JP7758926B2 - Urethane adhesive composition, vulcanized rubber bonding method, and conveyor belt - Google Patents

Description

The present invention relates to a urethane-based adhesive composition, a method for bonding vulcanized rubber, and a conveyor belt.

Conventionally, in order to make a belt such as a conveyor belt endless (for example, to make it longer and/or to form a ring), rubber pieces are joined together by joining vulcanized or unvulcanized rubber pieces. Commonly used joining methods include vulcanization joining, in which unvulcanized rubber pieces are joined together by vulcanization, and natural vulcanization joining, in which vulcanized rubber pieces are joined together by adhesive.
Vulcanization bonding requires equipment to vulcanize unvulcanized rubber together. This equipment must be large, especially when making large products such as conveyor belts into endless loops.
On the other hand, natural vulcanization bonding has the advantage that such large-scale equipment is not required. Adhesives that can be used for natural vulcanization bonding (these adhesives are also called natural vulcanization adhesives) are known from, for example, Patent Documents 1 and 2.

Patent No. 6733436 Japanese Patent Application Laid-Open No. 2021-031562

Under these circumstances, the present inventors prepared and evaluated a natural vulcanizing adhesive with reference to Patent Document 1, and found that an adhesive containing chloroprene rubber and polyisocyanate may have poor adhesion to vulcanized rubber of a rubber composition containing, for example, more than 30 mass % of butadiene rubber (BR) in the rubber component (Comparative Example 6).
Furthermore, adhesive compositions were prepared and evaluated with reference to Patent Document 2, and it was found that adhesive compositions containing a polyisocyanate compound and a polyester also sometimes exhibited poor adhesion to vulcanized rubber containing more than 30 mass % of butadiene rubber (BR) in the rubber component (Comparative Examples 3 to 5 and 8).

Therefore, an object of the present invention is to provide an adhesive composition that exhibits excellent adhesion to vulcanized rubber containing a high proportion of BR. It is also an object of the present invention to provide a method for adhering vulcanized rubber using the adhesive composition, and a conveyor belt manufactured using the adhesive composition.

As a result of intensive research to solve the above-mentioned problems, the present inventors have found that the desired effects can be obtained by including polyol 1 and polyol 2, which contain a polyol component and a polyisocyanate component, and the polyol component has a hydroxyl value and the like within a specific range, and have arrived at the present invention.
The present invention is based on the above findings and solves the above problems by specifically providing the following configurations.

[1]
A urethane adhesive composition containing a polyol component and a polyisocyanate component, wherein the polyol component contains the following polyol 1 and polyol 2, and which is used to bond vulcanized rubber.
Polyol 1: A polyol compound having a glass transition temperature of −30 to +60° C., a hydroxyl value of 1 to 20 KOHmg/g, and an ester bond. Polyol 2: A polyol compound having a hydroxyl value of more than 20 KOHmg/g and not more than 500 KOHmg/g, and having at least one skeleton selected from the group consisting of isoprene and/or butadiene polymers, hydrogenated products thereof, polyolefins, ester bonds, and carbonate bonds. [2]
The urethane adhesive composition according to [1], wherein the proportion of hydroxyl groups contained in the polyol 1 is 10 to 30 mol % of all hydroxyl groups contained in the polyol component.
[3]
The urethane adhesive composition according to [1] or [2], wherein the proportion of hydroxyl groups contained in the polyol 2 is 40 to 70 mol % of all hydroxyl groups contained in the polyol component.
[4]
The urethane adhesive composition according to any one of [1] to [3], wherein the polyol component further comprises polyol 3 having a hydroxyl value of more than 500 KOHmg/g and not more than 1300 KOHmg/g.
[5]
The urethane adhesive composition according to [4], wherein the hydroxyl value of the polyol 3 is 1000 to 1300 KOHmg/g.
[6]
The urethane adhesive composition according to [4] or [5], wherein the proportion of hydroxyl groups contained in the polyol 3 is 10 to 40 mol % of all hydroxyl groups contained in the polyol component.
[7]
The urethane adhesive composition according to any one of [1] to [6], wherein the molar ratio of all isocyanate groups in the polyisocyanate component to all hydroxyl groups in the polyol component is 1.0 to 3.0.
[8]
[8] The urethane adhesive composition according to any one of [1] to [7], wherein the glass transition temperature of the polyol 1 is 0 to +50°C.
[9]
[9] The urethane adhesive composition according to any one of [1] to [8], wherein the number average molecular weight of the polyol 1 is 6,000 to 23,000.
[10]
[10] The urethane adhesive composition according to any one of [1] to [9], wherein the polyol 2 has at least polyisoprene, polybutadiene, or a hydrogenated product thereof, or polycarbonate as a skeleton.
[11]
The urethane adhesive composition according to any one of [1] to [10], further comprising a solvent, wherein the solvent contains at least an acetate ester-based solvent.

[12]
A method for bonding vulcanized rubbers, comprising bonding vulcanized rubbers together using the urethane adhesive composition according to any one of [1] to [11].
[13]
A conveyor belt having its ends bonded together using the urethane adhesive composition according to any one of [1] to [11].

The urethane adhesive composition of the present invention has excellent adhesion to vulcanized rubber containing a high proportion of BR. Furthermore, it is possible to provide a method for adhering vulcanized rubber using the urethane adhesive composition of the present invention, and a conveyor belt manufactured using the urethane adhesive composition of the present invention.

1 is a schematic diagram showing an example of an adhesive type of a conveyor belt according to the present invention.

The present invention will be described in detail below.
In this specification, a numerical range expressed using "to" means a range including the numerical values written before and after "to".
In this specification, unless otherwise specified, each component may be used alone or in combination of two or more substances. When a component contains two or more substances, the content of the component means the total content of the two or more substances.
In this specification, the joining of vulcanized rubber pieces with an adhesive may be simply referred to as "adhesion."
In this specification, the adhesiveness to vulcanized rubber containing a high proportion of BR may be simply referred to as "adhesion." Furthermore, better adhesiveness to vulcanized rubber containing a high proportion of BR may be referred to as better effects of the present invention.

[Urethane-based adhesive composition]
The urethane adhesive composition of the present invention (the adhesive composition of the present invention) is
The urethane adhesive composition contains a polyol component and a polyisocyanate component, in which the polyol component contains the following polyol 1 and polyol 2, and is used to bond vulcanized rubber.
Polyol 1: A polyol compound having a glass transition temperature of −30 to +60° C., a hydroxyl value of 1 to 20 KOHmg/g, and an ester bond. Polyol 2: A polyol compound having a hydroxyl value of more than 20 KOHmg/g and not more than 500 KOHmg/g, and having at least one skeleton selected from the group consisting of isoprene and/or butadiene polymers, hydrogenated products thereof, polyolefins, ester bonds, and carbonate bonds.

