JPS624078B2 - - 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. As a result of intensive studies in light of the above circumstances, this invention was developed based on the results that when an ionic polyvalent metal salt consisting of iron or a metal with a greater ionization tendency than iron is used as a metal ion crosslinking agent, an appropriate amount of it can be added to an adhesive solution. When mixed with water, a cross-linked pressure-sensitive adhesive with excellent storage stability without the above-mentioned drawbacks is obtained, and when this is applied to a base film and dried to remove the water and solvent, cross-linking occurs. This was done because it was found that the reaction progressed to form an adhesive layer with appropriate adhesion and high adhesion retention. That is, this invention involves adding at least 2 parts by weight of water per 100 parts by weight of the polymer into an organic solvent solution containing a carboxyl group-containing polymer and an ionic polyvalent metal salt consisting of iron or a metal with a higher ionization tendency than iron. The present invention relates to a crosslinked adhesive having excellent storage stability, which is characterized in that it is mixed with a crosslinked adhesive. 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. The effect of suppressing crosslinking due to the presence of water can be obtained by using among these ionic multivalent metal salts, the type of metal being iron or a metal having a greater ionization tendency than iron. Typical examples of these metals include iron, calcium, zinc, magnesium, and aluminum. Note that even if a salt made of a metal other than the above-mentioned metals, that is, a metal having a smaller ionization tendency than iron, such as copper, nickel, or lead, is used without relying on the present invention, the effect of suppressing crosslinking due to the presence of water cannot be obtained. In this invention, the aforementioned 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 the ionic polyvalent metal salt described above are usually used as an adhesive agent. A polymer solution is prepared by dissolving optional components such as fillers, pigments, etc. in a common organic solvent such as toluene, benzene, heptane, octane, ethyl acetate, and methyl ethyl ketone, and an appropriate amount of water is added to the cross-linked polymer solution. Use pressure sensitive adhesive. The amount of water used is important, and if this amount is less than 2 parts by weight per 100 parts by weight of the carboxyl group-containing polymer, the effects of this invention will be very low. Therefore, it should be at least 2 parts by weight or more, preferably 5 parts by weight or more. However, if the amount is too large, problems may arise with coating conditions, so it is generally desirable to use 5 to 15 parts by weight. 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 concern that the crosslinking suppressing effect will deteriorate due to solvent volatilization, as would be the case, and the storage stability is extremely excellent. On the other hand, when this pressure-sensitive adhesive is applied to a base film, etc. and dried to volatilize the water and solvent, the crosslinking reaction immediately proceeds, forming an adhesive layer with moderate adhesive strength and high adhesive retention. . 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. To this solution, 10 parts of zinc chloride (ZnC ₂ ) was added to 100 parts of the polymer, and then 100 parts of the polymer
5 parts of water was added and mixed to obtain a crosslinked pressure-sensitive adhesive of the present invention. This adhesive shows no gelation during manufacturing,
Further, no increase in viscosity was observed even after this was left at 30° C. for one week. Next, this adhesive was cast onto a polyester film to a dry thickness of 50 μm and dried at 130°C for 3 minutes to make an adhesive tape. The results of the investigation 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 lists the test results for a product to which no zinc chloride was added as Reference Example 1. Comparative Example 1 An adhesive was prepared in the same manner as in Example 1 except that 10 parts of copper chloride (CuC ₂ ) was used in place of 10 parts of zinc chloride, but it gelled during production. Comparative Example 2 An adhesive was prepared in exactly the same manner as in Example 1, except that 10 parts of ethanol was used instead of 10 parts of water.
Although no gelation was observed in this adhesive during manufacture, an increase in viscosity was clearly observed when it was left at 30°C for one week. Example 2 50 parts of 2-ethylhexyl acrylate, 50 parts of butyl acrylate, and 3 parts of acrylic acid were copolymerized with toluene, and the average molecular weight was about 300,000 and the solid content concentration was
A 25% by weight polymer solution was obtained. Polymer
To 100 parts, 3 parts of calcium acetate and 10 parts of water were added and mixed to prepare a crosslinked pressure-sensitive adhesive of the present invention. Similar to Example 1, this adhesive had excellent storage stability. Next, an adhesive tape was prepared using this adhesive in the same manner as in Example 1, and its peeling adhesive strength and adhesive holding strength were examined, and the results were as shown in the table below. In the same table, the results of the investigation on the product without addition of calcium acetate are also listed as Reference Example 2. Example 3 Octyl acrylate 80 parts, ethyl acrylate 20 parts
and 15 parts of acrylic acid were copolymerized in a 1:1 mixed solvent of heptane and toluene to obtain a polymer solution with an average molecular weight of about 200,000 and a solid content concentration of 45% by weight. To this, ferrous chloride per 100 parts of polymer.
0.5 parts and 15 parts of water were added and mixed to prepare a crosslinked pressure-sensitive adhesive of the present invention. Similar to Example 1, this adhesive had excellent storage stability. Next, an adhesive tape was prepared using this adhesive in the same manner as in Example 1, and its peeling adhesive strength and adhesive holding strength were examined, and the results were as shown in the table below. In the same table, the results of the investigation on the product without the addition of ferrous chloride are also listed as Reference Example 3.

[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.

Claims (1)

[Claims] 1. Mixing at least 2 parts by weight of water per 100 parts by weight of the polymer into an organic solvent solution containing a carboxyl group-containing polymer and an ionic polyvalent metal salt consisting of iron or a metal with a greater ionization tendency than iron. A cross-linked pressure-sensitive adhesive with excellent storage stability.