JPH08173898A - Formation of coated film with ultraviolet rays irradiation - Google Patents

Abstract

PURPOSE: To produce an overprint cured film excluding a photopolymerization initiator and a photosensitizer unclear in safety to a human body due to oral intake on a surface of the coated film by curing a specified coated film with a chain carrier generated from a prescribed coated film cured by irradiating UV rays. CONSTITUTION: An ultraviolet curing resin ink or paint containing the photopolymerization initiator capable of generating the chain carrier with UV rays irradiation and the photosensitizer at need is printed or applied on the surface of a base material of a food container or a packaging material, and an overprint vanish which does not contain the photopolymerization initiator and the photosensitizer and comprises essentially a radical-polymerizable monomer and a cationic-polymerizable monomer is applied thereon. After that, UV rays are irradiated to cure a coated film of the ultraviolet curing resin ink or paint and to cure the coated film of the overprint vanish with the chain carrier generated from the coated film and a cured film of the overprint vanish which does not contain the photopolymerization initiator and the photosensitizer on the surface of the coated film is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coating a container or packaging material for foods, and in particular, a container for foods whose coated surface comes into direct contact with the mouth when ingesting food, drinking water or the like. Also, it relates to a method for coating a packaging material and a food container or packaging material coated by such a method. Specifically, a method of forming a cured coating film of overprint varnish by UV irradiation in which a photopolymerization initiator or a photosensitizer which is not supposed to come into direct contact with food is not present on the coating surface, and a photopolymerization on the coating surface by the method. An object of the present invention is to provide a container or packaging material for foods in which an overprint cured film without an initiator or the like is formed on the surface of the container.

[0002]

2. Description of the Related Art As a method of coating a container or packaging material for food, characters, patterns, etc. are printed directly on the surface of the base material of the container or packaging material or through an undercoat, and a transparent overcoat ( Overprinting) is performed. It has been recognized that most of the photopolymerization initiators and photosensitizers (hereinafter abbreviated as photopolymerization initiators) contained in the UV-curable resin paint are contained in the paint for the inner surface of containers that come into direct contact with food. In addition, since there are still uncertain points regarding the safety to the human body when orally ingested, it is desirable that there is no such coating on the outer surface of food cans, beverage cans, etc., which may also be in oral contact.

On the other hand, an ultraviolet-curable resin paint which uses a large amount of a photopolymerization initiator or the like has problems in storage suitability and suitability for coating such as viscosity change due to coating for a long time, but the curing system by ultraviolet irradiation is It has many advantages such as good productivity and less problem of solvent discharge. Therefore, although it is advantageous to be able to use this ultraviolet curing system as a method for coating food containers or packaging materials, it has been desired that there is no photoinitiator or the like even when coating varnish for overprinting by the system. .

By the way, looking at the fields of other industries, a pattern is formed on the surface of the substrate with an ink or a paint containing a photopolymerization initiator and the like, and a coating film of a photopolymerizable material containing no photopolymerization initiator or the like is formed thereon. A method of irradiating with ultraviolet light after providing is known. For example, as a method for producing a decorative plywood having a concavo-convex pattern, JP-A-48-60175 discloses that a pattern is formed with an ink or a paint containing a photopolymerization initiator. A method of irradiating with ultraviolet rays after coating a polymerizable liquid resin on this is disclosed. Further, in JP-A-61-290099, a PVC resin composition containing a photoreactive plasticizer which is printed on a substrate with an ink containing a photoinitiator and then cured by the photoinitiator Apply an object and irradiate it with ultraviolet rays to harden the pattern part and make that part a matte surface,
Then, there is described a method for producing a decorative material having a gloss / matte surface in synchronism with the design, in which the uncured resin composition is melted by heating to make a portion other than the design a glossy surface. However, in the former method, the photopolymerization initiator present in the ink containing the photopolymerization initiator migrates and diffuses into the polymerizable resin layer over time, and the polymerizable resin layer in which the photopolymerization initiator has diffused is UV-cured. This is a method of utilizing a means for allowing the migration and diffusion of the photopolymerization initiator to the overcoat layer. In the latter method, the photoreactive plasticizer contained in the overcoat composition is also reacted with the photoinitiator, so that migration and diffusion of the photopolymerization initiator into the overcoat layer cannot be denied. Therefore, even if these methods are applied to food containers, the most important issue to be solved by the present invention, that is, the safety of the human body due to ingestion is unclear in the presence of unclear photopolymerization initiators and the like. It is completely impossible to prevent migration and diffusion to the surface of the coated film. Moreover, a uniform overcoat film cannot be formed by these methods.

