HK1228941B - Bright ink composition for printing, paper container material made with the bright ink composition, and heat-insulating paper foam container - Google Patents

Description

Brightening ink composition for printing, paper container using the same Material and heat-insulating foamed paper container

The present invention is a divisional application of the invention application with application number 200980111748.6 (international application number PCT/JP2009/056513), filed on March 30, 2009, and entitled "Brightness ink composition for printing, paper container material using the same, and heat-insulating foamed paper container."

Technical Field

The present invention relates to a luminous ink composition for forming a printed layer by gravure printing that imparts design and aesthetic appeal to the surface of a thermally insulating foamed container, a paper container material using the same, and a thermally insulating foamed paper container. More specifically, the present invention relates to a luminous ink composition for forming a printed layer on a thermoplastic synthetic resin film having a thermally insulating layer, the thermally insulating layer being formed by foaming during heat treatment during the manufacture of the thermally insulating foamed paper container, and a paper container material using the same, and a thermally insulating foamed paper container. The printed layer provides a smooth surface with excellent foaming properties, minimal irregularities, and suppressed cracking of the ink film. Thermally insulating foamed paper containers having a printed layer formed from the luminous ink composition of the present invention exhibit excellent thermal insulation properties due to their smooth surface. Therefore, they are suitable for use as containers for foods containing high or low-temperature liquids. For example, the thermally insulating foamed paper containers of the present invention are suitable for use as cups or bowls for foods such as soup, rice cake and red bean soup, sauces, and noodles.

Background Art

In recent years, with the diversification of packaging containers, expectations for the ink and printing industries have also expanded significantly. For example, in the field of food containers such as cups used in food products such as ramen, udon, and soba, which are prepared by pouring a suitable amount of hot water into the container and consuming it within a few minutes, polystyrene cups are the primary choice due to their cost and thermal insulation properties.

However, with expanded polystyrene cups, printing must be performed separately after the cups are formed. Consequently, printing methods are limited to those using curved printing machines or stamp printers, resulting in issues such as poor printing speed and quality. Furthermore, the recent rise in polystyrene prices, coupled with the recent rise in oil prices, and the subsequent burden of recycling costs on food manufacturers due to the implementation of the Containers and Packaging Recycling Act, have led to a shift from polystyrene cups to paper cups.

One of the most representative paper container structures is a double-walled cup with an insulating air layer formed by laminating paper with flutes. However, double-walled cups are subject to issues such as high weight and cost. Consequently, in recent years, insulating foamed paper containers have attracted attention.

Thermally insulating foamed paper containers are generally manufactured using a paper container material having a thermoplastic synthetic resin film that forms a thermal insulation layer by foaming during heat treatment during container manufacturing. More specifically, the paper container material, for example, has a structure in which a high-melting-point polyethylene film with a melting point of approximately 130°C to 135°C is laminated on one side of a base paper (the inner side of the container), and a low-melting-point polyethylene film (hereinafter referred to as "low-MP film") with a melting point of approximately 105°C to 110°C is laminated on the other side of the base paper (the outer side of the container). A printed layer containing a pattern, such as a decorative pattern, company name, or barcode, is formed on the surface of the low-MP film.

In the manufacturing process of the above-mentioned thermally insulating foamed paper container, a paper container material with a pre-printed layer is formed into a predetermined shape and used as the main component of the cup to form a cup. Then, the low-MP film is heated near the melting point of the above-mentioned low-MP film to foam the above-mentioned low-MP film. The foaming occurs as follows: during the heating process, the moisture in the base paper evaporates and is squeezed toward the softened low-MP film. As a result, the low-MP film expands outward, generating foam. The thus-foamed low-MP film functions as an insulating layer, imparting thermal insulation properties to the paper container. Such thermally insulating foamed paper containers are disclosed, for example, in Japanese Patent Application Laid-Open No. 9-95368 (Patent Document 1), Japanese Patent Application Laid-Open No. 7-232774 (Patent Document 2), and Japanese Patent Application Laid-Open No. 11-189279 (Patent Document 3).

Forming a printed layer on the surface of the low-MP film of the thermally insulating foamed paper container material is typically accomplished by surface printing using gravure printing. In the field of gravure surface printing, ink is applied to the surface of printed materials, such as various base papers and plastic packaging containers. Therefore, gravure printing inks are required not only to be printable on the printed materials but also to have good adhesion to the base paper or plastic materials, to resist blocking to prevent printed materials from sticking to each other after printing, and to have various tolerances, such as friction resistance and heat resistance, which are necessary for container molding.

In addition, gravure printing inks typically contain an aromatic solvent such as toluene as a main solvent to achieve a balance between solubility and drying properties of the binder resin. However, in recent years, there has been a growing trend toward using printing inks that do not contain aromatic solvents to improve the printing environment.

Furthermore, considering the commercial value of thermally insulating foamed paper containers, it is desirable for the gravure printing ink used to form the printed layer of the container to provide an ink coating that does not interfere with but follows the foaming of the low-Mp film constituting the thermal insulation layer, thereby providing a container surface with few irregularities. Furthermore, it is desirable to provide a smooth printed surface with few cracks in the ink coating.

Ink for gravure printing, which is used to form the printed layer of thermally insulating foamed paper containers, has been known to contain polyamide resin and cellulose derivatives as binder components. However, when the ink film is exposed to heat or light for a long time, low-molecular-weight components such as oils and fats contained in the polyamide resin undergo oxidative decomposition into acetaldehyde, leading to the generation of a fatty odor. Furthermore, this fatty odor can potentially alter the taste of the contents of the container, creating a significant problem.

Furthermore, when the printing ink is formulated into a brightness ink containing a brightness material such as aluminum and used to form a printed layer, the ink coating tends to significantly inhibit foaming of the low-MP film. Consequently, when a printed layer formed from brightness ink is directly applied to a low-MP film, significant unevenness is produced between the printed and non-printed areas, making it difficult to achieve a smooth printed surface. Therefore, when using brightness ink to form a printed layer, a base layer of white ink is typically applied to the low-MP film. However, brightness ink has a greater ability to inhibit foaming of the low-MP film than white ink. Therefore, even when a white ink base layer is used and a brightness ink is printed over it, it is difficult to achieve a uniform thickness for the low-MP film after foaming.

Furthermore, on the surface of a container with such a printed layer, the printed area where the white ink/bright ink overlaps appears significantly concave compared to the white ink printed area, creating a noticeable height difference. Consequently, thermally insulating foamed paper containers suffer from issues such as a lack of smooth tactile feel, compromised product quality, and difficulty reading barcodes. Furthermore, because the foaming of the low-MP film is suppressed, a sufficient thickness of the thermal insulation layer cannot be achieved, resulting in the container heating up when hot water is added, further contributing to thermal insulation issues.

Meanwhile, Japanese Patent Application Laid-Open No. 2006-218708 (Patent Document 4) discloses a colored ink suitable for gravure printing, exhibiting a shimmering effect, high glossiness, and excellent design properties. The disclosed colored ink contains pearlescent pigments and silica as brightness agents and is primarily used to form a base layer for glossy cosmetic paper suitable for interior finishes such as building materials.

Patent Document 1: Japanese Patent Application Laid-Open No. 9-95368

Patent Document 2: Japanese Patent Application Laid-Open No. 7-232774

Patent Document 3: Japanese Patent Application Laid-Open No. 11-189279

Patent Document 4: Japanese Patent Application Laid-Open No. 2006-218708

Summary of the Invention

To improve the unevenness of the printed layer in thermally insulating foam paper containers, Patent Document 3 proposes a technique for forming a base layer by using an ink that does not hinder the foaming of the low-MP film and is compatible with the surface. However, even when using a bright ink to form the printed layer on such a base layer, unevenness still occurs, resulting in unsatisfactory properties such as tactile feel, design, and thermal insulation, and further improvements are desired. Furthermore, while Patent Document 4 discloses a colored ink containing a bright material, it does not provide any description or suggestion of a technique for providing a thermally insulating foam paper container with a printed layer having minimal unevenness by using such a colored ink. However, as mentioned above, inks containing a bright material have a strong inhibitory effect on the foaming of the low-MP film, so a printed layer formed with such a colored ink is more likely to have unevenness on the printed surface. Therefore, there is a need for a bright ink with excellent foaming properties that is well suited for specific applications such as thermally insulating foam paper containers.

