PROCESS OF MANUFACTURE OF A SINGLE LAYER THICK DRY FELT THROUGH A WET PROCESS AND SINGLE LAYER THICK DRY FELT OBTAINED THEREBY

Abstract: A process of manufacture of a single layer thick dry felt through a wet process is disclosed, comprising using at least a part of a thermoplastic resin under powder form having a large mean grain size, preferably of at least 200 micrometres and most preferably ranging between 300 micrometres and 1,000 micrometres. The preferred thermoplastic resin is polypropylene.

Description: Process of manufacture of a single Layer thick dry felt through a wet process and single layer thick dry felt obtained thereby. The present invention essentially relates to a process of manufacture of a single layer thick dry felt through a wet process like that industrially need according to the paper technology and a single layer thick dry felt obtained thereby. In the prior art, attempts have been made to manufacture thick felts but resulted in poor fiberglass dispersion and inefficient drying of the wet felt. To obtain good fiberglass dispersion for single thick felts, a large amount of very diluted suspension needs to deposit quickly on a wire screen. These conditions demand the physical state of the suspension to be amenable to the very fast drainage of the aqueous medium. If drainage is not fast enough, formation of the wet felt will not be possible and moreover when marginably acceptable wet fet is formed and passes through the drying oven, the felt would contain too much moisture to be dried efficiently. So, the only possible way to produce a thick felt is by using several layers laid one above the other, which are very sensitive to delamination. Examples of this prior art is GD patent DD-89,464. Therefore, the main purpose of the present invention is to solve the technical problem of manufacture of thick felts in a single step through a wet process, i.e. of single layer thick felts. Another main purpose of the present invention is to solve the technical problem of manufacture of single layer thick felts from any thermoplastic material, while accepting a significant amount of reinforcing fibers such as inorganic or organic reinforcing fibers. Another main purpose of the present invention is to solve the technical problem of manufacture of single layer thick felts containing a significant amount of reinforcing fibers well dispersed in the thermoplastic material. Another main purpose of the present invention is to solve the technical problem of manufacture of single layer thick felts at a high rate through a wet process according to the traditional paper technology, while using mild processing conditions, and notably low air depression. All these technical problems are solved simultaneously for the first time with the present invention according to a simple, reliable and low costly solution, which is therefore usable at industrial level. Thus, in a first aspect, the present invention provides a process of manufacture of a single layer thick dry felts through a wet process from a slurry containing in suspension a thermoplastic resin under powder form and a reinforcing material under fiber form, characterized in that at least a part of the thermoplastic resin under powder form is of a large mean grain size, preferably of at least 200 micrometres mean grain size. According to another specific process embodiment, the deposition of the thick felt is performed on an inclined wire, at the bottom part thereof, from bottom to top while draining water under moderate vacuum. In the description and the claims, moderate vacuum means a vacuum ranging between 500 and 650 mm Hg pressure. When pressure drops down below the 500 mm Hg level, the conditions will become industrially impractical to operate and the composite materials therefrom will not have good fiber dispersion. According to a particular embodiment, the mean grain size of the thermoplastic resin under powder form is ranging between 300 micrometres and 1,000 micrometres, more preferably 500 micrometres and 1,000 micrometres and most preferably between 600 micrometres and 1,000 micrometres. According to another specific embodiment, the thermoplastic resin is a polyolefine, in particular polyethylene, polypropylene and copolymers thereof, vinylpolychloride, polystyrene and copolymers, polyamide, saturated polyester, polyethylene ether, a polycarbonate and any plastic alloy. A most preferred thermoplastic resin is polypropylene. According to another specific embodiment, the reinforcing material under fiber form is selected from glass fibers, carbon fibers, ceramic fibers, boron fibers, glass wool, rock wool, metallic fibers, hot melt organic synthetic fibers, notably aromatic polyamides, polyesters and others. The length of the reinforcing fibers preferably ranges between 5 mm and 25 mm, and the diameter between 5 and 20 micrometres. According to another specific invention embodiment, the said slurry is a dilute slurry preferably having from 0.1 to 5 % by weight dry content. According to a preferred embodiment, the slurry composition, on a weight dry content basis, comprises : thermoplastic resin under powder form of large grain size as above defined 40 - 78% (preferably 45 - 78*, most preferably 50 - 75%) - reinforcing fibers 20 - 50% - dispersant 0.65 - 10% with respect to reinforcing fiber - optionally polyolefine pulp ... 