Coating of extruded profiles and apparatus therefor

Abstract: A coating apparatus and process for coating selected surface areas of an extruded substrate with decorative or functional coatings, passing the extruded substrates (52) emerging from the extrusion die (12) past a coating block (10). The coating block (10) contains a coating cavity die conforming to the selected surfaces to be coated, and liquid coating material is supplied to the coating cavity die in a manner to selectively coat the selected surfaces on the extruded substrate.

Description: This invention relates to the coating of extruded surfaces, and in particular aspects to processes and apparatus for selectively coating one or more surfaces of extrudate emerging from am extruder die by providing coating means for solution coating at the extruder die. Various types of extruded articles require surface coatings be applied to a plurality of selected surfaces without coating the entire surface of the extruded article. For instance, extruded elastomeric articles such as automotive window and door seals, fluid hoses, weather stripping and the like are extruded in specific cross-sectional designs which often require selective surface coating of separated surfaces. For example, automotive window seals require special slip- and abrasion-resistant surface coatings adjacent the window for engaging the glass so it can be raised or lowered easily without sticking to the window seal engaging surface. The remaining surfaces are generally maintained free of such coatings. In the prior art, US-A-4883690 describes a method for applying paint coatings to extruded substrates. The substrate is first extruded and then directed into a housing which guides it through a coating collar, where selected surfaces of the substrate are coated with paint. The aim herein is to provide new apparatus and methods for coating extruded substrates with liquid polymer solution coatings. In one aspect, we provide apparatus for applying a liquid polymer solution coating to an extruded substrate, comprising a coating block having a coating die cavity opening positioned to conform to an adjacent selected surface of a polymeric substrate emerging in use from an extrusion die; at least one liquid polymer solution supply source; a supply opening to receive liquid polymer solution from the source; and a channel communicating between the coating die cavity opening and the supply opening to supply the liquid polymer solution to the coating die cavity opening to coat the selected surface, characterised in that the coating block is abuttingly secured to the extrusion die, the channel being located at the back of the coating block adjacent the extrusion die whereby the surface of the extrusion die forms a wall of the channel, the coating block cooperating with and being adapted to receive extruded substrate from the extrusion die. Preferably the coating block has plural coating die cavity openings with respective supply channels. One or more liquid solution polymer coatings can be applied. In another aspect the invention provides a process for forming an extrudate with a liquid polymer solution coated selectively on a selected surface thereof, comprising the steps of: forming a polymeric extrudate, providing a coating block abuttingly secured to the extrusion die, the coating block having a coating die cavity opening which conforms to the selected surface of the polymeric extrudate emerging from the extrusion die, a supply opening to receive liquid polymer solution, and a channel communicating between the coating die cavity opening and the supply opening, the channel being located on the back of the coating block adjacent the extrusion die whereby the surface of the extrusion die forms a wall of the channel, and supplying liquid polymer solution to the supply opening to be communicated to the coating die cavity opening and thereby selectively coating the selected surface of the extrudate. It may be noted that FR-A-2572678 and FR-A-2200109 both describe the use of a second die block fixed onto the front of a first die block, so as to immediately coat extrudate emerging from the first die block. However these are co-extrusion processes, the second die being fed with plastisided polymer material from a screw extruder. Such processes and apparatus may be used to apply protective or functional solution coatings to multiple surfaces which may be laterally or vertically displaced from one another, depending on the cross-sectional configuration of the extruded substrate. In embodiments, we have been able to achieve essentially 100% transfer efficiency of solvent-based coating within the coating block to the selected extrudate surfaces without undesirable solvent emissions. Moreover, general surface areas of the extrudate substrate can be coated without masking. Post-extrusion coating steps displaced from the extruder such as brushing or spraying may thus be eliminated. Various protective or functional coatings which may be applied in accordance with the present invention include solution polymer cosmetic or decorative coatings, abrasion resistance or low friction slip coatings, weather-resistant coatings, freeze-resistant coatings and the like. Preferred technical features and advantages will become more apparent by referring to the drawings and detailed description of embodiments. FIG. 1 is a perspective view of apparatus embodying this invention, showing a coating block in conjunction with an extrusion die plate; FIG. 2 shows a front view