JPS5819709B2 - Photocurable pressure-sensitive adhesive composition - Google Patents

Description

[Detailed description of the invention] The present invention relates to a photocurable pressure-sensitive adhesive composition.

More specifically, the present invention relates to an acrylic photocurable pressure-sensitive adhesive composition that exhibits excellent adhesive properties in the absence of an organic solvent or almost no solvent.

Conventionally, in the case of known pressure-sensitive polyacrylic esters or acrylic ester copolymers, it is necessary to exert the desired adhesive properties, that is, the adhesive force to the adherend and the cohesive force of the pressure-sensitive adhesive itself. This requires the use of relatively high molecular weight, high viscosity polymers, which must therefore be applied to the substrate as a solution in an organic solvent.

However, in order to evaporate a large amount of the used solvent and obtain a pressure-sensitive adhesive with excellent adhesive properties, a long drying process is required after application.

Moreover, many of the solvents used for the above purpose are volatile, easily flammable, and have an adverse effect on the human body, so their use often causes fires and causes various pollution problems.

Furthermore, from an economical standpoint and the above-mentioned pollution prevention standpoint, the installation of a solvent recovery device, which is unavoidable, is generally expensive and requires a large space.

In order to prevent the above-mentioned drawbacks, in recent years, attempts have been made to make pressure-sensitive adhesives solvent-free.

As one of these, photocurable pressure-sensitive adhesives are attracting attention.

The reason for this is that photo-curable pressure-sensitive adhesives can be so-called solvent-free, meaning they do not, in principle, contain organic solvents, which are the disadvantages of solution-type pressure-sensitive adhesives, or even if they contain only a small amount. In addition, (1) the curing (polymerization) reaction is fast because it uses light, which is an active energy ray; (2) the curing reaction progresses only when the curing reaction is irradiated with light, so the pot life can be freely adjusted. (3) It does not require a large drying oven during production; this is because it has the following characteristics.

However, even this photocurable pressure-sensitive adhesive has the following drawbacks.

That is, in general, after light irradiation, the curing (polymerization) reaction proceeds from generated radicals to unsaturated double bonds, which are photosensitive groups, but the reaction rate is fast and excessive crosslinking is likely to occur.

(As a result, the glass transition temperature increases.

) Therefore, the formed film has low adhesion, is brittle, and in extreme cases of high polymerization shrinkage can crack.

Therefore, there is a drawback that a satisfactory adhesive force cannot be obtained.

On the other hand, if the amount of unsaturated double bonds in the molecule is reduced in order to suppress excessive cross-linking, the reaction will proceed locally, resulting in only scattered areas with a high degree of cross-linking, but the overall effect will be insufficient. This results in a gathering that does not have cohesive force.

That is, it has been extremely difficult to maintain cohesive strength without reducing adhesive strength.

In view of the above-mentioned situation, the present inventors have conducted intensive studies and have found that a comparative product containing tetrahydrofurfuryl (meth)acrylate monomer as a copolymerization component in the absence of an organic solvent or almost no solvent is The inventors have discovered that a low molecular weight acrylic copolymer has excellent adhesive strength and cohesive strength, that is, can be used as a pressure-sensitive adhesive with excellent adhesive properties, leading to the present invention.

That is, the gist of the present invention is to provide an acrylic copolymer with a relatively low molecular weight (molecular weight of about 1,000 to so, ooo), and a photopolymerizable monomer that undergoes an addition reaction with a functional group in the copolymer. In a pressure-sensitive adhesive made of a reaction product obtained by reacting a reaction product in which no organic solvent is present or almost no solvent is present, the component monomer of the acrylic copolymer has the general formula (provided that , R is H or CH3.

In the present invention, when the tetrahydrofurfuryl group of the tetrahydrofurfuryl (meth)acrylate monomer to be subjected to copolymerization is irradiated with light such as ultraviolet rays, the five-membered ring opens or generates an active radical of oxygen. .

Therefore, when it comes into contact with an adherend (particularly a metal plate such as a stainless steel plate), it is thought that the generated radicals and the metal are strongly bonded, increasing the interfacial adhesion force.

It is desirable to add a large amount of this tetrahydrofurfuryl group-providing monomer in order to improve the interfacial force.
Since the glass transition point of the entire system increases and the adhesion is impaired, it is preferable to copolymerize and use within the range of 5 to 40% by weight.

Other monomers constituting this acrylic copolymer include acrylic monomers such as ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate, or methacrylic monomers. Alkyl ester monomers of groups, (
Vinyl monomers containing side chain functional groups such as meth)acrylic acid, 2-hydroxyethyl (meth)acrylate, glycidyl (meth)acrylate, and N-methylol acrylamide can be mentioned.