It is believed that the adhesive composition of the present invention has the above-described structure and therefore exhibits the desired effects. The reason for this is not clear, but is presumed to be as follows.
When the adhesive composition of the present invention is applied to vulcanized rubber containing a high proportion of BR, polyol 2, which has a hydroxyl value of more than 20 KOHmg/g and not more than 500 KOHmg/g, migrates to and/or penetrates the surface of the vulcanized rubber, and in this state, the polyol component reacts with the polyisocyanate component, resulting in a crosslinking effect and an anchoring effect in the cured product (adhesive), which is thought to result in strong adhesion between the vulcanized rubbers.
Each component contained in the adhesive composition of the present invention will be described in detail below.

[Polyol component]
The polyol component contained in the adhesive composition of the present invention is a compound having a plurality of hydroxy groups. The number of hydroxy groups that the polyol component has may be at least two, and preferably from two to four, on average per molecule.
In the present invention, the polyol component contains polyol 1 and polyol 2. This provides the adhesive composition of the present invention with excellent adhesive properties.

[Polyol 1]
In the present invention, polyol 1 contained in the polyol component is a polyol compound having a glass transition temperature of −30 to +60° C., a hydroxyl value of 1 to 20 KOH mg/g, and an ester bond.

[Glass transition temperature of polyol 1]
In the present invention, the glass transition temperature (Tg) of Polyol 1 is −30 to +60° C. (−30° C. or higher and +60° C. or lower). When the Tg of Polyol 1 is within the above range, the adhesive composition of the present invention has excellent adhesive properties.

From the viewpoint of achieving better effects of the present invention and excellent early strength development, the Tg of polyol 1 is preferably 0 to +60°C, more preferably +10 to +50°C, and even more preferably +15 to +50°C.
From the viewpoint of achieving a superior effect of the present invention and a high initial strength, the Tg of polyol 1 is preferably 0 to +60°C, more preferably +10 to +50°C, and even more preferably +15 to +40°C.
In the present invention, the glass transition temperature of each polyol component can be measured by a differential scanning calorimeter. For example, the measurement is carried out at a temperature rise rate of 20°C/min, and the glass transition temperature can be calculated from the results by the midpoint method.

[Hydroxyl value of polyol 1]
In the present invention, the hydroxyl value (OH value) of polyol 1 is 1 to 20 KOHmg/g. When the OH value of polyol 1 is within the above range, the adhesive composition of the present invention has excellent adhesive properties.

The OH value of polyol 1 is preferably 5 to 20 KOH mg/g, more preferably 10 to 20 KOH mg/g, from the viewpoint of achieving better effects of the present invention and excellent early strength development.
In the present invention, the hydroxyl value of each polyol component can be measured in accordance with JIS K1557-1:2007.

(Proportion of Hydroxyl Groups in Polyol 1)
The proportion of hydroxyl groups in polyol 1 among all hydroxyl groups in the polyol component is preferably 10 to 30 mol %, more preferably 10.0 to 20.0 mol %, from the viewpoint of achieving better effects of the present invention and excellent early strength development.
The above ratio ranges also apply when the polyol component further contains polyol 3, which will be described later.

(Acid value of polyol 1)
The acid value of polyol 1 is preferably 1 to 20 KOHmg/g, more preferably 2 to 10 KOHmg/g, from the viewpoint of achieving better effects of the present invention and excellent early strength development.
In the present invention, the acid value of each polyol component can be measured in accordance with JIS K0070:1992.

[Ester bond of polyol 1]
In the present invention, Polyol 1 has an ester bond in addition to a plurality of hydroxy groups. The presence of an ester bond in Polyol 1 provides the adhesive composition of the present invention with excellent adhesive properties.
From the viewpoint of achieving a better effect of the present invention and exhibiting a better early strength, the skeleton of polyol 1 preferably has an ester bond, and more preferably has a polyester bond.

(Example of Polyol 1)
From the viewpoint of achieving a better effect of the present invention and exhibiting a better early strength, polyol 1 preferably contains a polyester polyol (a compound having a polyester polymer skeleton and a plurality of hydroxy groups).

(Number average molecular weight of polyol 1)
The number average molecular weight of polyol 1 is preferably 6,000 to 23,000 from the viewpoint of achieving better effects of the present invention and achieving excellent early strength development.
In the present invention, when each polyol component is a polymer (for example, a polyester polyol as polyol 1), the number average molecular weight of each polyol component can be a polystyrene-equivalent value determined by gel permeation chromatography using tetrahydrofuran as a solvent.

[Polyol 2]
In the present invention, polyol 2 contained in the polyol component is a polyol compound having a hydroxyl value of more than 20 KOHmg/g and not more than 500 KOHmg/g and having a skeleton of at least one selected from the group consisting of a polymer of isoprene and/or butadiene, a hydrogenated product thereof, a polyolefin, an ester bond, and a carbonate bond.

[Hydroxyl value of polyol 2]
In the present invention, the hydroxyl value (OH value) of polyol 2 is more than 20 KOHmg/g and not more than 500 KOHmg/g. When the OH value of polyol 2 is in the above range, the adhesive composition of the present invention has excellent adhesiveness.

From the viewpoint of achieving better effects of the present invention and excellent early strength development, the OH value of polyol 2 is preferably 21 to 400 KOHmg/g, more preferably 30 to 300 KOHmg/g, and even more preferably 45 to 225 KOHmg/g.
When polyol 2 includes a polyol having a polyester skeleton (polyester polyol), the OH value of the polyester polyol as polyol 2 is preferably 21 to 200 KOH mg/g, more preferably 21 to 100 KOH mg/g, from the viewpoint of achieving better effects of the present invention and exhibiting excellent early strength.
When polyol 2 contains a polyol having a polybutadiene skeleton (polybutadiene polyol), the OH value of the polybutadiene polyol is preferably 30 to 200 KOH mg/g, more preferably 35 to 90 KOH mg/g, from the viewpoint of achieving better effects of the present invention and providing excellent early strength.
When polyol 2 contains a polyol having a polycarbonate skeleton (polycarbonate polyol), the OH value of the polycarbonate polyol is preferably 30 to 300 KOHmg/g, more preferably 100 to 225 KOHmg/g, from the viewpoint of achieving better effects of the present invention and exhibiting excellent early strength.

(Ratio of hydroxyl groups in polyol 2)
The proportion of hydroxyl groups in polyol 2 among all hydroxyl groups in the polyol component is preferably 10.0 to 70.0 mol % from the viewpoint of achieving better effects of the present invention and exhibiting excellent early strength.
The proportion of hydroxyl groups in the polyol 2 can be the same when the polyol component further contains the polyol 3 described below.

[Polyol 2 skeleton]
In the present invention, polyol 2 has, in addition to a plurality of hydroxy groups, at least one selected from the group consisting of isoprene and/or butadiene polymers, hydrogenated products thereof, polyolefins, ester bonds, and carbonate bonds as a backbone. By having polyol 2 have the above structure in the backbone, the adhesive composition of the present invention has excellent adhesive properties.