[0005]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and an object of the present invention is to provide a photopolymerization initiator or the like whose safety to the human body by oral intake is unclear on the coating surface. Method for forming a uniform cured coating of overprint varnish that does not exist by UV irradiation, as well as for a metal food product in which a photopolymerization initiator or the like is not present on the coating surface by such a curing system To provide a container or packaging.

[0006]

Means for Solving the Problems As a result of intensive studies by the present inventors, a chain carrier (which is a radical or a cation, here, is a chain carrier) generated by irradiation of ultraviolet rays is used to emit light onto the surface of a coating film. It was found that a film without a polymerization initiator can be formed,
The present invention has been completed.

That is, the present invention comprises a photopolymerization initiator capable of generating a chain of carriers by UV irradiation and a photosensitizer, if necessary, on the surface of the substrate of a food container or packaging material (A). UV curable resin ink or paint containing (B)
Is printed or applied, and a varnish (C) for overprint which is mainly composed of a radically polymerizable monomer and / or a cationically polymerizable monomer but does not contain a photopolymerization initiator and a photosensitizer is applied thereon, and then UV rays are applied. And UV-curable resin ink or paint (B)
The coating of the overprint varnish (C) is cured by the chain transfer generated from the coating and the curing of the overprint varnish in which the photopolymerization initiator and the photosensitizer are not present on the coating surface. The present invention relates to a method for forming a coating film by irradiating ultraviolet rays, which comprises forming a coating film.

The method of the present invention completely controls the migration and diffusion of a photopolymerization initiator or the like whose safety to the human body is uncertain to the human body due to oral ingestion, and the photopolymerization initiator or the like is used for the food container or the like. This is a method for forming a film by an ultraviolet curing system that does not migrate and diffuse to the uppermost surface of the substrate, which was achieved for the first time by the knowledge of the present inventors.

Examples of the food container or packaging material (A) used in the method of the present invention include paper, plastic and metal. In particular, a container or a packaging material that comes into direct contact with food, drinking water, or the like when ingested is preferable, and typical examples thereof include food cans and beverage cans.

The photopolymerization initiator contained in the ultraviolet curable resin ink or coating material (B) of the present invention (hereinafter collectively referred to as "ultraviolet curable resin ink (B)") is chained by irradiation with ultraviolet rays. A photopolymerization initiator capable of generating a carrier (radical or cation), such as benzoin ether, α-acyloxime ester, benzyl ketal, acetophenone derivative, acylphosphine oxide, α-dicarbonyl, aromatic ketone, Examples thereof include thioxanthone, sulfonium salt, iodonium salt, benzoin tosylate and the like. The photosensitizer can be appropriately used from known ones depending on the kind of the photopolymerization initiator, if necessary. Naturally, these photopolymerization initiators and the like are not listed on the positive list of the Food Sanitation Law, US FDA and the like. The amount of photopolymerization initiator, etc. used in the ink or paint is sufficient to supply the chain to the varnish for overprinting, and also the migration of these initiators on the surface of the varnish for overprinting may cause migration. The range is 1 to 20% (by weight conversion) in total, and it is desirable.

