JPH11209726A - Granular pressure-sensitive adhesive composition, its bonding sheets and their production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a granular pressure-sensitive adhesive composition capable of carrying out the melt coating with an extruder at a low temperature or a high speed. SOLUTION: This granular pressure-sensitive adhesive composition contains polymeric grains comprising a copolymer of 60-99 wt.% main monomer consisting essentially of an alkyl acrylate or an alkyl methacrylate without substantially containing a carboxyl group-containing monomer and 40-1 wt.% nitrogen-containing monomer and having 0.1-10 mm grain diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solvent-free granular pressure-sensitive adhesive composition and to an adhesive sheet obtained by applying the composition onto a support by melt coating to form an adhesive layer. .

[0002]

2. Description of the Related Art Conventionally, a pressure-sensitive adhesive is prepared by mixing a tackifying resin or a crosslinking agent with a polymer solution, coating the mixture on a support, and drying the mixture. Has been used as an adhesive sheet. 2. Description of the Related Art In recent years, solvent-free pressure-sensitive adhesives have been actively developed from the viewpoint of environmental measures. Solvent-free methods include emulsification, hot melt, radiation curing, and the like, but have advantages and disadvantages in terms of characteristics and workability.

On the other hand, recently, there has been an attempt to use a granular pressure-sensitive adhesive. In this method, a granular material obtained by polymerization treatment in an aqueous system is directly charged into an extruder or the like, and is melt-coated on a support in a solvent-free state. For example, Japanese Unexamined Patent Publication No.
JP-A-42778 discloses a method of obtaining the above granular material by performing suspension polymerization in the presence of a copolymer of a hydrophilic monomer and a hydrophobic monomer. In the gazette,
There are disclosed methods of using vinyl acetate as a copolymer component and using a reactive zinc salt as a modifier to obtain the above-mentioned granular material having improved extrudability in an extruder.

[0004]

However, in all of the above-mentioned known pressure-sensitive adhesives, the melt viscosity of the granular material composed of polymer particles tends to be generally high, and it is difficult to apply the adhesive uniformly by using an extruder. Required high temperature or low speed coating. Therefore, the present invention overcomes this problem and provides a granular pressure-sensitive adhesive composition capable of performing melt coating at lower temperature or higher speed, and an adhesive sheet obtained by melt-coating the composition on a support. -It is intended to provide products and methods for producing them.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies in order to achieve the above-mentioned object. As a result, the above-mentioned known pressure-sensitive adhesive firstly has a particularly high holding force in order to improve the adhesive properties. In order to obtain the force characteristics,
Generally, acrylic acid, methacrylic acid, or the like is used as the polar component. However, it has been clarified that the use of such a polar component causes an increase in the melt viscosity of the polymer particles.

Based on this finding, further investigations have been made. As a result, when a nitrogen-containing monomer such as N, N-dimethylacrylamide is used in place of the carboxyl group-containing monomer, the polymerization treatment in an aqueous system can be performed. It can be performed stably without being affected by the type of dispersant or ions in the dispersion medium, and the obtained polymer particles do not have an extremely large melt viscosity, and can be melt-coated with an extruder at a lower temperature or at a higher speed, In addition, it was found that the formed adhesive layer had excellent adhesive strength and holding power, and the present invention was completed.

According to the present invention, 60 to 99% by weight of a main monomer mainly containing an alkyl ester of acrylic acid or methacrylic acid and containing substantially no carboxyl group-containing monomer.
And a polymer particle having a particle size of 0.1 to 10 mm, comprising a copolymer of 40% to 1% by weight of a nitrogen-containing monomer. 1) and an adhesive sheet comprising, on one or both sides of a support, an adhesive layer obtained by melt-coating the above-mentioned pressure-sensitive adhesive composition.
(Claim 2).

