JP2600360B2 - Adhesive for surface protection film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a surface having good adhesion to a coated plate having a rough surface, little change in adhesive force with time after application, and excellent weather resistance. The present invention relates to an adhesive for a protective film.

[Conventional technology]

Surface protection films are used to protect the surface of metal plates such as stainless steel plates and aluminum plates, painted plates such as painted metal plates and resin plates, resin plates, glass plates, etc. during transportation, processing or holding work. . Basically necessary properties for surface protection film, after pasting with these adherends,
That is, the adhesive does not transfer to the adherend when peeled off.
In order to maintain this non-transfer property, the surface protective film is generally subjected to severe conditions such as high temperature or outdoor exposure during sticking / peeling, so that a high degree of consideration is required. For this reason, commonly used adhesives include:
As shown in JP-A-53-49032, an acrylic copolymer is crosslinked with a methylol compound to such an extent that the tackiness is not lost, and the one having improved weather resistance by increasing cohesive strength has been used. I have.

When the adherend is a relatively flat plate such as a metal plate, a resin plate, or a glass plate, the adhesive has good sticking properties and peels off without being transferred even when exposed to severe conditions. Yes, no problem.

However, recent painted plates with rough surfaces, that is, the surface roughness is 10 μm or more, in some cases 20 μm or more. There was a problem.

(1) In the case of a conventional pressure-sensitive adhesive, the amount of the pressure-sensitive adhesive to be applied is required to correspond to the surface roughness of the coated plate from the viewpoint of sticking properties. As a result, the price of the surface protection film becomes high.

(2) Even if the high coating is allowed to be expensive as shown in (1), the pressure-sensitive adhesive flows over the rough surface of the adherend after a lapse of time, and the adhesive strength after the lapse of time increases. As a result, there is a problem that peeling becomes difficult.

(3) When a roof material or the like is an adherend, the construction period is often as long as six months or more, during which time the adhesive is transferred to the adherend. In order to solve this, it is conceivable to further increase the cohesive force by increasing the amount of the above-mentioned cross-linking agent, the methylol compound, but the cross-linking becomes denser, the tackiness decreases, and is applied to a rough painted plate. The problem that it becomes difficult arises.

[Problems to be solved by the invention]

An object of the present invention is to provide a pressure-sensitive adhesive for a surface protective film that shows good sticking properties to a rough coated plate, does not require an increase in amount, has little change over time, and has excellent weather resistance. Is what you do.

[Means for solving the problem]

In view of the above problems, the present inventor has reviewed the acrylic copolymer as a main component of the pressure-sensitive adhesive, and has completed the present invention.

That is, the present invention relates to an acrylic acid alkyl ester monomer (alkyl group having 1 to 8 carbon atoms) or a methacrylic acid alkyl ester monomer (alkyl group having 1 to 8 carbon atoms.
0.1) Functional group-containing copolymer monomer 0.1 per 100 parts by weight
Acrylic rubber having a glass transition temperature of −40 to −50 ° C. and a weight average molecular weight of 1,000,000 or more, and a general formula in one molecule. And a methylol compound having two or more functional groups represented by the formula _: CH ₂ OC _n H _{2n + 1} (where n represents 0, 1, 2, 3 or 4). It is intended to provide an adhesive for a protective film.

The acrylic acid alkyl ester monomer and the methacrylic acid alkyl ester monomer are components that impart desired adhesiveness, cohesiveness, flexibility, and the like to the adhesive for a surface protective film. The alkyl acrylate monomer and the alkyl methacrylate monomer used in the present invention have an alkyl group having 1 to 8 carbon atoms. Among these monomers, for example, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate and the like are preferably used. In the present invention, two or more acrylates and methacrylates can be used in combination regardless of the type.

In addition, together with the acrylic acid alkyl ester monomer and the methacrylic acid alkyl ester monomer, a suitable amount of a vinyl monomer copolymerizable with the monomer, for example, styrene, vinyl acetate, acrylonitrile, methacrylonitrile, or the like can be used.

