JPH0146547B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to general pressure-sensitive adhesive sheets such as labels and stickers, and more specifically to high-quality paper, coated paper, and polyvinyl chloride containing metal compounds as the surface base material of labels and stickers. The present invention relates to a pressure-sensitive adhesive sheet using a film or the like and an acrylic pressure-sensitive adhesive as the pressure-sensitive adhesive, which has excellent storage stability under moist heat or heating conditions. [Prior art] Adhesive sheets such as labels and stickers are usually
A base material such as high-quality paper, coated paper, polyvinyl chloride film, or polyethylene terephthalate film (hereinafter referred to as the surface base material), a rubber adhesive mainly composed of natural rubber or synthetic rubber, or an acrylic acid alkyl ester and methane. It consists of an acrylic adhesive made of a copolymer mainly composed of acrylic acid alkyl ester, and a release paper for the purpose of protecting the adhesive. A simple explanation of the process of processing adhesive sheets into labels, stickers, etc. First, a punching blade having a predetermined shape is used to insert the blade into the surface base material and the adhesive, leaving the release paper of the adhesive sheet. Next, unnecessary portions of the labels and stickers (usually called lees or matrix) are removed, so-called lees raising is performed, and the labels and stickers are left on the release paper. This process is a common process for manufacturing labels and stickers, but if the adhesive is not completely cut off during punching, the lees will break during lifting.
It becomes impossible to continuously produce labels and stickers. Acrylic adhesives are far superior to rubber adhesives in terms of ease of punching. Acrylic adhesives are copolymers mainly composed of alkyl acrylates and alkyl methacrylates, but the monomer composition may be changed or carboxyl groups in acrylic acid or methacrylic acid may be replaced with isocyanate, A wide range of adhesive properties can be developed by appropriately crosslinking with epoxy, melamine, aziridine, polyvalent metal chelate, etc. As described above, acrylic pressure-sensitive adhesives are widely used as pressure-sensitive adhesives for pressure-sensitive adhesive sheets because of their excellent label processability and the ability to obtain a wide range of adhesive properties. However, on the other hand, it is known that in a pressure-sensitive adhesive sheet whose surface base material contains a metal compound, a phenomenon in which the adhesive strength is extremely reduced occurs when the pressure-sensitive adhesive sheet is left at high temperature or under high temperature and high humidity. The present inventors have completed the present invention as a result of intensive research into the cause of the above-mentioned decrease in adhesive strength and countermeasures thereof. [Problems to be Solved by the Invention] Talc, calcium carbonate, and the like are used as paper fillers in high-quality paper, coated paper, and the like used as surface substrates. Particularly in recent years, there has been a strong tendency to use calcium carbonate to improve durability and reduce manufacturing costs through neutral papermaking. When left for a long time, the metal compound dissociates, and the free metal ions that have entered the adhesive combine with acrylic acid or methacrylic acid to cause excessive crosslinking, resulting in a decrease in the fluidity of the adhesive, and in other words, the adhesive strength. cause a decrease in This phenomenon can be confirmed by looking at the infrared absorption spectra of each pressure-sensitive adhesive before and after its adhesive strength has decreased, based on the absorption in the vicinity of 1,600 to 1,500 cm ^-1 , that is, the presence or absence of absorption due to the presence of ionized carboxyl groups. A similar phenomenon occurs when polyvinyl chloride film is used as the surface base material. In the case of polyvinyl chloride film, the metal stabilizer contained in the film penetrates into the adhesive along with the plasticizer when left at high temperatures, reacts with the acrylic acid or methacrylic acid in the adhesive, and causes over-crosslinking. It is. [Means for Solving the Problems] The present invention was developed as a result of intensive research into a method for preventing the crosslinking reaction between metal ions entering from the surface substrate and acrylic acid or methacrylic acid in the adhesive. It has been discovered that the use of sequestering agents is an extremely effective method. Substances that sequester metal ions include dibasic acids such as phthalic acid, succinic acid, oxalic acid, and aspartic acid;
Although ethylenediaminetetraacetic acid (EDTA) and condensed phosphates are known, the use of condensed phosphates is most effective for this purpose. As the condensed phosphate, sodium tripolyphosphate, acidic sodium metaphosphate, potassium pyrophosphate, sodium hexametaphosphate, sodium polyphosphate, potassium polyphosphate, potassium metaphosphate, etc. can be used. Metal ions from the surface substrate are removed by applying the condensed phosphate to the surface of the surface substrate in contact with the adhesive layer at 0.5 g/m ² or more, preferably 0.7 g/m ^{2 or} more. This can prevent the infiltration of acrylic adhesives and prevent the adhesive strength of acrylic adhesives from decreasing. If the amount of the condensed phosphate applied to the surface substrate is less than 0.5 g/m ² , the effect of preventing a decrease in adhesive strength will be small. Application amount is 1.2g/
If it exceeds m ² , although the effect of preventing a decrease in adhesive strength can be obtained, the adhesion between the surface base material and the adhesive will decrease slightly.
Furthermore, if economic efficiency is also considered, it is not practical. When the surface substrate is a paper product such as high-quality paper or coated paper, the application method may be to apply the condensed phosphate as an aqueous solution together with a water-soluble polymer (starch, carboxymethyl cellulose, polyvinyl alcohol, etc.). The coating location may be an on-machine coater such as a size press or a calender roll, or an off-machine coater, but is not particularly limited. When the surface substrate is a film product such as polyvinyl chloride film, the condensed phosphate may be applied together with an organic solvent-soluble resin (vinyl chloride, vinyl acetate copolymer, various acrylic binders). Below, an example in which a coated paper containing 15% calcium carbonate was used as a surface base material and a condensed phosphate was applied using a starch aqueous solution and the effects thereof will be explained in detail. The present invention is not limited to these embodiments. [Example] Example 1 A mixed aqueous solution of sodium tripolyphosphate and starch was applied to the surface of coated paper (trade name: SK Coat, manufactured by Sanyo Kokusaku Pulp Co., Ltd.) that was in contact with the adhesive.
Surface base material coated at a coating weight of 1.0g/m ² (sodium tripolyphosphate coating amount: 0.8g/m ² ). Comparative Example 1 Surface base material of uncoated coated paper used in Example 1. Comparative Example 2 A mixed aqueous solution of sodium tripolyphosphate and starch was applied to the coated paper used in Example 1 in a coating amount of 0.6 g/
m ² (as the coating amount of sodium tripolyphosphate
0.4g/m ² ) surface base material. Comparative Example 3 A mixed aqueous solution of sodium tripolyphosphate and starch was applied to the coated paper used in Example 1 in a coating amount of 1.4 g/
m ² (as the coating amount of sodium tripolyphosphate
1.2g/m ² ) surface base material. Emulsion-type acrylic adhesive (trade name: Tufftac 601, manufactured by Sanyo Kokusaku Pulp Co., Ltd.) was added to release paper (trade name: EK120D2, manufactured by Soken Kako Co., Ltd.) so that the solid content was 20 g/m ² After coating and sufficiently drying in a hot air dryer, it was applied to the surface substrate of Example 1 and Comparative Examples 1 to 3, and the adhesive strength after being left under predetermined conditions was
Shown in the table. Incidentally, the standing conditions and measurement conditions in Table 1 were based on the methods shown below. Normal storage: Each sample was left in an atmosphere of 20℃ and 65% RH for one week. Humid heat storage: Each sample was left in an atmosphere of 40℃ and 85%RH for one week. Adhesive strength: A sample with a width of 20 mm was attached to a polyethylene plate. Yes, 5Kg
Peeling resistance when crimped once with a loaded roll and peeled off 10 minutes later using a tensile testing machine at a tensile speed of 300mm/min, converted to a 10mm width.

[Table] It can be seen from Example 1 and Comparative Example 1 in Table 1 that by applying sodium tripolyphosphate to the surface substrate, it is possible to prevent the adhesive strength from decreasing after being left under moist heat. In addition, if the amount of sodium tripolyphosphate applied is small (Comparative Example 2), the effect is insufficient, and if the amount applied is too large (Comparative Example 3), although the moist heat deterioration prevention effect is recognized, the adhesive strength after standing under normal conditions is lower than that of Example 3. Although it is slightly lower than that of , it is not to the extent that it lacks practicality, but it is not practical when considering economic efficiency. Example 2 Potassium pyrophosphate was added to a polyvinyl chloride film containing a barium-zinc stabilizer (trade name: Viniban 80μ, manufactured by Band Kagaku Co., Ltd.) with acrylic resin (trade name: Thermolac S-2000, manufactured by Soken Kako Co., Ltd.) The surface base material was coated with potassium pyrophosphate in an amount of 1.0g/ ^m2 . Comparative Example 4 Polyvinyl chloride film surface base material used in Example 2. Solution-type acrylic adhesive (product name: Cybinol)
AT-201L, manufactured by Saiden Chemical Co., Ltd.) to release paper (product name: EK120D2, manufactured by Soken Kako Co., Ltd.) in terms of solid content.
It was applied to a weight of 30g/ ^m2 , and after drying, Example 2,
Table 2 shows the adhesive strength of Comparative Example 4 after it was attached to the surface substrate and left under predetermined conditions. Incidentally, the standing conditions and measurement conditions in Table 2 were based on the methods shown below. Leaving at room temperature: Same conditions as above; Leaving heated: Each sample was left in an atmosphere of 70°C for one week; Adhesive strength: Same conditions as above.

〔Effect of the invention〕

As shown in Example 1 and Example 2, by applying condensed phosphate to the surface base material, a surface base material containing a metal compound, and an alkyl acrylate ester and an alkyl methacrylate ester as main components are obtained. It was confirmed that the combination of adhesives can prevent a decrease in adhesive strength after exposure to moist heat or heating.

Claims (1)

[Scope of Claims] 1. In a pressure-sensitive adhesive sheet composed of a surface base material containing a metal compound, an acrylic adhesive layer, and a release paper, 0.5 g of a metal ion sequestrant is added to the surface of the surface base material in contact with the pressure-sensitive adhesive layer. An adhesive sheet characterized by being coated with a coating of /m ² or more. 2. The pressure-sensitive adhesive sheet according to claim 1, wherein the metal ion sequestering agent is a condensed phosphate-based substance.