JPS59179676A - Preparation of pressure-sensitive adhesive tape - Google Patents

Abstract

PURPOSE:To yield the titled tape excellent in water resistance, by the method wherein a raw material consisting mainly of an acrylic copolymer is neutralized and dispersed in water to give a hydrosol, which is incorporated with a crosslinker having aziridinyl groups to apply onto tape. CONSTITUTION:A raw material containing 0-20wt% solvent and consisting mainly of an acrylic copolymer comprising 80-99wt% monomer consisting chiefly of (meth)acrylate and 20-1wt% copolymerizable unsatd. monomer having an acidic group (e.g., acrylic acid), is prepd. An alkali and water is added to the raw material for neutralization and the copolymer is dispersed in water in a form of particles with a size 1-0.1mum. A crosslinker having two or more aziridinyl groups in a molecule, e.g. ethylene bis(2-aziridinylpropionate), is incorporated with the resulting hydrosol to yield a pressure-sensitive adhesive compn., which is then applied onto tape.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an acrylic pressure-sensitive adhesive tape.

More specifically, a solvent-free adhesive composition is produced by converting an acrylic copolymer into hydrosil having a fine particle size within a specific range without using an emulsifier, and blending this with an aziridinyl compound as a crosslinking agent. This invention relates to a method for producing a pressure-sensitive adhesive tape that can be used and has excellent water resistance.

In recent years, acrylic pressure-sensitive adhesives have become widely used in place of conventional natural rubber-based and synthetic rubber-based pressure-sensitive adhesives because of their excellent adhesive properties and durability.

Conventionally, adhesive tapes using acrylic pressure-sensitive adhesives have been manufactured by coating a solution of an acrylic polymer in an organic solvent onto a tape support and drying it, but this method requires a large amount of Since an organic solvent is required, various alternative methods have been proposed from the viewpoint of petroleum resource issues and pollution prevention.

Among these, adhesive tapes that use emulsion-based pressure-sensitive adhesives that do not use organic solvents have recently become particularly important from the viewpoints of resource saving, pollution-free, and environmental hygiene. The adhesive layer has poor water resistance and adhesive properties.

That is, the emulsifier used during polymerization or when blending additives with the tackifier resin after polymerization usually contains 3 to 10% of the emulsifier in the adhesive.
It contains a large amount by weight, has a high water absorption rate, has poor water resistance as an adhesive, and when immersed in water, it turns white within 24 hours and loses most of its functionality.

In addition, the average particle diameter of the emulsion is 0.1 to 171.
m, the ability to form a uniform film is slightly inferior to that of the organic solvent solution type.

On the other hand, from the viewpoint of film formation, polymer particles having carboxyl groups (particle size 0.3 ~07 μm) in the presence of an alkali such as caustic potash, caustic sorter, or ammonium hydroxide, the particle surface is scraped off, and the particle size is reduced to 0.07 μm.
A method for producing hydrosil by a so-called strippable method has been proposed, in which fine particles of 0.01 to 0.171 m are formed.

However, although this method shows an improvement in film-forming ability due to microparticulation, it is generally difficult to hydrosylate even if the weight average molecular weight is 10 or more because of the use of an emulsifier and the limited molecular weight of the polymer that can be hydrosylated. However, it has mainly been applied only to the paint field and paper size field.

The inventors previously discovered that a specific copolymer with acidic groups, which has a relatively high molecular weight (
We proposed a method for obtaining hydrosil in which the copolymer is emulsified and dispersed in fine particles by adding an alkali and water to a copolymer having a weight average molecular weight of 10 to 10 to neutralize the acidic groups.