Therefore, the present invention addresses the following issues in order to solve the conventional problems in the field of printing inks for thermally insulating foamed paper containers.

The present invention aims to provide a brightness ink composition for forming a printed layer of a thermally insulating foamed paper container, which not only exhibits excellent foaming followability to the foaming of the low-Mp film caused by the heat treatment during container production, but also minimizes cracking of the ink coating. It should be noted that "excellent foaming followability" in this specification means that the smooth ink coating of the printed layer formed on the surface of the low-Mp film foamed by the heat treatment does not significantly hinder the foaming of the film, and that the surface of the thermal insulation layer formed by the uniform expansion of the film maintains minimal irregularities.

Another object of the present invention is to provide a brightness ink composition that, in addition to the above-mentioned properties, has heat resistance and light resistance, and the ink coating does not generate odor even when exposed to heat or light for a long time, and has excellent friction resistance, blocking resistance, and adhesion to a low-MP film serving as a substrate.

Another object of the present invention is to provide a brightness ink composition that does not use an aromatic solvent and is excellent in the above-mentioned properties.

Another object of the present invention is to provide a heat-insulating foamed paper container material having a printed layer formed from a brightness ink composition having the above-mentioned excellent properties on a low Mp film that forms a heat-insulating layer by foaming under heat treatment.

Another object of the present invention is to provide a thermally insulating foamed paper container, wherein the thermally insulating foamed paper container is made of the above-mentioned container material having a printed layer formed from the above-mentioned brightness ink composition having excellent properties, thereby having a container surface with few irregularities and a smooth printed layer surface, that is, a smooth surface and an excellent appearance.

To address previous challenges in the printed layer of thermally insulating foamed paper containers, the inventors conducted extensive research on luminance inks. They discovered that when a luminance ink composition containing a luminance material such as aluminum and silica is used to form a printed layer, the ink film exhibits excellent conformability to foaming of low-MP films and suppresses the formation of ink cracks (fissures) in the ink film. Specifically, they discovered that the use of this luminance ink composition effectively reduces the height difference between the luminance ink-printed portion and other printed portions on the surface of a thermally insulating foamed paper container obtained by heat treatment. This allows for the realization of a thermally insulating foamed paper container with excellent printing quality, including smoothness, design, and aesthetics, and further, superior thermal insulation. Based on these findings, the present invention relates to the following matters.

The first aspect of the present invention relates to a brightness ink composition for forming a printed layer on the surface of a heat-insulating foamed paper container material comprising a base paper, a first thermoplastic synthetic resin film covering one side of the base paper, and a second thermoplastic synthetic resin film covering the other side of the base paper. The second thermoplastic synthetic resin film has a lower melting point than the first thermoplastic synthetic resin film and forms a heat-insulating layer by foaming under heat treatment. The brightness ink composition comprises a brightness material, silica, a binder resin, and a solvent. The brightness ink composition preferably also contains a colorant, if necessary.

The brightness material is preferably one or more materials selected from the group consisting of aluminum, pearlescent pigment, and glass. The brightness material preferably has a solids content of 2 to 30% by weight based on the total weight of the brightness ink composition. The aluminum material preferably has a particle size of 5 to 40 μm and is a non-leafing aluminum paste surface-treated with a fatty acid.

The silica has a particle size of 2 to 20 μm, and the content of the silica is preferably 0.2 to 5% by weight based on the total weight of the brightness ink composition.

The binder resin preferably comprises a polyurethane resin and a vinyl polymer. In addition, the ratio of the polyurethane resin to the vinyl polymer in the above components is preferably 95:5 to 5:95 based on the weight of solids.

The second aspect of the present invention relates to a thermally insulating foamed paper container material comprising a base paper, a first thermoplastic synthetic resin film covering one side of the base paper, a second thermoplastic synthetic resin film covering the other side of the base paper, and a printed layer provided on at least a portion of the surface of the second thermoplastic synthetic resin film, wherein the second thermoplastic synthetic resin film has a lower melting point than the first thermoplastic synthetic resin film and forms a thermally insulating layer by foaming under the action of a heat treatment, and the printed layer comprises at least one printed pattern formed from the brightness ink composition of the first aspect of the present invention.

The third aspect of the present invention relates to a heat-insulating foamed paper container, which is obtained as follows: a container is formed by combining a container main body component and a bottom plate component formed from the heat-insulating foamed paper container material of the second aspect of the present invention in such a manner that the first thermoplastic synthetic resin film forms the inner wall surface and the second thermoplastic synthetic resin film forms the outer wall surface, and the container is heat-treated to foam the second thermoplastic synthetic resin film.

The present application claims priority based on Japanese Patent Application No. 2008-092239 filed on March 31, 2008 by the same applicant, the specification of which is incorporated herein by reference as a part of the present specification.

According to the present invention, a brightness ink composition can be provided that overcomes conventional issues in the printed layer of a thermally insulating foamed paper container, achieving a smooth and aesthetically pleasing thermally insulating foamed paper container while also exhibiting excellent resistance to ink and print quality. Furthermore, a thermally insulating foamed paper container can be provided that exhibits minimal surface irregularities, a smooth printed surface, and excellent design, aesthetics, and heat resistance, even when the printed layer is configured with a brightness ink superimposed on a white ink using such an ink composition.

BRIEF DESCRIPTION OF THE DRAWINGS

[ Fig. 1] Fig. 1 is a schematic cross-sectional view showing one embodiment of the paper container material of the present invention.

[ Fig. 2] Fig. 2 is a schematic cross-sectional view showing the state of the paper container material shown in Fig. 1 after heat treatment.

[Fig. 3] Fig. 3 is a schematic cross-sectional view showing one embodiment of the paper container material of the present invention.

[ Fig. 4] Fig. 4 is a schematic cross-sectional view showing one embodiment of the paper container material of the present invention.

[Fig. 5] Fig. 5 is a perspective view showing one embodiment of the heat-insulating foamed paper container of the present invention.

[ Fig. 6] Fig. 6 is a schematic cross-sectional view showing an enlarged portion VI of the heat-insulating foamed paper container shown in Fig. 5 .

Description of Reference Numerals

10 base paper

20. First thermoplastic synthetic resin film (high MP resin film)

30. Second thermoplastic synthetic resin film (low Mp resin film)

30' thermal insulation layer (second thermoplastic synthetic resin film after foaming)

40 printing layers

42 Printing Pattern

42a No. 1 Printing Department

42b Second Printing Department

44 bottom floor

50 container body

50a container inner wall

50b Outer wall of container

60 container bottom plate

DETAILED DESCRIPTION

Hereinafter, the present invention will be described in more detail.

(Brightness ink composition)

The luminous ink composition of the present invention is characterized by being used to form a gravure-printed printed layer on the surface of the second thermoplastic synthetic resin film of a thermally insulating foamed paper container material comprising a base paper, a first thermoplastic synthetic resin film covering one side of the base paper, and a second thermoplastic synthetic resin film covering the other side of the base paper. The second thermoplastic synthetic resin film has a lower melting point than the first thermoplastic synthetic resin film and forms a thermally insulating layer by foaming under heat treatment. The luminous ink composition comprises a luminous material, silica, a binder resin, a solvent, and, if desired, a colorant. In the following description, the first thermoplastic synthetic resin film will be referred to as a "high-Mp resin film," and the second thermoplastic synthetic resin film will be referred to as a "low-Mp resin film," respectively.

The brightness material used in the brightness ink composition of the present invention can be any material that imparts, for example, a metallic brightness to the ink film, thereby visually enhancing the overall design and aesthetic appeal of the product. Generally speaking, the brightness of an ink film is a visually imparted color perception resulting from the interaction of the brightness material's inherent hue, structural factors such as the arrangement and orientation of the brightness material within or near the film's surface, and surface factors derived from the smoothness of the film's surface.

In the present invention, in order to impart an appropriate brightness to the ink coating through the use of the brightness material, it is necessary to optimize the properties of the brightness material, such as the surface treatment method, particle size, and concentration used. Furthermore, considering its applicability to thermally insulating foam paper containers, the ink coating containing the brightness material must not be a material that significantly hinders the foaming of the low-MP resin film during foaming.

