Method and apparatus for making cross-laminated non-woven fabrics

Abstract: In a method and apparatus for making a cross-laminated non-woven fabric composed of warp and weft webs (1, 2), the warp and weft webs (1, 2) are firmly gripped at least at their opposite selvages by and between the outer peripheral surface of a hot cylinder (3) and a pair of endless belts (8) as they are bonded together and heat-set on the hot cylinder (3). With this arrangement, the warp and weft webs (1, 2) are prevented from shrinking widthwise during heat-set on the hot cylinder (3).

Description: The present invention relates generally to the manufacture of cross-laminated non-woven fabrics, and more particularly to a method and apparatus for heat setting a cross-laminated non-woven fabric composed of warp and weft webs as they are bonded on and around a hot cylinder. Throughout the specification and claims, the term "warp web" is used to refer to a web formed of fibers arranged to extend substantially in the lengthwise direction of the web and hence having a larger strength in the lengthwise direction than in the transverse direction thereof, the term "weft web" is used to refer to a web formed of fibers arranged to extend substantially in the transverse direction of the web and hence having a larger strength in the transverse direction than in the lengthwise direction, and the term "cross-laminated non-woven fabric" is used to refer to a non-woven fabric composed of the warp and weft webs laminated together, with the fibers in the warp web extending crosswise the fibers in the weft web. Cross-laminated non-woven fabrics, cross-laminated films or the like cross-laminated sheet materials have recently been developed and placed on the market. In the manufacture of such cross-laminated sheet materials, warp and weft webs are bonded together into layers. In this instance, it is necessary to heat-set the warp and weft webs as they are bonded together. To meet this requirement, a hot cylinder is utilized in general. The hot cylinder has the advantage of its small installation space and high heat efficiency. The hot cylinder has a drawback however that the warp and weft webs while being heat-set on the hot cylinder are caused to shrink widthwise. This widthwise shrinkage lowers the productivity of the cross-laminated sheet material and also adversely affects the strength, Young's modulus and other physical properties of the cross-laminated sheet material. The foregoing widthwise shrinkage of the webs while being heat-set can be prevented by using a conventional tentering process in which the webs are held firmly at the opposite sides or selvages by pins or clips. The tentering process, however, requires an expensive apparatus which is large in size and hence occupies a large space for installation thereof. Another problem is that a hot air heating system employed in the tenter frame is low in thermal efficiency. Furthermore, the tentering process is totally unsatisfactory when used in the manufacture of a cross-laminated sheet material in which bonding of warp and weft webs is a major requirement. US 4,609,423 discloses the use of an endless belt to urge a laminated non-woven fabric into contact with a heating cylinder, wherein the web of non-woven material passes between an endless band and a roller, and is retained in such a manner as to control stretching or shrinkage of the material. The web is described as comprising two layers of non-woven fabrics of different fibres. French Patent 1,505,969 shows a method of making a non-woven criss-crossed fabric of a net structure from two groups of strands. In this known method, a first group of adhesive warp strands is laminated with a second group of criss-cross strands free of adhesive treatment with the latter strands gripped at their opposite selvages between an endless belt and a hot rotating cylinder. The criss-cross strands are thus prevented from widthwise shrinkage. Both these prior techniques require apparatus more cost intensive and complex than that of the present invention, and do not achieve the desired result. With the foregoing difficulties in view, the present invention seeks to provide a method of making a cross-laminated sheet material composed of warp and weft webs bonded together into layers and heat set on a hot cylinder without causing widthwise shrinkage which would otherwise lower the productivity and physical properties of the cross-laminated sheet material. The present invention further seeks to provide an apparatus for reducing the foregoing method into practice, which apparatus is simple in construction and can be manufactured less costly, and is small in size and occupies only a small space for installation thereof. According to a first aspect of the present invention, there is provided a method of making a cross-laminated non-woven fabric of the type having a warp web and a weft web bonded together, said warp web being stronger in the longitudinal direction than in the transverse direction, said weft web being stronger in the transverse direction than in the longitudinal direction and being shrinkable widthwise upon exposure to heat, said method comprising continuously feeding said warp and weft webs in cross-laminated relation to each other and onto a hot rotating cylinder via a pair of parallel spaced endless belts, characterised in that said weft web is a transversely stretched web of transversely parallel-laid weft fibres having selvage portions along its opposite marginal edges and gripping said warp web at its opposite side edges and said weft web at the selvage portions by and between an outer peripheral surface of said hot cylinder and said pair of endless belts, said endless belts being normally tensioned against the outer peripheral surface of said hot cylinder, whereby said warp and weft webs held in laminated relation are bonded together into a non-woven fabric structure free from widthwise shrinkage as they are passed around said hot cylinder. According to a second aspect of the present invention, there is provided an apparatus