JPS6087877A - Manufacture of painted article - Google Patents

Abstract

PURPOSE:To obtain a coated film having high hardness and excellent contamination resistance by curing with an electron beam a composition consisting of the specified first component or of the first and second components in an inert gas atmosphere. CONSTITUTION:A paint composition contg. >=50% acrylate monomer as an essential component or added with a (metha)acrylate oligomer when needed to increase the adhesion and hardness of a coated film is coated on an article to be coated, and cured by an electron beam. In this case, the acrylate monomer contg. >=3 acryloyl groups in a molecule, is used as a compd. having <=150 acryloyl group equivalents or the mixture thereof. The (metha)acrylate oligomer is obtained by esterifying an oligomer consisting of tetrahydrophthalic acid and trimethylolpropane or pentaerythritol with (metha)acrylic acid.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a method for manufacturing coated articles, such as coated steel plates, having a coating coated with an electron beam curable paint and exhibiting high hardness and excellent stain resistance.

(Prior art) In the past, expensive hollow-finished hollow products were mostly used for applications where oil-based contamination or scratches were expected, but in recent years, hollow products with a sagging coating film have been formed. The use of electron beam curable paints is attracting attention because they can be manufactured at low cost.

Electron beam-curing coatings, which are attracting attention as an alternative to hollow articles, have a higher crosslinking density than thermosetting coatings, but they also have higher hardness and surface resistance. 1. Many proposals have been made so far to exhibit characteristics such as poor stain resistance and solvent resistance.

For example, in Japanese Patent Publication No. 5 (I-8070), one type of methacrylate monomer containing two or more methacryloyl groups in one molecule and having a methacryloyl group equivalent of 1211 or less,
Esterification of three components, which contain two or more methacryloyl groups or acryloyl groups in the molecule and have a (meth)acryloyl group equivalent of 500 or less: tetrahydrofucric acid; trimethylolpropane or penquerythritol; and methacrylic acid or acrylic acid. The (meth)acrylate oligomer obtained by
It is disclosed to use a paint formulated in a range of 1/2.

Setting the blending ratio of methacrylate-I monomer and (meth)acrylate oligomer to 2/1 to 1/2 is (meth)
When using acrylay-1 oligomer alone, there is a possibility of
In other words, fine dust or stains adhering to the painted surface can cause spots where the paint does not adhere, making it impossible to obtain a beautiful paint job.Furthermore, the paint surface cannot be cured using methacrylate monomer alone. It's for a reason.

By the way, radiation-curable paints generally use oligomers containing carbon-carbon double bonds and a molecular weight of about 1,000 to 2,000 as the base resin, and react monomers that also contain double bonds and have a low molecular weight (low viscosity). It is used by adding it as a diluent to reduce the viscosity so that it can be coated.

In this way, in the conventional technology, the main component is an acrylic oligomer, which is a coating film forming component, and reactive monomers are added for viscosity adjustment and other purposes, so the amount of monomer added is usually 50%. There wasn't much to overcome.

(Summary of the Invention) The present inventors have continued their research in order to obtain a coating film that exhibits high hardness that exceeds conventional thermosetting coatings, and at the same time has excellent stain resistance and solvent resistance. In order to obtain such a coating film, the crosslinkable double bond equivalent (the value obtained by dividing the molecular weight by the number of crosslinkable double bonds present in the molecule, i.e., one crosslinkable double bond) in the coating composition must be by reducing the molecular weight (per unit molecular weight),
The crosslinking density in the cured coating must be high, and therefore a large amount of monomer must be used.

As a result of repeated investigations from the following viewpoints, the inventors of the present invention discovered that using an acrylate monomer, which is highly reactive even when used alone, as the main component, with a content of 550% or more, the paint film could not be as thin as the paint film. The present invention was completed by discovering that the following can be obtained.

