JPS5853673B2 - Manufacturing method of powder coating for chemical plating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a chemically plateable powder coating, which is suitably used for producing printed wiring boards with a metal core.

In recent years, as electronic devices have become more efficient, performance requirements for printed wiring boards have become more sophisticated, and at the same time, economic effects have also been required.

For example, it must have a high degree of dimensional stability without warping or twisting, it must have the rigidity to withstand the mounting of a large number of heavy parts, it must have a high degree of thermal conductivity to quickly remove the heat generated from the mounted parts, and scales that can be supplied at low cost.

Since conventional synthetic resin laminates cannot fully meet these demands, there is a trend toward printed wiring boards with metal cores such as iron, stainless steel, aluminum, and copper.

For printed wiring boards with metal cores, it is essential to insulate the metal core, and for this purpose, there are a wide range of resins that have the required properties such as heat resistance and the ability to easily form an insulating resin layer of uniform thickness. Powder coating methods are attracting attention because of their advantages such as being able to be used in a wide range of applications, being solvent-free, saving resources, and generating little pollution.

Conventionally, when forming printed circuits by chemical plating in the production of printed wiring boards, chemical plating directly on the thermosetting powder coating did not provide sufficient adhesion, so Furthermore, the process of providing a rubber composition (adhesive) layer to improve adhesion, that is, the process of applying adhesive varnish, is essential, which inevitably increases the complexity of the process and reduces economic efficiency. It was a burden.

The present invention provides a method for producing a powder coating, which is suitably used for producing a printed wiring board with a metal core, and is capable of forming a printed circuit directly on a powder coating by chemical plating.

Powder coating methods generally involve appropriately blending thermosetting resins such as epoxy resins, phenolic resins, acrylic resins, and polyester resins with curing agents, fillers, catalysts, pigments, and spreading agents, so that most of the crosslinking reaction takes place. Melt and knead at a low temperature that does not
After cooling, the powder coating is pulverized and adjusted to a particle size of about 300 parts or less, and then the heated object to be coated is immersed in the powder coating to adhere it. ■ One end of the object to be coated is A method using electrostatic spraying, in which a high voltage is applied to the tip of a grounded spray nozzle and powder and air are sent simultaneously, causing the charged powder to fly and adhere.■ Powder made with a perforated plate at the bottom. The object to be coated with one end grounded is placed on top of the paint tank, and ionized air is sent from under the perforated plate by a high voltage power source to form charged floating powder (cloud), and the object to be coated is placed in the cloud. Electrostatic dynamic immersion method to attach the powder
Alternatively, the powder is attached to the object to be coated and baked using a method such as the electrostatic vibration method, in which the powder is charged by contact between the DC negative electrode and the AC electrode to generate a cloud, which is then electrostatically attached to the grounded object to be coated. In this baking hardening process, the powder melts and flows to form a smooth cured coating.

Powder coatings must have the ability to be crushed to form a powder coating, have uniformly dispersed composition, have uniform powder charge, and have good paintability, and must be coated under no pressure after being applied to a metal plate. The necessary conditions are that a smooth coating film with good melt flowability and good leveling can be obtained.

In the case of manufacturing printed wiring boards with metal cores, it seems possible to achieve the goal by converting the aforementioned rubber-based adhesive directly into a powder coating, but this attempt was difficult because the rubber was difficult to disperse uniformly. There are other problems, such as the difficulty of pulverizing them unless special methods are used.

Furthermore, even if powderization is achieved, if the rubber particles are not uniformly and finely dispersed, the powder particles will not be uniformly charged and will have a polarized structure, resulting in poor paintability or electrostatic agglomeration of powder particles. Depending on the coating method, electrostatic adhesion may not occur.

Moreover, if the rubber particles are insufficiently dispersed, the beer strength of the printed circuit produced by chemical plating will be insufficient and unstable.

Therefore, it is necessary to increase the rubber content relatively more than necessary, which may deteriorate the electrical properties of the metal core printed wiring board, and furthermore, the dispersibility becomes worse.

Furthermore, since good melt flow is not achieved during the bake hardening process, a smooth coating surface cannot be obtained, which impairs circuit printing accuracy.

In view of these points, the present invention aims to improve the conditions for obtaining a powder coating that forms a coating film that enables printed circuit formation by direct chemical plating, such as uniform dispersion mixing, pulverization, and formation of a smooth coating film. This was done after considering the conditions under which this could be achieved.

