MXPA97006302A - Process to produce a protective coating on a surface of a glass or ceramic article - Google Patents

Abstract

The present invention relates to a process for producing a protective coating on a surface of a glass or ceramic article, the coating has an improved resistance to aqueous caustic treatments. To carry out the process of the invention, a stream of an oxygenated carrier gas containing a precursor that can be thermally decomposed state oxides (SnO2) and a precursor that can be thermally decomposed silicon dioxide (SiO2) in a molar ratio of the first precursor with respect to the last of between 0.6 and 3.0, the precursors which are present in the evaporated form, and which further contains water vapor in an amount of at least 1 mole per 100 moles of the carrier gas, are caused to collide uniformly on the surface to be coated, the surface has a temperature which is above the decomposition temperatures of the precursors and is quantified at least 550 ° C, to deposit a protective coating comprising tin oxide and silicon, and the deposition is continued until that a thickness of coatings between 240 and 15.00 angstroms is obtained

Description

PROCESS TO PRODUCE A PROTECTIVE COATING ON A SURFACE OF ON GLASS OR CERAMIC ARTICLES Field of the Invention The present invention relates to the surface coating of glass or ceramic articles, in particular to glass containers such as bottles, which are proposed for repeated use after they have been washed with a caustic solution.

Background of the Invention The treatment of the surface of glass articles is already known to improve the resistance to abrasion. For example, US-A-4 144 362 discloses the coating of glass bottles with a thin film of tin oxide. Tin oxide coatings are obtained by exposing the surface of the glass, heated to a temperature between 450 ° C and 600 ° C, in an oxygen atmosphere, for example in air, to an organic tin compound in the form of steam or in a finely divided form. When contacted with the hot glass surface, the R? F.25458 tin compound is decomposed and oxidized to form a tin oxide coating. The coating technique described and illustrated in US-A-4 144 362 leads to the production of tin oxide coatings having a thickness of the order of 45-120 angstroms. According to US-A-4 130 673, a thin layer of a natural wax or of a synthetic polymer is applied on of a surface coating of tin oxide produced as described above after the coated article with the tin oxide it has been cooled to a temperature of 350 ° C or less. The combination of the two coating layers is said to reduce scratches and breakage of glassware during handling and processing. There are increasing efforts to use glass containers, for example glass bottles, over and over again. Before the containers can be filled, they are subjected to a strong washing treatment, using for example caustic solutions. After 5-15 wash cycles at 80 ° C using 1-4% caustic solutions, a tin oxide coating which has been produced as described above, will be completely removed.

