JPH06179857A - Aqueous emulsion adhesive - Google Patents

Abstract

PURPOSE:To obtain an aqueous emulsion adhesive having suitable flow, excellent adhesion to plastic, resistance to thermal creeping and water resistance, and high initial tack and adhesive strength. CONSTITUTION:The adhesive contains a dispersoid comprising a (co)polymer comprising at least one kind of monomer units selected from among (meth) acrylic ester units, diene monomer units and styrene monomer units and having a glass transition temperature of -50 to 100 deg.C and a dispersant comprising a mercapto-terminated polyvinyl alcohol polymer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-based emulsion adhesive, and more specifically, it has excellent heat-resistant creep resistance and water resistance and high adhesive strength, and particularly adheres different or similar materials such as wood, paper, cloth and plastics. The present invention relates to an aqueous emulsion adhesive suitable for use in.

[0002]

2. Description of the Related Art In recent years, since an aqueous medium is used as an adhesive between similar or dissimilar materials such as paper, wood, cloth, aluminum foil and plastic, it is essentially non-polluting and highly solid. Aqueous emulsions, which have characteristics such as excellent workability because they have suitable flow characteristics for the minute, have been favored. Among them, vinyl acetate resin emulsion produced by an emulsion polymerization method using polyvinyl alcohol (PVA) as a protective colloid,
And ethylene-vinyl acetate resin emulsion,
Since it has excellent flow characteristics, adhesive performance (initial adhesiveness, adhesive strength) and heat-resistant creep resistance, it is mainly used as an adhesive for paper and woodworking. However, the above-mentioned vinyl acetate emulsion has the drawbacks of insufficient adhesion and water resistance to vinyl chloride resin and other plastics, and also has a problem that the glass transition temperature range that can be set is narrow. At the time of bonding, it is necessary for the adhesive to form a film at the bonding temperature,
The minimum temperature at which the film can be formed (minimum film forming temperature; MFT) is
Since the glass transition temperature of the resin is the main factor, vinyl acetate emulsions may require plasticizers, film-forming aids, etc. for adhesion at low temperatures. Also,
At high temperatures, the film softens, so heat resistance is generally difficult to develop.

On the other hand, adhesion to plastics, water resistance,
In the sense that a wide range of glass transition temperatures can be set, acrylic acid ester, methacrylic acid ester (hereinafter, acrylic acid ester and methacrylic acid ester may be referred to as “(meth) acrylic acid ester”), diene A homopolymer or copolymer resin emulsion obtained from a styrene-based monomer or a styrene-based monomer is desirable, but in the conventional method, emulsion polymerization using PVA as a protective colloid cannot be stably performed, and a surfactant is exclusively used. It is manufactured by the emulsion polymerization used. Therefore, the resin emulsion obtained from the (meth) acrylic acid ester, the diene-based monomer, and the styrene-based monomer is difficult to obtain the desired viscosity and viscosity so far, the initial adhesive strength is difficult to develop, and the film strength is high. It had many problems such as low heat resistance and low heat creep resistance. For the above reasons, it is desired to develop a homopolymer or copolymer emulsion obtained from a (meth) acrylic acid ester, a diene monomer, and a styrene monomer, which uses PVA as a protective colloid. It is the actual situation. On the other hand, it is known that a polyvinyl alcohol-based polymer having a mercapto group (hereinafter sometimes referred to as PVA-based polymer) is useful as an emulsion dispersion stabilizer (Patent Publication 3).
-24481 gazette).

[0004]

Under the circumstances described above, the present inventors have suitable flow characteristics (viscosity, viscosity) and have excellent adhesiveness to plastics, heat creep resistance and water resistance. The purpose of the present invention is to provide an aqueous emulsion adhesive which is excellent and has high initial adhesive strength and adhesive strength.