When polyol 2 has an ester bond in the skeleton, it is preferable that the skeleton of polyol 2 has a polyester. Examples of such polyol 2 include polyester polyols (compounds whose skeleton is a polyester polymer and which have multiple hydroxy groups).
When polyol 2 has a carbonate bond in the skeleton, the skeleton preferably has a polycarbonate. Examples of polyol 2 as described above include polycarbonate polyols (compounds whose skeleton is a polycarbonate polymer and has multiple hydroxy groups).

From the viewpoint of achieving better effects of the present invention and exhibiting excellent early strength, it is preferable that Polyol 2 have at least polyisoprene, polybutadiene, or a hydrogenated product thereof, or polycarbonate as the skeleton, and it is more preferable that it have at least polybutadiene, a hydrogenated product thereof, or polycarbonate.

(Viscosity of Polyol 2)
The viscosity of polyol 2 (for example, polybutadiene polyol) at 30° C. is preferably 6.0 Pa·s or less, from the viewpoint of achieving better effects of the present invention and achieving excellent early strength development.
The viscosity of polyol 2 (for example, polyisoprene polyol) at 75°C is preferably 1000 mPa·s or less, from the viewpoint of achieving better effects of the present invention and excellent early strength development.

(Example of Polyol 2)
From the viewpoint of achieving better effects of the present invention and exhibiting excellent early strength, polyol 2 preferably contains at least one selected from the group consisting of polyisoprene polyol, polybutadiene polyol, hydrogenated polyols thereof, and polycarbonate polyol, and more preferably contains at least one selected from the group consisting of polybutadiene polyol, hydrogenated polyols thereof, and polycarbonate polyol.

(Number average molecular weight of polyol 2)
The number average molecular weight of polyol 2 is preferably 500 to 5,000, more preferably 500 to 3,000, from the viewpoint of achieving better effects of the present invention and excellent early strength development.

(Polyol 3)
From the viewpoint of achieving better effects of the present invention and excellent early strength development, it is preferable that the above polyol component further contains polyol 3 having a hydroxyl value of more than 500 KOHmg/g and not more than 1300 KOHmg/g.

For the same reasons as above, the hydroxyl value of polyol 3 is more preferably 1000 to 1300 KOHmg/g.

(Ratio of hydroxyl groups in polyol 3)
When the polyol component further contains polyol 3, the proportion of hydroxyl groups in polyol 3 relative to the total hydroxyl groups in the polyol component is preferably 10 to 70 mol %, more preferably 20 to 65 mol %, from the viewpoint of achieving better effects of the present invention and providing excellent early strength.

(Proportion of hydroxyl groups in polyols 2 and 3 when the polyol component further contains polyol 3)
When the polyol component further contains polyol 3 and contains a polycarbonate polyol as polyol 2, the proportion of hydroxyl groups in the polyol 2 (including polycarbonate polyol) in all hydroxyl groups in the polyol component is preferably 10.0 to 50.0 mol %, more preferably 20.0 to 40.0 mol %, from the viewpoint of achieving better effects of the present invention and excellent early strength development.
In the above case, the proportion of hydroxyl groups in polyol 3 relative to the total hydroxyl groups in the polyol component is preferably 20.0 to 70.0 mol %, more preferably 40.0 to 65.0 mol %, from the viewpoint of achieving better effects of the present invention and providing excellent early strength.

(Structure of Polyol 3)
In view of achieving a better effect of the present invention and exhibiting a better initial strength, a preferred embodiment of the polyol 3 is a low molecular weight compound (monomer) having a plurality of hydroxy groups.
In polyol 3, the multiple hydroxy groups are preferably bonded to a hydrocarbon group, and more preferably to a hydrocarbon group formed only of carbon atoms and hydrogen atoms, from the viewpoint of achieving better effects of the present invention and excellent early strength development.
The number of carbon atoms in the hydrocarbon group is preferably 2 to 15, and more preferably 3 to 5, from the viewpoint of achieving better effects of the present invention and excellent early strength development.
The hydrocarbon group is preferably a linear or branched alkyl group, from the viewpoint of achieving a better effect of the present invention and exhibiting a better initial strength.
Examples of polyol 3 include butanediol, diethyl-1,5-pentanediol, butylethylpropanediol, and nonanediol.
From the viewpoint of achieving better effects of the present invention and exhibiting better early strength, polyol 3 preferably contains butanediol, and more preferably contains 1,4-butanediol.

(Molecular weight of polyol 3)
The molecular weight of polyol 3 is preferably less than 500, from the viewpoint of achieving better effects of the present invention and excellent early strength development.
In the present invention, when the polyol component has a low molecular weight (monomer), the molecular weight of the polyol component can be measured by a conventional method used for measuring the molecular weight of low molecular weight compounds.

[Polyisocyanate]
The adhesive composition of the present invention contains a polyisocyanate component. The polyisocyanate component is a compound having a plurality of isocyanate groups.
Examples of the polyisocyanate component include aromatic polyisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polymeric MDI, 1,4-phenylene diisocyanate, polymethylene polyphenylene polyisocyanate, xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), tolidine diisocyanate (TODI), 1,5-naphthalene diisocyanate (NDI), and triphenylmethane triisocyanate;
aliphatic (the aliphatic includes linear, branched and alicyclic) polyisocyanates, such as hexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate (TMHDI), lysine diisocyanate, norbornane diisocyanate (NBDI), transcyclohexane-1,4-diisocyanate, isophorone diisocyanate (IPDI), bis(isocyanatomethyl)cyclohexane (H ₆ XDI), and dicyclohexylmethane diisocyanate (H ₁₂ MDI);
These carbodiimide-modified polyisocyanates are exemplified.

From the viewpoint of achieving better effects of the present invention and exhibiting excellent early strength, the polyisocyanate component preferably contains an aromatic polyisocyanate, more preferably contains at least one selected from the group consisting of MDI, polymeric MDI, carbodiimide-modified products thereof, and triphenylmethane triisocyanate, and further preferably contains polymeric MDI and/or triphenylmethane triisocyanate.
The polymeric MDI is a polymethylene polyphenyl polyisocyanate. The polymeric MDI may be a mixture of polymethylene polyphenyl polyisocyanates having different degrees of polymerization. The polymeric MDI may further contain MDI in addition to the polymethylene polyphenyl polyisocyanate. The polymeric MDI is not particularly limited.
An example of triphenylmethane triisocyanate is triphenylmethane-4,4',4"-triisocyanate.

The polyisocyanate component is preferably liquid at room temperature (23° C.) from the viewpoint of achieving better effects of the present invention and exhibiting excellent early strength.
An example of the polyisocyanate component that is liquid at room temperature is polymeric MDI.
The polyisocyanate component may be in a state of being dissolved in a solvent.

