Patent Description:
It is known that, in order to seal hydrogen gas, oxygen gas or the like in fuel cells composed of a laminate structure of a number of cells, a gasket composed of a rubber material or a synthetic resin material having rubber-like elasticity and having a flat upper surface is provided on the surface of a substrate such as a separator constituting a fuel cell.

The gasket can be manufactured by a press molding method, an injection molding method or the like, but there has been a proposal of a manufacturing method in which screen printing is used in consideration of the takt time (for example, refer to Patent Literature <NUM> (<CIT>)).

In the case of forming the gasket by screen printing, a procedure of the following (<NUM>) to (<NUM>) is performed.

Incidentally, there has been a demand for, as the gasket, a gasket having a relatively thick thickness of approximately <NUM> to <NUM>.

However, studies by the present inventors showed that, in a case where an attempt is made to manufacture a gasket having a thick thickness by screen printing using an ink composition having a relatively low viscosity (paste composed of a non-crosslinked rubber material), the ink composition is likely to adhere to a screen mask, it becomes difficult for the ink composition to be extruded and a printing defect such as print sagging is likely to occur.

Therefore, as an ink composition for screen printing (paste composed of a non-crosslinked rubber material), the use of an ink composition having a high thixotropic property or an ink composition having a high viscosity has been considered; however, as a result of studies by the present inventors, it was clarified that, in the case of using an ink composition having a high thixotropic property or an ink composition having a high viscosity, rough surface portions such as mesh marks (screen marks) are likely to be generated on the surface of a gasket to be obtained, and the appearance or the performance is likely to become poor.

With such a circumstance, an objective of the present invention is to provide an ink composition for screen printing that does not easily allow the generation of a printing defect or a rough surface portion in a printed matter even in the case of forming the printed matter having a thick thickness and a method for producing a printed matter using such an ink composition for screen printing.

In order to achieve the above-described objective, as a result of intensive studies, the present inventors found that the above-described technical problem can be solved with an ink composition for screen printing containing (a) a rubber-forming component, (b) a crosslinking agent, (c) a main solvent that dissolves the rubber-forming component and (d) a poor solvent that dissolves in the main solvent but does not dissolve in the rubber-forming component, in which a viscosity (<NUM>/s) obtained with an E-type viscometer at a temperature of <NUM> is <NUM> to <NUM> Pa·s, a viscosity (<NUM>/s) obtained with the E-type viscometer at a temperature of <NUM> is <NUM> to <NUM> Pa·s, and a loss tangent (<NUM> rad/s) obtained with the E-type viscometer at a temperature of <NUM> is <NUM> to <NUM>, and completed the present invention based on the present finding.

Hereinafter, (c) the main solvent that dissolves the rubber-forming component will be referred to as "(c) main solvent", and (d) the poor solvent that dissolves in the main solvent and does not dissolve in the rubber-forming component will be referred to as "(d) poor solvent" as appropriate, respectively.

According to the present invention, (d) the poor solvent that dissolves in the main solvent but does not dissolve in the rubber-forming component is employed as a solvent that constitutes the ink composition for screen printing together with (c) the main solvent that dissolves the rubber-forming component, whereby the cohesion of the rubber-forming component in the ink composition is improved, the adhesion to screen masks is reduced, and the extrudability is improved, which makes it possible to reduce printing defects.

In addition, according to the present invention, the viscosity (<NUM>/s) of the ink composition for screen printing obtained with an E-type viscometer at a temperature of <NUM> is <NUM> to <NUM> Pa·s, whereby it is possible to suitably suppress print sagging, and, the viscosity (<NUM>/s) of the ink composition for screen printing obtained with an E-type viscometer at a temperature of <NUM> is <NUM> to <NUM> Pa·s, whereby it is possible to suitably guarantee printability.

Furthermore, according to the present invention, the loss tangent (<NUM> rad/s) of the ink composition for screen printing obtained with an E-type viscometer at a temperature of <NUM> is <NUM> to <NUM>, whereby the adhesion of the ink composition to screen masks is reduced, and the extrudability improves, which makes it possible to more effectively suppress the generation of printing defects.

