JP2002121517A - Bonded structure and bonding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bonded structure using a novel adhesive which strongly bonds to an extent equal to or more than the conventional polychloroprene (CR) solvent based adhesive without any problems in the aspects of safety and hygiene, and atmosphere. SOLUTION: The bonded structure can be obtained by bonding an adherend to a substrate with the use of an adhesive composition comprising a polychloroprene latex obtained by polymerizing 100 pts. mass chloroprene and more than 0 pt. mass to less than 2 pts. mass ethylenically unsaturated carboxylic acid in the presence of 0.5-4 pts. mass polyvinyl alcohol, and then adding a pH adjustor and a radical scavenger to the resulting product and having a gel content of the chloroprene polymer of 10-60 mass% and a pH of 6-9, a tackifying resin, and a metal oxide as the major components in an amount added of the tackifying agent of 10-100 pts. mass (in terms of the solid content) based on 100 pts. mass solid content of the polychloroprene latex.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for bonding a decorative plate to a base material for a top plate of office equipment such as desks, tables, kotatsu, counters, etc., housing equipment and furniture. The present invention relates to an adhesive structure using an adhesive and a method for bonding the same.

[0002]

2. Description of the Related Art Conventionally, when a decorative plate is bonded to a top plate base, a polychloroprene (CR) solvent-based adhesive is applied to the decorative plate and the top plate base. However, since organic solvents such as toluene, ethyl acetate, and methyl ethyl ketone are used for CR solvent-based adhesives, the organic solvents volatilize in the workplace during the application of the adhesive, resulting in safety and hygiene for workers and environmental protection. Undesirably, reduction of the organic solvent has been desired.

[0003]

SUMMARY OF THE INVENTION The present inventor has proposed a conventional C
Adhesive structure using a novel adhesive that does not have safety and hygiene and environmental problems as in the case of using an R-solvent-based adhesive, and is as strong as or more than conventional CR-solvent-based adhesives It is intended to provide a body and a bonding method.

[0004]

Means for Solving the Problems As a result of repeated studies to achieve the above object, the present inventors have found that the presence of polyvinyl alcohol and the polymerization of chloroprene with a specific amount of ethylenically unsaturated carboxylic acid can be achieved. By using the obtained polychloroprene latex, a tackifying resin and an adhesive mainly composed of a metal oxide, the present inventors have invented that a decorative plate can be firmly joined to a top plate base material.

That is, the present invention comprises a polychloroprene latex, a tackifying resin, and a metal oxide as main components, and the polychloroprene latex contains 100 parts by mass of chloroprene and more than 0 parts by mass of ethylenically unsaturated carboxylic acid in an amount of 2 parts by mass. Less than 0.5 parts by weight of polyvinyl alcohol
After polymerization in the presence of 10 parts by mass, the chloroprene polymer obtained by adding a pH adjuster and a radical scavenger has a gel content of 10 to 60% by mass, and a PH of 6 to 9,
Further, the addition amount of the tackifier resin (in terms of solid content) is based on 100 parts by mass of the solid content of polychloroprene latex.
An adhesive structure using an adhesive composition having an excellent balance of adhesive water resistance and heat resistance of 10 to 100 parts by mass.
Further, the present invention is an adhesive structure using the above-mentioned adhesive composition in which the metal oxide is zinc oxide, and applying these adhesive compositions to a decorative plate and / or a top plate base, Is a method for bonding a top plate.

Hereinafter, the present invention will be described in detail. The top plate substrate of the present invention is not particularly limited, and is usually used for office equipment such as a metal flat plate such as iron, stainless steel, aluminum and various alloys and a non-metal flat plate such as wood, housing equipment and furniture. Can be mentioned.

Specific examples of the ethylenically unsaturated carboxylic acid in the present invention include acrylic acid, methacrylic acid, crotonic acid, fumaric acid, maleic acid, citraconic acid, glutaconic acid and the like. More than one kind can be used in combination. In the present invention, it is preferable to use acrylic acid and methacrylic acid, and it is particularly preferable to use methacrylic acid.

