JPH1060382A - Pressure-sensitive urethane adhesive composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a pressure-sensitive urethane adhesive composition being nonproblematic in environmental pollution and safety, dispensing with previous heat treatment, freed from the restriction by a pot life, etc., and having improved general-purpose utility by adding two specified components to a composition so as to obtain a composition which can give a crosslinked product having pressure-sensitive adhesiveness. SOLUTION: This composition is used for pressure-sensitive adhesive sheets, pressure-sensitive adhesive tapes, pressure-sensitive labels, etc., and comprises 100 pts.wt. at least one urethane (meth)acrylate oligomer (A) and 50-120 pts.wt. reactive diluent (B) being a methacryloyl-containing methacrylate type monofunctional reactive diluent and optionally (when crosslinked by irradiation with electron beams or ultraviolet rays) 3-5 pts.wt. photopolymerization initiator and about 3 pts.wt. photopolymerization accelerator. This can be used without using any common organic solvent and may be in a solventless state. Therefore, unlike a water-based emulsion type, it can dispense with a long drying oven, unlike a hot melt type, can dispense with heating of the coating fluid and, unlike a thermosetting urethane type, is freed from the restriction by a pot life and aging.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a urethane-based pressure-sensitive adhesive composition used for a pressure-sensitive adhesive sheet, a pressure-sensitive adhesive tape, a pressure-sensitive adhesive label, etc., and relates to a reaction between a urethane (meth) acrylate oligomer and a methacrylate. A composition comprising a water-soluble diluent is cured by electron beam irradiation or ultraviolet irradiation to exhibit pressure-sensitive adhesiveness,
The present invention relates to a highly versatile urethane-based pressure-sensitive adhesive composition that can be coated without a solvent, can easily handle a coating liquid, and has high versatility.

[0002]

2. Description of the Related Art In recent years, the use of organic solvents has been desired to be solvent-free due to environmental pollution, effects on the human body during work, and problems related to safety. This solvent-free is similarly desired in the field of manufacturing pressure-sensitive adhesive products such as pressure-sensitive adhesive sheets, pressure-sensitive adhesive tapes and pressure-sensitive adhesive labels. As a method for eliminating the solvent of the pressure-sensitive adhesive product, a water-based emulsion type, a hot melt type, a thermosetting type, an electron beam curable type, an ultraviolet curable type, or another type curable by radiation are used. However, the water-based emulsion type requires a long drying oven in the drying step, and requires a large amount of heat energy. Also, since the softening point of the hot-melt type pressure-sensitive adhesive is about 80 to 120 ° C., it is necessary to heat the pressure-sensitive adhesive to a high temperature for coating, which also requires a large amount of heat energy. Is what you do. Also,
The thermosetting type uses a liquid polyol oligomer as a main component, a polyisocyanate monomer or a liquid polyisocyanate oligomer as a curing agent, and a urethane-based pressure-sensitive adhesive composition obtained by reacting the main component with a curing agent. I have. This is because, since the isocyanate compound is used, the reaction starts immediately after mixing the main agent and the curing agent, so that the pot life of the coating liquid is short and the coating is restricted in time. In addition, when the pot life is particularly short such as several hours or less, usually, in addition to the coating machine,
A mixing and discharging machine for mixing the main agent and the curing agent and supplying the coating liquid to the coating machine is required separately. Furthermore, after coating,
Aging at a certain temperature is required in order to promote the reaction between the main agent and the curing agent and to develop the desired adhesive properties. Aging can take anywhere from hours to days. The method of obtaining a pressure-sensitive adhesive using an electron beam-curable type, an ultraviolet-curable type, or another type of radiation-curable composition does not require a long drying oven as in the water-based emulsion type, in addition to solventless use. Because of the fact that there is no need to heat the coating liquid such as a hot-melt type, and that there is no need to limit or age due to pot life such as a thermosetting urethane-based pressure-sensitive adhesive, the above-mentioned problems are caused. In recent years, the curing method has been spotlighted because it is a simple method of merely irradiating radiation such as electron beam, ultraviolet light, or γ-ray. Conventional techniques for obtaining a pressure-sensitive adhesive using an electron beam-curable type, an ultraviolet-curable type, or another type curable by radiation are disclosed in patent publications. First, JP-A-61-207476, JP-A-63-196680, and JP-A-2-19
No. 9184 discloses a method of using a thiol-based chain transfer agent to prevent over-curing and to control the molecular weight so as not to become too large to develop pressure-sensitive adhesive properties such as tackiness and tack. Has been proposed. However, in this method, since the thiol and the acryloyl group cause a dark reaction, there is a problem that the coating solution gels during storage or the adhesive property of the cured pressure-sensitive adhesive changes. Also, JP-A-63-218359, JP-A-4-18.
The methods disclosed in JP-A-3770 and JP-A-5-43636 each relate to a urethane-based pressure-sensitive adhesive, and have the following characteristics. First,
Japanese Patent Application Laid-Open No. 63-218359 discloses a method of obtaining a pressure-sensitive adhesive by holding an ultraviolet-curable special polyurethane resin in a state immediately before it is completely cured when it is cured by ultraviolet irradiation. However, this method has a problem in that it is difficult to constantly maintain the manufacturing conditions so as to be in a state immediately before it is completely cured. Japanese Patent Application Laid-Open No. 4-183770 discloses that a polyol having a hydrogenated polybutadiene skeleton in the main chain is polymerized using a polyfunctional compound to obtain a polymerized hydrogenated polybutadiene polyol. Based on the hydroxyl groups remaining in the polybutadiene polyol, 25 to 100 mol% of (meth) acryloyl groups are introduced to form a urethane (meth) acrylate oligomer, and the urethane (meth) acrylate oligomer and the monofunctional (meth) acrylate This is a method for obtaining a pressure-sensitive adhesive by radiation-curing a composition contained therein. However, this method has low versatility due to the necessity of newly synthesizing a urethane (meth) acrylate oligomer, and a monofunctional (meth) acrylate is simply diluted to adjust the viscosity to an appropriate level for coating. It is used as an agent and does not attempt to contribute to the development of pressure-sensitive adhesiveness. JP-A-5-43636 discloses a urethane (meth) acrylate oligomer containing a dimer acid having 36 to 44 carbon atoms, a polyester diol obtained from a diol having 4 or more carbon atoms, and a copolymerizable with the oligomer. This is a method of converting a composition composed of various vinyl monomers into a pressure-sensitive adhesive mainly by electron beam curing. However, this method also has low versatility because it is necessary to newly synthesize a urethane (meth) acrylate oligomer. The expression of the pressure-sensitive adhesive property of the pressure-sensitive adhesive is attributable to the chemical structure of dimer acid. In other words, this is different from the method of the present invention in which the methacrylate-based reactive diluent itself directly contributes to the development of pressure-sensitive adhesiveness.

