JPH11292569A - Conductive paste and glass plate with conductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a glass sheet with a dark color conductor having <=30 brightness index L'. SOLUTION: A conductive paste containing a conductive material powder such as a silver powder, and a low melting point glass powder, an org. varnish and a silicon (Si) powder is prepared. The prepared conductive paste is applied on the surface of a glass sheet by screen printing to form three conductive stripes each comprising a line of 1.0 mm width and about 200 mm length and 10 mm squares attached to the both ends of the line. Then the pattern is dried at 120 deg.C for 10 min and fired at 680 deg.C for 5 min in an electric furnace to produce a glass sheet with a conductive body. The brightness index L' of the square pattern is <=30 by measuring through the surface of the glass where the conductive paste is not printed or fired.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a conductive paste and a glass plate with a dark conductor.

[0002]

2. Description of the Related Art In order to prevent fogging of a glass plate used for a rear window of an automobile, a large number of conductive wires for heating and a common wire connected to both ends of the conductive wire are provided on the glass plate. A power supply line (hereinafter, referred to as a bus bar) is printed and fired. Conductive wires and busbars (hereinafter referred to as
Both are called conductors. Is formed on the glass plate by printing the conductive paste on the glass plate and firing it. A metal terminal (hereinafter, referred to as a metal terminal) for taking out a lead wire is attached to the bus bar by soldering or the like. By applying a voltage between the metal terminals to generate heat in the conductor, the surface temperature of the glass plate is maintained at a dew point or higher, thereby preventing the glass plate from fogging.

In recent years, from the viewpoint of design, there has been a demand for making the color of a conductor darker, that is, darker. When a conventional silver powder-containing conductive paste is baked on a glass plate, the color of the conductor becomes yellow due to the color development of the silver colloid. Conventionally, to make this darker, copper oxide,
A method of directly adding a black pigment such as chromium oxide or cobalt oxide to a conductive paste has been adopted.

[0004]

SUMMARY OF THE INVENTION Copper oxide, chromium oxide,
With a conductive paste to which a black pigment such as cobalt oxide is directly added, there is a problem that the color of the conductor cannot be deepened as desired. Specifically, a glass plate with a conductor obtained by printing and firing a conductive paste on one surface of a glass plate is viewed from the side of the glass plate on which the conductive paste is not printed and fired. It was difficult to produce a glass plate with a conductor having a brightness index L ^* of 30 or less.

[0005] The reason is that when a conductive paste containing a black pigment such as copper oxide, chromium oxide, or cobalt oxide as a black pigment is used, sintering of silver powder particles is hindered and the specific resistance of the conductor increases. And the adhesion strength of the metal terminal to the conductor (hereinafter referred to as metal terminal adhesion strength) is reduced,
This is because black pigment cannot be sufficiently added. An object of the present invention is to provide a conductive paste and a glass plate with a conductor, which solve the above problems.

[0006]

SUMMARY OF THE INVENTION The present invention provides a conductive paste containing a conductive substance powder, a low-melting glass powder, an organic varnish, and silicon (Si) powder.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The conductor in the present invention is a conductive strip and a bus bar obtained by printing and firing a conductive paste on a glass plate or a ceramic color layer formed on the surface of the glass plate. The conductive paste in the present invention contains a conductive substance powder, a low-melting glass powder, an organic varnish, and a silicon powder.

[0008] The conductive substance in the present invention imparts desired conductivity to a conductor. As the conductive substance, silver, gold, platinum, a silver-platinum alloy, a silver-palladium alloy, a silver-rhodium alloy, rhodium oxide, or the like can be used, but high conductivity, easy availability, and low price are available. It is preferable to use silver for such reasons. Hereinafter, a case where silver is used as the conductive substance will be described.

The average particle size of the silver powder is preferably 20 μm or less in consideration of the printability of the conductive paste.
More preferably, it is 0.1 to 10 μm, particularly preferably 0.1 to 6 μm. In order to control printability and sinterability well, two or more silver powders having different average particle diameters or foil-like silver powders may be mixed and used as the silver powder.
Furthermore, in order to control the electrical resistance of the conductor and the solder erosion phenomenon, other conductive substances such as gold, platinum,
A silver-platinum alloy, a silver-palladium alloy, a silver-rhodium alloy, rhodium oxide, or the like may be added.

