Process for manufacturing superabsorbent-coated aramid yarn

Abstract: An aramid yarn, preferably poly(p-phenylene terephthalamide), is coated with a water swellable superabsorbent material. The swelling value of the yarn is at least 60. The superabsorbent provides water blocking capability to the yarn, so that it is suitable for use as a strength member in water tight optical communication cables. The yarn is made by successively treating an aramid yarn with a water-in-oil emulsion, a superabsorbent material being present in the water phase of the emulsion, and removing the liquid components from the treated yarn by evaporation.

Description: The invention relates to a process for manufacturing an aramid yarn coated with a superabordent material. Said yarn can be utilised in cables, more particularly optical communications cables, in this way functioning simultaneously as reinforcing member and as water blocking agent. An aramid yarn provided with a superabsorbent material and the manufacture of such a yarn are known from EP-A-0 351 100. According to this publication Kevlar®, a commercially available yarn of poly(p-phenylene terephthalamide) ex E.I. DuPont de Nemours, is impregnated with a superabsorbent material. After being impregnated the treated yarn is dried, so that a film is formed in and around the yarn's interstices. In one embodiment of this treatment method the yarn is impregnated with a superabsorbent material derived from an aqueous solution comprising acrylate polymeric material which combines acrylic acid and sodium acrylate functionalities and water. The resulting product is used as reinforcing material for the manufacture of a communications cable with water blocking properties. US-A-4 798 744 discloses a method of making superabsorbent fibrous porous support by impregnation of a porous support with a reverse suspension or emulsion. Said reverse suspension or emulsion results from the polymerization reaction and the removal of solvent from the support. The porous support can be a non-woven material, paper, fibre pile or a foam, of which the porosity is preferably greater than 0,5. Cellulose fibres are mentioned. The fibres treated are ment to comprise as much absorbent material as possible, so that the absorbent capacity is as large as possible. The superabsorbent material consists of a mixture of polyacrylic acid and an alkali acrylate, and a surfactant having an HLB value of 8-12. International Wire & Cable Symposium Proceedings 1988, pp. 307-308 describes a Kevlar® yarn treated with water swellable polymers. Such a yarn is used as reinforcing material in optical cables, providing them with water blocking properties. Said publication discloses neither the composition of the water swellable polymer, nor the manner in which treatment of the yarn with this polymer is carried out. Also, it is known that cables can be provided with a superabsorbent polymeric material by being contacted with said material in the powdered form, optionally with use being made of electrostatic forces. However, there are drawbacks to the above-mentioned methods of applying a superabsorbent material to a cable or yarn surface. The drawback to impregnating an aramid yarn with a superabsorbent material dispersed in an aqueous system is that, due to the superabsorbent material's high viscosity-enhancing action, uniform feeding of it is extremely difficult, if not impossible. Further, on account of the limited concentration of superabsorbent material in the impregnating liquid only a small quantity of it can be applied to the yarn per treatment. Another drawback to this method is that the comparatively large amount of impregnating liquid which is applied to the yarn with the superabsorbent material has to be removed again by evaporation. The disadvantage of handling superabsorbent materials in the powdered form is that special equipment is required and that, furthermore, it is hard to distribute the powdered material uniformly over the yarn. An additional drawback to handling powders is that dust is raised, with the attendant risk of explosions and health hazards. US-A-4,888,238 discloses a method of preparing superabsorbent synthetic fibres coated with a water absorbent polymer. As synthetic fibres which can be used are mentioned polyester, polyolefin, polyacrylonitrile, polyamide, rayon, cellulose