In addition, radiation-cured paints have a tendency to have poor adhesion due to the internal stress of the paint film, so if the object to be coated is a steel plate, etc., the adhesion of the paint odor tends to deteriorate. It has also been found that adhesion is improved by shot blasting and, if necessary, in combination with the present invention, better coated articles can be obtained.

Therefore, the present invention provides (1) containing three or more acryloyl groups in one molecule, or
The group consisting of trimethylolpropane triacrylate acrylate, pentaerythryl-1-ltetraacrylate, dipentaerythritol hexaacrylate, and mixtures thereof, each having an acryloyl group equivalent weight (molecules M per 11t!a of acryloyl groups) of 150 or less. A coating composition consisting of an acrylate monomer selected from
A method for producing a coated article having high hardness and excellent @1 staining properties; and (2) the above acrylate monomer is used as a first component, and the following second component is added to this at a weight ratio of first component/second component of 1/2. Production of coated articles having high hardness and excellent stain resistance, characterized by applying a coating composition blended in a ratio of 1 or more to coated articles and curing with electron beams in an inert gas atmosphere. Method: The second component is a (meth)acrylate oligomer which is a (meth)acrylic acid ester of an oligomer consisting of tetrahydrofucric acid and trimethylolpropane or pentaerythritol.

(Aspects of the Invention) Unlike methacrylate monomers, the acrylate monomer used in the present invention has high reactivity, so even if the acrylate monomer alone is not blended with an oligomer, it can be cured by electron beam irradiation to form a coating film. can. However, when painting on steel plates, etc., the adhesion of the coating film is insufficient, but the decrease in adhesion can be caused by: This can be supplemented by applying appropriate surface treatments such as the following, thereby maintaining practically sufficient adhesion.

Therefore, the present invention also includes a method using a coating composition containing only such acrylate monomer as a coating film-forming component.

The acrylate monomer must contain 3 (1''-) acryloyl groups in one molecule, and must have an equivalent weight of at least 150 acryloyl groups.According to the experiments conducted by the present inventors, 1 Those in which the number of acryloyl groups in the molecule is less than 2111 illu (e.g., 1 ribropylene glycol diacrylate, diethylene glycol diacrylate), and those in which the number is 31 or more but the acryloyl group equivalent exceeds 150, such as 160 However, even if a large amount of monomer (approximately 90%) was used, the coating film had a pencil hardness of 28 or less (η).
The higher the amount of monomer, the higher the hardness of the coating film). However, in the present invention, the following acrylate monomers are used. Such acrylates (compounds readily available that meet the monomer requirements include trimethylolpropane), 47. Engineering IJ,
', IJ l, -, +1/ l = IJ a, 1J.

-to, pentacorythritol, 1-acrylate, dipentaerythritol, and 1-acrylate.

Of course, mixtures of these can also be used. In addition, monomers other than those listed above may also be used, as long as they meet the above requirements.
It could be used.

The (meth)acrylate oligomer optionally blended into the coating composition used in the present invention as a second component is the same as that described in the aforementioned Japanese Patent Publication No. 56-8070, and this is tetrahydrofucric acid. and [-trimethylolpropane or pentaerythritol at the end)
It is obtained by reacting an alcohol component in excess so that one group remains, and then esterifying the resulting OH-containing polyester oligomer with acrylic acid or methacrylic acid. Such oligomers are also commercially available. Available.

The (meth)acrylate oligomer used in the present invention is 1
It is preferable that 1JJ contains two or more acryloyl groups and the (meth)acryloyl group equivalent is 500 or less.

When this (meth)acrylate oligomer is blended as the second component, as will be explained in detail later, the first component/
The blending ratio is such that the weight ratio of the second component is 1/1 or more.

However, based on the total amount of both components, acrylate monomer is used in an amount of 50% or more.

