Aqueous coating agent

Abstract

To provide an aqueous coating agent having superior heat sealability of a paper base material, particularly superior heat sealability even for a packaging body having a seal portion of a paper base material to which a content (more specifically, a powder) adheres.SOLUTION: Disclosed is an aqueous coating agent comprising: (A) thermally expandable microcapsule; and (B) a thermoplastic resin, wherein the aqueous coating agent comprises the component (A) in an amount less than 15 pts.mass based on 100 pts.mass of the total of the components (A) and (B).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aqueous coating agent applied to a paper substrate, and a paper substrate coated with the aqueous coating agent. Further, the present invention relates to a package (for example, a packaging bag, a container, a box, etc.) obtained by processing a paper substrate.

Background Art

[0002] In consideration of environmental problems, reduction of plastic products is globally recommended. Plastic products cannot be decomposed naturally and are difficult to dispose of. Further, when plastics are incinerated, dioxins may be generated, which may cause air pollution.

[0003] Furthermore, in recent years, plastic waste has been discarded into the ocean, decomposed into micro-levels to become small waste, and there is concern that fish in the ocean may eat this waste and humans may eat the fish.

[0004] Against such a background, replacement from plastic substrates to paper substrates has been considered in various fields. Particularly in the food field, attempts have been made to manufacture packages (for example, packaging bags for food, containers such as paper cups, boxes, etc.) by processing paper substrates instead of plastic substrates. In the construction field, packages (for example, powder packaging bags for cement, etc.) are manufactured by processing paper substrates.

[0005] As one form of the package, it is known to use laminated paper. Generally, laminated paper is obtained by laminating a polyethylene film or the like on a paper substrate. In recent years, environmental awareness has increased and recycling of laminated paper has been required. However, since special equipment is required for recycling laminated paper, a method of coating a film with an aqueous resin has been used.

[0006] Patent Document 1 teaches that an aqueous dispersion of an ethylene resin containing an ethylene-acrylic acid copolymer neutralized with ammonia or an amine and another olefinic thermoplastic resin is useful as a heat-sealing agent for a paper substrate or an aluminum foil substrate ([Claims],

[0025] ,

[0027] ,

[0028] ,

[0029] ,

[0030] ,

[0035] ,

[0044] , etc.). Patent Document 1 discloses that when the above-mentioned aqueous dispersion of an ethylene resin is applied to a paper substrate or an aluminum foil substrate, dried, and then the coated portion is heat-sealed at 80 or 120 °C, the heat-sealing property is excellent (

[0027] ,

[0030] ,

[0035] ,

[0044] , etc.).

[0007] Patent Document 2 manufactures an acrylic pressure-sensitive adhesive containing a copolymer of butyl acrylate and acrylic acid and thermally expandable microspheres (

[0039] to

[0040] ). Using this pressure-sensitive adhesive, a paper lid attached to a polymer tray containing a small amount of water is sealed (at room temperature) to manufacture a food package. Then, the food package is placed in a microwave oven and heated at 120 °C for 2 minutes to lose the adhesive force for emergency and peel off ([Claims],

[0003] ,

[0004] ,

[0040] to

[0041] ).

[0008] However, when the aqueous dispersions or pressure-sensitive adhesives of Patent Documents 1 and 2 are used as coating agents, it is difficult to heat-seal a package in which the contents adhere to the seal portion. In particular, when the contents of the package are substances such as powders that can easily scatter, such substances may float and adhere to the seal portion of the package, reducing the heat-sealing property. Therefore, it is required that the aqueous coating agent be able to heat-seal the package even at the seal portion where the contents of the package adhere. Furthermore, Patent Document 2 is a pressure-sensitive adhesive and cannot be used as a heat-sealing agent.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

[0010] The present invention has been made to solve the above problems, and provides an aqueous coating agent that is excellent in heat sealability of a paper substrate, and is particularly excellent in heat sealability even for a package having a sealed portion of a paper substrate to which a content (more specifically, a powder) adheres. Another object of the present invention is to provide a paper substrate coated with the coating agent. [Means for Solving the Problems]

[0011] As a result of intensive studies, the present inventor has found that an aqueous coating agent containing a thermoplastic resin and specific microcapsules and restricting the blending amount of the microcapsules within a specific range is excellent in heat sealability, and is particularly excellent in heat sealability even for a package having a sealed portion of a paper substrate to which a content (more specifically, a powder) adheres, and has thus completed the present invention. That is, this specification includes the following embodiments. 1. An aqueous coating agent containing (A) thermally expandable microcapsules and (B) a thermoplastic resin, wherein the amount of component (A) is less than 15 parts by mass with respect to 100 parts by mass of the total amount of components (A) and (B). 2. The aqueous coating agent according to 1, wherein the glass transition temperature of the (B) thermoplastic resin is 40°C or lower. 3. The aqueous coating agent according to 1 or 2, wherein the (A) thermally expandable microcapsules and the (B) thermoplastic resin are dispersed in an aqueous medium. 4. The aqueous coating agent according to any one of 1 to 3, wherein the (A) thermally expandable microcapsules have an outer shell and a foaming agent encapsulated in the outer shell and vaporized by heating. 5. (A) The thermally expandable microcapsules are the aqueous coating agent according to any one of 1 to 4, wherein the expansion start temperature is lower than the maximum expansion temperature, the expansion start temperature is 65 to 200°C, and the maximum expansion temperature is 100 to 350°C. 6. (B) The thermoplastic resin contains at least one structural unit selected from the structural units derived from polymers of (meth)acrylic acid esters and the structural units derived from styrene polymers, and is the aqueous coating agent according to any one of 1 to 5. 7. (B) The thermoplastic resin contains both a copolymer of methyl methacrylate and 2-ethylhexyl acrylate and a styrene-butadiene copolymer, and is the aqueous coating agent according to any one of 1 to 6. 8. A paper substrate coated with the aqueous coating agent according to 1 to 7. 9. A packaging body containing the paper substrate according to 8. 10. The packaging body according to 9, which contains powder.

