Method of manufacturing a glass container suitable for food contact and enhancing glass strength

Abstract

The invention relates to a method of manufacturing an inorganic silica-based hollow glass container, particularly a soda-lime-silica glass container in the form of a glass bottle. The method comprises the steps of providing a glass container with a hot coating; preparing a coating solution by mixing an amino-functional silane as a silica precursor compound, a solvent, and at least one alcohol and / or water to ensure controlled evaporation; applying the coating solution at least partially onto the external wall of the glass container; and, preferably at room temperature and an ambient temperature of up to 150°C, allowing controlled evaporation of the coating to obtain a food-grade coating layer with a thickness of <10 nm on the external surface of the glass container.

Description

[0001] DESCRIPTION

[0002] METHOD OF MANUFACTURING A GLASS CONTAINER SUITABLE FOR FOOD CONTACT AND ENHANCING GLASS STRENGTH

[0003] TECHNICAL FIELD

[0004] The invention relates to a method for coating a soda-lime-silica glass container that is suitable for contact with food and serves to increase strength, as well as to a glass container with enhanced strength produced by this method.

[0005] PRIOR ART

[0006] Reducing the weight of glass containers and producing lightweight or thin-walled glass containers require a focus on the mechanical strength values of the glass materials. In glass bottle products, producing wall thicknesses lower than the theoretical thickness for the purpose of weight reduction, or producing sheet glass at thicknesses below 2 mm, may pose significant risks.

[0007] For glass container products to maintain their durability against the various processes to which they are exposed — such as high line speeds, washing, filling, capping, labeling, packaging, and loading — a two-stage coating is routinely applied on the production line. In the first stage, the “hot coating” is performed by chemical vapor spraying when the glass temperature is around 550-600°C in a tunnel at the entrance of the annealing furnace. Through this process, a tin oxide (SnO2) coating of about 10 nm thickness fills the microcracks, thereby increasing the mechanical strength values. In the second stage, the surface roughness of the glass — which was made harder in the hot coating stage — is reduced and slipperiness is provided by applying a cold coating when the glass surfaces are at 80-150°C at the exit of the annealing furnace. After the cold coating dries, a film layer that is slightly soluble in water is formed, providing good slipperiness under relatively mild washing conditions. Currently, cold coating solutions are sprayed through nozzles in glass packaging production facilities.

[0008] EP2938584B1 discloses a coating composed of an amino-functional silane and water applied to the outer surface of a glass packaging material. The patent discloses three main steps for applying the coating material: (i) applying the amino-functional silane, (ii) obtaining an aminosiloxane via a curing step, and (iii) decomposing the organofunctional groups attached to the siloxane layer by heat treatment at 500-700°C.

[0009] SUMMARY OF THE INVENTION

[0010] The object of the invention is to facilitate the thinning of the wall thickness of a glass container by applying a coating solution for cold coating that increases the mechanical strength of the glass container.

[0011] In order to achieve the aforementioned objective, the invention concerns a method of manufacturing an inorganic silica-based hollow glass container — specifically, a soda-lime- silica glass container in bottle form. The method of manufacturing comprises the steps of: preparing a coating solution by mixing components including at least one amino-functional silane as a silica precursor compound, at least one solvent, and at least one alcohol and / or water to ensure controlled evaporation; directly applying this coating solution, at least partially, to the exterior surface of the glass container that already carries a hot coating; allowing controlled evaporation of the coating — preferably at room temperature and at an ambient temperature of at most 150°C — thereby creating a food-grade coating layer of <10 nm thickness on the exterior surface of the glass container.

[0012] Thus, a glass container with the desired mechanical strength and suitable for food contact can be obtained while using less raw material and, consequently, consuming less energy compared to standard production.

[0013] In a preferred application of the invention, during the evaporation step, the ambient temperature is chosen between 80°C and 150°C, particularly between 110°C and 150°C. It has been determined that these temperature ranges produce the best results in terms of the coating’s adhesion to the glass container.

[0014] In another preferred application of the invention, the coating solution is applied to the external surface of the glass container by spraying. Spraying yields a uniform coating thickness on the external surfaces.

[0015] In yet another preferred application, the amino-functional silane in the coating solution is selected from 3-aminopropyltriethoxysilane (APTES), 3-aminopropylmethoxysilane (APTMS), or a mixture thereof. Both of these compounds contain an amino group that can enhance adhesion to glass surfaces and participate in hydrolysis and condensation reactions to form siloxane networks. It has been found that APTES and APTMS with their high hydrolysis ability provide better adhesion performance on soda-lime-silica glass compared to other silane groups. This also promotes faster polymerization and network formation.

