JPS6068083A - Formation of surface protective layer - Google Patents

Abstract

PURPOSE:To form a satisfactory surface protective film by adhering a composite sheet formed by coating a specific water dispersible photosetting self-adhesive compsn. on a self-supportable sheet onto a surface to be adhered via a self- adhesive layer then irradiating light to said layer thereby curing the self-adhesive layer. CONSTITUTION:A water dispersible photosetting self-adhesive compsn. contg. an acrylic photocrosslinking polymer emulsion which is introduced with a photo polymerizable unsatd. group by covalent bond on the outside surface of emulsion particles having the double-layered structure obtd. by a two-stage emulsion polymn. method and has film forming power as well as a photosensitizer is prepd. A composite sheet having the photosetting self-adhesive layer formed by coating such compsn. on a self-supportable sheet is adhered via the above- described self-adhesive layer on the surface to be adhered and thereafter light is irradiated thereto to cure the self-adhesive layer. Only the self-supportable sheet is then stripped and the surface protective layer consisting of the polymerized and cured matter is formed on the surface of the body to be adhered.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a surface protective layer on the surface of an adherend, and more specifically, it relates to a method for forming a surface protective layer on an adherend, and more specifically, it relates to a method for forming a surface protective layer on an adherend, and more specifically, it relates to a method for forming a surface protective layer on an adherend. The present invention provides a method for forming a surface protective layer to semi-permanently prevent damage to the surface of an adherend.

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

These series of steps begin with the attachment of the film to a plate-shaped article, followed by processing such as bending, drawing, and punching, followed by film peeling, surface cleaning, painting, and drying. In addition to being complicated, cleaning solutions and paints contain a large amount of organic solvent, which poses various safety and hygiene problems.

Therefore, the inventors have conducted extensive research with the aim of finding a method for forming a surface protective layer that can easily protect the surface of a plate-shaped article before processing and after processing, and that does not require the use of organic solvents during construction. As a result, the above objective was achieved through the use of a photocurable adhesive layer, and the problem of poor dimensional stability due to volumetric shrinkage during curing, which is a wood-like drawback of photocurable resins, was applied to thin sheets. Problems such as low adhesion of the thin plate to the carno when the thin plate is applied can be solved by using an acrylic photocrosslinkable polymer emulsion in which a photopolymerizable unsaturated group is introduced into the outer layer of the emulsion particles by a two-step polymerization method, and a photosensitizer. The present inventors have discovered that the problem can be solved by creating a water-dispersible photocurable adhesive composition containing the following, and that an excellent surface protective film can be obtained, and this invention has been completed.

That is, the present invention provides an emulsion of an acrylic photocrosslinkable polymer having a film-forming ability in which a photopolymerizable unsaturated group is covalently introduced into the outer layer of emulsion particles having a two-layer structure obtained by a two-step emulsion polymerization method, and a photosensitizer. A composite sheet (or film) formed by coating a water-dispersible photocurable adhesive composition containing a photosensitive agent on a self-supporting sheet (or film) to form a photocurable adhesive layer is placed on the surface of the adherend. After laminating through the adhesive layer, the adhesive layer is cured by irradiation with light, and then the self-supporting sheet (or film)
2. A method for forming a surface protective layer, which is characterized in that a surface protective layer made of a polymerized cured product is formed on the surface of the adherend as described in 2.

According to this invention, the composite sheet (or film)
In addition to eliminating safety and hygiene problems by not using organic solvents in the manufacturing stage, damage to the surface of adherends such as plate-shaped articles before and during processing can be avoided by pasting composite sheets. After processing, the surface of the adherend is not damaged because it is protected by a surface protective layer formed by polymerizing and hardening the photocurable adhesive layer by irradiating it with light.

In addition, the surface protective layer has good adhesion to the adherend, and has little shrinkage due to photocuring, which reduces dimensional stability and prevents deformation such as curling of thin plates even when applied to thin plates. be done.

The acrylic photocrosslinkable polymer emulsion having a film-forming ability in which a photopolymerizable unsaturated group is covalently introduced into the outer layer of the above-mentioned two-layered emulsion particles used in the present invention is Examples include those obtained by adding a functional unsaturated monomer ([1) to the polymer [I].

