JPH09221644A - Delayed tack type adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject sheet excellent in adhesive force, blocking resistance and chalking resistance and useful for labels and tapes not requiring release paper sheets by disposing an adhesive layer comprising a solid plasticizer, an adhesive and a tackifier having a specific softening point on a substrate. SOLUTION: This delayed tack type adhesive sheet is obtained by disposing an adhesive layer comprising (A) a solid plasticizer, (B) an adhesive, and (C) a tackifier having a thermal softening point of 150-170 deg.C on a substrate. The component A includes various kinds of ester compounds having melting points of approximately 40-130 deg.C, such as diphenyl phthalate. The component B includes a thermoplastic resin emulsion having a glass transition temperature (Tg) of <=20 deg.C, preferably <=0 deg.C. The component C includes rosin derivative resins. The components A and C are preferably used in amounts of 50-300 pts.wt. and 50-250 pts.wt., respectively, per 100 pts.wt. (solid content weight) of the component B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a delayed tack type pressure-sensitive adhesive sheet which is non-tacky at room temperature but develops tackiness by heating and maintains tackiness even after the tackiness is developed. The delayed tack type adhesive sheet of the present invention develops adhesiveness only by being exposed to a heat source such as a heater or a hot air burner for a short time, and then can be attached as a tack label to a packaging material such as cans, bottles and boxes. It will be possible.
The present invention also relates to an adhesive sheet which has an advantage that unnecessary dust is not generated because a release paper is not required.

[0002]

2. Description of the Related Art The basic material constituting the adhesive layer of a delayed tack type adhesive sheet consists of a solid plasticizer, a thermoplastic adhesive and a tackifier, and a mixture of each of these is applied to a substrate. It is obtained by doing. The surface of the pressure-sensitive adhesive layer of the delayed tack type pressure-sensitive adhesive sheet is non-tacky at room temperature, but it develops tackiness by heating, and the tackiness is maintained for a while even if heating is not performed thereafter. It is considered that the delayed tack-type pressure-sensitive adhesive sheet exhibits the tackiness when the solid plasticizer is first dissolved by heating and then the thermoplastic pressure-sensitive adhesive and the tackifier are melted together as a solvent to dissolve.

However, in practice, the melting point of the solid plasticizer is 20
A phenomenon in which the adhesive layer composition begins to dissolve at a temperature lower by -30 ° C is observed from the analysis result of the differential calorimeter (DSC).
For example, when dicyclohexyl phthalate is used as a solid plasticizer, the delayed tack type pressure-sensitive adhesive sheet produced using this solid plasticizer should be stored in an atmosphere of about 40 ° C even though its melting point is 64 ° C. As a result, a phenomenon in which tackiness is developed and sheets are stuck to each other, that is, "blocking" occurs. Further, when the once melted solid plasticizer or pressure-sensitive adhesive composition is cooled again to a temperature below its melting point, a phenomenon in which these compositions crystallize into large particles, that is, "choking" occurs. The choking phenomenon not only lowers the adhesive strength but also causes troubles such as defective printing as a result of the crystallized substance transferring to the non-coated surface when wound in a roll.

As a method for solving blocking and choking, if a solid plasticizer having a melting point as high as possible, specifically, a solid plasticizer having a melting point of about 80 ° C. or higher is used, the activation temperature becomes high although it is improved to some extent. Not preferable. The activation temperature as referred to in the present invention means the minimum temperature necessary for the delayed tack type pressure-sensitive adhesive sheet to express sufficient adhesive force to adhere to the support, and is as low as possible in terms of the ease of expressing the adhesiveness. However, a higher value is more advantageous in order to improve the blocking resistance.

Further, the addition of a wax as an adhesive composition is disclosed in Japanese Patent Publication No. 62-21835, but it is not sufficient as an effect and, on the contrary, it causes a decrease in adhesiveness. An effective method has not yet been found, and in reality, it is transported and stored under low temperature conditions where blocking does not actually occur.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides a delayed tack type pressure-sensitive adhesive sheet which solves the following problems. Blocking does not occur even when exposed to an atmosphere of at least 50 ° C for a long time. Adhesion is exhibited at a low activation temperature, and strong adhesive strength is obtained on the surface of the base material.

[0007]

An object of the present invention is to provide a delayed tack type pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing a solid plasticizer, a pressure-sensitive adhesive, and a tackifier on a substrate, and having a heat softening point temperature of 150 to 170. It could be achieved by using a tackifier with a high softening point of ° C.

Usually, a terpene resin is used as a tackifier,
Aliphatic petroleum resin, aromatic petroleum resin, coumarone indene resin, styrene resin, phenol resin, terpene phenol resin, rosin derivative resin, etc. are used, but tackification of these used for delayed tack type adhesive sheet Agents having a softening point in the range of 80 to 130 ° C. have been used.

