JPS5896670A - Preparation of pressure-sensitive adhesive tape - Google Patents

Abstract

PURPOSE:To obtain the titled tape having improved adhesiveness and water resistance, by blending an acrylic polymer emulsion with a water dispersion by an alkali of an acrylic polymer using a specific amount of an acidic group-containing unsaturated monomer in a specific weight ratio, coating a substrate with the blend. CONSTITUTION:(A) An emulsion of an acrylic polymer having adhesivity at room temperature obtained by emulsion polymerization is blended with (B) a water dispersion by an alkali(preferably ammonia) of an acrylic polymer using 2-20wt% unsaturated monomer having an acidic group in the molecule, having adhesivity at room temperature, in a ratio of 100pts.wt. component A to 100- 900pts.wt. component B, and the blend is applied to a substrate, which is heated and dried to give the desired tape. A dispersion having a water dispersing index Q of 7-50 shown by the formula[m is number of parts by weight of the acidic group-containing unsaturated monomer based on 100pts.wt. other monomers; delta is a solubility parameter of the polymer consisting only of the other monomers; MW is molecular weight(10,000) of the acrylic polymer]is preferably used as the component B.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a new pressure-sensitive adhesive tape, and more specifically, to a water-dispersed acrylic pressure-sensitive adhesive that has excellent pressure-sensitive adhesive properties and uses almost no organic solvent. The present invention provides a method for manufacturing the pressure-sensitive adhesive tape used.

Conventionally, the method for manufacturing pressure-sensitive adhesive tapes using pressure-sensitive adhesives mainly composed of acrylic polymers has been to make the above-mentioned adhesive a solvent-based adhesive with a solid content of about 10 to 50% by weight, and to modify it. A commonly used method is to add a material and coat it on the tape support.

However, in recent years, due to issues such as oil resources and pollution prevention, there has been a trend toward so-called high-solid types that use less solvent, emulsion types that do not use solvents, and hot melt types. be.

However, because high-solid types generally use polymers with a molecular weight similar to or lower than that of conventional solvent-based systems,
In order to obtain good creep resistance, it is necessary to use some cross-linking means, and therefore, in many cases, the pot life of the pressure-sensitive adhesive composition (i.e., after the adhesive has been prepared, the gel is shortened to the point where it cannot be coated with a coater). The problem is that it is difficult to balance the amount of heat required to cure the coating after coating (the amount of time it takes to cure the coating), and because it is highly concentrated, high-precision coating equipment is required to obtain a uniform thickness. Due to certain problems, the present situation is that even if it is satisfactory in terms of adhesive properties, it has hardly been put into practical use industrially. In addition, although the emulsion type has excellent coating properties, it is difficult to obtain satisfactory properties such as adhesion and water resistance, and the hot melt type has only a few satisfactory properties such as heat resistance (this problem remains). It has only been put into practical use for certain purposes.

This invention provides a new method for producing a pressure-sensitive adhesive tape that solves these problems, and the gist of the invention is to provide an acrylic polymer that is adhesive at room temperature obtained by emulsion polymerization. A first liquid consisting of an emulsion of The acrylic polymer in the second liquid is 1 part by weight for 100 parts by weight of the acrylic polymer in the first liquid.
The t-water dispersion type acrylic pressure-sensitive adhesive obtained by mixing in a proportion of 00 to 900 parts by weight and adding a crosslinking agent, tackifier resin, softener, pigment, etc. as necessary, is applied to a tape support. A method for producing a pressure-sensitive adhesive tape is provided.

We have already proposed a method for producing a pressure-sensitive adhesive tape using an aqueous dispersion of an acrylic polymer obtained by bulk polymerization or the like using alkaline water. In this case, if the molecular weight of the polymer is small, a water-dispersed pressure-sensitive adhesive with a relatively high solids content can be obtained, but this does not provide perfect pressure-sensitive adhesive properties; However, in order to obtain a coatable viscosity, the solids content must be low, which leaves the problem that a relatively large amount of heat is required for drying.

