JP2019035048A - Adhesive and adhesive sheet - Google Patents

Abstract

To provide an adhesive that can form an adhesive layer that has excellent contrast after printing and resists coloring, and an adhesive sheet.SOLUTION: An adhesive contains an adhesive resin (A), and a bismuth laser color coupler (B). The bismuth laser color coupler (B) preferably has a D50 average particle size of 0.05-5 μm. Also preferably, the content of the bismuth laser color coupler (B) is 0.1-5 pts.mass relative to the 100 pts.mass of the adhesive resin (A).SELECTED DRAWING: None

Description

  The present invention relates to an adhesive.

In many cases, labels attached to various packaging materials and containers are printed with production lots and the like in addition to product names, and printing by an ink jet method or a laser marking method is common.
However, since the ink jet method uses heat-sensitive ink, its heat resistance is poor. For example, when it is used on a label for frozen foods, there is a problem that colors other than the printed part are colored by heating in a microwave oven, and the printed content cannot be decoded. It was. For this reason, printing by the laser marking method, whose application is not limited, is increasing.

  For example, Patent Document 1 discloses an adhesive containing copper oxide or molybdenum trioxide as a laser color former.

JP 2009-286864 A

  However, since the conventional adhesive contains copper oxide, there is a problem that the contrast between the laser coloring portion (printing portion) and the non-coloring portion is lowered, and the visibility of the printing portion is lowered. In addition, when molybdenum trioxide is included, the adhesive layer is colored yellow, so when used for this adhesive layer for transparent labels, the problem of reducing the merchandise of the label, and for example, when used for fresh food labels, There was a problem that the sales volume of the perishable food was likely to be reduced by giving a negative image to freshness from the yellow.

  An object of the present invention is to provide a pressure-sensitive adhesive and a pressure-sensitive adhesive sheet that have good contrast after printing and can form a pressure-sensitive adhesive layer with suppressed coloring.

  The pressure-sensitive adhesive of the present invention contains a pressure-sensitive resin (A) and a bismuth-based laser color former (B).

  According to the present invention, it is possible to provide a pressure-sensitive adhesive and a pressure-sensitive adhesive sheet that have good contrast after printing and can form a pressure-sensitive adhesive layer that suppresses coloring.

In this specification, a sheet, a film, and a tape are synonymous.
In this specification, the adherend is a counterpart to which the adhesive sheet is bonded.
As used herein, (meth) acrylic acid includes acrylic acid and methacrylic acid. The monomer means an ethylenically unsaturated group-containing monomer.

  In the present specification, unless otherwise specified, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are polystyrene-converted values determined by gel permeation chromatography (GPC) measurement, and are described later in [Examples]. It can be measured by the method described.

The pressure-sensitive adhesive of the present invention contains a pressure-sensitive resin (A) and a bismuth-based laser color former (B).
The pressure-sensitive adhesive of the present invention is preferably used as a pressure-sensitive adhesive sheet comprising a base material and a pressure-sensitive adhesive layer by forming a pressure-sensitive adhesive layer by coating.

  Since the pressure-sensitive adhesive of the present invention uses the bismuth-based laser color former (B), the pressure-sensitive adhesive layer is hardly colored and has high transparency. As a result, when used for labeling purposes, the entire label does not have a color derived from the adhesive layer. For example, when used for transparent labels and fresh food labels, it does not adversely affect the merchantability of the product that is the adherend. . Further, since the color developed by laser irradiation is good, the contrast between the printed portion and the non-printed portion is high, and the visibility of the printed portion is high.

(Adhesive resin (A))
The pressure-sensitive adhesive resin (A) is a resin that can be used for pressure-sensitive adhesives. After the pressure-sensitive adhesive layer is formed, moderate pressure-sensitive adhesiveness (tack) is obtained in the pressure-sensitive adhesive layer. The adhesive resin (A) preferably has a glass transition temperature (Tg) of 0 ° C. or lower, more preferably −10 ° C. or lower, and further preferably −20 ° C. or lower. Tg can be determined by the FOX equation using the glass transition temperature of the homopolymer of the monomer constituting the adhesive resin (A). As the monomer Tg, a known value such as a polymer handbook can be used. In addition, when Tg of a monomer is unknown, Tg of adhesive resin (A) can be calculated | required by DSC.

