JP2011187179A - Conductive paste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide conductive paste of an ultraviolet curing type, capable of being comparatively easily and perfectly transcribed from a surface of a silicone blanket onto a surface of a resin film, and, capable of granting desired curing physical properties to a conductive pattern after curing. <P>SOLUTION: The conductive paste is provided by adding unsaturated polyester resin, photopolymerization initiator and conductive powder into a solvent which gives a mass change rate ▵W, of a sample made of a silicone blanket cut out in 2 cm square before and after immersing the sample in the solvent at 23±1°C for 5 hours, of 30 mass% or more. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ultraviolet curable conductive paste used in a printing method using a so-called silicone blanket.

  For example, a conductive pattern such as a conductor wiring or an electrode is formed on a surface of a resin film such as a polyethylene terephthalate (PET) film or a polyimide (PI) film (one side or both sides, the same shall apply hereinafter) using a conductive paste, and a flexible print. When a wiring board or the like is manufactured, a thermosetting conductive paste containing a thermosetting binder resin and conductive powder is generally used as the conductive paste.

After the conductive paste is printed on the surface of the resin film so as to have a predetermined pattern shape, when the binder resin is cured by heating to about 120 to 200 ° C., the conductive paste is cured and adhered to the resin film. Conductivity and conductivity due to the conductive powder are manifested to form a conductive pattern.
As a printing method of the conductive paste, an intaglio offset printing method that can form a conductive pattern having a relatively large thickness and a uniform thickness is suitably employed.

In the intaglio offset printing method, a conductive paste filled in the concave portion of a plate (intaglio plate) having a concave portion corresponding to a conductive pattern to be printed is transferred from the plate to the surface of the blanket, and then the resin film from the surface of the blanket. By retransferring to the surface, a conductive pattern before curing is formed on the surface of the resin film.
The transfer rate of the conductive paste at the time of retransfer is 100%, that is, the conductive paste is completely transferred from the blanket surface to the resin film surface, so-called piling (separation of the conductive paste from the blanket side to the resin film side) Ideally, this should not occur. Therefore, as the blanket, a so-called silicone blanket in which at least the surface thereof is formed of silicone rubber excellent in releasability from the conductive paste is widely used.

However, when using a thermosetting conductive paste, the resin film may be damaged by heating when the conductive paste is printed and then subjected to a curing reaction.
Also, for example, while the resin film is fed out at a constant speed from a raw roll wound with a long resin film, a conductive paste is continuously printed on the surface and thermally cured, and then wound on a roll. When a flexible printed wiring board or the like is continuously produced by the roll-to-roll method, it is necessary to provide a heat treatment zone corresponding to the heating time required for the curing reaction on the line, resulting in a problem that the production equipment becomes large.

For example, when the transport speed (= printing speed) of the resin film is 5 m / min and the time required for heating is 10 minutes, a heat treatment zone as long as 50 m is required.
Therefore, the inventor applied an ultraviolet curable ink technique described in Patent Document 1 and the like to prepare an ultraviolet curable conductive paste that does not cause the above-described problem, and conducted using the conductive paste. We studied the production of flexible printed wiring boards by forming patterns.

  If it is an ultraviolet curable conductive paste, the resin film is less susceptible to damage because it does not need to be heated to a high temperature during the curing reaction by ultraviolet irradiation, and the curing reaction is much shorter than that of a thermosetting conductive paste. Since it can be completed in time, production facilities such as flexible printed wiring boards can be made compact.

JP 62-280804 A

Examples of the ultraviolet curable conductive paste include acrylate-based, unsaturated polyester-based ultraviolet curable components [resin content (prepolymer, oligomer), monomer (including reactive diluent, the same applies hereinafter) and the like], It is common to use a photopolymerization initiator and a conductive powder that basically does not contain a solvent.
When a solvent is included, the solvent inhibits the curing reaction of the ultraviolet curable component, or a large amount of solvent remains in the conductive pattern after curing. As a result, the conductive pattern has desired cured physical properties, that is, strength and goodness. It is because there is a possibility that it may not be possible to impart a good conductivity.