Examples of the luminance material that can be used in the present invention include aluminum, pearlescent pigments, and glass. In the present invention, one or more of these luminance materials can be used in combination.

Specific examples of the aluminum material include aluminum powder, aluminum paste, and aluminum flakes. Aluminum powder is a solvent-free metallic pigment, and also includes aluminum particles coated with a resin such as an acrylic resin. Aluminum paste is a surface-treated, paste-like material made from flaky aluminum particles using an organic solvent. Furthermore, an example of aluminum flakes is a pigmented aluminum vapor-deposited film.

An example of the pearlescent pigment is white pearls that have been surface-treated by micronizing mica. Another example of the glass material is a scaly glass flake, or a bright pigment-type material obtained by coating the flake with a metal or metal oxide.

The brightness material used in the brightness ink composition of the present invention is not particularly limited, but is preferably an aluminum material. Considering the dispersibility and stability in the brightness ink composition, aluminum paste is most preferred.

Aluminum paste is generally produced by crushing aluminum into flakes (scales) using a ball mill or other pulverizer, and then surface-treating it with a fatty acid. Depending on the type of fatty acid used, it can be broadly divided into two types: leafing and non-leafing.

The two types have different surface treatment agents, resulting in different arrangements of aluminum particles in the ink coating layer during printing.

More specifically, in the floating type, stearic acid is used as a surface treatment agent. Since the stearic acid acts as an oleophobic coating, the surface tension causes the aluminum particles to be exposed on the surface from the intermediate layer of the ink coating layer.

In contrast, non-leafing inks use oleic acid as a surface treatment agent. Oleic acid is less effective at reducing surface tension than stearic acid. Consequently, after printing, the aluminum particles are aligned parallel to each other in the center of the ink film, giving the ink film a shiny, metallic appearance.

When using leafing aluminum paste to prepare brightness ink, the ink coating exhibits excellent foaming properties. However, friction resistance and adhesion tend to be slightly inferior compared to using non-leafing aluminum paste. Therefore, in one embodiment of the present invention, non-leafing aluminum paste is preferably used as the brightness material.

The non-leafing aluminum paste used in the present invention is one in which the aluminum particles are surface-treated with oleic acid. The particle size after treatment is preferably in the range of 5 to 40 μm, and more preferably in the range of 8 to 25 μm. Particle sizes of 5 μm or less tend to increase the viscosity of the resulting brightness ink, resulting in poor ink quality. On the other hand, particle sizes of 40 μm or greater tend to reduce the hiding power of the ink film.

Aluminum particles in aluminum paste generally have a scaly shape, which is expressed by particle diameter and thickness. Particle diameter is the average particle diameter of the larger side of the particle, measured using a particle size distribution analyzer utilizing light scattering or direct observation using an electron microscope. In this invention, the D50 value (the cumulative weight 50% particle diameter) of the particle diameter measured by light scattering is used as the average particle diameter.

The solids content of the aluminum paste in the brightness ink composition of the present invention is preferably 2 to 30% by weight, based on the total weight of the brightness ink composition. A more preferred range is 5 to 20% by weight. A solids content of 2% or less tends to reduce the hiding power and brightness of the ink film, and also tends to reduce foaming followability. On the other hand, a solids content of 30% or more tends to increase the viscosity of the brightness ink, reducing ink fluidity.

In the brightness ink composition of the present invention, other brightness materials can be used in addition to the aluminum paste described above. However, when pearlescent pigments are used, the foaming properties tend to be slightly worse compared to when non-leafing aluminum paste is used. Furthermore, while excellent foaming properties can be achieved when thin aluminum flakes or glass flakes are used, they are very expensive and, therefore, are not suitable for the intended applications of the present invention from a cost perspective.

The silicon dioxide that can be used in the present invention may be, for example, a compound known as "synthetic silicon dioxide" produced by a known method. Representative methods for producing synthetic silicon dioxide include a wet method in which sodium silicate, made from high-purity silica sand, reacts with an acid to produce ultrafine hydrous silicic acid, and a dry method in which silicon tetrachloride is combusted and hydrolyzed in a gas phase.

The silica used in the present invention is not particularly limited by the synthesis method. For example, it may be any of treated silica whose surface has been modified using silicone wax or an organosilicon compound as a treatment agent, or untreated silica (untreated silica). The particle size of the silica used in the present invention is preferably in the range of 2 to 20 μm. When silica with a particle size of 2 μm or less is used, there is a tendency for the viscosity of the obtained ink composition to increase, thereby reducing the ink state. On the other hand, when silica with a particle size of 20 μm or more is used, there is a tendency for the ink coating to deteriorate in its ability to follow the foaming of the low-melting-point resin film during the heat treatment during container manufacturing. In the present invention, it is further preferred to use silica with a particle size in the range of 3 to 10 μm.

The particle size of silica is generally measured by the Coulter counter method utilizing electrical resistance change, the laser method utilizing light scattering, etc. In the present invention, the particle size is the average particle size obtained by the laser method.

The silica content in the brightness ink composition of the present invention is preferably in the range of 0.2 to 5% by weight, based on the total mass of the ink composition. A silica content of less than 0.2% by weight may not sufficiently improve the foaming properties of the ink film. Furthermore, a silica content of 5% or more may increase the ink viscosity, deteriorate the ink properties, and, in turn, reduce abrasion resistance. From the perspective of ink properties and foaming properties, the silica content is more preferably in the range of 0.5 to 3.5% by weight.

Typically, colored inks containing brightness materials or color pigments lack the ability to follow the foaming of low-MP resin films. This results in the printed area on the container surface becoming recessed relative to the rest of the printed area after foaming, creating a height difference. Especially with brightness inks containing brightness materials, this height difference on the printed surface is significant, significantly detracting from the container's appearance. However, according to the present invention, by combining a brightness material and silica to impart brightness, the ink film's ability to follow the foaming is improved, effectively suppressing the formation of unevenness on the printed surface of the brightness material-containing printed area.

Furthermore, according to the present invention, by using the brightness material and silica in combination, the occurrence of ink cracks (cracks) in the ink film of the printed layer can be suppressed when the low-Mp resin film is foamed, thereby improving foaming followability and providing a smooth printed surface.

Typically, when silica is added to an ink composition, the ink film loses its gloss, imparting a matte appearance and reducing its brightness. However, the brightness ink of the present invention, unlike the generally expected effects of silica, maintains the brightness of the ink film, providing excellent design and aesthetics. Without being bound by theory, it is believed that the addition of silica in the present invention suppresses cracks in the ink film, improves its ability to follow foaming, and maintains the uniformity and isotropy of the ink film.

The binder resin that can be used in the present invention may be any conventionally known binder resin for printing inks. Examples of such resins include polyurethane resins, vinyl copolymers, nitrocellulose, chlorinated polyolefin resins, alkyd resins, rosin resins, and nitrocellulose.

While not particularly limited, among the aforementioned resins, polyurethane resin is preferably used, considering the ink's foaming characteristics and sensory odor during foaming, as well as various resistance properties such as light resistance, heat resistance, friction resistance, and blocking resistance, as well as adhesion to the low-MP resin film serving as the substrate. By using a polyurethane resin or a resin mixture primarily composed of a polyurethane resin as the binder resin, odors emanating from the printed portion of paper containers such as paper cups can be nearly completely eliminated, even when stored under prolonged exposure to heat and light. Furthermore, excellent results can be achieved in terms of various properties of the ink coating, such as friction resistance, blocking resistance, and adhesion to the low-MP resin film serving as the substrate.

The term "polyurethane resin" used in the present invention means a polyurethane resin in a broad sense, including general polyurethane resins or modified polyurethane resins such as polyurethane urea resins used in the past in this technical field. In addition, the polyurethane resin used in the present invention is not particularly limited according to its different production methods, and can be: various polyurethane resins obtained by applying a known or well-known method involving polyurethane resins. Although not particularly limited, in the present invention, as a preferred embodiment of the polyurethane resin, there can be listed: a polyurethane resin obtained by reacting a polyol compound and an organic diisocyanate. In addition, as another embodiment, there can be listed: a modified polyurethane resin obtained by modifying a prepolymer of a polyurethane resin by an amine compound or an amide compound. Various polyurethane resins are described below.

