High durability low temperature lead-free glass and enamel...

Details High durability low temperature lead-free glass and enamel... High durability low temperature lead-free glass and enamel...

2001-07-30

2003-09-23

Marcheschi, Michael (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S014000, C501S016000, C501S017000, C501S020000, C501S021000, C501S025000, C501S032000, C501S077000

Reexamination Certificate

active

06624104

ABSTRACT:

This invention relates to low temperature melting lead-free glass and enamel compositions which have low boron content and possess high durability properties.
BACKGROUND OF THE INVENTION
Lead-free glass compositions are known in the art. As illustrative there can be mentioned the following:
Reinherz U.S. Pat. No. 4,892,847
Francel U.S. Pat. No. 4,554,258
Roberts U.S. Pat. No. 5,252,521
Klimas U.S. Pat. No. 4,970,178
Clifford U.S. Pat. No. 5,308,803
Murkens U.S. Pat. No. 5,093,285
Ryan U.S. Pat. No. 5,559,059
Newman U.K. Patent No. 2,301,100
Prunchak U.S. Pat. No. 5,629,247
Additional disclosures of lead-free glass compositions may be found in Francel et al., U.S. Pat. No. 4,446,241, Francel et al., U.S. Pat. No. 4,537,862, Reade, U.S. Pat. No. 4,224,074, Eppler, U.S. Pat. No. 4,312,951, Eppler, U.S. Pat. No. 4,376,169, Emlemdi, U.S. Pat. No. 5,504,045, Manabe et al., U.S. Pat. No. 5,578,533 and Evans et al., International Application No. PCT/EP94/00403.
Also, attention is directed to my prior filed application U.S. Ser. No. 08/908,953 Abr, filed Aug. 8, 1997 and my copending application Ser. No. 09/066,533 Abr, filed Apr. 27, 1998, entitled LEAD-FREE GLASS AND ENAMEL COMPOSITIONS WITH HIGH BISMUTH OXIDE CONTENT.
These glass compositions are generally used to form, in a well known manner, glass frits which are, in turn, used to formulate glass enamel compositions. These glass (or ceramic) enamel compositions are known to be useful for forming decorative coatings for glassware, chinaware, architectural glass and the like. They are especially useful in forming colored borders around glass sheets used for automotive windshields, sidelights and backlights. These colored borders enhance the appearance as well as prevent UV degradation of underlying adhesives.
In general, these enamel compositions consist essentially of a glass frit, a colorant and an organic vehicle. They are applied to a desired substrate and subsequently fired to burn off the organic vehicle and fuse the frit, thus bonding the enamel coating to the substrate.
Glass sheets for automotive use are generally coated with the ceramic enamel composition and then subjected to a forming process at elevated temperatures. During this treatment the enamel melts and fuses to the glass substrate and the glass is formed into a desired final shape. However, many prior art coatings exhibit a tendency to adhere to the materials covering the forming die, such as a fiberglass or metal fiber covered die, because these conventional enamels have a low viscosity after melting and stick to other materials at high temperature. Accordingly, these materials are not suitable for use in glass forming processes in which the heated glass coated with enamel contacts a material-covered forming die.
Various approaches have been suggested in order to facilitate the forming of glass sheets with a ceramic enamel coated thereon, withstanding of the elevated bending or forming temperatures, and repeated contact of the glass sheet and the covered forming die without the enamel adhering to the forming die. For example, U.S. Pat. Nos. 4,596,590 and 4,770,685 (issued to Boaz) and EP 201241 propose the addition of a low valent metal oxide powder, e.g., cuprous oxide, to the paint composition to provide a non-stick barrier between the coating and the fiberglass-covered forming die. U.S. Pat. Nos. 4,684,389; 4,857,096 and 5,037,783 (issued to Boaz), propose adding finely divided zinc metal powder for a similar effect. The use of an iron metal powder is proposed in U.S. Pat. No. 4,983,196 (issued to Stotka).
The use of other metal oxide powders, including bismuth oxide-containing formulations have been proposed in U.S. Pat. Nos. 4,029,605 (issued to Kosiorek); 4,098,949 (issued to Kosiorek); 4,892,847 (issued to Reinherz); 4,959,090 (issued to Reinherz); 4,970,178 (issued to Klimas et al.); 5,093,285 (issued to Murkens); 5,203,902 (issued to Murkens) and EP 370,693.