Advantages of the Invention

[0012] The aqueous coating agent of the embodiment of the present invention contains (A) thermally expandable microcapsules and (B) a thermoplastic resin. When the content of component (A) is less than 15 parts by mass with respect to 100 parts by mass of the total amount of components (A) and (B), the heat sealability with respect to the paper substrate (especially the heat sealability of a packaging body having a sealed portion of a paper substrate to which the content adheres) is remarkably improved. By reducing the content of component (A), the aqueous coating agent of the present invention is uniformly applied to the sealed portion of the paper substrate of the packaging bag, the adhesion and the peel strength are improved, and furthermore, the expansion rate can be maintained at a certain level.

[0013] Since the aqueous coating agent of the embodiment of the present invention expands by heat, even if the content (powder, more specifically, flour, cement powder, etc.) adheres to the sealing surface, the content is wrapped and the adhesion to the sealed portion is improved. By applying the aqueous coating agent of the embodiment of the present invention to the sealed portion, even if the content such as powder adheres to the sealed portion of the packaging body, the packaging body can be suitably heat-sealed. Thus, the aqueous coating agent of the embodiment of the present invention can suitably heat-seal the seal portion to which the contents of the package adhere. Therefore, the contents of the package are not limited to liquids and powders, and can be used in various packaging fields (for example, food, construction, etc.).

[0014] Since the paper substrate of the embodiment of the present invention is coated with the aqueous coating agent of the above-described embodiment, even when there is a possibility that the contents adhere to the seal portion, such as in a food packaging bag or a packaging bag containing powders such as cement, it becomes a package with excellent heat-sealability.

Mode for Carrying Out the Invention

[0015] The aqueous coating agent (also simply referred to as "coating agent") of the embodiment of the present invention contains (A) thermally expandable microcapsules (also referred to as "component (A)", "(A) microcapsules") and (B) a thermoplastic resin (also referred to as "component (B)").

[0016] The aqueous coating agent of the embodiment of the present invention contains less than 15 parts by mass of component (A) with respect to a total of 100 parts by mass of component (A) and component (B). Since the content of component (A) in the aqueous coating agent of the embodiment of the present invention is less than 15 parts by mass, it has excellent heat-sealability of the paper substrate and can be heat-sealed even if powder or the like adheres to the seal portion. In the present invention, the content of component (A) is more preferably 1 to 13 parts by mass, even more preferably 1 to 10 parts by mass, and most desirably 2 to 9 parts by mass with respect to a total of 100 parts by mass of component (A) and component (B).

[0017] Since the content of component (A) in the aqueous coating agent of the embodiment of the present invention is 1 to 13 parts by mass, it can maintain heat-sealability at a higher level and can more suitably heat-seal the seal portion in a state where powder or a liquid substance adheres to the seal portion.

[0018] The aqueous coating agent of the embodiment of the present invention refers to a coating agent in which a polymer (for example, component (B), etc.) can be dispersed and / or dissolved in an aqueous medium, and is preferably an aqueous emulsion (aqueous dispersion) in which the polymer is dispersed in the aqueous medium. By being an aqueous emulsion, the aqueous coating agent of the embodiment of the present invention can be used even in fields with strict hygiene requirements such as the food field.

[0019] In this specification, the "aqueous medium" refers to general water such as tap water, distilled water or ion-exchanged water, but may also include a water-soluble or water-dispersible organic solvent that has poor reactivity with the raw materials of the resin related to the present invention such as monomers, for example, acetone, ethyl acetate, etc., and may further include water-soluble or water-dispersible monomers, oligomers, prepolymers and / or resins, etc., and may also include emulsifiers, polymerizable emulsifiers, polymerization reaction initiators, chain extenders and / or various additives, etc. that are usually used when producing aqueous resins or water-soluble resins as described later. Hereinafter, the constituent elements of the aqueous coating agent of the embodiment of the present invention will be described.

