JP2865778B2 - Hot melt adhesive composition - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hot melt adhesive containing a thermoplastic resin and an isocyanate prepolymer and having an improved cohesive force at a high temperature and capable of being applied by a hot melt. .

(Prior Art) From the viewpoints of energy saving, resource saving, and de-pollution, hot melt adhesives have been widely used in place of solvent adhesives in which natural rubber or the like is dissolved and used in an organic solvent. As a base polymer of the hot melt adhesive, in a block copolymer composed of a block composed of an aromatic vinyl monomer and a block composed of a conjugated diene monomer, the carbon-carbon double bond of the block composed of the conjugated diene monomer has a value of 50%. % Or more hydrogenated block copolymers are known (see Japanese Patent Application Laid-Open No. 2-1788). These are base polymers which are excellent in adhesiveness and flexibility at low temperatures and ordinary temperatures, have good fluidity when heated, and have excellent heat resistance and ultraviolet ray deterioration resistance.

However, since it is inherently thermoplastic, it has drawbacks such as low cohesive strength at high temperatures and poor solvent resistance. Therefore, at present, its use range is limited.

(Problems to be Solved by the Invention) The present invention relates to a block copolymer composed of a block composed of an aromatic vinyl monomer monomer and a block composed of isoprene, wherein a carbon-carbon double bond of the block composed of isoprene is 50%. It is an object of the present invention to obtain a hot-melt adhesive composition which is based on a block copolymer hydrogenated by at least% and has excellent cohesive strength at high temperatures and excellent solvent resistance.

(Means for Solving the Problems) As a result of studies, the present inventors have found that a block copolymer composed of a block composed of an aromatic vinyl monomer and a block composed of isoprene (hereinafter simply referred to as a block copolymer). Is a polymer of a block copolymer in which the carbon-carbon double bond of the block composed of isoprene is hydrogenated by 50% or more and a liquid isoprene having a hydroxyl group or a mixture of isoprene-butadiene, Hot melt coating is performed by combining a liquid polymer in which 50% or less of carbon-carbon double bonds are hydrogenated (hereinafter simply referred to as a liquid polymer) with an isocyanate compound obtained by reacting with an isocyanate compound. Moisture curing afterwards introduces covalent crosslinking points and has high cohesion even at high temperatures, It found that hot melt adhesive excellent in solvent resistance.

That is, according to the present invention, the above-mentioned object is achieved by (a) having at least two blocks composed of an aromatic vinyl monomer and at least one block composed of isoprene, wherein the carbon-carbon A block copolymer in which at least 50% of heavy bonds are hydrogenated, and (b) 1
Liquid isoprene having 1.5 to 5.0 hydroxyl groups in the molecule or a polymer having a number average molecular weight of 700 to 7000, which is a mixture of isoprene and butadiene, wherein 50% or more of the carbon-carbon double bonds in the molecule are hydrogen. This is achieved by providing a hot melt adhesive composition containing an isocyanate prepolymer obtained by reacting an added liquid polymer with an isocyanate compound.

Block copolymer (a) used in the present invention
Is a block composed of an aromatic vinyl monomer,
Styrene, α-methylstyrene, paramethylstyrene,
It is obtained by polymerizing one or more monomers selected from vinyl naphthalene and the like. The monomer constituting the other block of the block copolymer (a) used in the present invention is isoprene. In the present invention, adhesion performance and low-temperature characteristics are improved due to the use of isoprene among conjugated dienes. In this block copolymer, it is necessary that 50% or more of the carbon-carbon double bonds of the block made of isoprene have been hydrogenated (hydrogenated). If the degree of hydrogenation is smaller than the above-mentioned value, there is a problem in the weather resistance, heat resistance and the like at the time of hot melt and the obtained adhesive, which is not preferable.

Further, this block copolymer has a number average molecular weight of 3000.
Preferably it is in the range of 0 to 500,000. The number average molecular weight of the block composed of an aromatic vinyl monomer is preferably in the range of 4,000 to 80,000. The weight ratio of the block composed of the aromatic vinyl monomer to the block composed of isoprene is preferably in the range of the former / latter = 5/95 to 50/50, and the amount of 1,4-bond of the block composed of isoprene is preferably Is preferably 50% or more.

When the number average molecular weight of the block copolymer is smaller than the above range, the cohesive force of the obtained adhesive is not sufficient, while when it is larger than the above range, the viscosity of the obtained adhesive at the time of melting is too high. Unsatisfactory properties are not preferred.

