NZ264561A - Method for coating a glass object with tin oxide - Google Patents

Description

k f- /, r r ■' Patents Form 5 \ \ Priority Date(s) !g\; Specification riled: XX*** \ Hn"'! puUticatio" Date P.O. Journal. No . 2.6 JU.U .1995. : ... f P ATr*!T.:rr:'Cr N.Z. No.

NEW ZEALAND Patents Act 1953 COMPLETE SPECIFICATION METHOD FOR THE HOT-END COATING OF HOLLOW GLASS OBJECTS We, TH GOLDSCHM1DT AG, Goldschmidtstrasse 100, D-45127 Essen, Germany do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- - I - 2 6 4 5 6 1 FIELD OF THE INVENTION The invention relates to a method for the hot-end coating of hollow glass objects by vapor deposition of tin compounds, optionally dissolved in organic solvents, on the outer surface of hollow glass objects, heated to 500* to 600*C, the tin compounds being pyrolyzed 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 vapor or as a spray, which contains a dissolved tin compound.

BACKGROUND INFORMATION AMD PRIOR ART In the US—C-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 hydrolyze 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. 2^561 9 • Per atom of tin, tin-IV chloride contains four atoms of chlorine and, for industrial applications, generally is stabilized 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.

The published patent specification Gli 1,520,124 discloses a method, for which the tin-IV oxide layer is produced by pyrolysis of a mono-organo tin trichloride of the general formula RSnClj, 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 vapor 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 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. 26£f56( r * The published patent specification US 5.314.534 discloses a method. for which hollow glass objects are coated by spraying on a solution, which contains 100 to 1,000 g/L of (OH)2SnCl2. Up to 50 mole percent of the compound can be replaced by equimolar amounts of the general compound (OH)xSn(C2Ojy, 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 publication C-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 th'-} 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 15 nm 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). 2 5 4 5 6 1 OBJECT or THE INVEMTIflH 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, at least, contain only minimal amounts of chloride. The tin oxide layer produced is to be as homogeneous as possible. gWMtfff TBS WYEWTISE Surprisingly, these requirements can be fulfilled by using the inventive method, which is characterized in that monobutyl tin tricarboxylates, which can be dissolved in organic solvents having a boiling point less than 180'C, are vapor deposited. In particular, the ability to vapor deposit these compounds and to produce tin oxide layers is surprising.

Preferably, carboxylates with up to 6 carbon atoms are vapor deposited as monobutyl tin tricarboxylates. The carboxylates can be linear or branched. Examples of suitable carboxylates are the acetates, propionates, butanatas, isobutanates, valerianates and hexanoates, the monobutyl tin triacetates, tripropionates and tributanates being particularly preferred. Mixed carboxylates, such as monobutyl tin diacetate 26^56 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 without solvents by means of a hot carrier gas on the surface of the glass objects that are to be coated. On the other hand, it is advisable to use the higher carboxylates with 4 to 6 carbon atoms in the form of their solutions, in order to obtain a uniform layer construction.

The homogeneity of the surface coating of hollow glass containers is ensured by tunnel-shaped vapor-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 vapor-deposition hood. Such coating hoods are state of the art and are described, for example in the 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, i-butanol, ketones, particularly acetone or butyl ethyl ketone and esters, particularly ethyl acetate or butyl acetate.

The solvents can be used as a mixture with water.

* A copy t ill is patent specification is available at the I'atcnl Ollice on iet.|iieil. -'545 SI Monobutyl tin tricarboxylates can be synthesized 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 precipitates are formed, even after prolonged standing. Concentrated solutions can readily be diluted again to the use concentrat ion.

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 100 g/L up to a maximum of 450 g/L and preferably of 200 g/L to 300 g/L.

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. 13 4 F. ' i . j EXAMPLE 1 a) Preparation of the Tln-IV oxide Laver White-glass bottles, which have not been coated and have a capacity of 250 mL, are heated to 560*C in a muffle furnace. After the bottle is removed from the tempering furnace, it is vapor-coated from a distance of about 35 cm with the experimental solution, which contains monobutyl tin triacetate in ethanol and has a tin content of 220 g/L. A hot current of air is passed over this solution. The temperature of the current of air is about 280'C and the vapor 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 furnace, heated to 560*C and cooled continuously over a period of 12 hours to room temperature. b) Determination of the Thickness of the Coating Laver 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, 1.5, 2, 2.5, 3, and 3.5 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 l shows the tin-IV oxide layer of three white glass bottles coated by the inventive method. The homogeneous structure of the layers can be recognized 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 vapor deposition under actual production conditions.

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

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

EXAMPLE 2 a) Preparation of the Tin-IV Oxide Laver The procedure of Example l is followed. Monobutyl tin tripropionate, in ethanolic solution, is used as layer-producing tin compound. The vapor-deposition phase requires 12 seconds. b) Determination of the Thickness of the Coating Laver The determination is carried out as in Example 1.

The thickness of the tin-rv 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 vapor-deposition phase requires 20 seconds. 2 * C 1 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. gjgWPMS 4 a) Preparation of the Tin-IV Oxide Laver The procedure of Example l 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 vapor-deposition 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 Laver The Determination is carried out as in Example 1. i ikfi \ 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 vapor-deposited monobutyl tin triacetate. The non-uniform coating over the height of the bottle results from the rigid vapor-deposition apparatus and the low air velocity. On an industrial scale, the vapor-deposition hoods guarantee uniform coating of the hollow glass due to their high air turbulence. 264 561 OIAIMfl

Claims (8)

WHAT WE CLAIM IS:

1. A method for coating a hollow-glass object by applying a tin compound, or its solution in an organic solvent, on a surface of the glass object heated to 500* to 600*C, the tin compound being pyrolyzed with the formation of a thin tin oxide layer, comprising depositing, in vapor form, on the glass surface, monobutyl tin tricarboxylate or its solution in an organic solvent having a boiling point below 180*C. depositing, in vapor form, the carboxylates having up to 6 carbon atoms. depositing, in vapor form, monobutyl tin triacetate, monobutyl tin tripropionate or monobutyl tin tributanate in solvent-free form.

2. The method of claim 1, comprising

3. The method of claim 1, comprising

4. The method of claim 1 or 2, cc depositing, in vapor form, a solution of monobutyl tin carboxylates comprising in alcohol , ketone ester or mixture thereof with water.

5. The method of claim 1 or 2, comprising depositing, in vapor form, solutions having a tin conten' substantially 100 g/L and 450 g/L. » 264 561

6. The method at claim 5, comprising depositing, in vapor form, solutions with a tin content between substantially 200 g/L and 300 g/L.

7. A method according to claim 1 substantially as herein described or exemplified.

8. A hollow-glass object coated in accordance with the method of any one of the preceding claims. - 14 - TH GOLDSCHMIDT AG By Their Attorneys HENRY HUGHES Per --rtfj.r \