GB2263478A

GB2263478A - Lead-and and cadmium-free glass composition for glazing, enameling and decorating

Info

Publication number: GB2263478A
Application number: GB9300476A
Authority: GB
Inventors: Erich Rodek; Werner Kiefer; Friedrich Siebers
Original assignee: Carl Zeiss AG
Current assignee: Carl Zeiss AG
Priority date: 1992-01-20
Filing date: 1993-01-12
Publication date: 1993-07-28
Anticipated expiration: 2013-01-12
Also published as: NL194123C; GB9300476D0; FR2686333B1; JPH05270860A; GB2263478B; NL9202217A; FR2686333A1; NL194123B; DE4201286A1; DE4201286C2

Description

2263478 1 LEAD- AND CADMIUM-FREE GLASS COMPOSITION FOR GLAZING, ENA14ELING

AND DECORATING, AND ITS USE expansion, as well as The invention relates to lead- and cadmiumfree glass compositions for glazing, enameling and decorating, and their use for glasses having low thermal such as, in particular, borosilicate glasses, glass ceramics.

The primary area of usage for such glasses or glass ceramics is constituted by laboratory appliances and cooking utensils resistant to temperature fluctuations, or especially also heatable plates, such as, for example, cooking surfaces.

Glazes are low-melting glasses utilized for protection, enhancement and/or alteration of the phsyical or chemical surface properties, for embedding, e.g. in electronics, or also simply for adornment and decoration of a great variety of glass articles, glass ceramic, ceramic, or porcelain.

Glazes usually consist of a transparent or translucent glass composition applied to the article in accordance with the conventional techniques, such as, for example, screen printing or brush application, in finely divided form, e.g. in the form, of a paste. The finely ground glass powder is frequentiy also called frit.

Enamels are glazes containing coloring components, such as pigments; the pigment proportion in the enamel can amount to up to 30% by weight.

2 - Pigments usually are oxides resistant with respect to the glaze, evoking the desired color impression in dependence on choice.

The glaze or the enamel is baked in at temperatures lying below the softening point of the article to be treated, the respective glass composition of the glaze and/or of the enamel being melted and forming a stable bond with the surface of the article.

Baking also serves for volatilization of the organic vehicles utilized as auxiliary agents for the application of the glaze or of the enamel.

In order to ensure an adequate and long-term adhesion of the alaze or enamel after baking and during subsequent practical usage, it is necessary in correspon- dence with previous theoretical considerations to carefully adapt, in particular, the thermal expansion coefficients of the article to be decorated and of the glaze or enamel to each other. in this connection, it has heretofore been considered desirable according to the state of the art for the glaze to exhibit a lower thermal expansion coefficient than the article to be glazed.

This was supposed to ensure that the glaze or the enamel, during cooling after baking, is exposed to tensile stress and accordingly does not exert on the properties of the support material any negative effects, especially strength-reducing effects.

Problems have been encountered heretofore in the glaze or enamel decoration of borosilicate glasses and, in particular, glass ceramics with low thermal ex- pansion based on S-eucryptite or h-quartz mixed crystals produced by thermal treatment, the so-called ceraming of a suitable starting glass. Such glass ceramics are distinguished by a thermal expansion of 0 1 x 10- 6 ", K in a temperature range of between 20 and 700 C.

4 is Considering the thermal stability of these glass types, decorating with glaze or, respectively, enamel must take place at temperatures of below 1000 C.

In glass ceramics, the baking of the glaze or enamel is preferably conducted simultaneously with the ceramic-producing process, as a socalled direct baking step.

The glazes and enamels used heretofore for coating and/or decorating glasses of low thermal expan- sion coefficients and glass ceramics contain, in most instances, even today still lead and frequently even, in addition thereto, still cadmium.

The reason for the use of lead and cadmium in glazes is their positive effect on the melting properties, a marked lowering of the melt temperature with simultaneously optimum viscosity characteristic of the glaze or enamel, respectively.

In addition, these glases or enamels, after direct baking, exhibit adequate adhesive strength with respect to the carrier material and well satisfy the requirements posed under practical conditions, even over long usage periods.

This is the more surprising inasmuch as, in contrast to the theoretical demand for approximately the same thermal expansion coefficients between carrier material and glaze or enamel, these lead- and cadmium containing glass compositions exhibit high thermal ex pansion coefficients of 5,x 106 /K up to even io X io -6 /K.

