JPS60248786A - Production of pressure-sensitive adhesive tape - Google Patents

Abstract

PURPOSE:Tapes as a support are coated with a photosetting, aqueous dispersion type pressure-sensitive adhesive containing an acrylic copolymer as a base, dried and irradiated with light to stabilize its cohesive power and give the titled tape with high adhesion. CONSTITUTION:Emulsion polymerization of a monomer mixture containing 0.01- 5pts.wt. of polymerizable unsaturated monomers bearing photosensitive groups together with (A) 100pts.wt. of (i) a (meth)acrylic ester and (ii) a polymerizable unsaturated monomer bearing polar groups is effected to give an acrylic copolymer. The photosetting, water-based pressure-sensitive adhesive is formed using the copolymer as a base and tape supports are coated with the adhesive, dried and irradiated with light to give pressure-sensitive adhesive tapes.

Description

Detailed Description of the Invention This invention involves applying a water-dispersed pressure-sensitive adhesive composition made of an acrylic base polymer into which a functional group with a photosensitizing effect has been introduced onto a tape support, drying it, and then irradiating it with light. The present invention relates to a method for producing a pressure-sensitive adhesive tape.

Conventionally, this type of tape has been manufactured by applying a solution of an acrylic polymer in an organic solvent to the tape support and drying it, but this method requires a large amount of organic solvent and requires a large amount of petroleum resources. There are many problems in terms of pollution prevention, fire safety, etc., and switching to alternative methods is actively being promoted. One such method is water-dispersible pressure-sensitive adhesives.

Water-dispersed pressure-sensitive adhesives do not have the above problems (and are widely used because they can achieve thickness accuracy more easily than hot-melt pressure-sensitive adhesives, but because they use water as a medium, There was a drawback that stable cohesive force could not be obtained because the base polymer crosslinking agent was difficult to become uniform.

That is, water-dispersed acrylic pressure-sensitive adhesives have conventionally been used with the addition of crosslinking agents such as polyisocyanate compounds, epoxy resins, melamine resins, peroxides, and metal salts in order to obtain sufficient cohesive strength. However, in either case, emulsion particles consisting of a crosslinking agent dissolved or dispersed in water and a base polymer exist as separate entities in the emulsion, and since the crosslinking agent participates in the crosslinking reaction only with the surface of the emulsion particles, the inside of the emulsion particles As a result, it is difficult to homogenize adhesive properties, especially cohesive force, and it is difficult to obtain a stable product.

The above-mentioned difficulty becomes more pronounced as the particle size of the emulsion particles made of the base polymer increases, and in this case, even if a large amount of crosslinking agent is added, sufficient cohesive force cannot be obtained. Moreover, since the above particle size varies considerably depending on conditions such as emulsion polymerization, the cohesive strength and adhesive strength of the adhesive obtained will change due to this variation even when the same crosslinking agent is used in the same amount. There was a problem in that consistent adhesive properties could not be expected.

In order to avoid such problems, a polyfunctional monomer having two or more carbon-carbon unsaturated bonds in one molecule is used as a type of monomer component when producing a polymer emulsion, thereby creating a three-dimensional polymer. Attempts have been made to obtain particles. In other words, the three-dimensional structure aims to improve the cohesive force similar to that of an external crosslinking agent. However, this method has the problem that the degree of three-dimensionalization tends to vary greatly due to slight differences in polymerization operations, and stable cohesive force similar to that obtained with external crosslinking agents cannot be obtained.

From this point of view, the inventors have conducted extensive studies and found that a uniform crosslinking reaction occurs within and between polymer particles in a water-dispersed acrylic pressure-sensitive adhesive, resulting in slight variations in the particle diameter of the polymer particles. We have now discovered a method for producing a pressure-sensitive adhesive tape with stable cohesive force and excellent adhesive properties regardless of the conditions.

That is, this invention provides a) a) acrylic acid alkyl ester and/or methacrylic acid alkyl ester, b)
consisting of a polymerizable unsaturated monomer having a polar group and C) a polymerizable unsaturated monomer having a functional group having a photosensitizing effect,
C based on 100 parts by weight of the total amount of the C component and b component.
After coating a tape support with a photo-crosslinkable water-dispersed pressure-sensitive adhesive whose base polymer is an acrylic copolymer obtained by emulsion polymerization of a monomer mixture containing 0.001 to 5 parts by weight of the component and drying it. , relates to a method for producing a pressure-sensitive adhesive tape characterized by light irradiation.

In this invention, a functional group that can easily generate radicals by light irradiation, that is, an oil-soluble functional group that has a photosensitizing effect, is uniformly and evenly introduced into each polymer in the water-dispersed polymer particles. Therefore, by coating this on a support, drying it, and then irradiating it with light, uniform crosslinking can be obtained both within and between the polymer particles, and stable cohesive force can be obtained regardless of the size of the polymer particles. Therefore, the pressure-sensitive adhesive tape obtained by this method has excellent cohesive strength even if the polymer particles have some variation in particle size, compared to the conventional method using a water-dispersed pressure-sensitive adhesive using an external cross-linking agent. is obtained, and the quality is stable.

In addition, according to the method of the present invention, compared to the above-mentioned conventional method using a water-dispersed pressure-sensitive adhesive, the crosslinking reaction proceeds only when irradiated with light, so the pot life can be freely adjusted. It is characterized by little change. Furthermore, the advantages of using water-dispersed pressure-sensitive adhesives include that there is no risk of fire or other hazards compared to solution-based adhesives, and that it is easier to achieve thickness accuracy equivalent to that of solution-based adhesives compared to hot-melt adhesives. It is extremely useful industrially.

The C component used in this invention includes acrylic acid alkyl esters such as ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and inoctyl acrylate, and methacrylic acid alkyl esters such as ethyl methacrylate and butyl methacrylate. Use one or more of them. Note that up to 20% by weight of component C may be replaced with other unsaturated monomers copolymerizable with component C, such as vinyl monomers such as vinyl acetate, acrylonitrile, and methacrylonitrile.

As the component b used in this invention, an acrylic polymerizable unsaturated monomer having a polar group such as a carboxyl group, a hydroxyl group, or an amine group is used, such as acrylic acid, methacrylic acid, itaconic acid, acrylic acid, etc. Examples include acid 2-hydroxyethyl ester and acrylic acid dimethylaminoethyl ester. The amount of component b to be used is usually 0.2% of the total amount of component C and component b.
It is preferable to adjust the amount to 20% by weight.

The C component used in this invention is a monomer represented by the following general formula; It can be obtained by converting a compound with a photosensitizing effect into a derivative having a hydroxyl group, and then reacting it with acrylic acid or methacrylic acid.

Compounds with photosensitizing effects include aromatic ketones with photosensitizing effects such as benzophenone, anthraquinone, and benzoin, aromatic aldehydes, aromatic carboxylic acids,
Examples include thioxanthone compounds.

A specific example of the C component is a compound represented by the following structural formula, which is commercially available from UCB under the trade name UVECRYLeP-36 (!:) and can be easily used.

The amount of component C to be used is 0.01 to 5 parts by weight, preferably 0.02 to 2 parts by weight, based on 100 parts by weight of the total amount of component C and component b. The amount of C component used is 0
If it is less than 0.01 parts by weight, crosslinking of the pressure-sensitive adhesive layer formed will be insufficient and the cohesive force will be low, which is not preferable. Furthermore, if the amount of component C used exceeds 5 parts by weight, the degree of crosslinking of the adhesive layer becomes too high and the adhesive strength decreases, which is not preferable.

Emulsion polymerization of the monomer mixture consisting of the above components a, b, and c is carried out by adding an appropriate emulsifier and polymerization initiator to water together with the monomer mixture, and adding a chain transfer agent if necessary. 3 at 50-85℃ under a nitrogen stream.
The reaction may be carried out for up to 10 hours, thereby obtaining the photocrosslinkable water-dispersed pressure-sensitive adhesive of the present invention.

As the emulsifier used here, any known nonionic or anionic emulsifier can be used, and the amount is preferably 5 parts by weight or less per 100 parts by weight of the acrylic copolymer. If the amount used exceeds 5 parts by weight, the adhesion strength decreases, resulting in poor water resistance.

Examples of polymerization initiators include persulfates such as ammonium persulfate and potassium persulfate, hydrogen peroxide, redox catalysts of these with sodium bisulfite, metal salts, amines, and organic peroxides such as benzoyl peroxide. can also be used. The amount of the polymerization initiator used is 0.01 to 5 parts by weight, preferably 0.05 to 2 parts by weight, per 100 parts by weight of the unsaturated monomer.

The molecular weight of the obtained acrylic copolymer is usually 1
The amount should be about 0,000 to 2,000,000, preferably about 200,000 to 1,000,000 (if necessary, lauryl mercaptan,
It is preferable to use a molecular weight regulator such as thioglycolic acid or to adjust the amount of polymerization initiator used, polymerization temperature, polymerization time, etc. so that the molecular weight falls within the above range.

The acrylic copolymer obtained as described above has a functional group having a photosensitizing effect in the molecule, and can be uniformly crosslinked both within the emulsion particles and between the particles when irradiated with light. The dispersion liquid of this acrylic copolymer after emulsion polymerization may be used as it is as the pressure-sensitive adhesive of the present invention, but various additives may be added thereto as necessary.

Examples of such additives include photoactive crosslinking agents such as ethylene glycol dimethacrylate and trimethylpropane triacrylate. This photoactive crosslinking agent is activated by receiving excitation energy from actinic rays or a photosensitizer and leads to crosslinking of the acrylic copolymer, thereby increasing the crosslinking efficiency. The amount added is usually 0 to 100 parts by weight of the acrylic copolymer.
-10 parts by weight, preferably 0 to 3 parts by weight. If too much is added, the crosslinking density of the pressure-sensitive adhesive will increase, resulting in a high degree of three-dimensionality and loss of tackiness, which is undesirable.

In addition, in order to further improve the initial adhesive strength (tack) of the pressure-sensitive adhesive layer formed by light irradiation, a tackifying resin, a softener such as a plasticizer, or a softener with an average molecular weight of s, oo, etc.
An acrylic polymer with a low molecular weight of 0 to 20,000 may be added. The amount of these additives is preferably up to 50 parts by weight per 100 parts by weight of the acrylic copolymer; if the amount is too large, the cohesive force and heat resistance of the pressure-sensitive adhesive layer will be impaired.

These additives can be used directly or by dropping a solution dissolved in a small amount of an organic solvent into water containing 1 to 5 parts by weight per 100 parts by weight of the additive, stirring, and emulsifying the water-dispersed type of the present invention. By adding it to pressure-sensitive adhesives, it can be easily and uniformly dispersed.

Furthermore, if necessary, polyvinyl alcohol and other emulsion stability improvers, thickeners, and the like can be added.

The photocrosslinkable water-dispersed pressure-sensitive adhesive obtained in this way has a low viscosity, and even when the solid content concentration is as high as about 30 to 60% by weight, it can be applied to plastic films, nonwoven fabrics, paper, foils, etc. It can be coated to a uniform thickness (usually 10 to 100 μm thick) on one or both sides of various types of tape supports using a commonly used coating equipment such as a reverse coater or a kiss coater.

By heating and drying after application and irradiating with light, the above-mentioned adhesive is crosslinked, and a pressure-sensitive adhesive tape with excellent adhesive properties, particularly excellent cohesion, and stable quality can be obtained.

The light irradiated here usually has a wavelength range of 180 to 4
Ultraviolet rays of approximately 00 nm are preferred, and sources include low-pressure, medium-pressure, and high-pressure mercury lamps. This light irradiation time is generally 3 to 12 hours using a 400W high-pressure mercury lamp as a standard.
0 seconds is appropriate.

Examples of this invention are shown below. In addition, in the following, parts mean parts by weight. Furthermore, in order to investigate the adhesive properties of the obtained pressure-sensitive adhesive tape, the adhesive force and cohesive force were measured as follows.

<Adhesive strength> Pressure-sensitive adhesive tape was cut into 20-thickness strips, and the tape was pressure-bonded to a stainless steel plate once with a 2Kg roller. After 30 minutes of crimping, a Schopper type peel tester was used for 20 minutes at a speed of 300 mm and 1 minute.
Measure the 180° peel adhesion at ℃.

<Cohesive force> A pressure-sensitive adhesive tape is pasted on a Bakelite plate in 10 mm x 20 pieces, a load of 900 y is applied at 40°C, and the displacement distance is measured after 1 hour.

Example 1 70 parts of butyl acrylate, 25 parts of 2-ethylhexyl acrylate, 5 parts of acrylic acid, UVECRYL P-36
(Polymerizable unsaturated monomer having the aforementioned photosensitizing functional group) 05 parts, dialkyl sulfur #fusuccinate sodium salt (emulsifier) 3 parts, potassium persulfate 03 parts
An acrylic polymer emulsion was obtained by reacting a mixture of 100 parts of ion-exchanged water and 100 parts of ion-exchanged water at 70° C. under a nitrogen stream for 8 hours. The average molecular weight of the polymer in this emulsion is 1 million, and the average particle size is about 1.
It was 70OA.

This acrylic polymer emulsion was used as a water-dispersed pressure-sensitive adhesive, and this was applied onto a support made of a 25/'' thick polyester film to a dry thickness of 80μ, and dried at 110°C for 10 minutes. After that, 40
30 seconds at 20σ irradiation distance with 0W high-pressure mercury lamp, 4
Pressure-sensitive adhesive tapes according to the invention were prepared by irradiating with light for 5 seconds and 60 seconds.

Comparative Example 1 A mixture consisting of 70 parts of butyl acrylate, 25 parts of 2-ethylhexyl acrylate, 5 parts of acrylic acid, 3 parts of dialkyl sulfosuccinate sodium salt, 0.3 parts of potassium persulfate, and 100 parts of ion-exchanged water was prepared. An acrylic polymer emulsion was obtained by reacting at 70° C. for 8 hours under a nitrogen stream. The average molecular weight of the polymer in this emulsion is 1 million, and the average particle size is approximately 1.
It was 600λ.

To this acrylic polymer emulsion, 2 parts of U dissolved in toluene per 100 parts of solid content of the emulsion was added.
Add 05 parts of VECRYL P-36 (mentioned above) and stir evenly to make a water-dispersed pressure-sensitive adhesive.
It was coated on a thick polyester film to a dry thickness of 80p, dried at 110'C for 10 minutes, and then
30 seconds at 20σ irradiation distance with 0W high-pressure mercury lamp, 4
Comparative pressure-sensitive adhesive tapes were prepared by irradiating with light for 5 seconds and 60 seconds.

Comparative Example 2 To the polymer emulsion obtained in Comparative Example 1, 0.5 parts, 1 part and 2 parts of water-soluble melamine resin were added to 100 parts of the solid content of this emulsion to form a water-dispersed pressure sensitive adhesive. was coated onto a 25 μm thick polyester film to a dry thickness of 80 μm, and dried at 130° C. for 10 minutes to obtain a pressure sensitive adhesive tape.

Comparative Example 3 The polymer emulsion obtained in Comparative Example 1 was added with 100 parts of solid content of this emulsion. Add 0.5 parts, 1 part and 2 parts of benzoyl peroxide dissolved in 1 part of toluene and stir evenly to form a water-dispersed pressure sensitive adhesive, which was spread onto a 25μ thick polyester film to a dry thickness of 80μ. It was coated to give a pressure-sensitive adhesive tape and dried at 150° C. for 10 minutes.

When the adhesive properties of the pressure sensitive adhesive tapes obtained in Example 1 and Comparative Examples 1 to 3 above were evaluated, the results shown in Tables 1 and 2 below were obtained.

Table 1 Table 2 Example 2 Butyl acrylate 70 parts, 2-ethylhexyl acrylate 25 parts, acrylic acid 5 parts, UVECRYL■P-36
A mixture consisting of 05 parts of (previously mentioned), 3 parts of dialkyl sulfosuccinate sodium salt, and 25 parts of ion-exchanged water was added dropwise over 8 hours to a mixture of 03 parts of potassium persulfate and 75 parts of ion-exchanged water under a nitrogen stream. An acrylic polymer emulsion was obtained by reacting.

The average molecular weight of the polymer in this emulsion was 1 million, and the average particle diameter was about 2,400λ.

This acrylic polymer emulsion was used as a water-dispersed pressure-sensitive adhesive, and this was applied onto a 25p thick polyester film to a dry thickness of 80PL.
After drying at 30° C. for 10 minutes, the tape was irradiated with light using a 400 W high-pressure mercury lamp at an irradiation distance of 20 c1n for 30 seconds, 45 seconds, and 60 seconds to produce a pressure-sensitive adhesive tape according to the present invention.

Comparative Example 4 A mixture consisting of 70 parts of butyl acrylate, 25 parts of 2-ethylhexyl acrylate, 5 parts of acrylic acid, 3 parts of dialkyl sulfosuccinate sodium salt, and 25 parts of ion-exchanged water was heated with 0 potassium persulfate under a nitrogen stream. An acrylic polymer emulsion was obtained by dropping the mixture into a mixture consisting of .3 parts and 75 parts of ion-exchanged water for 8 hours to react. The average molecular weight of the polymer in this emulsion was 1 million, and the average particle diameter was about 2.400λ.

To this acrylic polymer emulsion, 5 parts of UVECRYL@P-36C (mentioned above) dissolved in 2 parts of toluene was added to 100 parts of the solid content of this emulsion,
The mixture was stirred uniformly to obtain a water-dispersed pressure-sensitive adhesive. This was placed on a polyester film with a thickness of 25 mm to a dry thickness of 80 μm.
After drying at 110℃ for 10 minutes, it was coated with a 400W high-pressure mercury lamp at a distance of 20cm for 3 minutes.
Comparative pressure-sensitive adhesive tapes were prepared by irradiating with light for 0 seconds, 45 seconds, and 60 seconds.

Comparative Example 5 To the polymer emulsion obtained in Comparative Example 4, 0.5 parts, 1 part, and 2 parts of water-soluble melamine resin were added to 100 parts of solid content of this emulsion to prepare a water-dispersed pressure-sensitive adhesive. This was applied onto a polyethylene film having a thickness of 251 En to a dry thickness of 80 μm, and dried at 130° C. for 10 minutes to obtain a pressure-sensitive adhesive tape.

Comparative Example 6 To the polymer emulsion obtained in Comparative Example 4, 0, 5, 1, and 2 parts of benzoyl peroxide dissolved in 2 parts of toluene were added to the polymer emulsion obtained in Comparative Example 4, based on 100 parts of the solid content of this emulsion, and uniformly This was stirred to form a water-dispersed pressure-sensitive adhesive, which was coated onto a 25μ thick polyester film to a dry thickness of 807" and heated at 150°C for 10
It was dried for a few minutes to form a pressure sensitive adhesive tape.

When the adhesive properties of the pressure sensitive adhesive tapes obtained in the above Example 2 and Comparative Examples 4 to 6 were evaluated, the results shown in Tables 3 and 4 below were obtained.

Table 3 Table 4 As is clear from a comparison of Tables 1 and 2 and Tables 3 and 4 above, the photo-crosslinkable type water-dispersed pressure sensitive adhesive of the present invention was used to create a tape. The pressure-sensitive adhesive tape, which is formed by applying it to the support △, drying it, and then irradiating it with light, crosslinks uniformly both within and between the polymer particles in the polymer emulsion, so it is not affected by the particle size of the polymer particles. It can be seen that a pressure-sensitive adhesive tape with stable cohesive force, stable quality, and excellent adhesive properties can be easily provided.

Claims (1)

[Claims] +1) From a> acrylic acid alkyl ester and/or methacrylic acid alkyl ester, b) a polymerizable unsaturated monomer having a polar group, and C) a polymerizable unsaturated monomer having a functional group having a photosensitizing effect 001 parts by weight of component C for 100 parts by weight of the total amount of components a and b.
A photo-crosslinkable water-dispersed pressure-sensitive adhesive whose base polymer is an acrylic copolymer obtained by emulsion polymerization of a monomer mixture containing ~5 parts by weight is applied to a tape support, dried, and then irradiated with light. A method for producing a pressure-sensitive adhesive tape.