JPS61207476A - Radiation-curable self-adhesive for surface protective film used for drawing process - Google Patents

Abstract

PURPOSE:To obtain the titled self-adhesive capable of sticking to and imparting durability suitable for processing to an adherend, by incorporating a polyfunctional thiol and an acrylic monomer in a mixture of a radiation-curable prepolymer with a radiation curable oligomer. CONSTITUTION:A self-adhesive prepared by incorporating a mixture comprising 75-95 pts.wt. radiation-curable prepolymer (A) having a (meth)acryloyl group of 5,000-50,000 in molecular weight in its molecule and 5-25pts.wt. radiation-curable oligomer (B) having a (meth)acryloyl group of 500-3,000 in molecular weight in its both terminals with 0.2-20pts.wt. polyfunctional thiol (C) and 50-100pts.wt. acrylic monomer (D) having an alkali-reactive group. When the molecular weight of the component (A) is less than 5,000, the product does not have rubber properties which are necessary as a self-adhesive while when the molecular weight is more than 50,000 the product has a high viscosity in the absence of a solvent, leading to difficulty in coating it. When the molecular weight of the component (B) is less than 500, the properties thereof cannot sufficiently be displayed, while a molecular weight of more than 3,000 causes an insufficient radiation curing in the presence of a large amount of an alkali-reactive monomer.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a drawing process that provides good adhesion to adherends such as metal plates and provides durability suitable for processing such as drawing and bending. This invention relates to a radiation-curable adhesive for surface protection films.

[Conventional technology]

Conventionally, surface image layer films have been used to preserve the surfaces of metal plates such as stainless steel plates and aluminum plates, painted metal plates, resin plates, glass, etc., but the basic characteristics required are: The adhesive should stick to these adherends and not transfer when peeled off after transportation and processing.

The adhesives commonly used for this purpose have relatively high molecular weight,
Highly viscous polymers are crosslinked to the extent that they do not lose their tackiness, resulting in increased cohesive strength.

On the other hand, since the polymer is natural rubber, synthetic rubber, etc., it must be applied onto the substrate in the form of a solution in an organic solvent.

However, in recent years, from the viewpoints of pollution, safety, resource conservation, and energy conservation, solvent-free production has been attracting attention.

In particular, radiation-curable adhesives using liquid oligomers are attracting attention as a solvent-free solution.

Therefore, the present inventors proposed a radiation-curable adhesive that has both cohesive strength and adhesive properties by first adding a chain transfer agent and an acidic group-giving monomer to a liquid oligomer that has excessive unsaturated double bonds. (Special application 1986-128)
No. 224).

However, this is not suitable for metal processing surfaces! [Problems to be solved by the invention] When used in films, it has been found that the film does not have sufficient properties to withstand high-level drawing processing and can only be applied to light processing. [Problems to be solved by the invention] Drawing processing is generally After the stage or three stage drawing process,
The process is completed through processes such as trimming, drilling holes, and attaching parts, but as a general rule, if the surface protection film does not adhere well to the metal plate at each stage, the film may fold and overlap in the next process, causing the film to overlap on the metal plate. Leaves a mark.

That is, the conventional surface protection film has the disadvantage that it naturally peels off from the periphery during the intermediate process (hereinafter, this phenomenon is referred to as 1-floating 1).

Lifting occurs due to deformation or plastic deformation of the metal plate, whereas the base film contains an elastic element, so a stress corresponding to the deformation rate remains, and it is unable to withstand this stress.

In the case of highly drawn products such as the ball part of a stainless steel sink, the deformation rate of the metal plate locally reaches ±50%. In this case, there will be 3 to 6 steps, or each step will be done in principle as continuous work, and the floating will be at least 1 hour, and if holidays are included, it will be left in the middle for a week. It is required that it does not occur even if it occurs.

When observing the situation of floating when using a surface protection film, the adhesive often transfers onto the metal plate and breaks the interface. This indicates that it is necessary to strengthen the interfacial adhesion between the metal plate and the metal plate.

Therefore, the present inventors obtained some results by adding a monomer having an acidic group as described above. however,
In the case of high-level drawing processing, it was not sufficient and the situation was such that lifting occurred. In order to achieve this goal, we incorporated a large amount of the above acidic group-giving monomer to improve interfacial adhesion with good radiation curability.We reviewed the liquid oligomer and chain transfer agent, and as a result of extensive research, we arrived at the present invention. did.

