JPH09302264A - Method for forming surface protective layer of food packaging material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a surface protective layer of a food packaging material in order to permit a high-speed treatment in a narrow installation area. SOLUTION: The surface of a food packaging substrate material 6 unwound from an unwinding apparatus 1 is coated with an electron-beam-curable coating material, irradiated with an electron beam from an electron beam radiation apparatus 3 to cure the coating material, and irradiated with ultraviolet rays from an ultraviolet ray radiation apparatus 4 to treat the residual monomer after the electron beam irradiation. Thus, an electron beam capable of performing a high-speed curing can be utilized, enabling a safe surface protective layer of a food packaging material to be formed by a high-speed treatment in a narrow installation area.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for forming a surface protective layer in a food packaging material using an electron beam curable coating material.

[0002]

2. Description of the Related Art A food packaging material is printed with a display of contents, a picture or the like on the surface of a base material, and a transparent protective layer is formed thereon. This protective layer is formed not only to protect the printed matter but also to enhance the glossiness, scratch resistance, abrasion resistance, etc. of the food packaging material. Conventionally, this protective layer is formed on the substrate surface. It has been carried out by a so-called heat-curing method in which a heat-curable coating material is applied to and heat-dried.

[0003]

However, in the heat curing method, it takes a long time to cure the coating film, and in order to carry out mass production, a long heat drying oven is required and expensive equipment costs, There are drawbacks such as the need for a large installation area. As a method for curing a coating film that solves this drawback, it is possible to use an ultraviolet ray curing method and an electron beam curing method, which have recently been rapidly expanded.

[0004] However, the ultraviolet curing method allows inexpensive equipment costs and relatively high-speed processing with a small installation area, but the irradiation energy is small and it is necessary to add a photoreaction initiator to cure the ultraviolet curing method. Since the photoreaction initiator remains in the coating film, and its toxicity and odor may be generated in some cases, it is a serious drawback as a coating film for food packaging materials, and the ultraviolet curing method cannot be used as it is.

Further, the electron beam curing method can be said to be an ideal curing method because it can be processed at a higher speed than a UV curing method in a small installation area and does not require addition of a photoinitiator for curing. However, in the case of electron beam curing, since the curing reaction proceeds in an extremely short time, the monomer may be left behind in the cured product to a slight extent due to variations in electron beam irradiation. In this case, there is a disadvantage that the dissolution test method in the Food Sanitation Law does not meet the item of potassium permanganate consumption.

In order to completely eliminate this residual monomer, it is sufficient to irradiate it with an electron beam excessively, but this excessive irradiation is not only uneconomical, but also an overpolymerized cured coating film is formed in terms of quality. Therefore, it is not preferable because it becomes too hard and many problems occur such as cracking even if it is lightly bent, and it is difficult to properly irradiate the electron beam by the electron beam curing method.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for forming a surface protective layer in a food packaging material that enables high-speed processing in a small installation area.

[0008]

An object of the present invention is to coat a food packaging material with an electron beam curable coating material, cure the coating material by electron beam irradiation, and then treat the residual monomer by ultraviolet irradiation. And a method for forming a surface protective layer in a food packaging material.

According to the above feature of the present invention, unreacted free radicals remain immediately after the electron beam irradiation and the ultraviolet rays are irradiated in this state, so that the electron beam irradiation is performed without adding a photoinitiator. The reaction is promoted by an ultraviolet ray having far less energy than that, and only the residual monomer after electron beam irradiation can be reduced without substantially changing the physical properties of the cured coating film. Therefore, electron beams and ultraviolet rays capable of high-speed curing reaction can be used, and a safe surface protective layer of a food packaging material can be formed by a high-speed treatment in a small installation area.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An example of a method for forming a surface protective layer in a food packaging material according to the present invention will be described in detail below. 1 to 3 are device configuration diagrams applied to the method for forming a surface protective layer according to the present invention, in which 1 is an unwinding device and 2 is
Is a coater, 3 is an electron beam irradiation device, 4 is an ultraviolet irradiation device, 5 is a winding device, and 6 is a food packaging substrate.

FIG. 1 shows a state in which an electron beam irradiation device and an ultraviolet irradiation device are integrated, and a food packaging base material is continuously conveyed therein, and FIG. 2 shows an electron beam irradiation device and an ultraviolet irradiation device. , Which is installed separately, shows that the food packaging base material is exposed to an electron beam and then exposed to ultraviolet rays.
FIG. 3 shows a state in which after being irradiated with an electron beam, it is once wound and then irradiated with ultraviolet rays.