The reason why these high-thermal-expansion glass compositions show adequate adhesion to substrates with practically no thermal expansion, such as, for ex ample glass ceramic, is ascribed, insofar as this I- - tl - phenomenon has been understood thus far, especially also to these additions of lead and possibly cadmium.

However, in the meantime, unfavorable toxicological effects of these substances on humans and the environment have resulted in a partial or entire prohibition of such lead or cadium compounds in decorative coatings.

A number of lead-free and cadmium-free products of this type have been proposed, therefore, in the literature.

Thus, it has been known from DE 3,405,708 C2 to provide a lead-free, cadium-f-ree and zinc-free alass frit comoosition consisting of the components Al 2 0 3' B 0 Sio L.1 Z rO SnO, and of La 0 CaO, SrO, 2 3' 2' i2o- 2' 2 3' BaO, Na 2 0 and F, and using same --'--%r a colored enamel to decorate articles of glass, glass ceramic and ceramic.

These glass frit compositions exhibit high contents of B 2 0 3 and, in particular, also SnO 2 and/or La 2 0 3 ' Glass frit compositions with such high B 2 0 3 contents with simultaneouslv low SiO 2 contents are hardly capable of satisfying high requirements with regard to chemical resistance, =articularly acid resistance.

EP 0 267 154 Al relates to a lead- and cadmiumfree glass frit composition consisting of Na 2 0, ZnO, B 2 0 31 Sio 2 and optionally of K 2 0, Li 2 0, CaO, SrO, BaO, Bi 2 0 3' Al 2 0 3' ZrO 2' TiO 2 and WO 3 The glass frit composi-Lion contains 4.0 - 30.0 mol-% of ZnO. Also zinc compounds are con- sidered to be toxic already in small concentrations, though less than those of cadmium, and therefore are not without problems, and thus undesirable, as a substitute for lead. Also, the chemical resistance of -s frequenty unsatis- glasses having high ZnO contents factory in practical use.

WO 90/15782 discloses a lead-free glass composition with 30-51% by weight of Sio 2' 19-50% by weight of B 2 0 3' 2-20% by weight of Zro 2' up to 14% by weight of Na 2 0, up to 6% by weight of K 2 0, up to 19% by weight of ZnO, up to 5% by weight of Li 2 0, and 2-8 parts of fluorine compounds per 100 parts of the other components of the composition. Here again, lead is primarily substituted by zinc.

EP 0 402 007 A1 relates to a glass composition with 30-70% by weight of Sio 21 10-30% by weight of CaO, 0-20% by weight of ZnO, 3 -8% by weight of Moo,, 0-20% by weight of B 2 0 3' 0-25% by weight of Al 2 0 3' 0-10% by weight of K 2 0, 0-10% by weight of Na 2 0, 0-10% by weight of Mgo, 0-15% by weight of BaO, 0-7% by weight of L'2 0, 0-10% by weight of PbO, 0-5% by weight of Sro, 010% by weight of Ceo, 0-0.1% by weight of Coo, and 0-5% by weight of P 2 0 5 Here, too, the composition contains possibly up to 20% of ZnO and, in addition, necessarily still at least 3% of Moo 3, the alkali resistance of which is inadeauate due to the danger of the formation of molybdates. This composition furthermore will require a baking range of considerably above 1000 C.

U.S. Patent 4,970,178 claims a lead-free glass frit having the following components:

5.0-14.0 mol-% of Na 2 0, 8.0-25.0 mol-% of ZnO, 6.0-13.0 mol-% of B 2 0 3' 45.0-60.0 mol-% of SiO 21 0-8.0 mol-% of K 2 0, 0-5.0 mol-% of Lip ' 0-8.0 mol-% of CaO, 0-8.0 mol-% of SrO, 0-9.0 mol% of Bao, 0-10.0 mol-% of Bi 2 0 31 0-4.0 mol-% of A1 2 0 3' 0-6.0 mol-% of ZrO 2' 0-7.0 mol-% of TiO 21 0-1.0 mol-% of WO 3' Also this glass frit necessarily contains ZnO.

EP 0 412 336 Al discloses a pollutant-free orange-colored decorative paint ma!de up of 15-30% by weight of an orange-colored pigment and 70- 85% by weight of a glass frit wherein the frit consists of 35-60% by weight of Sio 21 15-35% by weight of B 2 0 3' 3-8% by weight of Zro 2' 2- 8% by weight of Al 2 0 3' 10-18% bv weight of Na 0 and/or K 0 and 2-6% by weight of L' 2 2 il - This frit does not contain any CaO and is baked at 1000 C onto tiles.