The proportion used is determined by the glass transition temperature of the entire system so as not to impair tackiness.

The low molecular weight acrylic copolymer is produced according to the usual synthesis method.
Catalytic systems that react only on the double bonds of monomer molecules, such as α,α′-azobisisobutyronyl-IJ, or radical generators such as benzoyl peroxide, or catalytic reactions with heavy metals. Although the polymerization is carried out using an initiator (polymerization catalyst) such as, for example, bulk polymerization, it is preferable to carry out the polymerization without using an organic solvent such as toluene or benzene or a diluent.

The polymerization conditions at this time are suitably adjusted by using a regulator such as lauryl mercaptan or carbon tetrachloride, or by increasing the concentration of a radical generator, and by changing the polymerization time and temperature.
By appropriate selection of , ooo to about 50,000 centipoise) and low viscosity (about 1103 to 105 centipoise at 30°C).

Next, by reacting the side chain functional groups present in such a copolymer with a photopolymerizable monomer having addition reactivity, it is possible to impart a double bond, which is a photosensitive group, to the side chain. I can do it.

Such monomers include glycidyl (meth)acrylate, (meth)acrylic acid, crotonic acid, maleic anhydride, 2-hydroxyethyl (meth)acrylate, vinyl isocyanate, 2-hydroxyethyl acrylate, and 2,4- reaction product of tolylene diisocyanate,
Examples include methylolated acrylamide.

This addition reaction is effective for tertiary amines such as triethylamine and quaternary amines such as triethylbenzylammonium chloride.
The reaction is carried out in the presence of a catalyst such as an ammonium salt compound and a thermal polymerization inhibitor such as hydroquinone at a temperature of from room temperature to about 140° C. for about 0.1 to 20 hours.

The reaction product obtained as described above is a photocurable acrylic copolymer, but in some cases, photopolymerizable monofunctional or polyfunctional monomers may be added to reduce the viscosity during coating. A photocurable pressure-sensitive adhesive composition is prepared by adding a tackifier or adding a softener, an antioxidant, a filler, a pigment, etc., if necessary.

In the present invention, light refers to active energy rays, including ultraviolet rays and ionizing radiation such as electron beams and gamma rays.

For ultraviolet light, the wavelength range is from about 180 nm to about 460 nm.
nm, and suitable sources include mercury arcs, low-pressure, intermediate-pressure, high-pressure, or ultra-high-pressure mercury lamps.

In addition, in the case of electron beams and gamma rays, the dose is 0.1 to 100
It can be used within the range of Mrad, but preferably 0.5~
It is about 50 Mrad.

Further, the irradiation time is generally about 0.1 to 30 seconds.

The photocurable pressure-sensitive adhesive composition of the present invention can be cured by light irradiation.
Although it cures rapidly, it can also contain a curing accelerator to further accelerate curing, which is often preferred.

If the light is ultraviolet light, a photosensitizer is used.

Examples of photosensitizers that can be suitably used include benzoin,
Benzoin compounds such as benzoin methyl ether, benzoin ethyl ether, benzoin isobutyl ether, benzoin octyl ether, etc., benzyl,
diacetyl, methylanthraquinone, amotophenone,
Examples include carbonyl compounds such as benzophenone, sulfur compounds such as diphenyl disulfide and dithiocarbamate, naphthalene compounds such as α-chloromethylnaphthalene, and metal salts such as anthracene and iron chloride.

The amount of photosensitizer used is 0.01 to 20 parts, more preferably 0.1 to 1 part, per 100 parts of the photocurable pressure-sensitive adhesive.
It is preferable that the amount is in the range of 0 parts.

When the light is ionizing radiation such as electron beams or gamma rays, curing occurs quickly without the use of a sensitizer, so there is no need to use a sensitizer.

This will be explained below using examples.

However, all parts below refer to parts by weight.

Example 1 In a four-eye flask equipped with a stirrer, thermometer, dropping funnel, and nitrogen gas blowing device, 80 parts of 2-ethylhexyl acrylate and tetrahydrofurfuryl acrylate were added.
A mixture of 5 parts of acrylic acid, 15 parts of acrylic acid, and 4 parts of α,α'-azobisisobutyronitrile was added thereto, and the mixture was heated to 80°C while stirring in a nitrogen stream.

By continuing the reaction for further 6 hours at the same temperature, a copolymer solution with a viscosity of about 104 centipoise (B-type viscometer, 30° C.) was obtained.