[Means for solving problems]

That is, the present invention uses 75 to 95 parts by weight of a radiation-curable prepolymer having a molecular weight of s, ooo to 5 Q, 000 and a molecular weight of 500 to 5,000 parts by weight.
02 to 20 parts by weight of a polyfunctional thiol and 50 to 1001 parts of an acrylic monomer having an acidic group are blended into a mixture of 5 to 25 parts by weight of a radiation-curable oligomer having meth)acrylic Ωyl groups at both ends. The gist of this paper is a radiation-curable adhesive for surface protection films that can be used in a drawing process.

In the adhesive of the present invention, the molecular weight of the main component (meta)
Radiation-curable prepolymers with acryloyl groups include acrylics copolymerized with (meth)acrylic acid alkyl esters in the main chain at a low degree of polymerization, as well as oligomers such as polyols, polyesters, polyurethanes, polybutadiene, polychloroprene, and polyisoprene. It is a prepolymer having one or more methacrylic or acrylic groups per molecule at the terminal or side chain.

Moreover, the oligomer is in a liquid state and does not require a solvent; even if a solvent is used, it is only a small amount.

The method of imparting a (meth)acryloyl group to the terminal or side chain is carried out by utilizing a reaction between an acid and an epoxy, as shown in Japanese Patent Laid-Open No. 57-10667.

Furthermore, its molecular weight is determined to be from 5,000 to 5,000 by measuring methods such as high performance liquid chromatography.
is within the range of

If it is less than 5,000, the intermolecular distance is short and a rubbery adhesive cannot be obtained, and if it is more than so or ooo, it is in a solvent-free state or has a high viscosity9, making it difficult to coat.

The radiation-curable oligomer having (meth)acryloyl groups at both ends is the same as the above-mentioned component or has a molecular weight of 500 to 000.

If it is less than 500, a large amount of the acidic group monomer blended will be sufficiently crosslinked and cured, but because the intermolecular distance is too short, the desired acidic group for strengthening the interfacial force will be incorporated, and the properties will be fully exhibited. Can not.

On the other hand, if it is 4,000 or more, (methacacryloyl group concentration is low) radiation curing will be poor for a large amount of acidic group monomer.

On the other hand, polyfunctional thiols as essential components include ethylene glycol dithioglycole), 1,4-butanediol dithioprobionate, trimethylolpropane tris-thioglycolate, trimethylolpropane trismothiopropionate). , pentaerythritol tetrakis + thioglycolate], pentaerythritol tetrakis + β-thiopropionate), and the like. These may be used alone or in combination of two or more. These can prevent excessive crosslinking during radiation curing through chain transfer by thiol groups.
Added to suppress.

For that purpose, it is necessary to select the elliptical amount in the range α2 to 20 parts by weight, preferably 2 to 15x parts by weight. If this amount is less than 0.2 parts by weight, the effect of suppressing crosslinking will be insufficient, and if it exceeds 20 parts by weight, curing will be insufficient and cohesive force will be insufficient, which will adversely affect the adhesive properties.

Next, examples of acrylic monomers having acidic groups include acrylic acid, methacrylic acid, acryloyloxyethyl hydrogen phthalate, acryloxyethyl hydrogen tetrahydroheptalate, caprolactone acrylate, dioxyethyl acrylate trimellitate, and 2-acrylamide-2- Methylpropanesulfonic acid, 3-chloro-2-7 phosphoxypropyl methacrylate, 2-acid phosphoxyethyl acrylate, di(2-methacryloyloxyethyl) phosphate, di(2-acryloyloxyethyl) phosphoric acid, etc. Can be mentioned. These may be used alone or in combination of two or more. The amount added is 50
n is selected in the range of ~100'N parts. This child is 50 copies M
If it is less than 100 parts by weight, the interfacial force effect is insufficient and it tends to float during processing. arise.

There is also a place for mixing tackifiers, softeners, antioxidants, fillers, pigments, etc., if necessary.

The radiation referred to in the present invention refers to active energy edges such as alpha rays, beta rays,
Refers to ionizing radiation such as gamma rays, neutron beams, accelerated electron beams, and ultraviolet radiation. Further, depending on the case, a curing accelerator may be included. When irradiating, particular care must be taken in the irradiation atmosphere. However, since the generated radicals are inhibited by oxygen in the air, depending on the case, the air may be replaced with an inert gas such as nitrogen, but the film may be covered with a film or the like.

The above will be explained using examples. In addition, in the following, parts indicate parts by weight.