[0020] <(A) Thermally expandable microcapsules> In this specification, the (A) thermally expandable microcapsules have a microcapsule structure composed of an outer shell (shell) and a foaming agent encapsulated in the outer shell. The foaming agent encapsulated in the outer shell vaporizes when heated, and the thermoplastic outer shell is expanded, so that the (A) thermoplastic microcapsules can expand. The outer shell is composed of a thermoplastic resin obtained by polymerizing the (a) polymerizable component, and the thermoplastic resin may be the same as or different from the (B) thermoplastic resin described later.

[0021] (a) The polymerizable component has (a1) polymerizable monomer as an essential component and may contain (a2) crosslinking agent. (a1) The polymerizable monomer is a monomer having one carbon-carbon double bond with radical polymerizability and is a monomer capable of addition polymerization. The crosslinking agent means a monomer having at least two carbon-carbon double bonds with radical polymerizability and is a component for introducing a crosslinked structure into the thermoplastic resin.

[0022] (a1) As the polymerizable monomer, for example, alkoxypolyoxyalkylene mono(meth)acrylate such as methoxypolyethylene glycol mono(meth)acrylate, methoxypolypropylene glycol mono(meth)acrylate, methoxypolybutylene glycol mono(meth)acrylate, methoxypolyethylene glycol-polypropylene glycol mono(meth)acrylate, methoxypolyethylene glycol-polybutylene glycol mono(meth)acrylate, methoxypolypropylene glycol-polybutylene glycol mono(meth)acrylate, octylpolyethylene glycol mono(meth)acrylate, lauroxypolyethylene glycol mono(meth)acrylate, stearoxypolyethylene glycol mono(meth)acrylate; phenoxypolyoxyalkylene mono(meth)acrylate such as phenoxypolyethylene glycol mono(meth)acrylate; polyalkylene glycol mono(meth)acrylate such as polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polybutylene glycol mono(meth)acrylate, polyethylene glycol-polypropylene glycol mono(meth)acrylate, polyethylene glycol-polybutylene glycol mono(meth)acrylate, polypropylene glycol-polybutylene glycol mono(meth)acrylate; succinic acid mono(2-acryloyloxyethyl); polylactone mono(meth)acrylate such as ω-carboxy-polycaprolactone mono(meth)acrylate and the like can be mentioned. In this specification, the notation (meth)acrylate means acrylate or methacrylate. The polymerizable monomer may be used alone or in combination of two or more.

[0023] (a1) The polymerizable monomer may further contain a nitrile monomer in addition to the monomer components exemplified above. When a nitrile monomer is further contained, the solvent resistance of the thermally expandable microcapsules is improved. When the polymerizable component contains a nitrile monomer, (A) the weight ratio of the nitrile monomer in the polymerizable component is preferably 5 to 95% by mass. More preferably, it is 10 to 90% by mass, still more preferably 15 to 85% by mass, particularly preferably 20 to 80% by mass, and most preferably 25 to 75% by mass.

[0024] (A) The content of the (a1) polymerizable monomer contained in the polymerizable component is preferably 5 to 100% by mass, more preferably 10 to 90% by mass, particularly preferably 15 to 80% by mass, and most desirably 20 to 75% by mass. When the content of the (a1) polymerizable monomer is 5 to 100% by mass, (A) the outer shell of the thermoplastic microcapsules becomes more likely to encapsulate the foaming agent.

[0025] (a2) As the crosslinking agent, for example, aromatic divinyl compounds such as divinylbenzene; Allyl methacrylate, triacryl formal, triallyl isocyanate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polytetramethylene glycol diacrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, PEG#200 di(meth)acrylate, PEG#400 di(meth)acrylate, PEG#600 di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, 2-butyl-2-ethyl-1,3-propanediol diacrylate, tricyclodecane dimethanol di(meth)acrylate and other polyfunctional (meth)acrylate compounds can be mentioned. These crosslinking agents may be used alone or in combination of two or more.

[0026] (a) The content of the (a2) crosslinking agent contained in the polymerizable component is preferably 0 to 5.0 parts by weight, more preferably 0.01 to 3.0 parts by weight, still more preferably 0.02 to 2.0 parts by weight, and particularly preferably 0.05 to 1.5 parts by weight with respect to 100 parts by weight of the (a) polymerizable component. (A) The thermally expandable microcapsules are excellent in expansion performance when the content of the (a2) crosslinking agent is within the above range.

[0027] In the present specification, the foaming agent is a component that vaporizes by heating and is enclosed in the outer shell constituting the (A) thermally expandable microcapsules. The (A) thermally expandable microcapsules have the foaming agent, so that the outer shell (shell) swells by heating and has thermal expandability.

[0028] The foaming agent is, for example, Straight-chain hydrocarbons such as propane, butane, pentane, hexane, heptane, octane, nonane, decane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane; Branched hydrocarbons such as isobutane, isopentane, isohexane, isoheptane, isooctane, isononane, isodecane, isododecane, 3-methylundecane, isotridecane, 4-methyldodecane, isotetradecane, isopentadecane, isohexadecane, 2,2,4,4,6,8,8-heptamethylnonane, isoheptadecane, isooctadecane, isononadecane, 2,6,10,14-tetramethylpentadecane; Hydrocarbons such as cyclododecane, cyclotridecane, hexylcyclohexane, heptylcyclohexane, n-octylcyclohexane, cyclopentadecane, nonylcyclohexane, decylcyclohexane, pentadecylcyclohexane, hexadecylcyclohexane, heptadecylcyclohexane, octadecylcyclohexane; Petroleum ether; Their halides; Fluorine-containing compounds such as hydrofluoroether; Tetraalkylsilane; Examples include compounds that generate gas by thermal decomposition upon heating.