As the resin type in the vehicle component of the ultraviolet curable resin ink (B), any known type can be used, for example, epoxy acrylate resin, urethane acrylate resin, polyester acrylate resin,
Examples thereof include alicyclic epoxy resins, vinyl ether compounds, caprolactane modified products and the like.

The prepolymer and the monomer used in the overprint varnish (C) are used depending on the type of chain carrier generated from the ultraviolet curable resin ink (B). Any conventionally known radical polymerization type or cationic polymerization type prepolymer or monomer may be used alone or in combination, and there is no particular limitation. Specific resin types of such varnish include rosin-modified phenolic resin, rosin-modified alkyd resin, fatty acid-modified polyester resin, silicon-modified alkyd acid resin, urethane-modified polyester resin, oil-free polyester resin, petroleum resin, epoxy resin, Epoxy ester resin,
Ketone resin, rosin-modified maleic acid resin, amino resin,
Examples thereof include benzoguanamine resin, acrylic resin and diallyl phthalate resin. If necessary, a solvent can be used in combination in this varnish. Further, if necessary, an auxiliary agent such as wax and silicone, a heat curing catalyst and the like can be used.

The method for forming a coating film of the present invention comprises the steps of applying light to a substrate surface of a pre-painted or unpainted food container or packaging material (paper, plastic, metal, etc.) (A) by ordinary offset, gravure or letterpress printing. A UV-curable resin ink (B) containing a polymerization initiator and a photosensitizer (hereinafter abbreviated as “photopolymerization initiator”) is printed, and then a varnish for overprint containing no photopolymerization initiator or the like. Applying (C) and then irradiating it with ultraviolet rays to cure the coating film of the ultraviolet curable resin ink (B) in the middle and at the same time, to use chain transfer carriers (radicals and cations) generated during curing of the ink It is a method of curing the coating film of the overprint varnish (C) on the upper surface by the chain reaction. After printing the UV-curable resin ink (B), it is irradiated with UV light until the photopolymerization initiator is not completely consumed, and then overprint varnish (C) is applied.
The coating film of the ultraviolet curable resin ink (B) in the middle is cured by irradiating with ultraviolet rays again, and the coating film of the overprint varnish (C) on the surface is formed by the chain reaction based on the chain carrier generated at that time. A method of curing can also be used.

When there is a portion where it is not necessary to print the ultraviolet curable resin ink (B) containing a photopolymerization initiator or the like depending on the design, a transparent ink (Victoria ink) is used for such a portion. You should print it. In addition, use inks other than UV-curable resin ink, such as when clear Victoria ink is printed on parts other than UV-curable resin ink (unhardened), or when it is necessary to cure ink such as overprinting or halftone printing. When a pattern or the like is printed, a varnish (B ') containing a photopolymerization initiator or the like is applied to the part or the entire surface, and an overprint varnish (C) containing no photopolymerization initiator or the like is further applied. ,afterwards,
By irradiating with ultraviolet rays, the coating film of the ultraviolet curable resin varnish (B and B ') in the middle is cured and the coating film of the overprinting varnish (C) on the surface is cured by the chain reaction based on the chain carriers generated there. You can also use the method.

When the cured film of the overprint varnish formed by the above-described method of the present invention is not completely cured, it is possible to take a means of heating and curing it after the irradiation of ultraviolet rays. For example, in the production of a beverage can in which the inside and the outside of the can are coated, even if the coating of the overprint varnish (C), which is the surface of the outer can, is not completely cured, the final curing is performed by heat curing during the coating of the inner can. A hardened coating may be applied.

UV curable resin ink (B) or (B ')
The coating thickness is arbitrary regardless of the types and concentrations of the photopolymerization initiator and the photosensitizer, but is preferably 0.05 to 10.00 μm, more preferably 0.50 to 5.00 μm.
The film thickness of the overprint varnish (C) of the present invention is preferably 1.0 to 20.0 μm. If it is less than 1.0 μm, the photopolymerization initiator or the like is likely to migrate to the surface of the varnish (C) for overprinting, and if it exceeds 20 μm, even if it is irradiated with ultraviolet rays, sufficient chain carriers are supplied from the substrate. As a result, a sufficient film cannot be formed.