acetate, dacron, nylon and bicomponent fibres. The fibres are added to an aqueous solution of an anionic polyelectrolyte, a polyvalent metal salt and a neutralizing agent. They are then fluff dried to evaporate the neutralizing agent and form a complex of the polyelectrolyte in situ as a coating thereon. Drawbacks to this method are that it can only be applied to short fibres, the evaporating neutralizing agent, i.e. ammonia, pollutes the atmosphere and the coating of the superabsorbent is resolubilized at a pH above 7. The present invention obviates the aforesaid drawbacks. The invention consists of a process for manufacturing an aramid yarn coated with a superabsorbent material. This process is characterized in that on the aramid yarn surface there is applied a layer of a water-in-oil emulsion containing in its aqueous phase a material having superabsorbant properties, and that next the emulsion's liquid ingredients are wholly or partially removed from the yarn by evaporation, the yarn being treated as such. The process according to the invention renders it possible to produce high quality aramid yarns having superabsorbent properties in an economical manner. The aramid yarn provided by the process of the invention may have a swelling value of at least 60. The swelling value is a measure of the quantity of water absorbed by the yarn when it is contacted with water in the liquid form. The method of experimentally determining the swelling value will be illustrated in greater detail below. It was found that the yarn obtainable according to the process of the invention may have a substantially higher swelling value than comparable prior art yarns. So far, it has proved impossible to explain this surprising property. It might be that the higher swelling value of the yarn obtainable according to the process of the invention is bound up with an improved uniformity of superabsorbent distribution in the yarn. The swelling value of the yarn obtainable according to the process of the invention may be at least 80, more particularly at least 100, and more particularly still at least 150. By aramid yarns is meant according to the invention yarns composed of polymers built up wholly or substantially from recurring units of the general formula Herein A 1 , A 2 , and A 3 represent different or the same divalent, one or more aromatic rings-containing rigid radicals which may also contain a heterocyclic ring, the chain-extending bonds of which radicals are in the position para to each other or are parallel and oppositely directed. Examples of such radicals include 1,4-phenylene, 4,4'-biphenylene, 1,5-naphthylene, and 2,6-naphthylene. They may contain substituents or not, e.g. halogen atoms or alkyl groups. In addition to amide groups and the aforementioned aromatic radicals the chain molecules of the aromatic polyamides may optionally contain up to 35 mole % of other groups, e.g. m-phenylene groups, non-rigid groups such as alkyl groups, or ether groups, urea groups or ester groups. Preferably the aramid yarn is made up wholly or in part, more particularly for over 90 wt.%, of poly(p-phenylene terephthalamide). By a superabsorbent is meant according to the invention a water-soluble or water-insoluble material having hydrophilic properties which is capable of absorbing and retaining a comparatively large quantity of water, optionally under pressure. So, the materials to be applied according to the present invention include, in addition to the insoluble superabsorbents mentioned on p. 198 of P.K. Chatterjee, ed.'s Absorbency , Elsevier, Amsterdam (1985) and in European Patent Application 0 351 100, superabsorbents that are wholly or partially water-soluble. Although the aramid yarn may be coated with any material having superabsorbent properties, preference is given to those superabsorbents which can be processed into stable water-in-oil emulsions. As will be illustrated in greater detail below, there are major advantages to such emulsions in the manufacture of said yarn. Particularly suitable for use are superabsorbent derivatives of polyacrylic acid. These include the homopolymers and copolymers derived from acrylamide, from acrylamide and sodium acrylate, and from acrylamide and dialkylaminoethyl methacrylate. These compounds are selected from the groups of non-ionic, anionic, and cationic (co)polymers, respectively. They are generally prepared by linking of the monomer units to form a water-soluble polymer. This can then be rendered insoluble by means of ionic and/or covalent cross-linking. Examples of superabsorbents that can be used in the manufacture of the yarns according to the invention include: cross-linked polyacrylic acid partially neutralised into the sodium salt, polypotassium acrylate, copolymers of sodium acrylate and acrylamide, terpolymers of acrylamide and carboxyl groups- and sulpho groups-containing monomers (sodium salt), polyacrylamide copolymers. Preferably, use is made of a terpolymer of acrylamide and carboxyl groups- and sulpho groups-containing monomers (sodium salt) or of a polyacrylamide copolymer. In the process according to the invention the superabsorbent material is applied to the aramid yarn via a water-in-oil emulsion, the superabsorbent being present in the emulsion's aqueous phase. The preparation of such an emulsion is as follows: using an emulsifier a water-soluble monomer admixed with a quantity of water is dispersed in a non-polar solvent immiscible with water and the monomer, and then polymerised to form a water-in-oil emulsion. The polymer formed is in the aqueous phase of the emulsion. In this manner a liquid product is obtained which contains highly concentrated superabsorbent while the liquid's viscosity remains low. Such emulsions and their preparation are known in themselves. A description with respect to the water-soluble superabsorbents can be found in, int. al., US-A-4 078 133, US-A-4 079 027, US-A-4 075 144, US-A-4 064 318, US-A-4 070 321, US-A-4 051 065, and DE-A-21 54 081, one with respect to the water-insoluble superabsorbents in Japanese laid-open Patent Application JP-A-147630/81. As continuous oil phase of the emulsion can be used liquids which are immiscible or poorly miscible with water, such as linear, branched, and cyclic hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons, etc. It is less desired to have liquids with a high boiling point, since it is difficult to remove them from the yarn by evaporation. Preferably, linear, branched, and cyclic hydrocarbons are employed, or petroleum fractions which are substantially made up of a mixture of such hydrocarbons and have a boiling point in the range of 150°-250°C. The emulsifiers employed are selected such that said mixture can be converted into a water-in-oil emulsion. This means that the emulsifier should have an HLB (hydrophile-lipophile balance) value of 3-12. The concentration of superabsorbent material in the emulsion used according to the invention is 1-90%, preferably 2-50%, calculated on the overall weight of the emulsion. Commercially available water-in-oil emulsions containing a superabsorbent generally have a solids content of 20-70 wt.%. In the process according to the invention these products can be employed either as such, i.e. undiluted, or in combination with additives, such as lubricants, stabilisers, emulsifiers, and/or diluents. Examples of materials suitable for use as emulsifier and as lubricant include ethoxylated oleyl alcohol and ethoxylated oleic acid. Examples of materials suitable for use as diluent include non-aromatic naphthenic and (iso)paraffinic hydrocarbons having a boiling point of 150°-280°C and isohexadecane, notably hydrogenated tetraisobutylene. To enhance their stability the dilute water-in-oil emulsions may contain 5-100 wt.%, preferably 20-80 wt.%, calculated on the undiluted emulsion, of one or more special stabilisers. These stabilisers should have an HLB value of less than 5. The meaning of the HLB (hydrophile-lipophile balance) value has been described in P. Becher, Emulsions, Theory and Practice , second ed., Reinhold Publishing Corp., New York (1965), pp. 232-255. As suitable stabilisers can be mentioned sorbitan trioleate, mixtures of sorbitan trioleate and ethoxylated sorbitan trioleate, sorbitan mono(iso)stearate, and sorbitan mono-oleate. In general, materials having a higher HLB value will cause the water-in-oil emulsion to have poorer stability. The stabilisers incorporated into the emulsion also have the favourable property of preventing the yarn from becoming electrostatically charged, so that filament spreading and filamentation are avoided. The viscosity of the commercially available water-in-oil emulsions is significantly reduced by their being diluted. As a result it becomes possible to apply the superabsorbent-containing water-in-oil emulsion to the yarn by means of a kiss roll. The amount of superabsorbent on the yarn is selected such that favourable water blocking properties are obtained when the yarn is used in cables. Favourable results are usually obtained if the yarn contains 0.3-10 wt.