The present inventor has noticed the heat softening point temperature of the tackifier and produced a delayed tack type pressure-sensitive adhesive sheet using a tackifier having a softening point higher than the above range. It was found that blocking is likely to occur, but when the temperature is 150 ° C. or higher, blocking hardly occurs even under storage conditions of, for example, 50 ° C. for 24 hours, and a delayed tack type pressure-sensitive adhesive sheet having sufficient adhesive strength during heating can be obtained. However, it has been found that when the temperature exceeds 170 ° C., it is difficult to produce the tackifier itself, or the activation temperature becomes extremely high, which is not preferable.

A rosin derivative resin is mentioned as an example of the tackifier having a high softening point used in the present invention, and a method for producing this high softening point rosin derivative resin will be described. Raw pine resin, which is the raw material for rosin derivative resin, consists of about 70-80% rosin, that is, resin acid and about 20% turpentine oil. The latter is usually removed by distillation to increase the ratio of resin acid. It is called gum rosin. The resin acid is a general term for organic acids existing in a free or ester form in a resin produced from natural wood, and specifically includes abietic acid, neoabietic acid, dihydroabietic acid and the like.

Resin acid monomer is toluene containing a catalyst such as sulfuric acid, hydrogen fluoride, aluminum chloride, titanium tetrachloride,
At a temperature of about 40 to 160 ° C in a solvent such as xylene.
By reacting for about 5 hours, a resin acid dimer, that is, a polymerized rosin is obtained, but this is a mixture in which gum rosin also remains. This mixture, that is, a resin acid mixture of gum rosin and polymerized rosin is further mixed with ethylene glycol, diethylene glycol, glycerin, pentaerythritol,
The softening point can be increased by esterifying with a polyhydric alcohol such as dipentaerythritol or polyglycerin. Usually, the softening point of the tackifier obtained by these methods is 80 to 130 ° C., but in order to further increase the thermal softening point, it is preferable that the ratio of the polymerized rosin in the resin acid mixture is 60% or more. The tackifier resin obtained by this method is finely pulverized by a wet or dry pulverization method to a particle size of 10 μm or less, preferably 5 μm or less.

As the pressure-sensitive adhesive used in the present invention, a thermoplastic resin emulsion having a glass transition temperature (Tg) of 20 ° C. or lower, preferably 0 ° C. or lower is used. For example, acrylic ester copolymer, styrene-acrylic acid Ester copolymer, styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, vinyl acetate-acrylic acid ester copolymer, ethylene-vinyl chloride copolymer, ethylene-acrylic acid ester copolymer, ethylene-acrylic Examples thereof include resins such as acid copolymers, polybutadiene and polyurethane. These may be used alone or in combination.

The solid plasticizer used in the present invention includes
Diphenyl phthalate, dihexyl phthalate, dicyclohexyl phthalate, dihydroabietyl phthalate, dimethyl isophthalate, sucrose benzoate, ethylene glycol dibenzoate, glyceride tribenzoate, pentaerythritol tetrabenzoate, sucrose octaacetate, citric acid The melting point of tricyclohexyl, etc., catechol dipalmitate, catechol distearate, catechol dibenzoate, stearyl stearate, behenic acid monoglyceride, stearic acid monoglyceride, etc. is about 40-130 ° C.
Although various ester compounds within the range are listed, these are used as an aqueous dispersion after being atomized by a wet or dry pulverization method. Also, instead of the above solid plasticizer,
Liquid plasticizers such as dimethyl phthalate, diethyl phthalate, dibutyl phthalate and dibutyl maleate can also be microencapsulated and used as apparently solid plasticizers. Further, various deterioration preventive agents having a melting point within the above-mentioned melting point range, particularly phenolic antioxidants, are particularly preferable because they have both the function of the solid plasticizer and the function of preventing embrittlement of the pressure-sensitive adhesive resin.

The mixing ratio of the tackifier in the present invention is preferably in the range of 50 to 250 parts by weight with respect to 100 parts by weight of the adhesive. When the mixing ratio is less than this range, the tackiness is extremely poor, and when it exceeds this range, the composition becomes too hard and the tackiness is poor. The mixing ratio of the solid plasticizer is 50 to 300 with respect to 100 parts by weight of the solid adhesive.
A range of parts by weight is preferred. If the mixing ratio is less than this range, blocking is very likely to occur, and if it exceeds this range, the adhesive strength is lowered and choking is likely to occur.

To the pressure-sensitive adhesive layer constituting the delayed tack type pressure-sensitive adhesive sheet of the present invention, a filler or the like can be added within a range not hindering the purpose of the present invention. For example, inorganic substances such as titanium oxide, alumina, kaolin, talc and silica, , Paraffin, natural wax, synthetic wax and the like can be used.