The colorant in the ultraviolet curable resin ink (B) containing the photopolymerization initiator and the like used in the method of the present invention, the varnish (B ') and the overprint varnish (C) may be organic or inorganic. Any pigment can be used without any particular limitation.

The UV irradiation lamp used for UV irradiation includes a metal halide lamp, a high pressure mercury lamp,
Any lamp that emits ultraviolet rays, such as an electrodeless lamp, can be used. The irradiation atmosphere can be any atmosphere such as air, inert gas, and dry air.

According to the method of the present invention, the varnish for overprinting is smoothly cured by the conventional ultraviolet irradiation system without using a special ultraviolet irradiation system, in which the photopolymerization initiator and the like are not easily present on the coating surface. It is possible to provide a food container or the like on which a film is formed. Further, since it is possible to form an overcoat (overprint) film by irradiation with ultraviolet rays, in the production of a drinking can in which the inner can is subsequently coated, the system can be simplified and the working efficiency becomes extremely good.

[0020]

EXAMPLES The present invention will be described in detail below with reference to examples in order to facilitate understanding of the present invention. The parts in the examples are based on weight.

(1) Preparation of UV-curable ink Ink 1 Shimla Fast Yellow 4181 (Dainippon Ink Chemicals pigment) 20 parts, UE-8200 (Dainippon Ink Chemicals epoxy acrylate) 50 parts, M-5700 (Toa Gosei) Chemically manufactured oligoester acrylate) 30 parts,
3 parts of Kayacure DETX-S (Nippon Kayaku's alkyl thioxanthone) was kneaded by stirring with a normal three-roll mill to obtain a yellow ink.

Ink 2 Shimla Red 3013 (Pigment manufactured by Dainippon Ink and Chemicals)
20 parts, UE-8200 (Dainippon Ink and Chemicals, epoxy acrylate) 50 parts, M-5700 (Toagosei Kagaku, oligoester acrylate) 30 parts, Kayakyu DETX-S (Nippon Kayaku alkylthioxanthone) 3 parts are usual. The meat was kneaded with a three-roll mill to obtain crimson ink.

Ink 3 Fastgen Blue TGR-L (manufactured by Dainippon Ink and Chemicals)
Pigment) 20 parts, UE-8200 (manufactured by Dainippon Ink and Chemicals)
50 parts of epoxy acrylate, 30 parts of M-5700 (oligoester acrylate manufactured by Toagosei Chemical Industry Co., Ltd.), and 3 parts of Kayacure DETX-S (alkylthioxanthone manufactured by Nippon Kayaku) are kneaded with an ordinary three-roll mill, and indigo ink. Got

Ink 4 10 parts Aerosil 200 (pigment manufactured by Nippon Aerosil),
UE-8200 (Dainippon Ink and Chemicals epoxy acrylate) 60 parts, M-5700 (Toa Gosei Chemical oligoester acrylate) 30 parts, Kayakyu DETX
3 parts of -S (alkyl thioxanthone manufactured by Nippon Kayaku Co., Ltd.) was kneaded with a normal three-roll mill to obtain a transparent Victoria ink.

(2) Overprint varnish (C)
Preparation Example of varnish UE-8200 (Epoxy acrylate manufactured by Dainippon Ink and Chemicals) 40 parts, M-5700 (oligoester acrylate manufactured by Toagosei Chemical Co., Ltd.) 60 parts by stirring and mixing, the safety to human body by oral intake An ultraviolet curable varnish for overprinting was obtained which did not use any unclear photopolymerization initiator or photosensitizer.

Varnish UE-8200 (manufactured by Dainippon Ink & Chemicals, Inc., epoxy acrylate) 40 parts, M-5700 (oligo ester acrylate manufactured by Toa Gosei Kagaku), 60 parts, Kayacure DET
3 parts of XS (Nippon Kayaku's alkyl thioxanthone) was mixed with stirring to obtain a UV-curable overprint varnish.