The respective glass compositions according to the state of the art exhibit various, in part desirable, proverties, but do not adequately meet high requirements.

Therefore, it is an object of this invention to indicate glass compositions free of lead, cadmium and other toxicologically objectionable components which satisfy high requirements, i.e. can be processed, in particular, without any problems in a broad and relatively low temperature range and, moreover, yield glazes and enamels, respectively, showing for use in industrial and domestic areas very good properties regarding adhesive strength, zhermal stability, resistance to temperature fluctuations, abrasive resistance, and conspicuous abrasion, spotting tendency upon contamination, and chemical resistance to acids and alkalis.

According to the present invention, this object has been attained by a glass composition with Li-20 0 12 % by wt.

MgO 0 - 10 % by wt.

CaO 3 - is % by wt.

B2()3 5 - 25 % by wt.

A1203 3 - 18 % by wt.

Na2O 3 - is % by wt.

K20 3 - IS % by wt.

BaO 0 - 12 % by wt.

Si02 25 - 55 % by wt.

TiO-> 0 - 5 % by wt.

ZrO-) 0 - <3 % bv wt.

1 With glass compositions according to this invention, glazes and enamels can be produced which satisfy in excellent fashion the high requirements of practical use, without employing toxic or environmentally relevant materials.

It has been found surprisingly that these compositions according to the invention exhibit all of the desired properties even without additions of lead, cadmium, zinc, tin, and fluorine compounds. that the CaO proportion which state of the art It is supposed lies markedly above the in conjunction with the selection and usage quantities of the other components in accordance with this invention,leads to an intensive and positive interaction between the substrate glass and the glaze or enamel during the baking step, and thus to a stress-free and firmly adhering bond over an adequately long time period in practical use.

Superior adhesive strengths have been found with the glass compositions according to this invention in the thus-formed glazes after baking, following quenching tests and in continuous operation at 670' C. Even in case of relatively large layer thicknesses of the glaze, for example up to 9 pm, no spalling or peeling tendencies were displayed by the substrate glass, and this holds true even at extreme fluctuating temerature loads over longer periods of time. The thermal stability of the compositions is satisfactory and shows practically no change in color even after 75 hours at 670 C.

With good chemical resistance to acids and alkalis, the glaze compositions according to this invention have high gloss, low abrasion, and practically no conspicuous abrasion in grid-like and also solid application.

Glazes according to the composition of this invention can also be mixed any time without problems with pigments up to a proportion of 30% by weight and can then be used for the production of colored coatings and/or decorations. The pigments employed are customary oxide materials resistant to the glass compositions at the baking temperature.

However, the glaze can also be inherently colored, for example bv the controlled addition of coloring oxides.

The composition of the glazing glass is first homogeneously melted and from the thus-formed glass, a glass powder having a grain size of < 10 pm, preferably 1 - 3 pm, is then produced by grinding, especially weL grinding. This powder is then made into a paste with a standard screen printing oil, e.g. on pine oil base, and applied according to generally known techniques, e.g. by screen printing, by transfer picture, or brush.

After baking on a glass of low thermal expansion or a glass ceramic, glaze layers are obtained with a thickness of between 2 and 9 pm. These layers, in spite of the very large differences in thermal expansion between the glaze or enamel and the substrate glass, show exellent adhesion and resistance to temperature fluctuations.

In a preferred embodiment, Li 2 0 on the order of magnitude of 4-10% by weight is added to the glass com- position of this invention, and the Cao proportion is raised.

Both measures improve the melting ability of the glass composition to a marked extent, the increased CaO proportion entirely overcompensating for the slight impair- ment in chemical resistance incurred by the addition of L j:F.

Other preferred embodiments contain, depending on the subsequent purpose of use, also additionally, for example, 8-10% by weight of BaO and/or, for instance, 6-10% by weight of MgO.

The addition of the facultative oxides proves advantageous, depending on the usage of the glass composition, where higher Li 2 0 contents generally entail a lowering of the baking temperature. Bao can serve as a replacement for Cao up to a certain proportion, but usually brings about an increase in baking temperature and thermal expansion.

Additions of Ti02 improve acid resistance while ZrO 2 can further improve the resistance to alkalis.

The invention will be described in greater detail by the following examples.