[0005]

Means for Solving the Problems As a result of intensive studies to develop an aqueous emulsion adhesive having the above-mentioned preferable properties, the present inventors have identified that the glass transition temperature of the dispersoid is within a predetermined range. It has been found that the object can be achieved by an aqueous emulsion containing the homopolymer or copolymer of 1) and a PVA polymer having a mercapto group at the terminal as a dispersant. The present invention is
It was completed based on such knowledge. That is, the present invention has a glass transition temperature of at least one monomer unit selected from a (meth) acrylic acid ester unit, a diene monomer unit and a styrene monomer unit as a dispersoid. It is intended to provide an aqueous emulsion adhesive characterized by containing a homopolymer or a copolymer at 50 to 100 ° C. and a PVA-based polymer having a mercapto group at a terminal as a dispersant.

In the aqueous emulsion adhesive of the present invention, as the dispersoid, a (meth) acrylic acid ester unit,
A homopolymer composed of at least one monomer unit selected from a diene monomer unit and a styrene monomer unit is used. The homopolymer or copolymer has a glass transition temperature of -50 to 100 ° C, preferably -40 to 40 ° C.
It must be in the range of 50 ° C. If the glass transition temperature is higher than 100 ° C., a high temperature is required for forming a film during bonding, which is not practical. Also, -50 ° C
When it is lower than the above range, the film becomes too flexible and the adhesive strength is not sufficiently exhibited.

Examples of the (meth) acrylic acid ester include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and dodecyl (meth) acrylate. , 2-hydroxyethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, and their quaternary compounds. Examples of the styrene-based monomer include styrene, α-methylstyrene, p-methylstyrenesulfonic acid and its sodium and potassium salts, and examples of the diene-based monomer include butadiene, isoprene and chloroprene. Is mentioned.

These monomers may be used alone or in combination of two or more. In the water-based emulsion adhesive of the present invention, in addition to the above (meth) acrylic acid ester, diene-based monomer, and styrene-based monomer, a copolymerizable monomer, if desired, in a range that does not impair performance The body can be copolymerized. Examples of the copolymerizable monomer include olefins such as ethylene, propylene and isobutylene, halogenated olefins such as vinyl chloride, vinyl fluoride, vinylidene chloride and vinylidene fluoride, vinyl formate and vinyl acetate,
Vinyl esters such as vinyl propionate and vinyl versatate, acrylic acid, methacrylic acid, itaconic acid,
Α, β-ethylenically unsaturated carboxylic acids such as crotonic acid, fumaric acid, maleic acid, citraconic acid and salts thereof,
(Meth) acrylamide-based monomers such as (meth) acrylamide, N-methylol (meth) acrylamide, N, N'-dimethylacrylamide, acrylamido-2-methylpropanesulfonic acid and its sodium salt,
Other examples include monomers such as vinyl pyridine and N-vinyl pyrrolidone.

The aqueous emulsion adhesive of the present invention needs to contain a PVA-based polymer having a mercapto group at a terminal as a dispersant. This aqueous emulsion adhesive is a monomer containing at least one selected from the above (meth) acrylic acid ester, diene monomer and styrene monomer in the presence of the PVA polymer. Those comprising an aqueous emulsion obtained by emulsion homopolymerization or copolymerization of the body are preferable.

The above-mentioned PVA-based polymer having a mercapto group has a sufficient effect even if it is a polymer having a mercapto group in the main chain of the PVA molecule, but in this case, by forming a disulfide bond by oxidation of PVA itself. , It may become insoluble. Therefore, in the present invention, a PVA-based polymer having a mercapto group only at one end of the molecule is easy to handle without fear of insolubilization and is preferably used.
P having a mercapto group only at one end of such a molecule
The VA polymer is obtained by saponifying a polyvinyl ester polymer obtained by polymerizing a vinyl monomer mainly containing vinyl esters in the presence of thiol acid by a conventional method. Will be described in detail. First, the thiol acid used here includes an organic thiol acid having a -COSH group. Examples thereof include thiol acetic acid, thiol propionic acid, thiol butyric acid, and thiol valeric acid. Among them, thiol acetic acid is most preferable because of its degradability. Further, vinyl esters can be used as long as they are radically polymerizable vinyl esters. For example, vinyl formate, vinyl acetate, vinyl propionate, vinyl versatate, vinyl laurate, vinyl stearate and the like can be mentioned. Among them, vinyl acetate is the most polymerizable and preferred. It is also possible to copolymerize these vinyl esters with a copolymerizable monomer.

