Flat filaments provided with ribs and raw fibres for pile fabrics

Abstract: Flat filaments have a flatness (A/B) of 7 to 25, where A is a length of two longer sides of a substantially rectangular, transverse cross-section of each filament and B is a length of two shorter sides of the substantially rectangular, transverse cross-section of each filament. The flat filaments also have a fineness of 0.5 to 40 denier, and are provided on each of the two longer sides with one or more ribs continuously extending in a direction of an axis of the filament and having a width W and a height H. The number of the ribs on each longer side ranges from 1 to A/2W, the width W ranges from B/2 to 3B, and the height H ranges from B/2 to 2B. The filaments have excellent non-tackiness and balkiness and permit easy elimination of crimps by polishing, and can be suitably used as raw fibers which, when formed into a pile product, provide the pile product not only with soft feeling but also with resilient and substantial feeling.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to filaments useful as a raw material for a pile product and also to raw fibers for pile fabrics. More specifically, this invention is concerned with flat filaments, which are provided with ribs, are excellent in brushing effect, namely, a property of filaments that they remain free from mutual cohesion or tangling, and bulkiness, can provide both soft surface feeling and resilient and substantial feeling, and are optimal for pile products such as stuffed toy animals, interior furnishings and clothing, and also with raw fibers for pile fabrics, said raw fibers containing the flat filaments and being capable of obtaining pile products which are equipped with both soft surface feeling and excellent resilient and substantial feeling. 2. Prior art As a natural fur is generally composed of hairs which are reduced in diameter at their free end portions compared with their basal end portions, touch feeling of its surface gives characteristic soft and flexible feeling despite its resilient and substantial appearance. There is a tendency in recent years toward avoidance of use of natural furs from the viewpoint of protection of the natural environment. This has led to a strong outstanding desire for the development of pile products which are made of synthetic fibers, have surfaces of soft feeling comparable with that available from natural furs and, when pressed, exhibit good resiliency and give substantial feeling. Among synthetic fibers, acrylic fibers can provide particularly soft feeling rather easily. Many pile products which are made of acrylic fibers and resemble furs have therefore been put on the market. However, the unavoidable use of fibers having a constant thickness results in coarse and hard feeling when fibers are formed with the same thickness as that of their basal portions, or leads to non-resilient feeling when the fibers are formed with the same thickness as their free end portions. The followings are examples of the prior art which are known to provide pile products owing to the use of synthetic fibers closer in feeling to natural furs: (1) a technique making use of the tendency that fibers having a flattened cross-section or an elongated circular cross-section are readily bent in at least one direction and give softer touch feeling compared with fibers having the same fineness but a circular cross-section (for example, Japanese Patent Laid-Open No. 59524/1975); (2) a technique that free end portions of piles of a pile product made of polyester fibers are pointed by dipping and hydrolyzing the free end portions in an aqueous alkali solution (Japanese Patent Laid-Open No. 16906/1980) or free end portions of bundled polyester fibers are pointed by dipping the free end portions in an aqueous alkali solution (Japanese Patent Laid-Open No. 134272/1981); (3) a technique that fibers with characteristic soft touch feeling despite the thickness of their basal portions are obtained by spinning fibers having a Y-shaped cross-section and applying force to the fibers so that free end portions of the fibers are split (Japanese Patent Publication No. 51564/1989); and (4) a technique that fibers, which have a fineness in a range of from 1.66 to 4.44 dtex (1.5 to 4 denier) and a flattened rectangular cross-section, are bendable in the direction of their shorter sides and have 1 to 6 asperities on an outer periphery of each fiber, are used to provide a pile product with improved soft surface feeling and brushing effect (Japanese Patent Laid-Open NO. 200808/1990). The approaches (1) to (4) are all to achieve both soft surface feeling and resilient and substantial feeling without using downy hairs. Described specifically, according to the technique (1), indentations are formed as viewed in an elongated circular cross-section so that the inherent tacky feeling of polyester fibers can be improved. However, the resulting feeling is more or less that available from the elongated cross-section, thereby failing to obtain soft surface feeling and, when pressed by a hand, resilient and substantial feeling, which are all comparable with those of natural furs and are intended by the present invention. According to the technique (2), the sharpness of fibers is hardly controllable and moreover, the hydrolysis in the aqueous alkali solution has to be practiced batchwise so that the efficiency of production is poor. Further, according to the technique (3), the drying load is substantially high due to a high water retention for which the cross-sectional shape is responsible. For industrial use, special consideration is needed. It is therefore difficult for this technique to achieve mass production at a low cost. Finally, according to the technique (4), the fibers tend to bend in the direction of the short sides thereof as viewed in their cross-section and because of the provision of the asperities, the fibers are provided with unduly high stiffness. According to the description of the examples in its specification, the fibers are stated to provide pile fabrics with greater bulkiness owing to the avoidance of close contact between the adjacent fibers compared with fibers having a "simple flat cross-sectional shape". However, such pile fabrics lack soft surface feeling. From the foregoing, it is possible to realize the difficulty in meeting numerous requirements required for pile products. In addition to the techniques (1) to (4), a still further method is known. According to this method, a pile product is formed using raw fibers composed in combination of non-shrinkable fibers and shrinkable fibers. Under dry hot or wet hot conditions, only the shrinkable fibers are then caused to shrink so that the non-shrinkable fibers and the shrunk fibers are allowed to remain as guard hairs and downy hairs, respectively. It is preferred for a pile product to have a surface which has soft feeling but, when pressed, gives resilient and substantial feeling. To provide the surface of the