When specifically illustrating an example of the polyol compound that can be used for producing the polyurethane resin, various well-known polyols such as those shown below are listed.

(1) Polyether polyols such as polymers or copolymers of ethylene oxide, propylene oxide, tetrahydrofuran, etc.;

(2) Polyester polyols obtained by dehydrating and condensing saturated and unsaturated low molecular weight glycols such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, methylpentanediol, hexanediol, octanediol, nonanediol, methylnonanediol, diethylene glycol, triethylene glycol, and dipropylene glycol, alkyl glycidyl ethers such as n-butyl glycidyl ether and 2-ethylhexyl glycidyl ether, and monocarboxylic acid glycidyl esters such as versatic acid glycidyl ester, with dibasic acids such as adipic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, fumaric acid, succinic acid, oxalic acid, malonic acid, glutaric acid, pimelic acid, azelaic acid, sebacic acid, and dimer acid, or their anhydrides;

(3) In addition, polycarbonate diols, polybutadiene diols, and diols obtained by adding ethylene oxide or propylene oxide to bisphenol A;

(4) Dimerdiols.

These various polyols may be used alone or in combination of two or more.

In the present invention, when the polyols exemplified in (2) above are used, diols in an amount of up to 5 mol% may be replaced with various other polyols. For example, polyols such as glycerin, trimethylolpropane, trimethylolethane, 1,2,6-hexanetriol, 1,2,4-butanetriol, and pentaerythritol may be used.

The number average molecular weight of the polyol is appropriately determined by considering properties such as the solubility, drying properties, and blocking resistance of the polyurethane resin obtained as the reaction product. While not particularly limited, it is generally preferably in the range of 500 to 10,000, and more preferably in the range of 500 to 6,000. A number average molecular weight of less than 500 tends to reduce printability due to decreased solubility. Furthermore, a number average molecular weight exceeding 10,000 tends to reduce drying properties and blocking resistance.

On the other hand, the organic diisocyanate compound that can be used in the production of the polyurethane resin in the present invention may be various known diisocyanates of aromatic, aliphatic or alicyclic types. Specifically, for example, 1,5-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyldimethylmethane diisocyanate, 4,4'-dibenzyl isocyanate, dialkyl diphenylmethane diisocyanate, tetraalkyl diphenylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, toluene diisocyanate, butane-1,4-diisocyanate, hexamethylene diisocyanate, isopropylidene diisocyanate, methylene ... diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, xylene diisocyanate, isophorone diisocyanate, lysine diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, methylcyclohexane diisocyanate, norbornane diisocyanate, m-tetramethylxylene diisocyanate, and dimer diisocyanates obtained by converting the carboxyl groups of dimer acids into isocyanate groups.

The method for producing the polyurethane resin may be a conventionally known or well-known method, and is not particularly limited. For example, when a polyol compound and an organic diisocyanate are reacted, other conditions are not limited except that the organic diisocyanate is used in excess relative to the polyol compound. In a preferred embodiment of the polyurethane resin production of the present invention, the molar equivalent ratio of isocyanate group/hydroxyl group is preferably set to be in the range of 1.2/1 to 3/1. If the molar equivalent ratio of isocyanate group/hydroxyl group is less than 1.2/1, the obtained polyurethane resin tends to be fragile. If a fragile polyurethane resin is used as a binder resin for printing ink, it is easy to cause caking. On the other hand, if the molar equivalent ratio of isocyanate group/hydroxyl group is 3/1 or more, the viscosity increases during the production of the polyurethane resin, and gelation is easily caused during the reaction. The polyurethaneization reaction in the production of the polyurethane resin is usually carried out at a reaction temperature in the range of 80°C to 200°C, preferably in the range of 90°C to 150°C.

The polyurethane reaction can be carried out in a solvent or in a solvent-free atmosphere. When a solvent is used, the solvent listed below can be appropriately selected from the viewpoints of controlling the reaction temperature, viscosity, and side reactions. Furthermore, when the polyurethane reaction is carried out in a solvent-free atmosphere, it is preferably carried out by raising the temperature to a level that allows for sufficient stirring and lowering the viscosity to obtain a uniform polyurethane resin. The reaction time of the polyurethane reaction is preferably set to 10 minutes to 5 hours. The endpoint of the reaction can be determined by methods such as viscosity measurement, confirmation of the NCO peak by IR measurement, and NCO% measurement by titration.

An example of a modified polyurethane resin used in the present invention is a polyurethane urea resin. A preferred polyurethane urea resin for use in the present invention is a resin obtained by reacting the polyol compounds listed above with an organic diisocyanate to synthesize a polyurethane resin prepolymer having terminal isocyanate groups, and then introducing urea bonds into the polyurethane resin prepolymer using an amine compound or an amide compound as a chain extender and reaction terminator. In the present invention, the use of such a polyurethane urea resin in the polyurethane resin further enhances various ink film properties.

As examples of the chain extenders that can be used to introduce urea bonds, various well-known amines can be used. Examples include ethylenediamine, propylenediamine, hexamethylenediamine, triethylenetetramine, diethylenetriamine, isophoronediamine, and dicyclohexylmethane-4,4'-diamine. Other examples include diamines having hydroxyl groups in the molecule, such as 2-hydroxyethylethylenediamine, 2-hydroxyethylpropylenediamine, di-2-hydroxyethylethylenediamine, di-2-hydroxyethylpropylenediamine, 2-hydroxypropylethylenediamine, and di-2-hydroxypropylethylenediamine, as well as dimer diamines obtained by converting the carboxyl groups of dimer acid into amino groups.

In addition, examples of compounds that can be used as the reaction terminator in the present invention include aliphatic amine compounds or fatty amide compounds having a long-chain alkyl group of C8 or greater and C22 or less. Examples of the aliphatic amine compound include octylamine, laurylamine, coconut amine, tetradecylamine, stearylamine, oleylamine, palmitamine, and dibutylamine, and these can be used alone or in combination of two or more. Examples of the fatty amide compound include caprylamide, caprylamide, laurylamine, myristylamide, palmitamide, stearylamide, behenamide, oleamide, erucamide, linoleamide, and linolenic acid amide, and these can be used alone or in combination of two or more.

By introducing a fatty amine or fatty amide compound having a long-chain alkyl group of C8 or greater and C22 or less into the terminal end of the polyurethane resin prepolymer, the blocking resistance of the ink film can be improved. Without being bound by theory, it is believed that the long-chain alkyl groups exhibit surface activity by aligning on the coating surface during film formation, thereby improving the blocking resistance of the polyurethane resin. By introducing these fatty acid amines or fatty amides into the polyurethane resin, the undesirable phenomenon of reduced gloss on the coating surface is avoided.

It should be noted that the method for introducing urea bonds into a polyurethane resin prepolymer is not particularly limited. For example, a two-step method can be used: a polyol compound and an organic diisocyanate compound are reacted in a ratio such that the isocyanate groups are in excess to prepare a prepolymer having isocyanate groups at the ends of the polyol; then, this prepolymer is reacted with a chain extender and a reaction terminator in a solvent. This two-step method is preferred because it more easily produces a uniform polymer solution. While not particularly limited, assuming the number of free isocyanate groups at both ends of the prepolymer is 1, the combined number of amino groups in the chain extender and reaction terminator used is preferably within the range of 0.5 to 1.3. If the combined number of amino groups is less than 0.5, the effects of improving drying properties, anti-blocking properties, and coating film strength tend not to be fully achieved. On the other hand, if the combined number of amino groups exceeds 1.3, the chain extender and reaction terminator tend to remain unreacted, resulting in a tendency for odor to remain in the printed layer.

The solvents used in the manufacture of the above-mentioned polyurethane resin and the above-mentioned polyurethane urea resin can generally be: well-known compounds that can be used as solvents for printing inks. For example, the following can be listed: alcohol solvents such as methanol, ethanol, isopropanol, n-propanol, n-butanol; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone; ester solvents such as ethyl acetate, propyl acetate, butyl acetate; non-aromatic hydrocarbon solvents such as methylcyclohexane and ethylcyclohexane. These solvents can be used alone or in a mixture of two or more. It should be noted that when the above-mentioned ketone solvent is used in the above-mentioned manufacture, a ketone imine group is generated between the ketone and the amine used as a chain extender, which will hinder the smooth progress of the reaction. Therefore, in order to suppress the generation of the ketone imine group and make the reaction proceed smoothly, it is preferred to use a small amount of water in combination.

