AU648880B2

AU648880B2 - Glass frits, a process for their production and their use in enamel barrier layers for stopping the migration of silver

Info

Publication number: AU648880B2
Application number: AU13156/92A
Authority: AU
Inventors: Jerome Anquetil; Alain Dauger
Original assignee: Degussa GmbH
Current assignee: Evonik Operations GmbH
Priority date: 1991-03-25
Filing date: 1992-03-24
Publication date: 1994-05-05
Anticipated expiration: 2012-03-24
Also published as: JPH0585770A; MX9201322A; BR9201007A; ZA922147B; KR100222156B1; AU1315692A; ES2097230T3; CA2063858A1; CA2063858C; FR2674519B1; JP3228994B2; DE69216883T2; FR2674519A1; EP0505892A1; DE69216883D1; KR920017963A; EP0505892B1

Description

S F Ref: 202918

AUSTRALIA

Patents Act 1990 44" 88 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

S e o o *e e* Name and Address of Applicant: Actual Inventors: Address for Service: Degussa Aktiengesellschaft, 9, Weissfrauenstrasse, D-6000 Frankfurt am Main, Germany Jerome Anquetil and Alain Dauger Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Invention Title: Glass Frits, a Process for their Production and their use in Enamel Barrier Layers for stopping the Migration of Silver The following statement is a full performing it known to me/us:description of this invention, including the best method of 584612 Last Modified 28/04/01 1 91 125 KF Glass frits, a process for their production and their use in enamel barrier layers for stopping the migration of silver Description This invention relates to the glass frits which, screen-printed on their own, in an overlayer or in an enamel, are capable of stopping the heat-activated migration of Ag' ions between a support of float glass and a silver-based resistive layer.

Enamel compositions for glass are well known among .experts: They are generally formed after firing by a vitreous phase supplied by the frit(s) used and a coloring and 10 opacifying crystalline pigment phase to which other compounds may be added to obtain various effects. They are suitable for various applications and may be used inter alia for forming borders at the periphery of sheets of flat float glass which are thermoformed and then tempered for :15 use as glazing in motor vehicles.

Originally used with the sole object of protecting the adhesive used to fix the sheets of glass (windscreens, rear windows, side windows) to bodywork against the ultraviolet radiation in sunlight, these strips of black or grey enamels were subsequently the subject of aesthetic re- Ssearch,. attempts having been made in particular to use these enamels to conceal the lateral silver collectors of heated rear windows and the welding spots of the connecting terminals of the current supply wires. Now, it has been found that, after the heat treatment required for curving and tempering, none of the enamels of conventional composition are capable of completely concealing the silver collectors applied in superposed form and heated with the 2 91 125 KF enamel or the above-mentioned weld spots.

Various studies have demonstrated the existence of heat-activated transport of the Ag' cations from the resistive layer through the enamel to the enamel/glass interface, thus revealing the presence of collectors behind the enamel by an intense colorimetric contrast.

Solutions have been proposed: It is known from US-PS 4,837,383 that it is desirable to prevent the migration of silver when using an enamel consisting of a glass flux based on a glass frit, pigments, elemental aluminium and/or lithium oxide and a vehicle for paste formation. European patent application EP-A 0 377 062 claims improvements in the silver-based opacity of 15 enamels by the Fddition before paste formation of silicon, boron, carbon, !iad and/or silver in their elemental forms.

0 For obvious reasons of cost (silver), special operatr ing conditions necessitated by the introduction of highly reducing elements, such as silicon or boron, stability to acids (lithium) or toxicity (lead), additions of the type mentioned have not proved entirely satisfactory. The enamels dk.veloped with additions such as these in conjunction with the present state-of-the-art in this field show that, despite the aesthetic interest there is in completely concealing the silver collectors by enamel, such solutions limit the range of colours currently useable by the automotive industry to a few blacks and to a few greys.

