WO2006098160A1

WO2006098160A1 - Conductive paste and glass structure

Info

Publication number: WO2006098160A1
Application number: PCT/JP2006/303959
Authority: WO
Inventors: Fumiya Adachi; Takuma Miyake
Original assignee: Murata Manufacturing Co., Ltd.
Priority date: 2005-03-14
Filing date: 2006-03-02
Publication date: 2006-09-21
Also published as: JPWO2006098160A1

Abstract

Disclosed is an environment-friendly conductive paste which is capable of forming a conductor on a glass substrate of window glass for automobiles. The conductor is able to have a dark color while having a low resistivity. Specifically disclosed is a conductive paste containing a silver powder, a glass frit, an organic vehicle, and at least one silver oxide selected from the group consisting of silver vanadate, silver molybdate and silver tungstate. The conductive paste is used for an antifog conductor (3) formed on the surface of a glass substrate (2).

Description

Specification

Conductive paste and glass structure

Technical field

[0001] The present invention relates to a conductive paste and a glass structure used for an antifogging conductor formed on the surface of a window glass of an automobile, for example.

Background art

A conductor for preventing fogging (hereinafter referred to as “anti-fogging”) called “defroster” is formed on the surface of a window glass of an automobile. By passing an electric current through the anti-fogging conductor to heat the conductor and keeping the surface temperature of the glass temperature above the dew point, fogging of the window glass is prevented. This anti-fogging conductor is formed by baking a conductive paste mainly composed of silver on a glass substrate. Further, glass frit is added to the conductive paste to increase the bonding strength with the glass substrate.

[0003] It is common to use soda-lime glass for a glass substrate for automobiles, and this glass contains Na. When a conductive paste composed mainly of silver is baked on a glass substrate, silver dissolves in the glass frit and silver ions are generated. This silver ion and Na ions in the glass substrate undergo ion exchange. Silver ions diffuse into the glass substrate. Silver ions are reduced in the glass substrate to form silver colloid, and due to the presence of this silver colloid, the interface between the conductor and the glass substrate is colored yellow or brown.

[0004] Further, since an automotive glass substrate is usually manufactured by a float glass method, thin tin (Sn) is diffused on one surface to form a thin layer of tin. When the conductive paste is baked on the surface on which the tin layer is formed, the formation of the silver colloid is promoted by Sn ions (Π), and the interface between the conductor and the glass substrate is colored darker brown.

[0005] However, in recent years, it has been desired to make the antifogging conductor inconspicuous from the viewpoint of design, and a technique for darkening the antifogging conductor is required. Thus, in order to darken the antifogging conductor, it is necessary to further increase the amount of silver colloid deposited on the interface between the antifogging conductor and the glass substrate.

[0006] In response to this, in Patent Document 1, V, Mn, Fe, Co and the like are included in the conductive paste. It has been proposed to add these oxides. Patent Document 2 proposes adding Rh, Cr, Cu, etc. to the conductive paste. In Patent Document 1 and Patent Document 2, the additive promotes the ion exchange reaction, thereby promoting the formation of silver colloid.

Patent Document 1: JP-A-5-290623

Patent Document 2: JP-A-9-92028

Disclosure of the invention

[0007] However, the additive disclosed in Patent Document 1 and Patent Document 2 reduces the amount of silver powder by colloiding it at the same time, and at the same time it remains as an oxide after baking. There was a problem that the specific resistance increased.

[0008] Each additive has the following problems.

V: When added alone, uneven coloring occurs.

Mn, Fe, Co: In order to obtain a desired color with a simple substance, it is necessary to increase the amount of applied force, and the resistance of the conductor increases.

Rh: The resistivity is very high, and it is difficult to control the added amount. Expensive.

Cr- · · · Environmentally favorable.

Cu- ■ · In order to obtain the desired color by itself, excessive addition amount is required, resulting in high resistance

[0009] Further, the conductive pastes disclosed in Patent Document 1 and Patent Document 2 are not preferable in terms of environmental problems because Pb is contained in the glass.