[0029] The foaming agent may be linear, branched, or alicyclic, and is more preferably aliphatic. These foaming agents may be used alone or in combination of two or more.

[0030] The average particle diameter of the (A) thermally expandable microcapsules of the present invention is preferably 0.5 to 200 μm, particularly preferably 1 to 150 μm, more preferably 2 to 75 μm, and most desirably 5 to 50 μm. When the average particle diameter of the (A) thermally expandable microcapsules is 0.5 to 200 μm, the balance between the thermal expandability and expansion stability of the component (A) is excellent. In addition, in this specification, the average particle diameter of the (A) thermally expandable microcapsules can be measured according to the method described in Example

[0077] of JP-A-2023-35309.

[0031] The encapsulation rate of the foaming agent is defined as the percentage of the weight of the foaming agent encapsulated in component (A) with respect to 100 parts by mass of component (A). The encapsulation rate of the foaming agent is preferably 1 to 50% by mass, particularly preferably 2 to 45% by mass, more preferably 5 to 40% by mass, and most desirably 10 to 35% by mass. The encapsulation rate of the foaming agent is calculated by the method described in Examples

[0079] to

[0080] of JP-A-2023-35309.

[0032] (A) The expansion start temperature (Ts) of the thermally expandable microcapsules is preferably 65 to 200°C, more preferably 65 to 150°C, particularly preferably 70 to 150°C, and most desirably 70 to 100°C. When the expansion start temperature (Ts) is 65 to 200°C, (A) the thermally expandable microcapsules can obtain more sufficient heat resistance.

[0033] (A) The maximum expansion temperature (Tmax) of the thermally expandable microcapsules is not particularly limited, but is preferably 100 to 350°C, more preferably 100 to 190°C, particularly preferably 110 to 185°C, and most desirably 110 to 135°C. When the maximum expansion temperature (Tmax) is 100 to 350°C, (A) the thermally expandable microcapsules are excellent in the balance between heat resistance and expansion ratio.

[0034] Incidentally, the expansion start temperature (Ts) and the maximum expansion temperature (Tmax) of the thermally expandable microcapsules are calculated by the method described in Example

[0078] of JP-A-2023-35309. In the present invention, the maximum volume expansion ratio of (A) the thermally expandable microcapsules is preferably 3 to 50 times, more preferably 5 to 20 times, particularly preferably 5 to 15 times, and most desirably 5 to 10 times. When the maximum volume expansion ratio of component (A) is 3 to 50 times, the aqueous coating agent of the embodiment of the present invention can more maintain the adhesion to the seal part while taking in the powder attached to the seal part into the inside of the coating agent.

[0035] In the present invention, (A) the thermally expandable microcapsules are different from so-called hollow particles. Hollow particles do not contain a foaming agent or the foaming agent has already vaporized, so they do not expand thermally.

[0036] (A) Commercially available products can be used as the thermally expandable microcapsules. Examples of commercially available products include Microsphere - F36D, F35D, F48D, F65D, FN100S, F100M, FN100M, FN180, F190D, F230D, F260D, F2800D, F2830D, F2860D, etc. manufactured by Matsumoto Yushi Seiyaku Co., Ltd. Examples of commercially available hollow particles include Microsphere - F30E, F50E, F65E, F65DE, F80DE, etc. manufactured by Matsumoto Yushi Seiyaku Co., Ltd.

[0037] <(B) Thermoplastic resin> In this specification, (B) the thermoplastic resin refers to a resin that becomes soft and moldable by heating and solidifies when cooled, and is obtained by polymerizing (b) a polymerizable unsaturated monomer.

[0038] In the present embodiment, the "polymerizable unsaturated monomer" refers to a radically polymerizable monomer having an ethylenic double bond. The "ethylenic double bond" refers to a double bond between carbon atoms that can undergo a polymerization reaction (radical polymerization). Examples of such functional groups having an ethylenic double bond include a vinyl group (CH2=CH-), a (meth)allyl group (CH2=CH-CH2- and CH2=C(CH3)-CH2-), a (meth)acryloyloxy group (CH2=CH-COO- and CH2=C(CH3)-COO-), a (meth)acryloyloxyalkyl group (CH2=CH-COO-R- and CH2=C(CH3)-COO-R-), and -COO-CH=CH-COO-. (b) The polymerizable unsaturated monomer may be a single monomer or a combination of two or more monomers.