In addition, the quality of the masking effect obtained is largely influenced by the firing cycle as a whole.

Accordingly, the problem addressed by the present invention was to provide an enamel barrier layer for stopping the migration of silver cations from the collectors to the glass during the firing of a combination of flat glass with an enamel- barrier layer and, above this 3 enamel layer, a resistive layer of silver which would have the disadvantages of the systems mentioned above.

Thus, by eliminating the need to form a paste of the additives mentioned above, the present invention offers a general solution to the problems discussed in the foregoing.

According to a first embodiment of the present invention there is provided glass frits based on an association of oxides in a vitrifiable composition comprising 15 to 40% by weight, silicon dioxide, 5 to 25% by weight boron trioxide, 15 to 70% by weight zinc oxide and 0.05 to 15 mol-% sulfur and/or sulfides dissolved in the vitreous structure whereby said sulfides are at least partly dissociated.

According to a second embodiment of the present invention there is provided an enamel barrier for stopping the migration of silver from a resistive silver layer to glass during firing of a combination of sheet glass with one or more enamel layers, which barrier comprises the glass frits of the first embodiment.

Preferably, the frits contain zinc oxide in a quantity of 30 to 65% by weight.

Preferably, the frits contain silicon dioxide in a quantity of 15 to 40% by weight and i boron trioxide in a quantity of 5 to 25% by weight.

Preferably, the frits contain coloring metal oxides.

According to a third embodiment of the present invention there is provided a process for the production of the glass frits of first embodiment, comprising melting a mixture of 20 oxides and/or non-oxide compounds at temperatures of 1,000 to 1,300 0 C, followed by sudden cooling.

According to a fourth embodiment of the present invention rovided an enamel barrier for stopping the migration of sil a resistive silver layrr to glass during firing of a combi s eet glass with one or more enamel layers, which barrf ises the glass frits of the first embodiment.

It has been found that the addition of 0.05 to 15.0 mol-% sulfur or sulfides (preferably zinc sulfide) to a mixture of oxides and/or non-oxide compounds for the Mt\LBnR)00252:AM 91 125 KF production of a glass frit provides the frit with the property of stopping the heat-activated diffusion within the frit of the Ag+ cations from the collectors of the resistive network based on silver.

In addition to sulfur and/or sulfides, the frits consist of a suitable association of oxides in a virtifiable composition. The expert knows many different associations of oxides which, after fusion, give glass frits, see for example US 4,892,847, EP-A-0 377 062 and EP-A-0 294 502.

The choice of the oxides determines the properties of the glass frits, for example their softening point, their thermal expansion coefficient and their stability to bases and acids. In general, the colorless glass frits contain 15 oxides selected from: 6 0 SiO 2 A1 2 0 3 TiOz, ZnO, MgO, Li 2 0,

B

2 0 3 Bi 2 03 SnO 2 PbO CaO La 2 03 ZrO 2 MnO BaO K 2 0 VzO 5 MoO 3 although other oxides, for example P205, Cr 2 0 3 Fe 2 0 3 CuO, NiO, CoO, W0 3 CeO 2 etc. may also be present. According to the invention, frits based on bc rosilicates, particularly zinc borosilicates, are preferred. It is for this reason that they contain silicon dioxide in a ruantity of 15 to 40% by weight and boron trioxide in a quantity of 5 to by weight and preferably 15 to 70% by weight and, above all, 30 to 65% by weight zinc oxide.

The introduction of sulfur during dry-mixing of the composition before melting may be carried out either in the form of flowers of sulfur or in the form of sulfides, although dissolution and retention in the structure of the glass vary according to the method of introduction selected. The advantage of ZnS over elemental sulfur and the 91 125 KF other sulfides is that it remains stable up to the fusion of the eutectics of the oxides of the mixture and it is only within this molten mixture that ZnS is progressively dissolved. Accordingly, the elimination of SO2 and the loss of elemental sulfur are avoided with ZnS. In addition, it has been found that zinc is an element which promotes stabilization of the sulfur in the vitreous atomic structure.

