JP2911917B2 - Heat sealable coating agent for coating film formation - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heat-sealable coating film-forming coating agent useful for imparting heat-sealing properties to a packaging film.

[Prior Art and Problems to be Solved by the Invention] Conventionally, moisture-proof cellophane or the like has been used as a packaging film for tea bags. However, this moisture-proof cellophane
Due to insufficient gas barrier properties and high cost, they are gradually being replaced by other plastic films. That is, in place of the moisture-proof cellophane, a heat seal layer is formed on one surface of a film such as polyethylene terephthalate,
On the other side, a laminate film in which a sealant such as an aluminum foil is laminated via an extruded laminate layer of polyethylene or the like is used. In order to enhance the gas barrier property and ensure the heat sealing property, the heat sealing layer is usually formed by coating an emulsion type coating solution of a vinylidene chloride-based polymer.

However, when a heat seal layer is formed using an emulsion type coating solution, the gas barrier properties are not yet sufficient. If the laminate layer is formed by melt-extruding polyethylene or the like, probably because of its low heat resistance, the heat seal layer is whitened, the appearance is impaired, and the commercial value is reduced.

On the other hand, when the heat seal layer is formed by using a solvent-type coating liquid of a vinylidene chloride polymer instead of the emulsion, although the whitening of the heat seal layer due to lamination can be prevented, the crystallinity of the vinylidene chloride polymer is large. Or, the heat sealability is not sufficient.

Therefore, an object of the present invention is to prevent a heat seal layer from whitening during lamination by melt extrusion molding, and to provide an excellent gas barrier property and heat seal property, despite containing a vinylidene chloride-based polymer. An object of the present invention is to provide a sealable coating film forming coating agent.

[Constitution of the Invention] The present inventor has found that when a vinylidene chloride-based polymer exhibiting a specific dissolution property with respect to a solvent is combined with a specific ratio of a good solvent and a poor solvent, a heat seal layer is formed during lamination by melt extrusion. The present inventors have found that whitening can be prevented and excellent heat sealability is exhibited, and the present invention has been completed.
That is, the present invention relates to a coating agent comprising a film-forming polymer and a good solvent and a poor solvent for the polymer, wherein the coating-forming polymer is a chlorinated polyolefin, a chlorosulfonated polyolefin, or a sulfonated polyolefin. Excludes polyolefins, polyester resins, copolymers containing vinyl esters and acrylates as monomers, and acrylate polymers, ketones and ethers as good solvents, alcohols, alicyclic hydrocarbons Substantially composed of a vinylidene chloride-based polymer containing aromatic hydrocarbons, halogenated hydrocarbons, esters, ethylene glycol mono- or dimethyl ether, ethylene glycol mono- or diethyl ether as a poor solvent, and a good solvent / poor solvent ratio. , The former / the latter = 70/30 to 90/10 (weight ratio) heat sealable coating The above problem is solved by a cloth material.

In the present invention, the film-forming polymer is a chlorinated polyolefin, a chlorosulfonated polyolefin, a sulfonated polyolefin, a polyester resin, a copolymer containing a vinyl ester and an acrylate as monomers,
And it does not contain an acrylate polymer and is substantially composed of a vinylidene chloride-based polymer. The vinylidene chloride-based polymer may be a homopolymer of polyvinylidene chloride.However, from the viewpoints of heat stability, weather stability, and film flexibility, copolymerization of vinylidene chloride with other polymerizable monomers. Coalescence is preferred. As the polymerizable monomer, for example, vinyl chloride, vinyl acetate, crotonic acid, acrylic acid, methyl acrylate, ethyl acrylate,
Various acrylates such as propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, tert-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, acrylonitrile, methacrylonitrile, methacrylic acid, and the above acrylates And the like. One or two or more of these polymerizable monomers are used. Among the above copolymers, vinylidene chloride-acrylonitrile copolymer, vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-vinyl acetate copolymer, vinylidene chloride-acrylic acid copolymer, vinylidene chloride-methacrylic acid copolymer, Copolymers such as a vinylidene chloride-acrylate copolymer and a vinylidene chloride-methacrylate copolymer are preferred. At least one of these vinylidene chloride polymers is used.