However, the solventless conductive paste has another problem that even when combined with a silicone blanket having excellent releasability, it is difficult to completely transfer to the surface of the resin film during retransfer.
That is, the conductive paste containing a solvent increases in concentration due to evaporation of the solvent from filling the intaglio indentation to retransferring it to the surface of the resin film, and penetration of the solvent and monomer into the silicone blanket. Along with this, the cohesive force gradually increases on the surface of the silicone blanket. Therefore, coupled with the use of a silicone blanket that is inherently more releasable from the conductive paste than the resin film, the conductive paste is relatively easily transferred from the surface of the silicone blanket to the surface of the resin film. Can be completely transferred.

However, with the useless-type conductive paste, complete transfer is difficult because the increase in cohesive force due to evaporation or penetration of the solvent cannot be expected.
An object of the present invention is to provide an ultraviolet curable conductive paste capable of relatively easily completely transferring from the surface of a silicone blanket to the surface of a resin film and imparting desired cured physical properties to a cured conductive pattern. There is to do.

  The inventor made the ultraviolet curable conductive paste contain a solvent and increased the concentration due to evaporation of the solvent or penetration of the liquid component containing the solvent into the silicone blanket, and the accompanying increase in cohesive force. This facilitates complete transfer at the time of retransfer, while reducing the amount of solvent remaining in the conductive pattern before curing printed on the surface of the resin film as much as possible to give the cured conductive pattern the desired cured physical properties. Various studies were made to do this.

  As a result, an unsaturated polyester resin was used as the resin, and in the conductive paste containing the unsaturated polyester resin, photopolymerization initiator, conductive powder, and solvent, the solvent penetrated as quickly as possible into the silicone blanket. What can be done, specifically, a sample in which a silicone blanket actually used for printing is cut into a 2 cm square, and a mass change rate ΔW before and after immersing at 23 ± 1 ° C. for 5 hours is 30% by mass or more. It was found that it should be used.

  As a result, the solvent blended in the conductive paste quickly penetrates into the silicone blanket after the conductive paste is transferred to the surface of the silicone blanket and re-transferred to the surface of the resin film. In combination with the amount of evaporation from the conductive paste, the cohesive force of the conductive paste is greatly increased, and the conductive paste can be completely transferred more reliably during retransfer.

In addition, after re-transferring to the surface of the resin film, the amount of solvent remaining in the conductive pattern before curing should be reduced as much as possible to give desired cured physical properties, that is, strength, good conductivity, etc. to the conductive pattern after curing. Is also possible.
Accordingly, the present invention relates to an ultraviolet curable conductive paste used in a printing method using a silicone blanket having at least a surface made of silicone rubber, comprising an unsaturated polyester resin, a photopolymerization initiator, a conductive powder, and a solvent. And a solvent having a mass change rate ΔW of 30% by mass or more before and after immersing a sample obtained by cutting the silicone blanket into 2 cm square in the solvent at 23 ± 1 ° C. for 5 hours. It is a conductive paste.

When two or more solvents are used in combination, the combination and blending are performed so that the mass change rate ΔW obtained in the same manner as described above using a mixed solvent of the two or more solvents is 30% by mass or more. Just choose.
When the conductive paste contains a liquid monomer, the combination and blending should be performed so that the mass change rate ΔW obtained in the same manner as described above using the mixture of the monomer and the solvent is 30% by mass or more. Just choose.

  That is, the present invention also includes a monomer, and a change in mass before and after immersing a sample obtained by cutting the silicone blanket into 2 cm square as the monomer and solvent in a mixed solution of the monomer and solvent at 23 ± 1 ° C. for 5 hours. It is an electrically conductive paste using what was combined and mix | blended so that ratio (DELTA) W might be 30 mass% or more.

  According to the present invention, there is provided an ultraviolet curable conductive paste that can be relatively easily transferred completely from the surface of the silicone blanket to the surface of the resin film and that can impart desired cured physical properties to the conductive pattern after curing. It becomes possible to do.

  The present invention is an ultraviolet curable conductive paste used in a printing method using a silicone blanket having at least a surface made of silicone rubber, comprising an unsaturated polyester resin, a photopolymerization initiator, a conductive powder, and a solvent. In addition, the solvent is characterized in that a mass change rate ΔW before and after immersing a sample obtained by cutting the silicone blanket into 2 cm square in the solvent at 23 ± 1 ° C. for 5 hours is 30% by mass or more. To do.

