Enamel paste composition and method for forming an enamel coating using the enamel paste composition

Abstract

The enamel paste composition includes a glass frit, a pigment, an organic carrier medium, and an oxygen source material that facilitates clean removal of the organic carrier medium components during firing, the oxygen source material including a combination of (i) a first oxygen source material that releases oxygen at a temperature less than 350° C. and (ii) a second oxygen source material that releases oxygen at a temperature greater than 350° C. The first oxygen source material can be magnesium peroxide and the second oxygen source material can be barium peroxide. The enamel paste composition is utilized to form an enamel coated product without the need for a pre-firing step.

Description

[Technical field]

[0001] The present specification relates to enamel paste compositions, enamel coated products, and methods of making enamel coatings. [Background technology]

[0002] In the automotive glazing industry, it is common to decorate windshields, backlights, sidelights, and other glass components with a band of black light-blocking enamel that extends around the peripheral area of ​​the component. Its primary function is to protect the adhesive that holds the glass components together from ultraviolet light that would break down the adhesive. A secondary function is to cover the electrical circuits, wiring, and connectors that ensure the functionality of any electrical or electronic components attached to or embedded in the glass components, and to ensure a clean aesthetic appearance.

[0003] Enamel typically contains glass frit and pigment in an organic carrier medium. The enamel is applied as a paste or ink to a flat glass substrate by screen printing or inkjet processes, then fired at high temperatures. During firing, the organic carrier medium of the paste or ink burns off, and the enamel fuses and establishes a bond to the substrate. The firing process also softens the substrate, allowing it to be bent and formed into its final shape during the firing process.

[0004] To form the enamel layer, a multi-step firing process is typically utilized that includes (i) a first "pre-firing" heating step at a temperature sufficient to remove the organic carrier medium component of the enamel paste to form a dry pre-fired layer, and (ii) a second "firing" heating step at a temperature above the glass transition temperature of the glass frit in the enamel paste to fuse the enamel. During the second firing step, the substrate can be formed into its final shape by bending.

[0005] Glass panels for automotive applications typically include two glass sheets bonded together by an interlayer sheet (e.g., a polymer film). One of the glass sheets forms the outer glass sheet of the glass panel, and the other glass sheet forms the inner glass sheet. The sides of the glass sheets in an automotive glass panel are typically numbered from the outside to the inside. Thus, the outside of the outer glass sheet is conventionally designated side 1, the inside of the outer glass sheet is conventionally designated side 2, the side of the inner glass sheet facing the outer glass sheet is conventionally designated side 3, and the inside of the inner glass sheet is conventionally designated side 4. In such automotive glass panels, it is common for an enamel layer to be formed on side 2 of the outer glass sheet. An example of such a process is shown in FIG. 1. An enamel paste composition is printed onto a first glass sheet. The enamel paste is then pre-fired at a temperature above 400° C., more typically above 500° C. A second glass sheet is then placed onto the pre-fired enamel on the first glass sheet, and the stack of glass sheets is fired at a temperature above 500°C, more typically above 600°C, to form a fired glass panel product.

[0006] In the process shown in Figure 1, a pre-firing step is performed before the deposited enamel paste is sandwiched between two glass sheets. This is done to remove organic components from the enamel while exposing it to an oxidizing atmosphere. If a glass sheet printed with a black light-blocking enamel is combined with another glass sheet and fired without pre-firing, undesirable results will occur. First, the organic material will decompose into low molecular weight substances and volatilize, creating excessive pressure between the two glass sheets. Second, decomposition will proceed in the absence of oxygen between the glass sheets, causing incomplete combustion of the organic matter. Incomplete decomposition will cause char formation, pigment loss, and delayed enamel fusion, which will have a significant impact on the product performance and aesthetics of the glass product.

[0007] To avoid the above problems, it is common in the industry to use a pre-firing step called pre-firing, which burns out the organic matter in the black enamel layer. Pre-firing is usually performed at high temperatures of 500-650°C (slightly below the softening point of the glass sheets), but is almost the same as the actual firing in terms of energy consumption. The implementation of both the pre-firing and firing steps significantly increases the energy consumption and the associated environmental impact and costs. In addition, if a cold glass sheet is placed on the hot pre-firing glass sheet for firing after pre-firing, optical distortions may occur, especially for deeply curved laminates. Alternatively, if the pre-firing glass sheet is cooled before combining it with a second glass sheet, this is also energy-intensive, time-consuming, and costly.

