SPONTANEOUSLY DEGRADABLE FIBERS

Abstract: A spontaneously degradable fiber excellent in bulkiness, softness, stretchability and feeling, which comprises (A) a low heat-shrinkable fiber component comprising a high crystalline aliphatic polyester and (B) a high heat-shrinkable fiber component comprising an aliphatic polyester, e.g., a low crystalline or non-crystalline aliphatic polyester, and a block copolymer or a mixture the main component of which is an aliphatic polyester and which comprises a high-melting component and a low-melting component. Further, fibers excellent in self-crimpability or self-adhesion property and dividable fibers are obtained by suitably combining the fiber components (A) and (B) to form conjugated fibers or composite yarns.

Description: The present invention relates to fibers which are spontaneously degradable and are capable of providing textile goods having excellent properties such as bulkiness, softness and feeling, and goods made thereof, and more particularly to spontaneously degradable fibers comprising aliphatic polyesters having different thermal characteristics, and goods made thereof. Conventional synthetic fibers made of synthetic resins are slow in rate of degradation under natural environment and generate a large amount of heat at burning and, therefore, have to be reconsidered from the viewpoint of environmental protection. For such a reason, spontaneously degradable fibers made of aliphatic polyesters are being developed, and their contributions to environmental protection have been expected. However, these spontaneously degradable aliphatic polyester fibers are not satisfactory in bulkiness, softness, feeling and so on, and an improvement thereof has been desired. Conventionally it is known that goods such as knitted and woven fabrics having excellent bulkiness and softness are obtained if fibers having a different shrinkability are combined in usual inter-fiber composites (blends of fibers). However, as to aliphatic polyester fibers having a spontaneous degradability, a manner of controlling the shrinkability has been scarcely known so far and, of course, it is not known at all to conjugate fibers having a different shrinkability and to improve the quality of knitted fabrics and woven fabrics by using it. Also, in order to obtain a fiber having a high softness and various functions based on a special shape of section and a large surface area, it has been conventionally practiced to divide a dividable conjugated fiber. By this method, there have been developed and widely used knitted and woven fabrics, non-woven fabric, artificial leather, artificial suede, high performance wiping cloth, high performance filter and so on. However, in the field of degradable fibers in natural environment, no dividable conjugated fiber has been proposed. The reason is that combination of spinning materials (polymers) suitable for division and how to divide have not yet been known. A self-adhesive (melt-adhesive) fiber that a part of a fiber melts by heating to adhere fibers to each other, has been widely used in the field of synthetic fibers. Melt-adhesive fibers using an aliphatic polyester are proposed in Japanese Patent Publications Kokai No. 6-207320 and Kokai No. 6-207324. However, in working examples thereof, a conjugated fiber composed of a sheath (adhesive component) of a polyethylene succinate having a melting point of 102°C and a core (strength-retaining component) of a polybutylene succinate having a melting point of 118°C is only disclosed, and the adhesive strength thereof is hot so strong. The reason is that the difference in melting point between both components is as small as only 16°C and the strength-retaining component is softened and deteriorated by heating for adhesion. Also, the optimum temperature for adhesion treatment of this fiber is limited within a very narrow range, so it is very difficult to exhibit desired adhesive force and strength. It is also very difficult to alter the adhesive strength in a wide range according to the purposes, so the uses are limited. In general, a low-melting component has been used for the adhesive component of melt-adhesive fibers. However, if a low-melting aliphatic polyester having a melting point of not more than 120°C is used, the glass transition temperature is lower than ordinary temperature, so the solidifying rate is slow and, therefore, there arise many problems in practical use such that fibers are easy to stick to each other at the time of melt-spinning, so not only production at a high speed is difficult, but also the heat resistance in use is low. An object of the present invention is to provide a spontaneously degradable fiber excellent in bulkiness, softness, feeling and stretchability, and textile goods prepared therefrom. A further object of the present invention is to provide a spontaneously degradable fiber having a self-crimpability. A still further object of the present invention is to provide a self-crimpable fiber which is spontaneously degradable, which reveals an excellent crimp by heating or the like so as to be able to provide goods excellent in softness, bulkiness and stretchability and, moreover, which can be easily prepared in high efficiency. As a result of repeating intensive study, the present inventors have found that the above objects can be achieved by combining spontaneously degradable aliphatic polyesters having different thermal properties such as heat absorption amount in melting (the heat of fusion), melting point and the like, thus having accomplished the present invention. Thus, the present invention provides a fiber comprising (A) a fiber component comprising an aliphatic polyester having a melting point of at least 100°C and a heat of fusion of at least 20 J/g and (B) a fiber component comprising an aliphatic polyester having a melting point of at least 100°C and a heat of fusion lower than that of said polyester (A) by at least 5 J/g. In the present invention, the fiber comprising the fiber components (A) and (B) is in the form of a composite yarn wherein fibers of respective components are blended in a weight ratio (A) to (B) from 10/1 to 1/10. Since this fiber comprises (A) high crystalline component having a high heat of fusion and (B) low crystalline component having a low heat of fusion, it has excellent bulkiness, softness and feeling based on a difference in heat shrinkability. Fig. 1 is cross sectional views showing various embodiments of a composite yarn comprising two kinds of fibers according to the present invention, wherein Fig. 1A shows a composite yarn that two kinds of fibers having a circular section are uniformly mixed, Fig. 1B shows a composite yarn that two kinds of fibers having a circular section are eccentrically non-uniformly mixed, Fig. 1C shows a composite yarn that two kinds of fibers having a circular section are concentrically non-uniformly mixed, Fig. 1D shows a composite yarn that a fiber having a triangular section and a fiber having a circular section are uniformly mixed, Fig. 1E shows a composite yarn that a fiber having triangular section and a fiber having a circular section are concentrically non-uniformly mixed, and Fig. 1F shows a composite yarn that a fiber having a triangular section, a fiber having a circular section and a third fiber are mixed; Fig. 2 is a fusion curve (DSC curve) showing heat exhaustion and heat absorption of a polymer at the temperature elevation, obtained by a differential scanning calorimeter (DSC); and Fig. 3 is a fusion curve (DSC curve) showing heat exhaustion and heat absorption of a block copolymer or mixture of two kinds of crystalline aliphatic polyesters having different melting points at the temperature elevation, obtained by a differential scanning calorimeter (DSC). Herein the aliphatic polyester is those containing, as a main component, namely in an amount of at least 50 % by weight (preferably at least 60 % by weight, more preferably at least 70 % by weight), components derived from the raw materials of the aliphatic polyester, e.g., (1) a hydroxyalkyl carboxylic acid such as glycolic acid, lactic acid or hydroxybutyl carboxylic acid, (2) an aliphatic lactone such as glycolide, lactide, butyrolactone or caprolactone, (3) an aliphatic diol such as ethylene glycol, propylene glycol, butanediol or hexanediol, (4) a polyalkylene glycol such as an oligomer of a polyalkylene ether such as diethyelene glycol, triethylene glycol, ethylene/propylene glycol or dihydroxyethylbutane, polyethylene glycol, polypropylene glycol or polybutylene glycol, (5) a polyalkylene carbonate glycol such as polypropylene carbonate, polybutylene carbonate, polyhexane carbonate, polyoctane carbonate or polydecane carbonate, and oligomers thereof, and (6) an aliphatic dicarboxylic acid such as succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid or decanedicarboxylic acid, and it encompasses all of homopolymers of an aliphatic polyester, block or random copolymers of aliphatic polyesters, and block or random copolymers of or mixtures of aliphatic polyesters and at most 50 % by weight of other components such as an aromatic polyester, a polyether, a polycarbonate, a polyamide, a polyurea, a polyurethane and a polyorganosiloxane. The modification of the aliphatic polyester by copolymerization or mixing is conducted for the purpose of decreasing the crystallinity and the melting point (decreasing the polymerization temperature or molding temperature), improvement of friction coefficient, softness or elasticity restoration, decreasing or increasing of heat resistance, glass transition temperature or heat shrinkability, improvement of dyability, hydrophilicity or water repellency, improvement or control of degradability and the like. Herein, the amount of heat absorption in melting (heat of fusion) is a value measured by a differential scanning calorimeter (hereinafter referred to as DSC) in nitrogen at a temperature elevation rate of 10°C/minute with respect to about 10 mg of a sample of thoroughly drawn, heat treated and dried yarm. A typical DSC curve is shown in Fig. 2. The figure shows an example of measurement of a sample which is scarcely crystallized, and numeral 19 shows a change of base line by glass transition, numeral 20 shows a peak of heat exhaustion owing to crystallization by heating at the time of the measurement, and numeral 21 shows a peak of heat absorption owing to fusion of crystals. In case of a sufficiently crystallized sample, the heat generation peak 20 disappears and is not observed. In the present invention, the temperature corresponding to the minimum value (central value) of the heat absorption peak 21 based on fusion of crystals is defined as the melting point, and the total heat absorption amount (integral value, proportional to the area of the oblique line area in Fig. 7) of the heat absorption peak 21 is defined as the heat of fusion. The unit of the heat of fusion is J/g. In case that a plurality of melting points are present with respect to a mixture, a block copolymer and the like, the highest temperature is defined as the melting point (in the present invention), provided that if the heat of fusion of a peak for the highest temperature is negligibly small, e.g., about 2 J/g or less, and a main