As a result of various studies on how to deal with this problem, we found that a blend system of the acrylic polymer emulsion conventionally produced by emulsion polymerization method and the aqueous dispersion according to the above proposal will improve pressure-sensitive adhesive properties, water resistance, and solid content concentration. This invention was developed based on the recognition that the balance between In other words, while the former emulsion can have a relatively high solids concentration and can take advantage of this property, the latter dispersion can compensate for its disadvantages of reduced water resistance and adhesive properties. can.

The acrylic polymer emulsion used as the first liquid in this invention may be one prepared by a conventionally known emulsion polymerization method.

As for the monomer composition, (meth)acrylic acid alkyl esters such as ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate are used as raw monomers, and vinyl acetate, methyl methacrylate, acrylonitrile, acrylamide, and copolymerizable monomers are used. Styrene, acrylic acid, methacrylic acid, itaconic acid, hydroxyethyl methacrylate, dimethylamine ethyl methacrylate, glycidyl methacrylate, and the like can be used. As the emulsifier, anionic, nonionic, or copolymerizable emulsifiers can be used, and an appropriate chain transfer agent may be used as necessary during emulsion polymerization. It is desirable that the acrylic polymer obtained by these methods and having tackiness at room temperature has good compatibility with the acrylic polymer of the second liquid. - The monomer composition may be the same as or different from that of the second liquid.

In this invention, the second liquid used in combination with the first liquid is an alkali-based acrylic polymer that is sticky at room temperature and contains 2 to 20% by weight of an unsaturated monomer having an acidic group in the molecule as a copolymerizable monomer. It is made by dispersing it in water. The above-mentioned acrylic polymer having tackiness at room temperature used here is preferably one synthesized by a bulk polymerization method, a solution polymerization method, or a pearl polymerization method, and most preferably one obtained by a bulk polymerization method. Good. However, in some cases, it may be synthesized by emulsion polymerization. In cases other than bulk polymerization, the medium is removed after predetermined polymerization, and each time the polymer is water-dispersed with an alkali.

In the medium removal step, impurities such as the emulsifier used during polymerization are removed. In addition, particularly in the pearl polymerization method, it is also possible to adopt a method in which an alkali is directly added to water as a medium without removing it to form an emulsion.

The monomers used in the synthesis of the acrylic polymer are essentially the same as those for the first solution, but the difference is that an unsaturated monomer having an acidic group in the molecule is essential as a copolymerization additive. do. That is,
It is necessary to use this monomer at 2 to 20% by weight of the total monomers; if it is less than 2% by weight, it will be difficult to water-disperse it with alkali, and if it exceeds 20% by weight, it will be difficult to obtain water dispersion. It becomes impossible to improve the water resistance and adhesive properties of the pressure-sensitive adhesive tape.

Examples of unsaturated monomers having an acidic group in the molecule include unsaturated carboxylic acids having a carboxyl group as an acidic group such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, and fumaric acid, styrene sulfonic acid, and allyl. Sulfonic acid, sulfopropyl acrylate, 2
-acryloyloxynaphthalene-2-sulfonic acid, 2
-methacryloyloxynaphthalene-2-sulfonic acid,
2-acrylamido-2-methylpropanesulfonic acid,
Examples of acidic groups such as 2-acryloyloxybenzenesulfonic acid include unsaturated sulfonic acids having a sulfonic group, and may also have other acidic groups, and one or more of these may be used. Use seven.

The weight average molecular weight of the acrylic polymer obtained using such a copolymerized monomer is generally from 100,000 to 1,000,000, preferably from 200,000 to 70,000. This is because if the molecular weight is too low, it is unfavorable in terms of adhesive properties, and if the molecular weight is too high, water dispersion by an alkali becomes difficult.

In addition, the above acrylic polymer has a water dispersibility index (
It is desirable that Q) be in the range of 7 to 50. If the above water dispersion index becomes too small, the stability of the dispersion obtained by emulsifying and dispersing with alkali and water in the subsequent process and the stability against shearing force when subjected to mechanical shearing force will decrease. Therefore, it is difficult to stably disperse acrylic polymers in water. Furthermore, if the water dispersion index becomes too large, a problem will arise in the water resistance of the pressure-sensitive adhesive tape finally obtained.

