JPS61103574A - Process for forming surface protecting layer - Google Patents

Abstract

PURPOSE:To stabilize an emulsion of a base polymer for a composition of a water-dispersible photo-curing adhesive compsn. and to improve the quality of a surface protecting layer by forming a compound sheet using a water- dispersible photo-curing adhesive compsn. contg. an emulsion of a base polymer prepd. by using an emulsifier together with a specified dispersion stabilizer. CONSTITUTION:An alkyl (meth)acrylate alone or a mixture of alkyl (meth) acrylate with other copolymerizable unsatd. monomer is emulsion-polymerized in the presence of an emulsifier and a dispersion stabilizer such as saponified polyvinyl acetate con- sisting of water-soluble polymers having >=10,000 weight average mol.wt., or polyalkylene glycol alkyl ester, etc. Then, a photopolymerizable compd. having at least one (meth)acryloyl group in a mole cule, and a photopolymerization initiator are added to prepare a water- dispersible photocuring adhesive compsn. When a surface protecting layer is formed by using the compsn. on the surface of a material to be coated, a layer having sufficient surface property, water resistance and adhesion to the base material is obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for forming a surface protective layer on an adherend surface, and more specifically to a method for forming a surface protective layer on an adherend surface, and more specifically to a method for forming a surface protective layer on an adherend surface, and more specifically, a method for forming a surface protective layer on an adherend surface, and more specifically, a method for forming a surface protective layer on an adherend surface. The present invention relates to a method for forming a surface protective layer for semi-permanently preventing damage to the surface of an adherend made of materials such as the like.

[Conventional technology]

Conventionally, the surface protection of adherends such as plate-shaped articles has been carried out by temporarily attaching a surface protection adhesive film before processing, and then applying paint etc. after processing. is common.

These series of steps begin with pasting the film onto a plate-shaped article, followed by bending and drawing.

Processing such as punching is performed, and then the film is peeled off, first cleaning the surface, painting, and drying, which is not only complicated, but also contains a large amount of organic solvent in the cleaning solution and paint, so it is not safe or safe. There were some hygiene issues.

Therefore, as an effective method to avoid the above problems, a photocurable adhesive layer is formed by coating a water-dispersible photocurable adhesive composition on a self-supporting sheet (or film). By laminating the composite sheet (or film) to the adherend surface, irradiating it with light, and then peeling off the self-supporting sheet (or film), a surface protective layer consisting of the polymerized and cured product of the above-mentioned adhesive layer is formed on the adherend surface. A method has been proposed to form a .

According to this method, the above composite sheet (or film)
Since no organic solvents are used in the manufacturing process, there are no safety or hygiene issues, and this composite sheet (or film) can be applied to prevent damage to the surface of adherends caused by plate-shaped articles before or during processing. This is prevented by keeping the
Moreover, after the J-processing, the adherend is protected by a surface protective layer formed by polymerizing and curing the photocurable adhesive layer by irradiation with light, thereby effectively preventing damage to the surface of the adherend.

In other words, this method has the advantage that it is possible to easily protect the surface of the plate-shaped article before processing and after processing.

[Problem that the invention seeks to solve]

However, the proposed method has the following problems due to the characteristics of the water-dispersible photocurable adhesive composition used to form the photocurable adhesive layer in the composite sheet (or film).

That is, the composition proposed above usually involves photopolymerization in an acrylic polymer emulsion obtained by emulsion polymerization of a (meth)acrylic acid alkyl ester alone or a mixture thereof with an unsaturated monomer copolymerizable with the alkyl ester (meth)acrylate. In this composition, a relatively large amount of a photopolymerizable compound and a photopolymerization initiator are added to the base polymer emulsion to improve its photocurability. When a polymerization initiator is added, the stability of the emulsion is extremely reduced.

