JPS592475B2 - pressure sensitive adhesive composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a novel acrylic pressure sensitive adhesive composition.

In recent years, pressure-sensitive adhesives based on acrylic polymers containing acrylic esters and methacrylic esters as main components have come into widespread use.

This type of adhesive has more diverse adhesive properties than conventional pressure-sensitive adhesives based on natural rubber, synthetic rubber, etc.
Moreover, it has excellent weather resistance, heat resistance, light resistance, oil resistance, ozone resistance, etc., and has the ability to withstand long-term use. By the way, although pressure-sensitive adhesives are extremely advantageous in terms of adhesive workability because they can be easily adhered with finger pressure, they generally have the disadvantage of being inferior in adhesive strength, particularly in creep resistance.

This is also the case with pressure-sensitive adhesives based on acrylic polymers, which pose the biggest problem when used as permanent adhesives. Conventionally, in order to improve such creep resistance, monomers having functional groups such as hydroxyl groups and carboxyl groups in the molecule were used together with acrylic monomers such as acrylic esters and methacrylic esters, and the resulting acrylic A method has been adopted in which the internal cohesive force is increased by adding a crosslinking agent made of a polyfunctional compound such as polyisocyanate or an epoxy compound to the polymer to finally make the polymer three-dimensional. .

However, this method has the disadvantage that it is difficult to achieve both creep resistance and adhesiveness.

In other words, if the three-dimensional reaction is progressed too much by using a large amount of a specific 7-mer or cross-linking agent, the tackiness or adhesion, especially the tackiness, will decrease significantly, and if the emphasis is on maintaining the tackiness, the cohesive force cannot be sufficiently maintained. If it cannot be made larger, the effect of improving creep resistance cannot be obtained. In light of these circumstances, the inventors have developed a pressure-sensitive adhesive based on an acrylic polymer, which is far more useful than pressure-sensitive adhesives based on natural rubber or synthetic rubber. This invention was arrived at as a result of extensive research into a method that can increase cohesive force without damaging it. That is, this invention uses a copolymerizable monomer containing two or more polymerizable carbon atoms per molecule for 100 parts by weight of a main monomer mainly consisting of an alkyl ester of acrylic acid or methacrylic acid having an alkyl group having 2 to 14 carbon atoms. 0.01 to 20 parts by weight of a polyfunctional isocyanate compound are blended into 100 parts by weight of an acrylic polymer made by using 0.001 to 0.5 parts by weight of a polyfunctional unsaturated monomer having a carbon double bond. The present invention relates to a pressure-sensitive adhesive composition characterized by the following.

As described above, this invention uses a specific amount of a polyfunctional unsaturated monomer in the synthesis of an acrylic polymer, and further blends a specific amount of a polyfunctional isocyanate compound into the acrylic polymer obtained by this method. This is the most important feature, and it has been found that with this, both good tackiness and adhesion as well as a large cohesive force can be obtained, and both characteristics can be satisfied.

It has already been reported that certain acrylic polymers using polyfunctional unsaturated monomers similar to those used in the present invention as copolymerized monomers are suitable as adhesive components capable of improving cohesive force. However, this proposed method disallows the use of acrylic acid or methacrylic acid as copolymerization monomers other than those mentioned above, and the cohesive force of the resulting adhesive is not very large, and this cohesive force and tackiness The balance characteristics with adhesiveness were not necessarily satisfactory. On the other hand, according to the adhesive composition of the present invention, which has the above-mentioned characteristics, that is, a polyfunctional isocyanate compound is further added to the acrylic polymer using a polyfunctional unsaturated monomer as a copolymerization monomer, the proposed method described above Better results can be obtained in cohesive force and tackiness or adhesion compared to conventional polymers, and these effects can be obtained even if acrylic acid or methacrylic acid is not used at all or only slightly in the synthesis of acrylic polymers. It has been found that small amounts, for example less than about 1% by weight of the acrylic monomer, can be used.

Generally, acrylic polymers containing a large amount of monomers having such functional groups tend to have problems in terms of moisture resistance, water resistance, solvent resistance, etc. when used as adhesives.

In addition, when this type of adhesive is used for masking purposes or for protecting the surface of metal plates, the presence of carboxyl groups causes the adhesive strength to become too strong, causing problems in removability when peeled off over time. There are also drawbacks. Therefore, the adhesive composition of the present invention, which can obtain good results in terms of cohesive force and tackiness even without the use of such monomers, can be extremely suitably used for the above-mentioned applications.

