0.5 3.84 3.12 Productivity ratio 1 .33 1 .40 Example 8 illustrates the efficacy of a (50 ; 50)6.6 s 6T copolymer nucleant in increasing the productivity in the manufacture of filaments from 6.8 nylon. Example s a control experiment.

The nucleating agent 7/as prepared as in the previous examples and dispersed in the base polymer "by the melt-dispersing method. Details of the polymer preparation and spun and drawn yarn properties are given in table 4 · TABLE 4 Examples 10, 11 and 12 illustrate the effectiveness in 6.6 nylon of different polyamide nucleating agents containing a terephthalamide linkage in the polymer chain, Example 13 is a 6.6 nylon control included for the purpose of comparison. under the conditions previously described. Details are given in table 5 · TABLE 5 * The solvent was 90i¾ aq. phenol and precipitant methanol.

TABLE 5 (continued) The following examples, 14 - » compare the effectiveness of various concentrations, from 0.01 to 5·0 b weight, of the preferred nucleating agent, ( 0 : 50)6.6 : 6.T nylon, in 6.6 nylon containing 0.3% iOg. Details are shown in Table 6.

TABLE 6 Example 14 15 16 17 18 19 Method of dispersing sol. sol. melt- sol. sol. melt- nucleating agent blendblenddisblendblenddie- ing ing persing ing ing persing Temperature of melt dispersing, °C - 325 - 325 i Ratio nucleating agent to base polymer in master batch 1 : 19 1 : 19 1 : 19 1 : 19 1 : 2 1 : 19 Chip blending/chip coating: ratio master batch to base polymer 1:499 1 : 49 1 : 9 1 : 4 1:32.2 Concentration of nucleating agent, 0.01 0.1 j 0. 1.0 2.0 •5.0 D.T.A. freezing point, i I °C 1 232 233 - - TABLE 6 (continued) The above examples indicate that, in the particular system employed and under the conditions of dispersion used, 0.01 of the nucleating agent is insufficient to yield filaments according to the present invention. Thus 0^ - 0q is less than 0.2 , there is substantially no increase in productivity, and the draw ratio at a nominal stress of 0.5 g/d and draw ratio for 3 °/o extension at break is lower than for the remaining examples which illustrate the invention. There are however indications that nucleation had occurred since the spun yarn has an increased D.T.A. freezing point compared with the control yarn of example 13. The results also indicate that there is no advantage in using a concentration of nucleating agent exceeding 0. 1 , although in practice a concentration of between about 0.5 and 1 . would be preferred for urel technical reasons associated with obtainin an ade uate Examples 20, 21 and 22 illustrate the use of different proportions of 6.6 and 6.T nylons in the preferred copolymer nucleant at the 1% level of nucleant in 6.6 nylon. In example 20 the nucleating agent wan prepared by mixing together aqueous solutions of hexamethylene diammonium adipate and hexamethylene diammonium terephthalate, in the correct proportions by weight, and polymerising the mixture an a continuous process in a coil such as that described in British Patent Specification No. 24, 630 In examples 21 and 22 the nucleating agents were prepared by the normal procedure adopted in the batch preparation of 6.6 nylon polymer. The nucleating agents were melt-dispersed with the 6.6 nylon to give a master batch and the master batch chip blended with 6.6 nylon chips to give a final concentration of 1 by weight of the nucleating agent in 6.6 nylon. Details are shown in table 7· TABLE 7 Example 20 21 22 i Ratio nucleating agent to base polymer in master batch 1 s 1 9 1 : 9 Temperature of melt-dispersing, °C 335 315 295 Ratio master batch to base polymer in chip blend - 1 : 4 1 : 9 Ratio 6. 6s 6.T nylon in nucleant 45 : 55 55 : 45 60.- 40 Spun yarn properties Denier/filament 1 2.5 13.3 9.0 Bi efringence 0.0131 0.0099 0 . 0. 21 -O.1 6 1 -0.26 0 0 -0.59 -0.42 -Q.52 ·:· . - 0 0 1 0 .80 0.26 0.26 TABLE 7 (continued) EXAMPLE 23 This example relates to the manufacture of 6.6 nylon monofil from polymer containing o of (50 ; 50) 6.6 s 6. T copolymer nucleating agent. A 1 ; nucleating agent to base polymer master batch was prepared by melt dispersion at 310°C and the master batch chip blended with more base polymer in a 1 ; 9 ratio to give the desired concentration of nucleating agent , The polymer was spun using conventional equipment to give a monofilament. Spinning speed and filament parameters are shown in table 8.

TABLE 8 Since a 66 d.p.f , monofil can normally only be spun at speeds The yarn could be drawn at speeds up to 4» 500 f.p.m. using a snubbing pin heated to 110 - 125°C at draw ratios of 4.0 to 4.2 to yield a drawn yarn having a tenacity of 4.34 g/d., extension at break of 2 .3 and an initial modulus of 26.5 g/d/ 100$ extension.

EXAMPLE 24 This example illustrates the effect of melt-dispersing a (50 s 50)6.6 : 6.T copolymer nucleating agent, having an optical melting point of 330°C, in 6.6 nylon at high a temperature.