(Combination of polyol component and polyisocyanate component)
The polyol component and the polyisocyanate component are, from the viewpoint of achieving the effects of the present invention more effectively and exhibiting excellent early strength, a combination 1 of a polyol component containing polyol 1, a polycarbonate polyol as polyol 2, and a polyol 3, and a polyisocyanate component containing triphenylmethane triisocyanate;
Combination 2 of a polyol component containing polyol 1, polybutadiene polyol or polyisoprene polyol as polyol 2, and polyol 3, and a polyisocyanate component containing polymeric MDI is preferred.

Combination 1
In the above combination 1, from the viewpoint of achieving a more excellent effect of the present invention and excellent early strength development and magnitude of the early strength, polyol 1 contains a polyester polyol having a Tg of 0 to +40°C, and/or
It is preferred that, of all hydroxyl groups in the polyol component, the proportion of hydroxyl groups in polyol 2 is 10.0 to 40.0 mol %, and the proportion of hydroxyl groups in polyol 3 is 20.0 to 70.0 mol %;
It is more preferable that polyol 1 contains a polyester polyol having a Tg of 0 to +40°C, that the proportion of hydroxyl groups contained in polyol 2 is 10.0 to 40.0 mol% of all hydroxyl groups contained in the polyol component, and that the proportion of hydroxyl groups contained in polyol 3 is 20.0 to 70.0 mol%.

Combination 2
In the above combination 2, from the viewpoint of achieving a more excellent effect of the present invention and excellent early strength development and magnitude of the early strength, polyol 1 contains a polyester polyol having a Tg of 0 to +40°C,
Polyol 2 comprises a polybutadiene polyol;
Polyol 2 contains a polybutadiene polyol having a hydroxyl value of 30 to 90 KOH mg/g, and/or
It is preferred that, of all hydroxyl groups in the polyol component, the proportion of hydroxyl groups in polyol 2 is 50.0 to 70.0 mol %, and the proportion of hydroxyl groups in polyol 3 is 20.0 to 40.0 mol %;
Polyol 1 comprises a polyester polyol having a Tg of 0 to +40°C;
It is more preferable that polyol 2 contains a polybutadiene polyol having a hydroxyl value of 30 to 90 KOH mg/g, and that the proportion of hydroxyl groups in polyol 2 is 50.0 to 70.0 mol % of all hydroxyl groups in the polyol component, and that the proportion of hydroxyl groups in polyol 3 is 20.0 to 40.0 mol %.

(NCO/OH molar ratio)
The molar ratio (NCO/OH) of all isocyanate groups in the polyisocyanate component to all hydroxyl groups in the polyol component is preferably 0.7 to 5.5, more preferably 1.0 to 3.0, and even more preferably 1.5 to 2.5, from the viewpoint of achieving better effects of the present invention and achieving excellent early strength.

(solvent)
The adhesive composition of the present invention preferably further contains a solvent, from the viewpoint of achieving better effects of the present invention and excellent early strength development.
The solvent is not particularly limited as long as it is soluble or compatible with the polyol component and non-reactive with the polyisocyanate component.
The solvent may be an organic solvent, and specific examples thereof include ester solvents, ketones such as methyl ethyl ketone, and ethers such as tetrahydrofuran.
From the viewpoint of achieving better effects of the present invention and exhibiting excellent early strength, the solvent preferably contains an ester-based solvent, more preferably contains an acetate ester-based solvent, and even more preferably contains ethyl acetate.

(Solvent content)
When the adhesive composition of the present invention further contains a solvent, the content of the solvent is preferably 30 to 80 mass% of the total amount of the adhesive composition of the present invention. In the above case, the total amount of the polyol component and the polyisocyanate component can be 20 to 70 mass% of the total amount of the adhesive composition of the present invention.
When the polyisocyanate component is in a state of being dissolved in a solvent, the amount of the solvent used together with the polyisocyanate component is included in the above-mentioned solvent content.

(Other ingredients)
In addition to the above-mentioned components, the adhesive composition of the present invention may further contain additives such as catalysts, carbon black, white fillers (e.g., silica, calcium carbonate, clay, talc), antioxidants, antioxidants, pigments (dyes), plasticizers, softeners, flame retardants, etc. The type and content of each of the above additives may be selected as appropriate.

(catalyst)
The adhesive composition of the present invention preferably further contains a catalyst, from the viewpoint of achieving better effects of the present invention and excellent early strength development.
Examples of the catalyst include carboxylic acids such as 2-ethylhexanoic acid and oleic acid; phosphoric acids such as polyphosphoric acid, ethyl acid phosphate and butyl acid phosphate; bismuth catalysts such as bismuth octoate; tin catalysts such as dibutyltin dilaurate and dioctyltin dilaurate; and amine catalysts such as 1,4-diazabicyclo[2.2.2]octane, 2,4,6-tris(dimethylaminomethyl)phenol (e.g., DMP-30), and bis(2-dimethylaminoethyl)ether.
The catalyst preferably contains a tin-based catalyst and/or an amine-based catalyst, and more preferably contains a tin-based catalyst and an amine-based catalyst.
The amount of the catalyst can be appropriately selected.

(Method 1 for producing adhesive composition)
The adhesive composition of the present invention can be produced, for example, by mixing the above-mentioned components. When produced as described above, the adhesive composition of the present invention can be a one-component system.

(Method 2 for producing adhesive composition)
The adhesive composition of the present invention is preferably a system of at least two components, from the viewpoint of excellent storage stability.
When the adhesive composition of the present invention is a two-component system, at least the polyol component is added to the first component, and the polyisocyanate component is added to the second component. Other components may be added to the first component and/or the second component as appropriate.
When the adhesive composition of the present invention is a two-component system, the first and second liquids may be mixed together before use.

[Urethane-based adhesive composition]
The adhesive composition of the present invention can become a polyurethane-based adhesive by reaction of the polyol component and the polyisocyanate component.

[Bonding vulcanized rubber]
The adhesive composition of the present invention can be used to bond vulcanized rubber.
The vulcanized rubber refers to rubber that has already been vulcanized. The adhesive composition of the present invention may be used as long as at least one adherend is a vulcanized rubber, and a preferred embodiment is one in which both adherends are vulcanized rubbers. When both adherends are vulcanized rubbers, the types of both vulcanized rubbers may be the same or different. When both adherends are vulcanized rubbers, the types of both vulcanized rubbers are preferably the same from the viewpoints of achieving better effects of the present invention and exhibiting excellent initial strength. Furthermore, when adhering adherends having layers of multiple different types of vulcanized rubber, it is preferable to adhere vulcanized rubbers of the same quality to each other for the same reasons as above. For example, when adhering adherends having a layer of vulcanized rubber A and a layer of vulcanized rubber B to each other, it is preferable to adhere the layers of vulcanized rubber A to each other and/or the layers of vulcanized rubber B to each other.
Examples of rubber components contained in vulcanized rubber include diene rubbers such as natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), aromatic vinyl-conjugated diene copolymer rubber (e.g., styrene-butadiene rubber), acrylonitrile-butadiene copolymer rubber (NBR), butyl rubber (IIR), halogenated butyl rubber (Br-IIR, Cl-IIR), and chloroprene rubber (CR).
In addition to the rubber component, the vulcanized rubber may further contain various additives commonly used in rubber compositions, such as fillers such as carbon black or silica, silane coupling agents, zinc oxide, stearic acid, antioxidants, processing aids, oils (e.g., process oils, aromatic oils), liquid polymers, vulcanizing agents (e.g., sulfur), and vulcanization accelerators.
The vulcanized rubber is preferably a sulfur vulcanized rubber. The vulcanization conditions are not particularly limited.

