JP2010235738A - Conductive ink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide conductive ink of which film strength after printed and dried is high and which further has excellent conductivity and good fine-line printability. <P>SOLUTION: In the conductive ink containing a conductive material and a binder resin, the binder resin is a polyester resin and a nitrocellulose resin, and the conductive material is silver powders with a BET specific surface area of 0.10-5.00 m<SP>2</SP>/g, a tap density of 1.0-10.0 g/cm<SP>2</SP>, an average particle diameter of 0.1-5.0 μm, and sphericity of 0.9-1.0. The conductive ink further includes aluminum chelate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a conductive ink for manufacturing a printed circuit board for forming a conductive circuit, and more particularly includes an aluminum chelate. The present invention relates to a conductive ink that has excellent conductivity, has a strong film strength after printing and drying, and also has high fine line printability.

  In general, an etching method and a printing method are known as patterning of electronic parts, thin film formation for electromagnetic wave shielding or conductive circuits. Regarding the etching method, the metal surface and shape are dissolved or removed chemically or electrochemically, and a processing technique in a broad sense including its surface treatment is used. Etching is a kind of chemical processing, and is mainly performed to obtain a desired pattern shape on the metal surface. However, since the process is generally complicated and waste liquid treatment is necessary in the subsequent process, there is a problem. Many. Moreover, since the conductive circuit formed by the etching method is formed only of a metal such as aluminum or copper, there is a problem that it is weak against physical impact such as bending.

  On the other hand, the printing method is a technique in which a circuit pattern is printed with a thermosetting or thermoplastic conductive ink and sintered by heat treatment. Since the conductive ink used for this printing method contains metal powders, such as silver, as a main component, it has favorable electroconductivity. As for printing, circuit patterns are formed on polyamide films, PET films, ceramics, glass, and the like by various methods such as screen printing.

  The conductive ink uses a thermosetting resin and a curing agent or a thermoplastic resin as a resin varnish, and contains an organic solvent and water as a metal powder and metal nanoparticles as a conductor and a solvent component. As the metal powder used here, silver is generally used and the shapes thereof are various. From the viewpoint of improving the conductivity of the printed conductive circuit, a flake shape or a flat shape having a large contact area is used. There are many examples used.

However, the silver powder having such a shape has a problem that the fine line printability is poor.
These conductive inks can be expected to reduce the size and weight of electronic components, improve productivity, and reduce costs, and can easily impart high conductivity by printing or coating on a substrate and drying, Since drying and curing processes can be performed at low temperatures, the substrate and electronic parts are not damaged by high heat, the process is short and the cost can be reduced, and the addition to the environment is very small compared to the etching method. In recent years, demand has increased rapidly.
Conductive inks have been proposed so far, and Japanese Laid-Open Patent Publication No. 2005-56778 and Japanese Laid-Open Patent Publication No. 2008-171828 have proposed a conductive ink using flaky silver powder. Although these have excellent conductivity, they have been proposed for conductive inks using flaky silver powder, but fine lines cannot be printed well when used for applications such as EMI shielding.

Furthermore, in recent years, examples of conductive inks that are cured with active energy rays have also been disclosed. Japanese Patent Application Laid-Open Nos. 2002-72468 and 2003-110225 disclose a volume resistivity of 10 ⁻⁴ Ω · cm, which is high resistance. Japanese Patent Laid-Open No. 2003-140330 discloses a conductive ink having a low resistance of 10 ⁻⁶ Ω · cm, which has high conductivity and a wide range of applications, but after generating radicals with a radical generator and ultraviolet rays. Heating at 250 ° C. for 30 minutes or more is required, and it is not suitable for a substrate affected by heat.

  Japanese Patent Application Laid-Open No. 2000-305260 discloses a photosensitive paste comprising an alkali-soluble negative photosensitive resin composition, a photopolymerization initiator, metal powder, and metal ultrafine particles as a photosensitive conductor paste. Therefore, in this publication, after patterning the photosensitive resin composition, an organic component is volatilized in a firing furnace such as an electric furnace or a belt furnace, and an inorganic powder is fired to form a conductive pattern film. The firing atmosphere is 500 ° C. or higher in the air, nitrogen atmosphere or hydrogen atmosphere, and is not suitable for a substrate affected by heat.

