CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority based on a Taiwanese patent application No. 098114756 filed on May 4, 2009, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a multi-layer yarn structure. More particularly, the present invention relates to a multi-layer yarn structure capable of achieving moisture management to remove perspiration away from the skin. 
     2. Description of the Prior Art 
     Due to the increasing demands of functional textiles/fabrics, the textile manufacturers not only focus on increasing additional value and practicability of textiles, but also intend to lead the fashion trend and develop all kinds of multi-functional textiles. Among all, moisture management or water transport property is one of primary standards for functional textiles. 
     Textiles with moisture management/water transport properties can absorb moisture of human bodies into the surface of the textile and then release the moisture to the atmosphere. In other words, textiles with moisture management/water transport properties exhibit the function of transporting sweat and moisture on the surface of skin to the surface of the clothing, thus preventing sweat from remaining on the skin, so as to keep the body dry and comfort. Moreover, in cold weather, the moisture management textiles can prevent heat loss of human body caused by evaporation of large amount of sweat. 
     According to conventional textiles having moisture transport properties, moisture and sweat are removed away from the skin by wicking, diffusion, and transmission processes via micro slits on the fibers and then diffused and evaporated quickly via the fibers of the clothing, so as to keep the skin dry and comfort and regulate the body temperature. As described above, due to the capillary or wicking phenomenon, the thinner the capillary is, the better the moisture absorption efficiency can be achieved. Therefore, fibers having numerous thin capillaries are desirable for excellent moisture absorption efficiency. Furthermore, when the moisture absorption efficiency of the fibers is better, the moisture absorption efficiency of the textile is increased. Therefore, the moisture absorption efficiency affects the comfort of the clothing. In the case that the moisture absorption and release efficiencies are better, the drying speed is faster and makes the skin more comfortable. 
     As the textiles quickly absorb moistures, it is possible to adjust the body temperature, improve vitality of body muscles, and delay fatigue. The textiles with good moisture transport properties are usually made from polyamide (PA) or polyester (PET). These textiles have light weight, absorb moisture/sweat quickly, and remove the moisture from the clothing rapidly. 
     However, the conventional textiles or fabrics with moisture transport properties are made by specific processing methods, e.g., adding chemicals to change the chemical structure of the surface of the fibers, or using mixed fibers for improving the moisture transport properties. As an example, the conventional push-pull fiber is a two-layer-yarn-structure consisting of a core layer which does not absorb moisture and a surface layer which can absorb moistures. That is, the surface layer absorbs moisture and sweat on the surface of skin, and then the core layer removes the moisture and sweat to keep the skin comfort and dry. 
     Therefore, in order to prevent the use of a great amount of chemical solvents and achieve other requirements, a new yarn structure is desirable. 
     SUMMARY OF THE INVENTION 
     It is an objective of the present invention to provide a multi-layer yarn structure and a method for making the same which is capable of regulating moisture released by human bodies and keeping the skin comfort and dry. 
     It is another objective of the present invention to provide a multi-layer yarn structure and a method for making the same, such that the composite yarn has a soft, smooth, and thick feel. 
     It is a further objective of the present invention to provide a multi-layer yarn structure and a method for making the same, which minimizes the use of chemical solvents to achieve the moisture transport properties. 
     It is yet another objective of the present invention to provide a multi-layer yarn structure and a method for making the same, so as to control humidity. 
     It is another objective of present invention to provide a multi-layer yarn structure and a method for making the same, wherein the fibers are micro-porous, and the moisture can be transported quickly. 
     The present invent provides a multi-layer yarn structure includes a core layer, a middle layer, and an outer layer. The core layer has a plurality of hydrophobic fibers; the hydrophobic fiber includes a hydrophilic fine denier fiber which has a fineness less than 75 denier. A plurality of noncircular fibers surrounds the core layer to form the middle layer while the outer layer surrounds the middle layer. Particularly, the core layer including a plurality of hydrophilic fibers is surrounded by the middle layer to form a three layer yarn structure as the multi-layer yarns structure. 
     In an exemplary embodiment, each noncircular fiber preferably has a crisscross shape; in other embodiments, however, the noncircular fiber may include Y-shape, cinquefoil shape, W-shape, micro porous structure or other proper shapes. The noncircular fibers preferably have better moisture transport properties and quicker moisture evaporation characteristic to regulate human body moisture rapidly. The material of the noncircular fibers includes artificial fibers and/or natural fibers. The artificial fiber may include polyester/polyethylene terephthalate (PET), polyamide 6 (PA6), polyamide 66 (PA66), nylon 6, nylon 66, polypropylene (PP), polyolefin, regenerated cellulose fibers (rayon, Tencel, Modal rayon, Tencel Sun) or other proper fibers. The nature fiber may include cotton, wool, flax, jute, ramie, sheng ma, hemp, or other proper fibers. 
