JPS6124426B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a pressure-sensitive adhesive for surface protection films and a pressure-sensitive adhesive film for surface protection coated with the pressure-sensitive adhesive. Surface protection adhesive films are used to protect the surfaces of plate-shaped articles such as stainless steel plates, metal plates such as aluminum plates, painted steel plates, resin plates and glass plates during transportation or processing. The adhesive used as the adhesive component of the film is a copolymer of an acrylic acid alkyl ester and a copolymerizable monomer crosslinked with a crosslinking agent, and this adhesive has excellent weather resistance and transparency. However, in order to achieve the above-mentioned surface protection, it is necessary to provide some additional performance. For example, it has a suitable adhesive strength to a plate-shaped article, has little increase in adhesive strength over time, and has no adhesive residue or stains on the surface of the article. However, if acrylic acid or the like having a carboxyl group is used as a copolymerizable monomer, the adhesive strength over time increases to the extent that the film breaks when peeled off, or the adhesive remains on the surface of the plate-shaped article. However, it is difficult to obtain improved performance, and N/N-dimethylaminoethyl acrylate, which has an amino group, or acrylamide, which has an amide group, is subject to restrictions on the crosslinking method of the copolymer. The current situation is that it has not yet reached the point where it is widely used. In addition, acrylic acid-2-hydroxyethyl ester having a hydroxyl group with relatively few such drawbacks has been used as an adhesive for surface protection films, but the rubber elasticity of the resulting adhesive has There is a problem that the lifting of the film after sheet metal processing, which is the underlying cause, cannot be solved satisfactorily, and the pot life of the adhesive solution is short, resulting in poor coating workability, and improvements are desired. As a result of various studies on a new adhesive for surface protection films that solves the various drawbacks of the conventional techniques, the present inventors discovered two types of copolymerizable monomers having specific functional groups, melamine and urea resin as crosslinking agents. The present inventors have discovered that the various drawbacks mentioned above can be overcome by using one or more selected from the group of compounds having two or more NCO groups in the molecule, and have thus arrived at the present invention. That is, the present invention provides a (meth)acrylic acid alkyl ester monomer (alkyl group having 1 to 8 carbon atoms)
The present invention provides an adhesive for a surface protection film, which is characterized by copolymerizing 100 parts by weight of the following components (i) and (ii) and crosslinking with (iii). (i) Hydroxyl group-containing copolymerizable monomer 0.1~
5 parts by weight. (ii) Carboxyl group-containing copolymerizable monomer 0.1~
10 parts by weight. (iii) Melamine, urea resin and 2 or more molecules in the molecule
0.5 to 10 parts by weight of one or more selected from the group of compounds having an NCO group. The above-mentioned (meth)acrylic acid alkyl ester monomer is a component that imparts desired tackiness, cohesiveness, flexibility, etc. to the adhesive for surface protection film, and examples include butyl acrylate, 2-ethylhexyl acrylate, methacrylic acid, etc. Methyl, ethyl methacrylate, etc. are preferably used, but other (meth)acrylic acid alkyl esters with an alkyl group of 8 or less carbon atoms may be used, or these may be used in combination. . In addition, an appropriate amount of a vinyl monomer copolymerizable with the above-mentioned (meth)acrylic acid alkyl ester monomer, such as styrene, vinyl acetate, acrylonitrile, methacrylonitrile, etc., can be used. Component (i) is a monomer that is effective in improving the wetting properties on the surface of a plate-shaped article with a hydroxyl group and suppressing an increase in adhesive strength after pasting on the surface of the article, and includes 2-hydroxyethyl acrylate,
These include 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, and the like. The amount of hydroxyl group-containing monomer is 0.1 per 100 parts by weight of the (meth)acrylic acid alkyl ester monomer.
If it is less than 5 parts by weight, no improvement in wetting properties can be obtained, and if it is less than 5 parts by weight, the pot life of the adhesive composition will be short and the coating operation will be poor, which is not preferable. Component (ii) imparts adhesion to the surface of the plate-like article through its carboxyl group, and also uses the crosslinking action of the hydroxyl group-containing monomer of component (i) and the crosslinking agent of component (iii) described below. , is a monomer that acts as a reaction site for crosslinking, and includes acrylic acid, methacrylic acid, maleic anhydride, itaconic acid, etc. If the amount of the carboxyl group-containing monomer is less than 0.1 parts by weight, adhesiveness cannot be obtained, and if it is more than 10 parts by weight, crosslinking takes a long time and the adhesive strength after pasting increases significantly, which is not preferable. Component (iii) is a component that crosslinks the hydroxyl group-containing monomer and the carboxyl group-containing monomer, and includes melamine such as n-butyl etherified melamine, iso-butyl etherified melamine, methyl etherified melamine, n-butanol ether urea, Urea resins such as butyl urea, and tolylene diisocyanate, diphenylmethane diisocyanate, m-phenylene diisocyanate, biphenylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate,
It includes compounds having two or more NCO groups (isocyanate groups) in the molecule, such as xylylene diisocyanate. If it is less than 0.5 parts by weight, the crosslinking effect will be small, and if it is more than 15 parts by weight, crosslinking will occur excessively.
This is undesirable because it reduces adhesive strength. The adhesive for surface protection film of the present invention has the above four components as essential components, but compounding agents such as an ultraviolet absorber, a rust preventive agent, a crosslinking accelerator, and a coloring agent may also be added. Of course. The adhesive configured in this way has a thickness of approximately 0.01~
It is applied to the surface of a 0.2 mm plastic film or paper to a thickness of 0.05 to 0.08 mm, and then used. The following examples of the present invention are shown. The words "part of the text" indicate parts by weight. Example 1 A copolymer solution (solid content 30%) obtained by copolymerizing ethyl acrylate: 2-ethylhexyl acrylate: 2-hydroxyethyl acrylate: acrylic acid at a ratio of 60:40:1:1 (weight ratio) ). To 100 parts of the solid content of the copolymer solution, 3 parts of tolylene diisocyanate and 0.5 parts of octyltin dilaurate as a crosslinking accelerator are added and mixed to obtain the adhesive for a surface protection film of the present invention. Next, in order to evaluate the properties of the adhesive, the adhesive was applied to the treated side of a polyethylene film (thickness 0.03 mm), which had been subjected to corona discharge treatment on one side, so that the thickness after drying was 0.05 mm. It is coated and dried at 90°C for 2 minutes to obtain an adhesive film for surface protection. The test results for the film are shown in Table 1. Examples 2 to 4 A surface protective adhesive film was prepared in the same manner as in Example 1, except that the following crosslinking agents (A), (B), and (C) were added in place of 3 parts of tolylene diisocyanate. obtain. The test results for the film are shown in Table 1. (A) 5 parts of iso-butyl etherified melamine (Example 2) (B) 5 parts of iso-butyl etherified melamine and 3 parts of tolylene diisocyanate (Example 3) (C) 5 parts of n-butanol ether urea (Example 4) ) Example 5 Butyl acrylate: Acrylonitrile: 2-hydroxyethyl acrylate: Acrylic acid = 80:
A copolymer solution (solid content 25%) is obtained by copolymerizing at a ratio of 20:1:1 (weight ratio). Thereafter, a surface protective adhesive film was obtained in the same manner as in Example 1. The test results for the film are shown in Table 1. Comparative Example A copolymer solution (solid content 30%) having the proportions shown in (a), (b), (c) and (d) below was prepared, and the following Example 1 was prepared.
In the same manner as above, 3 parts of tolylene diisocyanate and 0.5 part of octyltin dilaurate were added and mixed, and the mixture was coated on the polyethylene film of Example 1 and dried to obtain an adhesive film for surface protection. The test results for the film are shown in Table 1. (a) Ethyl acrylate 60 parts 2-ethylhexyl acrylate 40 parts Acrylic acid 1 part (b) Ethyl acrylate 60 parts 2-ethylhexyl acrylate 40 parts 2-hydroxyethyl acrylate 1 part (c) Butyl acrylate 80 parts Acrylonitrile 20 parts Acrylic acid 1 part (d) Butyl acrylate 80 parts Acrylonitrile 20 parts 2-Hydroxyethyl acrylate 1 part

