Enamel paste composition and coating method thereof, and chemically strengthened glass substrate

Abstract

1. A paste for coating glass substrates, which after coating is subjected to firing and chemical strengthening by ion exchange to form an enamel-coated, chemically strengthened glass product, the paste comprising an organic carrier liquid, a first inorganic frit having a first softening point, and a second inorganic frit having a second softening point, the softening point of the first inorganic frit being higher than the softening point of the second inorganic frit such that the second inorganic frit can be softened and sintered at a temperature lower than the softening point of the first inorganic frit, the first inorganic frit comprising a content of exchangeable ions capable of being ion-exchanged to chemically strengthen the first inorganic frit.

Description

Technical Field

[0001] field This specification relates to methods of coating and chemically strengthening enamel paste compositions and glass substrates.

Background Art

[0002] background Enamels are widely used, for example, for decoration or coating of substrates such as glass, metal, and ceramic. Applications include tableware, signs, tiles, cover glass for electronic devices, automotive glass, architectural glass, etc. Enamels are particularly useful, for example, in forming color borders around glass sheets used for windows and screens such as cover glass for electronic devices and front glass for automobiles. The color border can improve the appearance and prevent deterioration of the underlying adhesive by ultraviolet rays. Furthermore, it can also hide bus bars and connection parts of wiring.

[0003] Enamels usually consist of pigments and glass frit. Generally, they are applied to a substrate (e.g., glass surface) in an organic carrier liquid as pastes and inks, for example, by screen printing and inkjet printing. In this specification, the term "paste" is used, and it will be understood that this includes compositions that may also be referred to as inks for inkjet printing, for example.

[0004] Thus, enamel paste consists of particles of pigments and glass frit dispersed in a liquid dispersion medium. After applying the paste coating to a substrate, the paste is usually dried, and the applied coating is fired, i.e., heat-treated, so that at least a part of the frit particles softens and fuses (or melts; fuse), fuses to the substrate, thereby forming an enamel coating adhered to the substrate. During firing, the pigment itself usually does not soften and is fixed to the substrate by the frit or together with the frit.

[0005] Glass sheets used for certain applications are subjected to a pressure molding process to bend the glass into the desired final shape. Generally, before being subjected to high-temperature press bending, a paste is applied to the desired areas of such glass sheets in a printing process. The high temperature used in this process burns the coating, softens the glass sheet, and allows it to be molded into the desired final shape using a forming die or mold. Pressure molding is used, for example, in the manufacture of automobile windows, electronic device covers and screens, glass bottles, architectural glass, and appliance glass. In these examples, it may be desirable to apply enamel for decorative and / or functional reasons. [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] A problem with this method is that the enamel can adhere to the mold during press bending, damaging the enamel coating. Therefore, the enamel paste needs to be formulated to have low viscosity at press bending temperatures to mitigate the problem of adhesion to the mold.

[0007] In addition to the above, it is desirable for many applications to manufacture glass products with increased strength. This may be necessary to improve strength in a given application and / or to allow the use of thinner glass, while maintaining the desired level of strength, saving on material requirements, and reducing weight. In this regard, chemically strengthenable glass materials have been developed. Such glass materials consist of ions that can exchange for larger ions in an ion exchange process. For example, glass materials may consist of sodium ions that can exchange for potassium ions. Thus, chemical strengthening is the process of strengthening the surface of glass by exchanging smaller ions, such as sodium, for larger ions, such as potassium. This ion exchange creates a thin, highly compressible layer on the surface, resulting in a tensile layer in the center. This process is carried out by immersing the glass in a molten salt bath (e.g., molten KNO3).

[0008] In applications requiring non-planar chemically strengthened glass, the glass may be press-bent to the desired shape before undergoing the chemical strengthening process. This sequence is preferred because it facilitates press-bending the glass before strengthening. Furthermore, press-bending after chemical strengthening may reduce the strength of the final product.

[0009] Such molded and chemically strengthened glass screens are desired for mobile phone cover screens. In recent years, there has been a movement to use 3D-shaped glass cover screens. For example, the edges of the screen can be curved for aesthetic reasons and / or to avoid sharp edges, while the glass screen can be extended to the outer edge of the mobile device, increasing the screen area for a given device size. It is also desirable to have a screen with higher strength to mitigate damage in the event of a fall or other impact. Furthermore, it is desired to provide thin and lightweight devices that require thin screens. Chemical strengthening helps to reduce the thickness of the glass while achieving the strength required for robust mobile devices.

[0010] Such formed and chemically strengthened glass screens are also desired for other applications. For example, in automobiles, there is a demand for more efficient and lighter vehicles while maintaining or improving safety standards. By using chemically strengthened glass windows, it is possible to provide thinner and lighter windows while maintaining high strength performance. These characteristics are also expected to contribute to improving the performance of electric vehicles and hydrogen fuel cell vehicles.

[0011] Such applications often require the application of an enamel coating to chemically strengthened glass. This enamel coating may be applied after chemical strengthening. However, firing enamel paste on a chemically strengthened glass substrate generally reduces the strength of the glass substrate. For example, heating a chemically strengthened glass substrate to fire the enamel coating can cause ion migration within the glass substrate, reducing the chemical strengthening that had been imparted to it.

[0012] One possible approach is to use a coating that does not require such high-temperature firing. For example, organic ink could be used instead of enamel. However, such organic inks are not as hard or scratch-resistant as enamel coatings. Furthermore, if there is a process of shaping the glass before chemical strengthening, applying the coating after the shaping and chemical strengthening steps would require printing on a non-planar substrate, which is time-consuming and costly.

[0013] Therefore, it is desirable to apply the enamel coating before chemical strengthening, and in the case of non-planar products, before the molding process, so that the enamel coating is applied to the glass substrate in a form that is not yet planar and strengthened.