Japanese Laid-Open Patent Publication No. 2005-56778 Japanese Laid-Open Patent Publication No. 2008-171828 Japanese Laid-Open Patent Publication No. 2002-72468 JP 2003-110225 PR JP 2003-140330 PR JP 2000-305260 A

  Example of using a flake shape or flat shape with a large contact area as a conductive material in order to achieve excellent conductivity in the formation of a conductive circuit by printing using conventional thermoplastic conductive ink There were many. However, such a conductive ink has poor thin line printability, and has a drawback in terms of reliability as a conductive circuit. In addition, the binder of the polyester-based resin used in the present invention has a low heat resistance of the film and may cause surface peeling due to heat. Therefore, an object of the present invention is to provide a conductive ink having a strong film strength after printing and drying, further excellent conductivity, and good fine line printability.

In order to solve the above-mentioned object, the inventors have conducted intensive research. As a result, the conductive material has a tap density of 1.0 to 10.0 g / cm ³ and a BET specific surface area of 0.10 to 5.00 m ² / g. And a spherical silver powder having an average particle size of 0.1 to 5.0 μm, a polyester resin, and a nitrocellulose resin. The conductive substance has a tap density of 1.0 to 10.0 g / cm ³ and a BET specific surface area of 0.1. It has been found that a conductive ink containing 10 to 5.00 m ² / g and an aluminum chelate has a strong film strength after printing and drying, further has excellent conductivity, and good fine line printability.

That is, the conductive ink in the present invention is a conductive ink containing silver, a binder resin and an aluminum chelate,
Silver has a tap density of 1.0 to 10.0 g / cm ³ ,
BET specific surface area of 0.10 to 5.00 m ² / g,
Average particle size 0.1-5.0 μm
and
Sphericality 0.9-1.0
And
The binder resin is the following polyester resin (A) and a nitrocellulose resin.

The polyester resin (A)
Weight average molecular weight 23,000-60,000,
Glass point transfer temperature 50 ~ 120 ℃
and
Viscosity 10-30Pa · s
It is what is.

Furthermore, the present invention provides
Weight average molecular weight 3000-5000,
Glass transition temperature 50-120 ° C
and
Viscosity 100-300mPa · s
The polyester resin (B) is contained in the conductive ink and relates to the above conductive ink.

  The present invention also relates to the above conductive ink, wherein the aluminum chelate is a metal chelate having a molecular weight of 200 to 300 and containing one ethyl acetoacetate group in one molecule.

Furthermore, the present invention relates to a conductive film, wherein the conductive ink is applied onto a polyethylene terephthalate film substrate and dried.
Moreover, this invention relates to the electrically conductive circuit formed by apply | coating said electroconductive ink on a base material, and making it dry.

  The conductive ink obtained in the present invention is characterized by containing a polyester resin and a nitrocellulose resin as a binder resin. This polyester resin is preferably polyester (A) alone or a combination of polyester resin (A) and polyester resin (B). Further, since spherical silver having a small particle size is used, it has excellent fine line printability, and has excellent conductivity equivalent to that of conductive ink using a flake-shaped or flat-shaped conductive material having a large contact area. Furthermore, it has the property that the film strength after printing and drying is strong by using a nitrocellulose resin. Due to these properties, the conductive ink obtained in the present invention is excellent in practical properties.

  Hereinafter, the present invention will be described in more detail based on embodiments, but the present invention is not limited to these embodiments unless departing from the technical idea of the present invention.

  The conductive ink of the present invention contains silver powder, a polyester resin, a nitrocellulose resin, and an aluminum chelate. Since this conductive ink contains aluminum chelate, the dispersibility of silver powder is improved, and further, shrinkage due to curing is caused. Therefore, it can be presumed that the contact probability between silver is increased and excellent conductivity can be realized. Furthermore, it became possible to improve the film strength after printing and drying by including a nitrocellulose resin.

