JPH0456072B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field The present invention is a cross-linked pressure-sensitive adhesive that uses a functional isoprene oligomer at both ends and is cross-linked through both ends of the molecular chain via a polyfunctional isocyanate compound, and has excellent rough surface adhesion. and its adhesive member. Background of the Invention Cross-linked adhesives are made by dissolving a base polymer such as natural rubber or styrene-butadiene copolymer and a cross-linking material in a solvent. A drying process is required. As a result, there were problems such as poor production efficiency, environmental health and pollution problems, and the need for advanced safety measures against fire. As a result, a cross-linked pressure-sensitive adhesive that can be applied without solvent has been desired from the viewpoint of improved productivity, non-pollution, and fire safety. Such a cross-linked pressure-sensitive adhesive can be applied without using water or a solvent, and a cross-linked layer is formed by simply heat-treating the coated layer, which has the advantage of achieving energy savings. Conventional techniques and issues Conventionally, solvent-free cross-linked adhesives include:
It is known that a conjugated diene oligomer made of polybutadiene, which has functional groups at random positions on the molecular chain and is liquid at room temperature, is blended with a crosslinking agent and a tackifying resin (Japanese Patent Laid-Open No. 51-61537, same
51-69538). However, there has been a problem in that the adhesive layer obtained by crosslinking the crosslinked adhesive has poor adhesion to rough-surfaced adherends such as cardboard and plywood. Such recessiveness becomes particularly noticeable when used at low temperatures. Additionally, when sealing a cardboard box, there was a problem that the lid would peel off over time due to the repulsive force of the flap and the lid would open. Means for Solving the Problems The present inventor has conducted extensive research in order to overcome the above problems and develop a crosslinked adhesive that can be applied without solvent, has excellent rough surface adhesion, and has excellent stress relaxation properties. As a result of repeated efforts, the inventors discovered that the objective can be achieved by using a functional isoprene oligomer at both ends, which can be crosslinked through both ends of the molecular chain, leading to the present invention. That is, the present invention provides an isoprene-based oligomer having an average of 1.5 to 2 functional groups per molecule that can react with an isocyanate group, and having the functional groups only at the ends of the molecular chain, and A cross-linked adhesive characterized by comprising a polyfunctional isocyanate compound and a tackifying resin as components, and a double-terminally functional isoprene oligomer cross-linked through the ends of the molecular chain via the polyfunctional isocyanate compound. The present invention provides an adhesive member having a crosslinked adhesive layer made of the above-mentioned crosslinked adhesive on one or both sides of a supporting base material. Function: A double-end functional type isoprene oligomer, which has an average of 1.5 to 2 functional groups per molecule only at the ends of the molecular chain, is cross-linked through both ends or one end of the molecular chain, and is The formation of crosslinking points is avoided, and loose crosslinks with large distances between crosslinks are formed. In those that have a functional group in the middle of the molecular chain, crosslinking points are formed in the middle of the molecular chain, resulting in dense crosslinks with small distances between crosslinks, forming a highly modulus network structure with a small molecular weight between crosslinking points. That will happen. An isoprene oligomer crosslinked through both ends of its molecular chain via a polyfunctional isocyanate compound has a molecular chain that is efficiently extended and forms a molecular weight region that has a modulus etc. that is preferable as a base polymer for an adhesive. As a result, the adhesive layer made of such a base polymer has a suitable modulus,
Even on rough surfaces, a sufficient adhesive area can be formed with a light pressure force. In addition, it exhibits excellent stress relaxation properties due to cohesive failure shearing, has appropriate cohesive force, and has excellent retention properties after adhesion to rough surfaces. Examples of Constituent Elements of the Invention The isoprene oligomer used in the present invention has an average of 1.5 to 2, particularly 1.8 to 2, functional groups capable of reacting with isocyanate groups per molecule, and It is a functional type with both terminals only at the ends of the molecular chain. Therefore, in a molecular group consisting of isoprene oligomer molecules that have one functional group at each end of the molecular chain and no functional group in the middle of the molecular chain, a functional group may be added at one end of the molecular chain. Although there are isoprene-based oligomer molecules having the following, there are substantially no isoprene-based oligomer molecules having other molecular structures. The ideal in the present invention is a molecular group consisting only of isoprene oligomer molecules having one functional group at each end of the molecular chain and no functional group in the middle of the molecular chain. The aforementioned isoprene-based oligomers having an average number of functional groups per molecule of less than 1.5 have a poor molecular chain extension rate due to crosslinking, and when crosslinked via a polyfunctional isocyanate compound to form a crosslinked adhesive layer, the cohesive force is low. become scarce. The functional group capable of reacting with an isocyanate group in the isoprene oligomer may be any known functional group. Generally, hydroxyl group, carboxyl group,