[0008] EP1888333 proposes a method for making a decorated multi-layer glass structure in a single firing step, which involves the use of a crystallized glass enamel composition containing ingredients that allow the organic portion of the composition to burn off during firing and bending of a pair of glass sheets. It is stated that when applied to one of the pair of glass sheets, the organic portion of the composition burns off during the firing and bending process of the pair of glass sheets. The presence of an oxidizing agent in the composition ensures a supply of oxygen that allows the combustion of the organic vehicle during the firing of the glass sheets and before sintering the enamel composition to only one glass sheet of the pair of decorated or colored glass sheets.

[0009] The composition described in EP1888333 includes 20-80% by weight of a reactive glass component, 0.01-7% by weight of an oxidizer component, 10-40% by weight of a pigment, 10-40% by weight of an organic vehicle, and 1-20% by weight of a seed material. The oxidizer component includes an oxidizer selected from the group consisting of ammonium nitrate, antimony pentoxide, barium nitrate, bismuth pentoxide, bismuth subnitrate, bismuth tetroxide, calcium nitrate, calcium peroxide, cesium nitrate, cobalt nitrate, copper nitrate, lithium nitrate, magnesium peroxide, manganese dioxide, nickel (III) oxide, platinum monoxide, platinum dioxide, potassium nitrate, potassium peroxide, sodium nitrate, sodium percarbonate, sodium peroxide, strontium nitrate, strontium peroxide, silver nitrate, tellurium trioxide, tin nitrate, and zinc peroxide, and combinations thereof. The seed material includes Zn2SiO4, Bi 12 SiO 20 , Bi4(SiO4)3, Bi2SiO5, 2ZnO・3TiO2, Bi2O3・SiO2, Bi2O3・2TiO2, 2Bi2O3・3TiO2, Bi7Ti4NbO 21 , Bi4Ti3O 12 , Bi2Ti2O7, Bi2TiO 20 , Bi4Ti3O 12 , and Bi2Ti4O 11 The mixture includes at least one phase selected from the group consisting of:

[0010] The enamel composition is applied to a first glass substrate, and then a second glass substrate is stacked with the first substrate, with the green crystallized enamel composition present between the first and second glass substrates. The stacked glass substrates are then subjected to a firing operation to fuse the green crystallized enamel to the first substrate and completely burn off the organic vehicle, preventing the glass substrates from sticking to each other. Summary of the Invention [Problem to be solved by the invention]

[0011] While the aforementioned publications describe enamel compositions for use in processes without a pre-firing step, there remains a need to provide improved enamel paste formulations for use in such processes that burn out cleanly during firing while providing consistently good optical and color properties, as well as other desirable properties such as silver hiding / blocking, low optical distortion, and / or mechanical stability. It is an object of the present application to address this need. [Means for solving the problem]

[0012] According to one aspect of the present specification, an enamel paste composition is provided that includes a glass frit, a pigment, an organic carrier medium, and an oxygen source material for facilitating clean removal of the organic carrier medium components during firing, the oxygen source material including a combination of (i) a first oxygen source material that releases oxygen at a temperature below 350°C (i.e., releases some or all of its oxygen content below 350°C) and (ii) a second oxygen source material (different from the first oxygen source material) that releases oxygen at a temperature above 350°C.

[0013] Optionally, the first oxygen source material releases oxygen at a temperature below 330°C, below 300°C, below 280°C, below 260°C, or about 250°C (preferably above 100°C). Further, optionally, the second oxygen source material releases oxygen at a temperature above 370°C, above 400°C, above 420°C, above 440°C, or near 450°C (preferably below 800°C). The first and second oxygen source materials may include or consist of peroxide materials. The first oxygen source material may include or consist of magnesium peroxide or calcium peroxide, preferably magnesium peroxide. The second oxygen source material may include or consist of barium peroxide, barium oxide, barium oxide with glass frit, or strontium peroxide, preferably barium peroxide.