However, certain of the bismuth containing systems produce a weak glass, such as when lithium is present, and have poor silver bleed-through properties, as well as inadequate anti-stick properties.
U.S. Pat. No. 4,828,596 proposes introducing copper sulfide or copper sulfate into the ceramic enamel composition as an anti-stick agent. Sulfides or sulfates of other metals have been proposed as anti-stick agents in U.S. Pat. No. 4,8922,396 (issued to Reinherz).
A purportedly improved anti-stick ceramic enamel composition is proposed by U.S. Pat. Nos. 5,153,150 and 5,208,191 (issued to Ruderer et al.) wherein a seed powder containing Zn
2
SiO
4
is introduced into an oxide composition with or without the presence of bismuth oxide.
As a further problem, a number of previous ceramic enamel systems employ a lead-containing glass frit. For environmental considerations it is desirable to avoid the use of any lead-containing system.
Also, while some of the above-mentioned enamel systems may perform fairly well in conventional glass forming processes, some are not satisfactory for use in the newly-developed “deep bend” processes for forming automotive glass.
It is essential that the enamel compositions also possess adequate resistance to certain chemical agents, which they may contact, and many of the prior art compositions fail in this respect.
Each of the previously known enamel composition suffers from one or more of the deficiencies noted above, making it desirable to provide a composition which avoids these shortcomings. The present invention provides such ceramic enamel compositions, a method for employing the compositions, and substrates coated therewith.
The present invention provides a glass composition and glass frit produced therefrom which can be used in producing enamels having improved chemical durability properties to the fused enamel coating. Currently, the only lead-free glass frits suitable for automotive enamel use which pass sulfuric acid durability test specification required, for example, in Japan, use lithium ions. If not carefully controlled, however, the use of lithium can cause undesirable stresses and substrate breakage. The novel glass compositions of this invention avoid this problem. These compositions also impart excellent anti-stick properties.
DESCRIPTION OF THE INVENTION
The present invention provides new glass compositions from which can be obtained bismuth borosilicate-containing glass frits which have a lower boron oxide content. These systems do not require the use of zirconium oxide, titanium oxide or lithium oxide within the composition range.
The glass compositions of the present invention are as follows:
Oxide
Broad
Preferred
More Preferred
Component
Range (wt %)
Range (wt %)
Range (wt %)
Bi
2
O
3
40-70
50-65
54-63
SiO
2
25-40
28-38
29-37
B
2
O
3
0-3
  0-2.8
  1-2.7
Al
2
O
3
0-5
0-3
0.3-1.0
TiO
2
0-4
0-3
1-2
Na
2
O
0-8
1-6
  3-4.5
K
2
O
0-5
  0-1.5
0-1
Li
2
O
0-4
0-1
0
F
−1
0-4
0-2
0
Particularly suitable are compositions in which the B
2
O
3
content is not greater than 2 wt. %.
The glass compositions are formed in a known manner as, for example, blending the known starting materials and melting at a temperature of about 1000° to 1300° C. for about forty (40) minutes to form a molten glass having the desired composition. The molten glass formed can then be suddenly cooled, e.g., water quenched, in a known manner to form a frit. The frit can then be ground using conventional milling techniques to a fine particle size, preferably between 2 to 6 microns.
The invention also provides glass (ceramic) enamel compositions employing the above-described glass frit compositions. These compositions comprise from about 30 to 95 wt. % solids of a glass frit component.
This component comprises the disclosed glass frit compositions.
This glass frit component can be a single composition of the invention or, alternatively, can be a mixture of these frits. Also, at least one frit of the present invention may be combined with an additional low melting frit having a composition outside the scope of those of the invention to the extent

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