Here, the water dispersion index (Q) is expressed by the following equation.

Q=yn, xδ/V closed m; Number of parts by weight δ of the unsaturated monomer having an acidic group in the molecule relative to 100 parts by weight of other monomers; Polymer consisting of a monomer alone excluding the unsaturated monomer having an acidic group in the molecule Solubility parameter MW; weight average molecular weight of acrylic polymer (10,000) Also, the above solubility parameter (δ) is, as is well known, P,
A, J, Small I (J, , Appl, Ch.
Em, 3-71° 1953) proposed by the following equation.

81 Here, δ is the solubility parameter ([Cat/cl :l
), d is the density at 25°C (F/CI), G is 25
The molar attraction constant in °C, M is the molecular weight per repeating unit (g/mo+).

For example, in the homopolymer of methyl methacrylate, the basic structure is ~-CH2-C(CHs) (COOCHs
)-~, and the number of constituent groups G -CH2-1133 -CHa 2 214
-COO-1310 -C-1-93 ■ Therefore, ΣG= 133+214x2+310-9
3 = 778, and d = l, 18, 8 (= 100
Therefore, δPMMA= 1.18 x 778/
It becomes 100-9.2.

In the case of nitrile rubber (acrylonitrile 30 mol%), the basic structure is ~4 CH2-CH=CH-CH2+v(-CH2-C
H'+r-CN, and in the butadiene part, the number of constituent groups is G -CH2-2133 -CH= 2 111, and in the acrylonitrile part, the number of constituent groups is G -CH2-1133 -CH-128 -CN 1 410
Therefore, ΣG (butadiene) - (133 + 111)
X2 = 488, ΣG (acrylonitrile) - 133
+28+410=571, and d=0 for this rubber
．． 96, M=535, so δNBR=((488X7)+(571X3))xo,
961535=9.2.

In this way, the water dispersion index (Q) is determined by the dissolution of the polymer consisting of the weight average molecular weight of the acrylic polymer, the number of copolymerized parts of the unsaturated monomer having an acidic group in the molecule, and the single monomer other than the above monomer. Since the molecular weight of the acrylic polymer is determined by the above-mentioned parameters, the molecular weight of the acrylic polymer is appropriately adjusted within the above range depending on the type of monomer used and the proportion of unsaturated monomers having an acidic group in the molecule. It is recommended to set it to a value that is reasonable.

In particular, when such acrylic polymers are obtained by bulk polymerization, some organic solvents such as benzene, hexane, alcohol, etc. are added to the polymerization system, and the polymerization is carried out without removing the above-mentioned solvent and then water-dispersed with an alkali. It is also possible to do so. Further, in the above-mentioned bulk polymerization method and other polymerization methods, an appropriate chain transfer agent and a plasticizer such as dioctyl phthalate or polyethylene glycol may be added to the polymerization system.

The acrylic polymer thus obtained is prepared by adding alkali and water and stirring and mixing to neutralize part or all of the acidic groups in the polymer and to form a dispersion in which the above polymer is stably dispersed in water. It is said that The alkali used here is preferably one that easily scatters when the final adhesive is coated on the tape support and then heated and dried. By using such an alkali, it is possible to prevent the adverse effects of alkali contamination on the adhesive properties, and to obtain good adhesive properties. A typical splashable alkali is ammonia, but other substances such as α-amine ethyl alcohol, ethylamine, and flobylamine can also be used. In addition, general alkalis such as caustic potash and caustic soda can also be used together with these alkalis in small amounts.

The amount of alkali used is usually about 0.2 to 1.5 equivalents based on the acidic groups contained in the acrylic polymer; if this proportion is small, water dispersion will be difficult, and if it is too large, the adhesive properties will be affected. , unfavorable in terms of water resistance and economy. The amount of water used is preferably such that the solid content concentration of the resulting aqueous dispersion is usually about 20 to 50% by weight. The temperature during the neutralization treatment is kept at a constant temperature depending on the type and properties of the acrylic polymer, but is generally about 30 to 90°C.