[0016] In a further preferred application, the coating solution contains at least one acid selected from the group consisting of acetic acid, formic acid, ascorbic acid, citric acid, nitric acid, or mixtures thereof. The chosen acid can make the hydrolysis and condensation reactions of the silane more effective and provide a more homogeneous coating. The hydrolysis of silanes generally proceeds more controllably under acidic conditions.

[0017] In another preferred application, the coating solution contains an acid in a weight ratio of between 0.15% and 3%. It has been found that this range increases the stability of the coating solution.

[0018] In another preferred application, the coating solution, as a solvent, contains at least one component or a mixture of components selected from the group consisting of water, ethanol, butanol, 1 -propanol, 2-propanol, 1 -butanol, propylene glycol methyl ether, and propylene glycol methyl ether acetate. These solvents are suitable for providing a coating solution appropriate for cold coating.

[0019] In a further preferred application, the solvent includes at least two components selected from water, 1 -propanol, 2-propanol, and / or ethanol. These alcohols can effectively dissolve coating substances such as silanes. Moreover, by reducing the viscosity of the coating solution, they help the application become more homogeneous and uniform. Additionally, once applied, the solvent rapidly evaporates, accelerating the drying and curing of the coating.

[0020] In another preferred application, the solvent is present in a weight ratio of 95% to 99%, comprising at least one of water, 1 -propanol, 2-propanol, or ethanol. This ratio activates the hydroxyl groups on the glass surface, promoting better bonding of silanes to the surface.

[0021] In yet another preferred application, the amino-functional silane is included in the coating solution at 0.5% to 5% by weight of 3-aminopropyltriethoxysilane, 3- aminopropyltrimethoxysilane, ortheir mixture; 0.15% to 3% by weight of nitric acid; and 95% to 99% by weight of water and at least one ora mixture of 1 -propanol, 2-propanol, and / or ethanol. It has been found that this composition forms a food-grade coating layer while increasing strength.

[0022] In another preferred application, the coating solution includes 0.5% to 1 % by weight 3- aminopropyltriethoxysilane, 96% to 99% by weight water and ethanol, and 0.15% to 1 % by weight acetic acid.

[0023] In a further preferred application, the viscosity of the coating solution is between 1 and 1 .5 cP. This allows the solution to be applied by spraying onto the external surface of the glass container.

[0024] In a further preferred application, the resulting coating thickness is set to be <10 nm. The chosen thickness ensures optical transparency while sufficiently increasing mechanical strength.

[0025] In another preferred application, the structure is monolithic siloxane. This yields a homogeneous coating that ensures the structural integrity of the product.

[0026] Another aspect of the invention relates to a soda-lime-silica glass container obtained by the method of manufacturing described herein. Thus, for example, the use of cold coating is made possible in bottle production.

[0027] DETAILED DESCRIPTION OF THE INVENTION

[0028] In this detailed description, the invention relates to a coating solution with strength-enhancing properties aimed at addressing the technical problems encountered in reducing the weight of inorganic silica-based glass products. It is illustrated with non-limiting examples intended only to facilitate a better understanding of the subject matter.

[0029] The method of manufacturing according to the invention includes providing a soda-lime-silica- based bottle containing about 60-75% SiO2, 7-15% Na2O, 6-12% CaO, 0.1-3% Al2O3, 0.1-2% MgO, and 0.1-2% K2O in its composition. Following the forming and tempering processes, this bottle, which has the stated glass composition, is then coated by a coating solution obtained via the sol-gel method, as set forth in the present invention. A cold coating material is applied onto the coating solution. In the invention, the term “cold coating” refers to a mixture of polymer materials with polar and / or apolar structures. In one embodiment, the term “cold coating” refers to a mixture of polymer materials with polar structures. In another embodiment, the term “cold coating” refers to a mixture of polymer materials with apolar structures.

[0030] The coating solution used in the method of manufacturing of the invention fills the microcracks present on the glass surfaces, creating tensile stress. As a result of this increased mechanical strength, it becomes possible to reduce wall thicknesses of the described glass products without compromising their ultimate strength performance, thereby enabling lower-weight glass products.

[0031] Another aspect of the invention concerns a glass container coated with the coating solution.