The low-melting glass in the present invention is a glass which starts softening and flowing at a temperature lower than the softening point (about 730 ° C.) of soda lime glass generally used as a glass plate.

The low melting point glass powder in the present invention is an essential component for bonding the silver sintered body to a glass plate or a ceramic color layer formed on the surface of the glass plate during firing. When baking the conductive paste printed on the glass plate or the ceramic color layer formed on the surface of the glass plate at the same time as heating and bending the glass plate,
One or more crystals may precipitate on the low melting glass. As a result, an improvement in the mold releasability between the glass plate and the mold for bending can be expected. From such a viewpoint, at 570 to 700 ° C. which is a temperature range in which a glass sheet for an automobile is bent, at least one selected from the group consisting of lead titanate, lead zirconate, lead borate, and lead stannate is used. A crystallized glass that precipitates the above crystal as a main crystal can be used.

The organic varnish in the present invention is obtained by dissolving an organic resin having a binder function in a solvent, and is not particularly limited as long as it can impart printability to the conductive paste. However, since the raw materials are commercially available and easily available, one or more organic resins selected from the group consisting of ethylcellulose resin, acrylic resin, styrene resin and phenol resin are converted to α-terpineol,
It is preferable to use one dissolved in one or more solvents selected from the group consisting of butyl carbitol acetate and phthalate.

The silicon powder in the present invention is oxidized when the conductive paste printed on the glass plate is fired, and suppresses the generation of silver colloid which causes yellow color. The lightness index L ^* in the present invention is JIS Z87.
29 (method of displaying object color using L ^* a ^* b ^* color system and L ^* u ^* v ^* color system) It is defined by a lightness index, and JIS Z8 is used as Y in the specification.
701 is used.

The glass plate with a conductor according to the present invention is obtained by printing and firing the conductive paste of the present invention on a glass plate or a ceramic color layer formed on the surface of the glass plate. It is a dark-colored glass plate with a conductor, having a lightness index L ^* of 30 or less when viewed from the side where the paste is not printed and fired.

As a result of analyzing the conductor, the present inventors have found that the color development by silver colloid is mainly governed by the amount of silver colloid generated and the particle size of silver colloid. When the conductive paste of the present invention is used, the mechanism by which the color development due to silver colloid is suppressed and the lightness index L ^{* of the} glass plate with a conductor is reduced is unknown, but is speculated as follows. That is, the silicon powder in the conductive paste of the present invention reacts with oxygen during firing of the conductive paste. As a result, the supply of oxygen to the silver powder is suppressed, the generation of silver colloid and the increase in the particle size of the silver colloid are suppressed,
The lightness index L ^* decreases.

The conductive paste of the present invention preferably contains 0.1 to 5.0% by weight of silicon powder.
If the amount is less than 0.1% by weight, the effect of suppressing silver colloid generation is reduced, and the lightness index L ^* may not be 30 or less.
If it exceeds 5.0% by weight, the sintering of the silver powder particles may be insufficient and the metal terminal adhesive strength may be reduced.

The silicon powder in the present invention is preferably a spherical powder. Silicon powder includes spherical powder, flat powder,
However, when non-spherical powder is used, the dispersibility and fluidity of the powder are reduced, and as a result, the dispersibility of the silicon powder in the conductive paste is reduced and the effect of suppressing silver colloid generation is reduced. Variation may occur.

Whether the silicon powder is spherical or not is determined by S
Judge by EM observation. The volume shape factor K is determined for representative particles in the SEM observation field according to the method of Keywood, and those having K of 0.51 to 0.54 are defined as spherical powder. K is defined by the following equation. K = (π / 8) · (π ^1/2 P / α ^1/2 ) where P = (volume of particle) / (projected area × t), α =
(Projected area) / b · l, t = maximum particle height in the direction perpendicular to the projection plane, b = particle minor axis diameter, l = particle major axis diameter.

The volume average diameter of the silicon powder in the present invention is preferably 0.1 to 30 μm. 0.
If it is less than 1 μm, the silicon powder may agglomerate in the conductive paste to reduce the dispersibility, and the effect of suppressing silver colloid generation may vary. If it exceeds 30 μm, the reduction effect on the silver colloid may decrease due to a decrease in the specific surface area of the silicon powder. In addition, a filler, a pigment, and the like may be added to the conductive paste of the present invention as needed.

