Inkjet printable inks for the production of enamel coatings

Abstract

Inkjet printable ink for producing enamel coatings. 1. An inkjet printable enamel ink comprising: one or more glass frits; one or more pigments; crystalline bismuth silicate powder; and an organic medium, wherein the glass frits, pigments, and crystalline bismuth silicate powder in the organic medium have a d99 particle size distribution of less than 4 μm, and the enamel ink is inkjet printable at a shear rate of 100 s -1 and 30 mPa s at 35°C -1 and the enamel ink has a total solids content, including glass frit, pigments, and crystalline bismuth silicate powder, of 60% by weight or less.

Description

[Technical field]

[0001] The present invention relates to inkjet printable inks for producing enamel coatings. [Background technology]

[0002] Enamels are widely used to decorate and coat glass and ceramic substrates, including tableware, signage, tile, and architectural glass. Enamels are particularly useful for forming colored borders around the perimeter of glass sheets used in automobile windshields, side windows, and rear windows. The colored borders not only enhance appearance, but can also prevent degradation of the adhesive on the substrate by ultraviolet light. In addition, the colored borders can hide bus bars and wiring connections in glass defrosting systems.

[0003] Enamels usually contain pigments and glass frits. They are generally applied to a substrate (e.g. a windshield surface) as a paste or ink, for example by printing. The paste or ink may contain particles of pigment and glass frit dispersed in a liquid dispersion medium. Such pastes or inks are also called "inorganic ceramic pastes" or "inorganic ceramic inks". After applying a coating of the paste / ink to the substrate, the paste / ink is usually dried and the applied coating is fired, i.e. subjected to a heat treatment, so that the frit softens and fuses to the substrate, thereby adhering the enamel to the substrate. During firing, the pigment itself does not melt, but is adhered to the substrate by or together with the frit.

[0004] Various printing techniques can be employed to apply the inorganic ceramic paste / ink to the substrate. Screen printing and pad printing are commonly employed. These techniques usually use enamel pastes with high solids content and high viscosity. Digital inkjet printing has also been proposed as an alternative technique. After investigating such techniques, it has been found that enamel inks with smaller particle size, low solids content and / or low viscosity are advantageous for applying the ink to the substrate by inkjet printing.

[0005] Digital inkjet printing has various advantages over screen printing, such as reduced costs for storing screens and transfer equipment (since the desired pattern can be stored digitally), reduced costs for low-cost printing that is difficult to achieve with screen printing, improved ease and versatility for switching from one design to another, and the ability to print edge-to-edge. However, pastes suitable for screen or pad printing generally tend to be too viscous and contain glass frit or pigment particles with particle sizes that can clog the nozzles of inkjet printers, making them unsuitable for application by inkjet printing. Typically, inorganic ceramic inks suitable for inkjet printing (i.e., inkjet-able) have a viscosity (at the printing temperature) of less than 25 cps and the particles dispersed in the ink have a particle size of less than 2 μm, preferably less than 1 μm.

[0006] The selection of an appropriate frit is crucial in the formulation of inorganic ceramic inks, since the properties of the frit affect both the firing behavior and the properties of the final fired enamel. In general, inorganic ceramic inks contain particles of glass frit with a single glass composition. Typically, the composition of the glass frit includes silica, bismuth oxide, and boron oxide. For example, EP 1 658 342 describes an inkjet ink composition for printing on ceramic substrates, which ink composition comprises an organic solvent and SiO 2 , Bi 2 O 3 and B.2 O 3 and submicron particles of glass frit consisting of

[0007] WO 2020 / 021235 also describes an advantageous inkjet ink composition comprising particles of a first glass frit, which contains silica and little or no boron oxide, and particles of a second glass frit, which contains boron and little or no silica. It teaches that the temperature range at which the enamel fuses to the substrate during firing can be better controlled by using a composition containing two frits. Furthermore, the functional properties of the final enamel, such as color depth and bending strength, can be improved. That is, WO 2020 / 021235 describes an ink for forming an enamel, which comprises particles of a first glass frit, particles of a second glass frit, and a liquid dispersion medium, wherein the first glass frit has more than 5% by weight of silicon oxide (SiO 2 ) and less than 5% by weight of boron oxide (B 2 O 3 ), and the second glass frit comprises boron oxide (B 2 O 3 ) and less than 5% by weight of silicon oxide (SiO 2 ), wherein both the first glass frit particles and the second glass frit particles have a D90 particle size of less than 5 μm.

