Patent Application
20070270064
The invention will be more fully understood and further advantages will become apparent when reference is had to the following detailed description of preferred embodiments of the invention and the accompanying drawings, in which:
Carpets are routinely manufactured by tufting carpet yarn through the interstices of a woven or non-woven primary backing mat. The needling operation passes continuous or discontinuous staple yarn through the interstices of the backing mat, creating the carpet facing. The ability of the tufted yarns to be held within the primary backing mat is strongly related to the spring back characteristics of the primary backing mat. The spring back properties are a strong function of the primary backing mat's yarn type and weave pattern. The carpet is moved from the tufting station to a second station that applies an adhesive latex layer on the underside of the tufted primary mat. Frequently, after the tufting process, but before the latex adhesive has been applied, the tufts are susceptible to dislodgment from the primary backing. In such cases, rework is required between these steps to reinsert any tufts that were dislodged before the latex adhesive is applied. Traditionally, the latex application is burdensome, since it requires compounding, removing water, curing, and finally cooling. A secondary backing mat is generally applied under the primary mat to contain the latex adhesive and to securely trap the tufted carpet yarn. The use of the latex adhesive and the secondary backing mat increases the cost to manufacture the carpet. Furthermore, the use of the latex adhesive and the secondary backing mat results in a heavier carpet that is reflected in the cost of transporting the carpet. Lastly, the use of the latex and secondary backing yields a less bendable carpet that cannot be easily installed on stairs or around tight corners.
The present invention addresses the problems and costs associated with requiring the application of a substantial quantity of separate latex adhesive and the use of a secondary backing mat during carpet manufacturing. The present invention provides a primary backing for a carpet, which changes state via a post process and becomes an adhesive layer that permanently bonds the carpet fibers in place. Generally stated, the invention relates to a primary backing for a carpet that provides good gripping of the carpet fibers without the need of a substantial quantity of an adhesive layer, such as latex, or use of a secondary backing mat. The primary backing mat is constructed with high melting mat fibers that are bonded with lower melting polymeric particulate matter incorporated on its surface. The primary backing mat is tufted with carpet yarn, whereby the lower melting polymeric particles are placed in between the tufted carpet yarn and the primary backing mat fiber. During the post thermal heating process the underside of the carpet is heated to a temperature sufficient to change the state of the low melting polymeric particles. The low melting polymeric particles melt and completely surround the primary backing mat fiber, thereby capturing the tufted carpet yarn. When the carpet is cooled, the low melting polymer solidifies and thereby acts as an adhesive, providing complete contact of the tufted yarn loop with the primary backing mat fiber. This bond strength is sufficient to provide pull out resistance of the tufted carpet yarn, avoiding or reducing the need for a latex adhesive or a second backing mat. Since the adhesive is only present between the primary backing mat yarn and the tufted carpet yarn, the fabricated carpet is thin, lightweight, and is highly flexible.
The low melting polymeric particulate coating may be selected from a number of polymeric types. Low density polyethylene melts at a temperature of approximately 115° C. (e.g., approximately 115 to 120° C.) while high density polyethylene melts at a temperature of approximately 135° C. (e.g., approximately 135 to 140° C.). Polypropylene melts at temperatures of approximately 160° C. (e.g., approximately 160 to 175° C.). Nylon 6 has a melting temperature of approximately 210 to 220° C., while nylon 6,6 has a melting temperature of approximately 225 to 265° C. Also, jute fibers do not readily melt. Therefore, there are a number of combinations of high melting backing fibers that may be coated with the lower melting polymeric particulate matter. For example, a polypropylene backing fiber may be coated with particles of low or high-density polyethylene. Nylon 6 or 6,6 backing fibers may be coated with low or high-density polyethylene particles or polypropylene particles. A jute backing fiber may be coated with low- or high-density polyethylene particles or polypropylene particles or nylon 6 or 6,6 particles. The post heat treatment temperature must be chosen so that the coated polymeric particles melt to create a bonding adhesive. Also, the tuft fiber must be chosen so that it does not melt at the post heat treatment temperature. The tufted fiber yarn may be wool, cotton, nylon 6 or nylon 6,6 or polypropylene, and combinations of these. The lower melting polymeric particulate coating may be readily chosen based on the selection of the post heat treatment temperature. One of the unique characteristics of low or high-density polyethylene particles is that they readily bond to nylon 6 or nylon 6,6 fibers when melted. This unique characteristic defines a preferred combination of nylon backing fibers coated with low- or high-density polyethylene particulate matter tufted with nylon pile yarn. When polyethylene is used, the post heat temperature can be at approximately 115° C. or 135° C., depending on whether the polyethylene is low- or high-density.
