JP6760749B2 - Chloroprene rubber latex adhesive composition - Google Patents

Description

The present invention relates to a chloroprene rubber latex adhesive composition having properties suitable for the production of confidential postcards.

With the revision of the Postal Law, a confidential concealment postcard system has been put into practical use and has become widespread. This confidential concealment postcard folds a postcard containing various information such as personal matters, advertisements, guidance, etc., glues the overlapped part to hide the information content and mails it, and the recipient puts the overlapped part The information content can be viewed by peeling it off. Such information hiding means are used not only for postcards for mailing, but are collectively called information-carrying sheets.

As a method for manufacturing such an information-carrying sheet, a method is generally used in which a sheet coated with an adhesive is manufactured in advance, information is printed on the concealed surface, and then the concealed surface is bonded. Therefore, the adhesive for information-carrying sheets has not only adhesive strength that can hold a concealed surface until it is opened, removability without sheet breakage or contamination due to adhesive residue at the time of opening, but also sticking during storage before printing. No storage stability is required.

Conventionally, adhesives using natural rubber latex have been often used for information-carrying sheets, but it has been difficult to satisfy each required performance in a well-balanced manner. Therefore, Patent Document 1 discloses a method using a modified natural rubber latex. In addition, since natural rubber latex is derived from a natural product, variations in quality are unavoidable, and it is difficult to fine-tune the physical properties.
Japanese Unexamined Patent Publication No. 2004-137362

The problems of the present invention are properties suitable for manufacturing an information-carrying sheet, that is, adhesive strength capable of holding a concealed surface until opened, removability without sheet breakage or contamination due to adhesive residue at the time of opening, and storage before printing. It is an object of the present invention to provide a chloroprene rubber latex adhesive composition having a storage stability that does not stick.

The present invention contains chloroprene rubber latex (a) and silica (b) having a gel content of 35 % by weight or more and a crystallization time of 24 hours or more, based on the solid content of the entire adhesive composition. The chloroprene rubber latex adhesive composition is characterized by containing 25 to 75% by weight of the silica (b) .

The chloroprene rubber latex adhesive composition of the present invention is useful as an information-carrying sheet because it has excellent adhesive strength, removability and storage stability. In particular, since industrially manufactured chloroprene rubber latex is used, there is little variation in quality and fine adjustment of physical properties is easy.

The chloroprene rubber latex adhesive composition of the present invention contains the chloroprene rubber latex (a) having a gel fraction of 30% by weight or more and a crystallization time of 24 hours or more. When the gel fraction of the chloroprene rubber latex is 30% by weight or more, the peelability is improved, and when the crystallization time is 24 hours or more, the adhesive strength can be secured.

The gel content in the present invention is measured by the following method. THF is added to the chloroprene latex whose solid weight has been measured in advance, and the mixture is stirred and dispersed in a closed container for 3 hours, and then centrifuged. After centrifugation, the non-gel amount is measured by measuring the solid content of the supernatant so as not to suck up the gel at the bottom of the container, and the gel content is calculated using the remaining amount as the gel amount.

The crystallization time in the present invention is measured by the following method. Chloroprene rubber latex is dried on a glass pad in an atmosphere of 23 ° C. to prepare a dry film having a thickness of about 0.5 to 1 mm. A thickness of 1.5 to 5 mm is obtained by stacking a plurality of prepared dry films. At this time, push it sufficiently so that no air layer remains, and cut it into a size of about 50 × 50 mm to make a test piece. After heating the test piece in an atmosphere of 70 ° C. for 30 minutes, measure the type A hardness (elapsed time is 0 minutes), and immediately leave it in an atmosphere of -5 ° C. from the start of measurement until the hardness increases by 10. Let the crystallization time be. The hardness is measured at 5 points and evaluated by the average value. Further, the measurement is limited to 48 hours, and even if the hardness does not increase by 10 after 48 hours, the crystallization time is treated as 48 hours in the present invention.

The chloroprene rubber latex adhesive composition of the present invention contains silica (b). By containing silica, it is possible to prevent unintended adhesion such that the coated surfaces do not adhere to each other in normal contact and the coated paper can be wound up, and the adhesive performance can be adjusted. If silica is to be directly dispersed in chloroprene rubber latex, it tends to aggregate. Therefore, a method of once dispersing in a water-soluble polymer solution and then dispersing in chloroprene latex is preferable. Examples of such a water-soluble polymer include polyvinyl alcohol, hydroxyethyl cellulose, xanthan gum and the like.

The amount of silica blended is preferably 25 to 75% by weight based on the solid content of the entire adhesive composition. When the content is 25% by weight or more, sticking during storage can be prevented, and when the content is 75% by weight or less, the adhesiveness at the time of compression can be ensured.

By further blending the tackifier resin (c) with the adhesive composition of the present invention, the stability at the time of blending silica can be improved, and the peel strength can be adjusted.
Specific examples of the tackifier resin include gum rosin, tall rosin, wood rosin, asymmetric rosin, polymerized rosin, glycerin ester and pentaerythritol ester of these rosins, rosin-based resins such as these hydrogenated additives, terpene resins, and hydrocarbon-modified terpenes. Resins, terpene resins such as these hydrogen additives, terpene phenol resins, terpene phenol resins such as terpene phenol resin hydrogen additives, aliphatic petroleum resins, alicyclic petroleum resins, aromatic petroleum resins, Copolymerized petroleum resin, dicyclopentadiene petroleum resin, pure monomer based petroleum resin, petroleum resin such as these hydrogen additives, styrene resin, Kumaron inden resin, alkylphenol resin, xylene resin, dammar, Examples include copal and shelac.
Of these, a rosin-based resin is preferable, and an emulsion is more preferable from the viewpoint of dispersibility in chloroprene rubber latex.

The blending amount of the tackifier resin is preferably about 0 to 100 parts by weight with respect to 100 parts by weight of the chloroprene rubber latex based on the solid content.

In addition to the above-mentioned additives, the chloroprene rubber latex adhesive composition of the present invention includes inorganic fillers such as calcium carbonate and silica, antiaging agents, vulcanization accelerators, surfactants, preservatives, defoaming agents, and dispersions. Agents, leveling agents, freeze stabilizers and the like can be appropriately blended.

Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples. Further, as a matter of course, the present invention is not limited to the examples.

Example 1
Chloroprene rubber latex (a) as showprene 750 (manufactured by Showa Denko, trade name, gel content 60%, crystallization time 48 hours) 100 parts by weight, silica (b) as Nipsil E-150J (manufactured by Toso Silica), 75 parts by weight (trade name), 50 parts by weight of Superester E-865NT (manufactured by Arakawa Chemical Co., Ltd., trade name) as the tackifying resin (c), Amiradin 1820D (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name) 1.3 parts by weight and Latemuru AD-25 (manufactured by Kao, trade name) 0.4 parts by weight, as a heat deterioration inhibitor Adecastab LX-61 (manufactured by ADEKA, trade name) 1.5 parts by weight, as polyvinyl alcohol 2.3 parts by weight of PVA-224 (manufactured by Kuraray Co., Ltd., trade name) and 372.8 parts by weight of water for the pre-dispersed aqueous solution of silica were added to obtain the adhesive composition of Example 1.

Examples 2-3, Comparative Examples 1-2
In addition to the compounding materials used in Example 1, as chloroprene rubber latex, Shoprene 752 (manufactured by Showa Denko Co., Ltd., trade name, gel content 25%, crystallization time 48 hours), Shouprene 753 (manufactured by Showa Denko Co., Ltd., product Name, gel content 70%, crystallization time 48 hours), Choprene 654 (manufactured by Showa Denko Co., Ltd., product name, gel content 35%, crystallization time 24 hours), Choprene SD100 (manufactured by Showa Denko Co., Ltd., product) Name, gel content 0%, crystallization time 30 minutes) were used, and each compounding material was mixed according to the compounding (part by weight) shown in Table 1 to obtain each adhesive composition.

Each adhesive composition was applied to woodfree paper with a bar coater so as to have a solid content equivalent of 5 g / m ^2, and dried at 110 ° C. for 300 seconds. After drying, it was cured at 23 ° C. and 50% RH for 24 hours to obtain a coated paper. Each coated paper was evaluated by the following method. The numerical values on the left side in Table 1 are shown by peeling strength (N / 25 mm), and on the right side, the appearance at the time of peeling is shown by b: with substrate destruction and c: without substrate destruction.

After making the initial strength coated paper, it is cut to a width of 25 mm, the coated surfaces are put together and crimped with a load of 50 kgf / 25 mm, and a T-shaped peeling test is performed at a displacement speed of 100 mm / min using a tensile tester. Check the peel strength and appearance at the time of peeling.

Stability over time (normal temperature)
The uncrimped coated paper and the coated paper crimped with a load of 50 kgf / 25 mm are allowed to stand for 4 weeks in an atmosphere of 23 ° C. and 50% RH. After standing, the uncrimped coated paper is crimped with a load of 50 kgf / 25 mm, and the pre-crimped coated paper is peeled T-shaped at a displacement speed of 100 mm / min using a tensile tester as it is. Perform a test to check the peel strength and appearance at the time of peeling.

Stability over time (high temperature and high humidity)
The uncrimped coated paper and the coated paper crimped with a load of 50 kgf / 25 mm are allowed to stand at 40 ° C. in a 90% RH atmosphere for 4 weeks. After standing, move to a 50% RH atmosphere at 23 ° C and let stand for another 24 hours, crimp the coated paper that has not been crimped in advance with a load of 50 kgf / 25 mm, and leave the crimped coated paper as it is. A T-shaped peeling test is performed at a displacement speed of 100 mm / min using a tensile tester to confirm the peeling strength and the appearance at the time of peeling.

The adhesive composition of each example had good initial strength and stability over time (normal temperature and high temperature and high humidity). On the other hand, the adhesive composition having a low gel content shows paper breakage when stored under high temperature and high humidity, and the adhesive composition using chloroprene rubber latex having a fast crystallization time has low peeling strength and adheres. I was lacking in power.

Claims (3)

The silica (b) contains chloroprene rubber latex (a) and silica (b) having a gel content of 35 % by weight or more and a crystallization time of 24 hours or more, based on the solid content of the entire adhesive composition. ) Is contained in an amount of 25 to 75% by weight of a chloroprene rubber latex adhesive composition. The chloroprene rubber latex adhesive composition according to claim 1, further comprising a tackifier resin (c). An information-carrying sheet produced by using the chloroprene rubber latex adhesive composition according to claim 1 or 2 .