Water-based coating agent

Abstract

An aqueous coating agent comprising (A) a thermally expandable microcapsule; and (B) a thermoplastic resin is disclosed, wherein the aqueous coating agent comprises component (A) in an amount of less than 15 parts by mass based on a total of 100 parts by mass of components (A) and (B).

Description

Technology Field

[0001] The present invention relates to a water-based coating agent coated on a paper substrate and a paper substrate coated with the water-based coating agent. The present invention also relates to a packaging body (e.g., packaging bag, container, box, etc.) obtained by processing a paper substrate. Background Technology

[0002] Considering environmental issues, the reduction of plastic products is being recommended worldwide. These plastic products cannot decompose naturally, and disposing of them is difficult. Furthermore, the incineration of plastics can lead to the generation of dioxins and cause air pollution.

[0003] Furthermore, recently, plastic waste being dumped into the ocean and breaking down to the micro level to form small fragments is being recognized as a problem, as marine fish ingest these fragments, and there is a possibility that humans will consume these fish.

[0004] Against this backdrop, the replacement of plastic substrates with paper substrates has been considered in various fields, and in particular in the food industry, attempts have been made to manufacture packaging materials (e.g., food packaging bags, containers such as paper cups, boxes, etc.) by processing paper substrates instead of plastic substrates. In the construction industry, packaging materials (e.g., packaging bags for powders such as cement, etc.) have been manufactured by processing paper substrates.

[0005] Laminated paper is known to be used as a form of packaging. Generally, laminated paper is obtained by laminating a polyethylene film or the like onto a paper substrate. Recently, due to heightened environmental awareness, there is a demand for the recycling of laminated paper. However, since the recycling of laminated paper requires specialized equipment, a technology involving coating the film with a water-based resin is being used.

[0006] Patent Document 1 teaches that an aqueous ethylene-based resin dispersion comprising an ethylene-acrylic acid copolymer neutralized with ammonia or an amine and other olefinic thermoplastic resins is useful as a heat sealant for paper substrates or aluminum foil substrates (see [Claims],

[0025] ,

[0027] ,

[0028] ,

[0029] ,

[0030] ,

[0035] ,

[0044] , etc.).

[0007] Patent Document 1 discloses that excellent heat sealability is provided by coating the above-described aqueous ethylene-based resin dispersion onto a paper substrate or an aluminum foil substrate, drying the material, and then heat-sealing the coated portion at 80 or 120°C (see

[0027] ,

[0030] ,

[0035] ,

[0044] , etc.).

[0008] Patent Document 2 discloses that an acrylic adhesive comprising a thermally expandable microsphere and a copolymer of butyl acrylate and acrylic acid is manufactured (see

[0039] to

[0040] ), a paper lid attached to a polymer tray containing a small amount of water is bonded (at room temperature) using said adhesive to manufacture a food packaging, and subsequently, said food packaging is placed in a microwave oven and heated at 120°C for 2 minutes, thereby causing the adhesive strength of the adhesive layer to be lost and the lid to peel off (see [Claims],

[0003] ,

[0004] , and

[0040] to

[0041] ).

[0009] However, when an aqueous dispersion or adhesive according to Patent Documents 1 and 2 is used as a coating agent, it is difficult to heat-seal a package in which the contents are attached to the sealing portion. In particular, if the contents within the package are articles such as powder that can easily scatter, such articles may float and adhere to the sealing portion of the package, thereby reducing heat-sealability. Therefore, an aqueous coating agent is required that enables the package to be heat-sealed even at the sealing portion where the contents are attached. Furthermore, Patent Document 2 discloses an adhesive, which cannot be used as a heat-seal agent.

[0010] [Prior Art Literature]

[0011] [Patent Literature]

[0012] [PTL 1] JP 2000-7860 A

[0013] [PTL 2] JP 2000-302178 A The problem to be solved

[0014] The present invention was completed to solve the aforementioned problems. The object of the present invention is to provide an aqueous coating agent having excellent heat sealing properties for a paper substrate, and in particular, an aqueous coating agent having excellent heat sealing properties for a packaging body comprising a sealing portion of a paper substrate to which contents (more specifically, powder) are attached. Furthermore, the object of the present invention is to provide a paper substrate coated with a coating agent. means of solving the problem

[0015] As a result of repeating the aforementioned research, the inventors discovered that by making the aqueous coating agent comprise a thermoplastic resin and specific microcapsules and limiting the amount of the blended microcapsules to a specific range, an aqueous coating agent with excellent heat sealability is obtained, and in particular, excellent heat sealability for a packaging body including a sealing portion of a paper substrate to which contents (more specifically, powder) are attached, and accordingly, the present invention was completed.

[0016] That is, the present specification includes the following embodiments.

[0017] 1. As an aqueous coating agent, it comprises (A) thermally expandable microcapsules; and (B) a thermoplastic resin,

[0018] An aqueous coating agent in which the amount of component (A) is less than 15 parts by mass based on a total of 100 parts by mass of components (A) and (B).

[0019] 2. 1. A water-based coating agent in which the thermoplastic resin has a glass transition temperature of 40°C or lower.

