JP4667740B2 - Printed wiring board - Google Patents

Description

  The present invention relates to a protective ink mixture that is applied onto a conductor circuit of a printed wiring board such as a flexible printed circuit board (FPC) to protect and insulate the conductor circuit.

A membrane switch having a structure in which an electrically conductive paste such as silver paste is printed on a base film such as polyethylene terephthalate by screen printing to form a conductor circuit and an insulating protective layer is provided on the conductor circuit is known. Yes.
Such membrane switches are widely used as switches for various electric devices such as computer devices, audio devices, video devices, and OA devices.

  The insulation protective layer of this membrane switch is mainly made by applying a protective ink mixture and solidifying it. As this protective ink mixture, a polyethylene terephthalate film is often used as a base film. Therefore, an admixture mainly composed of a vinyl chloride resin, a saturated polyester resin, an acrylic resin or the like is mainly used from the viewpoint of adhesiveness.

  By the way, about such a membrane switch, the flame retardant property is calculated | required from the viewpoint of disaster prevention, and the flame retardant property is requested | required also for the insulating protective layer. For this reason, a blend of a halogen-based flame retardant such as decabromodiphenyl ether has been studied as a protective ink mixture for forming an insulating protective layer.

  However, in the flame retardant protective ink blend to which this kind of halogen flame retardant is added, harmful halogen-containing gas is generated during disposal by incineration of membrane switches etc. using this flame retardant protective ink blend. Therefore, there is a drawback that it must be avoided.

For this reason, a lot of non-halogen flame retardants such as metal hydroxides such as aluminum hydroxide and magnesium hydroxide are blended.
However, in the insulating protective layer containing a large amount of metal hydroxide, there is a big problem that the adhesion to the base film is lowered, and the sliding resistance and insulation are lowered.
Examples of prior art documents relating to the protective ink mixture used for such applications include the following.
JP 2002-189289 A Japanese Patent Laid-Open No. 11-18134

  Therefore, the problem in the present invention is that, in a protective ink mixture used for an insulating protective layer such as a printed wiring board such as a membrane switch, the adhesive strength to the base film is high, and the sliding resistance and the insulating property are reduced. The object is to obtain a flame-retardant protective ink mixture that is non-halogen and has sufficient flame retardancy.

To solve this problem,
The invention according to claim 1 is a printed wiring board in which a protective insulating film is formed on a conductive circuit on an insulating substrate made of polyethylene terephthalate using a protective ink mixture, and the protective ink mixture is 100 parts by weight of polyester resin and 60 to 150 parts by weight of melamine cyanurate having an average particle size of 5 μm or less, and 100 parts by weight of polyester resin is 60 to 80 parts by weight of polyester resin having a glass transition temperature of −15 ° C. to −18 ° C. Part and 20 to 40 parts by weight of a polyester resin having a glass transition temperature of 15 ° C. to 20 ° C., the weight average molecular weight of the polyester resin is 10,000 to 30,000, and the surface of the melamine cyanurate is not surface-treated. It is a printed wiring board .

The invention according to claim 2 is the printed wiring board according to claim 1 , wherein the protective ink mixture is one in which an isocyanate curing agent or an amine curing agent is added .

The invention according to claim 3 is the printed wiring board according to claim 1 or 2, which passes UL standard VTM-2.

The protective ink mixture of the present invention exhibits good adhesion and high flame retardancy, and no harmful halogen-containing gas is generated even when incinerated. Moreover, the coloring of the protective insulating layer can be made light and light, and the customer does not feel uncomfortable.
In addition, when a polyester resin containing 60 to 80 parts by weight of a polyester resin having a glass transition temperature of -15 ° C to -18 ° C and 20 to 40 parts by weight of a polyester resin having a glass transition temperature of 15 ° C to 20 ° C is used. Can prevent a decrease in bending resistance caused by the addition of melamine cyanurate, and the conductor resistance is not increased by bending the insulating substrate, and the protective insulating film is not cracked or cracked. .

  Moreover, in the printed wiring board of the present invention, the protective insulating layer exhibits a good adhesive force, has high flame resistance that passes UL standard VTM-2, and has sliding resistance. It will be excellent. In addition, since it is non-halogen, no harmful halogen-containing gas is generated even when incinerated. Further, the protective insulating layer is lightly colored and has an excellent appearance.

