Woven fabric made of shape memory polymer

Abstract: A woven fabric woven from fibers of a shape memory polymer alone or a blend of said fibers and ordinary natural or synthetic fibers.

Description: FIELD OF THE INVENTION AND RELATED ART STATEMENT The present invention relates to a woven fabric woven from fibers of a shape memory polymer alone or a blend of said fibers and ordinary natural or synthetic fibers. The conventional woven fabric is made of natural or synthetic fibers or a blend of both. These fibers are also used in combination with an adhesive to produce nonwoven fabrics. There has recently been proposed a nonwoven fabric which is composed of fibers of a resin having the shape memory property and an adhesive of a resin having the shape memory property. (See Japanese Patent Laid-open No. 252353/1986.) Being made by bonding short fibers to one another with an adhesive as disclosed in JP-61-252353, a nonwoven fabric has the following disadvantages. (1) It tends to be thick. (2) It tends to be uneven in thickness and hence in strength because it is difficult to distribute the adhesive uniformly. (3) It is high in cost owing to the expensive adhesive. The foregoing holds true of the nonwoven fabric made of shape memory resin mentioned above. Another disadvantage of the conventional nonwoven fabric made of shape memory resins is a high production cost attributable to additional processes. For example, where short fibers of a shape memory resin are used in combination with natural or synthetic long fibers, it is necessary to cut the latter short according to the length of the former. Also, there is an instance where a woven fabric of natural or synthetic fibers has to be laminated with an adhesive to a nonwoven fabric composed of fibers of a shape memory resin and an adhesive of a shape memory resin. The adhesive for lamination also adds to the production cost. JP-61 225 346 discloses a fabric using a shape memory alloy. This fabric is formed of said shape meory alloy in the form of fibrous lines weaving a cloth so that the fabric is shape-memorized to assume the required shape aimed at preventing wrinkle and shape collapse by shape recovery of said shape memory alloy over the temperature of its transformation and maintaining its shape for a long time. However, since this fabric is formed of metal, there are disadvantages such as discomfort when it is dressed and difficulty in processing at the time of cutting so that the use of the fabric is largely limited. DE-A-2 018 762 discloses a fabric made of yarns composed of a first film polymer and a second polymer conducted into the former, an appreciable number of the yarns of the fabric consisting of said first film shape polymer and said second polymer. However, DE-A-2 018 762 lacks the description that said polymer is a shape memory polymer utilizing changes in elasticity around the glass transition point. OBJECT AND SUMMARY OF THE INVENTION The present invention was completed to solve the above-mentioned problem associated with the conventional nonwoven fabric made of a shape memory resin. Accordingly, it is an object of the present invention to provide a woven fabric having the shape memory property. The gist of the present invention as claimed in claims 1 and 2, resides in a woven fabric of shape memory polymer which is formed by weaving yarns of shape memory polymer fibers alone or by weaving said yarns and yarns of ordinary natural or synthetic. fibers, and also in a woven fabric of shape memory polymer which is formed by weaving blended yarns of shape memory polymer fibers and ordinary natural or synthetic fibers. Further embodiments according to the invention are claimed in claims 3-7. The woven fabric of the present invention functions differently as follows depending on the glass transition point (Tg for short hereinafter) of the shape memory polymer in the woven fabric and the method of imparting the shape memory property. In the case where the Tg is lower than normal temperature (say, about -5°C) and the shape memory property is imparted at a temperature considerably higher than the Tg (say, a temperature at which the polymer begins to flow, or 150°C in the case of polyurethane), the woven fabric cut to an adequate size is caused to remember its shape when it is deformed as desired in a mold, and heated and held in the mold at a temperature at which the polymer begins to flow, and finally cooled to normal temperature in the deformed state. The woven fabric remembering the desired shape gives soft hand like an ordinary cloth when it is used at normal temperature, which is higher than the Tg. It does not wrinkle and deform even when it is washed or stored for a long time in a wardrobe. Therefore, the woven fabric having a low Tg can be favorably applied to the creases of slacks and the pleats of skirts if it is caused to remember the shape at a high temperature. In the case where the Tg is higher than normal temperature (say, about 40°C) and the shape memory property is imparted at a temperature (say, 150°C) at which the polymer begins to flow, the woven fabric gives hard hand at normal temperature. Even if it wrinkles or deforms after washing or storage for a long time in a wardrobe, it easily returns to its original shape it remembers when it is heated above the Tg. Therefore, the woven fabric having a high Tg can be favorably applied to the collars, cuffs, and shoulder pads of utility shirts. In the case where the Tg is higher than normal temperature (say, about 40°C) as mentioned above and the shape memory property is imparted in the softened state at a temperature (say, 90°C) slightly higher than the Tg (instead of the above-mentioned high temperature at which the polymer begins to flow) and then the woven fabric is cooled below the Tg, the woven fabric is set