[0003]

As described above, in the prior art, a long drying oven such as an aqueous emulsion type is required and a large amount of heat energy is required, and a coating method such as a hot melt type is required. Those requiring liquid heating, those subject to pot life limitations such as thermosetting urethane-based pressure-sensitive adhesives, those requiring aging, and electron beam-curing or ultraviolet-curing, or other In the case of curing by radiation, there were problems such as gelation of the pressure-sensitive adhesive coating solution due to a dark reaction, change in the adhesive properties of the pressure-sensitive adhesive film after curing, and low versatility. . SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in the prior art, and to deal with environmental pollution and the effect on human bodies during work due to the use of an organic solvent when handling a pressure-sensitive adhesive, and problems related to safety and the like. Solves the problem by eliminating the need for a solvent, eliminates the need for a long drying oven or pretreatment for heating the coating liquid, eliminates pot life and aging, does not cause gelation or change in adhesive properties due to dark reaction, and is highly versatile An object of the present invention is to provide a urethane-based pressure-sensitive adhesive composition.

[0004]

Means for Solving the Problems In order to achieve the object of the present invention, the present invention is configured as described in the claims. That is, as described in claim 1, the present invention provides a pressure-sensitive adhesive composition used for a pressure-sensitive adhesive sheet, a pressure-sensitive adhesive tape, a pressure-sensitive adhesive label, and the like, wherein the pressure-sensitive adhesive composition comprises at least And a urethane (meth) acrylate oligomer and a reactive diluent, each comprising at least one kind thereof. A crosslinked product obtained by cross-linking the composition by electron beam irradiation or ultraviolet irradiation is a pressure-sensitive composition. A urethane-based pressure-sensitive adhesive composition having adhesiveness is provided. According to a second aspect of the present invention, in the pressure-sensitive adhesive composition according to the first aspect, the reactive diluent is a urethane which is a methacrylate monofunctional reactive diluent having a methacryloyl group. This is a pressure-sensitive adhesive composition. In addition, the present invention provides a pressure-sensitive adhesive composition according to claim 1 or claim 2, wherein, when crosslinking by ultraviolet irradiation, a photopolymerization initiator or a photopolymerization initiator is used. The urethane-based pressure-sensitive adhesive composition contains a photopolymerization accelerator. The present inventors have conducted intensive studies and found that a pressure-sensitive adhesive sheet, a pressure-sensitive adhesive tape, a pressure-sensitive adhesive composition used for a pressure-sensitive adhesive label, and the like,
The pressure-sensitive adhesive composition is obtained by crosslinking a composition comprising at least one urethane (meth) acrylate oligomer (A) and at least one reactive diluent (B) by electron beam irradiation or ultraviolet irradiation. A pressure-sensitive adhesive composition, and wherein the reactive diluent is a methacrylate-based reactive diluent having a methacryloyl group, and contains a photopolymerization initiator (C) when cross-linked by ultraviolet irradiation; In addition, it has been found that the object of the present invention can be solved by using a urethane-based pressure-sensitive adhesive composition in which a crosslinked body comprising the above (A) and (B) has pressure-sensitive adhesive properties. is there. In the present invention, (meth)
Acrylate means acrylate or methacrylate. In addition, the reactive diluent of the present invention is handled separately from general organic solvents such as toluene. That is, the organic solvent in the present invention refers to a solvent excluding a reactive diluent, and the absence of a solvent means that a common organic solvent such as toluene as described above is not used. In addition, the reactive diluent is a methacrylate-based reactive diluent having a methacryloyl group, but the usual method of intentionally including an acrylate-based reactive diluent for the purpose of improving the reaction rate of methacrylate is used. It is possible to apply. Further, if necessary, additives such as a polymerization inhibitor, a photopolymerization accelerator or an antioxidant may be added. The urethane (meth) acrylate oligomer and methacrylate-based reactive diluent and acrylate-based reactive diluent, and the photopolymerization initiator and other additives used in the present invention are all commercially available general-purpose products. The urethane-based pressure-sensitive adhesive composition of the present invention is extremely excellent in versatility. As described in claim 1, claim 2 or claim 3, the urethane-based pressure-sensitive adhesive composition according