Patent Publication Number: US-2022234943-A1

Title: Dark-Colored, Low-Expansion Fillers

Description:
BACKGROUND 
     Glass frit systems are applied to various substrates and fired thereon to form an enamel that is bonded to the surface of the substrate. The fired enamel may be used to modify a characteristic, e.g. the appearance, of the substrate. If the coefficient of thermal expansion (CTE) of the fired enamel does not closely match that of the substrate, a significant interfacial stress will develop between the enamel and the substrate during the cooling cycle of the enamel firing process. This interfacial stress may cause a degradation in the bond between the enamel and the substrate, and may cause the enamel to craze, fracture, or de-bond from the substrate. 
     Ferro Corporation and other companies have long practiced the use of CTE modifiers, additives whose primary purpose is to enable modification of the enamel&#39;s overall CTE while minimizing its effect on the other enamel properties or the required firing profile. These additives serve to reduce the CTE difference between the substrate and the enamel, and therefore reduce the interfacial stress. This reduced CTE difference helps enhance the strength and durability of the enamel-substrate bonding because of the resulting reduced interfacial stress. 
     Glass frit systems for firing can be composed of glass frits, pigments, modifiers including CTE modifiers, and various other components such as fillers. The glass frit systems are formulated to give acceptable performance properties in terms of adhesion, appearance, strength, and durability. The fusion and flow properties of the glass frit systems are typically dominated by the glass frit components. However, modifiers, pigments, and fillers can interact with the glass components during the firing and affect the enamel&#39;s properties. These components often increase the required enamel firing temperature, which can be detrimental to the substrate upon which the enamel is formed. Therefore, novel approaches to formulate new glass frit systems that reduce the detrimental effects of the components on the enamel properties are beneficial. 
     In general, the glasses used in glass frit systems can aggressively attack, leach, or dissolve the other components to some degree during the enamel firing process. This affects primarily the surface of the glass particles, typically inhibiting their fusion and flow characteristics. The dissolution rate of the components within the glass frit system will depend on the chemistry, structure, surface area, and morphology of the components. Given the same chemistry for the components, larger specific surface areas and rougher surface textures will increase the dissolution rate of the components. Likewise, higher temperature enamel firing processes and longer soak times during firing will promote more dissolution of the components. Therefore, the choice of the specific components, the amount used, their particle size distributions, and their morphologies can affect the overall firing and performance of the enamel. 
     Many glass frit systems include pigments to modify the color of the fired enamels. In these cases, incorporation of conventional white or off-white CTE modifiers (i.e. “non-colored CTE modifiers”) to the glass frit systems results in changes the color values of the enamel in two ways. First, by diluting the percentage of pigment in the enamel, i.e. producing hue-changing; and second, by the light scattering produced by the whitish particles. These effects primarily increase the lightness of the enamel, i.e. increase the L-value. The L-value correlates to the lightness-darkness scale of the CIE Lab color system. 
     In order to counter this lightening and hue-changing effect from an addition of a conventional CTE modifier on the enamel color, the amount of pigment in the glass frit system may have to be increased. Unfortunately, any increase in the amount of pigment included in the glass frit system may have a significant negative impact on various characteristics (e.g. further increase the flow temperature) of the glass frit system or of the fired enamel. 
     BRIEF DESCRIPTION 
     According to one aspect, a glass frit system for forming an enamel adhered to a substrate includes a vehicle, a glass frit, a colored CTE modifier, and optionally one or more pigments. The colored CTE modifier includes (i) a modified Pseudo-Brookite type material having a formula Al 2 TiO 5 , wherein Al and/or Ti are partially substituted with one or more coloring ions including Fe, Cr, Mn, Co, Ni, and Cu; (ii) a modified Cordierite type material having a formula Mg 2 Al 4 Si 5 O 18 , wherein Mg and/or Al is partially substituted with one or more of the coloring ions; (iii) a Perovskite type material having a formula Sm 1−x Sr x MnO 3−δ , where x=0.0-0.5 and δ=0.0-0.25, or a modified version of the Perovskite type material wherein Sr is partially substituted with Ba and/or Ca; (iv) a modified magnesium pyrophosphate type material having a formula Mg 2 P 2 O 7  wherein Mg is substituted with Co and/or Zn ions; or (v) combinations thereof. 
     According to another aspect, method of forming an enameled substrate includes the steps of providing a substrate; providing a glass frit system including a vehicle, glass frit, a colored CTE modifier, and a pigment; applying the glass frit system to the substrate; and firing the glass frit system to thereby form a colored enamel adhered to the substrate. The colored CTE modifier includes (i) a modified Pseudo-Brookite type material having a formula Al 2 TiO 5 , wherein Al and/or Ti are partially substituted with one or more coloring ions including Fe, Cr, Mn, Co, Ni, and Cu; (ii) a modified Cordierite type material having a formula Mg 2 Al 4 Si 5 O 18 , wherein Mg and/or Al are partially substituted with one or more of the coloring ions; (iii) a Perovskite type material having a formula Sm 1−x Sr x MnO 3−δ , where x=0.0-0.5 and δ=0.0-0.25, or a modified version of the Perovskite type material wherein Sr is partially substituted with Ba and/or Ca; (iv) a modified magnesium pyrophosphate material having a formula Mg 2 P 2 O 7  wherein Mg is substituted with Co and/or Zn ions; or (v) combinations thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a dilatometry curve for Sr 0.15 Sm 0.85 MnO 3−x . 
     