Further, the present invention provides a method for producing the above-mentioned pressure-sensitive adhesive composition and an adhesive sheet thereof, which comprises an alkyl ester of acrylic acid or methacrylic acid as a main component and substantially contains a carboxyl group-containing monomer. Main monomer 6 not included
A monomer mixture composed of 0 to 99% by weight and 40 to 1% by weight of a nitrogen-containing monomer is polymerized in a state of being dispersed in water by a dispersant, and a copolymer of the above two monomers is obtained. A method for producing a granular pressure-sensitive adhesive composition, wherein polymer particles having a particle size of 0.1 to 10 mm are produced and separated and recovered; On one or both sides,
The method according to claim 4, wherein the pressure-sensitive adhesive composition obtained by the above method is melt-coated with an extruder to form an adhesive layer. It is.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The main monomer in the present invention is an alkyl ester of acrylic acid or methacrylic acid,
Esters of acrylic acid or methacrylic acid with alcohols having 12 or less carbon atoms, particularly those containing the above alkyl ester having an alkyl group having 4 to 12 carbon atoms as a main component. Here, the term "main component" means that the alkyl ester accounts for at least 50% by weight or more of the whole monomer. Therefore, within this range, other modifying monomers such as styrene, acrylonitrile, and 2-hydroxyethyl (meth) acrylate may be contained.

However, these modifying monomers do not substantially contain carboxyl group-containing monomers such as acrylic acid and methacrylic acid. Since these carboxyl group-containing monomers increase the melt viscosity of the polymer particles, their use is excluded in the present invention. However, as long as the above-mentioned melt viscosity hardly increases and the amount is extremely small so as not to adversely affect the coatability, it may be used in some cases. The term "substantially" means such a thing.

The nitrogen-containing monomer in the present invention contains a nitrogen atom in the molecule, and includes (meth) acrylamide, N, N-dimethyl (meth) acrylamide,
Acyclic (meth) acrylamide such as N-diethyl (meth) acrylamide, N- (meth) acryloylmorpholine, N- (meth) acryloylpyrrolidone, N-
Cyclic (meth) acrylamide such as (meth) acryloylpiperidine, N- (meth) acryloylpyrrolidine, N- (meth) acryloyl-4-piperidone, N-vinyl-2-pyrrolidone, N-vinyl-2-piperidone, N
Vinyl cyclic amides such as -vinyl-3-morpholinone,
And N-substituted maleimides such as N-cyclohexylmaleimide and N-butylmaleimide.

In the present invention, a mixture of the above-mentioned main monomer and nitrogen-containing monomer is used. The ratio of both monomers is 60 to 99% by weight, preferably 70 to 99% by weight. ~
97% by weight, nitrogen containing monomer is 40-1% by weight, preferably 30-3% by weight. If the content of the nitrogen-containing monomer exceeds 40% by weight, the adhesive properties will be impaired, the melt viscosity will increase, and the coatability will deteriorate. On the other hand, if the content of the nitrogen-containing monomer is less than 1% by weight, the adhesive properties, especially the holding power properties, deteriorate.

In the present invention, the above monomer mixture is polymerized in a state of being dispersed in water with a dispersant. In this treatment, first, the monomer mixture, the polymerization initiator and, if necessary, the chain transfer agent are uniformly mixed, and the mixture is added to water in which the dispersant is uniformly mixed, and the mixture is stirred and mixed. Disperse evenly in water.

The method of stirring and mixing is not particularly limited. For example, a stirring tank having a continuous blade structure in the height direction and increasing a water flow by rotating a stirring shaft is used for the stability and particle size distribution of particles during polymerization. Is preferably used for the uniformity of A stirring method in which a shearing stress is strongly applied is not preferable because it causes aggregation of particles.

The polymerization initiator includes a thermally active initiator such as a peroxide such as benzoyl peroxide and an azo compound such as azobisisobutyronitrile; A photoinitiator such as hydroxycyclohexylphenyl ketone is used. The amount used is usually 0.02 to 100 parts by weight of the monomer mixture.
It is preferable to use 3 parts by weight. If the amount is too small, the polymerization reaction will be slow and the polymerization rate will not be improved. If it is too large, the molecular weight will be reduced.

The chain transfer agent is used as needed for the purpose of improving the adhesive properties, particularly the tack, and reducing the molecular weight. As such a chain transfer agent, mercaptans are preferable, and based on 100 parts by weight of the monomer,
It is used in a proportion of 0.5 parts by weight or less. If the amount is too large, the molecular weight becomes too low, and the cohesive strength as a pressure-sensitive adhesive is disadvantageously lowered.

Examples of the dispersing agent include various inorganic powders, talc, bentonite, montmorillonite, silica, calcium carbonate, various salts having poor water solubility, inorganic substances such as barium sulfate, magnesium carbonate, and calcium phosphate, and water-soluble polymers. Polyvinyl alcohol, carboxymethyl cellulose, gelatin, polyacrylic acid soda and the like are used. In order to adjust the particle size, a small amount of an anionic surfactant or a nonionic surfactant can be used in combination.

The amount of the dispersant used varies depending on the monomer mixture used. However, in consideration of the workability of recovery and washing of the polymer particles, the particle size of the monomer oil droplets dispersed in water is preferably 0.1 to 0.1. 1 to 1
The thickness is determined in consideration of the type of the dispersant so as to be within the range of 0 mm. Usually, 0.01 to 100 parts by weight of the monomer is used.
10 to 10 parts by weight, preferably 0.05 to 5 parts by weight. If the amount is too large, the properties of the pressure-sensitive adhesive, particularly the water resistance, will be adversely affected. If the amount is too small, there are disadvantages such as aggregation during polymerization.

Next, the suspension (aqueous dispersion) obtained by uniformly dispersing the monomer mixture in water in this manner is subjected to a replacement treatment with an inert gas such as nitrogen to remove dissolved oxygen. The presence of dissolved oxygen in the suspension not only slows down the polymerization reaction of the monomer mixture, but also has the adverse effect of lowering the molecular weight. Therefore, it is better to perform sufficient nitrogen substitution. In particular, it is preferable that the dissolved oxygen be 2 ppm or less.

After the replacement with nitrogen, a polymerization treatment is carried out at a polymerization temperature of 40 to 90 ° C. for about 2 to 16 hours with a thermally activated initiator while flowing an inert gas such as nitrogen gas. The photoinitiator is irradiated with ultraviolet rays by a lamp capable of generating ordinary ultraviolet rays, such as a high-pressure mercury lamp or a metal halide lamp, to perform polymerization treatment. The irradiation amount of the ultraviolet ray may be appropriately determined depending on the type and amount of the photoinitiator, the type of the monomer, and the like, and is usually 20 to 8,000 mJ.
/ Cm ² .

By such a polymerization treatment, the suspension comprises a copolymer of the above-mentioned main monomer and nitrogen-containing monomer,
Polymer particles having a particle size of 0.1 to 10 mm are formed. The polymer particles are separated and recovered using a mesh or the like, washed with water or hot water, and then dried to obtain the granular pressure-sensitive adhesive composition of the present invention. The above drying treatment can be performed by drying with warm air or venting in an extruder.

In the present invention, such a granular pressure-sensitive adhesive composition is charged into an extruder, and if necessary, additives such as a tackifying resin, a filler and a pigment are added.
It is made into a uniform molten state, melt-coated on one or both sides of a support such as plastic film, paper, or non-woven fabric to form an adhesive layer having a thickness of usually 10 to 1,000 μm. And adhesive sheets such as tapes.

Here, the granular pressure-sensitive adhesive composition has a low melt viscosity of polymer particles and can be melt-coated at low or high speed by an extruder. Give good results. In addition, the adhesive sheets produced in this way are subjected to appropriate crosslinking treatment such as electron beam irradiation as required, so that the adhesive sheets and the holding force are both excellent and exhibit good adhesive properties. be able to.

[0024]

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

Example 1 70 parts of 2-ethylhexyl acrylate, 20 parts of n-butyl acrylate, 5 parts of i-boronyl acrylate,
To a monomer mixture of 5 parts of N, N-dimethylacrylamide, 0.15 part of lauryl mercaptan and 0.3 part of azobisisobutyronitrile were uniformly mixed to obtain a raw material for polymerization. The above-mentioned raw materials for polymerization were added to 200 parts of an aqueous solution in which 0.5 part of finely divided silica and 1 part of zinc oxide were uniformly dispersed in water, followed by stirring to prepare a suspension of a monomer mixture.

Next, nitrogen replacement is sufficiently performed to adjust the amount of dissolved oxygen to 1.5 ppm, and then the temperature is increased to 65 ° C.
Polymerization treatment was performed for 5 hours. This resulted in a suspension having polymer particles with a particle size of about 1 mm. This was filtered through a mesh, washed with warm water, and dried to obtain a granular pressure-sensitive adhesive composition comprising the above particles.

Example 2 Polymerization treatment was carried out in the same manner as in Example 1 except that 5 parts of N, acryloylmorpholine was used in place of 5 parts of N, N-dimethylacrylamide in the monomer mixture. About 1mm
A granular pressure-sensitive adhesive composition comprising polymer particles of the above was obtained.

Example 3 80 parts of i-octyl acrylate, 5 parts of styrene, N-
To a monomer mixture of 15 parts of acryloyl morpholine, 0.15 part of lauryl mercaptan and 0.3 part of azobisisobutyronitrile were uniformly mixed to obtain a raw material for polymerization. The above-mentioned raw material for polymerization was added to 200 parts of an aqueous solution in which 1 part of a polyvinyl alcohol-based dispersant was uniformly dispersed in water, and stirred to prepare a suspension of a monomer mixture.

Next, nitrogen replacement was sufficiently performed to adjust the amount of dissolved oxygen to 1.5 ppm, and then the temperature was increased to 65 ° C.
Polymerization treatment was performed for 5 hours. This resulted in a suspension having polymer particles with a particle size of about 1 mm. This was filtered through a mesh, washed with warm water, and dried to obtain a granular pressure-sensitive adhesive composition comprising the above particles.

Example 4 A polymerization treatment was carried out in the same manner as in Example 1 except that 70 parts of 2-ethylhexyl acrylate and 30 parts of N, N-dimethylacrylamide were used as the monomer mixture, and the particle size was reduced. A granular pressure-sensitive adhesive composition comprising polymer particles of about 1 mm was obtained.

Comparative Example 1 Polymerization was carried out in the same manner as in Example 1 except that 5 parts of methacrylic acid was used instead of 5 parts of N, N-dimethylacrylamide in the monomer mixture. A granular pressure-sensitive adhesive composition comprising polymer particles of the above was obtained.

Comparative Example 2 A polymerization treatment was carried out in the same manner as in Example 1 except that 50 parts of 2-ethylhexyl acrylate and 50 parts of N, N-dimethylacrylamide were used as a monomer mixture, and the particle size was reduced. A granular pressure-sensitive adhesive composition comprising polymer particles of about 1 mm was obtained.

Comparative Example 3 0.15 part of lauryl mercaptan, 0.1 part of azobisisobutyronitrile and 0.1 part of azobisisobutyronitrile were added to a monomer mixture of 75 parts of i-octyl acrylate, 20 parts of ethyl acrylate and 5 parts of styrene.
Three parts were uniformly mixed to obtain a raw material for polymerization. The above-mentioned raw material for polymerization was added to 200 parts of an aqueous solution in which 1 part of a polyvinyl alcohol-based dispersant was uniformly dispersed in water, and stirred to prepare a suspension of a monomer mixture.

Next, after sufficient nitrogen replacement and the amount of dissolved oxygen was adjusted to 1.5 ppm, the temperature was increased to 65 ° C.
Polymerization treatment was performed for 5 hours. This resulted in a suspension having polymer particles with a particle size of about 1 mm. This was filtered through a mesh, washed with warm water, and dried to obtain a granular pressure-sensitive adhesive composition comprising the above particles.

With respect to the granular pressure-sensitive adhesive compositions obtained in Examples 1 to 4 and Comparative Examples 1 to 3, the weight average molecular weight and melt viscosity of polymer particles were examined by the following methods. In addition, coating properties and adhesive properties (peeling force, holding force) were examined by the following methods. These results were as shown in Table 1.

<Weight Average Molecular Weight and Melt Viscosity> The weight average molecular weight of the polymer particles was determined by GPC analysis in terms of polystyrene. The melt viscosity is measured with a flow tester.
About 2 g of polymer particles after drying treatment using CFR-100
Temperature: 150 ° C, preheat: 5 minutes, load:
10kg, die diameter: 1mm, die length: 10mm,
It was measured.

<Coatability> The support has a thickness of 38 μm.
Polyethylene terephthalate film was used. The granular pressure-sensitive adhesive composition was coated on the surface of the support with an extruder under the condition A (extrusion temperature: 140 ° C., line speed:
Melt coating was performed under each of the following conditions: 10 m / min), condition B (extrusion temperature: 160 ° C., line speed: 10 m / min), and condition C (extrusion temperature: 160 ° C., line speed: 20 m / min). With respect to the adhesive layer having a thickness of 50 μm formed thereby,
The surface condition was visually observed, and the surface uniformly coated was evaluated as ○, and the surface unevenly coated was evaluated as ×.

<Adhesive Properties> The support has a thickness of 38 μm.
m of polyethylene terephthalate film, and on one side of the support, a granular pressure-sensitive adhesive composition was extruded by an extruder at an extrusion temperature of 140 ° C. (Comparative Examples 1 and 2 had a temperature of 16 ° C.).
(0 ° C.), line speed (extrusion speed): 10 m / min, and melt-coated to prepare an adhesive sheet having an adhesive layer having a thickness of 50 μm. After the adhesive layer was cross-linked by electron beam irradiation to reduce the gel fraction to about 10% by weight, the peeling force and the holding force were measured by the following methods.

The above gel fraction is determined by adding a predetermined amount (Mo) of the adhesive layer collected from the adhesive sheet to ethyl acetate so as to have a concentration of about 1% by weight, and then adding the gel at room temperature. After shaking for 7 days, the mixture was filtered through a 0.2 μm filter, the remaining polymer was dried, the weight (Mt) was measured, and the gel fraction (weight) was determined based on this and the amount (Mo) before treatment. %) =
(Mt / Mo) × 100.

(1) Measurement of Peeling Force The above adhesive sheet was cut into a size of 20 mm × 100 mm to prepare a test tape. This test tape was pressure-bonded to a stainless steel plate sanded with a # 280 sandpaper as an adherend in such a manner that a 2 kg roller was reciprocated once. After a lapse of 20 minutes at 23 ° C., the force required for peeling (180 ° peeling) was measured in an atmosphere of a pulling speed of 300 mm / min and 65% RH.

(2) Measurement of Holding Force A test tape having a width of 20 mm was prepared from the above-mentioned adhesive sheet. This test tape was placed on a phenol resin plate at 10 mm ×
Bonding was performed with a bonding area of 20 mm. After a lapse of 20 minutes, the plate was allowed to stand at 40 ° C. for 20 minutes, and then the phenol resin plate was suspended vertically, and a 500 g load was applied to the free end of the test tape.
At 80 ° C., the time (minutes) until the test tape dropped was measured.

[0042]

As is evident from the results in Table 1 above, the granular pressure-sensitive adhesive compositions of Examples 1 to 4 of the present invention have a low melt viscosity, and can be melt-coated at low or high speed by an extruder. It has good coating properties that can be performed at a time, and is excellent in the workability of producing adhesive sheets, and this adhesive sheet exhibits good adhesive properties that satisfy both peeling force and holding power It turns out that it is.

On the other hand, the granular pressure-sensitive adhesive composition of Comparative Example 1 was inferior in the above-described coating properties, and the granular pressure-sensitive adhesive composition of Comparative Example 2 was inferior in the above-mentioned composition. It can be seen that the coating properties and the adhesive properties are inferior, and that the granular pressure-sensitive adhesive composition of Comparative Example 3 is inferior in the adhesive properties (holding power).

[0045]

As described above, according to the present invention, the use of a nitrogen-containing monomer such as N, N-dimethylacrylamide as a polar component to be copolymerized with an alkyl ester of acrylic acid or methacrylic acid provides Low viscosity, melt coating by extruder can be performed at low temperature or high speed,
Moreover, it is possible to provide a granular pressure-sensitive adhesive composition exhibiting good adhesive strength and holding power, and an adhesive sheet thereof.

Claims (4)

[Claims] 1. 60 to 99% by weight of a main monomer mainly containing an alkyl ester of acrylic acid or methacrylic acid and substantially not containing a carboxyl group-containing monomer, and 40 to 1% by weight of a nitrogen-containing monomer. % Of a polymer having a particle size of 0.1 to 10 mm. 2. An adhesive sheet comprising a support having an adhesive layer obtained by melt-coating the granular pressure-sensitive adhesive composition according to claim 1 on one or both surfaces thereof. 3. A main monomer containing an alkyl ester of acrylic acid or methacrylic acid as a main component and substantially not containing a carboxyl group-containing monomer, and 60 to 99% by weight of a main monomer and 40 to 1% by weight of a nitrogen-containing monomer. % Polymerized in a state of being dispersed in water with a dispersant, and polymer particles having a particle size of 0.1 to 10 mm, which are composed of a copolymer of the above two monomers, are obtained. A method for producing a granular pressure-sensitive adhesive composition, comprising producing and separating and collecting the same. 4. The method of claim 1, wherein the granular pressure-sensitive adhesive composition obtained by the method according to claim 3 is melt-coated with an extruder on one or both surfaces of a support to form an adhesive layer. Characteristic method for producing adhesive sheets.