GB2067540A - Improved method for applying an inorganic titanium coating to a glass surface - Google Patents

Abstract

An inorganic titanium coating, such as a hot end coating for glass containers, is applied to a glass surface by contacting the glass surface, which is at an elevated temperature, for example at least 150 DEG C, with a mixture of a tetraalkyl titanate such as tetraisopropyl titanium, with a normally-liquid hydrocarbon such as kerosene.

Description

SPECIFICATION Improved method for applying an inorganic titanium coating to a glass surface This invention relates to an improved method for applying an inorganic titanium coating to a glass surface. More particularly, this invention is concerned with an improved method for applying an inorganic titanium hot end coating to a glass container.

It has long been known that inorganic coatings can be applied to a glass surface by contacting a hot glass surface with a metal bearing compound which decomposes to form what is believed to be a metal oxide layer on the surface of the hot glass. Processes of this type were disclosed by Lyle in U.S. Patent No. 2,375,482 for imparting an iridescent finish to glass.

More recently, processes of this type have been adapted for use in protective coatings for glass containers, particularly, beverage bottles and other similar containers. In these processes glass containers, such as glass bottles, while still hot from the bottleforming equipment and before passage through the annealing lehr, are treated with a thermally-decomposabie metal compound, such as stannic chloride or titanic chloride, under conditions such that a thin coating is formed on the container surface. This coating usually is thinner than that taught by Lyle, and serves to bond a lubricious organic polymer or wax coating applied to the container surface after the container exits from the lehr.This combination of metal oxide "hot end" coating and organic "cold end" coating has been found useful in improving the scratch resistance and lubricity of glass containers.

Although this combined coating has been found useful, the generally employed methods of applying a hot end coating have several drawbacks. Generally anhydrous compounds, especially anhydrous stannic or titanic chloride, were employed which led to numerous problems. First, it was necessary to entrain the metal halide vapors in a dry air stream, which normally is accomplished by bubbling dry air through a liquid metal halide. If moisture should be introduced into the resulting air stream, a precipitate results which may inhibit the flow of entrained metal halide vapors thereby causing a reduction in the amount of coating material supplied to the application chamber. Furthermore, reactions between the metal halide and water in the atmosphere or the pyrolysis of the metal halides results in a reaction product which is corrosive to the equipment employed in the production of glass articles.The reaction product also is noxious in odor, which often creates undesirable working conditions in the hot end of glass manufacturing plants. Other reaction products are particulate materials which are difficult to capture.

Next, it is difficult to ensure formation of a uniform hot end coating when anhydrous metal halide fumes are used because they can react with moistures in the atmosphere before contacting the glass surface. The results are non-uniform coating thickness and poor bottle-tobottle reproducibility. Moreover, the loss of metal halide through such a reaction seriously reduces the efficiency of the use of the expensive metal halide reagent.

Finally, it is essential to prevent formation of a metal oxide coating on the finish, or mouth, of bottles particularly to avoid corrosion of bottle caps and high removal torques. This control is difficult to achieve with air streams containing entrained metal halide vapors, especially with the so-called "stubby" beer bottles which are commonly employed today.

To some extent, these problems can be avoided through use of sprays of aqueous or alcohol solution of tin halide hydrates, as is disclosed in U.S. Patent No. 3,819,346. However, such solutions are highly acidic and special equipment are required to handle the corrosive liquids.

ThesE coating materials also create noxious and corrosive reaction products upon their pyrolytic decomposition.

Not only have inorganic compounds, such as metal halides, been employed, but considerable effort has been devoted to the use of organo-metallic compounds. For example, Deyrup, in U.S.

Patent No. 2,831,780 issued April 22, 1958, discloses applying vapors of a metallo-organic compound such as tetraisopropyl titanate to hot glass (450 -600 C). According to Deyrup the corresponding inorganic compounds are either too heat stable or insufficiently volatile without decomposition to be suitable for such use. Subsequently, Gray et al, in U.S. Patent No.

3,004,863 described a process in which aqueous solutions of certain aqueous acid-soluble titanates were applied to glass at room temperature and the glass was thereafter annealed, at which time the titanium oxide coating was formed. Still more recently, Green et al, in U.S.

Patent No. 3,667,926 issued June 6, 1 972, disclosed a process wherein an aqueous solution of a water-soluble titanium composition was sprayed onto hot glass. As was the case with Deyrup and Grey et al, Green et al employed solutions of organo-titanium compounds.