When the number average molecular weight of the block composed of an aromatic vinyl monomer is smaller than the above range, the cohesive force of the obtained adhesive is not sufficient.On the contrary, when the number average molecular weight is larger than the above range, the low temperature characteristics of the obtained adhesive are impaired sufficiently. Unsatisfactory adhesion performance cannot be obtained, which is not preferable.

When the weight ratio of the block composed of the aromatic vinyl monomer and the block composed of isoprene is smaller than 5/95, the obtained adhesive does not have sufficient cohesive force, and the weight ratio is 50/5.
When it is larger than 0, the obtained adhesive has insufficient adhesive performance especially at low temperature, and the viscosity at the time of melting is too high and the operability is not sufficient, which is not preferable.

In addition, the amount of 1,4 bonds in the block consisting of isoprene is 50
%, The resulting adhesive loses flexibility at low temperatures and does not exhibit sufficient adhesive performance, which is not preferable.

Such an unhydrogenated block copolymer is easily obtained by anionic polymerization. Examples of the synthesis method include a method of sequentially polymerizing an aromatic vinyl monomer and isoprene using an alkyl lithium such as butyl lithium as a catalyst, or a method of sequentially polymerizing an aromatic vinyl monomer and isoprene using an alkyl lithium such as butyl lithium as a catalyst. After that, a method of coupling with a coupling agent is exemplified. In these methods, a hydrocarbon solvent such as cyclohexane or toluene is used as the solvent.

Hydrogenation of this block copolymer can also be performed by a known method. Examples of hydrogenation include, for example, a transition metal and an organoaluminum compound, a Ziegler-based catalyst obtained by combining an alkylated product such as an alkaline earth metal or an alkali metal, or a metal such as nickel, palladium, and ruthenium alone or silica or alumina. And a method of reacting with hydrogen using a heterogeneous catalyst supported on a carrier such as diatomaceous earth. As a reaction condition, a method of contacting with hydrogen gas at normal temperature to 200 ° C. and normal pressure to 200 kg / cm ² for 0.1 to 100 hours is exemplified. The hydrogenation reaction is preferably performed in a solution state from the viewpoint of controlling the reaction, and a hydrocarbon solvent such as cyclohexane is used as a reaction solvent.

Next, the liquid polymer used to obtain the isocyanate prepolymer (b) used in the present invention is:
It is necessary that the number average molecular weight is in the range of 700 to 7000. When the number average molecular weight of the liquid polymer is smaller than the above range, the hot melt adhesive obtained using the isocyanate prepolymer does not show good adhesive performance after moisture curing. On the other hand, when the number average molecular weight of the liquid polymer is larger than the above range, the crosslink density of the prepolymer becomes too low, and good high-temperature cohesive force is not exhibited, which is not preferable.

Further, the liquid polymer needs to have 1.5 to 5.0 hydroxyl groups in one molecule. When the number of hydroxyl groups in one molecule is less than 1.5, the adhesive obtained using the isocyanate prepolymer does not exhibit good high-temperature cohesive strength due to insufficient crosslinking density after moisture curing. When the number of hydroxyl groups in one molecule is more than 5.0, the adhesive obtained using the isocyanate prepolymer is not preferable because it does not show good rubber elasticity after moisture curing. The hydroxyl group may be at the terminal of the molecular chain or at the end of the chain, but it is preferable that the hydroxyl group is present at least at the terminal.

Further, in this liquid polymer, it is necessary that 50% or more of the carbon-carbon double bond in the molecule is hydrogenated.
When the degree of hydrogenation is smaller than the above value, the adhesive obtained using the isocyanate prepolymer is not preferable because the heat resistance during hot melt and after bonding is insufficient.

The above liquid polymer is obtained by polymerizing isoprene or a mixture of isoprene and butadiene by a known method and then hydrogenating the mixture.

Polymerization of isoprene or a mixture of isoprene and butadiene is easily performed, for example, by radical polymerization. As a specific example, hydrogen peroxide and an azo compound having a hydroxyl group (for example, 2,2′-azobis [2-methyl-N- (2-hydroxyethyl)-
Propionamide]) or the like as a polymerization initiator. In these methods, an alcohol-based solvent such as ethanol or propanol is used as a solvent. Alternatively, the reaction may be carried out by polymerizing isoprene or a mixture of isoprene and butadiene using an anionic initiator such as a dilithium compound, and reacting the polymer with ethylene oxide, propylene oxide, or the like.

