JP7750002B2 - Water-based heat sealant and printed materials using it - Google Patents

Description

The present invention relates to a water-based heat-sealing agent and printed matter therewith.

More specifically, this relates to an aqueous heat sealing agent that can be stored for a long period of time, has good heat sealing properties, anti-blocking properties due to the absence of adhesion between the substrate and the heat sealing layer, oil resistance, water resistance, and printability, and is also environmentally hygienic.

In recent years, it has become common for product packaging and other packaging materials to be printed for decoration and surface protection. Furthermore, the quality of the print, such as its design, aesthetic appeal, and luxurious feel, can stimulate consumer purchasing desire and is of great industrial value.

In the packaging field, packaging materials are widely used in which a heat-sealing layer is formed by coating a paper substrate or various plastic film substrates with a heat-sealing agent. A commonly known method for forming a heat-sealing layer is to print a heat-sealable resin composition onto the substrate and then dry the medium, such as water or a solvent. Among these heat-sealing agents, water-based heat-sealing agents are desired for their environmental friendliness, and technological development is underway.

Examples of water-based heat-sealing agents that have been proposed include a water-dispersed heat-sealing composition (Patent Document 1) containing, as an essential component, an aqueous dispersion of an ethylene-unsaturated carboxylic acid copolymer in which a specific percentage of the carboxyl groups of the unsaturated carboxylic acid have been neutralized with monovalent alkali metal ions and which has a specific weight-average molecular weight; a coating composition (Patent Document 2) comprising a melt-kneaded product of a base polymer containing one or more thermoplastic polymers, a stabilizer containing at least one component selected from the group consisting of ethylene-acrylic acid copolymers, ethylene methacrylic acid copolymers, maleic anhydride-grafted polyolefins, and combinations thereof, a neutralizing agent, and water, and having a volume average particle size of less than about 5 μm; and a water-based heat-sealing agent (Patent Document 3) containing one or more acrylic polymer or copolymer emulsions, one or more molten waxes, and water. However, due to the range of thermal properties and molecular weight distribution, it has been difficult to obtain a water-based heat-sealing agent that satisfies the required heat-sealing properties, blocking resistance, oil resistance, and water resistance.

Japanese Patent Application Laid-Open No. 2006-282968 JP 2019-112637 A Special Publication No. 2020-517783

The objective of the present invention is to provide an aqueous heat-sealing agent that has good storage stability, water resistance, and printability, and is particularly excellent in heat-sealing properties, resistance to blocking on substrates, and oil resistance.

As a result of extensive research into the above-mentioned problems, the inventors discovered that the above problems could be solved by using the aqueous heat sealing agent described below, leading to the creation of the present invention.

That is, the present invention relates to an aqueous heat-sealing agent containing an acrylic resin (A) having a glass transition temperature of -20°C to 20°C and an acrylic resin (B) having a glass transition temperature of 40°C to 80°C.

The present invention also relates to the above-mentioned aqueous heat-sealing agent, in which the mass ratio of the solid contents of the acrylic resin (A) and the acrylic resin (B) (acrylic resin (A)/acrylic resin (B)) is 95/5 to 30/70.

The present invention also relates to the above-mentioned aqueous heat-sealing agent, in which the acid value of the mixture of acrylic resin (A) and acrylic resin (B) is 30 to 60 mgKOH/g.

The present invention also relates to the above-mentioned aqueous heat-sealing agent, in which, when the molecular weight distribution of the tetrahydrofuran (THF)-soluble portion of the mixture of acrylic resin (A) and acrylic resin (B) at 25°C is measured, the area percentage of molecular weights of 10,000 or less relative to the total peak area is 3 to 40%.

The present invention also relates to the above-mentioned water-based heat-sealing agent, which further contains a release agent.

The present invention also relates to a printed material having a heat seal layer made of the above-mentioned aqueous heat sealant on a substrate.

The present invention also relates to the above printed matter, which further has a coating layer.