  The conductive ink of the present invention contains a binder resin and a conductive substance, further contains an aluminum chelate as an additive for reducing the resistance value, a nitrocellulose resin for improving the film strength, and a polyester resin. It is characterized by that. The polyester resin as the binder resin can be used alone or in combination of the polyester resin (A) and the polyester resin (B). The polyester resin (A) and the polyester resin (B) can be used. By using together, printability is improved.

In the present invention, since the aluminum chelate undergoes curing shrinkage due to heat during drying, the contact probability between silver powders increases, and a low resistivity is obtained even in a polyester resin.
Here, the aluminum chelate used in the present invention preferably has a molecular weight of 200 to 300.

Furthermore, the aluminum chelate of the present invention is an ethyl acetoacetate complex, and is an aluminum chelate containing one or more ethyl acetoacetate groups in one molecule. Ethyl acetoacetate groups in the present _{invention, - (- OC-CH 3} -CH-CC 2 H 6 = O -) - and has a structure. An aluminum chelate having a molecular weight of more than 300 and / or containing a long-chain alkyl group inhibits so-called “wetting” between the polyester resin and silver powder, and contributes little to the decrease in resistance value.

  The addition amount is preferably 0.2 to 20% by weight based on the resin. 2 to 9 weight% is especially preferable. If it is less than 0.2% by weight, there may be no effect, and if it exceeds 20% by weight, the resistance value increases.

The conductive material contained in the conductive ink can be flaky, spherical, or agglomerated powder, but from the viewpoint of fine line printability, which is the object of the present invention, a spherical one with a small particle size is used. preferable. That is, the spherical silver powder has a tap density of 1.0 to 10.0 g / cm ³ , a BET specific surface area of 0.10 to 5.00 m ² / g, an average particle size of 0.1 to 5.0 μm, a true sphere The degree is preferably from 0.9 to 1.0. More preferably, it is a spherical silver powder having a tap density of 3.0 to 6.0 g / cm ³ , a BET specific surface area of 0.80 to 2.30 m ² / g and an average particle size of 0.3 to 1.2 μm. is there. If the average particle size is greater than 5.0 μm, the fine line printability is likely to be poor. is there.

In the present invention, the tap density is a value measured by a tap density measuring device. The BET specific surface area is described by defining a value calculated by the following calculation formula from the surface area measured using a flow type specific surface area measuring device “Flowsorb II” manufactured by Shimadzu Corporation as a specific surface area.
Specific surface area (m ² / g) = surface area (m ² ) / powder mass (g)

  The average particle size is described by defining the particle size (D50) of the cumulative particle size 50 of the volume particle size distribution measured using a laser diffraction particle size distribution analyzer “SALAD-3000” manufactured by Shimadzu Corporation as the average particle size (μm).

  The sphericity is described by defining the ratio of the shortest diameter (μm) / longest diameter (μm) of the particles by observing the shape with a scanning electron microscope. However, the true sphere has a sphericity of “1”.

  The binder resin contained in the conductive ink used in the present invention is preferably a polyester resin. This polyester resin is a polyester resin (A) having a weight average molecular weight of 23,000 to 60,000, a glass point transition temperature of 0 to 10 ° C., and a viscosity of 10 to 30 Pa · s, or a weight average molecular weight of 3000 to 5000, It is preferably used in combination with a polyester resin (B) having a glass transition temperature of 20 to 100 ° C. and a viscosity of 100 to 300 mPa · s.

  In the present invention, the viscosity is described as measured with an RB80 viscometer RB80L manufactured by Toki Sangyo Co., Ltd. The viscosity of the resin was measured by mixing 40 parts of each resin with 60 parts of ethyl diglycol acetate, heating and stirring, and then using the varnish. The measurement was performed at 25 ° C. The polyester (A) was measured using an M4 rotor and the rotational speed was 6 rpm, and the polyester resin (B) was measured using an M1 rotor and the rotational speed was 6 rpm. Moreover, although only a polyester resin (A) may be sufficient, printability improves by using a polyester resin (A) and a polyester resin (B) together.