peak of a large heat of fusion, e.g., 20 J/g or more, is present on the lower temperature side, there is a case that the substantial melting point (temperature at which a polymer is extremely softened and starts to flow) is regarded as being based on that main peak. Also, the heat of fusion is defined as the total of all heat absorption peaks. Firstly, an explanation is made with respect to a fiber (I) comprising (A) a fiber component comprising an aliphatic polyester having a melting point of not less than 100°C and a heat of fusion of not less than 20 J/g, preferably not less than 30 J/g and (B) a fiber component comprising an aliphatic polyester having a melting point of not less than 100°C and a heat of fusion lower than that of the polyester (A) by at least 5 J/g. The composite yarn (I) of the present invention is an inter-fiber composite wherein a fiber (A) comprising a polymer (A1) having a large heat of fusion and a fiber (B) comprising a polymer (B1) having a small heat of fusion are blended. Representative examples of the composite yarn of the present invention are a mixed filament (hereinafter referred to as "combined filament yarn"), a long/short composite yarn wherein a continuous filament and a staple are combined, and a blended yarn wherein plural kinds of staples are blended and spun. In these inter-fiber composites (fiber blends), it is known that goods such as knitted and woven fabrics excellent in bulkiness and softness are obtained if fibers having a different shrinkability are combined. However, as to aliphatic polyester fibers, a manner of controlling the shrinkability has been scarcely known so far and, of course, it is not known at all to conjugate fibers having a different shrinkability and to improve the quality of knitted fabrics and woven fabrics by using it. As a result of making intensive study about improvement in quality of knitted and woven fabrics of aliphatic polyester fibers, the present inventors have found that a fiber (A) comprising a polymer (A1) having a large heat of fusion is able to make the heat shrinkability small, and a fiber (B) comprising a polymer (B1) having a small heat of fusion is able to make the heat shrinkability large, thus excellent fiber structures can be obtained by combining the both fibers. In particular, goods having an excellent feeling are obtained based on difference in shrinkability between the fiber (A) and the fiber (B). The polymer constituting the fiber (A) of the composite yarn (I) is a component having a large heat of fusion and a small heat shrinkability and the polymers (11) noted below are used therefor. The polymer constituting the fiber (B) of the composite yarn (I) is a low-crystalline component having a small heat of fusion and a large heat shrinkability, and the polymers (B1) noted below are used therefor. The difference in heat of fusion between the polymer (A1) and the polymer (B1) is required to be at least 5 J/g for obtaining articles having a good feeling based on a sufficient difference in shrinkability. The difference is preferably at least 10 J/g, more preferably at least 15 J/g, most preferably at least 20 J/g. In general, a combination of fibers a difference in shrinkability of which is large (e.g., 20 to 50 %), is preferred for knitted and woven fabrics which require high bulkiness, stretchability and softness, but there are cases that a smaller difference in shrinkability (5 to 20 %) is preferred for imparting a bulkiness controlled to some extent and a desirable feeling. Thus, the polymer (B1) can be selected according to the purposes. Also, from the viewpoint of practical use, the melting point of the polymer (B1) is required to be not less than 100°C, and the melting point is preferably not less than 110°C, more preferably not less than 130°C, most preferably not less than 135°C. The polymer (A1) is a component having a high crystallinity and a low heat shrinkability. As the polymer (A1) are preferred crystalline homopolymers and those incorporated with a second component, a third component and the like in such a small amount that the crystallinity is not so impaired (for example, at most about 40 % by weight, especially at most 30 % by weight) by means of copolymerization and/or mixing. From the viewpoints of crimpability, strength and heat resistance of the fiber of the present invention, it is necessary that the heat of fusion of the polymer (A1) is not less than 20 or 30 J/g, and it is preferably not less than 35 J/g, more preferably not less than 40 J/g. In many cases, the heat. of fusion of crystalline aliphatic polyester homopolymers is around 50 J/g. Similarly, from the viewpoint of practical use, it is necessary that the melting point of the polymer (A1) is not less than 100°C, preferably the melting point is not less than 110°C, especially not less than 130°C, more especially not less than 140°C, most especially not less than 150°C. Preferable examples of the polymer (A1) are homopolymers such as polybutylene succinate (melting point about 116°C), poly-L-lactic acid (m.p. 175°C), poly-D-lactic acid (m.p. 175°C), polyhydroxybutyrate (m.p. 180°C) and polyglycolic acid (m.p. 230°C), copolymers or mixtures thereof with a small amount of other component, and mixtures thereof. In case of the block copolymers, the changes in crystallinity and melting point are mild, so preferably the content of the comonomer component is at most 50 %, especially 1 to 40 %, and in many cases, 1 to 30 %. In case of the random copolymers, the changes in crystallinity and melting point are marked, so preferably the content of the comonomer component is from 0.5 to 10 %, especially 