JPS6020427B2 - Radiation-curable pressure-sensitive adhesive composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radiation-curable pressure-sensitive adhesive composition having high cohesive strength and excellent adhesive properties.

Conventionally, in sensitive adhesive tapes, the desired cohesive strength,
Polymers with relatively high molecular weight and high viscosity (i.e., natural rubber, synthetic rubber, etc.) to exhibit adhesive properties such as adhesive strength.
needed to be used.

For this reason, during coating, it must be applied onto the substrate in the form of a solution in an organic solvent. however,
The drying process after application requires a long time to evaporate the large amount of solvent used. Furthermore, many of the solvents used for the above purposes are volatile and flammable, and have a negative effect on the human body, so their use can cause fires and cause various pollution problems.
Solvent recovery equipment, whose installation is unavoidable from an economic standpoint as well as from the above-mentioned pollution prevention point of view, is generally expensive and requires a large space. Therefore,
In recent years, the use of solvent-free pressure-sensitive adhesives has attracted attention from the standpoints of so-called resource saving, energy saving, and pollution-free production. There are emulsion-type and hot-melt-type adhesives as solvent-free solutions, but radiation-curable pressure-sensitive adhesives that use liquid oligomers are particularly in the spotlight. That music,
In principle, radiation-curable pressure-sensitive adhesives do not contain organic solvents, which is a disadvantage of solution-type pressure-sensitive adhesives mentioned above.
It is possible to be so-called solvent-free, or even if it contains only a small amount, {11 Since radiation, which is an active energy beam, is used, the curing (polymerization) reaction is fast: [21 As the curing reaction progresses, the pot life This is because it has the following characteristics: It can be freely adjusted; [3'] does not require a large drying oven during production; However, even in the case of this radiation-curable pressure-sensitive adhesive, there are the following difficulties.
In other words, the polymerization (curing) reaction generally progresses to unsaturated double bonds due to the generated radicals after radiation irradiation, but
The reaction rate is fast and it is easy to cause excessive crosslinking. (As a result, the glass transition temperature rises.) Therefore, the formed film is brittle, and in extreme cases, polymerization shrinkage is large and causes sharpness. Examining the properties of the film in this state shows that it has high breaking strength, but has almost no elongation and does not exhibit rubber-like properties. On the other hand, if the absolute amount of unsaturated double bonds in the molecule is reduced in order to suppress excessive crosslinking, the reaction proceeds locally, resulting in insufficient cohesive force as a whole. As described above, it has been difficult to appropriately control the curing reaction and maintain adhesive properties as a pressure-sensitive adhesive.

Therefore, as shown in JP-A-55-27311, the present inventors added a polyfunctional thiol compound to a compound having a vinyl group, which cured well with radiation and had high cohesive force and adhesive properties. We discovered and proposed that there is a Although the details of why such a composition provides good adhesive strength are not clear, the SH of the polyfunctional thiol compound
It is assumed that the radiation sensitivity of the group is high, and that the reaction between the pinyl group and the SH group competes with the chain polymerization reaction between the vinyl groups, resulting in a longer distance between crosslinking points in the cured product. . However, in the case of pressure-sensitive adhesives made of compositions containing such thiol compounds, there is a problem in that even if they are sufficiently cured by radiation, they have a slight unpleasant odor characteristic of thiols.

Therefore, as a result of further intensive research, it was found that the above drawbacks could be solved by using a reaction product of dithiol and diacrylate monomer, and the present invention was achieved. The present invention provides a pressure-sensitive adhesive that has good radiation curability and adhesive strength and does not have the unpleasant odor that thiol compounds tend to have.

That is, in the present invention, a compound obtained by reacting a dithiol with a diacrylate monomer is added to 0.5 parts by weight of a radiation-curable liquid oligomer 10 having a radically crosslinkable ethylenically unsaturated double bond in the molecule. This is a radiation-curable pressure-sensitive adhesive composition characterized by containing a cloud cover of .about.3.

In the composition of the present invention, the compound formed by reacting dithiol and diacrylate monomer to be added is as follows.

In other words, the unpleasant odor of dithiol is thought to be due to a final reaction during synthesis or a hydrolyzed monofunctional thiol. Therefore,
The thiol is generally removed by purification, such as by washing with water, but this is not sufficient. Furthermore, thiol has good reactivity with vinyl groups, especially acroyl groups.

