JPS6312109B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an adhesive composition based on a modified liquid isoprene rubber. In recent years, in the adhesive industry, from the standpoint of environmental pollution and energy conservation, emphasis has been placed on technology that reduces or eliminates solvents. A great deal of effort has been made to develop adhesive technology using this method, and the establishment of this technology is strongly desired. Such a technology cannot be solved by improving manufacturing technology alone, but rather should be solved by considering the raw materials for the adhesive. One approach from this point of view is to use a modified liquid polyisoprene rubber that is made by adding maleic anhydride or maleic ester to a liquid polyisoprene rubber with a specific structure, and then add tack to the liquid polyisoprene rubber. By adding resins and various crosslinking agents (e.g., metal crosslinking agents and epoxy crosslinking agents), it is expected that adhesives that are solvent-free to highly concentrated and have excellent adhesive performance can be obtained. However, for example, in the production of adhesive tapes using the same, various troubles occur, and in the end, it may not be possible to obtain an adhesive with excellent adhesive performance. In other words, in order to produce an adhesive tape with low production cost and easy process control, the adhesive composition must be sufficiently thickened and gelled in a short period of time before being applied. A sufficient crosslinking rate is required to reach a certain level of crosslinking rate by a heat treatment of at most 10 minutes after coating, but in many cases several minutes, and this pot life and a sufficient crosslinking rate are required. Since crosslinking speed and crosslinking speed are contradictory properties, a strict balance between the two properties is required for an industrially easier manufacturing method of adhesive tape. Although liquid polyisoprene rubber combined with a metal crosslinking agent has a sufficient crosslinking speed, its pot life is extremely short, and that of a combination of an epoxy crosslinking agent does not have a sufficient pot life. However, the crosslinking speed was too slow to be practical. In view of the problems of the prior art, the present inventors have developed a solvent-free or high-concentration adhesive that is industrially advantageous and has excellent performance as an adhesive, especially a pressure-sensitive adhesive. As a result of extensive research into methods for producing adhesives, we have developed an adhesive composition whose main component is a mixture of liquid rubber, tackifier resin, and polyisocyanate compound.
The liquid rubber has a molecular weight of 15,000 to 100,000,
Liquid isoprene rubber (especially preferably liquid isoprene homopolymer rubber) with a vinyl bond content of 25% or less and N-(hydroxyhydrocarbyl)
- Modified liquid isoprene rubber (a) to which maleimide (particularly preferably N-(hydroxyalkyl)-maleimide) has been added, and maleic acid hydroxyhydrocarbyl ester (particularly preferably maleic acid) to the liquid isoprene rubber. At least one hydroxyl group-containing liquid isoprene rubber selected from the group consisting of (b) a modified liquid isoprene rubber to which N-(hydroxyalkyl)-maleimide is added (particularly preferably a hydroxyl group-containing rubber to which N-(hydroxyalkyl)-maleimide is added) The inventors have discovered that the desired objective can be achieved by using a modified liquid isoprene rubber, and have completed the present invention. Especially glue mixture at 70-150℃ for 30 seconds ~
It has been found that a pressure-sensitive adhesive composition that is excellent in terms of manufacturing method and performance can be obtained by heat treatment for 10 minutes. The hydroxyl group-containing liquid isoprene rubber used in the present invention ultimately has at least one hydroxyl group selected from the group consisting of N-(hydroxyhydrocarbyl)-maleimide and maleic acid hydroxyhydrocarbyl ester. It means a modified liquid isoprene rubber with a maleic anhydride derivative added thereto. Here, liquid isoprene rubber is defined as having a molecular weight of
15000 to 100000 and vinyl bond amount is 25%
The following is an isoprene homopolymer or a copolymer of isoprene and butadiene. The copolymer may be a random copolymer or a block copolymer, but it is necessary to contain at least 20% by weight of isoprene. If the molecular weight is smaller than the above range, the adhesive composition will lack cohesive force, and if it exceeds the above range, the viscosity of the system will become too high when preparing a hydroxyl group-containing liquid isoprene rubber. Furthermore, the resulting hydroxyl group-containing liquid isoprene rubber has poor fluidity and poor processability, and furthermore, when made into an adhesive composition, its tackiness is low. From this point of view, the molecular weight is 20,000 ~
