JPH02199184A - Radiation-curable pressure-sensitive adhesive composition - Google Patents

Abstract

PURPOSE:To provide the title adhesive compsn. with excellent adhesiveness, water resistance, weatherability, shape retention, high-speed peelability, etc., by compounding a specified modified polybutadiene with each specified amt. of specified modified polypropylene glycol, chain transfer agent and heat polymn. inhibitor. CONSTITUTION:A modified polybutadiene consisting of 90% or more 1,2-type structure and having a number-average MW of 500-3,000, wherein at least 90% vinyl double bonds of the main chain or the side chains are hydrogenated and unsatd. double bonds are introduced into its terminals, is prepd. 100 pts.wt. said polybutadiene is compounded with 5-50 pts.wt. modified polypropylene glycol terminated with unsatd. double bonds and having a number-average MW of 1,000-20,000, 0.2-20 pts.wt. chain transfer agent with 2 or more functional groups in the molecule and 0.001-10 pts.wt. heat polymn. inhibitor (e.g. aluminum salt of N-nitrosophenylhydroxylamine) to produce a radiation-curable pressure- sensitive adhesive compsn.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a radiation-curable pressure-sensitive adhesive composition used for pressure-sensitive adhesive tapes, particularly for surface protection films of color steel plates.

(Prior art) Conventionally, surface protection films have been produced by applying adhesive T8 liquid, which is made by dissolving a high molecular weight polymer such as natural rubber or synthetic rubber in an appropriate organic solvent, onto a base material such as a plastic film and drying it. has been manufactured by. However, in recent years, the use of solvents has been considered from the viewpoints of resource saving, energy saving, non-pollution, and safety. As one of the measures to eliminate solvents,
There are radiation-curable adhesives that use liquid oligomers. Such adhesives have a relatively low molecular weight liquid oligomer coated on a base material and are irradiated with ionizing radiation to increase the molecular weight on the base material.

It is already known to use polybutadiene obtained by polymerizing butadiene to a low degree as such a liquid oligomer.

There are two types of polybutadiene: l,4-type and 1.2-type, but 1.4-type has too low a glass transition point, so it is not suitable for high-speed peeling and high-temperature adhesive strength, which is especially necessary for surface protection films. It was difficult to obtain adhesive properties such as JP-A-63-
As shown in Publication No. 196680, it is a 1.2-type,
tiX is an adhesive composition made by blending a chain transfer agent such as a thiol compound with a modified polybutadiene in which vinylic double bonds in the main chain or side chain are hydrogenated and unsaturated double bonds are introduced at the terminals. has been done. This composition has almost satisfactory basic adhesive properties as a surface protection film, such as normal adhesion and releasability.

(Problem to be Solved by the Invention) However, if a surface protection adhesive film of a radiation-curable adhesive composition made of a modified polybutadiene is used on a so-called colored steel plate coated with paint on an aluminum plate or iron plate, , there were the following problems. In other words, this adhesive film can be used after processing or transporting color steel sheets.
When Jl is released, the painted surface of the colored steel plate changes in gloss. When this phenomenon was investigated, it was found that it is different from the generally known transfer of adhesive to the colored steel plate or transfer of color steel plate paint to the adhesive, and that it is due to changes in the shape of the painted surface (unevenness). This is because the adhesive is harder than the paint.
A possible solution is to lower the Tg (glass transition temperature) of the adhesive.

As a specific method, first of all, a 1°4-type polybutadiene modified product having a low Tg is added.

Here, in the case of 1.4-type polybutadiene modified product, 1
．． Similar to type 2, hydrogenation of the vinyl double bonds in the main chain is necessary to maintain appropriate adhesive properties, including weather resistance. However, when type 1.4 is hydrogenated, it exhibits properties similar to polyethylene, as estimated from its chemical structure, that is, it becomes more crystalline and becomes a wax cane, making it an apparent low-T adhesive.
g, and the above problem of shape change is not solved, and new problems arise such as the viscosity of the pressure-sensitive adhesive composition increases and coating becomes difficult.

Next, the colored steel sheets in question are generally used for building materials such as roofs and walls, and for home appliances such as video decks and housings for stereo amplifiers and tuners. However, recently, as the purpose of streamlining such as simplifying the processing process,
Paints tend to become softer. That is, if the hardness of the paint is expressed in terms of pencil hardness, it is B or 2B instead of the conventional H or 2H. As a result, when a pressure-sensitive adhesive film made of a conventional pressure-sensitive adhesive composition is used, the problem of a change in the gloss of the coated surface due to the change in shape tends to become more and more noticeable.

The present invention has been carefully designed to address this situation, and while maintaining the basic characteristics of conventional adhesive films for surface protection such as adhesiveness and 8-meter properties, the present invention retains its color even when peeled off after going through processes such as drawing. The purpose of the present invention is to provide an excellent radiation-curable adhesive composition that does not cause changes in the shape of the surface of a steel plate.

