Glass-coating apparatus and methods

Abstract: Improved apparatus for coating containers having a minimal separation between the body and the finish region comprises a coating hood and means for supplying coating materials to the coating. The improvement consists of a controlled non-turbulent air supply (18) directed downward across the coating-material stream (12). A blower (19) provides process air to a plenum (22), and an angled attenuator plate with a plurality of small holes distributes the process air evenly, to avoid standing waves and regions of high or low air velocity. Several attenuator plates can be juxtaposed to permit removal of particulates by movement of the plates relative to each other.

Description: This invention is in the field of methods and apparatus for the application of coatings to glass containers. In some embodiments, the invention is in the field of methods and devices for the application of coatings of varying thicknesses to bottles, jars and the like, particularly where the distance between a closure region and a shoulder of the container is minimal. PRIOR ART 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. 4,389,234 and 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", by maintaining the finish region 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, its brittleness rendering 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, which can anchor a waxy lubricant added after annealing. Without the metal-oxide layer, such waxy lubricants do not adhere well to glass under the conditions encountered in a filling line. In our U.S. 4,668,268 and EP-A- 187 515 Lindner et al. teach 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 US 4,668,268 disclosure describes a coating hood for applying a uniform protective coating to a glass container as the container is 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 notably of glass bottles, one problem which is repeatedly encountered is that of applying adequate material to the body of the container while keeping the finish region of the container untreated. It is desirable to maintain the finish portion relatively free of coating material for both chemical and physical reasons. Where a 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 to 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 0.25 nm ; metal-oxide coatings of from about 30 to 40 CTU, or about 6 to 10 nm, 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 a finish-coating thickness of less than half that of the shoulder coating, proximity of finish to shoulder has heretofore made the desired separation difficult or impossible to achieve. The improvement in the art which US-A-4668268 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, this technique was able 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, such containers comprising beer, wine and soft-drink bottles and the like. However, while the utility of the apparatus of US-A-4668268 is excellent for beer, wine and other bottles with relatively long necks, it is only marginal for applications such as food and cosmetic bottles and jars having very short or non-existent necks, i.e., where the finish region is juxtaposed adjacent the body. 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. For the purposes of this specification, the terms "bottle" and "jar" may be used with substantial interchangeability, although generally, a jar has a relatively small separation of body and finish, while a bottle has a substantially larger separation. Our EP-A-425 307 proposed a more sophisticated way of blowing a non-coating flow horizontally across the container necks, preserving a laminar gas flow by matching the flow velocities. 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 in, e.g., 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. Further, even the best of the prior art devices tend to require careful attention in order to maintain adjustment of the parameters required for an acceptable differential between the body or shoulder and the finish region. In one general aspect, the invention provides apparatus for the chemical coating of glass containers, comprising a conveyor path along which the articles are conveyed for treatment, means for directing a coating flow containing coating precursor compound against the articles from one or both sides of the conveyor path, means for exhausting and optionally recirculating spent coating supply from the conveyor path, and means for inhibiting coating of an upper portion of the articles, characterised in that the means for inhibiting such coating comprise a blower for blowing a non-coating flow down onto the articles from above the conveyor path, by way of an accumulating plenum and a foraminous diffuses plate for distributing the non-coating flow. The non-coating flow is desirably vertically, or substantially vertically, downward. The non-coating flow desirably enters the conveyor path area through a downwardly-facing ceiling thereof. The non-coating downward flow is desirably applied all along a treatment zone of the conveyor path at which the coating supply is being applied. A preferred form of diffuses is a flat plate. The distribution of holes therein should be regular, and preferably symmetrical with respect to the articles on the conveyor path. To achieve a uniform downward flow, it is particularly preferred that the non-coating blower blows the non-coating supply into the plenum in a direction which is not the downward direction. Most preferably, it is blown in in a generally horizontal direction and then redirected within or by the plenum. For this purpose, an attenuator layer may be positioned within the plenum at an angle between horizontal and vertical, preferably an acute angle to the horizontal. The angle attenuator is desirably symmetrical to the conveyor path axis, i.e. angled up along rather than across that axis. Means may be provided for mechanically agitating the attenuator, to inhibit the accumulation of deposits thereon. In another aspect, the invention provides methods of coating treatment of glass articles, particularly glass containers, in which the articles are moved along a conveyor path, a coating supply containing a coating precursor compound is blown on the articles from at least one side, and a finish-coating inhibition flow is blown down on them from above by way of an accumulating plenum and a foraminous diffuses plate. In the method, features of the plenum and attenuator may be as specified above. In the drawings; Figure 