Title: Apparatus for applying a coating to glass containers
The present invention relates to an apparatus for applying a coating to glass containers, comprising a conveyor for passing the glass containers in the horizontal direction, first coating means in the form of a coating tunnel with a conveyor for passing the glass containers through the coating tunnel and with side walls in which slots are provided for supplying and exhausting a coating material containing gas-air mixture, and in which, in a selective hot-end coating process, a first coating can be applied to glass containers at high temperature, and second coating means in which, in a cold-end coating process, a second coating can be applied at a lower temperature.
To prevent glass containers, such as packaging glass, in particular bottles and jars, during successive conveyance to locations for carrying out various treatments, such as e.g. visual inspection, filling and labeling, from showing signs of wear in mutual contact through frequent scratching and rubbing, as a result of which the glass containers run a greater risk of breaking, it is conventional in practice, before these treatments take place, to coat the glass containers, thereby minimizing damage and substantially improving the above filling process because of the reduced mutual frictional resistance of the containers. Moreover, by preventing damage the appearance of the glass containers becomes more attractive When coating glass containers, a first coating is applied at a thickness of e.g. about 40 CTU (coating thickness units), which corresponds to about 10 nm, which first coating serves as support for a second coating, which otherwise hardly, if at all, adheres to the glass. The first coating often consists of tin oxide which, when supplying a mixture of air and a tin compound present therein in vapor form, forms on the glass by decomposition at high temperature, e.g.
in the order of 600 °C. Because the application of a coating occurs next to the manufacture of the glass containers, this high temperature is essentially the temperature the containers already have before they are passed into the coating" tunnel. Instead of tin oxide, a titanium oxide coating is, in practice, occasionally applied to the glass containers. It is, however, often not necessary to provide the whole glass container with such a coating. Thus, it is known to keep in particular the mouths of bottles free from coating by means of an air stream supplied from above, transversely to the coating material stream, or by means of an air stream supplied laterally against the necks of the bottles. This technique is described in e.g.
US-A 4,668,268 and US-A 5,584,903 and is known as finish protection. To apply this first coating, use is made of a coating tunnel in the side walls of which slots are provided for supplying and exhausting the coating material containing gas-air mixture, for brevity's sake occasionally referred to as coating gas. The height of the slots is adjustable, so that all kinds of forms and sizes of glass containers can be treated in this coating tunnel. In the above documents, the slots are vertically arranged, so that the bodies of the bottles are provided with a coating all over, while the mouths of the bottles are kept free from coating.
It is inter alia an object of the invention to save on the employed amount of coating material.
It has proved to be sufficient if only those parts of the bottles are provided with a coating with which they substantially touch each other. Therefore, according to the invention, the slots the side walls of the coating tunnel are horizontally provided in a longitudinal direction. As a result, the coating is applied m strips and preferably in strips at the lower sides of the bottles and in places where the bodies of the bottles merge into the necks. Exactly in these places the bottles are mostly thickest and will touch each other during conveyance over the conveyor. Through this
measure, a substantial saving on coating material is obtained. Of course, this manner of coating is not only applicable to bottles, but also to other types of glass packages and even to vases, tumblers, and the like.
After the hot-end coating has thus been applied, the glass containers are cooled in a controlled manner in a so-called cooling furnace to e.g. in the order of 120 to 140 °C, after which the second, cold-end coating is applied.
It is also possible that the second coating means are arranged to apply an overall coating, and that third coating means are present to apply, also in the cold-end coating process, a third, selective coating at a lower temperature. This overall coating will substantially be applied to offer some immediate protection of the containers against mutual damage in the further production line, that is to say until the third coating has been applied, which serves to provide the actual protection of the containers. In this situation, the third coating, like the first coating, will be applied selectively. The second coating is to be regarded as an intermediate coating. In the absence thereof, the third coating is actually to be regarded as the second coating.
Although in the cold-end coating process a powder coating technique or an immersion technique could be used, these methods are relatively expensive, so that use will nearly always be made of a spraying technique by means of a nozzle, which distributes a spray along the top between the glass containers. Although the glass containers are nearly completely provided with a second coating, this method has serious drawbacks. It proves to be difficult to prevent coating material from entering the glass containers. Furthermore, the coating material cannot be applied uniformly enough, particularly not if the glass containers are too close together or arranged insufficiently in line with each other. Moreover, the form of the glass containers plays a great role. Besides, the selection of the coating material is limited. In particular the adhesion of labels is strongly affected by the selection of the coating material and the degree in which this
material is applied to the glass containers. To face or at least substantially limit these problems, the second and/or the third coating means are designed according to the invention such that a relevant coating can be applied therewith in direct contact or nearly in contact with the glass containers. This measure can also be taken in those cases in which the hot- end coating process does not take place via slots horizontally provided in the side wall of the coating tunnel, but in a manner as e.g. described in the above US patents. The invention therefore also relates to an apparatus for applying a coating to glass containers comprising a conveyor for passing glass containers, first coating means in the form of a coating tunnel, in which, in a hot-end coating process, a first coating can be applied to the glass containers at high temperature, and at least second coating means, in which, in a cold-end coating process, a second coating can be applied at a lower temperature. This apparatus is characterized in that the second coating means are designed such that the second coating can be applied therewith in direct contact or nearly in contact with the glass containers. Of course, these second coating means can be used in combination with a coating tunnel in which the slots are horizontally arranged in the side walls thereof. In this connection, it is to be noted that in both above-described situations the height of these slots can be adjustable. Moreover, the application of the second coating can now take place selectively, in particular in the place where the first coating has also been applied. Because in the latter case it is mostly not necessary to make allowance for the adhesion of labels, the selection of coating material for this second coating is substantially increased. The places on the glass containers where now a coating is not found at all, render an adhesion of labels with simple glues, such as casein glue or starch glue, possible.