[0032] The coating solution used in the method of manufacturing of the invention comprises at least one silica precursor compound. In the invention, the silica precursorcrosslinkingcompound(s) in the coating solution form continuous film layers that strongly adhere to the glass surface via two reactive functional ends. In particular, the coating solution contains at least one of 3- aminopropyltriethoxysilane and / or 3-aminopropyltrimethoxysilane as the silica precursor compound in specific proportions.

[0033] In a preferred application, the coating solution contains 3-aminopropyltriethoxysilane (APTES) in certain weight ratios as the silica precursor compound. In the invention, 3- aminopropyltriethoxysilane, designated as Formula 1 , is used as the silica precursor compound.

[0034] Formula 1 In the 3-aminopropyltriethoxysilane compound shown in Formula 1 , the amino functional group provides properties that fill and heal the microcracks formed on the coating surface that cause breakage.

[0035] In the method of manufacturing of the invention, the coating solution contains 3- aminopropyltriethoxysilane (APTES) as a silica precursor compound. The amount of 3- aminopropyltriethoxysilane in the coating solution ranges from 0.3% to 5% by weight. Preferably, the amount is 0.5% to 1 % by weight. Specifically, it may be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1% by weight. Maintaining the 3-aminopropyltriethoxysilane content within these specific values is critical for crosslinking functions. If this content exceeds the upper specified value, the coating solution — applied to the glass while it is still hot — results in staining and agglomeration. Furthermore, exceeding the upper limit prevents achieving the desired form of coating material. If it is belowthe lower limit, the target mechanical strength values forthe glass cannot be achieved.

[0036] In one embodiment, the amount of 3-aminopropyltriethoxysilane in the coating solution ranges from 0.001 to 0.020 mol. In an alternative embodiment, it ranges from 0.001 to 0.015 mol, and in the most preferred application, from 0.001 to 0.009 mol. In a particularly preferred application, it is 0.002 to 0.005 mol, specifically 0.002 mol, 0.003 mol, or 0.004 mol.

[0037] As discussed above, including 3-aminopropyltriethoxysilane as the silica precursor in the coating solution makes the solution suitable for use in the food industry, and likewise, glass containers coated with this solution are also suitable for use in the food industry. The bond formed between the amino functional group in the 3-aminopropyltriethoxysilane molecule and the silicon atom is very strong, decomposing only at temperatures between 500°C and 600°C. According to the European Chemicals Agency (ECHA), 3-aminopropyltriethoxysilane has no known genotoxicity, and for food contact regulations (Food Contact Substances Listed in 21 CFR), its use is restricted to less than about 1-2%. Under Regulation (EU) No 10 / 2011 , it is restricted to about 10% or less, with a migration limit of 0.05 mg / kg.

[0038] The coating solution in the method of manufacturing of the invention also contains at least one component selected from water, ethanol, butanol, 1 -propanol, 2-propanol, 1 -butanol, propylene glycol methyl ether, or propylene glycol methyl ether acetate, serving as a solvent to control evaporation. Preferably, the coating solution includes at least one of water, ethanol, 1- propanol, and / or 2-propanol in order to ensure controlled evaporation. The solvent amounts to 95% to 99% by weight of the coating solution. If the solvent is below the lower limit, excessive gelation may occur, reducing stability and causing storage issues. If it is above the upper limit, the efficiency of hydrolysis processes necessary to obtain the coating solution is diminished, preventing the desired sol-gel form.

[0039] The coating solution used in the method of manufacturingof the invention also contains at least one acid to initiate hydrolysis and condensation reactions. The acid is at least one selected from the group consisting of acetic acid, formic acid, ascorbic acid, citric acid, nitric acid, or their mixtures. Preferably, acetic acid is included as the acid. The amount of acetic acid ranges from 0.15% to 3% by weight. This range is important because acetic acid acts as a catalyst for the reaction medium during the preparation of the coating solution. If the acetic acid is above the specified range, the reaction rate may become excessive, shortening synthesis times and causing stability problems. If it is below the lower limit, the required hydrolysis reaction conditions cannot be met, thus making it impossible to obtain the coating solution.

[0040] In the most preferred application, the coating solution used in the method of manufacturing comprises 0.3% to 3% by weight of at least one of 3-aminopropyltriethoxysilane and / or 3- aminopropyltrimethoxysilane, 96% to 98% by weight of at least two from water, ethanol, 1- propanol, and / or 2-propanol, and 0.15% to 2% by weight of acetic acid.