First, after some wash cycles, the spots or coarse stains of the tin oxide coating give an unacceptably strong blue color. In the subsequent wash cycles, the coating shows gray spots and finally disappears. EP-A-0 485 646 claims the production of refillable glass bottles which are provided with a metal oxide coating and which could withstand an eight-hour treatment with a 4% caustic solution at 80 ° C. The treatment comprises tin oxide or titanium oxide and has a thickness of 400 to 1,000 angstroms. The coating is made by contacting a tin compound such as tin tetraeloride or dimethyl dichloride and tin or a titanium compound such as titanium tetraeloride, with a glass bottle which has an external surface temperature of 550 to 700. ° C. The thicker tin oxide coatings prepared according to EP-A-0 485 646 provide better protection against caustic bath than the thinner coatings known from the US patents described above. However, the tests that have been carried out by the present inventors show that these coarser coatings become rather dark after 2 to 6 hours of washing (using a 4% caustic solution at 80 ° C), making to less acceptable bottles for repeated, long-lasting use. As far as the titanium oxide coatings are concerned, it can be seen that the titanium starting compound is hard and difficult to handle and is very inefficient in its use. WO Patent No. 93/13393 describes a process for coating glass by chemical vapor deposition (CVD) using a composition comprising a mixture of a tin oxide precursor, a silicon oxide precursor and an accelerator, preferably triethyl phosphite. The composition is deposited at a rate greater than about 350 angstroms / second to form a coating which according to the Examples has a thickness of between 2,000 and 4,930 angstroms. The coating thus obtained can be combined with other layers to produce an article with specific properties such as emissivity, refractive index, resistance to abrasion or appearance, controlled. In example 7 a clear glass bottle is coated with a vapor mixture comprising a tin oxide precursor, a silicon oxide precursor, a triethyl phosphite and hot air, the molar ratio of the tin oxide precursor with with respect to the silicon oxide precursor it is 0.2. The vapor mixture is deposited for 10 seconds at an estimated deposition rate of about 200 angstroms / second to produce a magenta-blue film having a thickness of approximately 2,000 angstroms. Without the presence of triethyl phosphite, the deposition rate is about 50 angstroms / second. The present invention provides a process for producing a protective coating for glass or ceramic articles, the coating is highly resistant to caustic washing treatments. The process of the present invention also provides an improved coating for glass containers, the coating remains clear and substantially unchanged when the glass container is subjected many times to the preparatory caustic washing treatments to a subsequent use thereof. According to a further object of the present invention a wax coating is applied to the upper part of the protective coating, thereby making the glass or ceramic articles more resistant to scratching. The present invention also provides a simple, efficient and reliable process for producing an improved protective coating on a surface of a glass or ceramic article, where thermally decomposable precursors are used which are easy to handle. In the production of a protective coating on a surface of a glass or ceramic article according to the present invention, a stream of an oxygenated carrier gas containing a thermally decomposable precursor of tin oxide (Sn02) and a precursor that can be thermally decomposed from silicon oxide (Si02) in a molar ratio of the first precursor to the latter of between 0.6 and 3.0, the precursors are present in an evaporated form, and which also contains water vapor in an amount of at least 1 mole per 100 moles of the carrier gas, it is made to strike uniformly on the surface to be coated, the surface has a temperature which is above the decomposition temperatures of the precursors and is quantified by at least 550 ° C , to deposit a protective coating of mixed oxide comprising tin oxide and silicon oxide, and the deposition is continued until a coating thickness of between 240 and 1,500 angstroms is obtained. The CTU (thickness unit of the coating) is an optical unit which is frequently used in the glass industry to define the thickness of the coatings and is based on the measurements of the reflection of the incident light. For an oxide coating according to the invention, a thickness of 1 CTU can be estimated to correspond to approximately 3 angstroms. For practical reasons and in accordance with what is usual in the art, CTU thickness units will generally be adopted throughout the description and the examples that follow. When a protective coating produced according to the invention is compared to a known coating having the same thickness of CTU, the coating of the invention in impressive form shows a considerably improved resistance to caustic washing treatments, while maintaining the coating its clear appearance. The excellent properties that have been established, for example a good resistance to 50 and even more washing cycles of 8 to 10 minutes, make the coating of the invention also very suitable for the protection of ceramic articles such as earthenware. Further, after a usual wax coating has been applied to the top of the coating of the invention, excellent scratch resistance is obtained. Possible explanations for the excellent properties of the protective coating produced according to the invention, could be that the silicon oxide produced in the coating and the silicon oxide contained in the substrate to be coated, at least in part, are melted jointly at the interface, and / or that the copresence of the silicon oxide leads to a more airtight coating or film that has almost no openings through which caustic attack can be carried out, and / or that the co-presence of the oxide Silicon increases the resistance of the coating layer to mechanical impact during contact with the cutlery or whatever is present in the washing equipment. At present, the mechanism (s) that cause the improvement is not yet (are) well understood (s) and therefore, the possible explanations detailed above have been considered as hypothetical only and are not proposed to be limited for the same.