[0039] In one aspect of the present invention, the polymerizable unsaturated monomer (b) that constitutes the thermoplastic resin preferably has a chemical structure derived from a carboxylic acid ester polymer. The "chemical structure derived from a carboxylic acid ester polymer" means a chemical structure including a polymer of a carboxylic acid ester having an ethylenic double bond (regardless of a homopolymer or a copolymer), and any modified product of the polymer. The "carboxylic acid ester polymer" is obtained by polymerizing a polymerizable unsaturated monomer (b) containing a carboxylic acid ester (b1) having an ethylenic double bond.

[0040] In the present specification, examples of the "carboxylic acid ester (b1) having an ethylenic double bond" (also simply referred to as "carboxylic acid ester (b1)") include (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; vinyl carboxylates such as vinyl acetate; allyl carboxylates such as allyl acetate; and the like can be exemplified. In the present specification, the (meth)acrylic acid ester represents both acrylic acid esters and methacrylic acid esters.

[0041] In the present invention, the "carboxylic acid ester (b1) having an ethylenic double bond" is preferably methyl methacrylate, butyl acrylate, or vinyl acetate, and particularly preferably vinyl acetate. In the present embodiment, the carboxylic acid ester polymer may be a copolymer of a carboxylic acid ester (b1) having an ethylenic double bond and a polymerizable unsaturated monomer (b2) other than the carboxylic acid ester having an ethylenic double bond (also referred to as "other monomer (b2)").

[0042] The other monomer (b2) is not particularly limited, and examples thereof include olefins such as ethylene and propylene, diolefins such as butadiene and isoprene, vinyl aromatic compounds such as styrene and α-methylstyrene, vinyl alcohol, acrylonitrile, and the like. In the present invention, (b1) preferably contains a (meth)acrylate, and particularly preferably contains methyl methacrylate, methyl acrylate, and 2-ethylhexyl acrylate. (b2) preferably contains styrene.

[0043] In the present invention, component (B) preferably contains at least one structural unit selected from the structural units derived from a polymer of a (meth)acrylate and the structural units derived from a styrene polymer. In particular, it is preferable to contain both the structural unit derived from a polymer of a (meth)acrylate and the structural unit derived from a styrene polymer. Furthermore, it is desirable to contain a copolymer of a copolymer of methyl methacrylate and 2-ethylhexyl acrylate and a styrene-butadiene copolymer.

[0044] Due to component (B) having the above-described composition, the aqueous coating agent of the present invention has excellent adhesion while maintaining excellent peel strength. In the present specification, the "structural unit derived from a polymer of a (meth)acrylate" has a chemical structure including a homopolymer or copolymer of a (meth)acrylate. The "structural unit derived from a styrene polymer" has a chemical structure derived from a homopolymer or copolymer of styrene.

[0045] In the present invention, the glass transition temperature of the thermoplastic resin (B) is preferably 40°C or lower, particularly preferably -50°C to 35°C, more preferably -40°C to 35°C, and most preferably 0°C to 35°C. When the glass transition temperature of component (B) is within the above range, the aqueous coating agent of the present invention has more excellent heat sealability.

[0046] In this specification, the glass transition temperature of the (B) thermoplastic resin is calculated from the glass transition temperature of the homopolymer obtained when the (b) polymerizable unsaturated monomer that is the raw material of the (B) thermoplastic resin is homopolymerized (hereinafter also referred to as "homopolymer Tg"). This homopolymer Tg is determined in consideration of the mixing ratio (parts by mass) of each (b) polymerizable unsaturated monomer (monomer). Specifically, the Tg of the copolymer can be obtained by calculating using the following formula.

[0047] 1 / Tg = C1 / Tg1 + C2 / Tg2 + ··· + Cn / Tgn [In the calculation formula, Tg is the theoretical Tg of the copolymer, Cn is the mass part ratio of the nth monomer n contained in the monomer mixture, Tgn is the homopolymer Tg of the nth monomer n, and n is the number of monomers constituting the copolymer, which is a positive integer.]

[0048] As the homopolymer Tg, values described in the literature can be used. Such literature includes, for example, "POLYMER HANDBOOK" (4th edition; published by John Wiley & Sons, Inc.). As an example, the homopolymer Tg of the monomers described in POLYMER HANDBOOK is shown below. Methyl methacrylate ("MMA", Tg = 105 °C) n-Butyl acrylate ("n-BA", Tg = -54 °C) 2-Ethylhexyl acrylate ("2EHA", Tg = -70 °C) Styrene ("St", Tg = 100 °C) Acrylic acid ("AA", Tg = 106 °C) Methacrylic acid ("MAA", Tg = 130 °C) n-Butyl methacrylate ("BMA", Tg = 20 °C)

[0049] The aqueous coating agent according to an embodiment of the present invention may further have, as additives, a viscosity modifier, a plasticizer, an antifoaming agent, a preservative, a colorant, etc., in addition to component (A) and component (B). These additives may be blended after the synthesis of (B) the thermoplastic resin, may be blended with the monomer which is the raw material of (B) the thermoplastic resin, or may be added to the aqueous coating agent after mixing component (A) and component (B).