[0020] 3. A water-based coating agent in which a thermally expandable microcapsule (A) and a thermoplastic resin (B) are dispersed in an aqueous medium, in accordance with 1 or 2.

[0021] 4. An aqueous coating agent comprising, in any one of 1 to 3, a thermally expandable microcapsule (A) included in the outer shell and a foaming agent that vaporizes upon heat.

[0022] 5. An aqueous coating agent in any one of 1 to 4, wherein the thermally expandable microcapsule (A) has an expansion start temperature lower than the maximum expansion temperature, has an expansion start temperature of 65 to 200°C, and has a maximum expansion temperature of 100 to 350°C.

[0023] 6. An aqueous coating agent comprising, in any one of 1 to 5, a thermoplastic resin (B) comprising at least one constituent unit selected from a constituent unit derived from a polymer of (meth)acrylate esters and a constituent unit derived from a styrene polymer.

[0024] 7. An aqueous coating agent in any one of 1 to 6, wherein the thermoplastic resin (B) comprises both a copolymer of methyl methacrylate and 2-ethylhexyl acrylate and a styrene-butadiene copolymer.

[0025] 8. A paper substrate coated with an aqueous coating agent according to 1 to 7.

[0026] 9. Packaging containing a paper substrate according to 8.

[0027] 10. In 9, the packaging contains powder. Effects of the invention

[0028] An aqueous coating agent of one embodiment of the present invention comprises (A) a thermally expandable microcapsule and (B) a thermoplastic resin, wherein the amount of component (A) is less than 15 parts by mass based on 100 parts by mass of the total of components (A) and (B). Accordingly, in the aqueous coating agent, the heat sealability for a paper substrate (in particular, the heat sealability for a packaging body including a sealing portion of a paper substrate to which contents are attached) is significantly improved.

[0029] The low content of component (A) allows the sealing portion of the paper substrate of the packaging bag to be uniformly coated with the aqueous coating agent of the present invention, resulting in improved adhesion and peel strength, and also allows the expansion rate to be maintained at a certain level.

[0030] The aqueous coating agent of the embodiment of the present invention expands upon heat. Therefore, even if the contents (powder, more specifically, flour, cement powder, etc.) adhere to the sealing surface, the aqueous coating agent encapsulates the contents and improves adhesion to the sealing portion.

[0031] Even if contents such as powder adhere to the sealing portion of the packaging, the packaging is preferably heat-sealed by coating the sealing portion with an aqueous coating agent of an embodiment of the present invention.

[0032] As described above, since the sealing portion to which the contents of the packaging are attached can preferably be heat-sealed with the aqueous coating agent of the embodiment of the present invention, the contents of the packaging are not limited to liquids and powders and can be used in various packaging fields (e.g., food, construction, etc.).

[0033] A paper substrate of one embodiment of the present invention is coated with the aqueous coating agent of the above-described embodiment, and becomes a packaging body with excellent heat sealability even when contents such as food packaging bags or packaging bags containing powder such as cement can be attached to the sealing portion. Specific details for implementing the invention

[0034] An aqueous coating agent (also simply referred to as "coating agent") of one embodiment of the present invention comprises a thermally expandable microcapsule (A) (also referred to as "component (A)" or "microcapsule (A)") and a thermoplastic resin (B) (also referred to as "component (B)").

[0035] The aqueous coating agent of the embodiment of the present invention comprises component (A) in an amount of less than 15 parts by mass based on a total of 100 parts by mass of components (A) and (B). Since the content of component (A) is less than 15 parts by mass, the aqueous coating agent of the embodiment of the present invention has excellent heat sealing properties for paper substrates and can heat seal the seal even if powder or the like adheres to the sealing part.

[0036] 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 preferably 2 to 9 parts by mass, based on a total of 100 parts by mass of components (A) and (B).

[0037] The content of component (A) in the aqueous coating agent of the embodiment of the present invention is 1 to 13 parts by mass, and thus the aqueous coating agent can maintain a higher level of heat sealability, and the sealing part to which powder or liquid material is attached can be more preferably heat sealed.

[0038] An aqueous coating agent of an embodiment of the present invention refers to a coating agent in which a polymer (e.g., component (B), etc.) can be dispersed and / or dissolved in an aqueous medium, and preferably, is an aqueous emulsion (aqueous dispersion) obtained by dispersing a polymer in an aqueous medium. When the aqueous coating agent of an embodiment of the present invention is an aqueous emulsion, the aqueous coating agent can be used in fields that are strict from a hygiene perspective, such as the food industry.

[0039] Here, "aqueous medium" means ordinary water such as tap water, distilled water, or ion-exchanged water, and may include organic solvents that are soluble or dispersible in water and have low reactivity with raw materials such as monomers of the resin related to the present invention, such as acetone, ethyl acetate, etc., and further may include monomers, oligomers, prepolymers, resins and / or similar substances that are soluble or dispersible in water, and may include emulsifiers, polymerizable emulsifiers, polymerization reaction initiators, chain extenders, various additives and / or similar substances that are commonly used when manufacturing aqueous resins or water-soluble resins as described below.