The dispersion obtained in this way may be used as it is as the second liquid in the present invention, but if necessary, a suitable solvent may be added as a dispersion aid in a small amount (usually 0 parts by weight per 100 parts by weight of the polymer). The second liquid can be prepared by adding a surfactant (up to .5 parts by weight) and other stabilizers such as methoxycellulose, polyvinyl alcohol, and polyacrylate.

In this invention, the first liquid and the second liquid as described above are
The second liquid for 100 parts by weight of the first liquid acrylic polymer.
The liquid acrylic polymer is mixed in a proportion of 100 to 900 parts by weight, preferably 150 to 500 parts by weight, to form a water-dispersible acrylic pressure-sensitive adhesive. The total solids concentration of this adhesive is usually in the range of 20 to 40% by weight. In addition, if the mixing ratio is such that the acrylic polymer in the second liquid is less than 100 parts by weight, the characteristics of the first liquid will be strongly expressed, and there is a risk that the adhesive properties and water resistance of the pressure-sensitive adhesive tape will deteriorate. On the other hand, if the mixing ratio exceeds 900 parts by weight, the amount of the second liquid becomes too large, resulting in a decrease in solids concentration as an adhesive, and it becomes difficult to maintain a balance with adhesive properties or water resistance. Further, when mixing the first liquid and the second liquid, it is preferable that the pH of both liquids is adjusted to be close to each other.
If the difference is too large, good results will not be obtained in terms of stability as an adhesive.

The water-dispersed pressure-sensitive adhesive of the present invention may contain various additives used in general pressure-sensitive adhesives, such as cross-linking agents, plasticizers, tackifying resins, and pigments, if necessary. can. These additives can be added as an aqueous dispersion or as a solution dissolved in an organic solvent after mixing the first liquid and the second liquid, or can be added alone or as an aqueous solution. It may be added in advance to one or both of the first liquid and the second liquid. In addition, especially when it is added to the second liquid, it may be added before the acrylic polymer is water-dispersed in an alkali.
In this case, it is also possible to add it when polymerizing the acrylic polymer.

In this invention, the water-dispersed pressure-sensitive adhesive prepared by the above method is uniformly applied onto a tape support such as paper or plastic film using a commonly used coating machine such as a reverse coater, gravure coater, or kiss coater. The desired pressure-sensitive adhesive tape can be obtained by heating and drying this with a drying means such as hot air or an infrared heater, and by removing scatterable alkali in this drying process.

As detailed above, according to the present invention, by blending a specific amount of a specific alkaline dispersion liquid into a conventional emulsion type adhesive, the balance between solid content concentration and adhesive properties and water resistance when made into an adhesive tape is achieved. Therefore, it is possible to provide a highly practical method for producing a pressure-sensitive adhesive tape.

Hereinafter, this invention will be explained in more detail with reference to Examples.

Example 1 Water in Step 11 in which 2 g of potassium persulfate was dissolved was added to a three-hole flask of Step 31, and the flask was thoroughly purged with nitrogen while stirring, and then heated to 75°C. While stirring and nitrogen purging, a mixed solution consisting of 2002 ethyl acrylate, 8009 butyl acrylate, 60 g of acrylic acid, 0.52 g of lauryl mercaptan, and 20 g of a nonionic emulsifier was added dropwise over 4 hours, and then heated for another 2 hours. The temperature was maintained at ℃. After that, it is cooled to room temperature to obtain an acrylic polymer emulsion liquid.
This was used as the first liquid. To this first solution, an equivalent amount of aqueous ammonia was added to the carboxyl group in the polymer to adjust the pH.

Next, a closed-type 21-capacity kneader equipped with a nitrogen gas inlet, a condenser outlet, a monomer dripping port, and a thermometer was sufficiently purged with nitrogen, and the kneader was heated to 80°C. While continuing rotation of the kneader and nitrogen substitution, ethyl acrylate 300iii', butyl acrylate 7009, acrylic acid 1009. A mixed solution consisting of 0.62% of thioglycol and 22% of adibisisobutyronitrile was added dropwise over 6 hours, while polymerization was carried out while maintaining the internal temperature at 80°C. After the dropwise addition was completed, the temperature was maintained at 80° C. for an additional hour.