The lower melting polymeric matter may be coated on the high melting primary backing fibers using processing steps selected from a number of options. The high melting fibers may be woven, knitted, or non-woven to define a backing mat and the lower melting polymeric particulate matter may be dispersed as a suspension in a liquid carrier and sprayed to coat the backing. The liquid carrier may be evaporated by heating. Alternatively, a dry powder coating of the low melting polymeric powder may be applied using an electrically charged sprayer. In this embodiment the woven or non-woven mat of fibers are charged with an electrostatic charge, and the thermoplastic particles are charged with an opposite charge and are distributed in an air stream that passes adjacent the charged mat so as to deposit the thermoplastic particles on the mat. In a second embodiment, the coated primary backing fiber mat may be heated to tack the lower melting polymeric particles to the high melting fiber. The resultant primary backing mat may be supplied as a roll for tufting of pile fibers to form a carpet.
The following advantages are made possible by the present invention: (i) elimination or reduction of the wet latex adhesive application process; (ii) immediate in-line adhesion of tufted yarn fibers to the backing after post heat treatment, resulting in less defects and need to rework; (iii) reduction of energy costs customarily needed to drive off a substantial quantity of latex water and cure; and (iv) overall improvement of process speeds that can be increased to the speed of the tufting machines. The end result provides the desired advantages of a lightweight, flexible carpet, while avoiding the undesired defect/re-work characteristics of the current carpet manufacturing process.
The key features associated with the enhanced carpet primary backing include, in combination: (i) a high melting carpet primary backing mat; (ii) the high melting backing mat fibers is covered with a coating of lower melting thermoplastic polymer particles; (iii) the carpet tufting yarn is needled into openings in between fibers of the primary backing mat; (iv) the resulting construction is subjected to a post process that melts the lower melting thermoplastic polymer particle coating of the primary backing mat to form an adhesive that bonds the tufted yarn with the backing; (v) the resulting construction is cooled; (vi) the adhesive forms a permanent bond between the carpet yarn and the primary backing; (vii) the need for a separate latex adhesive is reduced or is obviated, and (viii) the need for a carpet secondary backing is reduced or is completely obviated.
The primary backing mat may be made from a single polymeric composition or mixtures of polymeric compositions including weave patterns that use dissimilar yarns in the weaving process or use twisted or braided yarns of different polymeric compositions.
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The carpet primary backing having enhanced tufting and tuft securing characteristics is produced by a method comprising the steps of (i) selecting fibers for a primary backing mat that are higher melting polymeric materials; (ii) manufacturing the primary backing mat either by weaving or using non-woven mat preparation processes; and (iii) coating each mat fiber with lower melting polymeric particles. The lower melting polymeric particles may be bonded to the primary backing mat by electrostatic forces or Van der Waal type forces. The bond between the lower melting polymeric particles and the primary backing mat fibers may be improved by subjecting the coated primary backing mat to a temperature sufficient to make the particles sticky and tacks the particles without melting. The primary backing is subjected to carpet yarn tufting followed by a post heat treatment. The post heat treatment changes the state of the lower melting polymeric particles, causing the particles to adhere and permanently bond the tufted carpet yarns to the primary backing mat.
Having thus described the invention it is to be understood that such detail need not be strictly adhered to, but that additional changes and modifications may suggest themselves to one skilled in the art, all falling within the scope of the invention as defined by the following claims.