[0040] The compositional features of the aqueous coating agent of the embodiment of the present invention are described below.

[0041] (A) Thermally Expandable Microcapsules

[0042] Here, the thermoplastic microcapsule (A) comprises a microcapsule structure including an outer shell and a foaming agent contained in the outer shell. By heating the foaming agent contained in the outer shell, the foaming agent vaporizes, the thermoplastic outer shell expands, and the thermoplastic microcapsule (A) can expand.

[0043] The outer shell comprises a thermoplastic resin obtained by polymerizing a polymerizable component (a), and the thermoplastic resin may be the same as or different from the thermoplastic resin (B) described later.

[0044] The polymerizable component (a) includes a polymerizable monomer (a1) as an essential component and may include a crosslinking agent (a2).

[0045] The polymerizable monomer (a1) is a monomer having radical polymerizable carbon-carbon double bonds. The monomer is an addition polymerizable monomer. Additionally, the crosslinking agent refers to a monomer having at least two radical polymerizable carbon-carbon double bonds and is a component capable of introducing a crosslinked structure into a thermoplastic resin.

[0046] Examples of polymerizable monomers (a1) include the following:

[0047] Alkoxypolyoxyalkylene mono(meth)acrylates 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, and stearoxypolyethylene glycol mono(meth)acrylate; phenoxypolyoxyalkylene mono(meth)acrylates such as phenoxypolyethylene glycol mono(meth)acrylate; Polyalkylene glycol mono(meth)acrylates 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, and polypropylene glycol-polybutylene glycol mono(meth)acrylate;

[0048] Mono(2-acryloyloxyethyl) succinate; and

[0049] Polylactone mono(meth)acrylates such as ω-carboxy-polycaprolactone mono(meth)acrylate.

[0050] Here, the term "(meth)acrylate" means acrylate or methacrylate. These polymerizable monomers may be used alone or in combination of two or more of these.

[0051] The polymerizable monomer (a1) may additionally include a nitrile-based monomer in addition to the monomer component described as an example above. When a nitrile-based monomer is included, the solvent resistance of the thermally expandable microcapsule may be improved. When the polymerizable component includes a nitrile-based monomer, the weight ratio of the nitrile-based monomer to the polymerizable component (A) is preferably 5 to 95 mass%, more preferably 10 to 90 mass%, even more preferably 15 to 85 mass%, particularly preferably 20 to 80 mass%, and most preferably 25 to 75 mass%.

[0052] The content of the polymerizable monomer (a1) included in the polymerizable component (A) is preferably 5 to 100 mass%, more preferably 10 to 90 mass%, particularly preferably 15 to 80 mass%, and most preferably 20 to 75 mass%.

[0053] When the content of the polymerizable monomer (a1) is 5 to 100 mass%, the outer shell of the thermoplastic microcapsule (A) more easily contains a foaming agent.

[0054] Examples of crosslinking agents (a2) include the following:

[0055] Aromatic divinyl compounds such as divinylbenzene; and

[0056] Allyl methacrylate, triacrylformal, triaryl 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, Polyfunctional (meth)acrylate compounds such as 2-butyl-2-ethyl-1,3-propanediol diacrylate and tricyclodecane dimethanol di(meth)acrylate. These crosslinking agents may be used alone or in combination of two or more of these.

[0057] The content of the crosslinking agent (a2) included in the polymerizable component (a) is preferably 0 to 5.0 parts by weight, more preferably 0.01 to 3.0 parts by weight, even more preferably 0.02 to 2.0 parts by weight, and particularly preferably 0.05 to 1.5 parts by weight, based on 100 parts by weight of the polymerizable component (a).

[0058] Since the content of the crosslinking agent (a2) is within the range described above, the thermally expandable microcapsule (A) has better expansion performance.

[0059] Here, the foaming agent is a component that vaporizes upon heating and is contained in the outer shell of the thermally expandable microcapsule (A). By including the foaming agent, the outer shell of the thermally expandable microcapsule (A) swells upon heating, and the thermally expandable microcapsule has thermal expandability.

[0060] Examples of foaming agents include the following:

[0061] Straight-chain hydrocarbons such as propane, butane, pentane, hexane, heptane, octane, nonane, decane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, and nanodecane;

[0062] Branched-chain 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, isonanodecane, and 2,6,10,14-tetramethylpentadecane;

[0063] Hydrocarbons having a cyclic structure such as cyclododecane, cyclotridecane, hexylcyclohexane, heptylcyclohexane, n-octylcyclohexane, cyclopentadecane, nonylcyclohexane, decylcyclohexane, pentadecylcyclohexane, hexadecylcyclohexane, heptadecylcyclohexane, and octadecylcyclohexane;

[0064] Petroleum ethers;

[0065] Their halides;

[0066] Fluorine-containing compounds such as hydrofluoroethers;

[0067] Tetraalkylsilane; and

[0068] A compound that undergoes thermal decomposition by heating to generate gas.

[0069] The blowing agent may be any of straight-chain, branched-chain, and alicyclic blowing agents, and more preferably, an aliphatic blowing agent. Such blowing agents may be used alone or in combination of two or more of these.