    
    
     DETAILED DESCRIPTION 
     The formulation of enamels for such purposes as decoration on various substrates is challenging. Generally, a glass frit with a softening point below that of the desired substrate must be selected in order to minimize substrate distortion during the enamel firing process. However, a glass frit possessing a low softening point usually also has a high coefficient of linear thermal expansion (CTE) and poor acid durability. Additions can be made to the glass frit to address these concerns, but oftentimes all of the desired characteristics needed for an enamel cannot be met by the glass frit alone. The need for CTE-matching of the enamel to the substrate can in theory be met by the addition of CTE modifiers into the glass frit system. Three examples of conventional additives for the purpose of reducing the CTE of a fired glass enamel are β-Eucryptite (LiAlSiO 4 ), fused quartz (SiO 2 ), and Cordierite (Mg 2 Al 4 Si 5 O 18 ). 
     In some cases, such as for metal substrates like aluminum, the CTE of the glass enamel must typically be increased to match that of the substrate. Cristobalite, a crystalline form of silica with a large CTE, is sometimes used in such applications. 
     CTE modifiers are typically white or off-white in color. This property can be detrimental in achieving a desired enamel color, especially when black and other dark enamels are desired, while at the same time meeting other enamel requirements. 
     To address this concern, the present invention provides colored CTE modifiers produced by full or partial substitution of suitable metal ion chromophores (i.e. chromophoric cations or coloring ions) for one or more of the CTE modifier&#39;s original compositional ion components (i.e. original or substituted ions). For example, Cr(III) ions typically have similar ionic radii and coordination environments to Al(III) ions, and can be partially substituted as substitution ions into Al sites of Al 2 O 3 -corundum to form a red-ruby-colored CTE modifier. Similar substitutions can also be accomplished in CTE modifiers such as Al 2 TiO 5 . 
     Some of the useful CTE modifiers occur as naturally occurring oxide minerals. However, the naturally occurring low-CTE minerals such as cordierite and tialite, typically lack a sufficient amount of chromophoric cations to produce a useful coloring effect, and often contain such chromophoric cations only at contamination levels (i.e. below 0.05% substitution of the original ion), thus resulting in CTE modifiers having nearly white or off-white colors. With the advent of X-ray diffraction and chemical analysis techniques, it is possible to synthesize color-saturated, “clean” colored CTE modifiers based on chromophore-substituted versions of these minerals. Color optimization of the CTE modifiers is typically achieved by increasing the amounts and combinations of desired chromophoric ions and minimizing other impurities and secondary phases (i.e. secondary crystal structures). 
     The colored CTE modifiers of the present invention may be added to a glass frit system, such as an ink or paste to be fired on a substrate, in order to modify the CTE of the resulting fired enamel. 
     However, the CTE modifiers of this invention are highly colored compared to their naturally occurring counterparts, and therefore do not reduce the coloring effect from the pigment components on the enamels as much as the addition of conventional non-colored CTE modifiers. In many cases, in order to produce a desired coloring level in the enamel, the amount of the pigment component can be reduced due to the use of the colored CTE modifiers. This may be beneficial to the appearance and other enamel properties by reducing the crystalline-amorphous grain boundaries within the fired enamel that would ordinarily be present between the fired glass and the pigment. In addition, reduced pigment levels may advantageously reduce the enamel&#39;s flow temperature. 
     The colored CTE modifiers of this invention may be used to fully or partially replace a conventional combination of white-colored CTE modifiers and dark colored (e.g. black) pigments in a glass frit system. The colored CTE modifier may include a modified Pseudo-Brookite structure material having a formula Al 2 TiO 5  (tialite), wherein Al and/or Ti sites are partially substituted with one or more coloring ions. The coloring ions may include Fe, Cr, Mn, Co, Ni, and Cu. The colored CTE modifiers may include a modified Cordierite type material having a formula Mg 2 Al 4 Si 5 O 18 , wherein Mg and/or Al ions in the material are partially substituted with one or more of the coloring ions. The colored CTE modifiers may include a Perovskite type material having a formula Sm 1−x Sr x MnO 3−δ , where x=0.0-0.5 and δ=0.0-0.25; or the Perovskite type material modified by the substitution of coloring ions in the crystal structure. The colored CTE modifiers may include a modified magnesium pyrophosphate type material having a formula Mg 2 P 2 O 7  with partial substitution of Mg ions with chromophoric cations. The colored CTE modifiers may include a modified ZrSiO 4  material with appropriate chromophoric cation substitutions. The colored CTE modifiers may include combinations of these. These examples are not meant to limit the range of potential colored CTE modifiers of this invention. 
     There are several considerations that may be relevant in choosing appropriate chromophoric ions as substitutes in the various CTE modifiers, including the ionic radius, compatibility, and charge of the chromophoric cations. Suitable chromophoric cations may have a similar ionic radius as the substituted ions. The chromophoric cations may have an ionic radius that is +/−0.2 Å compared to the substituted ions for tetrahedral and octahedral sites, and larger ranges of +/−0.3 Å for higher coordination sites. The chromophoric cations may be compatible for substitution, i.e. capable of residing in the site&#39;s coordination environment. The chromophoric cations may also provide charge balance for the CTE modifiers, such as in scenarios that the chromophoric cations have a charge that is equal to the substituted ions. Alternatively, where the chromophoric cations have a charge that is different than the substituted ions, co-substitution ions may also be used so that the total charge of the chromophoric cations and co-substituted ions equals the charge of the substituted ions. In this case, another ion with a different charge may be substituted with the chromophoric cations for charge balancing purposes. 
     In the simplest case, Al 2 O 3 , Cr 2 O 3 , and Fe 2 O 3  are isostructural and can all form solid solutions with each other. As such, Cr(III) and Fe(III) can typically be used as direct substitutions for Al(III) octahedral sites in non-colored CTE modifiers. Likewise, CTE modifiers with spinel AB 2 O 4  structures are very amenable to ion substitutions in both their tetrahedral and octahedral sites, and in fact a number of cations can occupy either spinel site. Pigments based on doped-rutile structures demonstrate some routes to charge balancing by co-substitution, where a partial Cr(III) substitution can be balanced with an equal Sb(V) substitution to form solid solutions such as Cr 0.03 Sb 0.03 Ti 0.94 O 2  with an average formal cation charge being 4. Likewise, charge balancing of the CTE modifiers can also be accomplished with partial substitution of F anions at oxide sites. Finally, some colored CTE modifiers may have structures that can exist with various levels of oxygen vacancies. In these cases, the use of higher-valency cation co-substitutions may not be necessary. 
     Synthesis of the colored CTE modifiers typically includes a calcination process of an intimate mixture of raw materials that include a chromophoric component. The raw materials may include metal oxides, or compounds that convert to metal oxides during the calcination process, such as compounds including but not limited to metal hydroxides, metal carbonates, metal nitrates, and metal soaps (carboxylates). The term metal oxide is used here generically to represent any elemental oxide. The intimate mixture can be formed by a large variety of well-known blending and milling techniques. Likewise, the intimate mixture may be calcined in a wide variety of kilns, furnaces, and other heating techniques, including but not limited to box kilns, tunnel kilns, rotary kilns, and microwave furnaces. Multiple calcinations can be used, with or without intermittent milling, to enhance formation of the desired phase, but generally are restricted to single calcinations for industrial economic purposes. 
     Calcined colored CTE modifiers may or may not need sieving or to be ground to a finer size before incorporation into an glass frit system, depending on the fired particle size distribution and the process used for the enamel preparation. Any conventional milling technique can be used, including jet milling, attritor milling, bead milling, and ball milling. 
     Pseudo-Brookite Colored CTE Modifiers 
     Tialite (Al 2 TiO 5 ) is a mineral which has the Pseudo-Brookite (PBrookite) structure (Fe 2 TiO 5 ) and a CTE of 14×10 −7 /° C. The CTE of Tialite is virtually identical to the CTE of Cordierite (Mg 2 Al 4 Si 5 O 18 ), which is commonly used as a non-colored CTE modifier in enamels. Al 2 TiO 5  is a white-colored compound that can be synthesized by calcination of AlO(OH) with TiO 2  at 1450° C. Both the Al(III) and Ti(IV) cations occupy octahedral sites in this structure. 
     The colored CTE modifiers of the present invention include a modification of tialite, where transition metal chromophoric cations can be substituted in one or both of the Al(III) and Ti(IV) ion sites in tialite, since a number of these metal chromophoric cations have similar ionic radii to Al(III) and Ti(IV) ions and are compatible with the coordination geometry and size requirements of octahedral sites in the lattice. Applicable chromophoric cations suitable for substitution with the Al(III) and/or (Ti(IV) ions include ions of Fe(III), Cr(III), Mn(II), Mn(III), Mn(IV), Co(II), Ni(II), and Cu(II). In some cases, co-substitutions of the Al(III) and/or (Ti(IV) ions with higher valence cations such as Sb(V), Nb(V), Mo(VI), and W(VI) may be necessary to maintain charge balancing of the modified structure. 
     The more common transition metal chromophoric cations that are compatible with the coordination geometry and size requirements of octahedral sites may include metal ions with a net charge of 2+ or 3+, denoted herein M(II) and M(III) ions. Substitution of Al(III) with appropriate chromophoric M(III) cations would not require any charge balancing. Substitution at both the Al and Ti ion sites in Al 2 TiO 5  can produce a more saturated color in the colored CTE modifier, but substitution of M(II) or M(III) ions on the Ti site may require a co-substitution of higher valency cations to maintain charge balance. 
     Colored PBrookite structured materials can be formulated based on compounds with the formulas Al 2−x M x TiO 5  or Al 2 M x Ti 1−x O 5 , where “x” is the stoichiometric substitution amount and M is the chromophoric ion or ions (e.g. Fe, Cr, Mn, Co, Ni, Cu). Since the Al and Ti sites are both octahedral sites, some mixed sight occupancy is expected in both cases, which is not uncommon in mixed metal oxides, but the substitutions should be controlled primarily by the formulated stoichiometry. Table 1 below shows the useful, preferred, and most preferred ranges for the formula amount “x” of the various ions to be used in place of Al in the PBrookite structure formula, and ΣM represents the summation of multiple cation substitutions. In Table 1, the lower limit for “x” may be 0.01, 0.1, or more. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 x-values for Al 2−x MxTiO 5  formulation 
               