0 - 10% (preferably 2 to 10%) - optionally flocculent 0.25 - 1%. A further preferred embodiment comprises use of a thermoplastic resin under powder form having a mean grain size of about 700 micrometres, reinforcing fibers having a length from 6 to 25 mm and a diameter ranging between 10 to 17 micrometers. Most preferred reinforcing fibers are glass fibers, which can be additionally sized to have good dispersion in aqueous medium. In the present description and the claims, the term "thick felt" means a single layer felt having a minimum felt thickness of at least 4 kg per m 2 . According to a second embodiment, the invention also provides a single layer thick dry felt comprising a thermoplastic resin under powder form and a reinforcing material under fiber form, characterized in that at least a part of the thermoplastic resin under powder form is of a large grain size, as above defined. Other specific embodiments of the single layer thick felt clearly appear from the above description with regard to the process of manufacture thereof. Other purposes and technical advantages of the invention will appear from the following illustrative examples, which are not limiting the scope of the invention. In the examples, all parts are given by weight unless otherwise specified. INVENTION EXAMPLE 1 In 7 liters of water containing 3.2 g of a cationic dispersant based on fatty acid (Cartaspers DS1 of Sandoz), 32 g of glass fibers which are sized to have good dispersion in aqueous medium (reference M189 supplied by Manville of U.S.A.) having an average length of 13 mm and 16 microns diameter was added with strong stirring. 10 g of synthetic pulp was then introduced with moderate stirring. After suitable dispersion, 58 g of polypropylene powder, of mean particle size of 700 microns was added. After dilution until the suspension contains about 5 g of solids per liter, the mixture was then admitted on a wire screen, dewatered then dried according to the conventional paper making technique. A 595 mm Hg pressure at the dewatering section was required to produce a sheet of 4000 g/m 2 . The sheet thus obtained comprised sufficient cohesion to be handled, stored, transported and in which the various components of the formulation were perfectly retained. To make a final industrial product from this sheet, only one of such sheet needs to be preheated up to a temperature of the order of 180 β C to 210 C C and then moulded under pressures of 40 to 100 kg/cm 2 for a cycle less than 30 seconds. INVENTION EXAMPLE 2 This example differs from Example 1 in that 43.5 g of polypropylene powder of mean particle size of 700 microns and 14.5 g of polypropylene powder of mean particle size of 150 microns was used. The resulting vacuum pressure at the dewatering section was 565 mm Hg for producing a sheet of 4000 g/m 2 . INVENTION EXAMPLE 3 This example differs from Example 2 in that 29 g of polypropylene powder of mean particle size of 700 microns and 29 g of polypropylene powder of mean particle size of 150 microns was used. The resulting vacuum pressure at the dewatering section was 520 mm Hg for producing a sheet of 4000 g/m 2 . COMPARATIVE EXAMPLE 4 This example differs from Example 3 in that 14.5 g of polypropylene powder of mean particle size of 700 microns and 43.5 g of polypropylene powder of mean particle size of 150 microns was used. The resulting vacuum pressure at the dewatering section was 490 mm Hg for producing a sheet of 4000 g/m 2 . COMPARATIVE EXAMPLE 5 This example differs from Example 4 in that 58 g of polypropylene powder of mean particle size of 150 microns was used. The resulting vacuum pressure at the dewatering section was 450 mm Hg for producing a sheet of 4000 g/m 2 . The results from the above examples show that if the mean distribution size of the thermoplastic resin under powder form is decreased to a value lower than 200 micrometres, it is needed a deep vacuum pressure lower than 500 mm Hg to reach thick felts, which is extremely difficult to be obtained at the industrial level, and which is very costly. With the present invention, it has been discovered that by using significant amounts of a thermoplastic resin under powder form of mean particle size above 200 micrometres, it is possible to manufacture a single layer thick felt under mild processing conditions, and notably moderate vacuum pressure, not lower than 500 mm Hg pressure, which vacuum pressure is easily obtainable at industrial level. Further, with such large particle size of the thermoplastic resin, the single layer thick felts enable to prepare a final industrial product having excellent mechanical properties. In the description and claims, the terms "significant amount" of the thermoplastic resin under powder form of large size mean that at least 50 '/. of the thermoplast c resin is of a grain size larger than 200 micrometres.

