JP4539129B2 - Plastic package and its decoration method - Google Patents

Description

  The present invention relates to a plastic package and a decoration method thereof.

Plastics are suitable for mass production because they are easy to mold, and because they have excellent physical properties such as transparency and impact resistance, bottle containers, cups, pouches, etc. Widely used in various packages.
For these plastic packages, for example, for the purpose of protecting the contents that deteriorate due to light, such as beer and cider, and for the purpose of differentiating from similar products by giving aesthetics by decoration. Therefore, coloring is given.

Generally, a plastic package is colored by blending a colorant such as a pigment or a dye into the plastic that is the main material of the package. These colorants are colored by a chemical coloring mechanism.
In chemical color development, when white light including light in a plurality of wavelength ranges is incident on an object, the color is generated by the object absorbing light in a wavelength range indicating a specific color. For example, as shown in FIG. 6A, when the object absorbs light in the wavelength range indicating green, the light incident on the eyes as reflected light and transmitted light both appear red, which is a complementary color of green.
Since the wavelength of light absorbed by a substance is determined by the chemical structure of the substance, it is necessary to use a specific chemical substance in order to give a specific color.

However, in recent years, from the viewpoint of environmental burden, many restrictions have been imposed on the use of chemical substances, and reduction of the use of chemical substances has been demanded.
Resin recycling is promoted from the viewpoint of landfill saturation and resource saving, but colored packaging is difficult to reuse, especially for PET bottles when processed as recycled materials. It is required to be colorless.
Plastic packaging colored with a chemical substance has a problem in recyclability because it is difficult to decolorize the coloring, and has become unacceptable in the market.

As this correspondence, for example, the package is decorated by covering it with a colored label, and at the time of the regeneration process, the package body and the label are separated and processed.
In this method, the recyclability of the package body is satisfied, but the label is still problematic because the recyclability is still poor.

By the way, in the natural world, for example, there are those that do not develop by a chemical coloring mechanism, such as tropical fish scales and morpho butterflies, but develop a color by a physical coloring mechanism using light reflection and interference.
In the physical coloring mechanism, when white light is incident on an object, light in a wavelength region showing a specific color is colored by diffraction, interference, scattering, or the like on the object. For example, as shown in FIG. 6B, when the object strongly reflects light in the wavelength region indicating green, the light incident on the eye as reflected light appears green. Conversely, the transmitted light appears red, which is a complementary color of green.

Unlike the chemical coloring mechanism, coloring by this physical coloring mechanism does not emit light due to the inherent properties of the substance, but develops color by forming a certain structure on the light incident surface.
The color development by this mechanism has a vivid color tone having deep color and gloss, unlike the color development by conventional dyes and pigments.

As a coloring method applying a physical coloring mechanism, for example, a layer containing a scaly thin film having a high refractive index so as to be oriented in the surface direction of the container surface is provided on the outer layer of the thermoplastic resin layer. A package that emits a color has been proposed (see, for example, Patent Document 1).
However, a large amount of mica titanium pigment or the like is used as the scaly thin film, and there is still a problem in recyclability.
Accordingly, there is a need for a decoration method that is highly recyclable and can impart excellent aesthetics.

JP-A-8-80928

  In view of the above problems, an object of the present invention is to provide a plastic package that can be easily recycled even if it is decorated and a method for decorating the same.

  In order to solve this problem, the present inventors can decorate a plastic package by forming a fine periodic array structure having different optical characteristics on the surface of the plastic package, and this method. The packaging body decorated with can find that the periodic arrangement structure can be released by heating in the reprocessing step, so that it can be easily decolored and made colorless and transparent, and the present invention has been completed.

According to the first aspect of the present invention, there is provided a plastic package in which at least a part of the surface of the plastic package is periodically arranged with portions having different optical characteristics from this surface.
According to the second aspect of the present invention, the plastic packaging body that decorates the surface by periodically arranging at least a portion of the plastic packaging body a portion having optical characteristics different from the surface. A method of decorating is provided.