The base material for the delayed tack type pressure-sensitive adhesive sheet of the present invention includes paper, coated paper, synthetic paper, non-woven fabric and the like, but is not particularly limited. Although the coating amount of the adhesive layer varies depending on the material of the packaging material to be adhesive composition or adhesive, usually 1 to 30 g / m ² on a dry coating weight, preferably 5 to 25 g / m ²
It is coated in the range of.

[0017]

Next, the present invention will be described with reference to examples. still,
The% and the number of parts described in the examples indicate the number of parts by weight of solid.

Production Example 1 of tackifier: 100 parts of resin acid mixture (mixture of 34 parts of gum rosin and 66 parts of polymerized rosin of gum rosin) in a reactor equipped with a stirrer, a cooling pipe, a water divider and a nitrogen introducing pipe. After charging 14 parts of pentaerythritol, the system was heated under a nitrogen gas stream until the temperature in the system reached 250 ° C. After reacting at the same temperature for 2 hours, the temperature was further raised to 280 ° C.
Allowed to react for hours. Then, the low boiling fraction was removed under reduced pressure to obtain a pentaerythritol ester of a resin acid mixture, that is, a tackifier resin. The heat softening point temperature of this tackifier resin was 155 ° C. This tackifier was wet pulverized with water as a dispersion medium until it became about 2 μm to obtain an aqueous suspension of the tackifier.

Production Examples 2 to 6 of Tackifier The procedure of Production Example 1 was repeated except that the amounts of the resin acid mixture and the polyhydric alcohol were changed as shown in Table 1. Table 1 shows the softening points of the obtained tackifiers.

[0020]

[Table 1]

Examples 1 to 3 and Comparative Examples 1 to 3 The characteristics of the delayed tack type pressure-sensitive adhesive sheets using the tackifiers of Production Examples 1 to 3 are shown in Examples 1 to 3, and the tackifiers of Production Examples 4 to 6 are shown. Table 2 shows the results of evaluation of tackiness, blocking property, and chalking, using the delayed tack type pressure-sensitive adhesive sheets of Example 1 as Comparative Examples 1 to 3. In addition, the compounding parts number of the composition shown shows the weight part number in a dry state.

The adhesive composition and coating method for preparing the delayed tack type adhesive sheet are shown below. Ethylene-vinyl acetate copolymer (Tg = -20 ° C) 100 parts Dicyclohexyl phthalate (mp = 64 ° C) 150 parts Tackifier shown in Production Example 100 parts These adhesive compositions are mixed to give a solid content of 50 % To obtain an adhesive layer coating solution for delayed tack, which is applied to the uncoated surface of single-sided art paper so that the dry coating amount is 15 g / m ^2, and dried at 40 ° C. for 2 minutes to provide a delayed tack adhesive. Got the sheet.

The delayed tack type pressure-sensitive adhesive sheets obtained in Examples and Comparative Examples were heated in a 120 ° C. atmosphere for 1 minute to develop tackiness, and then rapidly adhered to a stainless steel plate to measure 180 ° peeling force. The following criteria were evaluated. A: 800 g / 25 mm or more B: 300 g / 25 mm or more and less than 800 g / 25 mm X ... 300 g / 25 mm or less

The blocking property is such that the adhesive surface of the delayed tack type adhesive sheet and the art surface of the one-sided art paper are overlapped with each other, and a weight of 500 g / cm ² is applied.
The 180 ° peeling strength after storage at 24 ° C. for 24 hours was measured and evaluated according to the following criteria. A: Less than 5 g / 25 mm O: 5 g / 25 mm or more and less than 50 g / 25 mm X ... 50 g / 25 mm or more

For choking, the delayed tack type pressure-sensitive adhesive sheet was stored in an atmosphere of 50 ° C. for 1 hour, and then the crystallized state of the plasticizer after storage in an atmosphere of 5 ° C. for 3 days was observed and evaluated according to the following criteria. ◎ ... Almost no chalking. ○… Chalking occurs in places. ×: A lot of choking occurred.

[0026]

[Table 2]

[0027]

As is clear from the examples, by using a tackifier having a specific softening point temperature in the pressure-sensitive adhesive layer constituting the delayed tack type pressure-sensitive adhesive sheet, the tackiness, blocking resistance and chalking resistance can be improved. A delayed tack seat with excellent performance is now available. The delayed tack sheet of the present invention is a label that does not require release paper,
It can be used as a tape.

Claims (1)

[Claims] 1. A delayed tack type pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing a solid plasticizer, a pressure-sensitive adhesive, and a tackifier on a substrate, wherein the heat-softening point temperature of the tackifier is 150 to 170.
A delayed tack type pressure-sensitive adhesive sheet characterized by being at a temperature of ℃.