As the copolymerizable monomer, for example, ethylene, propylene, isobutylene, acrylic acid, methacrylic acid or a salt thereof or an alkyl ester thereof, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, trimethyl- (3-acrylamide-) is used. 3-dimethylpropyl) -ammonium chloride, ethyl vinyl ether, butyl vinyl ether, N-vinyl pyrrolidone, vinyl chloride, vinyl bromide,
Vinyl fluoride, vinylidene chloride, vinylidene fluoride, tetrafluoroethylene, sodium vinyl sulfonate,
Examples include sodium allyl sulfonate and the like.

Polymerization of vinyl monomers mainly composed of vinyl esters such as vinyl acetate in the presence of thiol acid is carried out in the presence of a radical polymerization initiator in the bulk polymerization method, solution polymerization method, pearl polymerization method, emulsion polymerization method. Although any method such as a legal method can be used, the solution polymerization method using methanol as a solvent is industrially most advantageous. The amount and method of addition of the thiol acid present in the polymerization to the polymerization system are not particularly limited and should be appropriately determined according to the physical properties of the intended polyvinyl ester polymer. As a polymerization method, a known method such as a batch method, a semi-continuous method, or a continuous method can be adopted. Examples of the radical polymerization initiator include 2,
Known radical polymerization initiators such as 2'-azobisisobutyronitrile, benzoyl peroxide, and carbonate carbonate can be used, but azo initiators such as 2,2'-azobisisobutyronitrile are easy to handle. preferable. Radiation, electron beam, etc. can also be used. Although it is desirable to adopt an appropriate temperature as the polymerization temperature depending on the kind of the initiator used, it is usually selected from the range of 30 to 90 ° C. After polymerization for a predetermined period of time, unpolymerized vinyl esters are removed by a usual method to obtain a polyvinyl ester polymer having a thiol ester group at the terminal.

The polyvinyl ester polymer thus obtained is saponified by a conventional method, but it is usually advantageous to carry out the polymer as an alcohol solution, especially a methanol solution. As the alcohol, not only an anhydride but also a small amount of water-containing alcohol may be used according to the purpose, and an organic solvent such as methyl acetate or ethyl acetate may be optionally contained. The saponification temperature is usually selected from the range of 10 to 70 ° C. As the saponification catalyst, for example, an alkaline catalyst such as sodium hydroxide, potassium hydroxide, sodium methylate, potassium methylate is preferable, and the amount of the catalyst used is appropriately determined depending on the degree of saponification and the amount of water. It is desirable to use a molar ratio of 0.001 or more, preferably 0.002 or more based on the unit. On the other hand, if the amount of alkali is too large, it becomes difficult to remove the residual alkali from the polymer, and the polymer is colored, which is not preferable, and the molar ratio is preferably 0.2 or less. If the polyvinyl ester-based polymer contains a component that reacts with an alkali catalyst such as a carboxyl group or its ester group and consumes alkali, use the amount of the alkali catalyst added to the consumption amount. Is desirable.

By this saponification reaction, the terminal thiol ester of the polyvinyl ester polymer having a thiol ester group at the terminal and the vinyl ester bond in the main chain are saponified, and the polymer terminal becomes a mercapto group and the main chain becomes a vinyl alcohol. However, the degree of saponification of the vinyl ester unit in the main chain can be changed according to the purpose of use. The polymer precipitated after the saponification reaction can be usually obtained as a white powder by purifying by a known method such as washing with methanol and removing impurities such as residual alkali and an alkali metal salt of acetic acid and drying. The method for producing the PVA-based polymer having a mercapto group at the terminal used in the present invention has been described above. The degree of polymerization of this PVA-based polymer is 3500.
The following are preferred. The degree of saponification differs depending on the types of other modifying groups and cannot be unambiguously stated, but from the viewpoint of water solubility, it is preferably 70 mol% or more.

The amount of the PVA-based polymer thus obtained is 1 to 20% by weight based on the amount of the above-mentioned (meth) acrylic acid ester, styrene-based monomer, diene-based monomer and the like. , Particularly preferably 2 to 10% by weight. The P
When the amount of the VA polymer used is less than 1% by weight with respect to the amount of the monomer, emulsion polymerization stability is deteriorated and, in addition, the flowability characteristic of the PVA-protected colloidal aqueous emulsion,
The initial adhesiveness and the like are not sufficiently expressed, which is not preferable. on the other hand,
When the amount of the PVA-based polymer used exceeds 20% by weight,
Adhesion to plastics may be reduced, which may be a problem.

Emulsion homopolymerization or copolymerization of one or more monomers selected from (meth) acrylic acid esters, styrene-based monomers and diene-based monomers using the PVA-based polymer as a dispersant. In carrying out the method, the above-mentioned unsaturated monomers may be added temporarily or continuously in the presence of water, a dispersant and a polymerization initiator, and any ordinary emulsion polymerization method such as heating and stirring may be carried out. Alternatively, a method in which an unsaturated monomer is mixed with an aqueous PVA-based polymer solution and emulsified in advance and continuously added may be carried out. As the polymerization initiator,
A redox system using a mercapto group at the PVA end and a water-soluble oxidizing agent such as potassium bromate, potassium persulfate, ammonium persulfate, and hydrogen peroxide is also possible. Among these, potassium bromate is a radical alone under ordinary polymerization conditions. Is particularly preferable because it decomposes only by a redox reaction with a mercapto group at the PVA end and generates a radical, thereby effectively producing PVA and a block copolymer, and as a result, the stabilizing effect is increased. It is an initiator. It is also possible to use potassium bromate as a polymerization initiator and then use an oxidizing agent such that another oxidizing agent is additionally added.

PV having a mercapto group in the present invention
When emulsion homopolymerization or copolymerization is performed using a dispersant composed of the A-based polymer, it is important and desirable that the polymerization system is acidic. This is because the mercapto group, which exhibits extremely active reactivity in radical polymerization, is ionically added to the double bond of the monomer and disappears at a high rate under basic conditions, which significantly reduces the polymerization efficiency. However, depending on the type of unsaturated monomer, it is preferable to carry out all operations at pH 6 or less, preferably pH 4 or less. In the present invention, the dispersant composed of a PVA-based polymer having a mercapto group is preferably used alone as described above, but if necessary, a conventionally known anionic, nonionic or cationic surface active agent is used. The agent and the water-soluble polymer compound may be appropriately used in combination as long as the performance is not impaired.

The aqueous emulsion thus obtained is used as it is or as a filler such as conventionally known clay, kaolin, talc, calcium carbonate and wood flour, a bulking agent such as wheat flour, and a reaction accelerating agent such as boric acid and aluminum sulfate. Used for various adhesive applications by adding various additives such as agents, preservatives and rust preventives. In the aqueous emulsion adhesive of the present invention, if necessary, starch, modified starch, oxidized starch, sodium alginate, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, maleic anhydride / isobutene copolymer,
Maleic anhydride / styrene copolymer, maleic anhydride /
In the presence of water-soluble polymer compounds such as methyl vinyl ether copolymer, thermosetting resins such as urea / formalin resin, urea / melamine / formalin resin, phenol / formalin resin, polyvinyl acetate emulsion, and surfactant. Other aqueous emulsions such as produced (meth) acrylic acid esters, diene-based, styrene-based emulsions, polyvinyl chloride emulsions, polyvinylidene chloride emulsions, polyurethane emulsions may also be used.