     The present invention further provides a method for making a multi-layer yarn structure including the steps of: providing a plurality of hydrophobic fibers to form a core layer routing through a front roller of a first spinning area; conveying a plurality of noncircular fibers to the front roller of the first spinning area to overlap the core layer and wrapping the noncircular fibers around the core layer to form a semi-finished yarn; conveying the semi-finished yarn to a front roller of a second spinning area; and providing a plurality of hydrophilic fibers to the front roller of the second spinning area to overlap the semi-finished yarn and wrapping the hydrophilic fibers around the semi-finished yarn to form the multi-layer yarn. 
     In a preferred embodiment, conveying the noncircular fibers to the front roller of the first spinning area includes overlapping the noncircular fibers and the core layer in parallel and then rotating to form a composite yarn. In this step, before rotating the noncircular fibers, the method further includes conveying the noncircular fibers and the core layer to a twisting point of the first spinning area, by rotating the twisting point of the first spinning area to wrap the noncircular fibers around the core layer to form the composite yarn. In addiction, providing the hydrophilic fibers to a front roller of the second spinning area further includes overlapping the hydrophilic fibers and the semi-finished yarn in parallel and then rotating to form a three-layer yarn. In this step, before rotating the hydrophilic fibers, the method further includes conveying the hydrophilic fibers and the semi-finished yarn to a twisting point of a second spinning area, by rotating the twisting point of the second spinning area to wrap the noncircular fiber around the semi-finished fiber to form the three-layer yarn. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a schematic cross-sectional view of a multi-layer yarn structure of the present invention; 
         FIG. 2  illustrates another embodiment of a noncircular fiber of the present invention; 
         FIG. 3  illustrates yet another embodiment of the noncircular fiber of the present invention; 
         FIG. 4  shows a flow chart of a method of making the multi-layer yarn structure of the present invention; 
         FIG. 5A  illustrate a first embodiment of a method of making the multi-layer yarn structure of the present invention; 
         FIG. 5B  illustrates a side view of  FIG. 5A ; 
         FIG. 6A  illustrates a second embodiment of the method of making the multi-layer yarn structure of the present invention; 
         FIG. 6B  illustrates a side view of  FIG. 6A ; and 
         FIG. 7  shows another flow chart of the method of making the multi-layer yarn structure of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention provides a multi-layer yarn structure and a method for making the same which is capable of quick-drying and absorbing moisture to keep wearers comfort. In a preferred embodiment, the multi-layer structure includes three layer yarns and consists of hydrophobic fibers, noncircular fibers, and hydrophilic fibers. In general, the three-layer yarn structure preferably includes three different materials overlapping with each other to form the yarn structure. However, the number of layers or cycles of each yarn structure is not limited to the invention. In order to illustrate the present invention, various embodiments and structures thereof are described below with reference to the accompanied drawings. 
     As  FIG. 1  shows, the multi-layer yarn structure of the present invention includes a core layer  100 , a middle layer  200 , and an outer layer  300 . The core layer  100  has a plurality of hydrophobic fibers  110 . The hydrophobic fiber  110  preferably includes a hydrophobic fine denier fiber which includes a single fiber or multiple fibers having a fineness less than 75 denier. In the embodiment shown in  FIG. 1 , the hydrophobic fiber  110  can be a single bunch of fibers or multiple bunches of fibers to provide the yarn with better mechanical strength, such as tensile strength, etc. and in turn to achieve a high tenacity yarn. The material of the hydrophobic fiber  110  is preferably polyester/polyethylene terephthalate (PET). In other embodiments, however, the hydrophobic fiber  110  may include polyamide 6 (PA6), polyamide 66 (PA66), nylon 6, nylon 66, polypropylene (PP), polyolefin, or other proper fibers. 
     The middle layer  200  surrounds the core layer  100  with a plurality of noncircular fibers  210 . In the embodiment, the shape of each noncircular fiber  210  is preferably a crisscross shape. As  FIG. 2  or  FIG. 3  shows, however, the noncircular fiber  210  may include heart shape, W-shape, Y-shape, cinquefoil shape, micro porous structure, such that coolplus, or other proper shapes. 
     Due to the cross-section of the noncircular fiber  210  is a crisscross shape and its specific surface (m 2 /g) is relatively large while its fiber surface has numerous fine holes, the noncircular fiber  210  may use the capillarity effect to release the moisture to the atmosphere from the skin and keep the body dry and comfort. Moreover, the material of the noncircular fiber  210  may include artificial fibers and/or natural fibers. The artificial fiber may include polyester/polyethylene terephthalate (PET), polyamide 6 (PA6), polyamide 66 (PA66), nylon 6, nylon 66, polypropylene (PP), polyolefin, or other proper fibers. The nature fiber may include cotton, wool, flax, jute, ramie, sheng ma, hemp, or other proper fibers. 