[0014] In this regard, US9487439B2 proposes a method for decorating and strengthening glass substrates, which includes the following: a. Applying an enamel composition to a glass substrate, the enamel composition comprising a pigment and 45-100% by weight of glass enamel frit containing at least one replaceable alkali metal ion, b. To flow and sinter the glass enamel frit, thereby firing the glass substrate at a firing temperature sufficient to form colored enamel attached to the glass substrate, and c. Placing the enameled glass substrate in a bath of molten salt, the molten salt containing monovalent metal ions larger than the replaceable alkali metal ions in the glass, The glass enamel frit has a softening point between the temperature of the molten bath and the softening point of the glass substrate, so that the colored enamel remains as a decorative functional layer on the glass substrate.

[0015] US9487439B2 is "Useful frits will have a softening point that falls within the range between the temperature of the molten ion exchange bath and the softening point of the substrate glass. For example, molten potassium nitrate baths commonly used for ion exchange are generally operated in the range of about 350 to 400°C. Soda-lime substrate glass is generally processed at a temperature of about 600 to 700°C. Therefore, the softening point window for such systems is about 425 to 575°C." Identify.

[0016] The main characteristics of glass frit for enamel paste include: (i) having a softening point lower than the softening point of the substrate so that it can be fired on the substrate without damaging the substrate; (ii) having a softening point higher than the temperature of the molten bath so that the enamel coating is not damaged by the molten bath during the chemical strengthening process; (iii) the glass frit must contain exchangeable ions such that the glass in the enamel coating can be chemically strengthened; and (iv) the glass frit should have a coefficient of thermal expansion (CTE) close to the coefficient of thermal expansion of the substrate glass.

[0017] US9487439B2 lists numerous potential oxide components for glass frit and a range of potential quantities for these components. These components and quantities are shown to be typical for lead-free frit useful for glass decoration. All examples in US9487439B2 use commercially available lead-free sodium-containing glass frit in the paste.

[0018] Summary of the Invention The inventors have found it difficult to identify a commercially available frit that adequately meets all the requirements for coating and chemical strengthening glass products in specific, high-demand applications, such as mobile phone cover glass and automotive applications. A compromise is needed between the requirements for a frit to form a good enamel coating and the requirements for a frit to provide glass products with a very strong enamel coating. Commercially available frits that meet the softening point requirements to form a good enamel coating and then form an enamel coating on a substrate that has undergone a chemical strengthening process have been found to result in glass products that are not sufficiently strong to meet the requirements of the required applications.

[0019] Therefore, there is a need for enamel-forming compositions that can be well-treated on various chemically strengthened glass substrates, resulting in coated glass articles with improved properties. In particular, there is a need for enamel-forming compositions that allow for easy printing onto substrates subjected to chemical strengthening, resulting in coated glass products with excellent toughness and strength. The enamel should also provide a high-quality coating with good physical, optical, and chemical properties. [Means for solving the problem]

[0020] This specification is aimed at addressing these problems. In particular, this specification describes a solution where the enamel paste is formulated using at least two inorganic frits: a first frit that is adjusted to provide improved toughness and strength and that, in certain examples, is in powder form of the same material used for a substrate (e.g., Gorilla (trademark) glass from Corning (trademark)); and a second frit that has a lower softening temperature and is adjusted to provide a high-quality sintered enamel coating upon firing, but has a sufficiently high softening temperature so as not to be damaged by the chemical strengthening process that is carried out after coating and firing.

[0021] It has been found that using a material for the frit formulation of the paste that is the same as or similar to the substrate is advantageous for improving the toughness and strength of the enamel coating product after firing and chemical strengthening. This material is already optimized for the chemical strengthening process used for the chemical strengthening of the substrate. Thus, it can be said to be an ideal choice for the coating. Also, using the same or similar material for the coating and the substrate ensures a good matching of the thermal expansion coefficients between the coating and the substrate.

[0022] Of course, the problem with using the same inorganic material for the coating and the substrate is that the frit in the coating cannot be sintered unless it also softens the substrate. Therefore, this specification provides a paste having a second frit with a lower softening point that can be sintered at a temperature lower than the softening points of the substrate and the first frit in the paste composition. As a result, an enamel coating is obtained that comprises particles of the first frit embedded in a continuous matrix of the sintered second frit. To ensure that the first frit does not soften and sinter during the sintering of the second frit and to achieve a smooth and high-quality enamel coating, the first frit can be processed to provide fine powder with a small particle size.

[0023] Despite the fact that the first frit does not reach its softening point and sinter during the coating sintering step and remains as discrete particles dispersed in the sintered second frit, it has been found that a significant amount of the first frit can be incorporated into the paste formulation and yet a good quality enamel coating can be achieved.

[0024] Furthermore, despite the first frit remaining unsintered, it has been found that the toughness / strength of the final enamel-coated glass product after chemical strengthening is improved. Without being bound by theory, one possible mechanism is that the first frit, which is a material the same as or similar to the substrate, is strengthened in the same or a similar manner as the substrate material. The ion exchange process in which smaller ions are replaced by larger ions forms a thin layer of high compression on the surface of the enamel in a similar manner to the uncoated surface area of the substrate. As another mechanism, in-situ ion exchange between the first and second frits can occur prior to the chemical strengthening step. One or more of the aforementioned mechanisms may contribute to the chemical strengthening of the enamel coating. Regardless of the underlying mechanism, it has been found that the chemical strengthening of the enamel coating can be achieved without breaking the enamel coating. In addition, a better matching of the properties of the enamel and the substrate is achieved, leading to an improvement in the chemically strengthened enamel-coated glass product.