This invention was discovered as a result of intensive studies aimed at obtaining a solvent-free pressure-sensitive adhesive tape with excellent water resistance based on the above-mentioned proposed method. Copolymerizable unsaturated monomers 1 to 20 containing 80 to 99% by weight of raw monomers mainly composed of esters or methacrylic acid esters and acidic groups
A raw material containing an acrylic copolymer consisting of While neutralizing some or all of the acidic groups in the combined molecules, the above-mentioned copolymer is formed into hydrosil stably dispersed in water with an average particle size in the range of 0.01 to 0.1 μm, and this is added as a crosslinking agent. A method for producing a pressure-sensitive adhesive tape, which comprises applying a pressure-sensitive adhesive composition containing a compound having two or more aziridinyl groups in one molecule onto a tape support.

That is, in this invention, an acrylic copolymer having an acidic group is synthesized by various polymerization methods, and this is used as a raw material without a solvent or containing a small amount of solvent to form a hydrosil by the above-mentioned method, and this is applied onto a tape support. When applied, the adhesive tape exhibits high water resistance because it does not contain an emulsifier, and exhibits excellent film-forming properties due to the small particles, significantly improving water resistance compared to conventional emulsion adhesives. It has been found that adhesive properties can be obtained.

Furthermore, they discovered that when an aziridinyl compound is used as a crosslinking agent, a tape with no whitening phenomenon, almost no water absorption, extremely excellent water resistance, and well-balanced adhesion can be obtained, and the present invention has been made. I was able to complete it.

In addition, in this invention method, various additives such as tackifiers and softeners that are blended in general pressure-sensitive adhesives are mixed with the solid material whose main component is an acrylic copolymer, and then alkali and water are added. By forming hydrosil particles, the additive can be uniformly contained in each particle, so that the adhesive properties are extremely homogenized. Further, if these additives do not adversely affect the polymerization reaction, they can be mixed in advance into the system during polymerization.

On the other hand, in conventional emulsion adhesives, each of the above additives, especially the tackifier resin, is emulsified and dispersed in the emulsion obtained by emulsion polymerization, so each polymer particle and additive particle are separated. In this case, even if uniform dispersibility is obtained, it is difficult to homogenize the adhesive properties, and the adhesive properties tend to change over time.

As described above, the method of the present invention can avoid all the drawbacks of pressure-sensitive adhesive tapes using conventional emulsion adhesives, and can improve water resistance and adhesive properties. In addition, since hydrosil is a fine particle, during tape production, a coating film with excellent performance equivalent to that obtained from a general organic solvent solution can be obtained, and the coating workability is also good, and the solid content concentration is 25~25. With a relatively high concentration of about 45% by weight, coating with a uniform thickness is possible even with conventional coating equipment.

In this invention, 80 to 99% by weight of a raw monomer mainly composed of acrylic ester or methacrylic ester and 1 to 20% by weight of a copolymerizable unsaturated monomer having an acidic group.
In synthesizing an acrylic copolymer consisting of This is a solution polymerization method using a solvent.

Among these polymerization methods, in the bulk polymerization method, the resulting acrylic copolymer can be used as it is as a raw material for hydrosilation.

In the solution polymerization method, if the amount of solvent used is more than 20% by weight, the organic solvent is removed after synthesis by means such as distillation, but even if it is less than 20% by weight, the content can be reduced or eliminated by the above methods. This is desirable.

As the solvent used in this solution polymerization method, various general organic solvents can be used, but preferably alcohol-based hydrophilic solvents such as methanol, ethanol, n-butanol, n-propanol, isopropyl alcohol, and 5ec-butanol are used. Alternatively, it is desirable to use an oligomer or prepolymer having a hydrophilic group such as a hydroxyl group, a carboxyl group, or an amino group.

On the other hand, in other polymerization methods, the medium used in each method is removed by appropriate means after synthesis to obtain a solid material substantially free of medium. That is, for example, in the emulsion polymerization method, water is removed by coagulating and separating by salting out, and in the pearl polymerization method, water is removed by filtering the particulate copolymer.

At this time, it is desirable that the medium other than the organic solvent be completely removed, but a small amount of the medium is allowed to remain.