%, preferably 0.5-5 wt.%, and more particularly 0.6-2 wt.% of the superabsorbent material. In the process according to the invention the water-in-oil emulsion can be applied using a method known in itself, e.g. via a finishing bath, a kiss roll or a liquid applicator. The water-in-oil emulsion having been applied, the yarn is dried. In this process the non-polar solvent present in the emulsion and the water are wholly or for the most part removed from the yarn by evaporation, so that a uniform layer of the superabsorbent material is left on the yarn surface. Drying takes place according to the conventional methods, in which use may be made of means such as hot drums, hot sheets, hot rollers, hot gases, tube ovens, steam chests, infrared radiators, and the like. The drying temperature is 50°-300°C, preferably 100°-250°C. The process according to the invention can be carried out in several ways. In the fully continuous manner, which is linked directly to the aramid yarn spinning process, the water-in-oil emulsion containing the superabsorbent can be applied to the washed and dried yarn, after which the thus treated yarn is dried. According to another embodiment treatment of the yarn with the superabsorbent present in a water-in-oil emulsion takes places in a separate process not integrated with the spinning process. The process according to the invention is particularly suited to be used for combining, in one and the same process step, a heat treatment to improve the mechanical properties of the yarn, such as is employed in the production of high-modulus aramid yarns, with the yarn's treatment with the superabsorbent material. In Kirk-Othmer, Encyclopedia of Chemical Technology , 3rd Ed., Vol. 3 (1978), pp. 213-242 a summary of aromatic polyamide preparation and spinning is provided. A pre-eminently suitable technique for wet-spinning poly(p-phenylene terephthalamide) is described in US Patent Specification 4 320 081. The aramid yarns used in the process of the invention can have any linear density and any number of endless filaments common in actual practice. Generally the yarn will have a linear density of 10 to 20 000 dtex and be composed of 10 to 20 000 filaments. The superabsorbent material applied to the aramid yarn according to the process of the invention does not have a negative effect on the yarn's principal mechanical properties. The tenacity of the yarns according to the invention is 10-35 cN/dtex or higher, preferably 15-25 cN/dtex. The elongation at rupture is 0.5-10%, preferably 1-8%. The initial modulus is 200-1300 cN/dtex or higher, preferably 300-900 cN/dtex. Like the corresponding aramid yarn not treated with a superabsorbent, the yarn obtainable by the process of the invention has a relatively low water content after drying, even after it has been exposed to the air for a longer period of time. After the dried yarn has been conditioned at 20°C and a relative humidity of 65% for 4 weeks, it has a water content not exceeding 10 wt.% , more particularly not exceeding 7 wt.%. Apparently, the superabsorbent present in the yarn obtainable by the process of the invention absorbs only a small quantity of the water vapour present in the air. It is only when the yarn is contacted with water in the liquid form that it absorbs a large quantity thereof and so swells. By "yarn" are to be understood within the scope of the invention yarns comprising all usual fibre types, such as filaments of practically unlimited length and shorter fibres, e.g. staple fibres. Preferably the yarn of this invention comprises filaments of practically unlimited length. The procedure to determine the swelling value of the yarn obtained is as follows. About 10 g of the yarn to be examined are cut into non-intertwisted fibres of some 12 cm in length. Cutting may, of course, be omitted if the product consists of fibres shorter than about 12 cm. The fibre sample is immersed completely, without stirring, in 