Therefore, according to the present invention, it is possible to provide an ink composition for screen printing that does not easily allow the generation of a printing defect or a rough surface portion in a printed matter even in the case of forming the printed matter having a thick thickness and a method for producing a printed matter using such an ink composition for screen printing.

An ink composition for screen printing according to the present invention contains.

In the ink composition for screen printing according to the present invention, (a) the rubber-forming component means a component composed of (a-<NUM>) only a rubber component or (a-<NUM>) a mixture of a rubber component and a plasticizer.

In the ink composition for screen printing according to the present invention, as the rubber component constituting (a) the rubber-forming component, specifically, at least one selected from silicone rubber, acrylic rubber, chloroprene rubber, polysulfide rubber, urethane rubber, butyl rubber, natural rubber, ethylene-propylene rubber, nitrile rubber, fluoro rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene rubber, chlorosulfonated polyethylene rubber, polyisobutylene, modified silicone and the like can be exemplified, one or more selected from ethylene-propylene-diene rubber, fluoro rubber and acrylonitrile-butadiene rubber are preferable, and ethylene-propylene-diene rubber is more preferable.

In the ink composition for screen printing according to the present invention, in a case where (a) the rubber-forming component is composed of (a-<NUM>) the mixture of a rubber component and a plasticizer, the plasticizer is not particularly limited as long as the plasticizer is capable of adjusting the polymer viscosity of the rubber-forming component to be within a desired range and can be selected as appropriate from substances that are well known as plasticizers or softeners for rubber.

Specifically, for example, in a case where the rubber component is ethylene-propylene-diene rubber (EPDM), one or more selected from ethylene-propylene rubber (EPM), fatty acid ester, phthalate ester, aliphatic dibasic acid ester, phosphate ester, trimellitate, polyester, ricinoleic acid ester, acetate ester, mineral oil and the like can be exemplified as the plasticizer constituting the rubber-forming component.

In the ink composition for screen printing according to the present invention, the polymer viscosity (<NUM> rad/s) of (a) the rubber-forming component is preferably <NUM> to <NUM> Pa·s, more preferably <NUM> to <NUM> Pa·s and still more preferably <NUM> to <NUM> Pa·s.

In the ink composition for screen printing according to the present invention, since the polymer viscosity (<NUM> rad/s) of (a) the rubber-forming component is within the above-described range, when the ink composition has been extruded from a screen mask during screen printing and then an extruded matter has been dried or heated and cured with a crosslinking agent, it is possible to easily reduce the viscosity of the extruded matter to a desired range and to easily improve the leveling property (surface flatness) of the extruded matter.

In the present application document, the polymer viscosity (<NUM> rad/s) of the rubber-forming component means a value obtained by measurement with an E-type viscometer (RHEOMETER MCR301 manufactured by Anton Paar GmbH) using a parallel plate (PP12) having a diameter of <NUM> under conditions of <NUM>, an angular frequency of <NUM> radians/second and a strain of <NUM>% in a state where a polymer-forming component is dissolved in the main solvent and then dried with hot air at <NUM> for <NUM> hours or longer to completely remove the solvent.

The content of the rubber component in the ink composition for screen printing according to the present invention is preferably <NUM> to <NUM> mass%, more preferably <NUM> to <NUM> mass% and still more preferably <NUM> to <NUM> mass%.

In a case where the ink composition for screen printing according to the present invention contains a plasticizer in the rubber-forming component, the content of the plasticizer in the ink composition for screen printing according to the present invention is preferably <NUM> to <NUM> mass%, more preferably <NUM> to <NUM> mass% and still more preferably <NUM> to <NUM> mass%.

In addition, the content of (a) the rubber-forming component in the ink composition for screen printing according to the present invention is preferably <NUM> to <NUM> mass%, more preferably <NUM> to <NUM> mass%, still more preferably <NUM> to <NUM> mass% and far still more preferably <NUM> to <NUM> mass%.

In the ink composition for screen printing according to the present invention, (b) the crosslinking agent is not particularly limited as long as the crosslinking agent is capable of crosslinking the rubber component in (a) the rubber-forming component, can be selected as appropriate from well-known crosslinking agents and is preferably a thermal crosslinking agent.