Detailed description of the invention The present process for producing a protective coating comprising tin oxide and silicon oxide, is preferably carried out at the hot end of a production line to produce the glass or ceramic article, while the surface of the article is still hot enough for the precursor to be decomposed. In addition, a surface temperature of at least 550 ° C is essential to produce a coating having the desired good properties. The production of the protective coating by the decomposition and oxidation of the precursors can be carried out by means of the CVD (Chemical Vapor Deposition) method which comprises bringing the precursors in the vapor form in contact with the hot surface that goes to be coated According to the CVD method, the precursors are applied from a stream of a carrier gas, suitable air, which hits the surface to be coated and which contains the precursors in the evaporated form. For short deposition times, for example less than about 10 seconds, the deposition rate is proportional to the deposition time. However, when longer deposition times are applied, the surface temperature will be reduced leading to a corresponding decrease in the rate of deposition and the efficiency of the coating process. Therefore, depending on the thickness of the desired coating, it may be necessary to either start the coating at a rather high surface temperature or to supply additional heat to the surface to be coated during the coating itself. A rather high temperature of the surface to be coated is also advantageous for other reasons that will be described later. The tin compound for use as a precursor according to the invention can be any tin compound which is capable of being thermally decomposed at the surface temperature of the glass or ceramic article to be coated. During the decomposition reaction with the oxygen present in the carrier gas, the decomposition of the tin oxide is caused. Suitable thermally decomposable tin compounds can be selected from monoalkyl and tin trichlorides such as monomethyl and tin trichloride and monobutyl trichloride and tin, monoalkyl and tin tribromides, dialkyl and tin dihydrochlorides such as dihydrochloride dimethyl and tin, dialkyl and tin dibromides, and tin tetraeloride. The monobutyl trichloride and tin is most preferred for use as the tin oxide precursor, because it is easy to handle and very efficient in its use. The silicon compound for use as a precursor must also be capable of being thermally decomposed and then produce silicon oxide as described above with respect to the tin compounds. Suitable silicon compounds are compounds having the formula RnSiX (4-n), wherein R is an alkyl, alkenyl, alkynyl or alkoxy group having 1-5 carbon atoms, or a phenyl group; X is a halogen atom or a hydroxy group; and n is a number from 0 to 4. Trimethoxy silane, tetraethoxy silane and tetrapropoxy silane are examples of suitable silicon compounds. The tin compound is preferably present in an amount of 0.5 x 10 ~ 4 - 2 x 10 ~ 2 moles per 1 mole of the carrier gas. The molar ratio of the tin compound to the silicon compound is chosen between 0.6 and 3.0 in view of the high resistance to the caustic scrubbing sought. It has been established that, within the indicated range, the best results are obtained when the molar ratio is at most 2.0 and preferably at much 1.5. It is also essential that the carrier gas, preferably the air as mentioned above, contains water vapor, which is present in an amount of 1-50 mol (s) per 100 moles of the carrier gas. A sufficient amount of water vapor is usually contained in the air employed as the oxygenated carrier gas when the protective coating of the invention is produced by CVD at atmospheric pressure according to a preferred embodiment. It is evident that the carrier gas is at a temperature at which the precursors are in the evaporated form. In general, the temperature of the carrier gas is between 100 ° C and 210 ° C and a preferred temperature range is between 120 ° C and 180 ° C. The speed at which the gas stream containing the components detailed above collides on the surface to be coated is usually selected in the range of 1-10 m / s and more preferably in the range of 3-5 m / s. . It is essential that the temperature of the glass or ceramic surface to be coated is above the decomposition temperature of the precursors used, but obviously below the softening temperature of the article to be coated. Usually, the protective coating is applied to the hot end of the production line for example of glass bottles. A rather elevated temperature of the surface to be coated not only increases the rate of deposition, as described above, but has also been found to substantially improve the strength of the coated surface, in particular to the caustic wash. Therefore, the temperature on the surface of the article must be at least 550 ° C during the coating process, the preferred temperature is at least 570 ° C and the most preferred temperature is at least 600 ° C, such as between 600 ° C and 650 ° C. Additional heat can be supplied to the article during the coating process to maintain the surface temperature at the desired high value. Any suitable means for supplying additional heat is convenient, such as that of flame projection, etc. The coating treatment is continued until the thickness of the desired coating is obtained. In fact, the coating thickness, in combination with the molar ratio of the tin compound to the silicon compound and a sufficiently high coating temperature as described above, provides excellent resistance to caustic washing, while the coating maintains a clear appearance According to the invention, the thickness of the protective coating must be at least 80 CTU. At thicknesses of at least 150 CTU and preferably at least 180 CTU it has been found that the coatings withstand heavy washing treatments of 12 hours with 4% caustic solutions at 80 ° C without showing any darkening or unwanted colors provided that the temperature of the surface to be coated has been sufficiently high. Preferably, the thickness of the coating is between 150 CTU (450 angstroms) and 900 angstroms. In the following examples, given by way of illustration only, the tin and silicon compounds are introduced in a stream of hot air by means of syringes to evaporate these compounds. The air temperature is approximately 150 ° C. The gas mixture is directed towards the surface of the glass articles that are going to be treated by means of a tube, as is well known. In the examples, the opening of the tube is 15 x 35 mm. The 50 ml glass bottles are treated on two thirds of their height. They are heated in an oven to the desired temperature. The temperature is measured by means of a thermocouple placed inside the bottles. The bottles are fixed by any appropriate means, for example by means of a rod or rod which allows the bottles to be manipulated and rotated during their exposure in the treatment gas stream. The temperature of the gas at the beginning of the formation of the coating is measured by means of an infrared thermometer (CHINO IR-AHOT type / -50 ° C to + 1000 ° C) adjusted to an emissivity of 0.93, sensitive over a wavelength range from 4 to 13 μm.