1 to 5 %. Of course, since the changes in crystallinity and melting point by copolymerization vary depending on the kinds of comonomer component, it is necessary to pay attention to the heat of fusion of crystals and the melting point based on DSC. The changes in crystallinity and melting point by mixing with other component also vary depending on the kinds of component incorporated and the mixing ratio, but generally it is not so marked as the random copolymerization. The amount of the other components used for copolymerization or mixing is selected within the above-mentioned ranges so as not to impair the objects of the present invention. Examples of the other components are, for instance, aliphatic polyesters, e.g., polycaprolactones and polyesters derived from an aliphatic glycol such as ethylene glycol or octanediol and an aliphatic dicarboxylic acid such as succinic acid or decanedicarboxylic acid, aromatic polyesters, polyethers, polycarbonates, polyamides, polyureas, polyurethanes, polyorganosiloxanes, and raw materials for these polymers. The polymer (B1) is a component having a low crystallinity and a high heat shrinkability. As the polymers suitable for the polymer (B1), there are mentioned aliphatic polyesters modified to lower the heat of fusion of crystals by means of copolymerization or mixing. It is necessary that the difference in heat of fusion between the polymer (A1) and the polymer (B1) is at least 5 J/g, and for high crimp, preferably the difference is at least 10 J/g, especially at least 15 J/g. The heat of fusion of 5 J/g corresponds to about 10 % of the heat of fusion of crystalline aliphatic homopolyesters. That is to say, the degree of crystallinity of the polymer (B1) is approximately 90 % or less of that of the polymer (A1). In general, a strong crimp is preferred for knitted goods which require a high stretchability, but there are cases that a crimp controlled to some extent is preferred for imparting softness, bulkiness and desired feeling to woven fabric. Thus, the polymer (B1) can be selected according to the purposes. Also, from the viewpoint of practical use, it is necessary that the melting point of the polymer (B1) is not less than 100°C, and preferably the melting point is not less than 110°C, especially not less than 130°C, more especially not less than 135°C. Such polymers having a relatively high melting point are, for instance, mixtures and copolymers (block copolymers and random copolymers) containing the above-mentioned homopolymers with high melting point as the main component (not less than 50 % by weight). The component used for the copolymerization or mixing with the homopolymers with high melting point such as polybutylene succinate, polylactic acid, polyhydroxybutyrate and polyglycolic acid can be suitably selected from the raw materials for the preparation of the above-mentioned aliphatic polyesters. Preferable examples of the component used for the block copolymerization or mixing with the homopolymers are aliphatic polyesters having a glass transition temperature of not more than ordinary temperature, especially not more than 0°C, for example, a polycaprolactone; and a polyester produced from a combination of at least one aliphatic glycol such as ethylene glycol, propylene glycol, butanediol, hexanediol, octanediol, diethylene glycol or triethylene glycol and at least one aliphatic dicarboxylic acid such as succinic acid, adipic acid, sebacic acid, octanedicarboxylic acid or decanedicarboxylic acid, e.g., polyethylene succinate, .polybutylene succinate, polyethylene adipate, polybutylene adipate, polyethylene sebacate or polybutylene sebacate. The polymer (B1) is required to be low crystalline as mentioned above. The most effective manner of decreasing the crystallinity is random copolymerization. Examples of the cases wherein random copolymerization can be easily accomplished are mixing of optical isomers, different hydroxycarboxylic acids, or different lactones, e.g., L-lactic acid/D-lactic acid, L-lactide (LL-lactide)/D-lactide (DD-lactide, DL-lactide), lactic acid/glycolic acid, lactide/glycolide, and lactide/caprolactone; and copolymerization of at least two of a hydroxycarboxylic acid, a glycol, a dicarboxylic acid and the like. Further, mixtures of the random copolymers with the above-mentioned block copolymers or different kinds of polymers are also preferable. The different kinds of polymers include, for instance, aromatic polyesters, polyethers, polycarbonates, polyamides, polyureas, polyurethanes, polyorganosiloxanes and so on. The polymer (B1) must not be crystalline. In case of being non-crystalline, the melting point denotes the temperature at which the melt viscosity becomes 100,000 poises. The polymers (A1) and (B1) are separately formed into fibers and, if necessary, are subjected to molecular orientation through drawing, heat treatment or the like, thus giving the fibers (A) and (B). The fibers (A) and (B) are blended by various means to give the composite yarn (blended fiber product) of the present invention. The blending manner is not particularly limited, but in case that the fibers (A) and (B) both are filaments, there are preferably adopted spinning blending wherein filaments are simultaneously spun from a single or adjacent spinnerets and taken-up, air blending wherein filaments are separately spun and an air nozzle is applied thereto, and simple yarn doubling, doubling and twisting, combined filament false twist (composite false twist), and the like. In case that one of the fibers (A) and (B) is a filament and the other is a staple, a so-called core spinning method wherein