The good solvent for the vinylidene base polymer varies depending on the type of the vinylidene base polymer, and can be appropriately selected depending on the type of the polymer. As a good solvent,
For example, acetone, methyl ethyl ketone, ketones such as cyclohexanone, dioxane, diethyl ether,
Examples thereof include ethers such as tetrahydrofuran and a mixed solvent thereof.

The organic solvent in the coating composition is composed of a good solvent and a poor solvent. The ratio of the good solvent to the poor solvent is about the former / the latter = 70/30 to 90/10 (weight ratio), particularly about 80/20 to 90/10 (weight ratio). When the ratio of the good solvent increases, the crystallinity of the vinylidene chloride-based polymer decreases, and the heat sealing property is excellent. In addition, since a solvent-type coating agent is used instead of an emulsion-type coating agent, it has excellent gas barrier properties and does not whiten even when a laminate layer is formed by melt extrusion lamination.

As a poor solvent for the vinylidene base polymer,
For example, alcohols such as methanol, ethanol and propanol; alicyclic hydrocarbons such as hexane and cyclohexane; aromatic hydrocarbons such as benzene, toluene and xylene; halogenated hydrocarbons such as methylene chloride and ethylene chloride; ethyl acetate; Esters, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, ethylene glycol diethyl ether, and mixed solvents thereof.

The coating agent may contain another polymer as a component other than the vinylidene chloride-based polymer.

The coating agent preferably contains a lubricant in order to impart slipperiness and blocking resistance and enhance workability.

As the lubricant, wax or a fine powdery lubricant is preferable.
Examples of the wax include hydrocarbon waxes such as paraffin wax, polyethylene wax and microcrystalline wax, fatty acid waxes such as stearic acid, monoglyceride stearate, triglyceride stearate, zinc stearate, calcium stearate, oleic acid amide, and stearin Various waxes such as fatty acid amide waxes such as acid amide, erucamide, methylene bisstearic acid amide and ethylene bisstearic acid amide, and ester waxes such as carnauba wax can be exemplified. At least one of the above waxes is used. The content of the wax is usually about 0.1 to 10 parts by weight, preferably about 0.25 to 5 parts by weight, and more preferably about 0.5 to 2.5 parts by weight, based on 100 parts by weight of the vinylidene base polymer. If the amount of the wax is less than 0.1 part by weight, the slipperiness is not sufficient, and if it exceeds 10 parts by weight, the transparency and the like of the coating film are liable to decrease.

As fine powder lubricant, for example, kaolin, talc,
Inorganic lubricants such as diatomaceous earth, titanium oxide, calcium carbonate, magnesium carbonate, barium sulfate, silica, and alumina; organic lubricants such as polyethylene, polypropylene, polystyrene, acrylic resin, silicone resin, and phenolic resin; alumina valves, silica balloons, and foamed glass ,
A micro hollow body such as a micro balloon and Saran microsphere is exemplified. Among these fine powdery lubricants, silica fine powder, alumina fine powder, polyethylene fine powder,
Acrylic fine powder is preferred. The fine powdery lubricant may have an appropriate particle size as long as the transparency and heat sealability of the coating film are not impaired, but it is preferably 5 μm or less. If the particle size exceeds 5 μm, the lubricant tends to be missing, and the workability is reduced. The content of the fine powdery lubricant is usually 0.01 to 5 parts by weight, preferably 0.05 to 2.5 parts by weight, based on 100 parts by weight of the vinylidene chloride-based polymer. If the amount of the fine powdery lubricant is less than 0.01 part by weight, the lubricating property is not sufficient, and if it exceeds 5 parts by weight, the transparency and the like of the coating film are liable to be lowered.

The coating agent of the present invention can be applied to various packaging base films requiring heat sealing properties.

