JP2725558B2 - Emulsion type adhesive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates, without reducing the water resistance, synthetic resin Maerujon which allowed increased alkali solubility, methods and adhesives containing the synthetic resin emulsion produced in the synthetic resin emulsion.

[0002]

2. Description of the Related Art In recent years, under the slogan "Earth-friendly", recycling activities such as recovery of used paper and plastic bottles have been actively carried out. Against this background, the needs of the market have largely shifted from the conventional emphasis on performance, such as imparting alkali solubility to adhesives and the like, and imparting biodegradability to plastics, to environmental protection. Also in the adhesive field, there is a tendency to use tack paper labels as bottle labels. However, with conventional tack paper labels,
It could not be removed from the bottle during recycling.

Under these circumstances, the present inventors have started designing an alkali-soluble adhesive as a recyclable resin. Heretofore, in order to impart alkali solubility to a resin, it has been mainly used to blend a natural polymer having high alkali solubility (for example, starch or the like) into a resin emulsion. In this method, alkali solubility is certainly improved, but water resistance is necessarily reduced. Conventionally, a method of emulsifying and copolymerizing a large amount of a carboxyl group-containing monomer with an acrylate ester has been employed in order to impart alkali solubility to the acrylate resin in the acrylate resin emulsion. However, the copolymer resin obtained by this method is
Although it has alkali solubility, it is copolymerized with a large amount of a hydrophilic carboxyl group-containing monomer, so it has poor water resistance, and since a large amount of carboxyl groups are present on the surface of emulsion particles, it is used as an adhesive. There is a disadvantage that tack is hard to come out.

[0004]

An object of the present invention is to solve the above-said drawbacks of the conventional alkali-soluble synthetic resin emulsion and an adhesive comprising the same to overcome the water resistance and alkali soluble synthetic resin having excellent emulsion, synthetic resin Emaruji
And a pressure-sensitive adhesive containing the synthetic resin emulsion.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned drawbacks of the conventional alkali-soluble synthetic resin emulsion and the pressure-sensitive adhesive containing the same.
A synthetic resin emulsion obtained by emulsion polymerization using a composition containing a specific alkyl acrylate as a main component and a specific amount of an unsaturated carboxylic acid and β-mercaptopropionic acid and a pressure-sensitive adhesive containing the same, The inventors have found that the above-mentioned object can be effectively solved by combining excellent water resistance and alkali solubility, which could not be obtained with an alkali-soluble synthetic resin emulsion, and have completed the present invention.

That is, a first aspect of the present invention is to provide a vinyl monomer mixture containing an alkyl acrylate having an alkyl group of 2 or more as a main component and containing 5 to 40% by weight of an unsaturated carboxylic acid. The present invention relates to a synthetic resin emulsion obtained by emulsion polymerization using 0.01 to 10% by weight of β-mercaptopropionic acid based on the total weight of the vinyl monomer mixture, and having excellent water resistance and alkali solubility. A second aspect of the present invention is to provide a vinyl-based monomer mixture containing, as a main component, an alkyl acrylate having an alkyl group having 2 or more carbon atoms and containing 5 to 40% by weight of an unsaturated carboxylic acid. 0.01 to 10 based on the total weight of the monomer mixture
The present invention relates to a method for producing a synthetic resin emulsion excellent in water resistance and alkali solubility, which is characterized by emulsion polymerization in the presence of β-mercaptopropionic acid in an amount of 0.3% by weight.

Furthermore, a third aspect of the present invention relates to pressure-sensitive adhesive containing a synthetic resin emulsion obtained in the first invention.

The present invention is characterized in that an unsaturated carboxylic acid and β-mercaptopropionic acid are used together with an alkyl acrylate in the production of a synthetic resin emulsion in order to impart water resistance and alkali solubility to the synthetic resin emulsion. There is.

A dry film of a resin formed from a synthetic resin emulsion obtained by copolymerizing a large amount of an unsaturated carboxylic acid with a vinyl group-containing monomer and neutralizing with a volatile alkali such as ammonia or the like, It is known to dissolve by alkali. However, in view of the safety of the operation when the alkali is soluble, a weak alkali or a low-concentration strong alkali requires a very long time to dissolve even if the temperature is increased. This is because the unsaturated carboxylic acid serving as the soluble component is randomly dispersed in the resin, and its effect is reduced.

