JP2021038381A - Water dispersion composition for heat sealant, and heat seal material - Google Patents

Abstract

To provide a water dispersion composition for heat sealants that has excellent heat sealability and heat seal layer blocking resistance without using a lamination process.SOLUTION: A water dispersion composition for heat sealants contains an aliphatic conjugated diene copolymer latex with a toluene insoluble matter of 60 mass% or less and a glass transition temperature of 10°C or higher.SELECTED DRAWING: None

Description

The present invention relates to an aqueous dispersion composition for a heat sealant and a heat seal material.

A method of adhering (that is, heat-sealing) paper or film by superimposing them on top of each other and heating and pressurizing them is used for various purposes including packaging materials. As a means for forming heat sealability on paper, film, etc., for example, so-called laminated paper obtained by laminating a polyolefin resin, or a polymer compound such as a copolymer containing vinyl chloride or vinylidene chloride is used as a base material such as paper or film. A method of coating, laminating, or internally adding to the paper to develop heat-sealing properties is widely used because of its ease of manufacture and low manufacturing cost.

However, in recent years, due to the worldwide trend of deplasticization and resource saving, recycled paper has been reused, and in the case of the laminated paper, etc., from the viewpoint of biodegradability and the process of recycling. In the above, the laminated portion remains in the ecosystem or remains without being disintegrated in recycling, and the removal treatment of the residual residue becomes a problem. Therefore, it has been desired to develop a technology that can be recycled such as recovery and recycling and can replace the laminate.

In Patent Document 1, as an invention capable of imparting heat sealability, recyclability such as recovery and regeneration, and water resistance and oil resistance, a paint containing an acrylic dispersion and a styrene-butadiene dispersion in a specific blending ratio is used. Therefore, there is a description that the heat sealability can be improved.

Patent Document 2 discloses that the heat-sealing property can be improved by using a coating liquid containing an acrylic emulsion having a heat-sealing property as a main component.

Patent Document 3 shows that low-temperature heat-sealing property and water resistance can be improved by using an aqueous resin dispersion containing resin particles A and resin particles B in which the glass transition temperature and particle size are defined.

JP-A-2002-13095 Japanese Unexamined Patent Publication No. 2015-155582 Japanese Unexamined Patent Publication No. 2016-216533

However, the means described in the patent gazettes mentioned above are still insufficient to satisfy both the heat-sealing property and the blocking resistance of the heat-sealing layer.

An object of the present invention is to provide an aqueous dispersion composition for a heat sealant, which can improve the heat sealability and the blocking resistance of the heat seal layer without using a laminating process.

The present invention provides an aqueous dispersion composition for a heat sealant, which contains an aliphatic conjugated diene-based copolymer latex having an insoluble content in toluene of 60% by mass or less and a glass transition temperature of 10 ° C. or more.

Further, the present invention provides a heat-sealing material provided with a heat-sealing layer obtained by applying and drying the aqueous dispersion composition for a heat-sealing agent of the present invention on a base material.

According to the present invention, it is possible to provide an aqueous dispersion composition for a heat sealant, which can improve the heat sealability and the blocking resistance of the heat seal layer.

The aqueous dispersion composition for a heat sealant according to the present embodiment contains an aliphatic conjugated diene-based copolymer latex having an insoluble content in toluene of 60% by mass or less and a glass transition temperature of 10 ° C. or more.

The aliphatic conjugated diene-based copolymer latex is a copolymer latex having a structural unit derived from an aliphatic conjugated diene-based monomer and a structural unit derived from other copolymerizable monomers. For example, it can be obtained by emulsion polymerization of an aliphatic conjugated diene-based monomer and other copolymerizable monomers.

Aliphatic conjugated diene-based monomers include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chlor-1,3-butadiene, and substitutions. Examples include linear conjugated pentadienes and monomers such as substituted and side chain conjugated hexadienes. These can be used alone or in combination of two or more. In the present embodiment, 1,3-butadiene is preferably used from the viewpoint of easy industrial production, availability and cost.

As the other copolymerizable monomer, an ethylene-based unsaturated carboxylic acid monomer and an alkenyl aromatic monomer are preferable because the heat-sealing property and the blocking resistance of the heat-sealing layer can be improved.

Examples of the ethylene-based unsaturated carboxylic acid monomer include monocarboxylic acid monomers such as acrylic acid, methacrylic acid and crotonic acid, dicarboxylic acid monomers such as maleic acid, fumaric acid and itaconic acid, and anhydrides thereof. Can be mentioned. These monomers may be used alone or in combination of two or more.