Hereinafter, the present invention will be described in detail based on the embodiments.
1 and 2 each show an example of a printed wiring board of the present invention, and reference numeral 1 in the drawing indicates a base film that serves as an insulating substrate.
The base film 1 is a film having a thickness of 10 to 200 μm made of a saturated polyester such as polyethylene terephthalate or polyethylene naphthalate, a plastic such as polyimide, polyphenylene sulfide, polyethylene, polypropylene, or polyamide. Among these plastic films, polyethylene terephthalate film is preferable in terms of electrical characteristics, mechanical characteristics, cost, and the like.

  On one surface (FIG. 1) or both surfaces (FIG. 2) of the base film 1, a conductor circuit 2 having a desired pattern shape is formed. The conductor circuit 2 is formed by an additive method in which a conductive paste such as a silver paste is printed on the base film 1 by a printing method such as screen printing, and is solidified by a solidifying means such as heating. Is about 10 to 100 μm and the line width is about 0.05 to 10 mm.

A protective insulating layer 3 having a thickness of 10 to 300 μm is provided on the conductor circuit 2 so as to cover it. This protective insulating layer 3 only needs to cover at least the conductor circuit 2, and may cover a part or all of the base film 1 other than the conductor circuit 2. If necessary, two or more conductor circuits 2 and protective insulating layers 3 may be laminated to form a multi-layer electric circuit on the base film 1.
The protective insulating layer 3 is formed by printing or applying a protective ink mixture described below and solidifying and curing by heating.

  The protective ink mixture used here contains 100 parts by weight of a polyester resin and 60 to 150 parts by weight of melamine cyanurate having an average particle diameter of 5 μm or less as essential components.

  Examples of the polyester resin include acid components such as terephthalic acid, isophthalic acid, diphenylcarboxylic acid, adipic acid, succinic acid, and sabacic acid, ethylene glycol, 1,4-butanediol, 1,4-dicyclohexanedimethylol, neo Various saturated polyester resins and saturated copolyester resins obtained by a known condensation polymerization method using alcohol components such as pentyl glycol and diethylene glycol as raw materials are used.

The polyester resin preferably has a weight average molecular weight in the range of 500 to 50,000, preferably 10,000 to 30,000 because the mechanical strength of the protective insulating layer 3 is increased. The molecular weight is adjusted by appropriately controlling various polymerization conditions during the condensation polymerization reaction between the acid component and the alcohol component, such as polymerization temperature, polymerization time, polymerization pressure, and type of polymerization catalyst.
Although this is no particular limitation on the glass transition temperature of the polyester resin, the glass transition temperature in the range of -30 ° C. to 70 ° C. are preferred Nari high mechanical strength of the protective insulating layer 3 to be obtained.

  In addition, as a polyester resin, 100 parts by weight thereof includes 60 to 80 parts by weight of a polyester resin having a glass transition temperature of −15 ° C. to −18 ° C. and 20 to 40 parts by weight of a polyester resin having a glass transition temperature of 15 ° C. to 20 ° C. It is preferable to use this blend polymer because the protective insulating film is soft and flexible and the bending resistance is improved.

  Further, in this polyester resin, in order to improve the adhesion and bending resistance of the protective ink blend to the base film 1 made of a plastic film, a curing agent such as an isocyanate curing agent or an amine curing agent is blended, It is preferable to crosslink this at the polymer terminal of the polyester resin forming the binder.

  The blending amount of the curing agent is 3 to 30 parts by weight, preferably 5 to 20 parts by weight, with respect to 100 parts by weight of the polyester resin forming the binder. If it exceeds 30 parts by weight, the crosslinking proceeds excessively, the flexibility of the protective insulating layer 3 is lowered, and the bending resistance is lowered.

Melamine cyanurate is used as the flame retardant used in the protective ink blend of the present invention.
This melamine cyanurate is a non-halogen flame retardant and does not lower the electrical resistance of the protective insulating layer 3. As the melamine cyanurate, those whose surface is not surface-treated and whose average particle diameter is 5 μm or less are used. In the case of the surface treatment, the flame retardancy (UL standard VTM-2) of the printed wiring board using this is unacceptable, and in the case where the average particle diameter exceeds 5 μm, the dispersibility to the polyester resin is inconvenient. In addition, the bending property is reduced due to the deterioration of the coating properties of the protective insulating layer, and the insulating property is deteriorated due to moisture absorption and water immersion.