The present invention makes it possible to provide an aqueous heat-sealing agent that has good storage stability, water resistance, and printability, and is particularly excellent in heat-sealing properties, resistance to blocking on substrates, and oil resistance.

The following describes in detail an embodiment of the present invention. However, the following description of the constituent elements is merely one example (representative example) of an embodiment of the present invention, and the present invention is not limited to these details as long as it does not deviate from the gist of the invention.

In the following explanation, "aqueous heat-sealing agent" may be abbreviated simply as "heat-sealing agent." Unless otherwise specified, "parts" refers to "parts by mass" and "%" refers to "% by mass."

<Acrylic resin>
The acrylic resin used in the present invention may be, for example, an acrylic resin containing only acrylic monomers as constituent units, an ethylene-acrylic copolymer resin, a styrene-acrylic copolymer resin, or another copolymer resin form. More specifically, examples include an acrylic resin obtained by copolymerizing an acrylic monomer such as (meth)acrylic acid or a (meth)acrylic acid ester in the presence of a polymer emulsifier, and an acrylic resin having a core/shell structure obtained by emulsion polymerization of a (meth)acrylic acid ester. An acrylic emulsion is preferred, and the acrylic resin preferably has an ethylene-derived structure content of 50% by mass or less, more preferably 30% by mass or less, 10% by mass or less, or even more preferably 3% by mass or less. Forms not containing ethylene-derived structures can also be used suitably.

(Meth)acrylic acids that can form the shell portion of the core/shell structure include acrylic acid, methacrylic acid, etc.

Examples of (meth)acrylic acid esters that can form the shell portion or core portion of the acrylic resin of the present invention include (meth)acrylates having an alkyl chain such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and stearyl (meth)acrylate, (meth)acrylates having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate and 2-hydroxybutyl (meth)acrylate, and (meth)acrylates having an alicyclic structure such as cyclohexyl (meth)acrylate, and these can be used alone or in combination of two or more.
The (meth)acrylic acid ester in the shell portion and the (meth)acrylic acid ester in the core portion may be the same or different, and the shell portion and the core portion may be polymerized together with a component polymerizable with them other than (meth)acrylic acid and (meth)acrylic acid ester.

The core/shell ratio (mass ratio of core portion to shell portion) of the acrylic resin of the present invention is preferably 30:70 to 70:30. A core ratio of 30 or more results in good coating strength for the aqueous heat-sealing agent, while a core ratio of 70 or less results in good storage stability for the acrylic emulsion.

It is also preferable to use a neutralizing agent to make the acrylic resin aqueous during synthesis. Such neutralizing agents include ammonia, organic amines, and alkali metal hydroxides. Examples of organic amines include diethylamine, triethylamine, monoethanolamine, dimethylethanolamine, and diethylethanolamine. Examples of alkali metal hydroxides include sodium hydroxide and potassium hydroxide. Organic amines are preferred, and dimethylethanolamine is even more preferred. Using diethanolamine is preferable in terms of resolubility, resulting in good printability.

For the polymerization reaction of the acrylic resin of the present invention, a water-soluble thermally decomposable polymerization initiator such as a persulfate such as potassium persulfate or ammonium persulfate, or an azobis-based cation salt or a hydroxyl group adduct can be used.
Redox initiators can also be used, such as a combination of an organic peroxide such as t-butyl hydroperoxide, benzoyl peroxide, or cumene hydroperoxide with a reducing agent such as Rongalit or sodium metabisulfite, a combination of potassium persulfate or ammonium persulfate with Rongalit or sodium thiosulfate, or a combination of aqueous hydrogen peroxide and ascorbic acid.

The aqueous heat-sealing agent of the present invention contains two acrylic resins with different glass transition temperatures: acrylic resin (A) with a glass transition temperature of -20°C to 20°C and acrylic resin (B) with a glass transition temperature of 40°C to 80°C. Acrylic resin (A) provides heat-sealing properties and oil resistance, while acrylic resin (B) provides blocking resistance, thereby contributing to solving the problems described in this application.