In the present invention, the addition amount of the ethylenically unsaturated carboxylic acid is 0 to 100 parts by mass of chloroprene.
More than 2 parts by mass. More preferably, 0.
7 to 1.5 parts by mass. When the amount of the ethylenically unsaturated carboxylic acid is 0 parts by mass, the latex is inferior in stability and production is difficult, and the adhesive strength and heat resistance are inferior. When the addition amount of the ethylenically unsaturated carboxylic acid is 2 parts by mass or more, the decrease in water resistance is large.

Further, in the chloroprene polymer used in the present invention, other than chloroprene and ethylenically unsaturated carboxylic acid, other monomers copolymerizable therewith may be copolymerized in a small amount. Included in the invention. Examples of the monomer copolymerizable with chloroprene in the present invention include 2,3-dichloro-1,3-butadiene, 1-chloro-1,3-butadiene, butadiene, isoprene, styrene, acrylonitrile, and esters of acrylic acid. Kind,
Examples include esters of methacrylic acid, and two or more esters may be used as necessary.

The polyvinyl alcohol used in the present invention is not particularly limited, but preferably has a saponification degree of 60 to 98 mol%. More preferably, the degree of saponification is 75 to 95 mol%, and still more preferably, the degree of saponification is 7 to 95 mol%.
5 to 90 mol%. Further, those having a polymerization degree of polyvinyl alcohol in the range of 200 to 3000 are preferable. More preferably, the degree of polymerization is from 200 to 700. When the polyvinyl alcohol is in this range, the polymerization operation can be performed stably, and the stability of the obtained latex is excellent, and a stable latex at a high concentration can be obtained.

The amount of polyvinyl alcohol added in the present invention is 0.1 to 100 parts by mass of chloroprene.
Addition of 5 to 4 parts by mass is preferred. More preferably 2-4
Parts by mass, and more preferably 3 to 3.5 parts by mass. If the amount of the polyvinyl alcohol is less than 0.5 parts by mass, the emulsifying power is not sufficient, and the generation of aggregates tends to occur frequently during the polymerization reaction. If the amount exceeds 4 parts by mass, the viscosity may increase during the polymerization reaction, hindering the stirring, causing abnormal heat generation and making production difficult.

Further, the polychloroprene latex of the present invention has a gel content of 10-60
% By mass, preferably 15% by mass.
６０60% by mass. Gel content is 10% by mass
If it is less than the above, the adhesive strength and the heat resistance decrease. On the other hand, when the gel content exceeds 60% by mass, the initial adhesiveness is lowered and the water resistance is lowered.

The gel content of the polychloroprene latex can be controlled by controlling the use of the chain transfer agent, the amount used, the polymerization temperature, and the polymerization rate.

The chain transfer agent is not particularly limited as long as it is generally used in the production of polychloroprene. For example, long-chain alkyl mercaptans such as n-dodecyl mercaptan, n-octadecyl mercaptan and tert-dodecyl mercaptan , Dialkylxanthogen disulfides such as diisopropylxanthogen disulfide and diethylxanthogen disulfide, and known chain transfer agents such as iodoform.

Next, the polymerization temperature is preferably in the range of 0 to 55 ° C. from the viewpoint of polymerization control. In order to carry out the polymerization reaction more smoothly and safely, the polymerization temperature should be 30 to 50 ° C.
It is particularly preferred that

The final polymerization rate is preferably at least 80% by mass, more preferably at least 90% by mass.

In the present invention, the solid concentration of the polychloroprene latex can be adjusted to a necessary concentration by concentration or dilution with water, but is preferably in the range of 40 to 65% by mass, more preferably 43 to 60% by mass. It is.
By setting the solid content to be higher, a latex having a high drying rate and excellent initial adhesiveness can be obtained. The solid content can be adjusted by adjusting the ratio with the monomer at the time of polymerization, but can be adjusted by concentration after polymerization.

The chloroprene polymer in the present invention is acidic immediately after polymerization and is in an unstable state, so that the pH is 6 to
It is necessary to adjust to 9. Preferably PH is 6.
5 to 8.5. When the pH is less than 6, coagulation and separation and deterioration are liable to occur during long-term storage. An alkaline solution having a pH of more than 9 is not preferable in handling.