[0019]

The present invention will be described in more detail by way of examples, which should not be construed as limiting the invention thereto. The physical properties and adhesive performance of the emulsion were determined as follows.

(1) Physical Properties Tg: The emulsion was dried in a vacuum dryer at 60 ° C. and measured by a DSC (differential scanning calorimeter) at a temperature rising rate of 10 ° C./min. Solid content concentration: Determined from the weight after drying at 105 ° C. for 16 hours. Viscosity: Measured using a BM type viscometer at 30 ° C. and 60 rpm. Structural viscosity index: The viscosities (BM type viscometer) at 30 ° C., 60 rpm and 6 rpm were measured and determined by the following formula. Structural viscosity index = log (viscosity at 6 rpm) / log (viscosity at 60 rpm) Further, the adhesive performance of the obtained emulsion was evaluated by performing a wood / wood adhesion test and a vinyl chloride / plywood adhesion test. The results are shown in Table 1.

(2) Wood / wood adhesive strength test Adhering material: birch wood (measles) 2ply, specific gravity 0.62-0.6
8 Adhesive area: 25 × 25 (mm ² ) Applying amount: 125 g / m ² (wet) Normal adhesive force 6.25 kgf / cm ² After pressing for 16 hours, 20
It was pressed at 65 ° C. and 65% RH for 7 days, and the block shear adhesive strength was measured. Water-resistant adhesive strength 6.25 kgf / cm ² After pressing for 16 hours, 20
It was pressed at 65 ° C. and 65% RH for 7 days, immersed in water at 20 ° C. for 24 hours, and then the block shear adhesive strength was measured. The initial shear strength was 6.25 kgf / cm ² and the block shear strength was measured after pressing for 30 minutes.

(3) Polyvinyl chloride / plywood adhesion test Adhering material: soft polyvinyl chloride sheet (thickness 500 μm) plywood (thickness 5.5 mm, 3 ply, type 1 lauan plywood) Coating amount: 120 g / m ² pressure Tightening: 20 ° C, 65% RH or less, 0.5 kgf / cm ²
× 16 hours Curing: 7 days (20 ° C., 65% RH) Adhesive force: 25 mm width, 180 ° peel strength was measured. Heat-resistant creep: 60 ℃, load 500g / 25mm width 1
The creep length after time was measured.

Example 1 PVA having a mercapto group at the end in a 1-liter glass container equipped with a reflux condenser, a dropping funnel, a thermometer, and a nitrogen blowing port (PVA-1; polymerization degree 600, saponification degree 88.5 mol). %) 15 g by heating and dissolving in 280 g of ion-exchanged water,
The pH was adjusted to 3.5 with dilute sulfuric acid. Then, while stirring at 140 rpm, 50 g of methyl methacrylate and 50 g of butyl acrylate were charged, the temperature was raised to 60 ° C., and then 5 wt.
% 10% ammonium persulfate aqueous solution was added to initiate polymerization. 15 minutes after starting the polymerization, 100 g of methyl methacrylate and 100 g of butyl acrylate were continuously added over 2 hours. After 5 hours, the polymerization rate was 99.9% and the mixture was cooled. The produced emulsion is added with ammonia water.
After adjusting to H = 6.8, the physical properties and adhesive performance of the emulsion were measured. The results are shown in Table 1.

Example 2 12 g of PVA having a mercapto group at the end (PVA-2; degree of polymerization 400, degree of saponification 98.5 mol%) was dissolved by heating in 290 g of ion-exchanged water, which was blown with nitrogen and thermometer. It was placed in a pressure-resistant autoclave equipped with. P with diluted sulfuric acid
After setting H = 4.0, 165 g of styrene and then 135 g of butadiene were charged from a pressure resistance meter, the temperature was raised to 70 ° C., and 10 g of a 2 wt% potassium persulfate aqueous solution was injected under pressure to initiate polymerization. The internal pressure decreased from 4.8 kg / cm ² G as the polymerization progressed, and after 15 hours, 0.4 kg / cm ² G
Then, the polymerization rate was calculated and found to be 99.2%. The pH of the obtained emulsion was adjusted to 6.0 with aqueous ammonia, and the physical properties and adhesive performance of the emulsion were measured. The results are shown in Table 1.