[Table] Measurement and discrimination method in Table 1 Initial adhesion strength: The sample film immediately after production was
A specimen was created by attaching it to a SUS430 bright annealed stainless steel plate at room temperature, left for 30 minutes, and then peeled off at a speed of 300mm/
Measure by peeling 180 degrees at min. Adhesive strength over time: The sample is left at 70°C for 3 days (equivalent to about 1 year of indoor storage), then returned to room temperature, peeled 180 degrees at a peeling speed of 300 mm/min, and measured. Workability: Paste a sample film on a stainless steel disc with a thickness of 0.4 mm and a diameter of 100 mmφ, squeeze it by 10 mm using a punch with a diameter of 50 mmφ, and visually determine the lifting of the film and the adhesive residue after squeezing. Regarding lifting, cases where there is almost no lifting or even a slight amount of lifting is still effective in preventing scratches are marked as 0, and cases where lifting is large and there is no effect on preventing scratches are marked as ×. Regarding the adhesive residue, if there is no or almost no adhesive residue, mark it as 0.
Items that could be partially determined visually were marked with an x. As is clear from the above examples, the adhesive for surface protection film of the present invention is an adhesive formed by using a combination of a hydroxyl group-containing copolymerizable monomer and a carboxyl group-containing copolymerizable monomer and crosslinking with a specific crosslinking agent. The adhesive has a small increase in adhesive strength after pasting,
This sufficiently satisfies the characteristics required of a surface protection material that is peeled off after being pasted. Also, in terms of processability, it prevents the film from lifting,
The fact that the adhesive itself does not remain on the surface of a plate-shaped article is remarkable, and it has unique performance as a surface protection adhesive film.

Claims (1)

[Scope of Claims] 1 100 parts by weight of a (meth)acrylic acid alkyl ester monomer (alkyl group with 1 to 8 carbon atoms) is copolymerized with the following components (i) and (ii), and the following (iii)
An adhesive for surface protection films characterized by being crosslinked with. (i) Hydroxyl group-containing copolymerizable monomer 0.1~
5 parts by weight. (ii) Carboxyl group-containing copolymerizable monomer 0.1~
10 parts by weight. (iii) Melamine, urea resin, and 2 or more molecules in the molecule
0.5 to 15 parts by weight of one or more selected from the group of compounds having an NCO group.