Preferably in the 75000 range. Note that molecular weight here means viscosity average molecular weight (Mv), and at 30℃
It is determined using the intrinsic viscosity ([η]) measured in a toluene solution of [η] = 1.21×10 ^-4 Mv ^0.77 . Furthermore, the amount of vinyl bonds in liquid isoprene rubber, as determined by infrared absorption spectrum analysis, is 25% or less. The amount is 25
%, when preparing a hydroxyl group-containing liquid isoprene rubber, gelation tends to occur, especially during the maleation reaction, and the resulting crosslinked product of the hydroxyl group-containing liquid isoprene rubber with the polyisocyanate compound has poor rubber elasticity. This is not preferable in terms of the adhesive performance of the adhesive composition, especially the adhesive performance at low temperatures. From this point of view, the vinyl bond amount is
It is desirable that it be 20% or less. Furthermore, in the case of a copolymer, it is necessary that the amount of isoprene is 20% by weight or more. If there is too little isoprene, that is, if there is too much butadiene, gelation tends to occur in the maleation reaction when preparing a hydroxyl group-containing liquid isoprene-butadiene copolymer, making it difficult to obtain the desired modified copolymer. Moreover, the adhesive performance of the adhesive composition finally obtained will be low. From this point of view, it is desirable that the copolymer contains 60% by weight or more of isoprene. This particular liquid isoprene rubber is
Although it can be produced by various methods, it is preferably produced by an anionic polymerization method. Among these, living polymerization using a lithium-based catalyst such as metallic lithium or organic lithium such as methyllithium, propyllithium, butyllithium, or distyrenyllithium is effective for easily controlling the molecular weight and producing a microstructure with a small amount of vinyl bonds. Therefore, it is also easy to produce a copolymer, so it is preferably employed. The polymerization solvent is preferably used because it is easy to control the polymerization, and n-butane, isopentane,
An inert hydrocarbon such as n-hexane, n-heptane, benzene, toluene or xylene is used, but there is no problem even if it is not used depending on the case. The method for producing a hydroxyl group-containing liquid isoprene rubber from this liquid isoprene rubber is as follows: (1) Maleic anhydride is added to the liquid isoprene rubber (that is, a maleation reaction is carried out), and the resulting maleic anhydride is added to the liquid isoprene rubber. A modified liquid isoprene rubber was reacted with an amino alcohol represented by the general formula H ₂ N—R—OH (where R represents an alkyl group, an aryl group, or an aralkyl group) (that is, an amidation reaction was performed). )
(2) adding maleic anhydride or a maleic anhydride derivative such as maleic acid, maleic acid monoester or maleic acid monoamide to the liquid isoprene rubber ( The maleic anhydride or its derivative-modified liquid isoprene rubber obtained is reacted with a compound containing an oxirane ring in the molecule (that is, an esterification reaction is performed). Although it is possible to directly add N-(hydroxyhydrocarbyl)-maleimide or hydroxyhydrocarbyl maleate to liquid isoprene rubber, it is not practical due to its reactivity and economical efficiency. The reaction of adding maleic anhydride or its derivative to liquid isoprene rubber in (1) and (2) above, that is, the maleation reaction, can be carried out by various known methods. Preferred methods include mixing and stirring maleic anhydride or its derivatives under heating, or reacting liquid isoprene rubber with maleic anhydride or its derivatives in a solution. In the reaction, a catalyst such as a peroxide or an azo compound can be used, and an antigelation agent such as a copper compound or acetylacetone can also be present. Solvents used include inert hydrocarbons such as hexane, benzene or toluene. The reaction temperature is
The temperature is preferably 100 to 250°C, and the reaction time is generally 1 to 20 hours. The amount of maleic anhydride etc. to be added is closely related to the degree of modification of the hydroxyl group-containing liquid isoprene rubber, but it may be in the range of 0.35 to 10.5 mol per 100 monomer units of the liquid isoprene rubber. preferable. If the amount added is too small, the crosslinking efficiency with the polyisocyanate compound used as a crosslinking agent will be low, and adhesive performance will not be achieved when used as an adhesive composition. On the other hand, if the amount is too large, the viscosity will be high during the maleic reaction. This is not preferable because it becomes too hard, or even becomes hard and resin-like, resulting in a loss of fluidity. From this point of view, especially when used as an adhesive (pressure-sensitive adhesive), the amount added is preferably 0.5 to 5 moles from the viewpoint of various required performances. The amidation reaction and imidization reaction subsequent to the maleation reaction in (1) above are carried out by adding an amino alcohol to maleic anhydride-modified liquid isoprene rubber, performing a semi-amidation reaction, and then dehydrating it. . The amino alcohol used here is a compound represented by the general formula H ₂ N—R—OH (wherein R represents an alkyl group, an aryl group, or an aralkyl group), and typical examples thereof include is ethanolamine, 2-aminopropan-1-ol (isopropanolamine),
