JP4800609B2 - Conductive paste, conductive sheet and method for producing the same - Google Patents

Description

  The present invention relates to a conductive paste applied or printed on a resin substrate, a metal substrate, or a glass substrate. Furthermore, it is related with the electroconductive sheet in which the electroconductive coating film was formed on the base material, and its manufacturing method.

Membrane circuits in which a circuit is formed on a resin base material are widely used for keyboards and switches because they are flexible and lightweight. In order to manufacture this membrane circuit, for example, a method of forming a circuit by printing a conductive paste on a resin sheet is employed.
As a conductive paste used when producing a membrane circuit, a paste having high conductivity, heat resistance and bending resistance is required. As a conductive paste satisfying such requirements, a paste containing conductive powder and a polyester resin having a specific component and a specific molecular weight has been proposed (see Patent Document 1).
Japanese Patent Laid-Open No. 2002-8441

However, in the conventional products such as the conductive paste described in Patent Document 1, the leveling property of the conductive coating film formed by applying or printing on the resin substrate is not sufficient. If the leveling property is low, the coating thickness is not uniform, and a thin portion is generated. Since the resistance is increased at the thin part of the coating film, the conductivity of the coating film is lowered due to this.
In addition, as shown in FIG. 1, for example, when the insulating layer 12 is formed on the conductive coating 11 on the substrate 10 and the conductive layer 13 is formed on the insulating layer 12, the conductive coating 11 In some cases, the convex portion 14 of the surface protrudes from the insulating layer 12 and directly contacts the conductive layer 13. Therefore, conduction at an unintended place makes it difficult to form an accurate circuit. Therefore, it is conceivable to avoid the above problem by increasing the thickness of the insulating layer. However, if the insulating layer is increased in thickness, it becomes difficult to form circuits with high density.
Such a problem is not limited to a membrane circuit using a resin base material, but also occurs when a metal base material or a glass base material is used as the base material.

Furthermore, when a circuit is formed with a conductive paste on a flexible substrate, the circuit may be bent during manufacture or use of a device to which the circuit is mounted. Therefore, if the bending resistance is low, the circuit is disconnected, so that a conductive film having high bending resistance is required. In particular, the required characteristics have become more severe in recent years, and high bending resistance at high humidity is required.
This invention is made | formed in view of the said situation, and it aims at providing the conductive paste with high leveling property and bending resistance of a conductive coating film. Furthermore, it aims at providing an electroconductive sheet and its manufacturing method.

The conductive paste of the present invention contains a conductive powder and a polyester resin having an acid value of 0.3 to 2.2 mgKOH / g, and the polyester resin contains a polyhydric alcohol component and octadecanedioic acid or iconosan. It is comprised from the polybasic acid component containing a diacid, and the compounding quantity of the said electroconductive powder is 150-900 mass parts with respect to 100 mass parts of said polyester resins, It is characterized by the above-mentioned.
Moreover, it is preferable that the electrically conductive paste of this invention further contains the hardening | curing agent which can react with the said polyester resin.
The electroconductive sheet of this invention has the electroconductive coating film formed from the electroconductive paste mentioned above on a base material.
In the conductive sheet of the present invention, the conductive coating film preferably has an arithmetic average surface roughness (Ra) measured in accordance with JIS B0601 of 1.0 μm or less.
The method for producing a conductive sheet of the present invention is characterized in that the above-described conductive paste is applied on a substrate.
In the manufacturing method of the electroconductive sheet of this invention, it is preferable that the provision method of electroconductive paste is screen printing.

In the conductive paste of the present invention, the leveling property of the conductive coating film is increased, and the thin portions having high resistance are reduced, so that the conductivity of the conductive coating film can be increased. In addition, when the insulating layer is formed on the conductive coating and the conductive layer is formed on the insulating layer, the conductive coating of the conductive paste and the conductive layer are prevented from coming into direct contact. . Moreover, the bending resistance of a conductive coating film is high.
The conductive sheet of the present invention has high conductivity of the conductive coating film and excellent bending resistance after the moisture resistance test.
According to the method for producing a conductive sheet of the present invention, a conductive sheet having high conductivity and high bending resistance can be produced. A simple circuit can be formed.

The conductive paste of the present invention contains a conductive powder and a polyester resin, and these are mixed in a solvent.
Examples of the conductive powder contained in the conductive paste include metal and carbon powders, among which silver powder is preferable. Further, the shape of the powder may be any of flaky shape (scale-like shape), dendritic shape, spherical shape, and amorphous shape, but among these shapes, flaky shape is preferable from the viewpoint of conductivity.

  It is preferable that the compounding quantity of electroconductive powder is 150-900 mass parts with respect to 100 mass parts of polyester resins. When the blending amount of the conductive powder is less than 150 parts by mass, the conductivity of the conductive coating film obtained from the conductive paste may be insufficient, and when it exceeds 900 parts by mass, the conductivity in the conductive paste The dispersibility of the conductive powder may decrease, and the leveling property of the conductive coating film may decrease.