It consists of an amino group, etc., and a hydroxyl group is preferable. In view of the properties of the crosslinked adhesive layer to be formed, particularly in terms of suppressing performance deterioration at low temperatures, the isoprene-based oligomer with functionalized terminals at both ends is preferably one having a vinyl bond of 30% or less, especially 20% or less. . From the viewpoint of solvent-free coating, an isoprene-based oligomer that is liquid at room temperature and functionalized at both ends is used. Among these, those having a number average molecular weight of 5,000 to 100,000 are preferably used. If the number average molecular weight is less than 5,000, even if crosslinked, the molecular weight range that has a modulus etc. suitable for the base polymer will not be reached, and the resulting crosslinked pressure-sensitive adhesive layer will likely lack cohesive strength. On the other hand, 10
If it exceeds 10,000, the resulting adhesive will have a high viscosity, making it unsuitable for solvent-free coating. In the present invention, the number average molecular weight is based on polystyrene conversion using gel permeation chromatography. An example of a method for preparing isoprene-based oligomers with functional groups at both ends is to anionically polymerize isoprene monomers in the presence of a dilithium catalyst, and then react with a functional group-introducing agent such as alkylene oxide or carbon dioxide to form hydroxyl groups at both ends. Examples include a method of introducing a functional group capable of reacting with an isocyanate group such as a carboxyl group or a carboxyl group. Another example is a method of polymerizing isoprene monomers using a radical catalyst having a functional group capable of reacting with an isocyanate group. Examples of the dilithium catalysts mentioned above include reaction products of metallic lithium and aromatic compounds (Japanese Patent Publication No.
26592, 39-11090), and a reaction product of alkyllithium and divinylbenzene (US Pat. No. 3,862,251). Examples of radical catalysts having functional groups such as hydroxyl groups and carboxyl groups include hydrogen peroxide, 2,2'-azobis-[2-methyl-N-(2-hydroxyethyl)-propionamide], 4,4' -Azobis-
Examples include peroxides such as (4-cyanovaleric acid) and azo compounds. The amount of catalyst used is appropriately determined depending on the desired molecular weight. Generally, 0.1 to 50 parts by weight are used per 100 parts by weight of isoprene monomer. When preparing isoprene oligomers, it is preferable to use a solvent from the viewpoint of reaction control, but the reaction can also be carried out without using a solvent. The solvent used is inert towards the catalyst. In the case of anionic polymerization, aliphatic, aromatic, alicyclic, and other hydrocarbons are used. In the case of radical polymerization, in addition to the above-mentioned hydrocarbons, alcohols, ethers, etc. are used, and the polymerization conditions are generally -20 to 150°C for 0.1 to 30 hours. The cross-linked pressure-sensitive adhesive of the present invention is an isoprene-based oligomer having a functional type at both ends, which can be cross-linked with a polyfunctional isocyanate compound. As the polyfunctional isocyanate compound, it is preferable to use a difunctional one in a composition of 80% by weight or more, especially 90% by weight or more. In a composition in which trifunctionality or higher is 20% by weight or more, the formation of a network structure is prioritized over the extension of molecular chains, resulting in a small molecular weight between crosslinking points, and the resulting crosslinked adhesive layer has a low crosslink density. Excessive amount tends to result in poor adhesion. Typical examples of polyfunctional isocyanate compounds that can be used include tolylene diisocyanate, diphenylmethane diisocyanate, and polymers thereof;
Isophorone diisocyanate, hexamethylene diisocyanate, o-tolylene diisocyanate, tylphenylmethane triisocyanate, tris-(p-isocyanate phenyl) thiophosphite, adduct of trimethylolpropane and tolylene diisocyanate, trimethylolpropane and xylylene diisocyanate Examples include single-body compounds such as adducts of , and prepolymer compounds. The amount of the polyfunctional isocyanate compound to be used is suitably 0.6 to 1.5 equivalents, particularly 0.8 to 1.1 equivalents, based on the functional groups that can react with the isocyanate groups in the crosslinked adhesive. If the amount used is less than 0.6 equivalents, crosslinking will be insufficient, and if it exceeds 1.5 equivalents, there will be excessive crosslinking, which is unfavorable in terms of the properties of the resulting crosslinked pressure-sensitive adhesive layer. Examples of the functional groups in the crosslinked adhesive include those in isoprene oligomers and crosslinking aids used as necessary. In the crosslinked pressure-sensitive adhesive of the present invention, a known catalyst such as a tertiary amine or an organic tin compound may be used in combination to promote crosslinking, if necessary. Also,
A crosslinking aid may be added if necessary. As the crosslinking aid, one having two or more functional groups capable of reacting with an isocyanate group in its molecule is used. Examples include polyols such as glycerin, polyether polyols, polyester polyols,