[0014] Without wishing to be bound by theory, it is believed that when using barium peroxide as the second oxygen source material, in the temperature range of 350-450°C, the barium peroxide begins to decompose into barium oxide and oxygen, resulting in an equilibrium state where the barium oxide recombines with atmospheric oxygen to form barium peroxide. As the temperature increases, the equilibrium continues to shift toward the products, and at approximately 750°C, the reverse reaction no longer occurs.

[0015] TIFF2025502060000002.tif6150

[0016] This equilibrium begins at a relatively low temperature and persists over a wide temperature range, thus acting as an oxygen buffer and ensuring that oxygen evolution during the process coincides with the thermal decomposition of the organic components.

[0017] By providing at least two oxygen releasing materials with significantly different oxygen release temperatures, oxygen is released over a wider temperature range during application of the firing profile, improving the burn-off of organic matter and improving the optical, mechanical and / or chemical properties of the enamel coating when a single firing step (without a pre-firing step) is performed. Thus, the use of such a combination of oxygen releasing materials has the advantage of cleanly burning out during firing while still providing enamels with consistently good optical / color properties (e.g., better L values) as well as other desirable properties such as good silver hiding / blocking performance, low optical distortion, and high mechanical and chemical stability. The wider temperature range of oxygen release also improves the robustness of the firing process and allows greater flexibility in the firing profile.

[0018] The use of barium peroxide as an oxygen-releasing material has been found to be particularly advantageous in achieving good enamel properties when performing a firing method that does not include a pre-firing step.According to another aspect of the present specification, therefore, an enamel paste composition is provided that includes a glass frit, a pigment, an organic carrier medium, and an oxygen source material for facilitating clean removal of the organic carrier medium components during firing, the oxygen source material including barium peroxide.As explained in relation to the previous aspect, the barium peroxide is optionally / advantageously provided in combination with one or more further oxygen-releasing materials, for example, another peroxide material such as magnesium peroxide and / or another material that releases oxygen at a lower temperature than barium peroxide during firing of the enamel paste.

[0019] The present specification also provides a method of forming an enamel coating, the method comprising the steps of depositing an enamel paste composition on a substrate, drying the deposited enamel paste composition at a temperature below 400°C, and firing the dried enamel paste at a temperature above 400°C (e.g., 400°C to 800°C) without pre-firing to form an enamel coating on the substrate. Such a method does not require a pre-firing step, and drying may be carried out at a temperature below 350°C, below 300°C, below 250°C, below 200°C, or below 175°C, for example, about 150°C (optionally above 100°C). Advantageously, the method can be applied to the construction of glass panels comprising two substrates as described above. In this case, after drying, a second substrate is placed on the dried enamel prior to firing to form an enamel coating between the substrates. [Brief description of the drawings]

[0020] For a better understanding of the invention and to show how the same may be carried into effect, specific embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0021] [Figure 1] FIG. 1 shows a schematic diagram of a method for making a glass sheet, which includes both a pre-firing step and a firing step. [Diagram 2]FIG. 2 shows a schematic diagram of a method for producing a glass plate that does not require a pre-firing step. [Diagram 3] FIG. 3 shows a photograph of a glass pane made using a conventional enamel paste formulation and a method that does not include a pre-firing step. [Figure 4] FIG. 4 shows two photographs of glass panes made using an enamel paste formulation according to the present disclosure and a method that does not include a pre-firing step. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] As explained in the Summary of the Invention, the present specification relates to enamel paste compositions that do not require pre-firing. In this regard, it is common to utilize a process that includes both a pre-firing step and a firing step, as shown in Figure 1 and explained in the Background of the Invention. In such a process, the energy cost of the pre-firing is comparable to the firing cost, and cold glass on the pre-fired hot glass can cause optical distortions for deeply bent laminates.

[0023] In contrast, the enamel paste composition herein is designed in a manner as shown in FIG. 2. In such a manner, the enamel paste is printed onto a first glass sheet and dried at a temperature of about 150° C. without pre-firing at elevated temperatures above 400° C. or 500° C. A second glass sheet is placed onto the dried enamel coating, and the stack of glass sheets is fired in one step. The main advantages include reduced energy, cost, and environmental impact by eliminating the pre-firing step, increased manufacturing throughput (e.g., by using a pre-firing oven for the actual firing), reduced manufacturing footprint / capital investment (fewer ovens required), and minimization of optical distortion issues by firing two glass sheets simultaneously without pre-firing.