The adhesive composition of the present invention has excellent adhesion to vulcanized rubber containing a high proportion of BR (for example, a BR content of greater than 30% by mass in the rubber component). The adhesive composition of the present invention also has excellent adhesion to vulcanized rubber containing a low proportion of BR (for example, a BR content of less than 30% by mass in the rubber component) or to vulcanized rubber containing no BR.

The adhesive composition of the present invention can be cured under conditions of, for example, 5 to 40° C. and 10 to 80% RH.
The adhesive composition of the present invention can easily be used to bond rubber products (especially long ones) together in an endless loop, and is therefore preferably used to bond, for example, conveyor belts together.

[Vulcanized rubber adhesion method]
Next, the method for bonding vulcanized rubber of the present invention will be described.
The method for bonding vulcanized rubber of the present invention is a method for bonding vulcanized rubbers together using the urethane adhesive composition of the present invention.

The adhesive composition used in the vulcanized rubber bonding method of the present invention is not particularly limited as long as it is a urethane-based adhesive composition of the present invention.

The vulcanized rubber used in the method for adhering vulcanized rubber of the present invention is not particularly limited as long as it is rubber that has already been vulcanized. The vulcanized rubber can be the same as the vulcanized rubber described above in "Adhering vulcanized rubber."
As described above, the vulcanized rubber bonding method of the present invention uses an adhesive composition that has excellent adhesion to vulcanized rubber, and is therefore useful for bonding vulcanized rubber, particularly vulcanized rubber that contains a high proportion of BR (e.g., more than 30 mass % of the rubber component).
After vulcanization, the vulcanized rubber may be subjected to a physical surface treatment such as buffing or a chemical surface treatment such as the use of a surface treatment agent (for example, a primer), if necessary.
It is preferable that the vulcanized rubber has been subjected to a physical surface treatment such as buffing, from the viewpoint that increasing the surface irregularities and facilitating penetration of the adhesive composition will enhance the effects of the present invention.

In the method for bonding vulcanized rubber of the present invention, for example, the adhesive composition of the present invention is applied to the above-mentioned vulcanized rubber, and the vulcanized rubber is laminated with another vulcanized rubber, followed by curing under conditions of 15 to 35°C and 40 to 70% RH, thereby bonding the vulcanized rubbers together.
When vulcanized rubbers are bonded to each other, there are no particular limitations on the locations of the vulcanized rubbers to be bonded, and examples of such locations include the surface and end portions of the vulcanized rubbers.
When there are multiple vulcanized rubbers, the multiple vulcanized rubbers may be joined together to form a long piece.
Furthermore, in one vulcanized rubber or in the above-described integrated vulcanized rubber, the ends of the vulcanized rubber may be bonded together to form the vulcanized rubber into a ring shape (ring-like shape).

[Conveyor belt]
The conveyor belt of the present invention is a conveyor belt whose ends are bonded together using the urethane adhesive composition of the present invention.
The adhesive composition used in the conveyor belt of the present invention is not particularly limited as long as it is the urethane adhesive composition of the present invention.
The belt used in the conveyor belt of the present invention is not particularly limited as long as it can be used in a conveyor belt.
The belt (conveyor belt as raw material) may have a structure in which cover rubber is provided above and below a coating rubber in which a tensile strength material is embedded. The tensile strength material is not particularly limited, but examples thereof include canvas, steel cord, etc.
The vulcanized rubber constituting the belt is not particularly limited as long as it is a rubber that can be used for conveyor belts. For example, the vulcanized rubber can be the same as the vulcanized rubber described in the above section "Adhesion of vulcanized rubber."
After vulcanization, the vulcanized rubber may be subjected to a physical surface treatment such as buffing or a chemical surface treatment such as the use of a surface treatment agent (for example, a primer), if necessary.
The vulcanized rubber in the portion of the belt to be bonded is preferably subjected to a physical surface treatment such as buffing, from the viewpoint that the effect of the present invention is more excellent by increasing the surface irregularities and facilitating penetration of the adhesive composition.

[Belt ends together]
In the present invention, when the ends of the belt are bonded together, the bonding surfaces of the belt preferably contain vulcanized rubber.
When a plurality of belts are used in the conveyor belt of the present invention, the ends of the plurality of belts may be joined together to form a long, integrated belt.
Alternatively, the ends of a single belt may be bonded together to form the belt into a loop (ring shape). The same applies to the belt that is elongated and integrated as described above.
The conveyor belt of the present invention is preferably formed into an endless (ring-shaped) shape by bonding the ends of a single belt together with the adhesive composition of the present invention, or by bonding the ends of an elongated, integrated belt as described above together.

Conveyor belt manufacturing methods (adhesion methods, endless belting methods) of the present invention include, for example, conventional methods of vulcanizing a strip-shaped belt (conveyor belt as raw material; the same applies hereinafter) and then applying the adhesive composition of the present invention to the ends of the belt to bond the ends together. Before applying the adhesive composition of the present invention to the ends of the belt, the belt may or may not be processed as described below. Examples of processing (bonding methods) include the skiver method, in which the belt end is cut diagonally through its thickness relative to the direction of travel and then bonded; the step method, in which each layer of the belt end, such as the cover rubber, coat rubber, and tensile material, is peeled and cut in a stepped pattern and then bonded; the overlap method, in which the belt ends are overlapped and bonded (no particular belt processing required); the finger method (electrical joint method or insert method), in which the belt end is cut into a wedge shape and then butt-joined; the method in which the belt end is cut into a wedge shape relative to the direction of travel and then butt-joined; and improved or combined methods of each method.