1 is an elevation of apparatus of the prior art. Figure 2 is an elevation showing an initial concept of the invention. Figure 3 is a section taken along lines 3-3 of Figure 2. Figure 4 shows a sectional view of an embodiment of the invention. Figure 5 is another embodiment. Figure 6 is a plan view of an attenuator plate shown in Figures 4 and 5. Figure 1 is a sectional elevation of known apparatus 10 for maintaining a relatively low proportion of coating on the finish region 15 of bottle 13 . Briefly described, a process stream 12 under pressure from supply blower 28 impinges upon bottle 13 , the temperature of the surface of which is of the order of from about 350 to about 400 degrees Celsius; generally, bottle 13 , moving toward the observer in a direction perpendicular to the plane of the drawing, has recently emerged from a forming machine, not shown. Deflection stream 14 , flowing substantially in the same direction as process stream 12 , is intended to keep stream 12 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 12 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 this typical apparatus not germane to this invention are not further described here, being well within the understanding of one skilled in the art. In the operation of the depicted coating-hood apparatus 10 , process stream 12 is generally a mixture of glass-coating precursors such as, e.g., a volatile or finely dispersed tin or titanium compound in a carrier fluid such as, e.g., air or the like. Compounds which are useful with the apparatus of the present invention include those which are capable of reaction with air or other process-stream oxidizing moiety on the surface of the substrate to form a metal oxide, and comprise conveniently but not by way of limitation, materials such as 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 12 has a tendency toward turbulence on encountering bottle 13 , deflection stream 14 maintains a zone which is more, but not completely, free of the coating precursor carried in stream 12 . As a result, coatings secured by the prior-art apparatus provide a gradient of coating with a thickness of the order of 10 nm on the body of the container to about 1 nm in the finish region. However, in field application, it has not been possible to steepen the gradient, that is, to provide either more coating on the body or less on the finish, nor to apply the process of the apparatus in a consistently successful fashion to containers with necks shorter than about 25 millimeters. We have discovered that by providing a substantially vertical stream of process fluid, generally air, directed in a fashion perpendicular to the coating stream, it is possible to keep the deposition of material on the finish to a very low level. However, a simple approach as shown in Figure 2 tended to produce variable results, limiting the utility of the idea to long-necked ware such as, e.g., beer and wine bottles and the like. In Figure 2, blower 19 delivers air or other fluid through plenum 22 and diffuser plate 23 as vertical deflection stream 18 onto the finish region 15 of bottles 13 . Diffuser plate 23 contains a plurality of holes, and is designed to moderate the force of process fluid supplied by blower 19 . In attempting -to regulate the passage of air from plenum 22 through diffuser plate 23 into the treating zone, however, we discovered that the system caused the formation of standing waves and pressure nodes, causing the velocity of the protective stream 18 to vary along the length of the delivery apparatus. The nature of the problem is illustrated more fully in Figure 3. Figure 3 is a section taken along lines 3 - 3 of Figure 2. Bottles 13 are shown moving on conveyor 11 in the direction marked by the arrow A . Depending on the size and geometry of plenum 22 and the velocity of process fluid 21 delivered by blower 19 , standing waves represented vectorially by arrows 26 and 27 would develop in plenum 22 , producing differences in pressure along its length. As a result of the difference in pressure, the velocity of vertical deflection stream 18 would vary from point to point throughout the coating apparatus, making precise control of that stream extremely difficult. In Figure 4, apparatus is shown comprising relocated blower 29 which delivers process air or other suitable fluid 41 into an end, as opposed to between the ends, of upper plenum chamber 32 ; the air passes first through attenuator 34 plate into plenum lower chamber 36 , and then through diffuser plate 38 to provide a substantially uniform stream of process air 41 into the finish region of bottles 13 . Clean-out door 42 provides access to the interior of plenum upper chamber 32 and plenum lower chamber 36 for removing, replacing or servicing attenuator plate 34 and diffuser plate 38 as may be appropriate or necessary. It has been found preferable to position attenuator 34 substantially at an angle to the flow of process fluid as shown in Figure 3; it is our understanding of the operation of this apparatus that the fluid, in passing through attenuator 34 , is redirected to a plurality of small, low-energy jets 45 without the generation of substantial turbulence or formation of standing waves, and the subsequent passage of that fluid through lower diffuser plate 38 is quite uniform. With the availability of a uniform stream of non-turbulent process fluid, it becomes easier to adjust the flow rate of that stream with sufficient precision to maintain a zone free of coating material in the finish region without either starving the shoulder or body region of the ware being coated, or permitting the stream of coating material to rise into the finish region That adjustment is represented by the uniform vector arrows 37 in Figure 4. In the fashion described, the finish can be kept virtually free of coating, while the contact areas of the ware are provided with adequate coating. With apparatus as described, we have been able to provide a uniform coating thickness of about 5 nm on the body of a bottle, while the finish region was substantially uncoated. Throttle means 49 in Figure 4, such as, e.g., an iris valve, but chosen to avoid introducing turbulence into fluid stream 41 , permits an additional method of controlling the force and velocity of stream 41 , and therefore the force and velocity of jets 45 . A similar or conjunctive control can be achieved by regulating the force of blower 29 by means not shown, but well known to those skilled in the art. Figure 5 shows another embodiment of the apparatus of the present invention, where attenuator plate 34 is juxtaposed against an auxiliary or supplementary attenuator plate 44 ; by this juxtaposition, any clogging of the passages in the attenuator plates can be easily remedied by opening clean-out 42 and replacing the attenuators, or by moving one past the other, thus causing mechanical friction to dislodge accumulated particles such as atmospheric dust or partially reacted or hydrolyzed coating compound. In the alternative, attenuators 34 and 44 , or either, can be mounted in a fashion which would permit their substantially frequent or constant movement relative to each other, in order to maintain clean holes without the need for exterior manipulation. Such apparatus 46 can comprise, e.g., a motor having an eccentrically-mounted weight which would cause a low-amplitude vibration in attenuator 34 , by direct attachment 46 to that attenuator, or any other motive means for inducing relative movement, well known to those skilled in the art. It is sufficient if the attenuators are of complementary shape, and juxtaposed closely enough to permit particulate removal by moving either attenuator with respect to the other. Further, filtration means, not shown but well known to those skilled in the art, can be supplied to remove particulate and other deleterious matter from the input fluid stream prior to that fluid being urged into or through plenum upper chamber 32 . Figure 6 is a plan view of attenuator plate 34 , having a plurality of holes 61 therein, to permit the passage of process fluid, while moderating its velocity and changing its direction by up to 90°, in a plurality of low-energy jets 45 . Attenuator 44 is substantially similar in design, and those skilled in the art will realize that that the shape of the holes 61 is not critical to the operation of the present invention, it being a sufficient condition that the size of the holes 61 be adequate to permit the passage of air, and that their spacing be chosen to prevent the development of extraneous currents between the individual jets 45 . By the use of the coating apparatus embodying these concepts, it has been found possible to establish parameters for coating-stream flow, exhaust velocity and bottle travel rate, and then to set the volume and velocity of the vertical finish-protection stream to provide small or even substantially zero thickness of coating on the finish; thereafter, further adjustments to maintain the system in balance we found to be virtually unnecessary.

Claims: Apparatus for the application of coating material to glass containers (13), comprising a conveyor (11) to move the glass containers (13) along a conveyor path, means (28) for directing a coating flow containing coating precursor compound against the containers (13) from one or both sides of the conveyor path, means (16,17) for exhausting spent coating flow from the conveyor path, and means comprising a blower (19,29) for blowing a non-coating flow at an upper part of the conveyor path to inhibit coating of upper portions of the containers (13), characterised in that the output path from the blower (19,29) leads into a plenum (22;32,36) above the conveyor path and through a foraminous diffuser plate (22,23,28) facing downwardly onto the conveyor path, to create in use a diffuse non-coating flow distributed across and directed downwardly onto the conveyor path. Apparatus according to claim 1 in which the diffuser plate (22,23,38) has a regular distribution of holes. Apparatus according to claim 2 in which the distribution of holes is symmetrical with respect to the conveyor path. Apparatus according to any one of the preceding claims in which the plenum (32,36) is divided by a flow attenuator into an upper chamber (32) into which the blower output path leads and a lower chamber (36) from which the diffuser plate (38) leads. Apparatus according to any one of the preceding claims in which the blower output path leads into the plenum (32,36) in a direction other than the downward direction. Apparatus according to claim 5 in which the blower output path leads into the plenum (32,36) generally horizontally. Apparatus according to claim 4 or any claim dependent thereon in which the flow attenuator comprises a foraminous plate (34,44). Apparatus according to claim 7 in which the attenuator plate (34,44) is inclined in the plenum at an angle between vertical and horizontal. Apparatus according to claim 8 in which the attenuator (34,44) inclines up in the direction along the conveyor path axis, symmetrically with respect thereto, and the blower output path enters the plenum generally horizontally and at the lower end of the attenuator (34,44). Apparatus according to claim 4 or any claim dependent thereon in which means (46) is provided for mechanically agitating the attenuator (34,44) to inhibit the accumulation of deposits thereon. Apparatus according to claim 10 in which the attenuator comprises two superimposed plates (34,44) and the agitating means (46) is adapted to move the plates relative to one another. Apparatus according to any one of the preceding claims in which the plenum has an openable door (42) for cleaning access. Apparatus according to any of the preceding claims in which the means (16,17) for exhausting spent coating flow comprises means for recirculating the spent coating flow back into the coating flow. A method of coating glass containers (13), comprising moving the containers (13) along a conveyor path; blowing a coating stream containing coating precursor compound against the containers (13) from one or both sides of the conveyor path to coat them, and blowing a non-coating flow at upper portions of the containers (13) to inhibit coating of those upper portions, characterised in that the non-coating flow is blown down onto the containers (13) from above the conveyor path through an accumulating plenum (22;32,36) and a foraminous diffuser plate (22,38). A method according to claim 14 in which the containers (13) are jars. A method according to claim 14 or claim 15 in which the coating precursor compound is a tin or titanium compound. A method according to any one of claims 14 to 16, carried out using apparatus as defined in any one of claims 1 to 13.

Inventors: BARKALOW RAYMOND WILLIAM, GUTHRIE ROGER THACKSTON, BARKALOW, RAYMOND WILLIAM, GUTHRIE, ROGER THACKSTON
Applicants: ATOCHEM NORTH AMERICA ELF, ELF ATOCHEM NORTH AMERICA, INC.
Application year: 1992
Main classification: C03C17
IPC codes: C03C17, B05B15, B05D7, B65D23