[0070] The average particle size of the thermally expandable microcapsule (A) 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 preferably 5 to 50 μm. When the average particle size of the thermally expandable microcapsule (A) is 0.5 to 200 μm, the balance of thermal expandability and expansion stability of component (A) is better.

[0071] Here, the average particle size of the thermally expandable microcapsule (A) can be measured according to the method described in

[0077] of Example

[0077] of JP 2023-35309 A.

[0072] The content of the blowing agent is defined as the percentage of the weight of the blowing agent contained in component (A) relative to 100 parts by mass of component (A). The content of the blowing agent is preferably 1 to 50 mass%, particularly preferably 2 to 45 mass%, more preferably 5 to 40 mass%, and most preferably 10 to 35 mass%. The content of the blowing agent is calculated by the method described in Examples

[0079] to

[0080] of JP 2023-35309 A.

[0073] The expansion start temperature (Ts) of the thermally expandable microcapsule (A) is preferably 65 to 200°C, more preferably 65 to 150°C, particularly preferably 70 to 150°C, and most preferably 70 to 100°C. When the expansion start temperature (Ts) is 65 to 200°C, more sufficient heat resistance of the thermally expandable microcapsule (A) is obtained.

[0074] The maximum expansion temperature (Tmax) of the thermally expandable microcapsule (A) 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 preferably 110 to 135°C. When the maximum expansion temperature (Tmax) is 100 to 350°C, the thermally expandable microcapsule (A) has a better balance of heat resistance and expansion rate.

[0075] In addition, the expansion start temperature (Ts) and maximum expansion temperature (Tmax) of the thermally expandable microcapsule are calculated by the method described in

[0078] of the example of JP 2023-35309 A.

[0076] In the present invention, the maximum volume expansion ratio of the thermally expandable microcapsule (A) is preferably 3 to 50 times, more preferably 5 to 20 times, particularly preferably 5 to 15 times, and most preferably 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 allows a larger amount of powder attached to the seal to be blown into the interior of the coating agent, and also allows the adhesion with the seal to be maintained further.

[0077] In the present invention, the thermally expandable microcapsules (A) differ from so-called hollow particles. These hollow particles do not contain a blowing agent, or the blowing agent has already vaporized from these hollow particles. Therefore, these hollow particles do not thermally expand.

[0078] Commercial products may be used as thermally expandable microcapsules (A). Examples of commercial 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.

[0079] Examples of commercially available hollow particles include Microsphere F30E, F50E, F65E, F65DE, F80DE, etc., manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.

[0080] <(B) Thermoplastic Resin>

[0081] Here, the thermoplastic resin (B) refers to a resin having the characteristics of being softenable and moldable by heating and solidifying by cooling, and is obtained by polymerizing a polymerizable unsaturated monomer (b).

[0082] In the present embodiment, "polymerizable unsaturated monomer" refers to a radical polymerizable monomer having an ethylenically double bond. "Ethyleneenly double bond" refers to a double bond between carbon atoms from which a polymerization reaction (radical polymerization) may occur. Examples of functional groups having such an ethylenically double bond may 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-. The polymerizable unsaturated monomer (b) may be a single monomer or a combination of two or more monomers.

[0083] In one embodiment of the present invention, the polymerizable unsaturated monomer (b) included in the thermoplastic resin (B) preferably has a chemical structure derived from a carboxylic acid ester polymer.

[0084] "Chemical structure derived from a carboxylic acid ester polymer" means a chemical structure comprising a polymer of a carboxylic acid ester having an ethylenically double bond (regardless of whether it is a homopolymer or a copolymer) and any modification of said polymer. The "carboxylic acid ester polymer" is obtained by polymerizing a polymerizable unsaturated monomer (b) comprising a carboxylic acid ester (b1) having an ethylenically double bond.

[0085] Here, examples of "carboxylic acid esters (b1) having an ethylenetic double bond" (also simply called "carboxylic acid esters (b1)") may include the following:

[0086] (Meth)acrylate esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate;

[0087] Vinyl carboxylates such as vinyl acetate; and

[0088] Allyl carboxylates such as allyl acetate.

[0089] Here, (meth)acrylate esters refer to both acrylate esters and methacrylate esters.

[0090] In the present invention, "carboxylic acid ester (b1) having an ethylenically double bond" is preferably methyl methacrylate, butyl acrylate, or vinyl acetate, and particularly preferably vinyl acetate.

[0091] In this embodiment, the carboxylic acid ester polymer may be a copolymer of a carboxylic acid ester (b1) having an ethylenically double bond and a polymerizable unsaturated monomer (b2) other than the carboxylic acid ester having an ethylenically double bond (also referred to as "other monomer (b2)").

[0092] Other monomers (b2) are not particularly limited and examples include olefins such as ethylene and propylene; diolefins such as butadiene and isoprene; vinyl aromatic compounds such as styrene and α-methylstyrene; vinyl alcohols; and acrylonitrile.

[0093] In the present invention, (b1) preferably comprises a (meth)acrylate ester, particularly preferably comprises methyl methacrylate, methyl acrylate or 2-ethylhexyl acrylate, and (b2) preferably comprises styrene.

