JPH0196274A - Heat-sensitive coloring adhesive having delayed tackiness - Google Patents

Abstract

PURPOSE:To obtain the titled adhesive being non-tacky at ordinary temperature and capable of exhibiting tackiness on heating and maintaining the tackiness for a long period even in separating from heat source, by blending a polymer with a specific solid plasticizer, tackifier and colorless dye capable of coloring by an acid. CONSTITUTION:(A) A polymer (e.g. vinyl acetate or ethylene copolymer) is blended with (B) solid plasticizer (e.g. benzyl p-hydroxybenzoate) expressed by the formula (PHI is aromatic hydrocarbon ring; R is alkyl or alkenyl), (C) tackifier and (D) colorless dye capable of coloring by an acid to provide the aimed adhesive.

Description

Detailed Description of the Invention (4) Industrial Application Field The present invention is non-tacky at room temperature, but becomes tacky when activated by heating, and even after being separated from the heat source. The present invention relates to a heat-sensitive delayed tack adhesive that maintains tackiness for a long period of time and can adhere to or adhere to various objects.

That is, by applying the above-mentioned adhesive onto a substrate (base sheet) such as paper or film, a heat-sensitive adhesive sheet such as a heat-sensitive label or a heat-sensitive sticker can be obtained. Pressure-sensitive adhesive sheets are sticky at room temperature, so a protective sheet called release paper (1) is indispensable, whereas heat-sensitive adhesive sheets do not require it, and are therefore resource-saving and economically advantageous. In addition, the present invention relates to a thermochromic delayed tack adhesive that develops color when sensitive to heat so that it can be visually determined whether or not it has been thermally activated.

(B) Conventional technology A typical example of the types and quantitative ratios of various chemical materials used in heat-sensitive delayed tack adhesives is the 12th edition of "Adhesive Handbook" published by Kobunshi Kankai (1973). (annual publication), and basically polyvinyl acetate, polyvinyl acetate,
Polybutyl methacrylate, vinyl chloride-vinylidene chloride copolymer, synthetic comb, vinyl acetate-2-ethylhexyl allylate copolymer, vinyl-ethylene copolymer, vinylpyrrolidone-styrene copolymer, styrene-butadiene copolymer, vinylpyrrolidone - Polymers such as ethyl acrylate copolymer, dicyclohexyl heptatalate, diphenyl phthalate, dihexyl heptatalate, dihydroabethyl phthalate, dimethyl isophthalate, sucrose benzoate, ethylene glycol dibenzoate, tribenzoate acid trimethylolethane, tribenzoic acid glyceride, tetrabenzoic acid pentaerythritol,
sucrose acetate, tricyclohexyl citrate, N-
Solid preparations such as cyclohexyl-p-toluenesulfonamide, dehydroabiethylamine carbonate, methoxyethyl stearate-urea complex, indene resin, ethyl cellulose, petroleum resin (hydrocarbon resin), terpene resin, rosin derivative (polymerized rosin, hydrogenated rosin, rosin pentaerythritol ester, resin acid dimer, etc.)
Contains adhesion agents such as .

Furthermore, the present inventor has proposed in Japanese Patent Application No. 61-56157 as a novel solid plasticizer (where Φ is an aromatic hydrocarbon g which may have a tX fund).
R is alkyl, cycloalkyl/, alkenyl,
A whole group of compounds represented by n represents a group selected from the group consisting of aralkyl (the aromatic form of which may have a substituent).

In the above chemical materials, the polymer is the source of adhesion and without it, cohesive force cannot be obtained during adhesion.Solid plasticizers do not impart plasticity to the polymer at room temperature, so the adhesive Although it is non-tacky at room temperature, upon heating it first melts and becomes liquid, which swells or dissolves the polymer, softening it or turning it into a viscous solid, and exhibits tackiness. At this time, if a tackifier is also present, the tackiness will be more pronounced and the practical usefulness will be enhanced.