[0050] Examples of the viscosity modifier include nitrogen-containing substances such as urea, urea compounds, dicyandiamide, calcium hydroxide, calcium oxide, sodium carbonate, trisodium phosphate, diammonium hydrogen phosphate, borax, sodium fluoride, water glass, aqueous ammonia, etc. Examples of the plasticizer include glycerin; polyhydric alcohols such as ethylene glycol and propylene glycol; saccharides such as sucrose and sorbitol; organic solvents such as cellosolves, etc.

[0051] Examples of the antifoaming agent include silicone-based antifoaming agents such as dimethylpolysiloxane, polyoxyalkylene-modified silicone, organically modified polysiloxane, fluorosilicone; oil and fat-based antifoaming agents such as castor oil, sesame oil, linseed oil, animal and vegetable oils; fatty acid-based antifoaming agents such as stearic acid, oleic acid, palmitic acid; fatty acid ester-based antifoaming agents such as isoamyl stearate, diglycol laurate, distearyl succinate, distearic acid, sorbitan monolaurate, glycerin fatty acid ester, polyoxyethylene sorbitan, butyl stearate monolaurate, sucrose fatty acid ester, ethyl acetate alkyl ester of sulfonated ricinoleic acid, natural wax; alcohol-based antifoaming agents such as polyoxyalkylene glycol and its derivatives, polyoxyalkylene alcohol hydrates, diamylphenoxyethanol, 3-heptanol, 2-ethylhexanol; ether-based antifoaming agents such as 3-heptyl cellosolve, nonyl cellosolve-3-heptyl carbitol; Phosphate ester defoamers such as tributyl phosphate, sodium octyl phosphate, tris(butoxyethyl) phosphate; Amine defoamers such as diamylamine; Amide defoamers such as polyalkylene amide, acylamide polyamine, dioctadecanoyl piperidine; Metal soap defoamers such as aluminum stearate, calcium stearate, potassium oleate, calcium salt of wool oleic acid; Examples thereof include sulfonate ester defoamers such as sodium lauryl sulfonate and sodium dodecyl sulfonate.

[0052] The aqueous coating agent of the present invention can be applied to the surface of a paper substrate. As a method for applying the aqueous coating agent of the present invention onto a paper substrate, a normal coating method may be used. For example, the coating agent of the present invention is applied onto a paper substrate using a known coating machine such as a table coater, a bar coater, a two-roll size press coater, a gate roll coater, a blade metering coater, a rod metering coater, a blade coater, an air knife coater, a roll coater, a brush coater, a kiss coater, a squeeze coater, a curtain coater, a die coater, a gravure coater, or a dip coater.

[0053] The coating amount of the aqueous coating agent onto the paper substrate is not particularly limited, but is preferably, for example, 5 to 100 g / m 2 in terms of solid content (dry mass), more preferably 5 to 50 g / m 2 and particularly preferably 10 to 20 g / m 2 Here, the solid content of the coating agent refers to the solid content obtained by drying the coating agent at 105°C for 3 hours.

[0054] In other embodiments, the present invention relates to a paper substrate coated with the above aqueous coating agent on its surface. The paper substrate of the embodiment of the present invention has extremely excellent heat sealability and can be used for a package containing powders such as foods (retort) or building materials (for example, powders of foods such as matcha powder, wheat flour, rice flour, etc., powders of building materials such as cement, etc.). In this specification, the "powder" is defined as an aggregate of solid particles (fine solids). The powder preferably contains solid particles having a particle diameter of 5 mm or less. When the powder contains solid particles having a particle diameter of 5 mm or less, the aqueous coating agent of the embodiment of the present invention can more preferably heat-seal the seal portion to which the powder adheres.

[0055] Since the heat sealability of the aqueous coating agent of the embodiment of the present invention is extremely excellent, the seal portion of the package is hardly affected by the adhesion of the package contents. In particular, a package containing a substance that easily scatters such as a powder may stain the seal portion with that substance during heat sealing, and the sealability may decrease. However, by applying the aqueous coating agent of the embodiment of the present invention to the seal portion, it becomes possible to maintain the heat sealability of the packaging bag.

[0056] The paper substrate is not particularly limited, but as the paper substrate, known paper or synthetic paper obtained by papermaking using chemical pulp such as hardwood kraft pulp and softwood kraft pulp, or mechanical pulp such as GP (groundwood pulp), RGP (refiner ground pulp), and TMP (thermomechanical pulp) can be used. Further, as the above paper substrate, fine paper, medium paper, alkaline paper, glassine paper, semi-glassine paper, or paperboard, white paperboard, etc. used for corrugated board, building materials, white ball, chip ball, etc. can also be used. Note that the paper substrate may contain organic and inorganic pigments, as well as papermaking auxiliary chemicals such as paper strength enhancers, sizing agents, and yield improvers.

[0057] In still other embodiments, the present invention relates to a paper product having a paper substrate coated with the above aqueous coating agent. The paper products of the embodiments of the present invention can also be used for paper straws, toilet paper, paper cups, food packaging bags, cement bags, and the like.

Examples

[0058] Hereinafter, the present invention will be specifically and detailedly described with reference to examples and comparative examples. However, these examples are only one aspect of the present invention, and the present invention is not limited by these examples in any way. In addition, in the description of the examples, unless otherwise specified, the parts not considering the solvent are based on parts by mass and mass%.