for making a cross-laminated non-woven fabric of the type having a rotating hot cylinder for bonding and heat-setting a warp web having a larger strength in the lengthwise direction than in the transverse direction and a weft web having a larger strength in the transverse direction than in the lengthwise direction as they are continuously fed around the rotating hot cylinder in a superposed relating to one another, characterised in that said apparatus comprises a pair of endless belts held under tension against an outer peripheral surface of the rotating hot cylinder for gripping at least opposite selvages of the warp and weft webs therebetween as the warp and weft are fed around the hot cylinder, thereby preventing the warp and weft webs from shrinking widthwise as they are heat-set on the hot cylinder. Many other advantages and features of the present invention will become manifest to those versed in the art upon making reference to the detailed description and the accompanying sheets of drawings in which preferred structural embodiments incorporating the principles of the present invention are shown by way of example. Figure 1 is a diagrammatical view showing the general construction of an apparatus according to the present invention; Figure 2 is a schematic plan view of a rotating hot cylinder and associated endless belts of the apparatus shown in Figure 1; Figure 3 is an enlarged side view of a portion of the endless belt which is indicated by a circle A in Figure 1; Figure 4 is a view similar to Figure 2, but showing another embodiment of the present invention. Figure 1 diagrammatically shows the general construction of an apparatus for making a cross-laminated non-woven fabric or the like sheet material by bonding and heat-setting a warp web 1 and a weft web 2 as they are continuously fed on and along an outer peripheral surface of a hot cylinder 3 rotatably driven by a motor (not shown). At least one of the warp and weft webs 1, 2 has a certain degree adhesiveness or is treated with an adhesive. The apparatus further includes first and second pinch or nip rolls 4, 5 held in contact with the hot cylinder 3 and having their central axes spaced from one another at an angle of about 60 degrees relative to the central axis of the hot cylinder 3 so as to guide the warp and weft webs 1, 2 along about five-sixths of the full circumference of the hot cylinder 3. Disposed downstream of the second nip roll 5 is a cooling cylinder 6 for cooling a cross-laminated sheet material composed of the warp and weft webs 1, 2 which have been bonded together and heat-set on the hot cylinder 3. The cooling cylinder 6 is provided with a third pinch or nip roll 7 for holding the cross-laminated sheet material in intimate contact with the cooling cylinder 6 as the cross-laminated sheet material is withdrawn from the cooling cylinder 6. According to an important feature of the present invention, the warp and weft webs 1, 2 are gripped at least at opposite sides or selvages while they are fed around the hot cylinder 3 in superposed relation, so that the warp and weft webs 1, 2 are prevented from shrinking widthwise. To this end, the apparatus includes a pair of parallel spaced endless belts 8, 8 guided around the first nip roll 4 and first, second and third guide rolls 9a, 9b, 9c so as to be held under tension against the outer peripheral surface of the hot cylinder 3. In the illustrated embodiment, the third guide roll 9c is disposed upstream of the second nip roll 5 and circumferentially spaced at an angle of about 60 degrees from the second nip roll 5 so that the endless belts 8 travel about four-fifths of a longitudinal portion of the superposed warp and weft webs 1, 2 which is retained on the hot cylinder 3. The endless belts 8 may be arranged to further extend around the second nip roll 5 in which instance the endless belts 8 coextend with the respective selvages of the warp and weft webs 1, 2 retained on the hot cylinder 3. The endless belts 8 are made of a heat-resistant material so as to withstand a temperature of the hot cylinder 3. As shown in Figure 3, each of the endless belts 8 has a release coating layer 8a on one surface thereof which is engageable with the outermost web 1. The release coating layer 8a preferably comprises a fluorine plastic film or a silicone plastic film. Materials eligible for the warp web 1 includes a web of stretched or oriented tapes arranged in parallel juxtaposition in the lengthwise direction of the web, a reticular split fiber web spread widthwise 1.1 - 5.0 times its original width, and a non-woven fabric formed of fibers arranged to extend in the lengthwise directions. The weft web includes a laminated web which is composed of a continuous warp web of parallel-laid non-woven fabric, and a succession of discrete weft webs of parallel laid non woven fabric arrange lengthwise of and bonded with the continuous warp web, with their adjacent edges slightly overlapping one another. The laminated web may be made by a cross-laminating machine such as disclosed in U. S. Patent No. 4,052,243 proposed by the present inventors. In making the laminated web, a weft web is conveyed laterally over the warp web in the machine direction and overlaid onto the warp web in the manner of side by side arrangement without leaving any gaps between each other, after being cut by the length corresponding to the width of the warp web. Stated otherwise, one of two identical continuous warp webs of parallel laid non-woven fabric is fed transversely over the other warp web in timed relation to the movement of the other warp web. The one warp web is severed successively into individual lengths which are substantially equal to the width of the other warp webs. The thus severed individual lengths of warp web are united by bonding to the other warp web with their adjacent edges slightly overlapping one another, as stated above. The weft web may be a continuous transversely stretched web such as disclosed in U. S. Patnt No. 4,349,500, or a non-woven fabric formed of fibers arranged to extend in the