In the ink composition for screen printing according to the present invention, as (b) the crosslinking agent, specifically, one or more selected from sulfur, an organic peroxide, a quinoid compound, a phenolic resin, an amine, a metal oxide, a polyol compound and the like can be exemplified.

The content of (b) the crosslinking agent in the ink composition for screen printing according to the present invention is preferably <NUM> to <NUM> mass%, more preferably <NUM> to <NUM> mass% and still more preferably <NUM> to <NUM> mass%.

When the ink composition for screen printing according to the present invention contains (b) the crosslinking agent within the above-described range, it is possible to suitably crosslink the rubber component in (a) the rubber-forming component.

The ink composition for screen printing according to the present invention contains (c) the main solvent that dissolves the rubber-forming component.

In the ink composition for screen printing according to the present invention, (c) the main solvent that dissolves the rubber-forming component is not particularly limited as long as the main solvent is capable of dissolving (c) the rubber-forming component, and, for example, in a case where the rubber component is ethylene-propylene-diene rubber (EPDM), one or more selected from aromatic hydrocarbons such as toluene, benzene, styrene and xylene, and aliphatic hydrocarbons such as hexane, heptane, octane, nonane, decane, undecane and dodecane can be exemplified.

In the present application document, "dissolving the rubber-forming component" means that, when a <NUM>-thick rubber-forming component molded into a sheet is cut into a square that is <NUM> in length and <NUM> in width, and the obtained cut piece and the main solvent are introduced in proportions of <NUM>:<NUM> in terms of weight ratio, stirred with a stirrer for <NUM> hours and then further left still for <NUM> hours, there is no undissolved residue found by visual observation.

In the ink composition for screen printing according to the present invention, (d) the poor solvent that dissolves in the main solvent but does not dissolve in the rubber-forming component can be selected as appropriate depending on the kind of (a) the rubber-forming component, and, for example, in a case where the rubber component is ethylene-propylene-diene rubber (EPDM), one or more selected from ester-based solvents such as diethylene glycol monoethyl ether acetate or butyl lactate, ether-based solvents and the like can be exemplified.

In the present application document, "dissolving in the main solvent" means that, when the main solvent and the poor solvent are mixed in proportions of <NUM>:<NUM> in terms of volume ratio and left still for <NUM> hours in a glass container, no emulsification or separation is found by visual observation.

In the present application document, "not dissolving in the rubber-forming component" means that, when the rubber-forming component containing <NUM> to <NUM> mass% of a colored filler such as carbon black and the poor solvent are introduced in proportions of <NUM>:<NUM> in terms of weight ratio, stirred with a stirrer for <NUM> hours and then further left still for <NUM> hours, there is no rubber-forming component (colored with the filler) in a dispersed state found by visual observation.

The ink composition for screen printing according to the present invention contains (d) the poor solvent together with (c) the main solvent, whereby the cohesion of the rubber-forming component in the ink composition is improved, the adhesion of the ink composition to screen masks is reduced, and the extrudability is improved, which makes it possible to effectively suppress the occurrence of print sagging.

In the ink composition for screen printing according to the present invention, the boiling points of (c) the main solvent and (d) the poor solvent are not particularly limited as long as the influence on continuous printability of drying during screen printing is small and drying during drying is not difficult and are preferably <NUM> to <NUM>, more preferably <NUM> to <NUM> and still more preferably <NUM> to <NUM>.

In the ink composition for screen printing according to the present invention, regarding the content ratio between (c) the main solvent that dissolves the rubber-forming component and (d) the poor solvent that dissolves in the main solvent but does not dissolve in the rubber-forming component, the mass ratio, which is represented by the ratio of (c) the main solvent that dissolves the rubber-forming component: (d) the poor solvent that dissolves in the main solvent but does not dissolve in the rubber-forming component, is preferably <NUM>:<NUM> to <NUM>:<NUM>, more preferably <NUM>:<NUM> to <NUM>:<NUM> and still more preferably <NUM>:<NUM> to <NUM>:<NUM>.

In the ink composition for screen printing according to the present invention, the content ratio between (c) the main solvent that dissolves the rubber-forming component and (d) the poor solvent that dissolves in the main solvent but does not dissolve in the rubber-forming component is within the above-described range, whereby the cohesion of the rubber-forming component in the ink composition is improved, the adhesion of the ink composition to screen masks is reduced, and the extrudability is improved, which makes it possible to effectively suppress the occurrence of print sagging.