[0041] In another most preferred application, the coating solution comprises 0.5% to 1% by weight of 3-aminopropyltriethoxysilane, 96% to 99% by weight of at least two from water, ethanol, 1- propanol, and / or 2-propanol, and 0.15% to 1% by weight of acetic acid.

[0042] In yet another most preferred application, the coating solution comprises 0.5% to 1 % by weight 3-aminopropyltriethoxysilane, 96% to 99% by weight water and ethanol, and 0.15% to 1% by weight acetic acid.

[0043] In another most preferred application, the coating solution comprises 0.5% to 1% by weight 3- aminopropyltriethoxysilane, 96% to 99% by weight water, and 0.15% to 1% by weight acetic acid.

[0044] In another most preferred application, the coating solution comprises 0.5% to 1% by weight 3- aminopropyltriethoxysilane, 96% to 99% by weight ethanol, and 0.15% to 1% by weight acetic acid. Thanks to these constituents, the coating solution increases the mechanical strength of the coated glass by 10% to 20%, depending on the type of glass surface. Consequently, with increased mechanical strength, less raw material may be used to produce the glass. Especially in products such as glass packaging, the wall thickness may be reduced relative to current conventional glass container products. Moreover, glass container products can be obtained with increased durability without compromising on design. Through these technical advantages, it becomes possible to produce glass products with lower weight and more complex shapes using this coating solution.

[0045] In a preferred configuration of the invention, the coating solution is obtained by a sol-gel synthesis method. The components characterized in the invention are used to obtain the coating solution via the sol-gel production process. It is important for the components to be added in the specified weight ratios and for the coating solution to be prepared as characterized.

[0046] The coating solution used in the method of manufacturing of the invention can be coated onto glass by dip-coating, spraying, roll coating, etc. In a preferred application, it is sprayed onto the glass surface. Liquid application of the coating facilitates ease of use for shaped glass surfaces. Additionally, bringing the chemical bonding components into an appropriate form allows for the formation of strong chemical bonds with the glass surface. These bonds fill microcracks that negatively impact strength, thus improving mechanical strength. Thanks to its ingredients, the coating solution used in the method of manufacturing prevents the technical disadvantages caused by microcracks in the glass.

[0047] One innovative aspect of the invention is that the coating solution can be applied in-line during glass production, i.e., “on the production line.” In the most preferred application, the coating solution can be applied by spraying in-line onto glass packaging products. Producing the coating solution in a manner that enables it to be applied through in-line processes on glass packaging products is significant. A sol-gel technique is used to obtain the coating solution, because when the appropriate proportions of components are used, the mechanism of the solgel process ensures that hydrolysis and condensation reactions result in a continuous film layer that can form strong chemical bonds with glass surfaces. In the method of manufacturing of the invention, during production, a coating station is provided for applying the coating after hot coating and annealing. This station is located above the conveyor line where the glass containers pass and typically includes at least two nozzles that move along the y-axis relative to the production line (the nozzles move vertically in relation to the direction of bottle flow). At least one of these stations holds the coating solution, while at least one other station holds a cold coating material. At predetermined intervals, these stations spray the respective coating materials onto the glass containers. First, at least one nozzle applies the cold coating material onto the glass container, followed by spraying the strength-improving coating solution characterized in the invention. In a preferred application, these nozzles are adjacent to each other.

[0048] As mentioned, the bottles arrive at the coatingstation from the annealingfurnace. In a preferred application, prior to the coating application, the bottle surface is treated with 1 % acetic acid. Acetic acid enhances affinity on the bottle’s application surface. After this process, a polar cold coating is applied, followed by the strength-improving coating solution, and subsequently an apolar cold coating is applied. During these steps, the solution is applied to the glass at predetermined temperature values in the range of 80°C to 150°C, preferably 110°C to 150°C. At these temperatures, the glass is first contacted by the cold coating material and then by the sprayed strength-improving coating solution. By optimally applying the coating to hot glass surfaces, no high-temperature treatment is required, and the coating process can be incorporated in-line.

[0049] In the coating method of the invention, the spraying speed of the station(s) is preferably between 4.7 and 6.4 L / hour.

[0050] In the coating method of the invention, the viscosity of the coating solution is preferably between 1 and 1 .5 cP.