First, in principle, the ultraviolet curing method is
As mentioned earlier, the irradiation energy is low, so a photoinitiator is added, and this photoinitiator receives energy from ultraviolet rays and decomposes to generate radicals, and these radicals serve as the starting points for the polymerization reaction. Is progressing. Therefore, the polymerization reaction is not started without adding the photoreaction initiator. However, immediately after electron beam irradiation, unreacted free radicals remain, so by irradiating ultraviolet rays during the period when these free radicals remain, the free radicals can be the starting point of the photoreaction without adding a photoinitiator. Becomes By this reaction, the residual monomers are polymerized with each other and polymerized, so that the residual monomers can be reduced.

The life of free radicals generated by electron beam irradiation depends on the temperature, and has a property that the higher the temperature is, the shorter the life is. Usually, it is halved at room temperature for one hour.
Most of them disappear over time. Further, since free radicals easily react with oxygen, when the coating film surface is exposed to a large amount of oxygen atmosphere, the free radicals in the surface layer portion decrease, and the reaction with the residual monomer decreases.

On the other hand, in the electron beam irradiation treatment apparatus, the electron beam irradiation is inactive in order to prevent the generation of ozone due to the reaction between the paint and oxygen and the collision between the electron beam and oxygen in the reaction at the time of curing the coating film. It is designed to be carried out in a nitrogen atmosphere of gas, and naturally, a very small amount of oxygen exists in the apparatus.

Therefore, optimally, as shown in FIG. 1, the food packaging base material 6 is applied from the unwinding device 1 with the coater 2 onto the surface thereof with the electron beam curable coating material, and the electron beam irradiating device 3 is used to apply the electron beam. To cure the coating material, and subsequently, an ultraviolet ray irradiating device 4 integrated with the electron beam irradiating device 3 irradiates it with ultraviolet rays to treat the residual monomer by the electron beam irradiation,
The processed food packaging base material 6 is wound up on the winding device 5.

By doing so, ultraviolet irradiation can be carried out promptly after the electron beam irradiation, and there is no opportunity for the free radicals to react with oxygen after the electron beam irradiation until the irradiation of the ultraviolet rays ends, and therefore the residual monomer in the surface layer portion is not present. The remaining monomer can be reduced most effectively without reducing the reaction.

The base material as a food packaging material is polyvinyl chloride, polyethylene, polypropylene, polystyrene,
It is a single layer of polyvinylidene chloride, nylon, polyethylene terephthalate or the like, or a composite sheet or tube thereof.

The electron beam curable coating material is a monomer or oligomer having at least one acryloyl group as a functional group and is generically called an acrylic monomer.

Examples of monofunctional acrylic monomers include 2-ethylhexyl acrylate, 2-ethylhexyl EO adduct acrylate, 2-phenoxyethyl acrylate, and phenoxydiethylene glycol acrylate.

Examples of the bifunctional acrylic monomer include ethylene glycol diacrylate, polyethylene glycol diacrylate and tripropylene glycol diacrylate.

Examples of trifunctional or higher functional acrylic monomers include trimethylolpropane triacrylate, ditrimethylolpropane tetraacrylate, dipentaerythritol hexaacrylate, dipentaerythritol caprolactone adduct hexaacrylate, and other 3
Examples of the functional oligomers include ester-based oligomers, urethane-based oligomers, and epoxy-based oligomers.

In the electron beam irradiation, the acceleration voltage of the electron beam is 100.
~ 3000 KV, dose is 0.1-30 Mrad,
Preferably, the acceleration voltage is 150 to 300 KV and the dose is 1
Within the range of ˜15 Mrad. The irradiation atmosphere is an inert gas atmosphere such as nitrogen, and the residual oxygen concentration is 50
0 ppm or less is preferable.

The irradiation of ultraviolet rays may be any apparatus having a radiation source (generally, a high pressure mercury lamp, a metal halide lamp, etc.) which emits ultraviolet rays having a wavelength of 200 to 450 nm. The irradiation amount of ultraviolet rays is 30 mJ / cm ² or more, preferably 50 J / cm ² or more.

It is desirable that the irradiation is performed as quickly as possible from the irradiation of the electron beam to the irradiation of the ultraviolet ray, and it is desirable that the coating surface is not touched by air during the irradiation. Therefore, the surface shown in FIG. Although the method of forming the protective layer is most suitable, as shown in FIG. 2, ultraviolet irradiation is performed quickly even if the surface is in contact with air immediately after electron beam irradiation, or as shown in FIG. 3, immediately after electron beam irradiation. If the film is quickly wound, the air does not come into contact with the film until it is left to stand until it is irradiated with ultraviolet rays, so that the elimination of free radicals that react with the air can be prevented.