The ink composition for screen printing according to the present invention may contain, aside from (a) the rubber-forming component, (b) the crosslinking agent, (c) the main solvent that dissolves the rubber-forming component and (d) the poor solvent that dissolves in the main solvent but does not dissolve in the rubber-forming component, for example, one or more selected from a filler, a plasticizer, a dispersant, a crosslinking aid, an anti-foaming agent, a foaming agent and the like.

The total content of (c) the main solvent and (d) the poor solvent in the ink composition for screen printing according to the present invention is preferably <NUM> to <NUM> mass%, preferably <NUM> to <NUM> mass%, more preferably <NUM> to <NUM> mass% and still more preferably <NUM> to <NUM> mass%.

In the ink composition for screen printing according to the present invention, the viscosity (<NUM>/s) obtained with an E-type viscometer at a temperature of <NUM> is <NUM> to <NUM> Pa·s, preferably <NUM> to <NUM> Pa·s, more preferably <NUM> to <NUM> Pa·s and still more preferably <NUM> to <NUM> Pa·s.

In the ink composition for screen printing according to the present invention, the viscosity (<NUM>/s) obtained with an E-type viscometer at a temperature of <NUM> is within the above-described range, whereby it is possible to more effectively suppress the occurrence of print sagging even in a case where a printed matter having a thick thickness has been formed.

In the present application document, the viscosity (<NUM>/s) obtained with an E-type viscometer at a temperature of <NUM> means a viscosity that is measured using an E-type viscometer (RHEOMETER MCR301 manufactured by Anton Paar GmbH) at a temperature of <NUM> under a condition of a shear rate of <NUM>/s.

In the ink composition for screen printing according to the present invention, the viscosity (<NUM>/s) obtained with an E-type viscometer at a temperature of <NUM> is <NUM> to <NUM> Pa·s, preferably <NUM> to <NUM> Pa·s and more preferably <NUM> to <NUM> Pa·s.

In the ink composition for screen printing according to the present invention, the viscosity (<NUM>/s) obtained with an E-type viscometer at a temperature of <NUM> is within the above-described range, whereby screen printing is possible while the printability is suitably guaranteed.

In the ink composition for screen printing according to the present invention, the loss tangent (<NUM> rad/s) obtained with an E-type viscometer at a temperature of <NUM> is preferably <NUM> to <NUM>, preferably <NUM> to <NUM> and more preferably <NUM> to <NUM>.

In the ink composition for screen printing according to the present invention, the loss tangent (<NUM> rad/s) obtained with an E-type viscometer at a temperature of <NUM> is within the above-described range, whereby the adhesion of the ink composition to screen masks is reduced, and the extrudability improves, which makes it possible to effectively suppress the occurrence of print sagging.

In the ink composition for screen printing according to the present invention, the loss tangent (<NUM> rad/s) obtained with an E-type viscometer at a temperature of <NUM> can be easily controlled by adjusting the kinds and blending proportions of (c) the main solvent and (d) the poor solvent with respect to (a) the rubber-forming component and (b) the crosslinking agent.

In the present application document, the loss tangent (<NUM> rad/s) obtained with an E-type viscometer at a temperature of <NUM> means a value obtained by measurement with an E-type viscometer (RHEOMETER MCR301 manufactured by Anton Paar GmbH) using a parallel plate (PP25) having a diameter of <NUM> under conditions of a sample thickness of <NUM>, <NUM>, an angular frequency of <NUM> radians/second and a strain of <NUM>% in a state where the ink composition for screen printing has been stirred for <NUM> hours or longer, it has been visually confirmed that there is no rubber-forming component left undispersed or undissolved and then air bubbles inside have been removed by vacuum defoaming.

A method for preparing the ink composition for screen printing according to the present invention is not particularly limited.