The above-mentioned acrylic copolymer (I+ refers to the monomer or two or more unsaturated monomers described later (al component) and optionally the functional group-containing monomers described later (bl component) or the internal monomers described later (cl component). The first step of emulsion polymerization is carried out using a polyfunctional monomer as a crosslinking agent in the presence of an emulsifier and a polymerization initiator, followed by the second step of emulsion polymerization described later. It is obtained by a staged emulsion polymerization method.

The unsaturated monomer of the fa) component used in the first stage emulsion polymerization has an alkyl group with 1 to 1 carbon atoms.
Two (meth)acrylic acid alkyl esters, (meth)
Examples include esters of acrylic acid such as benzyl, cyclohexyl, and tetrahydrofurfuryl, vinyl acetate, vinyl propionate, (meth)acrylonitrile, diacetone acrylamide, and styrene.

In addition, if necessary, the functional group-containing monomer of the bl component used in the first stage emulsion polymerization includes carboxyl group-containing monomers such as (meth)acrylic acid, maleic acid, fumaric acid, and itaconic acid. or hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, acrylic alcohol, monoesteropentaerythritol triacrylate with polyethylene glycol and (meth)acrylic acid, triglycerol diacrylate, ethylene glycol or monovinyl ether of polyethylene glycol, Propylenec I
Examples include hydroxyl group-containing monomers such as J-col or monovinyl ether of polypropylene glycol.

Furthermore, (the functional monomer as an internal crosslinking agent of the Cl component is a polyfunctional monomer having two or more acryloyl groups or methacryloyl groups as a polymerizable carbon-carbon double bond in the molecule, For example, 1,4-butylene glycol di(meth)acrylate, 1,6-hexane glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyprolene glycol di(meth)acrylate,
meth) acrylate, trimethylol oil (
meth)acrylate, tetramethylolmethanetetra(
Examples include meth)acrylate.

As the emulsifier, any of the various emulsifiers used in normal emulsion polymerization can be used, and specific examples include fatty acid salts, higher alcohol sulfate ester salts, alkylbenzene sulfonates, alkylnaphthalene sulfonates, and dialkyl sulfosuccinates. Examples include anionic surfactants such as salts, alkyl phosphate salts, and polyoxyethylene sulfate salts, and nonionic surfactants such as fatty acid esters of polyethylene oxide and long-chain alkyl monoethers.

Polymerization initiators include persulfates such as ammonium persulfate and potassium persulfate, peroxides such as hydrogen peroxide and benzoyl peroxide, or reducing agents such as persulfates and alkali metal sulfites and bisulfites. and azo compounds such as azobisvaleric acid and azobis(2-amidinopropane) hydrochloride.

In the second stage emulsion polymerization, in the emulsion polymerization product of the first stage, the (relatively soft unsaturated monomer having one acryloyl group or methacryloyl group in the molecule among the al components), For example, 50 to 95 parts by weight of ethinoacrylate, petinoacrylate, 2-ethylhexyl acrylate, vinyl acetate, etc., as described in (1) above.
) a functional group-containing monomer of component [C) an epoxy group-containing monomer such as glycidyl acrylate or glycidyl methacrylate; - one or more functional group-containing monomers selected from methylol group-containing monomers 5
~50 parts by weight, the emulsifier and polymerization initiator as necessary,
A mixture containing a chain transfer agent such as thioglycolic acid, lauryl mercaptan, and carbon tetrachloride is added as it is or in a state dispersed in water. As a result, an acrylic copolymer is formed of emulsion particles having a two-layer structure, an inner and outer layer, with the emulsion particles produced in the first stage of emulsion polymerization as a nucleus and a polymer product layer formed in the second stage of emulsion polymerization on the outside. Coalescence (Il is obtained.

Incidentally, the ratio (weight ratio) of the unsaturated dose of the Al component used in the two-stage emulsion polymerization method described above is 97-3 to 20:8 for the first stage; for the second stage.
0, preferably in the range of 90:10 to 40:60.