[0094] In the present invention, component (B) preferably comprises at least one component unit selected from a component unit derived from a polymer of (meth)acrylate ester and a component unit derived from a styrene polymer, particularly preferably comprises both a component unit derived from a polymer of (meth)acrylate ester and a component unit derived from a styrene polymer, and more preferably comprises both a copolymer of methyl methacrylate and 2-ethylhexyl acrylate and a styrene-butadiene copolymer.

[0095] When component (B) has the composition described above, the excellent peel strength of the aqueous coating agent of the present invention is maintained, and the aqueous coating agent also has excellent adhesion.

[0096] Here, "constituent unit derived from a polymer of (meth)acrylate ester" has a chemical structure comprising a homopolymer or copolymer of (meth)acrylate ester. "Constituent unit derived from a styrene polymer" has a chemical structure derived from a homopolymer or copolymer of styrene.

[0097] 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 range described above, the aqueous coating agent of the present invention has better heat sealing properties.

[0098] Here, the glass transition temperature of the thermoplastic resin (B) is calculated based on the glass transition temperature of a homopolymer (hereinafter also referred to as "homomer Tg") obtained by homopolymerizing a polymerizable unsaturated monomer (b), which is a raw material for the thermoplastic resin (B).

[0099] The glass transition temperature of the thermoplastic resin (B) is determined by considering the homopolymer Tg and mixing ratio (parts by mass) of each polymerizable unsaturated monomer (b) (monomer). Specifically, the Tg of the copolymer can be determined by calculation using the following formula.

[0100] 1 / Tg = C1 / Tg1 + C2 / Tg2 + ... + Cn / Tgn

[0101] [In the formula, Tg represents the theoretical Tg of the copolymer, Cn represents the mass part ratio of the nth monomer n included in the mixture of monomers, Tgn represents the homopolymer Tg of the nth monomer n, and n is the number of monomers included in the copolymer and is a positive integer.]

[0102] Values ​​listed in literature may be used as homopolymer Tg. Such literature is, for example, the "POLYMER HANDBOOK" (4th edition, published by John Wiley & Sons, Inc.). As an example, the homopolymer Tg values ​​of monomers listed in the POLYMER HANDBOOK are listed below.

[0103] Methyl methacrylate ("MMA", Tg = 105℃)

[0104] n-butyl acrylate ("n-BA", Tg = -54℃)

[0105] 2-ethylhexyl acrylate ("2EHA", Tg = -70℃)

[0106] Styrene ("St", Tg = 100℃)

[0107] Acrylic acid ("AA", Tg = 106℃)

[0108] Methacryl acid ("MAA", Tg = 130℃)

[0109] n-butyl methacrylate ("BMA", Tg = 20℃)

[0110] The aqueous coating agent according to an embodiment of the present invention may include, in addition to components (A) and (B), a viscosity modifier, a plasticizer, an antifoaming agent, a preservative, a coloring agent, etc. as additives. These additives may be added after the synthesis of the thermoplastic resin (B), may be added to the monomer that is the raw material of the thermoplastic resin (B), or may be added to the aqueous coating agent after mixing components (A) and (B).

[0111] Examples of viscosity modifiers may include nitrogen-containing substances such as urea, urea compounds and dicyandiamide, calcium hydroxide, calcium oxide, sodium carbonate, trisodium phosphate, diammonium hydrogen phosphate, borax, sodium fluoride, water glass and ammonia water.

[0112] Examples of plasticizers may include glycerin; polyhydric alcohols such as ethylene glycol and propylene glycol; sugars such as sucrose and sorbitol; and organic solvents such as cellosolve.

[0113] Examples of antifoaming agents may include the following:

[0114] Silicone-based defoamers such as dimethylpolysiloxane, polyoxyalkylene modified silicone, organic modified polysiloxane, and fluorinated silicone;

[0115] Oil-based antifoaming agents such as castor oil, sesame oil, linseed oil, and animal and vegetable oils;

[0116] Fatty acid-based antifoaming agents such as stearic acid, oleic acid, and palmitic acid;

[0117] Fatty acid ester-based antifoamers such as isoamyl stearic acid, diglycol lauric acid, distearyl succinic acid, distearic acid, sorbitan monolauric acid, glycerin fatty acid ester, polyoxyethylene sorbitan, butyl monolaurate stearate, sucrose fatty acid ester, alkyl ethylacetate ester of sulfonated ricinate, and natural waxes;

[0118] Alcohol-based antifoaming agents such as polyoxyalkylene glycol and its derivatives, polyoxyalkylene alcohol hydrate, diamylphenoxyethanol, 3-heptanol, and 2-ethylhexanol;

[0119] Ether-based antifoaming agents such as 3-heptylcellosolve and nonylcellosolve-3-heptylcarbitol;

[0120] Antifoaming agents such as phosphate esters such as tributyl phosphate, sodium octyl phosphate, and tris(butoxyethyl)phosphate;

[0121] Amine-based antifoaming agents such as diamylamine;

[0122] Amide-based antifoaming agents such as polyalkylene amides, acylated polyamines, and dioctadecanoyl piperidine;

[0123] Metal soap-based defoaming agents such as aluminum stearate, calcium stearate, potassium oleate, and calcium salts of wool olein; and

[0124] Sulfonic acid ester-based antifoaming agents such as sodium lauryl sulfonate and sodium dodecyl sulfonate.

