Patent Publication Number: US-9845555-B1

Title: Stretch spun yarn and yarn spinning method

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to textiles and more particularly to stretch yarns and methods for making stretch yarn. 
     For certain types of clothing it is considered desirable to use fabrics exhibiting “stretch” properties, i.e. the ability to be extended under a relatively low force and to elastically return to the original shape and size. Stretch properties may be imparted by the type of fabric construction, such as knitting, and also by incorporating yarns which themselves have stretch properties. 
     It is known to make stretch fibers using urethane chemistry. One well-known stretch fiber is a polyester-polyurethane copolymer, sold under brand names such as SPANDEX. This fiber (in the form of a filament yarn) is often blended with or used alongside other fibers such as cotton or polyester to make fabrics and clothing. While effective to provide stretch properties, it has a high cost. 
     Accordingly, there have been attempts to make stretch yarns from other synthetics, in particular blends of bicomponent fibers comprising poly(ethylene terephthalate), also referred to as “PET”, and poly(trimethylene terephthalate), also referred to as “PTT”. Such fibers have a much lower cost that urethanes. However, these are still more expensive than cellulosic staple fibers (e.g. cotton) or other natural staple fibers. In the prior art it has been believed that relatively large amounts of such fibers are required to achieved adequate stretch properties in yarn. 
     Accordingly, there remains a need for a stretch yarn utilizing minimal amounts of synthetic fibers. 
     BRIEF DESCRIPTION OF THE INVENTION 
     This need is addressed by a blended stretch yarn suitable for making fabrics. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The yarn described herein may be spun from an intimate blend of a synthetic bicomponent fiber and natural staple fibers (such as cotton, linen, wool, or silk staple fibers), in a standard short-staple fiber drawing and spinning process. 
     The bicomponent fiber is a stretch staple fiber comprising poly(trimethylene terephthalate) (“PTT”) and another polymer such as poly(ethylene terephthalate) (“PET”). In a preferred embodiment, the bicomponent fiber has a side-by-side cross-sectional shape, with a weight ratio of the two components of approximately 50/50. Suitable fibers having these characteristics are available under the name ZENTRA from HUVIS of Seoul, Korea. 
     Blending of the bicomponent fiber with natural staple fibers can be accomplished by weight in the opening process described below, or by other known methods effective to produce an intimate blend of the two fibers. 
     The exact proportions of the bicomponent and natural staple fibers may be varied to suit a particular end use. It is believed that the majority of the stretch properties are dependent on the presence of PTT in the bicomponent fiber. Yarns made from a fiber blend of a 50/50 bicomponent have been tested at cotton-to-bicomponent ratios of 60/40, 70/30, 80/20, and 90/10. All of those blends demonstrated beneficial stretch properties, characterized by their crimp index measurements. Surprisingly and contrary to the prior art, it has been found that spun yarns made with less than 20% bicomponent fiber (that is, less than 10% PTT when using a 50/50 bicomponent fiber) have desirable stretch properties. Testing supports the reasonable conclusion that having PTT present at about 7.5 wt % of the spun yarn provides desirable stretch properties. When PTT is provided in a bicomponent fiber, the PTT/PET ratio could be increased or decreased as long as the percentage of PTT in the finished yarn is maintained. It is further believed that bicomponent fibers containing as little as 1-4 wt % PTT could provide some stretch benefit. 
     The yarn described above may be manufactured using known short staple yarn manufacturing machinery, an example of which will be briefly summarized. The cotton or other natural staple fibers are introduced in the process in the form of compressed bales. The bales are unstrapped and placed in a specific location under a top feeder machine according to their fiber properties. The top feeder machine traverses back and forth over the bales milling a few millimeters at a time introducing the fibers into the opening and cleaning process. 
     Since cotton is a natural fiber there are large, medium and fine particles of leaf, stem, trash, and seed coat fragments that must be cleaned from the natural fibers. The fibers are processed through a series of cleaning machines. During the cleaning process, tuft size is progressively reduced facilitating the cleaning and removal of the impurities. Furthermore, there is also a great amount of variation in natural fibers due to differences in the soils and the amount of rain in different cotton growth regions, farming practices and in cotton varieties. 
     The bicomponent staple fibers are also provided as bales and may be opened and cleaned separately. 
     Mixing machines are arranged in the cleaning line to receive the opened, cleaned fibers and provide a uniform mixing of the natural and bicomponent fibers. 
     Properly cleaned, mixed and blended fibers are transferred to carding machines where fibers are separated individually. Very fine trash, dust and foreign matter are removed, and the fibers are arranged in a continuous strand of uniform quality then coiled into a container that allows them to be transported to other processes. The end product of the carding process is sliver, which is a continuous strand of loosely assembled fibers without twist. The production of sliver is the first step in the textile operation that brings staple fiber into a form that can be drawn (or reduced in size) and eventually twisted into a spun yarn. 
     Multiple and continuous strands of fibers from the carding process are presented to drawing machines where they are passed through a series of rollers to provide further blending and to parallelize the fibers. 
     This doubling effect helps to blend out variation in the individual strands produced in the previous process. By passing fibers between a series of rollers with increasing speeds the fibers are straightened and made more parallel to the axis of the fiber strand. Also, the input weight is reduced to a weight that can be used by the next process. In addition, electronic devices called autolevelers, are used to reduce and control weight variation and to reduce objectionable imperfections. 
     Subsequent to drawing, the fibers are spun into yarn. Various spinning processes exist including ring spinning, open end spinning, air-jet spinning, and vortex spinning. Testing has been conducted with ring spinning and open end spinning. Air-jet spinning is believed to be suitable as well. The yarn cotton count and weight may vary to suit a specific end use of the yarn. 
     The completed yarn is suitable for being made into fabric using known methods. The yarn is especially suitable for being knitted into fabric, for example for use in articles of clothing, and imparts stretch properties to the fabric. 
     Example 
     A bicomponent staple fiber having a 50/50 composition of PET and PTT and a side-by-side cross-section was intimately blended with cotton staple fibers. The ratio by weight of cotton to bicomponent was 85/15. The fiber blend was drawn and spun into yarn using the process described above, using open-end spinning. The finished yarn had good stretch properties, with an average percent crimp (tested using industry standard protocols) of 57.5%. The yarn was subsequently knitted into fabric samples. The fabric exhibited desirable stretch properties as well as acceptable dyeing and processing characteristics. 
     At the same time, the spun yarn&#39;s overall cross-sectional properties were largely dominated by the cotton. For example, the elastic recovery, defined as the degree that the yarn will return to its original size after deformation from stress, was quite low. One industry standard, AS-L-1095, measures elastic recovery as a percentage of recovery from elongation of the yarn by 5% of its length. The test yarn of the Example had an average elongation at break of less than 5%, representing essentially no elastic recovery (at 5% elongation). Further testing indicates that any of the yarns described above should have an elastic recovery percentage of elongation (at 5% elongation) of less than 70%. 
     The foregoing has described a stretch spun yarn and a method for its manufacture. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. 
     Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. 
     The invention is not restricted to the details of the foregoing embodiment(s). The invention extends any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.