In the present invention, the pH adjusting agent includes sodium carbonate, potassium carbonate, trisodium phosphate, disodium hydrogen phosphate, tripotassium phosphate, and hydrogen phosphate.
Weak acid salts such as potassium, tripotassium citrate, dipotassium hydrogen citrate, trisodium citrate, disodium hydrogen citrate, sodium acetate, potassium acetate, and sodium tetraborate are added to 0.1 parts by mass of chloroprene per 100 parts by mass.
It is preferably contained in an amount of at least 1 part by mass, more preferably at least 0.3 part by mass. Weak acid salts are necessary to increase the buffer capacity of polychloroprene latex, and 0.1
If the amount is less than parts by mass, the decrease in pH during storage cannot be suppressed,
The storage stability of the adhesive composition also deteriorates. If the pH of the polychloroprene latex is less than 6 using only the weak acid salts, a basic substance such as sodium hydroxide, potassium hydroxide or diethanolamine can be optionally used in combination.

The method of adding the pH adjuster in the present invention is not particularly limited, and the pH adjuster powder can be directly added or diluted to an arbitrary ratio with water.

As the radical scavenger of the present invention, thiodiphenylamine, diethylhydroxylamine, hydroquinone, pt-butylcatechol, 1,3,5-
Polymerization inhibitors such as trihydroxybenzene and hydroquinone methyl ether, 2,6-di-t-butyl-4-methylphenol, 2,2-methylenebis (6-t-4-methylphenol), 4,4-butylenebis ( 6-t-butyl-3-methylphenol), ethylenebis (oxyethylene) bis [3- (5-t-butyl-4-hydroxy-m-tolyl) propionate], octadecyl-3
Antioxidants such as-(3,5-di-t-butyl-4-hydroxyphenyl) propionate and pentaerythritol tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] are exemplified. be able to. Examples of the radical scavenger of the present invention include polymerization inhibitors such as thiodiphenylamine, diethylhydroxylamine, hydroquinone, pt-butylcatechol, 1,3,5-trihydroxybenzene, and hydroquinone methyl ether; t-butyl-4-methylphenol, 2,2-methylenebis (6-t-4-methylphenol), 4,4-butylenebis (6-t-butyl-3-methylphenol), ethylenebis (oxyethylene) bis [3- (5-tert-butyl-4-hydroxy-
m-tolyl) propionate], octadecyl-3-
(3,5-di-t-butyl-4-hydroxyphenyl)
Propionate, pentaerythritol tetrakis [3
-(3,5-di-t-butyl-4-hydroxyphenyl) propionate] and the like.

As the radical scavenger of the present invention, it is preferable to use 0 to 0.5 parts by mass of the polymerization inhibitor and 0.1 to 1.5 parts by mass of the antioxidant. When the amount of the antioxidant is less than 0.1 part by mass, the increase in the amount of gel during storage of the polychloroprene latex composition cannot be suppressed, so that the adhesive composition has poor water resistance.

The method of adding the radical scavenger of the present invention is not particularly limited, but a method in which a radical scavenger dissolved in a chloroprene monomer is added to a chloroprene polymer to degas and remove the monomer, or the radical scavenger is treated with a surfactant It is preferable to add the agent emulsified by adding an agent or the like to the chloroprene polymer in consideration of the dispersion state of the radical scavenger in the polychloroprene latex composition.

The catalyst used in the polymerization of polychloroprene of the present invention includes inorganic peroxides such as potassium persulfate, ketone peroxides, peroxyketals, hydroperoxides, dialkyl peroxides, diacyl peroxides. And the like. The use of potassium sulphate as a catalyst is preferred from the viewpoint of performing stable polymerization. Further, potassium persulfate is preferably used as an aqueous solution of 0.1 to 5% by mass.

To enhance the activity of the catalyst used in the polymerization of the polychloroprene latex of the present invention, sodium sulfite, ferrous sulfate, sodium anthraquinone beta sulfonate, formamidinesulfonic acid, L-ascorbic acid, etc. are added. be able to.

Examples of the tackifier resin of the present invention include a rosin ester resin, a terpene phenol resin, a coumarone-indene resin, an aliphatic hydrocarbon resin and an aromatic resin. As the tackifier resin, an emulsion of a terpene phenol resin or a rosin acid ester resin is preferable from the viewpoint of developing the adhesive strength and water resistance of the adhesive composition.