[0024] As previously described herein, when such a method is used with conventional enamel paste, the organic materials in the enamel paste decompose into low molecular weight species that volatilize during firing, creating excess pressure between the two glass sheets. Furthermore, decomposition proceeds in the absence of oxygen, resulting in incomplete combustion of the organics. Incomplete decomposition can cause char formation, pigment loss, and retard enamel fusion, severely impacting the product performance and aesthetics of the glass product. Figure 3 shows photographs of glass sheets produced with a conventional enamel paste formulation and a method that does not include a pre-firing step. Many problems result from the non-clean combustion of organics, including uneven color development, highly porous enamel, adhesion between the glass sheets, and migration of enamel from one glass sheet to the other.

[0025] As explained in the Summary of the Invention, it has been found that the use of oxygen source materials including a combination of a first oxygen source material (e.g., magnesium peroxide) that releases oxygen at temperatures below 350°C and a second oxygen source material (e.g., barium peroxide) that releases oxygen at temperatures above 350°C is advantageous in achieving clean burnout during firing while providing enamels with consistently good optical / color properties, as well as other desirable properties such as low porosity and good silver hiding / blocking performance, low optical distortion, excellent non-stick properties, and high mechanical and chemical stability.

[0026] As explained in the Summary of the Invention, the use of barium peroxide as an oxygen releasing material has been found to be particularly advantageous in achieving good enamel properties when using firing methods that do not include a pre-firing step. Thus, the enamel paste composition according to the present invention comprises at least barium peroxide as an oxygen releasing material (e.g., 4-15 wt. % barium peroxide). Advantageously, the paste may also comprise one or more further oxygen releasing materials, e.g., another peroxide material such as magnesium peroxide, although optionally barium oxide may be used alone.

[0027] The enamel paste composition can comprise a total oxygen source material content of more than 4 wt.%, more than 5 wt.%, more than 6 wt.%, more than 7 wt.%, more than 7.5 wt.%, more than 8 wt.%, more than 9 wt.%, or more than 10 wt.%, including both the first oxygen source material and the second oxygen source material, or a total oxygen source material content of no more than 30 wt.%, no more than 20 wt.%, or no more than 15 wt.%, or within a range defined by any combination of the lower and upper limits set forth above.

[0028] Advantageously, the enamel paste composition may comprise at least 2%, 3%, 4%, 5%, or 6% by weight of barium peroxide, or no more than 15%, no more than 12%, no more than 10%, no more than 8%, or no more than 7% by weight of barium peroxide, or a barium peroxide content within a range defined by any combination of the aforementioned lower and upper limits. Advantageously, the barium oxide serves as a second high temperature oxygen releasing material in combination with the first low temperature oxygen releasing material.

[0029] The first low temperature oxygen releasing material can be a solid powdered complex of magnesium peroxide and magnesium oxide, MgO2·xMgO. An example of such an oxygen source material is Solvay's IXPER® 30MG. This material is sold for soil treatment, but has been found to be extremely effective as an additive for the enamel paste formulations described herein. This material comprises a stable complex of magnesium peroxide and magnesium oxide in solid powder form, and serves to consistently and reliably release oxygen within the enamel paste formulation during the initial stages of firing at temperatures ranging from 250°C to 400°C. This material provides very clean combustion of organic matter in an oxygen-deficient state during firing of the enamel paste formulation, achieving consistently good optical properties in the resulting enamel without the need for a pre-firing step. Moreover, relatively small amounts of such material are required to achieve such desirable results. For example, an enamel paste can include 3% to 15% by weight of oxygen source material, and optionally less than 10% by weight of oxygen source material.

[0030] Advantageously, the enamel paste composition herein has a low content of seed material or is free of seed material. For example, the enamel paste composition may contain less than 1 wt%, less than 0.8 wt%, less than 0.6 wt%, less than 0.4 wt%, less than 0.2 wt%, or less than 0.1 wt% of seed material, or more than 0 wt%, more than 0.01 wt%, or more than 0.05 wt%, or a seed content within a range defined by any combination of the above upper and lower limits. The seed material may include or consist of crystalline bismuth silicate seed powder (e.g., eulithite). The seeds promote crystallization to enhance non-stickiness and eliminate enamel transfer. It has been found that the paste formulations described herein do not require large amounts of seed material.

