KR20100029652A - Low temperature dryable conductive paste composite for solar cell and printing method using the same - Google Patents

Abstract

PURPOSE: A low temperature dryable conductive paste composite is provided to ensure screen printing applicability, adhesive force of a printing film, flexibility and electric conductivity, to form an electrode film through a low temperature drying, and to improve the reliability of products. CONSTITUTION: A low temperature dryable conductive paste composite for a solar cell comprises 100 wt% conductive paste, 60~90 wt% silver powder, and 10~40 wt% polyester-based binder resin. The silver powder comprises flake type powders with 1~10 micron size and 100~500 nm particle size distribution. The binder resin comprises 5~20 wt% resin solid and 5~35 wt% diluent based on 100 wt% conductive paste.

Description

Low temperature dryable conductive paste composite for solar cell and printing method using the same}

The present invention relates to an electrode paste composition used for electrode formation or packaging or assembly of various electric and electronic materials, and a printing method using the same, and more particularly, to screen printing for electric and electronic device parts including electrodes of solar cells. It relates to a low temperature dry electrode paste composition for a solar cell and a printing method using the same.

Generally speaking, printing of letters or image information onto paper is conceived using ink for giving color. However, current printing means forming a pattern in a necessary amount and a necessary amount (thickness) at a necessary place. Recently, screen printing technology has been widely applied to the electric and electronic fields because it is possible to print not only flat surfaces but also curved surfaces, and to shorten processes, reduce costs, and provide conductive materials to form electrodes. Screen printing is a printing method in which ink is placed on the line of the screen plate and pushed with a squeegee to be transferred to a to-be-printed object.

In the case of the etching method and the photolithography method which are conventionally used as the method of forming the conductive coating film, the process is complicated, the productivity is low, it requires a lot of equipment, the waste rate of the material is high, the generation of harmful substances, the environmental treatment cost are high. There were additional disadvantages such as occurrence.

Screen printing requires a screen printing paste, and in order to form an electrode, a material capable of providing conductivity to the paste is added. There are two types of electrode pastes for screen printing that impart conductivity, a high temperature baking type and a low temperature curing type, and most of the types currently used are high temperature baking type electrode pastes.

However, even if screen printing technology is used, the high temperature firing type requires more energy in the process line, thereby increasing the processing cost, and deteriorating the adhesive strength due to shrinkage of the conductive coating after firing, or inferior pattern precision. Problems such as the above appear.

Accordingly, the present invention is excellent in screen printing aptitude, adhesion of the print film and electrical conductivity, and a new mixture of a solid resin and a dilution solvent in a specific blending ratio to a specific silver filler to form an electrode coating by drying at a low temperature An electrode paste composition and a printing method using the same have been developed.

Conventionally, as the coating film is formed by firing at a high temperature, the wire resistance and the contact resistance are increased due to the shrinkage of the coating film, so that the conductivity is lowered, and the cost required for the production process increases.

Accordingly, it is an object of the present invention to provide a low temperature dry electrode paste composition for solar cells having excellent electrode properties by reducing the cost during the production process by drying the paste at a low temperature and increasing the electrical conductivity.

In addition, another object of the present invention is to provide a printing method using the electrode paste composition and the electrode paste composition further added to the composition, the specified additives for enhancing the performance of adhesion and electrical conductivity.

In order to solve the above technical problem, in the present invention, in the electrode paste used for screen printing, a specific silver powder is used as a component having electrical conductivity, and in addition, a solid resin of a specific formulation for imparting screen printability and A low temperature dry electrode paste for solar cells, comprising a binder composed of a diluent solvent, the content of silver powder being 60 to 90 wt% and the binder content of 10 to 40 wt% with respect to 100 wt% of the conductive paste; Disclosed is a printing method using the same.

Here, it is preferable to use the polyester resin which consists of a composition ratio of 5-20 wt% of resin solid content and 5-35 wt% of dilution solvent of resin solid content with respect to 100 wt% of electrode pastes for the said binder resin. This is because when the resin solid content is less than 5 wt% in the binder resin, the viscosity of the conductive paste is low, and when the resin solid content is more than 20 wt%, the viscosity is high so that workability during screen printing is low.