The amount of the tackifier resin (solid content)
The polychloroprene latex is 10 to 100 parts by mass, preferably 20 to 70 parts by mass, based on 100 parts by mass of the solid content. If the amount is less than 10 parts by mass, the adhesive strength and the water resistance will be low, and if it exceeds 100 parts by mass, the heat resistance will be poor.

Examples of the metal oxide in the present invention include zinc oxide, titanium oxide and iron oxide. Zinc oxide and titanium oxide are preferred for improving the water resistance of the adhesive composition, and the use of zinc oxide is particularly preferred.

The amount of the metal oxide added is 0.2 to 100 parts by mass of the solid content of polychloroprene latex.
8.0 parts by mass is preferable, and particularly 0.5 to 6.0 parts by mass is preferable. If the amount is less than 0.2 parts by mass, the water resistance and heat resistance of the adhesive composition may be insufficient, and if the amount exceeds 8.0 parts by mass, the adhesive strength tends to deteriorate.

The adhesive composition of the present invention comprises a curing accelerator such as isocyanate, an inorganic filler such as calcium carbonate, silica, talc or clay, a plasticizer or softener such as dibutyl phthalate or process oil, sodium polyacrylate,
Thickeners such as water-soluble polyurethanes and methylcellulose, polyoxyalkylene alkyl ethers, surfactants such as 1: 2 mol type aliphatic alkanolamide, 1: 1 mol type diethanolamide, polyoxyethylene stearate, and various antioxidants An ultraviolet absorber, an antioxidant and the like can be optionally added as needed.

The adhesive of the present invention is prepared by mixing a polychloroprene latex, a tackifying resin, a metal oxide and the like, but the mixing apparatus is not particularly limited, and a three-one motor, a homogenizer, a media mill, a colloid mill And other known devices.

For the purpose of improving the adhesive strength, the adhesive surface of the top plate substrate may be sanded and subjected to sandblasting, solvent treatment, or the like.

The adhesive composition of the present invention is applied by brushing,
Methods such as iron coating, spray coating, and roll coater coating are possible. The application of the adhesive composition is preferably applied to the bonding surface of each of the decorative board and the top plate base from the viewpoint of improving the adhesive strength.

The method of bonding the decorative plate and the top plate substrate of the present invention is not particularly limited. For example, there is a method in which the adherend is dried in a drier or at room temperature after application of the adhesive, and pressure-bonded with a hand roll, a press device, or the like, or a post home bonding process (bending bonding process).

[0035]

EXAMPLES The present invention will be described below with reference to examples, but these examples do not limit the present invention. In addition,
In the following examples, parts and% are based on mass unless otherwise specified.

[Example 1] [Production of polychloroprene latex] Using a reactor having an internal volume of 30 liters, 94 parts by mass of water and polyvinyl alcohol (Unitika UMR-20H,
3.5 parts by mass of a saponification degree of 79 mol% and a polymerization degree of 380) were added and dissolved by heating (60 ° C.). After cooling this aqueous solution to near room temperature, 99 parts by mass of chloroprene monomer
1.0 part by weight of methacrylic acid and 0.3 part by weight of octyl mercaptan were added. While maintaining this at 45 ° C., polymerization was carried out using sodium sulfite and potassium persulfate as initiators to obtain a polychloroprene latex. The final conversion was 98%.

Next, a 20% aqueous solution of diethanolamine and a 10% aqueous solution of disodium hydrogen phosphate are added to the polychloroprene latex to adjust the pH to neutral, and then the fatty acid alkanolamide (manufactured by Diamond Shimalloc Chemical Co., Ltd.) is used. Was added in an amount of 3 parts and a radical scavenger (Cellosol H633, manufactured by Chukyo Yushi Co., Ltd.) in an amount of 0.5 part by mass.

Next, the following measurement was performed on the polychloroprene latex. [Measurement of Gel Content] A polychloroprene latex sample was freeze-dried and precisely weighed as A. Dissolve in toluene (prepared to 0.6%), use a centrifuge, and
The gel was separated using a 0 mesh wire mesh. The gel component was air-dried and then dried for 1 hour in a 110 ° C. atmosphere. The gel content was calculated according to the following equation. Gel content = B / A × 100 (%) The results are shown in Table 1. [PH Measurement] After adjusting the latex sample to 20 ° C. in a constant temperature water bath, the pH was measured with a PH meter. [Storage stability test] After storing the latex sample at 40 ° C for 2 months in an environmental tester set at 40 ° C, the PH and gel content were measured to determine whether there was any change.