The acrylic resin (A) must have a glass transition temperature of -20°C to 20°C, and more preferably -15°C to 5°C.

The acrylic resin (B) must have a glass transition temperature of 40°C to 80°C, preferably 50°C to 70°C.

The glass transition temperature (Tg) of the acrylic resin referred to in the present invention is a glass transition temperature calculated based on the FOX formula from the Tg of each homopolymer that can be formed from each monomer and the mass fraction of each monomer, and is calculated jointly for both the share portion and the core portion.
1/Tg=Σ(Wn/Tgn)
Tg: calculated glass transition temperature (absolute temperature) of the copolymer
Wn: mass fraction of monomer n (%)
Tgn: glass transition temperature (absolute temperature) of the homopolymer of monomer n

The mixture of acrylic resin (A) and acrylic resin (B) is preferably contained in the aqueous heat-sealing composition in an amount of 10 to 60% by mass, more preferably 30 to 50% by mass, on a solids basis. A content of 10% by mass or more may improve the drying properties of the aqueous heat-sealing agent, while a content of 60% by mass or less may improve the fluidity and leveling properties of the aqueous heat-sealing agent, resulting in good printability.

In addition, the mass ratio of the solid contents of the acrylic resin (A) and the acrylic resin (B) in the aqueous heat-sealing agent of the present invention (acrylic resin (A)/acrylic resin (B)) is preferably 95/5 to 30/70, and more preferably 90/10 to 50/50. When the mass ratio of the acrylic resin (A) is 30 or more, the heat sealability and oil resistance may be improved, and when the mass ratio is 95 or less, the blocking resistance may be improved.

Furthermore, in the aqueous heat sealing agent of the present invention, the acid value of the mixture of acrylic resin (A) and acrylic resin (B) is preferably 30 to 60 mgKOH/g. An acid value of 30 mgKOH/g or more improves the resolubility of the acrylic resin, which can prevent plate fogging and clogging and improve printability, while an acid value of 60 mgKOH/g or less can improve water resistance.

Furthermore, in the aqueous heat-sealing material of the present invention, when the tetrahydrofuran-soluble portion at 25°C of the mixture of the acrylic resin (A) and the acrylic resin (B) is measured by gel permeation chromatography (GPC), the area ratio (area percentage) of the portion having a molecular weight of 10,000 or less is preferably 3 to 40%, more preferably 10 to 30%.
In the low molecular weight region of 10,000 or less, the acrylic resin melts at low temperatures and easily spreads onto the substrate, and an area ratio of 3 to 40% can result in good heat sealability and oil resistance.
The area ratio % is the area percentage % where LogM is in the range of 4 or less in a molecular weight distribution diagram with the area percentage % of molecular weight M on the vertical axis and the common logarithm LogM of molecular weight M on the horizontal axis.

The GPC measurement conditions can be polystyrene equivalent, with RI reflection as the detection method, a flow rate of 0.1 to 0.5 ml/min, a column temperature of 30 to 50°C, and a measuring instrument such as the Shodex GPC-104 manufactured by Showa Denko K.K.

As described above, when measuring the molecular weight distribution of the tetrahydrofuran (THF)-soluble portion of a mixture of acrylic resin (A) and acrylic resin (B), the area percentage of molecular weights of 10,000 or less relative to the total peak area can be adjusted to 3 to 40% by, for example, setting the weight-average molecular weight of acrylic resin (A) to 25,000 to 350,000 and the polydispersity index (weight-average molecular weight Mw/number-average molecular weight Mn) to 8 to 10, and by setting the weight-average molecular weight of acrylic resin (B) to 60,000 to 100,000 and the polydispersity index (weight-average molecular weight Mw/number-average molecular weight Mn) to 3 to 5.

