JPH11228926A - Radiation-curable pressure-sensitive adhesive composition, pressure-sensitive adhesive sheet or the like coated therewith, and production of them - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation-curable pressure-sensitive adhesive composition which exhibits improved applicability and radiation curability when used as a radiation-curable hot melt pressure-sensitive adhesive satisfactory in environmental hygienics, safety, water resistance, and heat resistance. SOLUTION: This composition contains an acrylic polymer essentially consisting of an alkyl (meth)acrylate, having weight-average molecular weight of 100,000-700,000 in terms of the polystyrene as determined by gel permeation chromatography and having an absolute molecular weight 2-20 times the above weight-average molecular weight as measured by multi-angle light scattering.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation-curable pressure-sensitive adhesive composition and radiation-curable sheet or tape-like pressure-sensitive adhesive sheets.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of environmental hygiene and safety,
In the production method of adhesive sheets, the shift to using no organic solvent is in progress. One of them is a method utilizing emulsion polymerization. However, the emulsifier at the time of polymerization tends to cause a problem in water resistance.

On the other hand, a method is known in which a hot-melt pressure-sensitive adhesive obtained by bulk polymerization or the like is melt-coated on a support. This method has attracted attention as a method satisfying environmental hygiene and safety without the above-mentioned problem of water resistance. Also, in this method, to improve heat resistance,
Generally, after the melt coating on the support, the support is irradiated with radiation such as an electron beam or an ultraviolet ray to be cured.

[0004]

However, the above-mentioned conventional hot-melt type pressure-sensitive adhesives have difficulty in coatability at the time of melt coating, and also have problems in radiation curability. Therefore, the present invention provides a radiation-curable hot-melt pressure-sensitive adhesive that satisfies environmental health, safety, water resistance, and heat resistance while avoiding such problems. An object of the present invention is to provide a curable pressure-sensitive adhesive composition and pressure-sensitive adhesive sheets thereof.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on the above object, and as a result, the absolute molecular weight measured by a multi-angle light scattering method by a specific bulk polymerization has been determined by gel permeation chromatography. When an acrylic polymer having a certain relationship with the weight average molecular weight in terms of polystyrene measured by the A method is obtained and used as an adhesive polymer, the polymer has a low melt viscosity and is improved. It has been found that the composition exhibits improved coating properties and gives good results in radiation curability, leading to the completion of the present invention.

That is, the present invention relates to a method for preparing a gel permeate comprising alkyl (meth) acrylate as an essential monomer.
The weight-average molecular weight in terms of polystyrene measured by the capillary chromatography method is 100,000 to 700,000, and the absolute molecular weight measured by the multi-angle light scattering method is 2 to 20 times the weight-average molecular weight described above. A radiation-curable pressure-sensitive adhesive composition containing an acrylic polymer (Claim 1), and a layer obtained by radiation-curing the pressure-sensitive adhesive composition having the above constitution on one or both surfaces of a support. Adhesive sheets (Claim 2).

Further, the present invention provides a method for producing the pressure-sensitive adhesive composition having the above-mentioned structure, which has a structure for continuously transferring the continuously supplied contents while renewing the surface, and has a predetermined temperature throughout the transferring process. In a reactor controlled by heating, the polymerization raw material essentially comprising alkyl (meth) acrylate is continuously bulk-polymerized, and the weight in terms of polystyrene measured by gel permeation chromatography is measured. A radiation-curable type having an average molecular weight of 100,000 to 700,000 and an acrylic polymer having an absolute molecular weight measured by a multi-angle light scattering method of 2 to 20 times the above weight average molecular weight. As a method for producing the pressure-sensitive adhesive composition (Claim 3) and a method for producing the above-mentioned pressure-sensitive adhesive sheets, the radiation-curable pressure-sensitive adhesive composition produced by the above method is coated on one or both surfaces of a support. After the, radiation is irradiated, characterized in that curing the adhesive sheet - which relates to a manufacturing method of preparative compound (claim 4).