As mentioned above, the two-step emulsion polymerization method is carried out by
The functional group-containing monomer f into which a photopolymerizable unsaturated group is introduced
The objective is to concentrate the functional groups that can undergo an addition reaction with the functional groups of lTl on the outer layer side of the emulsion particles, so that the reaction can be carried out effectively. On the other hand, in emulsion particles obtained by ordinary one-stage polymerization, functional groups are incorporated into the particles and become difficult to participate in the addition reaction.

The functional group-containing monomer (171) to be added to the two-layered acrylic copolymer +II obtained as described above has a functional group capable of reacting with the functional group of the copolymer fI+. Acrylic monomers are used, examples of which include the functional group-containing monomers of the l, (cl, and dl) components described above in (1).

This addition reaction of the functional group-containing monomer is carried out by blowing air into the aqueous medium after cooling the acrylic coelectric obtained by the two-step emulsion polymerization method, and then combining the monomer of the FBL component with the desired one. Then, amines such as triethylamine, tributylamine, dimethylaniline, etc. may be added as a catalyst, heated to about 60 to 100°C, and allowed to stand for about 2 to 24 hours. Through this addition reaction, a photopolymerizable unsaturated group is effectively covalently introduced into the outer layer of the two-layered emulsion particles, and an acrylic photocrosslinkable polymer emulsion having film-forming ability is obtained.

The amount of such a functional group-containing monomer (■1) is usually
1 to 40 parts by weight, preferably 5 parts by weight, per 100 parts by weight of the acrylic yarn copolymer obtained by two-stage emulsion polymerization.
The amount of amines used as the catalyst is preferably 20 parts by weight, and the amines as the catalyst are 0.5 to 5 parts by weight of functional group-containing monomers (0.5 to 5 parts by weight per Ill).
It is preferable to use less than % by weight.

The photosensitizer is not particularly limited as long as it promotes the photocrosslinking reaction of the polymer, but examples include dimethylbenzyl keter/Lz, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, Benzoins such as α-methylbenzoin, anthraquinones such as 1-chloroanthraquinone and 2-chloroanthraquinone, benzophenone,
Examples include benzophenones such as p-chlorobenzophenone and p-dimethylaminobenzophenone, and sulfur-containing compounds such as diphenyl disulfide and tetramethylthiuram disulfide. It is added in an amount of 0.05 to 20% by weight, preferably 0.5 to 10% by weight.

The method for adding this photosensitizer is to dissolve it using a small amount of solvent or liquid unsaturated monomer of the ial component and add it to the acrylic photocrosslinkable polymer emulsion and stir thoroughly. It is preferable to absorb and impregnate the emulsion particles.

The water-dispersible photocurable adhesive composition containing an acrylic photocrosslinkable polymer emulsion and a photosensitizer obtained as described above is a self-supporting, colored or colorless transparent adhesive composition that allows light to pass through. polyvinyl chloride sheets or films, polyolefin sheets or films (including sheets or films made of ethylene-vinyl acetate copolymers and their saponified products), polyester sheets or films (with a thickness of 10% ~300
1 to 100 μm thick on one side, such as (preferably 1 μm)
The composition is coated or transferred to form a photocurable adhesive layer, but suitable amounts of other compounding agents may be added to the composition 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, tert-butylcatechol, p-benzoquinone, 2,5-tert-butylhydroquinone, and phenothiazine. , pigments such as zinc white, yellow lead, and red iron oxide for coloring or decoration purposes, dyes such as toluidine red, phthalocyanine blue, and phthalocyanine green, other metal powders, glass peas, crow powder, glass flakes, etc., and adhering materials. For example, xylene resin, which aims to improve adhesive strength to body surfaces,
Adhesion-imparting resins such as coumaron resins, crosslinking agents such as triepoxypropyl isocyanurate and butoxymethylated melamine for the purpose of improving the cohesive force of the adhesive layer, and crosslinking agents for the purpose of improving the strength of the cured film, such as 1
・4-Ptylene gelicol di(meth)acrylate, 1
- Monomers such as 6-hexane gelicoldi(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethanetetra(meth)acrylate, etc. Examples include photopolymerizable unsaturated compounds such as epoxy acrylates, urethane-modified acrylates, and oligomers such as oligoester acrylates.