[0020]

EXAMPLE The composition of the low melting point glass is 65% by weight of PbO, 12% by weight of B ₂ O ₃ , and SiO ₂ :
_{10%, TiO 2: 5%} , ZrO 2: 1%, SnO 2:
0.5%, Al ₂ O ₃ : 0.5%, Li ₂ O: 0.5
_{%, Na 2 O: 0.5%} , ZnO: 5%, by compounding raw materials so as to. Put this raw material in a platinum crucible, 15
After melting at 00 ° C., the molten glass was flaked while being cooled by a roller. The flaked glass was pulverized with a ball mill to an average particle size of 3 to 5 μm to prepare a low-melting glass powder.

Next, silver powder, low-melting glass powder, organic varnish,
After blending the silicon powder and the black pigment (CuO, CrO, or CoO), the mixture was kneaded in a porcelain mortar for one hour, and further dispersed three times with three rolls to produce a conductive paste. The silver powder used was a mixture of foil silver powder having an average particle diameter of 10 μm and spherical silver powder having an average particle diameter of 1 μm in a ratio of 50:50. A spherical powder having a volume average diameter of 1.0 μm was used as the silicon powder. As the organic varnish, one obtained by dissolving ethyl cellulose resin having a polymerization degree of 7 in α-terpineol so as to have a concentration of 20% by weight was used.

This conductive paste is printed on the surface of a glass plate by a screen printer, and has a width of 1.0 mm and a length of about 2 mm.
Three conductive filaments each having a square pattern of 10 mm on each side attached to both ends of a 00 mm linear pattern were formed. Next, after drying at 120 ° C. for 10 minutes,
It was baked at 80 ° C. for 5 minutes to produce a glass plate with a conductor.
The lightness index L ^* , specific resistance (unit: μΩ · cm), and metal terminal adhesive strength (unit:
kgf) was measured. The results are shown in Tables 1 and 2. In Tables 1 and 2, Examples 1 to 7 are Examples and Examples 8 to 16
Is a comparative example.

Lightness index L ^* : Lightness index L ^* (JIS) when the conductive paste is viewed from the side where the conductive paste is not printed and fired, with respect to the square pattern portion of the conductive line of the glass plate with a conductor. Z8729) was measured using a CR200 type spectrophotometer (trade name) manufactured by Minolta Co., Ltd. Specific resistance: The electric resistance R was measured using a digital multimeter manufactured by Advantest Corporation. Furthermore, the cross-sectional shape was measured using Surfcom (trade name) manufactured by Tokyo Seimitsu Co., Ltd., and the cross-sectional area S was calculated by the integration method. R × S ÷ L was calculated using the above R and S, and this was defined as the specific resistance (Tables 1 and 2 show the average values of the specific resistances of the three conductive filaments). Here, L is the length of the conductive wire. The allowable range of the specific resistance for ensuring the conductivity is determined by the size of the glass for automobile, the shape of the defogger pattern, and the battery voltage. The present inventors set the allowable range to 12 μΩ · cm or less. Metal terminal adhesion strength: A force was applied to a Ni-plated copper terminal bonded to a conductor with a solder (adhesion area: 25 mm ² ) by applying a force, and the force when the Ni-plated copper terminal was peeled was measured using a small tensile gauge. . We have 15kgf
Greater than the acceptable range.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

According to the present invention, it is possible to provide a glass plate with a dark conductor having a lightness index L ^* of 30 or less when viewed from the side where the conductor is not formed.

Claims (4)

[Claims] 1. A conductive paste containing a conductive substance powder, a low-melting glass powder, an organic varnish, and silicon (Si) powder. 2. The conductive paste according to claim 1, containing 0.1 to 5.0% by weight of silicon powder. 3. The conductive paste according to claim 1, wherein the silicon powder is a spherical powder, and the silicon powder has a volume average diameter of 0.1 to 30 μm. 4. A glass plate with a conductor obtained by printing and baking the conductive paste according to claim 1, 2 or 3 on one surface of a glass plate, wherein the conductive paste of the glass plate is A glass plate with a conductor having a lightness index L ^* of 30 or less when viewed from the side of the surface not printed or fired.