<Release Agent>
The aqueous heat-sealing agent of the present invention may contain a release agent. The release agent is preferably a fatty acid amide, a hydrocarbon wax, or lecithin. Examples of the fatty acid amide include saturated fatty acid amides, unsaturated fatty acid amides, and modified fatty acid amides. Examples of the hydrocarbon wax include polyolefin wax and paraffin wax. Examples of the lecithin include paste-like lecithin prepared from by-products of vegetable oil refining such as soybeans or crude materials such as egg yolk. The aqueous heat-sealing agent composition preferably contains the release agent in an amount of 0.1 to 3% by mass, more preferably 0.2 to 1.5% by mass. Using the release agent in combination with the acrylic resin of the present invention further improves blocking resistance and water resistance.

<Aqueous medium>
In the present invention, the aqueous heat-sealing agent preferably contains an aqueous medium. The aqueous medium contains water as a main component (preferably 50% by mass or more of the total medium from the viewpoint of the storage stability and drying property of the aqueous heat-sealing agent), and may contain an aqueous organic solvent other than water as needed. Specifically, an alcohol-based organic solvent or a glycol-based organic solvent may be contained depending on the printing conditions (speed, plate depth, design, drying temperature). Specific examples of alcohol-based organic solvents include methanol, ethanol, propanol, isopropanol, isobutanol, normal butanol, tertiary butanol, hexanol, octanol, and decanol. Examples of glycol-based organic solvents include ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monooctyl ether, diethylene glycol, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, propylene glycol, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monopropyl ether, tripropylene glycol monobutyl ether, and dibutyl glycol.
Among these, isopropanol, ethylene glycol, propylene glycol, etc. are preferred. From the viewpoints of storage stability, viscosity increase, and drying properties of the aqueous heat-sealing agent, the amount of the aqueous organic solvent other than water is preferably 30 mass% or less, more preferably 10 mass% or less, of the total mass of the aqueous heat-sealing agent.

<Additives>
Various additives can be used in the aqueous heat-sealing agent of the present invention as needed. Examples include extender pigments, inorganic fine particles, leveling agents, antifoaming agents, and film-forming agents. Specific examples include extender pigments such as calcium carbonate, kaolin, barium sulfate, aluminum hydroxide, clay, and talc to improve drying properties and coating film hiding power, inorganic fine particles to impart antislip properties, leveling agents to improve leveling properties, antifoaming agents to impart antifoaming properties, basic compounds such as sodium hydroxide and potassium hydroxide to impart resolubility, and film-forming aids.

<Production of Water-Based Heat Sealing Agent>
The aqueous heat-sealing agent of the present invention can be produced by a known method. For example, it can be produced by adding acrylic resin (A), acrylic resin (B), and, if necessary, a release agent, water, an aqueous organic solvent, additives, etc., and then uniformly stirring and mixing them using a bladed mixer. Conventional bladed mixers can be used, including batch mixers such as vessels equipped with propeller blades, and continuous mixers such as in-line mixers.

<Base material>
The aqueous heat-sealing agent of the present invention can be used to form a heat-sealing layer on a substrate to produce a printed product. Note that "on a substrate" includes cases where the substrate and the heat-sealing layer are not in direct contact with each other.
Examples of the substrate (printing material) include plastic films such as polyolefin substrates such as polyethylene and polypropylene, polyester substrates such as polyethylene terephthalate, and polyamide substrates such as nylon, paper substrates, aluminum foil, and films and sheets made of composite materials thereof. In the present invention, paper substrates are particularly preferred. The paper substrate is preferably a paper substrate selected from kraft paper, art paper, coated paper, and high-quality paper.

<Printed material having a heat seal layer formed from an aqueous heat seal agent>
An example of a method for producing a printed matter having a heat seal layer formed from an aqueous heat sealant is a method in which the aqueous heat sealant of the present invention is used to print on a substrate using a gravure printer. The aqueous heat sealant can be appropriately diluted with a diluent consisting of water or an aqueous organic solvent as needed during printing, and then printed on various substrates using a gravure printing method.

<Printing method>
Various printing methods are used to form a printed layer from the aqueous heat-sealing agent of the present invention. Examples of such printing methods include rotary printing methods such as gravure printing and flexographic printing, and printing can be performed by known means. For example, when performing gravure printing, the aqueous heat-sealing agent can be diluted with water or a water/alcohol-based organic solvent to adjust the viscosity (20 to 30 seconds at 25°C using Zahn cup #3) and then printing can be performed appropriately.

