JP2003138235A - Pressure-sensitive adhesive composition having opacifying capability and pressure-sensitive adhesive sheet using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure-sensitive adhesive composition which exhibits an excellent opacifying capability without detriment to pressure-sensitive adhesive properties of an acrylic pressure-sensitive adhesive even when a substrate sheet is transparent or even when the pressure-sensitive adhesive layer is thin; and a pressure-sensitive adhesive sheet using the same. SOLUTION: This pressure-sensitive adhesive composition contains a copolymer consisting mainly of structural units derived from an alkyl (meth)acrylate monomer, a particle-surface-treated aluminum powder having an average particle size of 5-50 μm and an aspect ratio of 50-200, and titanium oxide. The pressure- sensitive adhesive sheet is prepared by using the composition.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a pressure-sensitive adhesive composition having a concealing property, which is used for indoor and outdoor decorations, marking films, name labels and the like, and more particularly to a pressure-sensitive adhesive sheet using the same. The present invention relates to a pressure-sensitive adhesive composition that has characteristics and has an excellent concealing property that shields the underlying color and characters of an adherend from the adhered portion, and a pressure-sensitive adhesive sheet using the same. The adhesive sheet is expressed by including tapes, labels, sheets and the like.

[0002]

2. Description of the Related Art Conventionally, marking films and name labels have been generally used as headings and displays on documents and shelves. Especially when the name label is overlaid on a document or when it is attached on a dark-colored adherend,
There is a problem that the letters and colors underneath become transparent and the letters and colors become unclear. to solve this problem,
It is required to improve the hiding power of the pressure-sensitive adhesive sheet.

Various methods have been considered to enhance the concealing property of the pressure-sensitive adhesive sheet. For example, there is a method of adding a large amount of filler to the base sheet, but the strength of the sheet decreases,
There is a problem that it breaks easily and cannot be used. Furthermore, there are a method of thickening the base material sheet and a method of thickening the pressure-sensitive adhesive layer. If the base sheet is made thick, the sheet becomes too stiff, and there is a problem in that the adhesion to the bent surface is poor and the base sheet is easily peeled off. If the pressure-sensitive adhesive layer is made thick, there is a problem in that a label or the like used for re-peeling causes adhesive residue on an adherend, which is also a cost problem.

Next, there is a method of forming an undercoat layer having a hiding property between the base sheet and the adhesive layer. For example, Japanese Patent Laid-Open No. 7-11202 discloses a concealable pressure-sensitive adhesive tape in which a transparent stretched polypropylene film is printed on one side and a metal-containing white ink layer and an adhesive layer are sequentially laminated on the printed surface. There is. JP-A-8-104848 discloses a pressure-sensitive adhesive tape in which a concealing layer having a titanium oxide pigment volume concentration of 50% or more and a pressure-sensitive adhesive layer are sequentially formed on one surface of a film substrate. Although the concealing property is obtained, the workability is poor because of two steps, and there is a problem in economical efficiency.

Further, there is a method of coloring the base sheet and the pressure-sensitive adhesive layer to impart a hiding property. For example, JP-A-5-438
Japanese Patent Publication No. 46 discloses an adhesive tape or sheet in which a beige colored adhesive layer is provided on one surface of a colored synthetic resin tape or sheet. Japanese Unexamined Patent Publication (Kokai) No. 5-108011 discloses an adhesive label in which an adhesive layer containing a white pigment as an adhesive is laminated on the back surface of a polyethylene terephthalate substrate containing a white pigment. Japanese Patent Laid-Open No. 11-106713 discloses a pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive comprising a pressure-sensitive adhesive base polymer and a pearl pigment is laminated on one surface of a synthetic resin sheet. However, in both cases, the hiding property is obtained because the substrate is made opaque by adding a pigment or the like, but there is a problem that the hiding property is difficult to obtain when the substrate sheet is transparent or the pressure-sensitive adhesive layer is thin. .

[0006]

An object of the present invention is to provide a pressure-sensitive adhesive having excellent concealing properties, even if the base sheet is transparent or the pressure-sensitive adhesive layer is thin, without impairing the pressure-sensitive adhesive properties of the pressure-sensitive adhesive. To provide a composition and a pressure-sensitive adhesive sheet using the same.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have identified a copolymer containing an alkyl (meth) acrylate ester as a main component as a main component. By using a combination of aluminum powder and titanium oxide, which are fine scale-like particles having a particle surface having physical properties treated, it is found that the hiding property is improved without lowering the adhesive property, and the present invention is completed. I arrived.

That is, according to the present invention, (a) 100 parts by weight of a resin component of a copolymer whose main component is a (meth) acrylic acid alkyl ester monomer having an alkyl group having 1 to 12 carbon atoms, (B) 0.1 to 5 parts by weight of aluminum powder having an average particle size of 5 to 50 μm and an aspect ratio of 50 to 200, the surface of which has been treated, and (c) 5 to 60 parts by weight of titanium oxide. And a pressure-sensitive adhesive sheet using the same.