For this reason, the emulsion may aggregate during storage or application of the composition, making it difficult to apply it onto a self-supporting sheet (or film) to form a composite sheet (or film), or cause streaks to form. Such streak coating makes it difficult to form a good surface protective layer. In addition, in order to avoid this problem, when the amount of emulsifier used during emulsion polymerization of the base polymer is increased, the emulsion.

Although the stability of the composite sheet (or film) is improved to some extent, the water resistance of the surface protective layer consisting of the photocurable adhesive layer when the formed composite sheet (or film) is applied to an adherend and photocured is There was a problem with extremely poor performance.

Therefore, the present invention uses a water-dispersible photocurable adhesive composition that does not have such problems to produce a composite sheet (or film) having a photocurable adhesive layer with good surface properties and no streaks. The object of the present invention is to provide a method of forming a surface protective layer with good surface properties (and good water resistance) on the surface of an adherend by using this composite sheet (or film).

[Means for solving problems]

As a result of intensive studies to achieve the above object, the inventors found that when a dispersion stabilizer is used together with a commonly used emulsifier during emulsion polymerization of a base polymer, the resulting base polymer emulsion has photopolymerizable properties. Addition of the compound and photoinitiator does not impair the stability of the emulsion, therefore, the water-dispersible photocurable adhesive composition obtained by this method is used to make the composite sheet (or film), and this sheet ( or film)
discovered that by forming a surface protective layer on the surface of an adherend in the same manner as the proposed method, it is possible to improve the surface properties of this protective layer and also to improve its water resistance.
This invention has been made.

That is, the present invention uses an alkyl (meth)acrylic ester alone or a mixture of this monomer and other unsaturated monomers copolymerizable with an emulsifier and a weight average molecular weight i.
After emulsion polymerization in the presence of a dispersion stabilizer consisting of a water-soluble polymer of o, ooo or more, a photopolymerizable compound having at least one (meth)acryloyl group in one molecule and a photopolymerization initiator are added. A composite sheet (or film) is prepared by coating a water-dispersible photocurable adhesive composition on the surface of a self-supporting sheet (or film) to form a photocurable adhesive layer, and the above adhesive layer is applied on the adherend surface. After bonding through the adhesive layer, the adhesive layer is cured by irradiation with light, and then only the self-supporting sheet (or film) is peeled off to form a surface protective layer made of a polymerized cured product on the surface of the adherend. The present invention relates to a surface protective layer forming method characterized by the following.

[Structure of the invention - Effect]

In this invention, the unsaturated monomer used as a raw material to obtain the base polymer emulsion is selected from the viewpoints of tackiness, adhesion, weather resistance, light resistance, transparency, etc. to be imparted to the adhesive composition. ) Acrylic acid alkyl ester alone or a mixture of this monomer and other unsaturated monomers copolymerizable is used.

Examples of (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, and (meth)acrylate. Examples include octyl acid, nonyl (meth)acrylate, decyl (meth)acrylate, and dodecyl (meth)acrylate.

Among these, those in which the alkyl group has 2 to 12 carbon atoms are particularly preferred. Further, the above alkyl group may be linear or branched (and two or more types may be used in combination if necessary).

Other unsaturated monomers that can be copolymerized with the above monomers include:
Carboxyl group-containing unsaturated monomers such as (meth)acrylic acid, crotonic acid, maleic acid, and itaconic acid, phosphoric acid (
(meth)acryloyloxyethyl, (meth)acryloyloxypropyl phosphate, etc. phosphoric acid group-containing unsaturated monomers, (meth)acrylic acid 2-hydroxyethyl, (
Hydroxyl group-containing unsaturated monomers such as 2-hydroxypropyl meth)acrylate, (meth)acrylic acid N-N
-dimethylaminoethyl, (meth)acrylic acid N -t
Alkylamino group-containing unsaturated monomers such as ert-butylaminoethyl, amide group-containing unsaturated monomers such as (meth)acrylamide, N-methylol (meth)acrylamide, n-butoxymethyl (meth)acrylamide,
Other examples include unsaturated monomers such as alkyl acid glycidyl ester, (meth)acrylonitrile, vinyl acetate, and styrene. The amount of these other unsaturated monomers to be added is in the range of 0 to 60 parts by weight based on 100 parts by weight of the alkyl (meth)acrylate, and is used to improve adhesion to the polar surface of the adherend and cohesion. Used for purposes such as granting.