[0008]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, a tacky polymer is used.
The acrylic polymer used as the reactor has a specific bulk polymerization reactor, that is, a structure that continuously transfers the continuously supplied contents while renewing the surface, and is heated to a predetermined temperature throughout the entire transfer process. Manufactured using a controlled reactor. Examples of the reactor include a single-screw or twin-screw extruder having a raw material supply port at one end and a take-out port at the other end. In this method, the polymerization raw material is continuously supplied from the above-mentioned raw material supply port, and is transferred toward the other end while rotating the screw to renew the surface. The polymerization is continuously carried out, and after reaching a predetermined polymerization rate, it is continuously taken out from the outlet, so that the heat of polymerization is removed and the necessary amount of heat is supplied and exchanged efficiently. ing.

The polymerization raw materials supplied to such a reactor are:
(Meth) acrylic acid alkyl ester is essential, and as the ester, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, isobutyl acrylate, isoamyl acrylate, hexyl acrylate, acrylic acid Examples thereof include an alkyl acrylate having an alkyl group having 14 or less carbon atoms, such as 2-ethylhexyl, isooctyl acrylate, and isononyl acrylate, and an alkyl methacrylate having an alkyl group similar to the above. Further, an appropriate modifying monomer may be used in combination with the above ester.
These monomer compositions should be such that the glass transition point of the acrylic polymer is 250 K or lower, and if the glass transition point is higher than this, good adhesive properties cannot be obtained.

Examples of the modifying monomers include (meth) acrylic acid, maleic acid, crotonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-hydroxyethylacryloyl phosphate, and 2-hydroxypropylacryloyl. Phosphate, vinyl acetate, styrene, glycidyl (meth) acrylate, acrylic acid 2-
Hydroxyethyl, 2-hydroxypropyl acrylate, N-vinyl-2-piperidone, N-vinyl-3-monomorpholine, N-vinyl-2-caprolactam, N-
Vinyl-2-pyrrolidone, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione and the like. These modifying monomers are generally preferably less than 50% by weight of the total amount of monomers.

As a raw material for polymerization, a polymerization initiator is used in addition to the above monomers. For example, peroxides such as benzoyl peroxide and azo initiators such as azobisisobutyronitrile, which are commonly used, are used. These initiators may be used alone or in combination of two or more. It is desirable to combine two or more initiators having different decomposition temperatures, since a polymer having a high polymerization rate and a high molecular weight can be obtained.
The amount of these initiators per 100 parts by weight of the monomer,
Usually, 0.01 to 3 parts by weight, preferably 0.03 to 2 parts by weight. Insufficient polymer with insufficient polymerization rate
If it is excessive, only a polymer having a low molecular weight can be obtained.

A polymerization raw material containing such a monomer and a polymerization initiator alone has a low viscosity, and a viscosity difference from a polymer after polymerization is too large, so that stable bulk polymerization is performed in the reactor. It can be difficult. In this case, the polymerization raw material is preliminarily polymerized, or a polymer having substantially the same composition as the polymerization raw material is preferably used as the polymerization raw material.
Alternatively, it is desirable to increase the viscosity of the polymerization raw material to some extent by previously dissolving the oligomer or in a reactor.

The supply of the polymerization raw material to the reactor is performed at a constant speed by a gear pump or the like.
In order to obtain a predetermined polymerization rate, the structure and operating conditions of the reactor, for example, in the single-screw or twin-screw extruder described above, the outer diameter of the screw, the barrel length, the interval between the barrel and the screw screw, the screw screw It may be appropriately selected according to the number of rotations and the like, in consideration of the type and amount of the monomer and the polymerization initiator used as the polymerization raw material. The reaction temperature at this time is also crucial, usually within the range of 60 to 150 ° C.
The temperature is controlled to an appropriate value over the entire area of the reactor. If the temperature is too high, the molecular weight of the polymer tends to be low, and if it is too low, the reaction rate is low and the polymerization reaction needs to be carried out for a long time, which tends to reduce the productivity.