[0009]

DETAILED DESCRIPTION OF THE INVENTION The constitution of the present invention will be described in detail below. The number of carbon atoms of the (a) alkyl group used in the present invention is 1
Specific examples of the (meth) acrylic acid alkyl ester monomer of 1 to 12 include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, and 2 -Ethylhexyl (meth) acrylate, octyl
Examples thereof include (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate, and lauryl (meth) acrylate. At least one selected from these groups can be used. Furthermore, other copolymerizable unsaturated group-containing monomers can be used. Specific examples of the other copolymerizable unsaturated group-containing monomer include (meth) acrylic acid, maleic acid, crotonic acid, maleic anhydride, hydroxyethyl (meth) acrylate, 4-hydroxybutyl acrylate and (meth ) Acrylonitrile, vinyl acetate, vinyl propionate, vinyl versatate, alkyl group having 13 to 20 carbon atoms
(Meth) acrylic acid alkyl ester and the like. At least one selected from these groups can be used. A copolymer in which the amount of the (meth) acrylic acid alkyl ester monomer used is 80 to 99.5% by weight and the other copolymerizable unsaturated group-containing monomer is 0.5 to 20% by weight is preferable. .

The copolymer of the present invention can be usually obtained by a bulk polymerization reaction or a solution polymerization reaction, preferably a solution polymerization reaction. The solvent used in the solution polymerization reaction, ethyl acetate, toluene, hexane,
An organic solvent such as acetone can be used. Further, as the polymerization initiator used in the solution polymerization reaction, an oil-soluble polymerization initiator which is an azobis compound such as penzoyl peroxide and lauryl peroxide, and azobisisobutyronitrile and azobisvaleronitrile is used. can do.

In the present invention, it is necessary to use aluminum powder and titanium oxide together in order to improve the hiding power. Although the hiding property can be obtained by using titanium oxide alone, higher hiding property, particularly when using a transparent base material sheet or in order to obtain high hiding property even when the coating amount of the adhesive is reduced. However, it cannot be obtained unless the amount of titanium oxide used is increased. If the amount of titanium oxide used is too large, the adhesive properties are likely to deteriorate, and adhesive residue on the adherend is liable to occur when peeling after bonding for a long time. However, by using a small amount of aluminum powder in combination, higher concealing property can be obtained even when the amount of titanium oxide used is small, and it is possible to reduce the amount of pigment used as a whole.

The (b) aluminum powder used in the present invention is required to have its surface treated. Aluminum powder may react with water, acid and alkali to generate hydrogen gas, so the surface of aluminum particles should be surface treated with a coupling agent or the surface of aluminum particles should be uniformly coated with a polymer compound. Must be present to prevent reaction with the acids present in the copolymer. A resin coating type is preferred.
A preferred embodiment of the aluminum powder is an aluminum paste type. The aluminum paste is a metal pigment obtained by processing aluminum into fine scale-like particles and forming a paste with an organic solvent such as mineral spirit, solvent naphtha, toluene and xylene, and the aluminum particles float on the coating surface layer and are arranged in parallel. And a non-leafing type in which aluminum particles are uniformly dispersed in the coating film and arranged in parallel, and a non-leafing type aluminum paste is preferable. As the aluminum paste, a commercially available aluminum paste manufactured by Asahi Kasei Co., Ltd. can be used.

The (b) particle surface-treated aluminum powder used in the present invention is required to have an average particle size of 5 to 50 μm, and preferably 10 to 30 μm, in order to enhance the hiding property. Is. If the average particle size is smaller than 5 μm, sufficient hiding property cannot be obtained and the particle size is 50 μm.
When it exceeds, the concealing property is deteriorated. In order to further improve the hiding property, it is necessary that the aspect ratio is 50 to 200, preferably 60 to 150. When the aspect ratio is 50 or less, sufficient hiding property cannot be obtained, and when the aspect ratio exceeds 200, dispersibility in the pressure-sensitive adhesive decreases. The average particle size is obtained by dispersing the sample in mineral spirits and using the laser diffraction / scattering method. The aspect ratio is calculated from the average particle diameter / thickness of aluminum particles.

The amount of aluminum powder used in the present invention is 0.1 to 100 parts by weight of the resin component of the copolymer.
5 parts by weight. If the amount used is less than 0.1 part by weight, the effect of the hiding property is low, and if it exceeds 5 parts by weight, the hiding property is high, but the metallic feeling becomes strong and the white hiding property is deteriorated.