pile product with soft feeling, it is an important point how to eliminate crips from guard hairs, which are buried in downy hairs, or how to convert them into readily straightenable fibers by a so-called polishing step in which the surface of the pile product is gently rubbed by a hot roller subsequent to shrinkage of downy hairs. To this end, it is known to be effective to reduce the proportion of acrylonitrile in an acrylonitrile copolymer to be employed for the production of the fibers so that the acrylonitrile copolymer can be provided with a reduced thermal distortion temperature. If the copolymerized amount of acrylonitrile in an acrylonitrile copolymer is reduced, the dye clarity and colorability of the fibers are deteriorated and moreover, the feeling of the pile product is prone to changes through a mild thermal history, for example, by drying or the like. The pipe product so obtained is therefore difficult to handle. According to this technique, the resilient and substantial feeling when the pile is pressed is developed by downy hairs. Here, the shrinkage factor of the fibers and their bulkiness and substantial feeling, which are associated with the cross-sectional shape of the shrinkable fibers, become important factors. As a method for overcoming such problems, Japanese Patents Laid-Open Nos. 21978/1985 and 209048/1985, for example, disclose a technique that shrinkable fibers, which have a shrinkage factor of at least 15%, an inter-fibers static friction coefficient of 0.23 or smaller and are susceptible to shrinkage, are used as downy hairs in piled products. To control the static friction coefficient below 0.23, use of an aminosiloxane softener is an essential requirement. However, an aminosiloxane softener tends to deposit in a rubbery form on drying rollers during a drying step of a spinning process of fibers and hence has tendency to become a cause for process troubles. A technique which does not use such a softener is therefore desired. JP-A-06 081207 discloses a flat filament having a flatness of 2≤A/b≤10 (A is the length of the flat part in the longitudinal direction of the cross section of the filament; b is the thickness at the centre of the flat part between two projecting parts separated in the longitudinal axis direction of the flat part) and provided with two longitudinal ribs having a height of 1/2 (B - b) with 1.2≤B/b≤5.0 (B is the distance between the tops of the two projecting parts existing in the direction crossing the flat part). SUMMARY OF THE INVENTION An object of the present invention is to provide flat filaments provided with ribs, which are excellent in brushing effect and bulkiness, permit easy elimination of crimps by polishing, and when formed into pile products, have soft feeling and can show resilient and substantial feeling and which are suited as raw fibers for pile fabrics and are optimal for stuffed toy animals, interior furnishings, clothing and the like. Another object of the present invention is to provide raw fibers for piled fabrics, which contain the above-described flat filaments provided with the ribs (which may hereinafter be called "ribbed flat filaments" for the sake of brevity) and, when formed into pile fabrics, show softer feeling. A further object of the present invention is to provide raw fibers, which comprise the above-described ribbed flat filaments and specific shrinkable fibers, do not require blending of raw fibers subjected to special treatment such as application of an aminosiloxane softener, and can obtain pile products equipped not only with soft surface feeling but also with excellent resilient and substantial feeling similar to that available from natural furs. In a first aspect of the present invention, there is thus provided a flat filament having a flatness (A/B) of 7 to 25, A being a length of two longer sides of a substantially rectangular, transverse cross-section of said filament and B being a length of two shorter sides of said substantially rectangular, transverse cross-section of said filament, and a fineness of 0.55 to 44.4 dtex (0.5 to 40 denier); and provided on each of said two longer sides with one rib continuously extending in a direction of an axis of said filament and having a width W and a height H, said width W ranging from B/2 to 3B, and said height H ranging from B/2 to 2B. In a second aspect of the present invention, there are also provided raw fibers for a pile fabric, which comprise at least 10 wt.% of ribbed flat filaments as defined above; and at most 90 wt.% of flat filaments having a flatness (A'/B') of 5 to 25, A' being a length of two longer sides of a substantially rectangular, transverse cross-section of each of said filaments and B' being a length of two shorter sides of said substantially rectangular, transverse cross-section of said filament, and a finenes of 1.11 to 44.4 dtex (1 to 40 denier). In a third aspect of the present invention, there are also provided raw fibers for a pile fabric, which comprise 20 to 60 wt.% of ribbed flat filaments as defined above; 20 to 50 wt.% of shrinkable fibers having a shrinkage factor of at least 15% and a fineness of 1.11 to 5.55 dtex (1 to 5 denier); and 60 wt% or less of non-shrinkable fibers. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will hereinafter be described in further detail. Incidentally, the term "fineness" as used herein by itself means "the fineness of a single filament". The ribbed flat filament according to the present invention is required to have a flatness of 7 to 25 as defined by a ratio of A/B where A is a length of two longer sides of a substantially rectangular, transverse cross-section of the filament, said cross-section being perpendicular to an axis of the filament, and B is a length of two shorter sides of the substantially rectangular, transverse cross-section of the filament. A flatness of 7 to 15 is more preferred. A flatness smaller than 7 is not preferred because such filaments tend to tangle with each other and, when formed into a pile product, result in a surface having rough feeling. On the other hand, a flatness greater than 25 makes it difficult to produce a pile product because such filaments have lower mechanical strength due to a reduction in stretchability upon spinning. The term "substantially rectangular" as used herein to define the shape of a cross-section of a base portion (i.e., a portion which still remains after removal of the ribs) of the ribbed flat filament according to the present invention should be interpreted to embrace not only rectangular shapes but also oval shapes, insofar as they can achieve the above-described objects of the present invention. It is required for the filament to be provided on each of the two longer sides with one rib as viewed in the transverse cross-section of the filament. The rib is required to continuously extend in a direction of the axis of the filament and to have a width W and a height H, said width W ranging from B/2 to 3B, and the height H ranging from B/2 