In this invention, the above-mentioned unsaturated monomer is emulsion polymerized to form a base polymer emulsion, but this emulsion polymerization is different from conventional methods except that a specific dispersion stabilizer is used in addition to a commonly used emulsifier. There is no difference.

That is, the above-mentioned emulsifier and dispersion stabilizer may be added to an appropriate amount of water, and emulsion polymerization may be carried out according to a conventional method using a known polymerization initiator such as ammonium persulfate.

Examples of the above emulsifiers include alkylbenzene sulfonates, alkylbenzene sulfonates, fatty acid salts,
Anionic surfactants such as higher alcohol sulfate ester salts, dialkyl sulfosuccinic acids, and alkyl phosphate salts are used.

The amount of surfactant added varies depending on the type, but
Generally, the amount can be selected within the range of 0.1 to 5 parts by weight based on 100 parts by weight of the unsaturated monomer. In order to improve the water resistance after photocuring, it is preferable to use the minimum amount that allows emulsion polymerization.

The dispersion stabilizer, which is an important component of this invention and is used in combination with the emulsifier, has a weight average molecular weight of 10,000 or more, usually 3.
It is a water-soluble polymer that does not form micelles. Specific examples include the following water-soluble polymers each having a weight average molecular weight of about 10.000 to 300.000.

b) Saponified polyvinyl acetate (saponification degree of 80% or more) RCO○ (CIIH2-0) -H or RCOO
(C-Hz -0), lOCR [R: alkyl group having 1 to 18 carbon atoms, m: an integer from 2 to 6, n: an integer from 50 to 3.000] alkylene glycol alkyl nistyl ha) RO (CIIHz-0) fiH or RO (C
IIHzsO), R [R: alkyl group having 1 or more carbon atoms and usually up to 18 carbon atoms, m: 2
polyalkylene glycol alkyl ether (R, R': an alkylene group having 1 to 6 carbon atoms, usually an integer from 50 to 3,000); n: an integer from 50 to 3,000;
R゛, π: Alkyl group with at least 18 carbon atoms, 1
: an integer from 2 to 6, m: an integer from 1 to 30, n: an integer from 30 to 2.000. It is generally preferable to use the amount in the range of 0.3 to 5 parts by weight per 10 parts by weight of the polymer.

In this invention, the photopolymerizable compound having at least one (meth)acryloyl group in one molecule to be blended into the base polymer emulsion obtained as described above is:
It is a polyfunctional type having at least one, preferably two or more, methacryloyl group or acryloyl group as a polymerizable double bond in one molecule, for example, 1.
4-butylene glycol di(meth)acrylate, 1.
6-hexane gelicoldi(meth)acrylate, neopentyl glycol di(meth)acrylate,
1 polyethylene glycol di(meth)acrylate,
trimethylolpropane tri(meth)acrylate,
Examples include monomers such as pentaerythritol tri(meth)acrylate and pentaerythritol tetra(meth)acrylate, and oligomers such as epoxy(meth)acrylate, urethane-modified (meth)acrylate, and oligoester (meth)acrylate. Two or more types may be used in combination if necessary.

The blending ratio of the photopolymerizable compound and the solid content of the base polymer emulsion is preferably such that the photopolymerizable compound accounts for 10 to 80i1% by weight, preferably 30 to 70% by weight of the total amount of both. . Too much of the photopolymerizable compound is undesirable because the cohesiveness of the photocurable adhesive layer before light irradiation is poor, and adhesive oozes out to the sides, and too little is undesirable because sufficient curing cannot be obtained. .