            
           
           
               
               
               
               
               
            
               
                   
                 M 
                 Useful Range 
                 Preferred 
                 Most Preferred 
               
               
                   
                   
               
               
                   
                 Fe 
                 0-2.0 
                 0.0-1.9 
                 0.0-1.8 
               
               
                   
                 Cr 
                 0-1.2 
                 0.0-1.0 
                 0.0-1.0 
               
               
                   
                 Mn 
                 0-1.6 
                 0.0-1.4 
                 0.0-1.2 
               
               
                   
                 Co 
                 0-1.6 
                 0.0-1.4 
                 0.0-1.2 
               
               
                   
                 Ni 
                 0-1.6 
                 0.0-1.4 
                 0.0-1.2 
               
               
                   
                 Cu 
                 0-1.6 
                 0.0-1.4 
                 0.0-1.2 
               
               
                   
                 ΣM 
                 0-2.0 
                 0.1-1.9 
                 0.2-1.8 
               
               
                   
                   
               
            
           
         
       
     
     Table 2 below shows suitable “x” ranges for various ions to be used in place of Ti in the formulated PBrookite structured material. The colored CTE modifier product will have a formula of Al 2 M x Ti 1−x O 5  where “M” is the chromophoric substitution ion (e.g. Fe, Cr, Mn, Co, Ni, Cu), and ΣM again represents the summation of multiple ion substitutions. For each coloring ion used, a “hyper-valent” ion may be needed for charge balancing since M(ll) and M(III) ions are replacing Ti(IV) ions. The hyper-valent ions may be chosen from Nb 5+ , Mo 6+ , W 6+ , P 5+ , As 5+ , and Sb 5+ , preferably Nb 5+ , Mo 6+ , W 6+ , and Sb 5+ , and most preferably Nb 5+ , Mo 6+ , and W 6+ . In Table 2, the lower limit for “x” may be 0.01, 0.1, or more. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 x-values for Al 2 MxTi 1−x O 5  formulation 
               
