JP5410176B2 - Membrane wiring board manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a membrane wiring board.

  Membrane wiring boards are used as connecting wiring materials for substrates of notebook computers and switch circuits for digital home appliances. The membrane wiring board is formed by printing a silver paste on a flexible film such as plastic to form a circuit layer (see Patent Document 1 below). Thus, the membrane wiring board can be easily manufactured at a lower cost than a flexible printed wiring board (FPC) in which a circuit layer is formed by etching or plating copper on a plastic film. It is becoming popular as a product.

JP 2006-261198 A

  By the way, in recent years, there has been a demand for further downsizing of the membrane wiring board, and accordingly, the circuit layer has been multilayered. In order to increase the number of circuit layers, it is necessary to coat each circuit layer with an insulating layer. As the conductive powder contained in the silver paste, flaky or spherical silver particles are used.

  However, if flaky silver particles are used as the conductive powder in the silver paste, the resistance of the circuit layer increases when the insulating coating layer is formed by applying the resin composition to the circuit layer and curing it. In some cases, the conductivity was lowered. This is an obstacle to manufacturing a membrane wiring board having multiple circuit layers.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for manufacturing a membrane wiring board capable of forming a circuit layer having excellent conductivity even when covered with an insulating coating layer. To do.

  As a result of intensive studies to solve the above problems, the present inventor has found that components (for example, solvents and low molecular weight components) in the resin composition are contained in the circuit layer when the resin composition is applied to the circuit layer and cured. It was thought that the conductive powder in contact with each other would be separated from each other by swelling or dissolving the binder resin contained in the circuit layer, thereby reducing the conductivity. Therefore, as a result of further earnest research, the present inventor applied a so-called solventless ultraviolet curable ink that does not use an organic solvent to the circuit layer and cured it to form an insulating coating layer. It has been found that the above-mentioned problems can be solved by suppressing swelling or dissolution of the binder resin therein, and the present invention has been completed.

That is, the present invention provides a first step of applying a conductive paste on a plastic substrate to form a first circuit layer, and coating the first circuit layer with a resin composition to form a first insulating coating layer. And a second step of applying a conductive paste to form a second circuit layer, and coating the second circuit layer with a resin composition to form a second insulating coating layer. The conductive paste contains conductive powder and a binder resin, the conductive powder is composed of flaky silver particles, and the resin composition is composed of ultraviolet curable ink. A method for manufacturing a membrane wiring board.

According to this method for manufacturing a membrane wiring board, the conductive paste is applied to form a first circuit layer, and the first circuit layer is coated with ultraviolet curable ink as a resin composition and cured to form a first insulating layer. When the coating layer is formed, since the ultraviolet curable ink usually does not contain an organic solvent, it is difficult to swell or dissolve the binder resin in the first circuit layer when applying the resin composition to the first circuit layer. It is difficult to separate the silver particles from each other. For this reason, an increase in the resistance of the first circuit layer is sufficiently suppressed. Similarly, the conductive paste is applied to the first insulating coating layer to form a second circuit layer, and UV curable ink is applied as a resin composition to the second circuit layer and cured to form the second insulating coating layer. When the resin composition is formed, when the resin composition is applied to the second circuit layer, the ultraviolet curable ink hardly swells or dissolves the binder resin in the second circuit layer, and the flaky silver particles are hardly separated from each other. For this reason, an increase in the resistance of the second circuit layer is sufficiently suppressed. Therefore, the first and second circuit layers having excellent conductivity even when covered with the insulating coating layer are realized.

In the method for manufacturing a membrane wiring board, the binder resin is preferably a saturated polyester resin. In this case, there is an advantage that adhesion to a substrate, particularly a PET substrate is improved.

  Here, it is preferable that the ultraviolet curable ink contains polyurethane (meth) acrylate.

  In this case, the ultraviolet curable ink is hardly swollen or dissolved by the binder resin in the conductive paste. For this reason, the circuit layer which has the more excellent electroconductivity is realizable.