[0059] The numerical values regarding the blending amounts of components (A) to (B) shown in Table 1 are the parts by number of "solid content (substance not containing moisture) excluding the solvent", and the unit is parts by mass. The total amount of components (A) to (B) is converted to 100 parts by mass, and the parts by mass of each component are shown in Table 1. Details of components (A) to (B) used in the examples and comparative examples are shown below.

[0060] (A) Thermoplastic microcapsules (A1) Thermally expandable microcapsules (Matsumoto Microsphere F48D, manufactured by Matsumoto Yushi-Seiyaku Co., Ltd., expansion start temperature: 90 - 100°C, maximum expansion temperature: 125 - 135°C, average particle diameter: 12 - 19μm) (A2) Thermally expandable microcapsules (Matsumoto Microsphere F36D, manufactured by Matsumoto Yushi-Seiyaku Co., Ltd., thermal expansion start temperature: 70 - 85°C, maximum expansion temperature: 120 - 130°C, average particle diameter: 12 - 19μm) (A’3) Hollow particles (Matsumoto Microsphere F50E, manufactured by Matsumoto Yushi-Seiyaku Co., Ltd., average particle diameter: 40 - 60μm)

[0061] (B) Thermoplastic resin (B1) Acrylic emulsion (AQUENCE EPIX BC9210, manufactured by Henkel Japan Co., Ltd., glass transition temperature (Tg): 34°C) (B2) Styrene-acrylic emulsion (AQUENCE EPIX BC900F, manufactured by Henkel Japan Co., Ltd., glass transition temperature (Tg): -28°C) (B3) Styrene-butadiene emulsion (SB latex A7301, manufactured by Asahi Kasei Chemicals Corporation, glass transition temperature (Tg): -8°C) (B4) Olefin dispersion (AQUECNE EPIX BC9220HS, manufactured by Henkel Japan Co., Ltd., glass transition temperature (Tg): -37°C) (B5) Ethylene-vinyl acetate emulsion (Sumika Flex S400HQ, manufactured by Sumitomo Chemical Tex Co., Ltd., glass transition temperature (Tg): 0°C)

[0062] <Preparation of aqueous coating agent and production of paper substrate> Example 1 <Preparation of aqueous coating agent> Into a 2000 ml separable flask equipped with a stirring blade with a diameter of 150 mm, 1000 g of (B) acrylic emulsion (trade name: AQUECNE EPIX BC9210, manufactured by Henkel Japan Co., Ltd., solid content: 50% by mass) as a thermoplastic resin was placed, and 50 g of (A1) thermally expandable microcapsules (trade name: Matsumoto Microfair F48D, manufactured by Matsumoto Yushi Seiyaku Co., Ltd.) was added under stirring. The contents of the flask were stirred for 30 minutes to obtain the aqueous coating agent of Example 1. <Production of paper substrate> Base weight 104.7 g / m 2 , thickness 126 μm, opacity 94% (trade name: Thunderbird high-quality paper, manufactured by Nakagoshi Pulp Industry Co., Ltd.) of white high-quality paper, the aqueous coating agent of Example 1 was coated with a bar coater so that the coating amount after drying was 20 g / m 2 . The paper substrate coated with the coating agent was put into a dryer and dried at 75 to 90°C to obtain the paper substrate of Example 1.

[0063] Example 2 (B) As the thermoplastic resin, except that (B2) (trade name: AQUECNE EPIX BC900F, manufactured by Henkel Japan Co., Ltd., solid content: 46% by mass) was used, the same conditions as in Example 1 were used for other conditions to obtain the aqueous coating agent and paper substrate of Example 2.

[0064] Examples 3 to 10, Comparative Examples 1 to 6 As the components (A) and (B) used in Example 1, the components shown in Tables 1 and 2 and their ratios were charged into a separable flask, and the respective aqueous coating agents and paper substrates were obtained under the same conditions as in Example 1. As shown in Tables 1 and 2, the heat sealability (adhesion, peel strength, swelling property) of the aqueous coating agents was evaluated with the aqueous coated papers of these Examples and Comparative Examples. The details of the heat sealability evaluation test are as follows.

[0065] <Adhesion of the Sealed Part with Powder Attached> The paper substrates obtained in Examples 1 to 10 and Comparative Examples 1 to 6 were cut into a size of 25 mm × 100 mm, and test pieces A and B for the adhesion test were prepared. Cement powder was sprinkled on the coating agent coated surface of test piece A. 1 m 2 The amount of cement powder sprinkled per surface was 15 to 20 g. The coating agent coated surface (with cement powder attached) of test piece A and the coating agent coated surface of test piece B (without cement powder attached) were overlapped and set in a press machine. The pressing conditions were a temperature of 130°C, a pressure of 0.6 MPa, and a time of 0.6 seconds. After the pressed test piece was cured at room temperature (23°C) for 2 hours, the coating surface was peeled off at a speed of 300 mm / min with a T-type peel tester (Tensilon), and the peeled part was visually observed and evaluated. The evaluation criteria are as follows. In this specification, material failure means that the paper substrate is broken as a result of peeling. ◎: Material failure of the heat seal part is 90% or more 〇: Material failure of the heat seal part is 50% or more and less than 90% △: Material failure of the heat seal part is 30% or more and less than 50% ×: The material breakage of the heat-sealing part is less than 30%, or it is not adhered