A composite sheet (or film) composed of a self-supporting sheet (or film) and a photocurable adhesive layer configured in this way can be used in the form of a plate made of a metal plate, glass plate, wood plate, decorative board, plastic plate, etc. It is attached to the surface of an adherend such as an article via an adhesive layer. Generally, the self-supporting sheet (or film) is irradiated for 0.3 seconds or more, preferably 3 seconds or more using a light source such as a high-pressure mercury lamp, ultra-high pressure mercury lamp, metal halide lamp, carbon arc lamp, or xenon lamp. Then, the adhesive layer is photopolymerized and cured.

Then, by peeling off only the self-supporting sheet (or film), a surface protective layer made of a polymeric hard material is formed on the surface of the adherend.

Note that the light irradiation may be performed after the composite sheet is attached to an adherend such as a plate-shaped article, and before or after the adherend is processed such as sheet metal cutting. Furthermore, 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.

As described above, according to the method of the present invention, a surface protective layer that can semi-permanently protect the surface of the adherend is formed by irradiating the composite sheet attached to the surface of the adherend and peeling off the self-supporting sheet. can do.

In addition, the adhesive layer of the composite sheet has good adhesion to the surface of the adherend, has very little hardening and shrinkage due to light irradiation, has excellent dimensional stability, and does not curl even when applied to various thin plates. There is no risk that this will occur.

The reason why the curing shrinkage of the adhesive layer due to light irradiation is small is because photopolymerizable unsaturated groups are introduced only in the outer layer of the emulsion particles, which is different from the case where unsaturated groups are introduced throughout the emulsion particles. In comparison, it is believed that a smaller amount of unsaturated groups is required to obtain equivalent curing properties, and therefore less volumetric shrinkage occurs due to photopolymerization.

Next, examples of the present invention will be shown. In the following, parts mean parts by weight.

Example 1 Ethyl acrylate 40 parts Methyl methacrylate 25 parts Trimethylolpropane triacrylate 5 parts Sodium dodecyl sulfate 1 part Ion exchange water 100 parts The above blended composition was charged into a 500mj' flask and heated to 70°C under an inert gas. After heating and stirring for 1 hour, 0.
0.5 parts of ammonium persulfate was added and the mixture was reacted at 70° C. for 3 hours to carry out the first stage of emulsion polymerization. Next, butyl acrylate 20 parts methacrylic acid 10 parts Sodium dodecyl sulfate 1 part Ion-exchanged water 53 parts Ammonium persulfate The mixture was added dropwise to the polymerized product at 70°C while stirring for 1 hour, and further reacted at this temperature for 1 hour to perform the second stage of emulsion polymerization.
An aqueous dispersion of an acrylic copolymer consisting of layered emulsion particles was obtained.

Subsequently, the above water dispersion was cooled to 25°C, air was blown into the liquid for 1 hour, and then 10 parts of glycidyl methacrylate and 0.1 part of dimethylaniline were added, and the reaction was carried out at 70°C for 3 hours. A photocrosslinkable polymer emulsion was obtained. Furthermore, 1 part of benzoin ethyl ether dissolved in 5 parts of neopentyl glycol diacrylate was added to this emulsion, and 70
Stirring was performed at ℃ for 1 hour to obtain a water-dispersible photocurable adhesive composition.

This composition was applied to one side of a polyethylene sheet with a thickness of 60 μm so that the thickness after drying was 10 μm, and the mixture was heated at 85°C.
The composite sheet was dried for 5 minutes to obtain a composite sheet.

This composite sheet was attached to a corona-treated polypropylene sheet with a thickness of 0.1 mm by applying pressure at 3 Q K9/cm2 for 5 seconds, and then the sheet was irradiated with light for 5 seconds from a distance of 10 cm using an IKW high-pressure mercury lamp. The adhesive layer was cured, and then the polyethylene sheet was peeled off to form a surface protective layer. When this polypropylene sheet with a surface protective layer was visually observed, no deformation such as curling was observed.