[0014] By such bulk polymerization in a reactor, a gel-pattern comprising alkyl (meth) acrylate as an essential monomer and, if necessary, an appropriate modifying monomer as a copolymer component. -Polystyrene equivalent weight average molecular weight of 10 measured by the migration chromatography method
Acrylics having a molecular weight of 10,000 to 700,000, preferably 200,000 to 500,000, and an absolute molecular weight measured by a multi-angle light scattering method of 2 to 20 times, preferably 3 to 15 times the above weight average molecular weight. Produce a polymer.

Here, it is said that the absolute molecular weight measured by the multi-angle light scattering method and the weight average molecular weight in terms of polystyrene measured by the gel permeation chromatography have the above-mentioned relationship. This means that the acrylic polymer has a branched structure and, when calculated from the radius of gyration of the polymer, has 1 to 8, preferably 2 to 6, branch points in the polymer main chain. Means

Such a branched acrylic polymer is as follows:
It has a low melt viscosity, exhibits excellent coatability, and has excellent radiation curability. On the other hand, when the absolute molecular weight measured by the multi-angle light scattering method is less than twice the weight average molecular weight, the number of branch points in the polymer main chain becomes insufficient, and the melt viscosity becomes high. The coatability decreases and the radiation curability also worsens. On the other hand, if the absolute molecular weight exceeds 20 times the weight average molecular weight, the number of branch points becomes too large to form a three-dimensional crosslinked structure, and the coating property is also lowered. When the weight-average molecular weight is less than 100,000, the adhesive property is reduced, and when it exceeds 700,000, the coating property is reduced.

The above weight average molecular weight can be set with good reproducibility by adjusting the amount of the polymerization initiator and the reaction temperature, and by adding a chain transfer agent such as mercaptan to the raw materials for polymerization. . Further, the above absolute molecular weight, and thus the number of branch points in the polymer main chain, controls the chain transfer to the polymer at the time of polymerization, for example, the chain transfer constant to the polymer by increasing the polymerization temperature. Can be easily set by using a method such as enlarging the amount of generated radicals or increasing the amount of generated radicals. Further, in addition to the above-mentioned monomers, it can be set by using a polyfunctional monomer such as di (meth) acrylate and tri (meth) acrylate.

The method of controlling the chain transfer is carried out by controlling the amount of the polymerization initiator, the reaction temperature and the monomer composition. First, when the number of radicals generated by the polymerization initiator is the same, the higher the reaction temperature (the higher the temperature-decomposition type polymerization initiator is used), the larger the absolute molecular weight can be set and the number of branch points can be increased. When the number of generated radicals is increased by adjusting the amount of the polymerization initiator and the reaction temperature, the absolute molecular weight can be increased, and the number of branch points can be increased. Further, when a monomer containing more tertiary carbon is used to control the monomer composition, the absolute molecular weight can be increased and the number of branch points can be increased. For example, using 2-ethylhexyl acrylate,
Compared to using butyl acrylate, the absolute molecular weight can be increased, and as a result, the number of branch points can be increased.

The radiation-curable pressure-sensitive adhesive composition of the present invention uses the acrylic polymer produced as described above as a pressure-sensitive adhesive polymer. A monomer having at least one radiation-reactive unsaturated bond in the molecule may be added. The radiation-reactive monomer may be added after being taken out of the reactor, or may be added before being taken out. The amount of addition is 30 parts by weight or less, preferably 20 parts by weight or less, per 100 parts by weight of the acrylic polymer. If too much is added, the adhesive strength decreases.

The above-mentioned radiation-reactive monomer includes 2-
Hydroxy-3-phenoxypropyl (meth) acrylate, dicyclopenteroxyethyl (meth) acrylate, ethyl carbitol (meth) acrylate, methyltriglycol (meth) acrylate, N , N'-dimethylaminopropyl (meth) acrylamide, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, neopentyl glycol di (Meth) acrylate, 1,6-hexanediol di (meth) acrylate, trimethylolpropanetri (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa ( (Meth) acrylate, divinylbenzene, vinyl (meth) acrylate, adip Vinyl acid, N, and the like N'- methylenebis (meth) acrylamide.