Hereinafter, the present invention will be described in detail.
In the present specification, “decoration” means that the package body is colored in chromatic color, or that light in a specific wavelength region is blocked so that the light does not pass inside the package body. is there.

  The plastic package of the present invention is decorated by applying a physical coloring mechanism. That is, light is interfered and diffracted and colored by periodically arranging portions having different optical characteristics on the plastic package.

Periodic arrangement of parts with different optical characteristics (formation of a periodic arrangement structure) means that optical characteristics such as refractive index, reflectance, transmittance, absorptivity, degree of polarization, etc. are regular and periodic. It means to change the order.
For example, spots and lines having a refractive index different from that of the surroundings may be formed at regular intervals on at least a part of the surface of the plastic package, or spots or lines having different absorption rates from the surroundings may be formed at least part of the plastic package. It may be possible to form them at regular intervals on the surface.
The periodic structure is preferably formed three-dimensionally, that is, in the thickness direction of the surface of the package, but it is sufficiently decorated even if formed in two dimensions (surface of the package). can do.
In the present specification, the “surface of the plastic packaging body” includes not only the surface of the surface forming the packaging body but also any surface formed inside the surface, for example, the surface formed by the inner layer in the multilayer container. Including the interface between layers.

  The arrangement period of the optical characteristics is determined by the color to be developed or the wavelength of light to be shielded. For example, when infrared light is shielded from the ultraviolet region, an appropriate range is 0.1 μm to 5 μm. Moreover, it can color in arbitrary colors by forming on the package the arrangement period which acts on the light of the wavelength range of 0.4 micrometer-0.7 micrometer which is visible region.

In this case, the periodicity does not necessarily have to be perfect, and there may be defects such as loss or variation of the periodicity, discontinuity of the periodic structure, and the periodicity is maintained as a whole. That's fine.
In addition, the arrangement period of the optical characteristics may be different for the entire decorative portion of the plastic package instead of the same pattern. A pattern with a plurality of colors can be formed by changing the pattern of the arrangement period.

  The repetitive period necessary for obtaining a color by the periodic structure is 10 periods or more, preferably 50 periods or more, particularly 100 periods or more.

Next, an example in which a periodic array structure having different optical characteristics is formed in a plastic package will be described as applied to a plastic bottle container.
The plastic bottle container can be formed by a normal bottle container forming means. For example, the preform can be obtained by stretch blow molding.
Specifically, first, the mouth of the bottomed cylindrical preform manufactured by an appropriate means such as an injection molding method, a compression molding method, a multilayer injection molding method, or a multilayer compression molding method is used by an appropriate means. Heat crystallization (spherulite formation) to impart heat resistance.
Next, the preform is heated to a stretching temperature equal to or higher than the glass transition point (Tg), and in a mold heated to a predetermined heat treatment (heat set) temperature, in the longitudinal direction (axial direction) by a stretching rod or the like. Moreover, it extends in the transverse direction (circumferential direction) by blow air.

  The blow mold described above is heated, and heat treatment (heat setting) is performed by bringing the outer wall of the blow molded body into contact with the inner surface of the mold for a predetermined time during biaxial stretching blow. Then, after the heat treatment for a predetermined time, the blow fluid is switched to the internal cooling fluid to cool the inside of the blow molded body.

A bottle container formed by stretch blow molding is stretched in the blowing direction and oriented and crystallized.
The blow molded product taken out from the mold is cooled by cooling or by blowing cold air.