[0010] The present invention solves the above-mentioned problems, and has as its main object to provide a conductive paste and a glass structure that can form a conductor that is environmentally friendly, can be darkened, and has a low specific resistance.

[0011] The conductive paste according to the present invention comprises silver powder, at least one silver oxide selected from the group consisting of silver vanadate, silver molybdate, and silver tungstate, and glass frit.

And an organic vehicle and used for an anti-fogging conductor formed on the surface of a glass substrate.

[0012] The silver oxide is contained at a ratio of 0.5 to 7 parts by weight with respect to 100 parts by weight of the silver powder. It is particularly preferable that it is contained in a proportion of 0.5 to 5 parts by weight.

[0013] The glass frit is preferably contained in a ratio of 3 to 10 parts by weight with respect to 100 parts by weight of the silver powder. The glass frit is composed of 2 to 13 wt% SiO, 2 to B

10% by weight, 60 to 85% by weight of BiO, 3 to 7% by weight of A10 are preferable. The glass frit preferably further contains ZnO in a proportion of 13 wt% or less.

[0014] The conductive paste according to the present invention is preferably used as an antifogging conductor in the automotive window glass as the glass substrate.

A glass structure according to the present invention comprises a glass substrate and an anti-fogging conductor formed on the surface of the glass substrate and formed by baking a conductive paste configured according to the present invention. To do. The glass structure is not particularly limited, and preferably includes a glass structure in which the antifogging conductor is formed on the surface of an automobile window glass as a glass substrate.

(The invention's effect)

[0015] When the conductive paste according to the present invention is baked, at least one silver oxide selected from the group consisting of silver vanadate, silver molybdate, and silver tungstate is dissolved in the glass frit to form silver ions. These silver ions diffuse into the substrate and become silver colloids, contributing to color development. Therefore, it is possible to suppress an increase in the specific resistance of the conductor that does not require a large amount of colloidal silver powder.

[0016] Further, for example, when silver molybdate is added, molybdenum reacts with the glass frit component during baking to form a stable complex salt with Bi. (The same reaction occurs when silver vanadate or silver tandastate is added.) This reaction facilitates the release of silver ions from the silver oxide, promotes the diffusion of silver ions, and darkens the conductor. Promote

[0017] As described above, when the conductive paste according to the present invention is used, darkening of the conductor can be promoted, and at the same time, the resistance of the conductor can be reduced. Further, even with a small amount of additive, it is possible to achieve a darkening effect equivalent to or higher than that of the conventional one and a specific resistance equivalent to or lower than that of the conventional one. Also, since only a small amount of additive is required, the conductor half A decrease in wettability of the rice field can be prevented.

[0018] Further, when the above-mentioned silver oxide is added, uneven coloring is unlikely to occur. This is presumably due to the stable supply of silver ions.

[0019] Furthermore, since the silver oxide is harmless, the conductive paste according to the present invention has a small load on the environment.

Brief Description of Drawings

FIG. 1 is a front view schematically showing a rear window of an automobile to which a conductive paste according to the present invention can be advantageously applied.

[FIG. 2] FIG. 2 is an enlarged sectional view taken along line II II in FIG.

Explanation of symbols

[0021] 1 ... Rear window

2 ... Glass substrate

3… Anti-fogging conductor

4 ... Lines

5 ... Bus bar

6 ... Solder

7 · · · Metal terminals

BEST MODE FOR CARRYING OUT THE INVENTION

[0022] The conductive paste according to the present invention contains silver powder, silver oxide, glass frit, and an organic vehicle.

[0023] As the silver powder, it is preferable to use a silver powder having an average particle size of 0.:! To 20 μm in consideration of the printability of the conductive paste. In addition, silver powder having a different average particle size can be used to accurately control printability and sinterability. The silver powder is not limited to spherical powder, and flake powder or a mixture of spherical powder and flake powder can be used.