Claims: AMENDED CLAIMS [received by the International Bureau on 21 February 1992 (21.02.92); original claims 1 and 2 amended; other claims unchanged (1 page)] 1. A process of manufacture of a single layer thick dry felt having a thickness of at least - kg per τn 2 through a wet process from a slurry containing in suspension a thermoplastic resin under powder form and a reinforcing material under fiber form, wherein at least a part of the thermoplastic resin under powder form is of a large mean grain size, preferably of at least 5QQ micrometres. 2. The process of claim 1, wherein the mean grain size of the thermoplastic resin under powder form ranges from 500 micrometres to 1000 micrometres, most preferably from 600 micrometres to 1000 micrometres . 3. The process of claim 1 or 2, wherein the thermoplastic resin is a polyolefine, such as polyethylene, polypropylene and copolymers; a polyvynylchloride; a polystyrene and copolymers; polyamide, a saturated polyester; a polyphenylene ether; a polycarbonate or a plastic alloy. 4. The process of claim 3, wherein the thermoplastic resin is polypropylene. 5. The process of any one of claims 1 to , wherein the thick felt is obtained from a dilute slurry preferably having from 0.01 to 5 % dry content. 6. The process of any one of claims 1 to 5, wherein the deposition is performed on an inclined wire at the bottom part thereof. 7. The process of any one of claims 1 to 6 , wherein the slurry- composition, on a weight dry content basis, comprises : - thermoplastic resin under powder form 45 - 78 * /. (preferably 50 - 75 '/.) - reinforcing fibers 20 - 50 % - dispersant 0.5 - 10 7. (with regard to the reinforcing fibers) - optionally flocculent 0.25 - 1 f. - optionally polyolefine pulp 0 - 10 V. (preferably 2 - 10 • /.) STATEMENT UNDER ARTICLE 19 The submitted amendments to claims 1 and 2 focus this application on preferred embodiments for achieving invention objectives of acceptable industrial methods of preparing thick felt intermediate products suitable for preparing reinforced thermoplastic sheet having high thermoplastic weight. The new lower limitation of 500 micron for thermoplastic powder size is derived from claim 2 as originally filed. EP-A-0281 475 does not address the objective of forming a thick felt under standard processing conditions and accordingly does not address particle size in the now claimed range. In column 3, lines 37-39, particle size is suggested to be greater than or equal to 100 micrometer, while the example of the invention teach particles with a diameter largely between 250 and 500 microns, column 4, lines 3635. No advantage or preference is described for particle size selection. EP-A-0039 292 similarly does not address forming a thick felt and accordingly teaches powder grains having dimensions smaller than 500 micron, page 3 lines, 6-9. WO-A-9 003 262 does not address a thick felt and is restricted to preparation of elastomeric sheet from elastomeric powder of granulometry less than 500 um, preferably between 40 and 300 um, see page 6, lines 30-33. EP-A-0329 200 is addressed to a foamed web that has decreased density by virtue of inclusion of dispersed air bubbles, no teaching as to particle size is apparent. The only relevant phrase may be the requirement for "particulate thermoplastics material" of claim 1, see page 9, line 26.

Inventors: MAILLE GERARD EMILE AMEDE, THIBAUDEAU JEAN PIERRE, MAILLE, GERARD, EMILE, AMEDE, THIBAUDEAU, JEAN, PIERRE
Applicants: EXXON CHEMICAL LTD, EXXON CHEMICAL PATENTS INC, EXXON CHEMICAL LIMITED, EXXON CHEMICAL PATENTS INC.
Application year: 1991
Main classification: D21H17
IPC codes: D21H13, D21H17, D21H21