JPS5833906B2 - Fast curing resistor coating composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fast-curing resistor coating composition, and relates to one whose curing properties are promoted by utilizing photocurability or the like.

Conventionally, for example, resistors used in printed circuit boards for electric circuits were made by blending carbon powder with a curable resin composition to form a paint, and the paint was applied to a laminated board made of phenol, epoxy, polyester, etc. using a screen to match the desired circuit. The coating is printed by printing, crosslinked and cured, thereby fixing the coating film to the substrate and exhibiting predetermined physical properties.

Curing of this resin (this is a so-called thermosetting material in which the resin composition is polymerized and crosslinked via a polymerization initiator that activates a prepolymer and monomer having radically polymerizable double bonds by thermal action). many.

This heating is usually done at 120-200℃ for 3 hours to 10 minutes.
This process is time consuming, has extremely poor workability, and also causes problems such as thermal deformation of the substrate.

- Photocurable photosensitive resin compositions are known as fast-curing resin compositions, but when these photosensitive resin compositions contain opaque materials such as carbon powder, their light transmittance is extremely poor. For example, in the case of a coating film applied to a substrate, a disadvantage arises in that the portion close to the substrate remains uncured.

The present invention has been made in view of these points, and provides a coating composition containing 2,2-dimethoxy-2-phenylacetophenone as a polymerization initiator, which can be used even when carbon powder is included. It can be cured in a short time of 1/60 to 1/240, and is subjected to G rubbing so that a stable resistor can be obtained.

The composition of the present invention is a coating composition in which carbon powder is blended into a resin composition of a radically crosslinkable prepolymer and a vinyl monomer, and further contains 2,2-dimethoxy-2-phenylacetophenone as a polymerization initiator. be.

All conventionally known radically crosslinkable prepolymers and vinyl monomers can be used, but for example, as prepolymers that have radically polymerizable unsaturated double bonds, epoxy compounds and (meth)acrylic acid can be used. Epoxy poly(meth)acrylate obtained by addition reaction of polyhydric alcohol, diisocyanate and hydroxyalkyl (meth)acrylate, urethane poly(meth)acrylate obtained by addition reaction of polyester carboxyl group and ( Polyester poly(meth)acrylate obtained by reacting hydroxyalkyl meth)acrylate or glycidyl methacrylate, Boss ester poly(meth)acrylate obtained by reacting the hydroxyl group of polyester with (meth)acrylic acid,
Polyether polyol poly(meth)acrylate obtained by reacting polyether glycol with (meth)acrylic acid, polyester poly(meth)acrylate obtained by reacting fatty acid with hydroxyalkyl (meth)acrylate or glycidyl methacrylate. -There are donas.

In addition, as vinyl monomers, styrene, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-
Hydroxypropyl (meth)acrylate, diethylene glycol di(meth)acrylate, neobentyl glycol di(meth)acrylate, 1゜3-butylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethanetetra These include (meth)acrylate, dipentaerythritol hexa(meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxytetraethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, and 2-hydroxydodecyl (meth)acrylate. The prepolymer and vinyl monomer may be used singly or in combination of two or more, if desired.

Carbon powders include furnace black, channel black, thermal black, acetylene black, graphite, grafted carbon, etc. depending on their manufacturing and processing methods, and these powders may be used alone or as a mixture.

As a polymerization initiator, 2,2-dimethoxy-2-phenylacetophenone (also referred to as benzyl dimethyl ketal) having the following structure and having the properties of a thermal polymerization initiator is used.

In addition, this composition (in addition to the above, it also contains colorants, wax,
Various additives used in general paints, such as polymerization inhibitors, organic peroxides, curing accelerators, thickeners, leveling agents, antifoaming agents, and inorganic pigments, can also be used.

In this composition, an inorganic extender pigment is often used to adjust the resistance value.

The composition ratio of the coating composition of the present invention is 25 to 85% of the resin composition containing a radically crosslinkable prepolymer and a vinyl monomer.
weight percent, preferably 40-80 weight percent, carbon powder from 5-70 weight percent, preferably 7-80 weight percent;
65 weight percent, 0.1 to 10 weight percent, preferably 0.5 to 8 weight percent of 2,2-dimethoxy-2-phenylacetophenone.

In order to produce the coating composition of the present invention, carbon powder is mixed with the prepolymer while stirring well, and the carbon powder is thoroughly coated with the prepolymer.

Then, mix the vinyl monomer and mix it evenly (
The mixture is stirred, and finally 2,2-dimethoxy-2-phenylacetophenone is mixed therein, and the mixture is diluted with a solvent such as a vinyl monomer as needed to obtain a product.

In addition, in order to use the coating composition of the present invention, if it is printed on a circuit board, for example, by an appropriate means such as silk screen printing, and irradiated with ultraviolet rays, the surface layer of the coating film mainly undergoes polymerization that is excited by the light. The agent acts on the prepolymer and the vinyl monomer and adds to the double bonds they have, and the prepolymer crosslinks with each other or via the vinyl monomer, forming a three-dimensional network (this becomes tack-free and hardens).

This surface layer portion is also thermally cured by heat rays emitted from, for example, an ultraviolet irradiation device, the coating film is solidified, and the carbon powder is firmly fixed to the substrate.

-Only heat curing occurs in the deep layers of the paint film where ultraviolet rays do not reach.

In this thermal curing, 2,2-dimethoxy-2-phenylacetophenone is excited by heat, which induces a reaction between the radical polymer and the vinyl monomer to crosslink and form a three-dimensional network, resulting in curing.

When solidified in this manner, the carbon powder is fixed and can function as a resistor in a circuit.

Next, examples of the present invention will be described in comparison with reference examples.

Table 1 shows the formulations, curing conditions, and sheet resistance values when thermosetting resins are used, and Table 2 shows the formulations, curing conditions, and sheet resistance values when using the coating compositions of the present invention.

As can be seen from Tables 1 and 2, heat curing requires 3 to 10 hours of curing time (on the other hand, UV curing resins require 3 to 5 minutes of UV irradiation to produce the same sheet. The resistance value was obtained.

Note that the binder refers to a mixture of a prepolymer and a vinyl monomer, which becomes the main component of the coating film when cured.

In addition, in the test, a paint was applied to a substrate, light was irradiated, and the resistance value of the paint film was measured.

In addition, the composition in the table shows parts by weight, and if the total does not add up to 100 parts by weight, the parts by weight are written in parentheses.

According to the present invention, since carbon powder is blended into a composition containing 2,2-dimethoxy-2-phenylacetophenone in a radically crosslinkable prepolymer and a vinyl monomer,
In addition to being characterized by fast curing through light curing, the deep parts of the coating film through which light does not pass are compensated for by heat curing, making it possible to obtain a coating film that cures quickly and with a high degree of hardening as a whole, significantly improving workability. It is possible to significantly reduce the manufacturing cost of printed circuit boards, for example, by improving the resistance and maintaining the function as a resistor.

Claims (1)

[Claims] 1 25 to 90 weight percent of a resin composition containing a radically crosslinkable prepolymer and a vinyl monomer, 5 to 70 weight percent of carbon powder, and 0% of 2,2-dimethoxy-2-phenylacetophenone as a polymerization initiator.
．． A fast-curing resistor coating composition comprising 1 to 10 percent by weight.