In this invention, the photopolymerization initiator used together with the photopolymerizable compound is not particularly limited as long as it promotes the photopolymerization reaction of the photopolymerizable compound. For example, benzoins such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, α-methylbenzoin, anthraquinones such as 1-chloroanthraquinone and 2-chloroanthraquinone, benzophenone, p-chloropentuphenone,
Examples include benzophenones such as p-dimethylaminobenzophenone, sulfur-containing compounds such as diphenyl disulfide and tetramethylthiuram disulfide, and dimethylbenzyl ketal. The amount of this photopolymerization initiator is 0.05 to 20 parts by weight based on 100 parts by weight of the total amount of the photopolymerizable compound and the solid content of the base polymer emulsion.
It is added in an amount of 0.5 to 10 parts by weight, preferably 0.5 to 10 parts by weight.

A water-dispersible photocurable adhesive composition comprising the above photopolymerizable compound, a photoinitiator, and a base polymer emulsion,
When the photopolymerizable compound is in a liquid state, the photopolymerizable compound can be prepared by adding and mixing a mixture of this compound and a photopolymerization initiator to the base polymer emulsion directly or, if necessary, using a small amount of an organic solvent. If it is solid, it can be obtained by dissolving it using a small amount of a solvent or other liquid compound, and then adding and mixing it according to the method described above. This adhesive composition has excellent stability as an emulsion even after the addition and mixing described above.

Appropriate amounts of other compounding agents may be added to the thus obtained water-dispersible photocurable adhesive composition of the present invention depending on the purpose. Examples of compounding agents include polymerization inhibitors that prevent thermal polymerization during production and reactions during storage, such as hydroquinone, hydroquinone monomethyl ether, and tert-
Butylcatechol, p-benzoquinone, 2.5-ter
Pigments for coloring or decoration such as t-butylhydroquinone and phenothiazine, such as zinc white, yellow lead, and red iron oxide; dyes such as toluidine red, phthalocyanine blue, and phthalocyanine green; other metal powders; glass, beads, and glass powder; , glass flakes, etc., and adhesion-imparting resins such as xylene resin and coumaron resin for the purpose of improving adhesion to the adherend surface.
Further examples include crosslinking agents such as triepoxyprobyl isocyanurate and butoxymethylated melamine for the purpose of improving cohesive force before irradiation with light.

In this way, a water-dispersible photocurable adhesive composition composed of a photopolymerizable compound, a photopolymerization initiator, and a base polymer emulsion is a colored or colorless transparent self-supporting sheet (or film) that transmits light. ), for example, polyvinyl chloride sheets or films, polyolefin sheets or films (including sheets or films made of ethylene-vinyl acetate copolymers and saponified products thereof),
Polyester sheet or film (thickness is 10-30
(preferably 0 μm), with a thickness of about 1 to 100 μm on one side.
It is coated or transferred in a range of m to form a photocurable adhesive layer. Since this adhesive layer has excellent stability as an emulsion of the adhesive composition, it has no defects such as streaks and has very good surface properties.
1 In this invention, a composite sheet (or film) consisting of a self-supporting sheet (or film) produced as described above and a photocurable adhesive layer is used as a metal plate, glass, wood board, decorative board, or plastic board. It is attached to the surface of an adherend, such as a plate-shaped article made of, etc., via the adhesive layer. Generally, from the self-supporting sheet (or film) side, a light source such as a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, a carbon arc lamp, a xenon lamp, etc. is used for 0.3 seconds or more, preferably 3 seconds or more. The adhesive layer is photopolymerized and cured by irradiation with light.

Then, by peeling off only the supporting sheet (or film), a surface protective layer made of a polymerized cured product is formed on the surface of the adherend. The supporting sheet (or film) can be easily peeled off by the loss of plastic fluidity of the adhesive layer due to photocuring.

