JPS5844432B2 - How to form a coating film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of curing a coating film by electron beam irradiation, and in particular a method for reducing the influence of inhibition of polymerization of a coating film that occurs when oxygen is present in the electron beam irradiation atmosphere. The present invention relates to a method for forming a coating film by electron beam irradiation that does not require inert gas atmosphere control.

Compared to the conventional heat curing method, the method of curing a coating film using electron beam irradiation has the following advantages: it can shorten the curing time of the coating film, it can be cured at room temperature, and it does not require a solvent. , which has the advantage of being able to cure a thick film at once, has attracted attention and has recently been put into practical use.

The coating-forming substances used in the electron beam curing method are mainly those that can be crosslinked by radical polymerization to form a coating film.

Radical polymerization of these radically polymerizable coating-forming substances is inhibited by oxygen, and the surface of the coating film is not sufficiently cured in air, making it impossible to form a coating film with sufficient performance.

In both the electron beam irradiation curing method and the photocuring method, polymerization is generally inhibited by oxygen in the air, but there are differences in the degree of inhibition. Using monomers, oligomers/
Although materials that can be sufficiently cured in air have been put into practical use by increasing the monomer ratio, the reality is that electron beam-cured coating forming materials do not cure unless in an inert gas atmosphere.

Therefore, even with ultraviolet curing paints used in an inert gas atmosphere, the atmosphere can generally be controlled more easily than with electron beam curing.

- Ultraviolet curable paints that fully cure in air have limitations on oligomers, monomers, and their composition ratios, and there are also limitations on the physical properties of the coating film, which limits its use as a single coating film.

In addition, like the electron beam irradiation method, the photocuring method has advantages over the heat curing method, such as shortening the curing time of the coating film and reducing environmental pollution due to the need for or reduction of solvents. It is impossible to harden to the point where

Therefore, when forming a coating film by radical polymerization crosslinking reaction by electron beam irradiation, the electron beam irradiation atmosphere needs to be an inert gas atmosphere that does not inhibit radical polymerization, such as nitrogen gas, carbon dioxide gas, combustion gas, etc. A method in which the atmosphere is controlled by air, and a method in which a film material with low oxygen permeability is attached to the surface of an unirradiated coating film and then irradiated with an electron beam in the atmosphere to cure the coating film are well known.

However, the method of controlling the electron beam irradiation atmosphere with an inert gas is expensive, and the cost associated with curing the coating film accounts for a large proportion of the cost.

Further, the film impregnation method also has drawbacks such as being expensive and not being able to form a coating film with excellent smoothness.

Furthermore, when applying a coating material to the object to be coated and curing it by direct electron beam irradiation, the coated surface cannot come into contact with rolls, shielding plates, etc., and it is necessary to leave a gap. It is difficult to prevent the generated brake X-rays, ozone, etc. from leaking outside the electron beam irradiation chamber area, and the apparatus itself must be complicated.

Furthermore, since the gap is open, the amount of inert gas required for atmosphere control must be increased, which is economically disadvantageous.

Therefore, the present invention was made to eliminate these drawbacks, and its purpose is to form a coating film with excellent curability and smoothness without requiring atmosphere control during coating film formation by electron beam irradiation curing. It is intended to provide a method.

The method of forming a coating film of the present invention is to cure the surface of a coating film containing a masking inorganic substance, pigment, etc. in a resin that hardens by light irradiation without controlling the atmosphere. A method of curing a part with an electron beam to form a coating film with excellent curability and smoothness, and a method of curing a coating-forming substance that cures with light irradiation without atmosphere control to form a coating film with electron beam irradiation. This method first hardens the surface of a coating layered on an uncured coating film by irradiating it with light to reduce polymerization inhibition caused by oxygen in the air, and then hardens the coating film deep down by irradiating it with electron beams. This results in the formation of an excellent coating film.

In the present invention, when the surface of the applied coating film is first irradiated with light and then irradiated with electron beam to cure it, the surface of the coating film is not damaged even if it comes into contact with a roll or a shielding plate. Braking X-rays, osone, etc. can be brought into contact with the surfaces of objects to be coated, such as rolls and shielding plates, to prevent them from leaking out of the electron beam irradiation room area, making their control easier.

Furthermore, since the irradiation chamber can be sealed with rolls, shielding plates, etc., even if atmosphere control is required, it can be easily controlled.

Particularly in continuous lines, the irradiation chamber can be under reduced pressure and the oxygen concentration can be controlled.

The photocurable coating used in the present invention is composed of monomers or oligomers containing photosensitive groups as main chains, side chains, or terminal groups, and when irradiated with light, polymerization and crosslinking reactions occur due to the photosensitive groups. Selected from those that are insolubilized in solvents and that change physical properties from fluid to solid.

The classification based on the type of photosensitive group is as follows.

■ Aku IJ Oyl group (-C3C-H
) and other monomers and oligomers with photopolymerizable unsaturated groups.

■ When excited by light or an electron beam, the ethylene group forms a cyclobutane ring, and by introducing a substance that trimerizes into the oligomer, the molecular weight can be increased by light irradiation, or it can be hardened by creating a three-dimensional structure. Monomers and oligomers having photodimerizable photosensitive groups.

