JPS61266480A - Aqueous dispersion of copolymer for adhesive - Google Patents

Abstract

PURPOSE:To reduce the lowering in adhesion of an aq. dispersion with time, by copolymerizing an ethylenically unsatd. dicarboxylic acid (monoester) with a (meth)acrylic ester and an ethylenically unsatd. monomer copolymerizable with them to prepare an aq. dispersion. CONSTITUTION:0.5-5wt% at least one monomer (A) selected from among ethylenically unsatd. dicarboxylic acids and their monoesters is copolymerized with 55-99.5wt% (meth)acrylic ester (B) having a 2-18C alkyl group and 0-40wt% other ethylenically unsatd. monomer copolymerizable with the components (A) and (B) to obtain an aq. dispersion of a copolymer having a glass transition temp. of -20--100 deg.C. It is required that the aq. dispersion contain a water-soluble component (as determined according to a specifically defined method) in an amount of 3wt% or less based on the total solid matter. The amount of the water-soluble component exceeding 3wt% brings about a remarkable change with time under wet heat conditions of adhesive products prepared therefore, which renders the products unsuitable for use as an adhesive.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an aqueous copolymer dispersion for adhesives having excellent moisture resistance.

BACKGROUND OF THE INVENTION Conventionally, acrylic emulsions have been mainly used as adhesives for adhesive products such as adhesive labels, adhesive sheets, and adhesive tapes.

When such an acrylic emulsion is used as a pressure-sensitive adhesive for a pressure-sensitive adhesive product, the adhesive strength may decrease over time if the resulting pressure-sensitive adhesive product is left in high temperature and high humidity conditions.

The degree of decrease in adhesive strength in this case varies depending on the type of base material used for the adhesive label, adhesive sheet, or adhesive tape.
Coated paper, which is often used as a base material, is affected by the decrease in adhesive strength (among coated papers, medium-strength coated paper has an even greater decrease in adhesive strength).

Problems to be Solved by the Invention As an improvement means to prevent this decrease in adhesive strength, a copolymer dispersion using a reactive emulsifier and a water-based solution consisting of a special highly functional copolymer have been developed. Mulsions have been proposed (for example, JP-A-60-38483), but the present invention provides an aqueous copolymer dispersion with even better adhesive strength.

The present invention was made against the background of the above-mentioned conventional technical problem, and its purpose is to minimize the decline in adhesive strength over time without sacrificing the adhesive properties (e.g. tack, cohesive strength, etc.). An object of the present invention is to provide an improved copolymer dispersion for adhesives.

Means for solving the problem, that is, the present invention, provides (a) at least one monomer selected from the group of ethylenically unsaturated dicarboxylic acids and monoesters of ethylenically unsaturated dicarboxylic acids. weight%
, (b) Acrylic ester or methacrylic ester having an alkyl group having 2 to 18 carbon atoms 55 to 99.5
% by weight, and (c) copolymerized with 0 to 40% by weight of another ethylenically unsaturated monomer copolymerizable with the components (a) and (b), and has a glass transition temperature of -20 to - A copolymer for adhesives, which is an aqueous dispersion of a copolymer at 100° C., and in which the water-soluble component as defined herein accounts for 3% by weight or less of the total solid content. A combined aqueous dispersion is provided.

In the present invention, examples of the ethylenically unsaturated dicarboxylic acid as monomer (a) include itaconic acid, maleic acid, fumaric acid, and maleic anhydride, preferably itaconic acid and maleic acid, and ethylenically unsaturated dicarboxylic acids. The saturated dicarboxylic acid monoester is a monoester of the ethylenically unsaturated dicarboxylic acid and a linear or branched aliphatic alcohol having 1 to 18 carbon atoms, and specifically, itaconic acid monomethyl ester, itaconic acid monoester, etc. Examples include monoethyl ester, monomethyl maleate, monoethyl maleate, monomethyl fumarate, monoethyl fumarate, mono-2-ethylhexyl itaconate, and these may be used alone or in combination of two or more. Ru.
(These monomers (a) have a content of 0.5 to 5 to contribute to the moisture and heat resistance of the adhesive.
% by weight, preferably 0.7-2.0% by weight.

If the amount of monomer (a) used is less than 0.5% by weight, the resulting aqueous copolymer dispersion will have poor cohesive strength, while if it exceeds 5% by weight, the adhesive strength of the resulting adhesive product after heat treatment will be poor. decreases.