Example 3 A 1-liter glass container equipped with a reflux condenser, a dropping funnel, a thermometer, and a nitrogen blowing port had PVA having a mercapto group at its end (PVA-3; polymerization degree 1000, saponification degree 92.
(0 mol%) 27 g was dissolved by heating in 280 g of water, and the pH was adjusted to 3.5 with dilute sulfuric acid. Then, with stirring at 140 rpm, 180 g of styrene and 120 butyl acrylate.
After charging g and raising the temperature to 65 ° C., 10 g of a 2 wt% potassium bromate aqueous solution was added to initiate polymerization. After 2 hours, 10 g of a 2 wt% potassium persulfate aqueous solution was added, and the temperature was raised to 70 ° C. After 5 hours, the polymerization rate was 99.9% and the mixture was cooled. PH of the resulting emulsion with ammonia water
= 6.5 and the physical properties and adhesive performance of the emulsion were measured. The results are shown in Table 1.

Comparative Example 1 PVA-205 as a dispersant (unmodified PVA; degree of polymerization: 5)
00, saponification degree 88.0 mol%, manufactured by Kuraray Co., Ltd. 15
The same procedure as in Example 1 was carried out except that g was used, but a large amount of coagulated product was generated during the polymerization, and an emulsion could not be obtained.

Comparative Example 2 Sandet BL (anionic surfactant; as a dispersant)
An emulsion was obtained in the same manner as in Example 1 except that 15 g of Sanyo Kasei Co., Ltd. was used. The physical properties and adhesive performance of the obtained emulsion were measured. The results are shown in Table 1.

Comparative Example 3 Example 1 except that 15 g of nonipol 200 (nonionic surfactant; Sanyo Kasei Co., Ltd.) was used as the dispersant.
An emulsion was obtained in the same manner as in. The physical properties and adhesive performance of the obtained emulsion were measured. The results are shown in Table 1.

Comparative Example 4 PVA-217 (unmodified PV) was placed in a 1 liter glass container equipped with a reflux condenser, a dropping funnel, a thermometer, and a nitrogen blowing port.
A, degree of polymerization 1700, degree of saponification 88 mol%) was dissolved in 280 g of deionized water by heating. Then 140 rp
While stirring at m, 300 g of vinyl acetate was charged, and 60
After the temperature was raised to ° C, polymerization was initiated using a hydrogen peroxide-Rongalite redox initiator. 2 hours and 30 minutes later,
The polymerization rate was 99.6% and the mixture was cooled. After adjusting the pH of the produced emulsion to 6.5 with aqueous ammonia, the physical properties and adhesive performance of the emulsion were measured. The results are shown in Table 1.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

PVA-1: polymerization degree 600, saponification degree 88.5 mol% PVA-2: polymerization degree 400, saponification degree 98.5 mol% PVA-3: polymerization degree 1000, saponification degree 92.0 mol%

[0034]

As is clear from the above results, the water-based emulsion adhesive of the present invention has an appropriate fluidity, is excellent in adhesiveness to plastics, heat creep resistance and water resistance, and has a high initial content. It is extremely excellent in that it has both adhesive strength and adhesive strength, and is particularly suitable for bonding different or similar materials such as wood, paper, cloth, and plastics.

Claims (1)

[Claims] 1. An acrylic ester unit as the dispersoid,
Glass transition temperature of -50 to 10 consisting of at least one monomer unit selected from methacrylic acid ester unit, diene monomer unit and styrene monomer unit
An aqueous emulsion adhesive containing a homopolymer or copolymer at 0 ° C. and a polyvinyl alcohol-based polymer having a mercapto group at a terminal as a dispersant.