Method and apparatus for controlled-profile coating of containers

Abstract: Apparatus for the coating of glass containers (212) has a series of vertical slots (202) for applying coating chemicals to a hot glass jar with a minimal neck and shoulder area. An opposing horizontal slot (210) exhausts spent coating material and reactants in a laminar flow. A center section (230) provides a current of gas without chemicals parallel to the coating stream, and flowing with low velocity relative to the coating stream, but with high velocity relative to the extraneous turbulent and convection currents.

Description: This invention is in the field of methods and apparatus for the application of coatings to containers. In embodiments the present invention relates to methods and devices for the application of coatings of varying thicknesses to glass bottles, jars and the like, particularly where the distance between a closure region and a shoulder of the container is small. The utility of glass bottles and jars has been broadened by surface coating to decrease abrasion and breakage, as taught by Carl, et al., U.S. 3,323,889; Gatchet, et al., U.S. 3,516, 811; Scholes, et al., U.S. 3,819,404; Hofmann, et al., U.S. 4,431,692; Lindner, et al., U.S. 4,668,268, and others. Gatchet observed the utility of avoiding all coating on the closure region of the container, known in the art as the "finish" region of the container. In U.S. 4,431,692, Hofmann taught maintaining the finish out of contact with the treatment gas. Several of the prior workers in this field have recognized the existence of non-linear currents in the coating-precursor stream, including omnidirectional turbulent currents and upwardly-moving convection currents. It is known in the art of glass manufacture that uncoated glass is generally unsuitable for handling in high-speed operations because its brittleness renders the surface susceptible to potentially catastrophic damage. Specifically, bottles and other glass containers made in large numbers are susceptible to breakage in the course of being transferred through various manufacturing steps, or during a subsequent filling operation. In order to minimize the problems thus encountered, a number of treatments have been applied to the containers as they are manufactured. Such treatments include, e.g., spraying with lubricant such as a wax or fatty acid, and applying reactive coatings by chemical-vapor-deposition (CVD) or spray pyrolysis methods. Treatment by CVD typically can involve propelling a vapor of metal-containing species onto the hot glass-container surface to produce a thin layer of metal oxide, typically stannic or titanic oxide. This metal-oxide layer anchors the waxy lubricant which is added after annealing. Without the metal-oxide layer, such waxy lubricants do not adhere well to glass under the conditions encountered in a wet filling line. Our U.S. 4,668,268, (equivalent to EP-A-0 187 515) teaches the application of a metal-containing compound, generally an organotin material, to the surface of a glass container immediately after that container has acquired sufficient mechanical integrity to maintain its shape on a material-handling line. The disclosure describes a coating hood for applying a uniform protective coating to a glass container as the container a transported by material-handling means, generally a conveyor belt, after its formation from molten glass. The described coating hood comprises a pair of side walls with a coating jet in at least one of the walls, and an exhaust system to remove the process stream from the coating zone. In the field relating to the coating of containers generally and glass bottles specifically, one problem which is repeatedly encountered is that of applying adequate material to the body of the container while keeping the area near the open end of the container untreated. The open end has a structure to accommodate a closure such as a cap with screw threads or a gasketed lid for a friction or vacuum seal. This portion of the container is referred to in the art as the "finish" of the bottle or jar. It is desirable to maintain the finish portion of the container relatively free of coating material for reasons of both chemical and physical importance. Where an improperly oxidized tin compound is deposited on the screw threads of, for instance, a jar for holding baby food, the chemical, electrochemical or mechanical interaction between the metal cap and the coating may be sufficient to discolor the glass or corrode the metal. Another disadvantage of coating on the finish is the possible effect on the frictional interaction between the glass and the cap or other closure; low friction can permit leakage, while too high a frictional value can impede both placement and removal of the closure. In either case, the utility of the treated container is adversely affected. In the art of coating glass containers, the film