It is practically required that the adhesive activated by heating maintains its tackiness even after being removed from the heat source and returning to room temperature.

This is because if time is taken between heat activation and application of the adhesive sheet to the adherend, assembly lines can be carried out continuously, making it very efficient. In recent years, it has become widely used in automatic labeling of bottles on the line, and the current situation is that the speed of the line is being increased rapidly. Tack the adhesive sheet to the activation point (
Heating to a temperature higher than the minimum temperature required for activation; this is determined mainly by the melting point of the solid plasticizer present in the adhesive (heating means include approaching a nichrome wire heater, blowing hot air, infrared irradiation, microwave irradiation) , etc.) When activated, it develops adhesive properties that can be identified by touching it with your fingers, but it is not always easy to tell visually, especially when flowing at high speed on a factory line. It is almost impossible to visually determine whether one label is completely thermally activated or not, and automatic detection using an optical detection mechanism is also difficult.

Therefore, in the past, troubles such as inactivation or insufficient activity ratio due to unheated or insufficiently heated labels, which rarely occur, and associated troubles such as unapplied labels, incompletely attached labels, and falling off, can be automatically prevented. It was difficult to prevent this from occurring, and it remained a problem.

The present invention aims to solve this problem, namely, the difficulty of determining whether a heat-sensitive delayed tack adhesive is activated or not by visual inspection or by an optical detection mechanism.

(D) Means for Solving the Problems In order to solve the above problems, it has been realized that the adhesive activated by heating should have a different hue than when it is not activated.

The principle applied to thermal recording paper is 4.
．． Organic solid acid microcrystals represented by 4'-isopropylidene diphenol (so-called bisphenol) and 3,
Triphenylmethane lactone type dye represented by 3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (so-called crystal violet lactone), 3-diethylamino-6-methyl-7-anilinofluorane Typical fluorane-type dyes, other lactam-type dyes such as rhodamine lactam, spiropyrafs,
When mixed with microcrystals of acid color-forming colorless dyes such as triphenylmethyl carbinol or its ethers, which were proposed in Japanese Patent Applications No. 60-265749, No. 60-268740, and No. 60-269392, they are colorless at room temperature. It seems possible to take advantage of the phenomenon of coloring when heated, and it is certainly possible.

However, in reality, the temperature at which the heat-sensitive delayed tack ointment is activated and the temperature at which it develops color do not match, and the adhesive contains an ester compound such as dicyclohexyl phthalate as a solid plasticizer. Perhaps because it contains such a large amount, it does not develop color when heated, or even if it develops, it is only a pale color.Furthermore, for adhesives such as bisphenol, if foreign substances are mixed into the adhesive, the adhesive It was found that the properties and performance of the adhesive were significantly impaired, resulting in insufficient adhesive strength.

Therefore, as a result of extensive research in search of a heat-sensitive color-forming delayed tack adhesive that does not impair the original performance of the adhesive and also has the same temperature for heat activation and color development, we finally found the following as (b) isotropic plasticizer: Using a compound represented by the general formula,
It has been found that the object can be achieved by mixing only a small amount of the above-mentioned acid color-forming colorless dye in addition to the printing polymer and the G/→ tackifier.

General formula: HO-Φ -00OR Here, φ is an aromatic hydrocarbon ring which may have a substituent, and R is a hydrocarbon residue which may have a substituent.

Representative examples of the compound group represented by the above general formula are shown below.

Methyl meta-hydroxybenzoate Ethyl meta-hydroxybenzoate Phenyl para-hydroxybenzoate Methyl para-hydroxybenzoate Ethyl para-hydroxybenzoate 1-propyl para-hydroxybenzoic acid Iso-propyl para-hydroxybenzoic acid n
-butyl para-hydroxybenzoic acid iso-butyl para-hydroxybenzoic acid secondary butylvaler hydroxybenzo@n-butyl para-hydroxybenzoic acid stearyl para-hydroxybenzoic acid cyclohexyl para-hydroxybenzoate Rose-hydroxybenzoic acid β-phenylethyl para-hydroxybenzoic acid 4-chlorobenzyl para-hydroxybenzoic acid 4-methylbenzyl para-hydroxybenzoic acid phenyl 4-hydroxyphthalate dimethyl 4-hydroxyphthalate diisol 4-hydroxyphthalic acid Dibenzyl di-n-propyl 4-hydroxyphthalate, diiso-propyl 4-hydroxyphthalate, dicyclohexyl 4-hydroxyphthalate, diethyl 5-hydroxysophthalate, and these may be used in combination with other solid plasticizers.

As acid color-forming colorless dyes, so-called leuco dyes, pressure-sensitive and heat-sensitive dyes, and electron-donating colorless dyes that are currently widely used in pressure-sensitive copying paper and heat-sensitive recording paper can all be used in the present invention.

If only an acid color-forming colorless dye (for example, crystal violet lactone) is added to a heat-sensitive delayed tack adhesive composition containing the above compound HO-(I)-00OR as a solid plasticizer, the adhesive becomes colorless (white) before activation. It turns blue at the same temperature as thermal activation, making it obvious that it has been thermally activated.

Also, if yellow dye is added in advance, the adhesive will change color to the post-activation edge color, and if pink dye is added, the adhesive will change to purple after heat activation.

Similarly, if only a black coloring colorless dye is used, the adhesive, which is colorless before activation, becomes black after heat activation.

Therefore, whether or not a heat-sensitive color-forming delayed tack adhesive sheet, in which such an adhesive is coated on a sheet such as paper, has been thermally activated can be visually determined by the change in color of the adhesive-coated surface.
The optical sensor will be able to detect it.

(Odor Example: Benzyl hydroxybenzoate 50 parts Polyvinyl alcohol 3 parts Nonionic activator
Water was added to 3 parts to make a plasticizer (4 times 25%), and wet milling was performed using a ball mill to make the solid plasticizer into fine particles.

Next, styrene-acrylic acid ester copolymer 5.0
parts (solid content 0 vinyl acetate-ethylene copolymer
5.0 parts (solid content) rosin ester
2.5 parts (solid content) of the above solid plasticizer fine particle suspension coating 16 parts (solid content) of crystal violet lactone finely ground suspension for thermal recording paper 1.6
(solid content) to obtain an aqueous coating liquid with a total solid content concentration of 50o4.

This coating liquid was applied to one side of a double-sided aft paper with a surface roughness of 801//m'' so that the dry coating amount was 20 Jl/7L'.
After drying at 0.degree. C., a pale white, non-stick coated paper was obtained.

When this coated paper was activated by heating for 30 seconds in a constant temperature chamber at 150° C., the surface coated with the adhesive developed a dark blue color and exhibited remarkable tackiness.

The degree of tack was measured according to the inclined pole tack measurement method (temperature 20° C., inclination angle 30 degrees), and the ball number was 7, which matched the value of the blank without crystal violet lactone.

(F) Effect of the invention As mentioned above, when an acid color-forming colorless dye is incorporated into a heat-sensitive delayed tack adhesive using a hydroxyl-substituted aromatic carboxylic acid ester compound as at least a portion of the solid plasticizer, when heated Color development occurs at the same time as activation, making it easier to visually determine the presence or absence of activation, and making it easier to detect using an optical detection mechanism.

Claims (1)

[Scope of Claims] A heat-sensitive delayed tack adhesive basically consisting of (a) a polymer, (b) a solid plasticizer, and (c) a tackifier, wherein (b) the solid plasticizer has the following general formula: A heat-sensitive color-forming delayed tack adhesive, which is the compound shown above, and further contains a (di) acid color-forming colorless dye. General formula: HO-■-COOR (However, in the formula, ■ is an aromatic hydrocarbon ring that may have a substituent, and R is alkyl, cycloalkyl, alkenyl, aralkyl (the aromatic ring has a substituent). ) and phenyl, respectively).