The coating composition used in the present invention can be made into either a clear coating containing no pigment or an opaque coating containing a pigment dispersed therein. Since this composition contains a large amount of acrylate monomer, it has a low viscosity, and depending on the coating method, it can be made into a paint without adding any non-reactive volatile organic solvents that cause air pollution. Even if it is necessary to add an organic solvent to adjust the viscosity, the amount added is very small, and the solvent evaporates shortly after application without heating or other solvent evaporation treatments.
In many cases, it can be handled in substantially the same way as solvent-free.

Examples of the article to be coated include metal plates such as steel plates and stainless steel plates, as well as plastic sheets and molded products thereof.

In the present invention, the coating film is cured by electron beam irradiation.

Electron beam irradiation itself is already known and is not particularly limited in the present invention, but in the case of the present invention, inert gas such as nitrogen is used to prevent curing inhibition due to oxygen and to prevent ozone generation. This will be done in an atmosphere. However, the presence of trace amounts of oxygen is allowed.

The reason why the blending ratio of acrylate oligomer and (meth)acrylate-1-oligomer is set to 1/1 or more in the coating composition of the present invention is as follows.

The attached image 1 shows the dry film thickness of a clear paint made by using pentaerythritol I/reacrylate as an acrylate monomer and varying the amount of acrylate oligomer on a 0.8+U thick electrogalvanized steel plate without a primer. 8 M
This is a graph in which the pencil hardness of a coating film obtained by curing by irradiation with a rad electron beam is plotted against the amount of acrylate oligomer. As is clear from the illustrated results, the pencil hardness of the coating film is determined by the amount of acrylate oligomer being 10 to 20%.
It is at its highest when and,
When the amount of acrylate oligomer exceeds 50%, the pencil hardness becomes lower than 6H, and the property of high hardness cannot be obtained. Therefore, in the present invention, the blending amount of the (meth)acrylate oligomer is limited to 50% or less, that is, the weight ratio of acrylate monomer/(meth)acrylate oligomer is 171 or more.

From the attached drawing f1, even when the first component acrylate monomer alone, that is, the acrylate oligomer is 0%,
It can be seen that a cured coating film with high hardness can be obtained.

In addition, in the above experiment, it was found that there is a general tendency that the adhesion of the cured coating film increases as the content of the acrylate oligomer increases. However, when painting a steel plate like the one used in the -1-2 experiment, even if a large amount of acrylic 1-oligomer is blended, the second test shows that
It is difficult to ensure adhesion of oo/100. However, as shown in the examples below, by applying an appropriate base treatment, such as organic primer/primer treatment, chemical conversion treatment, or shot plus 1 treatment to the steel plate before painting, it is possible to It was found that the adhesion of 1007100 was ensured regardless of the amount blended (including the case of 100% acrylate monomer). However, when using a primer, a slight decrease in hardness is inevitable. For example, if the pencil hardness without a primer is 6H or less, when a primer is used, the pencil hardness becomes 4 to 511 or less, making it impossible to obtain the "high hardness" performance that is one of the objectives of the present invention. Therefore, in the present invention,
When using primer treatment, the amount of acrylate oligomer in the paint is desirably within a range of 40% or less based on the total amount of acrylate monomer and acrylate oligomer. A primer coating thickness of several microns is sufficient. The surface treatment can be appropriately selected by those skilled in the art depending on the coating method, the type of paint and the article to be coated, etc.

Next, the present invention will be further explained by examples, which are shown merely for illustrative purposes and are not intended to limit the present invention.

Ado Ohba Pentaerythritol triacrylate-1 contains three acryloyl groups in one molecule and has an acryloyl group equivalent of approximately 99.
・A clear paint consisting of 70 parts and 30 parts of acrylate oligomer was applied to an electrogalvanized steel sheet with a thickness of 0.8 mm without a primer to a dry film thickness of 25 μm,
An electron beam of 8 Mrad was irradiated. The acrylate oligomer was an acrylic ester of an oligomer of 1° tetraphthalic acid and trimethylolpropane, and the viscosity of this clear paint was 400 cp. The pencil hardness of the resulting cured coating film was 75/100 in the 7H5 square test. Furthermore, even with red marker ink, which is one of the most severe stain resistance tests, no trace remained when wiped with methanol 24 hours after application. Therefore, it can be seen that it has poor not only stain resistance but also solvent resistance.