deposited onto the glass surface is measured in arbitrary coating thickness units (CTU), the unit thickness being about 2.5 Angstroms (Å); tin-oxide coatings of from about 30 to 40 CTU's, or about 75 to 100 Å, may be required for the body of the container, while acceptable coating on the finish may be one-half or even one-tenth of this amount, depending upon the ware and its intended use. While manufacturers of baby food state a preference for finish coating of less than half the shoulder coating, proximity of finish to shoulder has heretofore made the desired separation difficult or impossible to achieve under the teachings of the prior art. The improvement in the art which US-A-4 668 268 provided in partial response to the problem of differential wall and finish thickness was accomplished by directing a stream of air, in which no coating material was entrained, onto the finish in order to displace and dilute coating material which would otherwise coat the finish region almost as much as the shoulder or the body of the container. By selection of the geometry of the coating hood as a function of the containers to be coated, it was possible to effect acceptable coating thickness on the sidewalls, concomitant with protection of the finish for the large volume of glass containers having necks of appreciable length. However, the utility of the apparatus of US-A-4 668 268 is only marginal for applications such as food and cosmetic bottles and jars having very short or non-extent necks. The latter group comprises, e.g., jam, jelly and cold-cream jars, and containers for baby foods, peanut butter, thixotropic salad dressings, and the like. While the most effective prior art directs the vapor-laden air stream horizontally at the label panel of the ware, and a stream of vapor-free air at the finish region, some of the coating stream has been found inevitably to be displaced toward the finish by conditions within the coating hood. Displacement can originate, e.g. in the shearing interaction between adjacent coating streams traversing the hood in opposite directions; in the turbulence caused by the ware as it crosses the coating streams; in the strong convection currents caused by hot ware moving through a coating stream that is typically hundreds of degrees cooler than the ware; and in the induced draft caused by the finish-protection stream. This invention provides apparatus for applying a coating to glass containers, e.g. baby food jars and other substantially short-necked ware, comprising a tunnel having a roof and sides, a conveyor whereby the glass containers are conveyed through the tunnel along a conveyor path, and at least first and second coating stages along the conveyor path to blow respective first and second coating gas streams, across the conveyor path in opposite directions; (a) the first coating stage having (i) a first coating stream input opening in a first side of the tunnel opposite a first coating stream exhaust opening in the second side of the tunnel; (ii) means for blowing the first coating gas stream onto the conveyor path through the first coating stream input opening and exhausting it through the first coating stream exhaust opening; (iii) a first non-coating stream input opening above the first coating stream input opening, and (iv) means for blowing a first non-coating gas stream through the first non-coating stream input opening, above the first coating gas stream, to inhibit coating of a finish region of the glass containers, (b) the second coating stage having (i) a second coating stream input opening in the second side of the tunnel opposite a second coating stream exhaust opening in the first side of the tunnel; (ii) means for blowing the second coating gas stream onto the conveyor path through the second coating stream input opening and exhausting it through the second coating stream exhaust opening; (iii) a second non-coating stream input opening above the second coating stream input opening, and (iv) means for blowing a second non-coating gas stream through the second non-coating stream input opening, above the second coating gas stream, to inhibit coating of a finish region of the glass containers, characterised in that the paths of the first and second coating gas streams are longitudinally spaced from one another along the conveyor path, and the blowing means are adapted to blow the non-coating gas streams across the conveyor path at substantially the same velocity as the respective coating gas streams. Preferred features and specific embodiments are now described with reference to the drawings, in which: Figure 1 is an elevation of apparatus of the prior art. Figure 2 is partially cut-away perspective view of part of an apparatus embodying the invention; Figure 3 is an elevation of a portion of the device; Figure 4 shows a perspective view of a recirculation loop; Figure 5 is a perspective view of the center portion