  In the present invention, the flaky silver particles refer to particles having a ratio of the maximum length to the minimum length exceeding 1.1 when only the conductive powder is observed with an electron microscope having a magnification of 1000 to 3000 times. And

ADVANTAGE OF THE INVENTION According to this invention, even if it coat | covers with an insulation coating layer, the manufacturing method of the membrane wiring board which can form the circuit layer which has the outstanding electroconductivity is provided.

It is a top view which shows the membrane wiring board manufactured by one Embodiment of the manufacturing method of the membrane wiring board of this invention. It is sectional drawing along the II-II line of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 and 2.

  FIG. 1 is a plan view showing an embodiment of a membrane wiring board according to the present invention, and FIG. 2 is a sectional view taken along line II-II in FIG. As shown in FIGS. 1 and 2, the membrane wiring board 100 of the present embodiment includes a plastic substrate 1, a first circuit layer 2 a provided on the plastic substrate 1, and a first circuit on the plastic substrate 1. A first insulating covering layer 3 provided to cover the layer 2a, a second circuit layer 2b provided on the first insulating covering layer 3, and a second circuit layer 2b on the first insulating covering layer 3 And a second insulating coating layer 4 provided.

  Each of the first circuit layer 2a and the second circuit layer 2b includes conductive powder and a binder resin. The conductive powder is composed of flaky silver particles, and the flaky silver particles are held in contact with each other.

  The membrane wiring board 100 can be obtained as follows.

  First, a plastic substrate 1 is prepared. The plastic which comprises the plastic base material 1 will not be specifically limited if it is a plastic. Examples of such plastics include polyester resins such as polyethylene terephthalate resin (PET) and polyethylene naphthalate resin (PEN), polyimide, and polyetherimide.

  Next, a conductive paste is prepared. As the conductive paste, a paste containing conductive powder and a binder resin is used. The conductive powder is composed of flaky silver particles. That is, the content of the flaky silver particles in the conductive powder is 100% by mass.

The average particle size of the flaky silver particles in the conductive powder is not particularly limited, but is usually 0.1 to 20 μm, preferably 0.5 to 10 μm, and more preferably 1.0. ˜6.0 μm. The particle size of the flaky silver particles is the following formula when the silver particles are observed with an electron microscope:
Particle size = (minimum length + maximum length) / 2
The value calculated by.

  As the binder resin, a saturated polyester resin, an acrylic resin, an epoxy resin, or the like is used. Among these, a saturated polyester resin is preferable from the viewpoint of suppressing curing shrinkage of the conductive paste.

  The conductive paste usually contains a solvent in addition to the conductive powder and the binder resin. As the solvent, organic solvents such as ethanol, propanol, tetrahydrofuran, isophorone, terpineol, triethylene glycol monobutyl ether, butyl cellosolve acetate, and carbitol acetate can be used.

  In the conductive paste, the conductive powder is preferably added in an amount of 230 to 1900 parts by mass, more preferably 400 to 900 parts by mass, with respect to 100 parts by mass of the binder resin. When the addition amount of the conductive powder is within the above range, there is an advantage that the conductivity of the first circuit layer 2a and the second circuit layer 2b can be further improved, and the printability and coating film characteristics are also improved.

  Next, the conductive paste is applied onto the plastic substrate 1 by a printing method. As the printing method, for example, a screen printing method, a gravure printing method, a transfer printing method, a roll coating method, or the like can be employed.

  Next, the conductive paste is dried. The drying may be performed at a temperature of 120 ° C. to 180 ° C. for 30 to 120 minutes, for example. Thereby, the solvent in the conductive paste is removed, and the flaky silver particles come into contact with each other. Thus, the first circuit layer 2 a is obtained on the plastic substrate 1.

  Next, the first insulating coating layer 3 is formed on the plastic substrate 1 so as to cover the first circuit layer 2a (first step). The first insulating coating layer 3 can be obtained by applying a resin composition to the first circuit layer 2a on the plastic substrate 1 and curing it. At this time, ultraviolet curable ink is used as the resin composition. Here, the ultraviolet curable ink includes an ultraviolet curable resin and a photopolymerization initiator.