Examples of unsaturated polyester resins include unsaturated alkyds produced by polycondensation reaction of polybasic acids such as phthalic anhydride and maleic anhydride with polyhydric alcohols such as glycols, and if necessary, styrene. Any of various kinds of unsaturated polyester resins having radical polymerizability prepared by mixing with a radically polymerizable vinyl monomer can be used.
The unsaturated polyester resin is capable of undergoing a curing reaction by irradiation with ultraviolet rays in the presence of a photopolymerization initiator (radical photopolymerization initiator). The unsaturated polyester resin is supplied in any form of solid (powder to granular etc.) or liquid, and any of these forms can be adopted in the present invention.

  Examples of the unsaturated polyester resin include Iupica (registered trademark) 8523 manufactured by Nippon Iupika Co., Ltd. (softening point (conforms to JIS K2531: 1960, the same applies hereinafter): 92 to 98 ° C., granular), 8524 (softening point: 92 1 such as ~ 98 ° C, powder, 8542 (softening point: 100-104 ° C, powder), 8552 (softening point: 88-94 ° C, granular), 8553 (softening point: 88-94 ° C, granular), etc. A seed | species or 2 or more types is mentioned.

As the solvent, among the various solvents that can dissolve the unsaturated polyester resin satisfactorily, as described above, a sample obtained by cutting a silicone blanket actually used for printing into 2 cm squares is 5 at 23 ± 1 ° C. A solvent having a mass change rate ΔW before and after immersion for 30 hours or more can be selected and used.
For example, as a silicone blanket, on one side of a PET film as a substrate, a room temperature curable and two-component addition reaction type liquid silicone rubber [TSE3450, TSE34555 manufactured by Momentive Performance Materials Japan GK, or Shin-Etsu Chemical Co., Ltd. It has a two-layer structure in which a surface rubber layer is formed by applying a coating solution composed of a mixture of a main agent and a curing agent of Kogyo Co., Ltd. When using a thing, as the solvent,
(1) Propylene glycol monomethyl ether acetate (PGMEA): mass change rate ΔW = 33% by mass,
(2) α-terpineol (TPO): mass change rate ΔW = 81 mass%,
Etc.

A conductive paste is prepared by adding an unsaturated polyester resin, a photopolymerization initiator, and a conductive powder to the solvent. The solvent can be contained in the conductive paste in any ratio that can impart fluidity, viscosity, and the like suitable for a printing method (such as an intaglio offset printing method) in which printing is performed using the conductive paste.
Two or more solvents can be used in combination. In this case, as described above, the combination and blending are performed so that the mass change rate ΔW obtained in the same manner as described above using a mixed solvent of the two or more solvents is 30% by mass or more. Should be selected.

For example, when using the two-layer structure silicone blanket, as the mixed solvent,
(3) Mixed solvent of 60 parts by mass of PGMEA, 30 parts by mass of TPO, and 10 parts by mass of diethylene glycol monobutyl ether acetate (also known as butyl carbitol acetate, BCA): mass change rate ΔW = 45.4% by mass
Etc.

  A conductive paste is prepared by adding the unsaturated polyester resin, the photopolymerization initiator, and the conductive powder while maintaining the combination and blending of the solvents in the mixed solvent. The mixed solvent can be contained in the conductive paste in any proportion that can impart fluidity, viscosity, and the like suitable for a printing method (such as an intaglio offset printing method) in which printing is performed using the conductive paste. .

In addition, mass change rate (DELTA) W in BCA independent is 13 mass%.
The conductive paste of the present invention may contain a monomer. The monomer is in a liquid state, and various radical polymerization properties capable of undergoing a curing reaction with itself or with the unsaturated polyester resin by irradiation with ultraviolet rays in the presence of a photopolymerization initiator (radical photopolymerization initiator). Any monomer having can be used.

