JPS5933372A - Water-base adhesive excellent in initial adhesion and heat resistance - Google Patents

Abstract

PURPOSE:To provide a water-base adhesive excellent in initial adhesion and heat resistance, by incorporating a water-base high-molecular emulsion having a specific compsn. and salts such as an alkali metal or ammonium persulfate or a polyvalent metallic salt capable of reacting with carboxyl groups. CONSTITUTION:55-99.995wt% alkyl acrylate having 4C or higher alkyl groups (A), 0.005-2wt% polyfunctional monomer having double bonds in a molecule (B), and 0-44.995wt% other unsatd. monomer (C) are subjected to emulsion polymn. in an aq. medium contg. unsatd. polybasic carboxylic acids within a wt. ratio of unsatd. polybasic carboxylic acids to the total amt. of components A, B and C of 0.1 to 99.9-5 to 95. Salts selected from alkali metal persulfates, ammonium persulfates, and polyvalent metallic salts capable of reacting with carboxyl groups are incorporated with said water-base high-molecular emulsion to yield the intended water-base adhesive.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention develops extremely high adhesive strength in a short period of time,
The present invention also relates to a water-based adhesive with excellent heat resistance.

Conventionally, solution-type adhesives and pressure-sensitive adhesives using organic solvents as a medium have been widely used, but solution-type adhesives not only pose a risk of air pollution and fire, but also pose problems in terms of occupational safety and health and resource conservation. However, there are many problems with this system, and therefore, the current situation is that switching to other systems is being actively promoted. One such direction is the creation of aqueous emulsions for adhesives and pressure-sensitive adhesives.

Water-based emulsion adhesives and pressure-sensitive adhesives are used in a wide range of fields because they do not have the above-mentioned problems encountered with solution-based adhesives. Due to its poor performance, it has a fatal flaw in that the initial adhesive strength is extremely slow to develop.

In order to improve these drawbacks, methods have been proposed such as increasing the solid content in the emulsion, using an organic solvent in combination, or adding heat. However, none of these methods can be said to be satisfactory because they are not sufficiently effective or require special equipment.

Furthermore, a water-based adhesive mainly composed of rubber latex is combined with a film-forming agent (Japanese Patent Publication No. 56-9953), or an emulsion-type water-based adhesive is combined with an adhesion promoter (for example, Japanese Patent Publication No. 56-9953). No. 59874), a so-called two-component method of developing initial adhesion has also been proposed. Generally, if an aqueous solution of a metal salt is added to an aqueous polymer emulsion, salting out may occur, and if certain organic solvents or oppositely charged ions are added, the emulsion will not aggregate. well known. The second method focuses on the cohesive properties of emulsions, but in reality, the situation differs markedly depending on the type of emulsion, etc. For example, among the emulsions used in this method, some emulsions do not cause salting out or aggregation at all, or even if they do occur, their adhesion to the adherend is extremely reduced and they do not perform their function.
Alternatively, there is a problem that drying becomes poor and the initial adhesion property deteriorates considerably.

The present inventors have conducted various studies in order to overcome the drawbacks of these conventional techniques and obtain an aqueous adhesive with excellent initial adhesion properties. The water-based polymer emulsion, which has excellent film-forming properties due to adhesiveness and shear stress, and the water-based adhesive, which consists of specific salts, exhibit surprisingly large initial adhesion strength in an extremely short period of time, and also have significantly improved heat resistance. Therefore, the present invention has been completed based on the discovery that (4) an acrylic acid alkyl ester having an alkyl group having 4 or more carbon atoms in an aqueous medium containing an unsaturated polyhydric carboxylic acid. 55-99.995% by weight (B) 0,005-2% by weight of a polyfunctional monomer having two or more double bonds in one molecule (C) 0-2% of other unsaturated monomers, 995% by weight of unsaturated polyhydric carboxylic acid and the total weight ratio of components (4), (B) and (C) is within the range of 0.1:99.9 to 5:95. and at least one salt selected from alkali metal persulfates, ammonia persulfates, and salts of polyvalent metals that can react with carboxyl groups. Concerning superior water-based adhesives.

The aqueous adhesive of the present invention has superior initial adhesion and significantly increased heat resistance compared to when an aqueous polymer emulsion is used alone for adhesion. Furthermore, it has an excellent feature of high final adhesive strength.

The water-based adhesive of the present invention includes the type of monomer, the amount of monomer used,
It is an aqueous adhesive having a major feature in that it is a combination of an aqueous polymer emulsion obtained by a combination of specific polymerization conditions and the above-mentioned salts.

