AU672136B2 - Method for hot-end coating of hollow glass - Google Patents

Description

Method for Hot-End Coating of Hollow Glass Field of The Invention The invention relates to a method for the hot-end coating of hollow glass objects by vapour deposition of tin compounds, optionally dissolved in organic solvents, on the outer surface of hollow glass objects, heated to 500 0 C to 600 0 C, the tin compounds being pyrolysed with the formation of thin tin oxide layers.

Thin tin oxide layers are produced on the hot glass surfaces by the pyrolysis of tin compounds. The tin compounds can be applied either as a vapour or as a spray, which contains a dissolved tin compound.

Background Information and Prior Art In the US 3 414 429, a method is described, in which these layers are produced from tin-IV halides, such as tin tetrachloride. Compounds of this type hydrolyse easily in the presence of traces of moisture, producing highly corrosive compounds in the process.

Moreover, the yield during the build-up of the layer is very small. Since the portion of the tin-IV halides, which is not used for building up the layer, cannot readily be recycled, this method has only limited usefulness. Furthermore, the spontaneous decomposition of the tin tetrachloride leads to a non-uniform build-up of the layer, which becomes noticeable due to optically irritating interferences.

Per atom of tin, tin-IV chloride contains four atoms of chlorine and, for industrial 20 applications, generally is stabilised with additional hydrogen chloride. The main disadvantage of this system is the high chlorine content. During the thermal decomposition, hydrogen chloride gas is formed, which represents a danger to health and can attack or damage materials.

DE 25 41 710 discloses a method, for which the tin-IV oxide layer is produced by 25 pyrolysis of a mono-organo tin trichloride of the general formula RSnC13, wherein R represents an alkyl group with one to eight carbon atoms, on the hot glass surface. For this method, the compounds are applied by vapour deposition or spraying. Preferably, monobutyl tin trichloride is used. With respect to the emission of pollutants, it is a disadvantage here that three chlorine atoms are released and must be disposed of for every 30 tin atom.

If tin-II chloride is used, the calculated ratio of tin to chlorine admittedly is improved. However, because of the low hydrolytic stability of the aqueous solutions of the tin-II chloride, hydrogen chloride must once again be added to these solutions and the problem of increased corrosion of parts of the equipment by the strongly acidic solution of hydrochloric acid remains.

DE 41 24 136 discloses a method, for which hollow glass objects are coated by spraying on a solution, which contains 100 to 1000g/L of (OH) 2 SnC1 2 Up to 50 mole percent of the compound can be replaced by equimolar amounts of the general compound IN:\iIBCI00397:JOC 1 of 7 4 in which x has a value of 0.2 to 3.8, y a value of 1.9 to 0.1 and (2y+x) 4. Even with this, however, a tin to chlorine ratio of only 1:1, at best, can be attained.

Solutions of alkyl tin carboxylates, according to the US 3 414 429, can be sprayed to achieve hot-end coating. Application by spraying has, however, technical disadvantages, particularly a poor homogeneity and a low layer- forming efficiency. The poor yield (ratio of tin (incorporated in the layer) to tin (offered)) originates from the loss of the material, which either is sprayed next to the object or, as a result of inadequate contact, does not contribute to building up the layer and reaches the air that is exhausted in the form of tin oxide powder dust.

Within the scope of hot-end coating, tin oxide layers up to a thickness of about are obtained. These layers on the glass surfaces serve as coupling agent for the wax layers applied in a subsequent cold-end coating. These thin films of natural or synthetic waxes are transparent and protect the glass container against abrasion and scratching (cold-end coating).

Object of the Invention An object of the present invention is a method for uniformly coating the outer surfaces of hollow glass objects with tin compounds, optionally dissolved in solvents, with the formation of tin oxide layers. For this purpose, tin compounds are to be made available, which are stable also in the form of their solutions and are free of chloride or, 20 at least, contain only minimal amounts of chloride. The tin oxide layer produced is to be as homogeneous as possible.

Summary of the Invention Surprisingly, these requirements can be fulfilled by a method using monobutyl tin tricarboxylates, which can be dissolved in organic solvents having a boiling point less than 180 0 C, and which are vapour deposited. In particular, the ability to vapour deposit these compounds and to produce tin oxide layers is surprising.