Examples include diene oligomers other than isoprene oligomers with functional types at both ends. The crosslinked pressure-sensitive adhesive of the present invention uses one or more tackifying resins in combination to impart or improve tackiness. The tackifying resin used may be any resin that has adhesive strength. Representative examples include terpene resins (including phenolic and aromatic resins), coumaron indene resins, styrene resins, petroleum resins,
Examples include phenol resin, xylene resin, and rosin resin. The appropriate amount of the tackifier resin to be used is 20 to 300 parts by weight, particularly 50 to 200 parts by weight, per 100 parts by weight of the isoprene oligomer having both ends functionalized. If the amount used is less than 20 parts by weight, the resulting cross-linked adhesive layer will have poor initial adhesive strength, and if it exceeds 300 parts by weight, the resulting cross-linked adhesive layer will have poor cohesive strength, but in either case, the rough surface adhesion is satisfactory. Sexuality is not expressed. In the crosslinked adhesive of the present invention, if necessary,
A softener may also be added. Typical examples of softeners include tackifying resins that are liquid at room temperature, process oils,
Examples include polyester plasticizers, polybutene, and liquid rubber. Further, appropriate additives or compounding agents such as antioxidants, ultraviolet absorbers, pigments, extenders, and blowing agents may be added as required. The solvent-free coating type crosslinked adhesive of the present invention is prepared by mixing the components without using a mixing medium such as water or an organic solvent. If the viscosity of the mixed system is high and the mixability and coating properties are poor, the viscosity can be lowered by heating. moreover,
Addition of a small amount of organic solvent does not substantially impede solvent-free coating. In addition, when mixing each component under heating, the polyfunctional isocyanate compound and the crosslinking catalyst used if necessary can be mixed after mixing the other components and cooling the mixture to room temperature etc. preferable. From the viewpoint of coating properties, etc., the viscosity of the crosslinked pressure-sensitive adhesive is suitably 10,000 poise or less at 30°C. The adhesive member of the present invention is one in which a crosslinked adhesive layer made of the above-mentioned crosslinked adhesive is provided on one or both sides of a support base material. The cross-linked adhesive layer is formed by applying a cross-linked adhesive onto a supporting base material using an appropriate coating machine such as an extrusion coating machine, and then heat-treating this using an appropriate heating device such as a heating oven. This can be done by
Heating conditions are generally 80 to 180°C for 0.5 to 30 minutes, but may be determined as appropriate. Also, at low temperatures, especially
A crosslinked adhesive layer can also be formed by aging at room temperature to 80°C for a long time. This method can be preferably applied when the supporting base material has poor heat resistance. The thickness of the crosslinked adhesive layer may be determined as appropriate, and is generally 1 to 500 μm. As for the supporting base material, any suitable known adhesive tape or sheet may be used. Generally, materials made of paper, plastic film, metal foil, foam, etc. are used. The thickness of the supporting base material is typically 500 μm or less,
In some cases, it exceeds 1 mm. A separator from which the adhesive layer can be easily peeled can be used as a supporting base material, and the crosslinked adhesive layer can be used as an adhesive sheet to form an adhesive member. Effects of the Invention According to the present invention, since an isoprene-based oligomer having a functional type at both ends is used, a solvent-free coating type crosslinked adhesive can be obtained, and an adhesive layer formed by crosslinking the adhesive can be obtained. It has excellent flexibility and stress relaxation properties, and has excellent adhesion and retention properties to rough surfaces. Examples Reference Example 1 After dissolving 5.5 mmol of m-divinylbenzene in hexane and cooling it to -10°C, 11 mmol of n-butyllithium was added dropwise to form m-dilithiohexylbenzene, and 2.2 mmol of isoprene monomer was added to this solution. mol was added and polymerized at 40°C. Next, 12 mmol of ethylene oxide was added to the reaction system, and the obtained product was poured into a large amount of methanol to obtain a precipitate of the isoprene oligomer having hydroxyl groups at both ends. The number average molecular weight of this isoprene oligomer was 29,000, and the number of hydroxyl groups per molecule was 1.93. Reference Example 2 An isoprene oligomer having hydroxyl groups at both ends was obtained according to Reference Example 1, except that the amount of m-divinylbenzene used was 4.8 mmol and the amount of n-butyllithium was 9.6 mmol. The number average molecular weight of this isoprene oligomer is 32,000,
The number of hydroxyl groups per molecule was 1.74. Example 1 100 parts (parts by weight, same hereinafter) of the isoprene-based oligomer with both ends functionalized obtained in Reference Example 1, 80 parts of a tackifying resin consisting of an aliphatic petroleum resin (softening point 90°C),
20 parts of a softener consisting of a rosin resin that is liquid at room temperature;
80% of 1 part of antioxidant consisting of phenolic compound
After the mixture was kneaded at ℃ and cooled to room temperature, 0.9 equivalent of diphenylmethane diisocyanate was mixed based on the hydroxyl group in the isoprene oligomer, and 0.05 of dibutyltin dilaurate was added.