[0008] The present disclosure aims to provide inkjet printable inks suitable for producing enamel coatings. Summary of the Invention

[0009] The inventors have found that although enamel-forming inks have traditionally been formulated with suitable physical properties (e.g., low viscosity, low solids, low particle size) for the ink to exhibit good inkjet printability, the properties of the resulting enamel coating after firing tend to be different and generally inferior functional properties than state-of-the-art optimized commercial enamel pastes printed by screen printing methods. The functional properties of enamel coatings desired for end uses such as automotive glass include good color, good silver hiding properties, good anti-stick properties, good acid resistance, low firing temperature, good flexural strength properties, and low surface roughness.

[0010] The inventors have found that the functional properties (low solids, low viscosity, small particle size) of enamel coatings formed from inkjet inks can be significantly improved by including crystalline bismuth silicate powder (e.g. Eulytite) in the ink. Such crystalline bismuth silicate powders have been used in the past in certain screen printing enamel pastes (usually with much higher solids content, viscosity and particle size) to improve the anti-blocking properties of these pastes. The inventors have surprisingly found that including crystalline bismuth silicate powder in inkjet ink formulations significantly improves the enamel coatings formed from such inkjet ink formulations. It has been found that by using crystalline bismuth silicate powder, inkjet ink formulations can achieve enamel coatings with similar or better functional properties compared to enamel coatings formed from state-of-the-art commercial enamel pastes printed using screen printing methods.

[0011] That is, the present disclosure provides an enamel ink comprising one or more glass frits; one or more pigments; crystalline bismuth silicate powder; and an organic carrier, wherein the d99 particle size distribution of the glass frit, the pigment, and the crystalline bismuth silicate powder in the organic carrier is less than 4 μm (preferably less than 2 μm), and the enamel ink is heated at a shear rate of 100 s -1 and 30 mPa s at 35°C-1 and the total solids content in the enamel ink is 60% by weight or less.

[0012] The amount of crystalline bismuth silicate powder in the enamel ink can be 0.05% by weight or more, 0.08% by weight or more, or 0.1% by weight or more; 5% by weight or less, 2% by weight or less, 1% by weight or less, 0.5% by weight or less, or 0.2% by weight or less; or within a range defined by any combination of the above lower and upper limits. Preferably, the crystalline bismuth silicate powder has the chemical formula Bi 4 (SiO 4 ) 3 The most notable is Eulytite, a mineral having a crystalline bismuth silicate content of 100% by weight. It is noted that in the inkjet ink formulations of the present disclosure, small amounts (e.g., 0.1-0.2% by weight) of crystalline bismuth silicate powder make a significant difference in the performance properties of the enamel coating formed after inkjet printing and baking of the ink. Furthermore, since too much crystalline bismuth silicate powder can be detrimental to the enamel properties, it is preferred to include only small amounts of crystalline bismuth silicate powder to achieve good enamel performance properties. Thus, there is an optimal range for the amount of crystalline bismuth silicate powder included in the inkjet ink formulation to achieve the desired enamel properties.

[0013] The inkjet printable enamel inks of the present disclosure are capable of withstanding a shear rate of 100 s -1 and 30 mPa s at 35°C -1 Below, 28mPa·s -1 Below, 25mPa·s -1 Less than or equal to 20 mPa s -1 Shear rate is less than or equal to 100s -1 and 5 mPa s at 35°C -1 Below, 7mPa·s -1 Less than or equal to 10 mPa·s -1or within the range defined by any combination of the above upper and lower limits. The above viscosities are measured at 35° C. since this is the typical operating temperature for ink-jet inks for printing.

