JPS63152686A - Heat-sensitive tacky adhesive sheet - Google Patents

Abstract

PURPOSE:To obtain a heat-sensitive tacky adhesive sheet capable of keeping tackiness for a long period after separating from a heat source, by compounding a polymeric material, a tackifier and a specific solid plasticizer, etc., applying the obtained water-based dispersion composition to a surface of a substrate sheet and drying the coating layer. CONSTITUTION:An aqueous dispersion composition is produced by compounding, as basic components, (A) a polymeric material composed of a vinyl acetate- ethylene copolymer having a glass transition temperature of <0 deg.C and produced preferably by emulsion polymerization with (B) a tackifier composed of a rosin or terpene resin having a softening point of preferably 70-145 deg.C and (C) a solid plasticizer preferably composed of fine particles of dicyclohexyl phthalate crystal and having particle diameter of 21-31mum corresponding to the 90% cumulative volume of particle size distribution at normal temperature. The obtained composition is applied to a surface of a substrate sheet in aqueous state and dried to obtain the objective heat-sensitive tacky adhesive sheet.

Description

Detailed Description of the Invention (A> Industrial Application Fields 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. This invention relates to a heat-sensitive adhesive sheet obtained by coating a base sheet with a heat-sensitive adhesive that maintains tackiness for a long time and drying it.

(B) Conventional technology The heat-sensitive adhesive sheet is also called thermal delayed tack paper, and is described in, for example, the 12th edition of "Adhesive Handbook" (published by Kobunshi Kankai, 1981), and basically consists of (a ) Polyvinyl acetate, polybutyl methacrylate, vinyl chloride
Vinylidene chloride copolymer, synthetic rubber, vinyl acetate-acrylic 2-ethylhexyl copolymer, vinyl acetate-
(b) rosin derivatives (rosin, polymerized rosin, hydrogenated rosin and their glycerin, pentaerythritol esters, resin dimers, etc.), terpene resin systems,
Tackifiers such as petroleum resins, phenol resins, and xylene resins and (C) diphenyl phthalate, dihexyl phthalate, dicyclohexyl phthalate, dihydroabiethyl phthalate, dimethyl isophthalate, sucrose benzoate, ethylene dibenzoate Plasticizers that are solid at room temperature, such as glycol, trimethylolethane tribenzoate, glyceride tribenzoate, pentaerythritol tetrabenzoate, sucrose helacetate, tricyclohexyl citrate, N-cyclohexyl-p-toluenesulfonamide, etc. This sheet has a coating layer made of a heat-sensitive adhesive containing as a basic component. Here, the polymeric material is the source of adhesive strength, and the tackifier is a component that increases tackiness when activated by heating. A solid plasticizer is solid at room temperature, does not impart plasticity to the polymeric material, and melts when heated, causing the polymeric material to swell and dissolve and develop adhesive properties. Since it crystallizes slowly after it is once melted, it is possible to maintain the adhesion of the adhesive sheet for a long time after heat activation. In addition, the form of the coating liquid for producing heat-sensitive adhesive sheets is a hot melt type (e.g., JP-A-55-1
6055, JP-A-56-106984),
Organic solvent type (e.g. JP-A-51-111246) and water-based type ("Polymer Latex Adhesive" by So Muroi)
(Author, published by Kobunshi Kankankai) is a well-known example.

(C) Problem to be solved by the invention When a hot melt type or an organic solvent type (coating liquid) is adopted as the form of a composition prepared by blending a polymeric material, a tackifier, and a solid plasticizer, solid Because the plasticizer is melted by heat or organic solvents, the sheet immediately after being coated is activated and sticky, and it is necessary to wait for the solid plasticizer to recrystallize to make it non-stick. ,
It required a step of leaving it for a very long time, or it was necessary to apply it to a special base sheet coated with a mold release agent.

In the present invention, a water-based coating method was adopted in order to produce a heat-sensitive adhesive sheet that does not cause blocking even if it is coated on, for example, ordinary paper and directly rolled up after a short period of drying.

Conventional heat-sensitive adhesive sheets are made of plastic materials with particularly low polarity, such as polyethylene,
For polypropylene, polyester, etc., peeling from the adherend occurs early after adhesion, resulting in poor practical value.

The object of the present invention is to provide a heat-sensitive adhesive sheet that can maintain adhesive properties for a sufficiently long time even on plastic materials with low polarity, and which also has the contradictory properties of having good blocking properties. The purpose of the present invention is to provide a heat-sensitive adhesive sheet.