widthwise or transverse directions. In operation, the warp and weft webs 1, 2 are longitudinally fed successively around the first nip roll 4, the hot cylinder 3 and the second nip roll 5. During that time, the warp and weft webs 1, 2 are firmly gripped at their opposite selvages by and between the outer peripheral surface of the hot cylinder 3 and the respective endless belts 8, 8 with the result the warp and weft webs 1, 2 are heat-bonded together into a cross-laminated sheet material and heat-set on the hot cylinder 3 without causing heat-shrinkage in the widthwise direction. The cross-laminated sheet material is withdrawn from the hot cylinder 3 and then fed around the cooling cylinder 6 during which time the cross-laminated sheet material is cooled to set. The thus cooled cross-laminated sheet material is finally withdrown from the apparatus through the third nip roll 7. A modified apparatus shown in Figure 4 is substantially identical to the apparatus shown in Figures 1 and 2 with the exception that the superposed warp and weft webs 1, 2 are gripped substantially throughout the width thereof by and between the outer peripheral surface of the hot cylinder 3 and a single endless belt 10. The endless belt 10 has substantially the same width as the webs 1, 2 and includes a multiplicity of small pores or perforations 11 uniformly distributed over the entire surface thereof. The perforated endless belt 10 is permeable to vapor and hence allows smooth vaporization of the moisture content from the webs 1, 2 as the webs 1, 2 are heat-set on the hot cylinder 3. As described above, at least the selvages of warp and weft webs are gripped by and between the outer peripheral surface of a hot cylinder and two endless belts, so that the warp and weft webs are bonded together into a cross-laminated sheet material and heat-set without causing widthwise heat-shrinkage. The thus produced cross-laminated sheet material is sightly in appearance, is uniform in structure and posesses improved physical properties such as tensile strength and Young's modulus. The apparatus of the present invention which is composed of a hot cylinder and endless belts is simple in construction and hence can be manufactured easily at a low cost. Furthermore, the apparatus is small in size and hence occupies only a small space for installation thereof.

Claims: A method of making a cross-laminated non-woven fabric of the type having a warp web (1) and a weft web (2) bonded together, said warp web (1) being stronger in the longitudinal direction than in the transverse direction, said weft web (2) being stronger in the transverse direction than in the longitudinal direction and being shrinkable widthwise upon exposure to heat, said method comprising continuously feeding said warp and weft webs (1, 2) in cross-laminated relation to each other and onto a hot rotating cylinder (3) via a pair of parallel spaced endless belts (8), characterised in that said weft web (2) is a transversely stretched web of transversely parallel-laid weft fibres having selvage portions along its opposite marginal edges and gripping said warp web (1) at its opposite side edges and said weft web (2) at the selvage portions by and between an outer peripheral surface of said hot cylinder (3) and said pair of endless belts (8), said endless belts (8) being normally tensioned against the outer peripheral surface of said hot cylinder (3), whereby said warp and weft webs (1, 2) held in laminated relation are bonded together into a non-woven fabric structure free from widthwise shrinkage as they are passed around said hot cylinder (3). A method of Claim 1, wherein said warp web (1) is a split web stretched widthwise by 1.1 to 5.0 times its original width. A method of Claim 1, wherein said warp web (1) is a stretch type, a reticulate web formed of trunk and branch filaments, a slit reticulate web formed of trunk and branch filaments, a slit reticulate web formed of wide stretched film or a longitudinally stretched non-woven fabric, either alone or in combination. A method of Claim 1, wherein said warp web (1) or said weft web (2) or both comprise an upper layer, a lower layer and a core interposed therebetween, said core having a higher melting or softening point than said upper and lower layers. An apparatus for making a cross-laminated non-woven fabric of the type having a rotating hot cylinder (3) for bonding and heat-setting a warp web (1) having a larger strength in the lengthwise direction than in the transverse direction and a weft web (2) having a larger strength in the transverse direction than in the lengthwise direction as they are continuously fed around the rotating hot cylinder (3) in a superposed relating to one another, characterised in that said apparatus comprises a pair of endless belts (8) held under tension against an outer peripheral surface of the rotating hot cylinder (3) for gripping at least opposite selvages of the warp and weft webs (1, 2) therebetween as the warp and weft (1, 2) are fed around the hot cylinder (3), thereby preventing the warp and weft webs (1, 2) from shrinking widthwise as they are heat-set on the hot cylinder (3). An apparatus according to Claim 5, wherein said endless belts (8) have a multiplicity of perforations uniformly distributed over the entire surface thereof. An apparatus according to Claim 5, wherein said endless belts have a release coating layer (8a) on one surface thereof engageable with an outermost one of the webs (1, 2). An apparatus according to Claim 7, wherein said release coating layer (8a) comprises a fluorine plastic layer. An apparatus according to Claim 7, wherein said release coating layer (8a) comprises a silicone plastic film.

Inventors: KURIHARA KAZUHIKO, OHISHI TOSHIKAZU, TANI HARUHISA, YAZAWA HIROSHI, KURIHARA, KAZUHIKO, OHISHI, TOSHIKAZU, TANI, HARUHISA, YAZAWA, HIROSHI
Applicants: NIPPON PETROCHEMICALS CO LTD, POLYMER PROCESSING RES INST, NIPPON PETROCHEMICALS CO., LTD., POLYMER PROCESSING RESEARCH INSTITUTE LIMITED
Application year: 1989
Main classification: D04H3
IPC codes: D04H3