Test to measure resistance to scratching or scratching Two bottles that have had the same treatment are placed in the horizontal position, one above the other, and the same are pressed or pressed together, while causing them to slide together. When the pressure is increased, the moment of the formation of the scratch is clearly the moment when it is necessary to increase the force applied so that the bottles continue to slide on each other. The force of application is limited to 450 N with a higher force that could lead to one or both bottles being crushed. The bottles that have a suitable coating withstand a force of 450 N without experiencing scratches.

Test to measure the resistance to washing with a caustic solution The conditions correspond to those of the filling stations of the bottle. The bottles are submerged in a 4% sodium hydroxide solution maintained at 80 ° C. During the test the container containing the caustic solution has to be purged with nitrogen to avoid any conversion of sodium hydroxide to sodium carbonate as a result of the presence of carbon dioxide present in the ambient air. For the same reason, a freshly prepared sodium hydroxide solution was used for each test because sodium carbonate could cause less damage to the coating. For the test, 2 liter borosilicate glass containers of 150 mm diameter are used. These containers can contain 4 bottles. The bottles are placed on a plate placed 20 mm from the bottom of the container. Each bottle is retained by three pins of 6 mm in diameter and 15 mm in length, which are fixed in the holes in the plate. The plate, in the middle part of it, has a hole of 30 mm in diameter and 8 holes of 15 mm in length along its periphery. The caustic solution is agitated using a stirrer 40 mm in length and 10 mm in diameter, driven at 500 rpm by a heating plate with magnetic stirring. The thickness of the coating is measured using the device of the American Glass Research Co. (AGR). This device, commonly used in the bottle manufacturing industry, measures the reflection of the treated glass surface, the reflection value is then converted to CTU 's (Coating Thickness Units). 1 CTU for a tin oxide / mixed silicon oxide coating according to the invention, obtained by the CVD method as described here above, corresponds to about 3 angstroms. The following non-limiting examples illustrate the invention. Examples 1 and 2 are comparative examples. In Example 1, the bottles are covered with a tin oxide coating and with a wax coating in accordance with the teaching of U.S. Pat. No. 4,130,673. In Example 2, the bottles are treated to provide them with a thicker tin oxide coating. To avoid unacceptable dimming, these coatings were formed using larger concentrations of tin compound and larger carrier gas velocities.