            
           
           
               
               
               
               
               
            
               
                   
                 M 
                 Useful Range 
                 Preferred 
                 Most Preferred 
               
               
                   
                   
               
               
                   
                 Fe 
                 0-1.0 
                 0-1.0 
                 0.1-1.0 
               
               
                   
                 Cr 
                 0-0.8 
                 0-0.6 
                 0.1-0.5 
               
               
                   
                 Mn 
                 0-0.8 
                 0-0.6 
                 0.1-0.5 
               
               
                   
                 Ni 
                 0-0.8 
                 0-0.6 
                 0.1-0.5 
               
               
                   
                 ΣM 
                 0-1.0 
                 0-1.0 
                 0.1-1.0 
               
               
                   
                   
               
            
           
         
       
     
     Cordierite Based CTE Modifiers 
     The colored CTE modifiers may include modified materials from the Cordierite family, typified by such members as Beryl (Al 2 Be 3 Si 6 O 18 ), Cordierite (Mg 2 Al 4 Si 5 O 18 ), and Benitoite (BaTiSi 3 O 9  or Ba 2 Ti 2 Si 6 O 18 ). Colored, low-CTE modifiers may be obtained by partial or complete substitution of the various chemical components by appropriate metal cations. 
     The high compositional flexibility of the Beryl/Cordierite/Benitoite structures may allow substitutions to produce the colored CTE modifiers. The magnesium and aluminum sites can be substituted by Fe, Cr, Co, Mn, Cu and Ni. If the original formula for Cordierite is considered, at a maximum, about 36% (4/11) of the metal ions are in a 3+ oxidation state. If at least four Si atoms per unit formula are needed to maintain the structure type, then it is possible that the Cordierite structure may not provide the most saturated colors. In this regard, the level of coloring ions in the structure may be increased by substituting two Si 4+  ions with, for example, one Fe 3+  and one P 5+  ion, to produce the compound Mg 2 Fe 6 P 2 SiO 18  having a Cordierite structure. This compound may be produced by calcining a mixture of Cordierite with raw material oxides, or by seeding methods so as to yield a compound of the desired structure with a more saturated color. 
     Table 3 below shows broad ranges for the formula amount “x” of various cations partially substituting in the Al sites of Cordierite. The resultant modified Cordierite-materials will have a formula of Mg 2−x Al 4−y M x+y Si 5 O 18 . The lower limit for “x+y” may be 0.01, 0.1, or more. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 “x + y” values for Mg 2−x Al 4−y M x+y Si 5 O 18   
               
            
           
           
               
               
               
               
               
            
               
                   
                 M 
                 Useful Range 
                 Preferred 
                 Most Preferred 
               
               
                   
                   
               
               
                   
                 Fe 
                 0-3.0 
                 0-2.8 
                 0.0-2.5 
               
               
                   
                 Cr 
                 0-3.0 
                 0-2.8 
                 0.0-2.5 
               
               
                   
                 Mn 
                 0-3.0 
                 0-2.8 
                 0.0-2.5 
               
               
                   
                 Co 
                 0-3.0 
                 0-2.8 
                 0.0-2.5 
               
               
                   
                 Ni 
                 0-3.0 
                 0-2.8 
                 0.0-2.5 
               
               
                   
                 Cu 
                 0-3.0 
                 0-2.8 
                 0.0-2.5 
               
               
                   
                 ΣM 
                 0.1-3.0     
                 0.2-2.8     
                 0.5-2.5 
               
               
                   
                   
               
            
           
         
       
     
     Perovskite-structured CTE Modifiers 
     The colored CTE modifier may also include a Perovskite type material, for example Sm 0.85 Sr 0.15 MnO 3−δ , where δ represents some degree of oxygen vacancy. The Perovskite type material may have a formula of Sm 1−x Sr x MnO 3−δ , where x=0.0-0.5 and δ=0.0-0.25, or a modified version of the Perovskite type material wherein Sr is partially substituted with Ba and/or Ca. 
     This compound is black in color and can theoretically display a negative CTE behavior from approximately 90° C. to 600° C. Solid state synthesis of this material from heating an intimate mixture of non-colored Perovskite type material and metal oxide and metal carbonate raw materials, resulted in a black powder that when pressed into bars exhibited a CTE of −66×10−7/° C. from 200-360° C. The expansion curve is shown in  FIG. 1 , showing the range of negative CTE values. The discrepancy between the tested CTE and the theoretical CTE are likely due to small amounts of secondary phases that were present in the product. 
     Magnesium Pyrophosphate 
     The colored CTE modifier may also include Magnesium pyrophosphate (Mg 2 P 2 O 7 ), which may be a suitable colored CTE modifier since it has a negative CTE over a narrow temperature window due to a phase change when highly loaded in a phosphate glass. Partial substitution with Co(II), Zn(II), and other cations is possible and may make this phase change tunable to different temperature ranges. Mixes of different compositions can then broaden the overall phase transition temperature range and range of negative CTE behavior, giving this mix more utility in applications. This compound may also be used with Fe—Bi—Zn—B—O glasses and with V—Fe—Ti—Zn—P—O glasses. 
     CTE modifies with other structural types, including Ca 0.75 Sr 0.25 Zr 4 P 6 O 24  (NZP), NaZr 2 P 3 O 12 , Nb 2 O 5 , Zr 2 P 2 O 9 , ZrW 2 O 8 , and Y 2 (WO 4 ) 3 , may be modified by substitution with coloring ions to produce a colored CTE modifier according to the present subject matter. 
     EXAMPLES 
     Table 4 shows the compositions of PBrookite-structured colored CTE modifier examples. In examples 1-11, the raw materials were intimately mixed and the intimate mixture was fired at high temperature to form the colored CTE modifiers. Comparative example 1 was fired at 1450° C. for 60 hours to produce phase pure material. Partial substitution of Al with Fe, as in Examples 2 and 3, could be used to lower the firing temperature needed for synthesis to the range of 1350 to 1400° C. Substitutions of Cr for Al in any proportion without co-substitutions did not result in the formation of the PBrookite structure, as in Example 5. Provided that Al and Fe are present, Cr, Mn and Co can be added in attempts to neutralize the brown color of the materials from Examples 2 and 3. These doubly substituted trials appear as Examples 6 to 11 in Table 4. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Pseudo-Brookite Examples 
               
