JPS603435B2 - Adhesive for surface protection film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an adhesive for a surface protection film and a surface protection film coated with the adhesive.

Surface protection films are used for the purpose of preventing scratches and improving processability of adherends such as metal plates, painted plates, resin plates, and glass plates during transportation or processing.

The adhesive used in the above film is a copolymer of an acrylic acid alkyl ester and a copolymerized monomer that is crosslinked with a crosslinking agent, and in order to protect the surface, it must have several properties. be.

For example, it has a suitable adhesive strength to the adherend, the increase in adhesive strength is small over time after application, and there is no adhesive transfer or staining. There are several factors that affect the above performance, but first of all, from the point of view of the copolymerized monomer, using acrylic acid, methacrylic acid, itaconic acid, etc., which have carboxyl groups, has the ability to produce adhesive strength easily and is difficult to lift as a protective film. However, the adhesive strength increases significantly over time, and it may even become so difficult to peel that the film breaks. For this reason, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, etc., which have hydroxyl groups and have fewer such defects, have been used, but they do not have sufficient adhesive strength, or they do not float after sheet metal processing as a film. The drawbacks, such as the tendency to cause problems, have not been fully resolved.

Looking at the molecular weight of the adhesive as another factor, the higher the molecular weight, the higher the viscosity of a solution with a certain concentration, the lower the adhesive force will be, but the adhesive force will increase over time. is on the verge of being suppressed.

From the above, in order to have several properties as a protective film, it is necessary to make the molecular weight as high as possible.

However, the following problems remain unsolved. When using a copolymerizable monomer having a carboxyl group, the copolymerizable monomer having a carboxyl group may have poor copolymerizability with other acrylic acid alkyl esters during polymerization, or even if the copolymerizability is good, gel formation may occur. Because of this, stable copolymers with large molecular weights cannot be obtained. Further, even if it is obtained, there is hardly any effect on suppressing the increase in adhesive force at the time of bulging. On the other hand, when a copolymerizable monomer having a hydroxyl group is used, there are no problems with gelation during polymerization or copolymerizability, but problems such as poor adhesive strength still remain. Another method is to copolymerize a monomer having a carboxyl group and a monomer having a hydroxyl group with an alkyl (meth)acrylate to form a polymer, but in such a case, the monomer having a levoxy group Problems remain when copolymerizing only the carboxyl group and the hydroxyl group, and the carboxyl group and the hydroxyl group undergo an esterification reaction and crosslink.
Polymerization is extremely difficult.

Therefore, the present inventors conducted various studies on new pressure-sensitive adhesives in order to solve the various drawbacks of the prior art, and as a result, they developed a copolymer of two or more types of monomers having specific functional groups. It has been discovered that the above-mentioned drawbacks can be solved by a combination, leading to the present invention.

That is, the present invention provides (1) an alkyl ester (alkyl group having 1 to 8 carbon atoms) of acrylic acid and/or methacrylic acid (hereinafter abbreviated as (meth)acrylic acid) containing 1 to 10% of a copolymerizable monomer having a carboxyl group; ) is polymerized and has a viscosity of 1
Copolymer 10-9 cloud cover having PS/20°C (15% toluene solution) of 00-200 and (meth)acrylic acid containing 0.5-10% of a copolymerized monomer having a 'b} hydroxyl group A polymer consisting of a viscosity of 2,000 to 12,000 obtained by polymerizing an alkyl ester (alkyl group having 1 to 8 carbon atoms) and 90 to 1 part by weight of a copolymer having PS/2 and C (15% toluene solution). Coalescence mixture (provided that the total amount of ruboxyl groups in the polymer mixture is 0.1% to 10% in terms of acrylic acid, and the total hydroxyl group is 0.1% to 10% in terms of 2-hydroxyethyl acrylate)
0.5 to 10 parts by weight of a crosslinking agent selected from isocyanate compounds or alkyl etherified amino resins having two or more functional groups in the molecule.
The gist of the invention is an adhesive for a surface protection film containing 2 male parts by weight.