Further, since the radicals are slightly present even after one day, the starting point of the photoreaction occurs when the irradiation amount of ultraviolet rays is increased. In this case, however, it is uneconomical because a large dose of ultraviolet rays is irradiated. Depending on the material of the material, thermal deformation may occur.

[0026]

【Example】

In the apparatus configuration shown in Example 1 and FIG. 1, a corona-treated polyethylene film having a thickness of 50 μm was used as a substrate, and a mixed composition gravure coater having the following composition was added to the substrate.
The coating was performed so that the coating thickness was 5 μm. Acryloylmorphone (manufactured by ACMO Kojin Co., Ltd.) 30
Parts by weight tripropylene glycol diacrylate (Aronix M-220 manufactured by Toagosei Kagaku Kogyo Co., Ltd.) 40 parts by weight dipentaerythritol caprolactone adduct hexaacrylate (Kayarad DPCA-60 Nippon Kagaku Co., Ltd.)
Made) 30 parts by weight

After coating, using an area beam type electron beam irradiation apparatus, in a nitrogen atmosphere, an accelerating voltage of 150 KV and a dose of 10 M.
The coating film was cured under the conditions of rad and immediately irradiated with an ultraviolet irradiation device under the conditions of 10, 30, and 50 mj / cm ² . The results of potassium permanganate consumption by the dissolution test method in the Food Sanitation Law of this coating film are as follows. 10mJ / cm 2.0ppm ² in at 10.8ppm 30mJ / cm ² at 5.2ppm 50mJ / cm ²

Example 2 In the apparatus configuration shown in FIG. 2, a polyethylene film having a thickness of 50 μm and subjected to corona treatment was used as a base material, and a mixed composition having the following composition was applied thereto by a gravure coater. It was applied so as to have a thickness of 5 μm. Acryloylmorphone (manufactured by ACMO Kojin Co., Ltd.) 30
Parts by weight tripropylene glycol diacrylate (Aronix M-220 manufactured by Toagosei Kagaku Kogyo Co., Ltd.) 40 parts by weight dipentaerythritol caprolactone adduct hexaacrylate (Kayarad DPCA-60 Nippon Kagaku Co., Ltd.)
Made) 30 parts by weight

After coating, using an area beam type electron beam irradiation apparatus, in a nitrogen atmosphere, an accelerating voltage of 150 KV and a dose of 10 M.
The coating film was cured under the conditions of rad and immediately irradiated with an ultraviolet irradiation device under the conditions of 10, 30, and 50 mj / cm ² . The results of potassium permanganate consumption by the dissolution test method in the Food Sanitation Law of this coating film are as follows. 10mJ / cm 3.7ppm ² in at 13.5ppm 30mJ / cm ² at 10.6ppm 50mJ / cm ²

Example 3 In the apparatus configuration shown in FIG. 3, a polyethylene film having a thickness of 50 μm and subjected to a corona treatment was used as a substrate, and a coating composition of 5 μm was applied to this using a mixed composition gravure coater having the following composition. Was applied so that Acryloylmorphone (ACMO: manufactured by Kojin Co., Ltd.) 3
0 parts by weight tripropylene glycol diacrylate (Aronix M-220 manufactured by Toagosei Kagaku Kogyo Co., Ltd.) 40 parts by weight dipentaerythritol caprolactone adduct hexaacrylate (Kayarad DPCA-60 Nippon Kagaku Co., Ltd.)
Made) 30 parts by weight

After coating, using an area beam type electron beam irradiation apparatus, in a nitrogen atmosphere, an accelerating voltage of 150 KV and a dose of 10 M.
The coating film was cured under the conditions of rad. After 5 hours, irradiation was performed with an ultraviolet irradiation device under the conditions of 50, 100, and 200 mj / cm ² . The results of potassium permanganate consumption by the dissolution test method in the Food Sanitation Law of this coating film are as follows. 13.4ppm at 50mJ / cm ² 9.5ppm at 100mJ / cm ² 6.3ppm at 200mJ / cm ²