            
           
           
               
               
               
               
            
               
                 Example 
                 Formulation 
                 Single Phase 
                 Color 
               
               
                   
               
               
                 1-comparative 
                 Al 2 TiO 5   
                 Yes 
                 White 
               
               
                 2 
                 Al 1.5 Fe 0.5 TiO 5   
                 Yes 
                 Brown 
               
               
                 3 
                 AlFeTiO 5   
                 Yes 
                 Brown 
               
               
                 4 
                 Fe 2 TiO 5   
                 Almost 
                 Brown 
               
               
                 5 
                 AlCrTiO 5   
                 No 
               
               
                 6 
                 Al 1.5 Fe 0.4 Cr 0.1 TiO 5   
                 Almost 
                 Brown 
               
               
                 7 
                 Al 1.5 Fe 0.2 Cr 0.3 TiO 5   
                 Almost 
                 Brown 
               
               
                 8 
                 AlFe 0.8 Cr 0.2 TiO 5   
                 Almost 
                 Brown 
               
               
                 9 
                 AlFe 0.4 Cr 0.6 TiO 5   
                 Almost 
                 Brown 
               
               
                 10 
                 AlFe 0.8 Mn 0.2 TiO 5   
                 Almost 
                 Brown 
               
               
                 11 
                 AlFe 0.8 Co 0.2 TiO 5   
                 Almost 
                 Brown 
               
               
                   
               
            
           
         
       
     
     For reference, Table 5 below shows conventional CTE modifiers with their CTE values. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Literature CTE values of some non-colored CTE modifiers 
               
            
           
           
               
               
               
            
               
                   
                 CTE Modifier 
                 CTE × 10 7  (C −1 ) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 Al 2 TiO 5   
                 14 
               
               
                   
                 Cordierite (Mg 2 Al 3 Si 5 O 18 ) 
                 14 
               
               
                   
                 NaZr 2 P 3 O 12   
                 −4 
               
               
                   
                 Mg 2 P 2 O 7   
                 As low as −246 
               
               
                   
                 Zr 2 P 2 O 9   
                 4 
               
               
                   
                 Fused Silica 
                 5.4 
               
               
                   
                 Zircon (ZrSiO 4 ) 
                 4.5 
               
               
                   
                   
               
            
           
         
       
     
     Most conventional CTE modifiers are slightly off-white and have L*=85-95 when read with specular reflectance excluded. Three synthetic non-colored CTE modifiers (i.e. with L*=85-95) are included in Table 5b as comparative examples. In contrast, many of the colored CTE modifiers of this invention exhibit L* values in the range of 20-65. L* values of reference black pigments are about 20 when read under the conditions of specular reflectance excluded. Based on this data, it is anticipated that the amount of pigment component in the enamel can be significantly reduced or eliminated with the use of colored CTE modifiers. To be useful, the colored CTE modifier should have L*&lt;75 for dark colors or chroma C*&gt;8 for brighter colors, where C*=√(a* 2 +b* 2 ), preferably L*&lt;70 or C*&gt;10, and most preferably L*&lt;65 or C*&gt;12. 
     
       
         
           
               
             
               
                 TABLE 5b 
               
             
            
               
                   
               
               
                 Measured L* (packed powders, read specular excluded) and CTEs. 
               
            
           
           
               
               
               
            
               
                 CTE Modifier 
                 L* 
                 CTE × 10 7  (C −1 ) 
               
               
                   
               
            
           
           
               
               
               
            
               
                 LiAlSiO 4  (β-eucryptite) comparative 
                 94.6 
                   
               
               
                 example 
               
               
                 LiAl .5 Fe .5 SiO 4   
                 43.0 
               
               
                 Al 2 TiO 5  (PBrookite) comparative example 
                 92.9 
                 20.1 
               
               
                 AlCr .2 Fe .8 TiO 5   
                 53.5 
               
               
                 AlCo .2 Fe .8 TiO 5   
                 57.7 
               
               
                 Mg 2 Al 3 Si 5 O 18  (Cordierite) comparative 
                 94.7 
                 21.0 
               
               
                 example 
               
               
                 Mg 1.8 Al 3.8 Fe .2 Co .2 Si 5 O 18   
                 64.9 
                 37.0 
               
               
                 Perovskite (Sr .15 Sm .85 MnO 3−x ) 
                 21.7 
                 −66.0 
               
               
                 V-774 (ref black pigment) 
                 21.9 
               
               
                 10335 (ref black pigment) 
                 18.0 
               
               
                   
               
            
           
         
       
     