of a second embodiment of apparatus; and Figure 6 illustrates the second embodiment, in a view corresponding to Fig. 3. This invention embraces provision of apparatus for the coating of glass containers having a minimal neck region, the apparatus comprising a coating hood with a high-pressure portion and a juxtaposed low-pressure portion, with a center section for the introduction of air which is free of coating precursor, and traveling in essentially the same direction as the coating stream. The apparatus includes means for process-stream transfer and coating-precursor makeup. The invention further includes the article made by the apparatus, and coating methods using same. A preferred embodiment of the present apparatus enables the application of glass-treating material to a glass container having a minimal separation between the body of the container and the top portion, the apparatus comprising coating-supply means and exhaust or recirculation means, the coating-supply means having a plurality of coating-precursor slots on one side of the apparatus and a cooperating low-pressure area on the opposite side, the apparatus having a process-stream-directing means juxtaposed above the container and intermediate the two sides of the apparatus. As more fully described above, the coating-process stream maintains a substantially horizontal direction until it passes the ware. Means are provided for transfer of the process stream from the low-pressure to the high-pressure side of the device, and for makeup as necessary of the coating-precursor material. In one aspect the apparatus differs from the prior art, described above, in having at least one coating-precursor supply section in cooperation with at least one opposing exhaust section, and stream-deflection means consisting of a center section providing a stream of vapor-free air moving above and in the same direction as the coating stream. Turning now to the drawings, Figure 1 is a sectional elevation of the apparatus disclosed by Lindner et al., in U.S. 4,668,268. Briefly described, the Lindner et al. patent shows apparatus for the coating of a container, generally of glass, whereby a process stream 11 under pressure from blower 12 impinges upon bottle 13. Deflection stream 14 , flowing substantially in the same direction as stream 11 , is intended to keep stream 11 from depositing an undesirably thick coating of material on the finish 15 of bottle 13 . Recirculation blower 16 maintains a low pressure within plenum 17 to cause process stream 11 to move onto and around bottle 13 , thereby causing the coating precursor to react with the hot surface of the glass substrate. Other portions of the apparatus not germane to this invention are not further described here. As usually preferred, it is substantially isolated from ambient atmosphere. In the operation of the process of Lindner et al., in coating hood 10 , process stream 11 is generally a mixture of glass-coating precursors such as, e.g., an organotin compound In air or a titanium compound. Such compounds, also useful with apparatus of the present invention, include those which are capable of reaction with air or other process stream oxidizing moiety to form a metal oxide, and comprise, e.g., organotin compounds generally, monobutyltin trichloride, tin tetrachloride, titanium tetrachloride and tetraisopropyl titanate. Upon impinging on bottle 13, the organotin is converted to tin oxide as a coating on the glass surface. Volatile products and unreacted chemicals are recirculated by the action of blower 16 . While the process stream 11 has a tendency toward turbulence on encountering bottle 13 , deflection stream 14 maintains a zone which is essentially, but not perfectly, free of the coating precursor carried In stream 11 . As a result, coatings secured by the Lindner et al. apparatus provide a gradient of coating with a thickness of the order of 100 Å on the body of the container to about 10 Å in the finish region. However, in field application, it has not been possible to steepen the gradient, nor to apply the process to the apparatus in a consistently successful fashion to containers with necks shorter than about 25 millimeters (mm). Figure 2 depicts an embodiment of this invention, the apparatus being shown partially in phantom. Coating hood 200 differs from the prior art by minimizing the shearing interaction of adjacent coating and finish-protection streams. This improvement decreases the movement of coating precursor into the finish region by induced drafts and turbulent currents. In the apparatus depicted, vertical slots 202 in wall 204 provide a substantially laminar process-stream flow 206 across tunnel 216 . Wall 204 holds horizontal slot 210 , justaposed opposite vertical slot s 202 . A second, similar set of process stream input slots 202 and out-take slot 210 is provided on the opposite side of the conveyor, but with the out-take upstream