Next, the monomer (b) in the present invention, that is, the carbon number 2 to 1
Examples of acrylic esters or methacrylic esters having 8 alkyl groups include ethylenically unsaturated alkyl carboxylates such as ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate. Other ethylenically unsaturated monomers (c) copolymerizable with components (a) and (b) include esters, such as styrene, α-methylstyrene, p-methylstyrene, halogenated styrene,
Vinyl monomers such as acrylonitrile; vinyl acetate,
Examples include vinyl esters such as vinyl propionate; ethylenically unsaturated monocarboxylic acid monomers such as acrylic acid, methacrylic acid, and crotonic acid.

These monomers (b) and (c) can be used alone or in combination of two or more.

Monomer (c) also includes (meth)acrylamide, glycidyl (meth)acrylamide, N-
Functional group-containing vinyl monomers such as methylol (meth)acrylamide and 2-hydroxyethyl (meth)acrylamide; polyvinyl group-containing monomers such as divinylbenzene, diallyl phthalate, and allyl (meth)acrylate
It may be contained in an amount of about 10% by weight.

The copolymer constituting the copolymer aqueous dispersion of the present invention requires the copolymer composition as described above, but furthermore, since the copolymer dispersion of the present invention is for adhesive use, adhesive strength, It is necessary to balance the tack and cohesive force, and for this reason, the glass transition temperature (hereinafter rTg) of the copolymer constituting the dispersion is
) is -20 to -100°C, preferably -30
It is necessary that the temperature is ~-70°C.

In the present invention, when emulsion polymerizing monomers (b) and (c) to monomer (a) as described later, monomers (b) and (c)
By appropriately selecting the type and proportion of the copolymer, the glass transition temperature of the copolymer and the amount of the water-soluble component described later may be controlled within specified ranges.

If the Tg of the copolymer exceeds -20°C, the tack will be significantly reduced, while if it is less than -100°C, the cohesive force will be significantly reduced and the adhesive will lack balance, both of which are unfavorable.

Further, the amount of water-soluble components in the aqueous copolymer dispersion of the present invention is 3% by weight or less, preferably 1.5% by weight based on the total solid content.
It is necessary that the following is true.

The amount of water-soluble components can be adjusted by the type and amount of acidic monomer, the amount of emulsifier, the type and amount of polymerization catalyst, and the polymerization temperature.

Further, after polymerization, the aqueous dispersion can be treated with a thin film to separate and remove water-soluble components to keep it within a predetermined range.

Here, the method for measuring the amount of water-soluble components is that the total solid content is Log
500 ml of distilled water was added to the copolymer aqueous dispersion, and a filter with a pore size (PORESIzE) of 0.1 μm (manufactured by Toyo Roshi ■, Membrane Filter-TM-
5) to filter the water-soluble components under pressure, and repeat this operation in step 4.
A total of 4E of distilled water was collected as filtered water and dried, and the water-soluble component amount X (weight %) was determined from the solid content Ag obtained as a residue using the following formula.

X (weight%) = (A/10)XI 00 If the value of water-soluble component amount It is.

The copolymer aqueous dispersion of the present invention can be produced by an emulsion polymerization method.

That is, in water, which is an aqueous medium, the monomer (A) is mixed so that the Tg and the amount of water-soluble components of the copolymer obtained with respect to the monomer (A) are within the range of the present invention. Select the types and amounts of monomers (a), (b) and (c) l') obtained by selecting the types and amounts of (b) and (c), a polymerization initiator, an emulsifier, and a molecular weight regulator if necessary. Polymerization can be carried out by heating the mixture to about 40 to 90° C. while stirring.

In this case, it is particularly preferable to add the monomer mixture continuously or intermittently for polymerization.

The weight ratio of monomer/water during polymerization is 60 to 150 parts by weight of water per 100 parts by weight of the monomer mixture, taking into consideration the balance between the heat load during drying and the increase in viscosity during polymerization due to high solidification. parts, preferably 70 to 100 parts by weight.

As a polymerization initiator, persulfates such as ammonium persulfate, potassium persulfate, and sodium persulfate, or peroxidants such as hydrogen peroxide and cumene hydroperoxide are used, and if necessary, sodium thiosulfate and sodium sulfate are used. It is also possible to carry out emulsion polymerization by redox reaction in combination with a reducing agent such as monoferrous ammonium.

Examples of emulsifiers include anionic emulsifiers such as sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium dioctyl sulfosuccinate, and disodium dodecyl diphenyl ether disulfonate, and nonionic emulsifiers such as polyoxyethylene alkyl ether and polyoxyethylene alkyl phenyl ether. ,
Mention may be made of the usual emulsifiers.

The amount of these emulsifiers used is usually 0.05 to 3 parts by weight, preferably 0.1 to 2 parts by weight per 100 parts by weight of monomer.