Example 1 50 parts of ethyl acrylate, acrylic #! 40 parts of 2-ethylhexyl and 10 parts of glycidyl methacrylate were subjected to bulk polymerization in the presence of a catalyst to synthesize a solvent-free acrylic copolymer. Next, 5 parts of acrylic acid was subjected to an addition reaction (reaction rate 90%) to obtain an acrylic radiation-curable prepolymer having an acryloyl group in the side chain (Mw 15,000).
.

Next, 1 mole of diethylene glycol and 2 moles of tolylene diisocyanate were reacted, followed by addition of 2 moles of 2-hydroxyethyl acrylate to obtain an oligomer having acryloyl groups at both ends (Mi2: 2.000).

To a mixture consisting of 85 parts of the prepolymer and 15 parts of the oligomer, 10 parts of ethylene glycol dithioglycolate and 100 parts of di(2-methacryloyloxyethyl) phosphate (manufactured by Yushi Products Co., Ltd., trade name: Hosmer M) were added to form a radiation-curing type. Created an adhesive. The solvent-free adhesive was coated to a thickness of 5 μm on a 60 μm polyethylene film that had been corona-treated on one side. Next, a linear filament type electron beam irradiation device (Energy 5science Inc.
Manufactured by: Product name Electro Curtain), acceleration voltage 160k
V, Beam 1! Using a flow of 5 mAt, under a nitrogen atmosphere (
The film was irradiated with an electron beam at a dose of 4 Mrad at an oxygen concentration of 500 kg to obtain a surface image layer adhesive film. The characteristics test results are shown in Table 1.

Example 2 W ~ 1 mole of polypropylene glycol (M$-6,000) and 2 moles of tolylene diisocyanate were reacted, followed by an addition reaction with 2 moles of 2-hydroxyethyl acrylate to form a polyol having acrylic groups at both ends. The radiation-curable adhesive Lima was synthesized (M@212,000).

To 80 parts of the prepolymer, 20 parts of the oligomer of Example 1, 5 parts of trimethylolpropane tris-thioglycolate), and 75 parts of hydrogen phthalate and oxyethyl acrylate (Kyoeisha Yushi Kagaku, trade name IOA-mp) were mixed. A radiation-curable adhesive was created. Then, an adhesive film for a polyethylene surface retention film was prepared by irradiating the film with an electron beam in the same manner. The test results are shown in Table 1.

Comparative Example 1 An adhesive film was prepared in the same manner as in Example 1 using an adhesive made of carbon tetrabromide instead of ethylene glycol dithioglycolate. The results are shown in Table 1.

Comparative Example 2 A pressure-sensitive adhesive film was prepared from the pressure-sensitive adhesive of Comparative Example 1 except for the oligomer having 1 acryloyl group at both ends. Table 1 shows the results.
Shown below.

Comparative Example 3 An adhesive film was prepared by using the adhesive of Example 2 in which the amount of hydrogen phthalate oxyethyl acrylate was reduced to 20 parts. The results are shown in Table 1.

Comparative Example 4 Acrylic rubber (Toa Paint Door Akron PS-22
0) A 20% toluene solution of an adhesive consisting of 100 parts and 5 parts of thermally racked 11 type polyfunctional incyanate (manufactured by Nippon Polyurethane ■, product name: Coronate L) was prepared in the same manner as in Example 6.
Coating 6μ of solid content on 0μ polyethylene film, 9
The adhesive film was dried by heating at 0° C. for 5 minutes. Table 1 shows the results.
Shown below.

Table 1 Test results of surface adhesive film 1) Measured according to JIS-C-2107.

(Adherent: 5US430BA plate) 2) The adhesive strength was measured by leveling it for 24 hours under a pressure of 10 kg/alF using a hot platen press at 65°C.

3) Roll pasting on colored steel plate (surface roughness 5μ),
Leave it at 80°C for 24 hours and observe the condition of the patch.

4) JI 5US304BA board with adhesive film attached
Perform 10ffiIII Erichsen squeezing according to S-B-7777, and observe the floating state after one day of standing at room temperature.

(Same as evaluation = 3)) 5) The following symbols in the table indicate the state of transfer of the adhesive to the adherend.

〔Effect of the invention〕

Claims (1)

[Claims] 1. Radiation-curable prepolymer 75 having a (meth)acryloyl group with a molecular weight of 5,000 to 50,000
Radiation-curable oligomer 5 having (meth)acryloyl groups at both ends with ~95 parts by weight and a molecular weight of 500-3,000
~25 parts by weight of polyfunctional thiol 0.2
~20 parts by weight and an acrylic monomer having an acidic group 5
A radiation-curable pressure-sensitive adhesive for drawing-processed surface protection film, which contains 0 to 100 parts by weight.