<Curing test> Ink 1 to aluminum plate (A)
The ultraviolet curable ink (B) of No. 4 was printed so that the film thickness was 2 μm, or the varnish of Comparative Example was used as a paint,
This is coated to a thickness of 2 μm, and the overprint varnish (C) is coated to a film thickness of 4 μm when the ink or paint is in a wet state.
-1 (Using 160W / cm metal halide lamp made by Nippon Battery, irradiation distance 15cm, conveyor speed 2m /
UV light is irradiated at (min). The cured state of the coating after irradiation is evaluated by touching with a finger.

(Evaluation Method) When the varnish for overprinting was hardened into a film by touch with a finger, it was evaluated as ◯, and when the varnish for liquid was not formed into a film was evaluated as x.

[0029]

[Table 1]

<Surface Analysis> The presence of the photopolymerization initiator on the surface depends on the presence or absence of the sulfur S caused by the photopolymerization initiator “Kayacure DETX-S” (alkylthioxanthone manufactured by Nippon Kayaku Co., Ltd.). It is evaluated that the photopolymerization initiator is present, and if not detected, the photopolymerization initiator is not present on the surface. The coating film prepared in the curing test was analyzed by XPS under the following conditions.

KRATOS XSAM-800 type
X-ray photoelectron spectrometer Detector: Multi-channel detector Excitation X-ray source: MgKα ray Magnification ratio: Low resolution: Medium Step size: 0.10 seconds Sweep time: 60 seconds Accumulation frequency: 10 times Measurement element measurement range (binding energy eV ) O1s 553.0 to 523.0 C1s 310.0 to 280.0 S2p 184.1 to 154.1

[0032]

[Table 2] 1) N. D indicates not detected.

2) Surface analysis was measured only on the samples that formed cured films.

[0034]

Industrial Applicability According to the method for forming a film of the present invention, it is possible to obtain by UV irradiation an overprint cured film in which a photopolymerization initiator and a photosensitizer whose safety to the human body due to ingestion is unclear are not present on the surface of the film. Is possible.

Claims (5)

[Claims] 1. An ultraviolet curing agent containing a photopolymerization initiator capable of generating a chain-like transmission by UV irradiation on the surface of a base material of a container or packaging material (A) for food and, if necessary, a photosensitizer. Type resin ink or paint (B) is printed or applied, and a photopolymerization initiator and a photosensitizer are not contained thereon, and a radical polymerizable monomer and / or
A varnish (C) for overprinting composed of a cationically polymerizable monomer is applied, followed by irradiation with ultraviolet rays to cure the coating film of the above-mentioned UV-curable resin ink or paint (B), and a chain transfer agent generated from the coating film. A method for forming a coating film by ultraviolet irradiation, which comprises curing the coating film of the varnish (C) for overprinting by the above method to form a cured coating film of the overprint varnish in which a photopolymerization initiator and a photosensitizer are not present . 2. The total amount of the photopolymerization initiator and the photosensitizer contained in the ultraviolet curable resin ink or coating (B) is 1.
The method for forming a coating film according to claim 1, wherein the content is -20% by weight. 3. The coating thickness of the ultraviolet curable resin ink or coating (B) is in the range of 0.05 to 10.00 μm, and the coating thickness of the overprint varnish (C) is 1.0.
The coating film forming method according to claim 1, wherein the coating film thickness is in the range of 2 to 20.0 μm. 4. A container or packaging material for foods, which is formed by the method for forming a film by ultraviolet irradiation according to claim 1 and has an overprint cured film on the surface of which a photopolymerization initiator and a photosensitizer are not present. 5. A food can or a beverage can in which the overprint cured film without a photopolymerization initiator and a photosensitizer is formed on the surface of the film by the method for forming a film by ultraviolet irradiation according to claim 1.