■ Coatings that can be photocured by introducing azide compounds, bisazide compounds, diazonium salts, tetranium salts, etc., which decompose with light to produce radicals, into monomers and oligomers, or by mixing them with radically polymerizable monomers and oligomers.

** The above are applicable, but for light-curable paints and inks, it must be easy to set the base, have a viscosity suitable for painting and printing, and if necessary, be able to adjust the viscosity with a reactive diluent. Monomers and oligomers having photopolymerizable unsaturated groups are easy to use because the reactivity can be easily adjusted by adjusting the amount of photopolymerization initiator and well-balanced film characteristics can be easily obtained.

Therefore, for general purposes, photocurable coatings are basically ■ Reactive unsaturated oligomers ■ Reactive diluent ■Photosensitizer Consists of.

Photoreactive unsaturated oligomers can be classified based on their resin type: (1) Maleic anhydride-type unsaturated polyesters and their silicone-modified, ucrylic-urethane-modified, etc.

(2) Acryloyl group-reactive resin Rethane modification, With something (1) Polyester acrylate type (11) Epoxy acrylate type (m) Urethane acrylate type OV) Polyether acrylate type (■) Polyol acrylate type (vi) Melamine acrylate type (Vlo silicon acrylate type and so on.

The reactive diluent used in the method of the present invention is a photoreactive unsaturated oligomer or polymer base resin, which has too high a viscosity to be used as a paint or ink binder as it is, so it is generally used after being diluted with a polyfunctional monomer. Be it.

As a reactive diluent, 1,4-butanediol diacrylate, 1,
6-hexanediol diacrylate, neopentyl glycol diacrylate, diethylene glycol diacrylate, tetraethylene glycol diacrylate,
Commercially available diacrylates such as polyethylene glycol 400 diacrylate, triacrylates such as trimethylolpropane triacrylate, and pentaerythritol triacrylate can be used.

The photosensitizers that can be used in the method of the present invention are generally selected from those that are stable in the dark but generate radicals when exposed to light such as ultraviolet light, and include aromatic ketones such as benzophenone and its derivatives. ...Rogenated aromatic compounds should be used.

The electron beam curable coating material that can be used in the present invention basically consists of an electron beam-reactive unsaturated polymer and oligomer and a reactive diluent, each of which can be used in the photocurable coating material. You can choose from.

Examples of the present invention are listed below.

Example 1 100 parts by weight of polyfunctional oligoester acrylate (trademark registered Aronix M-8060), 2 parts by weight of benzyl as a photosensitizer, and titanium oxide (trademark registered Tybake R78)
0) were mixed to prepare a photocurable coating.

Spread this adjusted viscous liquid onto a clean aluminum plate for about 5 minutes.
After applying 0μ, it was irradiated with an ultraviolet curing device (registered trademark MiniCure 450) at an irradiation distance of 5CrfL for 20 seconds without controlling the irradiation atmosphere, and then an electron beam irradiation device (
5 at acceleration voltage 150KV with trademark ESH150-020)
As a result of irradiation without controlling the irradiation atmosphere, a glossy coating with a pencil hardness of 3H1 and a coating thickness of 50 μm was obtained.

Comparative Example 1 An aluminum plate coated in the same manner as in Example 1 was only irradiated with ultraviolet rays in the same manner as in Example 1. As a result, the inside of the coating film was not cured.

Comparative Example 2 An aluminum plate coated in the same manner as in Example 1 was directly cured by electron beam irradiation in the same manner as in Example 1 without being cured by ultraviolet rays. As a result, the inner surface of the coating was cured, but the coating was The surface was not sufficiently cured and was still sticky.

Example 2 Electron beam curable resin monofunctional acrylic oligoester (trademark registered Aronix M5700) was coated on a steel plate subjected to phosphate chemical conversion treatment by a curtain flow coater to approximately 20μ, and benzyl as a photocuring agent was further applied on top of the coating. Acrylic oligoester mixture containing 2% by weight (trademark registered Aronix M8060/Aronix M6300 1:1
) was coated with about 10 μm of chlorine using a curtain flow coater, and was irradiated with an ultraviolet curing device (registered trademark Minicure 450) at an irradiation distance of 5 CIrL for 30 seconds without controlling the irradiation atmosphere.
0-020) and 5 Mrad at acceleration voltage 150KV,
As a result of irradiation without controlling the irradiation atmosphere, a glossy coating with a pencil hardness of 2H1 and a coating thickness of about 30 μm was obtained.

Comparative Example 3 A test plate coated in the same manner as in Example 2 was subjected to ultraviolet curing alone in the same manner as in Example 2. As a result, the inside of the coating film was not cured.

Comparative Example 4 A test plate coated in the same manner as in Example 2 was directly cured with electron beam in the same manner as in Example 2 without irradiating it with ultraviolet rays. As a result, the inner surface of the coating was cured, but the surface of the coating was sufficiently cured. It was not sticky and had stickiness.

Claims (1)

[Scope of Claims] 1. A coating film characterized in that a photocurable coating material is applied to an object to be coated, the surface is cured by light irradiation, and then the inner surface of the coating film is further cured by electron beam irradiation. How to form. 2 Applying an electron beam curable coating material to the object to be coated, and then overcoating a photocurable coating material, then curing the surface by light irradiation, and then further curing the inner surface of the coating film by electron beam irradiation. Characteristic coating film formation method.