[0014] Inkjet printable enamel inks can be formulated to have a total solids content of 60% by weight or less, 58% by weight or less, 57% by weight or less, or 55% by weight or less; 30% by weight or more, 35% by weight or more, 40% by weight or more, or 45% by weight or more; or within a range defined by any combination of the above upper and lower limits. Screen printing pastes typically have a total solids content of more than 70% by weight. In contrast, inkjet inks typically have a lower solids content, for example less than 55% by weight.

[0015] According to one formulation, the ink comprises two or more different glass frits. For example, the two different glass frits may comprise particles of a first glass frit and particles of a second glass frit, where the first glass frit comprises more than 5 wt. % silicon oxide (SiO 2 ) and less than 5% by weight of boron oxide (B 2 O 3 ), and the second glass frit contains boron oxide (B 2 O 3 ) and less than 5% by weight of silicon oxide (SiO 2 In one embodiment, the first glass frit does not include boron oxide and the second glass frit does not include silicon oxide.

[0016] The formulation comprising the two glass frits may be similar to that described in WO 2020 / 021235. The main difference is the addition of crystalline bismuth silicate powder, which significantly improves the properties of the enamel coating formed after inkjet printing and firing of the ink. According to one formulation, in addition to the crystalline bismuth silicate powder, the composition of the first frit differs from that described in WO 2020 / 021235. In WO 2020 / 021235, the ink is disclosed as consisting of a mixture of: a first frit (Johnson Matthey Product No. 5466); and a second frit (Johnson Matthey Product No. 5317). The first frit in WO 2020 / 021235 (Johnson Matthey Product No. 5466) has the following composition:

[0017] TIFF2025504668000001.tif3160

[0018] In contrast, in the present disclosure, certain ink formulations include a new first frit composition that includes or consists of: More than 15% by weight and up to 50% by weight of SiO 2; 40% to 80% by weight of Bi 2 O 3 ; 0% or more (preferably, more than 0% by weight) and 5% or less by weight of ZnO; Lithium (0% by weight or more, preferably more than 0% by weight) 5% by weight or less 2 O(; 0% or more (preferably more than 0%) and 5% or less by weight of F; 0% by weight or more (preferably more than 0% by weight) 5% by weight or less of Na 2 O; 0% or more (preferably, more than 0% by weight) and 5% or less by weight of CuO; 0% by weight or more (preferably, more than 0% by weight) and 5% by weight or less of Al 2 O 3 ; 0% or more (preferably, more than 0% by weight) and 5% or less by weight of MnO; and Fe: 0% by weight or more (preferably, more than 0% by weight) 5% by weight or less 2 O 3 .

[0019] The main differences between the first frit of the present disclosure and the first frit described in WO 2020 / 021235 are the significantly lower ZnO content and the Li 2 O, F, Na 2 O, CuO, Al 2 O 3 , MnO and Fe 2 O 3 The addition of other components in the frit, which are one or more selected from the following: It has been found that the novel frit can be advantageously used in the inkjet printable ink formulations of the present disclosure. However, it is also envisioned that the novel frit can be used in other applications, particularly other enamel coating applications. Thus, the glass frit composition is also included in another aspect of the present disclosure.

[0020] The second glass frit may be the same as that disclosed in WO 2020 / 021235. For example, the second glass frit may include or consist of: 40% to 70% by weight of Bi 2 O 3 ; More than 5% by weight and up to 25% by weight of B 2 O 3 ; 5% to 25% by weight of ZnO; 0% by weight or more (preferably more than 0% by weight) and 25% by weight or less of SnO 2 .

[0021] Another difference between the particular ink formulations of the present disclosure and those of WO 2020 / 021235 and the like includes the relative amounts of the first and second glass frits. It has been found that the relative amounts of the first and second glass frits can be adjusted to achieve suitable firing conditions to produce an enamel coating. For example, the ink may include or consist of: 10-30 wt. % of a first frit (preferably, 12-20 wt. %); 10-30 wt. % of a second frit (preferably, 15-25 wt. %); 0.05-5 wt. % crystalline bismuth silicate powder (preferably, 0.1-0.5 wt. %); 10 to 20% by weight of pigment (preferably, 12 to 18% by weight); and 40-60% by weight of organic medium (preferably 45-60% by weight).