The plastic material forming the plastic bottle container is, for example, polyethylene terephthalate (PET), polyethylene isophthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyarylate, or a copolymer of monomers forming the above resin, cyclohexanedimethanol And thermoplastic polyester, such as a copolymer of the above-mentioned monomers forming the resin, polyethylene (PE), polypropylene (PP), polystyrene, cyclic olefin copolymer, ethylene-vinyl alcohol copolymer, nylon resin, vinyl chloride Resins, adhesive resins, blends with these resins or other resins are preferred, and ethylene terephthalate thermoplastic polyesters such as polyethylene terephthalate are particularly preferred.
The plastic material may be used as a material for forming a single-layer plastic bottle container, or as a material for forming an arbitrary part such as an inner / outer layer, an intermediate layer, an adhesive layer, etc. constituting a multilayer plastic bottle container. You may use it in combination.

Next, a method for decorating the plastic bottle container by forming a periodic array structure having different optical characteristics will be described.
The present invention is not limited to these embodiments.

[First embodiment]
1 to 3 are views for explaining a first embodiment of a method for forming a periodic array structure having different optical characteristics.
In the present embodiment, a periodic array structure is formed on a plastic bottle container using the diffraction phenomenon of laser light.
In this method, a laser light source 11, a lens 12, and a diffraction grating 13 are used.

The laser light source 11 oscillates laser light. For example, a carbon dioxide laser, a YAG laser, a semiconductor laser, a gas laser such as helium-neon or argon, an excimer laser, or the like can be used. Moreover, what converted the wavelength into these laser beams can also be used.
Laser light may be used in a continuous oscillation state or in a pulse oscillation state.
The lens 12 converts the laser light oscillated from the laser light source 11 into parallel rays.
The diffraction grating 13 diffracts laser light, and for example, a mesh having a grating interval of 0.1 μm to 2000 μm can be used.
A plastic bottle container 14 to be decorated is placed on the side of the diffraction grating.

Laser light oscillated from the laser light source 11 is converted into parallel rays by the lens 12.
The collimated laser beam passes through the diffraction grating 13 to form a periodic pattern due to interference fringes, that is, an intensity distribution of the laser beam.

FIG. 2 is an enlarged view of the vicinity of the diffraction grating, and shows a state of interference fringes of laser light.
In this way, the laser light that has passed through the diffraction grating 13 is diffracted and interfered to form a periodic (having a certain regularity) pattern.

  When the laser beam having such a periodic pattern is irradiated onto the wall surface 15 of the plastic bottle container, a part of the container wall surface 15 is locally heated by the portion 16 having a strong laser beam intensity. For example, in a PET bottle mainly made of polyethylene terephthalate, the wall surface 15 has a thickness of about 100 μm, and a depth portion of 1 to 5 μm in the vicinity of the surface layer is heat-treated.

When the heated part reaches a certain temperature or higher, only the part melts, the structure composed of the amorphous part and the oriented crystal part formed on the wall surface 15 of the container is released, and then the ball is cooled in the process of cooling. Crystals are formed. For example, in the case of polyethylene terephthalate, the temperature is about 190 ° C.
As shown in FIG. 3, when fine spherulite portions 16 are periodically formed on the container wall surface 15 by this method, the orientation crystal portions 17 and the spherulite portions 16 have different refractive indexes. The periodic array structure 18 having different characteristics (refractive index) can be formed.

[Second Embodiment]
FIG. 4 is a diagram for explaining a second embodiment of a method for forming a periodic array structure having different optical characteristics.
In the present embodiment, a periodic array structure is formed on a plastic bottle container using the refraction and condensing of laser light.
In the present embodiment, fine uneven portions 19 having a lens effect are formed on the container wall surface 15 of the plastic bottle container 14.
The concavo-convex portion 19 can be formed by, for example, forming a concavo-convex shape on the surface of the blow mold in the molding process of the plastic bottle container described above, and transferring it from the mold to the container wall surface during the heat treatment. it can.

