JP2873352B2 - Pressure sensitive adhesive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure-sensitive adhesive which has an excellent balance of adhesive strength, tackiness and holding power, has good weather resistance and transparency, and is suitable for packaging applications such as cardboard box sealing.

[0002]

2. Description of the Related Art Conventionally, rubber-based adhesives have been known as pressure-sensitive adhesives for packaging applications such as sealing cardboard boxes. Such a rubber-based pressure-sensitive adhesive is prepared by compounding a rubber-based polymer with a tackifier, a softening agent, and a filler to provide an adhesive force related to peel resistance, a tack related to wettability to an adherend, and a resistance to tack. It is made by adjusting the balance with the holding power related to creep properties. However, there is a problem that it is easily deteriorated by heat or oxygen, has poor weather resistance, and has poor transparency.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to develop a pressure-sensitive adhesive which is excellent in weather resistance and transparency in addition to a good balance between adhesion, tack and holding power.

[0004]

According to the present invention, 85 to 99% by weight of a monomer mainly composed of an acrylate ester having 4 to 12 carbon atoms in an alkyl group and a carboxyl group and / or a hydroxyl group are contained. An acrylic polymer having a glass transition point of 250 ° K or lower containing 1 to 15% by weight of a monomer as a main chain, having a weight average molecular weight of 1,000 or more and a glass transition point of 2
A graft weight having a carboxyl group-free compound having a temperature of 50 ° K or less as a side chain and having a ratio of molecular weight by laser scattering / polystyrene conversion of 1.3 or less in molecular weight measurement by gel permeation chromatography. An object of the present invention is to provide a non-ultraviolet curable pressure-sensitive adhesive characterized by being made of a united product.

[0005]

By using a graft polymer having a main chain and a side chain of a polymer having a glass transition point of 250 ° K or less, the tackiness can be improved even at a low temperature. Also,
In the molecular weight measurement by the graft polymer gel permeation chromatography, the ratio of the molecular weight by the laser scattering method / the molecular weight in terms of polystyrene is 1.3 or more, which indicates that the side chain shows good adhesion to the adherend. The balance between force, tack and holding force can be excellent. Furthermore, since it is an acrylic polymer, it can be made excellent in weather resistance and transparency.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The pressure-sensitive adhesive of the present invention uses a graft polymer, which is composed of a monomer 8 mainly composed of an acrylic acid ester having an alkyl group having 4 to 12 carbon atoms.
An acrylic polymer having a glass transition point of 250 ° K or less having a main chain of 5 to 99% by weight and 1 to 15% by weight of a monomer having a carboxyl group and / or a hydroxyl group as a main chain, and having a weight average molecular weight of 1000 With the above, the glass transition point is 250 ° K
It is composed of the following compounds having no carboxyl group as a side chain. In the present invention, the ratio of molecular weight by laser scattering / molecular weight in terms of polystyrene in the molecular weight measurement by gel permeation chromatography is 1.3 or more, especially 1.4 to 2.5.

The acrylic acid ester which is a component of the acrylic polymer has an alkyl group having 4 to 12 carbon atoms. Examples thereof include acrylic acid having a butyl group, isoamyl group, 2-ethylhexyl group, isooctyl group, isononyl group, decyl group, dodecyl group, etc.
And methacrylic acid esters. One or more acrylic acid esters are used for the synthesis of the acrylic polymer. When synthesizing the acrylic polymer, other monomers may be used as necessary. From the viewpoint of adhesive strength, it is appropriate to use 30% by weight or less of the acrylic acid ester. Examples of such monomers include vinyl acetate, styrene or derivatives thereof, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide and the like.

Examples of the monomer having a carboxyl group and / or a hydroxyl group as a component of the acrylic polymer include a monomer having a carboxyl group such as acrylic acid, methacrylic acid, maleic acid, itaconic acid and crotonic acid. And a hydroxyl group-containing monomer such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate and 2-hydroxypropyl methacrylate, and a carboxyl group such as mono-2-hydroxyethyl maleate. Examples include a monomer containing a hydroxyl group. The content of such a monomer in the acrylic polymer is 1 to 15% by weight. If the content is less than 1% by weight, the holding power is poor, and if it exceeds 15% by weight, the flexibility of the molecular chains is inferior and the tack and adhesion are poor. The weight average molecular weight of the acrylic polymer forming the main chain is preferably 50,000 or more, more preferably 100,000 to 2,000,000.