Examples of unsaturated polycarboxylic acids used in the present invention include maleic acid, fumaric acid, and itaconic acid.

Examples include citraconic acid and hymic acid. These unsaturated polyhydric carboxylic acids may be used alone or in combination of two or more.

The unsaturated polycarboxylic acid is added in advance to the aqueous medium before adding (4) the acrylic acid alkyl ester, (B) the polyfunctional monomer, and (C) the other unsaturated monomer. It is necessary to keep the unsaturated polycarboxylic acid in the aqueous medium without adding it to the aqueous medium in advance.
If components B) and (C) are added simultaneously to an aqueous medium and emulsion polymerization is carried out, not only will the reactivity be poor and the yield will be reduced, but also the storage stability of the resulting aqueous polymer emulsion will be poor. So I don't like it.

If an unsaturated monocarboxylic acid such as acrylic acid or methacrylic acid is used instead of an unsaturated polycarboxylic acid,
Since the unsaturated monocarboxylic acid is homopolymerized before adding components (A), (B), and 0, it does not work effectively, and the storage stability and film forming properties due to shear stress are affected by alkali metal persulfates and ammonia. The effect of improving coagulability and heat resistance by polyvalent metal salts that can react with persulfates and carboxyl groups is undesirable.

When an unsaturated polycarboxylic acid is used, it does not have the disadvantages of using an unsaturated monocarboxylic acid and gives preferable results.

The amount of the unsaturated polycarboxylic acid added to the aqueous medium is such that the weight ratio of the unsaturated polycarboxylic acid to the total weight of components (B) and (C) is 0.1:99.9 to 5: 95, preferably 0
．． It needs to be within the range of 2:99.8 to 2:98. When the weight ratio of unsaturated polyhydric carboxylic acid is less than 01,
Although the resulting aqueous polymer emulsion has good film-forming properties due to abrasion stress and excellent initial adhesion, it has poor storage stability and little improvement in heat resistance, making it unsuitable. When the weight ratio of unsaturated polyhydric carboxylic acid exceeds 5,
Not only does the film-forming property of the resulting aqueous polymer emulsion deteriorate, but also the polymerizability decreases, which is undesirable for practical use.

In addition to the aqueous medium containing this unsaturated polycarboxylic acid, the main component of the monomer to be copolymerized with this unsaturated polycarboxylic acid is (5) acrylic acid alkyl whose alkyl group has 4 or more carbon atoms. It is a gyl ester, and specific examples thereof include butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, and the like. These can be used alone or in combination.

(4) The amount of component used is 55 to 99.995% by weight, preferably 65 to 99.995% by weight based on the total weight of components (B) and (C).
It is 5% by weight. (4) If the amount of the component used is less than 55% by weight, or if the number of carbon atoms in the alkyl group of the prisoner component is less than 4, the resulting aqueous polymer emulsion will have insufficient tackiness and poor adhesion to various materials. However, it is not possible to obtain excellent initial adhesion properties that fully demonstrate the characteristics of the present invention. (4
If the amount of component ) used exceeds 99.995% by weight, the effect of improving the heat resistance of the resulting monoaqueous polymer emulsion will not be sufficient.

The unsaturated polycarboxylic acid used in the present invention and (4
) A polyfunctional monomer having two or more double bonds in one molecule that can be copolymerized with component (B) increases the internal cohesive force of the copolymer and provides good heat resistance. It is what you use. like this(
B) Examples of polyfunctional monomers include divinylbenzene,
Diallyl phthalate, diallyl maleate, ethylene glycol di(meth)acrylate, di(4-lene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate , dipropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, pentaerythritol di- or tri- or tetra(meth)acrylate, triallyl cyanurate, etc. The usage amount of component (B) is (] 3) In order to fully demonstrate the effect of using the ingredients, (B) and (C)
0.005 to 2% by weight, preferably 0.005% to 2% by weight of the total weight of the ingredients.
It is within the range of 0.01 to 1% by weight.

If the amount of component (B) used is less than 0.005% by weight, the effect of improving the heat resistance etc. of the resulting aqueous polymer emulsion will be insufficient; on the other hand, if the amount of component (B) used is less than 2% by weight
If it exceeds 20%, the tackiness and adhesion of the resulting aqueous polymer emulsion will be significantly reduced, and excellent initial adhesion will not be obtained.

Examples of other unsaturated monomers (C) that can be copolymerized with each of the above components include methyl acrylate, ethyl acrylate,
Propyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate.

Acrylic acid alkyl esters in which the alkyl group has less than 4 carbon atoms, such as glycidyl acrylate.