A preferred embodiment of the (c) titanium oxide used in the present invention is a titanium oxide paste type. The titanium oxide paste is a type in which an acrylic polymer is used as a dispersant and titanium oxide is made into a paste with an organic solvent such as mineral spirit, solvent naphtha, toluene, xylene, acetone, and isopropyl alcohol. The amount of titanium oxide used is 100% of the resin component of the copolymer.
It is 5 to 60 parts by weight, preferably 10 to 10 parts by weight.
40 parts by weight. When the amount used is less than 5 parts by weight, the effect of the hiding property is low, and when it exceeds 60 parts by weight, the hiding property is high, but the adhesive property is deteriorated and the adhesion to the substrate is also decreased.

As the base material of the pressure-sensitive adhesive sheet used in the present invention, various film base materials can be used. Specific examples include polyethylene film, polyester film, polypropylene film, polyvinyl chloride film, polycarbonate film, polyacrylic film and the like. The pressure-sensitive adhesive sheet of the present invention can be used for indoor and outdoor decorative tapes, marking sheets, name labels and the like.

The pressure-sensitive adhesive composition of the present invention is a terpene-based, terpene-phenol-based, coumarone-indene-based, styrene-based, rosin-based, xylene-based, phenol for the purpose of adjusting the tackiness and cohesive force as necessary. System, petroleum-based tackifying resins, melamine resins, cross-linking agents and the like can be added.

[0018]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. In the examples and comparative examples, parts or% means parts by weight or% by weight, unless otherwise specified.

Production Example 1 (Copolymer A-1) After nitrogen gas was charged into a reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube, 100 parts of ethyl acetate, 98 parts of butyl acrylate, and acryl. Charge 2 parts of acid and 0.2 part of polymerization initiator azobisisobutyronitrile. The mixture is reacted for 8 hours at the reflux temperature of ethyl acetate in a nitrogen gas stream with stirring. After completion of the reaction, 85 parts of toluene is added and cooled to room temperature. A copolymer A-1 having a viscosity of 2000 mPa · s and a solid content concentration of 35% was obtained.

Production Example 2 (Copolymer A-2) and Production Example 3
(Copolymer A-3) Copolymers A-2 and A-3 were obtained in exactly the same manner as shown in Table 1, except that the type and amount of the monomer of copolymer A-1 were changed. .

[0021]

[Table 1]

The monomers in Table 1 are described by the following abbreviations. BA: Butyl acrylate 2EHA: 2 ethylhexyl acrylate VAc: Vinyl acetate AAc: acrylic acid

Example 1 286 parts (100 parts by resin content) of the copolymer A-1 obtained in Production Example 1 and titanium paste ZC-300 (60% titanium oxide content concentration, manufactured by Mikuni Pigment Co., Ltd.) 25 parts (15 parts by titanium oxide content), aluminum paste HR-7000 (polymer coating type, average particle size 15 μ, aspect ratio 1
00, evaporation residue 50%, Asahi Kasei Co., Ltd. 0.6 part (aluminum 0.3 part), Coronate L-45 (Nippon Polyurethane Co., Ltd.) 1.0 part as a curing agent Then, the mixture was thoroughly mixed to obtain a concealing pressure-sensitive adhesive. The pressure-sensitive adhesive is applied to release paper so that the coating film thickness is 20 μm (dry), dried for 60 seconds in a dryer at 100 ° C., and then transferred to a transparent polyester film having a thickness of 50 μm to give a pressure-sensitive adhesive sheet. Was produced. The adhesive sheet was tested for hiding power, adhesive strength, holding power, adhesive residue, and total light transmittance, and all were good. The results are shown in Table 2.

Examples 2 to 4 In Examples 2 to 4, pressure-sensitive adhesive sheets were prepared in the same manner as in Example 1 using the materials shown in Table 2 and tested in the same manner. All test results were good. The results are shown in Table 2.

Example 5 Example 5 is an example except that the aluminum paste HR-7000 of Example 2 was changed to aluminum paste CR-300 (polymer coating type, average particle size 20 μ, aspect ratio 60, Asahi Kasei Co., Ltd.). Prepare an adhesive sheet in the same manner as in 2,
It tested similarly. The results were good. The results are shown in Table 2.

Comparative Example 1 Comparative Example 1 is an example excluding the aluminum paste of Example 2, and an adhesive sheet was prepared and tested in the same manner as in Example 1. As a result, the hiding property and the total light transmittance were poor. The results are shown in Table 2.

Comparative Examples 2 to 4 Comparative Example 2 is an example excluding the titanium oxide paste of Example 1. A pressure-sensitive adhesive sheet was prepared and tested in the same manner as in Example 1. The hiding power and total light transmittance were poor. Comparative Example 3
Is an example in which the titanium oxide paste of Example 2 is outside the scope of the present invention. A pressure-sensitive adhesive sheet was prepared and tested in the same manner as in Example 1. Although hiding power was obtained, the adhesive strength and adhesive residue were poor. Comparative Example 4 is an example in which the aluminum paste of Example 1 is outside the scope of the present invention. A pressure-sensitive adhesive sheet was prepared and tested in the same manner as in Example 1. Although the hiding property was obtained, a large amount of aluminum paste was added to give a metallic feeling, and the white hiding property was not obtained. The results are shown in Table 2.