The side chain of the graft polymer forms a compound having a weight average molecular weight of 1,000 or more and a glass transition point of 250 ° K or less. If the weight average molecular weight is less than 1,000, the interaction such as entanglement of side chains is inferior and the cohesive strength is poor. The upper limit of the weight average molecular weight of the compound forming the side chain is,
It is generally about 100,000 from the viewpoint of adjustability. By controlling the molecular weight and introduction ratio of the side chain in the graft polymer, the ratio between the molecular weight by laser scattering and the molecular weight in terms of polystyrene can be controlled in the molecular weight measurement by gel permeation chromatography. If the ratio of the molecular weight is less than 1.3, the holding power is poor,
When cross-linking treatment is carried out with a cross-linking agent, it is difficult to achieve a balance because of a decrease in adhesive strength.

The preparation of the graft polymer can be carried out by an appropriate method. A method of separately preparing a side-chain-forming compound having a radical polymerizable double bond at at least one end and copolymerizing it with a monomer for forming a main chain controls the molecular weight of the side chain and suppresses the formation of homopolymer. This is preferred from the viewpoint of the formation of a desired graft polymer and the like. The copolymerization treatment is, for example, a solution polymerization system, an emulsion polymerization system,
It can be performed by a suspension polymerization method or the like.

The side chain-forming compound is prepared, for example, by polymerizing a component monomer such as an acrylate ester with a polymerization initiator having a carboxyl group or a hydroxyl group such as azobis (4-cyano) valeric acid or thiaglycolic acid. Polymerization in the presence of an agent or a chain transfer agent to prepare an oligomer having a weight average molecular weight of about 1,000 to 50,000 and having a carboxyl group or a hydroxyl group at a terminal, and converting the oligomer into glycidyl acrylate, glycidyl methacrylate, methacryloyloxy. It can be carried out by a method of reacting a functional group capable of reacting with a carboxyl group or a hydroxyl group such as isocyanate with a compound having a radical polymerizable double bond. Therefore, the graft polymer in the present invention does not contain a carboxyl group in the side chain.

When the purpose of use of the pressure-sensitive adhesive is required to be excellent in holding power, for example, in the case of sealing a cardboard box having a strong repulsive force, a polyfunctional acrylic acid ester component is used as the main chain. And it is preferably contained in a side chain. Examples of the polyfunctional acrylic acid ester include, but are not limited to, polyethylene glycol diacrylate, 1,6-hexanediol diacrylate, polypropylene glycol diacrylate, 2,2
-Bis (4- (acryloxy-diethoxy) phenyl)
Examples thereof include propane trimethylol propane triacrylate, tetramethylol methane triacrylate, dipentaerythritol hexaacrylate, and those obtained by substituting the acrylic acid component with methacrylic acid.

The pressure-sensitive adhesive of the present invention can be prepared in a usual application form such as a non-UV curing type, that is, a solution type by a solvent, other than a type which is cured by irradiation with ultraviolet rays. At the time of its preparation, an appropriate compounding agent may be added, if necessary, in addition to the graft polymer.
Examples thereof include a crosslinking agent, an adhesion regulator, a tackifier,
Plasticizer, softener, antioxidant, UV absorber, filler,
Examples include bulking agents.

Examples of generally used crosslinking agents include polyisocyanates, melamine resins, amine-epoxy resins, peroxides, metal chelate compounds and the like.
The amount of the crosslinking agent is about 1 per 100 parts by weight of the graft polymer.
0 parts by weight or less is appropriate.

[0015] Commonly used adhesion regulators include:
Acrylic polymers and the like can be mentioned. As the tackifier, terpene-based resins, terpene-phenol-based resins,
Coumarone indene type resin, styrene type resin, rosin type resin, xylene type resin, phenol type resin, petroleum type resin and the like can be mentioned.

[0016] Examples of plasticizers generally used include process oils and polyesters. Examples of the softener include polybutene and liquid rubber.

In any of the above cases, from the viewpoint of transparency,
It is not preferable to use those exhibiting color or having poor compatibility. The total amount of the compounding agents used is generally equal to or less than the equivalent amount of the graft polymer.

The pressure-sensitive adhesive of the present invention can be applied to thin sheets such as plastic film, paper, cloth, metal foil, etc.
It can be used for ordinary applications such as an adhesive tape attached with a thickness of 0 μm. Particularly, it is preferably used for packaging applications such as sealing cardboard boxes.

Reference Example 1 In a container equipped with a cooling pipe, a nitrogen introduction pipe, a thermometer, and a stirring rod,
100 parts of methyl methacrylate (parts by weight, the same applies hereinafter), 4,
1 part of 4-azobis (4-cyano) valeric acid and 2 parts of thioglycolic acid are added, and reacted at 60 ° C. for 3 hours under a nitrogen atmosphere using 50 parts of methyl ethyl ketone and 50 parts of toluene as a solvent. Precipitation purification treatment was performed with a water-methanol mixed solvent to obtain a terminal carboxylated prepolymer.
The KOH equivalent of this prepolymer is 0.2 mmol / polymer 1
g.

Next, 100 parts of the above prepolymer, 200 parts of xylene, 7 parts of glycidyl methacrylate, 0.5 part of hydroquinone and 0.5 part of triethylamine were placed in a container similar to the above and reacted at 140 ° C. for 5 hours to obtain a mixture. The product is subjected to precipitation purification treatment with a water-methanol mixed solvent,
After drying under reduced pressure at 48 mmHg for 48 hours, a methyl methacrylate side chain-forming compound was obtained. This side chain-forming compound has a weight average molecular weight of 8200, a number average molecular weight of 5300, and a glass transition point of 31.
The temperature was 5 ° K (differential thermal analysis, the same applies hereinafter), and the conversion of the terminal carboxyl group was 95% (KOH equivalent, the same applies hereinafter). In the above, the conditions for measuring the molecular weight are as follows (the same applies hereinafter). Pump: TOYO SODA CCP
D. Thermostat: CO-8000. Light scattering: LS-800
0. Differential refractometer: RI-8011. Column: TSK-G
EL H-type organic solvent-based packed column for high-speed GPC.

Reference Example 2 According to Reference Example 1, terminal carboxylated prepolymer was obtained by using 100 parts of butyl acrylate, 1 part of 4,4-azobis (4-cyano) valeric acid and 1 part of thioglycolic acid. Using 100 parts of the prepolymer and 7.1 parts of glycidyl methacrylate, a butyl acrylate-based side chain-forming compound was obtained. This side chain-forming compound had a polymerization average molecular weight of 10,300, a number average molecular weight of 6,500, a glass transition point of 218 ° K, and a conversion of terminal carboxyl groups of 95%.

Reference Example 3 According to Reference Example 1, 85 parts of 2-ethylhexyl acrylate,
A terminal carboxylated prepolymer is obtained using 15 parts of methyl methacrylate, 1 part of 4,4-azobis (4-cyano) valeric acid and 0.5 part of thioglycolic acid, and the prepolymer is obtained.
Using 100 parts and 1.8 parts of glycidyl methacrylate, a side chain forming compound of 2-ethylhexyl acrylate was obtained. This side chain-forming compound had a weight average molecular weight of 40,000, a number average molecular weight of 16,000, a glass transition point of 228 ° K, and a conversion of terminal carboxyl groups of 95%.

Reference Example 4 According to Reference Example 1, 85 parts of methyl methacrylate, 15 parts of acrylonitrile, 4,4-azobis (4-cyano) valeric acid 1
And 0.5 part of thioglycolic acid were used to obtain a terminal carboxylated prepolymer, and 100 parts of the prepolymer and 3.4 parts of glycidyl methacrylate were used to obtain a methyl methacrylate-based side chain-forming compound. This side chain-forming compound has a weight average molecular weight of 26000, a number average molecular weight of 8200, a glass transition point of 326 ° K, and a reaction rate of terminal carboxyl group of 95.
%.

Example 1 In a vessel equipped with a cooling pipe, a nitrogen introduction pipe, a thermometer, and a stirring rod,
10 parts of the side chain forming compound obtained in Reference Example 2, 98 parts of 2-ethylhexyl acrylate, 2 parts of acrylic acid, benzoyl peroxide
0.2 part was added, and the mixture was reacted at 65 ° C. for 5 hours and then at 80 ° C. for 2 hours under a nitrogen atmosphere using 100 parts of toluene and 100 parts of ethyl acetate as a solvent to obtain a graft polymer. This graft polymer has a glass transition point of a main chain of 230 ° K and a molecular weight ratio (ratio of molecular weight by laser scattering method in molecular weight measurement by gel permeation chromatography / molecular weight by polystyrene conversion, the same applies hereinafter) of 1.80. Met. The glass transition point of the main chain is based on a polymer separately synthesized with a corresponding composition (the same applies hereinafter).

The pressure-sensitive adhesive of the present invention was obtained by adding 0.05 parts of a tetrafunctional epoxy crosslinking agent to the reaction solution containing the graft polymer.