     Glass Frit Systems 
     Glass frit systems may be in the form of a paste, ink, or green body (e.g. a tape), which may be applied to a substrate and fired thereon to form an enamel that is adhered to the substrate. The glass frit system may include glass frit, a colored CTE modifier, pigment, a vehicle, and other components as desired. 
     1. Colored CTE Modifier 
     The colored CTE modifiers can be incorporated into the glass frit system in order to modify the CTE of the resulting fired enamel, so as to more closely match the CTE of the substrate. Moreover, the colored CTE modifier is itself colored, and therefore its addition may reduce the amount of pigment needed in order to produce a desired coloring effect for the enamel as compared to using a conventional non-colored CTE modifier. The colored CTE modifier may be included at 0.5-50 wt % of the total weight of the solids portion. 
     2. Glass Frit 
     The glass frit is not particularly limited, and may be included at 18-95 wt % of the glass frit system. The glass frits used are not critical, and a variety of lead-containing and lead-free glasses may be utilized. 
     As used herein, the term “glass frit” means pre-fused glass material which is typically produced by rapid solidification of molten material followed by grinding or milling to the desired powder size. Glass frits generally includes alkali metal oxides, alkaline earth metal oxides, silica, boric oxide, and other metal oxides. 
     Generally, the glass frit useful herein include a variety of generally categorized glasses, including Pb—Si glass, Pb—B glass, a Pb—B—Si glass, Pb—Bi—Si glass, a Pb—Al—Si glass, a phosphate glass, or lead free glasses such as lead-free Bi—Si glass; lead-free alkali-Si glass; lead free Zn—Si glass; lead free Zn—B glass; lead free alkaline earth-Si glass; and lead free Zn—B—Si glass, all of which may contain additional elemental oxides or halides. Combinations of the foregoing are also possible. 
     In one embodiment, the glass frit may include from 0 to about 75 weight percent lead oxide, from 0 to about 75 weight percent bismuth oxide, from 0 to about 75 weight percent silica, from 0 to about 50 weight percent zinc oxide, from 0 to about 40 weight percent boron oxide, from 0 to about 15 weight percent aluminum oxide, from 0 to about 15 weight percent zirconium oxide, from 0 to about 8 weight percent titanium oxide, from 0 to about 20 weight percent phosphorous oxide, from 0 to about 15 weight percent calcium oxide, from 0 to about 10 weight percent manganese oxide, from 0 to about 7 weight percent copper oxide, from 0 to about 5 weight percent cobalt oxide, from 0 to about 15 weight percent iron oxide, from 0 to about 20 weight percent sodium oxide, from 0 to about 20 weight percent potassium oxide, from 0 to about 15 weight percent lithium oxide and from 0 to about 7 weight percent fluoride, as well as other oxides conventionally used in glass frit compositions. 
     The following Tables 6-11 set forth glass frit compositions useful in the practice of the invention. An entry such as Li 2 O+Na 2 O+K 2 O+Rb 2 O means that Li 2 O, Na 2 O, K 2 O, RbO 2  or any combination of them is present in the specified amount. Table 6 shows oxides amounts suitable for a bismuth and zinc frit. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 ZnBi frits including the listed composition ranges (mole %): 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Oxide 
                 Range 
                 Preferred 
                 Most Preferred 
               
               
                   
                   
               
               
                   
                 Bi 2 O 3   
                 5-85 
                  15-80 
                 50-80 
               
               
                   
                 SiO 2   
                 1-70 
                     2-45 
                 15-35 
               
               
                   
                 ZnO 
                 0-55 
                 0.1-25 
                  1-15 
               
               
                   
                 V 2 O 5   
                 0-30 
                 0.1-25 
                  1-15 
               
               
                   
                   
               
            
           
         
       
     
     Table 7 shows oxides amounts suitable for a bismuth frit. 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 Bi frits including the listed composition ranges (mole %): 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Oxide 
                 Range 
                 Preferred 
                 Most Preferred 
               
               
                   
                   
               
               
                   
                 Bi 2 O 3   
                 5-65 
                     5-55 
                 10-40 
               
               
                   
                 SiO 2   
                 15-70  
                  20-70 
                 30-65 
               
               
                   
                 B 2 O 3   
                 0-35 
                 0.1-35 
                  3-20 
               
               
                   
                 Alkali oxides 
                 0-35 
                 0.1-25 
                  5-25 
               
               
                   
                   
               
            
           
         
       
     
     Table 8 shows oxides amounts suitable for a lead frit. 
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 Pb frits including the listed composition ranges (mole %): 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Oxide 
                 Range 
                 Preferred 
                 Most Preferred 
               
               
                   
                   
               
               
                   
                 PbO 
                 15-75 
                 25-66 
                 30-64 
               
               
                   
                 SiO 2   
                  5-50 
                 15-40 
                 20-35 
               
               
                   
                 ZnO 
                  0-50 
                  5-35 
                 20-33 
               
               
                   
                 PbO + ZnO 
                 15-80 
                 — 
                 — 
               
               
                   
                   
               
            
           
         
       
     
     Table 9 shows oxides amounts suitable for an alkali-titanium-silicate (AlkTiSi) frit. 
     
       
         
           
               
             
               
                 TABLE 9 
               
             
            
               
                   
               
               
                 AlkTiSi frits including the listed composition ranges (mole %): 
               
            
           
           
               
               
               
               
            
               
                 Oxide 
                 Range 
                 Preferred 
                 Most Preferred 
               
               
                   
               
               
                 Li 2 O + Na 2 O + K 2 O + Rb 2 O 3   
                 5-55 
                 15-50 
                 30-40 
               
               
                 TiO 2   
                 2-26 
                 10-26 
                 15-22 
               
               
                 B 2 O 3  + SiO 2   
                 5-75 
                 25-70 
                 30-52 
               
               
                 V 2 O 5  + Sb 2 O 5  + P 2 O 5   
                 0-30 
                 0.25-25     
                  5-25 
               
               
                 MgO + CaO + BaO + SrO 
                 0-20 
                  0-15 
                  0-10 
               
               
                 F 
                 0-20 
                  0-15 
                  5-13 
               
               
                   
               
            
           
         
       
     
     Table 10 shows oxides amounts suitable for a zinc frit. 
     