[0025] In fact, the analysis results show that the second (lower softening point) frit not only acts as a sintering aid during enamel coating formation but also plays a crucial role in the chemical strengthening mechanism of the multi-frit system. Thus, the composition of the second (lower softening point) frit can be formulated in combination with the first (higher softening point) frit to provide a multi-frit system optimized for the chemical strengthening process. In this regard, the second frit is preferably bismuth silicate glass frit or zinc borosilicate glass frit (e.g., comprising 40-70% by weight of Bi2O3 and 10-40% by weight of SiO2). Furthermore, the first frit is preferably aluminosilicate glass frit (e.g., comprising 50-70% by weight of SiO2 and 15-25% by weight of Al2O3). The combination of aluminosilicate glass frit with bismuth silicate glass frit or zinc borosilicate glass frit has been found to be particularly advantageous in that it is optimized for the chemical strengthening process.

[0026] Advantageously, in the case of molded glass products, the step of sintering the second frit in the paste is performed simultaneously with the press bending of the glass substrate. Thus, this process comprises depositing / printing a dual frit paste onto a flat, unstrengthened glass substrate; pre-firing to remove the carrier liquid component of the paste; forming the substrate by press bending at a high temperature (e.g., between 700°C and 800°C) and sintering the second frit in the coating during the formation of the substrate to form an enamel coating; and then subjecting the enamel-coated glass substrate to chemical strengthening, for example, by immersion in a molten salt bath. The enamel thus obtained exhibits mechanical and optical properties that meet the requirements of demanding end-uses. For example, the obtained enamel may exhibit an exclusion L value measurement of less than 5 and an optical density greater than 3. [Brief explanation of the drawing]

[0027] Brief explanation of the drawing For a better understanding of the present invention and to illustrate how it can be put into practice, certain embodiments of the present invention are described only as illustrative, with reference to the accompanying drawings. [Figure 1] Figure 1 is a flowchart of the basic process steps for enamel coating and chemical strengthening a glass substrate. [Figure 2] Figure 2 is a schematic diagram of an enamel-coated and chemically strengthened glass product formed using the process shown in Figure 1. [Figure 3] Figure 3 is a flowchart illustrating the basic process steps of enamel coating, press bending, and chemical strengthening of a glass substrate. [Figure 4] Figure 4 is a schematic diagram of a molded, enamel-coated, and chemically strengthened glass product formed using the process shown in Figure 3. [Modes for carrying out the invention]

[0028] Detailed explanation This specification provides a paste for coating glass substrates, which, after coating, are subjected to sintering and ion exchange for chemical strengthening to form enamel-coated, chemically strengthened glass products. The paste comprises an organic carrier fluid, a first inorganic frit having a first softening point, and a second inorganic frit having a second softening point, wherein the softening point of the first inorganic frit is higher than that of the second inorganic frit, so that the second inorganic frit can be softened and sintered at a temperature lower than that of the second inorganic frit and lower than that of the substrate to which the coating is applied.

[0029] It should be noted that the "softening point" is a well-known and frequently used parameter in the field of glass materials. The softening point refers to the first temperature at which signs of softening or deformation of the frit are observed. This can be measured using a hot stage microscope (HSM). In addition or alternatively, the dilatometric softening point is defined as the temperature at which the viscosity of the frit reaches 10⁻¹⁰. 11.3This is the temperature at which the temperature becomes dPa·s, and it can also be measured by dilatometry.

[0030] An alternative or additional way to define the inorganic frits in the paste is in terms of their glass transition temperatures. In this case, the glass transition temperature of the first inorganic frit is higher than that of the second inorganic frit. Otherwise, the paste can be defined in the same manner as described herein.

[0031] Additional frit can be added to the mixture to improve the thermal expansion coefficient of the enamel or to improve the fluidity of the resulting mixture. The first inorganic frit comprises an exchangeable ion content that can be ion-exchanged to chemically strengthen the frit in the enamel coating, for example by in-situ ion exchange and / or during the same process used to chemically strengthen the glass substrate on which the enamel coating is placed. The second inorganic frit may also comprise an exchangeable ion content that, in addition to the first inorganic frit, can be ion-exchanged to chemically strengthen the second inorganic frit. However, since the composition of the second inorganic frit must be adjusted for its sintering properties rather than for glass strengthening, the chemical strengthening properties of the second inorganic frit (at least separately from the first frit) are generally lower than those of the first inorganic frit. Thus, the exchangeable ion content of the second inorganic frit is typically lower than that of the first inorganic frit, and / or the surrounding glass matrix prevents ion exchange from producing the same level of chemical strengthening as in the case of the first inorganic frit and glass substrate material, at least in the separation of the first frit. However, as mentioned earlier, preliminary analytical studies have also shown that, when present in a multi-frit system, the second (low softening point) frit contributes more to the chemical strengthening mechanism than expected, and that even if the exchangeable ion content of the second frit is lower than that of the first frit, it may still be just as important as the first frit in the chemical strengthening process.

[0032] As shown in the overview section, in one example, the first inorganic frit can be made from the same material as the glass substrate to which the enamel coating is applied. However, in other examples, the first inorganic frit can be made from a different material than that of the substrate, as long as it is a material adapted to have an exchangeable ion content that can be ion-exchanged to chemically strengthen the frit in the enamel coating by in-situ ion exchange and / or during the same process used to chemically strengthen the glass substrate to which the enamel coating is applied. In other words, the first inorganic frit is a material adapted to chemical strengthening properties and does not need to have a low softening point for sintering on the substrate. For example, the first inorganic frit can be formed from the same material as the substrate or a different type of glass material, adapted / optimized for chemical strengthening properties rather than the softening and flowing properties associated with conventional enamel coating formation.

[0033] One factor determining the ability of a glass material to be chemically strengthened by ion exchange is, obviously, the amount and type of exchangeable ions in the glass material. In this regard, the first inorganic frit may consist of an amount of exchangeable ions defined by the weight of equivalent oxides within the range defined by 6% or more by weight, 7% or more by weight, or 8% or more by weight; 15% or less by weight, 12% or less by weight, 10% or less by weight, or 9% or less by weight; or any combination of the aforementioned upper and lower limits. In this regard, it should be noted that a glass composition is conventionally defined by the weight percentage of oxide components used to manufacture the glass composition. Thus, it is appropriate to define the exchangeable ion content in terms of the equivalent oxide content used in the manufacture of the glass material.