  The blending amount of the melamine cyanurate is 60 to 150 weights in the form in which the conductor circuit 2 and the protective insulating layer 3 are provided on both surfaces of the base film 1 as shown in FIG. 2 with respect to 100 parts by weight of the polyester resin. 1 and 2, in the form in which the conductor circuit 2 and the protective insulating layer 3 are provided on both sides or one side of the base film 1 as shown in FIGS. 1 and 2, the amount is 80 to 120 parts by weight, and less than 60 parts by weight. The flame retardancy is insufficient, and if it exceeds 150 parts by weight, the adhesive strength is lowered and the kneadability is also lowered.

Further, various additives such as an organic solvent, an antioxidant, a metal corrosion inhibitor, a colorant, various coupling agents, a crosslinking agent, a crosslinking aid, and an antistatic agent are added as long as the effects of the present invention are not impaired. You may add suitably.
Examples of the organic solvent include ketones such as methyl ethyl ketone and methyl isobutyl ketone, esters such as ethyl acetate and butyl acetate, and aromatics such as toluene.

  The protective ink blend of the present invention can be produced by uniformly mixing 100 parts by weight of a polyester resin, 60 to 150 parts by weight of melamine cyanurate, and other additive components as required.

  Moreover, as a form of the protective ink mixture of the present invention, it can be a form of a solution, a paste or the like. In order to form the protective insulating layer 3, as a solution type, on the conductor circuit 2 of the base film 1 It can be used by being applied by a printing method such as screen printing or a bar coating method.

  In such a protective ink blend, since 100 parts by weight of a polyester resin and 60 to 150 parts by weight of melamine cyanurate are blended, sufficient flame retardancy is obtained, and when this is disposed of by incineration Does not produce halogen-containing compounds that are harmful to water.

  In the printed wiring board of the present invention, since the protective insulating layer 3 is made of a mixture of protective inks having the above composition, the adhesive strength to the conductor circuit 2 and the base film 1 is high, and the insulating property is high. High, excellent mechanical properties of the coating itself, good slidability, high flame retardancy, and no harmful halogen-containing gas is generated even when incinerated.

Further, since this protective ink mixture has high flame retardancy, the blending amount of melamine cyanurate is 60 to 150 parts by weight on the base film 1 made of a non-flame retardant polyethylene terephthalate film having a thickness of 20 to 80 μm, for example. In the case where the protective insulating layer 3 having a thickness of 20 μm or more is provided on both surfaces of the base film 1 using the admixture described above, the flame retardancy achieves the level of VTM-2 defined in UL94.
Moreover, VTM-2 is provided only when a protective insulating layer 3 having the same thickness is provided on only one surface of the base film 1 and an admixture having a melamine cyanurate content of 80 to 120 parts by weight is used. In this combustion test, even if the test is performed with the protective insulating film as the inner side or the outer side as the outer test, flame retardance at a level that passes the combustion test is exhibited.
For this reason, this printed wiring board can be used for wiring etc. of computer equipment etc. which require high adhesiveness and good flame retardance.

In addition, in the present invention, as the insulating substrate, in addition to the plastic film exemplified above, a plastic composite plate such as paper / phenolic resin or glass / epoxy resin can be used, and other insulating materials should be used. You can also.
Furthermore, the conductor circuit may be formed by a subtract method in which a metal foil such as a copper foil is formed by etching in addition to the additive method.

Specific examples are shown below.
(Example 1)
The protective ink mixture having the composition (parts by weight) shown in Table 1 was dissolved in a solvent composed of diethylene glycol monoethyl ether acetate to produce a protective ink mixture solution having a solid content of 70 wt%.

  A commercially available silver paste was screen-printed on both surfaces of a 75 μm thick polyethylene terephthalate film, and then heated to form a 20 μm thick conductor circuit. The protective ink mixture solution was screen-printed on this, heated and solidified to provide a protective insulating layer having a thickness of 40 μm, and a double-sided type printed wiring board as shown in FIG. 2 was produced.

The printed wiring board thus obtained was measured for flame retardancy (UL94, VTM-2), bending test (adhesiveness), and adhesion test.
In the bending test, the printed wiring board was repeatedly bent three times with a bending radius of 0.5 mm, and the presence or absence of disconnection or floating of the conductor circuit or a decrease in the insulation resistance between lines was measured. A simulated conductor circuit having a line width of 0.4 mm and a line spacing of 0.2 mm and having an insulation resistance of 1 × 10 ¹⁰ Ω or more was regarded as acceptable.

The adhesion test was performed by the cross-cut method defined in JIS K 5600-5-6, and those that were classified as 0 to 2 were accepted, and those that were classified as 3 to 6 were rejected. Moreover, the classification 0 is a state in which the edge of the cut is completely smooth and there is no peeling in any lattice eye.
The results are shown in Table 1.