An example of a method for manufacturing a conveyor belt according to the present invention is shown in the attached Fig. 1. The present invention is not limited to the attached drawings. Fig. 1 is a schematic diagram showing an example of a bonding method for a conveyor belt according to the present invention. Specifically, Fig. 1 shows an example of a step method for bonding by peeling and cutting each layer of cover rubber, coat rubber, and tensile material (not shown) at the end of the belt in a stepped manner.
As shown in Fig. 1(a), belt 1 is prepared as the belt (adherend rubber), in which the cover rubbers 2a and 2b, the coating rubber 3, and the tensile strength material (not shown) are peeled and cut in a stepped manner in the edge region 4, and belt 1' is prepared as the belt (adherend rubber), in which the cover rubbers 2a' and 2b', the coating rubber 3', and the tensile strength material (not shown) are peeled and cut in a stepped manner in the edge region 4'. Next, the adhesive composition of the present invention is applied to the adhesive interface in the edge region 4 and/or the adhesive interface in the edge region 4', and then the edge region 4 and the edge region 4' are bonded together as shown in Fig. 1(b), thereby producing a conveyor belt. In other words, the conveyor belt shown in Fig. 1(b) is produced by bonding the vulcanized rubbers at the belt edges together using the adhesive composition of the present invention. Combinations of vulcanized rubbers that can be bonded together include, for example, combinations of the same type of vulcanized rubber, such as cover rubbers 2a and 2a', cover rubbers 2b and 2b', and coat rubbers 3 and 3' in Figure 1(b), as well as combinations of different types (or blends) of vulcanized rubber, such as cover rubber 2a and coat rubber 3', and coat rubber 3 and cover rubber 2b'.

One example of a method for producing a conveyor belt of the present invention is to apply the adhesive composition of the present invention to the vulcanized rubber of the belt (which may be any vulcanized rubber contained in the belt, such as cover rubber or coat rubber) and dry it, then bond the vulcanized rubbers of the belt (adherend rubbers) together under pressure, and leave them at 0 to 35°C (preferably 15 to 30°C, more preferably 20 to 25°C) for 3 to 72 hours (preferably 3 to 24 hours, more preferably 6 to 18 hours). Furthermore, heating or pressurization can accelerate the reaction of the adhesive composition and shorten the time required for the bonding process. However, to avoid over-vulcanizing the vulcanized rubber, heating is preferably below 100°C.

The present invention will be explained in more detail below using examples. However, the present invention is not limited to these examples.

<Production of adhesive composition>
The components shown in the "First Liquid (mixture, parts by mass)" in the table below were used in the compositions (parts by mass) shown in the table, and these were mixed with a stirrer to prepare the first liquid.
The components shown in the "Second liquid (mixture, parts by mass)" in the table below were used in the compositions (parts by mass) shown in the same table, and these were mixed with a stirrer to prepare the second liquid.
Next, the first and second liquids prepared as described above were mixed in the amounts (parts by mass) shown in the "First Liquid/Second Liquid Mixture" in the table below to produce each adhesive composition.

<Preparation of Adherend Rubber 1>
An unvulcanized rubber composition was prepared by mixing the components (parts by mass) shown in the following (BR Compound 1) with a mixer. The following (BR Compound 1) is the same as the BR Compound 1 shown in Table 7 below.
(BR Compound 1)
- 100 parts by mass of rubber component with NR/SBR/BR = 28/36/36 (parts by mass) - Carbon black: ISAF carbon black 65 parts by mass - Oil: 6 parts by mass - Sulfur: 1.4 parts by mass - Vulcanization accelerator D: 0.2 part by mass - Vulcanization accelerator CZ: 1.0 part by mass

The unvulcanized rubber composition obtained as described above was then vulcanized at 148°C to obtain a vulcanized rubber sheet (6 inch x 4 inch square, 2 mm thick). The surface of the vulcanized rubber was buffed with sandpaper, and then a surface treatment agent (product name: Aftreat, manufactured by Tokyo Materials Co., Ltd.) was applied and dried to prepare Adherend Rubber 1.

<Preparation of Laminate 1>
Two sheets of adherend rubber 1 prepared as described above were prepared, and the adhesive composition produced as described above was applied to each of the adherend rubber 1. The adherend rubber 1 were then bonded together with the surfaces coated with the adhesive composition to form a sample. A weight of 10 kg was placed on the sample, and the sample was left to cure for 3 hours or 1 week under conditions of 23°C and 50% RH, thereby preparing each laminate 1.

<Evaluation>
The following evaluations were carried out using each of the laminates 1 prepared as described above. The results are shown in the "Evaluation Results" section of Tables 1 to 6.
<Adhesiveness>
Using each laminate 1 after one week of curing, a T-type peel test was performed at room temperature (23°C) and a peel rate of 50 mm/min to measure the peel strength (maximum peak strength, unit: N/25 mm), and the state of failure after the peel test was visually confirmed.
Peel strength (after 1 week)
A symbol ⊚ indicates that the peel strength of the laminate 1 after aging for one week was 80 N/25 mm or more.
A mark "◯" indicates that the peel strength was greater than 60 N/25 mm and less than 80 N/25 mm.
△ indicates that the peel strength was 40 to 60 N/25 mm.
"X" indicates that the peel strength was less than 40 N/25 mm.
- Breakdown state after peel test (after 1 week)
CF indicates cohesive failure. MF indicates that the vulcanized rubber has failed. "CF/MF" indicates that CF and MF are mixed.
AF indicates interfacial fracture. "CF/AF" indicates the coexistence of CF and AF.

Evaluation criteria for adhesion to vulcanized rubber In the present invention, adhesion to vulcanized rubber containing a high proportion of BR was evaluated based on the peel strength of each laminate 1 after aging for one week as described above and the state of failure after the peel test.
That is, in the present invention, when the peel strength of the laminate 1 after one week of aging exceeded 60 N/25 mm and the state of failure was CF and/or MF, the laminate was evaluated as having excellent adhesion to vulcanized rubber containing a high proportion of BR. The greater the peel strength above 60 N/25 mm, the better the adhesion.
On the other hand, if the peel strength of the laminate 1 after one week of curing was 60 N/25 mm or less, or if the state of failure was AF, the laminate was evaluated as having poor adhesion to vulcanized rubber containing a high proportion of BR.

<Early strength development>
Using each laminate 1 after 3 hours of curing, a T-type peel test was performed at room temperature (23°C) at a peel rate of 50 mm/min to measure the peel strength (maximum peak strength, unit: N/25 mm), and the state of failure after the peel test was visually confirmed.
Peel strength (after 3 hours)
A symbol ⊚ indicates that the peel strength of each laminate 1 after 3 hours of curing was 25 N/25 mm or more.
A symbol ○ indicates that the peel strength was greater than 10 N/25 mm and less than 25 N/25 mm.
△ indicates that the peel strength was 5 to 10 N/25 mm.
"X" indicates that the peel strength was less than 5 N/25 mm.
The state of destruction after the peel test (after 3 hours) is indicated in the same manner as the state of destruction after the peel test (after 1 week).

Evaluation criteria for early strength development In the present invention, the early strength development of vulcanized rubber containing a high proportion of BR was evaluated based on the peel strength of each laminate 1 after 3 hours of curing as described above and the state of failure after the peel test.
In the present invention, when the peel strength (after 3 hours) of each laminate 1 after 3 hours of curing exceeded 10 N/25 mm and the state of failure was CF and/or MF, it was evaluated as having excellent early strength development relative to vulcanized rubber containing a high proportion of BR. The greater the peel strength above 10 N/25 mm, the better the adhesion.
On the other hand, when the peel strength was 10 N/25 mm or less, or when the state of failure was AF, it was evaluated that the initial strength development for vulcanized rubber containing a high proportion of BR was poor.