As a result, if 0.1 to 1 mol of diacrylate monomer is reacted with 1 mol of dithiol at 50°C to 120 pm for more than 2 hours, and the molecular weight is increased,
It has been found that the compound has almost no unpleasant odor even after reaction and radiation irradiation. In the composition of the present invention, it is preferable to use 0.5 to 3 parts by weight of the reaction product of dithiol and diacrylate monomer per 100 parts by weight of the radiation-curable liquid oligomer in view of the characteristics of the resulting adhesive tapes. preferable.

If it is less than 0.5 parts by weight, there is almost no effect, and if it exceeds 3 parts by weight, radiation curability tends to deteriorate.

It can be used in the present invention. Examples of the dithiol include ethane dithiol, butane dithiol, hexamethylene dithiol, decane methylene dithiol, ethylene glycol bis(thioglycolate), ethylene glycol (8-mercaptopropionate) hexane dioldithiopropionate, and the like. . Also,
Examples of diacrylate monomers include ethylene glycol diacrylate, tetraethylene glycol diacrylate, 1.6-hexane glycol diacrylate, neobentyl glycol diacrylate, ethylene glycol dimethacrylate, 1.6-hexane glycol dimethacrylate, and bismethacrylate. Oxyethyl phosphate (e.g. KAYAMER PM-2 manufactured by Nippon Kayaku ■),
Polyester diacrylate (manufactured by Nippon Kayaku brand name MA)
NDA) etc. Next, in the radiation-curable liquid oligomer having a radically crosslinkable ethylenically unsaturated double bond in the molecule in the present invention, the primary mirror is copolymerized with alkyl ester acrylate or alkyl ester methacrylate to a low degree of polymerization. In addition to oligomers, polyol acrylate, polyester acrylate, urethane acrylate, epoxy acrylate, etc.
Acrylic oligomers with one or more terminals or side chains per molecule, as well as polybutadiene, polychloroprene,
It is a reactive prepolymer such as polyisoprene.

Moreover, the oligomer is liquid and solvent-free, and even if a solvent is used, only a small amount is used. Further, its viscosity is in the range of 1 cps to 5 x 1 cps at room temperature. In the present invention, particularly preferable results are obtained with oligomers having highly reactive acrylic double bonds. In addition, a tackifier may be added to this radiation-curable liquid oligomer, and if necessary, a softener, antioxidant, filler, pigment, etc. may be mixed therein. Radiation as used in the present invention refers to active energy rays, including ionizing radiation such as Q-rays, 8-rays, Y-rays, neutron beams, and accelerated electron beams, as well as ultraviolet rays.

In the case of fin-proximal radiation, the dose can be used in the range of 0.5 to MQd, but is preferably about 1 to 2 MQd. In the case of ultraviolet rays, the wavelength range is about 18 m to 46 m, and sources include high-pressure mercury lamps and the like.
Further, depending on the case, a curing accelerator (sensitizer in the case of ultraviolet rays) may be included, but when irradiating, particular attention must be paid to the irradiation atmosphere. That is, since the generated radicals are inhibited by oxygen in the air, they may be replaced with an inert gas such as nitrogen depending on the case, but the film may be covered with a film or the like. This will be explained below using examples. Note that in the following, parts indicate parts by weight. Example 1, Comparative Examples 1 and 2 a Synthesis of a polymer thiol compound A three-necked flask equipped with a rope sieve, a thermometer, and an injection port was charged with 1.
Pour 1 mol of 6-hexanediol thiopropionate and raise the temperature to 60°C.

Next, while maintaining the temperature, 0.5 mol of powdered 1.6 hexanediol diacrylate was gradually added to 30
The mixture was injected over several minutes, and after completion of the injection, the temperature was raised to 80°C, and the mixture was kept warm for 3 hours to react, thereby obtaining a colorless and transparent polymeric thiol compound. b Synthesis of radiation-curable oligomers Butyl acrylate 8 Boto, Glycidyl methacrylate 2
0 part was subjected to bulk polymerization in the presence of a catalyst to synthesize a solvent-free acrylic copolymer.

The weight average molecular weight of the obtained liquid oligomer was approximately 5000.
The viscosity was 2xl ps (30°C). Next, an addition reaction of 1 part of acrylic acid was carried out to synthesize an acrylic radiation-curable liquid oligomer having an unsaturated double bond in the side chain. To 10 parts of the oligomer synthesized as described above, 20 parts of the high molecular weight thiol compound synthesized in step a was added to prepare a radiation-curable sensitive adhesive composition.

Next, as Comparative Example 1, a composition containing only the oligomer not containing the above-mentioned thiol compound was selected, and as Comparative Example 2, a composition containing one base of butanedithiol in place of compound a was selected, and the film properties A comparison was made. The film was formed by applying each composition to a certain thickness (approximately 1 rib) on silicone-treated rattan paper, and using a resonant transformer-type fin beam accelerator (EBG) with a maximum acceleration voltage of 2 MeV under a nitrogen atmosphere (oxygen concentration 400 blood). ), the electron beam generated is 10 Mm at lmA.
It was created by polymerizing and forming a network by irradiating with d.

Then, the elongation rate and breaking strength of each film were measured using a Tensilon tensile tester.

The results are shown in Table 1. In addition, the tensile strength is 200
Ribs/min (20q○). Table 1 Film properties It was found that the composition of Example 1 sufficiently exhibited rubber-like genitalia.
Next, each composition was applied to a polyester film with a thickness of 0.025 mm (manufactured by Toray ■, trade name, Lumirror #25) so that the thickness of the adhesive layer was 0.015 mm. The adhesive force and cohesive force were measured by irradiation with a beam.

The results are shown in Table 2.

Table 2 Measurement according to JIS-C-2107 (adhesive tape special method)
The increase in adhesion over a period of days is shown in %.

(The smaller the increase, the better) 3. Measure the displacement distance after 30 minutes at 20°C under a load of 500 on a Bakelite plate.

The results show that the adhesive tape has no unpleasant odor due to thiol, has a certain cohesive force, and exhibits little change when raised, so it is clear that it is a pressure-sensitive adhesive with excellent properties.

Example 2, Comparative Example 2c Synthesis of High Molecular Weight Thiol Compound Using the same apparatus as in Example 1a, 1 mole of dicane methylene dithiol and 0.5 mole of tetraethylene glycol acrylate were reacted to synthesize a compound.

d Synthesis of liquid oligomer One part of ethyl acrylate, 70 parts of butyl acrylate, and two parts of glycidyl methacrylate were polymerized in the same manner as in Example 1, and then one part of acrylic acid was added to radiation-cure the acrylic system. After the liquid oligomer was synthesized, two thiol compounds (c) were added to this oligomer to prepare a radiation-curable sensitized adhesive composition.

Next, as Comparative Example 3, decane methylene dithiol was selected instead of the thiol compound in 1) and 1 part of decane methylene dithiol was added to prepare a composition. Each composition was applied to a polyethylene film with a thickness of 0.06 mm so that the thickness of the adhesive layer was 0.006 mm, and a linear filament type electron beam irradiation device (
Ener Battle Science IM. An adhesive film for surface protection was produced by irradiating electron beams with a standard AD in a nitrogen atmosphere (oxygen concentration 500 feet) using an accelerating voltage of 16 bulbs (manufactured by the product name Electrocurtain) and a beam current of 100 μm (hA). Characteristics were evaluated.

(Table 3) Table 3 Upper neck appearance 4 as adhesive film characteristics
The SUS board with the adhesive film attached was subjected to 8-side Eriksen drawing according to JISB7777, and the state of natural peeling of the film was observed after one day at room temperature.

From Table 3, it was found that the surface protection paper-based film had no unpleasant odor, had little change over time, and had good squeezing properties.

As described above, according to the present invention, by adding a reaction product of dithiol and alkyltin oxide to a radiation-curable liquid oligomer having an unsaturated double bond in the molecule, a high cohesive force without unpleasant odor can be achieved. It has become possible to provide a pressure-sensitive adhesive with excellent adhesive properties.

Claims (1)

[Claims] 1. For 100 parts by weight of a radiation-curable liquid oligomer having a radically crosslinkable ethylenically unsaturated double bond in the molecule, add 0.1 to 0.1 to 1 mole of dithiol and diacrylate monomer.
A radiation-curable pressure-sensitive adhesive composition containing 0.5 to 30 parts by weight of a compound obtained by reacting 1 mole of the compound.