[0034] The content of exchangeable ions can be provided, for example, by alkali metal ions such as lithium and / or sodium. Particularly useful is high-sodium content glass in which the sodium ion content is exchangeable for potassium ions when placed in a molten bath containing potassium ions. For example, if the exchangeable ion is sodium ions, the first inorganic frit may contain 7-10% by weight of Na2O. However, the use of other ion exchange systems is also conceivable. For example, it is known that glass can be chemically strengthened using cesium ions.

[0035] It is important to note that the chemical strengthening of glass materials is not solely governed by their exchangeable ion content, such as alkali metal content and, more specifically, sodium content. The amount of chemical strengthening also depends on the glass matrix surrounding the exchangeable ions. The amount, depth, and rate of ion exchange in a molten ion exchange bath are influenced by the surrounding glass matrix. Furthermore, the surrounding glass matrix affects the amount of stress generated by ion exchange. Thus, it should be noted that optimizing the chemical strengthening capacity of glass materials is not simply a matter of selecting glass materials with a high content of exchangeable ions (e.g., sodium).

[0036] In a particular example, the first inorganic frit may be an aluminosilicate glass frit comprising 50–70 wt% SiO2 and optionally 15–25 wt% Al2O3. As previously shown, the aluminosilicate glass frit may contain exchangeable ion content in the form of Na2O content, as previously defined. In addition, the first inorganic frit further comprises one or more (or one or more) of the following: 1–5 wt% Li2O; 0.2–2 wt% K2O; 0–1 wt% CaO; 0–1 wt% MgO; 0–1 wt% ZrO2; 0–1 wt% B2O3; and 1–5 wt% P2O5. These components and amounts correspond to commercially available glass materials prepared for chemical strengthening, such as Corning® Gorilla® glass.

[0037] When forming the enamel coating, the first inorganic frit does not need to soften and sinter, as these requirements are met by the second inorganic frit in the paste; therefore, the first inorganic frit does not need to have a softening point lower than the softening point of the glass substrate. The first inorganic frit may have a softening point within the range defined by 500°C or higher, 550°C or higher, 575°C or higher, 600°C or higher, 650°C or higher, 700°C or higher, 750°C or higher, or 800°C or higher; 1000°C or lower, 900°C or lower, or 850°C or lower; or any combination of the aforementioned upper and lower limits. In certain examples, for instance, if the first frit is made of the same material as the substrate, the softening point of the first inorganic frit will be the same as or substantially the same as the softening point of the glass substrate.

[0038] In addition to improving the chemical strengthening of the enamel coating, the first inorganic frit has the function of providing the enamel coating with a better thermal expansion coefficient match to that of the substrate. The glass substrate may have a thermal expansion coefficient that matches the first inorganic frit more closely than that of the second inorganic frit. This usually means that the first inorganic frit has a lower thermal expansion coefficient than that of the second inorganic frit. If the substrate is made of the same material as the first inorganic frit, the materials of the substrate and the first inorganic frit will exhibit the same thermal expansion coefficient.

[0039] The paste may contain an amount of first inorganic frit within the range defined by weight percentage of the paste's solid content: 50% by weight or less, 40% by weight or less, 30% by weight or less, 20% by weight or less, or 15% by weight or less; 2% by weight or more, 5% by weight or more, 8% by weight or more, or 10% by weight or more; or any combination of the aforementioned upper and lower limits. The lower limit is determined by the amount of chemically strengthened glass required to achieve the desired strength / toughness in the end application. The upper limit is determined by the amount of such material that can be incorporated into the enamel composition while providing a good quality enamel coating with good aesthetic, physical, optical, and chemical properties.

[0040] As previously stated, the second inorganic frit in the enamel paste composition is selected to have a lower softening temperature than the first glass frit and the substrate, and to provide a good quality sintered enamel coating during firing. The second inorganic frit must still have a sufficiently high softening temperature so as not to be damaged by chemical strengthening treatments performed after coating and firing. Thus, the second inorganic frit has softening and flow properties related to conventional enamel coating formation within a required temperature window, the lower end of which is defined by the temperature of the molten ion exchange bath and the upper end by the softening point of the glass substrate, but it can be selected as a more conventional glass frit used in enamel coating.

[0041] In other words, the second inorganic frit can be adjusted to optimize its compatibility with the first inorganic frit and the glass substrate in order to optimize the properties of the final product. As previously shown, the second frit can play a role in the chemical strengthening process in addition to its function as a sintering aid in the enamel coating. The second inorganic frit may be, for example, bismuth silicate glass frit, and may consist of 40-70% by weight or 45-70% by weight of Bi2O3 and / or 10-40% by weight or 20-40% by weight of SiO2. Alternatively, the second frit may be zinc borosilicate glass frit. In addition to the first inorganic frit, the second inorganic frit may contain exchangeable ion-containing materials that can be ion-exchanged to chemically strengthen the second inorganic frit. However, the exchangeable ion content of the second inorganic frit is usually lower than that of the first inorganic frit. For example, the second inorganic frit may contain an amount of exchangeable ions defined by the weight of equivalent oxides within the range defined by 0% by weight or more, 1% by weight or more, 2% by weight or more, or 2.8% by weight or more; 6% by weight or less, 5% by weight or less, 4% by weight or less, or 3.5% by weight or less; or any combination of the aforementioned upper and lower limits. In a particular example, the second inorganic frit consists of 1 to 5 wt% of Na2O.