U.S. Patent No. 3,387,994 to Dunton et al discloses that an improved process for applying a titanium coating to glass comprises spraying a heated glass surface with an inert, non-aqueous organic solvent solution of a titanium ester complex. According to the patent, the ester complex is the reaction product of one mole of a tetraallcyl titanate, e.g., tetraisopropyl ittanate, and one mole of a chelating agent, e.g., acetylacetone. Also according to the patent, the nature of the solvent can vary widely, and includes liquid hydrocarbons and halogenated derivatives and alcohols. Isopropyl alcohol is preferred, and was used in all of the Examples.It has been found, however, that the preferred process of Dunton et al using, e.g., tetraisopropyl titanate chelated with acetyl acetonate, in an alcohol solution does not yield a commercially practicable process.

As was the case with the inorganic compounds, the use of organo-metallic compounds was not entirely satisfactory. For example, the vapors of anhydrous organometallic compounds, such as tetraisopropyl titanate, react with moisture in the atmosphere and decompose. The results are non-uniform coating thicknesses and poor bottle-to-bottle reproducibility. When trying to spray liquid anhydrous organo-metallic compounds, the liquid reacts with moisture in the atmosphere and forms a solid deposit which tends to plug spray nozzles.

Furthermore, the techniques previously employed to apply such compounds typically form finely dispersed particles which are entrained in the air stream, and are difficult to remove from it in a simple and economic fashion.

It is an object of this invention to provide an improved method for applying a metal-containing coating to a glass surface, and especially to provide a simple, economical process which is free of the problems associated with the use of anhydrous and various alcohol or aqueous solutions of metal halide reagents.

These and other objects of this invention, which are evident from the specification and claims, are achieved by spraying onto a heated glass surface a mixture of a tetraalkyl titanate with a normally liquid hydrocarbon.

The tetraalkyl titanate employed in accordance with this invention may be represented by the general formula: (RO)Ti wherein R is alkyl of from 1 to about 3 carbons, and preferably from 2 to about 3 carbons.

Although in theory the alkyl groups need not be the same, the commercially-available tetraalkyl titantes typically do have the same four alkyl groups. Suitable tatraalkyl titanates include tetramethyl titanate, tetraethyl titanate, tetrapropyl titanate, and tetraisopropyl titanate. Tetraisopropyl titanate is preferred.

The tetraalkyl titanates are generally available as technical products which are normally liquid, i.e., liquid under ambient conditions.

The hydrocarbon employed may be any aliphatic, cycloaliphatic or aromatic hydrocarbon which serves as a carrier for the tetraalkyl titanate. is normally liquid (i.e., is a liquid at room temperature), and forms a liquid composition containing the tetraalkyl titanate which can be applied to the glass surface. It is unclear whether the mixture of tetraalkyl titanate and liquid hydrocarbon is a true solution, or is a dispersion of the tetraalkyl titanate in the hydrocarbon.

When first formed, the mixture has the appearance of a true solution, and phase separation does not occur on standing. However, if the mixture is frozen and then thawed, phase separation does occur but the tetraalkyl titanate is easily redispersed in the hydrocarbon carrier by stirring.

It is preferred that the mixture be sufficiently fluid that it can be sprayed. To this end, hydrocarbons which form a mixture having a viscosity of less than about 100 centipoises at room temperature are preferred, with those forming a mixture having a viscosity of less than about 10 centipoises being especially preferred. Suitable hydrocarbons include hexane, heptane, octane, cyclohexane, benzene, toluene, xylene, and the like. Petroleum fractions, such as gasoline and kerosene may be employed. The critical element is that the hydrocarbon which is employed be hydrophobic. It is believed that such a hydrocarbon avoids or minimizes the hydrolysis reaction which polymerizes tetraalkyl titanates and contributes to the nozzle plugging problem. Kerosene is preferred as the hydrocarbon because it is relatively inexpensive, readily available, and it can be purchased in an odorless form.

The use of solutions of tetraalkyl tita,.ates in anhydrous, or substantially anhydrous solvents, for coating purposes has been described by Haslam in U.S. Patent No. 2,768,909 issued October 30, 1956. In that patent, the tetraalkyl titanate solution is applied to a substrate at ambient temperature, and dried by evaporation of the solvent while exposed to the atmosphere.