In such emulsion polymerization, it is also possible to use a molecular weight regulator, such as n-dodecylmercaptan, t-dodecylmercaptan, dialkylxanthogen disulfide, etc., and these molecules! The amount of regulator used is 0 to 5 parts by weight, preferably O to 5 parts by weight per 100 parts by weight of monomer.
It is 1.0 part by weight.

When the aqueous copolymer dispersion of the present invention thus obtained is used as a pressure-sensitive adhesive, the pH of the aqueous dispersion is adjusted to 7 to 9, and colorants, fillers, anti-aging agents, and erasers are added as necessary. Foaming agents, thickeners, etc. are added.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples.

In addition, in the examples, parts and % are parts by weight and weight %.

Furthermore, the performance of the adhesive tapes obtained in the Examples was measured by the following method.

[Adhesive strength]

Thickness 0. 2cm, width 5. Ocm, length 12.5c
A 5US304111 plate with a width of 2.m is polished using the method specified in JIS 20237. 5an, length 5c
The strength is shown in g1cm width when the adhesive tape of I11 is crimped 5 times with a 2 kg hand roll and then peeled off at an angle of 1806 at a speed of 300 w/ll1n.

The measurement was carried out at a constant temperature of 23° C. and humidity of 60% RH.

〔tack〕

Based on JIS Z0237, the inclined plate angle is measured at 30'.

[Holding force (slip distance)]

Place the adhesive tape on a 5USfi board similar to the one used in the adhesive force measurement so that the overlapping part is 2.5cm x 2.5cm, press it 5 times with a 2kg hand roll, and place a 1kg weight on the bottom end of the tape. Hang it at a temperature of 40℃ and a humidity of 80%.
Measurement was carried out at a constant temperature of RH.

[Adhesive strength after heat treatment]

An adhesive tape with a width of 2.5 am with the release paper still attached was left for 7 days at a temperature of 40°C and a humidity of 100% RH, and then left for one day at a temperature of 23°C and a humidity of 60% RH to improve the adhesive strength. Perform similar measurements.

Example 1 40 parts of water, 0.0 parts of sodium dodecylbenzenesulfonate.
1 part of sodium persulfate and 0.6 parts of sodium persulfate were charged into a reactor with an internal capacity of 1001, and after raising the internal temperature to 80'C, 60 parts of water,
80 parts of butyl acrylate, 18.5 parts of styrene, 1.5 parts of itaconic acid, and 0.5 parts of sodium dodecylbenzenesulfonate were continuously added over 5 hours to advance the reaction.
After the addition was completed, the temperature was raised to 85°C, and the reaction was continued for an additional 3 hours.

As a result, a highly stable aqueous copolymer dispersion (hereinafter referred to as "emulsion") with a polymerization rate of 99% or more of the charged monomers was obtained.

When this emulsion was adjusted to pH 8 with 25% aqueous ammonia, the viscosity was 160 cps. The Tg of this emulsion polymer measured by a differential scanning calorimeter (hereinafter measured by the same method) was -34°C, and the amount of water-soluble components in the emulsion was 1.4%.

Furthermore, 0.05 part of sodium polyacrylate was added as a thickener in terms of solid content per 100 parts of this emulsion to obtain an aqueous adhesive dispersion having a viscosity of 3.200 cps.

This was applied to a commercially available release paper and dried for 2 minutes in a hot air dryer at 120°C. On this dry adhesive side,
The back side of the rd cast coated paper was placed on it, and the tape was pressed onto the adhesive, the adhesive was transferred, and the adhesive was cut to obtain an adhesive tape.

The thickness of the adhesive layer at this time was 20 to 25 μm.

Example 2 The same operations as in Example 1 were performed except that the monomers were 90 parts of 2-ethylhexyl acrylate, 8 parts of methyl methacrylate, 1 part of maleic acid, and 1 part of acrylic acid.

The polymerization rate of the monomer in the emulsion obtained here was 99%.
The viscosity after adjusting the pH to 8 with ammonia water is 230c.
ps and Tg were -62°C, and the amount of water-soluble components in the emulsion was 1.3%.

Example 3 In Example 1, the monomers were 90 parts of butyl acrylate, 6 parts of styrene, and 2 parts of 2-hydroxyethyl acrylate.
．． The same operation was carried out except that 7 parts of itaconic acid, 1.0 parts of itaconic acid, and 0.3 parts of methacrylic acid were used.

The polymerization rate of the monomer in the emulsion obtained here was 99%.
Above, the viscosity after adjusting to pH 8 with ammonia water is 130c
ps and Tg were -46°C, and the amount of water-soluble components in the emulsion was 0.6%.

Example 4 The same operations as in Example 1 were performed except that the monomers were 98 parts of butyl acrylate and 2 parts of itaconic acid.

