WO2002002473A1

WO2002002473A1 - Method of coating glass articles

Info

Publication number: WO2002002473A1
Application number: PCT/AU2001/000777
Authority: WO
Inventors: Atit Bhargava
Original assignee: Globaltele Pty Ltd
Priority date: 2000-06-30
Filing date: 2001-06-28
Publication date: 2002-01-10
Also published as: AUPQ848700A0

Abstract

A method of coating glass articles with a coating formed from at least portions of molecules of a first chemical utilising a spray technique, wherein a mixture of water and the first chemical is provided as a spray for the coating of the glass articles.

Description

METHOD OF COATING GLASS ARTICLES

Field of the invention

The present invention relates broadly to a method for coating glass articles. The invention will be described herein with reference to coating glass containers on a typical bottle production line, however, it will be appreciated that the present invention does have broad applications, for example for coating glass containers in a static configuration and coating flat glass articles.

Background of the invention

Glass containers such as bottles are commonly coated with chemicals that protect the surface from abrasion, weathering and chemical attack. Typically, the coating is formed from tin or titanium oxide, which can further be coated with an additional layer of a polymer.

The appropriate chemical is delivered to the surface of glass containers which are at relatively high temperatures on a production line conveyor belt. On contact with the hot glass bottle surface, the chemical is pyrolysed leaving behind an oxide film bonded to the glass, with volatile bi-products of the pyrolisis leaving the hot glass bottle surface.

Recently, a spray- technique has been proposed for the coating of glass containers. In the spray-technique, a spray which comprises molecules of a chemical suitable for forming the coating is directed towards the surface of the e.g. glass bottle whilst the glass bottles pass through a coating zone, with the coating being formed form at least portions of the molecules. The spray-technique can provide better control over the parameters of the coating process. h the spray-technique the chemical utilised for the formation of the coating is typically dissolved in alcohol to provide a liquid source from which the spray is formed, hi some instances, the solvent is a high alcohol mixture such as 95% alcohol and 5% water (e.g. PCT application PCT/JP97/00030, 1997, Nippon Sheet Glass). However, the addition of alcohol can have the disadvantage that because of the high temperatures involved in e.g. coating the glass bottles there may be safety issues associated with the use of alcohol in large quantities. This can put restrictions on the spray-technique, which may prevent utilising the technique in a most efficient way. In other instances, an admixture of chemicals is used which does not specifically improve stability of e.g. the tin chemical, improve properties or provide for addition of large variety of cations (e.g. US Patent 4,389,266, Brockway Glass Co, Inc.).

In other instances, different chemicals are applied sequentially to deposit elements other than tin. This method would provide sandwiched sequential layers rather than a uniform distribution of elements. Also, this typically requires two deposition equipments and would not be successful in a very fast production plant as is the instance these days. This method would also be inconvenient/in-efficient to implement in flat glass industry where a "sequential" deposition would be too expensive and improbably, (e.g. US Patent 4,021,218,1977, Yamamuor Glass Kabushiki Kaisha).

Summary of the invention

In accordance with a first aspect of the present invention there is provided a method of coating glass articles with a coating formed from at least portions of molecules of a first chemical utilising a spray technique, wherein a mixture of water and the first chemical is provided as a spray for the coating of the glass articles.

The applicants have found that water is suitable for forming a solution of chemicals suitable for the coating of glass articles, thus eliminating the need to use any alcohol in the spray-technique. The addition of water was also found to reduce and sometimes possibly to prevent altogether crystallisation of the chemicals during exposure to atmosphere. This stabilizes the chemicals and can reduce maintenance of e.g. spray nozzles and delivery tubes used in the spray-techniques typically caused by clogging through the formed crystals over time. Furthermore, the addition of water can also provide a source of cations for many applications such as e.g. for an ion-exchange reaction for increasing the mechanical strength of the surface of the glass article and for other additions such as colouring agents and for imparting physical, chemical and mechanical properties, h preferred embodiments, the resultant new chemical mixture is also environmentally friendly.

Preferably, the mixture comprises from about 10% to 70% by volume water.

