Classifications

• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F6/00—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof
  • D01F6/02—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D01F6/14—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds from polymers of unsaturated alcohols, e.g. polyvinyl alcohol, or of their acetals or ketals

Definitions

• This invention relates to polyvinyl alcohol (hereinafter referred to sometimes as PVA)-based synthetic fibers having a slender cross-sectional configuration and a large crystal length-to-breadth ratio.
• PVA polyvinyl alcohol
• the invention relates to shaped arti­cles reinforced with the same fibers.
• PVA-based fibers are characterized by the highest strength and tenacity of all conventional synthetic fibers and, because of these properties, have hereto­fore been used for the reinforcement of various molding materials inclusive of organic molding materials such as plastics and rubbers and hydraulic inorganic mate­rials such as cement and gypsum.
• any reinforc­ing PVA fiber must meet are high strength and a high modulus of elasticity. Unless the reinforcing fiber is adequate in strength and modulus, the finished reinforced article will necessarily lack toughness.
• the second important requirement of such a rein­forcing fiber is a high adhesive affinity for matrices (e.g. said plastics, rubbers, cement and gypsum). If the adhesion between the reinforcing fiber and the matrix is insufficient, the strength and modulus of the fiber will not be fully exploited when the article responds to an external stress, with the result that the article may undergo cracking or breakdown.
• matrices e.g. said plastics, rubbers, cement and gypsum.
• the most representative method for manufacturing such a PVA fiber comprises wet-extruding an aqueous PVA dope in a dehydrating salt-containing coagulation bath at ambient temperature and subjecting the resulting tow to drawing and heat treatment and, if necessary, to acetalization.
• the PVA fiber manufactured by the above method has a double-layer construction consisting of a skin layer and a core, resembling that of a cocoon, and as such has a com­paratively large surface area but can only be drawn or stretched in a total draw ratio of about 8.
• the strength of the fiber is only about 7 g/d which is far less than the requirement for a rein­forcing fiber.
• the total draw ratio is increased to about 22 and the mechanical properties are improved, providing a strength value of about 17 g/d, but the fiber has only a small surface area and is not yet satisfactory for reinforcing purposes.
• the latter patent literature refers to the length of fiber crystals but does not refer to the ratio of length (L) to width (W) (herein­after referred to as L/W ratio) of the crystals.
• L/W ratio ratio of length to width
• the total draw ratio of 16 and the strength value of 12 g/d as shown in the examples of this patent are considerably lower than the values obtainable according to this invention.
• the reinforcing effect is improved only when the L/W ratio, rather than the value of L, is increased.
• the fiber of this prior art is circular in cross section and has a low surface area, it is not satisfactory for use as a reinforcing material.
• Japanese Unexamined Patent Application KOKAI No. 126312/1985 (corresponding to U.S.P. 4,603,083 and European Patent Laid-open Specification No. 0146084) and Japanese Unexamined Patent Application KOKAI No. 108712/1986.
• This technology generally comprises dissolving PVA in a solvent such as dimethyl sulfoxide or glycerol, sub­jecting the solution to dry-jet-wet spinning (the spinning method in which the spinning dope extruded in the air from a spinneret nozzle is immediately dipped in a coagulation bath) or quench-gelation spinning, and, after removal of the solvent, drawing the resulting tow in a high draw ratio.
• the fiber obtainable by this technology has been remarkably improved in mecha­nical properties,but because of its exceptionally high homogeneity and circular cross section with a small surface area, it is not satisfactory for use as a reinforcing fiber.
• Another approach for obtaining an increased surface area per unit weight of fiber is to reduce the denier number of the fiber. Reducing the denier number, however, tends to reduce both spinnability and producti­vity and, in addition, adversely affects the dispersi­bility of the fibers in the matrix.
• the technical problem underlying the present invention is to provide PVA fibers of sufficiently high strength and modulus, with a slender cross-sectional configuration and a large surface area, all of which are the essential requirements for reinforcing fibers.
• This invention is, therefore, concerned with a PVA fiber having a degree of cross-sectional roundness not greater than 65% and a L/W ratio, as defined herein, of at least 2.1.
• the term cross-sectional roundness is defined below (see page 19).
• the reinforcing effect is more closely associated with the L/W ratio of the fiber than with the strength and modulus of the fiber.
• the L/W ratio should not be less than 2.1 and preferably not less than 2.3 and the degree of cross-­sectional roundness be not greater than 65 percent and preferably not greater than 60 percent.
• the length L of the fiber crystal taken independently, is not much correlated with the reinforcing effect and mechani­cal properties of the fiber but rather shows high correlation with them only in the context of L/W.
• this invention provides a process which com­prises wet-spinning an aqueous PVA solution containing boric acid or a salt thereof in a dehydrating salt-­containing alkaline coagulation bath at 55 to 95°C and drawing the resulting tow in a draw ratio of at least 17.
• the method of the invention uses a coagulation bath at a high temperature of 55 to 95°C.
• the drawability is markedly improved and the L/W ratio of the fiber is increased to realize a very large increase in the reinforcing effect and a marked improvement in mechanical properties.
• this invention permits a high draw ratio to fully exploit the effect of the degree of polymerization of vinyl alcohol, thereby yielding a fiber with a large L/W ratio and having a slender cross-sectional configuration.
• the ratio involved is not sufficiently clear but it is suspected that the mechanism of coagulation is completely different from that involved in conventional spinning tech­nology.
• this invention is concerned with shaped articles reinforced with the above-described PVA-based fibers,particularly fiber-reinforced plastic products (hereinafter referred to briefly as FRP), fiber-reinforced hydraulic products (hereinafter referred to briefly as FRC) and fiber-reinforced rubber articles.
• FRP fiber-reinforced plastic products
• FRC fiber-reinforced hydraulic products
• rubber articles fiber-reinforced rubber articles.
• the degree of polymerization of the PVA employed is at least 1,500, preferably at least 2,000, and more desirably at least 3,000.
• degree of polymerization of PVA is less than 1,500, crystal growth in the axial direction of the fiber is too small to assure an L/W ratio of not less than 2.1 and an improvement in mechanical properties.
• the spinning dope used in accordance with this invention is an aqueous solution containing 5 to 30 weight percent of said PVA and additionally 0.5 to 5 weight percent, based on said PVA, of boric acid or a salt thereof.
• the concentration of PVA is preferably 6 to 25 weight % and, for even better results, 7 to 18 weight %.
• the concentration of PVA may vary to some extent according to its degree of polymerization, but when the concentration is too low, the growth of crystals along the fiber axis will not be sufficient to assure a large L/W ratio, although the drawability will be satisfactory, and when conversely the concentration of PVA is too high, the drawability is greatly impaired.
• the temperature of the spinning dope is 85 to 125°C and preferably in the range of 95 to 120°C.
• an organic acid such as acetic acid or an inorganic acid such as nitric acid may be added to the spinning dope in an appropriate amount.
• the temperature of the coagulation bath is 55 to 95°C and preferably in the range of 60 to 80°C.
• the bath temperature is below 55°C, the fiber is not so slender in its cross-sectional configuration and the drawability is too low to assure a sufficiently large L/W ratio.
• the coagulation bath temperature is over 95°C, boiling of the bath and adhesion of mono­filaments tend to occur.
• an alkali hydroxide such as sodium hydroxide, potassium hydroxide, etc. is employed and its concen­tration is 2 to 200 g/l and preferably 5 to 50 g/l.
• the salt to be incorporated in the coagulation bath is a salt having dehydrating properties, such as sodium sulfate, sodium carbonate, etc. and its concentration is 100 g/l to saturation and preferably close to saturation.
• spinneret nozzle an ordinary circular-orifice nozzle or a nozzle similar thereto is employed.
• the fiber obtained can be post-treated by the conventional procedures of neutralization, wet heat drawing, rinsing, drying, heat drawing and heat treating (tempering).
• the draw ratio in wet condition is at least 3 and preferably not less than 5.
• the total draw ratio, inclusive of that in wet condition and that in dry condition, is not less than 17 and preferably not less than 20. The greater the total draw ratio, the larger is the L/W ratio. When the total draw ratio is less than 17, the L/W ratio does not reach 2.1.
• the size of PVA fibers may be similar to that used in the ordinary fiber-reinforced plastic (FRP) products, viz. in the range of 0.1 to 100 deniers, for instance.
• FRP fiber-reinforced plastic
• thermosetting resins such as unsaturated polyester resins, phenolic resins, epoxy resins and melamine resins, etc.
• thermoplastic resins such as polyester resins, polyamide resins, polyethylene resins, polypropylene resins, polyvinyl chloride resins and so on can be employed.
• the PVA fibers can be used e.g. in the form of short staples or chopped strands or, depending on use, may be used in the form of e.g.rovings, woven fabrics or nonwoven fabrics.
• the proportion of the PVA fibers in a shaped plastic article is preferably 1 to 50 weight percent.
• Such a shaped plastic article may further contain, in addition to PVA fibers and matrix resin, other fibers, fillers, curing or hardening agents, thixotropic agents, modifiers of flow properties, pigments and so on.
• the PVA fibers and a thermosetting resin are blended using a kneader and the resulting bulk molding compound is molded by compression molding or injection molding.
• Another method comprises laminating a sheet molding compound of a thermosetting resin with chopped strands of the PVA fibers, covering the laminate with a polyethylene film or the like on either side and molding the assemblage.
• Shaped articles may also be obtained by the usual hand lay-up method.
• the PVA fibers of this invention can be used in the same manner as glass fibers in the manufacture of shaped articles.
• the FRP obtainable by the method of this invention has the following characteristics.
• the fiber-reinforced resin composition according to this invention can be used in a wide range of purposes, such as architectural materials, building materials, indus­trial parts, transportation devices, automobiles, boats, and so on.
• the PVA fibers can be used in any form appropriate to the molding process or procedure. For example, they can be used as short monofilaments or chopped strands or in the form of continuous filament yarns or bundled filament yarns. They may also be used in the shape of fiber rods.
• the PVA fibers can also be used in such varied forms as nonwoven fabrics,mats,mesh sheets,knitted fabrics,or other two-dimensional or three-dimensional constructions.
• the PVA fibers can be used in combination with reinforcing steel or further used in combination with e.g. glass fibers, steel fibers, acrylic fibers.
• the molding method there is no limitation to the molding method that can be used; the ordinary molding processes for FRC can be employed with equal success.
• a wet-casting method can be used for the manufacture of sheets.
• the Hatschek process (see British patent 20 40 331) is typical of the method.
• the level of addition of the PVA fibers to a hydraulic molding composition is 0.2 to 20 weight percent and preferably 1 to 5 weight percent.
• the aspect ratio (the length of fiber divided by the diameter of a circle equivalent to the cross-section of the fiber) in the case of short staples is 50 to 2,000 and preferably 150 to 600.
• Portland cement is a representative hydraulic material and Portland cement is a typical example. Blast furnace cement, flyash cement, alumina cement, etc. may also be used. These hydraulic materials can be used singly or in combination. Furthermore, these cements may be used in admixtures with sand or gravel to provide a mortar or a concrete. As other examples of the hydraulic materi­al, gypsum, gypsum slag, magnesia, etc. can be mention­ed. After all, any hydraulic material suited to the intended application can be used.
• mica As auxiliary additives, mica, sepiolite, attapul­gite, etc. can be used.
• the FRC compositions of this invention Compared with the conventional FRC composition, the FRC compositions of this invention contain reinforcing PVA fibers having a larger L/W ratio and a slender cross-sectional configuration with a degree of cross-sectional roundness not greater than 65% and, as such, assure excellent mechanical properties. Therefore, the FRC composition of this invention can be used in all varieties of cement and concrete applications such as plates, pipes, blocks, wall panels, roof tiles, room dividers, road pavements, tunnel lining, surface protection and so on.
• the rubber to be used may be of any type.
• NR natural rubber
• various synthetic rubbers such as styrene-butadiene rubber SBR), chloroprene rubber (CR), nitrile rubber (NBR), ethylene-propylene diene rubber (EPDM), etc.
• SBR styrene-butadiene rubber
• CR chloroprene rubber
• NBR nitrile rubber
• EPDM ethylene-propylene diene rubber
• the PVA fibers of this invention are used in the form of a fabric or in the form of twisted yarn. Depending on uses, however, nonwoven fabrics, short staples, chopped strands, etc. may prove useful forms of application.
• the per se conventional technology can be utilized.
• the PVA fibers are twisted to form a cord and, if necessary, after treatment with an adhesive, the cord is woven or knitted into a fabric and super­posed on a rubber matrix.
• the PVA fibers are woven or knitted and, if necessary, after treatment with an adhesive, they are molded together with rubber.
• the shaped rubber articles of this invention have the following advantages.
• the fiber-reinforced rubber composition according to this invention can be used in various applications such as tire parts, tarpaulin, sheet, hoses, diaphragms, and so on.
• the PVA fibers of this invention have a large L/W ratio, superior mechanical properties and a large surface area due to a slender cross-sectional configuration with a degree of cross-sectional roundness not greater than 65% and therefore they are applied as reinforcing fibers for cement, plastics and rubber.Their excellent mechanical properties can be best exploited in such industrial products as ropes and cables.
• a photograph of the cross-section of a sample fiber is enlarged to the size of about 100 mm2 and the cross-sectional area F is measured.
• the degree of cross-sectional roundness is calculated by means of the following formula.
• the degree of cross-sectional roundness was calculat­ed for 20 randomly sampled monofilaments from a multi­filament yarn and the mean of the values was defined as the degree of cross-sectional roundness of the fiber constituting the multifilament yarn.
• This spinning dope was heated at 105°C and extruded into coagulation baths containing 15 g/l of sodium hydroxide and 350 g/l of sodium sulfate at 60°C (Exam­ple 1), 70°C (Example 2), 90°C (Example 3), 40°C (Comparative Example 1), 100°C (Comparative Example 2) and 30°C (Comparative Example 3) from nozzles having 1,000 circular orifices.
• the resulting tows were taken out from the baths at a rate of 6 m/min. Thereafter, the respective tows were subjected to the routine treatment of drawing between rolls, neutralization, 1.5 times wet heat drawing, rinsing and drying in a wet draw ratio of 6. The tows were then subjected to dry heat drawing at 230°C and taken up on bobbins.
• the non-heat drawn monofilaments obtained using a coagulation bath at 30°C or 40°C were comparatively transparent and had a high degree of cross-sectional roundness but as the temperature of the coagulation bath was increased, the monofilaments rapidly gained opacity and the degree of cross-­sectional roundness decreased.
• the properties of the yarns obtained are shown in Table 1.
• the yarn construction was invariably 1800d/1000f.
• the solution was heated at 100°C and extruded from a 1,000-circular orifice nozzle into a coagulation bath containing 30 g/l of sodium hydroxide and 340 g/l of sodium sulfate at 80°C.
• the resulting tow was taken from the bath at a rate of 8 m/min.
• the tow was then subjected to the routine treatment series of drawing between rolls, neutralization, 2 times wet heat drawing, rinsing and drying in a wet draw ratio of 7.
• the tow was further subjected to dry heat drawing at 225°C and taken up on a bobbin.
• the resulting yarn showed marked opacity and a cross-­sectional roundness of 50%.
• the total draw ratio was 25 and the L/W ratio was as large as 2.4. This fiber was very suitable for the reinforcement of cement.
• Example 2 The same procedure as Example 2 was followed up to the drying stage and the dry heat drawing ratio was decreased to give a total draw ratio of 16.
• the resulting yarn had the same degree of cross-sectional roundness of 36 %, as that of the yarn according to Example 2 but had a smaller L/W ratio of 2.0, thus being inferior in mechanical properties.
• the strength at break was 12.8 g/d and the modulus of elasticity was 280 g/d. Compared with the yarn according to Example 2, this fiber was by far inferior in its reinforcing effect.
• the resulting filament was approximately circular with a degree of cross-sectional roundness of as high as 92%. With an L/W ratio of as large as 2.6, the fiber showed excellent mechanical properties.
• the strength at break was 21.0 g/d and the modulus of elasticity was 530 g/d.
• This spinning dope was heated at 110°C and extruded from a 1,000-circular orifice nozzle into a coagulation bath containing 8 g/l of sodium hydroxide and 360 g/l of sodium sulfate. The resulting tow was taken from the bath at a rate of 4 m/min.
• the tow was subjected to the routine series of drawing between rolls, neutrali­zation, wet heat drawing, rinsing and drying and, then, to dry heat drawing and finally taken up on a bobbin.
• the draw ratio under wet conditions was 4 and the total draw ratio was 27.
• the monofilaments were very flat in cross-section with a cross-sectional roundness of 32%. With an L/W ratio of 2.9, the yarn had excellent mechanical proper­ties, i.e. strength at break was 22.9 g/d, elongation at break was 4.3%, and initial modulus of elasticity was 560 g/d. As anticipated, the yarn was excellent in its reinforc­ing effect on cement.
• the fibers prepared in Examples 1-3 and Comparative Examples 3 and 5 were used for reinforcing an unsaturated polyester resin.
• a kneader was charged with 150 parts of an unsaturated polyester resin (Polymar 6709, Takeda Chemical Industries, Ltd.), 2 parts of MgO (Kyowamag 40 F, Kyowa Chemical Co., Ltd.), 8 parts of a mold release agent (zinc stearate, Nippon Oils and Fats Co., Ltd.), 0.5 part of curing agent (Perbutyl Z, Nippon Oils and Fats Co., Ltd.) and 275 parts of CaCO3 (S light No.
• the PVA fibers having a monofilament fineness of 2 deniers, indicated in Table 3, were treated with 1%/monofilament of styrene-soluble polyvinyl acetate (Dainippon Ink and Chemicals, Inc.) and cut into 25,4 mm lengths, which were then constructed into chopped strand mats.
• Each mat was impregnated with a homogenous mixture of 100 parts of said unsaturated polyester resin, 2 parts of MgO, 8 parts of a mold release agent, 3 parts of a curing agent (Perbutyl Z) and 300 parts of CaCO3 to give a sheet molding compound (SMC).
• SMC sheet molding compound
• This SMC was compression-molded at 160°C and 100 kg/cm2 for 10 minutes to give an FRP with a thickness of 5 mm. It will be apparent from Table 3 that the FRPs manufactured from the SMCs reinforced with the PVA fibers according to this invention are superior in bending strength and impact resistance.
• the fibers prepared in Examples 1 and 2 and Comparative Examples 3-5 were cut into 6 mm lengths. Using a Hatschek machine, a composition of 2 parts of the fiber, 4 parts of pulp and 94 parts of Portland cement was wet-cast and subjected to spontaneous cure for 15 days to give cement plates with a thickness of 5 mm. The physical properties of such plates are shown in Table 4. The bending strength of each plate was measured in accordance with JIS K6911.
• each of the fibers was twisted at 30 T/10 cm for both first and final twists to provide 1,800 D/1 x 2 cords, which were then treated with RFL to give dipped cords.
• RFL means rubber latex containing a resorcinol-formaldehyde resin.
• the dipped cords were arranged in the form of tire cord fabrics and rubber was layed up and vulcanized to give a fiber-­reinforced rubber sheet. This sheet was bent on a flexural fatigue tester and the cords were then taken out and measured for residual strength. The results are set forth in Table 5.

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• Textile Engineering (AREA)
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Citations (5)

• 1988
  • 1988-10-21 EP EP88117568A patent/EP0313068B1/de not_active Expired - Lifetime
  • 1988-10-21 DE DE19883854253 patent/DE3854253T2/de not_active Expired - Fee Related
  • 1988-10-21 ES ES88117568T patent/ES2077560T3/es not_active Expired - Lifetime

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