Enamel paste composition, enamel coating product, and method for producing same

Abstract

An enamel paste composition is provided for producing a coated glass article comprising a glass substrate, an enamel layer disposed on the glass substrate, and a thin coating having a thickness of 0.5 micrometers or less disposed on the enamel layer. The enamel paste composition is formulated to provide a smooth surface and not crystallize during processing of the coated glass article, thereby improving the quality of the thin coating disposed thereon.

Description

[Technical field]

[0001] Field The present specification relates to an enamel paste composition, an enamel coating product, and a method for making the same. [Background technology]

[0002] background In the automotive glass industry, it is common to decorate windshields, backlights, sidelights, and other glass components with a black band of shielding enamel that extends around the perimeter of the component. Its primary function is to protect the adhesive that holds the glass component in place from ultraviolet light that would break down the adhesive. Its secondary function is to cover electrical circuits, wires, and connectors, ensuring the functionality of electrical or electronic components attached to or embedded in the glass component, and to ensure a clean aesthetic appearance.

[0003] Enamels typically comprise glass frit and pigments in an organic carrier medium. The enamel is applied to a flat glass substrate as a paste or ink by screen printing or inkjet processes and then fired at high temperatures. During this time, the organic carrier medium of the paste or ink burns off and the enamel fuses and establishes a bond with the substrate. The firing process also softens the substrate so that it can be formed into its final shape by a bending process during the firing process. It is also known to use a two-stage firing process to form the enamel layer, which comprises: (i) a first "pre-fire" heating step at a temperature below the melting temperature of the glass frit in the enamel paste to remove the organic carrier medium component of the enamel paste and form a dry pre-fired layer, and (ii) a second "fire" heating step at a temperature above the melting point of the glass frit in the enamel paste to melt the enamel. During the second firing step, the substrate can be formed into its final shape by a bending process.

[0004] In addition to the shielding enamel, electrical components can also be printed onto the glass part in a similar manner. In this case, the enamel formulation will typically include a metallic conductive powder (e.g., silver powder), a glass frit, and an organic carrier medium. Such a conductive enamel paste can be applied in addition to the shielding enamel paste and fired in the same process to form a glass part that includes both the electrical components (e.g., antennas and / or heating elements) and the shielding enamel, which is positioned to hide the electrical connections (such as bus bars) to the electrical components.

[0005] More recently, functional thin films have also been applied to glass components, for example using deposition processes. Such functional thin films have nanometer-scale thicknesses and can function, for example, as heating elements (replacing more conventional screen or inkjet printed conductive silver enamel heater lines) and / or IR reflective elements.

[0006] US Patent Application Publication No. 20170135160 (granted as US 10455645B2) describes an example of a method for manufacturing an automotive glass panel comprising a system of thin sputtered conductive layers for heating the glass panel. The glass panel configuration described in US Patent Application Publication No. 20170135160 is shown in FIG. 1 and comprises two glass sheets 2, 4 joined by an interlayer sheet 6. In use, glass sheet 2 forms the outer glass sheet of the glass panel, while glass sheet 4 forms the inner glass sheet. The sides of the glass sheets of an automotive glass panel are typically numbered from the outside to the inside. Thus, the outer side 8 of the outer glass sheet 2 is conventionally referred to as side 1, the interior side 10 of the outer glass sheet 2 is conventionally referred to as side 2, and the side 12 of the inner glass sheet 4 facing the outer glass sheet 2 is conventionally referred to as side 4, while the interior side 14 of the inner glass sheet 4 is conventionally referred to as side 3. In the configuration of US20170135160 shown in FIG. 1, an enamel layer 16 is formed on the side 2 of the outer glass sheet. A thin coating 18 is formed on the enamel layer 16 and on the uncoated portion of the side 2 of the outer glass sheet. In US20170135160, the thin coating is a system of heating conductive layers formed by cathode sputtering and including an assembly of metal layers and dielectric layers, the thickness of the assembly may be 0.1 micrometers or less. Electrical bus bars 20 are then formed in a thin coating 18 on the enamel layer 16. As previously mentioned, U.S. Patent Application Publication No. 20170135160 discloses that the system can be fired in a two-step firing process including a first pre-fire step to remove the organic carrier medium and a second firing step at a higher temperature to melt and fuse the glass frit and perform bending during the second firing step of the firing process to form a shaped glass article.