It is not necessarily clear what the reason for this effect of this invention is based on.

It is estimated that the polyfunctional isocyanate compound used absorbs moisture.
Water absorption results in a polyurethane with a high molecular weight and three-dimensional structure, which physically entangles with the acrylic polymer and greatly contributes to improving the cohesive force. This is thought to be because the movement is relatively free, so it does not have much of an adverse effect on tack or adhesion. On the other hand, in the present invention, it is of course possible to use polar monomers such as acrylic acid or methacrylic acid in the synthesis of acrylic polymers, and in this case, active hydrogen contained in the functional groups of the monomers mentioned above can be used. As a result of chemically reacting with the polyfunctional isocyanate compound, the cohesive force can be further increased. As already mentioned, the acrylic polymer in this invention consists of a main monomer mainly consisting of an alkyl ester of acrylic acid or methacrylic acid, in which the alkyl group has 2 to 14 carbon atoms, and 2 or more polymerizable carbon atoms in one molecule. It is obtained by copolymerizing a polyfunctional unsaturated monomer having a carbon double bond. Here, examples of the alkyl ester of acrylic acid or methacrylic acid in which the alkyl group has 2 to 14 carbon atoms include ethyl acrylate, isobutyl acrylate, n-butyl acrylate, hexyl acrylate,
Acrylic acid alkyl esters such as 2-ethylbutyl acrylate, heptyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, isooctyl acrylate, nonyl acrylate, decyl acrylate, n-butyl methacrylate, pentyl methacrylate, 2-methacrylate −
Examples include alkyl methacrylates such as ethylhexyl, octyl methacrylate, dodecyl methacrylate, and tetradecyl methacrylate.

In addition to these alkyl esters, the main monomers also include various monomers used in the synthesis of general acrylic polymers.

For example, there are alkyl esters of acrylic acid or methacrylic acid having an alkyl group other than those mentioned above, such as methyl methacrylate, and various vinyl monomers such as vinyl acetate, styrene, acrylonitrile, and methacrylonitrile, and maleic acid diesters. Diesters such as maleic anhydride, maleic acid monoester, itaconic acid, fumaric acid, acrylic acid,
Methacrylic acid, acrylamide, methylolacrylamide, hydroxyethyl acrylate, methoxyethyl acrylate, hydroxyethyl methacrylate, methoxyethyl methacrylate, ethoxyethyl acrylate, N-N-dimethylaminoethyl methacrylate, N
Examples include functional group-containing monomers such as -tert-butyl methacrylate. In this invention, when using a monomer having an active hydrogen that reacts with an isocyanate group as a functional group-containing monomer, typically a monomer having a carboxyl group or a hydroxyl group as a functional group,
The amount used is preferably about 10% by weight or less, preferably 1% by weight or less based on the main monomer.

Examples of polyfunctional unsaturated monomers having two or more polymerizable carbon-carbon double bonds in one molecule used together with these main monomers include the following general formula;
is hydrogen or a methyl group, n is 1-32, preferably 1-32
diacrylate or dimethacrylate of ethylene glycol or polyethylene glycol (an integer of 15), trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, 1.
Examples include 4-butanediol diacrylate.

The amount of this polyfunctional unsaturated monomer used is 10
The amount is within the range of 0.001 to 0.5 parts by weight relative to 0 parts by weight, but this range mainly depends on the molecular weight of the acrylic polymer obtained by copolymerization.

That is, in the case of a polymer having a low molecular weight, for example, an average molecular weight of 50,000 or less, it becomes difficult to achieve both cohesive force and tackiness as effects of the present invention unless the upper limit of 0.5 parts by weight is added. On the other hand, if the molecular weight is high, for example, the average molecular weight is about 700,000 or more, the lower limit of 0.00
An amount of 1 part by weight is sufficient; if more than 1 part by weight is added, it may gel during polymerization or gel when a polyfunctional isocyanate compound is blended, which may interfere with uniform coating on substrates such as plastic films. cause In this way, the amount of the polyfunctional unsaturated monomer to be used should be determined appropriately depending on the molecular weight of the acrylic polymer, but the optimal amount also depends on the type of other functional unsaturated monomers. will be different.

For example, when using diacrylate or dimethacrylate of polyethylene glycol, n of the general formula
The smaller the number, the smaller the number of parts to be added may be. The copolymerization reaction is generally preferably carried out using a solution polymerization method using an appropriate solvent.