of the extrusion die plate shown in FIG. 1; FIG. 3 is an enlarged front elevation view of the coating block shown in FIGS. 1 and 2, and also shows the coated extrudate; FIG. 4 is an enlarged cross-sectional view taken along lines 4-4 in FIG. 1. According to the present embodiment a coating block 10 is aligned and secured to an extrusion die plate 12 disposed on the front end of an extruder 14. The invention further contemplates the use of one or more coating supply sources which, desirably through individual pumps for each, are connected to specific supply lines. For example, as seen in FIG. 1, a coating block 10 is attached to the extruder die plate 12 and further interconnected to three coating supply pipes 16, 17, 18, and respective pumps 20, 21, 22, and coating supply sources 24, 25, and 26. As seen in FIGS. 2 and 3, the supply pipes 16, 17, 18 are attached to the front surface of the coating block 10 by individual quick-disconnect couplings 28, 29, 30, respectively, to enable simple interconnection with the coating supply sources. The use of three separate supply lines 16, 17, 18 permits use of three different coatings, if desired, and also provides individual control of each coating line where applied pump pressure to each line may be varied if desired to provide varied flow rates and/or applied pressure to form variable applied coating thicknesses to three separate extrudate surfaces. A single coating supply line containing a solution polymer can be used to supply the coating block with its total solution coating supply although separate coating supply lines 16, 17, 18 are preferred. As seen in FIG. 3, the coating block 10 is secured to the extrusion die plate 12 e.g. by plural bolts 32. The coating block 10 contains a multi-surface coating cavity 35 having the same general cross-sectional configuration as the extrusion die 12. The coating die cavity 35 has separate, independent coating surfaces 38, 40, 42 best viewed in cross-sectional FIG. 4 which particularly shows the coating means for supplying coating to the respective coating surfaces 38, 40, 42. The coating means comprises cylindrical chambers 16a, 17a, 18a disposed in the solid coating block 10 and communicating with coating feed lines 16, 17, 18 respectively. The solution coating such as a polymer coating material is supplied under moderate positive pressure actuated by the individual pumps 20, 21, 22, which can be independently adjusted to supply the coating under pressure to the internal cylindrical chambers 16a, 17a, 18a, as desired. As shown in FIG. 4, each individual chamber 16a, 17a, 18a communicates with generally downwardly depending narrow channels 46, 48, 50, respectively, which are generally located in the back of the coating block adjacent the extrusion die 12 and can communicate therewith, terminating in narrow slit applicator openings 60,61,62. The slit applicator openings 60,61,62 are narrow in depth (i.e., axial height of the coating block), but particularly broad in breadth to accommodate the coating profile breadth desired to be applied to the selected surfaces of the extruded substrate 52. In this regard, internal chamber 18a communicates with a wide profile channel 50 and a wide applicator slit 62 adapted to apply measured amounts of liquid coating to die cavity surface 42 within the coating block 10. Similarly, internal chamber 17a communicates with a narrow applicator slit 61 to supply measured amounts of coating to die cavity surface 40 while internal chamber 16a communicates with an intermediate channel 46 and an intermediate applicator slit 60 to supply measured amounts of liquid coating to die cavity surface 38. The downwardly depending channels 46,48,50 are all generally relatively narrow in thickness (depth), but vary in breadth to provide the breadth of coating profile desired. The double lines at 60,61,62 illustrate the "slit" layer thickness, determining coating thickness. These coating application surfaces may be recessed relative to the extrudate surface along their entire extent from the face of die 12, or may be stepped at some location downstream of the die surface, generally at or near where the channels 46,48,50 communicate into them. Each internal chamber 16a,17a,18a, in conjunction with the respective coating application channels 46,48,50, individually functions as flow coating means under minor positive pressure to provide separate linear coatings to separate surface areas. The desired linear coating surfaces can be laterally displaced, or vertically displaced, or both laterally and vertically displaced, as shown in Fig. 4. They furthermore can be of any desired configuration. The applied solution coatings can be continuous or intermittent, as desired, by operatively controlling pumps 20,21,22 or other coating supply control means. The coated extrudate is best seen in Fig. 3, showing linear coatings 55,56,57 applied to separate surfaces of the extrudate by liquid coating passing through channels 46,48,50, respectively, and through applicator openings 60,61,62 to apply coatings directly to the selected surfaces of the extruded substrate 52. The applied solution coatings can be dried or cured at ambient temperatures or heat-cured at elevated temperatures if desired. Preferred coatings are solvent-based polymers whereby preferably heat is not required to fuse coatings to extrudate surfaces. Using the means described, one or more solvent solution coatings can be transported and applied to one or more separate selected surfaces on an extruded