The present invention contains 1 to 30 parts of rubber having a conjugated double bond and a polar group in the molecule based on 100 parts (parts by weight, the same applies hereinafter) of the epoxy resin, and has a viscosity of 105 centipoise or less during at least one period of the heat curing step. Regarding the manufacturing method of thermosetting powder coating with epoxy resin having a melting point of 150°C or less, 3 to 50% (wt%, same hereinafter), inorganic filler 5 to 6
0% and less than 80% rubber and 2 in the final powder coating.
The kneaded composition is kneaded at a temperature equal to or higher than the melting point of the epoxy resin having a melting point of 150° C. or lower during at least one period of the kneading process, and the kneaded composition is kneaded together with the epoxy resin as a rubber-containing component, and then finely pulverized. It is characterized by:

As the rubber having a conjugated double bond and a polar group in the molecule, one type or a mixture thereof of acrylonitrile butadiene polymer, styrene butadiene polymer, acrylonitrile butadiene styrene resin, and polybutadiene resin can be used. Examples include nitrile groups, hydroxyl groups, carboxyl groups, and acid amide groups.

Rubbers that have conjugated double bonds and polar groups in their molecules are susceptible to proton-donating reactions due to their unsaturated nature, and are attacked by oxidizing acids, which promotes roughening and elution and generates hydrophilic groups. , improve the adhesion of printed circuits by chemical plating.

The rubber having conjugated double bonds is preferably one having 30% or more double bonds per constituent monomer from the viewpoint of improving circuit adhesion after chemical roughening.

A feature of the present invention is that a part of the epoxy resin, which is originally the main component in the final powder coating, is contained in the forced kneading process of a relatively large amount of high molecular weight rubber and an inorganic filler, and at least For a period of time, the entire system is heated above the melting point of the epoxy resin to melt and liquefy it, whereby the high molecular weight rubber, filler, and epoxy resin are easily mutually dispersed to obtain a highly concentrated rubber dispersion. It is in.

The molten epoxy resin not only acts as a lubricating component that moderately reduces the shear force of the dispersion effect between the high molecular weight rubber and the filler, but also acts as a lubricating component that moderately reduces the shear force of the dispersion effect. This results in a variety of finely dispersed particles.

In this case, if the epoxy resin content exceeds 50% of the system, that is, if the epoxy resin system has a large amount, the high molecular weight rubber will easily flow in the molten resin phase and will not be subjected to shearing force, resulting in a decrease in the dispersion effect; % or less, the lubricating effect is not sufficient.

If the melting point of the epoxy resin is 150°C or higher, thermal deterioration of the rubber will occur when the wires are crossed, various difficulties will arise in the kneading operation, and furthermore, the viscosity of the obtained powder coating will increase, and the heat curing process will be delayed. Since it does not exhibit a viscosity of 105 centipoise or less in one step, one with a melting point of 150° C. or less is used.

Further, if the inorganic filler content is 60% or more, the lubricating effect and solvent effect of the epoxy resin will be inhibited, and if it is less than 5%, the shearing force effect with the rubber will be insufficient, which is not preferable.

Further, the reason why the rubber content is limited to 80% or less is that the filler and epoxy resin contents are relatively reduced, which reduces the above-mentioned dispersion effect.

On the other hand, if the amount is less than twice the amount in the final powder coating, the efficiency of rubber dispersion is not good.

These high-concentration rubber dispersions are used in mixing rolls and kneaders.
Alternatively, it can be kneaded using a pressure kneader or the like.

Note that there is no need to add a crosslinking agent or the like in this step.

By using such a highly concentrated rubber dispersion as a rubber-containing component of the final powder coating, it is possible to easily uniformly and finely disperse the rubber particles in the powder coating.

The rubber content in the final powder coating is mixed in a range of 1 to 30 parts per 100 parts by weight of the epoxy resin as the main component.

Since the rubber particles are uniformly dispersed in advance, sufficient circuit adhesion can be obtained up to a lower limit of the rubber content of about 1 part, but below this it is insufficient.

If it exceeds 30 parts, it is not preferable because the heat resistance required for a coating film for printed circuits decreases.

Although it depends on the wiring board to be used, it is generally preferable to mix 2 to 10 parts of rubber.

As fillers, zirconium silicate, calcium carbonate, silicon oxide, zinc white, magnesium oxide, titanium oxide, etc. can be used, and it is also effective to use two or more types with different solubility in acids and alkalis. It is.

These are important in providing an auxiliary effect to create a roughened shape in the chemical roughening process, and the resin 1 in the final powder coating.
It can be used in an amount of 200 parts or less, preferably 100 parts or less.

In addition to being included in the high-concentration rubber dispersion, these fillers can also be added to the final powder coating.

Forming a smooth coating film on the surface of a metal plate by powder coating is extremely important in order to improve the mechanical properties required for a printed wiring board.

For this purpose, the viscosity of the powder must be 105 centipoise or less, preferably 103 centipoise or less, during at least one period of the heating step in which the thermosetting powder coating applied to the surface of the metal plate is heated to form a cured coating film. It is necessary that the following is true.

The viscosity in this heat curing step can be adjusted to a required value depending on the molecular weight of the powder and the curing speed.

Measurement of melt viscosity is carried out using ROTOVISKO manufactured by HAAKE.
.

This is carried out by using an R'Y-2 device, setting the temperature increasing rate at 45° C./min to the rotor PK-II, and measuring the flow torque in the rotational speed range of 0.1 to 10 rpm.

In order to powderize this composition, it is mixed with a mixing roll or an extrusion mixer to obtain a kneaded material, and then coarsely or finely ground with a grinder such as a conventional grinder or a fine micro pantum mill. .

It is preferable that the pulverization be carried out by a conventional method to the extent that substantially all particles of 300 μm or less are obtained.

Formation of printed circuits by chemical plating is performed, for example, according to the following table.

A coating film formed on the surface of a metal plate by powder coating can easily form a uniform surface roughening shape in the chemical roughening process, so it is difficult to remove Sn, Pd, etc. in the sensitizing and activating process. Adsorption of catalytic species is promoted,
Furthermore, the geometry of the surface and the properties of the surface resin ensure good adhesion with the deposited metal.

In addition, prior to chemical roughening, pre-soaking in an organic solvent is performed.
When the coating surface is swollen, the unsaturated polymer surrounded by the crosslinked resin can be easily roughened.

Examples of these organic solvents include mixed solvents of alcohols and methyl ethyl ketone, pyridine, dimethylformamide, trichloroethylene, and the like.

In the present invention, the surface of the metal plate is easily chemically roughened and made hydrophilic, and a cured coating film with improved circuit adhesion for printed circuits by chemical plating is applied to the surface of the metal plate using a powder coating method to create an excellent smooth surface. It can be formed with precision.

The present invention has been explained above mainly in connection with the production of printed wiring boards with metal cores, but the powder coating of the present invention can also be used to form a coating film that can be directly chemically plated on the surface of an insulating substrate. be.

Example 1 25 parts (62.5%) of acrylonitrile phytadiene copolymer (product name Nipol 1032, manufactured by Nippon Seon Co., Ltd., nitrile content 33%, Mooney viscosity 51), epoxy resin (trade name Epicote 1004, manufactured by Shell Co., Ltd., melting point 96-104°C)
) 5 parts (12.5%) and 10 parts (25.0%) of calcium carbonate as a filler were put into a pressurized Ni-Goo heated to 100-105°C and kneaded for 10 minutes, then the heating was stopped. The mixture was kneaded for 15 minutes.

The kneaded composition taken out was a dispersion containing 62.5% rubber.

In order to observe the dispersion state of this product, a flat plate about 1 inch thick was created by heat pressing at 160°C for 5 minutes, and then immersed in a chromium sulfuric acid mixture at 40°C for 15 minutes.The surface was then examined under a microscope. Upon observation, it was confirmed that each component was uniformly dispersed.

21 parts of the rubber dispersion, 14 parts of calcium carbonate, and 1 part of epoxy resin (trade name Epicoat 1004, manufactured by Shell)
30 parts were kneaded with a mixing roll, cooled and solidified, and then pulverized. To 160 parts of the resulting mixture, 6.5 parts of dicyandiamide, 1 part of finely powdered silica, and 1 part of a flow control agent (trade name: Modablo, manufactured by Monsanto) were added. The compositions were dry mixed using a Henschel mixer and then melt-kneaded using Konita PR-46 manufactured by Buss.

After cooling and solidifying, crush and pass through a 60-mesh sieve (openings 250μ).
) to create a powder.

The powder efficiency was also good, with a yield of 96% or more.

Next, the powder was applied to a 1.2 mm thick iron plate with through holes using an electrostatic dynamic coating device (080K).
V for 10 seconds) and then baked and cured at 180° C. for 60 minutes to form a cured coating film with a thickness of 150 μm.

During painting, a uniform charge reroud is generated continuously, and the coating is applied to the flat surfaces and holes of the iron plate with an average thickness. Screen printability was also good.

This sample was immersed in an organic solvent consisting of isopropyl alcohol and benzyl alcohol (volume ratio 50150) for 2 minutes at room temperature, washed with water, and dissolved in Na2Cr20720.
The surface was roughened by immersing it in a roughening solution in which 10 g of concentrated H2SO4 was dissolved in 48% HBF4 and the total amount was adjusted to 11.

The immersion conditions were as follows: 40 parts were soaked at 1° C. for 10 minutes, and then taken out, neutralized, and washed with water twice.

After roughening, a printed circuit is formed through the sensitizing, activating, and chemical plating steps shown in the table above.
Furthermore, a conductive circuit with a thickness of 35 μm was formed by electroplating.

After post-curing and drying this sample at 160°C for 60 minutes, the peel strength of the circuit portion was measured and was 1.7.
It had a value of 0 to 1.80 kg/am.

When the chemically roughened surface was observed using a scanning electron microscope, it was found that the entire surface had a complex protrusion shape averaged over the entire surface.

Further, when the metal surface after the circuit was peeled off, a portion of the resin was torn off and adhered to the peeled metal surface, indicating that good adhesion was achieved.

Example 2 10 parts of acrylonitrile phytadiene copolymer (trade name: Nipol 1001, manufactured by Nippon Zeon Co., Ltd.), styrene-butadiene polymer (trade name: Turprene 406, manufactured by Philips Corporation)
20 parts, epoxy resin (trade name Epicote 1 manufactured by Shell Co., Ltd.
001 (melting point 64-74°C) and 60 parts of calcium carbonate as a filler were put into a pressure kneader heated to 90°C and kneaded to prepare a dispersion with a rubber concentration of 31.3%.

Next, 30 parts of this dispersion and 170 parts of an epoxy resin (trade name Epicote 1004, manufactured by Shell) were kneaded in a pressure kneader, cooled and solidified, and coarsely pulverized. To the resulting mixture, 9 parts of dicyandiamide and a fine powder were added. 1.5 parts silica 1 part water conditioner
A powder coating was obtained in the same manner as in Example 1, and a printed wiring board was prepared in the same manner as in Example 1 using the powder coating.

The obtained printed wiring board was as good as that of Example 1, and the peel strength of the circuit portion was 1.65 to 1.75 kg.
/C111.

Comparative Example The final powder composition in Example 2 is the same composition as the epoxy resin (trade name Epicoat 1004 manufactured by Shell Co., Ltd.).
170 parts, acrylonitrile butadiene rubber (trade name: Ni-Ball 1001, manufactured by Nippon Zeon Co., Ltd.) 2.9 parts, styrene-butadiene polymer (trade name: Turprene, manufactured by Philips Corporation)
6.3 parts, epoxy resin (Meiko Pico-1 manufactured by Shell Co., Ltd.
-1001) and 18.8 parts of calcium carbonate were kneaded in a pressure kneader heated to 90'C.

After the epoxy resin is melted, there is almost no load on the torque meter of the kneader, indicating that no shearing force is applied.

When the composition was taken out after kneading for 30 minutes and the dispersion state was examined, small lump-like rubber substances were observed.

This composition was coarsely pulverized as it was, then made into a powder coating, electrostatically powder coated, and then a printed wiring board was prepared in the same manner as in Example 2.

In the powder coating process, the paint remaining in the sieve was repeatedly crushed due to poor crushing efficiency, but the yield dropped to less than 89%.

In addition, in the electrostatic dynamic dipping method, it was difficult to form a uniform coating because cloud formation was insufficient, probably because the powder particles were polarized and charged.

In this example, an electrostatic gun was used to paint a flat iron plate.
The printing accuracy of the obtained printed wiring board was poor because the leveling of the coating film was not sufficient and it became citron-like.

The peel strength of the circuit varies slightly, but it is 1.1
Values of about 0 to 1.45 ky/m were obtained.

As explained above, in the present invention, a relatively large amount of high molecular weight rubber and an inorganic filler are heated in advance to a temperature higher than the melting point of the epoxy resin during at least one period of the kneading process, and in the presence of a covering molten resin. By forming a powder coating using the high-concentration rubber dispersion obtained by kneading, a powder coating in which rubber particles are uniformly and finely dispersed can be obtained.

By uniformly finely dispersing the rubber in this way, (a) It becomes easier to pulverize powder coatings.

(b) Polarization electrification is reduced, and electrostatic coating properties are greatly improved due to uniform electrification.

(c) Printability is improved because good melt flow occurs during the baking hardening stage and coating film leveling is improved.

2) Uniform dispersion of rubber improves the peel strength of the circuit.

These effects of the present invention largely solve the problems of the prior art.

Claims (1)

[Claims] 1 Thermosetting powder containing 1 to 30 parts by weight of rubber having a conjugated double bond and a polar group in the molecule, based on 100 parts by weight of epoxy resin, and having a viscosity of 105 centivoise or less during at least part of the heat curing step. In the coating manufacturing method, 3 to 50% by weight of a thermosetting resin with a melting point of 150°C or less, 5 to 60% by weight of an inorganic filler, and 80% by weight or less of rubber, and at least twice as much as in the final powder coating. The melting point of the composition is 150° C. during at least one period of the kneading process.
A method for producing a powder coating for chemical plating, which comprises pre-kneading the following epoxy resin at a temperature equal to or higher than its melting point, further kneading the kneaded composition together with the epoxy resin, and pulverizing it.