[0125] The surface of a paper substrate may be coated with the aqueous coating agent of the present invention. Conventional coating methods may be used as a method for coating a paper substrate with the aqueous coating agent of the present invention. For example, the paper substrate is coated with the coating agent of the present invention using a known coater such as a table coater, a bar coater, a 2-roll size press coater, a gate roll coater, a blade metalling coater, a rod metalling 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.

[0126] The amount of water-based coating agent coated on the paper substrate is not particularly limited, but, for example, preferably 5 to 100 g / m² as a solid content (dry mass). 2 , more preferably 5 to 50 g / m² 2 , particularly preferably 10 to 20 g / m² 2 This is the case. 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.

[0127] In another embodiment, the present invention relates to a paper substrate whose surface is coated with the above-described aqueous coating agent. The paper substrate of the embodiment of the present invention has significantly excellent heat sealing properties and can be used in packaging materials containing powders such as food (retort), building materials, etc. (e.g., food powders such as tea powder, wheat flour or rice flour, building material powders such as cement, etc.).

[0128] Here, "powder" is considered to be an aggregate of solid particles (fine solids). A powder containing solid particles with a particle size of 5 mm or less is preferred.

[0129] When the powder contains solid particles with a particle size of 5 mm or less, the aqueous coating agent of the embodiment of the present invention enables the sealing part to which the powder is attached to be more preferably heat-sealed.

[0130] Because the heat sealing properties of the aqueous coating agent of the embodiment of the present invention are significantly excellent, the sealing portion of the packaging is less susceptible to the influence of adhesion of the contents of the packaging. In particular, the sealing portion of a packaging containing easily dispersed articles, such as powder, may be contaminated by said articles during heat sealing, and the sealing properties may be degraded. However, the heat sealing properties of the packaging bag can be maintained by coating the sealing portion with the aqueous coating agent of the embodiment of the present invention.

[0131] The paper substrate is not particularly limited, and known paper or synthetic paper obtained by papermaking from chemical pulp such as hardwood kraft pulp or softwood kraft pulp, mechanical pulp such as GP (groundwood pulp), RGP (refiner groundwood pulp), or TMP (thermomechanical pulp) may be used as the paper substrate. In addition, high-quality paper, medium-quality paper, alkaline paper, glassine paper, semi-glassine paper, or cardboard or white cardboard for use in corrugated cardboard, building materials, white liner chipboard, chipboard, etc. may be used as the paper substrate described above. Organic or inorganic pigments, or papermaking aids such as strength enhancers, sizing agents, or yield improvers may be included in the paper substrate.

[0132] In another embodiment, the present invention relates to a paper product having a paper substrate whose surface is coated with the above-described aqueous coating agent. The paper product of the embodiment of the present invention can also be used for paper straws, toilet paper, paper cups, food packaging bags, cement bags, etc.

[0133] [Example]

[0134] The present invention is described in detail below with reference to examples and comparative examples. Each of these examples is merely one embodiment of the present invention, and the present invention is not limited in any way to such examples. Unless otherwise noted, parts of the description of the examples in which the solvent is not considered are based on parts by mass or mass%.

[0135] The numerical values ​​related to the amounts of each of the formulation components (A) to (B) listed in Table 1 represent the portion of the "solids excluding solvent (materials excluding water)," 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 listed in Table 1. The details of components (A) to (B) used in the examples and comparative examples are described below.

[0136] (A) Thermoplastic microcapsules

[0137] (A1) Thermally expandable microcapsules (Matsumoto Microsphere F48D, manufactured by Matsumoto Yushi-Seiyaku Co., Ltd., expansion onset temperature 90 to 100°C, maximum expansion temperature 125 to 135°C, average particle size 12 to 19 μm)

[0138] (A2) Thermally expandable microcapsules (Matsumoto Microsphere F36D, manufactured by Matsumoto Yushi-Seiyaku Co., Ltd., thermal expansion onset temperature 70 to 85°C, maximum expansion temperature 120 to 130°C, average particle size 12 to 19 μm)

[0139] (A'3) Hollow particles (Matsumoto Microsphere F50E, manufactured by Matsumoto Yushi-Seiyaku Co., Ltd., average particle size 40 to 60 μm)

[0140] (B) Thermoplastic resin

[0141] (B1) Acrylic emulsion (AQUENCE EPIX BC9210, manufactured by Henkel Japan Ltd., glass transition temperature (Tg) 34℃)

[0142] (B2) Styrene acrylic emulsion (AQUENCE EPIX BC900F, manufactured by Henkel Japan Ltd., glass transition temperature (Tg) -28℃)

[0143] (B3) Styrene butadiene emulsion (SB Latex A7301, manufactured by Asahi-Kasei Chemicals Corporation, glass transition temperature (Tg) -8℃)