Preferably, carboxylates with up to 6 carbon atoms are vapour deposited as monobutyl tin tr' The carboxylates can be linear or branched. Examples of :.suitable carboxylates are the acetates, propionates, butanates, isobutanates, valerianates and hexanoates, the monobutyl tin triacetates, tripropionates and tributanates being particularly preferred. Particularly preferred is monobutyl tin triacetate and it is this compound which is used in the method of the invention. Mixed carboxylates, such as monobutyl tin diacetate monopropionate, can also be used.

The lower carboxylates (particularly the monobutyl tin triacetate, but also monobutyl tin tripropionate and monobutyl tin tributyrate) can be applied with or without solvents by means of a hot carrier gas on the surface of the glass objects that are to be coated. In the method of the invention monobutyl tin triacetate is used in solution in an organic solvent having a boilding point less than 180 0 C. It is advisable to use the higher -7 ;<(N:\LIBC|00397:KEH TO O carboxylates with 4 to 6 carbon atoms in the form of their solutions, in order to obtain a uniform layer construction.

Accordingly, there is provided according to a first embodiment of the invention a method for coating a hollow-glass object by applying monobutyl tin triacetate in solution in an organic solvent on a surface of the glass object heated to 500°C to 600°C, the monobutyl tin triacetate being pyrolysed with the formation of a thin tin oxide layer, the method comprising depositing, in vapour form, on the glass surface, monobutyl tin triacetate in solution in an organic solvent having a boiling point below 180 0

C.

According to a second embodiment of the invention there is provided a hollow glass object prepared by the method of the first embodiment.

The homogeneity of the surface coating of hollow glass containers is ensured by tunnel-shaped vapour-deposition hoods, through which a conveyor belt extends in the longitudinal direction for transporting the glass containers. At least one air cycle, enriched with the coating agent, is formed within this vapour-deposition hood. Such coating hoods are state of the art and are described, for example in EP-A-0 103 109, EP- A-0 378 116 and DE-C-37 27 632.

Particularly suitable as solvents are alcohols, ketones, esters or their mixtures with water, Especially preferred solvents are lower aliphatic alcohols, such as ethanol, propanol, isobutanol, ketones, particularly acetone or butyl ethyl ketone and esters, S 20 particularly ethyl acetate or butyl acetate.

SThe solvents can be used as a mixture with water.

Monobutyl tin tricarboxylates can be synthesised easily by the reaction of monobutyl tin oxide with carboxylic acids or carboxylic acid anhydrides. The monobutyl tin tricarboxylate can be dissolved in the desired solvent or solvent mixture. No 25 precipitates are formed, even after prolonged standing. Concentrated solutions can readily be diluted again to the use concentration.

If carboxylates are used for the inventive method, the monobutyl tin tricarboxylates should be contained in the solutions in such amounts, that the latter have a tin content from 100g/L up to a maximum of 450g/L and preferably of 200g/L to 300g/L.

30 The inventive method is to be described in greater detail by the following examples, it being understood that the examples are provided by way of illustration and not by way of limitations. The formation of the tin oxide layer on the outer surface of bottles is shown first, after which the thickness and uniformity of the tin oxide layers obtained are investigated.

Example 1 a) Preparation of the Tin-IV Oxide Laver White-glass bottles, which have not been coated and have a capacity of 250mL, are heated to 560 0 C in a muffle furnace. After the bottle is removed from the tempering furnace, it is vapour-coated from a distance of about 35cm with the experimental solution, ~^l0 which contains monobutyl tin triacetate in ethanol and has a tin content of 220g/L. A hot OT 0 [N:\L1BC100397:KEH current of air is passed over this solution. The temperature of the current of air is about 280°C and the vapour coating takes about 8 seconds.

The bottle is held here at the neck and is rotated at about 60 rpm.

After they are coated, the bottles are returned immediately to the muffle furn-ce, heated to 560 0 C and cooled continuously over a period of 12 hours to room temperature.

b) Determination of the Thickness of the Coating Layer The thickness of the tin-IV oxide layer on the glass surface is determined with a HOT END COATING METER of the AGR company. This measurement is an infrared reflection measurement and is carried out at various levels 1.5, 2, 2.5, 3, and inches from the glass bottom) of the surface of the bottle. The measuring instrument scans the whole periphery of the bottle at each of these levels.

Figure 1 shows the tin-IV oxide layer of three white glass bottles coated by the inventive method. The homogeneous structure of the layers can be recognised clearly on the glass walls. This shows that monobutyl tin tricarboxylate solutions decompose uniformly, as required for their technical use, and are thus suitable for hot-end coating.