substrate. Each coating for each respective selected surface is supplied through a pumping and feed line system to the coating block 10 which, by coating means, applies a coating to a preselected surface of the extrudate in specific metered amounts. Quick-disconnect couplings 28, 29 30 are provided at the coating block as well as being provided at various points in the coating supply lines 16, 17, 18, such as at the pumps 20, 21, 22, or the coating supply sources 24, 25, 26, and permit and facilitate interchange of coating sources with intended coating surfaces, if desired. In order to prevent running on the substrate surface, the solution coating viscosity should be from about 100 to about 500 centipoise, desirably from about 150 to about 500 centipoise, and preferably from about 200 to about 400 centipoise. The extrudate can be an elastomer, a thermoplastic elastomer, or a thermoset. Useful thermoplastics include polyvinyl chloride, acrylonitrile-butadiene-styrene, various polyolefins made from monomers having from 2 to about 7 carbon atoms with specific examples including polyethylene, polypropylene, etc., or other conventional polymers known to the art and to the literature. Useful thermosets include, for example, polyurethane and various types of rubber such as styrene-butadiene rubber, EPDM rubber (ethylene-propylenediene copolymer), natural rubber, butyl rubber, neoprene, blends of EPDM-SBR and EPDM-neoprene blends, as well as other rubbers known to the art and to the literature. Examples of suitable thermoplastic elastomers include blends of polypropylene and EPDM, e.g., Santoprene®, blends of PVC and EPDM, e.g., Sunprene®, as well as other compounds known to the art and to the literature. The extrudate, be it an elastomer, a thermoplastic elastomer, or a thermoset, can contain suitable reinforcing fibers such as glass, boron, graphite, polyester, nylon, and the like, as well as plastic, or metal reinforcement. The extruded substrate can also be aluminum. EPDM is a preferred substrate. The solution coatings which can be applied to the extrudate surfaces are generally unlimited so long as they can be dissolved by a suitable solvent known to the art and to the literature, usually organic, or water-based systems, i.e., where water is a solvent, or water-borne systems, i.e., where water is utilized with a co-solvent. An amount of solvent is generally utilized with the desired coating to conform to the above-noted viscosity range of from about 100 to about 500 centipoise. Organic solvents generally include hydrocarbon solvents such as aliphatic hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons, aliphatic substituted hydrocarbons, etc., as well as combinations thereof. The useful solution polymer coatings can be cosmetic or decorative coatings to achieve a desired aesthetic effect, or functional surface coatings to impart abrasion resistance, low friction, good weatherability, freeze resistance, and similar functional qualities to the surface coated. Exemplary cosmetic coatings can include polymers such as polyurethanes, polyesters, polyethers, fluorocarbons, silicones, acrylics, vinyls, and the like. Functional coatings include, for example, various polymers such as polyurethanes for high abrasion resistance, polyesters for weatherability, and silicones and Teflon® polymers for low friction resistance, and the like. Other coatings include flock adhesives, for example nylon or polyester fibers which are electrostatically applied while coating surfaces 55, 56, or 57 are still viscous. The type of extruder which can be utilized is not critical and can include a single screw, twin screw, a cross-head extruder, or one or more extruders but only one extrusion die. The extrudate substrate can include a wide variety of extruded articles such as automotive seals for windows or doors, fluid transport hoses, weather stripping, and similar extruded articles which require specifically selected surface coated areas. In accordance with the process of the present embodiment, liquid polymer solution coatings are supplied to a coating block containing a die cavity 35 having coating surfaces 38, 40, 42 conforming to the selected surfaces on the extruded substrate 52 to be coated. The extruded substrate emerges from the extrusion die plate 12 and enters the coating block 10 where the selected surface on the extruded substrate communicates with the conforming coating surfaces 38, 40, 42, whereupon liquid coating supplied to internal chambers 16a, 17a, 18a discharges through narrow channels 46, 48, 50, respectively. The liquid solution polymer coating passes through applicator openings 60, 61, 62 in the coating die cavity 35, and coating surfaces 38, 40, 42, to directly apply liquid coating as an applied film to the selected surfaces of the extruded substrate. While the above description relates to a preferred embodiment, it is apparent that the coating block can apply one or more solution coatings via one or more individual supply lines using one or more pumps through one or more coating block channels, each of which can communicate with one or more, but preferably only one, application openings to coat one or more surfaces. It should thus be obvious that the present invention includes a great number of permutations for applying a solution coating to a preselected surface of an extrudate. Another advantage which can be obtained is that inasmuch as the coating material is directly applied to a selected extrudate surface, there is no wasted solution coating.