  Examples of the adhesive resin (A) include acrylic resins and urethane resins. Among these, acrylic resins are preferable.

The acrylic resin is a resin obtained by polymerizing (meth) acrylic acid ester as a main component. As monomers other than (meth) acrylic acid esters, reactive functional group-containing monomers and other monomers can be used.
(Meth) acrylic acid ester is, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl ( Examples include meth) acrylate, t-butyl (meth) acrylate, n-pentyl (meth) acrylate, i-pentyl (meth) acrylate, neopentyl (meth) acrylate, and n-hexyl (meth) acrylate.
Examples of the hydroxyl group-containing monomer among the reactive functional group-containing monomers include 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate.
Among the reactive functional group-containing monomers, examples of the carboxyl group-containing monomer include (meth) acrylic acid, maleic acid, fumaric acid, itaconic acid, vinyl benzoic acid, and crotonic acid.
Examples of other monomers include acrylamide, vinyl acetate, styrene, and vinyl propionate.

  These monomers can be used alone or in combination of two or more.

The synthesis of the acrylic resin can be appropriately selected from, for example, solution polymerization, emulsion polymerization, and bulk polymerization. Solution polymerization with easy reaction control is preferable.
Examples of the solvent used for the solution polymerization include esters (for example, ethyl acetate and butyl acetate), hydrocarbons (for example, n-butane, cyclohexane, toluene, benzene), ketones (for example, acetone, methyl ethyl ketone, and methyl isobutyl ketone). .

  The solvent can be used alone or in combination of two or more.

The polymerization initiator used for the synthesis of the acrylic resin is preferably a peroxide or an azo compound.
Examples of the peroxide include benzoyl peroxide, di-t-butyl peroxide, and lauryl peroxide.
Examples of the azo compound include azobisisobutyronitrile, 2,2′-azobis (2-methylpropionitrile), 2,2′-azobis (2,4-dimethylvaleronitrile), and the like.

  The polymerization initiator can be used alone or in combination of two or more.

  The polymerization initiator is preferably used in an amount of 0.01 to 0.5 parts by mass with respect to the total amount of monomers.

  The weight average molecular weight of the acrylic resin is preferably 300,000 to 1,300,000, more preferably 400,000 to 1,000,000, and even more preferably 500,000 to 800,000. If the weight average molecular weight is 300,000 or more, the cohesive force of the pressure-sensitive adhesive layer is further improved, and the coating roll obtained by winding the pressure-sensitive adhesive sheet after continuous coating is difficult to shift into a bamboo shoot shape. Moreover, if it is 1.3 million or less, the surface smoothness of an adhesion layer will improve more and the commercial property of a label will improve. The weight average molecular weight is a value in terms of polystyrene obtained by GPC (gel permeation chromatography).

  An adhesive resin (A) can use single or 2 types or more.

In the present invention, a curing agent can be used. The curing agent is an optional component, but when the adhesive resin has a reactive functional group, a curing agent capable of reacting with the reactive functional group can be used.
When the adhesive resin (A) has a hydroxyl group, examples of the curing agent include an isocyanate curing agent. When the adhesive resin (A) has a carboxyl group, examples of the curing agent include an epoxy curing agent, a chelate curing agent, and an aziridine curing agent.

  The curing agent can be used alone or in combination of two or more.

  It is preferable that 0.1-10 mass parts is mix | blended with respect to 100 mass parts of adhesive resins (A) for a hardening | curing agent.

(Bismuth laser color former (B))
The bismuth-based laser color former (B) is preferably a bismuth oxide. The bismuth-based laser color former (B) carbonizes the surrounding adhesive resin (A) by absorbing laser light and generating heat. When the bismuth laser color former (B) is used, contrast after printing that cannot be obtained with the conventional laser color former can be obtained, and coloring of the adhesive layer can be suppressed. The carbonized portion is a laser coloring portion (printing portion).

Examples of the bismuth oxide include bismuth trioxide (Bi ₂ O ₃ ).

