United States Patent (19) 11 Patent Number: 4,847,218 Schittenhelm Et Al

United States Patent (19) 11 Patent Number: 4,847,218 Schittenhelm et al. (45) Date of Patent: Jul. 11, 1989

(54) ENAMEL FRITS FOR SHEET STEEL WITH Assistant Examiner-James M. Hunter, Jr. IMPROVED BONDING Attorney, Agent, or Firm-Sprung Horn Kramer & 75 Inventors: Hans-Joachim Schittenhelm, Woods Leverkusen; Werner Joseph, (57) ABSTRACT Cologne, both of Fed. Rep. of An enamel frit which provides improved bonding at Germany stoving temperatures below 800° C. after the frit has 73) Assignee: Bayer Aktiengesellschaft, been stoved on unalloyed steel which is capable of Leverkusen, Fed. Rep. of Germany being enamelled, the frit containing 1 to 6% by weight, based on the total quantity of the frit, of bonding oxides (21) Appl. No.: 167,222 and the other constituents so chosen that the following (22 Filed: Mar. 11, 1988 equation is fulfilled:

(30) Foreign Application Priority Data X monovalent atoms -- 2 S. divalent atoms - Mar. 31, 1987 (DE) Fed. Rep. of Germany ...... 3710608 X, fluorine atoms - 51 Int. Cl." ...... CO3C 8/00 52 U.S. Cl...... 501/21; 501/14 X pentavalent atoms 58 Field of Search ...... 501/14, 21 = x trivalent atoms (56) References Cited = X tetravalent atoms, FOREIGN PATENT DOCUMENTS 2746480 4/1979 Fed. Rep. of Germany ...... 501/21 in which the deviation from the ratio 1:1:1 is at most 0.109243 8/1980 Japan ...... 501/21 E8% for each of the monovalent atoms, divalent atoms 0977422 1/1982 U.S.S.R...... 501/21 and pentavalent atoms. 1081137 3/1984 U.S.S.R...... 501/21 1104118 7/1984 U.S.S.R...... 501/21 The enamel frits according to the invention being useful 1112016 9/1984 U.S.S.R...... 501/21 for electrostatic powder application. Primary Examiner-William R. Dixon, Jr. 9 Claims, 1 Drawing Sheet U.S. Patent Jul. 11, 1989 4,847.218

% adhesion Si1 B1 Nax Nio,06 Oz 1 OO A (770°C)--N

B (785oC) W \ C (805oC) \

0.6 O,8 10 1,2 14 X 4,847,218 1. 2 ENAMEL FRTS FOR SHEET STEEL WITH SUMMARY OF THE INVENTION IMPROVED BONDING It has now surprisingly been found that firing resis tant enamel frits which have excellent bonding proper BACKGROUND OF THE INVENTION 5 ties, especially at low temperatures, and flawless sur 1. Field of the Invention faces over a wide stoving range are always obtained This invention relates to enamel frits for sheet steel when the atomic numbers of the frit constituents fulfill with superior bonding at low stoving temperatures, in the following general condition: particular for use on substrates of steel which have not O been pickled or nickel plated. monovalent atoms - 2 X divalent atoms - 2. Background Information pentavalent atoms X fluorine atoms Base and direct enamel frits have the function of trivalent atoms establishing a firm bond between the metal workpiece tetravalent atoms. and the vitreous enamel layer. The enamelling should 15 withstand firing over a wide temperature range, have a More particularly, the frit constituents fulfill the follow smooth, flawless surface and undergo no loss of bond ing condition: ing even after repeated stoving. The development of these enamel frits has hitherto taken place empirically. (XLi-, Na, K-atoms -- 2XBa-, Ca-, Mg-atoms-Xfluorine So-called network forming oxides such as SiO2, TiO2, 20 ZrO2, B2O3 and Al2O3 were combined with network atoms-Xphosphorus atoms) migrators such as Li2O, Na2O, K2O, MgO, CaO, BaO or fluorides and phosphates and varied until the enamels = (Xboron atoms -- Xaluminum atoms) were satisfactory in the required commercial properties = Xsilicon atoms - Xzirconium atoms -- X titanium atoms, in such as fluidity, surface tension, thermal expansion, 25 surface quality and bonding. To improve the bonding of which the deviation from the ratio 1:1:1 is at most -- base enamels, heavy metal oxides such as CoO, NiO and CuO and occasionally iron oxide, manganese oxide, 8% for each of the three ratio components. molybdenum oxide or antimony oxide were added in The deviation from the ratio 1:1:1 should be at most varying quantities. 