When the uneven portion 19 formed on the wall surface 15 of the plastic bottle container is irradiated with laser light as in the first embodiment, the laser light is refracted by the lens effect of the uneven portion 19 as shown in FIG. Condensed from the apex of the part to a certain part in the thickness direction. A portion where the laser beam is condensed is heated by the energy of the laser beam because the intensity of the laser beam is increased.
When the heated part reaches a certain temperature or higher, only that part melts, the structure composed of the amorphous part and the oriented crystal part formed on the wall surface 15 of the container is released, and then the ball is cooled in the process of cooling. A crystal part 16 is formed.

Therefore, the spherulite portion can be periodically generated by periodically forming the uneven portion 19 on the wall surface 15 of the plastic bottle container. As described above, since the refractive indices of the oriented crystal part 17 and the spherulite part 16 are different, it is possible to form a periodic array structure having different optical characteristics (refractive index).
In addition, in this embodiment, it has the periodic uneven | corrugated | grooved part formed in the wall surface of a plastic bottle container, and the periodic arrangement | sequence structure in which the optical characteristics (refractive index) from which an orientation crystal part and a spherulite part differ are different. Therefore, it is possible to obtain a rainbow-colored gloss as seen in a hologram.

[Third embodiment]
FIG. 5 is a diagram for explaining a third embodiment of a method for forming a periodic array structure having different optical characteristics.
In the present embodiment, the container is formed by blending and dispersing the photothermal absorption fine particles 20 serving as the core of heat generation in the resin that is the main material of the plastic bottle container 14.
The photothermal absorption fine particles are fine particles that generate heat in response to a specific laser beam. Examples thereof include mica, kaolin, talc, and titanium oxide-coated mica.
The particle diameter of the photothermal absorption fine particles is 0.1 μm to 100 μm. If it is larger than 100 μm, it may become opaque when blended with the resin. Preferably,
0.2 μm to 30 μm.
The photothermal absorption fine particles 20 may be blended in the entire plastic bottle container (preform). For example, a multilayer preform may be used and blended only in the specific layer.

Next, the plastic bottle container 14 containing the photothermal absorption fine particles 20 is irradiated with laser light. When the photothermal absorption fine particle 20 is irradiated with laser light, it generates heat by its energy. With this heat, the resin around the photothermal absorption fine particles 20 is heated and vaporized to form a fine cavity 21.
The refractive index of the cavity portion shows the same value as air (about 1.0), and is different from the refractive index of the surrounding plastic (about 1.3 to about 1.5).
Therefore, by irradiating the plastic bottle container 14 containing the photothermal absorption fine particles 20 while controlling the irradiation position of the laser light, the cavity 21 can be periodically formed, and the optical characteristic (refractive index) is improved. Different periodic arrangement structures, that is, regions having different refractive indexes can be formed periodically at regular intervals.
According to this method, decoration can be performed by blending a relatively small amount of the photothermal absorption fine particles.
In addition, as a method for controlling the irradiation position of the laser beam, for example, as shown in FIG. 5A, a method of irradiating spot-shaped laser beam at a constant interval by a control method used in laser marking, As shown in FIG. 5B, there is a control method using the principle of interference fringes of laser light.

  An example using the principle of interference fringes of laser light will be described. In FIG. 5B, the laser light emitted from the laser light source 11 is converted into a parallel light beam by the lens 12 and divided into two directions of light α and β by the half mirror 23. The divided lights are reflected by the mirrors 23 and 24, respectively, and then irradiated to the wall surface 15 of the plastic container. At this time, since the interference fringes due to the optical path difference between the laser beams α and β are formed on the wall surface 15, a periodic pattern is formed.

  In addition to the first to third embodiments described above, for example, by utilizing the self-forming effect of a fine periodic structure that is manifested by irradiation with a short-time pulse laser such as a femtosecond laser, A periodic array structure can also be formed (Masaki Hashida, Journal of the Institute of Electrical Engineers of Japan, Vol. 122, No. 11, pp 749-753 (2002)).

