JPS58164669A - Preparation of pressure-sensitive adhesive tape - Google Patents

Abstract

PURPOSE:To provide the titled tape excellent in water resistance and adhesion, by removing unreacted matter and a medium from an acidic group-contg. acrylic copolymer and then applying onto a tape substrate a hydrosol formed by neutralizing by the addn. of an alkali and water. CONSTITUTION:After an acrylic copolymer comprising 80-99wt% major monomer consisting mainly of (meth)acrylate e.g., ethyl (meth)acrylate and 20- 1wt% copolymerizable unsatd. monomer having an acidic group e.g., (meth) acrylic acid is synthesized, unreacted matter or a medium together with it are removed. An alkali and water are added to the resulting compd. to neutralize part or the whole of the acidic groups of the copolymer molecule and convert the copolymer into a stably dispersed hydrosol with average particle diameter in the range of 0.01-0.1mum. The hydrosol is applied onto a support to give a pressure-sensitive adhesive tape markedly excellent in water resistance and adhesion.

Description

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

Traditionally, this type of tape has been manufactured by applying 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 organic solvent and requires a lot of petroleum resources. Various alternative methods have been proposed from the viewpoint of problems such as pollution and pollution prevention. For example, methods are known that use so-called high-solid adhesives, which are organic solvent solutions with as little amount of solvent as possible, and methods that use hot-melt adhesives or emulsion adhesives that do not require organic solvents. .

However, high-solid adhesives have the disadvantage of extremely high viscosity and the need for highly precise coating equipment, and the reality is that they are hardly ever put into practical use industrially. In addition, hot-melt adhesives that have a high viscosity when melted by heating are difficult to coat with a uniform thickness, while those that have a low viscosity generally have poor heat resistance and coating workability. There is a problem that it is difficult to achieve both heat resistance and heat resistance.

On the other hand, emulsion-type adhesives do not contain organic solvents, so they do not have a particularly negative effect on heat resistance and can provide relatively good coating workability, but on the other hand, they use emulsifiers. Therefore, the water resistance and adhesive properties of the coating film are difficult. In other words, the emulsifier used during polymerization or when blending additives such as tackifier resin after polymerization usually contains 3% in the coating film.
A large amount of ~10% by weight is also mixed in, which significantly impairs the water resistance of the coating film and also has an adverse effect on the adhesive properties. Furthermore, since the average particle diameter of the emulsion is about 0.1 to 1 μm, 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 to 1 0.7 μm) is stirred at high speed in the presence of an alkali such as caustic potash, caustic soda, or ammonium hydroxide...
.

A method for producing hydrosil by a so-called strippable method has been proposed in which the surface of the particles is scraped off to form fine particles with a particle diameter of 0.01 to 0.17 zm. deer,
According to this method, improvement in film-forming ability due to microparticulation is observed, but because of the use of emulsifiers and the limited molecular weight of the polymer that can be hydrosylated, it is generally difficult to hydrosylate even if the weight average molecular weight is 10' or more. However, it has mainly been applied only to the paint field and paper size field.

The inventors have previously developed polymers that have acidic groups and have a relatively high molecular weight (weight average molecular weight 10 to 10] Synthesize an acrylic copolymer, add alkali and water to it, neutralize the acidic groups 2 above, sv, = +c, i, and emulsify and disperse the 3-self copolymer into fine particles. We proposed a method for producing a pressure-sensitive adhesive (tape 0), which consists of a pressure-sensitive adhesive (tape 0), which is made of hydrosil and coated on a tape support. :, 7""" shows high water resistance, 5" small particles"
It has the advantage of exhibiting excellent film-forming properties and significantly improved water resistance and adhesive properties compared to conventional emulsion-type adhesives. However, when the amount of solvent and unreacted monomer (especially the latter amount) present after polymerization increases, hydrosilation becomes difficult and the stability of hydrosil particles tends to decrease somewhat. It was necessary to increase the amount of unreacted substances as much as possible and reduce the amount of unreacted substances.

