Preparation and method for coating glass vessels

Abstract

Glass vessels are coated by spraying a solution containing 86 to 1,290 g/L of (HO).sub.x Sn(C.sub.2 O.sub.4).sub.y on the 500.degree. to 600.degree. C. hot outer surface of the vessels. The solution may contain oxalic acid, HCl and a portion of the (HO).sub.x Sn(C.sub.2 O.sub.4).sub.y compound may be substituted by a compound (OH).sub.2 SnCl.sub.2. The coatings are uniform.

Description

FIELD OF INVENTION

The invention generally relates to the surface improvement of hollow glass bodies--hereinafter referred to as glass vessels--and is particularly directed to a liquid tin compound comprising a preparation suitable for spraying onto hot glass vessels to form a thin coating thereon.

Considered from another aspect, the invention is concerned with a coating method for applying tin compounds to the exterior surface of a glass vessel to improve its characteristics and the vessel obtained by the method.

More specifically, the invention provides a method for coating glass vessels by spraying a solution of tin compounds in water, alcohol or water/alcohol mixtures on the 500.degree. to 600.degree. C. hot outer surface of the glass vessels.

BACKGROUND INFORMATION AND PRIOR ART

It is known to coat thin tin oxide layers on glass surfaces by exposing the heated glass to a vaporized tin compound. The tin compound may be applied as a vapor or as a fine spray which contains a dissolved tin compound.

For example, U.S. Pat. No. 3,414,429 discloses a method for applying metal oxide layers on glass containers, wherein tin(IV) halides, such as tin tetrachloride, are used as tin compounds. However, these compounds hydrolyse readily in the presence of mere traces of moisture, with the formation of highly corrosive compounds. Since only a small portion of the tin halides introduced into the coating chamber is actually deposited on the glass surface and the unused portion of the tin halides cannot be recycled without considerable expenditure, the tin halides have only a limited suitability for coating or surface improving glass. Since tin tetrachloride, when used, generally is stabilized with additional hydrogen chloride, at least four chloride atoms per tin atom are obtained, which contaminate the effluent or waste water in the form of the chlorides. Moreover, because of spontaneous decomposition of tin tetrachloride, it is not unusual that a nonuniform build-up of the tin oxide layer takes place which results in optically confusing interferences.

If tin dichloride is used instead of tin tetrachloride, the amount of chloride that is to be disposed of is theoretically reduced. However, because of the hydrolytic instability of the aqueous solutions of tin dichloride, also in this instance hydrogen chloride has to be added to these solutions. As a result, the amount of chloride rises again above the value of 1 Sn: 2 Cl. In addition, the problem of the increased corrosion of the equipment by the hydrochloric acid-containing tin dichloride solution remains.

German Patent 25 41 710 discloses a method for applying a tin(IV) oxide layer on a glass container by the pyrolysis of a vaporized or finely divided, liquid tin compound on the surface of glass having a temperature of 450.degree. to 600.degree. C. For this method, a mono-organo tin trichloride of the general formula RSnCl.sub.3, wherein R is an alkyl radical with 1 to 8 carbon atoms, is used as tin compound. Preferably, butyl tin trichloride is used as monoalkyl tin trichloride. However, organo tin compounds are toxic products, which must be identified as such and the use of which requires special care. With respect to pollutant emission, it is a disadvantage that three chlorine atoms per tin atom are released and must be disposed of.

The glass containers provided with a tin(IV) oxide layer (hot end coated) can subsequently be additionally provided with a thin film of a natural wax or a synthetic polymer (cold end coating). Such a coating is usually transparent and makes the glass container even more resistant to scratching and abrasion, even when said container comes into contact with alkaline cleaning agents.

OBJECTS OF THE INVENTION

The present invention is concerned with this technical problem of coating the outer surface of glass vessels. A particular aspect of the invention is to provide solutions of tin compounds which are easily accessible, have a long shelf life and are not toxic or toxic to a slight extent only. Moreover, it is an object of the invention that upon the thermal decomposition of these compounds on hot glass surfaces, uniform tin oxide layers are formed on which the cold end coating materials (waxes, polyolefins, etc.) adhere well.

It is also an object of the present invention to provide a method for coating and thus surface improving glass vessels.

SUMMARY OF THE INVENTION

It has been ascertained that the objects can be attained by spraying a solution of tin compounds in water, alcohol or water/alcohol mixtures on the 500.degree. to 600.degree. C. hot outer surface of the glass vessels, with the distinguishing feature that the solution is sprayed which contains 86 to 1290 g/L of a compound of the general formula (HO).sub.x Sn(C.sub.2 O.sub.4).sub.y, 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.

Preferably, the subscript x has a value of 1.5 to 3 and the subscript y a value of 0.5 to 1.25.