The polyester resin is composed of a polybasic acid component and a polyhydric alcohol component. Examples of the polybasic acid component include terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid and other aromatic dicarboxylic acids, oxalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, Saturated aliphatic dicarboxylic acids such as octadecanedioic acid, eicosane diacid, hydrogenated dimer acid, unsaturated aliphatic dicarboxylic acids such as fumaric acid, maleic acid, itaconic acid, citraconic acid, dimer acid, 1,4-cyclohexanedicarboxylic acid 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 2,5-norbornenedicarboxylic acid alicyclic dicarboxylic acid, and the like. These may be anhydrous.
Among the polybasic acid components, aromatic dicarboxylic acids are preferable, and terephthalic acid and isophthalic acid are particularly preferable because they are industrially produced in large quantities and are inexpensive. Further, it is more preferable to use a combination of an aromatic dicarboxylic acid and a saturated aliphatic dicarboxylic acid, and the saturated aliphatic dicarboxylic acid has a higher bending resistance, so that the saturation represented by the above formula (1) is used. It is preferable to include an aliphatic dicarboxylic acid. Specifically, as a polybasic acid component, it is preferable to contain sebacic acid, dodecanedioic acid, octadecanedioic acid, and eicosanedioic acid, and since it has a long linear structure, bending resistance is particularly high, Octadecanedioic acid and aicosanedioic acid are more preferable.

As the polyhydric alcohol component, an aliphatic glycol having 2 to 10 carbon atoms, an alicyclic glycol having 6 to 12 carbon atoms, an ether bond-containing glycol, or the like is preferable. Specifically, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, 1,9 -Nonanediol, 2-ethyl-2-butylpropanediol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, dipropylene glycol and the like.
Moreover, ethylene oxide or propylene oxide adducts of bisphenols such as 2,2-bis (4-hydroxyethoxyphenyl) propane, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like can be mentioned.
Among the polyhydric alcohol components, ethylene glycol and neopentyl glycol are preferable because they are industrially produced in large quantities and are inexpensive.

The polyester resin may be copolymerized with monocarboxylic acid, monoalcohol, or hydroxycarboxylic acid. Examples of the component that may be copolymerized include lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, stearyl alcohol, benzoic acid, p-tert-butylbenzoic acid, p- Examples thereof include hydroxybenzoic acid, ε-caprolactone, lactic acid, β-hydroxybutyric acid and the like.
Various additives such as an antioxidant may be added to the polyester resin in order to increase the molecular weight.

Further, the polyester resin has an acid value of 0.3 to 2.2 mgKOH / g, preferably 0.5 to 2.0 mgKOH / g. When the acid value of the polyester resin is less than 0.3 mgKOH / g, the dispersibility of the conductive powder is lowered, so that the leveling property of the conductive coating film obtained from the conductive paste is lowered. And when leveling property falls, since a thin part will be formed and resistance in a thin part will become large, the electroconductivity of a conductive coating film will fall. Further, when an insulating layer is formed on the conductive coating film and the conductive layer is formed on the insulating layer, the conductive coating film is prevented from protruding from the insulating layer and directly contacting the conductive layer. .
On the other hand, when the acid value exceeds 2.2 mgKOH / g, the bending resistance after the moisture resistance test of the conductive coating film decreases, and the conductivity after repeated bending decreases.

  Here, the acid value is a value measured as follows. That is, it is a value obtained by dissolving 0.2 g of a sample in dioxane and titrating the solution with a 0.01N potassium hydroxide methanol solution. A cresol red solution is used as a titration indicator.

  The polyester resin preferably has a number average molecular weight of 4000 or more, more preferably 8000 or more, further preferably 12000 or more, and most preferably 15000 or more. If the number average molecular weight is less than 4000, processability tends to be insufficient. The number average molecular weight can be measured by gel permeation chromatography (GPC).

  The degree of dispersion of the molecular weight distribution of the polyester resin is preferably 8 or less, and more preferably 5 or less. Here, the degree of dispersion of the molecular weight distribution is a value obtained by dividing the mass average molecular weight measured by GPC by the number average molecular weight.

  The glass transition temperature (Tg) of the polyester resin is preferably −18 to 85 ° C., and the upper limit is more preferably 15 ° C. in order to obtain sufficient flexibility.