30 -8%, preferably --6% and is most preferably --4% For direct enamel frits, the addition of TiO2 increased for each of the components. the resistance of the enamelling to acid attack, while the addition of ZrO2 increased the resistance to alkalies. BRIEF DESCRIPTION OF THE DRAWING Molten mixtures of base enamel frits and direct The FIGURE is a graph of% binding versus variable enamel frits containing more than 12 oxidic constituents 35 Na content in the formula Si BNaNio,06Oz at three are therefore no rarity. In all multicomponent systems, temperatures. their development is difficult to oversee and compli cated and therefore expensive. The effect of any one DETALED DESCRIPTION OF THE component on certain properties of the frits is rarely INVENTION proportional to its ratio by weight and is independent of 40 The frits according to this invention contain the fol other components. An incremental calculation which is lowing constituents within the ranges indicated, obvi recommended for simple types of glass is only rarely ously so chosen that the above conditions are fulfilled: possible, e.g. in the case of thermal expansion, and then Na2O: 5-25% by weight only approximately. An added difficulty is that several K2O: 0-12 enamel frits are usually mixed together and inert sub 45 stances may be added for enamel commercial require BaO: 0-26 ments or reasons of economy. CaO: 0-16 For conventional two-layered or multi-layered enam MgO: 0-2 elling, frits with different viscosities and melting prop F: 0-10 erties were combined for the base enamel and inert 50 B2O3: 5-30 substances were added to facilitate the gas reactions Al2O3: 0-10 proceeding from the sheet steel. SiO2; 25-65 The base enamels which are viscous and hard at the ZrO2: 0-16 stoving temperature are described as filling bases, while TiO2: 0-14. low viscosity, soft frits which wet readily and are capa 55 If the general formula is applied to the components ble of dissolving iron oxides are known as network base used for base and direct enamel frits, the following enamels. The proportions in which they are mixed and formula is obtained: the amount of quartz added depend on the quality of the steel and the thickness of the steel sheet as well as on the 60 X alkali metal atoms -- 2X alkali earth metal atoms - stoving temperature and the dwell time. Here again, the X, fluorine atoms - X phosphorus atoms = proportion of frits and the additives used for the milling X boron atoms + X alumninum atoms = X, silicon atoms -- process are selected empirically and either accepted or X zirconium atoms -- X titanium atoms. varied under practical conditions. Predictions as to the The bonding oxides are normally obtained by melting optimum properties such as compatibility of the frits 65 nickel oxide either alone or together with cobalt oxide with one another, bonding to differently cast qualities of and/or copper, manganese or iron oxide, each in quanti steel and flow properties of the slips were rarely possi ties of 1 to 6% by weight, preferably 2 to 4% by weight, ble. based on the total quantity of frit. 4,847,218 3. 4. It is nowadays preferred for economical and ecologi nent base enamels described above were simplified to a cal reasons to apply the base and direct enamels to steel more easily overseen three-component system Na which has not been pickled or nickel plated. This new 2O/B2O3/SiO2 free from phosphorus, alkaline earth technology provides a considerable saving in energy by metals and fluorine, and the only bonding oxide intro dispensing with the heated pickling and rinsing baths. In duced was NiO. addition, the process of working up and disposing of the The atomic number formula now reduced to X, so spent pickling liquids, the nickel bath and the contami dium atoms=X, boron atoms=X silicon atoms was then nated rinsing liquid also becomes superfluous. modified over a wide range of Na contents while the It has now surprisingly been found that the enamels atomic number ratio Si:B= 1:1 was left unchanged, as according to this invention are exceptionally suitable 10 will be described in Example 2 herein below. for application to steel substrates which have not been pickled or nickel plated and are superior to the usual commercial base and direct enamels. Frit % by weight If the slip is to be applied by flooding, immersion or No. Formula SiO2 B2O3 Na2O NiO spraying, it is necessary to degrease the workpieces 15 1 SilB1 Nao.6 Nio,06Oz 50.9 29.5 15.8 3.8 which are to be enamelled but when the enamel frits 2 SiB Nao.7 Nio,06O2 49.6 28.8 7.9 3.7 described above are applied as powders by means of an 3 SiB Nao.8 Nio,06O. 48.4 28.0 20.0 3.6 4 SiBNao.9 Nio,06O. 47.2 27.4 2.9 3.5 electric field, this degreasing also becomes superfluous. 