[0031] Optionally, the enamel paste comprises 40% to 70% by weight of glass frit. The glass frit may comprise a mixture of a vitreous glass frit (e.g., a bismuth-boron-zinc glass system) and a crystallized glass frit (e.g., a bismuth-silicon glass system, or a combination of these systems). The enamel paste composition may comprise, for example, 40% to 60% by weight of the vitreous glass frit and 5% to 15% by weight of the crystallized glass frit. The crystallized glass frit may have a particle size distribution of D90 of 15 to 25 micrometers and D50 of 7 to 13 micrometers. Alternatively, the crystallized glass frit may be bead milled to a small particle size, e.g., D90 less than 4 micrometers. It has been found that such a combination of glass frit and oxygen source material can improve the optical properties of the resulting enamel when fired in a single firing step.

[0032] The enamel paste composition may comprise 15% to 30% by weight of a pigment, the pigment comprising or consisting of a Cu-Mn-Cr pigment.

[0033] Additionally, the enamel paste may include 7% to 15% by weight of an organic carrier medium, which may include one, more, or all of a wetting and dispersing agent, a binder, a solvent, and an organic additive.

[0034] The method herein includes forming an enamel coating, the method including depositing an enamel paste composition according to any of the above claims onto a substrate, drying the deposited enamel paste composition at a temperature below 400° C., below 350° C., below 300° C., below 250° C., below 200° C., or below 175° C., and firing the dried enamel paste at a temperature above 400° C., above 450° C., or above 500° C. to form an enamel coating on the substrate without pre-firing. After drying, a second substrate can be placed on the dried enamel prior to firing to form an enamel coating between the substrates.

[0035] Figure 4 shows two photographs of glass panes made using an enamel paste formulation according to the present disclosure and the method described above without the pre-firing step. The top photograph is an outside view of a glass windshield pane, showing good color development and a uniform, dark enamel. The bottom photograph is an inside view of a pair of glass panes that were fired together. The glass sheets were offset and shown to have excellent non-stick properties (easy to separate and process), no enamel transfer (clean top glass), and uniform, clean burn-out (no yellowing).

[0036] Examples of two enamel paste compositions according to the present invention are summarized in the table below. TIFF2025502060000003.tif93142

[0037] The glass frit compositions of the above example pastes are shown in the table below. TIFF2025502060000004.tif57142 TIFF2025502060000005.tif83148 TIFF2025502060000006.tif67138 ※Fe2O3 is an impurity attached to other raw materials.

[0038] In addition to changing the solid content of the enamel paste composition to achieve the desired functional performance, the performance of the paste can be improved, and the composition of the organic carrier medium (organic vehicle) can also be changed to burn out cleanly in a single firing process method.

[0039] The organic vehicle is designed to provide excellent printability, rheological stability, and clean combustibility in the presence of an oxygen source without using pre-firing. In this regard, a mixture of solvents, dispersants, and polymer components can be used to adjust the printability and rheological stability. According to the present specification, low decomposition point polymers such as polybutyl acrylate or isobutyl methacrylate polymers can be used to promote clean combustion while maintaining good printability and rheological stability. Examples of suitable organic carrier medium (organic vehicle) compositions are summarized in the following table. TIFF2025502060000007.tif52147

[0040] When the above enamel paste composition is used in a method that does not include pre-firing, it exhibits many advantageous features, including good non-stickiness between the glass and the enamel, good optical properties (L value < 5), good black color (-l < a < l and -l < b < l), good printability and stability, and compatibility with existing lamination processes.

[0041] Thus, the present disclosure provides an enhanced black enamel paste that does not require pre-firing. The paste helps to burn organics cleanly in oxygen-deficient conditions. Utilizing such paste compositions and methods, automotive glass manufacturers can reduce energy consumption / costs by 40-50%, increase throughput, and improve production yields. The only heating step before firing is to dry the enamel after printing. Drying can be performed in an infrared belt furnace. This method also simplifies the manufacturing lines and equipment used to make the glass.