[0022] Preferably, the weight ratio of the first frit to the second frit is in the range of 0.8:1 to 1:0.8, preferably 0.9:1 to 1:0.9.

[0023] The present disclosure further provides a method of forming an enamel coating on a substrate, the method comprising depositing a coating of the ink of the present disclosure on a substrate using a digital inkjet printer and baking the coating to form an enamel coating. In this regard, the deposition conditions of the digital inkjet printer can be selected / adjusted such that the optical density of the enamel coating after baking is greater than 3. Furthermore, the ink of the present disclosure can be formulated in the ranges described herein to achieve an enamel coating having comparable or better functional properties compared to an enamel coating formed from a state-of-the-art commercial enamel paste printed by a screen printing method, upon baking at a temperature ranging from 500° C. to 730° C. for a time ranging from 2 to 20 minutes. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] To better understand the invention and to show how it may be put into practice, specific embodiments of the invention will now be described by way of example.

[0025] As described in the Abstract, the present disclosure provides an inkjet printable enamel ink comprising one or more glass frits; one or more pigments; a crystalline bismuth silicate powder; and an organic medium, in which the glass frits, pigments, and crystalline bismuth silicate powder have a d99 particle size distribution of less than 4 μm (preferably less than 2 μm), and the enamel ink is inkjet printable at a shear rate of 100 s -1 and a temperature of 35° C., the enamel ink has a viscosity of less than 30 mPa, and the total solids content in the enamel ink is 60% by weight or less. Such inkjet printable ink compositions have been found to achieve enamel coatings with superior functional properties to conventional inkjet printable ink compositions, and have comparable or better functional properties compared to enamel coatings formed from state-of-the-art commercially available enamel pastes printed by screen printing processes. Thus, the inkjet printable ink compositions have the advantages of digital inkjet printing over screen printing (e.g., flexibility in changing print patterns, elimination of the need for custom hardware screens to form different patterns, etc.) and can provide an alternative to state-of-the-art commercially available enamel pastes printed by screen printing processes.

[0026] The composition ranges of the glass frit components and the crystalline bismuth silicate powder are described in the Summary of the Invention. With respect to glass frit compositions, as will be understood by those skilled in the art, glass materials such as glass frits are typically amorphous materials that exhibit a glass transition. In the glass frit compositions described in this disclosure, the amounts of the components are based on weight percentages. These weight percentages are based on the total weight of the glass frit composition. The weight percentages are based on the oxide of the components used as raw materials in the preparation of the glass frit composition. As will be understood by those skilled in the art, starting materials other than oxides of a particular element may be used in the preparation of the glass frits of the present disclosure. When a non-oxide starting material is used to provide an oxide of a particular element to the glass frit composition, an appropriate amount of starting material is used to provide the equivalent molar amount of the element as if the oxide of the element was provided at a given weight. The techniques for preparing such glass frit compositions are typical in the art. As one skilled in the art can readily appreciate, volatile components (such as oxygen) may be lost during the glass frit manufacturing process, and the resulting glass frit composition may not exactly match the weight percentages of the starting materials as expressed in this disclosure on an oxide basis. Methods for calculating the starting components of the glass frit composition may be employed as known to those skilled in the art, such as inductively coupled plasma optical emission spectroscopy (ICP-ES).

[0027] As will be readily understood by those skilled in the art, during the manufacture of glass frits, glass compositions may contain low levels of impurities. For example, in a melting / quenching glass forming process, such impurities may come from the refractory lining of the vessel used in the melting process. Thus, even if it is desirable to have a glass composition completely free of a particular component, this may be difficult to achieve in practice. Thus, the compositional information should be interpreted with this in mind. If a value of 0 (zero) is listed for a particular component, it means that no component was intentionally added during the manufacture of the glass frit and no raw materials were used that were intended to have that component in the final glass composition. If such a component is present in a glass frit composition at a low concentration, it is due to contamination during manufacture.