a filament is fed to a spinning step is applicable. In case that the fibers (A) and (B) both are a staple, a blended yarn is easily obtained by usual method such as fiber blending, sliver blending or web blending. Figs. 1A to 1F are cross sectional views showing examples of a combined filament yarn, core-spun yarn (long fiber/short fiber composite yarn) and a blended yarn. In the figures, 4 denotes the fiber (A), 5 denotes the fiber (B), and 6 denotes other fiber (C). Fig. 1A shows an example that 12 filaments of the fiber (A) having a circular cross section and 12 filaments of the fiber (B) having a circular cross section are relatively uniformly blended. Fig. 1B shows an example that 12 filaments of the fiber (A) having a circular cross section and 12 filaments of the fiber (B) having a circular cross section are disposed eccentrically (in the state that the respective centers of gravity are apart). Fig. 1C shows an example that 10 filaments of the fiber (B) having a circular cross section are disposed inside and 14 filaments of the fiber (A) having a circular cross section are concentrically disposed outside the fiber (B). Fig. 1D shows an example that 12 filaments of the fiber (B) having a circular cross section and 15 filaments of the fiber (A) having a triangular cross section are almost uniformly disposed. Fig. 1E shows an example that 6 filaments of relatively thick fiber (B) and 15 filaments of relatively thin fiber (A) having a triangular cross section are disposed in a core-sheath fashion. Fig. 1F shows an example that 4 filaments of relatively thick fiber (B) and 12 filaments of thin fiber (A) having a triangular cross section are blended with 12 filaments of another fiber (C) having a circular cross section. In the present invention, the cross sectional shape of fiber, fineness, blending ratio (by weight) of the fibers (A) and (B) and the like can be suitably selected without particular restriction. The blending ratio of the fibers (A) and (B) is selected according to the desired articles, but is from 10/1 to 1/10, preferably 5/1 to 1/5, more preferably 3/1 to 1/3, most preferably 2/1 to 1/2. The state of composite (blending) of the fibers (A) and (B) is not particularly limited, but the following three are basic and are often preferred and widely used, i.e., uniform and random disposition of the fibers (A) and (B) as shown in Fig. 1A, eccentric disposition as shown in Fig. 1B, and core-sheath or concentric disposition as shown in Fig. 1C. Also, another fiber (C) may be blended as shown in Fig. 1F. As the other fiber (C) are particularly preferred spontaneously degradable wool, cotton and aliphatic polyesters. In case of dress, blouse, under wear, lining cloth, coat and other light weight or medium weight woven and knitted fabrics which particularly require a softness, a process for weight reduction by alkali treatment has been conventionally carried out in a dye finishing step by treating a cloth of a polyester fiber with a strong alkali (aqueous solution of sodium hydroxide) to degrade and remove Apart (e.g., 5 to 50 %,especially 10 to 30 %) of the polymer. The alkali weight reduction processing is also applicable to aliphatic polyester fibers. However, in general the aliphatic polyester fibers are very sensitive to an alkali, and the weight reduction processing is carried out under milder conditions (low alkali concentration, low pH, low temperature and the like) than for conventional aromatic polyester fibers. In case of the alkali weight reduction processing of knitted and woven fabrics of the composite yarns of the present invention, the fiber (B) tends to have a higher speed of alkali weight reduction than the fiber (A). Therefore, if an alkali weight reduction is planned, it is desirable to make the filament (average) fineness of the fiber (B) larger than the fiber (A) in accordance with the weight reduction speeds, for example, by at least 10 %, especially about 20 to about 400 % (5 times). Another method for this purpose is to form the fibers such that the fiber (B) is formed to have a circular or analogous cross section so as to have a small surface area per unit weight, whereas the fiber (A) is formed into a polygonal or multi-blade shape having a lager surface area than the fiber (B) by at least 10 %, especially about 20 to about 400 % (5 times). Thus, it is desirable to pay attention so that the fibers (A) and (B) after the alkali weight reduction processing have adequate fineness and blending ratio. Of course, the above two methods may be combined. The aliphatic polyester fibers have the great advantage that a detrimental influence of the alkali weight reduction processing on environment is very small, since the consumption of an alkali is small and the resulting degradation products (lactic acid, etc.) can be easily degraded by microorganisms. Difference in boiling water shrinkage percentage (when treated for 10 minutes in boiling water under unloaded condition followed by air drying at room temperature) between the fiber (A) and the fiber (B) is not particularly limited, but the difference is usually at least 3 % and preferably from about 5 to about 50 %, and a difference within the range of about 10 to 40 % is the most widely used. Thus, the boiling water shrinkage percentage of the fiber (A) is preferably at most 15 %, more preferably at most 10 %. On the other hand, the boiling water shrinkage percentage of the fiber (B) is preferably at least 15 %, more preferably at least 20 %, and is often selected within the range of about 30 to about 60 %. The shape of the cross section of the fibers (A) and (B) can be suitably