Furthermore, the printing configuration of a printed matter having a heat seal layer can further include any combination of an anchor coat layer (anchor layer), a coating layer (OP layer) and an ink layer.
The composition of the printed matter is, for example,
Suitable examples include substrate/heat-seal layer, substrate/anchor layer/heat-seal layer ink layer, substrate/heat-seal layer ink layer, substrate/anchor layer/heat-seal layer OP layer/ink layer, substrate/heat-seal layer OP layer/ink layer, substrate/anchor layer/heat-seal layer OP layer/substrate/heat-seal layer OP layer/substrate/anchor layer/heat-seal layer OP layer/substrate/anchor layer/heat-seal layer OP layer/substrate/ink layer/heat-seal layer OP layer/substrate/ink layer/anchor layer/heat-seal layer OP layer/anchor layer/substrate/anchor layer/heat-seal layer OP layer/anchor layer/substrate/heat-seal layer, and the like.
Furthermore, printed matter having a heat seal layer and a coating layer can be post-processed according to various uses, and is suitable for use in packaging products such as food, particularly paper containers.

The OP layer can be preferably a coating material using polyurethane resin, polyamide resin, nitrocellulose resin, or the like, while the anchor layer can be preferably an anchor material using polyurethane resin, polyamide resin, nitrocellulose resin, polyether resin, acrylic resin, or the like. The ink layer can be preferably a gravure ink, flexographic ink, or other printing ink using polyurethane resin, polyamide resin, polyether resin, acrylic resin, or the like.

The present invention will be described in detail below using examples, but the present invention is not limited to these examples. Note that parts and percentages in the present invention represent parts by mass and percentages by mass unless otherwise noted.

<Acid value>
The acid value was measured in terms of the number of milligrams of potassium hydroxide required to neutralize the carboxyl groups contained in 1 g of sample, according to a method in accordance with JIS K0070.

<Weight average molecular weight and number average molecular weight>
The weight average molecular weight (Mw) and number average molecular weight (Mn) were determined by GPC (gel permeation chromatography). The molecular weight distribution was measured using a "Shodex GPC-104" manufactured by Showa Denko K.K., and the polystyrene equivalent molecular weight was determined. The measurement conditions are shown below.
Column: The following columns are connected in series.
Showa Denko Shodex LF-404 x 2 Showa Denko Shodex LF-G x 2
Detector: RI (differential refractometer),
Measurement conditions: column temperature 40°C,
Eluent: tetrahydrofuran Flow rate: 0.3 mL/min

Synthesis Example 1 (Synthesis of Acrylic Resin (A1))
A four-neck flask equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube was charged with 100 parts of isopropyl alcohol, and the temperature was raised to 80-82°C. A mixture of 5 parts of acrylic acid, 10 parts of methyl methacrylate, 25 parts of butyl acrylate, and 1.5 parts of benzoyl peroxide charged in a dropping funnel was then added dropwise over 2 hours. After the dropwise addition was completed, 0.3 parts of benzoyl peroxide was added, and the reaction was continued for another 2 hours. The temperature was then lowered to 40°C, and dimethylethanolamine and ion-exchanged water were added. The temperature of the reaction flask was then raised to 80-82°C, and stripping was performed, ultimately yielding a water-soluble resin with a solids content of 30%.
The entire amount of the water-soluble resin obtained above and 10 parts of ion-exchanged water were charged into a reaction flask, and the temperature was raised to 80°C to 82°C. Then, 0.5 parts of potassium persulfate was added, and a mixture of 26 parts of methyl methacrylate, 20 parts of butyl acrylate, and 14 parts of 2-ethylhexyl acrylate was added dropwise over 2 hours. After completion of the dropwise addition, 0.15 parts of potassium persulfate was added, and the mixture was allowed to react for 2 hours. In this way, an acrylic resin (A1) was obtained having a solids content of 40%, a calculated glass transition temperature of -12°C, an acid value of 38 mgKOH/g, a weight average molecular weight (Mw) of 141,100, and a number average molecular weight (Mn) of 16,800.