5 SiBiNal.0 Nio,06O2 46.1 26.7 23.8 3.4 The enamel frits according to the invention are ob 6 SiBiNa1. Nio,06O2 45.0 26.1 25.5 3.4 tained by melting ordinary commercial raw materials 20 7 SiB Na12 Nio,0602 440 25.5 27.2 3.3 for enamels, such as borax (Na2B4O7.5H2O), quartz 8 SilBNa1.3 Nio,06O2 43.0 24.9 28.9 3.2 powder, sodium tripolyphosphate, feldspar, zirconium 9 SilBiNa 14 Nio,06O2 42.1 24.4 30.4 3.1 sand, fluor spar, alkali metal and alkaline earth metal carbonates and the corresponding heavy metal oxides at Frits Nos. 1 to 9 were used as powders without mill 1100° C. until they are "thread smooth', and the molten 25 ing additives as described in German Patent Specifica mixture is then chilled over water-cooled steel rollers. tion No. 2025 072 and applied to test sheets under the The resulting flakes are applied to 1 mm test sheets both same experimental conditions and stoved for the same as enamel powders in an electrostatic field and as aque lengths of time at 770° C., 785 C. and 805 C. ous suspensions in the form of slips by immersion or The falling apparatus according to DEZ Merkblatt F spraying, and they are then stoved in a graduated tem 30 perature oven over a temperature range of from 770 to 6.2 was used for the bonding test. The results were 880 C. assessed visually on the deformed sample, bonding stage The thickness of the layer of stoved enamel was 0.15 No. 1 being given a value of 100% and bonding stage mm. The bonding test was carried out with a falling No. 5 given a value of 0%. apparatus with deformation of the sheet steel and visual The results of this experimental series are represented assessment of the bonding picture according to DEZ 35 in the accompanying diagram as stoving curves Merkblatt F 6.2. A=770° C., B=785 C. and C=805 C. The multi-component system given in Example 1 It is clear from this that the best bonding, especially in herein below fulfils the relationship according to this the range of low temperatures of base enamel frits, is invention of the atomic numbers: obtained with the atomic ratio Si:B:Na:(Ni 40 O)= 1:1:1:(0.06). When there is a deviation from the value Na=1, an XAlkali metal atoms (Na, K, Li) -- 2Xalkaline earth increase or reduction in the Na content in the system metal atoms (Mg, Ca, Ba) - Xfiuorine atoms - Xphosphorus SiB Nao.6-14Nio,06 results in a deterioration of the bonding even at elevated stoving temperatures, al atoms = Xboron atoms + Xaluminum atoms = Xsilicon 45 though the flow values of the frits according to DIN 51 atoms + Xzirconium atoms -- Xtitanium atoms with a devia 161 increase with increasing Na content. This is surprising and contradicts the known state of tion of c <1%. the art which proceeds on the basis that frits with a high Regardless of which method of application is em 50 B2O3 content promote wetting and soft base enamels ployed, the frit obtained after stoving is distinguished bond more firmly than hard base enamels (filling base by its smooth, flawless surface and excellent bonding enamels, network base enamels) having the same bond over the whole temperature range of from 770 to 880 ing oxide content. C. It may also be seen from the stoving series that the When the oxidic composition described in Example 1 55 more the frits deviate from the atomic ratio according is modified and simplified by replacing the tetravalent to the invention given by Si:B:Na=1:1:1, the weaker is Zr and Ti in ZrO2 and TiO2 by SiO2, replacing trivalent the bonding of the base enamel on steel substrates. As Al in Al2O3 by B2O3 and replacing divalent Mg and Ba may be expected, enamels having the composition SiB in MgO and BaO by CaO so that the sum of atomic Na1.4Nio,06 and SiB1 Nao.6Nio,06 show virtually no numbers in the formula according to the invention: X 60 bonding after they have been applied electrostatically Alkali metal atoms (Na, K, Li)--2X alkaline earth metal to 1 mm steel sheets and stoved at temperatures in the atoms (Ca)-X phosphorus atoms-X, fluorine region of 785 C. If, on the other hand, the two frits are atoms=X. boron atoms=X silicon atoms is again full mixed in equal parts so that the mixture again contains filled, then the base enamel obtained again has an excel the ideal atomic ratio: SilB1NaNio,06, then enamelled lent surface and very good bonding in the selected ten 65 metal sheets stoved at 785 C. are surprisingly found to perature range of from 770 to 880 C. show excellent bonding, To prove that the atomic number formula according This means that bonding at low stoving temperatures to this invention has general validity, the multi-compo can also be achieved with frit combinations in which the 4,847,218 5 6 individual components deviate from the atomic ratio according to the invention, but fulfil the requirement -continued Na:B:Si=1:1:1 when they are mixed together. % by Weight Atomic number per 10,000 The simple SilBiNa Nio,06 system is only in excep CoO 0.40 Co 24 Fe2O3 3.76 Fe 217 tional cases suitable for application as a slip. The rela- 5 CuO 2.47 Cu 43 tively high solubility of the frits when they are milled or MnO 0.58 Mn 38 stored alters the flow properties of the slip and hence its E(Na,Li,K) -- 2E(Ba,Ca,Mg) - F - EP = 2807 properties for application. Elements which stabilize the E(B,Al) = 2817 glass structure were therefore introduced to reduce E(Si, Zr,Ti) = 2811 leaching. 