[0028] The glass frit particles can be prepared by mixing the necessary raw materials, melting them to form a molten glass mixture, and then quenching to form a glass (melting / quenching glass formation). The skilled artisan will know suitable alternative methods for preparing the glass frit. Suitable alternative methods include water quenching, sol-gel processing, and spray pyrolysis. The process may further include grinding the resulting glass frit to provide glass frit particles of the desired particle size. For example, the glass frit can be ground using a bead grinding process, such as wet bead grinding in an alcohol-based or aqueous solvent. In the present disclosure, the glass frit is ground together with other solid components of the ink to a small particle size suitable for inkjet printing. In this case, the glass frit, pigment, and crystalline bismuth silicate powder are ground to a d99 particle size distribution in an organic medium of less than 4 μm (preferably less than 2 μm). In the present disclosure, the term "D99 particle size" refers to a particle size distribution, and the value of the D99 particle size corresponds to the particle size value below which 99% by volume of all particles in a particular sample are present. The D99 particle size can be measured by laser diffraction (eg, using a Malvern® 2000).

[0029] In some embodiments of the present disclosure, the glass frit may include a crystalline portion in addition to the amorphous glass phase. The use of such a glass frit may facilitate or induce crystallization of the frit during firing, which may be advantageous in certain applications.

[0030] In addition to the glass frit and crystalline bismuth silicate powder components, the inks of the present disclosure include pigments. The pigments may include complex metal oxide pigments or carbon black pigments. The type and amount of pigment may be selected depending on the range of color, luster, and opacity desired in the final enamel. Suitable pigments include complex metal oxide pigments such as corundum-hematite, olivine, priderite, pyrochlore, rutile, spinel, and the like. Other types such as baddeleyite, borates, garnets, periclase, phenacite, phosphates, sphenes, and zircons may also be more suitable for certain applications. Typical complex metal oxide pigments that may be used to produce black colors in the automotive industry include transition metal oxides with spinel structures, such as oxides with spinel structures of copper, chromium, iron, cobalt, nickel, manganese, and the like. These black spinel pigments are preferred for use in the automotive industry, although other metal oxide pigments for producing a variety of other colors may also be employed. Examples of other end uses include the architectural, home appliance, and beverage industries. Examples of commercially available pigments include CuCr 2 O4, (Co,Fe)(Fe,Cr) 2 O 4 , (NiMnCrFe), etc. Two or more pigments can also be mixed and used.

[0031] The glass frit, crystalline bismuth silicate powder, and pigment components are disposed in a flowable organic medium. The organic medium suspends the particle mixture under application conditions and is removed upon drying and / or baking (or pre-baking) of the applied ink coating. Factors influencing the selection of the medium include solvent viscosity, evaporation rate, surface tension, odor, and toxicity. When the ink is applied to the substrate by inkjet printing, preferred media include, but are not limited to, diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, dibasic acid esters, 1-methoxy 2-propanol, and the like. A particularly preferred medium includes dipropylene glycol monomethyl ether. The ink may further include one or more additives. These include, but are not limited to, dispersants such as BYKJET, disperBYK, Solsperse, or Dispex series additives, especially BYKJET 9151, resins, and / or rheology modifiers. EXAMPLES

[0032] The embodiments of the present disclosure provide a laminate inkjet ink using boron-free bismuth silicate frit and silicon-free boron bismuth frit. The ink is made using a newly developed boron-free bismuth silicate frit in combination with an existing silicon-free boron bismuth frit. A black pigment is added for coloring. The addition of crystalline bismuth silicate powder (e.g., eulithite) can significantly improve the performance of inkjet printing and enamel coating after firing. In certain preferred embodiments described herein, the crystalline bismuth silicate powder is applied in an inkjet ink formulation containing two different glass frits, but the crystalline bismuth silicate powder can also be used in an inkjet ink formulation containing only one glass frit.

[0033] The above components were applied separately in an organic medium to a bead mill and then mixed in a bead mill. Sieving and viscosity adjustment were performed to make the ink ready for use. The performance of the ink after inkjet printing and firing was confirmed to be equivalent to existing glass enamel paste applied by screen printing in automotive glass applications. Furthermore, the glass ink allows for quick switching to different designs without additional costs. Furthermore, the glass ink can increase the bending strength of decorative substrates by 30-50% compared to existing glass enamel paste applied by screen printing.