  Examples of the monomer include those that are classified as pure monomers and those that are classified as reactive diluents. Among them, the former monomers include, for example, dicyclopentenyloxyethyl acrylate, alkyl-modified dipentaerythritol acrylate. , Ε-caprolactone modified dipentaerythritol acrylate, caprolactone modified tetrahydrofurfuryl acrylate, caprolactone modified hydroxypivalic acid neopentyl glycol ester diacrylate, dipentaerythritol hexa (penta) acrylate, trimethylolpropane triacrylate, 1,6-hexanediol Diacrylate, neopentyl glycol diacrylate, neopentyl glycol hydroxypivalate ester diacrylate, etc. It is.

  Monomers classified as reactive diluents include, for example, isobornyl acrylate, 3-methoxybutyl acrylate, EO-modified bisphenol A diacrylate, ethoxydiethylene glycol acrylate, tetraethylene glycol diacrylate, tetrahydrofurfuryl acrylate, and tripropylene glycol. Examples include diacrylate, trimethylolpropane EO-modified triacrylate, and 1,9-nonanediol diacrylate.

When the monomer is included, the monomer is also involved in the cohesiveness of the conductive paste and has a property of penetrating into the silicone blanket, so that the mass change rate ΔW of the mixed solution of the solvent and the monomer is 30% by mass or more. The combination and formulation are selected as follows.
For example, when using the two-layer structure silicone blanket, as the mixed solution,
(4) Mixed solution of 40 parts by mass of PGMEA, 40 parts by mass of TPO, 10 parts by mass of BCA, and 10 parts by mass of trimethylolpropane triacrylate (TMPTA): mass change rate ΔW = 47% by mass,
(5) A mixed liquid of 35 parts by mass of PGMEA, 20 parts by mass of TPO, 35 parts by mass of BCA, and 5 parts by mass of TMPTA: mass change rate ΔW = 32.4% by mass,
(6) Mixed solution of 40 parts by mass of PGMEA, 40 parts by mass of TPO, 10 parts by mass of BCA, and 10 parts by mass of 1,6-hexanediol diacrylate (HDDA): mass change rate ΔW = 47% by mass,
(7) 35 parts by mass of PGMEA, 20 parts by mass of TPO, 35 parts by mass of BCA, and 5 parts by mass of HDDA: mass change rate ΔW = 32.4% by mass,
Etc.

  A conductive paste is prepared by adding an unsaturated polyester resin, a photopolymerization initiator, and a conductive powder while maintaining the combination and blending of the monomer and solvent in the mixed solution. The mixed liquid can be contained in the conductive paste at an arbitrary ratio that can impart fluidity, viscosity, and the like suitable for a printing method (such as an intaglio offset printing method) for printing using the conductive paste.

The mass change rate ΔW of TMPTA alone is 1% by mass. The mass change rate ΔW of HDDA alone is also 1% by mass.
The mass change rate ΔW of the solvent, the mixed solvent, or the mixed liquid is preferably 50% by mass or less even within the above range. When the mass change rate ΔW exceeds the above range, an excess solvent penetrates into the silicone blanket after the conductive paste is transferred to the surface of the silicone blanket and re-transferred to the surface of the resin film. As a result of the excessive increase in the viscosity of the conductive paste, there is a possibility that it is easy to produce a pile and difficult to complete transfer.

As the photopolymerization initiator, any of various compounds that can generate radicals by ultraviolet irradiation to cause the unsaturated polyester resin and the monomer to undergo a curing reaction can be used.
Examples of the photopolymerization initiator include Irgacure (registered trademark) 651 [2,2-dimethoxy-1,2-diphenylethane-1-one] and Irgacure 184 [1-hydroxycyclohexyl phenyl ketone] manufactured by Ciba. ], Darocur (registered trademark) 1173 [2-hydroxy-2-methyl-1-phenylpropan-1-one], Irgacure 500 [Eutectic mixture of Irgacure 184 and benzophenone], Irgacure 1000 [Irgacure 184 and Darocur 1173 1: 4 mixture], Irgacure 2959 [1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one], Irgacure 907 [2-methyl-1 [ 4- (Methylthio) phenyl] -2-morpholinopropane-1 -On], Irgacure 369 [2-Benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1], Irgacure 1700 [Bis (2,6-dimethoxybenzoyl) -2,4,4- 1: 3 mixture of trimethylpentylphosphine oxide and Darocur 1173], Irgacure 1800 [1: 3 mixture of bis (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide and Irgacure 184], Irgacure 1850 [1: 1 mixture of bis (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide and Irgacure 184], and Irgacure 819 [Bis (2,4,6-trimethylbenzoyl) -phenyl Phosphine oxide] etc. One or two or the like.