This is because not only is it advantageous in terms of workability, but also the molecular weight range of the obtained acrylic polymer is suitable for the purpose of the present invention. As a solvent, toluene, benzene,
Xylene, methyl ethyl ketone, vinyl acetate, hexane, heptane, etc. are suitable. Alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol are undesirable because they may react when mixed with a polyfunctional isocyanate compound. Of course, alcohols can be used if the alcohols are removed after the polymerization reaction and other solvents are added as necessary, or they can be gelled by reaction with isocyanate compounds in a mixed system with other solvents. There is no problem if the amount is small enough not to cause any problems. It is also possible to employ a bulk polymerization method or an emulsion polymerization method instead of using the solution polymerization method as described above. However, when employing the emulsion polymerization method, the acrylic polymer should be separated and dried by salting out after the polymerization reaction, and then it should be used by dissolving it in the above-mentioned solvent. This is because the polyfunctional isocyanate compound cannot be blended as is, and even if blended, the effects of the present invention cannot be expected. As an initiator for the copolymerization reaction, known polymerization initiators such as various peroxides such as benzoyl peroxide, methyl ethyl ketone peroxide, cumene hydroperoxide, and lauryl peroxide, and azo compounds such as azobisisobutyronitrile are used. Can be used widely.

The amount used is generally 0.01 per 100 parts by weight of monomer.
It may be about 5 parts by weight. The acrylic polymer according to the present invention obtained in this way has an average molecular weight of about 2.
It is desirable that the number is in the range of about 10,000 to 1,000,000, preferably 50,000 to 700,000.

If the molecular weight becomes too low, it becomes difficult to achieve both cohesive force and tackiness or adhesion. On the other hand, if the molecular weight becomes too high, it will gel very quickly during polymerization or when a polyfunctional isocyanate compound is added, making it impossible to coat uniformly, and if a large amount of solvent is used to prevent this, workability will be affected. becomes disadvantageous. In this invention, a pressure-sensitive adhesive composition is obtained by blending a polyfunctional isocyanate compound with the above-mentioned acrylic polymer (usually in a solution containing this polymer).

Examples of the polyfunctional isocyanate compound used here include tolylene diisocyanate, hexamethylene diisocyanate, polymethylene polyphenyl isocyanate, diphenylmethane diasocyanate, a dimer of diphenylmethane diisocyanate, and trimethylolpropane and tolylene diisocyanate. reaction product with cyanate,
Examples include reaction products of trimethylolpropane and hexamethylene diisocyanate, polyether polyisocyanates, and polyester polyisocyanates.
Among these, a reaction product of 1 mole of trimethylolpropane and 3 moles of tolylene diisocyanate is particularly preferred. This reaction product gives good results in terms of workability, reactivity and adhesive properties. The amount of the polyfunctional isocyanate compound to be used is 0.01 to 20 parts by weight, preferably 0.05 to 15 parts by weight, per 100 parts by weight of the acrylic perimer. If the amount is less than 0.01 part by weight, the effect of improving cohesive force will not be sufficiently obtained;
If the amount is more than 0 parts by weight, the gelation of the composition will be accelerated, and isocyanate compounds with poor compatibility with the polymer will tend to reduce tackiness and adhesion, which is unsuitable.

Various additives may be added to the pressure-sensitive adhesive composition of the present invention for the purpose of modifying adhesive properties.

These include resins such as rosin-modified resins, aromatic petroleum resins, coumaron-indene resins, and xylene resins, softeners such as coumaron oil, dioctyl phthalate, and dibutyl phthalate, fillers such as calcium carbonate, finely powdered silica, and colorants. , ultraviolet absorbers, and other known additives. Examples of this invention will be described below.

Note that in the following, parts mean parts by weight. In addition, measurements of adhesive strength, adhesion strength, and holding strength were performed using the following methods. (1) Adhesive strength: Measured according to JISZ-1528.

(2) Adhesive strength; J. DOw(:I) Old 111ngBa1
1Tack measurement method was used. (3) Holding power: A double-sided adhesive tape with an area of 25m71L x 25mm is attached to a stainless steel plate, lined with a 50μ thick polyester film, and the time until it falls is measured by applying a vertical load of 1kg at 40℃. did.

Example 1 70 parts of isooctyl acrylate, 30 parts of ethyl acrylate
parts, tetraethylene glycol dimethacrylate 0.0
3 parts and 100 parts of toluene were charged into a three-necked flask, and stirred for 2 hours while introducing nitrogen gas.