  The D50 average particle size of the bismuth-based laser color former (B) is preferably 0.05 to 5 μm, more preferably 0.1 to 3 μm, and still more preferably 0.3 to 1.5 μm. When the thickness is 0.05 μm or more, the specific surface of the particles of the bismuth-based laser color former (B) becomes large and the laser beam is absorbed and heat is easily generated, so that the printing accuracy is further improved. On the other hand, when it becomes 5 micrometers or less, coloring of the adhesion layer can be suppressed more. The bismuth-based laser color former (B) is preferably a dispersion treatment because it easily aggregates when blended with the adhesive resin (A). Therefore, the D50 average particle size of the bismuth-based laser color former (B) is the dispersed particle size after blending with the pressure-sensitive adhesive. The D50 average particle size is a particle size in which the integrated value of the volume average particle size measured with a Microtrac particle size distribution analyzer UPA250 (manufactured by Nikkiso Co., Ltd.) is 50%.

  The bismuth-based laser color former (B) is preferably blended in an amount of 0.1 to 5 parts by weight, more preferably 0.3 to 4 parts by weight, based on 100 parts by weight of the adhesive resin (A). 5-3 mass parts is more preferable. When 0.1 part by mass is blended, the contrast after printing is further improved. Moreover, when 5 mass parts or less are mix | blended, the cohesion force and adhesive force of an adhesion layer will improve more, and cost can be suppressed. When an appropriate amount of the bismuth-based laser color former (B) is blended, the contrast after printing is further improved, and coloring of the adhesive layer can be further suppressed.

In the pressure-sensitive adhesive, other laser color formers other than the bismuth-based laser color former (B) can be used in combination as long as the problems of the present invention can be solved.
Other laser color formers include, for example, molybdenum trioxide, copper phosphate, and the like.

  The pressure-sensitive adhesive can further contain an inorganic compound. When the bismuth laser color former (B) and an inorganic compound are used in combination, the contrast after printing may be further improved. The inorganic compound is preferably a metal oxide, inorganic salt, metal, metal hydroxide or the like other than the laser color former. Examples of the metal oxide include silica, titanium oxide, alumina, iron oxide, magnesium oxide, zinc oxide, cobalt oxide, lead oxide, tin oxide, antimony oxide, indium oxide, manganese oxide, nickel oxide, neodymium oxide, copper oxide, Examples include palladium oxide, lanthanum oxide, synthetic and natural zeolites; and composite metal oxides such as mica, montmorillonite, scumite, talc, and clay.

Inorganic salts include, for example, calcium carbonate, copper carbonate, nickel carbonate, manganese carbonate, cobalt carbonate, lanthanum carbonate, magnesium nitrate, manganese nitrate, iron nitrate, cadmium nitrate, zinc nitrate, cobalt nitrate, lead nitrate, nickel nitrate, copper nitrate Palladium nitrate, lanthanum nitrate, magnesium acetate, manganese acetate, cadmium acetate, zinc acetate, cobalt acetate, lead acetate, nickel acetate, copper acetate, palladium acetate and the like.
Examples of the metal simple substance include iron, zinc, tin, nickel, copper, silver, and gold. Examples of the hydroxide include aluminum hydroxide, magnesium hydroxide, zinc hydroxide, antimony hydroxide, cobalt hydroxide, nickel hydroxide, neodymium hydroxide, iron hydroxide, and lanthanum hydroxide.

A tackifier resin can be further mix | blended with an adhesive. When tackifying resin is included, the adhesive strength is improved.
The tackifying resin is preferably a rosin resin, a terpene resin, an aromatic petroleum resin, an aliphatic petroleum resin, or the like.
Examples of the rosin resin include natural rosin, rosin ester, hydrogenated rosin, hydrogenated rosin ester, polymerized rosin, polymerized rosin ester, disproportionated rosin, and disproportionated rosin ester.
Examples of the terpene resin include α-pinene resin, β-pinene resin, terpene phenol resin, hydrogenated terpene phenol resin, and the like.
Examples of aromatic petroleum resins include styrene oligomers and α-methylstyrene / styrene copolymers.
The softening point of the tackifying resin is preferably 60 ° C to 170 ° C.

  It is preferable that 3-30 mass parts of tackifying resin is mix | blended with respect to 100 mass parts of adhesive resin (A). When an appropriate amount of tackifying resin is blended, the adhesive strength is further improved.