The timing of the light irradiation may be after the composite sheet is bonded to an adherend such as a plate-shaped article, and before or after the adherend is processed such as sheet metal cutting or cutting. Furthermore, it goes without saying that the method of the present invention is applicable not only to the above-mentioned plate-shaped articles for processing, but also to mere surface protection of various articles.

[Effects of the Invention] As described above, according to the method of the present invention, as in the proposed method, the composite sheet used for surface protection of the adherend is irradiated with light and the self-supporting sheet is peeled off. In addition to being able to form a surface protective layer that can protect the surface semi-permanently, a specific dispersion stabilizer is used together with a normal emulsifier when preparing the base polymer emulsion in the water-dispersible photocurable adhesive composition for forming the above-mentioned composite sheet. By using the composition, the stability as an emulsion is improved, and the surface properties of the photocurable adhesive layer and the surface protection layer obtained by photocuring the adhesive layer can be improved. It can contribute to improving the water resistance and moisture resistance of the layer.

〔Example〕

Examples of this invention will be described below. In addition, in the following, parts mean parts by weight.

Example 1 2-ethylhexyl acrylate 60 parts Ethyl acrylate 35 parts Acrylic acid
2 parts ion exchange water
100 parts of the above blended composition was placed in a 500 ml flask, heated and stirred at 70°C for 1 hour under an inert gas, and then 0.1 part of ammonium persulfate was added and reacted at 7 liters for 5 hours to obtain a base polymer emulsion. Ta.

Next, 50 parts of tetraethylene glycol dimethacrylate and 3 parts of benzoin isobutyl ether were gradually added dropwise to 100 parts of this emulsion (solid content) while rapidly stirring the emulsion, and the mixture was uniformly mixed. A photocurable adhesive composition was obtained. This composition has a thickness of 60 mm.
One side of a μm polyethylene sheet has a dry thickness of 10 μm.
It was coated to a thickness of μm and dried at 85° C. for 5 minutes to obtain a composite sheet.

This composite sheet is BA finished stainless steel plate 5US304
After bonding to the sheet, the adhesive layer of this sheet is cured by irradiating ultraviolet rays for about 5 seconds from a loam distance with a high-pressure mercury lamp (80W/cm/lamp), and then the polyethylene sheet is peeled off to form a surface protection layer. did.

Example 2 Example 2 except that the same amount of polyethylene glycol di-n-butyl ester (weight average molecule 3118,000) was used instead of polypropylene glycol diethyl ether in the emulsion polymerization formulation described in Example 1. 1
In the same manner as above, a water-dispersible photocurable adhesive composition was prepared, a composite sheet was prepared, and a surface protective layer was formed.

Example 3 Saponified polyvinyl acetate (weight average molecular weight 10
A water-dispersible photocurable adhesive composition, a composite sheet, and a surface protective layer were prepared in the same manner as in Example 1, except that the same amount of 0.000, saponification degree 88%) was used.

Comparative Example 1 A water-dispersible photocurable adhesive composition was prepared in the same manner as in Example 1, except that polypropylene glycol diethyl ether was not used in the emulsion polymerization composition described in Example 1. I tried.

However, the emulsion coagulated at the stage of adding the photopolymerizable compound and the photopolymerization initiator, making it impossible to produce a composite sheet and form a surface protective layer.

Comparative Example 2 Polypropylene glycol diethyl ether was used in the emulsion polymerization composition described in Example 1, and the amount of sodium dodecylbenzenesulfonate was 1.5
A water-dispersible photocurable adhesive composition, a composite sheet, and a surface protective layer were prepared in the same manner as in Example 1, except that the amount was changed from 1 part to 3 parts.

Example 4 Butyl acrylate 30 parts Methyl methacrylate 50 parts Acrylonitrile
15 parts methacrylic acid
5 parts ion-exchanged water 150 parts A base polymer emulsion was obtained in the same manner as in Example 1 using the above acid compound. Next, to 100 parts of this emulsion (solid content), 60 parts of pentaerythritol triacrylate and 5 parts of dimethylbenzyl ketal were gradually added dropwise while rapidly stirring the emulsion, and mixed uniformly. A curable adhesive composition was obtained.