Example 2 Butyl acrylate 3 parts Cyclohexyl methacrylate 23 parts Lauryl ether 4 parts Ion-exchanged water 156 parts 500ml of the above blended composition! After heating and stirring at 70°C for 1 hour under an inert gas, 0.
0.5 parts of ammonium persulfate was added thereto and the mixture was reacted at 70° C. for 3 hours to carry out the first stage of emulsion polymerization. Subsequently, 0.05 parts of ammonium persulfate was added to this polymerization product, and 25 parts of 2-ethylhexyl methacrylate was added.
part and 15 parts of N-n-butoxymethylacrylamide and 2 parts
- 0.02 part of mercaptoethanol is added dropwise into the polymerization product at 70° C. over 1 hour with stirring, and further reacted at this temperature for 1 hour to perform emulsion polymerization on the second stage, An aqueous dispersion of an acrylic copolymer consisting of emulsion particles having a two-layer structure was obtained.

Next, the above water dispersion was cooled to 25°C, air was blown into the liquid for 1 hour, and then glycidyl meccrylate 13,
6 parts were added and the reaction was carried out at 70°C for 3 hours to obtain an acrylic photocrosslinkable polymer emulsion. Furthermore, a solution of 1 part of dimethylbenzyl ketal dissolved in 5 parts of toluene was added to this emulsion, and the mixture was stirred at 70°C for 1 hour to obtain a water-dispersible photocurable adhesive composition.

This composition was applied to one side of a polyethylene terephthalate sheet having a thickness of 50 μm so that the thickness after drying would be 30 μm, and dried at 100° C. for 5 minutes to obtain a composite sheet.

This composite sheet was used in the same manner as in Example 1 to a thickness of 0.
When a surface protective layer was formed on a 1 mm corona-treated polypropylene sheet, no deformation such as curling was observed.

Example 3 A blended composition consisting of 80 parts of styrene, 3 parts of sodium laurylbenzenesulfonate, and 154.5 parts of ion-exchanged water was placed in a 500 ml flask, heated and stirred at 70°C for 1 hour under an inert gas, and then stirred. , 0.05 part of ammonium persulfate was added and reacted at 70°C for 3 hours, and the first
Emulsion polymerization in the second stage was carried out. Subsequently, 0.05 parts of ammonium persulfate was added to this polymerization product, and a mixture consisting of 13 parts of ethyl acrylate and 8 parts of glycidyl methacrylate was added to the polymerization product at 70° C. while stirring. The mixture was added dropwise for 1 hour, and reacted at this temperature for another 1 hour to complete the second stage of emulsion polymerization, thereby obtaining an aqueous dispersion of an acrylic copolymer consisting of emulsion particles with a two-layer structure.

Next, the above aqueous dispersion was cooled to 25°C, air was blown into it for 1 hour, and then 3 parts of acrylic acid and 0.1 part of dimethylaniline were added, and the reaction was carried out at 70°C for 3 hours. A polymer emulsion was obtained. Furthermore, a solution of 1 part of benzophenone dissolved in 5 parts of pentaerythritol was added to this emulsion, and 1 part of benzophenone was dissolved in 5 parts of pentaerythritol.
Stirring was performed for a period of time to obtain a water-dispersible photocurable adhesive composition.

As shown in the above examples and the above test results, this composition can be applied to a polyvinyl chloride film having a thickness of 60 μm.As shown in the above examples and the above test results, the method of the present invention provides surface protection with good adhesion and excellent properties on adherends. It can be seen that the layer can be formed by a simple operation, and that there is little curing shrinkage of the adhesive layer due to light irradiation I during the formation of the surface protective layer.

Patent applicant: Nitto Electric Industry Co., Ltd.

Claims (1)

[Claims] (1) An acrylic photocrosslinkable polymer emulsion with film-forming ability in which a photopolymerizable unsaturated group is covalently introduced into the outer layer of two-layered emulsion particles obtained by a two-step emulsion polymerization method, and a photosensitizer. A composite sheet (or film) formed by coating a water-dispersible photocurable adhesive composition containing the following on a self-supporting sheet (or film) to form a photocurable adhesive layer, the adhesive layer on the surface of the adherend. 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.
A method for forming a surface protective layer, which comprises forming a surface protective layer made of a cured polymer on the surface of the adherend.