[0042] Furthermore, the second inorganic frit may further contain one or more of the following: 2.5–5.5 wt% B2O3; 3–5 wt% Li2O; 1–2 wt% ZnO; 0–1 wt% P2O5; 0–1 wt% MgO; and 0–1 wt% CuO. These components and amounts for the second inorganic frit have been found to be suitable for use in combination with the first inorganic frit and glass substrate formed in Corning® Gorilla® glass. It is also assumed that this formulation is suitable for use in similar chemically strengthened glass materials.

[0043] As previously stated, the second inorganic frit should be selected to have softening and flow properties for enamel coating formation within a temperature window defined at its lower end by the temperature of the molten ion exchange bath and at its upper end by the softening point of the glass substrate. The specific material selected and its softening point depend somewhat on the substrate, the material of the first glass frit, and the temperature of the molten ion exchange bath used, as these selections will set the temperature window for sintering the second inorganic frit. However, typically, the second inorganic frit is selected to have a softening point within the paste / enamel composition defined by a range of 650°C or less, 600°C or less, 575°C or less, 550°C or less, or 500°C or less; 350°C or more, 375°C or more, 400°C or more, 425°C or more, 450°C or more, or 475°C or more; or any combination of the aforementioned upper and lower limits.

[0044] The softening point of the second inorganic frit should be lower than its sintering temperature. Typically, the second inorganic frit should have a sintering temperature in the range of 700°C and 850°C (or optionally 700°C and 800°C). In this regard, it should be noted that the second inorganic frit may fuse at a lower temperature range on its own, but when used with the first frit (and other components of the paste, such as pigments), it provides a suitable sintering temperature range for the chemical strengthening process. That is, the second frit provides a suitable sintering temperature window for the chemical strengthening process only when used with other components in the paste / enamel, so the sintering behavior of the second frit described herein should be understood in this context. The softening and firing behavior of the second frit must be selected to provide the necessary properties when combined with other components in the paste / enamel. Furthermore, typically, the first inorganic frit does not sinter at this temperature, so the second inorganic frit sinters around the unsintered particles of the first inorganic frit, forming a continuous, fused, sintered glass matrix in which the particles of the first inorganic frit are distributed.

[0045] As mentioned above, for certain applications, the paste should provide an enamel coating with a dark color and a low L value. It has been found that the crystallization behavior of the secondary frit is important for achieving a low L value. Therefore, the secondary frit can be selected to be a low-crystallinity frit.

[0046] The paste may consist of a second inorganic frit in an amount defined by the weight percentage of the paste's solid content as 80% by weight or less, 60% by weight or less, 50% by weight or less, 45% by weight or less, or 43% by weight or less; 20% by weight or more, 30% by weight or more, or 40% by weight or more; or any combination of the aforementioned upper and lower limits. The lower limit is determined by the amount of second inorganic frit required to form a continuous molten sintered glass matrix in which the particles of the first inorganic frit are distributed. The upper limit depends on the amount of first inorganic frit required to achieve the desired strength after chemical strengthening.

[0047] For specific applications, it is desirable that the paste can be fired and press-bent at temperatures ranging from 700°C to 850°C (or optionally from 700°C to 800°C) without sticking to the press-bending equipment. Thus, the second inorganic frit should be formulated to sinter within this temperature range and possess anti-tack properties at this sintering temperature.

[0048] In applications where a colored enamel coating is desired, the paste may further contain a pigment. The type of pigment depends on the desired color, optical density, etc., for the final application. In certain applications, the pigment may consist of one or more of Cr, Cu, Co, and Mn. Furthermore, the paste may contain an amount of pigment within the range defined by the weight percentage of the paste's solids: 30% by weight or less, 25% by weight or less, or 22% by weight or less; 10% by weight or more, 15% by weight or more, or 19% by weight or more; or any combination of the aforementioned upper and lower limits.

[0049] The paste may also consist of seed frits, for example, ZnO and SiO2. The paste may consist of seed frits in amounts defined by the weight percentage of the paste's solids: 20% by weight or less, 15% by weight or less, or 12% by weight or less; 5% by weight or more, 7% by weight or more, or 9% by weight or more; or any combination of the aforementioned upper and lower limits.

[0050] The paste compositions described above can be used in methods for coating and chemically strengthening glass substrates. These glass substrates may be cover glass for electronic devices, cover glass for mobile phones, car windows, or building windows.

[0051] This specification also describes a method for coating a glass substrate, Depositing the paste described herein onto a glass substrate, The glass substrate is heated to sinter the second inorganic frit of the paste, forming an enamel-coated glass substrate, and The enamel-coated glass substrate is subjected to an ion exchange process to chemically strengthen it by exchanging at least some of the exchangeable ion content in the substrate with the first inorganic frit. It consists of, The glass substrate contains exchangeable ion-containing material that can be ion-exchanged to chemically strengthen the glass substrate, and the glass substrate has a softening point lower than the softening point of the second inorganic frit of the paste. Provide a method.

[0052] In the method described above, the glass substrate may contain the same or similar amounts of the same exchangeable ions as the first inorganic frit. For example, the glass substrate may contain exchangeable ions in amounts defined by the weight of the equivalent oxide within the range defined by any combination of the aforementioned upper and lower limits: 15% by weight or less, 12% by weight or less, 10% by weight or less, or 9% by weight or less; 6% by weight or more, 7% by weight or more, or 8% by weight or more; or any combination of the aforementioned upper and lower limits. In a particular example, the glass substrate may contain 7-10% by weight of Na2O.

[0053] Similarly, the softening point of the glass substrate may be the same as or similar to the softening point of the first inorganic frit. That is, the glass substrate may have a softening point within the range defined by 500°C or higher, 550°C or higher, 575°C or higher, 600°C or higher, 650°C or higher, 700°C or higher, 750°C or higher, or 800°C or higher; 1000°C or lower, 900°C or lower, or 850°C or lower; or any combination of the aforementioned upper and lower limits.