In principle, other sulfides than ZnS, for example sulfides of alkali metals, alkaline earth metals or of Mn, Fe, Co, Ni, Cu, Cd, Sn, Pb, Sb, Bi, may be introduced into the mixture to be melted. However, it should be pointed out that some of these sulfides, such as for example MnS, FeS, Cu 2 S, CdS, PbS, color the vitreous mass. In addition, 15 the introduction of these sulfides in large quantities can cause liquid-phase separation within the molten mass. I t is pointed out that the presence of elemental sulfur in the frits according to the invention is necessary for the interaction with the Ag cations and that, introduced in the form of sulfides, these sulfides are at least partly dissociated (ZnS begins to associate at around 900"C) during melting of the fusible mixture so that, thereafter, S' it is only the sulfur which reacts with the Ag' "ations in an enamel barrier layer containing the vitreous structure of such frits.

The principle of the process for producing the glass frits is known to the expert. To make the glass f.,its according to the invention, a mixture consisting of (a) oxides and/or compounds which form oxides by melting into a vitrifiable composition corresponding to the composition of the frit and one or more compounds selected from sulfur, zinc sulfide and other sulfides in a quantity of 0.05 to 15 mol-% of the mixture is melted at temperatures of 1,000 to 1,300 0 C, after which the molten glass is suddenly cooled in water.

91 125 KF Subsequent grinding of the granules obtained provides the ready-to-use frit powder.

The mixture mentioned above is preferably composed of oxides, although alkali metal and alkaline earth metal oxides are often introduced in the form of carbonates.

Melting is carried out conventionally in a refractory ceramic crucible or in a furnace having a suitable lining.

The fragments of the frits are ground after cracking (preferably 90% smaller than 20 10- 6 m) by known grinding techniques for glass frits.

By virtue of their ability to stop the migration of silver, the glass frits according to the invention may be used to form enamel barrier layers. These enamels may be I @9 colorless or colored, transparent or opaque. The enamel 15 barrier layers may contain other frits as the vitrifiable compound although the essential constituent is always a frit containing sulfur. The enamel barrier layers according to the invention stop the migration of silver during firing of the combinations of sheet glass with one or more enamel layers, including the barrier layer, and above the last enamel layer a resistive silver layer. The function which the vitreous structures of the enamel barrier layer perform in stopping the migration of silver is also effective at the temperatures required for curving and tempering the sheets of glass. The enamel barrier layer may be situated between the glass, for example a sheet of flat glass, and a resistive network based on silver and conceals *0 the silver collectors if the enamel is colored and preferably opaque. Now, the barrier layer may be situated between an opaque colored emanel applied to the glass and a resistive silver layer.

The enamel of the unfired barrier layer is formed by one or more frits according to the invention, colorants and/or opacifierr where a decorative effect is required and a vehicle for paste formation, for example a screen-printing oil based on solvents, natural resins and/or thermoplastics. The vehicle for paste formation is selected according to the final application envisaged. It must provide for effective suspension of the particles and must be completely consumed during firing and tempering.

The enamel of the barrier layer and/or a subjacent enamel of conventional composition have to meet certain requirements and, in the case of decorative enamels, must have above all a sufficient pigment content to satisfy the color and opacity requirements.

The enamels of the barrier layers according to the invention are applied by screen printing either directly or by way of a transfer or another intermediate support. The average thickness per layer after firing Is between 5 10- 6 m and 50 10- 6 m.

In cases where a barrier layer which is colorless or colored in the mass is Interposed between a crude and dry enamel which Itself is applied by screen printing and the resistive silver layer, disorientation of the meshes of the screen printing cloths used for one or other of the applications will be favourable. In this way, firing of the combination of Viss (with all the enamel layers) and the resistive silver layer (for example 60 to 80 by weight silver) is carried out in a single operation.