[0007] US Patent Application Publication No. 20170135160 discloses a problem with the configuration shown in FIG. 1 and described above. Namely, US Patent Application Publication No. 20170135160 identifies that the power supplied to the busbar is not fully transferred to the conductive layer, resulting in power losses and adversely affecting the heating performance of the glass panel. US Patent Application Publication No. 20170135160 identifies that this problem is caused, at least in part, by the surface roughness of the enamel layer, which adversely affects the connection of the busbar to the overlying conductive coating and the conductive coating on the enamel layer. Thus, US Patent Application Publication No. 20170135160 states that the surface roughness Ra of the enamel layer should be 0.5 micrometers or less, preferably 0.1 micrometers or less. Several methods have been described for reducing the roughness of an enamel layer, including: (i) the use of an enamel composition comprising a glass frit and a pigment; the pigment and optionally the glass frit having an average particle size of 5 micrometers or less, (ii) screen printing of the enamel paste using a printing screen having a coating surface with low surface roughness, (iii) modifying the surface tension and viscosity of the applied enamel paste layer to provide a smoothing effect, and (iv) inkjet printing of the enamel rather than using screen printing.

[0008] US Patent Application Publication No. 20170135160 states that the composition of the enamel paste is not specific to the application. For enamel layers produced by screen printing, it is disclosed that the average roughness Ra was 0.69 micrometers (i.e. too rough, exceeding the 0.5 micrometer threshold). For layers applied by inkjet technology, the resulting roughness was substantially reduced, with an average roughness of the order of 0.14 micrometers obtained using an enamel composition (JM1L6027) produced by Johnson Matthey.

[0009] The present invention is directed to an improved enamel paste composition specifically tailored for use in the methods as described in U.S. Patent Application Publication No. 20170135160. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] U.S. Patent Application Publication No. 2017-0135160 Summary of the Invention [Means for solving the problem]

[0011] overview As discussed in the Background section, US20170135160 indicates that the composition of the enamel paste is not specifically tailored for use in a thin functional coating beyond the particle size characteristics of the glass frit and pigment and the viscosity of the enamel paste provided by the organic carrier medium. US20170135160 does not provide any information about the type of glass frit used in the enamel other than the use of a commercially available enamel composition from Johnson Matthey. Furthermore, there is no indication that the chemical composition of the glass frit has any effect on the surface roughness of the enamel and the thin functional coating that is subsequently placed on it. Rather, US20170135160 indicates that a smoother enamel surface can be achieved by using small particle size pigments in the enamel composition and also suggests modifications to the printing process used to place the enamel.

[0012] The present inventors have developed an improved enamel paste formulation for the applications described in US Patent No. 20170135160. Specifically, the improved enamel paste formulation comprises a composition having the following characteristics: (i) a glass frit composition having a low firing (melting) temperature such that the glass frit can soften and flow at low firing temperatures to provide a smooth enamel layer at low temperatures for application of a thin coating thereon; (ii) a glass frit composition having a high crystallization temperature so that during heating and bending of the coated glass article, the glass enamel does not crystallize and damage the thin functional coating disposed thereon; (iii) A glass frit composition that satisfies the properties of (i) and (ii) while also having good silver hiding and UV blocking properties after heating and bending of the coated glass article.

[0013] That is, the chemical composition of the glass frit component of the enamel paste affects the quality of the thin coating placed thereon and the resulting coated glass article. In particular, the glass frit must be tailored to have a low firing temperature and a high crystallization temperature to produce a surface enamel layer with low roughness and to avoid damage to the thin functional coating, both during deposition of the thin functional coating and during processing of the coated glass article (i.e., heating and bending of the coated glass article). The enamel must also possess good silver hiding and UV blocking properties, which are affected by the type and firing temperature of the glass frit, as well as the pigment.

[0014] Accordingly, the present disclosure provides an enamel paste composition adapted for applying a thin functional coating thereto. The enamel paste comprises: 30-40% by weight of bismuth silicate glass frit; 20-30% by weight of zinc silicate glass frit; 15 to 25% by weight of a pigment; and 10-20% by weight of an organic carrier medium; wherein the bismuth silicate glass frit contains at least silicon, bismuth, boron, and lithium, and is free of lead and cadmium; The zinc silicate glass frit contains at least silicon, zinc, sulfur, and lithium, and is free of lead, cadmium, and bismuth; The glass frit and pigment in the enamel paste each have a D90 particle size distribution of less than 15 micrometers; Enamel paste is 100s -1 Shear rate of 5 to 150 Pa s -1 The viscosity is

[0015] The zinc silicate frit provides the silver hiding properties to the enamel. The bismuth silicate frit allows the enamel to be processed at low temperatures and develops a smooth surface at low firing temperatures. The frit also has a high crystallization temperature. Thus, the combination of the two frits provides a smooth surface at low firing temperatures, silver hiding properties over a wide temperature range, and a high crystallization temperature.

[0016] Optionally, the bismuth silicate glass frit has the following composition (expressed as oxide components):

[0017] [Table 1]

[0018] Optionally, the zinc silicate glass frit has the following composition:

[0019] [Table 2]

[0020] The pigment is optionally a CuCr black pigment.

[0021] The present specification also provides a use of an enamel paste for producing a coated glass article comprising a glass substrate, an enamel layer disposed on the glass substrate, and a thin coating having a thickness of 0.5, 0.4, 0.3, 0.2, or 0.1 micrometers or less disposed on the enamel layer.

[0022] The enamel paste is tailored to the method of making coated glass articles, including but not limited to the type of coated glass articles described in US20170135160.

[0023] This method is disposing an enamel paste on a portion of a glass substrate; Firing the enamel paste at a temperature T1 to form an enamel layer; disposing a thin coating over at least a portion of the enamel layer, where the thin coating has a thickness of 0.5, 0.4, 0.3, 0.2, or 0.1 micrometers or less; Firing and bending the glass substrate having the enamel layer and the thin coating thereon at a temperature T2 higher than T1 to form a coated glass article. Consisting of Here, the enamel paste is formulated so that the firing temperature is lower than T1 and the crystallization temperature is higher than T2.

[0024] The paste compositions described above can be used in this method. However, it is also envisioned that the firing temperature T1 and bending temperature T2 may be different for different applications. In this case, the formulation of the enamel paste can be modified to have a firing temperature lower than T1 and a crystallization temperature higher than T2 so that the thin coating placed on the enamel is not damaged during processing, while also achieving the color properties and / or silver hiding properties required for the end use after processing at T2. Thus, the method herein is not limited to a specific enamel paste composition tailored for an end use with a specially defined T1 and T2. That is, those skilled in the art of enamel paste formulation will be able to use the teachings herein to modify the composition of the paste described herein to suit thin coating applications with different T1 and T2 values ​​and utilizing various bending processes, including, for example, sag bending, press bending, and variations thereof.

[0025] Advantageously, the enamel layer has a roughness Ra of less than or equal to 1, 0.7, 0.5 or 0.3 micrometers and / or a roughness Rz of less than or equal to 5, 4, 3, 2 or 1 micrometers. Furthermore, for shielding applications, the enamel layer advantageously has an L value of less than or equal to 5, 4.5, 4 or 3.5.

[0026] The thin coating may be disposed via a vacuum deposition process, such as a cathode sputtering process, as in the application described in US Patent Publication No. 20170135160. In addition to being disposed on at least a portion of the enamel layer, the thin coating may also be disposed on at least a portion of the glass substrate. Additionally, as also described in US Patent Publication No. 20170135160, the thin coating is electrically conductive and can optionally include multiple sublayers (e.g., two or three silver sublayers), and at least one electrical connector can be disposed in the thin coating on the enamel layer.

[0027] Although the enamel paste of the present invention has been developed for applications such as those described in US20170135160, it is envisioned that the enamel paste according to the present disclosure is also useful for other functional thin coatings on glass substrates, including electrical, optical, and thermal functional coatings. [Brief description of the drawings]

[0028] BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, and to show how it may be carried into effect, specific embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 shows the construction of an automotive glass panel of the type described in U.S. Patent No. 20170135160. [Diagram 2] FIG. 2 shows a flow diagram of the steps involved in providing a coated glass sheet for use in the automotive glass panel construction shown in FIG. [Figure 3(a)]FIG. 3(a) shows a flow diagram illustrating that if the firing (melting) temperature of the enamel paste composition is not lower than the firing temperature T1 and the crystallization temperature of the enamel paste composition is not higher than the bending temperature T2, following the method of FIG. 2 will result in damage to the thin film during processing. [Figure 3(b)] FIG. 3(b) shows a flow diagram illustrating that if the firing (melting) temperature of the enamel paste composition is not lower than the firing temperature T1 and the crystallization temperature of the enamel paste composition is not higher than the bending temperature T2, following the method of FIG. 2 will result in damage to the thin film during processing. [Figure 4] FIG. 4 shows the color development characteristics of an enamel layer formed using an enamel paste composition according to the present specification in terms of its L value versus firing temperature, the enamel being formulated to have a low L value at the final firing (bending) temperature T2 of the method for producing coated glass without crystallization. [Diagram 5] FIG. 5 shows the silver hiding properties of an enamel layer formed using an enamel paste composition according to the present specification in terms of its dE value versus firing temperature, the enamel being formulated to have a low dE value (good silver hiding) at the final firing (bending) temperature T2 of the method for producing coated glass without crystallization. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Detailed Description As discussed in the Background section, the glass panel configuration described in U.S. Patent Publication No. 20170135160 is shown in FIG. 1 and comprises two glass sheets 2, 4 joined by an interlayer sheet 6. The outer surface 8 of the outer glass sheet 2 is conventionally referred to as face 1, the inner surface 10 of the outer glass sheet 2 is conventionally referred to as face 2, and the surface 12 of the inner glass sheet 4 that faces the outer glass sheet 2 is conventionally referred to as face 1, while the inner surface 14 of the inner glass sheet 4 is conventionally referred to as face 4. An enamel layer 16 is formed on face 2 of the outer glass sheet. A thin coating 18 is formed on the enamel layer 16 and on the un-enamelized portions of face 2 of the outer glass sheet. Electrical bus bars 20 are formed in the thin coating 18 on the enamel layer 16. The glass sheets 2, 4 are fired, shaped, and then laminated with an interlayer sheet 6 to form a glass panel.

[0030] 1 has an enamel layer 16 and a thin coating 18 disposed on face 2 of a laminated glass panel including two glass sheets 2, 4, it should be noted that the invention is not limited to this configuration. For example, the enamel layer and the thin coating may be applied to different faces of such a laminated glass panel, or may be applied to a glass panel including a single glass sheet.

[0031] Figure 2 shows a flow diagram of the steps involved in providing an outer coated glass sheet 2 for the automotive glass panel construction shown in Figure 1. The method comprises disposing an enamel paste on face 2 of the outer glass sheet, firing at a temperature T1°C, applying a thin layer coating on the enamel and on the un-enameled portions of the outer glass sheet, applying a silver bus bar to the thin layer coating on the enameled portions of the outer glass sheet, and bending the coated glass sheet at a temperature T2°C.

[0032] 3(a) and 3(b) show a flow diagram illustrating that as long as the firing (melting) temperature of the enamel paste composition is not lower than the firing temperature T1 and the crystallization temperature of the enamel paste composition is higher than the bending temperature T2, following the method of FIG. 2 will result in damage to the thin coating during processing.

[0033] FIG. 3(a) shows the case where the enamel paste is first fired at a temperature T1 below the firing / melting temperature of the glass frit, which would be the case for a standard pre-firing step designed simply to remove the organic carrier medium rather than melting and fusing the glass frit, resulting in a rough surface that could damage the coated thin film if deposited on such a surface, for example using deposition techniques.

[0034] Figure 3(b) shows that even if the enamel paste is first fired at a temperature T1 higher than the firing / melting temperature of the glass frit, it still provides a smooth surface for depositing the thin coating, which may be damaged when bending the coated glass sheet if the bending temperature T2 exceeds the crystallization temperature of the glass enamel.

[0035] Thus, Figures 3(a) and 3(b) show that the glass frit in the enamel composition must have both a firing / fusing / melting temperature lower than T1 and a crystallization temperature higher than T2 to produce low surface roughness after firing at T1, in order to ensure that the thin coating is deposited in an intact form and remains in an intact form during processing (bending) at T2.

[0036] In addition to the above, the resulting enamel must meet the functional properties required for the application. For example, in the application of the automotive glass panel of FIG. 1, the enamel must have good optical properties and good silver hiding properties to (i) protect the glue / adhesive from UV degradation, and (ii) mask the silver busbars placed behind the enamel. These properties depend on the chemical composition of the glass frit and also on the final firing / bending temperature T2 used to process the enamel-coated glass sheet. Therefore, in this application, the enamel paste composition must be tailored to meet multiple requirements including a firing / melting / fusion temperature lower than T1, a crystallization temperature higher than T2, and also the optical and silver hiding properties required for the enamel paste composition for the final application after processing at T2. The enamel must also be chemically and structurally resistant to the deposition processes that produce thin coatings and thin coatings on the enamel. Additionally, automotive applications require that the enamel be acid resistant (0.1N H2SO4, 80°C for 4 hours) and that the coated glass sheets meet minimum mechanical strength specifications.

[0037] Provided herein is an enamel paste composition that meets all of the above requirements for an enamel suitable for use in combination with a thin functional coating, such as, for example, a self-heating or IR-reflective coating.

[0038] The enamel paste comprises (1) a bismuth silicate glass frit, (2) a zinc silicate glass frit, (3) a pigment, and (4) an organic carrier. Details of two example frit compositions in terms of equivalent oxides are provided below.

[0039] Bismuth silicate frit: [Table 3]

[0040] Zinc silicate frit: [Table 4]

[0041] The pigment may be, for example, an automotive back pigment such as a CuCr black pigment.

[0042] The frits and pigments are milled to the desired particle size distribution with D90<15 micrometers and mixed with an organic carrier formulation at a shear rate of 100 s -1 5 to 150 Pa·s -1 A paste having a viscosity of

[0043] An example of a paste formulation is shown in the table below: [Table 5] As shown in.

[0044] The novelty of this paste formulation lies in the subtle combination of properties that are brought to the enamel to make it compatible with the manufacturing process of self-heated automotive laminated glass panels. Self-heated windshields are a relatively new product that was introduced to the market in the past five years at the time of writing, and this specification enables improved performance of such self-heated windshields. As previously indicated, the main features of the enamel paste formulation include: (i) low firing temperature, (ii) smooth surface after firing, (iii) good silver hiding properties, and (iv) high crystallization temperature. The zinc silicate frit brings the silver hiding properties to the enamel. The bismuth silicate frit allows the enamel to be processed at low temperatures and forms a smooth surface at low firing temperatures. Both frits have high crystallization temperatures. Thus, the combination of the two frits provides a smooth surface at low firing temperature, silver hiding properties over a wide range of temperatures, and a high crystallization temperature to avoid crystallization during bending of the coated glass sheet. This combination of features makes it possible to apply a nanometer-scale silver coating onto enamel and then subject it to bending without damaging the coating.

[0045] In addition to the above, the enamel paste composition provides an enamel layer with good optical properties and silver hiding properties after firing at T2. Figure 4 shows the color development properties of the enamel layer formed using the enamel paste composition in terms of its L value versus firing temperature. The enamel is formulated to have a low L value at the final firing (bending) temperature T2 of the method for producing coated glass without crystallization. Figure 5 shows the silver hiding properties of the enamel layer formed using the enamel paste composition in terms of its dE value versus firing temperature. The enamel is formulated to have a low dE value (good silver hiding) at the final firing (bending) temperature T2 of the method for producing coated glass without crystallization.

[0046] The resulting paste can then be used to construct improved automotive laminated glass panels. The enamel paste is placed on a glass substrate, usually soda-lime glass, and dried and fired at a predetermined temperature to obtain a smooth enamel surface. A thin multi-layer silver coating is then placed on the glass sheet and enamel to form a resistive heating element or IR reflective barrier, after which a busbar is placed on top of the enamel in contact with the thin coating. The coated glass sheet is then heated and bent to form a shaped windshield component.

[0047] The particular paste composition described above is tailored to a particular windshield manufacturing process having particular T1 and T2 temperatures. However, it is also envisioned that for different applications, the firing temperature T1 and bending temperature T2 may be different. In this case, the formulation of the enamel paste may be modified to have a firing temperature lower than T1 and a crystallization temperature higher than T2 such that the thin coating placed on the enamel is not damaged during processing and at the same time achieves the desired color properties required for the end application after processing at T2. Thus, the method herein is not limited to a particular enamel paste composition tailored to an end application having a specifically defined T1 and T2. That is, one skilled in the art of enamel paste formulation will be able to utilize the teachings herein to modify the composition of the paste described herein to suit thin coating applications having different T1 and T2 values. The main important feature of the modified paste is that the formulation of the enamel paste has a firing temperature lower than T1 and a crystallization temperature higher than T2 such that the thin coating placed on the enamel is not damaged during processing and also achieves the desired optical properties required for the end application after processing at T2. Variations of the examples described herein can achieve functional changes for such end uses. Thus, while variations may fall within the scope of the frit compositions defined in the Summary section, it is also envisioned that combinations of different frit types may also meet the functional requirements of the methods described herein. Thus, while the present invention has been particularly shown and described with reference to certain examples, it will be understood by those skilled in the art that various changes in form and details can be made without departing from the scope of the invention as defined by the appended claims.

Claims

1. 30-40% by weight of bismuth silicate glass frit; 20-30 wt. % zinc silicate glass frit; 15 to 25% by weight of a pigment; 10-20% by weight of an organic carrier medium; Consisting of the bismuth silicate glass frit comprises at least silicon, bismuth, boron, and lithium, and is free of lead and cadmium; The zinc silicate glass frit contains at least silicon, zinc, sulfur, and lithium, and is free of lead, cadmium, and bismuth; the glass frit and the pigment in the enamel paste each have a D90 particle size distribution of less than 15 micrometers; The enamel paste is subjected to a shear rate of 100 s －１ Viscosity at 5 to 150 Pa·s －１ 2. An enamel paste comprising:

2. The bismuth silicate glass frit has the following composition: 【Table 1】 2. The enamel paste according to claim 1, having

3. The zinc silicate glass frit has the following composition: 【Table 2】 3. The enamel paste according to claim 1 or 2, wherein

4. 3. An enamel paste according to claim 1 or 2, wherein the pigment is a CuCr black pigment.

5. 3. Use of the enamel paste according to claim 1 or 2 for the manufacture of a coated glass article comprising a glass substrate, an enamel layer disposed on the glass substrate, and a thin coating having a thickness of 0.5 micrometers or less disposed on the enamel layer.

6. Placing the enamel paste according to claim 1 or 2 on a part of a glass substrate; Firing the enamel paste at a temperature T1 to form an enamel layer; disposing a thin coating over at least a portion of the enamel layer; firing and bending the glass substrate having the enamel layer and the thin coating thereon at a temperature T2 greater than T1 to form a coated glass article; Consisting of the thin coating has a thickness of less than 0.5 micrometers; 11. A method for producing a coated glass article, wherein the enamel paste is formulated to have a firing temperature below T1 and a crystallization temperature above T2.

7. The method according to claim 6 , wherein the enamel layer has a roughness Ra of 1 micrometer or less and / or a roughness Rz of 5 micrometers or less.

8. The method of claim 6 , wherein the enamel layer has an L value of 5 or less.

9. The method of claim 6 , wherein the thin coating is disposed on at least a portion of the glass substrate in addition to being disposed on at least a portion of the unfired enamel layer.

10. The method of claim 6 , wherein the thin coating is electrically conductive and at least one electrical connector is disposed in the thin coating on the pre-fired enamel layer.

11. The method of claim 6 , wherein the thin coating comprises multiple sub-layers.

12. The method of claim 6 , wherein the thin coating is deposited by a vacuum deposition process.

13. The method of claim 6 , wherein the thin coating has a thickness of 0.4, 0.3, 0.2, or 0.1 micrometers or less.

14. A coated glass article produced according to the method of claim 6.

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