In the present invention, the number average molecular weight of the polyurethane resin used as the binder resin is preferably within the range of 5,000 to 100,000. When a printing ink composition is prepared using a polyurethane resin with a number average molecular weight of less than 5,000, the ink composition's properties, such as drying properties, blocking resistance, film strength, and oil resistance, tend to be reduced. On the other hand, when a polyurethane resin with a number average molecular weight exceeding 100,000 is used, the viscosity of the printing ink tends to increase, and the gloss of the printed ink film tends to decrease.

In one embodiment of the ink composition of the present invention, the polyurethane resin described above is preferably combined with another binder resin, such as a vinyl copolymer and nitrocellulose. Combining a polyurethane resin with another resin not only improves various properties but also tends to enhance the foamed appearance. Without being bound by theory, it is believed that by adding components with different elongations from the polyurethane resin, these components act as a binder when the polyurethane component expands under heat treatment to form a foamed layer.

The nitrocellulose that can be used in the present invention can be any nitrocellulose compound known to those used in printing inks. On the other hand, ethylene copolymers that can be used include copolymers obtained by copolymerizing vinyl chloride monomers, fatty acid vinyl ester monomers, and various vinyl monomers with other polymerizable monomers having unsaturated carbon atom-carbon double bonds in one molecule and having functional groups as required. From the perspective of improving the foaming appearance, it is preferred to use a polyurethane resin and an ethylene copolymer in combination. Specific examples of ethylene copolymers that can be used in the present invention are described below.

Examples of the fatty acid vinyl ester monomers that can be used as monomers for producing the ethylene-based copolymer include vinyl acetate, vinyl propionate, vinyl monochloroacetate, vinyl versatate, vinyl laurate, vinyl stearate, and vinyl benzoate.

Examples of the functional group in the other polymerizable monomers having a carbon-carbon unsaturated double bond in one molecule and optionally having a functional group include a hydroxyl group, a carboxyl group, an isocyano group, and an epoxy group.

For example, as an example of the above-mentioned monomer having a hydroxyl group, there can be listed: vinyl alcohol, 2-hydroxyethyl (meth)acrylate, 1-hydroxypropyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, hydroxystyrene and N-hydroxymethyl acrylamide.

Examples of the monomer having a carboxyl group include (meth)acrylic acid, itaconic acid, isovaleric acid, maleic acid, fumaric acid, and their derivatives. Examples of the derivatives include (meth)acrylonitrile, (meth)acrylates, alkyl (meth)acrylates such as methyl (meth)acrylate, butyl (meth)acrylate, ethylhexyl (meth)acrylate, and stearyl (meth)acrylate, and benzyl (meth)acrylate.

Examples of the monomer having an isocyanate group include (meth)acryloyloxyethyl isocyanate, (meth)acryloyloxypropyl isocyanate, and the like, as well as reactants obtained by reacting hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate with polyisocyanates such as toluene diisocyanate and isophorone diisocyanate.

Examples of the monomer having an epoxy group include glycidyl methacrylate, glycidyl cinnamate, glycidyl allyl ether, glycidyl vinyl ether, vinylcyclohexane monoepoxide, and 1,3-butadiene monoepoxide.

In the present invention, one or more of the aforementioned monomer compounds may be appropriately selected and used, depending on the various properties required of the ink composition. A preferred embodiment of the binder resin in the present invention includes a combination of a vinyl chloride/vinyl acetate copolymer and a polyurethane resin.

The manufacturing of the ethylene copolymer that uses in the present invention is not particularly limited, can be implemented by being applicable to known method in the past.For example, applicable suspension polymerization, that is, water adds water, dispersion agent and polymerization initiator in the polymerization vessel, after degassing, is pressed into a part for vinyl chloride monomer and fatty acid vinyl ester monomer and begins reaction, then on one side remaining vinyl chloride monomer is pressed into in the reaction, on one side implements polyreaction.The ethylene copolymer that obtains like this, also can be used as commercially available product and obtain.For example, in the present invention, as vinyl chloride-vinyl acetate copolymer, can use commodity " Nissin ethylene (Nissin vinyl) " of Nissin Chemical Industry Co., Ltd.

The polymerization initiator used in the production of the ethylene copolymer can be a representative peroxide or azo compound in the art. For example, benzoyl peroxide, azoisobutylvaleronitrile, azobisisobutyronitrile, di-tert-butyl peroxide, tert-butyl perbenzoate, tert-butyl peroctoate, cumene hydroxyperoxide, etc. can be used. The polymerization temperature is 50-140°C, preferably 70-140°C. The number average molecular weight of the obtained ethylene copolymer is preferably 5,000-100,000.

During the polymerization, a non-aromatic solvent is used. Examples include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ethers such as tetrahydrofuran, dioxane, ethylene glycol dimethyl ether, and diethylene glycol dimethyl ether; and esters such as ethyl acetate and butyl acetate. A mixture of two or more solvents may also be used.

In the present invention, when a polyurethane resin and a vinyl copolymer are used together as the binder resin, the content ratio of the polyurethane resin to the vinyl copolymer (solid weight ratio) is preferably in the range of 95:5 to 5:95. Furthermore, from the viewpoints of adhesion to base paper, anti-blocking properties, ink dispersibility, abrasion resistance, and ink followability during foaming, the content ratio is more preferably in the range of 50:50 to 90:10.

In the brightness ink composition of the present invention, the total binder resin content is preferably 30% by weight or less, more preferably 5 to 25% by weight, based on the total weight of the ink composition. By ensuring that the binder resin content falls within this range, a suitable ink viscosity is easily achieved, thereby improving the efficiency of ink production and printing operations.

Specific examples of solvents used in the ink composition of the present invention include: alcohol-based organic solvents such as methanol, ethanol, n-propanol, isopropanol, and butanol; ketone-based organic solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ester-based organic solvents such as methyl acetate, ethyl acetate, propyl acetate, and butyl acetate; aliphatic hydrocarbon-based organic solvents such as n-hexane, n-heptane, and n-octane; and alicyclic hydrocarbon-based organic solvents such as cyclohexane, methylcyclohexane, ethylcyclohexane, cycloheptane, and cyclooctane. Considering the solubility and drying properties of the binder resin, it is preferable to use a mixture of the above-mentioned solvents. These organic solvents are typically used in an amount of 30% by weight or more in the ink composition. Thus, the present invention allows the use of non-aromatic solvents, thereby preventing deterioration of the printing environment.

The brightness ink composition of the present invention may contain a colorant as needed. The colorant used in the present invention may be any of the inorganic and organic pigments commonly used in printing inks and coatings. Examples include inorganic pigments such as titanium oxide and carbon black, and organic pigments such as soluble azo pigments, insoluble azo pigments, azo chelate pigments, condensed azo pigments, copper phthalocyanine pigments, and condensed polycyclic pigments. By adding a colorant to the brightness ink composition containing the various components described above, various brightness effects can be imparted, further enhancing the design and aesthetics of the printed product.

Furthermore, the brightness ink composition of the present invention may contain various hard resins as needed. Examples of hard resins include dimer acid resins, maleic acid resins, petroleum resins, terpene resins, ketone resins, dammar resins, copal resins, and chlorinated polypropylene. Adding a hard resin to the brightness ink composition is expected to improve the adhesion of the ink film to the substrate. Therefore, this is particularly effective when forming a printed layer on an untreated plastic film.

Furthermore, the brightness ink composition of the present invention may contain a crosslinking agent or a wax component as needed for the purpose of improving heat resistance, oil resistance, and abrasion resistance.

Examples of crosslinking agents include alkyl titanate-based and isocyanate-based crosslinking agents. More specifically, examples of alkyl titanate-based crosslinking agents include tetraisopropoxytitanium, tetra-n-butoxytitanium, tetra(2-ethylhexyl)titanium, tetrastearyl titanium, triisopropoxytitanium monostearate, tri-n-butoxytitanium monostearate, diisopropoxytitanium distearate, and di-n-butoxytitanium distearate. Furthermore, examples of isocyanate-based crosslinking agents include aliphatic polyisocyanate compounds, alicyclic polyisocyanate compounds, aromatic aliphatic polyisocyanate compounds, aromatic polyisocyanates, and various biuret compounds and isocyanate compounds. Among these, alkoxytitanium stearate-based compounds are more preferred from the perspective of heat resistance, and isocyanate-based crosslinking agents are also effective from the perspective of improving adhesion to the film.