If it is in the range which can solve the subject of this invention, other additives can be mix | blended with an adhesive.
Examples of other additives include pigments, dyes, fillers, diluents, anti-aging agents, dispersion stabilizers, polymerization inhibitors, ultraviolet absorbers, and ultraviolet stabilizers. Other additives can be used alone or in combination of two or more. Moreover, the addition amount of an additive should just be taken as the quantity from which the desired physical property is obtained, and is not specifically limited.

(solvent)
The pressure-sensitive adhesive can contain the solvent already described, if necessary, in addition to the use in solution polymerization.

  The pressure-sensitive adhesive of the present invention is preferably produced by blending a pressure-sensitive resin (A) and a bismuth-based laser color former (B) and subjecting it to a dispersion treatment. As a result, the bismuth-based laser color former (B) is not easily dispersed uniformly in the adhesive. Further, a dispersion obtained by previously dispersing a part of the adhesive resin (A) and the bismuth-based laser color former (B) can be mixed with the remaining adhesive resin (A). The dispersed particle diameter of the bismuth-based laser color former (B) can be appropriately adjusted according to the size of the laser color development portion required by the dispersion treatment.

  A known disperser can be used for the dispersion treatment. Examples of the disperser include a ball mill and a bead mill.

It is preferable that the adhesive sheet of this invention is equipped with a base material and the adhesion layer containing an adhesive. The pressure-sensitive adhesive layer can be formed by applying a pressure-sensitive adhesive. The surface of the pressure-sensitive adhesive layer that is not in contact with the base material is usually attached with a peelable sheet until just before the pressure-sensitive adhesive sheet is used to prevent foreign matter from adhering.
The pressure-sensitive adhesive sheet is produced, for example, by forming a pressure-sensitive adhesive layer by applying a pressure-sensitive adhesive to a substrate and drying it. Moreover, a pressure-sensitive adhesive layer is formed by applying and drying a pressure-sensitive adhesive on a peelable sheet, and a base material is bonded thereto. Alternatively, the pressure-sensitive adhesive layer can be formed by applying a pressure-sensitive adhesive to the peelable sheet and drying, and further bonding another peelable sheet. An adhesive sheet that does not use a substrate is called a cast adhesive sheet.

  The pressure-sensitive adhesive can be adjusted in viscosity by using an appropriate solvent during coating. The viscosity can also be adjusted by heating the pressure-sensitive adhesive.

  The pressure-sensitive adhesive layer is formed by applying a pressure-sensitive adhesive by a known method and drying it. Examples of the coating method include Mayer bar, applicator, brush, spray, roller, gravure coater, die coater, lip coater, comma coater, knife coater, reverse coater, and spin coater. Examples of the drying method include hot air drying, infrared rays, and a decompression method. The drying temperature is usually about 60 to 160 ° C.

  The thickness of the adhesive layer is preferably 5 to 150 μm, and more preferably 10 to 50 μm. By adjusting to 5 to 150 μm, an appropriate adhesive strength can be obtained.

Examples of the substrate include sheets or plate materials such as plastic, paper, and metal foil.
Examples of the plastic include polyethylene, polypropylene, polyester (for example, polyethylene terephthalate (PET)), polystyrene, polyvinyl chloride, polycarbonate, cellophane, and the like.

  The thickness of the substrate is about 5 to 200 μm.

In the release sheet, a known release layer formed from a silicone compound, a fluorine compound, or the like is usually formed on a film or paper substrate.
The thickness of the peelable sheet is usually about 10 to 200 μm.

  The pressure-sensitive adhesive sheet of the present invention can be suitably used for pressure-sensitive adhesive products such as film labels and paper labels used for general and industrial purposes.

  Hereinafter, synthesis examples, examples according to the present invention, and comparative examples will be described. However, it goes without saying that the present invention is not limited to the examples. In the following description, “part” means “part by mass” and “%” means “mass%” unless otherwise specified. The compounding quantity in a table | surface is a mass part.