  The binder resin used in the present invention can be used alone or in combination with the polyester resin (B). Furthermore, other resins can be used in combination. Resins that can be used in combination include acrylic resin, styrene resin, epoxy resin, modified epoxy resin, polyester resin, vinyl chloride-vinyl acetate copolymer, butyral resin, acetal resin, phenol resin, polyurethane resin, alkyd resin, polyolefin resin, fluorine Resins, ketone resins, benzoguanamine resins, melamine resins, urea resins, silicone resins, nitrocellulose, rosin, rosin esters, and the like. The resin to be used in combination can be used in combination with a polyester resin and a nitrocellulose resin depending on the type of printing method, the type of printing substrate, the printing conditions, and the circuit application.

  Moreover, the solvent for diluting these resins can be selected according to the solubility of the resin used. The content of the binder resin in the conductive ink is preferably 5 to 30% by weight, preferably 8 to 25% by weight based on the total solid weight of the conductive ink (100% by weight). More preferred. This is because when the content of the conductive material is less than 70% by weight, the conductivity is not sufficient, and when it exceeds 95% by weight, the printability and conductivity are lowered.

  The polyester resin (A) has a weight average molecular weight of 23,000-60,000, Tg of 0-10 ° C., 40 parts of this resin are mixed with 60 parts of solvent ethyl diglycol acetate, heated and stirred to dissolve the varnish. The viscosity measured by Toki Sangyo Co., Ltd. RB80 viscometer RB80L is preferably 10-30 Pa · s at 25 ° C. and 6 rpm. If it exceeds 60,000, the viscosity becomes high and the printability may be deteriorated. Moreover, if it is less than 23,000, the fine line printability may be deteriorated.

  The polyester resin (B) that can be used in combination with the above polyester resin (A) has a weight average molecular weight of 3,000 to 5,000, Tg of 20 to 100 ° C., and 40 parts of this resin as a solvent ethyl diglycol acetate. The viscosity of the varnish mixed with 60 parts, heated and stirred and dissolved with an RB80 type viscometer RB80L manufactured by Toki Sangyo Co., Ltd. is preferably 100 to 300 mPa · s at 25 ° C. and 6 rpm. Since this polyester resin (B) is added to improve printability, there is no point in mixing when the weight average molecular weight is greater than 5,000, and when the weight average molecular weight is less than 3,000, the viscosity is low. Therefore, there is a high possibility that the fine line printability is deteriorated.

  The ratio of the conductive material to the binder resin is based on the total solid content weight of the conductive ink (100% by weight), the conductive material is 70 to 95% by weight, and the binder resin is 5 to 30% by weight. The binder resin is preferably 8 to 20% by weight with respect to 80 to 92% by weight of the active substance. This is because when the content of the conductive material is less than 70% by weight, the conductivity is not sufficient, and when it exceeds 95% by weight, the printability and conductivity are lowered.

  The solvent contained in the conductive ink used in the present invention is a glycol ether solvent, a ketone solvent, an aromatic solvent, a petroleum solvent, an ester solvent, an aliphatic solvent, depending on the type of printing method, etc. An appropriate amount of an alcohol solvent, water or the like can be used, and two or more kinds can be mixed and used.

  As glycol ether solvents, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol mono n-butyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono n -Propyl ether, propylene glycol mono n-butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol mono n-propyl ether, and dialkyl ethers such as acetic acid ester, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and dipropylene glycol dimethyl ether And examples of the ketone solvents, acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, methyl amyl ketone, isophorone, .gamma.-butyrolactone, and cyclohexanone. In addition, examples of the aromatic solvent include toluene, xylene, alkylbenzene, and the like. Examples of the ester solvents include methyl acetate, ethyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, (iso) amyl acetate, cyclohexyl acetate, ethyl lactate, 3-methoxybutyl acetate, and the like. Examples of the solvent include n-heptane, n-hexane, cyclohexane, methylcyclohexane, and ethylcyclohexane. Examples of the alcohol solvent include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, cyclohexanol, 3- Examples include methoxybutanol and diacetone alcohol. Examples of petroleum solvents include naphthalene hydrocarbon solvents and paraffin hydrocarbon solvents. Other liquid media include dimethyl carbonate, ethyl methyl carbonate, and di-n-butyl carbonate. The said solvent is an illustration and is not limited to these.