10 It has been found advantageous to replace sodium The melt, which had become homogeneous and within certain limits by other alkali metals, such as potassium and/or lithium, and to replace part of the "thread smooth' after 20 to 30 minutes, was chilled boron by aluminium and part of the silicon by zirco between steel rollers and the glass band obtained was nium. Enamels of this type are again distinguished by 15 broken. The resulting flakes were applied to steel sub their good bonding at low temperatures, so long as the strates by electrostatic means as a powder and by spray atomic ratio Me:Met 3:Mei i = 1:1:1 remains un ing as a slip and stoved in a graduated oven at a temper changed. The atomic numbers Na1-x(Li-i-K)xB1-xAlx ature range of from 770 to 880 C. Sil-Zr-Nio,06 then represent the limit for this compen Powder Application sation. 20 It has also been found that alkaline earth metals such 100 g of enamel flakes and 0.4 g of methyl-hydrogen as calcium and/or barium may be introduced instead of siloxane were ground in a porcelain ball mill as de alkali metals without any significant change in the scribed in Example 2, herein below until the residue of bonding properties, provided the atomic numbers for powder on the 16,900 mesh screen (width of mesh 40 the alkali earth metal equivalent (Me/2) do not exceed 25 um) was less than 20%. 20% of the Na. The formula alkali metals 1-alkaline The powder, which had a surface resistance of more earth metal/2Met 31.0Met'10Nio,06 (x up to 0.2) then than 1012 (), was sprayed on steel sheets 60X 450 mm applies. The introduction of other elements, such as from an electrostatic spray gun with application of a fluorine in the form of fluoride or phosphorus in the voltage of 70 kV to form a uniform layer 1 mm in thick form of phosphate, may occasionally have an advanta- 30 ness. After the application of 14 g of powder (5.2 geous effect on the flow properties of the slips, the g/dm2), the steel sheets were stoved in a graduated melting properties and the surface smoothness. The furnace for 10 minutes. The strips of steel sheet were combination rule according to the invention based on (a) degreased the valencies of the elements again applies: X. Alkali (b) not degreased. metal atoms +2X alkaline earthmetal atoms-2 fluo Application of Slip rine atoms-X phosphorus atoms=X boron atoms--X. aluminum atoms=X silicon atoms--X zirconium atoms. 1000 g of flakes were ground in a ball mill containing The best results were obtained with 4% by weight 3500 g of heavy grinding balls to form a slip according NiO. No further improvement in bonding may be ob to the following formulation: tained by increasing the Ni content. Cobalt oxide and copper oxide may be used as bonding oxides in addition % by weight to nickel oxide; and manganese oxide and iron oxide Frit 100 may be added for color. On economical grounds alone, Clay 6 the ratio Ni:Co (Cu) should not be less than 3:1. Sodium nitrite 0.1 The object of the present invention will now be ex- 45 Borax 0.2 plained with reference to the following Examples. Calcium silicate hydrate 0. Water about 50 EXAMPLES Degree of grinding 1 % residue on a 3600 mesh screen EXample le 1 50 Density 1.70 g/ml. An enamel frit of the following composition was obtained by melting commercially available enamel raw This slip was applied to the above-mentioned steel materials in a fire clay crucible of 500 ml capacity at strips by spraying to form an enamel layer which had a 1100° C.: thickness of 0.15 mm after stoving. After drying, the 55 sample strips were stoved in a graduated oven in a tem perature range of from 770 to 880 C. for 10 minutes. % by Weight Atomic number per 10,000 The steel had previously been prepared by degreasing Na2O 15.61 Na 2,320 Li2O 1.90 Li 585 in the usual manner. The bonding test with falling appa K2O 140 K 137 ratus showed excellent bonding over the whole temper BaO 1.83 Ba 55 60 ature range. CaO. 0.65 Ca 54 MgO 