According to the patent, moisture present in the atmosphere hydrolyzes the tetraalkyl titanate, and causes it to polymerize to form an insoluble transparent, adherent, flexible polyoxide film.

The resulting film, however, is not the same type of coating as is obtained through thermal decomposition of-a tetraalkyl titanate. In particular, it is not as well bonded to the glass and thus does not provide as effective a protective coating as is obtained through thermal decomposition.

As has been noted above, Dunton et al in U.S. Patent No. 3,387,994 describe the use of non-aqueous solutions in certain tetraalkyl titanate complexes. According to this patent, the use of such complexes is superior to use of solutions containing uncomplexed tetraalkyl titanate. It has been found in accordance with this invention that mixtures of tetraalkyl titanates with hydrocarbons are far superior to the preferred alcoholic solutions of complexes such as acetylacetonates in providing a commercially practical process capable of operating for long periods of time while applying a satisfactory titanium coating. In particular, the use of tetraisopropyl titanate/acetylacetonate complexes is characterized by nozzle clogging, especially in a humid atmosphere, which precludes sustained operation.In this respect, it is noted that Dunton et al used one-to-two second spray bursts. In contrast, when using tetraisopropyl titanate/kerosene mixtures in accordance with this invention under commercially-encountered conditions (relative humidity of 75% and higher), sustained operations of up to 8 days are possible without nozzle clogging. When a mixture of a tetraisopropyl titanate-acetylacetonate complex in kerosene is employed, however, nozzle clogging was encountered within 20 minutes at 60 percent relative humidity.

The concentration of the tetraalkyl titanate in the mixture is not highly critical, provided sufficient titanate is present to permit formation of a titanium coating of adequate thickness on the glassware. To some extent, this can be controlled by varying the rate of application of the mixture to the glass surface, with higher rates of application being required with more dilute mixtures. In any event, the concentration of the titanate in the mixture, and the rate of application of the mixture should be sufficient to provide an inorganic titanium coating having a thickness of at least about 25 CTU's and preferably at least about 40 CTU's, as measured with an American Glass Research, Inc. Hot End Coating Meter. The maximum thickness is not critical, although thickness in excess of about 100 to about 120 CTU's ordinarily have an iridescence which may be considered to be undesirable.It is believed that the hydrocarbon carrier is effective because it is hydrophobic, and thus it tends to inhibit the absorption of water by the tetraalkyl titanate solution. Accordingly, the amount of hydrocarbon should be sufficient to inhibit the absorption of water by the mixture. In general, mixtures wherein the concentration of titanate is in the range of from about 25 to about 99 volume percent have been found useful, and permit practical rates of application. Preferred concentrations are in the range of from about 40 to about 80 volume percent, with a concentration of from about 50 to about 75 volume percent being especially preferred.

The hydrocarbon composition containing the titanate is readily applied by spraying onto the surface of glassware which has been heated at a temperature above the thermal decomposition point of the compound in question. Such procedures are well known to the art, and do not per se form a part of this invention.In general, however, the temperature of the glassware should be at least 1 50,C (300 F), preferably at least 3715C (700 F), and most preferably is in the range of from about 482go (900oF) to about 593 C (1100 F). It has been found that the solid reaction product of the use of such sprays is in the form of relatively large particles which are easily removed from the air stream in which they are entrained by simple filtration. Furthermore, the presence of noxious and corrosive hydrogen chloride vapors is avoided.

After application of the titanium hot end coating in accordance with the present invention, glassware may then be provided with a "cold end" coating in accordance with known techniques.

Example I Employing apparatus similar to that described in U.S. Patent No. 3,926,103, sold by American Glass Research, Inc. as the AGR Pentahood, a mixture of 75 volume percent tetraisopropyl titanate and 25 volume percent kerosene was sprayed onto glass bottles which had been heated to a temperature of 538 C (1000 F). Two series of tests were run, one at a flow rate of 40 and the other at a flow rate of 60 (Gilmont No. 2 flowmeter setting). In each series, the nozzle-to-glass distance was varied from 2 to 6 inches. The average coating thickness in CTU's was determined with an AGR Hot End Coating Meter. The results of these tests are summarized as follows: Nozzle-to-Glass Average Coating Thickness (CTU) Distance, in.Flow = 40 Flow = 60 2 < 200 < 200 3 88 < 200 4 38 132 5 5 28 85 6 15 45 The optimum coating at a flow rate of 40 was obtained at a nozzle-to-glass distance of 3 inches, whereas, at a flow rate of 60, the optimum coating was obtained at a nozzle-to-glass distance of about 5 inches.