  In the method for producing a conductive ink of the present invention, silver powder, binder resin, aluminum chelate and solvent are mixed with a disper. If necessary, it is further mixed and dispersed with three rolls. Finally, filtration is performed to produce a conductive ink.

  Finally, a conductive circuit formed using the conductive ink of the present invention will be described. The conductive ink of the present invention is conventionally known, such as flexographic printing, gravure printing, gravure offset printing, offset printing, screen printing, rotary screen printing, on one or both sides of a substrate such as paper or plastic depending on the intended use. A conductive circuit can be formed by printing using this printing method.

  By using the conductive ink of the present invention, a conductive circuit can be formed by a normal printing method, so that design utilizing existing equipment is possible. In other words, it is possible to print and form the conductive circuit as it is after performing normal printing to enhance the design of the design etc., so compared with the circuit forming method conventionally performed by etching method or transfer method. It is far superior in terms of productivity, initial investment cost, and running cost.

  EXAMPLES The present invention will be described in more detail with reference to the following examples. However, the following examples do not limit the scope of rights of the present invention. In the present invention, “part” means “part by weight”, and “%” means “% by weight” unless otherwise specified.

[Binder 1]
40 parts of polyester resin Byron 300 (weight average molecular weight 23 × 10 ³ , Tg 7 ° C.) manufactured by Toyobo Co., Ltd. was mixed with 60 parts of ethyl carbitol acetate and heated and stirred to prepare varnish-like binder 1.

[Binder 2]
40 parts of polyester resin Byron 630 (weight average molecular weight 23 × 10 ³ , Tg 7 ° C.) manufactured by Toyobo Co., Ltd. was mixed with 60 parts of ethyl carbitol acetate, and heated and stirred to prepare varnish-like binder 2.

[Binder 3]
40 parts of polyester resin Byron 220 (weight average molecular weight 3 × 10 ³ , Tg 53 ° C.) manufactured by Toyobo Co., Ltd. was mixed with 60 parts of ethyl carbitol acetate, and heated and stirred to prepare varnish-like binder 3.

[Binder 4]
40 parts of polyester resin Byron 226 (weight average molecular weight 8 × 10 ³ , Tg 65 ° C.) manufactured by Toyobo Co., Ltd. was mixed with 60 parts of ethyl carbitol acetate, and heated and stirred to prepare varnish-like binder 4.

[Binder 5]
30 parts of Sekisui Chemical Co., Ltd. butyral resin BL-S (calculated molecular weight 2.3 × 10 ⁴ , Tg 61 ° C.) was mixed with 70 parts of butyl carbitol acetate and heated and stirred to prepare varnish-like binder 5.

[Binder 6]
Nitrocellulose resin (33.7 parts) was mixed with propylene glycol monomethyl ether acetate (PGMAC) (51.8 parts) and isopropyl alcohol (IPA) (14.5 parts), followed by heating and stirring to prepare varnish binder 6.

[Silver powder A]
Spherical silver (specific surface area 0.93 m ² / g, tap density 5.5 g / cm ² , average particle size 0.9 μm, sphericity 0.9 to 1.0) made by DOWA Electronics Co., Ltd. It was.

[Silver powder B]
Dowa Electronics Co., Ltd. spherical silver (specific surface area 1.77 m ² / g, tap density 4.0 g / cm ² , average particle size 0.5 μm, sphericity 0.9 to 1.0) silver powder B It was.

[Silver powder C]
Flake silver foil powder Co., Ltd. flake silver (average particle diameter 6.2 μm, specific surface area 0.8 m ² / g) was used as silver powder C.

[Chelate a]
Aluminum chelate (general formula (1)) manufactured by Kawaken Fine Chemical Co., Ltd. was designated as aluminum chelate a.
General formula (1)

[Adjustment of conductive ink]
Silver powder, binder resin, aluminum chelate, and solvent were mixed with a disper at the blending ratios of Examples 1 to 5 and Comparative Examples 1 to 4 shown in Table 1, and mixed and dispersed with three rolls to adjust the conductive ink. And the characteristic of the obtained conductive ink was measured by the following method.

[Production of conductive circuit]
A 15 mm × 60 mm pattern of the conductive ink described in Examples 1 to 5 and Comparative Examples 1 to 4 is screen-printed on a 75 μm thick PET film and dried in a box oven at 180 ° C. for 30 minutes. A conductive circuit was formed.