The use of industrial hot-end coating hoods in the glassworks ensures uniform coating of the surface in order to achieve a tin oxide layer by vapour deposition under actual production conditions.

In Figure 1, the thickness of the tin-IV oxide layer is shown in CTU (coating S 20 thickness units) for the entire rotated surface of the bottle for three white-glass bottles Scoated with ethanolic monobutyl tin triacetate solutions.

CTU is a conventional, industrial unit, 1 CTU corresponding approximately to 0.25nm.

Example 2 25 a) Preparation of the Tin-IV Oxide Layer The procedure of Example 1 is followed. Monobutyl tin tripropionate, in ethanolic solution, is used as layer-producing tin compound. The vapour-deposition phase requires 12 seconds.

Sb) Determination of the Thickness of the Coating Layer 30 The determination is carried out as in Example 1.

The thickness of the tin-IV oxide layer over the whole of the rotated surface of the bottle is shown in Figure 2 for a white-glass bottle coated with an ethanolic monobutyl tin tripropionate solution.

Example 3 a) Preparation of the Tin-IV Oxide Laver The procedure of Example 1 is followed. Monobutyl tin trihexanoate in ethanolic solution is used as the layer-producing tin compound. The vapour-deposition phase W RAa eauires 20 seconds.

IN:\LIBC100397:KEH b) Determination of the Thickness of the Coating Laver The determination is carried out as in Example 1.

The thickness of the tin-IV oxide layer over the whole of the rotated surface of the bottle is shown in Figure 3 for a white glass bottle coated with an ethanolic monobutyl tin trihexanoate solution.

Example 4 a) Preparation of the Tin-IV Oxide Layer The procedure of Example 1 is followed. Monobutyl tin triacetate, in pure form, is used as the layer-producing tin compound. For applying the monobutyl tin triacetate, a hot current of air, laden with monobutyl tin triacetate, is directed onto the rotating bottle.

The temperature of the air current is about 280°C. The vapour-depo ition phase requires 8 seconds. The heat treatment of the treated bottle is carried out as described in Example 1.

b) Determination of the Thickness of the Coating Layer The determination is carried out as in Example 1.

The thickness of the tin-IV oxide layer in CTU over the whole of the rotated bottle surface is shown in Figure 4 for a white-glass bottle coated with vapour-deposited monobutyl tin triacetate. The non-uniform coating over the height of the bottle results from the rigid vapour-deposition apparatus and the low air velocity. On an industrial 20 scale, the vapour-deposition hoods guarantee uniform coating of the hollow glass due to their high air turbulence.

1N:\LIBC100397:KEH

Claims (7)

1. A method for coating a hollow-glass object by applying monobutyl tin triacetate in solution in an organic solvent on a surface of the glass object heated to 500°C to 600 0 C, the monobutyl tin triacetate being pyrolysed with the formation of a thin tin oxide layer, the method comprising depositing, in vapour form, on the glass surface, monobutyl tin triacetate in solution in an organic solvent having a boiling point below 180 0 C.

2. The method of claim 1 wherein the monobutyl tin triacetate is in a solution of an organic solvent selected from an alcohol, ketone, ester or a mixture of the organic solvent with water.

3. The method of claim 1 or 2, wherein solutions having a tin content between 100g/L and 450g/L are deposited, in vapour form.

4. The method of claim 3, wherein solutions having a tin content between about 200g/L and 300g/L are deposited, in vapour form.

5. A method for coating a hollow-glass object by applying monobutyl tin triacetate in solution in an organic solvent on a surface of the glass object, which method is substantially as herein described with reference to Example 1.

6. A hollow glass object coated by the method of any one of the preceding claims. 20

7. The object of claim 6 wherein said object is a container. o Dated 25 July, 1996 Th. Goldschmidt AG 25 Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON IN:\LIBCi00397:KEH *A4 SO* *J /VT L* !1__1 *LB]037:E Method for Hot-End Coating of Hollow Glass Abstract A method is described for the hot-end coating of hollow- glass objects by the application of tin compounds, optionally dissolved in organic solvents, on the surface of s hollow glass objects heated to 500 0 C to 600 0 C, the tin compounds being pyrolysed with the formation of thin tin oxide layers. For this method, monobutyl tin tricarboxylates, which can be dissolved in organic solvents having a boiling point below 180°C, are vapour deposited on the glass surfaces. No Figure IN:\LIBC100397:JOC 0 of 7