Details of each component shown in Tables 1 to 6 are as follows.
[First liquid]
(Polyol 1)
Polyester polyol 1-1: Vylon GK-810, manufactured by Toyobo Co., Ltd. Tg 46°C, hydroxyl value 19 KOH mg/g, acid value 5 KOH mg/g, Mn 6,000.
Polyester polyol 1-2: Vylon GK-890, manufactured by Toyobo Co., Ltd. Tg 17°C, hydroxyl value 13 KOH mg/g, oxidation value 5 KOH mg/g, Mn 11,000.
Polyester polyol 1-3: Vylon 630, manufactured by Toyobo Co., Ltd. Tg 7°C, hydroxyl value 5 KOH mg/g, acid value <2 KOH mg/g, Mn 23,000.
Polyester polyol 1-4: Vylon 500, manufactured by Toyobo Co., Ltd. Tg 4°C, hydroxyl value 5 KOH mg/g, acid value <2 KOH mg/g, Mn 23,000.
Polyester polyol 1-5: Vylon 550, manufactured by Toyobo Co., Ltd. Tg -15°C, hydroxyl value 4 KOH mg/g, acid value <2 KOH mg/g, Mn 28,000.
Polyester polyol 1-6: Vylon UR-3210, manufactured by Toyobo Co., Ltd. Tg -3°C, hydroxyl value 2.5 KOH mg/g, acid value <1 KOH mg/g, Mn 40,000.
Polyester polyol 1-7: Vylon UR-6100, manufactured by Toyobo Co., Ltd. Tg -30°C, hydroxyl value 5 KOH mg/g, acid value <1 KOH mg/g, Mn 32,000.
Comparative polyester polyol: Vylon 200, manufactured by Toyobo Co., Ltd. Tg 67°C, hydroxyl value 6 KOH mg/g, acid value <2 KOH mg/g, Mn 17,000.

(Polyol 2)
Polyester polyol 2-1: Vylon GK-680, manufactured by Toyobo Co., Ltd. Tg 10°C, hydroxyl value 21 KOH mg/g, acid value <2 KOH mg/g, Mn 6,000.

Butadiene-skeleton polyol 2-1: Poly bd 15HT, manufactured by Idemitsu Kosan Co., Ltd. Hydroxyl value: 102.7 KOH mg/g, Mn: 1,200. Hydroxyl-terminated liquid polybutadiene. Viscosity: 1.5 Pa·s @ 30°C
Butadiene-skeleton polyol 2-2: Poly bd 45HT, manufactured by Idemitsu Kosan Co., Ltd. Hydroxyl value: 46.6 KOH mg/g, Mn: 2,800. Hydroxyl-terminated liquid polybutadiene. Viscosity: 5.0 Pa·s @ 30°C
Isoprene-skeleton polyol 2: Poly ip, manufactured by Idemitsu Kosan Co., Ltd. Hydroxyl value: 46.6 KOH mg/g, Mn: 2,500. Hydroxyl-terminated liquid polyisoprene. Viscosity: 7.5 Pa·s @ 30°C
Polyolefin-based polyol 2: Epol, manufactured by Idemitsu Kosan Co., Ltd. Hydroxyl value: 50.5 KOH mg/g, Mn: 2,500. Hydroxyl-terminated liquid polyolefin. 75 Pa·s @ 30°C

Polyester polyol 2-2: Polyester polyol of 2,4-diethyl-1,5-pentanediol and phthalic anhydride. HS 2N-226P, manufactured by Toyokuni Oil Mills. Hydroxyl value: 56.1 KOH mg/g, Mn: 2,000
Polycarbonate polyol 2-1: EATERNACOLL PH200D, manufactured by Ube Industries, Ltd. Hydroxyl value: 57.3 KOH mg/g, acid value: 0.03 KOH mg/g, Mn: 2,000. Polycarbonate polyol made from 1,5-pentanediol and 1,6-hexanediol. Viscosity: 2200 to 3400 mPa·s @ 75°C (liquid).
Polycarbonate polyol 2-2: EATERNACOLL UP-50, manufactured by Ube Industries, Ltd., hydroxyl value 224.4 KOH mg/g, Mn 500, 300 mPa·s @ 75°C (liquid at room temperature), polycarbonate polyol made from 2-methyl-1,3-propanediol

Comparative polyether polyol 1: EXCENOL 2020, manufactured by Asahi Glass Co., Ltd., hydroxyl value 56.1 KOH mg/g, Mn 2,000
Comparative polyether polyol 2: VORANOL ^™ P 400 Polyol, manufactured by The Dow Chemical Company, hydroxyl value 260 KOH mg/g, Mn 431

(Polyol 3)
1,4BD: 1,4-butanediol (commercially available product, manufactured by Mitsubishi Chemical Corporation), hydroxyl value 1245 KOHmg/g, molecular weight 431
PD-9: 2,4-diethyl-1,5-pentanediol (commercially available product, manufactured by KH Neochem Co., Ltd.), hydroxyl value 700 KOHmg/g, molecular weight 160.3
BEPG: 2-butyl-2-ethyl-1,3-propanediol (commercially available product, manufactured by KH Neochem Co., Ltd.), hydroxyl value 700 KOHmg/g, molecular weight 160.3
ND: 1,9-nonanediol (commercially available product, manufactured by Kuraray Co., Ltd.), hydroxyl value 700 KOH mg/g, molecular weight 160.3

(catalyst)
Metal catalyst: dioctyltin dilaurate, product name U-810, manufactured by Nitto Kasei Co., Ltd. Amine catalyst: bis(dimethylaminoethyl) ether, product name BL-19, manufactured by Evonik

[Second liquid]
Aromatic polyisocyanate 1: Polymeric MDI, Sumidur 44V-10, manufactured by Sumika Covestro Urethane Co., Ltd., solids content 100%, NCO% 32.0%
Aromatic polyisocyanate 2: Carbodiimide-modified MDI. Product name: Millionate MTL, manufactured by Tosoh Corporation. Solid content: 100%, NCO content: 29.0%
Aromatic polyisocyanate 3: triphenylmethane-4,4',4''-triisocyanate (Mw 367.36) Desmodur RE, manufactured by Sumika Covestro Urethane Co., Ltd. Solid content 27% by mass, NCO % 9.3%
Aliphatic polyisocyanate: a mixture of pentamethylene diisocyanate isocyanurate and pentamethylene diisocyanate allophanate, STABIO D-376N, manufactured by Mitsui Chemicals, Inc., solids content 100%, NCO % 22.0%

From the results shown in Tables 1 to 6, Comparative Examples 1 and 2, which did not contain Polyol 1, had poor adhesion to vulcanized rubber containing a high proportion of BR.
Comparative Examples 3 to 5 and 8, which did not contain polyol 2, had poor adhesion to vulcanized rubber containing a high proportion of BR.
Comparative Example 6, which did not contain Polyols 1 and 2 but contained chloroprene rubber instead, had poor adhesion to vulcanized rubber containing a high proportion of BR.
Comparative Example 7, which did not contain Polyol 1, had poor adhesion to vulcanized rubber containing a high proportion of BR.

In contrast, the adhesive composition of the present invention exhibits excellent adhesion to vulcanized rubber containing a high proportion of BR.

<Adhesion to various rubber substrates>
The adherend rubbers used were six types of belts commonly used as cover rubber for conveyor belts (BR-based compounds 1 to 3, abrasion-resistant belt, heat-resistant belt, and oil-resistant belt) and a general-purpose coating rubber. The main components and vulcanization systems of each belt are shown in Table 7. In the following examples, adhesion between vulcanized rubbers of the same quality was evaluated.
In the polymer column in the table, "NR" means natural rubber, "NBR" means nitrile rubber, "SBR" means styrene butadiene rubber, and "BR" means butadiene rubber.
In the carbon black column, "ISAF" stands for "Intermediate Super Abrasion Furnace,""HAF" stands for "High Abrasion Furnace," and "GPF" stands for "General Purpose Furnace."
Also, in the vulcanization system column (vulcanization component column),
"D" is a guanidine vulcanization accelerator (manufactured by Sanshin Chemical Industry Co., Ltd. under the trade name "Suncerer D-G"),
"CZ" is a sulfenamide vulcanization accelerator (manufactured by Ouchi Shinko Chemical Industry Co., Ltd. under the trade name "Noccela CZ-G");
"NS" is a sulfenamide vulcanization accelerator (manufactured by Sanshin Chemical Industry Co., Ltd. under the trade name "Suncerer NS-G");
"TS" is a thiuram vulcanization accelerator (manufactured by Sanshin Chemical Industry Co., Ltd. under the trade name "Suncerer TS-G");
"M" means a thiazole-based vulcanization accelerator (trade name "Noccela M" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.).
In the carbon black column, oil/plasticizer column, and vulcanization system column, "phr" represents parts by mass per 100 parts by mass of polymer.
BR-based compound 1 in the table is the same as (BR-based compound 1) used in <Preparation of adherend rubber 1> above.

<Preparation of Adherend Rubber 2>
Each adherend rubber was prepared in the same manner as in <Preparation of Adherend Rubber 1> above (all steps up to the application of the surface treatment agent were the same) using the components (parts by mass) shown in the rubber formulation in Table 7 above, and the adhesive composition shown in "Adhesive composition used" in Table 7 was applied to each of two pieces of each adherend rubber prepared as above. Adherend rubbers of the same type (formulation) were bonded together using the surfaces coated with the adhesive composition to prepare a sample, and a weight of 10 kg was placed on the sample. The sample was then left to age for one week under conditions of 23°C and 50% RH, thereby preparing each laminate 2.

<Evaluation>
Each laminate 2 prepared as described above was evaluated in the same manner as in the above-mentioned <Adhesion>. The evaluation criteria were also the same as above. The results are shown in Table 7.

The results shown in Table 7 show that when the adhesive composition of Comparative Example 6, which did not contain Polyols 1 and 2 but instead contained chloroprene rubber, was used on vulcanized rubbers containing a high proportion of BR (BR-based compounds 1 to 3), adhesion between the vulcanized rubbers was poor.

In contrast, the adhesive composition of the present invention has excellent adhesion to vulcanized rubber containing a high proportion of BR, such as more than 30 mass % of BR in the vulcanized rubber (for example, cover rubber of a BR-based compound in a conveyor belt).
The adhesive composition of the present invention also has excellent adhesion to vulcanized rubbers (for example, heat-resistant belts or coated rubbers in conveyor belts) that do not contain BR or that contain BR in a low proportion (30 mass % or less in the vulcanized rubber).

1, 1' belt 2a, 2b, 2a', 2b' cover rubber 3, 3' coating rubber 4, 4' end region

Claims (12)

A urethane adhesive composition containing a polyol component and a polyisocyanate component, wherein the polyol component contains the following polyol 1 and polyol 2, and which is used to bond vulcanized rubber.
Polyol 1: A polyol compound having a glass transition temperature of -30 to +60°C, a hydroxyl value of 1 to 20 KOHmg/g, a number average molecular weight of 6,000 to 23,000, and having an ester bond. Polyol 2: A polyol compound having a hydroxyl value of more than 20 KOHmg/g and not more than 500 KOHmg/g, and having a skeleton of at least one selected from the group consisting of a polymer of isoprene and/or butadiene, a hydrogenated product thereof, a polyolefin, an ester bond, and a carbonate bond. A urethane adhesive composition containing a polyol component and a polyisocyanate component, wherein the polyol component contains the following polyol 1 and polyol 2, and which is used to bond vulcanized rubber.
Polyol 1: A polyol compound having a glass transition temperature of −30 to +60° C., a hydroxyl value of 1 to 20 KOH mg/g, and an ester bond.
Polyol 2: A polyol compound having a hydroxyl value of more than 20 KOHmg/g and not more than 500 KOHmg/g and having at least polyisoprene, polybutadiene, or a hydrogenated product thereof, or polycarbonate as a skeleton. 3. The urethane adhesive composition according to claim 1, wherein the proportion of hydroxyl groups contained in said polyol 1 is 10 to 30 mol % of all hydroxyl groups contained in said polyol component. The urethane adhesive composition according to claim 1 or 2, wherein the proportion of hydroxyl groups contained in polyol 2 is 40 to 70 mol % of the total hydroxyl groups contained in the polyol component. The urethane adhesive composition according to claim 1 or 2 , wherein the polyol component further comprises a polyol 3 having a hydroxyl value of more than 500 KOHmg/g and not more than 1300 KOHmg/g. 6. The urethane adhesive composition according to claim 5 , wherein the polyol 3 has a hydroxyl value of 1000 to 1300 KOHmg/g. 6. The urethane adhesive composition according to claim 5 , wherein the proportion of hydroxyl groups contained in said polyol 3 is 10 to 40 mol % of all hydroxyl groups contained in said polyol component. 3. The urethane adhesive composition according to claim 1, wherein the molar ratio of all isocyanate groups contained in the polyisocyanate component to all hydroxyl groups contained in the polyol component is 1.0 to 3.0. 3. The urethane adhesive composition according to claim 1 , wherein the polyol 1 has a glass transition temperature of 0 to +50°C. The urethane adhesive composition according to claim 1 or 2 , further comprising a solvent, the solvent including at least an acetate ester-based solvent. A method for bonding vulcanized rubbers, comprising bonding two vulcanized rubbers together using the urethane adhesive composition according to any one of claims 1 to 10 . A conveyor belt, the ends of which are bonded together using the urethane adhesive composition according to any one of claims 1 to 10 .