As the base film, for example, polyethylene, ethylene-ethyl acrylate copolymer, ionomer, polypropylene, ethylene-propylene copolymer, poly-4
Olefin resins such as methylpentene-1; polyvinyl chloride; polyvinylidene chloride resins such as polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-acrylonitrile copolymer; polystyrene, styrene-acrylonitrile copolymer Styrene resins such as styrene-acrylonitrile-butadiene copolymer; polyesters such as polyethylene terephthalate and polybutylene terephthalate; nylon 6, nylon 11, nylon
Nylon or polyamide such as 66; Polyacrylonitrile; Polycarbonate; Polyimide; Polyvinyl alcohol; Ethylene-vinyl acetate copolymer or saponified product thereof;
Various films made of a material such as hydrochloric acid rubber can be used.

Among the above-mentioned base films, a film made of an olefin resin, particularly a polypropylene film, and a film made of a polyester, particularly a polyethylene terephthalate film are excellent in transparency, mechanical strength and packaging suitability.

The base film may be unstretched, or may be uniaxially or biaxially stretched. As the stretching method, for example, a conventional stretching method such as roll stretching, rolling stretching, belt stretching, tenter stretching, tube stretching, or a combination thereof can be applied. The stretching ratio can be appropriately set according to the desired film properties, for example, 1.5 to 20 times, and preferably 2 to 20 times.
It is about 15 times. If the stretching ratio is less than 1.5 times, the stretching effect is small, and if it exceeds 20 times, excessive stretching occurs and the productivity decreases.

The stretching treatment is performed at a temperature not higher than the melting point of the polymer constituting the film and not lower than the secondary transition point.
Further, after stretching the film, a heat treatment may be performed under tension to fix the molecular orientation.

The surface of the base film may be surface-treated. Examples of the surface treatment include conventional surface treatments such as corona discharge treatment, high-frequency treatment, flame treatment, chromic acid treatment, and solvent treatment. Of these surface treatments, corona discharge treatment is preferred.

The base film may be a single-layer film or a composite film in which two or more films are laminated. The thickness of the substrate film is not particularly limited, and for example, a substrate film having a thickness of 1 to 250 μm, preferably about 5 to 100 μm can be used.

The coating agent and / or the base film may contain various additives such as an antioxidant, an ultraviolet absorber, a heat stabilizer, a plasticizer, an antistatic agent, a tackifier, a plasticizer, a filler, and a dye / pigment. It may be contained.

The coating agent of the present invention is applied to at least one surface of a base film. The application means is not particularly limited,
Conventional means such as a dip coater, a roll coater, a gravure coater, an air knife coater, and a spray can be used. The thickness of the coating is usually from 0.01 to
It is about 5 μm, preferably about 0.1 to 3 μm. Thickness 0.0
If it is less than 1 μm, it is difficult to impart high heat sealing properties, and if it exceeds 5 μm, it is not economical,
In some cases, the properties of the base film may be reduced.

Since the coating agent of the present invention can easily form a coating film having excellent heat sealability, the film on which the coating film is formed is excellent in bag making properties, and the coating film is also excellent in gas barrier properties. . In addition, since the coating does not whiten during the melt extrusion lamination, the above coating agent is applied to one surface of the base film, and if necessary, polyethylene or the like is melt extruded to the other surface to form a laminate layer. An aluminum foil or the like can be laminated via a layer. Therefore, the coating composition of the present invention is suitable for application to various packaging films, especially food packaging films and fragrance retaining films.

[Effects of the Invention] As described above, according to the coating composition for heat-sealable coating film of the present invention, a vinylidene chloride-based polymer exhibiting a specific solubility characteristic in an organic solvent and a good solvent having a specific ratio And a poor solvent, the heat seal layer is not whitened at the time of melt extrusion in spite of containing the vinylidene chloride polymer, and a coating film having excellent gas barrier properties and heat seal properties can be formed.

EXAMPLES Hereinafter, the present invention will be described in more detail based on examples.

Example 1 100 parts by weight of a vinylidene chloride (90% by weight) -acrylic acid ester (10% by weight) copolymer, 1 part by weight of a wax having a melting point of 78 ° C., 0.1 part by weight of a silica fine powder having an average particle diameter of 3 μm were mixed with tetrahydrofuran / Toluene = 70/30 (weight ratio)
To prepare a coating solution.