Temporary implementation ↓ In this example, the same clear paint as in Example 1 was used, but
After applying an epoxy type primer, painting was performed, and the material was cured by the same electron beam irradiation. Pencil hardness is 6
II. Adhesion was secured at 100/100.

Further, there was no 9 staining with magic ink.

A paint was prepared by adding 20% by volume of titanium white to the same resin system as in Example 1. It was painted using a primer under the same conditions as in Example 1, and was cured. The pencil hardness was IOQ/100 in the 6H1 second test. There was also no contamination with the marker ink, and the gloss level at 60' was 91.

Practical implementation The same paint as in Example 3 was applied to a stainless steel plate (DF) at the same thickness and cured under the same conditions as in Example 1. Pencil hardness was 7 II, adhesion was 100/100. Met.

No contamination from marker ink, gloss level 9 at 60'
A beautiful painted stainless steel plate of No. 1 was obtained.

The results of Examples 1 to 4 are summarized in the table below.

2 Nashi '34Jm 6H' 100/1003 Titanium white 3 μm 6 H100/100 In the above examples, a small amount (5% or less) of solvent was used, but the solvent was irradiated with an electron beam after coating. It was virtually the same as using no solvent. Furthermore, as a general tendency, the hardness of the coating film was higher when titanium white was added.

The present invention has been described in detail above, but the present invention uses acrylate as a monomer and the monomer/oligomer blending ratio is 1.
By increasing the crosslinking density above, it is possible to increase the crosslinking density of the coating film, and it is possible to manufacture a coated plate having high hardness and poor stain resistance that cannot be obtained with conventional thermosetting paints. As for steel plates, coated steel plates can be manufactured that are cheaper than hollow metal plates and have performance comparable to hollow metal plates. In the case of stainless steel, f1 cannot be heated to high temperatures.
Although lightning hollow treatment is not possible, the method of the present invention makes it possible to produce colored stainless steel plates with irregular physical properties.

Furthermore, using a large amount of acrylate monomer, as in the present invention, not only provides excellent physical properties to the coating film, but also reduces the amount of oligomer, which lowers the viscosity of the coating material, which is a cause of air pollution. NaruntJ
The use of the Mi agent can be eliminated or the amount used can be reduced.

Therefore, it is believed that the present invention will greatly contribute to the development of this field due to its unique effects.

[Brief explanation of the drawing]

The accompanying drawing is a graph obtained by plotting the pencil hardness of the cured coating film against the amount of acrylate oligomer. Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent Attorney Akira Hirose −

Claims (1)

[Scope of Claims] (111) containing 3 or more acryloyl groups in the molecule and having 150 or less acryloyl groups; A coating composition comprising an acrylate monomer selected from the group consisting of erythritol tetraacrylate-1, dipentaerythritol hexaacrylate, and mixtures thereof is applied to the article to be coated, and cured with an electron beam under an inert gas atmosphere. A method for producing a coated article having high hardness and excellent stain resistance, characterized by A method for producing a coated article having high hardness and excellent stain resistance, the method comprising applying a coating composition blended in the above ratio to an article to be coated and curing it with an electron beam in an inert gas atmosphere. First component: Trimethylolpropane triacrylate-1, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol, which contains three or more ataryloyl groups in one molecule and has an acryloyl group equivalent of 150 or less. Acrylate monomer second component selected from the group consisting of hexaacrylate and mixtures thereof...(meth)acrylate which is a (meth)acrylic acid ester of an oligomer consisting of telorahydrophthalic acid and trimethylolpropane or pentaerythritol. oligomer