1-Aminobutan-2-ol, 2-aminobutan-1-ol, 3-aminobutan-1-ol, 1-amino-2-methylpropan-2-ol, 1-aminopentan-4-ol or 1-
Examples include aminoalkyl alcohols such as aminopentan-5-ol, aminoaralkyl alcohols such as aminophenol, aminocresol, aminoxylenol, or aminonaphthol. Among them, aminoalkyl alcohols such as ethanolamine and isopropanolamine are preferably used. Amino alcohol easily reacts with the maleic anhydride group added to liquid isoprene rubber, but it is necessary to pay attention to the reaction temperature in the semi-amidation reaction. At this time, if the reaction temperature is too high, gelation reactions and other undesirable side reactions occur. Therefore, it is necessary to keep the reaction temperature low until the second half of the amidation reaction after addition of the amino alcohol is completed. The reaction temperature is room temperature to 130°C, preferably 50 to 100°C.
is desirable. After the half-amidation reaction is completed, the half-amide is imidized by performing a dehydration reaction.
At this time, the reaction temperature should be 150-220°C. When carrying out the dehydration reaction, the reaction may be carried out in the presence of a dehydrating agent such as sulfuric acid, phosphoric acid or phosphorus pentoxide to accelerate the reaction, or the reaction may be carried out while distilling the water produced under reduced pressure. There is no harm in doing so. In addition, the reaction of the above (2) maleic anhydride or its derivative modified liquid isoprene rubber with a compound containing an oxirane ring in the molecule is carried out by mixing and heating the two, which facilitates the esterification reaction. happens. The oxirane ring-containing compounds used here include alkyl oxides such as ethylene oxide, propylene oxide, 1-butene oxide or cyclohexene oxide, butyl glycidyl ether, butyl glycidyl ester,
or phenyl glycidyl ether. Among them, alkyl oxides such as ethylene oxide are preferably used. In this reaction, the system may be diluted with a solvent in order to lower the viscosity of the system and facilitate the reaction. Examples of solvents that can be used include aliphatic and alicyclic hydrocarbons such as hexane, heptane or cyclohexane, aromatic hydrocarbons such as benzene or toluene, halogenated hydrocarbons such as chloroform or carbon tetrachloride, alcohols or ethers. They can be used alone or in combination of two or more. In addition, to increase the reaction rate, pyridine,
Amine compounds such as quinoline, 2-methylimidazole, 2-ethyl-4-methylimidazole, tributylamine or tris(dimethylamino)phenol are used as catalysts. The reaction temperature at this time is room temperature to 200°C, preferably 50 to 150°C, and the reaction is carried out for 0.5 to 20 hours, preferably 1 to 10 hours. Oxirane-containing compounds have a concentration of 1.0 to 2.0 per added maleic anhydride group, etc.
Used within the equivalent range. After the reaction is completed, the product is
The solvent, catalyst, unreacted oxirane ring-containing compound, etc. are removed by a conventional method, and the product is used. The product obtained in this way is a product in which hydroxyhydrocarbyl maleic acid ester is added to liquid isoprene rubber. It may be esterified with a hydrocarbon compound. Typical tackifier resins used in the present invention include terpene resins, terpene phenol resins, rosin resins, aromatic hydrocarbon petroleum resins, alicyclic hydrocarbon petroleum resins, and aliphatic hydrocarbon resins. Examples include petroleum resins, coumaron indene resins, and phenolic resins. These tackifier resins may be used alone or in combination of two or more. The amount used is in the range of 5 to 250 parts by weight, preferably 20 to 60 parts by weight, per 100 parts by weight of the hydroxyl group-containing liquid isoprene rubber. If the amount used is too small, it will not be possible to obtain an adhesive composition with sufficient tack and adhesive strength, while if it is too large, an adhesive composition with sufficient cohesive strength will not be obtained. In the present invention, a polyisocyanate compound is used as a crosslinking agent for the hydroxyl group-containing liquid isoprene rubber. What is this polyisocyanate compound?
It is an isocyanate compound containing at least two or more isocyanate groups in the molecule, an example of which is 2,4-tolylene diisocyanate (TDI).
2,6-tolylene diisocyanate (TDI), diphenylmethane-4,4'-diisocyanate (MDI), P-phenylene diisocyanate, 1,
5-naphthalene diisocyanate, hexamethylene diisocyanate, triphenylmethane triisocyanate, triisocyanate phenyl thiophosphate, polymethylene polyphenyl polyisocyanate, MDI derivatives such as polymeric MDI and carbodiimide modified MDI, or hydrogenated
Examples include TDI derivatives such as TDI and trimethylolpropane-TDI adduct. In addition, blocked isocyanates blocked with various blocking agents such as phenol and oxime may also be used. The amount of polyisocyanate compound used is expressed relative to the amount of isocyanate groups in the hydroxyl group-containing liquid isoprene rubber.
It is in the range of 0.5 to 3 equivalents, more preferably 0.7 to 2 equivalents. If the amount of the polyisocyanate compound used is too small, an adhesive composition with sufficient cohesive force cannot be obtained, and on the other hand, if it is too large, an adhesive composition with sufficient adhesive strength and adhesive force cannot be obtained. Incidentally, in order to promote the reaction between the hydroxyl group and the isocyanate, a catalyst such as a metal compound such as dioctyltin laurede or dibutyltin laurate, an amine compound, or an organic acid may be used as necessary. In the adhesive composition of the present invention, in addition to the essential components of hydroxyl group-containing liquid isoprene rubber, polyisocyanate, and tackifying resin, if necessary, antioxidants, fillers such as calcium carbonate, silica, or clay, Softeners such as process oil and dioctyl phthalate, medicinal ingredients used in adhesive plasters, and the like can be added. Further, there is no problem in adding a liquid polymer such as unmodified liquid polyisoprene rubber or liquid polyptadiene rubber. The adhesive composition of the present invention is produced, for example, in the following manner. In other words, it may be produced by simultaneously mixing a hydroxyl group-containing liquid isoprene rubber, a tackifier resin, a polyisocyanate compound, and other ingredients at an appropriate temperature, but generally it is made by mixing a hydroxyl group-containing liquid isoprene rubber, a tackifier resin, and other ingredients simultaneously. A method in which a polyisocyanate compound as a crosslinking agent is added and mixed after mixing and other ingredients, or a method in which a composition based on a hydroxyl group-containing liquid isoprene rubber and a composition mainly based on a polyisocyanate compound as a crosslinking agent is used. A method in which both compositions are prepared separately and then mixed prior to coating on a substrate is preferred because it has the advantage that crosslinking can be appropriately controlled. During mixing, work must be carried out at an appropriate temperature and atmosphere depending on the softening temperature of the tackifying resin used, the viscosity of the hydroxyl group-containing liquid isoprene rubber, and the viscosity of the composition required after mixing. However, heat treatment may be performed at an appropriate temperature to speed up the crosslinking rate after coating the substrate. At this time, the industrially advantageous temperature condition is a temperature that does not damage the base material, specifically 70°C.
The temperature is preferably ~150℃, and the heat treatment time is 30 seconds to 10 minutes, preferably 30 minutes, considering production efficiency.
A period of seconds to 5 minutes is appropriate. Although it is most desirable not to use any solvent in preparing these mixed compositions, small amounts of solvent may be used in some cases. For the above-mentioned mixing, a general mixing tank with an agitator, a kneader, a Banbury mixer, an open roll, or the like is used. Typical practical examples of the adhesive composition of the present invention include adhesive tapes such as craft tape, cellophane tape, cloth tape, washi tape, and film tape, adhesive plasters, and adhesive labels. Further, the adhesive composition can be sufficiently used as an adhesive without coating the tape base material. EXAMPLES The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to these Examples in any way. Note that "parts" in Examples and Comparative Examples mean "parts by weight" unless otherwise specified. Example 1 and Comparative Examples 1 to 4 Liquid polyisoprene rubber with a molecular weight of 47,000 and a vinyl bond content of 6% (cis-1,4 bond content of 82%) (however, M _W /M _N is 2.0) .Kuraprene LIR-50) manufactured by Kuraray Soprene Chemical Co., Ltd.