<Synthesis Examples 2 to 9> (Synthesis of acrylic resins (A2) to (A9))
In Synthesis Examples 2 to 5 and 8 and 9, polymerization was carried out in the same manner as in Synthesis Example 1 to obtain acrylic resins (A2) to (A5) and acrylic resins (A8) to (A9).
In Synthesis Examples 6 and 7, polymerization was carried out in the same manner as in Synthesis Example 1, except that the amount of benzoyl peroxide and potassium persulfate were changed, to obtain acrylic resins (A6) to (A7). The formulations of these monomers are shown in Table 1.
In all synthesis examples, the water-soluble resin constituting the shell portion was adjusted to have a solid content of 30%, and the entire amount was used. The solid content of the final acrylic emulsion was adjusted to be 40%.
Dimethylethanolamine was used as the neutralizing agent in the synthesis of the shell portion, and taking into consideration distillation by stripping, the carboxyl groups were ultimately neutralized to 110%.

Synthesis Example 10 (Synthesis of acrylic resin (B1))
A four-neck flask equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube was charged with 100 parts of isopropyl alcohol, and the temperature was raised to 80-82°C. A mixture of 6 parts of methacrylic acid, 34 parts of methyl methacrylate, 10 parts of butyl acrylate, and 2.5 parts of benzoyl peroxide charged in a dropping funnel was then added dropwise over 2 hours. After the dropwise addition was completed, 0.5 parts of benzoyl peroxide was added, and the reaction was continued for another 2 hours. The temperature was then lowered to 40°C, and dimethylethanolamine and ion-exchanged water were added. The temperature of the reaction flask was then raised to 80-82°C, and stripping was performed, ultimately yielding a water-soluble resin with a solids content of 30%.
The entire amount of the water-soluble resin obtained above and 10 parts of ion-exchanged water were charged into a reaction flask, and the temperature was raised to 80°C to 82°C. Then, 0.8 parts of potassium persulfate was added, and a mixture of 42 parts of methyl methacrylate and 8 parts of 2-ethylhexyl acrylate was added dropwise over 2 hours. After completion of the dropwise addition, 0.2 parts of potassium persulfate was added, and the mixture was allowed to react for 2 hours. In this way, an acrylic resin (B1) was obtained having a solids content of 40%, a calculated glass transition temperature of 61°C, an acid value of 45 mgKOH/g, a weight average molecular weight (Mw) of 73,800, and a number average molecular weight (Mn) of 21,700.

Synthesis Examples 11 to 14 (Synthesis of acrylic resins (B2) to (B5))
In Synthesis Examples 11 to 14, polymerization was carried out in the same manner as in Synthesis Example 10 to obtain acrylic resins (B2) to (B5). The formulations of these monomers are shown in Table 1.
In all synthesis examples, the water-soluble resin constituting the shell portion was adjusted to have a solid content of 30%, and the entire amount was used. The solid content of the final acrylic emulsion was adjusted to be 40%.
Dimethylethanolamine was used as the neutralizing agent in the synthesis of the shell portion, and taking into consideration distillation by stripping, the carboxyl groups were ultimately neutralized to 110%.

Example 1
53.4 parts of acrylic resin (A1), 35.6 parts of acrylic resin (B1), 0.5 parts of lecithin, 0.2 parts of a silicone-based antifoaming agent, and 10.3 parts of water were mixed with stirring to obtain an aqueous heat sealing material S1.

<Examples 2 to 19>
Aqueous heat sealing agents S2 to S19 were obtained in the same manner as in Example 1, except that the raw materials and compounding ratios shown in Table 2 were used.

<Comparative Examples 1 to 6>
Aqueous heat-sealing agents T1 to T6 were obtained in the same manner as in Example 1, except that the raw materials and compounding ratios shown in Table 3 were used.