The water is advantageously used as a source of cations for an ion-exchange reaction at the surface of the glass articles. The first chemical may comprise mono-butyl-tin-tri-chloride (MBTC). The method may further comprise the step of adding a second chemical to the mixture prior to providing the mixture as a spray for the coating.

The second chemical may be utilised as a further source of cations for the ion-exchange.

The second chemical may comprise lithium. The lithium may be provided as a soluble salt such as lithium chloride.

The second chemical may alternatively or additionally comprise soluble salt of titanium such as titanium di isopropoxide di-ionate.

The second chemical may alternatively or additionally comprise tungstosilicic acid.

The second chemical may alternatively or additionally comprise soluble metal salts such as cobalt nitrate or mixtures with manganese nitrate and/or copper nitrate and/or iron nitrate.

The glass articles may comprise non-planar articles or planar articles. The glass articles may comprise glass containers such as e.g. glass bottles.

In accordance with a second aspect of the present invention there is provided a glass article coated in accordance with the method of the present invention. The glass article may be a non-planar article or a planar article. The glass article may comprise a glass container such as e.g. a glass bottle. h accordance with a third aspect of the present invention there is provided a coated glass article, wherein a mechanical strength of the surface of the glass article has been modified through an ion-exchange reaction, wherein a cation of the glass surface has been replaced by a water cation.

The glass article may be a non-planar article or a planar article. The glass article may comprise a glass container such as e.g. a glass bottle.

Preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings. Brief description of the drawings

Figure 1 shows a schematic diagram illustrating the coating of bottles using the spray- technique. Figure 2 shows a plot of internal (bursting) pressure of bottles versus line simulation time illustrating the effect of different coating chemicals/solutions.

Figure 3 shows a plot of internal (bursting) pressure of bottles versus line simulation time illustrating the effect of the addition of lithium. Detailed description of the embodiments

The preferred embodiments described provide a method of coating a glass article in which mixtures not containing any alcohol are utilised for coating of glass articles utilising a spray technique.

Figure 1 shows a schematic drawing of a device 10 utilised in the spray-technique. The device 10 comprises two nozzles 12, 14, for provision of the spray 16. A liquid containing the chemical from which the coating is to be formed is provided to the nozzles 12, 14 through tubes 18, 20 from reservoirs 22, 24 respectively. The reservoirs 22, 24 are being pressurised from sources 26, 28 of compressed gas. The generated spray is directed towards the glass article to be coated, in the example shown in figure 1 bottles e.g. 29 being conveyed through the device 10. In the following, two examples embodying the present invention will be described also, results of line simulation experiments will be presented with reference to Figures 2 and 3. Line simulation is a technique of quality control and testing used in the container glass industry to evaluate performance of bottles. In this test, bottles are placed in a certain manner inside a chamber which is subjected to rapid motion simulating wear and tear in transportation and handling of the bottles. The time for which the equipment is run is called in the line simulation time. With increasing line simulation time, the strength of the bottle (as measured by internal bursting pressure tests) decreases due to formation and propagation of cracks. It is desired to have a slow fall in the internal bursting pressure of bottles with increasing line simulation times.

Example 1: Using a 50% by volume mixture of water and mono-butyl-tin-tri-chloride (MBTC), bottles were coated in a production plant using the spray-techniques.

A comparison of results obtained with this mixture embodying the present invention and the prior art is shown in Figure 2. hi Figure 2, the internal bursting pressure is lotted as a function of line simulation time. The results for the mixture of example 1 embodying the present invention are represented in curve 30 in Figure 2. As can be seen, the internal bursting pressure as measured after a line simulation time of 6 minutes is improved when compared with the prior art (curves 32, 34). More specifically, curve 32 shows the results for coatings obtained utilising conventional stannic chloride (SnCl ) as the liquid for the generation of the spray, whereas curve 34 shows the results obtained utilising MBTC without add-mixture of water as the liquid for the creation of the spray. Furthermore, it is noted that the coating obtained utilising the mixture of example 1 embodying the present invention (curve 30) was observed to be generally more homogenous than those made by the prior art (curve 32, 34).