The radiation-curable pressure-sensitive adhesive composition of the present invention comprises:
In addition to the above components, tackifier resin, surfactant, filler,
Additives such as pigments and colorants may be blended. These additives, as in the case of the radiation-reactive monomer described above,
It may be added after being taken out of the reactor or may be added before being taken out. Further, an antioxidant or a polymerization inhibitor may be added in the same manner as described above in order to suppress the modification of the polymer during bulk polymerization or coating. However, the ratio of these antioxidants and polymerization inhibitors is preferably 0.05 to 2 parts by weight per 100 parts by weight of the acrylic polymer. If too much is added, polymerization control during bulk polymerization and radiation curability after coating are impaired, which is not preferable.

In the present invention, the radiation-curable pressure-sensitive adhesive composition thus prepared is melt-coated on one or both sides of a support. The coating thickness can be set in a wide range depending on the application purpose of the adhesive sheet, but it is generally preferable that the thickness of the adhesive layer after the subsequent radiation curing be 5 to 120 μm.

The support used herein includes plastic film, paper, nonwoven fabric, foam, metal foil and the like.
For roll coating on the support, either a roll coater or a die coater can be used, but a die coater is particularly suitable for uniform coating. In this case, the manifold of the die coater may be plural, and a plurality of radiation-curable pressure-sensitive adhesive compositions having different compositions may be applied in a laminated manner.

In the present invention, after the above-mentioned coating, radiation is irradiated to cure the radiation-curable pressure-sensitive adhesive composition.
As the radiation, ionizing radiation such as α-rays, β-rays, γ-rays, neutron rays, and electron beams, and active rays such as ultraviolet rays are used. Irradiation dose is usually 0.5 to ionizing radiation
20 Mrad, preferably 1 to 10 Mrad, and usually 400 to 3,000 mj /
It is cm ^2. When the irradiation amount of the radiation is too small, the crosslinking and curing of the pressure-sensitive adhesive composition is insufficient, and a decrease in holding power and heat resistance is observed.
If the amount is excessive, there is a concern that the support may deteriorate.

The ultraviolet light preferably has a wavelength range of 180 to 460 nm, and a mercury lamp, a metahalide lamp or the like is preferably used as a source. When the composition is cured by irradiation with ultraviolet rays, it is desirable to add a photoreaction initiator (photosensitizer) in advance when preparing the radiation-curable pressure-sensitive adhesive composition. Examples of the photoreaction initiator include radical initiators such as benzoin, benzoin methyl ether, benzoin ethyl ether, dibenzyl, benzyl dimethyl ketal, and bis (dodecylphenyl)
Iodonium hexafluoroantimonate, (1-6
-Η-cumene) (η-cyclopentadienyl) iron (1
+) Cationic initiators such as hexafluorophosphoric acid (1-).

The adhesive sheet in the form of sheet or tape obtained in this manner is excellent in water resistance because it does not contain an emulsifier in the adhesive composition, and it can be exposed to radiation. Because it is cured, it has excellent heat resistance. In addition, since it has excellent melt coatability and radiation curability to the support, the production work of adhesive sheets is easy,
After radiation curing, in addition to the above-described water resistance and heat resistance, it is possible to exhibit adhesive properties excellent in balance between adhesive strength and holding power.

[0027]

Next, an embodiment of the present invention will be described in more detail. Hereinafter, “parts” means “parts by weight”.

Example 1 To a monomer mixture consisting of 95 parts of 2-ethylhexyl acrylate and 5 parts of acrylic acid was added 0.05 part of 2,2'-azobisisobutyronitrile and 1,1'-azobis (cyclohexane- The polymerization raw material obtained by adding 0.05 part of 1-carbonitrile) was sufficiently purged with nitrogen, and then a biaxial screw having a screw outside diameter of 37 mm, a barrel length of 1,800 mm, and a distance between the barrel and the screw mount of 0.4 mm was used. The mixture was fed into a reactor consisting of an extruder to continuously perform bulk polymerization.