Thereafter, using this composition, a composite sheet was prepared and a surface protective layer was formed in the same manner as in Example 1.

Surface properties, pencil hardness, and adhesion of the surface protective layers obtained in Examples 1 to 4 and Comparative Example 2.

The results of water resistance measurements are shown in the table below. Regarding the adhesion strength, Example 1 was used with a copper plate and an acrylic plate as adherends.
-4 and Comparative Example 2, the values obtained when the surface protective layer was formed are also shown.

In addition, the adhesive strength of the adhesive composite sheet before light irradiation (initial adhesive strength) in forming the surface protective layer and the adhesive strength when peeling off the self-supporting property after light irradiation (self-supporting property - tJI
The results of the investigation regarding separation force are also listed in the table below. Note that the above measurements were performed by the following method.

Initial adhesion strength> The composite sheet was attached to a BA finished stainless steel plate 5US304, left for 30 minutes, and then peeled off at 180 degrees to measure the adhesive strength (peel speed: 300 cuts/min, 20°C x 65cm).
%RH).

Peeling force of self-supporting sheet> The composite sheet was attached to a BA-finished stainless steel plate 5US304 and exposed to ultraviolet light, and then the peeling force of the self-supporting sheet was measured (peeling speed 300fi/min, 20°C
×65%RH).

Surface quality> Visually observe the deterioration of the surface condition of sushi etc. due to the coating properties when forming the photocurable adhesive layer in the surface protective layer, and evaluate the surface condition of sushi etc. with good surface quality. Those with slight deterioration in surface properties were evaluated as Δ, and those with significant deterioration in surface properties were evaluated as ×.

<Pencil hardness> The hardness of the surface protective layer was measured according to JIS-5400.

Adhesion Strength> 100 cuts were made in the surface protection layer at intervals of 1 square in the shape of a base grid, and commercially available cellophane tape was pasted thereon.The tape was then peeled off and the remaining percentage of the base grids was expressed.

Water Resistance〉 Stainless steel plate with a surface protective layer is ion-exchanged ~ After being immersed in water at room temperature for one week, the surface protective layer is visually inspected for whitening or blistering, and if no whitening or blistering is observed, then O1 is applied. Δ indicates that there is a difference, × indicates that it is significant
It was evaluated as

As is clear from the above results, according to the method of the present invention, the adherend has good surface properties and excellent water resistance.
It is also clear that a surface protective layer with excellent hardness and adhesion can be easily formed.

Claims (3)

[Claims] (1) Dispersion of (meth)acrylic acid alkyl ester alone or a mixture of this monomer and other unsaturated monomers copolymerizable with an emulsifier and a water-soluble polymer having a weight average molecular weight of 10,000 or more. After emulsion polymerization in the presence of a stabilizer, a water-dispersible photocurable adhesive composition is prepared by adding a photopolymerizable compound having at least one (meth)acryloyl group in one molecule and a photopolymerization initiator. A composite sheet (or film) that is coated on the self-supporting sheet (or film) surface to form a photocurable adhesive layer is laminated onto the adherend surface via the adhesive layer, and then irradiated with light to form the above-mentioned adhesive layer. A method for forming a surface protective layer, which comprises curing the adhesive layer and then peeling off only the self-supporting sheet (or film) to form a surface protective layer made of a polymerized cured product on the surface of the adherend. (2) The method for forming a surface protective layer according to claim (1), wherein the emulsifier is an anionic surfactant. (3) Claim (1) wherein the dispersion stabilizer is at least one selected from saponified polyvinyl acetate, polyalkylene glycol alkyl ester, polyalkylene glycol alkyl ether, and water-soluble polyurethane resin. Or the method for forming a surface protective layer according to item (2).