0.30 Mg 34 EXAMPLE 2 F 0.96 F 232 POs 4.45 P 289 To prepare frits 1 to 9 of the system SiB1 Nao.6. B2O3 19.94 B 2,638 1-4Nio,06Oz, the raw materials, borax Na2B4O7, soda Al2O3 1.98 Al 179 65 SiO2 33.32 Si 2,554 Na2CO3, quartz powder SiO2 and nickel oxide NiO, ZrO2 5.81 Zr 217 were weighed out in stoichiometric proportions, mixed, TiO2 0.69 Ti 40 and melted in fire clay crucibles at 1100° C. for 25 min NiO 3.95 Ni 244 utes, using an electrically heated muffle furnace, and the 4,847,218 7 8 melt was chilled between steel rollers and the resulting -continued glass band was broken up into flakes. weight % 100 g portions of these flakes were ground up in a BaO 0 to 26 Bloch-Rosetti mill containing 30 grinding balls with a CaO 0 to 16 5 MgO 0 to 2 total weight of 240 g with the addition of 0.4 g of meth F 0 to 10 yl-hydrogen-siloxane until the residue of powder on the B2O3 5 to 30 40 um screen (16,900 meshes/cm) was less than 20%. Al2O3 O to 0 The enamel powder was applied to conventionally SiO2 25 to 65 ZrO2 0 to 16 degreased steel sheets 100x100mm x 1.0 mm in thick O ness by means of a commercial electrostatic spray gun TiO2. 0 to 14 with application of a voltage of 70 kV to the corona the frit comprising 1 to 6% by weight, based on the total discharge electrode. After the application of 5.2 g of quantity of the frit, of bonding oxides and the other powder/dm2, the coated sample plates were stoved at constituents so chosen that the following equation is 770° C., 785 C. and 805 C., respectively. 15 fulfilled: The bond strength was tested by means of the falling apparatus according to DEZ Merkblatt F 6.2. In this test, a striking pin which was hemispherical at one end (XLi-, Na, K-atoms -- 2XBa-, Ca-, Mg-atoms - Xfluorine and weighed 2000 g was dropped on the enamelled test atoms - Xphosphorus atoms) plate from a height of 750 mm. The bond strength was assessed visually on the deformed sample. = (Xboron atoms -- Xaluminum atoms) It is found that optimum bonding, especially at low = Xsilicon atoms + Xzirconium atoms + X titanium atoms, temperatures, is obtained with frits which correspond Q approximately to the atomic ratio Si:B:Na:- 25 in which the deviation from the ratio 1:1:1 is at most E8% for each of the three ratio components. Ni=1:1:1:0.06. 2. An enamel frit according to claim 1, wherein the EXAMPLE 3 deviation is at most E6%. 3. An enamel frit according to claim 1, wherein the Frits Nos. 1 and 9 of Example 2, which alone pro deviation is at most 4%. vided no bonding over the whole temperature range of 30 4. An enamel frit according to claim 1, wherein the from 770 to 830 C., were milled in equal amounts (in frit comprises 2 to 4% by weight of bonding oxides, each case 50 g) with 0.4% by weight of polysiloxane in based on the total quantity of the frit. a ball mill, as already described. The powder was 5. An enamel frit according to claim 1, wherein the sprayed on pretreated steel sheets 60X450 mm and 1 bonding oxide is selected from the group consisting of mn in thickness by means of a commercial electrostatic 35 nickel oxide and nickel oxide with cobalt oxide, nickel spray gun and stoved in a graduated oven adjusted to a oxide with copper oxide, nickel oxide with manganese temperature range of from 770° C. to 880 C. oxide, nickel oxide with iron oxide and nickel oxide The bonding test with the falling apparatus showed with cobalt oxide and one or more of copper oxide, excellent bonding over the whole temperature range. 40 manganese oxide and iron oxide. It will be appeciated that the instant specification and 6. An enamel frit according to claim 1, wherein the claims are set forth by way of illustration and not limita frit has the formula tion and that various modifications and changes may be SiB1 Nao.6tal.4Nio,06. without departing from the spirit and scope of the pres ent invention. 45 7. An enamel frit according to claim 1, wherein the We claim: frit has the formula 1. A base or a direct enamel frit which provides im proved bonding at stoving temperatures below 800° C. after the frit has been stoved on unalloyed steel which is 50 where x is up to 0.2. capable of being enamelled, which frit comprises the 8. An enamel frit according to claim 1, wherein the following composition - frit has the formula alkali metals 1-alkaline earth metal /2Me! 31.0Me'10Nio,06, where x is up to 0.2. weight % 9. An enamel frit according to claim 1, wherein the 55 sum of Mg, Ca and Ba atoms is at most 10% of the Na Na2O 5 to 25 atOnS. K2O 0 to 2 ck k cit k it Li2O 0 to 8