[0066] <Peeling strength of the sealed part with powder adhered> The paper substrates obtained in each of the examples and comparative examples were cut into a size of 25 mm × 100 mm, and test specimens A and B for the peeling strength test were prepared. Cement powder was sprinkled on the coating agent application surface of test specimen A. 1 m 2 The amount of cement powder sprinkled per 1 m was 15 to 20 g. The coating agent application surface of test specimen A (with cement powder adhered) and the coating agent application surface of test specimen B (without cement powder adhered) were overlapped and set in a press machine. The pressing conditions were a temperature of 130°C, a pressure of 0.6 MPa, and a time of 0.6 seconds. After the pressed test specimens were cured at room temperature (23°C) for 2 hours, the coating agent application surface was peeled off at a speed of 300 mm / min using a T-peeling tester (Tensilon), and the peeled part was visually observed and evaluated. The evaluation criteria are as follows. ◎: The peeling strength of the heat-sealing part is 2 N / 25 mm or more 〇: The peeling strength of the heat-sealing part is 1 N / 25 mm or more and less than 2 N / 25 mm △: The peeling strength of the heat-sealing part is 0.5 N / 25 mm or more and less than 1 N / 25 mm ×: The peeling strength of the heat-sealing part is less than 0.5 N / 25 mm or it is not adhered

[0067] <Adhesion of the sealed part without powder adhered> The paper substrates obtained in Examples 1 to 10 and Comparative Examples 1 to 6 were cut into a size of 25 mm × 100 mm, and test specimens A and B for the adhesion test were prepared. The coating agent application surface of test specimen A and the coating agent application surface of test specimen B were overlapped and set in a press machine. The pressing conditions were a temperature of 130°C, a pressure of 0.6 MPa, and a time of 0.6 seconds. After the pressed test specimens were cured at room temperature (23°C) for 2 hours, the coating agent application surface was peeled off at a speed of 300 mm / min using a T-peeling tester (Tensilon), and the peeled part was visually observed and evaluated. The evaluation criteria are as follows. ◎: Material breakage of the heat-sealing part is 90% or more 〇: Material breakage of the heat-sealing part is 50% or more and less than 90% △: Material breakage of the heat-sealing part is 30% or more and less than 50% ×: Material breakage of the heat-sealing part is less than 30% or not sealed

[0068] <Expansion rate of the seal part without powder adhesion> The heat-sealing papers obtained in each example and comparative example were cut into a size of 25 mm × 100 mm, and test specimens A and B for the adhesion test were prepared. The coated surface of test specimen A and the coated surface of test specimen B were overlapped and set in a press machine. The pressing conditions were a temperature of 130°C, a pressure of 0.6 MPa, and a time of 0.6 seconds. The base material thicknesses of test specimens A and B before pressing were measured in advance, the base material thicknesses of test specimens A and B after pressing were measured, and the expansion rate after heat-sealing was calculated. The evaluation criteria are as follows. ◎: Expansion rate of the heat-sealing part is 200% or more 〇: Expansion rate of the heat-sealing part is 150% or more and less than 200% △: Expansion rate of the heat-sealing part is 110% or more and less than 150% ×: Expansion rate of the heat-sealing part is less than 110%

[0069]

Table 1

[0070]

Table 2

[0071] As shown in Tables 1 and 2, the aqueous coating agent of the example has a content of component (A) of less than 15 parts by mass with respect to a total of 100 parts by mass of components (A) and (B), and thus is remarkably excellent in heat sealability. It has been demonstrated that the aqueous coating agent of the example can maintain high levels of adhesion and peel strength even when cement powder adheres to the seal portion.

[0072] For the aqueous coating agent of the comparative example, compared with that of the example, since it does not contain component (A) or the content of component (A) is too high, the heat sealability is poor. In particular, with respect to the peel strength of the seal portion to which cement powder adheres, all of Comparative Examples 1 to 6 are marked with an "×".

Industrial Applicability

[0073] The present invention can provide an aqueous coating agent. The aqueous coating agent of the embodiment of the present invention is applied to a paper substrate to produce a package. Examples of the package include food packaging bags, paper cups, and powder packaging bags for cement and the like.

Claims

Claim 1 An aqueous coating agent comprising (A) thermally expandable microcapsules and (B) a thermoplastic resin, wherein the amount of component (A) is less than 15 parts by mass per 100 parts by mass of the total amount of components (A) and (B). Claim 2 The aqueous coating agent according to claim 1, wherein the thermally expandable microcapsules (A) include an outer shell and a blowing agent encapsulated in the outer shell and vaporized by heating. Claim 3 A paper substrate coated with the aqueous coating agent according to claim 1 or 2.

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