[0024] The silver oxide is at least one selected from the group consisting of silver vanadate, silver molybdate, and silver tungstate, and contributes to darkening of the conductor as a color former. Silver vanadate is synonymous with silver metavanadate. As the silver oxide, it is preferable to use a powder having an average particle size of 0.5 to ΟΟ ΟΟ μm. [0025] The silver oxide is preferably contained in a proportion of 0.5 to 7 parts by weight with respect to 100 parts by weight of the silver powder. When the content ratio of the silver oxide is 0.5 parts by weight or more, the effect of adding the silver oxide can be sufficiently exhibited. If the content of silver oxide is more than 7 parts by weight, the specific resistance of the antifogging conductor may become too high. Further, when the content ratio of the silver oxide is 5 parts by weight or less, it is particularly preferable because various properties of the antifogging conductor are stabilized.

[0026] Among the silver oxides, silver vanadate and silver molybdate in particular have a high coloration effect at low temperatures. Specifically, the effect of darkening can be obtained sufficiently even at a temperature 40 ° C lower than the firing temperature of the conventional conductive paste. As a result, when the conductive paste is baked onto the glass substrate, it is possible to achieve darkening without generating unnecessary thermal stress on the glass substrate.

[0027] As the glass frit, it is preferable to use a glass that starts softening flow at a temperature lower than a softening point (about 730 ° C) of soda lime glass generally used as a glass substrate. Specific examples include PbO—B 2 O—Si 0 series, Bi 0 1 B 2 O—SiO series, Si 0 1 B 0 series low melting point glass, and the like. Considering the environmental impact, a glass frit containing no Pb is preferred.

[0028] The glass frit is preferably contained in a ratio of 3 to 10 parts by weight with respect to 100 parts by weight of the silver powder. If the glass frit content is less than 3 parts by weight, the bonding strength between the substrate and the conductor may decrease, and the color developability may decrease. If the glass frit content is greater than 10 parts by weight, the glass may float on the surface of the conductor after firing, solder wettability may be reduced, and the bonding strength between the substrate and the conductor may be reduced. As the glass frit, it is preferable to use one having an average particle diameter of 0.5 to 5.0 / im.

[0029] The glass frit 2 a SiO: 13 wt ^_0/0, 2 and B_〇: 10 weight ^_0/0, Bi_〇 60 to 85 by weight%, A1_rei a 3-7%, of the It is preferable to contain by a ratio. Glass frit is

ZnO is preferably contained in a proportion of 13% by weight or less.

[0030] SiO is a network-forming oxide of glass and contributes to improvement of chemical, thermal and mechanical properties. If the SiO content is less than 2% by weight, chemical durability may be reduced. If the SiO content is more than 13% by weight, the softening point of the glass may become too high. [0031] BO is a network-forming oxide of glass and functions as a flux component. If the BO content is less than 2% by weight, the glass softening point may be too high. If the BO content exceeds 10% by weight, chemical durability may be reduced.

[0032] BiO functions as a flux component. If the content ratio of Bi 2 O is less than 60% by weight, the softening point of the glass becomes too high, and the fluidity of the glass is lowered, and the bondability between the antifogging conductor and the glass substrate may be lowered. When the content ratio of BiO is more than 85% by weight, the glass is easily crystallized at the baking temperature, and the fluidity of the glass is lowered, and the bonding property between the antifogging conductor and the glass substrate may be lowered. At the same time, chemical durability may decrease.

[0033] A10 contributes to the improvement of chemical durability, and particularly shows strong durability against attacks of salt ions. Since glass frit containing BiO is easily corroded by salt water or the like, it can be prevented by including forces S and A10 that may deteriorate the antifogging conductor. If the Al 2 O content is less than 3% by weight, the effect of improving chemical durability is poor. If the content of A10 is greater than 7% by weight, the soft spot of the glass becomes too high.

There is power.

[0034] ZnO is contained as necessary and functions as a flux component. If ZnO is more than 15% by weight, chemical durability may be reduced.

[0035] The organic vehicle contains an organic binder and a solvent. As the organic binder, one or more kinds of resins selected from the group consisting of ethyl cellulose resin, nitrocellulose resin, alkyd resin, acrylic resin, styrene resin and phenol resin can be used. As the solvent, one or more solvents selected from the group consisting of a-terbineol, butyl carbitol, butyl carbitol acetate, diacetone alcohol and methyl isobutyl ketone can be used.