(Means for solving 1!111) The radiation-curable adhesive WI&I composition according to the present invention comprises an adhesive component mainly composed of two types of liquid oligomers having a specific structure, a chain transfer agent, and a thermally polymerized adhesive component. More specifically, it consists of 90% or more of the 1,2 type structure, and 90% or more of the vinyl double bonds in the main chain or side chain are hydrogenated, and an unsaturated double bond is introduced at the terminal. The number average molecular weight is 5
5 to 50 parts by weight of modified polypropylene glycol having a number average molecular weight of i, ooo to 20,000 with an unsaturated double bond introduced at the terminal, per 1 molecule, per 100 parts by weight of modified polybutadiene having a molecular weight of 00 to 3°000. 0.2 to 20 parts by weight of a chain transfer agent having two or more functional groups;
The present invention further relates to a radiation-curable adhesive composition containing 0.001 to 10 parts by weight of a thermal polymerization inhibitor.

The present invention will be explained in detail below.

The modified polybutadiene used in the present invention has the following general formula (1) (wherein R1 and R1 are a hydrogen atom, an alkyl group,
Represents a hydrocarbon group such as a cycloalkyl group or an aryl group, or a substituent such as a halogen atom, where R is preferably a hydrogen atom, methyl group, or chlorine atom, and R8 is preferably a hydrogen atom). One or two selected from the butadines represented
The skeleton structure is a polybutadiene oligomer obtained by living anionic polymerization which results in a 1.2-type structure of 90% or more.

Furthermore, the vinyl group in the molecule of this polybutadiene oligo 7, that is, the vinyl double bond in the main chain or side chain is 90
% or more hydrogenated.

If the hydrogenation rate is less than 90%, since it is used in combination with a chain transfer agent, it may cause a dark reaction and thicken during storage, making it unusable as an adhesive. Also, adhesive strength may change over time and become brittle. Can be mentioned.

Furthermore, this polybutadiene oligomer has an average of 1 to 2 unsaturated double bonds (ie, at both ends) introduced into each molecule at the molecular ends. However, if there is less than one, radiation curability will be poor.

Examples of this unsaturated double bond include vinyl ester, vinyl ether, and acrylic ester.

Examples include methacrylic acid ester type, acrylamide type, methacrylic acid amide type, etc. 6. Based on these specific examples, vinyloxy group, vinyloxycarbonyl group, acryloyl group, methacryloyl group, acryloyl acid group, methacryloyl acid group,
Examples include an allyl group, an allyl ether group, an allyl thioether group, and a vinyl thioether group.

In particular, from the viewpoint of curability, highly reactive acryloyl groups and methacryloyl groups are preferred.

Although there is a method of directly introducing the unsaturated double bond at the molecular end of the polybutadiene oligomer, numerically it can be introduced through the intervention of a terminal modifier or chain extender as shown below.

In other words, there are hydroxyl groups at both ends of the hydrogenated molecule.

After passing a diisocyanate as a chain extender to a polybutadiene oligomer (commercially available products can be used) having active hydrogen such as a carboxyl group and 2 amino groups, it is treated with hydroxyethyl (meth)acrylate, etc. It is modified to introduce an unsaturated double bond at the end. Here, as the diisocyanate as a chain extender, there are tolylene diisocyanate 9, trimethylhexamethylene diisocyanate, hexamethylene diisocyanate, etc., but tolylene diisocyanate is particularly excellent from the viewpoint of heat resistance.

The molecular weight of the modified polybutadiene used in the present invention is expressed as a number average molecular weight determined by a conventional measurement method, such as an osmotic pressure method, a vapor pressure method, or a high performance liquid chromatography method.
If it is less than 00, it lacks flexibility as an adhesive and the adhesive force per coated thickness is small, and if it is more than 3,000, the viscosity becomes too high, making it difficult to form a solvent-free type and making it difficult to apply.

Next, the modified polypropylene glycol used in the present invention with an unsaturated double bond introduced at the terminal and having a molecular weight of several thousand from 1.000 to 20°000 has the following general formula [...] (n is a constant). It has the structure shown, and the skeleton is polyether obtained by ordinary condensation polymerization.

Therefore, the hydroxyl groups present at both ends of the molecule are reacted with tolylene diisocyanate, hydroxyethyl acrylate, etc. in the same manner as the modified polybutadiene described above, and an unsaturated double bond is created at the end of the molecule, with an average of one or more per molecule. Regarding the molecular weight to obtain modified propylene glycol with 2 or less introduced, from the point of view of adhesive strength and viscosity, the number average molecular weight is t, ooo
A range of 2o, ooo is desirable.