The ink composition for screen printing according to the present invention can be prepared by, for example, collecting each of (a) the rubber-forming component, (b) the crosslinking agent and, furthermore, other components as necessary in a desired amount, then, kneading the components using a well-known kneader such as an intermix, a kneader or a Banbury mixer or a well-known kneading device such as an open roll, furthermore, adding (c) the main solvent that dissolves the rubber-forming component and (d) the poor solvent that dissolves in the main solvent but does not dissolve in the rubber-forming component to the obtained kneaded matter and, furthermore, kneading the components using a well-known stirrer.

A method for screen printing using the ink composition for screen printing according to the present invention is as described in detail in the description of a method for producing a printed matter according to the present invention to be described below.

The ink composition for screen printing according to the present invention can be suitable used at the time of printing printed matters having a thick thickness by screen printing.

The ink composition for screen printing according to the present invention can be suitably used at the time of, for example, forming gaskets by screen printing and can be suitably used at the time of forming gaskets for fuel cells by screen printing.

According to the present invention, it is possible to provide an ink composition for screen printing that does not easily allow the generation of a printing defect or a rough surface portion in a printed matter even in the case of forming the printed matter having a thick thickness.

Next, a method for producing a printed matter of the present invention will be described.

The method for producing a printed matter of the present invention is characterized by screen-printing the ink composition for screen printing according to the present invention and then curing it to form a printed matter.

The details of the ink composition for screen printing according to the present invention, which is used in the method for producing a printed matter of the present invention, are as described above.

In the method for producing a printed matter of the present invention, for example, a procedure of the following (<NUM>) to (<NUM>) can be performed.

The thickness of the printed matter can be easily controlled by adjusting the thickness of the screen mask.

The thickness of the printed matter obtained by the production method according to the present invention is preferably <NUM> or more, more preferably <NUM> or more, still more preferably <NUM> to <NUM> and far still more preferably <NUM> to <NUM>.

In the present application document, the thickness of the printed matter means the maximum value when a cross section of the printed matter is cut out and eight points are measured with a microscope.

In the method for producing a printed matter of the present invention, since the ink composition for screen printing according to the present invention is used, it is possible to conveniently form a printed matter while the generation of a printing defect such as print sagging or a rough surface portion is suppressed even when the thickness of a printed matter to be obtained is thick.

In the method for producing a printed matter of the present invention, a gasket can be exemplified as the printed matter to be obtained, and a gasket for fuel cells can be exemplified as the gasket.

In a case where the printed matter that is obtained by the production method according to the present invention is a gasket for a fuel cell, a separator or the like constituting the fuel cell can be exemplified as the substrate forming the printed matter.

In a case where the substrate is a separator, it is possible to easily form an integrated matter of the separator and the gasket.

According to the present invention, it is possible to provide a method for producing a printed matter enabling a printed matter to be conveniently formed while the generation of a printing defect such as print sagging or a rough surface portion is suppressed even when the thickness of a printed matter to be obtained is thick.

Next, the present invention will be more specifically described using examples, which are simply examples and do not limit the present invention.

As shown in Table <NUM>, <NUM> parts by weight of ethylene propylene diene rubber <NUM> (EPDM1) as (a) a rubber-forming component, <NUM> parts by weight of (b) a crosslinking agent and <NUM> parts by weight of carbon black were kneaded with an open roll to produce a kneaded matter, <NUM> parts by weight of dodecane, which was (c) a main solvent, and <NUM> parts by weight of diethylene glycol monoethyl ether acetate (EDGAC), which was (d) a poor solvent, were further added to the obtained kneaded matter and stirred with a stirrer, thereby preparing an ink composition for screen printing.

The polymer viscosity (<NUM> rad/s) of the rubber-forming component was <NUM> Pa·s.

In addition, for the obtained ink composition for screen printing, the loss tangent (<NUM> rad/s) obtained with an E-type viscometer at a temperature of <NUM> was <NUM>, the viscosity (<NUM>/s) obtained with the E-type viscometer at a temperature of <NUM> was <NUM> Pa·s, and the viscosity (<NUM>/s) obtained with the E-type viscometer at a temperature of <NUM> was <NUM> Pa·s.

Screen printing was performed under the following conditions in the same manner as in Example <NUM> using the obtained ink composition for screen printing to obtain a gasket having a thickness of <NUM>, and the proportion of the ink composition adhering to a screen mask and the number of rough surface portions in the obtained printed matter were measured. The results are shown in Table <NUM>.