<Printed materials and evaluation>
The aqueous heat-sealing agents and printed materials thereof obtained in Examples 1 to 19 and Comparative Examples 1 to 6 were used to carry out the evaluations described below.
The results are shown in Tables 2 and 3.

<Heat sealability>
The aqueous heat-sealing agents obtained in Examples 1 to 19 and Comparative Examples 1 to 6 were diluted with water and adjusted to a viscosity of 25 seconds (25°C) using a Zahn cup No. 3 to prepare diluted heat-sealing agents for printing.
Next, a heat seal layer was formed by printing twice on the matte side of one-side gloss bleached kraft paper (Oji Paper Co., Ltd.) using a gravure proofing press with a 35 micron deep etching plate (drying temperature 100°C, printing speed 40 m/min). A polyamide/nitrocellulose release varnish was printed as a coating layer on the glossy side of the one-side gloss bleached kraft paper using a 20 micron deep etching plate (drying temperature 50°C, printing speed 40 m/min).
The printed matter was cut into a size of 15 mm x 100 mm, and the heat seal layer surfaces were heat sealed together using the following device and conditions to evaluate the heat seal strength. Note that a strength of 2.0 N/15 mm or more is within the range where there are no practical problems.
(Heat sealing conditions)
Apparatus: Heat seal tester manufactured by Tester Sangyo Co., Ltd., seal width: 10 mm, heater temperature: 120°C, seal pressure: 2 kg/cm ² , seal time: 1 sec
(Heat seal strength measurement)
Apparatus: Intesco small tensile testing machine (model: IM-20), test piece width: 15 mm, peel mode: 90° peel, tensile speed: 300 mm/min

<Blocking resistance>
The aqueous heat-sealing agents obtained in Examples 1 to 19 and Comparative Examples 1 to 6 were diluted with water and adjusted to a viscosity of 25 seconds (25°C) using a Zahn cup No. 3 to prepare diluted heat-sealing agents for printing.
Next, a heat seal layer was formed by printing twice on the matte side of one-side gloss bleached kraft paper (Oji Paper Co., Ltd.) using a gravure proofing press with a 35 micron deep etching plate (drying temperature 100°C, printing speed 40 m/min). A polyamide/nitrocellulose release varnish was printed as a coating layer on the glossy side of the one-side gloss bleached kraft paper using a 20 micron deep etching plate (drying temperature 50°C, printing speed 40 m/min).
The printed matter was cut into 4 cm squares, and the heat seal layer surface and the coating layer surface were pressed together. The printed matter was then left to stand for 24 hours in an environment of a temperature of 40°C, a humidity of 80% RH, and a load of 100 N/ ^cm2 . After that, the blocking resistance was evaluated based on the peel resistance when the pressed surface was peeled off and the state of the peeled surface according to the following criteria.
A. There is no peel resistance and no heat sealant removal is observed.
B. There is slight peel resistance, but no heat sealant removal is observed.
C. Peel resistance is observed, but no heat sealant removal is observed.
D. There is resistance to peeling, and small amounts of heat sealant have been removed in spots.
E. Peel resistance is strong, and heat sealant removal is observed over 50% or more of the printed area.
A, B and C are within the ranges that do not pose any practical problems.

<Oil resistance>
The aqueous heat-sealing agents obtained in Examples 1 to 19 and Comparative Examples 1 to 6 were diluted with water and adjusted to a viscosity of 25 seconds (25°C) using a Zahn cup No. 3 to prepare diluted heat-sealing agents for printing.
Next, a gravure proofing press was used to print twice on the non-glossy side of a single-sided bleached kraft paper (manufactured by Oji Paper Co., Ltd.) using a 35 micron deep etching plate (drying temperature 100°C, printing speed 40 m/min) to form a heat seal layer.
The oil resistance of the printed matter was evaluated in accordance with JAPAN TAPPI Paper and Pulp No. 41:2000 "Paper and Paperboard - Oil Repellency Test Method - Kit Method."
Evaluation by kit value: Evaluation was made within the range of kit value 1 to 16, with 1 (poor) ⇔ 16 (excellent), and a kit value of 5 or more was judged to be in a range where there is no problem in practical use.