       
         
           
               
             
               
                 TABLE 10 
               
             
            
               
                   
               
               
                 Zn frits including the listed composition ranges (mole %): 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Oxide 
                 Range 
                 Preferred 
                 Most Preferred 
               
               
                   
                   
               
               
                   
                 ZnO 
                 5-65 
                 7-50 
                 10-32 
               
               
                   
                 SiO 2   
                 10-65  
                 20-60  
                 22-58 
               
               
                   
                 B 2 O 3   
                 5-55 
                 7-35 
                 10-25 
               
               
                   
                   
               
            
           
         
       
     
     Table 11 shows oxides amounts suitable for another lead frit. 
     
       
         
           
               
             
               
                 TABLE 11 
               
             
            
               
                   
               
               
                 Pb frits including the listed composition ranges (mole %): 
               
            
           
           
               
               
               
               
            
               
                 Oxide 
                 Useful Range 
                 Preferred 
                 Most Preferred 
               
               
                   
               
               
                 PbO 
                 25-75  
                 30-70 
                 40-60 
               
               
                 SiO 2   
                 20-50  
                 25-45 
                 30-40 
               
               
                 ZnO 
                 0-35 
                  0-25 
                  0-15 
               
               
                 Al 2 O 3   
                 0-15 
                  0-10 
                 0-5 
               
               
                 Ta 2 O 5   
                 0-5  
                 0-3 
                 0-2 
               
               
                 P 2 O 5   
                 0-5  
                 0-5 
                 0-5 
               
               
                 HfO 2  + In 2 O 3  + Ga 2 O 3   
                 0-10 
                 0-8 
                 0-5 
               
               
                 ZrO 2   
                 0-15 
                  0-10 
                 0-5 
               
               
                 B 2 O 3   
                 0-30 
                  0-20 
                  0-10 
               
               
                 Sb 2 O 5   
                 0-5  
                 0-5 
                 0-5 
               
               
                 TiO 2   
                 0-20 
                  0-15 
                  0-10 
               
               
                 Bi 2 O 3   
                 0-25 
                  0-20 
                  0-15 
               
               
                 Nb 2 O 5   
                 0-5  
                 0-5 
                 0-5 
               
               
                 Alkali Glasses 
                 0-15 
                  0-15 
                  0-15 
               
               
                   
               
            
           
         
       
     