The content of the photopolymerization initiator is 1 part by mass or more, particularly 3 parts by mass or more per 100 parts by mass of the unsaturated polyester resin (when no monomer is included) or 100 parts by mass of the total amount of the unsaturated polyester resin and the monomer. Is preferably 10 parts by mass or less, and particularly preferably 8 parts by mass or less.
When the content ratio is less than the above range, there is a possibility that good ultraviolet curability cannot be imparted to the conductive paste. Moreover, not only the effect beyond it is not acquired even if it exceeds the said range, but there exists a possibility of producing a thickening by a time-dependent change.

  Examples of the conductive powder include silver, copper, gold, platinum, nickel, aluminum, iron, palladium, chromium, molybdenum, tungsten, manganese, cobalt and other metal powders, and powders of two or more alloys of the above metals, silver Examples thereof include one or more of a powder of a plating complex such as plated copper and a powder of a metal oxide such as silver oxide, cobalt oxide, iron oxide, and ruthenium oxide.

Among them, silver that can form a conductive pattern with excellent conductivity because it has high conductivity and is excellent in oxidation resistance that hardly generates a highly insulating oxide is preferable.
The conductive powder preferably has a 50% cumulative diameter D ₅₀ of a particle size distribution of 0.05 μm or more, particularly 0.1 μm or more, preferably 10 μm or less, particularly 2 μm or less. By setting the particle size of the conductive powder within the above range, it is possible to prepare a conductive paste that is excellent in printability when used in the intaglio offset printing method and can finely reproduce fine conductive patterns in detail.

  Further, the shape of the conductive powder is preferably spherical or granular for improving the printing suitability, and is scaly for increasing the contact area between the conductive powders and increasing the conductivity of the conductive pattern. Is preferred. Further, in order to further densely fill the conductive powder and further increase the conductivity of the conductive pattern, the scale-like conductive powder and the spherical or granular conductive powder may be used in combination.

The content of the conductive powder is 500 parts by mass or more, particularly 700 parts by mass or more per 100 parts by mass of the unsaturated polyester resin (when no monomer is included) or 100 parts by mass of the total amount of the unsaturated polyester resin and the monomer. Is preferably 1500 parts by mass or less, and particularly preferably 1100 parts by mass or less.
If the content ratio is within this range, the conductive pattern formed by printing the conductive paste can be provided with good conductivity suitable for, for example, the conductor wiring or electrode of the flexible printed wiring board.

The conductive paste of the present invention is used in a printing method using a silicone blanket having at least its surface formed of silicone rubber, such as an intaglio offset printing method as described above.
As the silicone blanket, the whole is made of a single layer of silicone rubber, or has a two-layer structure in which a surface rubber layer made of silicone rubber is laminated on one side of a base material made of PET film, metal foil or the like, or Examples thereof include those having a multilayer structure in which any one layer or two or more layers are interposed between the base material and the surface rubber layer.

The silicone rubber is preferably, for example, a silicone rubber that is liquid or pasty when uncured.
For example, in the case of a two-layer silicone blanket, when the liquid rubber or paste-like silicone rubber is applied on a substrate and cured to form a surface rubber layer, the surface of the surface rubber layer is liquid or paste when cured. Can be smoothed by the self-leveling effect. Therefore, it is possible to obtain a silicone blanket having an extremely small surface roughness suitable for forming a highly accurate conductive pattern.

Alternatively, the blanket may be produced by injecting the liquid or pasty silicone rubber into a mold and curing it while forming it into the shape of the surface rubber layer.
In addition to the intaglio offset printing method, a printing method using the silicone blanket and the conductive paste of the present invention includes, for example, a reverse printing method.
In the reversal printing method, a conductive paste is applied to substantially the entire surface of the silicone blanket and brought into contact with a plate having a non-image area protruding thereon, so that the conductive paste corresponding to the non-image area is applied to the surface of the plate. By selectively transferring, a conductive pattern is formed on the surface of the silicone blanket. Thereafter, the formed conductive pattern is transferred to the surface of the resin film, and then irradiated with ultraviolet rays to cause a curing reaction, whereby a flexible printed wiring board or the like is manufactured.