As the functional group-containing comonomer used in the present invention, a large number of monomers are applicable depending on the type of the functional group. The functional groups include (1) hydroxyl group, (2) carboxyl group, (3)
Examples thereof include an amino group or an acid amide group (4), and specific monomers are as follows. (1) Examples of the hydroxyl group-containing copolymerizable monomer include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, and the like.

(2) Examples of the carboxyl group-containing copolymerizable monomer include acrylic acid, methacrylic acid, maleic anhydride, and itaconic acid. (3) Examples of the amino group-containing comonomer include N, N-dimethylaminoethyl acrylate and N, N-dimethylaminoethyl methacrylate.
(4) Examples of the acid amide group-containing copolymerizable monomer include acrylamide and methacrylamide. In particular, 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate having an alcoholic hydroxyl group as a functional group are preferably used from the viewpoint of reactivity with a methylol compound serving as a crosslinking agent. Two or more of these functional group-containing copolymer monomers can be used in combination.

The functional group-containing copolymer monomer is copolymerized in an amount of 0.1 to 10 parts by weight with respect to 100 parts by weight of the alkyl acrylate monomer or the alkyl methacrylate monomer. When the amount of the functional group-containing comonomer is less than 0.1 part by weight, the crosslinking density due to the reaction with the methylol compound as a crosslinking agent is low, and a sufficient cohesive force cannot be obtained. On the other hand, if the amount exceeds 10 parts by weight, it is not preferable because the pot life of the pressure-sensitive adhesive is short and the coating operation is easily affected.

The acrylic rubber used in the present invention is obtained by copolymerizing the above-mentioned alkyl acrylate monomer or methacrylic acid alkyl ester monomer with a functional group-containing copolymerizable monomer, and has a glass transition temperature (hereinafter, Tg).
Is in the range of -40 to -50C. The Tg is adjusted by appropriately selecting the above-mentioned alkyl acrylate monomer, alkyl methacrylate monomer or functional group-containing copolymer monomer. Tg is -40 ° C
If it is higher, the sticking property to the rough coated plate is reduced, and if it is lower than −50 ° C., the sticking property is good, but floating tends to occur in a high-temperature atmosphere, and the effect intended by the present invention cannot be obtained.
This Tg can be measured by the following general method. That is, as a thermal method, DTA (Differential Therma
l Analysis), DSC (Differential Scanning Calorimet)
er) and TBA (T
traditional Braid Analysis), TMA (Thermal Mechanical
Analysis).

The weight average molecular weight (Mw) of the acrylic copolymer used in the present invention is 1,000,000 or more,
It is a copolymer, that is, an acrylic rubber. The Mw is generally measured by high performance liquid chromatography (HLC) recently, but may be measured by a conventional light scattering method, ultracentrifugation method, vapor pressure method, or the like.

The copolymerization method is not particularly limited, and is not particularly limited as long as it is a method generally used for synthesizing an acrylic rubber. However, it is difficult to polymerize Mw to 1,000,000 or more by a solution polymerization method, and synthesis by an emulsifier, such as an emulsion polymerization method or a pearl polymerization method, is generally performed.

On the other hand, methylol compounds used in the present invention has the general formula _{-CH 2 OC n H 2n + 1} ( wherein, n has the same meaning as above.) In one molecule with functional groups two or more represented Having a methylol compound.

Examples of such a methylol compound include an initial condensate of an alkyl etherified methylol melamine, for example, an initial condensate of an n-butyl etherified methylol melamine, iso
An initial condensate of butyl etherified methylolmelamine,
An initial condensate of methyl etherified methylol melamine; an initial condensate of alkyl etherified methylol urea, for example, an initial condensate of n-butyl etherified methylol urea; an initial condensate of alkyl etherified methylol melamine-urea; No.

The amount of the methylol compound is preferably 0.5 to 15 parts by weight based on 100 parts by weight of the acrylic rubber. If the amount is less than 0.5 part by weight, the crosslinking effect is small. If the amount exceeds 15 parts by weight, crosslinking occurs excessively, and the adhesive strength may be reduced.

When this methylol compound is used, an acid catalyst is usually used in many cases, and specific examples include paratoluenesulfonic acid, hydrochloric acid, ammonium chloride, oxalic acid, and phosphoric acid.