This invention was discovered through intensive studies aimed at further improving the proposed method, and its gist is that the main monomer 80 to 99 weight it%
After synthesizing an acrylic copolymer consisting of 1 to 20% by weight of a copolymerizable unsaturated monomer having an acidic group, unreacted substances or unreacted substances and a medium are removed to obtain substantially unreacted substances. A solid material containing no medium is prepared, and an alkali and water are added thereto to neutralize some or all of the acidic groups in the copolymer molecules, and the copolymer has an average particle diameter of 0.01. The present invention provides a method for producing a pressure-sensitive adhesive tape, characterized in that the hydrosil is stably dispersed in a range of 0.1 μm to 0.1 μm, and is applied onto a tape support.

That is, in this invention, an acrylic copolymer having an acidic group is synthesized by various polymerization methods, and a solid material is obtained by removing medium components such as organic solvents and water and unreacted monomers from this copolymer. When converted into hydrosil by the above method, hydrosilation becomes easier compared to the proposed method since it does not contain unreacted substances and medium components, and the stability of the hydrosil dispersion is greatly improved, and the viscosity of the dispersion is It has been found that the coating properties and coating workability on the tape support are improved because the coating properties are relatively low, making it possible to use a high base. In addition, the pressure-sensitive adhesive tape obtained by the method of this invention has high water resistance because it does not contain an emulsifier, and has excellent film-forming properties because of its small particles, making it easier to use than conventional emulsion-type adhesives. It was found that significantly improved water resistance and adhesion properties were obtained compared to V1.

Moreover, in this invention method, after mixing various additives such as tackifiers, softeners, crosslinking agents, etc. that are blended in general pressure-sensitive adhesives into the solid material whose main component is an acrylic copolymer, By forming hydrosil particles with alkali and water, the above-mentioned additives 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.

In addition, when the additive is a crosslinking agent, whereas in conventional emulsion adhesives, the crosslinking agent dissolved or dispersed in water participates in the crosslinking reaction only with the surface of the emulsion particles.
In the present invention, if the crosslinking agent is mixed into the solid material in advance, a uniform crosslinking reaction can occur inside the resulting particles, so that the effect of improving adhesive properties, especially cohesive force, is noticeable. , and very good results in quality stabilization.As described above, according to the method of this invention, all the drawbacks of conventional emulsion type adhesives can be avoided and water resistance and adhesive properties can be improved. For this reason, a coating film with excellent performance comparable to that obtained using a general organic solvent solution can be obtained.

In addition, the coating workability is good, and the solid content concentration is 25 to 45.
It is possible to apply the coating at a relatively high concentration of about % by weight and to a uniform thickness even with conventional coating equipment.

In this invention, first, solution polymerization method, emulsion polymerization method,
By a conventionally known method such as a pearl polymerization method or a bulk polymerization method, an unsaturated monomer having an acidic group with a weight of 2 to 20% by weight and 80 to 98% by weight of other unsaturated monomers that can be copolymerized are used. A copolymer with a weight average molecular weight of 1° and a weight of 10 to 10 is synthesized. Thereafter, depending on each polymerization method, the organic solvent used, a medium such as water, and unreacted monomers are removed to obtain a solid material substantially free of medium and unreacted substances. In other words, in the solution polymerization method and the bulk polymerization method, organic solvents and unreacted materials are removed by means such as distillation, in the milk polymerization method, water and unreacted materials are removed by coagulation and separation by salting out, and in the pearl polymerization method, water and unreacted materials are removed by coagulation separation by salting out. Then, the particulate copolymer is separated from water and unreacted substances by filtration. In addition, in the emulsion polymerization method and pearl polymerization method, the emulsifier used during polymerization partially adheres to the surface of the polymer particles, but this emulsifier is removed during the removal operation described above, and if necessary, it must be removed by washing. Bye.

Raw 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. Other monomers mentioned above 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, acrylonitrile, styrene, 2-methoxyethyl acrylate, and vinyl ether. In addition, various functional monomers such as glycidyl acrylate, glycidyl methacrylate, hydroxyethyl methacrylate, acrylamide, and methylolacrylamide are widely included.