Details are given in table 9· TABLE 9 The temperature employed in melt-dispersing the nucleating agent in the polymer was greater than that preferred, i.e. 1.08 times the optical melting point of the nucleating agent, and in

Claims (33)

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed* we declare that what we claim is :

1. . A yarn comprising one or more undrawn polyamide filaments having molecular orientations exhibiting X-ray reflect patterns in which O^- q , 0.2. as hereinbefore defined

2. A yarn according to Claim 1 wherein - 0 .

3. A yarn according to Claim 1 having a molecular orientation in which 0 - 0q > 0.7.

4. A yarn to Claims 1 , 2 and 3 comprising filaments of polyhexamethylene adipamide.

5. A yarn according to Claims 1 , 2 and 3 comprising filaments of polyhexamethylene suberamide,

6. A yarn according to any one of the recedin claims polyamide comprising/filaments containing a as hereinbefore defined agent/ dispersed therethrough.

7. A yarn according to Claim 6 containing at least 0.05$ by weigh

8. ' A yarn according to Claim 7 containing 0.5 - 1 . $ by weight of the nucleating agent.

9. · A yarn according to Claims 6, 7 an 8 wherein the nucleating agent is polymeric and has an optical melting point greater than the melt holding temperature at spinning as hereinbefore defined.

10. A yarn according to Claim 9 wherein the nucleating agent is polymeric and has an optical melting point at least 10°C above the melt holding temperature at spinning.

11. 1 1 . A yarn according to Claim 10 wherein the nucleating agent is polymeric and has an optical melting point at least 30°C above the melt holding temperature at spinning.

12. A yarn according to any one of Claims 9, 0 or 11 wherein the nucleating agent comprises a polyamide or copolyamide containing aryl linkages in the polymer chain.

13. A yarn according to Claim 12 wherein the nucleating agent comprises pol (methylene)x terephthalamide where x is an integer between 2 and 12.

14. A yarn according to Claim 12 wherein the nucleating agent is polyhexamethylene terephthalamide.

15. A yarn according to Claim 12 wherein the nucleating agent is polydecamethylene terephthalamide.

16. A yarn according to Claim 12 wherein the nucleating agent is a copolymer of polyhexamethylene adipamide and polyhexamethylene terephthalamide.

17. A yarn according to Claim 16 wherein the nucleating agent is a copolymer of polyhexamethylene adipamide and polyhexamethylene terephthalamide containing at least 30$¾ by weight of polyhexamethylene terephthalamide.

18. A yarn according to Claim 17 wherein the nucleating agent is a copolymer of polyhexamethylene adipamide and polyhexamethylene terephthalamide containing at least 40$ by weight of polyhexamethylene terephthalamide.

19. 1 . A yarn according to Claim 17 wherein the nucleating agent is a copolymer of polyhexamethylene adipamide and polyhexamethylene terephthalamide, in equal proportions by weight,

20. A process for the manufacture of a yarn comprising one or more undrawn polyamide filaments comprising incorporating a finely as hereinbefore defined divided nucleating agent/ in a polyamidef forcing the molten polyamide containing the nucleating agent through a filtering medium^extruding the said polyamide through orifices contained in a spinneret plate and winding up the filaments.

21. A process according to Claim 20 wherein the nucleating agent is polymeric.

22. A process according to Claims 20 and 21 wherein the polyamide contains at least 0.05 by weight of the nucleating agent.

23. A process according to Claim 22 wherein the polyamide contains 0.5 o to 1 .5 ¾ weight of the nucleating agent.

24. · A process according to any one of claims 21 - 23 wherein the nucleating agent has an optical melting point greater than the melt holding temperature at spinning.

25. A process according to Claim 24 where the nucleating agent has an optical melting point of not less than 10°C above the melt holding temperature at spinning.

26. A process according to Claim 25 wherein the nucleating agent has an optical melting point at least 30°C above the melt holding temperature at spinning.

27. · A process according to any one of Claims 20 - 26 wherein the nucleating agent is incorporated into the polyamide by preparing a master batch with a portion of the said polyamide by coprecipitation of mixed solutions thereof, forming the master batch into a paste,coating the said master batch onto the remaining portion of the polyamide and melting together at spinning.

28. A process according to any one of Claims 20 - 26 wherein the nucleating agent is incorporated in the polyamide by melt-dispersing the nucleating agent in the polyamide prior to extrusion into filaments.

29. · A process according to Claim 27 wherein the melt dispersion is solidified, formed into chips and subsequently extruded into filaments by melt spinning.

30. A process according to any one of Claims 20 - 26 wherein the nucleating agent is incorporated into the polyamide by preparing a master batch with a portion of the said polyamide by melt dispersing the nucleating agent in the polyamide, forming the master batch into chips and blending the said chips with the remaining portion of the polyamide and melting together at spiiining.

31. . A process according to any one of Claims 28 - 30 wherein ' dispersing the temperature of the melt- £ is less than 1 .08 timos the optical melting point of the nucleating agent.

32. A process according to Claim 31 wherein the temperature . dispersing times of the melt- £ is less than 1.04 the optical melting point of the nucleating agent.

33. A process according to any one of Claims 28 - 32 wherein the nucleating agent is incorporated in the polyamide by melt dispersion in a screw extruder. 34· A process for the manufacture of a yarn comprising one or more undrawn polyamide filaments according to any one of Claims 1 - 19 substantially as described herein with reference to Examples. DATED the 12th day of SEPTEMBER, 1966 S. Horowitz, &)Co. Agents for Applicants DJA/CRF - 34 -