The present inventors have paid attention to this point and used β-mercaptopropionic acid having a carboxylic acid in the chain transfer agent to improve the alkali solubility of the resin in the synthetic resin emulsion. When the carboxylic acid is selectively added, the alkali solubility is remarkably improved even when the amount of the unsaturated carboxylic acid is smaller than the conventional amount. It has been found that a synthetic resin emulsion having good properties can be obtained.

In general, a method of improving the alkali solubility by copolymerizing an unsaturated carboxylic acid with a vinyl group-containing monomer is known. However, an example in which β-mercaptopropionic acid is used as a chain transfer agent to improve the alkali solubility is known. Is not known. The present invention is based on the finding that a synthetic resin emulsion obtained by emulsion polymerization using a specific amount of β-mercaptopropionic acid is easily dissolved in a low-concentration alkali.

The alkyl acrylate used in the present invention has an alkyl group having 2 or more carbon atoms, preferably 2 to 12, and has a relatively low glass transition temperature when formed into a resin. Lower ones are used,
Representatives include ethyl acrylate, n-propyl or iso-propyl acrylate, n-butyl, iso-butyl or t-butyl acrylate, n
-Amyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl or iso-octyl acrylate, nonyl acrylate and the like. These alkyl acrylates are used at least 50% by weight in the vinyl monomer mixture. When the amount of the alkyl acrylate having an alkyl group having 2 or more carbon atoms is less than 50% by weight,
It has the disadvantage that the glass transition temperature of the resin is high, and tackiness and wetting property during drying are reduced, and further, the adhesion property is reduced accordingly.

When the alkyl group of the acrylic acid alkyl ester has less than 2 carbon atoms, the resultant synthetic resin emulsion has a drawback that the tackiness of the pressure-sensitive adhesive is inferior.

In the present invention, the unsaturated carboxylic acid is used for imparting alkali solubility. The unsaturated carboxylic acid used contains a monovalent or divalent or higher carboxylic acid, and specifically includes acrylic acid, methacrylic acid,
Maleic acid, maleic anhydride, phthalic acid, crotonic acid,
And itaconic acid.

The amount of the unsaturated carboxylic acid used is 5 to 40% by weight, preferably 5 to 10% by weight in the vinyl monomer mixture. If the amount of the unsaturated carboxylic acid is less than 5% by weight, the alkali solubility is insufficient. If the amount is more than 40% by weight, tackiness as tackiness is not produced and water resistance is lowered, which is not preferable.

The vinyl monomer mixture may contain other vinyl monomers in addition to the alkyl acrylate having an alkyl group of 2 or more carbon atoms and the unsaturated carboxylic acid. For example, in order to give cohesive force to the produced resin,
A monomer having a relatively high glass transition temperature when formed into a resin, for example, methyl (meth) acrylate, ethyl methacrylate, propyl methacrylate, or the like can be blended within a range that does not impair the object of the present invention. Other typical vinyl monomers that can be used include vinyl acetate, vinyl propionate, styrene, α-
As methylstyrene, acrylonitrile, vinyl chloride, vinylidene chloride, and an appropriate amount of hydrophilic vinyl monomer,
Sodium vinyl sulfonate, sodium methallyl sulfonate, 2-acrylamide 2-methylpropanesulfonic acid, sodium p-styrenesulfonate, (meth) acrylamide, N-methylol (meth) acrylamide, hydroxyethyl (meth) acrylate, hydroxypropyl ( (Meth) acrylate and the like.

The amount of β-mercaptopropionic acid used is
0.01 to 10 based on the total weight of the vinyl monomer mixture
%, Preferably 0.1 to 5% by weight. If the amount of β-mercaptopropionic acid is less than 0.01% by weight, the alkali solubility of the resin will not be obtained, and if it exceeds 10% by weight, the cohesive strength of the resin will be too low and the heat resistance as an adhesive will be maintained. It is not preferable because it cannot be performed. In the present invention, β
-Another chain transfer agent may be used in combination with mercaptopropionic acid.

The synthetic resin emulsion of the present invention can be produced by a usual emulsion polymerization method, but may be produced by a seed polymerization method, a two-stage polymerization method or a power feed polymerization method.