of the input so as to complement the set-up shown in Fig. 2. This gives two longitudinally-spaced process paths, reducing shearing turbulence therebetween while achieving good coverage. In the operation of the apparatus, process stream 206 impinges upon container 212 carried on conveyor 214 through tunnel 216 in the direction indicated as C in the drawing; container 212 with body portion 220 and finish region 222 may be at a temperature of about 250 to 315 degrees Centigrade, but in any event at a surface temperature sufficient to cause the reaction at that surface of the coating precursor in the process stream with ambient air in order to provide the desired coating, generally an oxide of tin or titanium. With the exception of the unavoidable deflection of the process stream by the containers 212 moving through the apparatus, the present apparatus maintains a smooth, laminar, flow of the process stream 206 over the surface of container 212 , avoiding the turbulence encountered in the prior art. The process stream is removed through slots 210 and recirculated, as shown in Figures 2, 3 and 4. Although the minimization of turbulent flow of the process stream 206 is an improvement in coating of containers over the prior art, the further use of center section 230 provides even better control over the process stream in the finish region 222 of container 212 . Channel or duct portion 232 is adjusted to permit close clearance of container 212 , and the size of the channel is chosen to provide clearance between channel 232 and finish region 222 of container 212 with a tolerance of from about 2 to about 5 mm (these values are merely exemplary). Referring to Figure 3, a fluid 236 not containing coating precursor is urged through slot 239 in a manner such that the direction and velocity of flow does not create turbulence, nor substantially interact, with process stream 206 . After traversing the finish region 222 of container 212 , fluid 236 leaves the treatment region through exhaust channel 234 while the effluent of process stream 206 is drawn off through slots 210 . The fluid stream 236 is introduced at approximately the same velocity as the process stream 206, in order to achieve the reduced turbulence. A further feature, as seen in Fig. 3, is for the input opening 239 of flow 236, to open directly adjacent the projection across the tunnel of process stream input opening 202. Upon traversing the full width of tunnel 216 , process-stream flow 206 may be at least partially exhausted or gently deflected downward and drawn into low-pressure slot 210 ; see further the discussion hereinbelow with reference to Figure 6. By the design set forth herein, there is minimal interaction between process stream 206 and fluid 236 until they are no longer in proximity to the finish region 222 of bottle or jar 212 which so is substantially uncoated by the action of the precursor materials carried in process stream 206 . Thus, the action of the fluid 236 , generally air, is to preclude reaction on finish region 222 of coating-precursor chemicals carried In process stream 206 . By this cooperation of the fluid flow from openings 234 and the flow of process stream 206 from vertical slots 202 into horizontal slots 210 , precise coating of container 212 is achieved, depositing sufficient coating on body 220 while minimizing the thickness of coating on finish region 222 . Figure 3 shows a greater detail of center section 230 disposed in tunnel 216 . Impelled by pressure from blower or other source 302 , non-coating fluid stream 236 flows from openings 239 and is directed by the conformation of curvilinear portion 234 as shown by arrows 308 . The conformation of the curvilinear portion 234 of channel 232 is preferably complementary with the finish region of the container. After non-coating stream 236 has passed across finish region 222 of container 212 , it is given a stint vertical component by the conformation 234 of center section 230 ; the major portion of stream 236 is then removed through air exhaust 238 which directly opposes input opening 239. Figure 4 shows wall 204 of the apparatus in greater detail. Recirculation loop 250 comprises a conduit 252 drawing process-stream materials and spent reactants through duct 254 and in turn recycling them by means of duct 256 back through slots 202 . Blower or other fluid-motive device 258 serves as the means to move the process and reactant stream; conduit arm 260 provides a make-up port for the introduction of reactants or stream adjustment as may be required to meet process conditions such as line speed, temperature fluctuation, coating-thickness specifications and the like. As discussed in relation to Figure 2, vertical slots 202 provide a laminar flow of the process stream; the height 402 of slots 202 is conveniently, although not necessarily, chosen to be identical with the height of the body of the container 212 shown in Figure 