The adhesive of the present invention is a copolymer having a high molecular weight hydroxyl group {tb} while taking advantage of the excellent adhesiveness obtained by the copolymer having a carboxyl group (al) and the prevention of film lifting during sheet metal processing. This makes it possible to suppress the increase in adhesive strength over time.

Further, the adhesive according to the present invention will be explained. That is, the carboxyl group provides adhesiveness to the adherend and has the effect of suppressing lifting after sheet metal processing as a protective film, and copolymerizable monomers having such groups include acrylic acid, methacrylic acid, and maleic acid. Contains acids such as itaconic acid. If the amount of copolymer 'a' is 10% or more, it tends to gel during polymerization, making it impossible to obtain the desired viscosity, or causing extremely poor copolymerizability. The hydroxyl group has the effect of suppressing the increase in adhesive strength over time, and an example of a copolymerizable monomer having such a group is acrylic acid-2-hydride. These include quichethyl, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, and the like. Ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, etc. are often used as (meth)acrylic acid alkyl esters, but other (meth)acrylic acid alkyl esters also have an alkyl group. It can be used if the number of carbon atoms is 8 or less.

In addition, ethylene monomers copolymerizable with the above monomers, such as styrene, Q-methylstyrene, vinyl acetate,
Appropriate amounts of acrylonitrile, methacrylonitrile, etc. may be used.

In addition, the copolymer 'a} has a viscosity of 10, PS/20°C, 1
A 5% toluene solution (hereinafter simply referred to as CPS) indicates the viscosity under these conditions.

) or less tends to cause staining, and conversely, if the PS is higher than 200, it tends to gel during polymerization, making it impossible to obtain a stable copolymer, or the mixture with a high molecular weight copolymer having a high viscosity. Excessive coating will interfere with coating work. Note that 'a'
When producing a copolymer, a monomer having a hydroxyl group may be copolymerized and used as long as there is no problem in polymerization. However, in such a case, the monomer having a hydroxyl group should be contained in an amount of 1 to 5%, and if it exceeds 5%, gelation tends to occur during polymerization. The copolymer [b] has a viscosity of 20
If it is less than 00 PS, there is no effect of suppressing the increase in adhesive strength over time, and if it is more than 12,000 PS, the adhesive film will become rough and unstable even if it is mixed with 'a} and applied after dilution. This is not preferable because adhesive strength cannot be obtained.

Moreover, it is meaningless to copolymerize {b} with a monomer having a carboxyl group. Furthermore, regarding the adhesive obtained by mixing {a) and [b-, if the total amount of ruboxyl groups is less than 0.1% in terms of acrylic acid, it tends to lift as a protective film after sheet metal processing, and if it is more than 10%, It cannot be said that it is more effective than when it is less than 10%.

Further, if the total hydroxyl group is 0.1% or less in terms of 2-hydroxyethyl acrylate, there is no effect of suppressing the increase in adhesive strength over time, and conversely, if it is 10% or more, no increase in the effect is observed. The polymerization method is not particularly limited as long as the viscosity-concentration relationship does not deviate from the above conditions, but suspension polymerization or emulsion polymerization is preferred when solution polymerization is used to obtain a high viscosity product.

In addition, [a} and {b Harinaru adhesives may contain (meth)acrylic acid alkyl ester copolymer, tackifier resin, etc. as a third component unless the above conditions are met.
'b} It is also possible to mix in a range of 0 to 7 parts by weight per 100 parts by weight.

In order to improve the cohesive force of the above-mentioned adhesive, the adhesive is usually crosslinked by reacting with a part of the carboxyl group and/or hydroxyl group in the polymer. Included are isocyanate compounds having reactive groups, alkyl etherified melamines, and alkyl etherified ureas.

Isocyanate compounds include hexamethylene diisocyanate (HMDI), tolylene diisocyanate (T
DI), TDI/trimethylolpropane adduct, diphenylmethane diisocyanate, HMDI/trimethylolpropane adduct, HMDI piuret adduct, and the like.

As the alkyl etherified melamine, n-butyl etherified melamine, ls.

