JPH0312260A - Powder painting method - Google Patents

Abstract

PURPOSE:To enhance the heat cycle resistance and humidity resistance of a part by a method wherein an under coating material containing a phenol resin and epoxidized polybutadiene is applied to an electric/electronic part and, after curing, powder paint is applied to the under coating layer. CONSTITUTION:About 15-85wt.% of a phenol resin and about 85-15wt.% of epoxidized polybutadiene are used to the sum amount of the phenol resin and epoxidized polybutadiene and dissolved in a solvent such as a hydrocarbon solvent to prepare an under coating material. This under coating material is applied to the surface of an electric/electronic part and, after curing, powder painting is applied thereon. As the phenol resin there are a resole type phenol resin and a novolac type phenol resin and expoxidized polybutadiene is obtained by adding a plurality of epoxy groups to the main chain or terminal of polybutadiene.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention applies an undercoat paint with good adhesion to powder coating of electrical and electronic components such as ceramic capacitors, varistor resistance networks, and high-print ICs. The present invention relates to an electrical insulation method that improves moisture resistance and thermal shock resistance, and also improves coating defects such as pinholes.

[Conventional technology]

There are various methods for insulating and encasing electronic components such as capacitors, varistors, resistor networks, and hybrid ICs with resin, such as casting with liquid resin, dip, drop, sealing, encapsulation molding with molding materials, and powder coating. Powder coating is widely used as a highly productive coating method that allows devices of various shapes to be easily coated at relatively low cost.

Powder coating methods include fluidized dipping method, static 1 * dynamic dipping method,
There are methods such as rolling method, sprinkle method, and electrostatic spray method.

Even in these powder coated products, the reliability level of the parts is becoming increasingly sophisticated, and in particular, improvement of the heat cycle resistance and moisture resistance of the insulating coating film is a challenge.

Regarding heat cycle resistance, since the linear expansion coefficients of the powder coating and the substrate are different, if thermal stress is applied, internal stress will cause cranking. In severe cases in large hybrid ICs, this may lead to peeling of the conductor pattern.

In order to solve the second problem, reduce the stress of powder coating,
Studies are being carried out from the perspectives of both methods and improvement of coating methods.

As for powder coatings, if heat cycle resistance is improved, moisture resistance tends to deteriorate, and it is currently difficult to achieve both.

Furthermore, in order to improve the heat cycle properties of powder coatings by coating methods, a method of applying an undercoat material having a buffer effect such as silicone resin or urethane resin has been adopted. However, silicone resin has poor adhesion and moisture permeability, while urethane resin has shortcomings in solvent resistance and water resistance.Although both improve heat cycle resistance, they have poor moisture resistance under severe conditions such as PCT. There are some things that cannot be expected to improve, and instead deteriorate.

As an undercoat material, it is desirable that the material has good adhesion to various parts and exterior materials, has excellent moisture resistance, solvent resistance, and heat cycle resistance, is fast curing, and can be molded.

[Problem to be solved by the invention]

An object of the present invention is to use a powder coating material that has good adhesion and moisture resistance to improve both heat cycle resistance and moisture resistance of electrical and electronic components. It is in providing the law.

[Means to solve the problem]

When coating electrical and electronic components with a powder coating, the present invention applies an undercoating material containing phenol resin and epoxidized polybutadiene as essential components in advance, and after curing the coating material, the powder is coated with a powder coating. It is a painting method.

Phenolic resins that are one component of the undercoating material used in the present invention include resol type phenolic resins and novolanc type phenolic resins. The resol type phenolic resin usually contains 1 mol or more of formaldehyde, preferably 1.1 to 1.8 mol, per 1 mol of phenol, and also contains a nitrogen-containing compound catalyst, or a nitrogen-containing compound and an alkaline earth metal catalyst as a catalyst. These resins are used in combination and are condensed and dehydrated using conventional methods.

The phenols mentioned here include phenol, cresol, xylenol, resorcinol, and alkylphenols such as paratertiary butylphenol, paraoctylphenol, paranonylphenol, and paraphenylphenol.

Formaldehyde may be usually paraformaldehyde in addition to formalin aqueous solution.

Examples of nitrogen-containing compounds include ammonia, triethylamine, triethanolamine, diethyleneamine, aniline, hexamethylenetetramine, and the like.

Alkaline earth metals are oxides and hydroxides of alkaline earth metals such as calcium, magnesium, and barium.

The resol type phenolic resin is preferably an ammonia resol using ammonia or hexamethylenetetramine as a reaction catalyst. A preferred amount of catalyst is NH per 100 parts of phenol.

The total amount is 3 to 15 parts.

The novolak type phenolic resin is produced by condensation and dehydration using the phenols and formaldehyde described in the resol type phenol resin using a conventional method using an monic acid such as Scherer's acid and an inorganic acid such as hydrochloric acid or sulfuric acid as a catalyst. It is a resin.

Furthermore, if necessary, these phenolic resins may be modified with xylene resin, melamine resin, silicone resin, vegetable oil, or the like.

Epoxidized polybutadiene, which is another component of the undercoating material used in the present invention, is polybutadiene with a plurality of epoxy groups added in the main chain and at the ends, and has a number average molecular weight (Mn
) is 600 to 5000 liquid rubber. For example, Nippon Soda ■ B F-1000, Adeka Argus Chemical ■ B
F-1000, Poly bd R4 manufactured by Idemitsu Petrochemical ■
5EPT, Poly bd R45EP+, and the like.