[0034] Thus, a black, inkjet printable enamel ink was prepared that included (1) BiSi glass frit, (2) BiB glass frit, (3) black pigment, (4) crystalline bismuth silicate powder, and (5) an organic medium. For comparison, an example of a BiSi glass frit (frit 1 of the present disclosure) is shown below along with an existing commercially available BiSi frit:

[0035] [Table 1]

[0036] An example of a BiB frit (frit 2 of this disclosure) is shown below:

[0037] Frit 2 (BiB frit) [Table 2]

[0038] The frit, pigment and crystalline bismuth silicate powder were applied individually to a bead mill to the desired particle size distribution (d99<2 μm) in an organic medium, then mixed together and stirred at 35 °C and a shear rate of 100 s -1 , the viscosity is 15-20 mPa s using a 5 cm spindle at an angle of 1°. -1Two examples of ink formulations and the associated ranges of component amounts are shown in the table below.

[0039] [Table 3]

[0040] The ink was used to manufacture laminated automotive glass panels by depositing the ink onto a glass substrate (typically soda-lime glass) by digital inkjet printing, drying and firing the process as follows: (1) Using a digital printer, deposit ink onto a glass substrate. The deposition parameters are adjusted so that the optical density after firing is 3 or more. (2) Firing in a gradient kiln at 540 / 615 / 705°C for 600 seconds.

[0041] The ink of Example 1 had a higher firing temperature than the ink of Example 2. Therefore, the ink of Example 2 is preferred for applications requiring a lower firing temperature. The lowering of the firing temperature could be achieved by adjusting the relative amounts of the first and second glass frits. It was confirmed that a ratio of about 1:1 (wt%) between the two glass frits provided good firing conditions.

[0042] The enamel coating made with the ink of Example 2 was tested and compared to an enamel coating made with the current enamel paste and screen printed. The test results of the enamel coating are shown in the table below.

[0043] [Table 4]

[0044] As can be seen from the values ​​in the table, the performance properties are similar for both enamel samples. However, the flexural strength is much higher for the enamel formed with the inkjet ink and the surface roughness is lower. Thus, the enamel formed with the inkjet ink has advantages over the enamel formed with the screen printing paste.

[0045] Although the present invention has been shown and described with reference to specific embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention as defined by the claims.

Claims

1. one or more glass frits, one or more pigments, Crystalline bismuth silicate powder; and 1. An inkjet printable enamel ink comprising an organic medium, The d99 particle size distribution of the glass frit, the pigment, and the crystalline bismuth silicate powder in the organic medium is less than 4 μm; The enamel ink was heated at a shear rate of 100 s －１ and 30 mPa·s at a temperature of 35°C. －１ and having a viscosity of less than The enamel ink has a total solid content including the glass frit, pigment, and crystalline bismuth silicate powder of 60% by weight or less.

2. 10. The inkjet printable enamel ink of claim 1, wherein the crystalline bismuth silicate powder is eulytite.

3. 10. The inkjet printable enamel ink of claim 1, wherein the amount of crystalline bismuth silicate powder contained in the enamel ink is 0.05 wt.% or more, 0.08 wt.% or more, or 0.1 wt.%; 5 wt.% or less, 2 wt.% or less, 1 wt.% or less, 0.5 wt.% or less, or 0.2 wt.% or less; or within a range defined by any combination of said lower and upper limits.

4. The viscosity of the enamel ink was measured at a shear rate of 100 s －１ and 28 mPa·s at a temperature of 35°C. －１ Below, 25mPa・s －１ or less or 20 mPa·s －１ or less, or shear rate 100 s －１ and 5 mPa·s at a temperature of 35°C. －１ Above, 7mPa・s －１ or more or 10 mPa·s －１ or greater than or within a range defined by any combination of the above upper and lower limits, 10. The inkjet printable enamel ink of claim 1.

5. the total solids content of the enamel ink is 58% by weight or less, 57% by weight or less, or 55% by weight or less; 30% by weight or less, 35% by weight or less, 40% by weight or less, or 45% by weight or less; or within a range defined by any combination of the above upper and lower limits.