On the other hand, various known waxes such as polyolefin wax and paraffin wax can be used as the wax.

Furthermore, various ink additives such as a pigment dispersant, a leveling agent, a surfactant, and a plasticizer may be added to the ink composition of the present invention as needed.

The brightness ink composition of the present invention can be produced by mixing the various components described above using known techniques. More specifically, a method can be used in which the brightness material, binder resin, organic solvent, and, if necessary, pigment dispersant, surfactant, etc., are first stirred and mixed, followed by grinding using a grinder such as a bead mill, ball mill, sand mill, attritor, roll mill, or pearl mill, and then the remaining materials are added and mixed.

(Thermal insulating foam paper container material)

The thermally insulating foamed paper container material of the present invention is a material used to manufacture thermally insulating foamed paper containers, characterized by being constructed using the aforementioned brightness ink composition of the present invention. More specifically, as shown in FIG1 , the thermally insulating foamed paper container material of the present invention (hereinafter referred to as the "paper container material") comprises: a base paper 10; a first thermoplastic synthetic resin film 20 covering one side of the base paper 10; a second thermoplastic synthetic resin film 30 covering the other side of the base paper, having a lower melting point than the first thermoplastic synthetic resin film and foamed by heat treatment to form a thermal insulating layer; and a printed layer 40 disposed on at least a portion of the surface of the film 30; the printed layer 40 comprising at least one printed pattern 42 formed from the ink composition of the present invention.

The base paper used to produce the paper container material of the present invention is not particularly limited. However, from the perspective of container weight, a base paper having a basis weight (grammage) in the range of 80 g/ ^m² to 400 g/ ^m² is preferred. Furthermore, from the perspective of foamability during container production, the base paper preferably has a moisture content in the range of approximately 5 to 10% by weight.

The first thermoplastic synthetic resin film (high-MP resin film) and the second thermoplastic synthetic resin film (low-MP resin film) laminated on the base paper can be formed from resin materials commonly known as container materials. For example, films formed from thermoplastic synthetic resins such as stretched and unstretched polyolefins such as polyethylene and polypropylene, polyester, nylon, cellophane, and vinylon can be appropriately selected. However, when manufacturing a container using the container material of the present invention, the low-MP resin film is used so that the outer wall of the container body is formed. Therefore, the melting point of the low-MP resin film must be lower than that of the high-MP resin film forming the inner wall of the container body. For example, as described above in the prior art, a high-melting-point polyethylene film having a melting point of approximately 130°C to 135°C can be used as the first thermoplastic synthetic resin film. Alternatively, a low-melting-point polyethylene film having a melting point of approximately 105°C to 110°C can be used as the low-MP resin film.

However, the various thermoplastic synthetic resin films that can be used in the present invention are not limited to combinations of polyethylene films having different melting points; films formed from other resin materials may be appropriately selected for use. In the present invention, a high-Mp resin film need only not melt or soften when a low-Mp resin film is foamed by heat treatment. In other words, the terms "high melting point" and "low melting point" are described from a relative perspective, and the various resin films are not limited to specific melting points. However, in general, in order to allow hot water to be poured into insulating foamed paper containers for foods such as cup noodles, the melting point of the resin film used as the low-Mp resin film must be above 100°C.

For example, when the inner and outer walls of the container's main body are each formed of polyethylene film, one side of the base paper (the inner wall of the container) must be laminated with a medium-density or high-density polyethylene film, and the other side (the outer wall of the container) must be laminated with a low-density polyethylene film. The thickness of each film laminated to the base paper is not particularly limited. However, the thickness of the low-MP resin film forming the outer wall of the container's main body is preferably set to a sufficient thickness, as the foamed film layer functions as a thermal insulation layer when the film is foamed.

For example, when the outer wall surface of the container body is composed of a low-density polyethylene film, the thickness of the film laminated on the base paper can be 25 to 80 μm. On the other hand, when the inner wall surface of the container body is composed of a medium-density or high-density polyethylene film, the thickness of the film laminated on the base paper is not particularly limited. However, when a heat-insulating foamed paper container is made, it is preferred to appropriately set the thickness of the film to ensure the permeability resistance of the contents. As for the thickness of the film laminated on the base paper, since it varies depending on the resin material of the film used, it is preferred that a person skilled in the art appropriately set it in consideration of the characteristics of the resin material.

The printed layer in the paper container material constructed as described above is formed by surface gravure printing on a low-MP resin film forming the outer wall of the container using the brightness ink composition of the present invention. The structure of the printed layer is not particularly limited; known techniques may be applied. Figure 1 is a schematic cross-sectional view of one embodiment of a paper container material. In the embodiment shown in Figure 1, the printed layer 40 includes a printed pattern 42, such as a decorative pattern, formed on a low-MP resin film 30 using the brightness ink composition of the present invention.

In the past, when a printing layer as shown in FIG1 was formed on a low-Mp resin film using a colored ink, the printing layer hindered the foaming of the low-Mp resin film, and the thickness of the foamed film did not become uniform, and the printed portion was sunken, resulting in a significant height difference with the non-printed portion. However, according to the present invention, the formation of depressions on the printed surface after the low-Mp resin film is foamed can be effectively suppressed. FIG2 is a schematic cross-sectional view showing the state after foaming by heat-treating the paper container material of the present invention shown in FIG1. As shown in FIG2, according to the present invention, since the printing layer has excellent foaming followability, the thickness of the low-Mp resin film (insulating layer 30') after foaming by heat treatment becomes uniform. As a result, with respect to the surface of the printing layer 40, the foamed surface of the film becomes uniform with respect to the non-printed portion, and the formation of bumps and depressions can be suppressed.

FIG3 is a schematic cross-sectional view showing another embodiment of the paper container material of the present invention. The printed layer 40 of the paper container material shown in FIG3 is composed of a base layer 44 formed on a low-MP resin film 30 and a printed pattern 42 formed on the base layer 44. Forming such a printed layer can be achieved by first printing white ink on the entire surface of the film 30 and then pattern-printing a brightness ink. With a paper container material having such a structure, when a printed pattern is formed using conventional brightness ink, even with a base layer of white ink, the printed portion of the brightness ink remains concave, easily creating unevenness on the printed surface. However, according to the present invention, by using a specific brightness ink to form the printed pattern of the printed layer, the ink coating does not significantly hinder the foaming of the low-MP resin film. Therefore, the thermal insulation layer formed by the foaming of the low-MP resin film under heat treatment becomes uniform in thickness, making it easy to obtain a printed surface with fewer unevenness.

FIG4 is a schematic cross-sectional view showing another embodiment of the paper container material of the present invention. The printed layer of the paper container material shown in FIG4 is composed of a base layer 44 formed on a film 30, and a pattern 42 including a first printed portion 42a and a second printed portion 42b formed on the base layer 44. Such a printed layer is formed by initially printing white ink on the entire surface of the film as the base layer 44 on the first layer. Next, the first printed portion 42a is formed by pattern-printing the white ink on the second layer, and a brightness ink is further printed on the non-printed area of the second layer other than the first printed portion 42a formed by the white ink, thereby forming the second printed portion 42b. In this way, a printed layer having a two-layer structure (for example, white ink/white ink and white ink/brightness ink) can be formed, in which the printed pattern 42 including the first printed portion 42a and the second printed portion 42b is formed on the base layer 44. The order of printing the white ink and brightness ink forming the first and second printed patterns of the second layer is not particularly limited.

For the paper container material of the present invention having a structure as shown in Figure 4, in conjunction with Figure 3 and as described above, not only is it easy to obtain a printed surface with fewer bumps, but also because the thickness of the printed layer formed on the low-Mp resin film becomes uniform, it is easier to obtain a printed surface with fewer bumps even after the above-mentioned low-Mp resin film is foamed by heat treatment. From this point of view, it is preferred.