[Manufacture of Adhesive] 100 parts by mass of polychloroprene latex, 30 parts by mass of tackifying resin 1 (Tamanol E-100 manufactured by Arakawa Chemical Industry Co., Ltd.) and 3 parts of zinc oxide (AZ-SW manufactured by Osaki Industry Co., Ltd.) The mixture was stirred with a three-one motor at a mixing ratio of parts by mass to prepare an adhesive.

[Shear Peel Adhesive Strength] An adhesive was applied to a melamine resin decorative board (size 25 × 100 × 1 mm) by 100
g (solid content) / m ² , iron plate (JIS G3141-9)
0; 100 for SPCC, size 25 x 100 x 1 mm)
g (solid content) / m ²
Dried for minutes. Both adherends were pressed by a press. Crimp 2
After 4 hours, the tensile speed is 2.5 mm / m using a tensile tester.
The shear peel adhesion strength was measured under the conditions of in.

[Water resistance]
After 4 hours, immersed in water for 2 days and in a tensile test,
The shear peel strength was measured under the same conditions as above.

[80 ° C. creep test] After pressing for 24 hours, the iron plate side was fixed to a fixing jig in an atmosphere of 80 ° C., and a 1 kg weight was hung on the decorative plate side and peeled after 24 hours. Was observed. Samples that did not drop for more than one hour were marked with a circle in the table for good heat resistance. 1
Samples that were peeled and dropped within a period of time were marked X in the table in the sense that heat resistance was not good.

Example 2 A 10% aqueous sodium carbonate solution was added to the polychloroprene latex of Example 1 to adjust the pH to neutral.

Example 3 Polymerization was carried out in the same manner as in Example 1 except that 98.5 parts by mass of chloroprene and 1.5 parts by mass of methacrylic acid were used. The gel content and the adhesive properties were measured in the same manner as in Example 1, and the results are shown in Table 1.

Example 4 In Example 1, 0.38 parts by mass of octyl mercaptan and polyvinyl alcohol were added to B-05 manufactured by Denki Kagaku Kogyo Co., Ltd. (a saponification degree of 88 mol%,
The polymerization was carried out in the same manner as in Example 1 except that the polymerization degree was 550). The gel content and the adhesive properties were measured in the same manner as in Example 1, and the results are shown in Table 1.

Example 5 100 parts by mass of the polychloroprene latex of Example 1, 30 parts by mass of tackifying resin 1 (Tamanol E-100 manufactured by Arakawa Chemical Industry Co., Ltd.) and zinc oxide (AZ-SW manufactured by Osaki Industry Co., Ltd.) ) Was stirred with a three-one motor at a mixing ratio of 5 parts by mass to prepare an adhesive.

Example 6 A polychloroprene latex was obtained in the same manner as in Example 1 except that 0.02 parts by mass of diethylhydroxylamine and 0.3 part by mass of Cellosol H633 were used as the radical scavenger. 100 parts by mass of the above polychloroprene latex, 40 parts by mass of tackifying resin 1, 10 parts by mass of tackifying resin 2, and 3.0 parts by mass of zinc oxide were stirred with a three-one motor to prepare an adhesive.

Example 7 A polychloroprene latex was obtained in the same manner as in Example 1 except that the radical scavenger was 1.0 part by mass of Cellsol H633. 100 parts by mass of the above polychloroprene latex, 30 parts by mass of Superester E-650, and 3.0 parts by mass of zinc oxide were stirred with a three-one motor at a mixing ratio to prepare an adhesive.

Comparative Example 1 Polymerization was carried out in the same manner as in Example 1 except that 96.0 parts by mass of chloroprene and 4.0 parts by mass of methacrylic acid were used. The gel content and the adhesive properties were measured in the same manner as in Example 1, and the results are shown in Table 2.

Comparative Example 2 100 parts by mass of the polychloroprene latex of Example 2 and 30 parts of Tamanol E-100
The mixture was stirred with a three-one motor at a mixing ratio of parts by mass to prepare an adhesive.