After removing oxygen from the system in this manner, 0.02 part of azobisisobutyronitrile was added and the temperature was raised to 57°C.
After 4 hours, 0.02 part of azobisisobutyronitrile was further added, and the polymerization reaction was continued for 4 hours.

Then, 0.02 part of azobisisobutyronitrile was added again, the temperature was raised to 65°C, and the polymerization reaction was continued for 5 hours. The obtained acrylic polymer had an average molecular weight of about 320,000.

Dismodule (B) is added to the reaction solution containing this polymer.
1 part of a reaction product of trimethylolpropane and tolylene diisocyanate (manufactured by Ayer) was added thereto, and the mixture was thoroughly stirred and mixed to obtain a pressure-sensitive adhesive composition of the present invention. Next, this composition was applied to a thickness of 50 μm on release paper and dried by heating at 100° C. for 5 minutes to produce a pressure-sensitive adhesive film. 5 coats of Shikaru Watari's film on both sides of a 30μ thick rayon non-woven fabric.
Laminate with a heated roller at 0°C to create double-sided adhesive tape. The adhesive strength of this double-sided adhesive tape is 7509/20
mm, adhesive strength was 22, and retention strength was 1830 minutes.

Example 2 In the synthesis of acrylic polymer, 0.5% of 2-hydroxyethyl acrylate was used as a copolymerization monomer.
An acrylic polymer was synthesized in exactly the same manner as in Example 1, except that part was added.

The average molecular weight of this polymer was approximately 340,000. Thereafter, a pressure-sensitive adhesive composition and a double-sided adhesive tape of the present invention were prepared in the same manner as in Example 1. The adhesive strength of the double-sided adhesive tape thus obtained was 8109/20 mm.
The adhesive strength was 24 and the retention strength was 15,860 minutes.

Comparative Example 1 A pressure-sensitive adhesive composition, a composition, and a double-sided adhesive tape were prepared in exactly the same manner as in Example 1, except that 0.03 part of tetraethylene glycol dimethacrylate was not used in the synthesis of the acrylic polymer. .

The adhesive strength of this tape is 28009/20m7! Cohesive failure occurred at L. The holding power was 12 minutes. Comparative example 2
In the synthesis of the acrylic polymer, 0.5 part of 2-hydroxyethyl acrylate was added as in Example 2 as a copolymerization monomer, while 0.03 part of tetraethylene glycol dimethacrylate was not used. An acrylic polymer was prepared in exactly the same manner as in Example 1.

A pressure-sensitive adhesive composition was prepared by adding 1 part of Dismodule L similar to Example 1 and 0.3 part of dioctyltin dilaurate to the reaction solution containing this polymer. The purpose of adding dioctyltin dilaurate is to promote the reaction between the isocyanate and (the hydroxyl groups of) the polymer, thereby giving the resulting composition a large holding power similar to that in Example 2. Using this composition, a double-sided adhesive tape was prepared in the same manner as in Example 1.

The adhesive strength of this tape is 6809/20mm, and the adhesive strength is 8
The retention force was 10150 minutes. Comparative Example 3 A double-sided adhesive tape was prepared in exactly the same manner as in Example 1, except that Dismodule L was not blended into the reaction solution containing the acrylic polymer and the above reaction solution was used as it was as a pressure-sensitive adhesive composition. I made it.

The adhesive strength of this tape was 30009 or more/20 mm and cohesive failure occurred. Moreover, the adhesive strength was 30 or more, and the retention strength was 6 minutes. Comparative Example 4 A double-sided adhesive tape was prepared in exactly the same manner as in Example 2, except that the reaction solution containing the acrylic polymer was used as it was as a pressure-sensitive adhesive composition as in Comparative Example 3.

The adhesive strength of this tape is over 30009/20m77! Cohesive failure occurred, the adhesive strength was 30 or more, and the holding power was 8 minutes. Example 3 95 parts of isooctyl acrylate, 5 parts of acrylic acid, 0.01 part of tetraethylene glycol dimethacrylate, and 100 parts of toluene were placed in a three-hole flask, and the same procedure as in Example 1 was carried out to obtain an acrylic polymer.

The average molecular weight of this polymer was approximately 350,000. Next, 1 part of Dismodule L was added to the reaction solution containing this polymer 1 to prepare a pressure-sensitive adhesive composition of the present invention, and a double-sided adhesive tape was made from this composition in the same manner as in Example 1. The adhesive strength of this tape is 820f)/20m1L
The adhesive strength was 28, and the retention strength was 1000 minutes or more.