In addition, in the emulsion polymerization method and the pearl polymerization method, a portion of the emulsifier used during polymerization adheres to the surface of the polymer particles, but this emulsifier is almost completely removed during the above-mentioned medium removal operation or by washing if necessary.

In addition, in the emulsion polymerization method, highly three-dimensional copolymers may be produced, but such three-dimensional polymers hinder hydrosylation in the subsequent process, so It is desirable to prevent the formation of such polymers as much as possible.

If a portion of this is formed, it is desirable to masticate it using a mixing roll or a Banbury mixer under conditions where high shearing force is applied.

The main monomers used to obtain the acrylic copolymer include ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, inoctyl acrylate,
It is mainly composed of alkyl esters of acrylic acid or methacrylic acid in which the alkyl group has 2 to 15 carbon atoms, such as ethyl methacrylate and butyl methacrylate, and other monomers copolymerizable therewith may be used in combination.

Examples of monomers having the above functions include alkyl esters of acrylic acid or methacrylic acid in which the number of carbon atoms in the alkyl group is outside the above range, such as methyl acrylate and methyl methacrylate, vinyl acetate, acrylonyl, styrene, and acrylic acid. - In addition to methoxyethyl, vinyl ether, etc., various functional monomers such as glycidyl acrylate, glycidyl methacrylate, hydroxyethyl methacrylate, acrylamide, and methylolacrylamide are widely included.

Copolymerizable unsaturated monomers having an acidic group used together with the above main monomers include, for example, acrylic acid,
Methacrylic acid, crotonic acid, itaconic acid, maleic acid,
Unsaturated carboxylic acids having a carboxyl group as an acidic group such as fumaric acid, styrene sulfonic acid, allyl sulfonic acid, sulfopropyl acrylate, 2-acryloyloxynaphthalene-2-sulfonic acid, 2-methacryloyloxynaphthalene-2-sulfonic acid, Examples of the acidic group include unsaturated sulfonic acids having a sulfonic group, such as 2-acrylamido-2-methylpropanesulfonic acid and 2-acryloyloxybenzenesulfonic acid.
It may also have other acidic groups, and one or more of these may be used.

The usage ratio of the raw monomer and the copolymerizable unsaturated monomer having an acidic group is 80 to 99% by weight for the former and 20 to 99% by weight for the latter.
It is necessary to make it 1% by weight, and the former is particularly preferably 90% by weight.
The content is preferably 97% by weight, and the latter is preferably 10-3% by weight. The copolymerizable unsaturated monomer having an acidic group is 1
When it is less than % by weight, hydrosilation becomes difficult;
If the amount is more than 20% by weight, it is still unsuitable because the tackiness and other adhesive properties deteriorate.

It is generally desirable that the molecular weight of the acrylic copolymer synthesized at the above-mentioned usage ratio is in the range of 10 to 10 in terms of weight average molecular weight. If the molecular weight is too low, the cohesive force of the adhesive tape will be poor and a large amount of crosslinking agent will be required to improve this, but in this case there is a problem that the stability of the hydrosil will be impaired. Furthermore, if the molecular weight becomes too high, hydrosilation with alkali and water becomes difficult, which is undesirable in terms of adhesive properties.

In this invention, an alkali and water are added to a raw material mainly composed of the acrylic copolymer prepared as described above (including various additives as described above) and mixed by stirring. This neutralizes some or all of the acidic groups in the copolymer while producing hydrosils in which the copolymer is stably dispersed in water.

The alkali used here is selected from one that can easily scatter when the hydrosil 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 example of a splashable alkali is ammonia. Others α-aminoethyl alcohol, ethylamine,
Propylamine and the like can also be used.

The amount of alkali used may be generally about 0.1 to 2 equivalents relative to the acidic groups contained in the acrylic copolymer.