[Example 1]
In a polymerization apparatus equipped with a reaction vessel, a stirrer, a thermometer, a dropping funnel, a catalyst vessel, and a reflux condenser, in a nitrogen atmosphere, 30 parts of butyl acrylate, 69 parts of 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate 0.7 parts, 0.2 part of acrylic acid, 0.1 part of 2,2′-azobisisobutyronitrile and 60 parts of ethyl acetate were charged, and the reaction vessel was heated while stirring. After confirming the start of the reaction, the reaction was carried out for 7 hours under reflux. After completion of the reaction, the reaction mixture was cooled and diluted with ethyl acetate to adjust the nonvolatile content to 45% to obtain an acrylic resin (A-1) solution having a weight average molecular weight of 650,000. For 100 parts of the acrylic resin (A-1) in the resulting acrylic resin (A-1) solution, 25 parts of rosin resin (Pine Crystal KE-359, rosin ester, manufactured by Arakawa Chemical Industries, Ltd.) Mixed.
Next, 1.0 part of commercial bismuth trioxide (99% molybdenum trioxide content, 1% neodymium trioxide) having an average particle size of 1.0 μm per 100 parts of the acrylic resin (A-1) in the mixed solution. A part was added and the dispersion process was performed with a bead mill disperser. Next, 0.8 parts of Takenate D-110N (trimethylolpropane adduct of xylylene diisocyanate, manufactured by Mitsui Chemicals Co., Ltd.) with respect to 100 parts of the acrylic resin (A-1) in the obtained mixed liquid was converted into non-volatile content. Was added to obtain an adhesive having a viscosity of 3000 mPa · s and a nonvolatile content of 40%. It was 1.4 micrometers when D50 average particle diameter of bismuth trioxide in an adhesive was measured. The viscosity is a value measured with a B-type viscometer (# 3 rotor, 12 rpm) at 25 ° C.

  The pressure-sensitive adhesive obtained on the release surface of the peelable sheet (thickness 38 μm, made of polyethylene terephthalate) was applied so that the thickness of the pressure-sensitive adhesive layer after drying was 20 μm. Subsequently, it dried at 100 degreeC for 2 minute (s), and formed the adhesion layer. On this adhesive layer, a polyethylene terephthalate film (PET film, Lumirror T-60: manufactured by Toray Industries, Inc.) having a thickness of 50 μm was stuck as a substrate to obtain an adhesive sheet. After curing at 23 ° C. for 7 days, the following evaluation was performed.

[Measurement of molecular weight]
The weight average molecular weight (Mw) and the number average molecular weight (Mn) were measured by gel permeation chromatography (GPC) method. The measurement conditions are as follows. Mw and Mn are both polystyrene equivalent values.
Apparatus: LC-GPC system “Prominence” (manufactured by Shimadzu Corporation),
Column: 4 GMHXL (Tosoh Corp.), 1 HXL-H (Tosoh Corp.) connected in series,
Detector: differential refractive index detector,
Mobile phase solvent: tetrahydrofuran (THF),
Column temperature: 40 ° C
Flow rate: 1.0 ml / min,
Sample concentration: 0.02%
Sample injection volume: 100 μL

(Examples 2-6, Comparative Examples 1-3)
Except having changed the mixing | blending of Example 1 as having described in Table 1, it carried out similarly to Example 1 and obtained the adhesive and adhesive sheet of Examples 2-6 and Comparative Examples 1-3, respectively. The titanium oxide dispersion used in Example 4 (“Multilac S-161”, manufactured by Toyochem Co., Ltd.) was blended with the isocyanate curing agent so that the titanium oxide was 0.5 parts with respect to 100 parts of the acrylic resin. did. In addition, bismuth trioxide was used by preparing bismuth trioxide having different dispersion particle sizes by appropriately adjusting dispersion conditions.