The blending amount is 5 to 50 parts by weight per 100 parts by weight of the modified polybutadiene. Less than 5 parts by weight, low T
g, the problem of shape change of the colored steel sheet cannot be solved. On the other hand, if it exceeds 50 parts by weight, the Tg becomes too low, leading to problems such as a decrease in high-temperature adhesive strength and a tendency to float. Note that even if the molecular weight of the modified polybutadiene changes, the amount of modified polypropylene glycol to be blended may be considered to be the same within the above molecular weight range.

Next, as chain transfer agents used in the present invention, ethylene glycol dithioglycole), 1. 4-Butanediol dithiopropionate, polyfunctional thiol compounds such as trimethylolpropane tris-(β-thiopropionate), pentaerythritol tetrakis-(β-thiopropionate), disulfides such as diphenyl disulfide, or Carbon tetrachloride, carbon tetrabromide, chloroform.

Examples include halogen compounds such as dichlorobenzene. These may be used alone or in combination of two or more, preferably having a chain transfer constant of 108
The above thiol compounds are suitable.

These chain transfer agents are added to suppress excessive crosslinking during radiation curing. For that purpose, it is necessary to select the amount in the range of 0.2 to 20% by weight, preferably 2 to 15% by weight. If this amount is less than 0.2% by weight, the effect of suppressing crosslinking will be insufficient;
If it exceeds % by weight, curing is insufficient and cohesive force is insufficient, which adversely affects adhesive properties.

Next, the thermal polymerization inhibitors used in the present invention include phenols such as hydroquinone and hydroquinone monomethyl ether, quinones such as β-naphthoquinone and 2-ethylanthraquinone, phenothiazine, triphenylmethane, diphenylvicrylhydrazyl, N Examples include nitroso-based compounds such as ammonium salts or metal salts of -nitrosodiphenylamine, N-nitrosodipropylamine, nitrosonaphthol, nitrosopiperidine, and N-nitrosophenylhydroxyamine.

Among them, the metal salts of N-nitrosophenylhydroxyamine are effective, particularly the aluminum salts are very advantageous. In addition, if the amount is less than 0.001 parts by weight, the storage stability effect will be small (and if it exceeds 10 parts by weight, polymerization will be inhibited in the radiation polymerization reaction. It is preferably from 0.001 to 10 parts by weight, especially from 0.01 to 1 part by weight.

The thermal polymerization inhibitor may be added to the chain transfer agent in advance or may be added at the time of blending, and the effect will not vary depending on the addition method.

Furthermore, in addition to the above-mentioned components, the adhesive composition of the present invention also contains a diluent monomer, a tackifier, and a 1M tackifier.

It may contain additives such as radiation curing accelerators and ultraviolet absorbers, and it may also contain small amounts of solvents.
It can be adjusted and used.

The adhesive composition of the present invention is obtained by blending the various components as described above. This pressure-sensitive adhesive composition is applied to a base material such as a polyethylene film to an appropriate coating thickness, and then irradiated with radiation to be cured to obtain a pressure-sensitive adhesive film.

The radiation referred to in the present invention refers to active energy rays, α
Ionizing radiation such as rays, β-rays, T-rays, neutron beams, and accelerated electron beams can be used at a dose in the range of 0°5 to 50 Mrad, but preferably about 1 to 10 Mrad. When doing so, care must be taken regarding the irradiation atmosphere. That is, since the generated radicals are inhibited by oxygen in the air, it may be necessary to use an inert gas such as nitrogen to maintain an appropriate oxygen concentration.

(Function) The pressure-sensitive adhesive composition according to the present invention can be cured by radiation, and exhibits various excellent effects.
Since the modified polybutadiene and modified polypropylene glycol used in the present invention have radiation functional groups at both ends,
After radiation curing, there are no free end chains and the molecular weight between crosslinking points becomes large. Therefore, it has a flexible crosslinked structure and provides excellent adhesiveness and application temperature characteristics.

In particular, while the ether bonds of modified polypropylene glycol are sufficiently compatible with modified polybutadiene, which is the main component,
It seems that the adhesive has a well-balanced low Tg and excellent rubber elasticity. As a result, it seems possible to maintain the water resistance, light resistance, and heat resistance obtained only with modified polybutadiene.

(Example) Next, the present invention will be described in detail based on Examples, but the present invention is not limited thereto. In addition, unless otherwise specified, parts in the examples mean parts by weight.

<Synthesis of modified polybutadiene> Type 1 and 2 polybutadiene synthesized by living anionic polymerization of butadiene (trade name: Nl5SOPB G-10)
00, both terminal hydroxyl groups, number average molecular weight approximately 1000. (manufactured by Nippon Soda) in an autoclave under a platinum catalyst at 150°C for 1
Hydrogen was reacted at 0 kgf/- for 3 hours to produce polybutadiene with hydrogenated vinyl double bonds. The hydrogenation rate at that time was 90% due to the absorption of 1600 clI-' of IR.

Next, droxyethyl acrylate and tolylene diisocyanate, which is a chain extension side, were mixed in equimolar amounts and heated at 70°C for 4 hours.
2 moles of the vinyl group-containing isocyanate compound obtained by the stirring reaction for hours were mixed with 1 mole of the hydrogenated 1,2-polybutadiene, and the mixture was reacted at 80° C. for 5 hours.
A modified polybutadiene having an acryloyl group at the end (theoretical number of terminal double bonds=2) was obtained.

Modified polybutadiene B having a theoretical terminal double bond number of 1.5 was synthesized in a similar manner.

<Synthesis of modified polypropylene glycol> Polypropylene glycol (product name: PPG-3000, manufactured by Asahi Denka Special Co., Ltd.)
After mixing 2 mol of tolylene diisocyanate per 1 mol (number average molecular weight approximately 1000) and heating at 80°C for 5 hours, 2 mol of hydroxyethyl acrylate was added and 8 mol of hydroxyethyl acrylate was added.
The mixture was heated at 0° C. for 4 hours to obtain modified polypropylene glycol (theoretical number of terminal double bonds=2).

In a similar manner, three types of modified polyethers shown in Table 2 were synthesized.

The properties of the obtained modified polybutadiene and modified polypropylene glycol are shown in Tables 1 and 2.

Table 1 Characteristics of modified polybutadiene Examples and comparative examples In addition to the modified polybutadiene and modified polypropylene glycol as basic components, aluminum salt of trimethylolpropane tris (β-thiopropionate) and N-nitrosophenylhydroxylamine (trade name q -t
3ot: manufactured by Wako Pure Chemical Industries, Ltd.) to obtain a radiation-curable adhesive composition (details of formulation are shown in Table 3).

The obtained adhesive composition was spread on a polyethylene film (thickness 6
0 μ) to a coating thickness of 10 #s, and then using an electron beam irradiation device (linear filament type, En6rgy 5cke) with an acceleration voltage of 200 KV and a beam current of 10 mA.
5 Mra under a nitrogen gas atmosphere (oxygen concentration 500 ppm) using CE Inc., product name Electrocurtain).
d irradiation to create an adhesive film for surface protection.

This adhesive film was attached to a 5OS-430BA plate and a color steel plate, and various tests were conducted. The results are summarized in Table 4.

Margin below (Effects of the Invention) As is clear from the results of the above examples, according to the present invention, the adhesive composition containing modified polybutadiene and modified polypropylene glycol as basic components has a high adhesive strength per coating thickness. High temperature adhesive strength, low temperature adhesion, water resistance, weather resistance, shape change over time.

It has excellent high-speed peelability and well-balanced adhesive properties, making it very useful as a pressure-sensitive adhesive.

Claims (1)

[Claims] 1,90% or more of the 1,2-type structure, 90% or more of the vinyl double bonds in the main chain or side chain are hydrogenated,
The number average molecular weight with an unsaturated double bond introduced at the end is 500.
5 to 50 parts by weight of modified polypropylene glycol having a number average molecular weight of 1,000 to 20,000 with an unsaturated double bond introduced at the terminal, per 1 molecule, per 100 parts by weight of modified polybutadiene having a molecular weight of 1,000 to 3,000. 2 functional groups
1. A radiation-curable pressure-sensitive adhesive composition, characterized in that it contains 0.2 to 20 parts by weight of a chain transfer agent having at least 100% of the chain transfer agent, and 0.001 to 10 parts by weight of a thermal polymerization inhibitor. 2. The radiation-curable pressure-sensitive adhesive composition according to claim 1, wherein the terminal unsaturated double bond of the modified polybutadiene and modified polypropylene glycol is an acryloyl group or a methacryloyl group. 3. The radiation-curable pressure-sensitive adhesive composition according to claim 1, wherein the modified polybutadiene and the modified polypropylene glycol have an average theoretical number of terminal double bonds of 1 or more per molecule. 4. The radiation-curable pressure-sensitive adhesive composition according to any one of claims 1 to 3, wherein the modified polybutadiene and the modified polypropylene glycol are polymers using tolylene diisocyanate as a terminal modifier or chain extender. 5. The radiation-curable pressure-sensitive adhesive composition according to claim 1, wherein the chain transfer agent is a thiol compound having a chain transfer constant of 10^2 or more. 6. The radiation-curable pressure-sensitive adhesive composition according to claim 1, wherein the thermal polymerization inhibitor is a nitroso compound. 7. The radiation-curable pressure-sensitive adhesive composition according to claim 6, wherein the nitroso compound is a metal salt of N-nitrosophenylhydroxylamine. 8. The radiation-curable pressure-sensitive adhesive composition according to claim 7, wherein the metal salt of N-nitrosophenylhydroxylamine is an aluminum salt.