to 2B. Owing to the provision of these ribs which continuously extend in the direction of the axis of the filament, adjacent filaments remain loose without cohesion, thereby having excellent brushing effect and bulkiness and, when formed into a pile product, exhibiting soft feeling and even resilient and substantial feeling. If the width W of the ribs is smaller than B/2 or greater than 3B, effects of ribs cannot be observed so that such filaments merely show feeling and brushing effect which are not different at all from those available from simple flat filaments are used. If the height H of the ribs is smaller than B/2, effects of ribs cannot be observed so that such filaments merely show feeling and brushing effect which are not different at all from those available from simple flat filaments are used. If the height H of the ribs exceeds 2B, such filaments cannot be produced with good productivity. Further, the number of ribs per longer side of the filament is 1. The fineness of the ribbed flat filament according to the present invention should be 0.55 to 44.4 dtex (0.5 to 40 denier), with 2.22 to 27.7 dtex (2 to 25 denier) being preferred and 3.33 to 22.2 dtex (3 to 20 denier) being particularly preferred. A fineness small-er than 0.55 dtex (0.5 denier) is not preferred because such filaments tend to tangle with each other and, when formed into a pile product, result in a surface having rough feeling. On the other hand, a fineness greater than 44.4 dtex (40 denier) cannot show soft feeling when formed into a pile product. No particular limitation is imposed on the position of each rib in the ribbed flat filament, insofar as it is located on the longer side of a basal portion of the filament. From the standpoint of feeling, it is particularly preferred that a midpoint of a width of the rib is located within a distance of A/4 from a midpoint of the longer side. Although no particular limitation is imposed on the cross-sectional shape of each rib, the rib preferably has a cross-sectional shape that does not form any pocket between the rib and the basal portion of the filament since its water retention can be controlled at low level in a spinning step. Illustrative examples of the cross-sectional shape include triangular, square, rectangular, other polygonal and semicircular shapes. In particular, a cross-sectional shape defined by curved lines only without edges is preferred, because such raw filaments also show good cohesion in a spinning step and moreover, when formed into a pile product, mutual hooking of the filaments is reduced and the pile product is provided with still enhanced soft surface feeling. The term "cohesion" as used herein indicates performance as to whether or not any inconvenience such as sliver breakage takes place when forming such filaments into slivers as an intermediate material for the pile product. If the cohesion is poor, it is necessary to make longer the cut length of raw fibers to be spun. When the cross-sectional shape of each rib is formed of curved lines alone, the cut length of the raw fibers can be chosen from a broader range so that such a cross-sectional shape is advantageous for adjusting the feeling. The preferred ranges of the width W and the height H, in which the above-described characteristic features of the filament according to the present invention can be most enhanced, are a range of B/2 to 2B, notably a range of B to 2B for the width W and a range of B/2 to B for the height H. Setting of W and H within these ranges makes it possible, in addition to the availability of excellent characteristic features of the raw fibers, to produce filaments with good productivity in the spinning step and further to achieve the best cohesion in the spinning step. The ribbed flat filaments are preferably acrylic filaments made of an acrylonitrile polymer because among synthetic fibers, acrylic filaments are particularly easier in obtaining soft feeling and are excellent in dye clarity and colorability. The ribbed flat acrylic filaments can be produced as will be described hereinafter. The acrylonitrile polymer suitable for the production of the ribbed flat acrylic filaments is an acrylonitrile copolymer which is composed of 50 wt.% or more of acrylonitrile and an unsaturated monomer copolymerizable with acrylonitrile. Especially when the ribbed flat filaments are used in combination with shrinkable acrylic fibers and/or other acrylic fibers, an acrylonitrile polymer containing acrylonitrile in an amount of 90 wt.% or more is preferred. An acrylonitrile content lower than 50 wt.% leads to filaments which are poorer in thermal properties, dye clarity and colorability. No particular limitation is imposed on the unsaturated monomer which is employed as a copolymerizable component. Usable examples include acrylic acid, methacrylic acid and derivatives thereof; vinyl acetate, acrylamide, methacrylamide, vinyl chloride, and vinylidene chloride; and depending on the application, ionic unsaturated monomers such as sodium vinylbenzenesulfonate, sodium methallylsulfonate, and sodium acrylamidomethylpropanesulfonate. No particular limitation is imposed on the polymerization process for the acrylonitrile polymer. For example, a conventional suspension polymerization or solution polymerization process can be used. Further, no particular limitation is imposed on the molecular weight of the acrylonitrile polymer provided that the molecular weight falls within a range of molecular weights generally employed for the production of acrylic filaments. It is however preferred to have a reduced viscosity at 25°C within a range of 1.5 to 3.0 when measured in the form of a 0.5 wt.% dimethylformamide solution. A spinning solution is prepared by dissolving the acrylonitrile polymer in a solvent so that the concentration of the acrylonitrile polymer falls within a range of 15 to 28 wt.%. The spinning solution is then spun through a spinneret having a hole configuration substantially similar to the cross-sectional shape of desired filaments. If the concentration of the acrylonitrile polymer in the spinning solution is lower than 15 wt.%, the configuration of the fine spinning holes and the cross-sectional shape of the filaments substantially differ from each other at the time of coagulation. This makes it difficult to obtain the desired cross-sectional shape. Such a low concentration is not preferred. If the concentration exceeds 28 wt.