This coating solution was applied to one surface of a biaxially stretched polyethylene terephthalate film having a thickness of 12 μm using a roll coater so that the coating amount after drying was 2.0 g / m ² ,
The coating was formed by drying.

Example 2 Instead of the mixed solvent of Example 1, tetrahydrofuran /
Other than using a mixed solvent of toluene = 90/10 (weight ratio),
A coating film was formed in the same manner as in Example 1.

Example 3 Instead of the coating solution of Example 1, 100 parts by weight of a vinylidene chloride (90% by weight) -acrylonitrile (10% by weight) copolymer, 1 part by weight of a wax having a melting point of 78 ° C., and fine silica having an average particle diameter of 3 μm were used. A coating film was formed in the same manner as in Example 1 except that 0.1 part by weight of the powder was mixed with a mixed solvent of methyl ethyl ketone / toluene = 80/20 (weight ratio) and used.

Comparative Example 1 A commercially available moisture-proof cellophane (film thickness: 20 μm) was used.

Comparative Example 2 A wax having a melting point of 78 ° C. was added to 100 parts by weight of the solid content of an emulsion containing a vinylidene chloride (85% by weight) -methacrylic acid (15% by weight) copolymer in place of the coating liquid of Example 1. A coating film was formed in the same manner as in Example 1, except that 0.1 parts by weight of a silica fine powder having an average particle diameter of 3 μm was added and mixed.

Comparative Example 3 Instead of the mixed solvent of Example 1, tetrahydrofuran /
Other than using a mixed solvent of toluene = 60/40 (weight ratio),
A coating film was formed in the same manner as in Example 1.

Then, of the films obtained in each of Examples and Comparative Examples, polyethylene was
The mixture was melt-extruded at a temperature of 0 ° C. to form a polyethylene layer having a thickness of 20 μm, and an aluminum foil having a thickness of 7 μm was laminated on the molten polyethylene layer.

Excellent: No whitening Good: Slightly whitening Impossible: Whitening over the entire surface Further, among the obtained laminated films, the coating surfaces were heat-sealed under the conditions of a temperature of 110 ° C., a pressure of 1 kg / cm ² , and a pressing time of 1 second. And 15mm width corresponding to the heat seal part
The heat seal strength of each sample was measured using a Tensilon tensile tester.

Further, the water vapor transmission rate and the oxygen gas transmission rate of the films obtained in the respective examples and comparative examples were measured under the following conditions.

Water vapor transmission rate: Measured under the conditions of a temperature of 40 ° C. and a relative humidity of 90% RH in accordance with JIS Z 0208. The unit is g / m ^2/24 hours.

Oxygen gas permeability: Gas chromatographic method (Measuring device Lyssy Gas Pe
rmeablity Testing Apparatus L-66)
% Oxygen gas and helium gas as a compensation gas were measured at a temperature of 20 ° C. The unit is cc / m ^2/24 hours. The results are shown in the table.

As is clear from the table, the films of Comparative Example 1 and Comparative Example 2 not only whiten
Gas barrier properties were not sufficient. Further, the film of Comparative Example 3 did not have sufficient heat sealability. In contrast, the films of Examples 1 to 3 did not whiten during lamination, and were excellent in heat seal strength and gas barrier properties.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C08J 7/04 C08L 27/08 C09D 127/08

Claims (1)

(57) [Claims] 1. A coating composition comprising a film-forming polymer and a good solvent and a poor solvent for the polymer, wherein the film-forming polymer is chlorinated polyolefin, chlorosulfonated polyolefin, sulfonated Excludes polyolefins, polyester resins, copolymers containing vinyl esters and acrylates as monomers, and acrylate polymers, ketones and ethers as good solvents, alcohols, alicyclic hydrocarbons Substantially composed of a vinylidene chloride-based polymer containing aromatic hydrocarbons, halogenated hydrocarbons, esters, ethylene glycol mono- or dimethyl ether, ethylene glycol mono- or diethyl ether as a poor solvent, and a good solvent / poor solvent ratio. The heat characterized by the former / latter = 70/30 to 90/10 (weight ratio) Sealing coating agent.