As stated, the second and, optionally, the third coating can be applied to the glass containers in direct contact with the glass containers, in which case reference will further he made to contact coating or coating nearly in
contact with the glass containers. In the first case, the second and/or, optionally, the third coating means will be provided with coating liquid adsorbing means, such as sponges, brushes, and the like, while in the second case the second and/or, optionally, the third coating means will be provided with coating liquid nozzles, which are arranged at a very short distance from the glass containers, that is to say at a distance of a few mm.
For the coating process to be carried out efficiently, the conveyor comprises a first section for passing the glass containers in a single row through the coating tunnel and a second section for passing the glass containers in parallel rows through the second coating means. In particular for the purpose of applying the second coating, rotating means are provided to realize a rotation of the further coating means relative to the glass containers. It is possible to rotate the glass containers and successively pass them along the coating liquid absorbing means or the coating liquid nozzles. There is also the possibility that these second coating means are movable along and around the step wise moving parallel glass containers of a simultaneously presented row of glass containers, while, since the further coating means must always be lifted, so that a row of glass containers can be moved under them without coating liquid still entering the glass containers, the further coating means operate intermittently. After application of the second coating, the conveyance in parallel rows of glass containers can be converted again into a single serial container conveyance. If third coating means are also present, then a third, selective coating can be applied by means thereof during the last-mentioned serial container conveyance. Without third coating means, it is also possible to provide the second coating means in the serial conveyor path.
The invention will now be explained in more detail with reference to the accompanying drawing. In this drawing:
Fig. 1 is a diagrammatically shown arrangement of the coating process with bottles;
Fig. 2 is a horizontal cross-section through the hot-end coating tunnel in this arrangement; Fig. 3 is a vertical cross-section transverse to the conveying direction for a coating tunnel according to the state of the art;
Fig. 4 is a side view of a row of bottles coming out of the coating tunnel, provided with a coating according to the state of the art;
Fig. 5 is a vertical cross-section transverse to the conveying direction for a coating tunnel according to the invention; and
Fig. 6 is a side view of a row of bottles coming out of the coating tunnel, provided with a coating according to the invention.
In the Figures, similar parts are indicated by the same reference numerals. The arrangement shown in Fig. 1 comprises a bottle production machine 1, which delivers the manufactured bottles to a conveying unit 2. The bottles are supplied in series to a hot-end coating tunnel 3 and, subsequently, in parallel to a cooling furnace 5 by means of a converting unit 4. The bottles are then supplied per row to a cold-end coating unit 6 and, subsequently, taken over in serial form and passed further, e.g. to an inspection location. In the tunnel 3, the bottles are provided with a tin oxide coating layer at a temperature of about 600 °C. The bottles are successively exposed on both sides to a mixture of air and a tin compound present in vapor form; as shown in Fig. 2, the remainder of this mixture are alternately exhausted on the opposite side. In the state of the art, as appears from the above US patents, only the necks of the bottles are kept free from coating; this situation is shown in Figs. 3 and 4. The coating vapor mixture is supplied via vertical slots. By adjusting the height of the slots, it can he ensured that only the bodies of the bottles are provided with a coating layer. If necessary, by means of a horizontally or vertically directed
air stream, a coating layer can be prevented from still being formed on the neck of the bottle. According to the invention, the coating tunnel shown in Fig. 1 is provided with horizontal slots, via which the coating vapor mixture is successively supplied and exhausted on both sides. By adjusting the height of these horizontal slots, it can be ensured that only a few horizontal strips of the bottles are provided with a coating layer. In Fig. 5, the coating tunnel is provided with two horizontal slots, via which the coating vapor mixture is supplied, which slots are adjusted such that only coating is applied to the lower side of the bottles and to the body of the bottles where thoy merge into the neck. To ensure that the coating is exclusively applied to the desired glass strips, the distance between the horizontal 'slots and the bottles to be passed along is kept small.
After the first coating, which functions as support for the final coating, has been applied, the bottles are passed in a parallel arrangement through a cooling furnace 5. The bottles are cooled therein in a controlled manner to about 130 °C. Then the bottles are passed in parallel arrangement to the cold-end coating unit 6, in which a final coating is applied. This coating adheres to the first coating and, only with great difficulty, to the glass, so that, even if the bottles are sprayed with the second coating all over, this coating substantially adheres to the strips provided with the first coating. The second coating is applied by means of a nozzle provided in the coating unit 6, which nozzle is moved between the individual TOWS of bottles.
By selectively coating in the coating tunnel according to the invention, as stated before, a substantial saving on coating can be obtained. For e.g. a wine bottle having a surface area of about 500 cm2, the coating area can be limited to about 150 cm2. To obtain an acceptable coating, a coating thickness of 40 CTU is usual. If the whole bottle is provided with a coating, then the amount of coating material thereon is 20,000 cm2. CTU. If a coating 40 CTU in thickness is applied over a surface area of 150 cm'2,
while it is assumed that a coating having an average thickness of 15 CTU still lands on the rest of the surface, then the amount of coating material is 11,250 cm2 CTU, which therefore means that a saving of about 44 % of coating material is obtained. By increasing the accuracy of selectively coating, a further saving can be obtained.
The invention is not limited to the exemplary embodiment described herein with reference to the drawing, but comprises all kinds of modifications thereof, of course as far as falling within the scope of protection of the appended claims. Thus, it is possible to add a coating unit 7 (see Fig. 1), through which the bottles are passed in serial form so as to be provided with a third coating layer. The coating applied in the coating unit 6, also in a cold-end coating process, then serves to offer some protection when the parallel conveyance form changes to the serial conveyance form of the bottles. In the coating unit 7, the final coating, preferably also selective, can then be applied.