2, and less than the height of the finish region of that container. In this fashion, process stream 206 impinges on the body 220 , but not on the finish region 222 , of container 212 . The function of horizontal slots 210 is to remove the spent process stream and reaction by-products without inducing turbulence. It has been surprisingly discovered that by controlling the rate of flow of process stream 206 , turbulence is avoided, and the removal of by-products and unreacted material through slots 210 helps to maintain a laminar aspect of that flow; concurrently, by applying a parallel control flow of stream 236 through openings 239 of center section 230 , any tendency of the process stream 206 to flow onto or around finish region 212 is minimized almost to the point of exclusion. Figures 5 and 6 illustrate the function and construction of another embodiment of this invention In Figure 5, center section 530 is shown in perspective. Finish-protection stream 236 exits through slot 239 , traverses surface 502 , and follows conformation 534 , the effect of which is to provide a downward vector to maintain finish 222 of container 212 essentially free of coating. From a review of this disclosure, those skilled in the art will recognize that the lower portion of finish-protection stream 236 will become enriched with coating-precursor stream 206 by diffusion, convection, and impingement of coating-precursor stream 206 upon container 212. Figure 6 shows center section 530 in coating hood 200. As noted hereinabove with reference to center section 230 of Figure 3, center section 530 of this embodiment is disposed in tunnel 216 . Impelled by pressure from blower or other source 302, non-coating fluid stream 236 flows from openings 239 and is directed by the conformation of curvilinear portion 534 as shown by arrows 608 . The conformation of the portion 534 of channel 632 is preferably complementary with the finish region of the container. After non-coating stream 239 has passed across finish region 222 of container 212 , it is given a vertical component by the conformation of the curvilinear portion 534 of center section 530. The mixed coating-precursor and finish-protection streams 640 are then recirculated for further application to more containers 212 after the manner noted above in connection with Figure 2. Surprisingly to highly skilled professionals who have long sought the sharp coating separation between shoulder and finish only rarely and fleetingly obtainable with appratus of the prior art, the ordinary worker can now, with apparatus embodying this invention, accurately set the balance of exhausted and recirculated process streams by comparing coating thickness on the shoulder with that on the finish, and then adjusting the apparatus controls to maximize that ratio. In contrast to the apparatus of the prior art, the present apparatus may maintain the desired ratio almost indefinitely.

Claims: Apparatus for applying a coating to glass containers, comprising a tunnel (216) having a roof (230) and sides (204), a conveyor (214) whereby the glass containers (212) are conveyed through the tunnel along a conveyor path, and at least first and second coating stages along the conveyor path to blow respective first and second coating gas streams (206), across the conveyor path in opposite directions; (a) the first coating stage having (i) a first coating stream input opening (202) in a first side of the tunnel opposite a first coating stream exhaust opening (210) in the second side of the tunnel; (ii) means (252,256,258) for blowing the first coating gas stream (206) onto the conveyor path through the first coating stream input opening (202) and exhausting it through the first coating stream exhaust opening (210); (iii) a first non-coating stream input opening (239) above the first coating stream input opening (202), and (iv) means (302) for blowing a first non-coating gas stream (236) through the first non-coating stream input opening (239), above the first coating gas stream (206), to inhibit coating of a finish region (222) of the glass containers, (b) the second coating stage having (i) a second coating stream input opening (202) in the second side of the tunnel opposite a second coating stream exhaust opening (210) in the first side of the tunnel; (ii) means (252,256,258) for blowing the second coating gas stream onto the conveyor path through the second coating stream input opening (202) and exhausting it through the second coating stream exhaust opening (210); (iii) a second non-coating stream input opening (239) above the second coating stream input opening (202), and (iv) means (302) for blowing a second non-coating gas stream (236) through the second non-coating stream input opening (239), above the second coating gas stream (206), to inhibit coating of a finish region (222) of the glass containers, characterised in that the paths of the first and second