The polymerization rate of the monomer in the emulsion obtained here was 99%.
Above, the viscosity after adjusting to pH 8 with ammonia water is 180c
It was ps.

Comparative Example 1 The same operations as in Example 1 were performed except that the monomers were 60 parts of butyl acrylate, 38.5 parts of styrene, and 1.5 parts of itaconic acid.

The polymerization rate of the monomer in the emulsion obtained here was 99%.
Above, the viscosity after adjusting to pH 8 with ammonia water is 150c
ps and Tg were -12°C, and the amount of water-soluble components in the emulsion was 1.3%.

The Tg of the obtained copolymer was outside the range of the present invention, and both adhesive strength and thermal adhesive strength were poor.

Comparative Example 2 The same operation as in Example 1 was carried out except that the monomers were 80 parts of butyl acrylate, 18.2 parts of styrene, 1.8 parts of itaconic acid, and the amount of continuously added emulsifier was 1.9 parts. Ta. The monomer polymerization rate of the emulsion obtained here was over 99%, and the viscosity after adjusting the pH to 8 with aqueous ammonia was 1.
40 cps.

Tg was -32°C, and the amount of water-soluble components in the emulsion was 4.0%. The amount of water-soluble components in the obtained copolymer emulsion was outside the scope of the present invention, and the thermal adhesive strength was poor.

Comparative Example 3 The same operations as in Example 1 were performed except that the monomers were 80 parts of butyl acrylate, 1967 parts of styrene, and 0.3 parts of itaconic acid.

The polymerization rate of the monomer in the emulsion obtained here was 99%.
Above, the viscosity after adjusting to pH 8 with ammonia water is 170c
ps and Tg were -36°C, and the amount of water-soluble components in the emulsion was 0.5%.

The composition of the resulting emulsion was outside the scope of this invention and had no holding power at all.

Comparative Example 4 In Example 1, the monomer was butyl acrylate! ) The same operation was performed except that 80 parts of styrene, 13 parts of itaconic acid, and 7 parts of itaconic acid were used.

The polymerization rate of the monomer in the emulsion obtained here was 99%.
Above, the viscosity after adjusting to pH 8 with ammonia water is 160c
ps and Tg were -30°C, and the amount of water-soluble components in the emulsion was 6.0%.

The composition of the obtained emulsion was outside the scope of the present invention, had a large amount of water-soluble components, and had low thermal adhesive strength.

Comparative Example 5 The same operations as in Example 1 were performed except that the monomers were 80 parts of butyl acrylate, 18.5 parts of styrene, and 1.5 parts of acrylic acid.

The polymerization rate of the monomer in the emulsion obtained here was 99%.
The viscosity after adjusting the pH to 8 with ammonia water is 220c.
It was ps.

The composition of the obtained emulsion was outside the scope of the present invention and had low thermal adhesive strength.

Table 1 shows the charging compositions and physical properties of the emulsions produced in Examples 1 to 4 and Comparative Examples 1 to 5, as well as the performance of the adhesive tapes obtained using the emulsions.

Effects of the Invention The copolymer aqueous dispersion of the present invention is: - Mechanically and chemically stable and has excellent handling properties; - Adhesive labels,
When used as an adhesive for tapes, sheets, etc., compared to conventional copolymer aqueous dispersions, adhesive strength decreases less when stored under high temperature and humidity conditions, and is especially effective as a base for adhesive labels, tapes, and sheets. When the material is coated paper, or even cast-coated paper, conventional aqueous copolymer dispersions cause a further decrease in adhesive strength, but the aqueous copolymer dispersions of the present invention have less of this effect and are excellent. It can maintain adhesive strength and has other effects such as excellent cohesive strength and tack.

Since the copolymer aqueous dispersion of the present invention has the excellent performance shown above, it can be used as an adhesive label with excellent productivity and quality.
Tapes, sheets, etc. can be manufactured more favorably especially when the base material is coated paper.

Claims (1)

[Claims] (1) (a) 0.5 to 5% by weight of at least one monomer selected from the group of ethylenically unsaturated dicarboxylic acids and monoesters of ethylenically unsaturated dicarboxylic acids, (b) 2 to 5 carbon atoms; 55 to 99.5% by weight of acrylic ester or methacrylic ester having 18 alkyl groups, and (c) 0 to 0 to 99.5% of other ethylenically unsaturated monomers copolymerizable with the components (a) and (b) above. Made by copolymerizing 40% by weight,
It is an aqueous dispersion of a copolymer having a glass transition temperature of -20 to -100°C, and the water-soluble component as defined herein is 3% by weight or less of the total solid content. Characteristic copolymer aqueous dispersion for adhesives.