Table I contains the compositions of Examples 1-17 of the glazes according to this invention in percent by weight, based on the oxide:

T A B L E I No. 1 2 3 5 6 L4 o 0 4 0 0 ,L 1.0.0 4,0 10.0 a & B-)O- 10,0 20.0 12.0 10.0 1040 10.0 Na-)O 5,0 15.0 5.0 5,0 15,0 5.0 Mao 0,0 0.0 800 6.0 0.0 8.0 Al'203 5.0 5.0 15.0 15.0 15,0 5.0 S i-02 50.0 30.0 30.0 30.0 4660 48.0 K20 5,0 15.0 5,0 15.0 5,0 15,0 cao 5.0 11.0 15,0 540 5,0 5,0 BaO 10.0 0.0 0.0 10.0 0.0 0.0 No. 7 8 9 10 11 12 Li) 0 4.0 10.0 4.0 10.0 10.0 10.0 10,0 20.0 20,0 20.0 20.0 10.0 NaiO 15.0 15,0 5.0 5.0 5.0 5.0 Mao 8.0 8.0 0.0 0,0 8.0 0.0 A1203 5.0 7.0 5.0 150 5,0 15,0 0 S102 30,0 30,0 46.0 30,0 32.0 30,0 K20 5.0 5.0 5,0 5.0 15.0 15.0 CaO 13.0 5.0 15,0 5.0 5.0 15.0 BaO 10.0 0.0 0,0 10.0 0.0 0.0 No.

L120 B203 Na20 MaO A1203 Si02 K.) 0 CaO BaO 1 3 14 is 16 17 4.0 20.0 5.0 6.0 5.0 30.0.

5.0 15.0 10.0 1040 10.0 15#0 0..0 560 30.0 15.0 5,0 10.0 10.0 11.3 6.8 0 0 12.8 g 5,0 5.0 0,0 9 & 4 10.0 5,0 0,0 11.4 41,7 5&0 15,0 2.5 6,4 10,0 7,6 3.3 7 & 6 45. 'L & 0 5.0 10,0 Table II shows, for the compositions 1-17 of Table I, in each case the transition temperature (Tg) in 0 C, the softening temperature (ST) in 0 C, the processing temperature (PT) in ' C, as well as the thermal expansion coefficient (CTE) between 20' and 300' -in 10- 6 /K.

T A B L E II No. Tg ST PT CTE 454 567 690 --0.18 469 596 14.49 433 533 840 11,41 382 495 830 12,38 444 557 750 11.50 6 447 568 756 10.98 7 374 490 700 13,62 8 365 447 597 13.65 9 511 610 765 9.20 422 513 639 10.83 ii 378 456 630 12 385 515 755 13 466 567 689 10.51 14 300 400 430 16.40 is 435 537 780 16 432 531 750 11.48 11 436 543 705 11.14 1 Examples especially preferred according to this invention herein are compositions 1, 11, 15, 16, and 17, with transition temperatures in a range from 3800 to 4500 C, softening temperatures in a range from 4601 to 570' C, processing temperatures from 630' to 780 C, and thermal expansion coefficients of 10.18 to 13.13. 10- 6 /K.

These compositions also display very good adhesive strengths, a high thermal and chemical re- sistance, and excellent usage properties during the course of the investigations performed according to the customary and conventional standard methods, as well as in lonc-term tests.

Claims

A lead-and cadmium-free glass composition for glazing, enameling and/or decorating with up to 30% by weight of a pigment stable at the baking temperature, characterized in that the glass composition comprises the components Li70 0 - 12 % by wt.

Mgo 0 - 10 % by wt.

CaO 3 - 18 % by wt.

B203 5 - 25 % by wt.

A1203 3 - 18 % by wt.

Na20 3 - 18 % by wt.

K20 3 - 18 % by wt.

BaO 0 - 12 % by wt.

Si02 25 - 55 % by wt.

Ti02 0 - 5 % by wt.

Zr02 0 - <3 % by wt.
2. A glass composition according to claim 1, characterized in that it comprises the components Li20 4 - 10 % by wt.

Mgo 0 - 8 % by wt.

CaO 5 - 15 % by wt.

B203 10 - 20 % by wt.

A1203 5 - 15 % by wt.

Na20 5 - 15 % by wt.

K20 5 - 15 % by wt.

BaO 0 - 10 % by wt.

Sio, 30 - 50 % by wt.

Ti02 0 - 5 % by wt.

Z-r02 0 - <
3 % by wt.

17 3. A glass composition according to claim 1, characterized in that it comprises the components Li20 8 - 12 % by wt.