Example II An in-plant trial was conducted by applying a 75 percent by volume mixture of the tetraisopropyl titanate in kerosene in an AGR Pentahood, as described in U.S. Patent No.

3,926,1 03, using a flowmeter setting of 40 and a nozzle-to-glass distance of from about 2 to about 4 inches. The oxide coating thickness on 6 randomly selected bottles was measured with an AGR Hot End Coating Meter. For each bottle, the thickness was measured at 45 intervals around the bottle at the upper-, mid- and lower-sidewall.The average thickness values, in CTU, are summarized as follows: Metal Oxide Thickness, CTU at Various Angular Positions 05 45 90 135 180 225' 270 335t Upper Sidewall 12 12 10 12 26 39 27 12 Mid Sidewall 35 71 40 27 77 123 86 22 Lower Sidewall 37 65 42 28 57 74 50 28 Example 111 Employing procedures and equipment similar to those described in Example I, a 75 percent by volume mixture of tetraisopropyl titanate in kerosene was sprayed at a nozzle setting of 40 and a nozzle-to-glass distance of 4 inches onto glass bottles which had been heated at various temperatures.The variation in average coating thickness with glass temperature is summarized as follows: Coating Temperature, C ( F) Thickness, CTU 149 (300) 95 204 (400) 80 260 (500) 80 316(600) 80 371(700) 95 427 (800) 35 482 (900) 45 538(1000) 45 593 (1100) 30 Example IV In an effort to compare the efficiency of tetraisopropyl titanate (TPT) and a chelate of tetraisopropyl titanate with acetylacetonate (TPT-AA)," mixtures of equal parts by volume of each titanium compound and kerosene were sprayed onto glass bottles heated at a temperature of 525 C i 25 C. The heated bottles were placed on a rotating turntable, and the mixture were applied for one revolution of each bottle.The coating was applied using a Spraying System 1 /8" JBC internal mix nozzle equipped with a 60 atomization tip, a flowmeter setting of 40 (approximately 6 ml/mn), air atomization pressure of 20 psi, tank pressure of 10 psi and a nozzle-to-glass distance of 3 inches.

*Supplied as a 75% solution in isopropanol by duPont as "Tyzor" AA.

Coating thicknesses were measured on an AGR Hot End Coating Meter, and were repeated three times with six bottles per sample set (i.e., for a total of 18 bottles for each coating system). The average coating thicknesses which were observed were as follows: Titanium Coating Thicknesses, CTU Compound Minim m Maximum Average TPT-AA 50 135 80 TPT 200 + 200 + 200 f These data clearly indicate that the TPT/kerosene mixture is much more efficient than the TPT-AA/kerosene system in applying an inorganic titanium coating to a heated glass surface.

Not only is the thickness of the coating much less with TPT-AA, but it is very non-uniform, as is indicated by a ratio of maximum to minimum thickness of 135 -, or about 2.7:1.

50 Normally, there should be little or no variation of coating thickness when using a rotating turntable. The large variation in coating thickness obtained with TPT-AA is believed due to clogging of the spray nozzle when the acetylacetonate compound is used.

Claims (8)

1. A method for applying a metal-containing coating to a glass surface by contacting said surface at elevated temperature with a tetraalkyl titanate in admixture with a normally-liquid hydrocarbon.

2. A method according to claim 1 wherein the concentration of the tetraalkyl titanate is from about 25 to about 99 volume percent.

3. A method according to claim 1 or claim 2 wherein said hydrocabon is a saturated aliphatic hydrocarbon.

4. A method according to any preceding claim wherein said hydrocarbon is a petroleum fraction.

5. A method according to any preceding claim wherein the concentration of said tetraalkyl titanate in said mixture is from about 40 to about 80 volume percent.

6. A method according to any preceding claim wherein said tetraalkyl titanate is tetraisopropyl titanate.

7. A method according to any preceding claim wherein said hydrocarbon is kerosene.

8. A method according to claim 1 substantially as described herein with reference to any one of the Examples.