GB2139997A - Surface treatment of glassware - Google Patents

Abstract

A hot end treatment of glassware, e.g. glass containers, comprises applying to the ware a solution or dispersion containing compounds of tin and aluminium, while the ware is at a temperature sufficient to cause reaction to occur between the glass at the surface of the ware and the tin and aluminum compounds, and thereafter cooling the ware. The hot glassware may be treated with a solution made by dissolving stannic chloride and aluminium chloride in n-butyl acetate.

Description

SPECIFICATION Surface treatment of glassware This invention relates to the surface treatment of glassware, such as glass containers (e.g. bottles, jars) and tableware (e.g. drinking glasses).

For many years it has been an established practice in the manufacture of glass containers to subject the containers to a surface treatment after forming and before the containers are passed into the annealing lehr. This is commonly referred to as the "hot end" treatment of containers, and in conjunction with a second treatment taking place as the containers emerge from the lehr (the "cold end" treatment) a glass surface is produced which is lubricious and extremely resistant to abrasion when contacted by similar glass surfaces. Hence bottles and other glassware given this treatment can be passed along conveyors and the like wherein glass-to-glass contact takes place without resulting in jam-u ps due to frictional contact, or to any damage to the glass itself which may subsequently diminish its strength in use.

A number of methods are in commercial use for applying hot end coatings. They all basically revolve around the deposition of either tin oxide ortitanium oxide on the glass surface by chemical reaction of the hot glass with a suitable compound of tin or titanium. Typical processes are described in U.K.

Patent Specifications Nos: 1115342 and 1024468.

Generally speaking, tin compounds are expensive to apply, but they form a coating readily, and control of the thickness of the coating can easily be exercised.

Titanium coatings are much cheaper to produce in terms of material costs, but greater care is needed in orderto obtain a coating and particularly to control its thickness. Compounds of other metals have been tried as coatings for glass containers, and indeed as coatings for flat glass for other types of application.

In general, however, such materials have not found commercial acceptance as coatings for containers, either because they do not readily produce a coating, or because the coating produced is coloured, or because the material from which the coating is produced or any material extracted from the glass as a result of such coating is unduly toxic.

A number of methods are available for applying hot end coatings, but again these resolve down to two basic methods. In one case the coating material is applied as a vapour of the active material, generally incorporated in specially dried air so that premature reaction of the vapour can be avoided. In the other method, the coating material is dissolved in or reacted with a suitable solvent, which may be aqueous or organic, and is sprayed on to the containers. The coating material in both methods is applied to the glassware in treatment hoods or tunnels located between the forming machine and the annealing lehr.

One of the disadvantageous features of most existing hot end treatment procedures is the low efficiency in the use of the material, and, in general, the amount of material deposited on the glass containers is only of the order of 5-10% of the total amount of material applied into the treatment hood.

Apart from the cost of this unused material, it also produces a disposal problem since the excess material will appear either as a deposit in the treatment hood and associated ducting, or as a vapour issuing from an exhaust stack.

The present invention is particularly concerned with providing a method of applying a hot end treatment to glass containers and other glassware which substantially reduces the cost of the treatment both by use of low cost material and by increasing the efficiency of coating deposition. We have found that this can be achieved by replacing part of the tin in a tin-containing solution or dispersion used for spraying containers by aluminium.

According to the invention, therefore, we provide a method of treating glassware which comprises applying to the ware a solution or dispersion containing compounds of tin and aluminium while the ware is at a temperature sufficient to cause reaction to occur between the glass at the surface of the ware and the said compounds, and thereafter cooling the ware.

The amount of tin replaced by aluminium is of some of importance. A worthwhile effect, so far as operating efficiency is concerned, is observed when 25% of the tin is replaced by its molar equivalent of aluminium, and even greater effect is observed at 50% replacement. Up to this point, there is no observable change in the handling properties of the material or in its chemical properties. As the mix approaches the 75% replacement value (i.e. a molar ratio of Sn:AI of 1.3), some deterioration in the coating performance is observed, as well as some instability in chemical behaviour, although even at this point the material saving generated may be worth the additional cost of dealing with handling problems. Beyond 75% replacement, the coating performance falls off substantially, and handling problems increase significantly.For this reason, we believe the practical application of this method of treatment to be confined essentially to a material in which at least 50% of the active ingredient is present as tin and at most 50% as aluminium, both expressed on a molar basis.

The hot end treatment of the invention may be used alone, or in combination with a subsequent "cold end" treatment, of which details are widely known in the art.