  Since the ultraviolet curable ink generally does not contain an organic solvent, it is difficult to swell or dissolve the binder resin in the first circuit layer 2a when the resin composition is applied to the first circuit layer 2a. For this reason, an increase in resistance of the first circuit layer 2a is suppressed, and the first circuit layer 2a having higher conductivity is realized.

  Examples of the ultraviolet curable resin include polyester (meth) acrylate, polyurethane (meth) acrylate, and polyether (meth) acrylate. When a saturated polyester resin is used as the binder resin in the first circuit layer 2a, polyurethane (meth) acrylate is preferable because the binder resin in the conductive paste is less likely to swell.

  The resin composition is cured by irradiating the resin composition with ultraviolet rays.

  Next, a conductive paste similar to the above is applied onto the first insulating coating layer 3 by a printing method and dried. Drying can be performed in the same manner as in the case of drying the conductive paste. Thus, the second circuit layer 2 b is obtained on the first insulating coating layer 3.

  Finally, the second insulating coating layer 4 is formed on the first insulating coating layer 3 so as to cover the second circuit layer 2b (second step). Similarly to the first insulating coating layer 3, the second insulating coating layer 4 is also applied and cured on the first insulating coating layer 3 so as to cover the second circuit layer 2 b. At this time, as the resin composition, an ultraviolet curable ink is used as in the case where the first insulating coating layer 3 is formed. Thus, the membrane circuit board 100 is obtained.

  According to the manufacturing method of the membrane circuit board 100 described above, the conductive paste is applied on the plastic substrate 1 and dried to form the first circuit layer 2a. Further, the first circuit layer 2a is UV cured as a resin composition. When the first insulating coating layer 3 is formed by applying and curing the mold ink, the binder resin in the conductive paste is sufficiently suppressed from being swollen or dissolved by the components in the resin composition. For this reason, the flaky silver particles are held in contact with each other. Therefore, an increase in resistance of the first circuit layer 2a can be suppressed, and the first circuit layer 2a having excellent conductivity can be realized. Similarly, a conductive paste is applied on the first insulating coating layer 3 and dried to form the second circuit layer 2b. Further, an ultraviolet curable ink is applied to the second circuit layer 2b as a resin composition and cured. Even when the second insulating coating layer 4 is formed, the binder resin in the conductive paste is sufficiently suppressed from being swollen or dissolved by the components in the resin composition. For this reason, the flaky silver particles are held in contact with each other. Therefore, an increase in resistance of the second circuit layer 2b can be suppressed, and the second circuit layer 2b having excellent conductivity can be realized. For this reason, the membrane wiring board 100 is extremely useful for multilayering circuit layers.

  The present invention is not limited to the above embodiment. For example, in the above embodiment, two circuit layers are formed, but three or more circuit layers may be formed. In this case, the step of forming a circuit layer using the conductive paste, applying the resin composition to the circuit layer, and curing it to form an insulating coating layer may be repeated.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and the content of this invention is demonstrated more concretely, this invention is not limited to a following example.

Example 1
First, a conductive paste was prepared as follows. That is, flaky silver particles, a binder resin, an organic solvent, and a curing agent were mixed and kneaded with three rolls to obtain a conductive paste. At this time, the flaky silver particles and the binder resin were mixed in the ratio shown in Table 1, and 20 parts by mass of the curing agent was added to 100 parts by mass of the binder resin. In addition, the ratio shown in Table 1 shows a ratio when the solid content base, that is, the total solid content is 100% by mass. Specifically, the following were used as the flaky silver particles, binder resin, organic solvent and curing agent.
Flaky silver particles: S-303 (average particle size 2.4 μm) manufactured by Daiken Chemical Industry Co., Ltd.
Binder resin: Byron 300 manufactured by Toyobo Co., Ltd.
Organic solvent: Carbitol acetate curing agent: Dismodule TPLS2759 (Block HMDI)

  Next, the conductive paste was applied onto a plastic substrate made of polyethylene terephthalate having a thickness of 75 μm by a screen printing method so as to form a printing pattern of a predetermined shape, and dried at 150 ° C. for 30 minutes. The printed pattern is composed of a linear portion and a rectangular lead terminal portion provided at both ends of the linear portion, and the linear portion has a thickness after drying of 8 μm, a width of 0.4 mm, and a length of 5 cm. The extraction terminal portion was formed so that the thickness after drying was 8 μm, the width was 3 mm, and the length was 5 mm. A first circuit layer was thus obtained on the plastic substrate.