The ink composition for screen printing was supplied onto the screen mask (<NUM> meshes/inch), opening parts of the screen mask were filled with the ink composition with a scraper, and then the ink composition filling the opening parts was transferred to a base material with a squeegee. The transferred ink composition was dried at <NUM> for <NUM> minutes with a hot air oven and then heated at <NUM> for <NUM> minutes to be crosslinked and cured, thereby obtaining an intended gasket.

Four arbitrary sites in the printed part on the screen mask used during the screen printing were each observed at a magnification of <NUM> times using a microscope, and the degree of adhesion to the screen mask at each observation site was obtained by the following equation.

Degree of adhesion to screen mask = (the number of screen openings to which the ink composition adheres/the number of all screen openings except openings in the peripheral parts of the observation sites) × <NUM>.

After that, the arithmetic average value of the degrees of adhesion was obtained as the proportion of the ink composition adhering to the screen mask, and the property of the ink composition for suppressing adhesion to the screen mask was evaluated according to the following standards.

O: The proportion of the ink composition adhering to the screen mask is <NUM>% to <NUM>%.

X: The proportion of the ink composition adhering to the screen mask is more than <NUM>% and <NUM>% or less.

An arbitrary site on the surface of the gasket obtained by the screen printing was observed at a magnification of five times using a microscope, and (the number of rough surface portions such as screen marks/the total observation area) × <NUM> in such an observation site was obtained as the number of rough surface portions.

As shown in Table <NUM>, <NUM> parts by weight of ethylene propylene diene rubber <NUM> (EPDM1) as (a) a rubber-forming component, <NUM> parts by weight of a plasticizer <NUM>, <NUM> parts by weight of (b) a crosslinking agent and <NUM> parts by weight of carbon black were kneaded with an open roll to produce a kneaded matter, <NUM> parts by weight of dodecane, which was (c) a main solvent, and <NUM> parts by weight of diethylene glycol monoethyl ether acetate (EDGAC), which was (d) a poor solvent, were further added to the obtained kneaded matter and stirred with a stirrer, thereby preparing an ink composition for screen printing.

Screen printing was performed in the same manner as in Example <NUM> using the obtained ink composition for screen printing to obtain a gasket having a thickness of <NUM>, and the proportion of the ink composition adhering to a screen mask and the number of rough surface portions in the obtained printed matter were measured in the same manner as in Example <NUM>. The results are shown in Table <NUM>.

As shown in Table <NUM>, <NUM> parts by weight of ethylene propylene diene rubber <NUM> (EPDM1) as (a) a rubber-forming component, <NUM> parts by weight of (b) a crosslinking agent and <NUM> parts by weight of carbon black were kneaded with an open roll to produce a kneaded matter, and <NUM> parts by weight of dodecane, which was (c) a main solvent, was further added to the obtained kneaded matter and stirred with a stirrer, thereby preparing an ink composition for screen printing.

As shown in Table <NUM>, <NUM> parts by weight of ethylene propylene diene rubber <NUM> (EPDM2) as (a) a rubber-forming component, <NUM> parts by weight of (b) a crosslinking agent and <NUM> parts by weight of carbon black were kneaded with an open roll to produce a kneaded matter, <NUM> parts by weight of dodecane, which was (c) a main solvent, and <NUM> parts by weight of diethylene glycol monoethyl ether acetate (EDGAC), which was (d) a poor solvent, were further added to the obtained kneaded matter and stirred with a stirrer, thereby preparing an ink composition for screen printing.

As shown in Table <NUM>, <NUM> parts by weight of ethylene propylene diene rubber <NUM> (EPDM3) as (a) a rubber-forming component, <NUM> parts by weight of (b) a crosslinking agent and <NUM> parts by weight of carbon black were kneaded with an open roll to produce a kneaded matter, and <NUM> parts by weight of dodecane, which was (c) a main solvent, was further added to the obtained kneaded matter and stirred with a stirrer, thereby preparing an ink composition for screen printing.