Example 1 (comparative) Using the procedure described above, a tin oxide coating is deposited in 4 bottles, starting from monobutyl trichloride and tin. For this purpose, there is struck on the surface of the glass bottles brought up to a temperature of 600 ° C, a mixture of gases comprising air as the carrier gas, the tin compound in a ratio of 1.5 x 10 ~ 4 moles per mole of air and water vapor at a concentration of 2.3 moles per 100 moles of air. The air speed is 3 m / second. The deposition is made in 2.5 seconds. A tin oxide coating having a thickness of about 35 CTU is obtained. Two of these bottles are then treated to be coated with a wax coating by spraying an aqueous suspension of poly (ethylene oxide) according to the process described in U.S. Pat. 4130,673. These two bottles show excellent resistance to scratching at 450 Newtons. Coated bottles as described in each of the Examples given below, show the same excellent scratch resistance after they have been coated in the same manner with a wax coating. The other two bottles suffer the severe wash test in a 4% caustic solution at 80 ° C. The tin oxide coating is much more damaged after 15 minutes of washing and was completely removed after 30 minutes of washing.

Example 2 (comparative) The general coating process described in Example 1 is used, including the temperature of 600 ° C on the surface of the glass bottles. Tin oxide coatings having thicknesses of 100 CTU, 150 CTU and 200 CTU were formed, starting from a gas mixture containing monobutyl trichloride and tin in a ratio of 1 x 10 ~ 3 moles per mole of air and steam. water at a concentration of 2.3 moles per 100 moles of air. The air speed is 5 m / second. The deposition periods are, respectively, 3 seconds, 4.5 seconds, and 6 seconds. The thickness of these coatings is larger than that of the coating of Example 1. Still, after one hour of washing under the conditions of Example 1, all of the tin oxide films were damaged and partially removed.

Example 3 The general coating process described in Example 1 is used, including the temperature of 600 ° C on the surface of the glass bottles. In this example, bottles having two different coating thicknesses are prepared. The gaseous mixture used to form the coatings on the bottles, comprises monobutyl trichloride and tin in a ratio of 1 x 10 ~ 3 moles per 1 mole of air, tetraethoxy silane in a ratio of 50% mole of the mixture of the two metal compounds, and water vapor in a concentration of 2.3 moles per 100 moles of air. The air speed is 5 m / second. The deposition periods are, respectively, 4.5 seconds and 6 seconds. The coatings obtained have thicknesses of 150 CTU and 200 CTU. They do not show any turbidity or darkening. With respect to the resistance to washing with a caustic solution when performed under the conditions of the preceding examples, after 12 hours of washing the coating having a thickness of 150 CTU shows only a slight darkening and the coating of 200 CTU does not show no harm.

Example 4 The coatings are formed on the bottles as in Example 3, but the tetrapropoxy silane is used in place of the tetraethoxy silane. Results similar to those of Example 3 are obtained.

Example 5 Coatings of a thickness of 150 CTU are formed as described in Example 3. However, the concentration of water vapor in the gas mixtures used is varied. These concentrations are, respectively, 8 moles and 14 moles per 100 moles of air. All coatings obtained show an excellent resistance similar to washing with the caustic solution than that of the 200 CTU coating of Example 3.

Example 6 The procedure is as in Example 3, except that in place of the monobutyl trichloride and tin, tin tetraeloride or monomethyl tin trichloride was used. In both cases, similar results are obtained as those of Example 3.

Example 7 The procedure is as in Example 3, except that temperatures different from the surface of the glass bottles are used: ie 575 ° C and 625 ° C. Since at these elevated temperatures the deposition rates are approximately the same, the deposition times are, respectively, 4.5 seconds for a coating thickness of 150 CTU and 6 seconds for a coating thickness of 200 CTU. For both coating thicknesses, the resistance to washing with the caustic solution is completely acceptable when the temperature of the glass surface is 575 ° C, and it is excellent when the temperature of the glass surface is 625 ° C.

