GB2230260A - Strengthening of glass containers - Google Patents

Abstract

Glass containers of increased strength are produced by a process in which the containers are treated, immediately after forming and while still hot therefrom, e.g. at a temperature in the range 450-600 DEG C, simultaneously with a silane and an organic fluorine compound. Suitable silanes are methacryl-oxypropyl trimethoxy-silane and methyltri-ethoxy-silane; suitable fluorine compounds are mono-choro-fluoro-methane and 1,1-difluoro-ethane. The containers are suitably treated between the forming machine and the annealing lehr, wherein a "hot end" treatment of the containers may also be applied.

Description

STRENGTHENING OF GLASS CONTAINERS This invention relates to glass containers and other glass articles, and is especially concerned with a process for producing such articles having increased strength.

Many methods have been disclosed by which glass containers may be strengthened, albeit at a cost which may make the resulting glass container uncompetitive as a package. Such methods have included chemical ion exchange at the surface in order to impart a permanent compressive stress; laminating while hot with an outer layer of lower coefficient of expansion such that on cooling a permanent compressive stress is induced; surface cyrstallisation to achieve the same effect; melting the skin glass to remove large flaws; and many other methods.

Another approach which has been used, particularly in the manufacture of glass fibre for optical lines, has been to apply to the glass surface a protective polymer which inhibits the access of water vapour to the glass surface. This in turn reduces the fatigue effect which occurs when the glass surface is placed under stress in the presence of moisture, and which would otherwise result in considerable loss in strength.

It is common practice to apply coatings to glass containers for the purpose of protecting against abrasion once the bottles are cool. These coatings may comprise a "hot end" coating of tin oxide or titanium oxide which is applied by contacting the bottles at a temperature in the region of 5000C with a tin or titanium compound, and subsequently, when the bottles are at about 1000C, applying a suspension of an oxidised polymer or a fatty acid to give a lubricant film. These coatings, while protecting the glass against further loss in strength during handling and transport, do not increase the strength of the glass container at the time of manufacture.

A significant proportion of glass containers are used for the packing of foodstuff, and these tend to be widemouthed containers which are manufactured by a process known as "press-and-blow" (a preform is made in a press mould, and this is transferred to a blow mould for blowing into final shape). Such containers have a weaker internal surface than narrow-necked containers made by the "blow-and-blow" process (in which the preform is made in a blow mould), and while this is not a serious problem, it reflects on the impact resistance of the container. Those made by the "pressand-blow" process may fail by impact from the weakened internal surface, and the prior art does not disclose any method for overcoming this problem.

It is the object of the invention herein described to strengthen glass containers using an economic process.

According to the invention glass containers are treated, immediately after forming and while still hot therefrom, simultaneously with a silane and an organic fluorine compound.

The containers may also be provided with standard "hot end" and "cold end" coatings to protect against abrasion. The process may be applied to the internal surface of jars manufactured by the press-and-blow method such as to increase resistance to impact.

The silane and the organic fluorine compound may be applied separately, although at the same time, or they may be applied in admixture. Alternatively, the two functional groups may be present in the same compound and this comprises another method of application. The materials are preferably applied immediately before the containers pass into an annealing lehr or, when a "hot end" treatment is being given, immediately before they pass into the hood where they are given the tin oxide or titanium oxide treatment. Alternatively, treatment can be effected in the same hood as that used to apply the hot end coating of e.g. tin oxide or titanium oxide, or immediately after the containers, e.g. bottles have emerged from that hood.

Suitable silanes are those having three alkoxy groups attached to a silicon atom, the fourth group being a saturated or unsaturated hydrocarbon group or substituted hydrocarbon. We have found methacryl-oxypropyl trimethoxy-silane and methyltriethoxy-silane to be especially useful.

Suitable organic fluorine compounds are those with one or two carbon atoms, with at least two fluorine atoms bonded to one of the carbon atoms. We have found monochlorotrifluoro-methane and 1,1-difluoro-ethane to be especially useful.

The treatment of the invention is preferably conducted while the containers are at a temperature in the range 450-6000C, preferably at least 5000C, and suitably a mist or spray of the treatment materials in solution or suspension is applied to the containers.

The residence time of the containers in the treatment area is of the order of one second.

The prior art discloses the use of organic fluorine compounds to improve the chemical durability of glass, and the use of silanes, when applied to cooled glass, for modi fying the wettability of the surface. Application of either material separately to hot glass has no effect whatsoever on its strength, but when the materials are applied together in accordance with the invention, a quite unexpected effect is observed. Although the strength of the treated glass surface when measured by a rapid loading technique may not be changed, strength measured by a slow loading technique is significantly increased. This is related to the fatigue, and suggests that the treatment is reducing the extent of fatigue, resulting in a stronger glass after such has been exposed to stress.Since in practice glass containers are continually exposed to stress raising factors during the course of their normal use, e.g. impact during filling and transport, carbonation pressure, vertical load during storage of stacked pallets of empty and filled containers, thermal stress during washing and pasteurising etc., the provision of meansofpreventing strength loss should result in a container which in practice is stronger.

Treatment may be applied to the external surface of bottles. In this case a strengthening of this external surface is obeserved, and this will reflect on the strength of the bottles to withstand stress caused by internal pressure, impact and vertical loading.

Treatment may also be applied to the internal surface, particularly of those items manufactured by the press-andblow process. In this case a significant strength increase of the internal surface is observed, resulting in a corresponding improvement in impact resistance.

The method of the invention may be further explained by reference to the following examples which are given for the purpose of illustration and not of limitation.