As shown in Table <NUM>, <NUM> parts by weight of ethylene propylene diene rubber <NUM> (EPDM2) as (a) a rubber-forming component, <NUM> parts by weight of (b) a crosslinking agent and <NUM> parts by weight of carbon black were kneaded with an open roll to produce a kneaded matter, and <NUM> parts by weight of dodecane, which was (c) a main solvent, and <NUM> parts by weight of butyl lactate, which was (d) a poor solvent, were further added to the obtained kneaded matter and stirred with a stirrer, thereby preparing an ink composition for screen printing.

As shown in Table <NUM>, <NUM> parts by weight of ethylene propylene diene rubber <NUM> (EPDM1) as (a) a rubber-forming component, <NUM> parts by weight of (b) a crosslinking agent and <NUM> parts by weight of carbon black were kneaded with an open roll to produce a kneaded matter, and <NUM> parts by weight of decane, which was (c) a main solvent, was further added to the obtained kneaded matter and stirred with a stirrer, thereby preparing an ink composition for screen printing.

As shown in Table <NUM>, <NUM> parts by weight of ethylene propylene diene rubber <NUM> (EPDM1) as (a) a rubber-forming component, <NUM> parts by mass of a plasticizer <NUM>, <NUM> parts by weight of (b) a crosslinking agent and <NUM> parts by weight of carbon black were kneaded with an open roll to produce a kneaded matter, <NUM> parts by weight of dodecane, which was (c) a main solvent, and <NUM> parts by weight of diethylene glycol monoethyl ether acetate (EDGAC), which was (d) a poor solvent, were further added to the obtained kneaded matter and stirred with a stirrer, thereby preparing an ink composition for screen printing.

As shown in Table <NUM>, it is found that the ink compositions for screen printing obtained in Example <NUM> to Example <NUM> contain (a) the rubber-forming component and (b) the crosslinking agent, have a viscosity (<NUM>/s) of <NUM> to <NUM> Pa·s obtained with the E-type viscometer at a temperature of <NUM> and a viscosity (<NUM>/s) of <NUM> to <NUM> Pa·s obtained with the E-type viscometer at a temperature of <NUM> and contain, as solvents constituting the ink composition for screen printing, (d) the poor solvent that dissolves in the main solvent but does not dissolve in the rubber-forming component together with (c) the main solvent that dissolves the rubber-forming component, whereby the cohesion of the rubber-forming component in the ink composition is effectively improved by controlling the loss tangent (<NUM> rad/s) obtained with the E-type viscometer to <NUM> to <NUM>, and the extrudability can be improved by suppressing the adhesion amount of the ink composition during screen printing.

In addition, as shown in Table <NUM>, it is found that the ink compositions for screen printing obtained in Example <NUM> to Example <NUM> contain, as solvents constituting the ink composition for screen printing, (c) the main solvent and (d) the poor solvent, and (d) the poor solvent volatilizes during a drying treatment or during a heating and curing treatment with (b) the crosslinking agent after screen printing, whereby the viscosities of extruded matters during drying reduce compared with those immediately after extrusion with the screen mask, the leveling property (surface flatness) is easily improved, and the number of rough surface portions can be reduced.

In contrast, as shown in Table <NUM>, it is found that the ink compositions for screen printing for comparison obtained in Comparative Example <NUM> to Comparative Example <NUM> do not contain (d) the poor solvent that dissolves in the main solvent but does not dissolve in the rubber-forming component together with (c) the main solvent that dissolves the rubber-forming component, and thus the adhesion amounts of the ink composition during screen printing are high, additionally, it is not possible to improve the leveling properties (surface flatness) of extruded matters after extrusion with the screen mask, and the numbers of rough surface portions exhibit high numerical values.

Claim 1:
An ink composition for screen printing comprising:
(a) a rubber-forming component;
(b) a crosslinking agent;
(c) a main solvent that dissolves the rubber-forming component; and
(d) a poor solvent that dissolves in the main solvent but does not dissolve in the rubber-forming component,
wherein a viscosity (<NUM>/s) obtained with an E-type viscometer at a temperature of <NUM> is <NUM> to <NUM> Pa·s,
a viscosity (<NUM>/s) obtained with the E-type viscometer at a temperature of <NUM> is <NUM> to <NUM> Pa·s, and
a loss tangent (<NUM> rad/s) obtained with the E-type viscometer at a temperature of <NUM> is <NUM> to <NUM>.