coating gas streams (206) are longitudinally spaced from one another along the conveyor path, and the blowing means (258,302) are adapted to blow the non-coating gas streams (236) across the conveyor path at substantially the same velocity as the respective coating gas streams. Apparatus according to claim 1 in which the paths of the first and second non-coating gas streams (236) are adjacent. Apparatus according to claim 1 or claim 2 in which each coating stream input opening (202) has a series of upright slots, to induce laminar flow of the coating gas streams (206). Apparatus according to any one of the preceding claims in which the coating stream exhaust openings (210) are horizontal slots. Apparatus according to any one of the preceding claims in which the non-coating gas stream (236) is exhausted, together with the respective coating gas stream (206), through the respective coating stream exhaust opening (210). Apparatus according to claim 5 in which the tunnel roof has a downwardly-curving portion (534) opposite the non-coating stream input opening (239), to guide the non-coating gas stream 236) down to the coating stream exhaust opening (210) after crossing the conveyor path. Apparatus according to any one of the preceding claims in which the roof of the tunnel has a horizontal flat centre portion (232,502) extending across the conveyor path from immediately above the non-coating stream input opening (239). Apparatus according to any one of the preceding claims, comprising a recirculation duct (250) for recirculating gas from a said coating stream exhaust opening (210) to a said coating stream input opening (202). Apparatus according to claim 8, in which the recirculation duct has a makeup port (260) for replenishing the recirculating gas with a substance for forming the coating. Apparatus according to claim 8 or claim 9 in which gas is recirculated from the first coating stream exhaust opening (210) to the second coating stream input opening (202), and vice versa . Apparatus according to any one of claims 8 to 10 in which the means for blowing the coating gas stream (206) comprises a blower (258) acting on the flow in the recirculation duct (250). A method of applying a coating to glass containers, comprising moving the containers (212) along a conveyor path in a tunnel (216) and at a first coating stage, blowing a first stream (206) of coating gas across the conveyor path from a first coating stream input opening (202) in a first side of the tunnel to contact the glass containers (212), and exhausting the first coating gas stream (206) through a first coating stream exhaust opening (210) in the second side of the tunnel, opposite the input opening; while blowing a first non-coating gas stream (236) through a first non-coating stream input opening (239), across the conveyor path above the first coating gas stream (206) to inhibit coating of a finish region (222) of the glass containers, and at a second coating stage, blowing a second stream (206) of coating gas across the conveyor path in a direction opposite to that of the first coating gas stream, from a second coating stream input opening (202) in the second side of the tunnel to contact the glass containers (212), and exhausting the second coating gas stream through a second coating stream exhaust opening (210) in the first side of the tunnel, while blowing a second non-coating gas stream (236) through a second non-coating stream input opening (239), above the second coating gas stream (206) to inhibit coating of the finish region (222) of the glass containers, characterised by providing longitudinal spacing between the first and second coating gas streams (206) along the conveyor path, to avoid shearing interaction between them, and blowing each non-coating gas stream (236) across the conveyor path at substantially the same velocity as the respective coating gas stream (206). A method according to claim 12 in which each non-coating gas stream (236) is exhausted from the tunnel through the respective coating stream exhaust opening (210). A method according to claim 12 or claim 13 in which the paths of the first and second non-coating gas streams (236) are adjacent. A method according to any one of claims 12 to 14 in which the coating gas contains an organotin compound to coat the glass containers. A method according to claim 15 in which the organotin compound is monobutyltin trichloride. A method according to any one of claims 12 to 16 in which the roof (230,530) of the tunnel is immediately above the non-coating gas streams, and is shaped to conform to the finish regions of the glass containers.

Inventors: BARKALOW RAYMOND WILLIAM, GUTHRIE ROGER THACKSTON, BARKALOW, RAYMOND WILLIAM, GUTHRIE, ROGER THACKSTON
Applicants: ATOCHEM NORTH AMERICA, ATOCHEM NORTH AMERICA, INC. ELF ATOCHEM NORTH AMERICA, INC.
Application year: 1990
Main classification: C03C17
IPC codes: C03C17, C23C16, B65D23