In addition, in the present invention, it is preferable to further add 0.1 to 3 wt% of the additive to impart the properties such as conductivity, adhesion, dispersibility, storage stability, printability, etc. to the paste 100 wt%. This is because it is difficult to impart the above-described characteristics when the additive is used in an amount of less than 0.1 wt%, and the conductivity or printing aptitude may be lowered when the additive is added in excess of 3 wt%.

More preferably, in consideration of conductivity, adhesion, dispersibility, storage stability, printing aptitude, etc., 100 wt% of an electrode paste consisting of 5 to 20 wt% of a resin solid content and 5 to 35 wt% of a diluting solvent of the resin solid content is made of silver powder. It is preferable that 0.1-3 wt% of additives are further contained with respect to%.

In the binder resin, the solid resin is preferably a polyester resin having a glass transition temperature in the range of 5 to 40 ° C. or a molecular weight in the range of 10,000 to 50,000. This is because it is applicable to various printed materials and has the characteristics of a binder that can be cured at low temperatures.

The diluent solvent is preferably a boiling point in the range of 150 ~ 240 ℃ so that the resin solid content can be dried within 1 hour at room temperature or 200 ℃ or less, specifically N-methylpyrrolidone, butyl cellosolve, Diethylene glycol monobutyl ether acetate, ethyl cavitol, ethyl cavitol acetate and butyl cavitol, ethoxyethyl acetate, ethyl cellosolve, butyl acetate, propylene glycol monomethyl ether and propylene glycol monomethyl ether acetate and the like. It is preferable to use any one or more selected from the group consisting of.

At this time, the diluent is more specifically terpineol, N-methylpyrrolidone (N-Methylpyrrolidone, bp 202 ℃), butyl cellosolve (bp 171.2 ℃), ethylene glycol monobutyl ether acetate (Ethylene glycol monobutyl ether acetate, bp 192 ° C.), ethyl carbitol (bp 201.9 ° C.), ethyl cabitol acetate (Ethyl cabitol acetate, bp 217.4 ° C.), butyl capitol (Butyl cabitol, bp 230.6 ° C.) ethoxyethyl acetate ( Ethoxyethyl acetate (bp 156.3 ° C), Ethyl cellosolve (bp 135 ° C), Butyl acetate (Butyl acetate, bp 126 ° C), Propylene glycol monomethyl ether (bp 121 ° C), Propylene glycol mono Methyl ether acetate (Propylene glycol monomethyl ether acetate, bp 146 ℃) and the like can be used, among them terpineol (Terpineol bp: 2 in consideration of the adhesion and printability of the print film to the printed material). 17 ° C.) is most preferred.

The silver powder is preferably used by mixing a flat plate (flake type) having a micron size of 1 ~ 10㎛ and a particle size distribution of 100 ~ 500nm, more preferably a micron size of silver and Nano-size silver is used by mixing 1: 1 to 1: 5 by weight. This is because when the shape of the silver powder is not a plate-shaped sphere type, the silver powder of the screen-printed film does not have surface contact with each other and is in point contact with each other, so that a conductive path is difficult to be formed and the required electrical conductivity is not obtained. In addition, in the case of using a small-volume spherical silver powder in forming the conductive paste based on the weight part, the volume of the silver powder becomes smaller in the total volume of the printed film, resulting in pinholes in the printed conductive pattern. This is because a poor packing of silver powder may cause a problem of poor electrical conductivity, and when silver powders having different particle sizes are mixed, the conductivity may be improved by reducing the air gap between the silver powders to make the density uniform. . In this case, when the nano-size silver is less than 1 or more than 5 based on the micron-sized silver 1 by weight, the effect of filling the above-mentioned voids is reduced, and it is preferable to mix within the above-mentioned range.

In the present invention, in terms of cost and conductivity, the silver powder may use pure silver or conductive silver selected from the group consisting of zirconia, tin oxide, antimony oxide and indium tin oxide (ITO), nickel oxide, and aluminum oxide powder. Addition of a substance can be used, and preferably a mixture of 1 to 30 wt% based on 100 wt% of the mixture is preferable. If it is less than 1 wt%, the effect of improving conductivity is insignificant, and if it is used in excess of 30 wt%, the necessary silver is not sufficiently used. Therefore, it is preferable to use it within the above-mentioned range.