     In any given embodiment, the frit need not contain all oxide ingredients, and various combinations are possible. 
     3. Vehicle 
     The vehicle may include solvents, binders, dispersants, and other common additives such as anti-settling and antifoam agents. The vehicle system may constitute 3.5-80 wt % of the glass frit system. The binder may include a resin, and typically impacts the rheological properties, green strength, or package stability for the compositions. The vehicle may include epoxies, polyesters, acrylics, cellulosics, vinyls, natural proteins, styrenes, polyalkyls, carbonates, rosins, rosin esters, alkyls, drying oils, and polysaccharides such as starches, guar, dextrins and alginates, and the like. 
     4. Pigment 
     The pigment is not particularly limited, and may be included at 1-50 wt % of the glass frit system. The pigment may be lead-free and cadmium-free compositions, and may include one or more pigments, including metal oxide pigments, carbon blacks, mixed-metal oxide pigments; metallic pigments, and others. The pigment may include the CICPs (Complex Inorganic Color Pigments (CICP&#39;s), including corundum-hematite, pyrochlore, rutile, zircon, spinel and other mineral based-structured pigments as outlined in the CPMA handbook, 4 th  edition. Examples of commercially available black pigments include CuCr 2 O 4 , (Co,Fe)(Fe,Cr) 2 O 4 , and (NiMnCrFe) 3 O 4  spinel pigments. 
     5. Additional Components 
     The glass frit system may include various additives or fillers such as crystalline material, reducing agents, dispersants/surfactants, rheological modifiers, flow aids, adhesion promoters, stabilizers, etc., as desired to modify characteristics of the glass frit system or fired enamel. When forming ceramic glazes, rather that glass enamels, other minerals such as kaolin or other silicate materials can be included. 
     Surfactants or dispersants aid in coating the substrate with the glass frit system and, in combination with particle size optimization, inhibits coalescing or clumping of the particles. If the particles are subjected to a particle size reduction operation, the dispersant can be added during size reduction to inhibit the particles from agglomerating together to form larger bodies. 
     Methods 
     The invention can provide a substrate having fired enamel thereon, which fired enamel is produced by firing a glass frit system according to the invention. Any suitable substrate can be used in the subject invention. Examples of substrates include glass, ceramic, metal, or other non-porous substrates. Specific examples of substrates include an automotive glass substrate, architectural or structural glass, appliances and beverage containers. The fired coating may be a glass enamel or ceramic glaze, which may include glass frit and minerals such as kaolin or other silicate material and included on the surface of a tile. 
     To prepare the glass frit systems of the invention, glass frit is combined with the other components, including the vehicle and the colored CTE modifying component, and if necessary, a pigment to form a glass frit system in the form of a paste, ink, or green body. 
     Once the glass frit system is prepared, it can be applied to the substrate by any suitable technique. The glass frit system can be applied by screen printing, decal application, spraying, brushing, roller coating, tape casting, or the like. Screen printing can be preferred when the glass frit system is in the form of a paste and is to be applied to a glass substrate. 
     After application of the glass frit system to a substrate in a desired pattern, the applied glass frit system is then fired to form an enamel adhered to the substrate to form a glass enamel or ceramic glaze. The firing temperature is generally dependent on the sintering temperature of the frit. Typically, the firing range is in the range of about 500° C. to about 1500° C. 
     A substrate can be colored and/or decorated by applying any glass frit system described herein to at least a portion of the substrate. The substrate can be for example, a glass substrate such as a glass sheet, or automotive glass, (e.g., windshield). A glass frit system can be applied in the form of a paste as disclosed herein. 
     The glass frit system may be applied to the entire surface of a substrate, or to only a portion thereof, for example the periphery. The method involves forming an enameled or ceramic glazed substrate whereby the substrate and glass frit system applied thereto is heated to sinter the glass frit to the substrate and burn off any organic materials in the glass frit system. 
     The method may include further processing after the enamel is formed on the substrate, including heating and bending the substrate with the enamel thereon. 
     It will be appreciated that various of the above-disclosed and other features and functions, or alternatives or varieties thereof, may be desirably combined into many other different systems or applications. In addition, various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art are also intended to be encompassed by the following claims. 
     The present subject matter is further defined by the following items. 
     Item 1. A glass frit system for forming an enamel adhered to a substrate, including a vehicle, a glass frit, a colored CTE modifier, and optionally one or more pigments, the colored CTE modifier including: 
     a modified Pseudo-Brookite type material having a formula Al 2 TiO 5 , wherein Al and/or Ti are partially substituted with one or more coloring ions including Fe, Cr, Mn, Co, Ni, and Cu; 
     a modified Cordierite type material having a formula Mg 2 Al 4 Si 5 O 18 , wherein Mg and/or Al is partially substituted with one or more of the coloring ions; 
     a Perovskite type material having a formula Sm 1−x Sr x MnO 3−δ , where x=0.0-0.5 and δ=0.0-0.25, or a modified version of the Perovskite type material wherein Sr is partially substituted with Ba and/or Ca; 
     a modified magnesium pyrophosphate type material having a formula Mg 2 P 2 O 7  wherein Mg is substituted with Co and/or Zn ions; or 
     combinations thereof. 
     Item 2. The glass frit system according to Item 1, wherein: 
     the CTE modifier includes the modified Pseudo-Brookite type material; and 
     the modified Pseudo-Brookite type material has a formula Al 2−x M x TiO 5 , wherein M includes one or more of the coloring ions, and x is 0.1-2, or has a formula Al 2 Ti 1−x M x O 5 , where M includes one or more of the coloring ions and x is 0.01-0.4. 
     Item 3. The glass frit system according to Item 1, wherein: 
     the CTE modifier includes the modified Cordierite type material; and 
     the modified Cordierite type material has a formula Mg 2−x Al 4−y M x+y Si 5 O 18 , wherein M is one or more of the coloring ions, and x+y is 0.1-3.0. 
     Item 4. The glass frit system according to Item 1, wherein the CTE modifier includes the Perovskite type material having the formula Sm 1−x Sr x MnO 3−δ . 
     Item 5. The glass frit system according to Item 1, wherein the CTE modifier includes the modified magnesium pyrophosphate type material. 
     Item 6. The glass frit system according to Item 1, wherein relative to the total weight of the glass frit system: 
     the vehicle in included at 3.5-80 wt %, 
     the glass frit is included at 18.5-95 wt %, 
     the colored CTE modifier is included at 0.5-50 wt %, and 
     the pigment is included at 1-50 wt %. 
     Item 7. The glass frit system according to Item 1, further including one or more of a filler, a reducing agent, a dispersant/surfactant, a rheological modifier, a flow aid, and adhesion promoter, or a stabilizer. 
     Item 8. A method of forming an enameled substrate, comprising: 
     providing a substrate; 
     providing a glass frit system including a vehicle, glass frit, a colored CTE modifier, and a pigment, the colored CTE modifier including:
         a modified Pseudo-Brookite type material having a formula Al 2 TiO 5 , wherein Al and/or Ti are partially substituted with one or more coloring ions including Fe, Cr, Mn, Co, Ni, and Cu;   a modified Cordierite type material having a formula Mg 2 Al 4 Si 5 O 18 , wherein Mg and/or Al are partially substituted with one or more of the coloring ions;   a Perovskite type material having a formula Sm 1−x Sr x MnO 3−δ , where x=0.0-0.5 and δ=0.0-0.25, or a modified version of the Perovskite type material wherein Sr is partially substituted with Ba and/or Ca;   a modified magnesium pyrophosphate material having a formula Mg 2 P 2 O 7  wherein Mg is substituted with Co and/or Zn ions; or   combinations thereof;       

     applying the glass frit system to the substrate; 
     firing the glass frit system to thereby form a colored enamel adhered to the substrate. 
     Item 9. The method according to Item 8, wherein: 
     the CTE modifier includes the modified Pseudo-Brookite type material; and 
     the modified Pseudo-Brookite type material has a formula Al 2−x M x TiO 5 , wherein M includes one or more coloring ions, and x is 0.1-2.0, or has a formula Al 2 Ti 1−x M x O 5 , wherein M includes one or more of the coloring ions, and x is 0.01-0.4. 
     Item 10. The method according to Item 8, wherein: 
     the CTE modifier includes the modified Cordierite type material; and 
     the modified Cordierite type material has a formula Mg 2−x Al 4−y M x+y Si 5 O 18 , wherein M is one or more of the coloring ions, and x+y is 0.1-3.0. 
     Item 11. The method according to Item 8, wherein the CTE modifier includes the Perovskite type material having the formula Sm 1−x Sr x MnO 3−δ . 
     Item 12. The method according to Item 8, wherein the CTE modifier includes the modified magnesium pyrophosphate type material. 
     Item 13. The method according to Item 8, wherein relative to the total weight of the glass frit system: 
     the vehicle in included at 3.5-80 wt %, 
     the glass frit is included at 18.5-95 wt %, 
     the colored CTE modifier is included at 0.5-50 wt %, and 
     the pigment is included at 1-50 wt %. 
     Item 14 The method according to Item 8, wherein the glass frit system further includes one or more of a filler, a reducing agent, a dispersant/surfactant, a rheological modifier, a flow aid, and adhesion promoter, or a stabilizer. 
     Item 15. The method according to Item 8, wherein the substrate is glass.