A cross-linked pressure-sensitive adhesive that is fluid at room temperature was obtained. Next, on a 38 μm thick polyester film whose back side was treated with a release agent, the cross-linked adhesive was applied to a thickness of 30 μm using an extruder, and then passed through a heating zone at 130°C for 2 minutes. After cross-linking treatment,
An adhesive tape having a crosslinked adhesive layer was obtained. Example 2 100 parts of the isoprene-based oligomer with functionalized terminals at both ends obtained in Reference Example 2, aliphatic petroleum resin (softening point 95°C,
70 parts of tackifier resin), 10 parts of terpene phenol resin (softening point 115℃, tackifier resin), 20 parts of a softener made of terpene resin that is liquid at room temperature, and 80 parts of antioxidant made of phenol compound. ℃, and the resulting mixture was cooled to room temperature.
An equivalent amount of diphenylmethane diisocyanate was mixed, and 0.05 part of dibutyltin dilaurate was further added to obtain a crosslinked adhesive that was fluid at room temperature. Next, an adhesive tape having a crosslinked adhesive layer was obtained according to Example 1 using the crosslinked adhesive. Comparative Example 1 2.2 mol of isoprene monomer was polymerized using 3.5 mmol of n-butyllithium to prepare an isoprene-based oligomer having a number average molecular weight of 45,000 and having no functional groups, and then 100 parts of the oligomer was dissolved in hexane. Add 2 parts hydrogen peroxide and 1 part acetic acid
After the reaction was carried out at 30°C, water was added and stirring was continued, and the obtained product was poured into a large amount of methanol to obtain an isoprene oligomer having hydroxyl groups at random positions on the molecular chain consisting of the precipitate. The number of hydroxyl groups per molecule in this isoprene oligomer was 1.8. Next, a pressure-sensitive adhesive tape having a cross-linked pressure-sensitive adhesive fluid at room temperature and a cross-linked pressure-sensitive adhesive layer made of this cross-linked pressure-sensitive adhesive was obtained in the same manner as in Example 1, except that the above-mentioned isoprene-based oligomer was used. Comparative Example 2 An isoprene oligomer having hydroxyl groups at random positions in the molecular chain was obtained in accordance with Comparative Example 1, except that the amount of n-butyllithium used was 6.2 momol. The number of hydroxyl groups per molecule in this isoprene oligomer was 2.5, and the number average molecular weight was 24,000. Next, a pressure-sensitive adhesive tape having a cross-linked pressure-sensitive adhesive fluid at room temperature and a cross-linked pressure-sensitive adhesive layer made of this cross-linked pressure-sensitive adhesive was obtained in the same manner as in Example 2, except that the above-mentioned isoprene-based oligomer was used. Test Evaluation The following tests were conducted on the adhesive tapes obtained in Examples and Comparative Examples. [Sealability] Commercially available cardboard box (A-1, 640mm x 255mm x
After repeatedly pasting and peeling adhesive tape around the folding part of the flap (300mm) to peel off the skin of the flap and roughen it, the flap was folded and the roughened central part was heated at 18 to 20℃. A 50 mm square piece of adhesive tape was attached to the flap, lightly pressed by hand, and left to stand, and the time taken for the adhesive tape to peel off and the flap to open was measured. [Retention] Adhere adhesive tape to a cut piece of commercially available plywood board with an adhesive area of 25 mm width x 25 mm length at 18 to 20 degrees Celsius, press it lightly with your fingertips, and then hang it so that the adhesive tape hangs vertically. A load of 1 kg was applied to the end of the tape so that the stress was uniform, and the time until the adhesive tape peeled off was measured. The above results are shown in the table. All displayed values are 5
This is the average value of the sample.

[Table] From the table, it can be seen that the adhesive tape made of the double-terminally functional isoprene oligomer of the present invention has excellent sealing properties and adhesion properties to rough surfaces, as well as excellent retention properties.

Claims (1)

[Scope of Claims] 1. A double-end functional isoprene oligomer having an average of 1.5 to 2 functional groups per molecule that can react with isocyanate groups, and having the functional groups only at the ends of the molecular chain. , a crosslinked pressure-sensitive adhesive characterized by containing a polyfunctional isocyanate compound and a tackifying resin as components. 2. The crosslinked adhesive according to claim 1, which has fluidity at room temperature and can be applied without solvent. 3. A crosslinked adhesive layer consisting of the crosslinked adhesive according to claim 1, in which a double-end functional isoprene oligomer is crosslinked through the ends of the molecular chain via a polyfunctional isocyanate compound, is applied to one or both sides of a supporting substrate. An adhesive member comprising: