JP7533676B1 - Packaging material and method for manufacturing the same - Google Patents

Abstract

[Problem] The present invention provides a packaging material that is excellent in substrate adhesion, appearance, light-shielding properties, and hot lamination strength. [Solution] A packaging material having a substrate, a white printed layer, a light-shielding printed layer, an adhesive layer, and a sealant in this order, wherein the white printed layer contains a white pigment, the light-shielding printed layer contains at least one pigment selected from the group consisting of carbon black, aluminum particles, iron oxide, and zinc oxide, the white printed layer and the light-shielding printed layer contain a urethane resin, the urethane resin contains a constituent unit derived from a polyester polyol that is a condensate of a dibasic acid and a diol, and the dibasic acid contains at least one selected from the group consisting of sebacic acid, succinic acid, and dimer acid. [Selected Figures] None

Description

The present invention relates to packaging materials and methods for manufacturing packaging materials.

Packaging materials may contain light-blocking materials such as aluminum foil, aluminum-deposited film, milky film, and black film in order to prevent deterioration of the contents due to light. However, the use of aluminum foil and aluminum-deposited film has issues such as a large amount of _CO2 emissions during production, which places a heavy burden on the environment, and the difficulty of recycling the packaging material, and the use of milky film and black film has issues such as the loss of design of the packaging material. For this reason, in recent years, there have been an increasing number of cases in which light-blocking properties are imparted to packaging materials by using a printed layer that uses a light-blocking ink containing titanium oxide, carbon black, or aluminum particles.

For example, Patent Document 1 discloses a packaging material including a printed layer consisting of a white ink layer and a gray ink layer, which is said to have good light-shielding properties, whiteness, and lamination strength without the use of an aluminum compound, but has problems with adhesion to substrates without an isocyanate compound. Patent Document 2 discloses a packaging material including a concealing layer using silver ink made of aluminum paste and two overlapping white solid layers, which is said to have good light-shielding properties and concealing properties, but there is a concern that the adhesion to substrates and lamination strength may decrease with inks using conventional urethane resins in processes where heat is applied, such as extrusion lamination and retort processing.
In addition, pigments that have light-blocking properties, such as carbon black, aluminum particles, and iron oxide, are generally difficult to disperse in ink, and it is difficult to form and maintain a uniformly dispersed state, which tends to result in poor printability, particularly ink transfer (trapping properties) during overprinting, and therefore poor appearance of the packaging material.

Patent No. 6864774 JP 2022-082716 A

The objective of the present invention is to provide a packaging material that has excellent adhesion to substrates, appearance, light blocking properties, and hot lamination strength.

In light of the above problems, the inventors conducted intensive research and discovered that the above problems could be solved by using the packaging material described below, which led to the creation of the present invention.

That is, the present invention relates to the following [1] to [5].

[1] A packaging material having a substrate, a white printed layer, a light-shielding printed layer, an adhesive layer, and a sealant in this order,
The white printing layer contains a white pigment,
the light-shielding printed layer contains at least one pigment selected from the group consisting of carbon black, aluminum particles, iron oxide, and zinc oxide,
the white printed layer and the light-shielding printed layer contain a urethane resin,
the urethane resin contains a structural unit derived from a polyester polyol which is a condensation product of a dibasic acid and a diol,
The packaging material, wherein the dibasic acid comprises at least one selected from the group consisting of sebacic acid, succinic acid, and dimer acid.

[2] The packaging material described in [1], wherein the dibasic acid includes sebacic acid.

[3] The packaging material according to claim [1] or [2], wherein the white printed layer and/or the light-shielding printed layer contains a cured product derived from an isocyanate-based curing agent.

[4] A method for producing a packaging material having a substrate, a white printed layer, a light-shielding printed layer, an adhesive layer, and a sealant in this order, comprising:
A step of forming a white printing layer by gravure printing or flexographic printing with white ink;
and forming a light-shielding printed layer by gravure printing or flexographic printing a light-shielding ink on the white printed layer,
the light-shielding ink contains at least one selected from the group consisting of carbon black, aluminum particles, iron oxide, and zinc oxide;
the white ink and the light-shielding ink contain a urethane resin,
the urethane resin contains a structural unit derived from a polyester polyol which is a condensation product of a dibasic acid and a diol,
The method for producing a packaging material, wherein the dibasic acid comprises at least one selected from the group consisting of sebacic acid, succinic acid, and dimer acid.

[5] The method for producing a packaging material described in [4], wherein the amount of light-shielding ink applied by printing is 0.5 g/ ^m2 or more and less than 5 g/ ^m2 .

The present invention makes it possible to provide a packaging material that has excellent adhesion to substrates, appearance, light blocking properties, and hot lamination strength.

The following describes in detail the embodiments of the present invention. However, the following description of the components is merely an example (representative example) of the embodiment of the present invention, and the present invention is not limited to these contents as long as it does not exceed the gist of the invention.

The packaging material of the present invention will be described in detail below.
The packaging material of the present invention is a packaging material having a base material, a white printed layer, a light-shielding printed layer, an adhesive layer, and a sealant, in this order, wherein the white printed layer contains a white pigment, the light-shielding printed layer contains at least one selected from the group consisting of carbon black, aluminum particles, iron oxide and zinc oxide, the white printed layer and the light-shielding printed layer contain a urethane resin, the urethane resin contains a structural unit derived from a polyester polyol, which is a condensation product of a dibasic acid and a diol, and the dibasic acid contains at least one selected from the group consisting of sebacic acid, succinic acid and dimer acid.
It is believed that by providing the white printed layer and the light-shielding printed layer with the above-mentioned components, the affinity between the ink interfaces is improved, resulting in good trapping properties and good hot lamination strength.