[0144] (B4) Olefin dispersion (AQUECNE EPIX BC9220HS, manufactured by Henkel Japan Ltd., glass transition temperature (Tg) -37℃)

[0145] (B5) Ethylene-vinyl acetate emulsion (SUMIKAFLEX S400HQ, manufactured by Sumika Chemtex Company, Limited, glass transition temperature (Tg) 0℃)

[0146] <Manufacture of Water-based Coating Agents and Paper Substrates>

[0147] Example 1

[0148] <Manufacture of Water-based Coating Agents>

[0149] As a thermoplastic resin (B), 1000 g of (B1) acrylic emulsion (product name: AQUECNE EPIX BC9210, manufactured by Henkel Japan Ltd., solid content 50 mass%) was placed in a 2000 mL volume separable flask equipped with a stirring blade with a diameter of 150 mm, and 50 g of (A1) thermally expandable microcapsule (product name: Matsumoto Microsphere F48D, manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.) was added under stirring.

[0150] The contents of the flask were stirred for 30 minutes to obtain the aqueous coating agent of Example 1.

[0151] Manufacture of paper substrates

[0152] Basis weight 104.7 g / m² 2 On white high-quality paper (product name: Premium Grade (manufactured by Chuetsu Pulp & Paper Co., Ltd.)) having a thickness of 126 μm and an opacity of 94%, the coating amount of the water-based coating agent after drying is 20 g / m² 2The aqueous coating agent of Example 1 was coated by a bar coater so as to be.

[0153] A paper substrate coated with a coating agent was placed in a dryer and dried at 75 to 90°C to obtain the paper substrate of Example 1.

[0154] Example 2

[0155] The aqueous coating agent and paper substrate of Example 2 were obtained using conditions similar to those of Example 1, except that (B2) (product name: AQUECNE EPIX BC900F, manufactured by Henkel Japan Ltd., solid content 46 mass%) was used as the thermoplastic resin (B).

[0156] Examples 3 to 10 and Comparative Examples 1 to 6

[0157] As components (A) and (B) used in Example 1, the components and their proportions listed in Tables 1 and 2 were added to a separable flask, and an aqueous coating agent and a paper substrate were obtained, respectively, under conditions similar to Example 1.

[0158] The heat sealing properties (adhesion, peel strength, and expansion) of the water-based coating agents were evaluated for the water-based coated papers of these examples and comparative examples as described in Tables 1 and 2.

[0159] The details of the evaluation test for heat sealability are as follows.

[0160] <Adhesion of the powder-attached seal>

[0161] The paper substrates obtained in Examples 1 to 10 and Comparative Examples 1 to 6 were cut to a size of 25 mm x 100 mm to prepare test specimens A and B for adhesion testing. Cement powder was sprinkled onto the coating surface of test specimen A. The amount of cement powder sprinkled per square meter of the coating surface of test specimen A was 15 to 20 g.

[0162] The coated surface of specimen A (with cement powder attached) and the coated surface of specimen B (without cement powder attached) were laminated and set in a press machine. The press conditions were a temperature of 130℃, a pressure of 0.6 MPa, and a time of 0.6 seconds.

[0163] The pressed specimens were cured at room temperature (23℃) for 2 hours, after which the coating surface was peeled off at a speed of 300 mm / min using a T-type peel tester (TENSILON), and the peeled portion was visually observed and evaluated. The evaluation criteria are as follows.

[0164] Here, material destruction refers to the destruction of the paper substrate after peeling.

[0165] Excellent: Material failure in over 90% of the heat-sealed area

[0166] Good: Material failure in 50% to less than 90% of the heat seal

[0167] Normal: Material failure in 30% to less than 50% of the heat seal

[0168] Defect: Material failure in less than 30% of the heat seal, or lack of adhesion

[0169] <Peel strength of powder-attached seal>

[0170] The paper substrates obtained in each example and comparative example were cut to a size of 25 mm x 100 mm to prepare test specimens A and B for peel strength testing. Cement powder was sprinkled on the coating surface of test specimen A. The amount of cement powder sprinkled per square meter of the coating surface of test specimen A was 15 to 20 g.

[0171] The coated surface of specimen A (with cement powder attached) and the coated surface of specimen B (without cement powder attached) were laminated and set in a press machine. The press conditions were a temperature of 130℃, a pressure of 0.6 MPa, and a time of 0.6 seconds.

[0172] The pressed specimens were cured at room temperature (23℃) for 2 hours, after which the coating surface was peeled off at a speed of 300 mm / min using a T-type peel tester (TENSILON), and the peeled portion was visually observed and evaluated. The evaluation criteria are as follows.

[0173] Excellent: Peel strength of heat-sealed parts 2 N / 25 mm or greater

[0174] Good: Peel strength of heat seal 1 N / 25 mm or greater and less than 2 N / 25 mm

[0175] Normal: Peel strength of heat seal 0.5 N / 25 mm or more, less than 1 N / 25 mm

[0176] Defective: Peel strength of heat seal less than 0.5 N / 25 mm, or no adhesion

[0177] <Adhesion of the sealing part without powder attachment>

[0178] The paper substrates obtained in Examples 1 to 10 and Comparative Examples 1 to 6 were cut to a size of 25 mm x 100 mm to prepare test specimens A and B for adhesion testing.