Example 2: Using a 50% volume mixture of water and mono-butyl-tin-tri-chloride as used in Example 1, lithium chloride is dissolved in the mixture. In one mixture, called Li (1) a small amount of lithium chloride is used. In another example, called Li (2), a larger amount of lithium chloride is used. Both these amounts are less than about 10% of the solubility limit of lithium chloride in water at 25 degrees Celsius.

A comparison of the two mixtures embodying the present invention with the prior art is shown in Figure 3. In Figure 3, the bursting pressure of the coated glass bottles is shown as a function of line simulation time. The results for the two mixtures embodying the present invention, called Li(l) and Li (2) are shown in curves 40 and 42 respectively. As can be seen from Figure 3, the bursting pressure of glass bottles coated with either one of the mixtures embodying the present invention (curves 40, 42) is higher than for bottles utilising the conventional SnCl liquid (curve 44). Furthermore, the results shown in Figure 3 indicate a potential of even higher bursting pressures with the use of higher amounts of lithium chloride in other mixtures embodying the present invention, as illustrated by a comparison of curves 42 (higher lithium chloride amount) and curve 40 (lower lithium chloride amount).

The results shown in Figure 3 further indicate a potential of even higher bursting pressures with the use of higher amounts of lithium chloride in the mixture.

It will be appreciated by the person skilled in the art that numerous modification and/or variations may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.

For example, it will be appreciated by the person skilled in the art that whilst the present invention has been described herein with reference to the coating of glass bottles, the invention does have broader applications to the coating of other glass articles, including planar articles such as glass panels. In the claims that follow and in the summary of the invention, except where the context requires otherwise due to express language or necessary implication the word "comprising" is used in the sense of "including", i.e. the features specified may be associated with further features in various embodiments of the invention.

Claims

I . A method of coating glass aiticles with a coating formed from at least portions of molecules of a first chemical utilising a spray technique, wherein a mixture of water and the first chemical is provided as a spray for the coating of the glass articles.

2. A method as claimed in claim 1, wherein the mixture comprises from about 10% to 70% by volume water.

3. A method as claimed in claims 1 or 2, wherein the water is used as a source of cations for an ion-exchange reaction at the surface of the glass articles.

4. A method as claimed in any one of the preceding claims, wherein the first chemical may comprise mono-butyl-tin-tri-chloride (MBT).

5. A method as claimed in any one of the preceding claims, wherein the method further comprises the step of adding a second chemical to the mixture prior to providing the mixture as a spray for the coating.

6. A method as claimed in claim 5, wherein the second chemical is utilised as a further source of cations for the ion-exchange.

7. A method as claimed in claims 5 or 6, wherein the second chemical comprises lithium.

8. A method as claimed in claim 7, wherein the lithium is provided as a soluble salt.

9. A method as claimed in claim 8, wherein the lithium is provided as lithium chloride.

10. A method as claimed in any one of claims 5 to 9, wherein the second chemical comprises a soluble salt of titanium.

I I. A method as claimed in claim 10, wherein the soluble salt of titanium comprises titanium di isopropoxide di-ionate.

12. A method as claimed in any one of claims 5 to 11, wherein the second chemical comprises tungstosilicic acid.

13. A method as claimed in any one of claims 5 to 12, wherein the second chemical comprises a soluble metal salt.

14. A method as claimed in claim 13, wherein the soluble metal salt comprises one or more of the group of cobalt nitrate, mixtures with manganese nitrate, copper nitrate, and iron nitrate.

15. A method as claimed in any one of the preceding claims, wherein the glass articles comprise non-planar articles or planar articles.

16. A method as claimed in claim 15, wherein the glass articles comprise glass containers.

17. A method as claimed in claim 16, wherein the glass articles comprise glass bottles.

18. A glass article coated in accordance with the method of any one of the preceding claims.

19. A glass article as claimed in claim 18, wherein the glass article comprises a non- planar article or a planar article.

20. A coated glass article, wherein a mechanical strength of the surface of the glass article has been modified through an ion-exchange reaction, wherein a cation of the glass surface has been replaced by a water cation.