The weight average molecular weight of the obtained polymer was approximately 280,000, and the water dispersibility index (Q) was approximately 18. Note that the solubility parameter (δ) of the 7:3 copolymer of ethyl acrylate and butyl acrylate is 9.6.

Next, 3 for the carboxyl group contained in this polymer.
/4 equivalent of ammonia and water were added and stirred at 65° C. for 2 hours to obtain an alkaline aqueous dispersion with a solid content of 25% by weight, which was used as a second liquid.

The pH of the first liquid and the second liquid are made equal and mixed so that the solid content (polymer) ratio is as shown in the table below, and water-soluble melamine resin is added to the total solid content. They were added and mixed in the proportions shown in the table to form a water-dispersed pressure-sensitive adhesive.

Each adhesive was applied to a polyester film having a thickness of 25 μm so that the dry thickness was 35 μm, and dried at 120° C. for 5 minutes to obtain pressure-sensitive adhesive tapes of samples Nα1 to 6. The adhesive properties and water resistance of each tape were as shown in the same table.

Example 2 Ethyl acrylate 200! i', butyl acrylate 5o
OP, 1505' methacrylic acid, 1 part polyvinyl alcohol, 2 parts benzoyl peroxide and 2,30 parts water.
After putting 5,0001 OP into a three-bottle flask, the flask was purged with nitrogen for about 1 hour while being slowly stirred. After sufficiently eliminating internal oxygen, the temperature was raised to 75°C and the reaction was carried out for about 7 hours to obtain an aqueous dispersion of particulate polymer. In addition, 1. /2 equivalent of 2-aminoethanol was added and stirred at 70° C. for 5 hours to obtain a milky white alkaline aqueous dispersion in which the particulate matter was partially dissolved, which was used as the second liquid. The weight average molecular weight of the polymer of this second liquid is 360,000, and the water dispersion index (Q) is about 23.
It was 3. The solubility parameter (δ) of a 2:8 copolymer of ethyl acrylate and butyl acrylate is approximately 9.
．． It is 3.

Next, the above-mentioned second liquid was blended with the first liquid obtained in Example 1 so that the solid content ratio was 100:300 (parts by weight), and 50v of polyether isocyanate was added to form a water-dispersed type. It was made into a pressure sensitive adhesive.

This was applied and dried on a polyester film in the same manner as in Example 1 to obtain a pressure-sensitive adhesive tape. The adhesive strength of this tape to the stainless steel plate is 480P/10mm, and the adhesive strength to the stainless steel plate after 7 days underwater is 4702/10mm, and it has excellent adhesive properties and water resistance like Nα2 to 4 in Example 1. It was something.

Patent applicant: Nitto Electric Industry Co., Ltd.

Claims (3)

[Claims] (1) a first liquid consisting of an emulsion of an acrylic polymer that is sticky at room temperature and obtained by emulsion polymerization;
A second liquid is prepared by dispersing an acrylic polymer, which is sticky at room temperature, in water using an alkali, using 2 to 20% by weight of an unsaturated monomer having an acidic group in the molecule as a copolymerization monomer, to the first liquid. The amount of acrylic polymer in the second liquid is 100 to 90 parts by weight based on 100 parts by weight of acrylic polymer.
A method for producing a pressure-sensitive adhesive tape, which comprises mixing the mixture in a proportion of 0 parts by weight, applying the mixture onto a tape support, and drying it by heating. (2) As for the acrylic polymer of the second liquid, the ratio is δ/Pi (where m is the number of parts by weight of unsaturated monomers having an acidic group in the molecule based on 100 parts by weight of other monomers, δ is the solubility parameter of a polymer consisting of a heptamer alone excluding unsaturated monomers with acidic groups in the molecule, Mw
is the weight average molecular weight (10,000) of the acrylic polymer)
The method for producing a pressure-sensitive adhesive tape according to claim 1, wherein a pressure-sensitive adhesive tape having a water dispersion index (Q) expressed by Q is in the range of 7 to 50. (3) A method for producing a pressure-sensitive adhesive tape according to claim 1 or 2, wherein the alkali is a splashable alkali such as ammonia.