%, on the other hand, the spinning solution has lower time-based stability so that its spinnable properties are lowered. Such a high concentration is not preferred either. Usable examples of the solvent include organic solvents such as dimethylformamide, dimethylacetamide and dimethyl sulfoxide; and other solvents such as nitric acid; aqueous thiocyanate solutions; and aqueous solution of zinc chloride. When it is intended to control the cross-sectional shape of filaments by the configuration of fine spinning holes, an organic solvent is advantageous. By performing spinning and taking up in such a way that a spinning draft defined in terms of a ratio of a taking up speed of coagulated filaments to a linear delivery speed of a spinning solution falls within a range of 0.7 to 2.0, flat acrylic filaments having a cross-sectional shape substantially similar to the configuration of the fine spinning holes can be obtained. A spinning draft greater than 2.0 results in more frequent end breakage in the coagulation bath solution, thereby making it difficult to obtain filaments themselves. The thus-obtained coagulated filaments are then stretched, washed and dried under known conditions by known methods, whereby flat acrylic filaments according to the present invention can be obtained. Depending on the application, the filaments so obtained are subjected thermal relaxation treatment or the like to impart well-balanced mechanical properties, and are then cut into raw fibers. A description will next be made about raw fibers for a pile fabric, which comprise flat filaments having a flatness (A'/B') of 5 to 25, A' being a length of two longer sides of a substantially rectangular, transverse cross-section of said filaments and B' being a length of two shorter sides of said substantially rectangular, transverse cross-section of said filament, and a fine-ness of 1.11 to 44.4 dtex (1 to 40 denier), and ribbed flat filaments according to the present invention. If raw fibers for a pile fabric are formed of mere flat filaments alone, the filaments closely cohere as described above so that their brushing effect is reduced and, when formed into a pile product, the pile product has rough feeling. If raw fibers are formed of super flat filaments having a large flatness to impart soft feeling, the resulting pile product has the above-mentioned drawback and also low resiliency. However, blending of ribbed flat filaments according to this invention with flat fibers results in insertion of the ribbed filaments between the flat filaments which by themselves tend to closely cohere with each other. The filaments are therefore prevented from cohesion, resulting in an improvement in brushing effect. Further, as the individual filaments are independent from each other, they can be brought into direct contact with a hot roller when they are heated in a polishing step. This facilitates transfer of heat from the hot roller to the individual filaments so that the elimination of crimps from the filaments is easier than that of crimps from raw fibers composed only of ribbed flat filaments according to the present invention. The resulting pile product is therefore of a structure in which the flat filaments are reinforced by the ribbed flat filaments, so that the pile product has resilient and substantial feeling while its surface has soft feeling. Here, the flat filaments which are blended to the ribbed flat filaments are required to have a flatness (A'/B') of 5 to 25, A' being a length of two longer sides of a substantially rectangular, transverse cross-section of the flat filament and B' being a length of two shorter sides of the substantially rectangular, transverse cross-section of the flat filament, and a fineness of 1.11 to 44.4 dtex (1 to 40 denier), preferably of 2.22 to 33.3 dtex (2 to 30 denier), more preferably of 5.55 to 16.6 dtex (5 to 15 denier). If the flatness of the blended flat filaments is smaller than 5, it is difficult to exhibit the softness specific to such flat filaments, thereby making it difficult to obtain a pile product resembling a natural fur. If the flatness exceeds 25, on the other hand, the blended flat filaments have strong tendency to cohere each other so that, even when the ribbed flat filaments are blended, improving degree of the brushing effect of the ribbed flat filaments cannot be exhibited fully. If the fineness of the blended flat filaments is smaller than 1.11 dtex (1 denier), the filaments tend to tangle with each other so that, when formed into a pile product, the pipe product has a surface having rough feeling. If the fineness exceeds 44.4 dtex (40 denier), the filaments cannot exhibit soft feeling despite their flat configurations when they are formed into a pile product. It is therefore difficult to obtain a pile product resembling a natural fur. Concerning the blending proportions of the ribbed flat filaments and the blended flat filaments, the former should be 10 wt.% or more, more preferably 30 wt.% or more. If this proportion is smaller than 10 wt.%, the proportion of the ribbed flat filaments which are located between the blended flat filaments is too small so that the ribbed flat filaments cannot effectively prevent mutual tacking or cohesion of the blended flat filaments. When formed into a pile product, the pile product tends to have a surface of rough feeling. Needless to say, the raw fibers for the pile fabric can be composed solely of ribbed flat filaments according to the present invention. The flat filaments which are used to form the raw fibers according to the present invention for the pile fabric are preferably flat acrylic filaments because among synthetic fibers, the acrylic filaments are easier to obtain particularly soft feeling and are excellent in dye clarity and colorability. The flat acrylic filaments can be produced in a similar manner as the above-described production process of the ribbed flat acrylic filaments except that the configuration of the fine spinning holes has to be changed to a configuration substantially similar to the cross-sectional shape of the flat acrylic filaments. Raw fibers for a pile fabric can be obtained by blending the ribbed flat filaments and the flat filaments, in the above-described proportions or by using only the ribbed flat filaments. The raw fibers can then be formed into a pile fabric such as a boa, high-pile fabric or carpet. A description will next be made of raw fibers according to the present invention for a pile fabric, which is composed of shrinkable fibers, which have a shrinkage factor of at least 15% and a single fibers finenes of 1.11 to 5.55 dtex (1 to 5 denier), and the ribbed flat acrylic filaments. These raw fibers will hereinafter be called "shrinkable-fiber-blended raw fibers for a pile fabric". A natural fur exhibits characteristic resilient and substantial feeling not only when pressed strongly but also pressed lightly. The feeling of the above-mentioned raw fibers for the pile fabric is very close to the feeling of the natural fur when pressed gently, but when pressed strongly, resilient and substantial feeling such as that available from the natural fur cannot be obtained from the raw fibers for the pile fabric. With a view to improving the feeling further, shrinkable filaments which become downy hairs when formed into a pile product are therefore used in combination. The shrinkable-fiber-blended raw fibers for the pile fabric are obtained by blending the ribbed flat filaments, shrinkable fibers having a shrinkage factor of at least 15% and a single fibers fineness of 1.11 to 5.55 dtex (1 to 5 denier) and non-shrinkable fibers together. It is necessary to set the proportions of the respective fibers at 20 to 60 wt.% for the ribbed flat filaments, 20 to 50 wt.% for the shrinkable fibers and 60 wt.% or less for the non-shrinkable fibers. In this case, the ribbed flat filaments have high stiffness so that they tend to remain upright in the pile fabric. When a hot roller is brought into contact with the ribbed flat filaments upon so-called polishing step in the production process of the pile fabric, the ribbed flat filaments can contact the hot roller without flexion. This makes it possible to improve the efficiency of heat transfer from the hot roller to the ribbed flat filaments, whereby crimps can be easily straightened out. If the proportion of the ribbed flat filaments in the shrinkable-fiber-blended raw fibers for the pile fabric is smaller than 20 wt.%, it is impossible to provide the resulting pile fabric with a surface of soft feeling. On the other hand, a proportion greater than 60 wt.% makes it difficult to fully draw out the effect of the thus-blended shrinkable fibers, that is, to achieve improvements in the resilient and substantial feeling of the resulting pile fabric when the pile fabric is strongly pressed. The shrinkage factor of the shrinkable fibers which are converted to downy hairs when formed into the pile fabric is 15% or greater, preferably 20% or greater. A shrinkage factor smaller than 15% leads to fluffs sunken to basal portions of the ribbed flat filaments so that, when strongly pressed, the downy hairs cannot play a role in imparting resilient and substantial feeling to the pile fabric. Incidentally, the term "shrinkage factor of at least 15% (20%)" as used herein indicates that either the wet thermal shrinkage factor (as measured after treatment for 3 minutes in boiling water) or the dry thermal shrinkage factor (as measured after treatment at 130°C for 10 minutes) is at least 15% (20%). If the proportion of the shrinkable fibers in the shrinkable-fiber-blended raw fibers for the pile fabric is smaller than 20 wt.%, the resulting pile fabric cannot exhibit strong resiliency and substantial feeling when strongly pressed. On the other hand, a proportion greater than 50 wt.% leads to a pile fabric whose surface has a low filament density, whereby the pile fabric is not provided with surface smoothness. The shrinkable fibers are required to have a fineness of 1.11 to 5.55 dtex (1 to 5 denier). A fineness smaller than 1.11 dtex (1 denier) results in tangling of the shrinkable fibers themselves or tangling of the shrinkable fibers with the ribbed flat filaments as guard hairs, thereby making it difficult to allow the shrinkable fibers to undergo even shrinkage. A fineness greater than 5.55 dtex (5 denier), on the other hand, results in a pile fabric which is felt rough at the basal portions of its filaments and is hence of lower quality. Further, if the proportion of the non-shrinkable fibers which may be used in addition to the ribbed flat filaments and the shrinkable fibers as needed exceeds 60 wt.%, the proportions of the ribbed flat filaments as guard hairs and the shrinkable fibers as downy hairs are reduced accordingly, thereby resulting in a pile fabric with a surface whose soft feeling, resiliency and substantial feeling are all reduced. Moreover, use of shrinkable and/or non-shrinkable fibers having a specific cross-sectional shape as the shrinkable fibers and/or the non-shrinkable fibers leads to a pile fabric of still improved quality. As the cross-sections of fibers of such a specific cross-sectional shape, it is necessary to concurrently meet the following three requirements. (1) The contour of each cross-section should be defined only by edge-free curves. (2) Each cross-section should satisfy the following formula: 2 ≤ a/b ≤ 5 where, when the cross-section is sandwiched between two parallel straight lines, a is a maximum distance between the two parallel straight lines and b is a minimum distance between the two parallel straight lines. (3) Each cross-section defines at least two indentations at different locations. When the requirements (1) to (3) are met, the chance of mutual hooking of the single fibers is reduced upon causing the shrinkable fibers to shrink into downy hairs. The shrinkable fibers are therefore allowed to undergo even shrinkage, leading to a pile fabric with still improved, excellent resilient and substantial feeling. It is a role of the non-shrinkable fibers to prevent the ribbed flat filaments from cohering together in the pile fabric so that the pile fabric is provided with stilled improved quality. The cohering-preventing effect of these non-shrinkable fibers can also enhanced further if the contours of their cross-sections are each defined only by curves. Any fibers available by a known process and having the above-described characteristics are usable as the sinkable fibers in the shrinkable-fiber-blended raw fibers for the pile fabric. No particular limitation is imposed on their production process. Shrinkable acrylic fibers are particularly preferred for their superb dye clarity and colorability. Shrinkable acrylic fibers can be produced by a known process, and to provide them with a cross-sectional shape which can meet the above-described requirements (1) to (3), the configuration of fine spinning holes and spinning conditions are suitably selected and combined to obtain shrinkable acrylic fibers of the desired cross-sectional shape. Concerning the individual types of fibers making up the shrinkable-fiber-blended raw fibers for the pile fabric, no particular limitations are imposed on their spinning steps or on finishing oils which are used in post-treatments after dyeing or the like. When colored raw fibers are desired, it is only necessary to conduct dyeing by a method known per se in the art such as dyeing after the formation of the raw fibers, or using of producer dyed fibers or pigmented fibers. The ribbed flat filaments, the shrinkable fibers and, if necessary, the non-shrinkable fibers are blended in the above-described proportions, and as raw fibers for a pile fabric, are formed into a pile product such as a boa, a high-pile fabric or a carpet by a known piling process. The present invention will hereinafter be described further by the following examples, in which the individual measurement data were measured by the following methods. (Reduced viscosity of acrylonitrile polymer) The reduced viscosity of each acrylonitrile polymer was determined by dissolving it with dimethylformamide into a 0.5 wt.