Example 4 In the apparatus configuration shown in FIG. 3, a corona-treated polyethylene film having a thickness of 50 μm was used as a substrate, and a mixed composition gravure coater having the following composition was used to apply a coating thickness of 5 μm. Was applied so that Acryloylmorphone (manufactured by ACMO Kojin Co., Ltd.) 30
Parts by weight tripropylene glycol diacrylate (Aronix M-220 manufactured by Toagosei Kagaku Kogyo Co., Ltd.) 40 parts by weight dipentaerythritol caprolactone adduct hexaacrylate (Kayarad DPCA-60 Nippon Kagaku Co., Ltd.)
Made) 30 parts by weight

After coating, using an area beam type electron beam irradiation apparatus, in a nitrogen atmosphere, an accelerating voltage of 150 KV and a dose of 10 M.
The coating film was cured under the conditions of rad. One day later, irradiation was performed with an ultraviolet irradiation device under the conditions of 200, 500 and 1000 mj / cm ² . The results of potassium permanganate consumption by the dissolution test method in the Food Sanitation Law of this coating film are as follows. 200 mJ / cm ² 29.4 ppm without deformation 500 mJ / cm ² 17.3 ppm with deformation 1000 mJ / cm ² 7.4 ppm with deformation

Comparative Example 1, with an electron beam irradiation apparatus only, a corona-treated polyethylene film having a thickness of 50 μm was used as a substrate, and a mixed composition gravure coater having the following composition was applied to the coating thickness. The thickness was 5 μm. Acryloylmorphone (manufactured by ACMO Kojin Co., Ltd.) 30
Parts by weight tripropylene glycol diacrylate (Aronix M-220 manufactured by Toagosei Kagaku Kogyo Co., Ltd.) 40 parts by weight dipentaerythritol caprolactone adduct hexaacrylate (Kayarad DPCA-60 Nippon Kagaku Co., Ltd.)
Made) 30 parts by weight

After coating, using an area beam type electron beam irradiation apparatus, in a nitrogen atmosphere, an acceleration voltage of 150 KV, a dose of 10,
The coating film was cured under the conditions of 30,50 Mrad. The consumption amount of potassium permanganate and the 180-degree bending test result of the coating film by the dissolution test method in the Food Sanitation Law of this coating film are as follows. 10 Mrad: 38.2 ppm No coating cracks 30 Mrad: 18.9 ppm No coating cracks 50 Mrad: 8.7 ppm Coating cracks

The standard value is 10 ppm or less in the item of overpotassium consumption in the dissolution test method in the Food Sanitation Law. Example 1 is a method in which irradiation is performed immediately after electron beam irradiation without touching the air. A value that passed the Food Sanitation Law was obtained at 30 mj / cm ² . In Example 2, ultraviolet irradiation is performed immediately after electron beam irradiation. However, during that time, because of the condition of being exposed to air, a value that passed the Food Sanitation Law was obtained at 50 mj / cm ² .

In Examples 3 to 4, there is a storage time of 5 hours and 1 day before irradiation with ultraviolet rays after electron beam irradiation, but when the irradiation amount of ultraviolet rays increases, a value that passes the Food Sanitation Law can be obtained, but the irradiation amount is large. There is some problem because the film is deformed.

Since Comparative Example 1 did not irradiate with ultraviolet rays, the value up to 30 Mrad failed the Food Sanitation Law, but when the dose increased up to 50 Mrad, the value passed, but cracking of the coating film caused a problem. is there.

[0039]

As described in detail above, according to the present invention,
Apply electron beam curable paint to food packaging materials, cure the paint by electron beam irradiation, and then quickly irradiate ultraviolet rays within the time when unreacted free radicals remain, so that It is possible to reduce the elution of residual monomer, and it is possible to pass the item of potassium permanganate consumption in the elution test method in the Food Sanitation Law. Therefore, an electron beam capable of high-speed curing reaction can be used, and a safe surface protective layer of a food packaging material can be formed by a high-speed treatment in a small installation area.

[Brief description of drawings]

FIG. 1 is an apparatus configuration diagram of an example applied to a method for forming a surface protective layer according to the present invention.

FIG. 2 is an apparatus configuration diagram of another example applied to the method for forming a surface protective layer according to the present invention.

FIG. 3 is a device configuration diagram of still another example applied to the method for forming a surface protective layer according to the present invention.

[Explanation of symbols]

 1 Unwinding device 2 Coater 3 Electron beam irradiation device 4 Ultraviolet irradiation device 5 Winding device 6 Food packaging base material

Claims (1)

[Claims] 1. Surface protection in a food packaging material, characterized in that an electron beam curable coating material is applied to the food packaging material, the coating material is cured by electron beam irradiation, and then residual monomers are treated by ultraviolet irradiation. Method of forming layer.