[0042] Although the present invention has been particularly shown and described with reference to specific examples, it will be understood by those skilled in the art that various changes in form and details can be made therein without departing from the scope of the invention as defined by the appended claims.

Claims

1. Glass frit, pigment, organic carrier medium, and an oxygen source material to facilitate clean removal of the organic carrier medium components during firing Including, The oxygen source material comprises a combination of (i) a first oxygen source material that releases oxygen at a temperature less than 350°C, and (ii) a second oxygen source material that releases oxygen at a temperature greater than 350°C.

2. 10. The enamel paste composition of claim 1, wherein the first oxygen source material releases oxygen at a temperature below 330°C, below 300°C, below 280°C, below 260°C, or at about 250°C.

3. 3. The enamel paste composition of claim 1 or 2, wherein the second oxygen source material releases oxygen at a temperature above 370°C, above 400°C, above 420°C, above 440°C, or near 450°C.

4. An enamel paste composition according to any of the preceding claims, wherein the first oxygen source material comprises or consists of magnesium peroxide or calcium peroxide, preferably magnesium peroxide.

5. 5. An enamel paste composition according to any of the preceding claims, wherein the second oxygen source material comprises or consists of barium peroxide, barium oxide, barium oxide containing glass frit, or strontium peroxide, preferably barium peroxide.

6. 6. The enamel paste composition of claim 1, wherein the enamel paste composition comprises more than 7 wt. % of oxygen source materials in total, including both the first oxygen source material and the second oxygen source material.

7. 7. The enamel paste composition of claim 6, wherein the enamel paste composition comprises more than 7.5 wt.%, more than 8 wt.%, more than 9 wt.%, or more than 10 wt.% in total of the oxygen source material.

8. 8. The enamel paste composition of claim 6 or 7, wherein the enamel paste composition comprises a total of no more than 30 wt%, no more than 20 wt%, or no more than 15 wt% of oxygen source material.

9. 9. An enamel paste composition according to any preceding claim, wherein the enamel paste composition comprises less than 1% by weight of seed material.

10. 10. The enamel paste composition of claim 9, wherein the enamel paste composition comprises less than 0.8%, less than 0.6%, less than 0.4%, less than 0.2%, or less than 0.1% by weight of seed material.

11. 11. The enamel paste composition according to claim 9 or 10, wherein the enamel paste composition is free of seed material or comprises a seed material content of greater than 0 wt.% and less than 1 wt.%.

12. An enamel paste composition according to any one of claims 9 to 11, wherein the seed material comprises or consists of a crystalline bismuth silicate seed powder.

13. An enamel paste composition according to any one of claims 1 to 12, wherein the enamel paste comprises 40% to 70% by weight of glass frit.

14. 14. The enamel paste composition according to any one of claims 1 to 13, wherein the glass frit comprises a mixture of vitreous glass frit and crystallized glass frit.

15. 15. The enamel paste composition of claim 14, wherein the enamel paste composition comprises 40% to 60% by weight of vitreous glass frit and 5% to 15% by weight of crystallized glass frit.

16. 16. An enamel paste composition according to claim 14 or 15, wherein the vitreous glass frit comprises or consists of a bismuth-boron-zinc glass system and the crystallized glass frit comprises or consists of a bismuth silicate glass system.

17. An enamel paste composition according to any preceding claim, wherein the enamel paste composition comprises from 15% to 30% by weight of the pigment.

18. An enamel paste composition according to any preceding claim, wherein the enamel paste comprises from 7% to 15% by weight of the organic carrier medium.

19. Depositing an enamel paste composition according to any one of claims 1 to 18 onto a substrate; drying the deposited enamel paste composition at a temperature of less than 400° C.; and Firing the dried enamel paste at a temperature in excess of 400° C. to form an enamel coating on the substrate without pre-firing.

13. A method for forming an enamel coating comprising:

20. 20. The method of claim 19, wherein the enamel paste composition is dried at a temperature of less than 350°C, less than 300°C, less than 250°C, less than 200°C, or less than 175°C.

21. 21. The method of claim 19 or 20, wherein after drying, a second substrate is placed on the dried enamel before firing to form an enamel coating between the substrates.

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