600 ml of demineralised water of 20°-22°C in an 800 ml beaker. For 60 seconds (measured by stopwatch) the fibre sample remains immersed in the water in a condition of complete rest, i.e. without being stirred, shaken, vibrated, or subjected to some other form of movement. Immediately afterwards the overall contents of the beaker, i.e. fibres and water, are transferred to a bag (dimensions: about 10 cm x 15 cm) made of polyester curtain netting (mesh size 1.5 mm x 1 mm). In this process the water for the most part runs out through the meshes of the curtain netting, while the fibres are left in the bag. Next, the bag and its contents are straightaway transferred to a centrifuge and then centrifuged for 120 seconds (measured by stopwatch), thus removing the still adhering water from the impregnated fibre sample. The centrifuge used is an AEG of the type SV 4528 (ex AEG Aktiengesellschaft, D-8500 Nuremberg), operates at a rate of 2800 revolutions per minute, and has a centrifugal drum with an inner diameter of about 24 cm. Immediately after it has been centrifuged the fibre sample is transferred from the bag to a weighing box with a pair of tweezers and weighed to an accuracy of 0.0001 g (fibre weight: a grammes). The fibre sample in the weighing box is thereupon dried to constant weight in an air oven at 105°C. Usually a drying time of 24 hours will suffice. After that the weight of the dried fibre sample in the weighing box is determined to an accuracy of 0.0001 g (fibre weight: b grammes). The swelling value of the yarn is calculated by means of the following formula: swelling value = (a-b).100 b . Each determination is carried in duplicate and the results are averaged. Because of the properties mentioned hereinbefore the yarn obtaineble according to the process of the invention is extremely well suited to be used as a reinforcing yarn of high water blocking capacity. Consequently, it is pre-eminently suitable for use in cables, more particularly optical communications cables. The invention will be further illustrated with reference to the following examples. Example I At a yarn rate of 20 m/min and using a split applicator and a feed pump (geared pump or tubing pump) an unfinished filament yarn of an aramid composed of poly(p-phenylene terephthalamide) with a linear density of dtex 1680 f 1000 was provided with a water-in-oil (W/0) emulsion. The emulsion contained in its aqueous phase a material having superabsorbent properties. Next, the yarn was dried. The water blocking action of the resulting yarn was determined using the through-flow test. In this test the inner cylindrical space of a section of PVC (polyvinyl chloride) hose open on both sides is filled with a bundle of the yarn, such that the longitudinal axis of the yarn bundle is substantially parallel with the longitudinal axis of the cylindrical space in which the yarn bundle is positioned. The hose filled with the yarn is cut through in a direction perpendicular to its longitudinal axis in two places, such that a cylinder-shaped test tube of a length of 50 mm is formed and the ends of the yarn bundle present in the thus obtained test tube by and large coincide with the test tube ends. Next, one of the ends of the test tube is contacted with the contents of a vessel of liquid and subjected to the pressure of a head of water of a particular height. The time required to wet the entire yarn bundle in the test tube is referred to as the through-flow time. This time is a measure of the water blocking action of the yarn. The through-flow time is taken to be the time which passes after the application of water pressure to the one end of the test tube and prior to the first drop appearing at the other (free) end. The through-flow test is carried out under the following conditions: Type of hose polyvinyl chloride Hose, inner diameter 5 mm Hose, outer diameter 7 mm Length of test tube 50 mm Number of yarns in test tube 100 Number of measurements 1 Height of liquid head 100 cm Testing liquid demineralised water The number of yarns in the test tube should be chosen such that the bundle formed from them will fully fill the inner cylindrical space of the test tube. For a yarn linear density of dtex 1680 f 1000 this number was found to be 100, giving an overall linear density for the yarn bundle of dtex 168 000 f 100 000. The composition