The pressure-sensitive adhesive for a surface protective film of the present invention contains two components of the acrylic rubber and the methylol compound as essential components, but a tackifier, a softener, an ultraviolet absorber, a rust inhibitor, a crosslinking accelerator, Needless to say, a compounding agent, such as a coloring agent, which is usually compounded in the adhesive may be added.

[Action]

The technical point of the pressure-sensitive adhesive for a surface protective film of the present invention is to make the adhesiveness and weather resistance compatible with a rough coated plate. In the present invention, an acrylic copolymer is used as a main component, and this is cross-linked by melamine cross-linking, urea cross-linking using a specific methylol compound as a cross-linking agent, and its weather resistance is increased by increasing cohesive force. I have. However, although increasing the cohesive force increases the weather resistance, on the other hand, the adherence is reduced because the adherend has a rough surface. Therefore, as a means for preventing a decrease in the sticking force and further improving the sticking force, a feature of the present invention is that an appropriate region of Tg and Mw of the acrylic copolymer has been found. That is, acrylic rubber having a Tg of −40 to −50 ° C. has a good sticking property because it is appropriately deformed and adhered to a rough surface under pressure sensitivity, and further has an Mw of 10
It is believed that the entanglement of high molecular weight molecules of not less than 100,000 and the crosslinking by a crosslinking agent such as melamine maintain weather resistance, and as a result, exhibit a well-balanced adhesive property as a whole.

〔Example〕

Hereinafter, the present invention will be described with reference to Examples, but the scope of the present invention is not limited by these Examples. However, all parts are parts by weight.

Example 1 butyl acrylate, acrylonitrile and 2-hydroxyethyl acrylate were obtained by mixing butyl acrylate: acrylonitrile: 2-hydroxyethyl acrylate = 85 parts: 10
Parts: after emulsion polymerization with a mixture of 5 parts (initiator: hydrogen peroxide, emulsifier: nonionic surfactant, reaction temperature: 75 ° C.,
Polymerization time: 3 hours), washed with water and dried, acrylic rubber (Tg
-42 ° C, Mw 1.35 million).

Next, the obtained acrylic rubber was used as a toluene solution. In this toluene solution, 100 parts of rubber solids were added to melan 22 (a product of Hitachi Chemical Co., Ltd.) as a methylol compound.
3 parts (as solids), butyl etherified methylol melamine), and paratoluenesulfonic acid as an acid catalyst
0.3 parts were mixed to prepare an adhesive solution.

The obtained pressure-sensitive adhesive solution is applied to a corona-treated surface of a PE film (thickness: 60 μm) containing an ultraviolet absorbent that has been corona-treated on one side so as to have a solid content of 10 μm and dried by heating at 100 ° C. for 5 minutes. Thus, a surface protective film was obtained. Table 1 shows the properties of the obtained surface protective film.

Example 2 Butyl acrylate, acrylonitrile and 2-hydroxyethyl methacrylate were converted into butyl acrylate: acrylonitrile: 2-hydroxyethyl methacrylate = 90
Parts: 5 parts: After the pearl polymerization in a composition of 5 parts (initiator: hydrogen peroxide, emulsifier: nonionic anionic surfactant, reaction temperature: 65 ° C, polymerization time: 5 hours), washed with water and dried, An acrylic rubber (Tg-46 ° C, Mw 1.07 million) was obtained.

Next, the obtained acrylic rubber was used as a toluene solution. In this toluene solution, 100 parts of rubber solids were added to melan 14 (a product of Hitachi Chemical Co., Ltd.) as a methylol compound.
Butyl etherified methylol melamine-urea) (5 parts (as solid content)) and 0.5 parts of paratoluenesulfonic acid as an acid catalyst were mixed to prepare an adhesive solution.

Using the obtained pressure-sensitive adhesive solution, a surface protective film was produced in the same manner as in Example 1. Table 1 shows the properties of the obtained surface protective film.

Comparative Example 1 Butyl acrylate, acrylonitrile and 2-hydroxyethyl acrylate were obtained by mixing butyl acrylate: acrylonitrile: 2-hydroxyethyl acrylate = 85 parts: 10
Parts: 5 parts by weight, solution polymerization was carried out in an ethyl acetate solvent to obtain an acrylic copolymer (Tg-42 ° C, Mw 450,000) solution.