Next, the temperature was raised to 100°C, and 5 parts of dilycidyl methacrylate was added. A mixed solution containing 0.5 part of IJ ethylbenzylammonium chloride and 0.1 part of a thermal polymerization inhibitor was added dropwise through a dropping funnel over 30 minutes, and the reaction was continued for about 20 hours at the same temperature to form a side chain. An acrylic photocurable prepolymer with double bonds was obtained.

A photocurable pressure-sensitive adhesive composition was prepared by adding 5 parts of benzophenone as a photosensitizer to this prepolymer.

This composition was applied to a polyester film (Toshi ■ trade name Lumirror #25) to a thickness of 0.02 mm, and a commercially available high-pressure mercury lamp (intensity 80 W/cIrL) was applied for about 5 seconds from a height of 20 cm. By irradiating it with ultraviolet rays, it was polymerized and reticulated to produce an adhesive tape, and its properties were investigated.

The results are shown in Table 1.

Comparative Example 1 A copolymer solution containing 80 parts of 2-ethylhexyl acrylate, 5 parts of methyl methacrylate, 15 parts of acrylic acid, and 4 parts of α,α'-azobisisobutyronide IJ was prepared in the same manner as in Example 1. Then, a mixture of 5 parts of glycidyl methacrylate, 0.5 part of triethylbenzylammonium chloride, and 0.1 part of a thermal polymerization inhibitor was used to synthesize acrylic light with double bonds in the side chain. A curable prepolymer was obtained.

5 parts of benzophenone was added to this prepolymer to prepare a photocurable pressure-sensitive adhesive composition, and a polyester adhesive tape was produced in the same manner as in Example 1.

Its characteristics are shown in Table 1.

Note) 1) According to JIS-C-2107 measurement.

(Substrate: 5US430BA board) 2) 65°C heating acceleration test for 7 days and the increase in adhesion strength is shown in %. did.

(The smaller the increase, the better) 3) Measure the displacement distance after 30 minutes with a Bakelite plate under a load of 500 g and 120°C.

As can be seen from Table 1, in the case of Example 1, which has a tetrahydrofurfuryl group, it is an excellent pressure-sensitive adhesive because it has easy adhesive strength, has a certain cohesive force, and has little change over time. That is clear.

Example 2 In the same manner as in Example 1, 75 parts of 2-ethylhexyl acrylate, 15 parts of tetrahydrofurfuryl acrylate
parts, 10 parts of acrylic acid and α.

A photocurable prepolymer was synthesized by blending 4 parts of α'-azobisisobutyronitrile.

A composition prepared by adding 5 parts of benzophenone to this prepolymer was applied to a 0.06 mm thick polyethylene film to a thickness of 0.06 mm.
The film was coated to a thickness of 0.008 mm and irradiated with ultraviolet rays in the same manner as in Example 1 to produce an adhesive film for surface protection, and its properties were evaluated.

The results are shown in Table 2.

Comparative Example 2 An example of an adhesive consisting of 100 parts of acrylic rubber (manufactured by Toa Paint ■, trade name Door Akron PS-220) and 3 parts of a polyfunctional isocyanate (trade name Coronate L, manufactured by Nippon Polyurethane Industries ■) as a crosslinking agent. 2, the thickness is 0.
The adhesive film was coated on a 0.06 mm polyethylene film to a thickness of 0.005 mm and dried at 100'C for 3 minutes to produce an adhesive film.

Table 2 summarizes and compares the evaluation of the characteristics.

Note) ■)', 2)': Same as 1) and 2) of Note) in Table 1 3)' JISB
7777, and the state of natural peeling of the film was observed after 1 day (z).

From Table 2, it can be seen that not only does it exhibit the same adhesive strength as the ordinary thermosetting adhesive film shown in Comparative Example 2, and has good drawing properties, but also has excellent cohesive strength because it is a photocurable film. It can be seen that this is an adhesive film for surface protection with little change in adhesive strength over time.

As described above, the photocurable pressure-sensitive adhesive composition of the present invention, which is made of a relatively low molecular weight acrylic copolymer having a tetrahydrofurfuryl group, has excellent adhesive strength in a solvent-free or small solvent state. In addition, it is possible to provide a pressure-sensitive adhesive having excellent adhesive properties and cohesive force.

Claims (1)

[Scope of Claims] 1. Relatively low molecular weight (molecular weight approximately 1,000 to 50.00
There is no organic solvent obtained by reacting the acrylic copolymer of 0) with a photopolymerizable monomer that undergoes an addition reaction with a functional group in the copolymer, or almost no solvent is present. In the pressure-sensitive adhesive consisting of a reaction product of A photocurable pressure-sensitive adhesive composition characterized by containing 40% by weight.