The temperature during neutralization treatment is kept at a constant temperature depending on the type and properties of the acrylic copolymer, but generally it is between 30 and 30°C.
It is 80'C. The method of neutralization and production of hydrosyl is
This can be done by adding a predetermined amount of alkali and water at once and stirring well, or by adding a predetermined amount of alkali or alkaline aqueous solution and stirring thoroughly, and then gradually adding water. By making them phase, water becomes a continuous phase and copolymer particles are dispersed therein.
A dispersion of types may be generated.

The dispersion thus obtained is a hydrosil in which copolymer particles as dispersed particles are uniformly and stably dispersed in water, and its viscosity is generally 30 to 1,000 poise at 25°C, and the solid content concentration is is 25 to 45% of electric power.

In addition, when producing this hydrosil, as already mentioned, additives such as tackifiers, softeners, plasticizers, fillers, and colorants can be added to the solid raw material before hydrosilation. In this case, it is usually added after polymerization, but it can also be added before polymerization depending on the case. Of course, it is also possible to hydrosilate each of the above additives and then add them to the sol.

Examples of compounds having at least two aziridinyl groups in one molecule that are added to the hydrosyl thus obtained include 1,1-(methylenedi-P-phenylene)bis-3,3-aziridinyl urea,・1-(hexamethylene)bis-3.3-aziridinyl urea, ethylene bis(2-aziridinylpropionate), tris(1-aziridinyl)phosphine oxide, 2.4
・6-triaziridinyl-1,3,5-triazine,
2,2-bishydroxymethylbutanol-tris[3
-(1-aziridinyl)propionate], and these can be used alone or in combination of two or more.

The amount of these aziridinyl compounds used is 0.01 to 5 parts by weight per 100 parts by weight of the acrylic copolymer in the hydrosil.
It is preferable to use parts by weight. If the amount used is too small, the water resistance of the pressure-sensitive adhesive tape will be low, and if it is too large, the adhesiveness will be low, which is not preferable.

The above-mentioned hydrosil can be coated to a uniform thickness on one or both sides of various tape supports such as plastic films, non-woven fabrics, woven fabrics, paper, and foils using conventional coating equipment. By removing moisture and scattering the scatterable alkali, it is possible to obtain a pressure-sensitive adhesive tape with desired water resistance and good adhesive properties.

EXAMPLES Hereinafter, this invention will be specifically explained with reference to Examples, but this invention is not limited to these Examples. In addition, all parts in the following text mean parts by weight.

Furthermore, the pressure-sensitive adhesive tapes obtained in Examples were evaluated by the following method.

Adhesive Strength> A pressure-sensitive adhesive tape with a width of 20 mm and a length of 150 mm was prepared, and it was peeled off at 180 degrees according to JIS-Z-1528, and its adhesive strength (g/20 mm) was measured.

<Holding force> Create a pressure-sensitive adhesive tape with a width of 10 mm and a length of 150 mm, paste the 0 mm width x 20 mm length on a Bakelite plate, apply a load of 500 g at 40°C, and calculate the time until the load falls. (minutes) was measured.

Water resistance〉 Pressure-sensitive adhesive tape was immersed in water at 20°C for 7 days, and oral changes were examined. No whitening phenomenon was observed after 7 days (○), and slight whitening phenomenon was observed after 3 days. The case was evaluated as (△), and the case where the whitening phenomenon was observed significantly after one day was evaluated as (×).

<Water absorption rate> A pressure-sensitive adhesive was applied to one side of a 25 μm polyester film so that the thickness after drying was 50 μm.
After drying at °C for 3 minutes, it was immersed in water and pulled out after 7 days, the water droplets on the surface were removed and the weight was measured to determine the water absorption rate (%).
I asked for

Example 1 2-ethylhexyl acrylate 80 g 1 ethyl acrylate 2 (1, 5 acrylic acid, 2-hydroxyethyl acrylate 51. Azobisisobutyronitrile 0.1.5
10 g of a composition consisting of 0.05 P of lauryl mercaptan and 0.05 P of lauryl mercaptan were charged into a 14-piece four-bottle flask, and the flask was purged with nitrogen for 40 minutes while stirring. Next, the remaining amount was added dropwise from the dropping funnel, and the mixture was reacted at 83°C for 4 hours to synthesize a copolymer having a weight average molecular weight of 6×10 (according to GPC).