of the water-in-oil emulsions with which the aramid yarn was treated is listed in Table A. The emulsions were supplied by Chemische Fabrik Stockhausen GmbH, D-4150 Krefeld 1, Federal Republic of Germany. Emulsion no. Trade name Chemical composition Solids content (%) Viscosity ) (25°C) mm 2 /s A A 3024 poly(potassium)acrylate as W/0 emulsion, non-cross-linked 36 appr. 250 B A 3116 copolymer of (sodium) acrylate and acrylamide as W/0 emulsion, non-cross-linked 30 appr. 170 C W 41934 terpolymer of acrylamide, carboxyl groups- and sulpho groups-containing monomers (sodium salt) as W/0 emulsion, cross-linked 30 appr. 800 The results of the experiments are given in Table B. Exp. no. Emulsion no. Superabsorbent content of emulsion (wt.%) Amount of superabsorbent on yarn (wt.%) Through-flow time (100 cm water head) Swelling value 1 A1 2.1 0.5 appr. 30 min. 27 2 A2 4.2 1 >6 days - 3 A3 12.6 3 >14 days 79 4 A4 21.0 5 >6 days - 5 A5 31.5 7.5 >6 days - 6 A 36 0.5 >5 days - 7 B 30 1 >4 days 115 8 B 30 2 >6 days 115 9 B 30 0.5 >5 days - 10 C 30 1 >4 days 183 11 C 30 2 >6 days 295 12 C 30 0.5 18 hrs. - In Experiments 1 through 5 use was made of an emulsion obtained by diluting commercial product A 3024 with a mixture of non-aromatic naphthenic and (iso)paraffinic hydrocarbons having an atmospheric boiling range of 153°C to 188°C (Exxsol D 40, supplied by Exxon Chemical Holland B.V., Schiedam). In the experiments listed in Table B the yarn was successively dried in a tube oven (2 sec., 200°-250°C) and on a hot sheet (4.5 sec., 130°C). The through-flow time of the starting yarn, which was not treated with a superabsorbent-containing water-in-oil emulsion, was less than 1 minute. It is clear from the data in Table B that the process according to the invention permits the manufacture of an aramid yarn which, under the conditions of the through-flow test, is capable of withstanding water at a pressure of 1 m head for more than 14 days. It was found that when emulsions A and B were employed, white deposits were formed on the various yarn guiding members. However, when emulsion C was used, there were no such deposits at all. Example II An aramid yarn was treated with a superabsorbent material. The starting yarn and the process used were the same as in Example I, unless otherwise specified. The composition of the water-in-oil (W/0) emulsions used in the experiments is given in Table C. The viscosity value given in Table C was determined according to the method disclosed for Table A. Emulsion no. Trade name Chemical composition Solids content ) (%) Viscosity (25°C) mm 2 /s D Nalco 4755 polyacrylamide copolymer as W/0 emulsion 50 appr. 170 E Nalco 7863 polyacrylamide copolymer as W/0 emulsion 42 appr. 290 F Nalco 7862 copolymer of sodium acrylate and acrylamide as W/0 emulsion 34 appr. 270 Emulsions D, E, and F were supplied by Nalco Chemical B.V., Tilburg, the Netherlands. Various materials were added to the emulsions mentioned in Table C to reduce their viscosity, enhance their stability, and/or prevent the formation of deposits on yarn guiding members. In Table D the composition of the resulting W/0 emulsions is given in parts by weight. Emulsion no. A2 A6 C1 D1 E1 F1 Content (%) 4.2 11.0 8.3 9.2 8.5 7.8 A 3024 (36%) 11.7 16.7 W 41934 (30%) 16.7 Nalco 4755 (50%) 8.3 Nalco 7863 (42%) 8.3 Nalco 7862 (34%) 8.3 Span 85 4.15 3.3 4.15 5.0 5.0 Tween 85 0.85 0.85 Exxsol D40 88.3 Exxsol D80 78.3 Exxsol D120 80 Isohexadecane 86.7 86.7 86.7 The compositions listed in Table D are of the following composition: Span 85 is sorbitan trioleate, supplied by: ICI Holland B.V. Tween 85 is ethoxylated sorbitan trioleate, supplied by: ICI Holland B.V. Exxsol D80 and Exxsol D120 are non-aromatic naphthenic and (iso)paraffinic hydrocarbons having an atmospheric boiling range of 196°C to 237°C, and 255°C to 294°C, respectively, supplied by: Exxon Chemical Holland B.V., Schiedam. Isohexadecane is a mixture of C 16 -isoparaffinic hydrocarbons with small amounts of C 12 -paraffines, supplied by EC Erdölchemie GmbH, Köln, Federal Republic of Germany. The water-in-oil emulsions listed in Table D were used in the treatment of the aramid yarn disclosed above. The conditions under which the experiments were carried out and the results thereof can be found in Table E. Exp. no. Emulsion no. Composition concentration (wt.%) Amount of superabsorbent on yarn (wt.%) Amount of stabiliser on yarn (wt.%) Through-flow time (100 cm head) Swelling value 13 A2 4.2 1.0 - >6 days - 14 A6 11.0 1.2 1.0 >3 days - 15 C1 8.3 1.0 0.7 4 days - 16 D1 9.2 1.0 1.2 >3 days 117 17 E1 8.5 0.7 1.0 >7 days - 18 F1 7.8 0.5 0.9 1 hour 53 For comparison an experiment was carried out in which the aramid yarn was only provided with 0.8 wt.% of Breox 50A50, a conventional yarn finishing, i.e. without a superabsorbent-containing water-in-oil emulsion being applied to the yarn. Breox 50A50 is composed of ethoxylated and propoxylated butanol and supplied by B.P. Chemicals Benelux, Zwijndrecht, Belgium. The through-flow time for the yarn obtained in this comparative experiment was found to be less than 1 minute. Example III In this example the effect of stabilisers on the stability of the utilised W/0 emulsions is demonstrated. Also demonstrated is the effect of 4 weeks of conditioning at 20°C and a relative humidity of 65% on the moisture content of the aramid yarn manufactured using the process according to the invention. An aramid yarn was treated according to the process described in Example I, except that the linear density of the starting yarn was dtex 1610 f 1000 and drying of the yarn was with the aid of steam in steam chests (2-3 sec. at 240°C). In Table F the composition of the W/0 emulsions used in the experiments is given in parts by weight. Emulsion no. C3 D2 E2 C4 D3 E3 Content (%) 25.0 30.0 24.2 15.0 18.0 15.1 W 41934 (30%) 50 50 Nalco 4755 (50%) 36 36 Nalco 7863 (42%) 36 36 Span 85 10 12 9.1 Exxsol D80 40 52 54.9 50 64 64 Determined was the stability of the compositions listed in Table F. By stability is meant in this context the time between preparation and the moment when the first deposit becomes visible in the emulsion. The data in question is compiled in Table G. Emulsion no. Concentration of superabsorbent in the composition (wt.%) Concentration of stabiliser in the composition (wt.%) Stability in relative units of time C3 15 10 3.6 D2 18 12 30 E2 15.1 9.1 30 C4 15 - 1 D3 18 - 2 E3 15.1 - 1 Several of the water-in-oil emulsions listed in Table F were employed in the above-mentioned treatment of the aramid yarn. The conditions under which the experiments were carried out and the results thereof are given in Table H. Exp. no. Emulsion no. Conc. of composition wt.% Amnt. superabsorb. on yarn wt.% Amnt. stabiliser on yarn wt.% Residence time in steam chests sec. Moist. cont. after winding ) wt.% Moist. cont. after conditioning ) wt.% Through flow time ) days 19 C3 25 1.5 1.0 3 1.6-2.3 3.7 >17 20 D2 30 1.5 1.0 3 1.4-1.5 3.0 >17 21 D2 30 1.5 1.0 2 2.0-2.1 3.1 >17 22 E2 24.2 1.2 0.8 3 1.5-1.5 3.2 >14 The swelling value for the yarns obtained in Experiments 21 and 22 was 163 and 107, respectively. For comparison experiments were carried out to determine the moisture content and through-flow time of the aramid yarn not treated with a W/0 emulsion of a superabsorbent material. After having been conditioned at 20°C and a relative humidity of 65% such a yarn was found to have an equilibrium moisture content of 3.0% by weight. The yarn through-flow time was less than 1 minute. The swelling value of this untreated yarn was 19. Example IV This example demonstrates the favourable effect of stabilisers as regards the yarns manufactured according to the invention being electrostatically charged. An aramid yarn was treated according to the process described in Example I, except that the yarn rate was 75 m/min and drying was carried out using a hot sheet (temperature: 140°C, contact time: 2.4 sec.) In Table I the composition of the W/0 emulsions is given in parts by weight. Emulsion no. D4 E4 D5 E5 Content (%) 25 21.6 50 42 Nalco 4755 (50%) 25 100 Nalco 7863 (42%) 21.6 100 Span 85 10 12.5 Tween 85 2.5 Exxsol D80 62.5 65.9 The composition of emulsion C3 is given in Example III. The water-in-oil emulsions listed above were used to treat the aramid yarn. The conditions under which the experiments were carried out and the results thereof are listed in Table J. Exp. no. Emulsion no. Amount of superabsorb. on yarn (wt.%) Amount of stabiliser on yarn (wt.