Aqueous solutions of (HO).sub.x Sn(C.sub.2 O.sub.4).sub.y can be easily prepared in high concentrations by preferably the electrolytic oxidation of metallic tin in solutions acidified with oxalic acid. The solutions are resistant to hydrolysis. No precipitate is formed even after prolonged standing. Thickened, highly concentrated solutions can easily be diluted again to the concentrations at which they are to be used. The solutions are free of chlorine which is bound to tin.

With the inventive method, uniform tin oxide layers with a thickness of about 10 to 30 nm are obtained on the glass surfaces. During a subsequent cold end coating, the wax or polyolefin layers applied adhere well and withstand a larger number of washing cycles than was possible according to the previous state of the art.

A modification of the inventive method is that a solution is sprayed which additionally contains 0.01 to 0.5 moles of oxalic acid per mole of (HO).sub.x Sn(C.sub.2 O.sub.4).sub.y. This is of advantage particularly when compounds having the formula (HO).sub.x Sn(C.sub.2 O.sub.4).sub.y are used, the y value of which is low and falls within the range from about 0.1 to 0.5. Due to the addition of the oxalic acid, the formation of particularly uniform tin oxide layers is promoted and the adhesion of the layers to the substrate is improved even more.

The development of the tin oxide layer can be improved further by spraying on a solution, which additionally contains 0.01 to 0.5 moles of HCl. Due to this slight addition of HCl, the effluent and emission problems are still kept within limits; however, clearly thicker layers of SnO.sub.2 are attained.

It has been ascertained that it is of particular advantage if a solution is sprayed in which up to 49.9 mole percent of the compound (HO).sub.x Sn(C.sub.2 O.sub.4).sub.y is replaced by equimolar amounts of the compound (OH).sub.2 SnCl.sub.2. With this particularly preferred embodiment of the inventive method, extremely uniform tin oxide layers up to 100 nm thick are obtained. Moreover, the solutions used are resistant to hydrolysis and show no deposits even after prolonged standing.

The tin oxalate of formula (HO).sub.x Sn(C.sub.2 O.sub.4).sub.y, used pursuant to this embodiment of the inventive method, can be synthesized like the tin oxydichloride by electrolytic oxidation of metallic tin in aqueous solutions, which have been acidified with oxalic acid.

A further aspect of the invention are the preparations for carrying out the inventive method. Such a preparation is characterized in that it consists of an aqueous solution which contains the compound (HO).sub.x Sn(C.sub.2 O.sub.4).sub.y, 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, in such an amount that the tin content of the solution is 0.45 to 4.5 moles/L. This corresponds to a concentration of 86 to 1,290 g/L of (HO).sub.x Sn(C.sub.2 O.sub.4).sub.y. Moreover, as stated above, up to 49.9 moles percent of the compound (HO).sub.x Sn(C.sub.2 O.sub.4).sub.y can be replaced by equimolar amounts of the compound (OH).sub.2 SnCl.sub.2. In that case, the ratio of Sn to Cl preferably is at least approximately equal to 1, that is, 49.9 mole percent of the compound (HO).sub.x Sn(C.sub.2 O.sub.4).sub.y are replaced by (OH).sub.2 SnCl.sub.2. Furthermore oxalic acid can be added to the solution in such amounts that the solution additionally contains 0.01 to 0.5 moles of oxalic acid per mole of (HO).sub.x Sn(C.sub.2 O.sub.4).sub.y . The addition of oxalic acid is to be recommended particularly when the value of the subscript y in the compound (HO).sub.x Sn(C.sub.2 O.sub.4).sub.y lies in the lower range from 0.1 to about 0.5.

A further preferred preparation additionally contains 0.01 to 0.5 moles of HCl per mole of (HO).sub.x Sn(C.sub.2 O.sub.4).sub.y. In much the same way as with the addition of (OH).sub.2 SnCl.sub.2, the uniform build-up of the tin oxide layer is also favored by the addition of HCl.

Examples of the inventive preparations are solutions of the following composition:

______________________________________ Oxalic(HO).sub.x Sn(C.sub.2 O.sub.4).sub.y Acid (OH).sub.2 SnCl.sub.2 HClSolution x = y = g/L g/L g/L g/L______________________________________1 2 1 340 -- -- --2 3.2 0.4 980 -- -- --3 2 1 820 60 -- --4 2 1 550 93 -- --5 3.2 0.4 490 -- 226 --6 3.2 0.4 490 50 226 --7 2 1 334 -- -- 10______________________________________

The inventive method is further described in more detail by the following examples, it being understood that these examples are given by way of illustration and not by way of limitation. The method of coating the outersurface of bottles is shown first and the coatings obtained are examined for thickness of the layer and for uniformity. The coated bottles are subsequently cold end coated and the resistance to washing of the cold endcoatings is determined.