Copolymerizable unsaturated monomers having an acidic group that can be used together with the raw monomers mentioned above 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, 2-Acrylamido-2-methylpropanesulfonic acid, 2-7'ri IJ
Examples of the acidic group such as loyloxybenzenesulfonic acid include unsaturated sulfonic acids having a sulfonic group, and also those having other acidic groups may be used, and one or more of these may be used.

The ratio of the main monomer to the copolymerizable unsaturated monomer having an acidic group is 80 to 99 monomers for the former and 20 to 99 monomers for the latter.
It may be 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. Copolymerizable unsaturated upper layer having 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 becomes poor, and a large amount of crosslinking agent is required to improve this, but in this case there is a problem that the stability of the hydrosil is impaired. Also, if the molecular weight is too high, hydrosilation with alkali and water becomes difficult, which is undesirable in terms of adhesive properties.

In this invention, methanol, ethanol, n-furopanol,
After adding an alcohol-based water-soluble solvent such as isopropyl alcohol or 5ec-butanol, alkali and water are added under stirring for neutralization. This produces hydrosil 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. Other α−
Aminoethyl alcohol, ethylamine, flobylamine, etc. can also be used. The amount of alkali used is usually about 0.1 per acid group eaten into the acrylic copolymer.
A ratio of ~2 equivalents is sufficient.
1. The temperature during neutralization treatment depends on the type of acrylic copolymer,
It is kept at a constant temperature depending on its properties, but generally it is kept at a constant temperature of 3.
The temperature is 0 to 80°C. Neutralization and generation of hydrosil may be carried out by adding a predetermined amount of alkali and water at once and stirring and mixing, or by first adding a predetermined amount of alkali or alkaline aqueous solution and stirring and mixing thoroughly. Then, by gradually adding water and inverting the phase, water becomes a continuous phase and the copolymer particles are dispersed in it.
/W type dispersion may also be produced.

The dispersion thus obtained is a hydrosil in which copolymer particles as dispersed particles are uniformly and stably dispersed in water with an average particle diameter in the range of 0.01 to 0.1 μm, and its viscosity is generally 30 to 1,000 voids, and solid content concentration is 25 to 45% by weight.

In addition, when producing this hydrosil, as already mentioned, additives such as tackifiers, softeners, plasticizers, crosslinking agents, fillers, and colorants should be added to the solid raw material before hydrosilation. In this case, it is usually added during polymerization, but it can also be added before polymerization in some cases.

Of course, it is also possible to hydrosilate each of the above additives and then add them to the sol.

The above 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, and this coating is heated and dried. 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. Note that in the following, parts mean parts by weight, and the water resistance and adhesive strength of the pressure-sensitive adhesive tapes obtained in Examples and Comparative Examples were measured by the following methods.

Water Resistance> Pressure-sensitive adhesive tape was immersed in water at 20°C for 7 days and its changes over time were examined. No whitening was observed after 7 days (0), while some whitening was observed after 3 days. (mu), and cases where bleaching phenomenon is noticeable every day (mu).
×).

<Adhesive Strength> A pressure-sensitive adhesive tape with a width of 20+m and a length of 150m was prepared, and the adhesive strength (!9/20m) was measured by peeling it off at 180 degrees according to JIS Z-1528.

Example 1 Ethyl acrylate 50g 2-ethylhexyl acrylate 50g methacrylic acid
15g Azobisisobutyronitrile 0115g Benzene
200. ! The above raw material composition was charged into 11 flasks and reacted with stirring at 65° C. for 4 hours to synthesize a copolymer with a weight average molecular weight of 4×10 (according to GPC). Benzene and unreacted monomers were distilled off from this polymerization reaction product by reduced production distillation.

・・：′・、−・ , □″.

115 for the carboxyl group of this copolymer.
Add an equivalent amount of ammonia aqueous solution (25% by weight) to 80
The mixture was neutralized at a temperature of .degree. C., and then, while stirring, 200 parts of water was added to 100 parts of the copolymer for phase inversion to obtain a transparent hydrosil.

The hydrosil thus obtained has a viscosity (25
℃) was 120 poise, the solid content concentration was 32%, and the average particle size was 0.05 μm (according to Nanosizer).