to the present invention comprises a urethane (meth) acrylate oligomer and a reactive diluent. It is used and does not require the use of a normal organic solvent, and can be used without a solvent. In addition, a long drying oven such as an aqueous emulsion type is not required, and there is no need to heat a coating liquid such as a hot melt type, and there is a limitation due to a pot life such as a thermosetting urethane type pressure sensitive adhesive. No need for aging or aging. The reason is that the method for curing the urethane-based pressure-sensitive adhesive composition of the present invention is a simple method of merely irradiating an electron beam or an ultraviolet ray, and the coating liquid before the pressure-sensitive adhesive is cured before heating. The coating liquid can be applied without treatment, and the coating liquid before curing of the pressure-sensitive adhesive has an effect of obtaining good storage stability by a simple method such as addition of a polymerization inhibitor or storage in a dark place. Further, the urethane-based pressure-sensitive adhesive of the present invention has an effect that gelation and change in adhesive properties due to a dark reaction do not occur. This is presumably because the urethane-based pressure-sensitive adhesive composition of the present invention uses a reaction product of a urethane (meth) acrylate oligomer and a methacrylate-based reactive diluent for the expression of pressure-sensitive adhesiveness. It is considered that the urethane-based pressure-sensitive adhesive composition of the present invention exhibits pressure-sensitive adhesive properties by electron beam curing or ultraviolet curing due to the following effects. First, it is well known that a polyurethane obtained by curing a urethane (meth) acrylate oligomer can be a pressure-sensitive adhesive. However, instead of simply curing the urethane (meth) acrylate oligomer, it is necessary to devise, for example, the above-described conventional technique. In the urethane-based pressure-sensitive adhesive composition of the present invention, the following is shown. Such ingenuity has been made. First, by controlling the molecular weight not to become too large,
The adhesive strength and tackiness are exhibited. That is, when considering the reaction between the urethane (meth) acrylate oligomer and the methacrylate-based reactive diluent in the present invention, the methacryloyl group has a relatively slow reaction rate as compared with the acryloyl group, and the crosslinking reaction is difficult to proceed.
It has the property of preventing the molecular weight from becoming too large, and therefore exhibits adhesive strength and tack. At this time, when a methacrylate-based monofunctional reactive diluent having one methacryloyl group is used, the adhesive strength and tackiness are more easily developed. This seems to be due to the fact that the use of the monofunctional reactive diluent makes the cured product closer to the linear polymer. Next, it is mentioned that an appropriate cohesive force required for the pressure-sensitive adhesive is obtained. The urethane-based pressure-sensitive adhesive of the present invention is characterized in that the molecular weight is adjusted so as not to become too large as described above, but this has an effect of reducing the cohesive force of the pressure-sensitive adhesive. Nevertheless, the urethane-based pressure-sensitive adhesives of the present invention show good cohesion. It is generally well known that the addition of a reactive diluent improves the cohesive strength after curing of a urethane (meth) acrylate oligomer. It is considered that this contributes to the pressure-sensitive adhesive. Therefore,
The urethane-based pressure-sensitive adhesive composition of the present invention has excellent holding power.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described more specifically with reference to embodiments of the present invention. Note that “parts” in the embodiments indicates parts by weight. <Embodiment 1> As shown in Table 2, using the materials shown in Table 1, five types of compounded liquids (1-1), (1-2), (1)
-3), (1-4), and (1-5) were prepared, and each compounded solution was coated on a 38 μm-thick PET (polyethylene terephthalate) film using a doctor blade with a coating layer thickness of 50 μm to 50 μm. Coating was performed so as to be 60 μm. Subsequently, using a high-pressure mercury lamp (lamp output: 120 W / cm), the composition was cured by irradiating ultraviolet rays under an irradiation distance of 20 cm in a nitrogen gas atmosphere to obtain a urethane-based pressure-sensitive adhesive sheet. Irradiation with ultraviolet light was performed until curing sufficiently proceeded, and the confirmation was performed by infrared spectrophotometry. Regarding the characteristics of the produced pressure-sensitive adhesive sheet, JIS Z 0237
(Adhesive tape / adhesive sheet test method)
0 degree peeling adhesive strength, inclined ball tack (tilt angle 3
As a result, as shown in Table 3, it was confirmed that good pressure-sensitive adhesiveness was exhibited.