[0054] The glass substrate may have a coefficient of thermal expansion closer to that of the first inorganic frit than to that of the second inorganic frit.

[0055] The substrate may also have other components identical or similar to those forming the material of the first inorganic frit. For example, the substrate may be an aluminosilicate glass, which may consist of, for example, 50-70% by weight of SiO2 and 15-25% by weight of Al2O3. In addition, the glass substrate may further contain one or more of the following: 1-5% by weight of L2O, 0.2-2% by weight of K2O, 0-1% by weight of CaO, 0-1% by weight of MgO, 0-1% by weight of ZrO2, 0-1% by weight of B2O3, and 1-5% by weight of P2O5. These components and amounts are equivalent to those of commercially available glass materials prepared to chemically strengthen, for example, Corning®'s Gorilla® glass. According to a particular example, the glass substrate is formed of the same material as the first inorganic frit in the paste.

[0056] In a method for forming an enamel coating, the heating step includes, for example, heating to a temperature in the range of 700°C to 800°C, and heating the glass substrate to a temperature between the softening temperatures of the first and second inorganic frits of the paste to sinter the second inorganic frit that forms the enamel-coated glass substrate without softening the first inorganic frit or the glass substrate.

[0057] This method may further include a press-bending step for shaping the glass substrate. In this regard, after applying paste to the glass substrate, the glass substrate is further press-bent to shape it before chemically strengthening the glass substrate by ion exchange treatment. It is preferable to shape the substrate by press-bending at the same time as sintering a second inorganic frit to form an enamel coating on the glass substrate. In this way, the coating is sintered simultaneously with the shaping of the substrate without requiring an additional processing step for forming the enamel coating.

[0058] After sintering the enamel coating and forming the glass substrate, the enamel-coated product is subjected to chemical strengthening by ion exchange. The ion exchange process involves placing the enamel-coated glass substrate into a molten ion exchange bath, such as a molten bath of KNO3. The resulting coated and chemically strengthened glass products have been found to have improved strength and toughness compared to other enamel-coated and chemically strengthened glass products, making them advantageous for use in a variety of applications. For example, the coated glass product could be a cover glass for an electronic device, a cover glass for a mobile phone, a car window, or an architectural window.

[0059] Figure 1 shows a flowchart of the basic process steps for chemical strengthening of enamel coatings and glass substrates. The method comprises the following steps: (a) Start with an unreinforced, flat glass substrate made of glass material. The glass material is formulated to have smaller ions (e.g., sodium ions) that can exchange with larger ions (e.g., potassium ions) when placed in a molten salt bath. The glass substrate material also has a matrix structure that allows for ion exchange and generates stress in the surface layer when exchange occurs, thereby increasing the strength / toughness of the glass substrate. An example of a glass material suitable for a substrate is Corning®'s Gorilla® glass. (b) Print an enamel paste comprising the first and second frit components onto a flat, untempered glass substrate. As previously stated, the first frit component is selected for chemical strengthening and has a composition and properties similar to or identical to the substrate material. In contrast, the second frit has a composition and properties selected to provide a good quality enamel coating when sintered on the substrate. (c) Pre-sinter the enamel paste to remove the liquid carrier component. When forming an enamel coating, it is typical to heat the paste on the substrate after deposition to evaporate the liquid carrier before the main firing step. This heating is at a temperature lower than the main firing / sintering temperature. (d) After pre-firing, the main firing step is carried out to sinter the second frit component of the enamel paste and form a sintered enamel coating on the glass substrate. In this step, the second frit of the enamel coating softens and flows, and the frit particles fuse to form a continuous glass matrix that forms the enamel coating. Typically, the first frit does not soften and flow during this step, but rather remains as discrete particles embedded in the continuous glass matrix formed by the second frit. (e) Finally, the coated enamel-coated glass substrate is chemically strengthened by immersion in a molten salt bath. Smaller ions in the glass substrate and the first frit component of the enamel coating are exchanged for larger ions that generate stress in the surface layer, strengthening the glass substrate and the enamel coating. The second frit component of the enamel coating (formed on the sintered coating in the previous firing step) may also contain some amount of exchangeable ions, but the amount of such ions and / or the amount of stress and / or the strengthening / strengthening component generated in the second frit is generally less than the amount of the substrate and the first frit component.

[0060] Figure 2 shows a schematic diagram of an enamel-coated chemically strengthened glass product formed using the process shown in Figure 1. Note that this is an illustrative drawing only and is not to scale. The product comprises a chemically strengthened glass substrate 2 and an enamel coating 4. The enamel coating 4 comprises particles of first frit 6 arranged within a continuous glass matrix 8 formed by second frit.

[0061] Figure 3 shows a flowchart of the basic process steps for enamel coating, press bending, and chemical strengthening of a glass substrate. The process is very similar to the process shown in Figure 1, except that in step (d), the coated glass substrate is fired to form the enamel coating, and then press-bent to shape the coated glass substrate into the desired shape (non-planar) for end applications such as molded cover screens for mobile electronic devices or automotive windows. In this regard, the second frit component of the enamel paste is selected to be sintered at the temperature used for heating and shaping the substrate.

[0062] Figure 4 shows a schematic diagram of a molded, enamel-coated, chemically strengthened glass product formed using the process shown in Figure 3. The structure is similar to the product shown in Figure 2, but it includes a molded, non-planar substrate. The product comprises a chemically strengthened molded glass substrate 2 and an enamel coating 4. The enamel coating 4 comprises particles of a first frit 6 arranged within a continuous glass matrix 8 formed by a second frit.