Examples of the alkenyl aromatic monomer include styrene, α-methylstyrene, methyl-α-methylstyrene, vinyltoluene and divinylbenzene. These can be used alone or in combination of two or more. In the present embodiment, it is preferable to use styrene from the viewpoint of easy industrial production, availability and cost.

Examples of copolymerizable monomers other than ethylene-based unsaturated carboxylic acid monomer and alkenyl aromatic monomer include vinyl cyanide-based monomer, unsaturated carboxylic acid alkyl ester monomer, and hydroxyalkyl group. Examples thereof include unsaturated monomers containing unsaturated carboxylic acid and unsaturated carboxylic acid amide monomers. These monomers may be used alone or in combination of two or more.

Examples of the vinyl cyanide-based monomer include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, and the like. These can be used alone or in combination of two or more. In the present embodiment, it is preferable to use acrylonitrile or methacrylonitrile from the viewpoint of easy industrial production, availability and cost.

Examples of the unsaturated carboxylic acid alkyl ester monomer include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, and dimethyl itaconate. Examples thereof include monomethyl fumarate, monoethyl fumarate and 2-ethylhexyl acrylate. These can be used alone or in combination of two or more. In the present embodiment, it is preferable to use methyl methacrylate from the viewpoint of easy industrial production, availability and cost.

Examples of unsaturated monomers containing a hydroxyalkyl group include β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, and 3-chloro-2-hydroxypropyl. Examples thereof include methacrylate, di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis (2-hydroxyethyl) maleate and 2-hydroxyethyl methyl fumarate. These can be used alone or in combination of two or more.

Examples of the unsaturated carboxylic acid amide monomer include acrylamide, methacrylamide, N-methylolacrylamide, N-methylolmethacrylamide and N, N-dimethylacrylamide. These can be used alone or in combination of two or more.

Further, in addition to the above-mentioned monomers, monomers used in ordinary emulsion polymerization such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride and vinylidene chloride can be used.

The content of the structural unit derived from the aliphatic conjugated diene-based monomer is preferably 5% by mass or more, more preferably 10% by mass or more, and 15% by mass or more in the copolymer. It is more preferable to have. Further, it is preferably 32% by mass or less, more preferably 30% by mass or less, and further preferably 28% by mass or less. Within the above range, the film-forming property of the aqueous dispersion composition for a heat sealant and the blocking resistance of the heat seal layer tend to be excellent.

The content of the structural unit derived from the ethylene-based unsaturated carboxylic acid monomer is preferably 5% by mass or less, more preferably 3% by mass or less, and 2.5% by mass in the copolymer. It is more preferably less than or equal to%. Within the above range, the heat-sealing material tends to be excellent in heat-sealing property and disintegration property. Further, from the viewpoint of dispersion stability of the aqueous dispersion composition for a heat sealant, it is preferably 0.1% by mass or more, and more preferably 0.5% by mass or more.

The content of the structural unit derived from the alkenyl aromatic monomer is preferably 55% by mass or more, more preferably 60% by mass or more, and 65% by mass or more in the copolymer. Is even more preferable. Further, it is preferably 95% by mass or less, more preferably 85% by mass or less, and further preferably 75% by mass or less. Within the above range, the blocking resistance of the heat seal layer tends to be excellent.

The content of structural units derived from other copolymerizable monomers other than ethylene-based unsaturated carboxylic acid monomer and alkenyl aromatic monomer is 0% by mass or more and 40% by mass or less in the copolymer. Is preferable.

Next, the emulsion polymerization according to the present embodiment will be described.

In the reaction system of emulsion polymerization according to the present embodiment, in addition to the monomer components constituting the copolymer, an emulsifier (surfactant), a polymerization initiator, and if necessary, a chain transfer agent and a reducing agent. Etc. can be blended.

Examples of the emulsifier include sulfate ester salts of higher alcohols, alkylbenzene sulfonates, alkyldiphenyl ether disulfonates, aliphatic sulfonates, aliphatic carboxylates, dehydroavietates, formalin condensates of naphthalene sulfonic acids, and non-aliphatic sulfonates. Examples thereof include anionic surfactants such as sulfate ester salts of ionic surfactants, alkyl ester type of polyethylene glycol, alkyl phenyl ether type, and nonionic surfactants such as alkyl ether type. These can be used alone or in combination of two or more.