These epoxidized polybutadienes can be expected to have the effect of preventing paint from sagging, as well as impart flexibility to the coating film, improve thermal shock resistance, and improve the high frequency properties of the cured product.

Among these epoxidized polybutadienes, an epoxidized polymer having 50% or more of 1,4 bonds is preferable from the viewpoint of imparting flexibility and compatibility with other components.

Further, the durability of the coating film can be adjusted by partially substituting a part of the epoxidized polybutadiene with, for example, a bisphenol A type epoxy resin having an average molecular weight of 770 or more.

The composition of the undercoat component according to the present invention is 15 to 85% by weight of phenolic resin and 85% by weight of epoxidized polybutadiene, based on the total amount of phenolic resin and epoxidized polybutadiene.
It can be used in a range of 15% by weight.

Furthermore, polyvinyl butyral resin, phenoxy resin, Evoquine resin other than those mentioned above, etc. can also be appropriately blended.

The solvent used for the undercoat material used in the present invention is toluene,
Hydrocarbon solvents such as xylene, alcohol solvents such as ethyl alcohol, gent solvents such as methyl ethyl Kent, ester solvents such as cellosolve acetate and butyl acetate, cellosolve solvents such as methyl cellosolve and ethyl cellosolve, Use one or more types.

Regarding other additives, it is preferable to include a silane coupling agent or a titanium coupling agent in order to further improve adhesion.

In addition, appropriate amounts of curing accelerators such as imidazoles, aromatic amines, and organoaluminum compounds, antifoaming agents, anti-sagging agents, leveling agents, dyes and pigments, etc. can be added as necessary.

The liquid-type undercoating material obtained in this way has excellent adhesion to parts, substrates, and exterior powder coatings, and in particular, has excellent moisture resistance, solvent resistance, and heat cycle resistance with a thin film of 100 μm or less. It can be effective.

(Example) The present invention will be explained below using examples.

Table 1 shows the resin composition used for the undercoat and its application results.
Shown below.

Resol type phenolic resin is made by mixing 1.2 moles of formadehyde with 1 mole of phenols, reacting with each catalyst shown in Table 1 in a conventional manner, and after vacuum dehydration, mixing methyl ethyl ketone/methyl cellosolve = 1/2. It was dissolved with a solvent and the resin content was adjusted to 50%.

Novolak type phenolic resin is formulated with 0.9 mol or less of formaldehyde per 1 mol of phenols, reacted in a conventional manner with the catalyst shown in Table 1, and after vacuum dehydration, dissolved in a mixed solvent of methyl ethyl ketone/methyl cellosolve = 1/2. The resin content was adjusted to 50%.

The urethane resin is a flexible two-component curing type (Sumitomo Bakelite rG CR-3200J), and the silicone resin is a room temperature curing type (Shin-Etsu Silicon KR-2S).
IJ) were used respectively.

During the characteristic measurement test, the device was 40m wide and 20m long.
A comb-shaped resistor with a circuit width of 0.3 mm and a circuit spacing of 0.3 mm was baked with Ag/Pd paste, and a lead frame was attached to the alumina with a thickness of 0.71 m and a lead frame was used.

Each of the undercoating materials shown in Table 1 was diluted with methyl heptatoroso to adjust the viscosity and applied to this element to give a film thickness of 20 μm. After drying at room temperature for 1 hour, at 110°C for 1 hour,
It was baked and hardened at 50°C for 1 hour.

Powder coating was carried out as follows.

(1) Powder coating: Epoxy resin powder coating PR-5213
5 (manufactured by Sumitomo Durez ■) (2) Painting machine: Fluid immersion coating machine ■ Seiken PC-2S (3) Painting conditions: The element coated with the undercoat material was preheated at 150'C for 30 minutes.
After preheating for 1 minute, immersion in a powder fluidization tank 3 times to adhere powder coating, and curing at 150°C for 1 hour to achieve a film thickness of 0.6
An element for evaluation of the torso was created.

In addition, in the reference example, no undercoat material was applied, and only powder paint was applied.

The evaluation method for each characteristic is as follows.

Solvent resistance of undercoat material: The element coated with the undercoat material was immersed in a methyl ethyl Kent solution for 1 hour, and the swelling of the coating film of the undercoat material was observed.

Those that did not swell and those that swelled with O1 were indicated as ×.

Moisture resistance: After the evaluation element was subjected to moisture absorption treatment at 121° C. for 1150 hours using a pressure cutter tester, moisture resistance was evaluated based on changes in insulation resistance between circuits. (Initial value 10') Ω) The heat cycle resistance second evaluation element was subjected to thermal shock at 125°C for 30 minutes and at 140°C for 30 minutes, and the number of cycles until cracks occurred in the coating film in 50% of the samples ( times) was calculated.

〔Effect of the invention〕

According to the method of the present invention, the drawbacks of conventional undercoating methods using silicone resins and urethane resins can be overcome, and not only heat cycle resistance but also moisture resistance can be improved.

Particularly when applied to varistors and high print ICs, coated products with high reliability can be obtained. Furthermore, when applied to products with molded components, this coating method can also improve coating film defects such as blisters and pinholes caused by air pockets in the gaps between individual components and the board.

Procedural amendment (voluntary) November 1999

Claims (1)

[Claims] (1) When coating electrical/electronic parts with powder coating, the parts are first coated with an undercoat containing phenolic resin and epoxidized polybutadiene as essential components, and after the coating has hardened, powder coating is applied. Body painting method.