In the present invention, the additive is (a) an acid additive selected from stearic acid, acetic acid, formic acid phosphoric acid, maronic acid, maric acid, hydrochloric acid and sulfuric acid; (b) a polysiloxane antifoaming agent selected from dimethylpolysiloxane, methylethylpolysiloxane, diethylpolysiloxane, etc., a silicone leveling agent selected from silicone diacrylate or silicone polyacrylate, or an alcohol leveling agent selected from methanol, ethanol, butanol, etc., hexafluoroanti It is preferable in view of the properties of the conductive paste to use an additive consisting of an additive selected from an ammonium, an inorganic filler, and the like blocked with triflic acid. However, the present invention is not limited to the above-described additives and may be commercially available in the conductive paste field.

The viscosity of the conductive paste according to the present invention is preferably in the range of 5,000 to 1,000,000 cps in consideration of the printability and workability of screen printing.

The electrode paste composition according to the present invention is dried at a temperature of up to 200 ° C. or at a temperature from room temperature to 200 ° C. within 1 hour to form an electrode coating film.

In addition, in screen printing using the electrode paste composition according to the present invention, in order to further improve the conductivity, the first screen printing is carried out using a liquid consisting of a conductive paste on the printed object, and again, as a mixed additive. Car screen says to print.

Specifically, in the present invention, a screen printing method using a conductive paste, comprising: (a) forming an electrode paste containing 60 to 90 wt% of silver powder and 10 to 40 wt% of polyester binder resin in the printed object; Primary screen printing step; And

(b) on the primary screen printing,

(Iii) an acid additive selected from the group consisting of sulfuric acid, acetic acid, formic acid, phosphoric acid, maronic acid, maleic acid, hydrochloric acid and stearic acid;

(Ii) an additive selected from the group consisting of a polysiloxane antifoaming agent, a silicone leveling agent or an alcohol leveling agent, hexafluoroantimonate, ammonium blocked with triflic acid and an inorganic filler; a mixed additive consisting of 0.01 to 3.0 wt% It provides a screen printing method using a conductive paste, characterized in that the second screen printing. It is preferable to use it within the range of use as the use of a mixed additive of less than 0.01 wt% on the primary screen printing may cause a slight increase in conductivity and cause an electrical damage to the surrounding when it exceeds 3.0 wt%. Do.

The conductive paste of the present invention is excellent in screen printing aptitude of the paste, adhesion of the print film, flexibility, and electrical conductivity, and the coating film is formed even by low temperature drying, so that the production process cost is reduced, so it is very efficient for screen printing for various electric and electronic devices. It is applicable and the print quality is also very good, which can improve the reliability of the product.

[Publication Materials]

1.silver filler

In the present invention, silver powder is used as the conductive metal material, and physical properties thereof are shown in Table 1 below. 1 is a SEM photograph of the silver powder of the present invention, showing a plate-like shape having a particle size distribution of the micron size (A) and a particle size distribution of the nano size (B).

2. Binder Resin

2-1. Resin solids

In the present invention, a polyester resin is used as the resin of the binder for imparting viscosity to the conductive paste, and the physical properties and the diluting solvent are shown in Table 2 below.

At this time, the viscosity of the polyester resin was selected to be 2,000 ~ 50,000 cps.

[ Example  1] electrode paste manufacturing

[ Example  2] screen printing

1.1 part 1 degree

The conductive paste of Example 1 was applied by rolling on a screen plate with a scraper, and then plate-separated while being discharged to the caustic part of the screen plate with a squeegee, and then screen-printed while leveling the printed object, and then at 200 ° C. It dried for 30 minutes and formed the electrode.

2. 2-part 2 degree

The conductive paste of Example 3-1 was applied by rolling on a screen plate with a scraper and then plate-separated while being discharged to the wire portion of the screen plate with a squeegee to be leveled on the printed object, followed by primary screen printing. Second screen printing was carried out with the acid additive of Example 3-2 on the primary printing in the same manner, and dried at 200 ° C. for 30 minutes to form an electrode.

Experimental Example

1.adhesive

As a result of confirming the adhesion test of the test electrode printed in Example 2, it can be seen that the same characteristics as the electrode formed by firing at a high temperature. The adhesion test is based on KS M ISO 2409 (Paint Adhesion Test Method). Cross-cut the printed electrodes in cross shape, attach them with cellophane tape, and check whether the printed pattern cells are good as falling numbers. Judged. Among the 100 cells formed by the electrode printed in Example 2, all of the 100 cells were attached even after cross-cutting.