selected, e.g., circle, ellipse, gourd shape, polygon, multi-blade, alphabet shapes, other various non-circular shapes (modified cross sections) and hollow shapes. Similarly, the fineness is suitably selected according to the purposes. In case of fibers for usual clothes, the fineness of a filament is from about 0.1 to about 50 d, preferably from 0.5 to 30 d, and a fineness within the range of 1 to 20 d is widely used: The thinner or thicker fibers are adaptable for non-woven fabrics, leathers and materials. Each of the fibers (A) and (B) may be a mixture of two or more fibers having different cross section, fineness and shrinkage percentage. The composite yarn (I) of the present invention can be prepared, using the polymer (A1) and the polymer (B1), by spinning in a manner such as melt spinning, wet spinning, dry spinning, dry-wet spinning and others. Melt spinning is particularly preferred since the efficiency is high. In case of the melt spinning, low speed spinning at a taking-up speed of 500 to 2,000 m/minute, a high speed spinning at a taking-up speed of 2,000 to 5,000 m/minute and a ultra-high speed spinning at a taking-up speed of not less than 5,000 m/minute are possible. As occasion demands, drawing and heat treatment can be further conducted. In general, drawing is conducted at a drawing ratio of about 3 to about 8 in low speed spinning, and at a drawing ratio of about 1.5 to about 3 in high speed spinning, and drawing is not conducted or is conducted at a drawing ratio of about 2 or less in a ultra-high speed spinning. A so-called spin-draw method wherein spinning and drawing are conducted simultaneously is also suitably adoptable. A unique self-extendable yarn that is a fiber prepared at a relatively low drawing ratio and heat-treated at a low temperature and characterized in that the fiber whose crystallization and orientation have proceeded extends when heated later at a high temperature, can also be preferably used as the fiber (A). The composite yarn of the present invention can be formed into a suitable form according to the purposes, such as continuous filament combined yarn, doubling and twisting yarn, composite false twist yarn, blended yarn and analogous yarns, and by using them, knitted fabrics, woven fabrics, non-woven fabrics and other fiber structures can be prepared. During the preparation steps and processing steps thereof or after the preparation, it is possible to produce a difference in shrinkage percentage by suitably heating or swelling the fibers, thereby imparting desirable bulkiness, softness and feeling to articles. The heating can be conducted in a suitable manner such as dry heating, wet heating, infrared rays and a combination thereof. For the swelling, a solvent, swelling agent or water is used. Of course, it is also possible to conduct the heat shrinking after mechanically imparting a crimpability by false twisting or thrusting in the form of yarn. The heat shrinking is also widely conducted, for example, in the dye finishing step of woven and knitted fabrics. In general, the shrinking treatment is conducted in a relaxation state, but it is possible, to control the shrinkage, by applying an adequate tension. The respective fibers which constitute the composite yarn of the present invention can contain various kinds of pigment, dye, colorant, water repellent, water absorbent, flame retarder, stabilizer, antioxidant, ultraviolet absorber, metallic particles, inorganic compound particles, nucleating agent, lubricant, plasticizer, fungicide, perfume, and other additives. The composite yarns of the present invention can be used alone or in combination with other fibers for the preparation of yarn; braid, rope, knitted fabric, woven fabric, non-woven fabric, paper, composite materials and other structures. In case of using with other fibers, natural organic fibers such as cotton, wool or silk and spontaneously degradable fibers such as aliphatic polyester fiber are particularly preferable as other fibers, since fully spontaneously degradable articles are obtained. The fibers of the present invention are spontaneously degradable and scarcely pollute environment and, moreover, they can provide articles having excellent softness, bulkiness, elasticity, heat resistance and stretchability such as knitted fabrics, woven fabrics and non-woven fabrics and can be suitably utilized in various clothes, industrial materials, household goods and the like. The fibers of the present invention are superior in preparation efficiency and are inexpensive, since the melt spinning is easy. Further, the self-crimpable fibers have the advantages that they are easy to use and the range of application is very wide, since crimping of various strengths can be achieved. In general, aliphatic polyester fibers are not only degradable under natural environment, but also are small in heat generation amount in burning as compared with conventionally used synthetic fibers and, therefore, incineration is easy. Especially polylactic acid does not cause an increase of carbon dioxide gas in air, because the raw material lactic acid is obtained from agricultural products by a fermentation method or the like and polylactic acid is put into a cycle of matter in nature. Thus, aliphatic polyesters containing polylactic acid as a main component are the most preferable from the viewpoint of environmental protection. The present invention is then explained on the basis of examples, but it is to be understood that the present invention is not limited to these examples. In the examples, % and parts are by weight unless otherwise noted. In the present invention, the molecular