%) Observation during experiment Yarn tenacity cN/dtex 23 C3 1.2 0.8 good bundle cohesion 18.75 24 D4 1.0 1.0 good bundle cohesion 18.56 25 D5 1.0 - charging ) 16.88 26 E4 0.7 1.0 good bundle cohesion 18.57 27 E5 0.7 - charging ) 17.46 Also determined was the yarn tenacity of the starting yarn without superabsorbent. It was 18.80 cN/dtex. The experiments show that in the process according to the invention charging of the yarn is inhibited by using a stabiliser. It was also found that there is no filament lapping around rolls. In this way filamentation, which results in reduced yarn tenacity, is avoided. Comparative Example This comparative example relates to experiments in which an aramid yarn was treated with a superabsorbent according to the method described in EP-A-0 351 100. An unfinished yarn of poly(p-phenylene terephthalamide) having a linear density of dtex 1610 f 1000 was impregnated with Aridall 1125 (Fine) Superabsorbent Polymer, supplied by Chemdal Corporation, Arlington Heights, Illinois, U.S.A. In this process the yarn to be treated was first passed through a suspension of the superabsorbent in water and then, to promote a more uniform distribution of the superabsorent over the aramid yarn's surface, through a drawing die of which the passage had a diameter of 0.81 mm. In the experiments the content of superabsorbent in the aqueous suspension was varied. The thus treated yarns were dried in an air oven for 2.5 min at 100°C. The conditions under which the experiments were carried out and the properties of the resulting yarns are given in Table K. Exp. no. Superabsorbent suspension Superabsorb. on yarn wt.% Yarn water content after drying and conditioning wt.% ) Through-flow time (100 cm head) Swelling value Content wt.% Viscos. (25°C) mm 2 /s V1 0.5 700 0.66 2.7 7 min 38 V2 0.7 2000 0.92 2.8 15 min 43 V3 1.0 5000 1.33 2.9 8-15 hr. 51 The untreated yarn had a swelling value of 21. The results of the through-flow test, as given in Tables B, E, H, and K, demonstrate the enhanced water blocking capacity of the yarns according to the invention. According to Table K the swelling value of the yarns manufactured as described in EP-A-0 351 100 does not exceed 51. Example V An aramid yarn was treated according to the process described in Example I under the following conditions. The linear density of the starting yarn was dtex 1610 f 1000. The yarn rate was 150 m/min. Drying of the yarn was with the aid of steam in steam chests (2.4 sec. at 240°C). In Table L the composition of the W/0 emulsions used in the experiments is given in parts by weight. Emulsion no. G1 G2 G3 Content (%) 26.6 33.2 33.1 Mirox W 45985 (33.1%) ) 50 70 100 Span 85 10 10 Exxsol D80 40 20 Stability ) 84 288 576 The relatively stable water-in-oil emulsions listed in Table L were employed in the above-mentioned treatment of the aramide yarn. The conditions under which the experiments were carried out and the results thereof are given in Table M. Exp. no. Emulsion no. Conc. of composition wt.% Amnt. superabsorb. on yarn wt.% Amnt. stabiliser on yarn wt.% Moist. cont. after winding ) wt.% Swelling value Through flow time ) 28 G1 27 1.6 0.9 1.8-1.8 84 >3 days 29 G2 33 1.1 0.5 1.5-1.6 63 about 20 hours 30 G2 33 1.4 0.6 1.7-1.7 80 >3 days 31 G3 33 1.5 - 1.7-1.7 99 >3 days

Claims: A process for the manufacture of an aramid yarn coated with a superabsorbent material, characterized in that on the aramid yarn surface there is applied a layer of a water-in-oil emulsion containing a superabsorbent in its aqueous phase, and that next the emulsion's liquid ingredients are wholly or partially removed from the yarn by evaporation, the yarn being treated as such. A process according to claim 1, characterized in that the aramid yarn to be treated is made up wholly or in part of poly(p-phenylene terephthalamide). A process according to claim 1 or 2, characterized in that the water-in-oil emulsion used contains 2-50 wt.% of the superabsorbent material. A process according to any one of the claims 1-3, characterized in that the superabsorbent material is a derivative of polyacrylic acid. A process according to any one of the claims 1-4, characterized in that the water-in-oil emulsion contains 20-80 wt.%, calculated on the undiluted emulsion, of a stabiliser having an HLB value of less than 5.

Inventors: GEURSEN HERMAN JOHAN, WILLEMSEN STEPHANUS, GEURSEN, HERMAN JOHAN, WILLEMSEN, STEPHANUS
Applicants: AKZO NOBEL NV, AKZO NOBEL N.V.
Application year: 1991
Main classification: D06M15
IPC codes: G02B6, D02G3, D06M101, D06M15, D01F6