Example 2 Example 1 was repeated using 5 parts of the side chain-forming compound obtained in Reference Example 3, 90 parts of isooctyl acrylate, 6 parts of vinyl acetate, 4 parts of acrylic acid, and 0.01 part of trimethylolpropane triacrylate. A similar graft polymer was obtained to obtain the pressure-sensitive adhesive of the present invention. The graft polymer had a glass transition point of the main chain of 210 ° K and a molecular weight ratio of 1.72.

Example 3 15 parts of the side chain-forming compound obtained in Reference Example 2 and acrylic acid 2-
97 parts of ethylhexyl, 3 parts of acrylic acid, 2-acrylic acid
Using 0.1 part of hydroxyethyl, a graft polymer was obtained in the same manner as in Example 1 to obtain a tube pressure-sensitive adhesive of the present invention. The graft polymer had a glass transition point of the main chain of 225 ° K and a molecular weight ratio of 1.70.

Comparative Example 1 15 parts of the side chain-forming compound obtained in Reference Example 1 and acrylic acid 2-
Example 1 using 98 parts of ethylhexyl and 2 parts of acrylic acid
And a pressure-sensitive adhesive was obtained. In the graft polymer, the glass transition point of the main chain was 225 ° K, and the molecular weight ratio was 1.75.

Comparative Example 2 Using 10 parts of the side chain-forming compound obtained in Reference Example 4, 95 parts of butyl acrylate, and 5 parts of acrylic acid, a graft polymer was obtained according to Example 1, and a pressure-sensitive adhesive was obtained. Was. The graft polymer has a glass transition point of a main chain of 215 ° K and a molecular weight ratio of
1.62.

Comparative Example 3 A commercially available rubber-based pressure-sensitive adhesive for sealing cardboard (containing two parts of a trifunctional isocyanate-based crosslinking agent) composed of natural rubber having a glass transition point of 233 ° K was used.

Comparative Example 4 Pressure-sensitive according to Example 1 using a polymer having a side chain composed of 90 parts of dodecyl acrylate, 5 parts of acrylonitrile and 5 parts of acrylic acid (glass transition temperature 230 ° K., molecular weight ratio 1.2). An adhesive was obtained.

Evaluation Test The pressure-sensitive adhesive obtained in each of Examples and Comparative Examples was coated on one surface of a uniaxially stretched polypropylene film having a thickness of 60 μm to a thickness of 30 μm after drying.
m and then dried by heating to obtain an adhesive tape, which was left at 50 ° C. or lower for 3 days, and then examined for the following characteristics.

Adhesive force Measured according to JIS Z 0237.

Retention force Measured in accordance with JIS Z 0237. The condition is 40
C., a suspension load (weight) of 2 kg, and a suspension time of 30 minutes. During that time, the time until the weight dropped was measured when the weight fell, and the displacement of the adhesive tape was measured when the weight did not fall.

Transparency Ten adhesive tapes were superimposed, adhered to the paper on which the characters were printed, and examined to see if the characters could be read.

Weather Resistance The pressure-sensitive adhesive tape was pressed back and forth on a stainless steel plate by reciprocating a 2 kg roll, and after 7 days of outdoor exposure, the pressure-sensitive adhesive tape was peeled off, and it was examined whether or not any adhesive residue was left on the stainless steel plate.

Sealability A lid (width: 10) in which both ends of the cardboard box can be freely bent.
5mm, length 260mm) and close the butted part (center)
Join with 50mm, 260mm long adhesive tape, fix the cardboard box with the joint side down through the side, apply a 5kg load to the joint through the lid, and until the weight falls And the state after standing for 23 days.

The results are shown in Table 1.

[Table 1]

[0039]

The pressure-sensitive adhesive of the present invention has an excellent balance of adhesive strength, tackiness and holding power, and also has excellent weather resistance and transparency, and is excellent when used for sealing cardboard boxes and the like. Shows the initial adhesive force and maintains the adhesive state for a long time.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-271471 (JP, A) JP-A-63-301282 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C09J 151/00-151 / 10,155 / 00 C08F 299/00

Claims (1)

(57) [Claims] (1) 85 to 99% by weight of a monomer mainly composed of an acrylic acid ester having 4 to 12 carbon atoms in an alkyl group;
Monomers 1-1 having a carboxyl group and / or a hydroxyl group
An acrylic polymer having a glass transition point of 250 ° K or less containing 5% by weight as a main chain and having a weight average molecular weight of 100
A carboxyl group-free compound having a glass transition point of 250 ° K or less and a glass transition point of 0 or more is used as a side chain, and the ratio of molecular weight by laser scattering / polystyrene conversion in molecular weight measurement by gel permeation chromatography is 1.3 or more. A non-ultraviolet curable pressure-sensitive adhesive, comprising: a graft polymer.