The screw rotation speed is 300 rotations /
The feed rate of the polymerization raw material was 250 g / min, and the barrel temperature in the extruder was controlled to be 100 to 140 ° C. for each region. The acrylic polymer discharged from the extruder by this method has a conversion of 94% by weight, a weight average molecular weight in terms of polystyrene measured by gel permeation chromatography which is 280,000, and The absolute molecular weight measured by the multi-angle light scattering method was 1.5 million, which was 5.4 times the above weight average molecular weight. Further, the melt viscosity of this acrylic polymer was 450 poise at 100 ° C.

This acrylic polymer is directly used as a radiation-curable pressure-sensitive adhesive composition, which is melt-coated on a polyester film as a support by a die coater heated to 120 ° C., and then irradiated with 5 Mrad of electron beam. Adhesive tape with an adhesive layer with a thickness of 50 μm
Was prepared.

Example 2 100 parts of the acrylic polymer obtained in Example 1 was mixed with 3 parts of trimethylolpropane trimethacrylate and 1 part of benzyl dimethyl ketal to obtain a radiation-curable pressure-sensitive adhesive composition. Was prepared. This radiation-curable pressure-sensitive adhesive composition,
After being melt-coated on a polyester film as a support by a die coater heated to 120 ° C., ultraviolet rays were applied for 5 minutes.
The coating was cured by irradiating it with 00 mj / cm ² to prepare an adhesive tape having an adhesive layer having a thickness of 50 μm.

COMPARATIVE EXAMPLE 1 0.02 parts of 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile) and lauryl were added to a monomer mixture consisting of 95 parts of 2-ethylhexyl acrylate and 5 parts of acrylic acid. The polymerization raw material obtained by adding 0.03 part of mercaptan is sufficiently purged with nitrogen, and then supplied into the same twin-screw extruder as used in Example 1 to continuously perform bulk polymerization. I went.

The screw rotation speed is 300 rotations /
The feed rate of the polymerization raw material was 120 g / min, and the barrel temperature in the extruder was controlled to be 50 to 70 ° C. for each region. The acrylic polymer discharged from the extruder by this method has a conversion of 90% by weight, a weight average molecular weight in terms of polystyrene measured by gel permeation chromatography, of 230,000, and The absolute molecular weight measured by the multi-angle light scattering method was 400,000, which was 1.7 times the above weight average molecular weight. Further, the melt viscosity of this acrylic polymer was 520 poise at 100 ° C.

This acrylic polymer was directly used as a radiation-curable pressure-sensitive adhesive composition, which was melt-coated on a polyester film as a support by a die coater heated to 120 ° C., and then irradiated with 5 Mrad of electron beam. Adhesive tape with an adhesive layer with a thickness of 50 μm
Was prepared.

Comparative Example 2 A radiation-curable pressure-sensitive adhesive composition was prepared by mixing 3 parts of trimethylolpropane trimethacrylate and 1 part of benzyldimethylketal with 100 parts of the acrylic polymer obtained in Comparative Example 1. Was prepared. This radiation-curable pressure-sensitive adhesive composition,
After being melt-coated on a polyester film as a support by a die coater heated to 120 ° C., ultraviolet rays were applied for 5 minutes.
The coating was cured by irradiating it with 00 mj / cm ² to prepare an adhesive tape having an adhesive layer having a thickness of 50 μm.

Comparative Example 3 95 parts of 2-ethylhexyl acrylate, 5 parts of acrylic acid, 0.04 part of 2-mercaptoethanol, and 2 parts of a reactor equipped with a cooling pipe, a nitrogen introducing pipe, a thermometer and a stirrer. ,
0.2 part of 2'-azobisisobutyronitrile and 40 parts of toluene were added, and polymerized in a nitrogen stream to obtain an acrylic polymer. This polymer had a polystyrene-equivalent weight average molecular weight of 260,000 as measured by gel permeation chromatography, and an absolute molecular weight of 270,000 as measured by multi-angle light scattering. Was 1.0 times the weight average molecular weight of further,
The melt viscosity after removing the toluene was 650 poise at 100 ° C.