[0006]

[Table 1]

[0007]

[Table 2]

[0008]

[Table 3]

<Embodiment 2> From the formulations shown in Table 2, a formulation was prepared by removing a photopolymerization initiator and a photopolymerization accelerator, and was prepared by using a doctor blade on a 38 μm-thick PET film. Coating was performed so that the coating layer thickness was 50 μm to 60 μm. Subsequently, using a linear filament type electron beam irradiation apparatus, an acceleration voltage of 200 kV and an acceleration current of 10 m
A, An electron beam was irradiated and cured in a nitrogen gas atmosphere to obtain a urethane-based pressure-sensitive adhesive sheet. The irradiation with the electron beam was performed until the curing sufficiently proceeded, and the confirmation was performed by infrared spectrophotometry. Regarding the properties of the produced pressure-sensitive adhesive sheet, as a result of measuring 180-degree peeling adhesive force, inclined ball tack (inclination angle of 30 degrees) and holding force according to JIS Z 0237 (Testing method of adhesive tape and adhesive sheet), As shown in Table 4, it was confirmed that good pressure-sensitive adhesiveness was exhibited.

[0010]

[Table 4]

<Comparative Example 1> As shown in Table 5, compounding was performed to cure only the urethane (meth) acrylate oligomer. Compounding liquids 5-1 and 5-2 were irradiated with ultraviolet light, and compounding liquid 5-3 was mixed. A test sheet was prepared by coating and curing with an electron beam in the same manner as in Embodiments 1 and 2, respectively. In addition, Table 6 shows the results of the adhesion, tack, and holding force performed in the same manner as in the above embodiment. As is clear from the table, although the holding power was excellent, both the adhesion and the tack were low, and the polyurethane film remained a very small pressure-sensitive adhesive film as usually shown.

[0012]

[Table 5]

[0013]

[Table 6]

[0014]

As described above, the urethane-based pressure-sensitive adhesive composition of the present invention comprises at least urethane (meth)
A composition containing at least one acrylate oligomer and one or more reactive diluents, wherein the reactive diluent is a methacrylate-based reactive diluent having a methacryloyl group, and is irradiated with ultraviolet light or electron beam. Thus, a urethane-based pressure-sensitive adhesive can be easily obtained. And, the urethane-based pressure-sensitive adhesive composition of the present invention is a solventless type, does not require a long drying oven such as an aqueous emulsion type, and does not require heating of a coating liquid such as a hot melt type, It is not limited by the pot life like thermosetting urethane-based pressure-sensitive adhesives, does not require aging, and gels the pressure-sensitive adhesive coating liquid due to dark reaction, and sticking of the pressure-sensitive adhesive film after curing. The characteristics are not changed, and a commercially available material can be used as it is.

Claims (3)

[Claims] 1. A pressure-sensitive adhesive composition used for a pressure-sensitive adhesive sheet, a pressure-sensitive adhesive tape, a pressure-sensitive adhesive label, and the like, wherein the pressure-sensitive adhesive composition comprises at least a urethane (meth) acrylate oligomer and a And a diluent, each comprising at least one kind thereof, wherein a cross-linked product obtained by cross-linking the composition by irradiation with an electron beam or ultraviolet light has a pressure-sensitive adhesive property. Urethane-based pressure-sensitive adhesive composition. 2. The pressure-sensitive adhesive composition according to claim 1, wherein the reactive diluent is a methacrylate monofunctional reactive diluent having a methacryloyl group. Composition. 3. The pressure-sensitive adhesive composition according to claim 1, wherein when crosslinking by irradiation with ultraviolet rays, a photopolymerization initiator or a photopolymerization initiator and a photopolymerization accelerator are contained. A urethane-based pressure-sensitive adhesive composition characterized by the following: