JPS624079B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a crosslinked pressure-sensitive adhesive that can form an adhesive layer that has excellent storage stability, appropriate adhesive strength, and high adhesive retention. Pressure-sensitive adhesives have moderate adhesion to the surface to which they are adhered, resistance to displacement in the shear direction on the surface to which they are adhered,
In other words, it must be able to satisfy both adhesion and retention strength. However, in general, even if the adhesive strength is satisfied, the adhesive retention strength is often inferior, and in order to increase the adhesive retention strength, a crosslinking agent is usually used and an adhesive solution containing the crosslinking agent is applied to the base film etc. A method of carrying out a crosslinking reaction after drying has been adopted. Conventionally, as a type of cross-linked adhesive,
A type in which the resin component is a carboxyl group-containing polymer and is ionically crosslinked with an ionic polyvalent metal compound is known. However, because this type of adhesive has a particularly high reactivity with ionic polyvalent metal compounds, crosslinking reactions occur before it is applied to the base film, that is, during manufacturing or storage, resulting in increased viscosity and gelation. This is a difficult problem that can easily occur. Therefore, in recent years, as a solution with fewer such problems, a solution has been proposed in which a polar organic solvent such as an alcohol, tetrahydrofuran, dioxane, or dimethylformamide is added to a polymer solution using an organometallic compound as a crosslinking agent. This adhesive uses a polar organic solvent that delays the crosslinking of carboxyl group-containing polymers in a mixed system with ordinary non-polar organic solvents for dissolving polymers such as toluene, benzene, and heptane, and this is removed by coating and drying. A cross-linking reaction occurs quickly and gives the adhesive layer appropriate adhesive strength and good adhesion retention. However, this adhesive also has a few drawbacks.
For example, by using a carboxyl group-containing polymer with a large molecular weight, or by solvent volatilization during manufacturing or storage, polar organic solvents and non-polar organic solvents (especially mixed non-polar organic solvents) may be used.
When the ratio of the polar organic solvent to the polar organic solvent changes, there is a problem that the crosslinking suppressing effect of the polar organic solvent is greatly reduced. Furthermore, when compounds such as nickel, lead, and copper, which generally have a smaller metal ionization tendency than iron, are used as organometallic compounds, the desired effects are hardly obtained. This invention was developed as a result of intensive studies in light of the above circumstances.When aqueous ammonia is mixed in the adhesive solution when an ionic polyvalent metal salt is used as a metal ion crosslinking agent, the above-mentioned drawbacks may occur. A cross-linked pressure-sensitive adhesive with excellent storage stability is obtained, and when it is applied to a base film and dried to remove the ammonia water and solvent, the cross-linking reaction progresses, resulting in moderate adhesion and high adhesion retention. It was found that a strong adhesive layer could be formed.
It has been done. That is, this invention relates to a cross-linked adhesive with excellent storage stability, which is characterized in that aqueous ammonia is mixed into an organic solvent solution containing a carboxyl group-containing polymer and an ionic polyvalent metal salt. . The carboxyl group-containing polymer used in this invention generally has an average carbon number of 3 to 12
The main monomer is an ester of acrylic acid or methacrylic acid having an alkyl group of Those obtained by copolymerizing with acids, etc., or those obtained by using other copolymerizable monomers such as vinyl acetate, acrylonitrile, acrylamide, etc. in the above copolymerization are used. Of course, other polymers may be used as long as they have a carboxyl group in the molecule and are effective as the resin component of the pressure-sensitive adhesive. The metal ion crosslinking agent used in this invention is an ionic polyvalent metal salt, and typical examples thereof include chlorides of divalent or higher-valent metals and organic acid salts. Organic acids include acetic acid, propionic acid,
These include aliphatic carboxylic acids such as caproic acid, capric acid, lauric acid, and stearic acid, aromatic carboxylic acids such as benzoic acid, oxalic acid, citric acid, and tartaric acid. Examples of divalent or higher metals include calcium,
There are metals that have a higher ionization tendency than iron, such as magnesium, aluminum, and iron, and metals that have a lower ionization tendency than iron, such as copper, nickel (divalent), mercury (trivalent), and lead, and any of them can be used. It is. In this invention, the above-mentioned carboxyl group-containing polymer and, if necessary, a polymer partially having no carboxyl groups in the molecule are used as the resin component, and this and an ionic polyvalent metal salt are usually used as a tackifying agent and a filler. A polymer solution is prepared by dissolving optional components such as agents and pigments in common organic solvents such as toluene, benzene, heptane, octane, ethyl acetate, and methyl ethyl ketone, and ammonia water is further added to this to create a cross-linked pressure-sensitive adhesive. as a drug. The amount of ammonia water used is usually 1/50 to 1/1 of the carboxyl group of the carboxyl group-containing polymer.
It is sufficient if the amount is equivalent. The cross-linked pressure-sensitive adhesive of the present invention thus obtained can suppress cross-linking reactions during storage even if the resin component has a high molecular weight, and is unique to the proposed method using a polar organic solvent. There is no inevitable reduction in the crosslinking suppressing effect due to solvent volatilization, as would be the case with
It has excellent storage stability. On the other hand, when this pressure-sensitive adhesive is applied to a base film or the like and dried to volatilize the ammonia water and solvent, the crosslinking reaction immediately proceeds, forming an adhesive layer with appropriate adhesive strength and high adhesive retention. Ru. Next, examples of this invention will be described. In the following, parts shall mean parts by weight. Example 1 90 parts of butyl acrylate and 10 parts of methacrylic acid were copolymerized in toluene to obtain a polymer solution having an average molecular weight of 150,000 and a solid content concentration of 40% by weight. In this solution, zinc chloride (ZnC ₂ ) (No. 1),
Add 10 parts each of copper chloride (CuCl ₂ ) (No. 2),
Further, aqueous ammonia was added and mixed in an amount of 1/2 equivalent to the carboxyl group in the polymer to obtain two types of crosslinked pressure sensitive adhesives, Nos. 1 and 2 of the present invention. None of these adhesives showed any gelation during manufacture, and no increase in viscosity was observed even after the adhesives were left at 30°C for one week. Next, each of these adhesives was cast onto a polyester film to a dry thickness of 50μ.
An adhesive tape was prepared by drying at 130° C. for 3 minutes, and the peeling adhesive strength and adhesive holding strength of this tape were examined by conventional methods, and the results were as shown in the table below. The adhesion retention strength was determined by measuring the time required for the test piece to fall under a load of 200 g/cm ² at 30°C. For reference, the same table also includes test results for samples to which no metal salts were added as reference examples.

[Table] As is clear from the above table, it can be seen that the adhesive of the present invention provides a suitable adhesive strength and high adhesive holding power. Comparative Example 1 Two types of adhesives were prepared in exactly the same manner as in Example 1, except that 10 parts of ethanol was used instead of aqueous ammonia. No gelation was observed during manufacturing with the adhesive that used zinc chloride (which has a greater tendency to ionize than iron) as the ionic polyvalent metal salt;
When left at 30°C for one week, an increase in viscosity was clearly observed. On the other hand, when copper chloride (which has a lower ionization tendency than iron) was used as the ionic polyvalent metal salt, it gelled during production. Example 2 70 parts of 2-ethylhexyl acrylate, 28 parts of vinyl acetate, and 2 parts of acrylic acid were copolymerized in a mixed solvent of ethyl acetate and toluene to produce a polymer with an average molecular weight of about 450,000 and a solid content concentration of 20% by weight. A polymer solution was obtained. Add 0.1 part of lead acetate to this and add ammonia water to the carboxyl group in the polymer at a rate of 2/2.
The crosslinked pressure-sensitive adhesive of the present invention was prepared by adding and mixing them in an amount of 3 equivalents. Similar to Example 1, this adhesive had excellent storage stability. Next, using this adhesive, an adhesive tape was made in the same manner as in Example 1, and its adhesive retention strength was examined, and it was found to have a high adhesive retention strength of over 1000 minutes. In addition, those without lead acetate added are 180
It was hot in minutes. Comparative Example 2 Adhesives were prepared in the same manner as in Example 2 using various alcohols instead of aqueous ammonia, but none of them could prevent gelation during manufacture.

Claims (1)

[Claims] 1. A crosslinked pressure-sensitive adhesive with excellent storage stability, characterized in that aqueous ammonia is mixed into an organic solvent solution containing a carboxyl group-containing polymer and an ionic polyvalent metal salt.