% solution and then measuring its viscosity at 25°C with a Cannon-Fenske viscometer. (Measurement of shrinkage factor) The measurement of the shrinkage factor of each filament was conducted by the following procedures. The filament length (Lw) before shrinkage was measured under a load of 9 mg/dtex (10 mg/denier) and subsequent to shrinking processing, the temperature of the filament was allowed to drop down to room temperature and the filament length (L'w) was likewise measured under a load of 9 mg/dtex (10 mg/denier). Its shrinkage factor was then determined in accordance with the following formula: Shrinkage factor (%) = {(Lw - L'w)/Lw} x 100 (Ranking of pile product) Based on the surface softness of each pile product as determined by human hand in an organoleptic test and the resiliency and substantial feeling of the pile product when the pile product was pressed by hand, the pile product was ranked in accordance with the following standards. Surface softness: A: Excellent B: Good C: Average D: Poor E: Bad Resiliency and substantial feeling: A: Excellent (good resiliency and substantial feeling were obtained not only when the pile product was strongly pressed but also when the pile product was lightly pressed). B: Good (good resiliency and substantial feeling were obtained when the pile product was lightly pressed). C: Average D: Poor E: Bad (Water retention) After filaments were washed, a sample was collected in a wet state before processing them with drying rollers. The sample was dried at 105°C for 2 hours. From the weights of the sample before and after drying, its water retention was calculated in accordance with the following formula: Water retention (%) = {(W 1 - W 0 )/W 0 } x 100 where W 0 is the weight (g) of the filaments after drying and W 1 is the weight (g) of the filaments before drying. (Positions of ribs) In each example, the position of each rib was indicated by expressing a midpoint of a bottom side of the rib in terms of (x,y) in a coordinate system composed in such a way that a point of intersection between diagonal lines of a substantially rectangular cross-section obtained by cutting the rib along a plane, which extends vertically relative to a filament axis of the associated flat filament, is located at the origin of coordinate axes x,y, said coordinate axis x extending in parallel with both longer sides of the substantially rectangular cross-section while said coordinate axis y extending in parallel with both shorter sides of the substantially rectangular cross-section. Examples 1-12 & Reference Examples 13-15 & Comparative Examples 1-11 In each of the examples, reference examples and comparative examples, an acrylonitrile copolymer composed of 93 wt.% of acrylonitrile and 7 wt.% of vinyl acetate and having a reduced viscosity of 2.0 was obtained by an aqueous suspension polymerization process. The acrylonitrile copolymer was then dissolved in dimethylacetamide so that a spinning solution containing the acrylonitrile copolymer at a concentration of 24 wt.% was obtained. In Comparative Example 1, however, the concentration of the acrylonitrile copolymer was set at 20 wt.%. Through fine spinning holes of the corresponding one of hole configurations which are similar to cross-sectional shapes of desired types of filaments, respectively, the spinning solution was spun in a 40% aqueous solution of dimethylacetamide, said aqueous solution having been controlled at 40°C, so that the corresponding spinning draft shown in Table 1 was obtained. The resultant filaments were stretched 5-fold in hot water (6.5-fold in Comparative Example 1 only), washed and then dried by drying rollers. After they were subjected to thermal relaxation treatment under a pressurized steam atmosphere of 2.5 kg/cm 2 , crimps were applied at a population of 3.74 crimps/cm (9.5 crimps/inch) and a crimp degree of 10.3%, whereby ribbed flat acrylic filaments were obtained. These ribbed flat acrylic filaments were cut into 51 mm lengths to form raw fibers. From the raw fibers, slivers of 10 g/m in thickness were produced. By a sliver knitting machine, they were formed into a sliver knit. The sliver knit was then subjected to polishing step, whereby a high-pile fabric of a metsuke (basis weight) of 700 g/m 2 and a pile length of 18 mm was obtained. Evaluation results of this high-pile fabric are shown in Table 1. Comparative Examples 12 and 13 In each comparative example, spinning was conducted in a similar manner as Example 2 except that the configuration of each fine spinning hole was modified at the rib-forming portions thereof. The water retention of filaments before their drying step was measured, and is shown in comparison with that of the filaments of Example 2 in Table 2. The pre-drying water retention varies substantially depending on the rib shape, and the rib shapes of Comparative Examples 10 and 11 are expected to result in significant drying loads. Examples 16-18 & Comparative Examples 14-18 In each of the examples and comparative examples, an acrylonitrile copolymer composed of 93 wt.% of acrylonitrile and 7 wt.% of vinyl acetate and having a reduced viscosity of 2.0 was obtained by an aqueous suspension polymerization process. The acrylonitrile copolymer was then dissolved in dimethylacetamide so that a spinning solution containing the acrylonitrile copolymer at a concentration of 24 wt.% was obtained. Through fine spinning holes of a corresponding flat configuration, the spinning solution was spun in a 40 wt.% aqueous solution of dimethylacetamide, said aqueous solution having been controlled at 40°C, while taking them up at a spinning draft of 1.01 to 1.91. The resultant filaments were stretched 5-fold in hot water, washed and then dried by drying rollers. After they were subjected to thermal relaxation treatment under a pressurized steam atmosphere of 2.5 kg/cm 2 , crimps were applied at a population of 3.74 crimps/cm (9.5 crimps/inch) and a crimp degree of 10.3%. The ribbed flat acrylic filaments were then cut into 51 mm lengths. In this manner, six types of flat acrylic fibers shown in Table 3 were obtained. Each of the six types was blended with the 51-mm long ribbed filaments, which had been obtained in the corresponding one of Examples 1 to 3 and Comparative Examples 2 and 4, in the proportions shown in Table 3, and slivers of 10 g/m in thickness were produced. By a sliver knitting machine, they were formed into a sliver knit. The silver knit was then subjected to polisher processing, whereby a high-pile fabric of a metsuke of 700 g/m 2 and a pile length of 8 mm was obtained. Evaluation results of this high-pile fabric are also shown in Table 3. Examples 19-23 and Comparative Examples 19-22 In each of the examples and comparative examples, a spinning solution of the same composition as that employed in Example 16 was spun into a 40 wt.