[0063] As previously stated, the paste compositions, coatings, and chemical strengthening methodologies described herein can be used in a variety of applications. One application is the cover screen of a curved 3D mobile phone. In recent years, certain manufacturers have introduced mobile phone designs that incorporate screens made of, for example, Gorilla Glass 5, particularly those with curved edges. Because the 3D forming and molding process for Gorilla Glass 5 must be carried out at temperatures exceeding 750°C, and organic inks cannot withstand such extreme conditions, manufacturers need to decorate the substrate with organic ink after the bending process. Although 3D decoration techniques for organic ink deposition have also been developed, this is a complex process and has become one of the bottlenecks in the manufacturing process.

[0064] This specification solves the problem of 3D decoration by providing an enamel paste composition that is suitable for both bending processes (760°C in a graphite mold) and chemical strengthening processes (in molten KNO3) and results in a tough / strong coated product. One of the main challenges is to maintain the high glass strength / toughness provided by the use of Gorilla Glass 5 and chemical strengthening. Since the use of enamel tends to weaken the glass, it is important to limit this weakening. The front cover glass of commercially available mobile phones typically has a break value of 600 MPa. The process steps correspond to the steps shown in Figure 3. This process begins with a sheet of glass decorated with the enamel paste described herein by screen printing. After drying at 150°C for several minutes, the enamel is pre-fired and the coated product is bent at 760°C in a graphite mold. After shaping the coated glass, for chemical strengthening, the coated glass is treated in a molten KNO3 bath (450°C) for 24 hours.

[0065] In this 3D mobile phone glass manufacturing process, the enamel has the following properties: - Firing temperature between 700°C and 850°C (for example, 700°C to 800°C) Non-stick properties between -700°C and 850°C (e.g., 700°C to 800°C) - Low glass weakening - Resistance to molten KNO3 treatment.

[0066] One enamel composition developed for this application comprises two different glass components, a pigment, and a seed component. One of the glass components (~42% by weight of the solids content of the enamel paste) is a bismuth silicate glass frit with a relatively low alkali metal content (lower compared to the substrate and other glass components of the enamel composition). This glass frit has a softening point higher than the temperature of the molten KNO3 bath used for chemical strengthening and lower than the softening point of the Gorilla glass substrate. The other glass component of the enamel paste (~25% by weight of the solids content of the enamel paste) is formed from crushed glass powder of the same Gorilla Glass as the substrate being coated, i.e., a high sodium content glass used for ion exchange with potassium to chemically strengthen the glass. It has been found that including Gorilla Glass in the enamel paste reduces the weakening of the substrate glass by the enamel coating. The entire enamel composition could be made of Gorilla Glass, as the enamel paste needs to soften and flow at a lower temperature than the substrate. Therefore, the 2-glass component of the enamel composition is an important feature of the enamel composition described herein, and the proportion of the sintered glass component in the enamel paste to the solid content of the enamel paste is less than that of the enamel paste without the addition of unsintered Gorilla Glass component. During sintering, only the bismuth silicate-based glass frit is sintered—the sintering temperature is lower than the temperature required to sinter the Gorilla Glass component of the enamel paste.

[0067] One of the developed paste compositions contains the following components (percentages are relative to the total solids content of the paste and do not include liquid carrier components):

[0068] TIFF0007854434000001.tif2886

[0069] The composition of the bismuth silicate glass used in the aforementioned paste composition is as follows (by weight): TIFF0007854434000002.tif4761

[0070] The composition of Gorilla® glass is as follows (by weight %): TIFF0007854434000003.tif5365

[0071] The seed composition is as follows (by weight %): TIFF0007854434000004.tif1455

[0072] The pigment composition is as follows (by weight): TIFF0007854434000005.tif1853

[0073] Subsequent research has shown that seed materials are not essential to the composition and can be omitted. Furthermore, different examples of paste compositions have been developed using different frits and pigments. Table 1 below shows 13 different examples of paste compositions. The compositions of frits A-I are shown in Table 2. Table 3 shows the optical properties of the items obtained after firing at 800°C on a Gorilla glass substrate. For certain applications, darker colors (lower L values) and higher optical density (higher OD) are preferred.

[0074] [Table 1]

[0075] [Table 2]

[0076] [Table 3]

[0077] Thus, a series of enamel coating compositions have been developed for use in coating glass substrates, which are then press-bent and subjected to a chemical strengthening process. The enamel compositions survive the subsequent processing steps while maintaining a good aesthetic appearance. Furthermore, the enamel coatings retain good mechanical adhesion properties. Importantly for the end application, the coated articles have higher mechanical strength compared to previously enamel-coated and chemically strengthened articles, which have been found to have significantly lower strength compared to chemically strengthened glass substrates without enamel coating. Finally, it has been shown that by adjusting the composition, a range of optical properties can be achieved, including dark, high optical density coatings for obscuration applications.

[0078] Although the present invention has been specifically shown and described with reference to certain embodiments, those skilled in the art will understand that various modifications in form and detail can be made without departing from the scope of the invention as defined by the appended claims.

Claims

1. A paste for coating glass substrates, which, after coating, is subjected to firing and chemically strengthened by ion exchange to form an enamel-coated, chemically strengthened glass product, wherein the paste is Organic carrier liquid, A first inorganic frit having a first softening point, and Second inorganic frit having a second softening point, It consists of, The softening point of the first inorganic frit is higher than the softening point of the second inorganic frit, so that the second inorganic frit can be softened and sintered at a lower temperature than the softening point of the first inorganic frit. The first inorganic frit comprises an amount of exchangeable ions that can be ion-exchanged and chemically strengthened, The first inorganic frit is an aluminosilicate glass frit, The second inorganic frit is a paste, which is bismuth silicate glass frit or zinc borosilicate glass frit.

2. The paste according to claim 1, wherein the first inorganic frit is an aluminosilicate glass frit comprising 50 to 70% by weight of SiO₂ and 15 to 25% by weight of Al₂O₃.

3. The paste according to claim 1 or 2, wherein the first inorganic frit contains alkali metal ions as an exchangeable ion content for chemical strengthening.