10. The inkjet printable enamel ink of claim 1.

6. The d99 particle size distribution of the glass frit, the pigment, and the crystalline bismuth silicate powder in the organic medium is less than 2 μm.

10. The inkjet printable enamel ink of claim 1.

7. The enamel ink contains two or more different glass frits.

10. The inkjet printable enamel ink of claim 1.

8. the two different glass frits include particles of a first glass frit and particles of a second glass frit; The first glass frit contains more than 5 wt. % silicon oxide (SiO ２ ) and less than 5% by weight of boron oxide (B ２ O ３ ), The second glass frit is boron oxide (B ２ O ３ ) and less than 5 wt. % silicon oxide (SiO ２ 8. The inkjet printable enamel ink of claim 7, comprising:

9. The first glass frit may be: More than 15% by weight and not more than 50% by weight of SiO ２ ; 40% by weight or more and 80% by weight or less of BiO ３ ; ZnO of 0% by weight or more and 5% by weight or less; 0% by weight or more and 5% by weight or less of Li ２ O; 0% by weight or more and 5% by weight or less of F; 0% by weight or more and 5% by weight or less of Na ２ O; 0% or more and 5% or less by weight of CuO; 0% by weight or more and 5% by weight or less of Al ２ O ３ ; 0% to 5% by weight of MnO; and 0% by weight or more and 5% by weight or less of Fe ２ O ３ 9. The inkjet printable enamel ink of claim 8, comprising:

10. The inkjet printable enamel ink of claim 8 , wherein the first glass frit does not include boron oxide.

11. The second glass frit may be: 40% by weight or more and 70% by weight or less of Bi ２ O ３ ; More than 5% by weight and not more than 25% by weight of B ２ O ３ ; 5% by weight or more and 25% by weight or less of ZnO; 0% by weight or more and 25% by weight or less of SnO ２ 9. The inkjet printable enamel ink of claim 8, comprising:

12. The inkjet printable enamel ink of claim 8 , wherein the second glass frit is silicon oxide-free.

13. below: 10 to 30 wt. % of a first glass frit; 10 to 30 wt. % of a second glass frit; 0.05 to 5 wt. % crystalline bismuth silicate powder; 10 to 20% by weight of a pigment; and 40 to 60% by weight of organic medium 9. The inkjet printable enamel ink of claim 8, comprising:

14. 9. The inkjet printable enamel ink of claim 8, wherein the weight ratio of the first glass frit to the second glass frit ranges from 0.8:1 to 1:0.

8.

15. 1. A method for forming an enamel coating on a substrate, comprising: depositing a coating of the enamel ink of any one of claims 1 to 14 onto a substrate using a digital inkjet printer; and baking the coating to form an enamel coating; A method comprising:

16. 16. The method of claim 15, wherein deposition conditions in the digital inkjet printer are selected such that the optical density of the fired enamel coating is greater than 3.

17. 16. The method of claim 15, wherein the firing temperature is in the range of 500°C to 730°C and the firing time is 2 to 20 minutes.

18. A glass frit composition for use in an inkjet printable enamel ink according to any one of claims 1 to 14, comprising: The glass frit composition comprises or consists of: More than 15% by weight and not more than 50% by weight of SiO ２ ; 40% by weight or more and 80% by weight or less of Bi ２ O ３ ; 0% or more (preferably, more than 0%) and 5% or less by weight of ZnO; 0% by weight or more (preferably, more than 0% by weight) and 5% by weight or less of Li ２ O; 0% by weight or more (preferably, more than 0% by weight) and 5% by weight or less of F; 0% by weight or more (preferably more than 0% by weight) and 5% by weight or less of Na ２ O; 0% or more (preferably, more than 0%) and 5% or less by weight of CuO; Al of 0% by weight or more (preferably, more than 0% by weight) and 5% by weight or less ２ O ３ ; 0% or more (preferably, more than 0%) and 5% or less by weight of MnO; and, 0% by weight or more (preferably, more than 0% by weight) and 5% by weight or less of Fe ２ O ３ Glass frit composition.