In the present invention, when forming overlapping printed layers as shown in Figures 3 and 4, the white ink used to form the base layer, etc., is not particularly limited. However, the white ink preferably has a composition that significantly inhibits the foaming of the low MP resin film. In one embodiment of the present invention, the white ink contains a binder resin, a white pigment, and a solvent. From the perspectives of concealment and light resistance, titanium dioxide is preferably used as the white pigment. In addition, the binder resin and solvent can be selected from the binder resins and solvents previously exemplified as structural components of the brightness ink composition of the present invention. In one embodiment of the present invention, the binder resin in the white ink is preferably a combination of a polyurethane resin and an ethylene copolymer, and a polyurethane urea resin is more preferably used as the polyurethane resin. The mixing ratio (solids) of the polyurethane resin/ethylene copolymer is not particularly limited, but as a preferred embodiment, a mixing ratio of 90/10 is exemplified. The content (solids) of the binder resin in the white ink is preferably 30% by weight or less, based on the total weight of the ink.

In the present invention, the method for printing the ink composition used to form the printed layer is not particularly limited, and known techniques may be employed. For example, when printing white ink on the entire surface of the film to form a base layer, a coating machine such as a bar coater, a roll coater, or a reverse roll coater may be used.

(Thermal insulating foam paper container)

The thermally insulating foamed paper container of the present invention is characterized by comprising a container body member and a base member, wherein the container body member is formed from the paper container material of the present invention. More specifically, as shown in Figure 5 , the thermally insulating foamed paper container of the present invention comprises a container body 50 formed from the paper container material of the present invention, which is combined with a base member 60 such that the high-MP resin film in the paper container material forms the container's inner wall 50a, and the printed layer on the low-MP resin film forms the container's outer wall 50b. The container is then heat-treated to foam the low-MP resin film.

The molding process of the heat-insulating foamed paper container of the present invention can be implemented by applying well-known techniques. For example, using a commonly used container manufacturing device, the container main body component obtained by first beating the heat-insulating foamed paper container material of the present invention into a predetermined shape according to a mold, and the bottom plate component obtained by similarly beating the bottom plate material into a predetermined shape are assembled into the shape of the container and molded. The assembly molding of the container by the container manufacturing device is implemented in such a manner that the high-Mp resin film of the container main body forms the inner wall surface, the low-Mp resin film forms the outer wall surface, and the laminated surface of the bottom plate component becomes the inner side. After the container is assembled and molded by the container manufacturing device in this way, the low-Mp resin film is foamed by heat treatment to form an insulating layer, thereby obtaining a heat-insulating foamed paper container.

The heating temperature and heating time during the heat treatment used to form the thermal insulation layer vary depending on the properties of the base paper and thermoplastic synthetic resin film used. Those skilled in the art can appropriately determine the optimal combination of heating temperature and heating time for the film used. While not particularly limited, the heat treatment performed during the container molding process generally involves a heating temperature of approximately 100°C to 200°C and a heating time of approximately 20 seconds to 10 minutes. When using low-density polyethylene (70 μm thickness), the preferred heating temperature is 100°C to 130°C and a heating time of approximately 5 to 6 minutes. Any heating method, such as hot air, electric heating, or electron beams, can be used. If heating is performed using hot air or electric heating within a conveyor-equipped transport channel, large quantities of insulating foamed paper cups can be produced inexpensively.

FIG5 is a perspective view showing the structure of a heat-insulating foamed paper container obtained by heat treatment after the container is assembled and formed. In the figure, reference symbol 50 is the container body, and reference symbol 60 is the bottom plate. FIG6 is a schematic cross-sectional view showing an enlarged portion of the container body of the heat-insulating foamed paper container shown in FIG5 , indicated by reference symbol VI. The container body is composed, in order from the outer wall surface 50b of the container, of a printed layer 40, a heat-insulating layer 30' formed of a low-Mp resin film, base paper 10, and a high-Mp resin film 20 forming the inner wall surface of the container. In addition, the layer structure of the container body component of the container shown in FIG6 corresponds to the structure of foaming the paper container material shown in FIG3 .

As shown in Figure 6, the printed layer 40 forming the container surface shown in Figure 5 is composed of a base layer 44 formed of white ink, applied to the entire surface of the thermal insulation layer 30', and a printed pattern 42 formed thereon, comprising a bright ink. Thus, according to the present invention, since the printed layer 40 forming the outer wall of the container body is composed of an ink composition with excellent foaming properties, the printed layer (reference numeral 40 in Figure 3) on the low-Mp resin film (reference numeral 30 in Figure 3) does not hinder the foaming of the film, and the low-Mp resin film forms a uniform thermal insulation layer 30' upon heat treatment. Furthermore, during the foaming of the low-Mp resin film, the printed layer's excellent foaming properties prevent the formation of irregularities on the container surface and cracks in the ink film. As described above, by applying the ink composition of the present invention to form a thermally insulating foam container, a smooth container surface with excellent thermal insulation properties can be achieved.

Example

The present invention will be described in more detail below by way of examples, but the present invention is not limited to these examples. It should be noted that, unless otherwise specified, "parts" and "%" in the examples represent "parts by weight" and "% by weight."

(Preparation Example 1: Preparation of Polyurethane Resin Varnish)

A prepolymer was obtained by adding 313 parts of polypropylene glycol (number-average molecular weight: 2,000), 63 parts of isophorone diisocyanate, and 60 parts of ethyl acetate to a four-necked flask equipped with a stirrer, thermometer, reflux condenser, and nitrogen inlet tube. The mixture was reacted at 90°C under a nitrogen stream for 6 hours. This prepolymer was then chain-extended by adding it dropwise to a mixture of 21 parts of isophorone diamine, 360 parts of ethyl acetate, and 180 parts of isopropyl alcohol. This polyurethane resin varnish (PU varnish) had a solids content of 40%, a viscosity of 200 mPaS at 25°C, and a weight-average molecular weight of 9,000. Molecular weight was measured using a Shodex DS-4 (Showa Denko K.K.) equipped with a UV detector and a refractometer.

(Preparation Example 2: Preparation of Vinyl Chloride-Vinyl Acetate Copolymer Varnish)

A vinyl chloride-vinyl acetate copolymer varnish (PVC-PVAc varnish) for testing was obtained by mixing and dissolving 25 parts of a vinyl chloride-vinyl acetate copolymer (SOLBIN TA5R, manufactured by Nissin Chemical Industry Co., Ltd.) in 75 parts of ethyl acetate.

(Example 1)

1. Modulation of brightness ink

A brightness ink was obtained by mixing 45 parts of the polyurethane resin varnish obtained in Preparation Example 1, 8 parts of the vinyl chloride-vinyl acetate copolymer varnish (PVC-PVAc varnish) obtained in Preparation Example 2, 15 parts of a non-leafing aluminum paste (aluminum paste 1100TA manufactured by Toyo Aluminum Co., Ltd., solid content 65%, particle size 12 μm), 2.5 parts of untreated silica (SYLYSIA 450 manufactured by Fuji Silysia Chemical Ltd., particle size 5.2 μm), and 29.5 parts of a mixed solvent consisting of methylcyclohexane: isopropyl alcohol: ethyl acetate = 40:40:20 (weight ratio), and then stirring for 20 minutes using a homogenizer.

2. Preparation of white ink

12 parts of the polyurethane resin varnish obtained in Preparation Example 1, 19.2 parts of the vinyl chloride-vinyl acetate copolymer varnish (PVC-PVAc varnish) obtained in Preparation Example 2, 40 parts of titanium oxide (TITANIX JR800 (manufactured by TAYCA Co., Ltd.), and 28.8 parts of a mixed solvent consisting of methylcyclohexane: isopropyl alcohol: ethyl acetate = 40:40:20 (weight ratio) were mixed and then dispersed and kneaded using a sand mill to obtain a white ink for the base.

3. Formation of the printing layer

Using the white ink and brightness ink prepared above, respectively, a gravure proofreading machine was used to form overlapping printed layers of white ink/brightness ink having the structure of a printed layer as shown in Figure 3 on the above-mentioned low-melting-point film of a paper container material, which had previously been laminated with a high-melting-point polyethylene film (melting point 133°C) on one surface of the base paper and a low-melting-point polyethylene film (melting point 106°C) on the other surface of the base paper.