[0051] In the coating method of the invention, the nozzles spray coating materials continuously. As the glass moves along the +x axis on the production line, the nozzles move along the y axis. At least two nozzles are present: one first sprays the cold coating material, while another subsequently sprays the coating solution. The stations operate periodically for 10-20 seconds along the y axis. In a preferred application, the stations operate periodically for 10-15 seconds along the y axis. In this manner, the coating processes on the production line can be completed in a short period without any change in temperature. Having consecutively coated the glass surfaces with the cold coating material and then with the coating solution while the glass is still hot providing a synergistic effect on the mechanical strength of glass products such as bottles. This synergistic effect has been demonstrated through slip angle, heel impact, shoulder impact, and burst pressure tests conducted on coated glass products. In these tests, the reference sample refers to a glass product with only cold coating applied (i.e., without the strength-improving coating solution as characterized in the invention), as shown in Table 1 .

[0052] Table 1 . Strength improvements in bottles obtained through the applied coating

[0053] The coating solution used in the method of manufacturing of the invention is formulated with 3-aminopropyltriethoxysilane and / or 3-aminopropyltrimethoxysilane as the silica precursor compound such that it remains below the limits specified by EU and FDA regulations. Furthermore, it has been observed that the mechanical strength of glass products coated with this solution can increase by up to 20%.

[0054] Another aspect of the invention relates to a method of applying the coating solution to glass products. The coating method of the invention ensures that the coating solution delivers the desired technical benefits and effects on glass materials. Additionally, through the method of the invention, the coating solution can be applied in-line, thus not incurring additional process costs.

Claims

CLAIMS1. A method of manufacturing an inorganic silica-based hollow glass container, particularly a soda-lime-silica glass container in the form of a glass bottle, comprising the following steps of• providing a glass container with a hot-coating;• preparing a coating solution by mixing components including at least one amino-functional silane as the silica precursor compound, at least one solvent, and at least one alcohol and / orwaterto ensure controlled evaporation;• applying the coating solution at least partially onto an external wall of the glass container;• controlled evaporation of the coating — preferably at room temperature and at an ambient temperature of up to 150°C — so that a food-grade coating layer with a thickness of <10 nm is formed on the external wall of the glass container.

2. A method of manufacturing according to claim 1 , wherein the ambient temperature is selected between 80°C and 150°C, in particular between 110°C and 130°C in the evaporation step.

3. A method of manufacturing according to any of the preceding claims, wherein the coating solution is applied to the external wall of the glass container by spraying.

4. A method of manufacturing according to any of the preceding claims, wherein the amino-functional silane in the coating solution comprises 3- aminopropyltriethoxysilane, 3-aminopropylmethoxysilane, or a mixture thereof.

5. A method of manufacturing according to any of the preceding claims, wherein the coating solution comprises at least one acid selected from the group consisting of acetic acid, formic acid, ascorbic acid, citric acid, nitric acid, ortheir mixtures.

6. A method of manufacturing according to any of the preceding claims, wherein the coating solution contains 0.15% to 3% by weight of an acid.

7. A method of manufacturing according to any of the preceding claims, wherein the coating solution comprises, at least one component or a mixture of components selected from the group consisting of water, ethanol, butanol, 1 -propanol, 2-propanol,1 -butanol, propylene glycol methyl ether, and propylene glycol methyl ether acetate as a solvent.

8. A method of manufacturing according to claim 7, wherein at least two components selected from the group consisting of water, 1 -propanol, 2-propanol, and / or ethanol as a solvent.

9. A method of manufacturing according to claim 8, wherein the solvent is 95% to 99% by weight of at least one of water, 1 -propanol, 2-propanol, or ethanol.

10. A method of manufacturing according to any of the preceding claims, wherein the amino-functional silane is 0.5% to 5% by weight of 3-aminopropyltriethoxysilane, 3- aminopropyltrimethoxysilane, ora mixture thereof; 0.15% to 3% by weight of nitric acid; and 95% to 99% by weight of water and at least one or a mixture of 1 -propanol, 2- propanol, and / or ethanol.

11. A method of manufacturing according to any of the preceding claims, wherein the coating solution comprises 0.5% to 1 % by weight 3-aminopropyltriethoxysilane, 96% to 99% by weight water and ethanol, and 0.15% to 1% by weight nitric acid.

12. A method of manufacturing according to any of the preceding claims, wherein the viscosity of the coating solution is between 1 cP and 1 .5 cP.

13. A method of manufacturing according to any of the preceding claims, wherein the resulting coating thickness is set to <10 nm.

14. A method of manufacturing according to any of the preceding claims, wherein the coating structure is a monolithic siloxane.

15. Asoda-lime-silica glass container obtained by a method of manufacturing according to any of the preceding claims.