The polymer thus obtained is hydrogenated according to a known method. As an example thereof, for example, nickel, palladium, a metal such as ruthenium alone, or silica, alumina, using a heterogeneous catalyst supported on a carrier such as diatomaceous earth, at normal temperature to 200 ° C, under normal pressure to 200 kg / c
For example, a method of contacting with hydrogen gas of m ² for 0.1 to 100 hours is exemplified. The hydrogenation reaction may be carried out in the presence of a solvent. Examples of the solvent that can be used for this purpose include hydrocarbon solvents such as hexane, ether solvents such as tetrahydrofuran, and alcohol solvents such as ethanol.

In the present invention, an isocyanate compound having two or more isocyanate groups in one molecule is used. Examples of the compound having two isocyanate groups in one molecule include tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate. Examples of the compound having three isocyanate groups in one molecule include triphenyl Examples include methane triisocyanate and polymethylene polyphenyl polyisocyanate. One or two or more isocyanate compounds can be used in combination.

In the present invention, an isocyanate prepolymer obtained by reacting the above liquid polymer with an isocyanate compound is used as a component of the adhesive composition. By using such a prepolymer, the obtained adhesive composition can be cross-linked by water, and can be cross-linked by moisture in the air, which is a so-called moisture-curable composition. The isocyanate compound is usually used at a ratio of isocyanate group / hydroxyl group of 1.05 to 10/1, under an inert gas atmosphere, at a temperature of normal temperature to 150 ° C.
It is reacted for 0.1 to 10 hours. In this reaction, an organic compound containing tin, lead, or the like, or an amine can be used as a catalyst.

When the ratio of isocyanate group / hydroxyl group is smaller than the above range, the obtained adhesive is not sufficiently cured and does not show good high-temperature cohesive strength. On the other hand, when the ratio of isocyanate group / hydroxyl group is larger than the above range, the crosslinking density becomes too high, and the resulting adhesive lacks flexibility, and sufficient adhesive performance cannot be obtained.

The preferred mixing ratio of the block copolymer (a) and the isocyanate prepolymer (b) in the adhesive composition of the present invention is the former / the latter = 95/5 to 5/95.

The adhesive composition of the present invention is within a range that does not impair the purpose thereof, a tackifier resin, an antioxidant, a plasticizer such as process oil, calcium carbonate, a powder filler such as titanium oxide, a glass fiber, an organic reinforcing fiber and the like. May be included.

Tackifying resins are roughly classified into rosin-based, terpene-based and terpene-phenol-based natural resin-based resins, and paraffin-based, coumarone-indene-based, styrene-based, and phenol-based synthetic resin-based resins. Any of these tackifying resins can be used, but hydrogenated rosin, styrene-based resins, and the like are preferably used.

In the present invention, the mixture of the block copolymer (a), the isocyanate prepolymer (b), and other compounding agents used as necessary is usually mixed using a kneader, an extruder, a mixing roll, a Banbury mixer, or the like.
It can be performed in a temperature range of ~ 220 ° C.

The adhesive composition of the present invention, in a molten state paper, cellophane,
Used by coating on a substrate such as polypropylene or polyester. The adhesive composition then forms a cross-linking point of the isocyanate prepolymer component in the adhesive composition due to moisture in the air, etc., resulting in excellent high-temperature cohesive strength,
Develops solvent resistance.

(Examples) Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist.

Reference Example 1 Styrene and isoprene were sequentially added and polymerized using sec-BuLi as a catalyst.
Styrene having physical properties such as styrene / isoprene ratio
An isoprene-styrene triblock copolymer (SIS) was obtained. The molecular weight of each SIS was determined by the GPC method, and the styrene / isoprene ratio and 1,4 bond amount were determined by infrared absorption analysis.

These block copolymers were dissolved in cyclohexane in an autoclave to form a 20% by weight solution. To this solution, 5% by weight of a palladium (5% by weight) -carbon supported catalyst was added to and dispersed in the block copolymer, and the pressure was increased to 50 kg / cm ² with hydrogen to perform a hydrogenation reaction at 50 ° C. After completion of the reaction, the catalyst was separated by filtration and dried under vacuum to obtain a hydrogenated product of block copolymer (hydrogenated SIS). The hydrogenation rate determined by measuring the iodine value was as shown in Table 1.

Reference Example 2 By polymerizing isoprene using hydrogen peroxide as a catalyst, a liquid polymer having physical properties such as a molecular weight shown in Table 2 and the number of hydroxyl groups in one molecule was obtained. The number average molecular weight of the liquid polymer was determined by the VPO method.