The polymerization was carried out in a toluene solution at 120 ° C. for about 3 hours using azobisisobutyronitrile as an initiator.

To the obtained acrylic copolymer solution, 223 parts of melan and 0.3 part of p-toluenesulfonic acid as an acid catalyst were mixed with 100 parts of the solid content of the copolymer to obtain an adhesive solution. Using the obtained pressure-sensitive adhesive solution, a surface protective film was produced in the same manner as in Example 1. Table 1 shows the properties of the obtained surface protective film.

Comparative Example 2 Solution polymerization was carried out at 95 ° C. for about 8 hours in a toluene solution using azobisisobutyronitrile as an initiator in the same formulation as in Comparative Example 1 to obtain an acrylic copolymer having a Tg of −42 ° C. and a Mw of 800,000. Thus, a surface protective film was produced in the same manner as in Comparative Example 1 using this. Table 1 shows the properties of the obtained surface protective film.

Comparative Example 3 Emulsion polymerization of butyl acrylate and 2-hydroxyethyl acrylate was carried out in a mixture of butyl acrylate: 2-hydroxyethyl acrylate = 95 parts: 5 parts to give an acrylic rubber (Tg-52 ° C., Mw 1.4 million). Obtained. A surface protection film was produced in the same manner as in Example 1 except that the acrylic rubber thus obtained was used. Table 1 shows the properties of the obtained surface protective film.

[Effect of the Invention] The pressure-sensitive adhesive for a surface protective film of the present invention has a surface roughness of 10
It is an excellent pressure-sensitive adhesive for surface protective films that has good sticking properties to rough coated plates of μm or more, has little change over time, and exhibits long-term weather resistance.

Continued on the front page (72) Inventor Akihiko Dobashi 1500 Oji Ogawa, Shimodate City, Ibaraki Prefecture Inside the Shimodate Research Laboratory, Hitachi Chemical Co., Ltd. (72) Inventor Yutaka Yamaguchi 1500 Oji Ogawa Shimodate City, Ibaraki Prefecture (56) References JP-A-61-91277 (JP, A) JP-A-53-49032 (JP, A) JP-A-62-138576 (JP, A) JP-A-61-47772 (JP, A) JP-A-56-14565 (JP, A) JP-A-1-178567 (JP, A)

Claims (4)

(57) [Claims] 1. An acrylic acid alkyl ester monomer (alkyl group having 1 to 8 carbon atoms) or a methacrylic acid alkyl ester monomer (alkyl group having 1 to 8 carbon atoms)
A copolymer obtained by copolymerizing 0.1 to 10 parts by weight of a functional group-containing copolymer monomer with respect to parts by weight, has a glass transition temperature of −40 to −50 ° C., and further has a weight average molecular weight of 100
Acrylic rubber is 10,000 or more, the formula _{-CH 2 OC n H 2n + 1} ( wherein, n represents. 0, 1, 2, 3 or 4) in a molecule a functional group represented by 2 A pressure-sensitive adhesive for a surface protective film, comprising a methylol compound having at least one compound. 2. The pressure-sensitive adhesive according to claim 1, wherein the functional group-containing copolymerizable monomer is 2-hydroxyethyl acrylate or 2-hydroxyethyl methacrylate having a hydroxyl group as a functional group. 3. A molecule having two or more functional groups represented by the general formula --CH ₂ OC _n H _{2n + 1} (wherein n represents 0, 1, 2, 3 or 4). The pressure-sensitive adhesive for a surface protective film according to claim 1, wherein the methylol compound is an initial condensate of an alkyl etherified methylol urea, an initial condensate of an alkyl etherified methylol melamine, an initial condensate of an alkyl etherified methylol melamine-urea, or a mixture thereof. Agent. 4. A methylol having two or more functional groups represented by the general formula -CH ₂ OC _n H _{2n + 1} (wherein n represents 0, 1, 2, 3 or 4) in one molecule. The pressure-sensitive adhesive for a surface protective film according to claim 1, wherein the compound is compounded in an amount of 0.5 to 15 parts by weight based on 100 parts by weight of the acrylic rubber.