100 parts of maleic anhydride and 1.8 parts of maleic anhydride were heated at 180°C for 5 hours to form a maleic anhydride-modified liquid polyisoprene rubber (hereinafter referred to as maleic anhydride-modified liquid polyisoprene rubber) in which 1.3 moles of maleic anhydride was added per 100 isoprene monomers of the liquid polyisoprene rubber. , MAn-LIR(A)) was obtained. For comparison, this maleic anhydride-modified liquid polyisoprene rubber MAn-LIR (A) was reacted with methanol to produce a maleic acid (mono)ester-modified liquid polyisoprene rubber (hereinafter referred to as E-MAn-LIR (B)).
It is abbreviated as. ) was prepared. On the other hand, to the maleic anhydride-modified liquid polyisoprene rubber MAn-LIR (A), ethanolamine was added in an amount twice as much as the added maleic anhydride to cause a semi-amidation reaction, and then The temperature was raised to 160°C and a dehydration reaction was carried out under reduced pressure to form a hydroxyl group-containing polyisoprene rubber (hereinafter referred to as I-MAn) to which N-(2-hydroxyethyl)-maleimide having an imide ring and a hydroxyl group was added.
- Abbreviated as LIR(C). ) was prepared. According to infrared absorption spectrum analysis, all of the added maleic anhydride groups in this hydroxyl group-containing polyisoprene rubber were imidized. Three types of modified liquid polyisoprene rubbers obtained in this way MAn-LIR (A), E-MAn-LIR (B),
and I-MAn-LIR (C) to prepare the adhesive compositions shown in Table 1. In preparing the adhesive composition, components other than the crosslinking agent, that is, modified liquid polyisoprene rubber, tackifying resin, or other compounded components, and the crosslinking agent component are separately mixed in a high concentration toluene solution (solid content concentration). 90%) and mixed the two. A part of the adhesive composition thus obtained was made into an adhesive tape, and its adhesive strength and cohesive force were evaluated, and the other part was used to evaluate its pot life characteristics and crosslinking rate characteristics. In addition, the evaluation of the pot life characteristics of the adhesive paste composition is as follows:
When the adhesive composition is left to stand at room temperature for 15 minutes after adding and mixing the crosslinking agent, the adhesive composition significantly thickens and becomes impossible to apply, making it unusable for practical use (No. 1)
(represented by an x mark in the table) or one with a relatively small rate of thickening and easy to coat (represented by an ○ mark in Table 1).
The evaluation of the crosslinking speed characteristics of adhesive compositions was conducted when the cohesive force level was 60 minutes or more after heat treatment with hot air at 90°C for 3 minutes (represented by a circle in Table 1).
or the cohesive force level was 20 minutes or less (represented by an x in Table 1). The adhesive strength of the adhesive tape was determined by the J. Dow rolling ball tack method (measurement temperature: 25°C). ball
The higher the number, the greater the adhesive force. In addition, the cohesive force of adhesive tape is 15% when adhesive tape is applied to a stainless steel plate.
Evaluation was carried out by measuring the time until it falls when an area of mm x 12 mm is pasted and a load of 1 kg is applied (at a temperature of 25°C).

[Table] As can be seen from this table, the adhesive composition of formulation a, which is mainly composed of hydroxyl group-containing liquid polyisoprene rubber to which N-(2-hydroxyethyl)maleimide has been added, has good pot life characteristics. It has a good balance with the crosslinking rate characteristics, and the adhesive tape obtained from it has adhesive strength and cohesive strength within a range suitable for practical use. The adhesive compositions b, c, d, and e are unbalanced in pot life characteristics and crosslinking speed of the adhesive composition, and the adhesive tapes obtained therefrom cannot be put to practical use. be. Example 2 By alternately polymerizing isoprene monomer and butadiene monomer using butyllithium as a catalyst, the molecular weight was 41000 and the vinyl bond content was 12%.
The weight composition ratio of isoprene/butadiene is 70/30.
A liquid isoprene-butadiene block copolymer (hereinafter abbreviated as liquid rubber LIBR (D)) in which the arrangement of polyisoprene and polybutadiene is (polyisoprene-polybutadiene) ₃ was prepared. 1.2 parts of maleic anhydride was added to 100 parts of this liquid rubber LIBR (D) and subjected to a maleation reaction. Modified liquid rubber (hereinafter referred to as
MAn-LIBR(E)) was prepared. Next, maleic anhydride modified liquid rubber MAn-
1.2 times the mole of maleic anhydride to which isopropanolamine was added was added to LIBR (D) maintained at 100°C, subjected to a half-amidation reaction, and then heated to 160°C and dehydrated under reduced pressure. Hydroxyl group-containing liquid rubber (hereinafter referred to as I-
MAn-LIR(E)) was prepared. The formation of imide rings was confirmed by infrared absorption spectrum analysis. Hydroxyl group-containing liquid rubber I obtained in this way
-MAn- 100 parts of LIBR(E), 40 parts of terpene resin (YSPX800 manufactured by Yasushi Oil Chemical Co., Ltd.) and 0.2 parts of antioxidant were mixed at 130°C to prepare a homogeneous mixture. An adhesive composition was prepared by adding an isocyanate crosslinking agent solution containing 1.1 parts of tolylene diisocyanate and 0.1 part of dibutyltin laurate to this mixture while maintaining the mixture at 40°C. This adhesive composition had sufficient coating properties even 15 minutes after preparation, and was applied to a polyester adhesive tape base material and heat-treated at 120°C for 2 minutes to form an adhesive tape. The adhesive force and cohesive force were measured in the same manner as above, and the adhesive force was 120 minutes or more for Ball No. 18, indicating that it had excellent adhesive performance. On the other hand, an adhesive composition in which a maleic anhydride-modified liquid rubber MAn-LIBR (D) is used in place of the hydroxyl group-containing liquid rubber I-MAn-LIBR (E), An adhesive composition prepared by adding 15 parts of calcium-cured rosin to the composition was investigated for its pot life characteristics and the performance of the adhesive tape when made into an adhesive tape.
None of the adhesive tapes were satisfactory in terms of pot life characteristics and performance of the adhesive tape. Example 3 Modified polyisoprene rubber E-MAn-LIR to which maleic acid monoester was added used in Example 1
By adding propylene oxide to the toluene solution of (B) using tris(dimethyl)phenol as a catalyst and reacting at 130°C for 5 hours,
Hydroxyl group-containing liquid polyisoprene rubber (hereinafter referred to as OH
-MAn-LIR(F)) was obtained. The introduction of hydroxyl groups was confirmed by infrared absorption spectrum analysis. A petroleum resin (Quinton U-185 manufactured by Nippon Zeon Co., Ltd.) was added to 100 parts of the hydroxyl group-containing liquid polyisoprene rubber OH-MAn-LIR (F) thus obtained.
45 parts, 3 parts of process oil, 2 parts of antioxidant and 15 parts of hexane were added to prepare a homogeneous mixture. To this mixture, 1.3 parts of tolylene diisocyanate and 0.2 parts of dibutyltin laurate were added and mixed to prepare an adhesive composition. When the performance of this adhesive composition was investigated, it was found that the pot life was sufficient and it was easy to apply even 30 minutes after preparation. In addition, a cellophane-based adhesive tape was prepared by coating it on cellophane paper and heat-treating it at 100°C for 5 hours, and its performance was evaluated in the same manner as in Example 1. It was ball tack No. 18. It had adhesive strength and creep resistance (cohesive strength) at 25°C for 120 minutes or more, and had performance equivalent to or better than commercially available solution-based adhesive tapes.

Claims (1)

[Scope of Claims] 1. An adhesive composition containing a mixture consisting of a liquid rubber, a tackifying resin, and a polyisocyanate compound as a main component, wherein the liquid rubber has a molecular weight of
Modified liquid isoprene rubber (a) in which N-(hydroxyhydrocarbyl)-maleimide is added to a liquid isoprene rubber having a molecular weight of 15,000 to 100,000 and a vinyl bond content of 25% or less; An adhesive composition comprising at least one hydroxyl group-containing liquid isoprene rubber selected from the group consisting of (b) a modified liquid isoprene rubber to which an acid hydroxy hydrocarbyl ester has been added. 2. The adhesive composition according to claim 1, wherein the adhesive composition is an adhesive obtained by heat-treating the mixture at 70 to 150°C for 30 seconds to 10 minutes.