Claims: Apparatus for applying a liquid polymer solution coating to an extruded substrate, comprising a coating block (10) having a coating die cavity opening (60,61,62) positioned to conform to an adjacent selected surface (55,56,57) of a polymeric substrate (52) emerging in use from an extrusion die (12); at least one liquid polymer solution supply source; a supply opening to receive liquid polymer solution from the source, and a channel (16a,17a,18a) communicating between the coating die cavity opening (60,61,62) and the supply opening to supply the liquid polymer solution to the coating die cavity opening (60,61,62) to coat the selected surface (55,56,57), characterised in that the coating block (10) is abuttingly secured to the extrusion die (12), the channel (16a,17a,18a) being located at the back of the coating block (10) adjacent the extrusion die (12) whereby the surface of the extrusion die (12) forms a wall of the channel (16a,17a,18a), the coating block (10) co-operating with and being adapted to receive extruded substrate (52) from the extrusion die (12). Apparatus according to claim 1 in which an internal chamber is defined in the coating block (10) at the supply opening and is adapted to be in fluid connection with a source of coating material. Apparatus of claim 2 wherein there are at least two supply openings and respective internal chambers. Apparatus of any one of the preceding claims wherein a coating die cavity (35) having the opening (60,61,62) essentially conforms to the upper surface profile of said extrudate (52). Apparatus of any one of claims 1 to 3 wherein the extrusion die (12) has an upper profile configuration and a coating die cavity (35) having the opening (60,61,62) conforms to said extrusion die upper profile configuration. Apparatus of any one of the preceding claims wherein the channel (16a,17a,18a) terminates in a narrow slit opening (60,61,62) and wherein the narrow dimension of the slit is adapted to determine the thickness of the liquid coating applied to said extruded substrate surface (55,56,57). Apparatus according to claim 6, wherein there are plural channels and respective slit openings, and each said slit opening (60,61,62) has a different breadth and is adapted to deposit a surface coating on said extruded substrate (52). Apparatus according to claim 6, wherein there are plural channels and respective slit openings, and said slit openings (60,61,62) are different to enable each opening to apply a different thickness of applied coating to said extruded substrate (52). Apparatus of any one of the preceding claims wherein the supply opening to receive liquid polymer solution and the channel (16a,17a,18a) communicating between the coating die cavity opening (60,61,62) and the supply opening to supply liquid polymer solution to the coating die cavity (35) to coat the selected surface (55,56,57) on the extruded substrate is adapted to apply a continuous surface coating on said extrudate substrate (52). Apparatus of any one of claims 1 to 9 wherein the supply of liquid polymer solution is intermittently interrupted to apply a non-continuous linear surface coating on said extruded substrate. A process for forming an extrudate with a liquid polymer solution coated selectively on a selected surface (55,56,57) thereof, comprising the steps of: forming a polymeric extrudate, providing a coating block (10) abuttingly secured to the extrusion die (12), the coating block having a coating die cavity opening (60,61,62) which conforms to the selected surface (55,56,57) of the polymeric extrudate (52) emerging from the extrusion die (12), a supply opening to receive liquid polymer solution, and a channel (16a,17a,18a) communicating between the coating die cavity opening (60,61,62) and the supply opening, the channel (16a,17a,18a) being located on the back of the coating block (10) adjacent the extrusion die (12) whereby the surface of the extrusion die (12) forms a wall of the channel (16a,17a,18a), and supplying liquid polymer solution to the supply opening to be communicated to the coating die cavity opening (60,61,62) and thereby selectively coating the selected surface of the extrudate (55,56,57). The process of claim 11 wherein said coating solution is applied continuously on selected surfaces of said extrudate. The process of claim 11 wherein the supply opening to receive liquid polymer solution and the channel communicating between the coating die cavity opening and the supply opening to supply the liquid polymer solution to the coating die cavity to coat the selected surface on the extruded substrate are operative to coat, in conjunction with said coating die cavity opening, a selected surface of the extruded substrate by applying a thin curtain of liquid coating to said extruded substrate. The process of claim 11 wherein said coating solution is applied intermittently on selected surfaces of said extrudate. The process of claim 11 wherein one of plural said channels applies a continuous coating to selected surfaces of the extruded substrate and the other said channel applies a coating intermittently on other selected surfaces of said extruded substrate. The process of claim 11 comprising applying different thickness coatings to different selected surfaces of said extrudate by having narrower or larger openings provided in plural said channels.

Inventors: GOEWEY JAMES R, WILSON KEITH E, GOEWEY, JAMES R., WILSON, KEITH E.
Applicants: GENCORP INC, GENCORP INC.
Application year: 1992
Main classification: B05C3
IPC codes: B29C47, B60J10, B05C3, B29L9