     The outer layer  300  consists of a plurality of hydrophilic fibers  310  surrounding the middle layer  200 ; thus, the three-layer yarn structure is formed. The hydrophilic fiber  310  is preferably a nature fiber or cellulose fiber, such as cotton fiber, wool fiber, jute fiber, ramie fiber, flax fiber, sheng ma fiber, hemp fiber, cupra rayon fiber, viscose rayon fiber, tencel, modal rayon, tencel sun, bamboo fiber, cellulose acetate fiber, acetate fiber, or regenerated cellulose fiber. 
     In the embodiment of  FIG. 1 , the first layer of the three-layer yarn structure, i.e. the core layer  100 , preferably contains non-absorbent PET fibers to provide the yarn with greater elastic extensibility. The second layer of the three-layer yarn structure, i.e. the middle layer  200 , is preferably noncircular PET fibers and its moisture regain (index of moisture present in a material, expressed as a percentage of the moisture-free weight, as determined under definite prescribed conditions) is below 0.4%. The third layer of the three-layer yarn structure, i.e. the hydrophilic fiber  310  of the outer layer  300 , is preferably cotton and its moisture regain is 8%. In other embodiments, however, the three-layer yarn structure may be constructed in a manner that the core layer  100  serves as the first layer, the hydrophilic fiber  310  serves as the second layer, and the crisscross shape PET fiber serves as the third layer. The material of each layer is set forth as above and can be modified depending on the required functionality. 
     As  FIG. 4  shows, the present invention further provides a method of making a multi-layer yarn structure including: a step  400  of providing a plurality of hydrophobic fibers to form a core layer routing through a front roller of a first spinning area, a step  410  of conveying a plurality of noncircular fibers to the front roller of the first spinning area to overlap the core layer and wrapping the noncircular fibers around the core layer to form a semi-finished yarn, a step  420  of conveying the semi-finished yarn to a front roller of a second spinning area, and a step  430  of providing a plurality of hydrophilic fibers to the front roller of the second spinning area to overlap the semi-finished yarn and wrapping the hydrophilic fibers around the semi-finished yarn to form the multi-layer yarn. 
     In the embodiment of  FIG. 4 , in the step  410 , before conveying the noncircular fibers to the front roller of the first spinning area, the method further includes overlapping the noncircular fibers and the core layer in parallel and then rotating to form a composite yarn. In addition, before rotating the noncircular fibers, the method further includes conveying each noncircular fiber and the core layer to a twisting point of the first spinning area, by rotating the twisting point of the first spinning area to wrap each noncircular fiber around the core layer to form the composite yarn. In step  430 , before providing the hydrophilic fibers to the front roller of the second spinning area, the method further includes overlapping the hydrophilic fibers and the semi-finished yarn in parallel, and then rotating to form a three-layer yarn. Moreover, before rotating the hydrophilic fibers, the method further includes conveying the hydrophilic fibers and the semi-finished yarn to the twisting point of the second spinning area, by rotating the twisting point of the second spinning area to wrap the noncircular fiber around the semi-finished fiber to form the three-layer yarn. 
     Hereinafter, the method for making the multi-layer yarn structure will be described with reference to the process equipment, wherein  FIGS. 5A and 6A  illustrate front views of the process equipment, and  FIGS. 5B and 6B  illustrate side views of the process equipment. 
     As  FIGS. 5A and 5B  show, the hydrophobic fibers  110  and the noncircular fibers  210  are preferably overlapped with each other and wrapped together after providing/conveying the two different fibers through the front roller  500  of the first spinning area. Moreover, before routing through the front roller  500  of the first spinning area, the hydrophobic fiber  110  and the noncircular fiber  210  are conveyed by distinct guiding devices in different routes, as shown in  FIG. 5B . In the embodiment shown in  FIG. 5B , the guiding device for conveying the noncircular fibers  210  includes three sets of extendable rollers  500 ,  520 , and  550  to extend and align each noncircular fiber. In order to control the spinning requirement of the yarn, the speed of the guiding devices can be adjusted. For example, in this stage, the twist multiplier (T.M., T.M.=Twist per inch÷√yarn count) and the yarn ratio is preferably 1.5˜4. In other embodiments, the T.M. may be more than 4, and the guiding device for conveying the noncircular fibers  210  may include more than three sets of extendable rollers, depending on the demand. Furthermore, two sets of guiding devices can be employed to convey the hydrophobic fibers  110 ; in addition to the front roller  500  of the first spinning area, a stable guiding roller  560  is provided to ensure the yarn to have steady tensional force and control the feeding position of the hydrophobic fibers  110 . Therefore, by means of the stable guiding roller  560 , the hydrophobic fibers  110  and the noncircular fibers  210  are routed and twisted through a twisting point  800  of the first spinning area to ensure the hydrophobic fiber  110  stably warped by the noncircular fiber  210  to form the semi-finished yarn  600 , as shown in  FIG. 5A . 