2. Electrical conductivity

The electrical conductivity of the formed electrode pattern was measured on the surface of the electrode pattern by the 4-point probe method using a surface resistance measuring instrument (CMT-series, Korea), and the thickness was measured by SEM photographing. In conversion, it is shown in Table 4 below.

As a result of measuring the specific resistance, it can be seen that the results are shown in Table 4. Compared with the general electrode pattern, it can be seen that it shows good physical properties for use as the electrode pattern.

As a result, it was found that the printed film prepared according to the present invention had the same or superior conductivity as well as the adhesive strength as compared with the high temperature baking in forming the electrode.

1 is a SEM photograph of the silver powder of the present invention, showing a plate-like shape having a particle size distribution of the micron size (A) and a particle size distribution of the nano size (B).

Claims (9)

In the electrode paste, A low-temperature dry electrode paste composition for a solar cell, wherein the content of the silver powder is 60 to 90 wt% and the content of the polyester-based binder resin is 10 to 40 wt% with respect to 100 wt% of the electrode paste. The method of claim 1, The silver powder is a low-temperature dry type electrode paste composition for solar cells, characterized in that it is mixed with a flat plate (flake type) having a particle size distribution of 1 ~ 10㎛ micron size and 100 ~ 500nm particle size distribution. The method of claim 1, The binder resin is a low-temperature dry electrode paste composition for a solar cell, characterized in that consisting of 5 to 20 wt% of resin solids and 5 to 35 wt% of a diluent of resin solids with respect to 100 wt% of the conductive paste. The method of claim 3, wherein The additive may include (a) an acid additive selected from stearic acid, acetic acid, formic acid, phosphoric acid, maronic acid, maleic acid, hydrochloric acid, sulfuric acid, and the like; (b) a polysiloxane antifoaming agent selected from dimethylpolysiloxane, methylethylpolysiloxane, diethylpolysiloxane, etc., a silicone leveling agent selected from silicone diacrylate or silicone polyacrylate, or an alcohol leveling agent selected from methanol, ethanol, butanol, etc., hexafluoroanti Additives selected from monates, ammonium blocked with triflic acid and inorganic fillers; 0.01-3.0 wt% of an additive comprising a further low temperature dry electrode paste composition for a solar cell. The method of claim 1, Solid binder resin in the binder resin is a low temperature dry electrode paste composition for a solar cell, characterized in that the polyester has a molecular weight in the range of 10,000 ~ 50,000. The method of claim 1, The diluents are terpineol, NMP, butyl cellosolve, ethylene glycol monobutyl ether acetate, ethyl cavitol, ethyl cavitol acetate and butyl carbitol, ethoxy ethyl acetate, ethyl cellosolve, butyl acetate, propylene glycol A low temperature dry electrode paste composition for solar cells, characterized in that the diluent is selected from the group consisting of monomethyl ether and propylene glycol monomethyl ether acetate. The method of claim 1, The silver powder is pure silver or low temperature drying type for solar cells, characterized in that 1 to 30 wt% of a conductive material selected from the group consisting of zirconia, tin oxide, antimony oxide and indium, nickel oxide, and aluminum oxide powder is added to pure silver or silver. Electrode paste composition. The method according to any one of claims 1 to 7, The electrode paste is dried at a temperature of up to 200 ℃ within 1 hour to form an electrode coating film, low temperature dry electrode paste composition for a solar cell. In the screen printing method using a conductive paste, (a) primary screen printing an electrode paste having a content of silver powder of 60 to 90 wt% and a polyester binder resin of 10 to 40 wt% in the printed object; And (b) on the primary screen printing, (Iii) an acid additive selected from the group consisting of sulfuric acid, acetic acid, formic acid, phosphoric acid, maronic acid, maleic acid, hydrochloric acid and stearic acid; (Ii) an additive selected from the group consisting of a polysiloxane antifoaming agent, a silicone leveling agent or an alcohol leveling agent, hexafluoroantimonate, ammonium blocked with triflic acid and an inorganic filler; 0.01 to 3.0 wt% of a mixture consisting of Screen printing method using a conductive paste, characterized in that the secondary screen printing using the added conductive paste.

Images