These liquid polymers were dissolved in cyclohexane in an autoclave to form a 50% by weight solution. To this solution, a reduced nickel (35% by weight) -diatomaceous earth-supported catalyst was added at 10% by weight with respect to the polymer and dispersed, and 50 kg / cm ² was added with hydrogen.
And a hydrogenation reaction was carried out at 200 ° C. After the completion of the reaction, the catalyst was separated by filtration and dried under vacuum to obtain a hydrogenated product of a liquid polymer. The hydrogenation rate was as shown in Table 2.

Further, the isocyanate compound was reacted with the hydrogenated product under the conditions shown in Table 3 to obtain an isocyanate prepolymer.

Examples 1 to 6 and Comparative Examples 1 to 3 The isocyanate prepolymer, tackifier resin, plasticizer and antioxidant shown in Table 3 were blended with the hydrogenated SIS shown in Table 1 in a mixing ratio shown in Table 4. The mixture was mixed at 200 ° C. for 20 minutes using a melting and mixing tank to obtain an adhesive composition. This composition was coated on a commercially available polyester film having a thickness of 50 μm with a coating thickness of 50 μm at 150 ° C. using a coater to form an adhesive tape, adhered to various substrates, and allowed to stand at room temperature and humidity for 3 days. The moisture-absorbing curing of the isocyanate prepolymer was completed, and the performance was evaluated by the following method. Table 4 shows the results.

(1) Holding force Affixed in an area of 25 mm x 25 mm, a 1 kg load was applied thereto, left in an atmosphere at a temperature of 25 ° C or 60 ° C, and measured for a drop time or a deviation distance.

(2) Adhesive force The above adhesive tape was adhered to a stainless steel or polyethylene sheet having a thickness of 1 mm, and a 180 ° peel force was measured.

(3) Solvent resistance The above adhesive tape is pressure-bonded to a 1mm long stainless steel plate,
According to a method of observing the state after immersion in various solvents.

According to Table 4, the pressure-sensitive adhesive tape performance of the adhesive composition of the present invention shown in Examples was 60 ° C. lower than that of the adhesive composition containing no isocyanate prepolymer shown in Comparative Examples. It can be seen that the high-temperature cohesive force seen in the holding power and the solvent resistance seen in trichloroethane and toluene are excellent.

Reference Example 3 Styrene-butadiene-styrene triblock copolymer (SBS) having the physical properties such as the molecular weight and styrene / butadiene shown in Table 5 by sequentially polymerizing styrene, butadiene, and styrene in the same manner as in Reference Example 1. I got The obtained SBS was hydrogenated in the same manner as in Reference Example 1 to obtain a hydrogenated SBS (SEBS). The molecular weights of SBS and SEBS were determined by the GPC method, the styrene / butadiene ratio and the amount of 1,4-bond were determined by an infrared absorption method, and the hydrogenation ratio was determined by iodine value measurement.

Comparative Examples 4 and 5 The isocyanate prepolymer, tackifier resin, plasticizer and antioxidant shown in Table 3 were blended with the SBS and SEBS obtained in Reference Example 3 in the mixing ratios shown in Table 6, and An adhesive composition was obtained in the same manner. Using the obtained adhesive composition, a pressure-sensitive adhesive tape was prepared in the same manner as in Example 1 and bonded to various substrates.
After allowing to stand for a day, the moisture-absorbing curing of the isocyanate prepolymer was completed, and the performance was evaluated in the same manner as in Example 1.
Table 6 shows the results.

(Effect of the Invention) According to the present invention, coating with hot melt is possible,
A hot melt adhesive composition having improved cohesion at high temperatures and excellent solvent resistance is provided.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-64-54089 (JP, A) JP-A-63-120785 (JP, A) JP-A-1-284577 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) C09J 153/00-153/02 C09J 175/00-175/16

Claims (1)

(57) [Claims] (A) a) two or more blocks composed of an aromatic vinyl monomer and one block composed of isoprene;
And b) a liquid isoprene or isoprene having 1.5 to 5.0 hydroxyl groups in one molecule, wherein at least 50% of carbon-carbon double bonds of the isoprene block are hydrogenated. And a butadiene mixture having a number average molecular weight of 700 to 7000, obtained by reacting an isocyanate compound with a liquid polymer in which at least 50% of carbon-carbon double bonds in the molecule have been hydrogenated. A hot melt adhesive composition comprising the isocyanate prepolymer obtained.