in the deformed shape which has been given when softened and remembers this shape. In this case, the woven fabric gives hard hand when used at normal temperature, which is lower than the Tg, as with the above-mentioned case. Even if it wrinkles or deforms after washing or storage for a long time in a wardrobe, it easily returns to its original shape it remembers when it is heated above the Tg. Therefore, in this case, too, the woven fabric can be favorably applied to the collars, cuffs, and shoulder pads of utility shirts. Incidentally, in the case where the Tg is lower than normal temperature (say, about -5°C) and the shape memory property is imparted in the softened state at a temperature slightly higher than the Tg as mentioned above, the woven fabric cannot be used in the shape it remembers because the normal use temperature is higher than the Tg. This is not the case, however, if the woven fabric is used at low temperatures below -5°C. In other words, the woven fabric can be used in the shape it remembers only in special districts under special conditions. The above-mentioned shape memory function can be freely controlled by many factors in the following manner. (1) In the case where the woven fabric is composed of yarns of shape memory polymer alone, the ability of the woven fabric to retain the shape depends on the fineness of the yarn and the set of the cloth. (2) In the case where the woven fabric is composed of yarns of the shape memory polymer fibers and yarns of ordinary natural or synthetic fibers, whether the woven fabric has hand similar to or different from that of the woven fabric of natural or synthetic fibers depends on the blending ratio and fineness of the polymer yarns. (3) In the case where the woven fabric is composed of blended yarns of shape memory polymer fibers and ordinary natural or synthetic fibers, the ability to retain the shape and the hand of the woven fabric depends on the amount, the fineness and cross-section of the blended yarns, and the set of the woven cloth. In the case where the woven fabric is composed of blended yarns, the woven fabric exhibits the shape memory function easier or harder as the amount of the shape memory polymer increases or decreases, respectively. Therefore, the amount of the shape memory polymer should preferably be 10 to 96 wt% in the blended yarns. As the shape memory polymer that can be used in the present invention may be cited urethane polymers, styrene-butadiene polymers (not claimed), crystalline diene polymers (not claimed), and norbornane polymers (not claimed). Their Tg can be freely controlled by properly selecting the kind of the raw materials (monomers, chain extender, etc.) and their mixing ratio. The woven fabric of the present invention has an advantage inherent in woven fabrics. That is, the fibers (or yarns) of the shape memory polymer can be easily blended with ordinary natural or synthetic fibers (or yarns thereof). Unlike the conventional nonwoven fabric mentioned above, there is no need for cutting long fibers short, or laminating with an adhesive nonwoven fabrics separately prepared from shape memory polymer fibers and natural or synthetic fibers. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The present invention will be described in more detail with reference to the following examples which are not intended to restrict the scope of the invention. [1] Preparation of shape memory polymer Polyurethane elastomers as the shape memory polymers were prepared by prepolymer process in the following manner according to the formulation shown in Table 1. First, the diisocyanate and polyol were reacted in a specific molar ratio of [NCO]/[OH] to give a prepolymer. When the reaction was complete, the chain extender was added in an amount sufficient to establish a desired molar ratio of [chain extender]/[prepolymer]. After defoaming, the resulting mixture was cured for crosslinking reaction at 80°C for one or two days in a constant temperature dryer. This process may be carried out with or without solvent. The polyurethane elastomer produced as mentioned above will have a Tg and other physical properties as desired, if the following six factors are properly selected. (1) the kind of the isocyanate, (2) the kind of the polyol, (3) the kind of the chain extender, (4) the [NCO]/[OH] molar ratio, (5) the [chain extender]/[prepolymer] molar ratio, and (6) the curing condition. In Table 1, the crystallinity (wt%) was measured by X-ray diffractometry. [2] Weaving of shape memory polyurethane Example (1) A cloth was woven only from yarns spun from the shape memory polyurethane, sample No. 2 in Table 1. The Tg of this cloth was -10°C. Example (2) A cloth was woven from the yarns of the shape memory polyurethane in Example (1) as warps and ordinary cotton yarns as wefts. The Tg of this cloth was -10°C. Example (3) A cloth was woven from a 50:50 blended yarns of fibers of the shape memory polyurethane, sample No. 2 in Table 1, and ordinary cotton fibers. The Tg of this cloth was -10°C. Example (4) A cloth was woven only from the yarns spun from the shape memory polyurethane, sample No. 39 in Table 1. The Tg of this cloth was 40°C. Example (5) A cloth was woven from the yarns of the shape memory polyurethane in Example (4) as warps and ordinary cotton yarns as wefts. The Tg of this cloth was 40°C. Example (5) A cloth was woven from a 50:50 blended yarns of fibers of the shape memory polyurethane, sample No. 39 in Table 1, and ordinary cotton fibers. The Tg of this cloth was 40°C. [3] Use of the shape memory woven cloth Example (A) Each of the cloths prepared in Examples (1) to (3) was folded over and heated in a trouser press at a temperature at which the polyurethane, sample No. 2, begins to flow. After being kept at this temperature for 5 minutes, the cloth was