[Example 7]
In a four-necked flask equipped with a stirrer, reflux condenser, nitrogen inlet tube, thermometer, and dropping funnel, under a nitrogen atmosphere, 81 parts by weight of Kuraray polyol P-1010 (bifunctional polyester polyol, manufactured by Kuraray), Sanix GP3000 ( 101 g of trifunctional polyether polyol (manufactured by Sanyo Chemical Industries), 19 parts by weight of Desmodur H (hexamethylene diisocyanate, manufactured by Sumika Cobestrourethane), 134 parts by weight of toluene, 0.05 part by weight of dibutyltin dilaurate as a catalyst, 0.02 part by weight of tin 2-ethylhexanoate was charged, the temperature was gradually raised to 90 ° C., and the reaction was performed at 90 ° C. for 2 hours. Next, sampling was performed, and after the disappearance of the remaining isocyanate groups was confirmed by IR, the reaction was terminated by cooling. Subsequently, toluene was added as appropriate to obtain a urethane resin (A-2) solution having a nonvolatile content of 60% and a weight average molecular weight of 100,000. The viscosity of the urethane resin solution (A-2) was 3,300 mPa · s.
Next, 1.0 part of the above-mentioned commercial bismuth trioxide was added to 100 parts by mass of the urethane resin (A-2) in the urethane resin (A-2) solution, and dispersion treatment was performed with a bead mill disperser. Next, with respect to 100 parts of the urethane resin (A-2) in the obtained mixed liquid, 3.0 parts of Duranate 301-75E (trimethylenepropane adduct of hexamethylene diisocyanate, manufactured by Asahi Kasei Co., Ltd.) in terms of nonvolatile content was added. Blended to obtain an adhesive. It was 1.4 micrometers when D50 average particle diameter of bismuth trioxide in an adhesive was measured. Furthermore, it carried out similarly to Example 1 and obtained the adhesive sheet.

[Evaluation items and methods]
Evaluation items and evaluation methods are as follows.

(Visibility)
The obtained adhesive sheet was prepared to have a width of 100 mm and a length of 100 mm, and used as a measurement sample. Next, under an atmosphere of 23 ° C.-50% RH, a Q-switched pulsed laser light amplification light wave using an yttrium vanadate crystal (i-MarkerLT-010, a wavelength of about 1064 nm manufactured by YVO) was applied from the substrate side of the measurement sample. The laser beam was set to be perpendicular to the substrate surface, and the laser beam was scanned in parallel to the substrate surface to produce a laser coloring portion. The irradiation conditions were a switch frequency of 30000 Hz, an output of 46%, and a drawing speed of 2000 mm / S. Visibility of blackness developed by irradiation was visually determined. The evaluation criteria are as follows.
A: A clear and high contrast blackness was obtained. Good.
B: Necessary blackness is obtained, but contrast is slightly lower than A. Practical area.
C: Blackness is insufficient and contrast is low. Not practical.

(transparency)
The obtained adhesive sheet was prepared to have a width of 100 mm and a length of 100 mm, and used as a measurement sample. Next, the peelable sheet was peeled off from the measurement sample in an atmosphere of 23 ° C.-50% RH, and the transparency of the exposed adhesive layer was visually evaluated. The evaluation criteria are as follows.
○: The adhesive layer is not colored. Good.
(Triangle | delta): The adhesion layer had slightly yellow coloring. Practical area.
X: The adhesive layer was colored yellow. Not practical.

(Printability)
The obtained adhesive sheet was prepared to have a width of 100 mm and a length of 100 mm, and used as a measurement sample. Similar to the visibility test, a barcode was printed by irradiating a laser beam from the substrate side of the measurement sample to cause color development. The printing was evaluated using a bar code verifier (REA Check ER manufactured by Ainix Co., Ltd.) with an alphabet score.
○: A to C. Good.
Δ: D. Can be used.
X: F. Usage prohibited.

  From the results shown in Table 1, the pressure-sensitive adhesive of the present invention has a good contrast after printing and can provide a pressure-sensitive adhesive and a pressure-sensitive adhesive sheet that can form a pressure-sensitive adhesive layer.

Claims (5)

  An adhesive comprising an adhesive resin (A) and a bismuth laser color former (B).   The pressure-sensitive adhesive according to claim 1, wherein the bismuth-based laser color former (B) has a D50 average particle diameter of 0.05 to 5 µm.   The adhesive of Claim 1 or 2 containing 0.1-5 mass parts of bismuth type | system | group laser color former (B) with respect to 100 mass parts of said adhesive resins (A). The said adhesive resin (A) is an adhesive of any one of Claims 1-3 containing 1 or more types selected from the group which consists of an acrylic resin and a urethane resin.   The adhesive sheet provided with the base material and the adhesion layer containing the adhesive of any one of Claims 1-4.