(D> Means for Solving the Problems As mentioned above, the present inventors used an aqueous dispersion of the coating liquid in order to apply the solid plasticizer in the solid state as the coating composition. We decided to do so.

As a result, it was possible to directly produce a heat-sensitive adhesive sheet that does not cause blocking even when wound into a roll, by selecting drying conditions that do not cause the adhesive sheet to be thermally activated. However, it has been discovered that the smoothness of the coated surface can be prevented and blocking can be further prevented by adjusting the pulverized particle size of the solid plasticizer within a certain numerical range. In this way, no literature describes that a heat-sensitive adhesive sheet with excellent performance can be obtained only by controlling the pulverized particle size of the solid plasticizer within a suitable numerical range.

Once it was discovered that the blocking properties of this sheet could be improved by precisely controlling the particle size of the finely powdered solid plasticizer, it became clear that solid plasticizers whose particle size had not been previously controlled had poor blocking properties and could not be used. Even polymer materials, adhesives, that were previously unavailable,
Now you can use it. This point is the main point of the present invention. For example, adhesive polymers with a low glass transition point are soft at room temperature and exhibit remarkable tackiness, so they are extremely suitable as materials for adhesives and are commercially available. While it could not be used in the past, it can now be used satisfactorily in the present invention.

As a result, the present invention has made it possible to obtain, for the first time, a practical heat-sensitive adhesive sheet that can be sufficiently applied to non-polar adherends such as polyethylene.

In the present invention, the polymeric material of component (a) is a material that is amorphous at room temperature, particularly has a glass transition temperature of less than O'C, such as acetic acid obtained by emulsion polymerization and having a monomer weight ratio of 70:30. When a vinyl-ethylene copolymer (glass transition point -15°C) is used, tackiness becomes noticeable and the tackiness lasts for a long time.
Improves practicality. In such a case, the effect is particularly noticeable when the adherend is made of various types of polyethylene.

Adhesive properties to various adherends (adhesive strength, adhesive strength, cohesive strength,
etc.) In order to delicately control blocking resistance, etc., it is preferable to use two or more types of polymer materials in combination. Examples include emulsions of the conventionally known polymeric materials, and particularly preferred examples include vinyl acetate copolymers (e.g. vinyl acetate-ethylene copolymers), acrylic copolymers (e.g. styrene-acrylic acid alkyl esters). copolymers), chlorinated polypropylene, and the like.

In particular, when vinyl acetate-ethylene copolymer and chlorinated polypropylene are combined, tackiness becomes noticeable when heated, and an excellent heat-sensitive adhesive with great adhesion to non-polar adherends can be obtained. I understand.

Conventionally, the adhesive ability and blocking property of heat-sensitive adhesive sheets were not compatible, and increasing the adhesive ability usually resulted in worsening of the blocking property, but with the present invention, a high-performance polymer material is used. As a result, it has become possible to create sheets with high performance in practical use.

As the tackifier for component (b), conventionally known tackifiers can be used, but preferred examples include softening point (JIS
K-5903> is preferably a rosin or terpene resin having a temperature of 70 to 145°C, and examples of the rosin include abietic acid rosin, its hydrogenated product, and its maleic acid adduct, metal salts, glycerin, pentaerythritol, ethylene glycol, Examples include processed rosins such as esterified products with alcohols such as diethylene glycol. Further, as the terpene resin, homopolymers such as α-pinene, β-pinene, dipentene, copolymers thereof, terpene/phenol copolymers, water additives thereof, etc. are used. These are available as aqueous emulsions.

The solid plasticizers of component (C) include the aforementioned diphenyl heptathalate, dihexyl phthalate, dicyclohexyl phthalate, dihydroabiethyl phthalate, dimethyl isophthalate, sucrose benzoate, ethylene glycol dibenzoate, and tribenzoate. Plasticizers that are solid at room temperature such as methylolethane, tribenzoic acid glyceride, tetrabenzoic acid pentaerythritol, sucrose helacetate, tricyclohexyl citrate, and N-cyclohexyl-p-toluenesulfonamide can be used, but in the present invention, Dicyclohexyl phthalate is preferred because it is the most versatile.