As a method for forming a periodic array structure in a plastic bottle package, it is possible to utilize the fact that the optical characteristics of the plastic material differ depending on the wavelength.
The optical properties of the plastic material, in particular the transmittance (or absorption) vary with wavelength.

For a specific wavelength, the plastic material is either transparent with a transmittance of about 70% or more, translucent with a transmittance of 10% or more and less than 70%, or opaque with a transmittance of less than 10%. Show properties.
When the plastic material is transparent for a certain wavelength, the effect of light giving energy to the plastic package is weak.

On the other hand, when the plastic material is opaque or translucent, light has a strong effect of giving energy to the plastic package.
On the other hand, when the plastic material exhibits opacity, light penetrates only near the surface of the package.
On the other hand, when the plastic material exhibits translucency or transparency, light penetrates into the package.

By utilizing the wavelength dependence of these optical properties, a three-dimensional periodic structure can be formed on the surface of the plastic package if the plastic material constituting the plastic package is irradiated with light having a wavelength that is translucent. Can do.
Moreover, if the plastic material which comprises a plastic package is irradiated with the light of the wavelength which is opaque, a two-dimensional periodic structure can be formed in the surface of a plastic package.

The periodic structure once formed in this way can be decorated by exhibiting physical coloring effects such as diffraction, interference, and scattering even in a wavelength region where the plastic material exhibits transparency.
When this method is used, it is possible to decorate a part or all of the plastic packaging body that is originally transparent in a certain wavelength region by physical coloring.

For example, polyethylene terephthalate (PET) exhibits transparency with respect to a wavelength of 0.38 μm to 1.0 μm including a visible light region (0.4 μm to 0.7 μm), and a near ultraviolet light region (0.3 μm to 0). .38 μm) is translucent, and in the deep ultraviolet region (0.3 μm or less) is opaque.
Moreover, although it shows transparency in the infrared light region of 1.0 μm or more, there is a region showing opacity or translucency corresponding to the absorption spectrum of the molecule.

  A plastic package made of a PET material having such a wavelength characteristic of light transmittance includes a third harmonic of a YAG laser having a wavelength of 0.355 μm, or a wavelength of 0, which is included in a wavelength region showing translucency. By irradiating with XeF excimer laser light having a wavelength of .351 μm, it is possible to form a periodic structure that develops physical coloring in the visible light region (0.4 μm to 0.7 μm).

  In addition, a plastic package made of a PET material having such a wavelength characteristic of light transmittance includes a fourth harmonic of a YAG laser having a wavelength of 0.266 μm, or a wavelength included in a wavelength region showing opacity. By irradiating light of 0.248 μm KrF excimer laser or ArF excimer laser having a wavelength of 0.193 μm, a periodic structure that develops physical coloring in the visible light region (0.4 μm to 0.7 μm) Can be formed.

As a method for forming the periodic structure, any method such as the first to third embodiments described above or a method using the self-forming effect of the fine periodic structure can be used.
The method for forming the periodic structure may be applied to a single-layer plastic package or may be applied to a multilayer plastic package.

  Transparency of light of the specific wavelength to a multilayer plastic package with a layer composed of a plastic material transparent to a specific wavelength and a layer composed of an opaque or translucent plastic material. Irradiating from the material layer side and passing through the transparent material layer, a periodic structure can be formed at the interface between the opaque material layer and the transparent material layer or inside the translucent material layer.

  The optical characteristics of the plastic material can be given arbitrary optical characteristics by blending an absorbing material for a specific wavelength in addition to using the characteristics specific to the plastic material.

Since the plastic bottle container of the present invention does not use a colorant by chemical coloring such as a pigment or a dye, the amount of chemical substances used can be reduced, so that it is a container with a small environmental load.
In addition, a periodic array structure is formed by the difference in crystal structure and the formation of cavities, and the decoration using the physical coloring mechanism is applied, so it is easy to heat and knead (repelletize) during recycling. Can be decolored. Therefore, although it is decorated when used as a container, it is colorless and transparent after reprocessing, so that recyclability is very good.
Furthermore, unlike chemical coloring, a vivid color tone having deep colors and gloss can be obtained, which is also effective for differentiation of products due to a decoration effect.