[0179] The coated surface of test specimen A and the coated surface of test specimen B were laminated and set in a press machine. The press conditions were a temperature of 130℃, a pressure of 0.6 MPa, and a time of 0.6 seconds.

[0180] The pressed specimens were cured at room temperature (23℃) for 2 hours, after which the coating surface was peeled off at a speed of 300 mm / min using a T-type peel tester (TENSILON), and the peeled portion was visually observed and evaluated. The evaluation criteria are as follows.

[0181] Excellent: Material failure in over 90% of the heat-sealed area

[0182] Good: Material failure in 50% to less than 90% of the heat seal

[0183] Normal: Material failure in 30% to less than 50% of the heat seal

[0184] Defect: Material failure in less than 30% of the heat seal, or no seal

[0185] <Expansion rate of the seal without powder attachment>

[0186] Test specimens A and B for adhesion testing were prepared by cutting the heat sealing paper obtained from each example and comparative example into a size of 25 mm x 100 mm.

[0187] The coated surface of test specimen A and the coated surface of test specimen B were laminated and set in a press machine. The press conditions were a temperature of 130℃, a pressure of 0.6 MPa, and a time of 0.6 seconds.

[0188] The thickness of the substrates of test specimens A and B was measured in advance before pressing, and the thickness of the substrates of test specimens A and B was measured after pressing, and the expansion rate after heat sealing was calculated. The evaluation criteria are as follows.

[0189] Excellent: Expansion rate of heat-sealed part 200% or more

[0190] Good: Expansion rate of heat seal 150% or more and less than 200%

[0191] Normal: Expansion rate of the heat seal 110% or more and less than 150%

[0192] Defective: Expansion rate of heat seal less than 110%

[0193] Examples 1 2 3 4 5 6 7 8 (A)(A') A1 9.0 9.0 3.8 2.0 9.0 9.0 9.0 A2 9.0 A'3 (B) B1 91.0 96.2 98.0 45.5 45.5 B2 91.0 B3 45.5 45.5 B4 91.0 B5 91.0 aggregate 100 100 100 100 100 100 100 100 evaluation Adhesion of the powder-attached seal Good Good Good commonly excellence excellence Good Good Peel strength of the powder-attached seal excellence excellence Good Good excellence excellence Good Good Adhesion of the sealing part without powder attachment Good Good excellence excellence excellence excellence Good Good Expansion rate of the seal without powder attachment excellence excellence Good commonly excellence excellence Good Good

[0194] Examples Comparative example 9 10 1 2 3 4 5 6 (A)(A') A1 13.0 1.0 16.7 28.6 44.4 A2 A'3 9 (B) B1 43.5 49.5 91 83.3 71.4 55.6 B2 B3 43.5 49.5 B4 100 B5 100 aggregate 100 100 100 100 100 100 100 100 evaluation Adhesion of the powder-attached seal excellence commonly error commonly commonly error error error Peel strength of the powder-attached seal Good Good error error error error error error Adhesion of the sealing part without powder attachment excellence excellence commonly Good Good error excellence excellence Expansion rate of the seal without powder attachment excellence commonly error excellence excellence excellence error error

[0195] As described in Tables 1 and 2, each of the aqueous coating agents of the examples has significantly excellent heat sealing properties because the content of component (A) in each of the aqueous coating agents of the examples is less than 15 parts by mass based on 100 parts by mass of the total of components (A) and (B). It has been proven that the aqueous coating agents of the examples allow the adhesion and peel strength to be maintained at a high level even when cement powder adheres to the sealing part.

[0196] In contrast to the aqueous coating agent of the example, each of the aqueous coating agents of the comparative example does not contain component (A) or has an excessively high content of component (A) in each of the aqueous coating agents of the comparative example, so the aqueous coating agent of the comparative example has inferior heat sealing performance. In particular, the peel strength of the sealing part to which cement powder is attached in Comparative Examples 1 to 6 is all poor.

[0197] [Industrial Applicability]

[0198] The present invention may provide a water-based coating agent. A water-based coating agent of one embodiment of the present invention is coated onto a paper substrate to manufacture a packaging body. Examples of packaging bodies include food packaging bags, paper cups, and packaging bags for cement powder, etc.

[0199] [Cross-reference to related applications]

[0200] This application claims priority under Article 4 of the Paris Convention based on Japanese Patent Application No. 2023-210165 filed in Japan on December 13, 2023. The entirety of this priority patent application is incorporated herein by reference.

Claims

Claim 1 A water-based coating agent comprising (A) thermally expandable microcapsules; and (B) a thermoplastic resin, wherein the water-based coating agent comprises component (A) in an amount of less than 15 parts by mass based on a total of 100 parts by mass of components (A) and (B). Claim 2 In claim 1, the thermally expandable microcapsules (A) comprise an outer shell and a foaming agent contained in the outer shell that vaporizes upon heat, an aqueous coating agent. Claim 3 A paper substrate coated with an aqueous coating agent according to claim 1 or 2.

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