Example 8 The general coating procedure described in Example 3 is used, including the temperature of 600 ° C on the surface of the glass bottles. In this example, coatings with a thickness of 200 CTU were prepared, while varying the ratio of the tin compound to the silicon compound in the gas mixture used to form the coatings. The monobutyl trichloride and tin was used in a ratio or ratio of 1 x 10"3 moles to 1 mole of air The concentration of tetraethoxy silane was varied The water vapor was present in a molar ratio of the tin compound + silicon compound of 11.5, which corresponds to an amount of water vapor of 1.3 - 3.45 moles per 100 moles of air. The coated bottles were subjected to a 6 hour wash with the caustic solution as described in the preceding Examples. The ratios of the tin compound / silicon compound and the results of the washing tests are given in the Table given below.

TABLE Compound ratio result of tin test / silicon wash compound 0. 5 (comparative) strong dimming; severely attacked coating 0.6 light dimming 0.9 no darkening (= totally clear) 1.2 light dimming 1. 5 light dimming 3. 4 (comparative) darkening; coating attacked; 10.1 (comparative) strong dimming; coating severely attacked.

Since "no dimming" is the most desired result and a "light dimming" is still an acceptable result, it will be clear that the molar ratio of the tin compound to the silicon compound is preferably chosen in the range of 0.6 to 1.5. It is noted that in relation to this date the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following

Claims (14)

1. A process for producing a protective coating on a surface of a glass or ceramic article, characterized in that a stream of an oxygenated carrier gas containing a thermally decomposable precursor of tin oxide (Sn02) and a precursor that can be thermally decomposing silicon dioxide (Si02) in a molar ratio of the first precursor to the latter of between 0.6 and 3.0, the precursors that are present in the evaporated form, and that contain other water vapor in an amount of at least 1 mole per 100 moles of the carrier gas, it is caused to collide uniformly on the surface to be coated, the surface has a temperature which is above the decomposition temperatures of the precursors and is quantified by at least 550 ° C, to deposit a mixed oxide protective coating comprising tin oxide and silicon oxide, and the deposition is continued until a coating thickness between 240 and 1,500 angstroms.

2. The process according to claim 1, characterized in that the molar ratio of the tin oxide precursor to the silicon oxide precursor is at most 2.0.

3. The process according to claim 2, characterized in that the molar ratio of the tin oxide precursor to the silicon oxide precursor is at most 1.5.

4. The process according to any of claims 1-3, characterized in that the carrier gas contains 0.5 x 10 ~ 4 - 2 x 10"2 moles of the tin oxide precursor per 1 mole of the carrier gas.

5. The process according to any of claims 1-4, characterized in that the carrier gas has a temperature between 100 ° C and 210 ° C, preferably between 120 ° C and 180 ° C.

6. The process according to any of claims 1-5, characterized in that the gas stream hits the surface to be coated at a speed of 1-10 m / s.

7. The process according to claims 1-6, characterized in that the temperature of the surface to be coated is maintained at a value of at least 570 ° C during the coating process.

8. The process according to claim 7, characterized in that the temperature of the surface to be coated is maintained at a value of at least 600 ° C during the coating process.

9. The process according to any of claims 1-8, characterized in that the thermally decomposable precursor of tin oxide is selected from monoalkyl and tin trichlorides, monoalkyl and tin tribannes, dialkyl tin dichlorides, dialkyl dibromides and tin and tin tetraeloride.

10. The process according to claim 9, characterized in that the thermally decomposable precursor of tin oxide is selected from monomethyl and tin trichloride, monobutyl trichloride and tin and dimethyl tin dichloride.

11. The process according to any of claims 1-10, characterized in that the thermally decomposable precursor of silicon oxide is a compound having the formula RnSiX (4-n), wherein R is an alkyl, alkenyl group, alkynyl or alkoxy having 1-5 carbon atoms, or a phenyl group; X is a halogen atom or a hydroxy group; and n is a number from 0 to 4.

12. The process according to any of claims 1-11, characterized in that the deposition is continued until a coating thickness of between 450 and 900 angstroms is obtained.

13. The process according to any of claims 1-12, characterized in that the deposition is carried out by CVD at atmospheric pressure using the air as the carrier gas.

14. The process according to any of claims 1-13, characterized in that the protective coating is produced on the external surface of a glass container proposed for repeated use, or on the earthenware.