This acrylic polymer is directly used as a radiation-curable pressure-sensitive adhesive composition, which is melt-coated on a polyester film as a support by a die coater heated to 120 ° C., and then irradiated with 5 Mrad of electron beam. Adhesive tape with an adhesive layer with a thickness of 50 μm
Was prepared.

Comparative Example 4 A radiation-curable pressure-sensitive adhesive composition was prepared by mixing 100 parts of the acrylic polymer obtained in Comparative Example 3 with 3 parts of trimethylolpropane trimethacrylate and 1 part of benzyldimethylketal. Was prepared. This radiation-curable pressure-sensitive adhesive composition,
After being melt-coated on a polyester film as a support by a die coater heated to 120 ° C., ultraviolet rays were applied for 5 minutes.
The coating was cured by irradiating it with 00 mj / cm ² to prepare an adhesive tape having an adhesive layer having a thickness of 50 μm.

With respect to each of the pressure-sensitive adhesive tapes of Examples 1 and 2 and Comparative Examples 1 to 4, the adhesive force and the holding force were examined in the following manner. These results were as shown in Table 1 below.

<Adhesive Strength> An adhesive tape of 20 mm × 100 mm was pressure-bonded to a stainless steel plate, which was sanded with an # 280 sandpaper as an adherend, by reciprocating a 2 kg roller once, at 23 ° C. After 20 minutes at 23 ° C, 65%
Under an atmosphere of RH and a pulling speed of 300 mm / min, 18
The force required for 0 ° peeling was measured.

<Holding force> An adhesive tape is attached to the phenol resin plate.
The tape was adhered with an adhesion area of 10 mm x 20 mm, and after 20 minutes, left at 80 ° C for 20 minutes. Then, a phenol resin plate was hung down and 500 g of uniform adhesive was applied to the free end of the adhesive tape. A load was applied, and the time until the adhesive tape dropped at 80 ° C. was measured.

[0042]

As is clear from the above Table 1, the adhesive tapes of Examples 1 and 2 are superior in coating property and radiation curability as compared with the adhesive tapes of Comparative Examples 1 to 4. It is easy to manufacture, has excellent balance between adhesion and holding power after radiation curing, and has sufficient advantages as a radiation-curable hot melt adhesive with excellent environmental hygiene, safety, water resistance and heat resistance. You can see that it can be used for

[0044]

As described above, according to the present invention, the absolute molecular weight measured by a multi-angle light scattering method by a specific bulk polymerization is a polystyrene-equivalent weight average measured by a gel permeation chromatography method. By obtaining an acrylic polymer that has a certain relationship to the molecular weight and using it as a tacky polymer, it has improved coating properties with low melt viscosity and radiation curability. An excellent radiation-curable pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet thereof can be provided.

Claims (4)

[Claims] 1. An alkyl (meth) acrylate ester as an essential monomer, having a polystyrene equivalent weight average molecular weight of 100,000 to 700,000 as measured by gel permeation chromatography, and a multi-angle The absolute molecular weight measured by the light scattering method is 2 to the above weight average molecular weight.
A radiation-curable pressure-sensitive adhesive composition comprising an acrylic polymer that is 20 times as large. 2. A pressure-sensitive adhesive sheet having a radiation-cured layer of the pressure-sensitive adhesive composition according to claim 1 on one or both surfaces of a support. 3. An alkyl (meth) acrylate in a reactor having a structure for continuously transferring contents continuously supplied while renewing its surface and heating and controlling the content to a predetermined temperature throughout the entire transfer process. The polymerization raw material containing an ester as an essential component is continuously bulk-polymerized, and the weight average molecular weight in terms of polystyrene measured by gel permeation chromatography is 100,000 to 700,000. The measured absolute molecular weight is 2 to the above weight average molecular weight.
A method for producing a radiation-curable pressure-sensitive adhesive composition, comprising obtaining an acrylic polymer having a ratio of 20 times. 4. A pressure-sensitive adhesive sheet characterized in that the radiation-curable pressure-sensitive adhesive composition produced by the method according to claim 3 is applied to one or both surfaces of a support and then irradiated with radiation to be cured. Manufacturing methods.