4. The paste according to claim 3, wherein the exchangeable ion content of the first inorganic frit is the content of sodium ions that can be exchanged for potassium ions when placed in a molten bath containing potassium ions.

5. The paste according to any one of claims 1 to 4, wherein the first inorganic frit comprises an amount of exchangeable ions defined by the weight of equivalent oxides within the range defined by 15% by weight, 12% by weight, 10% by weight or less, or 6% by weight, 7% by weight or more, or any combination of the aforementioned upper and lower limits.

6. The paste according to any one of claims 1 to 5, wherein the first inorganic frit has a softening point within the range defined by 500°C, 550°C, 575°C, 600°C, 650°C, 700°C, 750°C, or 800°C or higher; 1000°C, 900°C, or 850°C or lower; or any combination of the aforementioned upper and lower limits.

7. The paste according to any one of claims 1 to 6, wherein the paste contains, in weight percentage of the solid content of the paste, an amount of the first inorganic frit within the range defined by 50% by weight, 40% by weight, 30% by weight, 20% by weight, or 15% by weight or less; 2% by weight, 5% by weight, 8% by weight, or 10% by weight or more; or any combination of the aforementioned upper and lower limits.

8. The second inorganic frit is 40-70% by weight of Bi ２ O ３ and 10-40% by weight of SiO ２ A paste according to any one of claims 1 to 7, comprising bismuth glass frit silicate.

9. The paste according to any one of claims 1 to 8, wherein the second inorganic frit also comprises an amount of exchangeable ions that can chemically strengthen the second inorganic frit.

10. The paste according to claim 9, wherein the content of the exchangeable ions in the second inorganic frit is lower than the content of the exchangeable ions in the first inorganic frit.

11. The paste according to any one of claims 1 to 10, wherein the second inorganic frit comprises an amount of exchangeable ions defined by the weight of an equivalent oxide within the range defined by any combination of the aforementioned upper and lower limits: 6% by weight, 5% by weight, 4% by weight or less, or 3.5% by weight or less; 0% by weight, 1% by weight, 2% by weight or more, or 2.8% by weight or more; or the amount of an equivalent oxide within the range defined by any combination of the aforementioned upper and lower limits.

12. The paste according to any one of claims 1 to 11, wherein the second inorganic frit has a softening point within the range defined by 650°C, 600°C, 575°C, 550°C, or 500°C or less; 350°C, 375°C, 400°C, 425°C, 450°C, or 475°C or more; or any combination of the aforementioned upper and lower limits.

13. The paste according to any one of claims 1 to 12, wherein the second inorganic frit has a sintering temperature in the paste composition in the range of 700°C to 850°C.

14. The paste according to any one of claims 1 to 13, wherein the first inorganic frit is not sinterable at temperatures in the range of 700°C to 850°C.

15. The paste according to any one of claims 1 to 14, wherein the paste comprises an amount of the second inorganic frit as a weight percentage of the solid content of the paste within the range defined by 80% by weight, 60% by weight, 50% by weight, 45% by weight or less; 20% by weight, 30% by weight or more, or any combination of the aforementioned upper and lower limits.

16. The paste according to any one of claims 1 to 15, wherein the first inorganic frit has a lower coefficient of thermal expansion than the coefficient of thermal expansion of the second inorganic frit.

17. The paste according to any one of claims 1 to 16, further comprising a pigment.

18. The use of the paste according to any one of claims 1 to 17 in a method for coating and chemically strengthening a glass substrate.

19. A method for coating a glass substrate, Depositing the paste according to any one of claims 1 to 17 onto a glass substrate, The process involves heating the glass substrate to form an enamel-coated glass substrate, thereby scorching the second inorganic frit of the paste, and The enamel-coated glass substrate is subjected to an ion exchange process to chemically strengthen the enamel-coated glass substrate by exchanging at least a portion of the exchangeable ions in the substrate with the first inorganic frit. It consists of, The glass substrate comprises an exchangeable ion content that can be ion-exchanged and chemically strengthen the glass substrate, and the glass substrate has a softening point higher than the softening point of the second inorganic frit of the paste.

20. The method according to claim 19, wherein the glass substrate comprises the same exchangeable ions as the first inorganic frit.

21. The method according to claim 19 or 20, wherein the glass substrate is aluminosilicate glass.

22. The method according to any one of claims 19 to 21, wherein the glass substrate comprises an amount of exchangeable ions defined by the weight of an equivalent oxide within the range defined by 15% by weight, 12% by weight, 10% by weight or less, or 9% by weight or less; 6% by weight, 7% by weight or more, or 8% by weight or more; or any combination of the aforementioned upper and lower limits.

23. The method according to any one of claims 19 to 22, wherein the glass substrate has a softening point within the range defined by 500°C, 550°C, 575°C, 600°C, 650°C, 700°C, 750°C, or 800°C or higher; 1000°C, 900°C, or 850°C or lower; or any combination of the aforementioned upper and lower limits.

24. The method according to any one of claims 19 to 23, wherein the glass substrate has a coefficient of thermal expansion that is more closely matched to the first inorganic frit than to the second inorganic frit.

25. The method according to any one of claims 19 to 24, wherein the heating comprises heating the glass substrate to a temperature between the softening temperatures of the first and second inorganic frits of the paste, without exceeding the softening point of the first inorganic frit or the glass substrate, thereby firing the second inorganic frit to form the enamel-coated glass substrate.

26. The method according to any one of claims 19 to 25, wherein the glass substrate is formed by depositing the paste onto the substrate and then pressing and bending it, before chemically strengthening the glass substrate by subjecting the glass substrate to the ion exchange process.

27. The method according to claim 26, wherein the substrate is formed by pressing and bending at the same time as firing the second inorganic frit to form the enamel coating on the glass substrate.

28. The method according to any one of claims 19 to 27, wherein the ion exchange process comprises placing the enamel-coated glass substrate in a cast ion exchange bath.

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