Process for the production of a dense stitched fleece
United States Patent Fleissner 5] Apr. 8, 1975 [5 1 PROCESS FOR THE PRODUCTION OF A 3.515.609 6/l970 Rudlofi 264/113 3.620.892 11/1971 Wincklhofer et al. 264/122 DENSE STITCHED FLEECE Primary E.\&#39;ami11erRobert F. White Assistant Examiner-.1. R. Hall Attorney. Agent. or F inn-Craig &amp; Antonelli [57] ABSTRACT A continuous process for producing a dense and compact stitched fleece is disclosed wherein a stitched fleece comprised of at least two fibers having defined melting points. one of the fibers having a melting point lower than the other fibers and being used as binding fibers. is heated in the range of the temperature of the binding fibers to soften said binding fibers; the stitched fleece is compressed while said binding fibers are in the softened state; and the stitched fleece is cooled to solidify the fleece while the fleece is in the compressed state. In addition. the product of this process and the apparatus for effecting the process are disclosed.  
 18 Claims, 2 Drawing Figures [75] Inventor: Heinz Fleissner, Egelsbach, Germany [73] Assignee: Vepa AG, Basel. Schweiz.  
 Switzerland [22] Filed: Feb. 17, I970 [21] Appl. No.: 14,808  
 [30] Foreign Application Priority Data Feb. 25. 1969 Germany 1909345 Feb. 17. 1969 Germany 1907860 [52] US. Cl 264/122; 264/92 [51] Int. Cl D04h 1/54 [58] Field of Search 264/122, 113, 92  
 [56] References Cited UNITED STATES PATENTS 2,852,485 9/1958 Stoff et al. 264/122 3.431.334 3/1969 Williams et al. 264/122 PROCESS FOR THE PRODUCTION OF A DENSE STlTCl-IED FLEECE BACKGROUND OF THE INVENTION The present invention relates to a process for producing a dense stitched fleece suitable base material (substrate) for synthetic leather, and in particular to a process for producing a densely stitched fleece comprising at least two types of fibers, one of which is employed as the binding fiber. This fleece, which is suitable as a base material for synthetic leather, can be strengthened by means of a thermal treatment.  
  It is conventional to utilize fleeces as a base material for synthetic leather. These fleeces generally contain a large proportion of high-shrinkage fibers, for example about 30-50%, or more. In case high-shrinkage fibers of polyesters or polyamides are employed. the shrinking step is most advantageous conducted in a water bath heated to a temperature of about 90-95C. However, in this connection, considerable difficulties are encountered in obtaining a uniform shrinkage over a specific width of the material. A uniform shrinkage is necessary since this produces the desired closeness density in the material. Only when the density is uniform is it possible to obtain uniform properties in synthetic leather. When using polypropylene as the shrinkage fiber, the shrinking step is carried out in heated air. By means of the shrinking process, a very close, dense and compact fleece is obtained exhibiting a correspondingly good flexural elasticity. Becuase of the difficulty encountered in obtaining a uniform shrinkage, it is also known to employ knitted and woven fabrics as the base. These fabrics are expensive in their manufacture, and the final products do not possess properties equal to a synthetic leather utilizing a shrunk fleece as a base material. In order to avoid the difficult shrinking process, it has also been suggested to use a stitched fleece as a base (carrier or substrate) material, said fleece having a certain proportion of binding fibers. These fleeces are very voluminous and do not exhibit the closeness of a shrunk fleece and thus do not exhibit the good properties of a shrunk fleece.  
 SUMMARY OF THE INVENTION An object of the present invention is to avoid the prior art disadvantages in providing a process for pro ducing a stitched fleece suitable as a base material for synthetic leather.  
  Another object of the present invention is to provide an improved process for producing a base material for synthetic leather wherein a good bonding of the individual fibers and a uniform compactness of the fibers is achieved.  
  A further object of the present invention is to avoid the difficulties encountered in the treatment of shrunk fleece but, at the same time, imparting to the base material the similar advantageous properties of a shrunk fleece.  
  Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it would be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications with the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.  
  Pursuant to the present invention, it has been found that the above-mentioned disadvantages may be eliminated and a much improved process for producing a base material for synthetic leather may be obtained by heating the stitched fleece to the melting or softening temperature of the binding fiber, compressing the fleece, and then cooling the fleece during the compression step. The compression (pressing) step effects, on the one hand, a very good bonding of the individual fibers to one another by welding, and, on the other hand, a considerable compacting of the fleece. By cooling the fleece during the pressing step, the fleece is simultaneously solidified in the compressed condition, so that as a result thereby a very close fleece is produced which, additionally, is also extremely uniform, particularly in its closeness (compactness).  
  it is advantageous to conduct the heating process utilizing air, steam, or a steam-air mixture as the treat ment medium, wherein this treatment medium is drawn through the fleece. ln order to compress the fleece, at least one pair of cooled rolls can be employed, and for cooling purposes, air can be utilized.  