Examples of the chain transfer agent include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, and n-stearyl mercaptan; Xanthogen compounds such as sulfide; thiuram compounds such as tetramethylthiuram disulfide, tetraethylthiuram disulfide and tetramethylthiuram monosulfide; phenolic compounds such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; Allyl compounds such as allyl alcohols; halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, carbon tetrabromide; vinyl ethers such as α-benzyloxystyrene, α-benzyloxyacrylonitrile, α-benzyloxyacrylamide; triphenylethane, penta Chain transfer agents such as phenylethane, achlorine, metaacrolein, thioglycolic acid, thioapple acid, 2-ethylhexylthioglycolate, turpinolene, α-methylstyrene dimer and the like can be mentioned. These can be used alone or in combination of two or more. The blending amount of the chain transfer agent can be appropriately adjusted in consideration of the combination of other additives and the like.

Further, in the reaction system according to the present embodiment, saturated hydrocarbons such as pentane, hexane, heptane, octane, cyclohexane and cycloheptene; penten, hexene, heptene, etc., for the purpose of controlling the molecular weight and crosslinked structure of the copolymer. Unsaturated hydrocarbons such as cyclopentene, cyclohexene, cycloheptene, 4-methylcyclohexene and 1-methylcyclohexene; hydrocarbon compounds such as aromatic hydrocarbons such as benzene, toluene and xylene can be blended. These can be used alone or in combination of two or more. Of these, cyclohexene and toluene are preferably used.

Further, in the reaction system according to the present embodiment, if necessary, an electrolyte, an oxygen supplement, a chelating agent, a dispersant, a defoaming agent, an antiaging agent, a preservative, an antibacterial agent, a flame retardant, an ultraviolet absorber, etc. Additives may be blended. These additives can be used in appropriate amounts in terms of both type and amount used.

In the present embodiment, it is preferable that the reaction system at the start of charging the polymerization initiator contains a part of the monomer components constituting the copolymer, an emulsifier, a reducing agent, and a chain transfer agent.

It is preferable that all of the emulsifier and the polymerization initiator are contained in the reaction system at the start of charging the polymerization initiator.

Further, it is preferable that the unreacted monomer and other low boiling point compounds are removed from the aliphatic conjugated diene-based copolymer latex by a method such as hot vacuum distillation.

The average particle size of the aliphatic conjugated diene-based copolymer latex is preferably 250 nm or less, and more preferably 220 nm or less. If it exceeds 250 nm, the film-forming property of the aqueous dispersion composition for a heat sealant tends to decrease. Further, it is preferably 70 nm or more, and more preferably 80 nm or more. If it is less than 70 nm, the dispersion stability of the aqueous dispersion composition for a heat sealant tends to decrease or the viscosity tends to increase. The average particle size can be adjusted, for example, by changing the amount of water or emulsifier used to prepare the copolymer latex. The average particle size is based on JIS Z8826, and the average particle size by the photon correlation method is measured by the dynamic light scattering method.

The insoluble content of the aliphatic conjugated diene copolymer latex in toluene is 60% by mass or less, preferably 50% by mass or less, and more preferably 40% by mass or less. If it exceeds 60% by mass, the heat sealability is lowered. Further, from the viewpoint of the surface strength of the heat seal layer, it is preferably 2% by mass or more, and more preferably 5% by mass or more. The insoluble content in toluene can be adjusted, for example, by changing the amount of the chain transfer agent. The insoluble matter in toluene is measured by the method described in Examples.

The glass transition temperature (Tg) of the aliphatic conjugated diene-based copolymer latex is 10 ° C. or higher, preferably 20 ° C. or higher, and more preferably 25 ° C. or higher. If the temperature is lower than 10 ° C., the blocking resistance of the heat seal layer is lowered. Further, from the viewpoint of the film-forming property of the aqueous dispersion composition for a heat sealant, the temperature is preferably 80 ° C. or lower, and more preferably 70 ° C. or lower. The glass transition temperature is measured by the method described in Examples.

If necessary, the aqueous dispersion composition for a heat sealant of the present embodiment may contain functional additives such as a dispersant, a preservative, an antiaging agent, a printability improver, and a surfactant. These additives can be used in appropriate amounts in terms of both type and amount used.

The heat-sealing material of the present embodiment is provided with a heat-sealing layer obtained by applying and drying the aqueous dispersion composition for a heat-sealing agent of the present embodiment on a base material.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the following examples. Unless otherwise specified,% and parts are based on mass.