[0036] The organic vehicle is preferably contained in a proportion of 10 to 40 parts by weight with respect to 100 parts by weight of the silver powder. If the content of the organic vehicle is less than 10 parts by weight, the organic vehicle may not be sufficiently wetted with the solid content in the conductive paste, and the viscosity of the conductive paste may become too high. If the organic vehicle content is greater than 40 parts by weight, it will become conductive. The viscosity of the paste becomes too low, or residual charcoal tends to be generated during firing, which may reduce the sinterability of the conductor.

[0037] For the purpose of adjusting the resistance value, Ni powder or the like may be added to the conductive paste. The resistivity of the conductor can be increased by adding Ni powder.

[0038] Further, amorphous silica may be added as a color former for the purpose of adjusting the hue.

The amount of amorphous silica added is preferably 0.5 to 5.0% by weight with respect to 100 parts by weight of glass. 5. If the content exceeds 0% by weight, the specific resistance of the conductor may become too high.

[0039] Next, the rear window of an automobile to which the conductive paste according to the present invention is advantageously applied will be described as an example. FIG. 1 is a front view schematically showing the rear window, and FIG. 2 is an enlarged sectional view taken along line II-II in FIG.

As shown in FIG. 1, the rear window 1 includes a glass substrate 2 and a conductor circuit including a defogging conductor 3 formed on the glass substrate 2. The antifogging conductor 3 includes a plurality of wires 4 and bus bars 5 connected to both ends of each wire 4. The antifogging conductor 3 is formed by applying and baking the conductive paste according to the present invention on the glass substrate 2 by printing or the like in a predetermined pattern.

As shown in FIG. 2, each bus bar 5 is attached with a metal terminal 7 for connecting a lead terminal via solder 6. When a voltage is applied between the metal terminals 7, a current flows through the conductor circuit including the antifogging conductor 3 and the metal terminal 7, and the antifogging conductor 3 (particularly the wire 4) generates heat. This heat generation keeps the surface temperature of the rear window 1 above the dew point and prevents fogging.

[0042] Note that a film made of a black color ceramic, which is a mixture of glass and ceramic, is baked on the glass substrate 2 where the bus bar 5 is formed. The bus bar 5 may be formed on the film made of the color ceramic. Needless to say, the conductive paste according to the present invention can also be used when forming an anti-fogging conductor on the windshield of an automobile.

Experimental example 1

[0043] 1. Preparation of glass frit

Prepare SiO, HBO, BiO, Al (OH) and ZnO as starting materials. They were blended so that the composition ratio shown in Table 1 was obtained, put in an alumina crucible and melted at a temperature of 1200 ° C., and then rapidly cooled to vitrify. Thereafter, the obtained glass was pulverized using a zircoyour ball to prepare glass frit samples A to J shown in Table 1. The average particle size of each glass frit was 1. O zm.

[0045] 2. Preparation of conductive paste

Samples A to J of silver powder, silver vanadate, silver molybdate, silver tungstate, chromium oxide, glass frit and organic vehicle were mixed by a three roll mill in the ratio shown in Table 2 below, and shown in Table 2. Samples 1 to 26 of the conductive paste were produced. Samples marked with * in Table 2 are comparative examples.

[0046] [Table 2]

[0047] For the samples shown in Table 2:! ~ 12, 14 ~: 16, 60% by weight of spherical powder with an average particle size of 1 / m and 40% by weight of flake powder with a major axis of 3-5 μm Blended silver powder was used. For Sample 13, silver powder was used in which spherical powder with an average particle size of l z m was blended at a ratio of 70% by weight and spherical powder with an average particle size of 0.1 × m at 30% by weight. For Samples 17 to 26, silver powder containing spherical powder having an average particle diameter of 2 μm and 70% by weight of amorphous powder having an average particle diameter of 1 μm and 30% by weight was used.

[0048] The average particle size for silver vanadate is 2.6 μm, the average particle size for silver molybdate is 1.3 μπι, the average particle size for silver tungstate is 1.8 μπι, and the average particle size for chromium oxide. A powder having a uniform particle size of 1.5 μm was used.