<Water resistance>
The aqueous heat-sealing agents obtained in Examples 1 to 19 and Comparative Examples 1 to 6 were diluted with water and adjusted to a viscosity of 25 seconds (25°C) using a Zahn cup No. 3 to prepare diluted heat-sealing agents for printing.
Next, a gravure proofing press was used to print twice on the non-glossy side of a single-sided bleached kraft paper (manufactured by Oji Paper Co., Ltd.) using a 35 micron deep etching plate (drying temperature 100°C, printing speed 40 m/min) to form a heat seal layer.
The heat seal layer surface of the printed material was rubbed 50 times with a cotton swab soaked in water, and the water resistance was evaluated based on the degree of removal of the heat seal agent, as determined by visual inspection.
A. The heat sealant does not come off the cotton swab.
B. There is a small amount of heat sealant on the cotton swab, but the substrate is not visible.
C. There is heat sealant on the cotton swab, but the substrate is not visible.
D. There is heat sealant on the cotton swab and the base material is also slightly visible.
E. The swab has the heat seal removed and the substrate is clearly visible.
A, B and C are within the ranges that do not pose any practical problems.

<Printability>
The viscosity of the aqueous heat-sealing agents obtained in Examples 1 to 19 and Comparative Examples 1 to 6 was adjusted with water to 25 seconds (25°C) using a Zahn cup No. 3, and printing was performed using a gravure proofing press with a etched plate having a plate depth of 35 microns (drying temperature 100°C, printing speed 40 m/min). The plate was then run idle for 60 minutes, and printing was performed again, and the degree of printing unevenness on the printed matter was visually determined and evaluated.
A. The area of uneven printing is less than 1%.
B. The area of printing unevenness is 1% or more and less than 3%.
C. The area of printing unevenness is 3% or more and less than 6%.
D. The area of uneven printing is 6% or more and less than 10%.
E. The area of uneven printing is 10% or more.
A, B and C are within the ranges that do not pose any practical problems.

The present invention has provided an aqueous heat-sealing agent that has good storage stability, water resistance, and printability, and is particularly excellent in heat-sealing properties, blocking resistance to substrates, and oil resistance.
In particular, in Comparative Examples 1 and 2 in which the glass transition temperature of the acrylic resin (A) was outside the range, Comparative Examples 3 and 4 in which the glass transition temperature of the acrylic resin (B) was outside the range, and Comparative Examples 5 and 6 which did not contain the acrylic resin (A) or the acrylic resin (B), the heat sealability, blocking resistance, or oil resistance were evaluated as not meeting the standards.

Claims (6)

An aqueous heat-sealing agent containing an acrylic resin (A) having a glass transition temperature of -20°C to 20°C and an acrylic resin (B) having a glass transition temperature of 40°C to 80°C ,
An aqueous heat-sealing agent, wherein the mass ratio of the solid contents of the acrylic resin (A) and the acrylic resin (B) (acrylic resin (A)/acrylic resin (B)) is 95/5 to 20/80 . 2. The aqueous heat-sealing agent according to claim 1 , wherein the mixture of the acrylic resin (A) and the acrylic resin (B) has an acid value of 30 to 60 mgKOH/g. 3. The aqueous heat-sealing agent according to claim 1, wherein, when a molecular weight distribution of a tetrahydrofuran (THF)-soluble portion of a mixture of the acrylic resin (A) and the acrylic resin (B) at 25°C is measured, the area percentage of molecular weights of 10,000 or less relative to the total peak area is 3 to 40%. The aqueous heat-sealing agent according to any one of claims 1 to 3 , further comprising a release agent. A printed matter having a heat seal layer made of the aqueous heat sealant according to any one of claims 1 to 4 on a substrate. The printed matter according to claim 5 , further comprising a coating layer.