Next, as a resist ink (resin composition), an ultraviolet curable ink (PTF-6D manufactured by Kyoyo Chemical Industry Co., Ltd.) is applied so as to cover the straight portion of the first circuit layer and expose the lead terminal portion. By using a metal halide lamp to output light having an intensity of 1000 mJ / cm ² , the ultraviolet curable ink was cured by irradiating the ultraviolet curable ink with ultraviolet rays. Subsequently, in the same manner as described above, the ultraviolet curable ink is applied on the ultraviolet curable ink cured by ultraviolet irradiation, and the ultraviolet curable ink is irradiated with ultraviolet rays in the same manner as described above. Then, the ultraviolet curable ink was cured. Thus, a first insulating coating layer having a thickness of 24 μm was obtained.

  Next, the conductive paste was applied onto the first insulating coating layer so as to form a pattern with a predetermined shape by screen printing, and dried at 150 ° C. for 30 minutes. This pattern is the same pattern as the first circuit layer, and the dimensions are the same as those of the first circuit layer. Thus, a second circuit layer was obtained on the first insulating coating layer.

  Finally, an ultraviolet curable ink, which is a resist ink used in the manufacture of the first circuit layer, is applied so as to cover the second circuit layer so as to cover the linear portion of the second circuit layer and expose the lead terminal portion. The ultraviolet curable ink was cured by irradiating the ultraviolet curable ink with ultraviolet rays in the same manner as described above. Subsequently, in the same manner as described above, the ultraviolet curable ink used for the production of the first circuit layer was applied over the ultraviolet curable ink cured by ultraviolet irradiation, and the ultraviolet curable ink was applied to the ultraviolet curable ink. The ultraviolet curable ink was cured by irradiating with ultraviolet rays in the same manner as described above. A second insulating coating layer having a thickness of 24 μm was thus obtained. A membrane wiring board was obtained as described above.

(Example 2)
As flaky silver particles in the conductive paste, S-302 (average particle size) manufactured by Daiken Chemical Industry Co., Ltd. was used instead of S-303 (average particle size 2.4 μm) manufactured by Daiken Chemical Industry Co., Ltd. A membrane wiring board was obtained in the same manner as in Example 1 except that the material of 6.2 μm) was used.

(Example 3)
As the conductive paste, FA-353N manufactured by Fujikura Kasei Co., Ltd. was used, and as a resin composition for forming the first and second insulating coating layers, instead of PTF-6D manufactured by Reciprocal Chemical Industry Co., Ltd. A membrane wiring board was obtained in the same manner as in Example 1 except that the average particle diameter of the flaky silver particles and the resin material of the ultraviolet curable ink were changed by using PTF-250G manufactured by Chemical Industry Co., Ltd. In addition, Fujikura Kasei Co., Ltd. FA-353N contains the flaky silver particle and binder resin in the mixture ratio shown in Table 1.

Example 4
A membrane wiring board was obtained in the same manner as in Example 1, except that FA-353N manufactured by Fujikura Kasei Co., Ltd. was used as the conductive paste.

(Comparative Example 1)
As a resist ink (resin composition) for forming the first and second insulating coating layers, a polyester resin composition (XB-101G manufactured by Fujikura Kasei Co., Ltd.), which is a solvent-type ink, is used instead of the ultraviolet curable ink. In the same manner as in Example 1 except that the polyester resin composition was cured by heating at 150 ° C. for 30 minutes in a box-type heating furnace to form the first insulating coating layer and the second insulating coating layer. A membrane wiring board was obtained.

(Comparative Example 2)
As a resist ink (resin composition) for forming the first and second insulating coating layers, a polyester resin composition (XB-101G manufactured by Fujikura Kasei Co., Ltd.), which is a solvent-type ink, is used instead of the ultraviolet curable ink. In the same manner as in Example 2 except that the first insulating coating layer and the second insulating coating layer were formed by heating and curing the polyester resin composition at 150 ° C. for 30 minutes in a box-type heating furnace. A membrane wiring board was obtained.