A typical hot end treatment according to the invention will comprise spraying into a treatment hood, through which hot newly formed glassware (at a temperature in excess of 350"C, suitably greater than 500"C) is passing, a spray or mist of a solution or dispersion of a tin compound and an aluminium compound in an aqueous or organic solvent.

The treatment liquid may be prepared by dissolving or dispersing a tin halide, e.g. stannic chloride, and an aluminium halide, e.g. aluminium chloride, in suitable amounts in an organic solvent, e.g. n-butyl acetate.

Following the hot coating the ware may be sprayed with a lubricating agent, e.g. a polyalkylene glycol, in a cold end treatment (e.g. at approximately 1 00 C).

It should be mentioned that aluminium-containing materials have in the past been mentioned in the literature as suitable for use in the hot end treatment of glassware. However, they have not found use commercially because their coating performance is poor and the solutions unstable. It was therefore quite unexpected that the replacement of part of the tin in a hot end treatment by aluminium resulted in a treatment which was every bit as satisfactory as that using tin alone, as well as providing a more efficient treatment in terms of material usage.

The following Examples will serve to illustrate the benefits of this Application.

Example I (for comparison) A solution was prepared containing 20% by weight of stannic chloride dissolved in n-butyl acetate, corresponding to a tin content of 8% by weight, and this solution was sprayed on to hot bottles issuing at a temperature in excess of 500"C from a forming machine, using four spray heads each delivering 12.5ml per minute of solution into a tunnel through which the bottles were passing. After this treatment the bottles were annealed, and when at a temperature of approximately 1 00 C were passed into a hood where they were sprayed with a solution of 0.2% polyethylene glycol 4000.The treated bottles were found to be quite lubricious when contacted one against another, and upon attempting to scratch one bottle against another it was found extremely difficult to obtain any evidence of abrasion. By use of a standard abrasion test it was found that the abraded surface of these bottles retained 89% of the unbraded strength, whereas similar bottles without the tin treatment retained 40% only of the unabraded strength. Surface analysis showed the presence of 5 micrograms of tin per cm2 of surface, and by reference to the quantity of material sprayed per minute, and the number of bottles passing through the treatment hood per minute, the efficiency of deposition was found to be 4%.

Example 2 (for comparison) This was carried out as described in Example 1, except that the tin-containing solution was applied using four spray heads at a rate of 9 ml per minute through each spray. The lubricity and abrasion resistance of the bottles was good, with a strength retention in a standard test of 74%. The efficiency of tin deposition was 5%.

Example 3 (for comparison) This was carried out as described in Example 1, except that the treatment solution used contained no tin instead 10% by weight of aluminium chloride (corresponding to 2% by weight aluminium). Treatment of bottles using four spray heads each at a flowrate of 12.5ml per minute gave bottles with poor abrasion resistance.

Example 4 This was carried out as described in Example -d 2, except that the treatment solution used con- estained 10% by weight of stannic chloride (corresponding to 4% by weight tin) and 5% by weight of aluminium chloride (corresponding to 1% by weight aluminium). Treatment of bottles using four spray heads each at a flow rate of 9ml per minute gave bottles with good lubricity and abrasion resistance, the standard test showing 82% retention of strength.

Surface analysis showed efficiency of 8% for tin and 45% for aluminium.

Example 3 confirms that aluminium materials alone are poor treatment agents for glass containers.

Example 4 clearly shows, however, that substitution of some of the tin by aluminium brings about an enhanced degree of treatment, represented by the increased abrasion strength retention, accompanied by a substantial increase in efficiency of material usage, represented by greater tin deposition.

Claims (7)

1. A method of treating glassware which comprises applying to the ware a solution or dispersion containing compounds of tin and aluminium while the ware is at a temperature sufficient to cause reaction to occur between the glass at the surface of the ware and the said compounds, and thereafter cooling the ware.

2. A method as claimed in claim 1 wherein the solution or dispersion contains tin and aluminium in a molar ratio in the range 3:1 to 1:3.

3. A method as claimed in claim 1 wherein the solution contains tin and aluminium in a molar ratio in the range 3:1 to 1:1

4. A method as claimed in any of claims 1 to 3 wherein the solution is applied to the ware while the ware is at a temperature in excess of 500"C.

5. A method as claimed in any of claims 1 to 4 wherein the solution is made up by dissolving stannic chloride and aluminium chloride in n-butyl acetate.

6. A method as claimed in any of claims 1 to 5 wherein, during the cooling of the ware, it is treated with a lubricating agent.

7. A method as claimed in claim 6 wherein the ware, during cooling, is sprayed with a solution of polyethylene glycol.