A preferable blending ratio of (a) polymeric material, (b) tackifier, and (C) solid plasticizer is that the tackifier is 10 to 120 parts by weight per 100 parts by weight of the polymeric material, and the solid plasticizer is 10 to 120 parts by weight. The amount of the agent is 50 to 300 parts by weight.

If the tackifier contains less than 10 polymers, the tackiness and adhesive strength after heat activation will be low, and if it exceeds 120 polymers, the blocking phenomenon will become severe when wound into a roll. Solid plasticizer is 5
If it is less than 0 parts by weight, it is difficult to develop adhesiveness due to heat activation, and if it exceeds 300 parts by weight, the cohesive force of the adhesive part after heat activation will decrease, and the duration of adhesion after heat activation (open time) will decrease. is not practical as it becomes shorter.

To prepare a heat-sensitive adhesive composition made of the aqueous resin dispersion of the present invention, a mixture of (a>polymer material, (b) tackifier, and (C) solid plasticizer) is placed in one multi-screw It may be supplied to a screw extruder, melt-kneaded, and supplied with a glass retaining colloid from a supply port provided in the middle of the extruder, and mixed with this to prepare the product.

Alternatively, aqueous emulsions of each of the components (a), (b) and (c) may be prepared individually and then mixed.

The solid content concentration of the resin aqueous dispersion is usually 25 to 60% by weight.
and may be diluted with water if necessary.

A heat-sensitive adhesive sheet is obtained by applying this aqueous resin dispersion containing components (a), (b), and (C) onto a base sheet and drying it.

As the water-based coating method, commonly used roll coaters, wire bar coaters, air knife coaters, blade coaters, gravure coaters, etc. can be used, and the coating amount is 5 to 30 g/Td in dry solid content. preferable.

As the base sheet, pulp, paper, polyethylene terephthalate film, polypropylene film, polyvinylidene chloride film, cellulose acetate film, art paper, synthetic paper (Japanese Patent Publication No. 46-40794, Japanese Patent Application Laid-Open No. 1983-1989)
141339) etc. can be used.

This heat-sensitive adhesive sheet is useful, for example, as a label material for carbonated beverage bottles, shampoo bottles, motor oil packaging, tissue paper polyethylene packages, and the like.

As mentioned above, in particular (a) a polymeric material containing a glass transition point below 0° C., (b) a tackifier, and (
C) Using a coating liquid prepared in the form of an aqueous dispersion containing dicyclohexyl phthalate as a solid plasticizer as a basic component, that is, a heat-sensitive adhesive composition, aqueous coating is applied onto a base sheet,
When dried, 1 q of extremely excellent heat-sensitive adhesive sheet is obtained. However, if the particle size of the crushed product of dicyclohexyl phthalate, which is a solid plasticizer, is not precisely controlled, a long roll of the obtained heat-sensitive adhesive sheet is produced. It was observed that a blocking phenomenon was observed when the cut paper, which had been hung to dry, was stored at room temperature for a long period of time.

The suitable particle size range of the solid plasticizer in the heat-sensitive adhesive composition is described in a previous application by the present inventor (Japanese Patent Application No. 61-60
No. 94 specification) proposed a numerical range of 14 microns (IIn> or more), but subsequent research progress has led to the introduction of a polymer material (in the above-mentioned earlier application), which is an essential component in the composition. It has been found that when a material with a low glass transition point is included in (as described above), the long-term adhesive stability is significantly improved, especially for non-polar adherends such as polyolefins. It has been found that, rather than controlling the average particle size of the agent, the performance can be significantly improved by precisely controlling the numerical value of the ratio.

In other words, the particle size distribution (frequency of particle existence relative to particle size) of solid plasticizer fine particles at room temperature is measured, a mountain-shaped distribution curve is obtained, and particles existing from small to a certain size are determined. 9 of the total particle amount when integrated.
It has been found that the particle diameter including 0% (volume cumulative 90% value) shows a strong correlation with the performance of the heat-sensitive adhesive sheet, especially the blocking property.

As shown in the examples below, as a result of numerous experiments, the optimum particle diameter corresponding to 90% volume cumulative value is between 21 and 3.
It was found to be in the range of 1 micron (*). When it is smaller than this value, blocking worsens, and when it is larger than this value, the smoothness of the sheet deteriorates and the thermal activation response speed of the sheet decreases.

A fine powder of a solid plasticizer, such as dicyclohexyl phthalate, can be obtained by any number of known atomization methods, but this method is especially effective when using a fine powder aqueous dispersion obtained by a wet milling method using a ball mill. Good results were obtained in the invented system.