(Comparative Example 3)
As a resist ink (resin composition) for forming the first and second insulating coating layers, a polyester resin composition (CRA manufactured by Asahi Chemical Research Co., Ltd.), which is a solvent-type ink, is used instead of the ultraviolet curable ink. 18G), and the polyester resin composition was heated at 150 ° C. for 30 minutes in a box-type heating furnace and cured to form the first insulating coating layer and the second insulating coating layer. Thus, a membrane wiring board was obtained.

(Comparative Example 4)
As a resist ink (resin composition) for forming the first and second insulating coating layers, a polyester resin composition (XB-101G manufactured by Fujikura Kasei Co., Ltd.), which is a solvent-type ink, is used instead of the ultraviolet curable ink. In the same manner as in Example 4 except that the polyester resin composition was heated and cured at 150 ° C. for 30 minutes in a box-type heating furnace to form the first insulating coating layer and the second insulating coating layer. A membrane wiring board was obtained.

<Evaluation of conductivity of first circuit layer and second circuit layer>
The following characteristics were evaluated for the membrane wiring boards obtained in Examples 1 to 4 and Comparative Examples 1 to 4.
During the manufacture of the membrane wiring boards obtained in Examples 1 to 4 and Comparative Examples 1 to 4, the resistance (R1) immediately after printing / drying of the first circuit layer was measured, and the first after the membrane wiring board was completed. The resistance (R1 ′) of one circuit layer was measured. The results are shown in Table 1. At this time, the resistances R1 and R1 ′ were measured by a four-terminal method. And the resistance increase rate is given by the following formula:
Resistance increase rate = 100 × (R1′−R1) / R1
Calculated based on The results are shown in Table 1.

In addition, during the manufacture of the membrane wiring boards obtained in Examples 1 to 4 and Comparative Examples 1 to 4, the resistance (R2) immediately after printing and drying of the second circuit layer was measured, and after completion of the membrane wiring board The resistance (R2 ′) of the second circuit layer was measured. The results are shown in Table 1. At this time, the resistances R2 and R2 ′ were also measured by the four-terminal method. And the resistance increase rate is given by the following formula:
Resistance increase rate = 100 × (R2′−R2) / R2
Calculated based on The results are shown in Table 1.

  In addition, the resistance value and resistance increase rate of each Example and comparative example in Table 1 show the average value of the resistance value and resistance increase rate measured about ten membrane wiring boards.

  From the results shown in Table 1, the membrane wiring boards of Examples 1 to 4 are able to realize a circuit layer having excellent electrical conductivity with a marked increase in resistance compared to the membrane wiring boards of Comparative Examples 1 to 4. I understood.

Therefore, according to the method for manufacturing a membrane wiring board of the present invention, it was confirmed that a circuit layer having excellent conductivity can be formed even when covered with an insulating coating layer.

  DESCRIPTION OF SYMBOLS 1 ... Plastic base material, 2a ... 1st circuit layer, 2b ... 2nd circuit layer, 3 ... 1st insulating coating layer, 4 ... 2nd insulating coating layer, 100 ... Membrane wiring board.

Claims (3)

A first step of applying a conductive paste on a plastic substrate to form a first circuit layer, and coating the first circuit layer with a resin composition to form a first insulating coating layer; the forming a second circuit layer by applying, met manufacturing method of the second step and, the way to membrane wiring board obtained the second circuit layer forming a second insulating coating layer coated with a resin composition And
The conductive paste includes conductive powder and a binder resin,
The conductive powder is composed of flaky silver particles,
The resin composition is composed of ultraviolet curable ink;
A method for manufacturing a membrane wiring board characterized by the above. The method for manufacturing a membrane wiring board according to claim 1, wherein the binder resin is a saturated polyester resin. The method for producing a membrane wiring board according to claim 2, wherein the ultraviolet curable ink contains polyurethane (meth) acrylate.

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