Production of the following silicone blankets, preparation, measurement and testing of conductive pastes in Examples and Comparative Examples were carried out in an environment with a temperature of 23 ± 1 ° C. and a relative humidity of 55 ± 1%, unless otherwise specified.
<Production of silicone blanket>
After mixing 10 parts by mass of the main agent and 1 part by mass of the curing agent of liquid silicone rubber (TSE3450 manufactured by Momentive Performance Materials Japan GK) that is a room temperature curing type and a two-component addition reaction type, defoaming is performed. A coating solution for the surface rubber layer was prepared, and the coating solution was applied on one side of a PET film having a thickness of 0.25 mm as a substrate using a bar coater, and then allowed to stand at room temperature for 24 hours to undergo a curing reaction. A surface rubber layer having a thickness of 0.70 mm and a type A durometer hardness (conforming to JIS K6253: 2006) of A30 / S was formed to prepare a silicone blanket having a two-layer structure.

Example 1
<Preparation of conductive paste>
90 parts by mass of unsaturated polyester resin [Yupika (registered trademark) 8524 manufactured by Japan Upica Co., Ltd.], 900 parts by mass of silver powder [AgC-A manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.], radical photopolymerization initiator [ 2-methyl-1 [4- (methylthio) phenyl] -2-morpholinopropan-1-one, 3 parts by mass of Irgacure (registered trademark) 907 manufactured by Ciba, and radical photopolymerization initiator [2-hydroxy 2-methyl-1-phenyl-propan-1-one, Darocur (registered trademark) 1173 manufactured by Ciba, Ltd.] and the following monomers and solvent were blended and kneaded using three rolls. A conductive paste was prepared.

(monomer)
Trimethylolpropane triacrylate (TMPTA): 10 parts by mass (solvent)
Propylene glycol monomethyl ether acetate (PGMEA): 40 parts by mass Diethylene glycol monobutyl ether acetate (BCA): 10 parts by mass α-terpineol (TPO): 40 parts by mass (Measurement of mass change rate ΔW)
A mixture is prepared by blending only the one type of monomer and three types of solvent in the same proportion as that contained in the conductive paste, and the previously prepared two-layer silicone blanket is added to the mixture. A sample cut into a 2 cm square was weighed and then immersed at 23 ± 1 ° C. for 5 hours.

At this time, the entire sample is completely immersed in the mixed solution, and even if a decrease in the mixed solution and an increase in the volume of the sample occur due to the penetration of the mixed solution into the sample, 5 hours have passed. In the meantime, attention was paid to the amount of the mixed solution and the relative state so that the entire sample was kept completely immersed in the mixed solution.
When 5 hours have passed since the immersion, the sample was pulled out of the mixed solution, and after removing the mixed solution adhering to the surface without penetrating into the sample, the sample was weighed immediately, and the mass change rate ΔW from the measured value before and after the immersion. Was 47% by mass.

Example 2
A conductive paste was prepared in the same manner as in Example 1 except that the amount of the unsaturated polyester resin was 95 parts by mass and the amounts of the monomer and the solvent were the following values.
(monomer)
TMPTA: 5 parts by mass (solvent)
PGMEA: 35 parts by mass BCA: 35 parts by mass TPO: 20 parts by mass Further, when the mass change rate ΔW was determined in the same manner as in Example 1 for the mixture of the monomer and the solvent, it was 32.4% by mass.

Example 3
A conductive paste was prepared in the same manner as in Example 1 except that the amount of the unsaturated polyester resin was 100 parts by mass, the monomer was omitted, and the amount of the solvent was the following value.
(solvent)
PGMEA: 60 parts by mass BCA: 10 parts by mass TPO: 30 parts by mass Further, when the mass change rate ΔW was determined in the same manner as in Example 1 for the mixed solvent containing only the three solvents, it was 45.4% by mass.