% aqueous solution of dimethylacetamide, said aqueous solution having been controlled at 40°C, through fine spinning holes of a configuration similar to the cross-sectional shape of the desired filaments. The resultant filaments were then stretched 5-fold in boiling water while washing off the solvent, followed by drying-through hot rollers controlled at 150°C. After they were subjected to thermal relaxation treatment in pressurized steam of 2.5 kg/cm 2 , crimps were applied at a population of 3.74 crimps/cm (9.5 crimps/inch) and a crimp degree of 10.3%. In this manner, different types of ribbed flat acrylic filaments, which were different in fineness and flatness as shown in Table 4, were obtained. Each type of ribbed flat acrylic filaments was then cut into 51 mm lengths to provide raw fibers. Further, spinning was also performed likewise through fine circular holes. After the resultant filaments were subjected to thermal relaxation treatment in pressurized steam, they were stretched 1.5-fold in steam of normal pressure, thereby obtaining shrinkable acrylic fibers having a broad-bean-shaped cross-section. [fineness: 2.22 dtex (2 denier), a/b = 2.6, number of indentation(s): 1]. The shrinkage factor of these fibers was 26% when measured by treating them for 3 minutes in boiling water and 17% when measured by treating them for 10 minutes at 130°C dry heat. These fibers were cut into 38 mm lengths to provide conventional raw fibers of shrinkable acrylic fibers. Additional spinning was also performed likewise through the same fine circular holes. The resultant fibers were subjected only to pressurized steam treatment, thereby obtaining shrinkable acrylic fibers having a broad-bean-shaped cross-section [fineness: 5.55 dtex (5 denier), a/b = 2.6, number of indentation(s): 1]. These fibers were cut into 38 mm lengths to provide conventional raw fibers of shrinkable acrylic fibers. The above-obtained three types of raw fibers were blended together in proportions such that the ribbed flat acrylic filaments, the shrinkable fibers and the conventional acrylic fibers accounted for 40 wt.%, 40 wt.% and 20 wt.%, respectively, and slivers of 20 g/m in thickness were then produced. By a sliver knitting machine, they were formed into a sliver knit. Subsequent to shrinking treatment, the silver knit was subjected to polisher processing, whereby a high-pile fabric of a metsuke of 700 g/m 2 and a pile length of 18 mm was obtained. Its feeling was ranked and is also shown in Table 4. Examples 24-31 & Comparative Examples 23-25 In each of the examples and comparative examples, the same acrylonitrile copolymer as in Example 1 was dissolved in dimethylacetamide so that a spinning solution containing the acrylonitrile copolymer at a concentration of 25 wt.% was obtained. The spinning solution was spun into a 40 wt.% aqueous solution of dimethylacetamide, said aqueous solution having been controlled at 40°C, through fine spinning holes of a configuration similar to the cross-sectional shape of the desired fibers. The resultant fibers were then stretched 5-fold in boiling water while washing off the solvent, followed by drying through hot rollers controlled at 150°C. After they were subjected to thermal relaxation treatment in pressurized steam of 2.5 kg/cm 2 . In this manner, four types of fibers which had edge-free cross-sectional shapes and were different in shape [a/b, number of indentation(s)] were obtained. Each type of fibers was then stretched 1.5-fold in steam of normal pressure, whereby shrinkable acrylic fibers having a fineness of 2.22 dtex (2 denier) were obtained. The shrinkage factor of these filaments was 27% when measured by treating them for 3 minutes in boiling water and 18% when measured by treating them for 10 minutes at 130°C dry heat. These fibers were cut into 38 mm lengths to provide raw fibers of shrinkable acrylic fibers. In a similar manner as described above, spinning was performed through the fine circular holes and the resultant fibers were subjected to the treatment or processing up to the pressurized steam treatment, whereby conventional acrylic fibers having a fineness of 5.55 dtex (5 denier) were obtained. These fibers were cut into 38 mm lengths to provide conventional raw fibers of acrylic fibers. The above-obtained two types of raw fibers were blended with the ribbed flat acrylic filaments (fineness: 11.1 dtex (10 denier), flatness: 13), which had been obtained in Example 1, in proportions shown in Table 5, whereby slivers of 10 g/m in thickness were produced. By a sliver knitting machine, they were formed into a sliver knit. Subsequent to shrinking treatment, the silver knit was subjected to polisher processing, whereby a high-pile fabric of a metsuke of 700 g/m 2 and a pile length of 18 mm was obtained. Its evaluation results are also shown in Table 5. Example 32 The filaments obtained in Example 27, which had an edge-free cross-sectional shape (a/b = 3.4, number of indentations: 2), were stretched 1.5-fold in steam of normal pressure subsequent to their treatment in pressurized steam, whereby shrinkable acrylic fibers having a fineness of 2.22 dtex (2 denier) were obtained. The shrinkage factor of these fibers was 27% when measured by treating them for 3 minutes in boiling water and 18% when measured by treating them for 10 minutes at 130°C dry heat. These fibers were cut into 38 mm lengths to provide raw fibers. In a similar manner as described above, spinning was performed and the resultant fibers were subjected to post treatment or processing up to the pressurized steam treatment, whereby non-shrinkable acrylic fibers having a similar edge-free cross-sectional shape (a/b = 3.7, number of indentations: 2) and a fineness of 5.55 dtex (5 denier) were obtained. These fibers were cut into 38 mm lengths to provide raw fibers. The above-obtained two types of raw fibers were blended with the ribbed filaments of the flat cross-section (fineness: 11.1 dtex (10 denier), flatness: 13), which had been obtained in Example 1, in proportions such that the ribbed flat acrylic filaments, the shrinkable acrylic fibers and the non-shrinkable acrylic fibers accounted for 30 wt.%, 40 wt.% and 30 wt.%, respectively, and slivers of 10 g/m in thickness were then produced. By a sliver knitting machine, they were formed into a sliver knit. The sliver knit was subjected to shrinking treatment for 5 minutes at 130°C dry heat and then to shrinking treatment, whereby a high-pile fabric of a metsuke of 700 g/m 2 and a pile length of 18 mm was obtained. A surface of this high-pile fabric has soft feeling and also had excellent resiliency and substantial feeling. It was therefore a pile fabric of very high quality. The ribbed flat filaments according to the present invention have excellent brushing effect and bulkiness, permit easy elimination of crimps by polishing and, when formed into a pile product, provide not only soft feeling but also resilient and substantial feeling. They are hence suited as raw fibers for a pile fabric. The raw fibers according to the present invention for the pile fabric exhibit still softer feeling when formed into the pile fabric. Further, the shrinkable-filament-blended raw fibers for a pile fabric according to the present invention obviate blending of raw fibers subjected to special treatment such as application of an aminosiloxane softener, and can be formed into a pile product equipped with not only soft surface feeling but also excellent resiliency and substantial feeling, all of which are highly comparable with those of natural furs.