-butyl etherified melamine, methyl etherified melamine, etc., and the alkylated urea includes butyl etherified urea, etc. The amount of the crosslinking agent added is within the range of 0.5 to 20 parts by weight per 10 parts by weight of {a'+'b}. If it is less than 0.5 parts by weight, the crosslinking effect will be small, and if it is more than 2 parts by weight, the time available for coating will be extremely short, crosslinking will be excessive, and the adhesive force will be reduced, which is not preferable.

In addition to the above, compounding agents such as an ultraviolet absorber, an antioxidant, and a crosslinking accelerator may be added to the adhesive for a surface protection film of the present invention. The adhesive with the above structure has a thickness of 12 to 1
0.5~50W on the surface of 50 Buddha plastic film
It is coated and used to a thickness of .

Next, examples of the present invention will be shown.

All parts in the text indicate parts by weight, and in the case of polymers, the solid content is indicated, and the amount of carboxyl groups is expressed as the amount of acrylic acid, and the amount of hydroxyl groups is expressed as the amount of 2-hydroxyethyl acrylate. Polymer A butyl acrylate 8
3 parts of acrylonitrile, 12 parts of acrylic acid, and 5 parts of acrylic acid were polymerized in a toluene solution using penzoyl peroxide as a catalyst, and after polymerization, the concentration was adjusted to 15% to obtain a polymer solution with a PS/2000 of about 80.

Polymer B 42 parts of butyl acrylate, 4 parts of 2-ethylhexyl acrylate, 12 parts of methyl methacrylate, 3 parts of acrylic acid, and 3 parts of 2-hydroxyethyl acrylate in a toluene solution using penzoyl peroxide as a catalyst. polymerize,
After polymerization, the concentration was adjusted to 15% to obtain a polymer solution with PS/2000 of about 40.

Polymer C butyl acrylate 82 parts, acrylonitrile 1
2 parts and 6 parts of 2-hydroxyethyl methacrylate were subjected to suspension polymerization in water using Pensoyl peroxide as a catalyst,
After polymerization, salting out and washing with water were repeated, and after drying, a 15% toluene solution was prepared to obtain a polymer solution with a PS/20oo of about 700.

Polymer D: Emulsion polymerization of 6 groups of butyl acrylate, 20 parts of ethyl acrylate, 13 parts of acrylonitrile, and 5 parts of 2-hydroxyethyl acrylate in water using ammonium persulfate as a catalyst, and after polymerization, salting out and washing with water. After drying, prepare a 15% toluene solution and give a P of about 2000.
A polymer solution of S/2000 was obtained.

Polymer E Solution polymerization was carried out using the same monomer composition as Polymer C, and after polymerization, the concentration was adjusted to 15% to obtain a polymer solution with PS/20 qo of about 40.

Example 1 Tolylene diisocyanate/trimethylolpropane adduct (manufactured by Nippon Polyurethane; trade name Coronate L) was added to Polymer A6 Pus B and 40 parts of Polymer C (the total amount of ruboxyl groups below is 3%, the total amount of hydroxyl groups is 22%). ) A 15% solution containing 3 parts of solids was applied to the corona-treated surface of 60 μm of low-density polyethylene film in 50% solids.
A protective film was prepared by drying for 0.02 minutes.

The test results are shown in Table 1. Example 2 5 parts of butyl etherified melamine (manufactured by Hitachi Chemical Co., Ltd.; trade name Melan-23) was added to 40 parts of polymer A6 and fat B,
A protective film similar to that in Example 1 was prepared using a 15% solution to which 0.2% of para-toluene sulfonic acid was added.

The test results are shown in Table 1. Example 3 Polymer A3 base part and Polymer C 70 parts (the total amount of ruboxyl group is 1.5%)
, total hydroxyl group content was 3.7%) and 3 parts of Coronate L was added thereto to prepare a protective film similar to that in Example 1.