     After the semi-finished yarn  600  is formed, the semi-finished yarn  600  is conveyed to the front roller  510  of the second spinning area, as shown in  FIGS. 6A and 6B . In the embodiment shown in  FIGS. 6A and 6B , the hydrophilic fibers  310  are also routed through the front roller  510  of the second area to overlap the semi-finished yarn  600 . Before this operation, the semi-finished yarns  600  and the hydrophilic fibers  310  are conveyed by distinct guiding devices in different routes, as shown in  FIG. 6B . In the embodiment shown in  FIG. 6B , the guiding devices for conveying the hydrophilic fibers  310  includes three sets of extendable rollers  510 ,  530 , and  540  to extend and align each hydrophilic fiber  310 . In order to control the spinning requirement of the yarn, the speed of the guiding devices can be adjusted. For example, in this stage, the twist multiplier and its yarn ratio is preferably be 2˜4.5. In other embodiments, however, the T.M. may be more than 4.5, and the guiding devices for conveying the hydrophilic fibers  310  may include more than three sets of extendable rollers, depending on the demand. Furthermore, two sets of guiding devices can be employed to convey the semi-finished yarn  600 ; in addition to the front roller  510  of the second spinning area, a stable guiding roller  570  is provided to ensure the yarn to have steady tensional force and control the feeding position of the semi-finished yarn  600 . Therefore, by means of the stable guiding roller  570 , the semi-finished yarn  600  and the hydrophilic fibers  310  are routed and twisted through a second twisting point  810  of the second spinning area to ensure the semi-finished yarn  600  stably warped by the hydrophilic fiber  310  to form the multi-layer yarn  610 , as shown in  FIG. 6A . 
     It is noted that, in this embodiment, though a respective equipment of different spinning area is employed to make the semi-finished yarn  600  and the multi-layer yarn  610 . In other embodiment, however, the same equipment can be employed to make the semi-finished yarn  600  and the multi-layer yarn  610 . In other words, the front roller  510  and the twisting point  810  of the second spinning area may be replaced by the front roller  500  and the twisting point  800  of the first spinning area, and the stable guiding roller can be used replaced as well. In such a case, only the CTF has to be adjusted depending on whether the semi-finished yarn  600  or the multi-layer yarn  610  to be formed. Moreover, the thickness of the semi-finished yarn  600  or the multi-layer yarn  610  can be controlled by controlling the rotation speed (rpm) of the twisting point  800  and the speed (cm/sec) of the front roller  500  of the first spinning area or the rotation speed (rpm) of the twisting point  810  of the second spinning area and the speed (cm/sec) of the front roller  510  of the second spinning area. On the other hands, when the rotation speed of the twisting point  800  of the first spinning area or the twisting point  810  of the second spinning area is constant, the conveying speed of the front roller  500  of the first spinning area or the front roller  510  of the second spinning area is increased faster, the thickness of semi-finished yarn  600  or the multi-layer yarn  610  becomes thicker. 
     As  FIG. 7  shows, the present invention further provides a method of making the multi-layer yarn structure including the steps of: a step  710  of conveying a core layer, a step  720  of providing a plurality of noncircular fibers and wrapping around the core layer to form a semi-finished yarn, a step  730  of conveying the semi-finished yarn, and a step  740  of providing the hydrophilic fiber and wrapping the semi-finished yarn to form a multi-layer yarn. 
     In step  720 , wrapping the core layer to form the semi-finished yarn further includes overlapping each noncircular fiber and the core layer in parallel and then wrapping the core layer. In step  740 , wrapping the semi-finished yarn to form the multi-layer yarn further includes overlapping each hydrophilic fiber and the semi-finished yarn in parallel and then wrapping the semi-finished yarn. 
     Although the preferred embodiments of the present invention have been described herein, the above description is merely illustrative. Further modification of the invention herein disclosed will occur to those skilled in the respective arts and all such modifications are deemed to be within the scope of the invention as defined by the appended claims.
A multi-layer yarn structure and a method for making the same are provided. The multi-layer yarn structure includes a core layer, a layer of noncircular fibers, and an outer layer. The core layer has a plurality of hydrophobic fibers. The noncircular fibers surround the core layer to form a middle layer. The outer layer surrounds the middle layer and has a plurality of hydrophilic fibers. The method spins different fibers into multi-layer yarn for making textile with a soft, smooth, and thick feel. By utilizing inherent characteristics of the multi-layer yarn structure, the textile may regulate moisture released from the human body and keep the body dry and comfort.