[0049] In each sample, as the organic binder in the organic vehicle, ethyl cellulose is used. And a mixture of alkyd resins. Further, as a solvent in the organic vehicle, a mixture of butyl carbitol, butyl carbitol acetate and tervineol was used.

[0050] 3. Evaluation of conductive paste

The characteristics of samples:! -26 were evaluated as follows. The results are shown in Table 2.

[0051] (1) Evaluation of fading

Samples of conductive paste:! -26 were printed by screen printing on a slide glass substrate (soda lime glass, dimensions 260 mm X 760 mm X I. 4 mm) having a tin coating formed on the surface. The printed shape was a rectangle with a long side of 20 mm and a short side of 10 mm. The target thickness is 10 to 15 zm in terms of the thickness of the conductive paste after drying, and 7 to 4 in the thickness of the conductor after firing.

[0052] Next, each printed sample was dried at 150 ° C for 10 minutes, and then fired at a peak temperature in the atmosphere of 600 ° C for 2 minutes (5 minutes before entering the furnace and then exiting) to form a thick film A conductor was formed.

[0053] Next, L * (brightness) was obtained by irradiating the back surface of the thick film conductor with light having a wavelength of 300 to 800 nm through a glass substrate and measuring the reflected light. For measurement of L *, UV-2400U (manufactured by Shimadzu Corporation) was used. A product with an L * force of ¾0 or less was regarded as a non-defective product.

[0054] (2) Evaluation of specific resistance value

By screen printing, conductive paste samples:! -26 were printed on a slide glass substrate (soda lime glass, dimensions 260 mm X 760 mm X I. 4 mm) having a tin coating formed on the surface. The printed shape was a rectangle with a long side of 200 mm and a short side of 0.4 mm. The target thickness was 10 to 15 / im in terms of the thickness of the conductive paste after drying, and 4 to 8 μπι in terms of the thickness of the conductor after firing.

[0055] Next, each printed sample was dried at 150 ° C for 10 minutes and then calcined at an atmospheric peak temperature of 600 ° C for 2 minutes (5 minutes before entering the furnace and 5 minutes). A thick film conductor was formed.

Next, the resistance value and film thickness of the thick film conductor were measured, and the specific resistance value was measured by the following equation.

Formula: Specific resistance value = resistance value X film thickness X short side length of pattern ÷ long side length of pattern

The resistance value was measured using a multimeter (manufactured by HIOKI) as a resistance measuring device. The film thickness is a contact-type film thickness measurement system Surfcom (TOKYO SEIMITSU ). For the resistance value and film thickness to be substituted into the above formula, the average value of the measured values measured five times for each sample was used.

[0057] (3) Measuring method of terminal strength

Sample of conductive paste on a slide glass substrate (soda lime glass, dimensions 260mm X 760mm X I .4mm) with a tin coating formed on the surface by screen printing:! ~

26 was printed. The printed shape was a square with a side of 2 mm. The target thickness was 10-15 μm for the conductive paste thickness after drying, and 4-8 μm for the conductor thickness after firing.

[0058] Next, after each printed sample was dried at 150 ° C for 10 minutes, the atmospheric peak temperature 60

Thick film conductors were formed by firing at 0 ° C for 2 minutes (5 minutes from entering the furnace until exiting).

Next, the slide glass substrate on which the thick film conductor was formed was placed on a plate heated to 150 ° C., and a lead terminal was soldered on the thick film conductor. As the lead terminal, an L-shaped solder bow I copper wire with a diameter of 0.6 mm was used.

As the solder, Sn—Pb—Ag solder was used, and a flux in which rosin was dissolved in isopropyl alcohol was used.

[0061] Then, the lead terminal was pulled, and the strength at which the lead terminal was peeled off from the thick film conductor was determined as the joint strength of the terminal. The bonding strength of this terminal is 10N or more.