Claims: A flat filament having a flatness (A/B) of 7 to 25, A being the length of the two longer sides of a substantially rectangular, transverse cross-section of said filament and B being the length of the two shorter sides of said substantially rectangular, transverse cross-section of said filament; and provided on said two longer sides with ribs continuously extending in the direction of the axis of said filament and having a width W and a height H, said width W ranging from B/2 to 3B, and said height H ranging from B/2 to 2B, characterized in that the fineness of said flat filament is 0.55 to 44.4 dtex (0.5 to 40 denier) the number of said ribs on each longer side is 1. The flat filament according to claim 1, wherein a midpoint of said width W of each rib is located within a distance of A/4 from a midpoint of the associated longer side. The flat filament according to claim 1 or 2, wherein said flatness (A/B) ranges from 7 to 15 and said fineness ranges from 3.33 to 22.2 dtex (3 to 20 denier). The flat filament according to claim 1, 2 or 3, wherein each rib has a shape defined only by edge-free curves as viewed in said transverse cross-section of said filament. The flat filament according to claim 1, 2, 3 or 4, wherein said flat filament is an acrylic filament. Raw fibers for a pile fabric, comprising: at least 10 wt.% of ribbed flat filaments as defined in claim 1; and at most 90 wt.% of flat filaments having a flatness (A'/B') of 5 to 25, A' being a length of two longer sides of a substantially rectangular, transverse cross-section of each of said filaments and B' being a length of two shorter sides of said substantially rectangular, transverse cross-section of said filament, and a fineness of 1.11 to 44.4 dtex (1 to 40 denier) The raw fibers according to claim 6, wherein said latter flat filaments have a fineness of 2.22 to 33.3 dtex (2 to 30 denier). The raw fibers according to claim 6, wherein the latter flat filaments have a fineness of 5.55 to 16.6 dtex (5 to 15 denier). Raw fibers for a pile fabric, said raw fibers including shrinkable fibers, comprising: 20 to 60 wt.% of ribbed flat filaments as defined in claim 1; 20 to 50 wt.% of shrinkable fibers having a shrinkage factor of at least 15% and a fineness of 1 to 5 denier; and 60 wt% or less of non-shrinkable fibers. The raw fibers according to claim 9, wherein each of said shrinkable fibers has a transverse cross-section defined only by edge-free curves, defines at least two indentations at different locations as viewed in the transverse cross-section, and satisfies the following formula: 2 ≤ a/b ≤ 5 where, when said transverse cross-section is sandwiched between two parallel straight lines, a is a maximum distance between said two parallel straight lines and b is a minimum distance between said two parallel straight lines. The raw fibers according to claim 9 or 10, wherein each of said non-shrinkable fibers has a transverse cross-section defined only by edge-free curves, defines at least two indentations at different locations as viewed in the transverse cross-section, and satisfies the following formula: 2 ≤ a/b ≤ 5 where, when said transverse cross-section is sandwiched between two parallel straight lines, a is a maximum distance between said two parallel straight lines and b is a minimum distance between said two parallel straight lines. The raw fibers according to claim 9, 10 or 11, wherein said shrinkable fibers are acrylic fibers. The raw fibers according to claim 9, 10, 11 or 12, wherein said non-shrinkable fibers are acrylic fibers.

Inventors: HOSOKAWA HIROSHI, MASAOKA HIDEO, NISHIHARA YOSHIHIRO, OISHI SEIZO, TAKEMOTO FUMIO, HOSOKAWA, HIROSHI, MASAOKA, HIDEO, NISHIHARA, YOSHIHIRO, OISHI, SEIZO, TAKEMOTO, FUMIO, Hosokawa, Hiroshi, c/o Mitsubishi Rayon Co., Ltd., Masaoka, Hideo, c/o Mitsubishi Rayon Co., Ltd., Nishihara, Yoshihiro, c/o Mitsubishi Rayon Co., Oishi, Seizo, c/o Mitsubishi Rayon Co., Ltd., Takemoto, Fumio, c/o Mitsubishi Rayon Co., Ltd.
Applicants: MITSUBISHI RAYON CO, MITSUBISHI RAYON CO., LTD.
Application year: 1996
Main classification: D01D5
IPC codes: D01F6, D01D5