Comparative Example 3 In Example 1, a polychloroprene latex was prepared in the same manner as in Experimental Example 1 without adding a 10% aqueous solution of disodium hydrogen phosphate, and stored under the conditions of the storage stability test described above. did. As a result, PH decreased to 5.4. The gel content, pH and adhesive properties of the latex before storage were measured in the same manner as in Example 1, and the results are shown in Table 2. The latex after storage was lower than the range of the present invention, so that polychloroprene latex and heavenly latex were used. It is obvious that the latex of the adhesive composition for boards is unstable and easily solidifies.

Comparative Example 4 100 parts by mass of the polychloroprene latex of Example 2 and 10 parts of Tamanol E-100
0 parts by mass and zinc oxide were mixed at a mixing ratio of 3 parts by mass with a three-one motor to prepare an adhesive.

[0053]

[Table 1]

[0054]

[Table 2]

Note 1) Polyvinyl alcohol: PVA;
UMR-20H, degree of saponification 79 mol%, degree of polymerization 380
(Manufactured by Unitika) Note 2) Polyvinyl alcohol: PVA; B-05, saponification degree 88 mol%, polymerization degree 550 (manufactured by Denki Kagaku Kogyo Co., Ltd.) Note 3) Cellosol H633: 2,6-di-t-butyl-4- Methylphenol emulsion (manufactured by Chukyo Yushi Co., Ltd.), the added amount is converted to solid content. Note 4) Tackifying resin 1: terpene phenol resin emulsion; Tamanol E-100 (manufactured by Arakawa Chemical Industries),
Addition amount is solid content Note 5) Tackifying resin 2: rosin acid ester resin emulsion; Superester E-650 (manufactured by Arakawa Chemical Industries), addition amount is solid content conversion Note 6) Zinc oxide: zinc oxide emulsion (Osaki Manufactured by Kogyo Co., Ltd.)

[0056]

As is clear from Table 1, the adhesive of the present invention is excellent in adhesive strength, adhesive water resistance and heat resistance, so that it can be applied to adherends and substrates, especially decorative plates and top plate substrates. As the best.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C09J 151/04 C09J 151/04 201/00 201/00 // B29K 9:00 B29K 9:00 F term ( Reference) 4F211 AA19 AA45 AB03 AB04 AB16 TA03 TN51 TN53 4J011 KA16 KA25 KB14 PA54 PC06 4J026 AA71 BA25 BA34 DB04 FA04 GA01 GA06 4J040 BA202 CA161 DD022 DK012 DN032 DN072 GA01 GA07 GA12 HA136 HA196 HA286 HB26 HDB JA03 KA42 LA07 LA08 LA11 MA08 MA10 NA05 NA12 PA30

Claims (6)

[Claims] 1. A method for polymerizing 100 parts by mass of chloroprene and more than 0 parts by mass and less than 2 parts by mass of ethylenically unsaturated carboxylic acid in the presence of 0.5 to 4 parts by mass of polyvinyl alcohol, followed by radical scavenging with a pH adjuster. A polychloroprene latex having a chloroprene polymer gel content of 10 to 60% by mass and a pH of 6 to 9, a tackifying resin and a metal oxide as main components. The addition amount of the tackifier resin (in terms of solid content) is determined by using the adhesive composition, which is 10 to 100 parts by mass with respect to 100 parts by mass of the polychloroprene latex in terms of solids. Adhesive structure characterized by being obtained by adhering. 2. The polyvinyl alcohol has a degree of saponification of 75.
The adhesive structure according to claim 1, wherein the amount is from 90 to 90 mol%. 3. The adhesive structure according to claim 1, wherein the pH adjuster is a weak acid salt. 4. The adhesive structure according to claim 1, wherein the metal oxide is zinc oxide. 5. The adhesive structure according to claim 1, wherein the adherend is a decorative plate and the base is a top plate base. 6. A polychloroprene latex, a tackifier resin and a metal oxide as main components, and the polychloroprene latex contains 100 parts by mass of chloroprene and more than 0 parts by mass of ethylenically unsaturated carboxylic acid and less than 2 parts by mass, After polymerization in the presence of 0.5 to 4 parts by mass of polyvinyl alcohol, the chloroprene polymer obtained by adding a pH adjuster and a radical scavenger has a gel content of 10 to 10.
A bonding method, comprising bonding an adherend and a substrate using an adhesive composition having a pH of 6 to 9 by mass.