4. Evaluation

First, the adhesiveness, heat resistance, and friction resistance of the printed layer of the paper container material formed as described above were evaluated by the following evaluation methods.

(Evaluation of Adhesion)

Cellotape (registered trademark) was applied to the printed surface of a paper container material and pressed five times with fingers before being peeled off. Adhesion to the base paper was evaluated by comparing the area where the tape was applied with the area where the ink film had peeled off from the base paper (laminated layer).

A: The ink coating was not peeled off at all.

B: The area where the ink film peeled off from the base paper or the white ink composition was 20 to 50% of the adhesive tape adhesion area.

C: The area where the ink film peeled off from the base paper or the white ink composition exceeded 50% of the adhesive tape adhesion area.

(Evaluation of heat resistance)

Aluminum foil cut to the same size as the printed material was overlapped with the printed surface. The aluminum foil was pressed at a pressure of 2 kg/ ^cm2 for 1 second using a heat seal tester. The heat resistance was evaluated by measuring the minimum temperature at which the bright ink was transferred to the aluminum foil.

A: The minimum temperature is above 160℃

B: The minimum temperature is 140°C or higher and less than 160°C.

C: The minimum temperature is less than 140°C.

(Abrasion resistance)

Using a textile rubbing color fastness tester, a load of 2.5 N/ ^cm2 is applied to the printed surface of the brightness ink, and rubbed with printing paper. Evaluation is performed by the number of times when 20% or more of the entire printed surface is removed.

A: More than 100 times

B: More than 50 times, less than 100 times

C: Less than 50 times

Next, the paper container material with the printed layer formed as described above was heated at 120°C for 5 minutes to foam the low-melting-point film. The printed layer's foaming followability, foam appearance, and sensory odor testing were then conducted according to the following methods. The results are shown in Table 2.

(Evaluation of Foaming Followability)

The printed surface of the low melting point film after foaming was touched with a finger to determine the height difference between the white ink printed portion and the brightness ink printed portion, and the degree of depression of the brightness ink printed portion was evaluated.

A: There is almost no difference in height from the white ink printed part.

B: A slight difference in height from the white ink printed portion is felt.

C: A difference in height from the white ink printed portion is clearly felt.

(Evaluation of Foaming Appearance)

The brightness and appearance of the ink printed surface after the low melting point film was foamed were visually observed, and the degree of ink cracking (cracks) was evaluated based on the area ratio of the cracked portion to the entire printed surface.

A: No ink cracks

B: The total area of ink cracks is 50% of the printed surface

C: The total area of ink cracks is more than 80% of the printed surface

(Sensory odor test)

A 0.2 ^m² sample of bright ink printed material, obtained by foaming a low-melting-point membrane, was placed in a 500 ml Erlenmeyer flask and sealed tightly to produce a sensory odor sample. After allowing the sample to stand in sunlight for 10 days, the odor within the flask was sensory evaluated. The results are shown in Table 1.

A: I didn't detect any odor in the flask.

B: A slight odor is detected in the flask.

C: The odor in the flask was strongly felt.

(Examples 2 to 19, Comparative Examples 1 to 4)

Brightness inks were prepared by blending the components shown in Tables 1 to 3 using the same stirring method and preparation steps as in Example 1. Subsequently, using each brightness ink, a printed layer was formed on a low-melting-point film of a paper container material using the same method as in Example 1. The base layer was formed using the same white ink as in Example 1.

Regarding Tables 1 to 3, details of the luminance materials used in Examples 2 to 19 and Comparative Examples 1 to 4 are as follows.

Floating aluminum paste: Altop 18TH (manufactured by Asahi Kasei Corporation, solid content 80%, particle size 7 μm)

Non-leafing aluminum paste: (Toyo Aluminum Co., Ltd., aluminum paste 1100TA, solids 65%, particle size 12 μm)

Aluminum flakes: Metasheen KM100 (manufactured by Toyo Aluminum Co., Ltd., particle size 12 μm)

Pearl pigment: Iriodin 120BS (Merck Japan Co., Ltd., particle size 5-25 μm)

Treated silica: Sylophobic 200 (Fuji Silysia Chemical Co., Ltd., particle size 3.9 μm)

Untreated silica: (manufactured by Fuji Silysia Chemical Co., Ltd., SYLYSIA 450, particle size 5.2 μm)

Next, similar to Example 1, paper container materials having the printed layers produced in Examples 2 to 19 and Comparative Examples 1 to 4 were used to evaluate the adhesiveness, heat resistance, and friction resistance of each printed layer. Furthermore, similar to Example 1, the paper container materials having the printed layers were heated at 120°C for 5 minutes to foam the low-melting-point film. The printed layers were then evaluated for their foaming followability and appearance, as well as for sensory and odor testing. The evaluation results are shown in Tables 1 to 3.

[Table 1]

[Table 2]

[Table 3]

As is apparent from Tables 1-3, the luminous ink composition of the present invention, which contains a luminous material such as aluminum and silica, is highly suitable as an ink for forming the printed layer of thermally insulating foamed paper containers because the ink coating does not significantly hinder the foaming and following of the low-Mp resin film, and does not produce cracks (fissures) in the ink coating. Furthermore, the printed surface of the foamed low-Mp resin film has minimal height differences between the luminous ink-printed portion and other printed portions, resulting in a generally smooth printed surface, thereby enhancing the container's design and aesthetic appeal. Furthermore, because the luminous ink-printed portion does not significantly hinder the foaming of the low-Mp resin film, a uniform thermal insulation layer can be formed through foaming, resulting in excellent heat resistance. Similar results were achieved when the paper container material of the present invention was used as a container body and the container was actually molded. Furthermore, Comparative Examples 1-4 achieved excellent results in the evaluation of foam appearance. However, in the evaluation of foam following performance, significant height differences were observed on the printed surface, indicating poor foam following performance. That is, the reason for the excellent foam appearance results in Comparative Examples 1 to 4 is interpreted to be that the ink coating further inhibits the foaming of the low-melting-point film.

It is apparent from the above description that a wide variety of embodiments can be constructed without departing from the spirit and scope of the present invention, and the present invention is not limited to the specific embodiments thereof except as defined in the claims.

Claims (5)

1. A brightness ink composition for forming a printing layer on the surface of a second thermoplastic synthetic resin film of a heat-insulating foamed paper container material having a base paper, a first thermoplastic synthetic resin film covering one side of the base paper, and a second thermoplastic synthetic resin film covering the other side of the base paper, wherein the second thermoplastic synthetic resin film has a lower melting point than the first thermoplastic synthetic resin film and foams under heat treatment to form a heat-insulating layer. The ink composition comprises a brightness material, silica, a binder resin, and a solvent. The brightness material comprises a non-floating aluminum paste with a particle size of 5–40 μm, and the solid content of the aluminum paste is 2–30% by weight, based on the total weight of the brightness ink composition. The silica has a particle size of 2–20 μm, and the silica content is 1.0–3.5% by weight, based on the total weight of the brightness ink composition. The adhesive resin contains polyurethane resin and ethylene copolymer. 2. The brightness ink composition according to claim 1, wherein, in the adhesive resin, the ratio of the polyurethane resin to the ethylene copolymer is 95:5 to 5:95, calculated by solid weight. 3. The brightness ink composition according to claim 1, characterized in that it further contains a colorant. 4. A thermally insulating foamed paper container material, comprising a base paper, a first thermoplastic synthetic resin film covering one side of the base paper, a second thermoplastic synthetic resin film covering the other side of the base paper, and a printed layer disposed on at least a portion of the surface of the second thermoplastic synthetic resin film, wherein the second thermoplastic synthetic resin film has a lower melting point than the first thermoplastic synthetic resin film and foams under heat treatment to form a thermally insulating layer. The printed layer comprises at least one printed pattern formed by the brightness ink composition according to any one of claims 1 to 3. 5. A heat-insulating foamed paper container, which is obtained as follows: The container body and the bottom plate are formed by combining the container body component and the bottom plate component made of the heat-insulating foamed paper container material as described in claim 4, with the first thermoplastic synthetic resin film forming the inner wall surface and the second thermoplastic synthetic resin film forming the outer wall surface. The container is then heated to cause the second thermoplastic synthetic resin film to foam.