(E) Example In this example, "part" means "part by weight" unless otherwise specified.
represents.

Example 1 Dicyclohexyl phthalate (melting point 64
°C white crystals, manufactured by Tokyo Kasei Kogyo (Tai) 100 parts A small amount of henonionic surfactant and water were added to give a concentration of 40 to 50% by weight, and the solid plasticizer was ground to different degrees by changing the grinding time using a ball mill. Fifty-two samples of aqueous suspensions of microparticles were prepared.

For each sample, the particle size distribution was determined using a Franhonois diffraction measurement method of forward scattered light from a laser light source (using a Microtrac particle size analyzer sold by Nippon Iso).

Furthermore, heat-sensitive adhesive sheet samples were prepared using each suspension sample in the following manner.

(a) As a polymer material, vinyl acetate-ethylene copolymer emulsion (0 parts to 30 parts compared to monomer, TC1 = -15°C) 60 parts (solid content) Vinyl acetate-ethylene copolymer emulsion (0 parts to 20 parts compared to 7-mer) (Tg=O°C) 40 parts (solid content) (b) Polymerized rosin pentaerythritol ester emulsion as tackifier 50 parts (solid content) (C) Solid plasticizer 150 parts (solid content) of dicyclohexyl phthalate pulverized fine particle aqueous suspension minutes), mix,
The aqueous dispersion composition was applied onto one side of art paper having a basis weight of 185 g/rd using a wire bar so that the coating amount after drying was 15 g/TIt, and dried at 50°C.

All of these coated paper samples showed no stickiness at room temperature, but were activated and became sticky only by heating at 120° C. for 20 seconds.

In order to examine the blocking properties, unheated coated papers were stacked so that the front and back sides were facing each other, and a weight was placed on them to give a weight of 1 kg/crA. The presence or absence of blocking was investigated.

The results are shown in Table 1. In Table 1, the degree of blocking is expressed in five levels: 1.2, 3, and 4.5.
, 4 and 3 are practically acceptable, and 2 and 1 are practically defective.

(Left below) Table 1 (Continued from Table 1) As shown in Table 1, the cumulative volume of solid plasticizer fine particles is 90%
The particle size corresponds to the value and the blocking property corresponds well, and 2
A value of 11 Irt or more falls within the practical range, and a value of more than 31 Irt results in poor smoothness of the coated surface.

The heat-sensitive adhesive sheet prepared in this manner also exhibited good adhesive properties against polyethylene sheets after heat activation.

Of course, the sheet using a solid plasticizer having a particle size of less than 21p at 90% volume cumulative value also had extremely good adhesive properties, but the blocking property was poor and it could not be used as a practical product.

(F) Effect of the invention As mentioned above, for the fine particles of the solid plasticizer, which is an essential component in the adhesive composition for producing a heat-sensitive adhesive sheet, the particle size corresponding to 90% volume cumulative value of the particle size distribution at room temperature is 21. When controlled within the range of 31 microns (*) from As a result, it has become possible to produce a heat-sensitive adhesive sheet with extremely excellent adhesive properties.

[Brief explanation of the drawing]

FIG. 1 is a particle size distribution diagram of the solid plasticizer fine powder aqueous suspension of sample number N052 of Example 1. In the figure, the bar graph represents the volume frequency (%) of particles at each particle size.
and the curve shows volume accumulation (%). Procedural City Official Book (Voluntary) 2nd year of 1986! 6th

Claims (1)

[Claims] 1) (a) polymeric material, (b) tackifier, and (C)
In a heat-sensitive adhesive sheet obtained by aqueous coating of an aqueous dispersion composition containing three powder plasticizers as basic components on a base sheet and drying, (C) solid plasticizer at room temperature A heat-sensitive adhesive sheet characterized in that a particle diameter corresponding to 90% volume cumulative value of viscosity distribution is in the range of 21 to 31 microns (μm). 2) The heat-sensitive adhesive sheet according to claim 1, wherein the solid plasticizer is fine particles obtained by pulverizing crystals of dicyclohexyl phthalate. 3) The thermosensitive material according to claims 1 and 2, wherein the polymer material contains a vinyl acetate-ethylene copolymer emulsion obtained by emulsion polymerization and having a glass transition temperature of less than 0°C. adhesive sheet.