In the first to third embodiments, the plastic bottle container molded in advance is decorated, but after the preform is decorated by the above method, it is molded into the bottle container which is the final product. May be.
In addition to plastic bottle containers, the present invention can be applied to packaging bodies such as cups, pouches, trays, and tube containers.

  ADVANTAGE OF THE INVENTION According to this invention, even if it decorates, the plastic packaging body which can be recycled easily and its decorating method can be provided.

It is a figure for demonstrating 1st embodiment of the decorating method of this invention. It is an enlarged view around the diffraction grating, and is a view showing a state of interference fringes of laser light. It is a figure which shows the periodic arrangement | sequence structure formed on the plastic bottle container wall surface. It is a figure for demonstrating 2nd embodiment of the decorating method of this invention. It is a figure for demonstrating 3rd embodiment of the decorating method of this invention, (a) is the figure which irradiated the laser beam in the spot form, (b) is a laser beam using an interference fringe pattern. It is the figure which irradiated. It is a figure for demonstrating the difference of a chemical coloring mechanism and a physical coloring mechanism, (a) shows a chemical coloring mechanism, (b) shows a physical coloring mechanism.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Laser light source 12 Lens 13 Diffraction grating 14 Plastic bottle container 15 Plastic bottle container wall surface 16 Spherulite part 17 Oriented crystal part 18 Periodic arrangement structure 19 Concavity and convexity 20 Photothermal absorption fine particle 21 Cavity part 22 Half mirror 23, 24 Mirror

Claims (9)

By irradiating the wall surface of the plastic packaging body having a predetermined thickness with laser light, portions having different optical characteristics are periodically arranged inside the wall surface of the plastic packaging body isolated from the surface and interface of the plastic packaging body. A plastic package characterized by forming a periodic structure that expresses physical coloration, and light that enters the periodic structure interferes or diffracts and develops color .   2. The plastic package according to claim 1, wherein the plastic package includes a crystalline resin as a main material, and the portions having different optical characteristics have a crystal structure different from the crystal structure of the surface.   The plastic package according to claim 1, wherein the portion having different optical characteristics is a cavity formed on a surface of the plastic package. By irradiating the wall surface of the plastic packaging body having a predetermined thickness with laser light, portions having different optical characteristics are periodically formed inside the wall surface of the plastic packaging body isolated from the surface and interface of the plastic packaging body. A method for decorating a plastic package , characterized by arranging and forming a periodic structure that expresses physical coloration, and performing decoration by coloring light incident on the periodic structure by interference or diffraction .   The method of decorating a plastic package according to claim 4, wherein the plastic package is formed by forming a crystalline resin as a main material and providing the portion having different optical characteristics by providing a spherulite portion on the surface.   The method for decorating a plastic package according to claim 5, wherein the spherulite portion is formed using light diffraction or interference phenomenon.   At least a part of the surface of the plastic package made of a plastic material having a wavelength region showing transparency and a wavelength region showing translucency or opacity, the wavelength included in the wavelength region showing translucency or opacity. The method for decorating a plastic package according to any one of claims 4 to 6, wherein a portion having different optical characteristics in a wavelength region exhibiting the transparency is formed by irradiating light.   6. The plastic package according to claim 5, wherein an uneven portion for condensing light is formed in advance on the surface, and the spherulite portion is formed on the surface by irradiating the uneven portion with light. Decoration method.   Light heat absorbing fine particles are blended and dispersed in the plastic package, the package is locally irradiated with a laser beam, the light heat absorbing fine particles are heated, and the resin around the light heat absorbing fine particles is vaporized to form a cavity. The method for decorating a plastic package according to claim 4, wherein the portions having different optical characteristics are formed.

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