cooled to normal temperature, so that the crease was set (or the cloth was caused to remember the crease). These cloths gave exactly the same hand as the cloths of ordinary natural or synthetic fibers. When they were washed for 1 hour using a washing machine and then dried, they did not wrinkle. Example (B) Each of the cloths prepared in Examples (4) to (6) was heated in a shoulder pad press at a temperature at which the polyurethane, sample No. 39, begins to flow. After being kept at this temperature for 5 minutes, the cloth was cooled to normal temperature, so that the shape of shoulder pad was set (or the cloth was caused to remember the shape of shoulder pad). These cloths gave hard hand at normal temperature, but they are not so hard as plastic plate. They gave the hand of cloth and did not give unpleasant feeling when kept in contact with the human skin for a long time. The cloths in the shape of shoulder pad were washed in a washing machine for 1 hour and then dried. They slightly wrinkled and deformed; but they restored their original shape when heated with a hair drier at a temperature higher than the Tg. They retained their shape even when they were cooled below the Tg. Incidentally, when the wrinkled and deformed cloths were heated by bringing them into contact with the human arm instead of using a hair drier, they restored their original shape in 20 seconds to 1 minute. Example (C) Each of the cloths prepared in Examples (4) to (6) was softened at 50°C (higher than the Tg) and folded over and pressed between two flat plates under a pressure of 0.5-2.0 kgf/mm². Then, it was cooled to a temperature lower than the Tg in the folded state so that the folded state was set. These cloths gave hard hand at normal temperature as in Example (B), but they are not so hard as plastic plate. They gave the hand of cloth and did not give unpleasant feeling when kept in contact with the human skin for a long time. The cloths in the folded shape were washed in a washing machine for 1 hour and then dried. They slightly wrinkled and deformed as in Example (B); but they restored their original shape when heated with a hair drier at a temperature higher than the Tg. They retained their shape even when they were cooled below the Tg. Incidentally, when the wrinkled and deformed cloths were heated by bringing them into contact with the human arm instead of using a hair drier, they restored their original shape in 20 seconds to 1 minute. As mentioned in detail above, the woven cloth of the present invention offers the following advantages inherent in woven cloth. (1) The thickness of the woven fabric can be easily controlled by properly selecting the fineness of yarns. (2) The woven fabric does not need any adhesive. Therefore, unlike the conventional nonwoven fabric which absolutely needs an adhesive, the woven fabric has no fear of becoming uneven in thickness and strength due to the uneven distribution of adhesive. (3) The woven fabric is low in production cost because it needs no adhesive. (4) The woven fabric can be woven from a blend composed of the fibers (or yarns) of the shape memory polymer and ordinary natural or synthetic fibers (or yarns thereof). The blend may be in the form of blended yarn or different yarns. (5) The woven fabric can be produced at a low production cost for the reasons given in (3) and (4) above. (6) Owing to its shape memory performance, the woven fabric can be used in various ways depending on the Tg of the shape memory polymer used in the woven fabric or the way in which the woven fabric was caused to remember the shape. It can be used in various application areas and in various places ranging from cold districts to hot districts.

Claims: A woven fabric of shape memory polymer characterised in that it is formed by weaving yarns of shape memory polymer fibers alone or by weaving said yarns and yarns of ordinary natural or synthetic fibers wherein said shape memory polymer fibers are made of a polyurethane elastomer having a shape memory property. A woven fabric of shape memory polymer characterised in that it is formed by weaving blended yarns of shape memory polymer fibers and ordinary natural or synthetic fibers wherein said shape memory polymer fibers are made of a polyurethane elastomer having a shape memory property. A woven fabric as claimed in Claim 1 or 2, wherein the yarns or fibers of the shape memory polymer have a glass transition point lower than room temperature and the setting of the shape is performed at a temperature higher than room temperature. A woven fabric as claimed in Claim 1 or 2, wherein the yarns or fibers of the shape memory polymer have a glass transition point lower than room temperature and the setting of the shape is performed at a temperature approximate to the temperature at which said polymer begins to flow. A woven fabric as claimed in Claim 1 or 2, wherein the yarns or fibers of the shape memory polymer have a glass transition point higher than room temperature and the setting of the shape is performed at a temperature approximate to the temperature at which said polymer begins to flow. A woven fabric as claimed in Claim 1, wherein the yarns of the shape memory polymer fibers and the yarns of natural or synthetic fibers are blended in the ratio of 10-95/90-5 wt%. A woven fabric as claimed in Claim 2, wherein the blended yarns are composed of the shape memory polymer fibers and natural or synthetic fibers in the ratio of 10-95/90-5 wt%.

Inventors: HAYASHI SHUNICHI NAGOYA TECHNI, KOBAHASHI KAZUYUKI NAGOYA MACH, HAYASHI, SHUNICHI NAGOYA TECHNICAL INSTITUTE, KOBAHASHI, KAZUYUKI NAGOYA MACHINERY WORKS
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI JUKOGYO KABUSHIKI KAISHA
Application year: 1989
Main classification: D03D15
IPC codes: C08L75, D02G3, D01F6, D03D15, C08L101