The synthetic resin emulsion of the present invention is excellent in water resistance and alkali solubility, and is useful as an alkali-soluble adhesive or adhesive.

[0020]

The present invention will be described below in more detail with reference to examples and comparative examples. In Examples and Comparative Examples,
Parts and percentages are by weight unless otherwise specified. The measurements of adhesion, alkali solubility and water resistance in the examples and comparative examples were performed according to the following.

A) Adhesiveness A test piece from which a release paper cut to a width of 25 mm and a high-quality paper were bonded, and the release paper was peeled off, was bonded to a glass plate by reciprocating a roller of 2 kg in weight five times. After standing for 20 minutes, a 180 ° peeling force was measured at a peeling speed of 300 mm / min.

B) Alkali-Soluble A 25 mm × 25 mm test piece from which a release paper and a high-quality paper are adhered to the inside of a beaker of 1000 ml and peeled off, and left at room temperature for 24 hours, A 4% aqueous solution of sodium hydroxide was placed in a beaker at 70 ° C. in a water bath, and the time until the test piece was peeled was measured while stirring at 800 rpm with a disper.

C) Water resistance A 25 mm × 25 mm test piece from which a release paper and a high quality paper are bonded to a φ20 mm glass tube, and the release paper is peeled off, is left at room temperature for 24 hours. Measured the state after 24 hours of immersion in water at ℃ and the time until peeling.

Example 1 1000 equipped with a stirrer, a nitrogen inlet tube and a reflux condenser tube
0.4 part of potassium persulfate and 200 parts of ion-exchanged water are put into a ml reactor, and heated to 80 ° C. under a nitrogen stream.
Then, 2-ethylhexyl acrylate 2 was added to the reactor.
15 parts, butyl acrylate 215 parts, methacrylic acid 6
0 parts, β-mercaptopropionic acid (β-MPA)
3 parts, an anionic surfactant having a reactivity represented by the following formula (Hitenol A-10, Daiichi Kogyo Seiyaku Co., Ltd.)
12 parts of water previously emulsified with 284 parts of water using a homomixer are dropped continuously over 3 hours while maintaining the above temperature.

Embedded image To the resulting emulsion, 3 parts of an ether type nonionic surfactant (Bissurf 1400, manufactured by Kao Corporation) was added.
The solid content concentration of the synthetic resin emulsion thus obtained was 50.8%, and the viscosity was 9,600 cps. This emulsion is applied to release paper at 50 to 60 μm,
After drying at 1 ° C for 1 minute, 55 g of high quality paper was stuck and
After standing in a constant temperature and humidity room at 0 ° C. and 65% for one day, the adhesion, water resistance, alkali solubility, and peeling force were measured. The results are shown in Table 1.

Examples 2 to 5 and Comparative Examples 1 to 6 The same procedures as in Example 1 were carried out except that emulsion polymerization was carried out with the composition shown in Table 1. The results are shown in Table 1.

[0026]

[Table 1]

[Table 2]

[0027]

As is clear from the above results, when the synthetic resin emulsion of the present invention is used as a pressure-sensitive adhesive, it is excellent in alkali solubility without lowering the water resistance of the pressure-sensitive adhesive. It is found to be useful as

Claims (3)

(57) [Claims] 1. A vinyl monomer mixture containing an alkyl acrylate having an alkyl group having at least 2 carbon atoms as a main component and containing 5 to 40% by weight of an unsaturated carboxylic acid. 0.01 to 10 based on the total weight of
A synthetic resin emulsion excellent in water resistance and alkali solubility, obtained by emulsion polymerization using β-mercaptopropionic acid in an amount of 1% by weight. 2. A vinyl monomer mixture containing, as a main component, an alkyl acrylate having an alkyl group having 2 or more carbon atoms and containing 5 to 40% by weight of an unsaturated carboxylic acid. 0.01 to 10 based on the total weight of
A process for producing a synthetic resin emulsion having excellent water resistance and alkali solubility, which comprises carrying out emulsion polymerization in the presence of β-mercaptopropionic acid in an amount of 0.5% by weight. 3. An adhesive containing the synthetic resin emulsion according to claim 1.