Methyl methacrylate, ethyl methacrylate.

Methacrylic acid esters such as butyl methacrylate, hydroxyethyl methacrylate, glycidyl methacrylate, vinyl formate, vinyl acetate.

Vinyl esters such as vinyl propionate and vinyl persate, acrylamide, methacrylamide,
Unsaturated amides such as N-methylolacrylamide, vinyl halides such as vinyl chloride and vinylidene chloride, aromatic vinyls such as styrene, α-methylstyrene and sodium styrene sulfonate, and unsaturated amides such as acrylic acid and methacrylic acid. Saturated carboxylic acids, unsaturated nitriles such as acrylonitrile and methacrylonitrile, or ethylene.

Examples include olefins such as isobutylene.

The amount of component (C) used is 0 to 44.995% by weight based on the total weight of components (B) and (C). If the amount of component (C) used exceeds 44.995% by weight, the resulting aqueous polymer emulsion will have low adhesive strength and poor adhesion to various materials, making it impossible to obtain excellent initial adhesion. .

To produce the aqueous polymer emulsion of the present invention, conventional emulsion polymerization methods are employed. For example, a surfactant, a polymerization initiator, a reducing agent, Pi (regulator), deionized water, and an unsaturated polyhydric carboxylic acid are charged into a reactor, and the reactor is stirred while purging with nitrogen as necessary to maintain a predetermined temperature. (For example, 30 to 1
After heating to 00° C.), components (4), (B) and (2) are added all at once, continuously or in portions.

In the present invention, continuous addition or divided addition is preferred. Components (A), (B) and (C) may be mixed in advance and then added, or each component may be added separately.

After the addition of components (B) and 0 is completed, the unreacted monomers may be aged at the same temperature, or the unreacted monomers may be removed by further raising the polymerization temperature or adding a polymerization initiator. Polymerization is completed so as to eliminate the

As the surfactant used during emulsion polymerization, an anionic type surfactant represented by sodium alkylbenzenesulfonate is used in an amount of 25% by weight or less, preferably 1.0% by weight or less based on the total system. It is preferable to do so. If the amount used exceeds 2.5% by weight, the film-forming properties of the resulting aqueous polymer emulsion will deteriorate, resulting in a decrease in initial adhesion as well as poor water resistance as an adhesive.

Although the polymerization temperature varies depending on the type of monomer and the polymerization initiator, it is usually preferably carried out in the range of 3o-J'+oooC. The monomers are preferably used in proportions such that the final polymer concentration in the emulsion is in the range of 20 to 65% by weight.

The aqueous polymer emulsion of the present invention thus obtained has good adhesion and storage stability, and is easily formed into a film by shear stress etc., giving excellent initial adhesion. When the pH of the emulsion is adjusted to 7 or less, especially 6 or less, this effect becomes even more pronounced, and the initial adhesion is further improved. In addition, examples of the alkali metal persulfate and ammonia persulfate used to further improve the initial adhesion and heat resistance include sodium persulfate, potassium persulfate, and ammonium persulfate. Examples of polyvalent metal salts that can react with carboxyl groups include calcium, magnesium, zinc, copper,
Hydrochlorides and sulfates of barium, iron, aluminum, zirconium, etc.

Examples include sulfites, nitrates, nitrites, phosphates, and carboxylates. These salts may be used alone or as a mixture, but particularly effective are systems in which alkali metal persulfates or ammonia persulfates are combined with polyvalent metal salts. , better heat resistance can be obtained than when each is used alone.

The amount of salt used is 10% of the solid content of the aqueous polymer emulsion.
The solid content is preferably 0.2 to 20 parts by weight based on Q parts by weight. If the amount of salt used is less than 0.2 parts by weight, the remarkable effect of the present invention cannot be obtained, and if it exceeds the weighted kick part, the adhesive strength will be significantly reduced, which is not preferable.

As a method of combining an aqueous polymer emulsion and salts, the aqueous polymer emulsion and salts may be separately applied to each surface of the adherend to be bonded, and the coated surfaces may be overlapped and pressure bonded. Salts may be made into a solution and simultaneously sprayed onto the adherend with an aqueous polymer emulsion using a spray or the like, followed by pressure bonding. Either method can exhibit the effects of the present invention.