It is preferable that the conductive paste further contains a curing agent capable of reacting with the polyester resin for the purpose of enhancing the mechanical properties of the conductive coating film. It is preferable that the compounding quantity of a hardening | curing agent is 1-20 mass parts with respect to 100 mass parts of polyester resins. When the blending amount of the curing agent is less than 1 part by mass, the effect of blending the curing agent is not exhibited. When the blending amount exceeds 20 parts by mass, the mechanical properties of the conductive coating film may be changed.
As the curing agent, an isocyanate compound is preferable because the bending resistance is further improved. Examples of the isocyanate compound include tetramethylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, and isophorone diisocyanate. Moreover, these derivatives may be sufficient. Further, these isocyanate compounds are preferably blocked blocked isocyanates. When the isocyanate compound is blocked, the storage stability of the conductive paste is increased.

  Examples of the solvent in which the above components are dispersed include, for example, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, propylene glycol monopropyl ether, diethylene glycol Propylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, ethyl Glycol monoisobutyl ether, diethylene glycol monoisobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, ethylene glycol mono 2-ethylhexyl ether, ethylene glycol monoallyl ether, ethylene glycol monophenyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl Examples include ether, diethylene glycol dibutyl ether, triethylene glycol dimethyl ether, and glycol ether derivatives such as esterified products thereof. These may be used alone or in combination of two or more.

  This conductive paste is produced by mixing a conductive powder, the above-described polyester resin, and, if necessary, a curing agent in a solvent. In this production, each component is mixed so as to have a viscosity according to the application.

The electroconductive sheet of this invention has the electroconductive coating film formed from the electroconductive paste mentioned above on a base material.
Here, the base material is a polyester sheet such as polyethylene terephthalate or polyethylene naphthalate, a resin sheet made of plastic such as polyimide, polyphenylene sulfide, polyethylene, polypropylene or polyamide, a metal substrate such as a silicon substrate, or a glass substrate. In the case where the conductive sheet is a membrane circuit, among these, a sheet made of polyester is preferable in terms of flexibility, electrical characteristics, mechanical characteristics, cost, and the like.

  In the conductive coating film of this conductive sheet, the arithmetic average surface roughness (Ra) measured in accordance with JIS B0601 is preferably 1.0 μm or less. If the arithmetic average surface roughness (Ra) of the conductive coating film is 1.0 μm or less, the irregularities on the surface of the conductive coating film are sufficiently small, and therefore the conductivity is sufficiently high.

  Moreover, this electroconductive sheet is manufactured by providing the said electroconductive paste on a base material. As a method for applying the conductive paste, various coating methods or printing methods can be adopted, and among these, the screen printing method is preferable. If the method for applying the conductive paste is screen printing, a circuit made of a conductive coating can be precisely formed on the substrate.

(Production Example 1)
A mixture of 490 g of terephthalic acid, 490 g of isophthalic acid, 350 g of octadecanedioic acid, 342 g of ε-caprolactone, 335 g of ethylene glycol, and 531 g of neopentyl glycol is heated in an autoclave at 240 ° C. for 3 hours with stirring to conduct an esterification reaction. It was. Next, the temperature was raised to 260 ° C., and 2.0 g of tetrabutyl titanate was added as a catalyst, and the pressure in the autoclave was gradually decreased to 13 Pa after 1.5 hours to carry out a polycondensation reaction. After 4 hours, the pressure was returned to normal pressure, isophthalic acid was added, and the mixture was stirred at 260 ° C., then the inside of the autoclave was pressurized with nitrogen gas and the contents were extracted into a sheet to obtain a polyester resin (1).

(Production Example 2)
A mixture comprising 498 g of terephthalic acid, 498 g of isophthalic acid, 343 g of eicosandioic acid, 342 g of ε-caprolactone, 335 g of ethylene glycol and 531 g of neopentyl glycol is heated in an autoclave at 240 ° C. for 3 hours with stirring to perform an esterification reaction. It was. Subsequently, with the temperature kept at 240 ° C., 2.0 g of tetrabutyl titanate was added as a catalyst, and the pressure in the autoclave was gradually decreased to 13 Pa after 1.5 hours to carry out a polycondensation reaction. After 4 hours, the pressure was returned to normal pressure, isophthalic acid was added, and the mixture was stirred at 260 ° C., then the inside of the autoclave was pressurized with nitrogen gas and the contents were extracted into a sheet to obtain a polyester resin (2).

(Production Example 3)
A mixture comprising 449 g of terephthalic acid, 449 g of isophthalic acid, 323 g of sebacic acid, 342 g of ε-caprolactone, 335 g of ethylene glycol and 531 g of neopentyl glycol was heated in an autoclave at 240 ° C. for 3 hours with stirring to perform an esterification reaction. . Subsequently, with the temperature kept at 240 ° C., 2.0 g of tetrabutyl titanate was added as a catalyst, and the pressure in the autoclave was gradually decreased to 13 Pa after 1.5 hours to carry out a polycondensation reaction. After 4 hours, the pressure was returned to normal pressure, isophthalic acid was added, and the mixture was stirred at 260 ° C., then the inside of the autoclave was pressurized with nitrogen gas and the contents were extracted into a sheet to obtain a polyester resin (3).