The heat treatment, i.e. firing followed by tempering, of the combinations of glass/enamel barrier layer/resistive silver layer or glass/conventional enamel layer/enamel barrier layer/resistive silver 0 layer is carried out in various types of furnace, according to the intended application of the enamelled glass. The firing temperature Is S 25 also determined by the composition of the frit(s) used In the enamels.

In general, the firing temperature varies from 450 0 C to 800°C and preferably from 550 C to 750 0

C.

In tests (see Example 10) It was found that, in the enamels described in DE-OS 38 32 937 and DE-OS 38 38 196 which are formed by a conventional frit, a vehicle and, in TCH/8353T 8 91 125 KF addition, a sulfide of copper, zinc, iron, tin or aluminium, there was no favorable action in stopping the Ag cations, i.e. there was no effective interaction between sulfide and Ag The S Ag interaction and the resulting arrest of the Ag cations is thus a quality unique to enamels of which the frits contain elemental sulfur and/or a sulfide dissolved in the vitreous mass. Frits which do not contain dissolved sulfur and which are applied on their own or in association with pigments do not provide the layer formed all other things being equal with the property of stopping the Ag cations during their heat-activated migration towards the interface with the glass. In addition, the direct introduction of sulfides into the enamel, as in the documents 15 cited above, i.e. as an associated pigment charge, causes a significant colorimetric drift whereas the use of a frit according to the invention (containing sulfur) causes no such drift.

The invention is illustrated by the following Examples in conjunction with the accompanying drawing.

t S.

S

5e Examples 1 to 4 Frits having the following composition are barrier layers: prepared for colorless 4 Composition of the frit mol-%

S

SS

a I ZnS 1.98 3.99 4.82 5.00

SIO

2 21.86 34.99 19.76 29.00

B

2 0 3 12.64 20.08 11.42 18.00 ZnO 63.52 30.09 64.00 35.45 6.30 6.00 BaO 4.55 4.65 ZrO 2 1.90 S. S 9

SS

S* SC a 'S a 55 *S

S

Dry mixing of the oxides except for NaO2 and BaO, which were added with Na 2

CO

3 and BaCO 3 melting at 1,150 to 1,200 0 C, quenching in water, grinding, stoving. To obtain the enamel barrier layer, the frits are made into a paste with vehicle and the enamel Is applied by screen printing.

Figure 1 shows the X ray diffraction spectrum obtained with the 20 frit of Example 3.

TCH/8353T 91 125 KF Examples 5 and 6 Introduction of the sulfur in the form of flowers of sulfur or cadmium sulfide.

Composition of the 5 6 mixture for melting mol-% S 15.00 CdS 6.04 Si0 2 18.95 20.95

B

2 0 3 10.97 12.11 15 ZnO 55.08 60.89 The frits are produced in the same as in Examples 1 to 4.

Example 7 The frit may be pigmented as such without affecting its barrier properties. In Example 7, the dissolution of a black colored inorganic pigment of the copper chromite spinel type enables a brown frit to be obtained with its barrier properties intact.

Dry mixing of the frit of Example 2 (85.36% by weight) with a black spinel pigment (14.64% by weight), melting, quenching, grinding and stoving to obtain an intermediate frit.

30 The brown frit consists of 70% by weight of the frit of Example 1 and 30% by weight of the intermediate frit mentioned above. To obtain the enamel for a barrier layer: disintegration of the two frits in alcohol to form a homogeneous mixture, stoving, paste formation.

91 125 KF Examples 8 and 9 Black and grey opaque enamels maskingq the silver collectors.

Composition of the enamel 8 9 by weight Frit of Example 4 75 77.5 Black pigment, copper chromite spinel type 25 12.5 Titanium dioxide 10.0 Color of the enamel Black Grey A a a

A.

a a a 0* 08 A. a a *0*AA* S A Disintegration of the compounds in alcohol, stoving and paste formation for application as a barrier layer.

a. a 9* a.