The aqueous polymer emulsion used in the present invention can be used for bonding as it is without any modification; however, depending on the use and purpose, other aqueous polymers may be added to the emulsion. Molecular emulsions and tackifiers, or inorganic powders such as calcium carbonate and clay, organic fillers such as flour and starch, or solvents and plasticizers, thickeners, antifoaming agents, stabilizers, and rust preventives. agents, preservatives, pigments,
It is also possible to mix and use various additives such as colorants and crosslinking agents. The same applies to persulfates of alkali gold D3, persulfates of ammonia, and salts of polyvalent metals that can react with carboxyl groups, and it is also possible to use them by blending various additives with them. It is.

Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the present invention is not limited in any way by these Examples.

Example 1 1 g of sodium dodecylbenzenesulfonate, 2 g of sodium pyrophosphate, and 1 g of itaconic acid were placed in a four-eye flask with an internal volume of 11 equipped with a hygrometer, stirrer, condenser, dropping funnel, etc.
0 g and 180 g of deionized water were added. While stirring, the mixture was uniformly dissolved and the temperature was raised to 85°C. Thereinto was added a monomer mixture consisting of 375 g of 2-ethylhexyl acrylate, 125 g of styrene, and 0.40 g of divinylbenzene, and 4 g of sodium dodecylbenzenesulfonate and 250 g of divinylbenzene.
A monomer emulsion obtained by emulsifying with 1 g of deionized water and 40 I of an ammonium persulfate aqueous solution having a concentration of 10% by weight were added dropwise over 3.5 hours. Thereafter, the mixture was further aged for 15 hours with stirring at the same temperature. The reaction was favorable.

After cooling, 7 ml of aqueous ammonia was added to partially neutralize. The resulting aqueous polymer emulsion had a polymer concentration of 7% by weight, a pH of 5.8, good storage stability, and remained stable even after 3 months.

The amount of wet coating of this emulsion on the tin plate is approximately 1
After applying with an applicator so as to reach 50 g/m and air drying for 1.5 minutes at a temperature of 20'C, a 10% by weight ammonium persulfate aqueous solution was applied on top of it in advance to a wet weight of about 809 g/m. 9 obtained by applying it to a thickness of m and drying it in air.
The No. 1 cotton canvas was overlapped and bonded by pressing with a roller with a load of 1 kg. After 2 minutes, use Tensilon and 200 mu
The 180° peel strength measured by pulling the cotton canvas at a speed of 2 adhesives made of canvas
After air drying for more than 4 hours, a weight of 100 μm was attached to one end of the cotton canvas and hung in a hot air dryer, and the temperature was increased at a rate of 1°C/acid to measure the temperature at which the weight fell (adhesion length 50 m
m). The softening temperature thus measured was 86°C.

Examples 2 to 4 and Comparative Example 1 Magnesium chloride (Example 2) and aluminum sulfate (Example 3) were used instead of ammonium persulfate used in Example 1.
The initial adhesive strength and softening temperature were measured in the same manner as in Example 1, except that a mixture of ammonium persulfate and aluminum sulfate (Example 4) was used. In addition, the case where these salts are not used is compared with Example 3: 10% by weight aluminum sulfate
720 98 Example 5 Instead of the monomer mixture consisting of 2-ethylhexyl acrylate, styrene and divinylbenzene used in Example 1, 450 g of butyl acrylate,! An aqueous polymer emulsion was produced in the same manner as in Example 1, except that a monomer mixture consisting of 50 g of ethyl acrylate and 0.3 g of triethylene glycol dimethacrylate was used. Concentration: 51°3% by weight, pH: 5.5. The storage stability was good and remained stable even after 3 months.

Next, this emulsion and an aqueous salt solution containing 0.5% by weight of ammonium persulfate and 5% by weight of magnesium chloride were sprayed onto a cotton canvas in the same manner so that the wet coating amount was about 120 mm. 2 at room temperature.
After air-drying for a minute, it was pressed and bonded to an aluminum plate. below,
When the initial adhesive strength and softening temperature were measured using the same method as in Example 1, the initial adhesive strength was 480! ? /25+z and the softening temperature was 115°C.

Comparative Example 2 An aqueous polymer emulsion was produced in the same manner as in Example 1, except that ethyl acrylate was used instead of 2-ethylhexyl acrylate used in Example 1. The resulting aqueous polymer emulsion has a polymer concentration of 50.9%
, PH is 60. Although the storage stability was good and remained stable even after 3 months, when the initial adhesive strength was measured using the same method as in Example 5, the adhesiveness was poor and a peel strength of less than 50 g/25 mm was obtained. . Moreover, the softening temperature was 95°C.

Comparative Example 3 An aqueous polymer emulsion was produced in the same manner as in Example except that 150 g of 2-ethylhexyl acrylate and 350.9 g of styrene were used as monomer components.