Mgo 0 - 3 % by wt.

CaO 5 - 10 % by wt.

B203 5 - 13 % by wt.

A1203 5 - 10 % by wt.

Na20 5 - 10 % by wt.

K20 5 - 10 % by wt.

BaO 8 - 12 % by wt.

Si02 45 - 55 % by wt.

Ti02 0 - 5 % by wt.

Zr02 0 - <3 % by wt.
4. A glass composition according to claim 1, characterized in that it comprises the components Li20 8 - 12 % by wt.

Mgo 6 - 10 % by wt.

CaO 5 - 10 % by wt.

B203 15 - 20 % by wt.

A1203 5 - 10 % by wt.

Na20 5 - 10 % by wt.

K20 10 - 15 % by wt.

BaO 0 - 5 % by wt.

Si02 30 - 40 % by wt.

TiO2 0 - 5 % by wt.

Zr02 0 - <3 % by wt.
5. A glass composition according to claim 1, characterized in that it comprises the components Li20 8 12 % by wt.

Mgo 0 - 3 % by wt.

CaO 5 - 10 % by wt.

B203 5 - 13 % by wt.

A1203 10 - 15 % by wt.

Na20 5 - 10 % by wt.

K20 5 - 10 % by wt.

BaO 0 - 5 % by wt.

Si02 45 - 55 % by w.

Ti02 0 - 5 % by wt.

Zr02 0 - <3 % by wt.
6. A glass composition according to claim 1, characterized in that it comprises the components LI-20 8 - 12 % by wt.

Mgo 0 - 3 % by wt.

CaO 10 - 15 % by wt.

B203 5 - 13 % by wt.

A1203 10 - 15 % by wt.

Na20 5 - 10 % by wt.

K20 5 - 10 % by wt.

BaO 0 - 5 % by wt.

S102 35 - 45 % by wt.

Ti02 0 - 5 % by wt.

Zr02 0 - <3 % by wt.
7. A glass composition according to claim 1, characterized in that it comprises the components z Li20 4 8 % by wt.

Mgo 0 - 5 % by wt.

CaO 5 - 10 % by wt.

B203 5 - 13 % by wt.

A1203 5 - 10 % by wt.

Na20 5 - 10 % by wt.

K20 5 - 10 % by wt.

BaO 8 - 12 % by wt.

Si02 40 - 50 % by wt.

Ti02 0 - 5 % by wt.

Zr02 0 - <3 % by wt.
8. A glass composition according to claim 1, characterized in that it comprises the components Li20 4 - 8 % by wt.

Mgo 0 - 3 % by wt.

CaO 10 - 15 % by wt.

B203 15 - 20 % by wt.

A1203 5 - 10 % by wt.

Na20 5 - 10 % by wt.

K20 5 - 10 % by wt.

BaO 0 - 5 % by wt.

Si02 40 - 50 % by wt.

Ti02 0 - 5 % by wt.

Zr02 0 - <3 % by wt.
9. A glass composition according to any preceding claim, having a transition temperature of 300 - 5100C, a softening temperature of 400 6100C and a processing temperature of 430 - 8400C.
10. A glass composition according to claim 9, having a transition temperature of 380 - 4500C.
11. A glass composition according to claim 9 or 10, having a softening temperature of 450 - 5700C.
12. A glass composition according to claim 9, 10 or 11, having a processing temperature of 630 - 7801C.
13. A glass composition according to any preceding claim, characterized in that a glaze formed from the composition exhibits a thermal expansion coefficient of 9.20 to 16.40 x 10-6 /K.
14. A glass composition according to claim 13, wherein said glaze has a thermal expansion coefficient of 10.18 to 13.13 x 10-6 /K.
15. A glass composition according to claim 1, substantially as hereinbefore described in any one of Examples 1 - 17.
16. The use of a glass composition according to any preceding claim for the glazing, enameling and/or decorating of a glass having a thermal expansion of less than 5.0 x 10-6 /K.
17. A method decorating a glass having a thermal expansion of less than 5. 0 x 10-6 /K, comprising baking a glass composition as claimed in any one of claims 1 to 15 onto said glass having a thermal expansion of less than 5. 0 X 10-6 1K.
18. A method according to claim 17, wherein said glass is a borosilicate glass.
19. A method according to claim 17, wherein said glass is a glass ceramic.
20. A method according to claim 17, wherein said baking is effected whilst converting the glass to a glass ceramic.