<< Comparative Example 1 >>
A conductive paste was prepared in the same manner as in Example 1 except that the amounts of monomer and solvent were set to the following values.
(monomer)
TMPTA: 10 parts by mass (solvent)
PGMEA: omitted BCA: 75 parts by mass TPO: 15 parts by mass Further, the mass change rate ΔW was determined in the same manner as in Example 1 for the mixed solution of the monomer and the solvent, and found to be 22% by mass.

<< Comparative Example 2 >>
In place of the unsaturated polyester resin, 100 parts by mass of a modified epoxy acrylate resin [EBECRYL (Evecryl, registered trademark) 3708 manufactured by Daicel-Cytec Co., Ltd.] was used, the nomer was omitted, and the amount of the solvent was changed to the following value: A conductive paste was prepared in the same manner as in Example 1 except that.

(solvent)
PGMEA: omitted BCA: 40 parts by mass TPO: 60 parts by mass The mass change rate ΔW was determined in the same manner as in Example 1 for the mixed solvent containing only the two solvents described above, and it was 53.8% by mass.

《Printing test》
The previously prepared silicone blanket was mounted on an intaglio offset printing machine (Original Printing Machine Co., Ltd.). As the intaglio plate, a soda lime glass plate having a stripe-shaped recess having a line width of 80 μm, a pitch of 200 μm, and a depth of 30 μm was used.

And while supplying the conductive paste prepared in Examples and Comparative Examples to the intaglio, a stripe-shaped conductive pattern corresponding to the recess was printed on one side of the PET film by an intaglio offset printing method, and then a metal halide lamp was used. The conductive pattern was cured by irradiating ultraviolet rays under conditions of 3000 J / cm ² .
Of the series of printing operations, the transferability in the process of retransferring the conductive paste from the surface of the silicone blanket to the surface of the PET film, that is, the conductive paste is not completely transferred to the surface of the PET film. Whether or not there was a transfer failure (pyring) in which the portion remained on the surface of the silicone blanket was determined by observing the surface of the silicone blanket and the surface of the PET film.

Specifically, a part of the conductive paste remaining on the surface of the silicone blanket was evaluated as having a piling (x), and a part not remaining was evaluated as a complete transfer (◯).
For the completely transferred material, the specific resistance [μΩ · cm] of the conductive pattern after being cured by ultraviolet irradiation was measured.
The results are shown in Table 1.

From the results of Comparative Example 2 in Table 1, when a modified epoxy acrylate resin was used instead of the unsaturated polyester resin, even when the mass change rate ΔW of the mixed solvent was set to 30% by mass or more, during retransfer It was found that the conductive paste could not be completely transferred.
Further, from the result of Comparative Example 1, even when an unsaturated polyester resin was used, the specific resistance of the conductive pattern after curing was significantly increased when the mass change rate ΔW of the mixed liquid was less than 30% by mass. It was found that a large amount of solvent remained in the pattern and the desired cured properties could not be obtained.

  On the other hand, from the results of Examples 1 to 3, the unsaturated polyester resin was used, and the mass change rate ΔW of the mixed liquid or mixed solvent was set to 30% by mass or more, so that the resin film was removed from the surface of the silicone blanket. It has been found that it can be completely transferred onto the surface relatively easily, and the desired cured properties can be imparted by minimizing the amount of solvent remaining in the conductive pattern after curing.

Claims (2)

  An ultraviolet curable conductive paste used in a printing method using a silicone blanket having at least a surface made of silicone rubber, comprising an unsaturated polyester resin, a photopolymerization initiator, a conductive powder, and a solvent, As a conductive paste, a sample having a mass change rate ΔW before and after immersing a sample obtained by cutting the silicone blanket into 2 cm square in the solvent at 23 ± 1 ° C. for 5 hours is 30% by mass or more. .   A mass change rate ΔW before and after immersing a sample obtained by cutting the silicone blanket into a 2 cm square as the monomer and solvent in a mixed solution of the monomer and the solvent at 23 ± 1 ° C. for 5 hours is 30%. The conductive paste according to claim 1, wherein a combination and a combination so as to be at least% are used.