[0062] 4. Evaluation results

From Table 2, samples with silver oxide added:! ~ 12, 17 ~ 26 have lower L * (brightness) of thick film conductors compared to sample 14 without any addition I understand. In addition, when compared to Samples 15 and 16 to which chromium oxide was added, the low L * (brightness) and low specific resistance values were achieved even though the amount added was equal or less. Recognize. It can also be seen that despite the addition of a small amount, low L * (lightness), low specific resistance and high terminal strength are achieved.

Experimental example 2

[0063] 1. Preparation of glass frit

As a starting material, Si_〇, H BO, Bi O, and prepared Al (OH), Si_〇 force weight ^_0/0, BO force wt%, Bi O force ¾1 wt%, the composition of Al O force ¾ wt% ratio So that

After being put in an alumina crucible and melted at a temperature of 1200 ° C., it was rapidly cooled to be vitrified. So Thereafter, the obtained glass was pulverized using zirconia balls to prepare a glass frit. The average particle size of the glass frit was 1 · 0 / m.

[0064] 2. Preparation of conductive paste

Silver powder, silver vanadate, silver molybdate, silver tungstate, chromium oxide, glass frit and organic vehicle were mixed by a three-roll mill at the ratio shown in Table 3 below, and the conductive paste samples shown in Table 3 were mixed. 4:! -53 were produced. Samples marked with * in Table 3 are comparative examples.

[0065] [Table 3]

[0066] As the silver powder, 50% by weight of spherical powder having an average particle diameter of 1.3 μm and 50% by weight of amorphous powder having an average particle diameter of 0.8 μm were used.

[0067] Average grain size for silver vanadate 2.6 μm, average grain size for silver molybdate

For 1.3 / im, silver tungstate, powder with an average particle size of 1 · 8 μΐη and for chromium oxide with an average particle size of 1.5 _β m were used.

[0068] In each sample, as the organic binder in the organic vehicle, a mixture of ethyl cellulose and alkyd resin was used. As a solvent in the organic vehicle, a mixture of butyl carbitol, butyl carbitol acetate and terpineol was used.

[0069] 3. Evaluation of conductive paste The characteristics of Samples 41 to 53 were evaluated in the same manner as in Experimental Example 1. The results are shown in Table 3.

[0070] As can be seen from Table 3, L * (brightness) of samples 41-46 is L * (brightness) of samples 50-53, even at a baking temperature 40 ° C lower than that of samples 50-53. ) Or less. In other words, it can be seen that when silver vanadate or silver molybdate is added, the effect of darkening can be sufficiently obtained even at a low baking temperature.

[0071] It should be noted that the samples 47 to 49 to which silver tungstate was added had a noticeable effect of fading at low temperatures, but were superior to the comparative samples 50 to 53. Is clear.

Claims

The scope of the claims

Silver powder,

At least one silver oxide selected from the group consisting of silver vanadate, silver molybdate and silver tungstate;

Glass frit,

Containing an organic vehicle,

A conductive base characterized in that it is used for an anti-fogging conductor formed on the surface of a glass substrate.

2. The conductive paste according to claim 1, wherein the silver oxide is contained in a ratio of 0.5 to 7 parts by weight with respect to 100 parts by weight of the silver powder.

3. The conductive paste according to claim 1, wherein the silver oxide is contained in a ratio of 0.5 to 5 parts by weight with respect to 100 parts by weight of the silver powder.

The conductive paste according to any one of claims 1 to 3, wherein the glass frit is contained in a ratio of 3 to 10 parts by weight with respect to 100 parts by weight of the silver powder. Glass frit

SiO2: 13% by weight,

B〇 2 ~: 10% by weight,

Bi-O 60-85% by weight,

A10 3-7% by weight,

The conductive paste according to any one of claims 1 to 4, wherein the conductive paste is contained at a ratio of

6. The conductive paste according to claim 5, wherein the glass frit further contains ZnO at a ratio of 13 wt% or less.

The conductive paste according to claim 1, wherein the glass substrate is a window glass of an automobile.

A glass substrate;

The conductive substrate according to any one of claims 7 to 7, wherein the conductive substrate is formed on the surface of the glass substrate. A glass structure comprising an anti-fogging conductor formed by baking a conductive paste.

The glass structure according to claim 8, wherein the glass structure is a window glass of an automobile.