<Measurement of insoluble content of aliphatic conjugated diene copolymer latex in toluene>
A copolymer latex film is prepared in an atmosphere having a temperature of 40 ° C. and a humidity of 85%. After that, about 1 g of the latex film is weighed to make X g. This is placed in 400 ml of toluene and swelled and dissolved for 48 hours. Then, this is filtered through a weighed 300 mesh stainless wire mesh, and then toluene is evaporated and dried, the mesh weight is subtracted from the dried weight, and the dried weight of the sample is weighed to Yg.
Insoluble content in toluene (mass%) = Y / X × 100

<Measurement of glass transition temperature (Tg) of aliphatic conjugated diene copolymer latex>
The copolymer latex is poured on a glass plate and dried at 70 ° C. for 4 hours to prepare a film, which is packed in an aluminum pan and set in a differential scanning calorimeter (DSC6200: manufactured by Seiko Instruments). After cooling the device to a temperature about 50 ° C. lower than the expected Tg in advance, the temperature is raised at a heating rate of 10 ° C./min to draw a DSC curve.

In the differential curve of the DSC measurement chart, the glass transition temperature in the present invention is (a) the temperature at the top of the peak when there is one peak, and (b) the temperature of the area when there are two or more peaks. The temperature of the peak top of the largest one is (c) if it has a peak top but the shape is broad, the temperature of the peak top is (d) a broad (trapezoidal) shape that does not have a peak top. In the case of, the temperature of the central part is (e) when there are two or more peaks and the shape of the part with the largest area corresponds to (c) and (d), respectively ( c) Refers to the temperature obtained based on the criteria of (d).

<Measurement of average particle size of aliphatic conjugated diene copolymer latex>
The average particle size of the copolymer latex is based on JIS Z8826, and the average particle size by the photon correlation method is measured by the dynamic light scattering method. FPAR-1000 (manufactured by Otsuka Electronics Co., Ltd.) was used for the measurement.

<Manufacture of aliphatic conjugated diene copolymer latex>
The materials shown in Table 1 were blended in the blending amounts (unit: parts by mass) shown in the same table, and the reaction was carried out to synthesize copolymer latex A to I. The specific synthesis procedure is shown below.

10% by mass of each monomer shown in Table 1, an emulsifier, a polymerization initiator, a chain transfer agent, and a polymerization water were charged into a pressure-resistant polymerization reactor, and after sufficient stirring, the temperature inside the reactor became 65 ° C. From that point on, the remaining components of each monomer shown in Table 1 were continuously added over 360 minutes. Then, the temperature inside the polymerization reactor was raised to 80 ° C., and the polymerization was terminated when the polymerization conversion rate exceeded 95%. Next, the obtained copolymer latex was adjusted in pH to 9.0 with NaOH to obtain copolymer latex A to I.

Each component in Table 1 below is indicated by the following abbreviations.
BDE: 1,3-butadiene STY: Styrene ACN: Acrylonitrile MMA: Methyl methacrylate HEA: Hydroxyethyl acrylate IA: Itaconic acid FA: Fumaric acid AA: Acrylic acid EML: Dodecylbenzene sulfonate sodium (manufactured by Kao Co., Ltd., Neoperex G) -15) (Anionic emulsifier)
TDM: t-dodecyl mercaptan (chain transfer agent)

<Evaluation method of heat sealability>
Heat sealant manufactured by Tester Sangyo Co., Ltd. is coated on synthetic paper YUPO (YUPO Corporation) with a coating amount of 20 g / m ^{2 of copolymer latex as an aqueous dispersion composition for heat sealant on one side.} After heat-sealing was performed using a tester TP-701A at a heat-sealing width of 10 mm, a sealing temperature of 120 ° C. and a sealing pressure of 1.3 MPa × 10 sec, the adhesive strength was measured by a T-shaped peeling test.

<Evaluation method of blocking resistance>
A copolymer latex is applied to a PET film as an aqueous dispersion composition for a heat sealant with a wire bar # 20, dried at 130 ° C. for 1 minute, cut into strips having a width of 1 cm, and attached side by side on a mount. Black Kent paper was placed on top of it and pressure-bonded through hot rolls at 100 ° C. using a thermal calendar for laboratory testing, and the state of adhesion of fibers after the black Kent paper was peeled off was visually evaluated. Those with less fiber adhesion have excellent blocking resistance. Those with a large amount of fibers attached were evaluated as having inferior blocking resistance as follows.
(Excellent) ◎ ＞ 〇 ＞ △ ＞ × (Inferior)

Claims (3)

An aqueous dispersion composition for a heat sealant containing an aliphatic conjugated diene-based copolymer latex having an insoluble content in toluene of 60% by mass or less and a glass transition temperature of 10 ° C. or more. The aqueous dispersion composition for a heat sealant according to claim 1, wherein the aliphatic conjugated diene-based copolymer latex contains 5% by mass or less of a structural unit derived from an ethylene-based unsaturated carboxylic acid monomer. A heat-sealing material comprising a base material provided with a heat-sealing layer obtained by applying and drying the aqueous dispersion composition for a heat-sealing agent according to claim 1 or 2.