In Table 1, “Polyester resin” is “Byron GK-140” (trade name, manufactured by Toyobo Co., Ltd., glass transition temperature 15-20 ° C., polyester resin) and 100 parts by weight “Coronate 2513” (trade name, Nippon Polyurethane Industry). 10 parts by weight of an isocyanate curing agent)
“Melamine cyanurate” indicates “MC-860” (trade name, manufactured by Nissan Chemical Industries, Ltd.) having an average particle diameter of 3 μm which is not surface-treated.
The results are shown in Table 1.

(Example 2)
The protective ink blends having the blending compositions (parts by weight) shown in Tables 2 to 4 were dissolved in a solvent comprising diethylene glycol monoethyl ether acetate to produce a protective ink blend solution having a solid content of 70 wt%.

  A commercially available silver paste was screen-printed on one side of a base film of a polyethylene terephthalate film having a thickness of 75 μm and heated to form a conductor circuit having a thickness of 20 μm. The protective ink mixture solution was screen-printed on this, heated and solidified to provide a protective insulating layer having a thickness of 40 μm, and a printed wiring board having a structure as shown in FIG. 1 was produced.

The printed wiring board thus obtained was measured for flame retardancy (UL94, VTM-2), bending test 1 (adhesiveness), bending test 2 (repeat bending resistance), and blocking properties.
In the combustion test of UL94 and VTM-2, the protective insulating film formed on both sides of the base film and the protective insulating film formed only on one side were used with the protective insulating film forming surface inside or outside.

In the bending test 1, a printed wiring board was repeatedly bent three times with a bending radius of 0.5 mm, and the conductor circuit was confirmed to be disconnected and lifted, and the conductor resistance in the unbent state and the bent state was measured. A simulated conductor circuit having a line width of 0.4 mm and a line spacing of 0.2 mm and having an increase in circuit resistance from the initial unbent state was 5Ω or less was accepted.
Bending test 2 occurs when a printed wiring board similar to the above is bent 5 times in a reciprocating manner with a bending radius of 0 mm, the appearance is observed, and the protective insulating film is cracked and has no cracks. Was rejected. Those having an insulation resistance of 1 × 10 ¹⁰ Ω or more were regarded as acceptable.
Bending tests 1 and 2 were carried out with both the single-sided and double-sided structures shown in FIGS. 1 and 2, and when either one failed, the test was rejected.

The blocking property was obtained by superposing two 50 mm × 50 mm printed wiring boards described above and leaving them in an atmosphere of 40 ° C. and 95 RH% for 7 days with a load of 5 kg / cm ² applied. Was accepted as a pass. And it tested by the thing of the single side | surface and double-sided type shown in FIG. 1 and FIG. 2, and the case where either one failed was made disqualified.
The results are shown in Tables 2-4.

  In Tables 2 to 4, “Polyester resin A” is “Byron 550” (trade name, manufactured by Toyobo Co., Ltd., polyester resin having a glass transition temperature of −15 ° C. to −18 ° C.), and “Polyester resin B” is “Byron GK-140” (trade name, manufactured by Toyobo Co., Ltd., glass transition temperature 20 to 15 ° C., polyester resin). The curing agent is “Coronate 2513” (trade name, manufactured by Nippon Polyurethane Industry Co., Ltd., an isocyanate-based curing agent). The average particle diameter is 3 μm.

It is a schematic sectional drawing which shows an example of the printed wiring board concerning this invention. It is a schematic sectional drawing which shows the other example of the printed wiring board concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Base film, 2 ... Conductor circuit, 3 ... Protective insulating layer.

Claims (3)

A printed wiring board in which a protective insulating film is formed on a conductor circuit on an insulating substrate made of polyethylene terephthalate, using a protective ink mixture,
The protective ink blend includes 100 parts by weight of a polyester resin and 60 to 150 parts by weight of melamine cyanurate having an average particle diameter of 5 μm or less. The polyester resin 100 parts by weight has a glass transition temperature of −15 ° C. to −18 ° C. 60 to 80 parts by weight of polyester resin and 20 to 40 parts by weight of polyester resin having a glass transition temperature of 15 to 20 ° C. The weight average molecular weight of the polyester resin is 10,000 to 30,000, and the melamine cyanurate has its surface Is a printed wiring board that is not surface-treated. The printed wiring board according to claim 1, wherein the protective ink mixture is an isocyanate-based curing agent or an amine-based curing agent added thereto. The printed wiring board of Claim 1 or 2 which passes VTM-2 of UL specification.

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