SPIN COATING APPARATUS

Abstract: Continuous filament glass fiber bundles are coated with a molten thermoplastic polymer, without the addition of a size to the glass, by passing the filaments through an unpressurized pool of the polymer contained in a passage. The forces between the filaments and the unpressurized polymer interact to center the filaments in the passage as they pass through.

Description: This invention relates to an apparatus for coating bundles of freshly spun continuous filament glass fibers. Traditionally, water or water-based sizings are sprayed or coated onto glass fibers as they are formed to lubricate and protect the filaments during subsequent processing steps. These steps may include initial wind-up, chopping, drying, re-winding, packaging, shipping, and finally unwinding into an end use. Since glass fibers are inherently flaw sensitive, any "uncoupled" composite process (where the formed glass must be handled before introducing the matrix resin) will require the use of such sizings and finishes on the glass roving. In addition to added water and chemicals, moisture and other contaminants from the surrounding atmosphere will also degrade the quality of glass fibers by rapidly adsorbing onto the high energy pristine glass surface. Since all of these added surface species (whether applied intentionally or adsorbed from the atmosphere) tend to mask the glass surface, it is very difficult to wet and adhere matrix resins onto glass fibers in composite applications. This wetting and adhesion problem is especially important for viscous thermoplastic resins and systems without intensive mixing. Organometallic materials (e.g. silanes, titanates and chromates) are commonly added to the sizing formulation to overcome these problems. Although these three component systems (glass + sizing + resin) have been under development and optimization, evidence in the literature suggests that superior wetting and adhesion could be realized if all additives and contamination were kept away from the glass surface before the matrix resin is applied, U.S.-A 2,919,970 discloses an apparatus for coating bundles of freshly spun continuous filament glass fibers. The glass fiber bundle is drawn through a passage which comprises successive conical and straight lengths. Molten polymer is applied to the glass fibers at the exit end or at some location along the conical or straight length. At the beginning of the coating process, the glass fibers have to be introduced into the coating apparatus from the top through the passage. A similar apparatus is known from EP-A-21677 wherein the passage has only a conical length extending from the top to the bottom of the apparatus. The invention solves the problem of how to design an apparatus for coating bundles of continuous filament glass fibers such that the stringup procedure is simplified. That problem is solved by an apparatus with the features set forth in claim 1. Preferred embodiments of the invention are the subject matter of the subclaims. By removing the detachable cover from the body member of the apparatus, the glass fiber bundle can be inserted sidewise. The misalignment of the passage from the longitudinal axis prevents filaments which are drawn through the passage from catching or being snagged in the mating line. The apparatus of the invention is especially useful as a coating shoe for coating bundles of bare continuous filament glass fibers with one of several molten thermoplastic polymers (e.g. polyethylene terephthalate) without the need to apply lubricants to protect the bare filaments from abrasion and damage. Streams of glass are drawn into a bundle of continuous filaments, then the filament bundle is passed through a molten unpressurized pool of thermoplastic polymer maintained at a controlled level in the coating passage of a coating shoe. The filaments are centered in the passage by means of forces produced by interaction between the polymer and the filaments flowing through the passage. Upon entering the coating shoe, the filament bundle has a surface coating of polymer. The bundle is then heated and the polymer is worked into the bundle to coat each individual filament. The glass filaments are drawn in an inert atmosphere prior to coating. The product formed, a fiber reinforced thermoplastic material, is essentially a two component material, i.e. an array of continuous glass filaments coated with thermoplastic resin that has retained the same proportion of the as-spun glass filament properties as those using three components of glass, water-based sizing and resin. Brief Description of the Drawings Fig. 1 is a schematic diagram illustrating the spin coating method. Fig. 2 is an isometric view of the coating shoe. Fig. 3 is a partial front elevation view of Fig. 2 with the detachable cover removed. Fig. 4 is a partial side elevation view of Fig. 2 with the detachable cover in place. Fig. 5 is a schematic cross-sectional view greatly enlarged of the coated filament bundle following the working step subsequent to coating. D etailed Description of the Preferred Embodiment The method chosen for purposes of illustration in Fig. 1 includes a bundle 10 of continuous filament glass fibers 12 being drawn from a bushing 14. The bundle 10 is forwarded through an inert nitrogen atmosphere supplied through nozzles 11 and 13 directed at bushing 14 and chamber 15 to a coating shoe 16 where in passing through a passage in the shoe the bundle is coated with molten polyethylene terephthalate polymer supplied to the shoe from a source indicated by flow arrow 18. The coating operation in the shoe is unpressurized, thus eliminating the need for a guide-seal at the entry to a pressurized polymer chamber. The interaction between the filaments and the polymer as they move through the passage centers the filaments in the passage so they do not abrade by rubbing on a surface of the passage. Upon exiting the coating shoe, the polymer coated filament bundle 10′ is passed over heated rework shoes 20 and 22 and wound into a package 26. A water spray device 28, is used to spray water on the filament bundle 10′ to cool it prior to winding into package 26. Referring now to Figs. 2-4, the coating shoe 16 is seen to include a body member 30 into which is machined an upper surface portion 32 and a lower surface portion 34 connected by a passage 36. The passage 36 has successive conical and straight lengths 36 a , 36 b , respectively, and each length of the passage has a cross-sectional area greater than the cross-sectional area of the fiber bundle 10 during its passage through the passage. The coating shoe includes a detachable cover 31 held against a mating surface of the body 30 by means of arm 33 attached to the body member 30 and screw 35 threaded through arm 33 to contact detachable cover 31. As best seen in Fig. 4, the surface of detachable cover 31 which mates with body member 30 at mating line 37 has a portion of the passage lengths 36 a , 36 b machined therein to match up with similar portions in the body member for the passage 36. The mating line 37 is angularly displaced from the longitudinal axis 39 of the passage by an angle A to minimize the possibility of filaments being snagged as they pass through the conical length 36 a of the passage and are consolidated into polymer coated bundle 10′ in passage length 36 b . Molten polymer is introduced into passage length 36 a at directly opposed locations at the mating line 37 via passage ways 40, 42 supplied with molten polymer 18 through passageways 40 a , 42 a , respectively. Another passage 44 through body members 30 is used to supply nitrogen in the proximity of the upper surface 32. Fig. 5 shows the resultant filament bundle 10″ after passing over rework shoes 20, 22 wherein the molten polymer has penetrated the bundle and coated each filament. In operation, the interaction of the unpressurized molten polymer in passage 36 and the filament bundle 10 moving through the passage gathers the filaments together and aligns them to center them with respect to passage length 36 b without the need for centering guides resulting in a coated bundle as shown in Figs. 5 and 6 wherein the glass filaments have not been abraded by the guides. Further, the polymer streams from passageways 40, 42 are directed laterally against the filament bundle from each side of the cover mating line 37 as it passes through passage 36 to keep filaments away from the mating line to minimize the risk of their being snagged at the mating line. The slight angular displacement of the mating line 37 from the longitudinal axis of the passage 36 also assists in preventing snagging of the filaments in the mating line.

Claims: Apparatus for coating a bundle of continuous filament glass fiber (12) being drawn in a path from a source (14) with a molten thermoplastic polymer (18), said apparatus comprising a body member (30) having an upper (32) and lower (34) surface connected by a passage (36), said passage encompassing sail path and having a cross-sectional area along its entire length greater than the cross-sectional area of the bundle of filaments and having successive conical (36a) and straight (36b) lengths; and a means for introducing said molten polymer (18) into said passage at an intermediate location in said conical length (36a) characterized by a detachable cover (31) secured to said body member (30), one surface of said cover (31) mating along a longitudinal mating line (37) with a surface of said body member (30) said surface having a portion of passage lengths (36a, 36b) machined therein to match up with similar portions in the body member (30) to form said passage (36) and the longitudinal mating line (37) of said body member (30) and said cover (31) being angularly displaced from the longitudinal axis of said passage (36) and said means for introducing molten polymer (18) into said passage (36) including a pair of passage ways (40, 42) connected to a source of polymer and being at directly opposed intermediate locations in said conical length (36a) of said passage (36). The apparatus according to claim 1 wherein said opposed locations are at the longitudinal mating line (37) whereby polymer is directed away from that mating line (37). The apparatus according to claim 1 or 2 including means (44) located in said body member (30) for introducing an inert gas in the proximity of said upper surface (32) to blanket said passage (36) at said upper surface (32) with said gas.

Inventors: HECKROTTE, ROBERT SHERWOOD
Applicants: E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1989
Main classification: C03C25
IPC codes: B05C3, C03C25, B29B15