Next, 0.4 to the carboxyl group of this copolymer.
Add 5 equivalents of ammonia and 20 oy of water for neutralization at a temperature of 69°C, and phase inversion to create a human 000000000000000000000000000000000000000000000000000000000000000000 Although the continuous layer is water.
-/I got it. The hydrosil obtained in this way is
Viscosity (25°C) 120 poise, solid content concentration 32.5% by weight, average particle size 0.07 μm (according to Nanosizer)
Met.

For 100 parts of the polymer solid content of the above hydrosil, 1.
1-(methylene-di-P-phenylene)bis-3.3-
A crosslinking agent solution prepared by dissolving 0.5 parts of aziridinyl urea in 5 parts of dimethylformamide was blended to prepare a pressure-sensitive adhesive composition.

This composition was applied to a polyester film having a thickness of 50 μm and dried by heating at 130° C. for 4 minutes to obtain a pressure-sensitive adhesive tape having an adhesive thickness of 50 μm.

Comparative Example 1 To the hydrosil obtained in Example 1, 1.2N of triglycidyl isocyanurate was added as a crosslinking agent to the polymer solids content of 1
A pressure sensitive adhesive tape was obtained in the same manner as in Example 1 using this adhesive composition.

Comparative Example 2 To the hydrosil obtained in Example 1, 2.2 parts of tributoxymethylmelamine was added as a crosslinking agent to 100% of the polymer solid content.
A pressure-sensitive adhesive tape was obtained in the same manner as in Example 1 using this adhesive composition.

Comparative Example 3 A monomer mixture having the same composition as in Example 1 was emulsion polymerized using 2 parts of sodium lauryl sulfate as an emulsifier, thioglycolic acid as a chain transfer agent, and potassium persulfate as a polymerization initiator. A polymer emulsion having a weight average molecular weight of 5×10 5 and an average particle diameter of 0.23 μm was obtained. A crosslinking agent was added to this emulsion in the same manner as in Example 1, and a pressure-sensitive adhesive tape was obtained in the same manner as in Example 1 using this adhesive composition.

The performance of each pressure-sensitive adhesive tape of Example 1 and Comparative Examples 1 to 3 was evaluated, and the results are shown in Table 1 below.

Example 2 Hydrosil and pressure-sensitive adhesive tape were obtained in the same manner as in Example 1 except that the amount of acrylic acid used was 20 F/.

Comparative Example 5 An attempt was made to obtain a pressure-sensitive adhesive in the same manner as in Example 1 except that the amount of acrylic acid used was 11, but even by ammonia neutralization, hydrosil with a minute particle size was not obtained, and the particle size was The resulting aqueous dispersion had a large amount of water and very poor stability, and a coatable adhesive could not be obtained.

Example 3 80 g of n-butyl acrylate, 20 g of ethyl acrylate
, methacrylic acid 10g, benzoyl peroxide 0.
1g of 5ec-butanol, 10g of the monomer mixture and 5g of 5ec-butanol.
The mixture was placed in a four-bottle flask (No. 4), and the mixture was purged with nitrogen at 40°C for 40 minutes while stirring. Thereafter, 0.1y of benzoyl peroxide was added, and after completely dissolving, the temperature was raised to 80°C.

The remaining monomer mixture is then added from the dropping funnel to approximately 0.000 g.
It took 2 hours to drip at a rate of 871 parts, and the temperature was 85±5°C.
The weight average molecular weight was 3×105 (GP
A copolymer of C) was synthesized.