Comparative Example 5 A pressure-sensitive adhesive composition and a double-sided adhesive tape were prepared in exactly the same manner as in Example 3, except that 0.01 part of tetraethylene glycol dimethacrylate was not used in the synthesis of the acrylic polymer.

The adhesive strength of this tape is 8409/20mm 1 The adhesive strength is 2
8. Retention power was 120 minutes. Example 4 20 parts of ethyl acrylate, 80 parts of octyl acrylate, 1 part of acrylic acid, 0.002 parts of trimethylolpropane triacrylate (Acryx TMP: manufactured by Toagosei Co., Ltd.) and 100 parts of ethyl acetate were charged into a three-necked flask. .

Stirring was continued for about 60 minutes while introducing nitrogen gas. After removing oxygen from the system in this manner, 0.02 part of azobisisobutyronitrile was added and the temperature was raised to 57°C. After 4 hours, 0.02 part of azobisisobutyronitrile was further added, and the polymerization reaction was continued for 4 hours.

Then, 0.02 part of azobisisobutyronitrile was added again, the temperature was raised to 65°C, and the polymerization reaction was continued for 5 hours. The obtained acrylic polymer had an average molecular weight of about 700,000.

0.02 part of polymethylene polyphenyl isocyanate was added to the reaction solution containing this polymer, and the mixture was thoroughly stirred and mixed to obtain a pressure-sensitive adhesive composition of the present invention. Using this composition, a double-sided adhesive tape was prepared in the same manner as in Example 1. The adhesive strength of this tape was 8609/20 mu1, the retention strength was 1000 minutes or more, and the adhesive strength was 26. Comparative Example 6 In the synthesis of acrylic polymer, Acryx TMPO. Example 4 except that 2 parts OO was not used.
A pressure-sensitive adhesive composition and double-sided adhesive tape were prepared in exactly the same manner as described above.

The adhesive strength of this tape was 7909/20ml1L1 adhesive strength was 28, and the retention strength was 48 minutes. Examples 5-9 20 parts of ethyl acrylate, 80 parts of 2-ethylhexyl acrylate, 0.5 part of acrylic acid and AcryxTM
Five types of acrylic polymers were synthesized in the same manner as in Example 4 using P in the amounts shown in the table below.

The average molecular weight of each polymer was as shown in the same table. The molecular weight was adjusted by adding lauryl mercaptan to the polymerization system and adjusting its amount. Also, the average molecular weight is 8
00,000 (Example 9), benzene was used as the solvent. Dismodule L was added to the solution containing each acrylic polymer thus obtained in the proportions shown in the same table, and five types of double-sided adhesive tapes were prepared in the same manner as in Example 4.

Claims (1)

[Scope of Claims] 1. Polymerization of two or more monomers in one molecule as a copolymerized monomer with respect to 100 parts by weight of a main monomer mainly consisting of an alkyl ester of acrylic acid or methacrylic acid having an alkyl group having 2 to 14 carbon atoms. 0.01 to 20 parts by weight of a polyfunctional isocyanate compound to 100 parts by weight of an acrylic polymer made by using 0.001 to 0.5 parts by weight of a polyfunctional unsaturated monomer having a carbon-carbon double bond. 1. A pressure-sensitive adhesive composition comprising: 2. The pressure-sensitive adhesive composition according to claim 1, wherein the main monomer of the acrylic polymer does not contain any functional group-containing monomer having active hydrogen that reacts with an isocyanate group. 3. The pressure-sensitive adhesive composition according to claim 1, which contains a functional group-containing monomer having an active hydrogen that reacts with an isocyanate group as one of the main monomer components in the acrylic polymer. 4. The pressure-sensitive adhesive composition according to claim 3, wherein the functional group-containing monomer having active hydrogen that reacts with an isocyanate group has a hydroxyl group or a carboxyl group as a functional group. 5. The pressure-sensitive adhesive composition according to claim 3 or 4, wherein the proportion of the functional group-containing monomer having an active hydrogen group that reacts with an isocyanate group in the main monomer is 1% by weight or less. 6. The pressure-sensitive adhesive composition according to any one of claims 1 to 5, wherein the acrylic polymer has an average molecular weight of about 50,000 to 700,000. 7. The pressure-sensitive adhesive composition according to any one of claims 1 to 6, wherein the polyfunctional isocyanate compound is a reaction product of 1 mol of trimethylolpropane and 3 mol of tolylene diisocyanate.