Comparative Example 5 In Comparative Example 5, the aluminum paste HR-7000 of Example 2 was used as the aluminum paste C having an aspect ratio outside the range of the present invention.
R-50FM (polymer coating type, average particle size 20μ,
An adhesive sheet was produced in the same manner as in Example 2 except that the aspect ratio was changed to 40 and the product was changed to Asahi Kasei. As a result, hiding power and total light transmittance were not obtained. The results are shown in Table 2.

[0029]

[Table 2]

The abbreviations in Table 2 indicate the following materials. L-45: Crosslinking agent, manufactured by Nippon Polyurethane Industry Co., Ltd.
Product name Coronate L-45 HR-7000: Asahi Kasei Corporation, product name Aluminum Paste HR-7000, polymer coating type, average particle size 15
μ, aspect ratio 100, evaporation residue 50% CR-300: Asahi Kasei Co., Ltd., trade name Aluminum Paste CR-300, polymer coating type, average particle size 20 μ,
Aspect ratio 60 CR-50FM: Asahi Kasei Corporation, trade name Aluminum paste CR-50FM, polymer coating type, average particle size 20
μ, aspect ratio 40 ZC-300: manufactured by Mikuni Pigment Co., Ltd., trade name titanium paste ZC-300, titanium oxide concentration 60%,

Test Method Concealment Property The pressure-sensitive adhesive compositions shown in Tables 2 and 3 were used to form coating films having a thickness of 20 μm.
The release paper was coated so as to be (dry), dried for 60 seconds in a dryer at 100 ° C., and then transferred to a transparent polyester film having a thickness of 50 μm to prepare an adhesive sheet sample. The sample is affixed to a white mount on which black characters are printed, and the hiding property is visually determined. ○: Almost no characters are visible. ▲: Almost no letters are visible, but the sheet has a metallic feel. Δ: Characters are slightly visible. X: Almost all characters are visible.

The pressure-sensitive adhesive sheet sample obtained in the adhesive power hiding test was JIS Z02.
According to 37, paste in an atmosphere of 23 ° C, 65% HR,
Twenty minutes after application, 180 ° peeling adhesion is measured with a Tensilon universal tensile tester (manufactured by Orientec Co., Ltd.) within that temperature. Adhesive strength is 7.5N / 25m
It is preferably m or more.

The pressure-sensitive adhesive sheet sample obtained in the holding power hiding test was JIS Z02.
According to 37, measure the number of seconds until a load of 1 kg is dropped in a constant temperature bath at 40 ° C. If it does not fall in 5 hours,
The degree of deviation of the adhesive surface was measured, and NC represents no deviation.

The pressure-sensitive adhesive sheet sample obtained in the adhesive residue hiding test was tested at 23 ° C. and 65%.
In a HR atmosphere, attach it to a stainless steel plate whose surface has been polished and cleaned beforehand, and leave it at room temperature for 3 days, then JIS
According to Z0237, peeled by 180 ° with Tensilon universal tensile tester (manufactured by Orientec Co., Ltd.),
Observe the amount of glue left. ⊚: No glue residue ○: 0 to 5% glue residue △: 6 to 50% glue residue ▲: 51 to 90% glue residue ×: 91 to 100% glue residue

Total light transmittance (%) The pressure-sensitive adhesive sheet sample obtained in the hiding test was tested at 23 ° C. and 65%.
The total light transmittance (%) is measured in RH using an NDH2000 haze meter (manufactured by Nippon Denshoku Industries Co., Ltd.). It is preferably 20% or less.

[0036]

EFFECTS OF THE INVENTION The pressure-sensitive adhesive composition of the present invention and the pressure-sensitive adhesive sheet using the same have excellent masking ability even when the base sheet is transparent or when the pressure-sensitive adhesive layer is thin. It can be suitably used for a sheet, a masking tape, and a masking label.

Claims (2)

[Claims] 1. The (a) alkyl group having 1 to 12 carbon atoms
With respect to 100 parts by weight of the resin component of the copolymer mainly composed of the (meth) acrylic acid alkyl ester monomer, (b) the particle surface having an average particle diameter of 5 to 50 μm and an aspect ratio of 50 to 200 is A pressure-sensitive adhesive composition comprising 0.1 to 5 parts by weight of treated aluminum powder and (c) 5 to 60 parts by weight of titanium oxide. 2. A pressure-sensitive adhesive sheet obtained by applying and drying the pressure-sensitive adhesive composition having the concealing property according to claim 1 on a substrate sheet.