Next, 0.2 to the carboxyl group of this copolymer.
1 for 5 equivalents of ammonia and 100 parts of copolymer
70 parts of water was added to neutralize the mixture at a temperature of 50±3°C, and the phase was inverted to obtain hydrosil whose continuous phase was water.

The hydrosil thus obtained has a viscosity (25
°C) was 520 poise, the solid content concentration was 33% by weight, and the average particle diameter was 0.05 μm.

0.2 parts of 2,2-bishydroxymethylbutanol-tris(3-(1-aziridinyl)propionate) was blended with 100 parts of the hydrosil polymer to prepare a pressure-sensitive adhesive composition.

A pressure-sensitive adhesive tape was obtained from this composition in the same manner as in Example 1.

Example 4 2-ethylhexyl acrylate 60 Q Ethyl acrylate 40 9 Meccrylic acid
15 1Azohisisobutyronitrile
0.15y toluene 200
g The above composition was placed in a 14 flask and reacted at 65°C for 4 hours with stirring, resulting in a weight average molecular weight of 7XLO.
A copolymer of (by GPC) was synthesized.

Toluene was distilled off from this polymerization reaction product by vacuum distillation.

1/8 of the carboxyl group of this copolymer
250 parts per equivalent amount of ammonia water and 100 parts of copolymer
of water was added to neutralize the mixture, and the phase was inverted to obtain hydrosil in which the continuous phase was water. This hydrosil was strained in the same manner as in Example 3 to obtain a pressure-sensitive adhesive tape.

Example 5 [I]-octyl acrylate 65 9 Methyl methacrylate 35 9 Methacrylic acid
10 1 lauryl mercaptan
0.15 g water
160 g of the above composition was placed in a No. 14 flask and heated to 70°C while stirring, and then a polymerization initiator solution prepared by dissolving 0.1 g of potassium persulfate in No. 51 water was added to the flask.
After reacting at 70°C for 3 hours, the weight average molecular weight was 1.5.
A copolymer emulsion of X 105 (by GPC) was synthesized. This copolymer emulsion was salted out, and the precipitated copolymer was filtered, washed with water, and dried.

Next, the mixture was neutralized and phase inverted in the same manner as in Example 1 to obtain hydrosil.

Using this hydrosil, a pressure-sensitive adhesive tape was obtained in the same manner as in Example 1.

Example 6 n-butyl acrylate 65 1 ethyl acrylate 85 g acrylic acid
7g benzoyl peroxide 0.
1yaxto 280g of an aqueous solution of polyvinyl alcohol with weight i% was placed in a flask No. 11, and the above composition was added and reacted at 79°C for 4 hours with stirring to obtain a copolymer with a weight average molecular weight of 6 x 10 (according to GPC) and an average particle size. Pearl particles of 1.5 mm were obtained.

The particles were filtered, washed with water, and dried.

At the same time, 15 parts of n-propyl alcohol was added to 100 parts of this copolymer, and after sufficiently dissolving the copolymer, hydrosil was obtained in the same manner as in Example 3. Using this hydrosil, a pressure-sensitive adhesive tape was obtained in the same manner as in Example 3.

The performance evaluation results for each of the pressure-sensitive adhesive tapes of Examples 2 to 6 above are shown in Table 2 below.

Table 2

Claims (1)

[Claims] (1) A solvent whose main component is an acrylic copolymer consisting of 80-99% by weight of raw monomers mainly composed of acrylic esters or methacrylic esters and 1-20% by weight of copolymerizable unsaturated monomers having acidic groups. Content is 0-2
preparing a raw material substantially free of other media at 0% by weight;
Alkali and water are added to this to neutralize some or all of the acidic groups in the copolymer molecules, and the copolymer is stably dispersed in water with an average particle size in the range of 0.01 to 0.1 μm. A pressure-sensitive adhesive composition is prepared by blending a compound containing two or more aziridinyl groups in one molecule as a crosslinking agent onto a tape support. Method of manufacturing adhesive tape.