weight of aliphatic polyesters indicates a weight average molecular weight of a polymer component excepting a component having a molecular weight of not more than 1,000, measured by GPC analysis of a 0.1 % solution of a sample in chloroform. The crimp elongation of conjugated fibers is obtained by forming sample filaments to a tow having a thickness of about 1,000 (950 to 1,050) deniers and a length of 50 cm, treating it in boiling water for 10 minutes under unloaded condition, dehydrating by centrifugation, air-drying in a room of 23°C and a humidity of 65 % for at least 24 hours under unloaded condition, measuring a length L1 of the sample 1 minute after applying a load of 0.5 g, then measuring a length L2 of the sample 1 minute after applying a load of 500 g, and calculating according to the equation: [(L2-L1)/L1]×100 (%). The heat shrinkage percentage of fibers is obtained by forming sample filaments to a tow having a thickness of about 1,000 deniers and a length of 50 cm, treating it in boiling water for 10 minutes under unloaded condition, air-drying in a room of 22°C and a humidity of 65 % for 24 hours, and calculating from the length L3 of the sample before the treatment and the length L4 of the sample treated and dried according to the equation of [(L3-L4)/L3]×100 (%). The length of a fiber is measured 1 minute after applying a load of 10 mg per denier. EXAMPLE 1 (Reference Example) Three parts of polyethylene glycol (PEG) having a molecular weight of 8000 and containing hydroxyl groups at the both molecular ends, 98 parts of L-lactide, 100 ppm of tin octylate and 0.1 part of Irganox 1010, i.e. an antioxidant produced by Ciba Geigy Corp. were mixed, and then polymerized by melting and stirring in a nitrogen atmosphere at 190°C for 12 minutes by a twin-screw extruder. Then after cooling and forming into chips, the chips were treated (solid phase polymerization) in a nitrogen atmosphere at 140°C for four hours to give a block copolymer P1 of polylactic acid and PEG. The polymer P1 had a molecular weight of 153000, a content of a PEG component of about 3 %, a melting point of 174°C and had a heat of fusion of 55 J/g when sufficiently orientated and crystallized. Further a polymer P2 was obtained in the same manner as in the polymer P1 except that a mixture of 95.5 parts of L-lactide and 2.5 parts of D-lactide was used as the lactide. The polymer P2 had a molecular weight of 158000, a melting point of 163°C and a heat of fusion of 27 J/g. The polymers P1 and P2 were melted separately by a screw extruder of 220°C, and supplied to two polymer feed parts of a spinneret for production of conjugated yarn. The both polymers were conjugated in a parallel type (conjugation ratio 1/1) as shown in Fig. 1A and spun out through an orifice of 225°C having a diameter of 0.25 mm. While cooling in air and oiling, the spun filament was wound at a speed of 1500 m/min and then drawn at 80°C in a drawing ratio of 4.5 to give a drawn yarn F1 of 70deniers/24filaments. The drawn yarn F1 was excellent one having a tenacity of 4.6 g/d and an elongation of 29 % and showing a crimp elongation of 226 % after revelation of the crimp. For comparison, a polylactic acid homopolymer P3 was prepared in the same manner as in the polymer P1 except that PEG was not used. The polymer P3 had a molecular weight of 162000, a melting point of 175°C and a heat of fusion of 55 J/g. Further a polymer P4 was prepared in the same manner as in the polymer P1 except that 6 parts of PEG and 95 parts of L-lactide were used. The polymer P4 was one having a molecular weight of 155000, a melting point of 173°C and a heat of fusion of 55 J/g though PEG was contained as a copolymerizing component in an amount of about 6 %. By using the polymers P3 and P4, a drawn yarn F2 (Comparative Example) was produced in the same manner as in the drawn yarn F1. The drawn yarn F2 had a strength of 4.8 g/d. and an elongation of 31 % and showing a crimp elongation of 19 % after revelation of the crimp, and was very low in crimpability. EXAMPLE 2 (Reference Example) A polymer P5 was prepared in the same manner as in the preparation of the polymer P1 of Example 1 except that instead of the PEG, 30 parts of polybutylene succinate having a molecular weight of 127000 and containing hydroxyl group at the molecular end was used. The polymer P5 had a molecular weight of 129000, a melting point of 162°C and a heat of fusion of 35 J/g. A polymer P6 was prepared in the same manner as in the polymer P1 except that instead of the PEG, 10 parts of polybutylene succinate having a molecular weight of 127000 and containing hydroxyl group at the molecular end and instead of the L-lactide, 88.5 parts of L-lactide and 2.52 parts of D-lactide were used. The polymer P6 had a molecular weight of 134000, a melting point of 151°C and a heat of fusion of 26 J/g. A drawn yarn F3 was produced in the same manner as in the drawn yarn F1 of Example 1 by using the polymers P1 and P5. The drawn yarn F3 had a tenacity of 4.7 g/d, an elongation of 28 % and a crimp elongation of 223 %, and thus was excellent in crimpability. Similarly a drawn yarn F4 was produced in the same manner as in the drawn yarn F1 of Example 1 by using the polymers P1 and P6. The drawn yarn F4 had a tenacity of 4.6 g/d, an elongation of 29 % and a crimp elongation of 236 %, and thus was excellent in crimpability. EXAMPLE 3 The block copolymer P1 of polylactic acid and PEG was prepared in the same manner as in Example 1. The polymer P1 was melted by a screw extruder of 230°C, and spun out through an orifice of 225°C having a diameter of 0.2 mm. With cooling in air and oiling, the