DESCRIPTION OF THE METHOD

Uncoated white glass bottles of a volume capacity of 250 mL are heated in amuffle furnace to 560.degree. C. After the bottles are removed from the tempering furnace, they are each sprayed at a distance of about 55 cm withthe test solution. For this purpose, the bottles are held at the neck and rotated at 60 rpm.

The spraying lasts about 4 seconds. The amount of coating material applied in each case is 4 mL. The solution to be applied is sprayed with a spray gun using compressed air at 3.5 bar.

After being coated, the bottles are immediately returned to the muffle furnace at 560.degree. C. and cooled continuously over a period of 12 hours to ambient temperature.

DETERMINATION OF THE LAYER THICKNESS

The thickness of the tin(IV) oxide layers is determined with a HOT END COATING METER of the AGR Company. This method involves an infrared reflection measurement. This measurement is carried out from the bottom ofthe bottle at heights of 1, 1.5, 2 and 3 inches. At each height, the measuring instrument scans the whole circumference of the bottle and carries out a measurement at each degree (360 measurements/circumference).

COLD END COATING

To determine the adhesion of cold end coating agents, the coated bottles are sprayed with a 1:40 diluted solution of a cold end coating agents based on a polyethylene wax emulsion (commercially available under the name of TEGOGLAS-RP-40.TM.). For this purpose, the bottles are heated to 120.degree. C. and placed on a plate rotating at 30 rpm. By means of a spray gun (3.5 bar), 2 mL of the cold end coating solution is applied.

DETERMINING THE SCRATCH RESISTANCE

Two identical, coated glass bottles are fastened in a holding device so as to be offset 90.degree. to one another and rubbed against one another witha pressure of 5.5 bar on a 10 cm rubbing section. The number of lifts or strokes until scratching noises or scratches can be perceived acousticallyand optically is a measure of the scratch protection of the cold end coating solution. The bottles are tested in the wet as well as in the dry state for scratch resistance.

WASHING LIQUID STABILITY

The resistance of the coatings is determined in a dishwasher (Miele-Desinfektor G 7736), which has been modified for this purpose. For this test, the bottles are washed for 10 minutes at 85.degree. C. with a 2% sodium hydroxide solution.

HOT END COATING

______________________________________ Film Thickness/CTU.sup.1) Measurement Zone/InchesSolution 1 1.5 2 3______________________________________1 29 22 33 232 29 30 31 293 41 39 39 404 33 32 29 235 48 39 38 416 53 84 55 677 22 29 30 26______________________________________ .sup.1) 1 CTU = 0.3 nm

COLD END COATING

All the test solutions applied have an excellent primer effect for the coldend coating agents employed. The cold end coating in the case of chloride-free hot end coating solutions has a scratch resistance of more than 5 lifts or strokes, while the test of the chloride-containing variation does not yet show any negative effects after 10 lifts or strokes. After two washing cycles with sodium hydroxide solution, the scratch resistance is reduced by less than 10% relative to the initial number of lifts or strokes.

Claims

1. A preparation suitable for coating hot glass vessels to improve the exterior surface of the vessels, said preparation comprising a solution of the compound (HO).sub.x Sn(C.sub.2 O.sub.4).sub.y wherein x has a value of 0.2 to 3.8, y has a value of 1.9 to 0.1 and (2y+x)=4, in such an amount that the Sn content of the solution is 0.45 to 4.5 moles/L.

2. The preparation of claim 1, wherein the solution also contains 0.01 to 0.5 moles of oxalic acid per mole of (HO).sub.x Sn(C.sub.2 O.sub.4).sub.y.

3. The preparations of claims 1 or 2, wherein the ratio of Sn to Cl in the solution is at least approximately equal to 1.

4. The preparation of claim 1, wherein the solution also comprises a compound (OH).sub.2 SnCl.sub.2, the amount of (OH).sub.2 SnCl.sub.2 in the solution being such that it replaces equimolarly up to 49.9 mole % of the compound (HO).sub.x Sn(C.sub.2 O.sub.4).sub.y.

5. The preparation of claim 4, wherein the solution also contains 0.1 to 0.5 moles of oxalic acid per mole of (HO).sub.x Sn(C.sub.2 O.sub.4).sub.y.

6. The preparation of claims 1, 2 or 3, wherein the solution also contains 0.01 to 0.5 moles of HCl per mole of (HO).sub.x Sn(C.sub.2 O.sub.4).sub.y.

7. The preparation of claims 1, 2 or 3, wherein the liquid phase of the solution is water, a mixture of lower aliphatic alcohols and water, or ethanol.