  It is furthermore advantageous to hold the fleece compressed between a perforated drum and a perforated belt, at least during the cooling step, and to guide it therebetween, with a gaseous or liquid cooling medium. e.g., air, steam, or water, being conducted through the fleece and through the drum and belt during the cooling process. The feature of starting the compression of the fleece while it is in the plastic condition of the melt fiber afford the advantage that a more satisfactory welding is achieved due to the relative movement of the individual fibers with respect to one another. A particularly good fleece for a base material for synthetic leather is obtained according to the present process by providing that the fleece contains up to about 50% binding fibers, preferably about l0-l 5% binding fibers, and is strengthened by a thermal treatment and a pressure treatment as described above. By increasing the proportion of binding fibers within the desired proportions noted above, the closeness of the fleece can be enhanced.  
  A fleece consists of a specific fiber having a specific melting point. If another fiber having a different chemical composition and a lower melting point is added to this fiber, it serves as a binding fiber when the temperature of the fleece is increased in the range of the melt ing point of said another fiber. Thus, the fleece as defined by the present invention comprises at least two of any material of synthetic fibers having a defined melting point, at least one of said fibers having a melting point lower than that of the remaining fibers.  
  The fibers which can be utilized by the present inven tion include any of the natural or synthetic fibers. The natural fibers can include cotton, wool, silk, cellulose, etc., and the synthetic fibers may comprise synthetic polymers such as polyolefins, e.g., polyethylene, polypropoylene, etc., polyamides, e.g., Nylon 6 obtained by condensation of caprolactam, Nylon 66 obtained by the condensation of hexamethylenediamine with adipic acid, etc., polyesters, e.g., polyethylene terephthalate, etc., phenolic resins, e.g., phenol formaldehyde resins, urea formaldehyde resins, etc., polyvinyl materials, e.g., polyvinyl chloride, polyvinyl acetate etc., and acrylate resins, such as polymethylmethacrylate. Copolymers of these materials with one another or with ethylenically unsaturated monomers, and similar type polymers are also encompassed by the present invention. Typical fleece compositions include. for example. polyester fibers utilizing polypropylene or polyamidcs as the biniding fiber.  
  A good. uniform coaiescence and thus a fleece which possesses an extraordinary uniform strength is obtained by combining the two types of fibers to a bi-component fiber. Such a fleece can also be advantageously produced as a spun fleece from endless fibers. A fleece of this type exhibits an especially high flexural elasticity and a wrinkle-recovery angle of about l7()l 80C. Ex amples of bicomponent fibers include Nylon 66 and Nylon 6. Orlon 2l. 2] and 27 a polyester with a polyamide. and HS] and Nylon.  
  For the manufacture of such fleeces. it is suggested to employ an apparatus containing at least one sieve drum subjected to a suction draft. for heating the binding fibers to the melting temperature. Also, a perforated belt which is associated with the sieve drum is provided in the proximity ofthe outlet of the treatment chamber. said belt applying an initial pressure against the sieve drum and the fleece disposed thereon. It is also advantageous to draw in by suction fresh air for cooling the fleece. at least in a portion of this zone.  
  It is also possible. in the case of certain fleeces. to provide after the sieve drum at least one pair of cooled compression rolls. in place of such a perforated belt. A cooled pair ofcompression rolls can be advantageously employed when treating thin fleeces wherein the cooling is extensively effected by contact with the compression rolls. In the case of thick fleeces, an apparatus with the above-described perforated belt is more desirable.  
 BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only and thus are not limitative of the present invention and wherein FIG. 1 shows a longitudinal section through the apparatus for carrying out the process of this invention;  
  FIG. 2 shows a cross-section through the apparatus of FIG. I along line AA of FIG. I.  
 BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings. the apparatus for effecting the process of the present invention comprises a heat-insulated housing 1, containing a sieve drum 2, sujbected to a suction draft. Above and beneath the sieve drum 2, heating elements 3 are provided for heating the circulated treatment medium. for example air and/or steam. At the front face thereof, the sieve drum is provided with a fan 4, which draws the treatment medium out of the sieve drum and blows medium back to the outer surface of said sieve drum, via additional heating elements 5. In the sieve drum 2, a cover plate 6 is arranged at that side of the sieve drum, which is free from the material being treated. The cover plate 6 prevents the treatment medium from entering the sieve drum 2 at this side. The fleece 7 to be strengthened is fed to the sieve drum 2 on a conveyor belt 8, in the apparatus shown in the drawing, and is suddenly heated. in a shock-like manner i.e.. the fleece is rapidly heated. to the treatment temperature. by drawing the treatment medium into the drum through the fleece disposed on the sieve drum. A perforated belt 9 is associated with a portion of the periphery of the sieve drum. said belt. which is under tension or pressure. functioning to compress the fleece. By utilizing this compressing step, a more satisfactory welding together of the binding fibers with the other fibers is accomplished. AT the same time, the fleece is prevented from lateral shrinking by means of the bilateral guidance provided by the drum and the perforated belt. This is particularly important when polypropylene is employed as the binding or shrinking fiber. In the prox mity of the outlet of the apparatus. fresh air is drawn into the treatment chamber through an opening 10. This fresh air cools the fleece between the perforated belt 9 and the sieve drum 2, and thus the fleece structure is solidified in the compressed state. In place of cooling by means of fresh air. it is also possible to effect the cooling by a pair of cooled compression rolls ll arranged at the outlet of the apparatus. However. this pair of compression rolls 11 can also be additionally provided. The fan drive 12 and the drum drive 13 are attached at the outside of the housing I.  
  The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention. and all such modifica tions as would be apparent to one skilled in the art are intended to be included.  
 What is claimed is:  
  l. A continuous process for producing a uniformly compacted stitched fleece, which comprises:  
 a. providing a stitched fleece consisting essentially of at least two types of fibers having defined melting points, at least one type ofsaid fibers having a melting point lower than the others and being employed as binding fibers;  
 b. heating the stitched fleece to soften said binding fibers in the fleece;  
 c, compressing the heated stitched fleece while said binding fibers are in said softened state; and  
 d. cooling the heated stitched fleece while said fleece is in the compressed state whereby the fleece is retained in said compressed state upon solidification of said binding fibers.  
  2. The process of claim I, wherein the stitched fleece is cooled during at least a portion of the compressing step.  
  3. The process of claim 1, wherein the stitched fleece is cooled subsequent to the compressing step.  
  4. The process of claim 2, wherein the stitched fleece is further cooled subsequent to the compressing step.  
  5. The process of claim I wherein the heating step (B) is conducted by utilizing a heating medium selected from the group consisting of air, steam and a steam-air mixture, said heating medium being drawn through the stitched fleece.  
  6. The process of claim 2, wherein the stitched fleece is cooled by drawing air therethrough.  
  7. The process of claim 1, wherein the binding fiber is present in an amount of at least about 10%.  
  8. The process of claim 1, wherein the binding fiber is present in an amount of about 10 t0 l5% by weight.  
  9. The process of claim 1, wherein the fleece comprises polyester fibers containing polypropylene as the binding fiber.  
  10. The process of claim 1, wherein the fleece comprises polyester fibers containing polyamides as the binding fiber.  
  11. The process of claim 1, wherein the fleece contains a bi-component fiber selected from the group consisting of Nylon 66 -Nylon 6. Orlon 2l-23-27 and a polyester-polyamide mixture.  
  12. The process of claim 1, wherein the stitched fleece is heated to a temperature near the melting temperature of the binding fibers to soften said binding fibers.  
  13. A continuous process for producing a uniformly compacted stitched fleece which comprises:  
 a. providing stitched fleece consisting essentially of at least two types of fibers having defined melting points, at least one type of said fibers having a melting point lower than the others and being employed as binding fibers;  
 b. heating the stitched fleece to soften the binding fibers by conveying said fleece on the surface of at least one sieve drum means subjected to a suction draft and by drawing a heated gaseous treatment medium through said fleece;  
 c. simultaneously compressing the fleece between at least a portion of the surface of the sieve drum means and a perforated belt operativcly associated with said sieve drum means; and  
 d. cooling the heated stitched fleece to solidify the binding fibers in said fleece while said fleece is still in the compressed state.  
  14. The process of claim 13, wherein said gaseous treatment medium is selected from the group consisting of air. steam and a steam-air mixture.  
  15. The process of claim 13, wherein the fleece is cooled by drawing air through said fleece while still disposed between the sieve drum means and the perforated belt 16. The process of claim 13, wherein the fleece is cooled after being removed from the sieve drum means by conveying the fleece through a pair of cooling rolls.  
  17. The process of claim l5, wherein the fleece is further cooled after being removed from the sieve drum means by conveying it through a pair of cooling rolls.  
  18. The process of claim 13, wherein the compressed stitched fleece exhibits a high flexural elasticity and a wrinkle-recovery angle of about ll80.