The reaction proceeded smoothly, and the resulting aqueous polymer emulsion had a polymer concentration of 50.3% by weight, a pH of 55, and good storage stability.

The initial adhesion strength was measured in the same manner as in Example 1, each separately combined with 10% by weight of aluminum sulfate.

The initial adhesive strength was 50 g/25 mm or less in all cases, and they were easily peeled off.

Comparative Example 4 A polymerization reaction was carried out in the same manner as in Example 1 except that acrylic acid was used instead of itaconic acid used in Example 1. Polymerization stability was poor, and a large amount of resin adhered to stirring blades, etc. .

The aqueous polymer emulsion obtained by removing these deposits has a polymer concentration of 49.5% by weight and a pH of 5.9.
Met.

The aqueous polymer emulsion of 10% by weight aqueous ammonium persulfate solution used in Example J and the
The initial adhesion strength was measured in the same manner as in Example 1 by combining each with a magnesium chloride aqueous solution of % by weight.

Initial adhesion strength is 60 g/25mm1110 each
g/25mm was not good.

This aqueous polymer emulsion also had poor storage stability and showed significant thickening within a few days.

Comparative Example 5 Same as Example 1, except that in Example j, itaconic acid was not dissolved in the aqueous medium in advance, but was added dropwise to the monomer emulsion consisting of 2-ethylhexyl acrylate, styrene, and divinylbenzene. The polymerization reaction was carried out by the method.

Although the emulsion was stably obtained, the polymerization property was poor and the polymer concentration in the emulsion was as low as 46.8% by weight, and the monomer odor was extremely strong.Also, this emulsion had poor storage stability, and the polymer concentration in the emulsion was as low as 46.8% by weight. Since the viscosity increased and hardened, the initial adhesive strength was not measured.

Examples 6-8 Into the four-eye flask used in Example 1, add 0.5 g of sodium dodecylbenzenesulfonate, 15 g of sodium acetate, 5 g of maleic acid, 3 g of ascorbic acid, and 18 g of deionized water.
Added 0g. The temperature was raised to 70°C while stirring under a nitrogen atmosphere to uniformly dissolve the mixture.

Into it 425 g of 2-ethylhexyl acrylate, 5
Monomer emulsion obtained by emulsifying a monomer mixture consisting of 0.9 g of styrene, 20 g of ethyl acrylate, 5 g of methacrylic acid and 1.0 g of divinylbenzene with 3 g of sodium dodecylbenzenesulfonate and 250 g of deionized water. was soaked for 4 hours with 50 g of 5% by weight hydrogen peroxide solution, and then the temperature was raised to 85° C. and aged for 1 hour. The reaction went well, and after cooling, 4 ml of aqueous ammonia was added to partially neutralize it. The resulting aqueous polymer emulsion had a polymer concentration of 51.1% by weight and a pH of 5.3. The storage stability was good and remained stable even after 3 months.

Next, this aqueous polymer emulsion and aqueous solutions of various salts were applied in a wet coating amount of 150% each! i'
/m and 30jj/7d at the same time on cotton canvas, air-dried for 2 minutes at room temperature, and then crimped and bonded to a tin plate. Hereinafter, the initial adhesive strength and softening humidity were measured using the same method as in Example 1.

The results were as shown in the table below: Example 620 weight type magnesium chloride 440
87 Example 720 Shigesato% Zinc Chloride 5]0
95 Initial adhesive strength was measured in the same manner as in Example 1, except that instead of the aqueous polymer emulsion used in Example 1, polyvinyl acetate emulsion, which is currently widely used after removing the emulsion mold, was used. . The initial adhesive strength was less than 50 g/2.5 mm.

Patent applicant: Showa Kobunshi Co., Ltd. Representative Patent Attorney Sei Kikuchi

Claims (1)

[Scope of Claims] 55 to 99.995% by weight of an acrylic acid alkyl ester having an alkyl group having 4 or more carbon atoms (B) 55 to 99.995% by weight of an acrylic acid alkyl ester having an alkyl group containing 4 or more carbon atoms in an aqueous medium containing an unsaturated polycarboxylic acid; 0.005 to 2% by weight of a polyfunctional monomer having a double bond (C) 0 to 44.995% by weight of other unsaturated monomers and unsaturated polycarboxylic acid pair (4), (B) and (an aqueous polymer emulsion obtained by emulsion polymerization at a weight ratio of the total weight of component Q within the range of 0.1:99.9 to 5:95, an alkali metal persulfate, an ammonia persulfate) and at least one salt selected from salts of polyvalent metals capable of reacting with carboxyl groups, and has excellent initial adhesion and heat resistance.