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

Comparative Example 1 A monomer mixture having the same composition as in Example 1 was subjected to emulsion polymerization using thioglycolic acid as a chain transfer agent and potassium persulfate as a polymerization initiator, resulting in a weight average molecular weight of 3 to 1.
A polymer emulsion of 0 was obtained. This was applied onto a tape support in the same manner as in Example '1, to obtain a pressure-sensitive Roumon tape.

Example 2 '''' A n-octyl acrylate 80.!9 Methyl methacrylate 109 Acrylic acid 2
-Hydroxyethyl 10g methacrylic acid
6I benzoyl peroxide
0.1g thioglycolic acid
0.05 g 15 g of the above composition was charged into a four-bottle flask (No. 11), and the flask was purged with nitrogen for 40 minutes while stirring.

After that, while dripping the remaining amount from the dropping funnel, it was heated to 85℃ for 4 hours.
A copolymer with a weight average molecular weight of 3×105 (according to GPC) was synthesized by reacting for a time. Unreacted monomers were distilled off from this polymerization reaction product by vacuum distillation.

Next, 1/2 of the carboxyl group of this copolymer
Add an equivalent amount of ammonia aqueous solution (25% by volume) and heat to 70°C.
After that, the copolymer 10 was added with further stirring.
A translucent hydrosil was obtained by adding 150 parts of water to 0 parts and inverting the phase.

%, and the average particle diameter was 0.08 μm (according to Nanosizer). A pressure-sensitive adhesive tape was obtained in the same manner as in Example 1 using this hydrosil.

Example 3 n-octyl acrylate s5g Methyl methacrylate 15.9 Acrylic acid
5g lauryl mercaptan
0.15.9 Polyoxyengineered tyrene alkyl phenol ether g Water 16
0g of the above composition was placed in a 1j flask and heated to 70°C with stirring. Then, a polymerization initiator solution containing potassium persulfate 0, II dissolved in 5g of water was added, and the mixture was heated at 70°C for 30 minutes.
A copolymer emulsion having a weight average molecular weight of 6×10 (according to GPC) was synthesized by reacting for a period of time. This copolymer emulsion was salted out, and the precipitated copolymer was filtered with E, washed with water, and dried.

Next, 1/4 of the carboxyl group of this copolymer
Add an equivalent amount of ammonia aqueous solution (25% by weight) and heat to 80°C.
After that, 250 parts of water was added to 100 parts of the copolymer while stirring to effect phase inversion, and a translucent hydrosil was obtained.

The hydrosil thus obtained has a viscosity (25
℃) was 100 poise, the solid content concentration was 28% by weight, and the average particle diameter was 0.06 μm. A pressure-sensitive adhesive tape was obtained in the same manner as in Example 1 using this hydrosil.

Example 4 n-octyl acrylate 65.9 ethyl acrylate 35g methacrylic acid
4g benzoyl peroxide 0.194 x 10% by weight polyvinyl alcohol aqueous solution 250g 11! The above raw material composition was added and reacted at 70°C for 4 hours with stirring to obtain pearl particles with a weight average molecular weight of 5 x 10 (according to GPC) and an average particle diameter of 1 ms (7)''. .

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

Next, 15 parts of n-propyl alcohol was added to 100 parts of this copolymer to sufficiently dissolve it, and then translucent hydrosil was obtained in the same manner as in Example 1.

The hydrosil thus obtained has a viscosity (25
℃) was 170 poise, the solid content concentration was 37% by weight, and the average particle diameter was 0.07 μm. Using this hydrosil, a pressure-sensitive adhesive tape was obtained according to Example 1 below.

The water resistance and adhesive strength of the pressure sensitive adhesive tapes obtained in the above Examples and Comparative Examples were measured and the results are shown in the following table.

Claims (1)

[Claims] (1) After synthesizing an acrylic copolymer consisting of 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, Unreacted substances or unreacted substances and medium are removed to prepare a solid substance substantially free of unreacted substances and medium, and an alkali and water are added to this to remove the acidic groups in the copolymer molecules. While partially or completely neutralized, the copolymer has an average particle size of 0.01 to 0.0.
A method for producing a pressure-sensitive adhesive tape, which comprises forming hydrosil stably dispersed in a range of 1 μm and coating the same on a tape support.