spun filament was wound at a speed of 1500 m/min, drawn at 80°C in a drawing ratio of 4.5 and heat-treated at 110°C under a tension to give a drawn yarn A1 of 40deniers/12filaments. The drawn yarn A1 had a tenacity of 4.5 g/d, an elongation of 29 % and a shrinkage of 12 % in boiling water. Further the polymer P2 was prepared in the same manner as in Example 1. The polymer P2 was melted by a screw extruder of 220°C, and spun out through an orifice of 225°C having a 0.2 mm diameter. With cooling in air and oiling, the spun filament was wound at a speed of 1500 m/min, drawn at 80°C in a drawing ratio of 4.5 to give a drawn yarn B1 of 60deniers/12filaments without heat-treating. The drawn yarn B1 had a tenacity of 4.4 g/d, an elongation of 33 % and a shrinkage of 27 % in boiling water. Each one of the drawn yarns A1 and B1 was mixed by means of an air nozzle to give a combined filament yarn MY 1 having the both drawn yarns uniformly mixed in its section. A twill fabric was produced by using a yarn obtained by twisting the combined filament yarn at 600 T/m as a warp and a twisted yarn of 30T/m as a weft in a ratio of 2/1. The obtained twill fabric was, after scouring, heat-treated at 120°C for 15 minutes by dry heating under relaxation and further was subjected to treatment (decrease in weight) at 80°C for 10 minutes with a 0.5 % aqueous solution of caustic soda, followed by washing, adding 0.2 % of a soft-finishing agent and then heat-treating at 135°C under a tension to give a woven fabric MF1. For comparing purpose, a polylactic acid homopolymer P3 having a melting point of 175°C and a heat of fusion of 55 J/g and a polylactic acid/PEG block copolymer P4 having a melting point of 174°C and a heat of fusion of 55 J/g were prepared in the same manner as in Example 1. By using the polymer P3, a drawn yarn A2 of .40deniers/ 12fila-ments was produced in the same manner as in the drawn yarn A1. The drawn yarn A2 had a tenacity of 4.6 g/d, an elongation of 30 % and a shrinkage of 12 % in boiling water. By using the polymer P4, a drawn yarn B2 of 60deniers/12filaments was produced in the same manner as in the drawn yarn A1. The drawn yarn B2 had a tenacity of 4.5 g/d, an elongation of 29 % and a shrinkage of 15 % in boiling water. Each one of the drawn yarns A2 and B2 was blended uniformly by means of an air nozzle to give a combined filament yarn MY2. A woven fabric MF2 was produced in the same manner as in the woven fabric MF1 except that the process for weight reduction by alkali treatment was carried out with a 0.6 % of caustic soda for 30 minutes by using the combined filament yarn MY2. Characteristics of the woven fabrics MF1 and MF2 are shown in Table 1. Woven fabric Softness Bulkiness Feeling Remarks MF1 Good Good Good Present Invention MF2 Not good slightly Not good slightly Not good slightly Comparative Example EXAMPLE 4 Polylactic acid/polybutylene succinate block copolymers P5 and P6 were prepared in the same manner as in Example 2. By using the polymer P5, a drawn yarn B3 was obtained in the same manner as in the drawn yarn B1 of Example 3 except that a one-step method for spinning and drawing continuously was employed, a spinning speed was 4000 m/min, a drawing temperature was 80°C, a drawing ratio was 1.6 and heat-treatment was not carried out. The drawn yarn B3 had a tenacity of 4.7 g/d, an elongation of 33 % and a shrinkage of 38 % in boiling water. A drawn yarn A3 was produced in the same manner as in the drawn yarn B3 except that the polymer P1 of Example 3 was used and after the drawing, heat-treatment was carried out at 120°C. The drawn yarn A3 had a tenacity of 4.9 g/d, an elongation of 29 % and a shrinkage of 13 % in boiling water. A drawn yarn B4 was produced in the same manner as in the drawn yarn B3 except that the polymer P6 was used. The drawn yarn B4 had a tenacity of 4.6 g/d, an elongation of 29 % and a shrinkage of 35 % in boiling water. The drawn yarns A3 and B3 were blended by an air nozzle, and a woven fabric MF3 was produced in the same manner as in the woven fabric MF1 of Example 3. Softness, bulkiness and feeling of the woven fabric MF3 were all excellent. Similarly softness, bulkiness and feeling of the woven fabric MF4 obtained from the combined filament yarn comprising the drawn yarns B4 and A3 were excellent.

Claims: A fiber comprising (A) a fiber component comprising an aliphatic polyester (a) having a melting point of not less than 100°C and a heat of fusion of at least 20 J/g, and (B) a fiber component comprising an aliphatic polyester (b) having a melting point of not less than 100°C and a heat of fusion lower than that of said polymer (A) by at least 5J/g, wherein said fiber is a composite yarn wherein a fiber made of said fiber component (A) and a fiber made of said fiber component (B) are blended in a blending weight ratio of fiber component (A) to fiber component (B) from 10/1 to 1/10. The fiber of claim 1, wherein the blending ratio of said fiber made of component (A) to said fiber made of component (B) is from 1/5 to 5/1 by weight. The fiber of any one of claims 1 or 2, wherein the heat of fusion of said polymer (A) is at least 30 J/g. The fiber of any one of claims 1 to 3, wherein the difference in heat of fusion between said polymer (A) and said polymer (B) is at least 10 J/g.

Inventors: KAJIYAMA HIROSHI, KONDO YOSHIKAZU, MATSUI MASAO, OZEKI EIICHI, KAJIYAMA, HIROSHI, KONDO, YOSHIKAZU, MATSUI, MASAO, OZEKI, EIICHI, MATSUI, Masao, Shimadzu Corporation, Sanjo-Work, OZEKI, Eiichi, Shimadzu Corporation, Sanjo-Work
Applicants: KANEBO LTD, KANEBO LTD.
Application year: 1997
Main classification: D01F8
IPC codes: D01F8