.5O* A el A. A A. 98 A A 9 a a ~a.

*4 4 A S A *6 91 125 KF Example (for comparison with DE-OSS 38 32 937 and 38 38 196) Tests for introduction of sulfides into the (composition in parts by weight): a b b d enamel e Vitreous enamel powder VA 641 (DPC LIMOGES) ZnS (ALDRICH) ZnS (PROLABO) Cu 2

S

FeS CdS S 15 MnS VEHICLE MX 54 (DPC LIMOGES) COLOUR OF

ENAMEL

7.2 1.6 7.2 7.2 7.2 7.2 7.2 1.6 1.6 1.6 1.6 1.6 2.8 2.8 2.8 2.8 2.8 2.8 BLUISH BLUISH GREY GREY

DEEP

GREY-

RED

BROWN-

ISH

GREY

GREEN GREEN GREY GREY rS S 0 *4 Sb OS i~ S

COLORIMETRIC

DIFFERENCES

A E IN RELATION 13.40 10.11 6.15 14.80 5.30 11.40 25 TO THE ENAMEL VA 641 AS

REFERENCE

30 Application of the enamels to glass (4 mm); superposition of the enamelled glass with the silver paste SP 1230 (Degussa AG); vertical firing and tempering for 3.5 minutes at 680°C. None of the enamels of Example 10 is effective in stopping the migration of the silver.

W

S~

5900 S. a S

Claims

1. Glass frits based on an association of oxides in a vitrifiable composition comprising 15 to 40% by weight, silicon dioxide, 5 to 25% by weight boron trioxide, to 70% by weight zinc oxide and 0.05 to 15 mol-% sulfur and/or sulfides dissolved in the vitreous structure whereby said sulfides are at least partly dissociated.

2. Glass frits as claimed in claim 1, wherein said sulfide is zinc sulfide.

3. Glass frits as claimed in claim 1 or claim 2, which comprise 30 to 65% by weight zinc oxide.

4. Glass frits as claimed in any one of claims to 3, which further comprise one or more metal oxides. Glass frits, substantially as hereinbefore described with reference to any one of Examples 1 to 9.

6. A process for the production of the glass frits claimed in any one of claims 1 ito comprising melting a mixture of oxides and/or non-oxide compounds at temperatures of S 15 1,000 to 1,300°C, followed by sudden cooling.

7. A process as claimed in claim 6, wherein said non-oxide compounds are fluorides and/or carbonates.

8. A process for the production of the glass frits, substantially as hereinbefore described with reference to any one of Examples 1 to 9. 20 9. Glas frits when prepared by the process of any one of claims 6 to 8. An enamel barrier for stopping the migration of silver from a resistive silver layer to glass during firing of a combination of sheet glass with one or more enamel layers, which barrier comprises glass frits as claimed in any one of claims 1 to 5 or 9.

11. A colored or colorless enamel barrier layer, substantially as hereinbefore 25 described with reference to any one of the Examples. Dated 9 December, 1993 Degussa AG Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON N:ibR00262:KEH 13 of 2 91 125 KF ABSTRACT Glass frits, a process for the production and their use in enamel barrier layers for stopping the migration of silver 0e 0 0 4 a *0 1,0 S 0o *0 0 a P a) Glass frits, a process for their production and their use in enamel barrier layers for stopping the migration of silver. b) Glass frits, characterized in that they contain 0.05 to 15.0 mol-% sulfur and/or sulfides and in that they contain zinc sulfide and a process for producing a glass frit by melting a mixture of oxides and/or non-oxide compounds (fluorides, carbonates) at temperatures of 1,000 to 1,300*C, followed by sudden cooling, characterized in that the glass frit contains between 0.05 and 15 mol-% sulfur, zinc sulfide or other sulfides. c) The invention relates to glass frits and their use in enamel barrier layers for stopping the migration of silver. r*