[Measurement of surface resistivity]
A pattern of 3 mm x 90 mm was screen-printed with the conductive ink described in Examples 1 to 5 and Comparative Examples 1 to 4 on a PET film having a thickness of 75 μm, and obtained after drying for 30 minutes in a box oven at 180 ° C. The resistivity of the printed matter was measured with a resistivity meter Loresta GP manufactured by Mitsubishi Chemical Analytech Co., Ltd.

[Measurement of film thickness]
The film thickness of the printed matter was measured using an MH-15M type measuring instrument manufactured by Sendai Nikon Corporation.

[Calculation of volume resistivity]
The volume resistance value was calculated from the surface resistance value and the film thickness measured by the above method.
The target value of the volume resistance value is 2.5 × 10 ⁻⁵ Ω · cm or less. Although 2.5 to 8.0 × 10 ⁻⁵ Ω · cm has practicality for the time being, it can be determined that there is no practicality at 8.0 × 10 ⁻⁵ or more.

[Measurement of dry film strength]
The film strength of the printed matter was measured using a heat seal tester. Place the aluminum foil on the surface of the printed material printed and dried by the above method, heat seal, peel off the printed material and the aluminum foil by hand, observe the surface of the aluminum foil on the side in contact with the printed material, and visually check the ink. The abundance of was confirmed. The heat sealing condition was performed by applying pressure for 10 seconds at 180 ° C. and 1 fkg / cm 2. In addition, it evaluated with the following evaluation methods.
○: No ink △: There is ink at the edge ×: There is ink

[Confirmation of fine line printability]
A conductive ink described in Examples 1 to 5 and Comparative Examples 1 to 4 was screen printed with a 0.1 mm × 50 mm pattern on a 75 μm thick PET film and dried in a 180 ° C. box oven for 30 minutes. It was. The line width of the printed matter was confirmed with a two-dimensional measuring machine manufactured by Nakamura Seisakusho.
○: Line width is 0.2 μm or less △: Line width is 0.2 μm to 0.4 μm
×: Line width is 0.4 μm or more

[Examples 1 to 5]
The obtained conductive circuit had high conductivity with a volume resistance of 2.5 × 10 ⁻⁵ or less under a dry condition of 180 ° C. for 30 minutes. Further, fine line printability, film strength and the like were good.

[Comparative Examples 1-4]
Comparative Example 1 in which the binder and silver powder are the same as in the example, and no metal chelate is added, and Comparative Example 2 in which the resin of the example is changed, have a high resistance and no practical volume resistance compared to Examples 1-5. Value. In Comparative Example 3 using flake silver, the resistance value and heat seal test were good, but the fine line printability was poor. In Comparative Example 4 in which no nitrocellulose resin was added, the film strength was weak and out of the practical range.

Claims (5)

In a conductive ink containing silver, a binder resin and an aluminum chelate,
Silver has a tap density of 1.0 to 10.0 g / cm ³ ,
BET specific surface area of 0.10 to 5.00 m ² / g,
Average particle size 0.1-5.0 μm
and
Sphericality 0.9-1.0
And
A conductive ink, wherein the binder resin is the following polyester resin (A) and nitrocellulose resin.
The polyester resin (A)
Weight average molecular weight 23,000-60,000,
Glass point transfer temperature 50 ~ 120 ℃
and
Viscosity 10-30Pa · s
It is what is. Furthermore, the weight average molecular weight is 3000 to 5000,
Glass transition temperature 50-120 ° C
and
Viscosity 100-300mPa · s
The conductive ink according to claim 1, wherein the polyester resin (B) is contained in the conductive ink.   The conductive ink according to claim 1 or 2, wherein the aluminum chelate is a metal chelate having a molecular weight of 200 to 300 and containing one ethyl acetoacetate group in one molecule.   A conductive film obtained by applying the conductive ink according to any one of claims 1 to 3 onto a polyethylene terephthalate film substrate and drying it.   The electroconductive circuit formed by apply | coating the conductive ink in any one of Claims 1-3 on a base material, and making it dry.