EXAMPLE 1 Immediately after manufacture, and whilst still at a temperature of 500 C, 500ml soft drink glass bottles were transferred into a hood wherein normal "hot end" application of a tin-containing compound was made. At the entrance to this hood, a separate auxiliary hood was installed in which the bottles were subjected to treatment by two sprays each providing a mixture of -methacryl-oxypropyl trimethoxy silane (Union Carbide A-174) and chloro-trifluoro methane (CFC11 fluorocarbon). The silane has previously been dissovled in butyl acetate to provide a 10% w/w solution and was atomised by air at 151bs per sq.inch.

After treatment the bottles were passed into the hood applying tin compound and were subsequently annealed in the normal way.

Strength tests were carried out by supporting a bottle on its side on two horizontal rollers and loading with a ball in the mid-sidewall at a predetermined rate of loading until failure of the bottle occurred. Two loading rates differing by a factor of 10 were used to assess the effect of fatigue on strength. Table 1 shows the results obtained on bottles treated in the manner described in this Example, compared with bottles produced immediately prior to the application of the treatment, but in all other respects manufactured by the same process, on the same machine and taken from the same mould. It is seen that the major effect of the treatment is to reduce the fatigue effect, thus enhancing the strength of the glass under prolonged conditions.

EXAMPLE 2 Bottles similar to those described in Example 1 were treated similarly to the method described in Example 1 except that 1:1 di-fluoro ethane (CFC 152a) was used as the fluorocarbon. The results shown in Table 1 indicate that the presence of chlorine in the fluorocarbon is not essential for the treatment to be successfully applied.

EXAMPLE 3 Bottles similar to those described in Example 1 were treated in a similar manner to that described in Example 1 except that the fluorocarbon treatment was omitted, the bottles being treated in this part of the process only with the silane solution. The results shown in Table 1 indicate that the fluorocarbon is an essential part of the fatigue suppresion effect.

EXAMPLE 4 Bottles similar to those described in Example 1 were treated in a similar manner to that described in Example 1 except that the silane solution was replaced by butyl acetate only, so that no silane was used in the treatment procedure. The results shown in Table 1 indicate that the silane constituent is an essential part of the fatigue suppression process.

EXAMPLE 5 Bottles similar to those described in Example 1 were treated in a similar manner to that described in Example 1, except that application of the fluorocarbon and silane materials was made after the bottles had been treated with a tin-containing compound. The results shown in Table 1 indicate that the fatigue suppression effect is also obtained when this order of treatment takes place.

EXAMPLE 6 Glass jars produced by the press-and-blow process were treated in a similar manner to the bottles described in Example 1, except that the application of the material was made by a single spray situated overhead and spraying downwards so that the interior surface of the jar received treatment. When tested by the method described in Example 1, the failure origin was on the internal surface immediately under the loading point and the results shown in Table 2 indicate that the effect of treatment was to suppress the fatigue behaviour of the internal surface..

Such jars failed by impact from internal surface failure and Table 2 also shows that the treated jars had a higher resistance to impact than jars not given this treatment.

EXAMPLE 7 Bottles were treated as described in Example 2 except that a solution of methyltriethoxy-silane (Union Carbide A-162) was used. The strength under slow loading was some 5% less than that under fast loading, whereas for untreated bottles the difference was 20%.

TABLE 1 - TREATMENT OF EXTERNAL SURFACE MEAN LOAD TO FAILURE (KN) FAST LOADING SLOW LOADING Standard Treatment 11.9 10.5 Treated as described in Example 1 11.9 11.4 Treated as described in Example 2 (CFC 152a) 11.9 11.4 Treated as described in Example 3 (CFC omitted) 11.8 10.5 Treated as described in Example 4 (silane omitted) 11.9 10.5 Treated as described in Example 5 11.8 11.4 TABLE 2 - TREATMENT OF INTERNAL SURFACE FAILURE STRESS (MPa) MEAN IMPACT RESISTANCE FAST LOADING SLOW LOADING INS/SEC AGR TESTER No Internal surface treatment 680 490 60 Treated as described in Example 6 700 650 80

Claims (13)

1. CLAIMS 1. A process for treating glass containers which comprises treating them, immediately after forming and while still hot from forming, simultaneously with a silane and an organic fluorine compound,
2. 2. A process as claimed in claim l wherein the silane and the organic fluorine compound are applied to the glass containers in admixture.
3. 3. A process as claimed in claim 1 or claim 2 wherein the silane is one having three alkoxy groups attached to the silicon atom, the fourth group attached to the silicon atom being a saturated or unsaturated hydrocarbon group or a substituted hydrocarbon.
4. 4. A process as claimed in claim 3 wherein the silane is methacryl-oxypropyl trimethoxy-silane or methyl triethoxy-silane.
5. 5. A process as claimed in any preceding claim wherein the organic fluorine compound has one or two carbon atoms, at least two fluorine atoms being attached to one of the carbon atoms.
6. 6. A process as claimed in claim 5 wherein the organic fluorine compound is mono-chlorotrifluoro-methane or l,l-difluoro-ethane.
7. 7. A process as claimed in claim 1 wherein the silane and the organic fluorine compound are the same compound.
8. 8. A process as claimed in any preceding claim wherein the glass containers are treated whilst at a temperature in the range 45O6O00C.
9. 9. A process as claimed in claim 8 wherein the glass containers are treated at a temperature of at least 5000C.
10. 10. A process as claimed in any preceding claim wherein the silane and organic fluorine compound are applied to the containers in solution or suspension form as a mist or spray.
11. 11. A process as claimed in any preceding claim wherein the glass containers are subjected to treatment for a time of the order of 1 second.
12. 12. A process as claimed in any preceding claim wherein both the internal and external surfaces of the containers are treated.
13. 13. A process as claimed in claim 1, substantially as described in any of the Examples.