  In the polyester resins (1) to (3), the acid value was adjusted by changing the amount of isophthalic acid to be added later. The amount of isophthalic acid added is shown in Tables 2 to 4 below.

(Examples 1-8 , Comparative Examples 1-5 , Reference Examples 1 and 2 )
Polyester resins having various acid values, blocked isocyanate which is a curing agent, and silver powder were blended in the ratios shown in Table 1, and kneaded with three rolls. Then, ethylene glycol monobutyl ether acetate is added as a solvent so that the viscosity when measured with a viscometer VT-04 (measurement temperature 23 ° C., using a No. 2 rotor) manufactured by Rion is about 150 dPa · s. A paste (conductive paste) was obtained.
This silver paste is applied to a Toray PET film (Lumilar S, annealed at 155 ° C. for 1 hour) by silk screen printing so that the film thickness after drying becomes 8 to 11 μm, the line width is 0.4 mm, Five patterns made of a conductive coating film having a length of 50 mm were formed at intervals of 5 mm. And it was made to dry for 30 minutes at 150 degreeC box-type hot air dryer, and it hardened | cured, and produced the membrane circuit for evaluation (electroconductive sheet).

  The polyester resin was used as an ethylene glycol monobutyl ether acetate solution having a concentration of 36% by mass. As blocked isocyanate which is a curing agent, Duranate TPA-B80E (a derivative of hexamethylene diisocyanate) manufactured by Asahi Kasei Corporation was used. Moreover, as silver powder, flake silver powder with a particle size of 3-10 micrometers was used.

The obtained membrane circuit for evaluation was evaluated as follows. The evaluation results are shown in Tables 2-4.
<Resistivity>
The sheet resistance film thickness was measured with a 4 deep needle resistance measuring device, and the specific resistance was calculated from this value and the film thickness.
<Pencil hardness>
About the pattern which consists of an electroconductive coating film formed with the silver paste, pencil hardness was measured based on JISK5400.
<Bending resistance>
The evaluation membrane circuit was left in an environment of a temperature of 65 ° C. and a humidity of 95% RH for 1000 hours (moisture resistance test). Then, it is folded so that the pattern made of the conductive coating film is located inside, a load of 333 g / cm ² (5 kg / 15 cm ² ) is applied for 5 seconds, and then folded so that the pattern is located outside in the same place. A load of 333 g / cm ² (5 kg / 15 cm ² ) was applied for 5 seconds. This was repeated 11 times as one cycle, and the resistance value was measured. And bending resistance was calculated | required by the following formula.
(Folding resistance) = {(R−R ₀ ) / R ₀ } × 100 (%) R ₀ : Resistance value before moisture resistance test R: Resistance value after bending 11 <Surface roughness>
The center line average roughness (Ra75) was measured according to JIS B0601 using SE3500 manufactured by Kosaka Laboratory Ltd. as a measuring device.

As shown in Tables 2 to 4, the silver paste (Examples 1 to 8 ) containing a polyester resin having an acid value in the range of 0.3 to 2.2 mgKOH / g has both high bendability and leveling property. It turned out that it is excellent in electroconductivity.
On the other hand, the silver paste (Comparative Examples 2 to 4) containing a polyester resin having an acid value exceeding 2.2 mgKOH / g has a low surface roughness value, but its bending resistance is so low that it cannot be measured.
Silver paste (Comparative Examples 1 and 5) containing a polyester resin having an acid value of less than 0.3 mg KOH / g had a large surface roughness value and low dispersibility of silver powder.

  The electrically conductive paste of this invention is used suitably when forming a circuit on a resin base material, a metal base material, and a glass base material.

It is a figure which shows the coating film formed from the conventional electrically conductive paste.

Claims (6)

A polybasic acid containing conductive powder and a polyester resin having an acid value of 0.3 to 2.2 mg KOH / g , wherein the polyester resin contains a polyhydric alcohol component and octadecanedioic acid or eicosanedioic acid. The conductive paste is composed of components, and the blending amount of the conductive powder is 150 to 900 parts by mass with respect to 100 parts by mass of the polyester resin . The conductive paste according to claim 1, further comprising a curing agent capable of reacting with the polyester resin.
A conductive sheet comprising a conductive coating film formed from the conductive paste according to claim 1 or 2 on a substrate. The conductive sheet according to claim 3 , wherein the conductive coating film has an arithmetic average surface roughness (Ra) measured in accordance with JIS B0601 of 1.0 μm or less. A method for producing a conductive sheet, comprising applying the conductive paste according to claim 1 or 2 on a substrate. The method for producing a conductive sheet according to claim 5 , wherein the method for applying the conductive paste is screen printing.

Images