The test results are shown in Table 1. Example 4 L$ part of Coronate was added to Polymer B5 Ikarito and 50 parts of Polymer D (1.5% of total ruboxy groups, 4% of total hydroxyl groups), and the same protective film as in Example 1 was prepared. Created.

The test results are shown in Table 1. Example 5 40 parts of Polymer B, 20 parts of Polymer E, and 40 parts of Polymer D (total amount of carboxyl groups is 2%, total amount of hydroxyl groups is 3%).
1%) and 3 parts of Coronate L were added thereto to prepare a protective film similar to that in Example 1.

The test results are shown in Table 1. Comparative Example 1 3 parts of Coronate L was added to 9 parts of polymer A and 9 parts of polymer CI (total amount of ruboxyl groups 5.0%, total amount of hydroxyl groups 0.05%), and the same protection as in Example 1 was carried out. created a film.

The test results are shown in Table 1. Comparative Example 2 3 parts of Coronate L was added to BI part of polymer and 9 parts of polymer D (total amount of ruboxyl groups 0.03%, total amount of hydroxyl groups 5.0%), and the same protection as in Example 1 was carried out. created a film.

The test results are shown in Table 1. Comparative Example 3 3 parts of Coronate L was added to polymer A5 and 50 parts of polymer E (total amount of ruboxyl groups 2.5%, total amount of hydroquine groups 2.7%), and the same protection as in Example 1 was carried out. created a film.

The test results are shown in Table 1. The above evaluation was conducted through the following tests.

m Adhesive strength and change over time after pasting 0.4 Willow thickness SUS
-1 hour after applying the roll to 430BA 30 enemies/minute 18
The adhesive force measured at 0 degrees was used as the initial value, and the change over time was evaluated using the measured value after 7 days of the 6500 heating acceleration test (equivalent to about 1 year at room temperature).

It is desirable that the adhesive strength be as low as possible without interfering with workability, but if it exceeds 300 mm/25 mm, it will be difficult to peel it off. ■
Sheet metal workability (drawability) A 50x50 plate with a film pasted in the same manner as '1}
One day after heating the willow at 65° C., a 6-side drawing test was performed using an Eriksen tester as shown in FIG. 1, and the lifting of the film and changes in the board surface when left at room temperature were observed.

As is clear from Table 1, the surface protection film coated with the adhesive of the present invention shows little change in adhesive strength over time and exhibits excellent sheet metal workability.

Table 1 G Note) The alphabet for drawability (floating position) is the second
It corresponds to the figure, and the closer it is to , the less the film lifts and the better the drawing workability (sheet metal workability).

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram showing the state of drawing by an Eriksen testing machine, and FIG. 2 is a cross-sectional view of a sheet metal workpiece showing the floating position of the film after drawing. Explanation of symbols, 1...Erichsen tester punch, 2...Erichsen tester die, 3...
...Surface protection film, 4...Stainless steel plate, 5...Depth of drawing, 7...0, A to F film floating position. Figure 1 Figure 2

Claims (1)

[Claims] 1 (a) Copolymerizable monomer 1 having a carboxyl group
A copolymer obtained by polymerizing an acrylic acid alkyl ester and/or a methacrylic acid alkyl ester (however, the alkyl group has 1 to 8 carbon atoms) containing ~10% (by weight) (however, the viscosity of the 15% toluene solution is 100-2000
CPS/20°C) 10 to 90 parts by weight, and (b
) Copolymerizable monomer having hydroxyl group 0.5-1
A copolymer obtained by polymerizing an acrylic acid alkyl ester and/or a methacrylic acid alkyl ester (however, the alkyl group has 1 to 8 carbon atoms) containing 0% (by weight) (however, the viscosity of a 15% toluene solution is ~12000
0CPS/20°C) 90 to 10 parts by weight (however, the total amount of carboxy groups in the mixture is 0.1 to 10% by weight in terms of acrylic acid, and the total amount of hydroxyl groups (c) isocyanate compound or alkyl etherified amino resin having two or more functional groups in the molecule. An adhesive for a surface protection film, which contains 0.5 to 20 parts by weight of a crosslinking agent selected from the following.