In this specification, the printed layers that do not contain light-blocking pigments are referred to as "other ink layers" in contrast to the "white printed layer" and "light-blocking printed layer" that have light-blocking properties. In addition, the white printed layer, the light-blocking printed layer, and the other ink layers are collectively referred to as "printed layers."

<Packaging materials>
The packaging material of the present invention is a packaging material having a structure in which a base material, a white printed layer, a light-shielding printed layer, an adhesive layer, and a sealant are laminated in this order from the outer layer side. Specific examples of the laminate structure can be exemplified below, in order from the outer layer side (left side). In the following structure notation, "/" means the boundary between each layer.
(1) Substrate/white printed layer/light-shielding printed layer/adhesive layer/sealant (2) Substrate/white printed layer/light-shielding printed layer/adhesive layer/intermediate substrate layer/adhesive layer/sealant (3) Substrate/other ink layer/white printed layer/light-shielding printed layer/adhesive layer/sealant (4) Substrate/white printed layer/other ink layer/light-shielding printed layer/adhesive layer/sealant (5) Substrate/white printed layer/light-shielding printed layer/other ink layer/adhesive layer/sealant (6) Substrate/other ink layer/white printed layer/light-shielding printed layer/adhesive layer/intermediate substrate layer/adhesive layer/sealant (7) Substrate/white printed layer/other ink layer/light-shielding printed layer/adhesive layer/intermediate substrate layer/adhesive layer/sealant (8) Substrate/white printed layer/light-shielding printed layer/other ink layer/adhesive layer/intermediate substrate layer/adhesive layer/sealant Although the layer configuration can be selected arbitrarily, it is preferable that the light-shielding printed layer be visible from the outside (substrate side).

<White printing layer, light-shielding printing layer>
The packaging material of the present invention has a white printed layer and a light-shielding printed layer between the substrate and the sealant. The white printed layer and the light-shielding printed layer may be provided on the entire surface of the substrate, or may be provided on the substrate. The white printed layer and the light-shielding printed layer of the packaging material of the present invention may be formed on a part of the surface of the packaging material. Also, as described above, an ink layer may be further formed. The packaging material of the present invention further comprises a white printed layer containing a white pigment, and a light-shielding printed layer containing a urethane resin and carbon black. The ink contains at least one pigment selected from the group consisting of aluminum particles, iron oxide, and zinc oxide.

(white ink)
The white print layer can be formed by printing a white ink. The white ink can be produced by dissolving and/or dispersing a white pigment such as titanium oxide, zinc oxide, zinc sulfide, barium sulfate, calcium carbonate, or the like, and a urethane resin in an organic solvent.
As the white pigment, titanium oxide is preferred from the viewpoints of coloring power, shielding properties, and light-shielding properties.

(Light-blocking ink)
The light-shielding printed layer can be formed by printing a light-shielding ink. The light-shielding ink can be produced by dissolving and/or dispersing a light-shielding pigment and a urethane resin in an organic solvent.
From the viewpoint of achieving both sufficient light-shielding properties and adhesion to the substrate, the amount of the light-shielding ink applied by printing is preferably 0.5 g/ ^m2 or more and less than 5 g/ ^m2 immediately after application, more preferably 0.6 g/ ^m2 or more and 4.9 g/ ^m2 or less, and even more preferably 0.7 g/ ^m2 or more and 4.5 g/ ^m2 or less, or 4 g/ ^m2 or less.

(Light-blocking pigment)
The light-shielding printed layer contains at least one light-shielding pigment selected from the group consisting of carbon black, aluminum particles, iron oxide, and zinc oxide. The light-shielding pigment may be used alone or in combination of two or more. The content of the light-shielding pigment in the light-shielding printed layer (i.e., the content of the light-shielding pigment in the total solid content of the light-shielding ink) is preferably 20 to 65 mass% of the total mass of the light-shielding printed layer (total solid content of the light-shielding ink), more preferably 35 to 63 mass%, and even more preferably 45 to 60 mass%. By making the content of the light-shielding pigment in the light-shielding printed layer 20% or more, the light-shielding properties are improved. By making the content 65% or less, the laminate properties are improved.

(Carbon Black)
Specifically, the carbon black is preferably C.I. Pigment Black 7. The average particle size of the carbon black is preferably 20 to 120 nm, more preferably 23 to 100 nm, and even more preferably 25 to 100 nm. When the average particle size of the carbon black is within the above range, good pigment dispersibility and a vivid hue can be obtained. Here, the above average particle size is an arithmetic mean size determined by observing the carbon black particles under an electron microscope.

(Aluminum particles)
The aluminum particles are preferably aluminum flakes. The aluminum flakes may be either leafing or non-leafing metal flakes. The metal flakes have a higher fatty acid adsorbed on the metal surface, and among these, a fatty acid having a carbon number of 12 to 18 is preferably adsorbed on the metal surface, and a fatty acid having a carbon number of 16 to 18 is more preferably adsorbed on the metal surface. Suitable examples of the higher fatty acid include lauric acid, palmitic acid, stearic acid, oleic acid, vaccenic acid, elaidic acid, linoleic acid, and linolenic acid. Stearic acid and oleic acid are particularly preferred. Metal flakes that have been surface-treated with a resin may also be used.

(iron oxide, zinc oxide)
As the light-shielding pigment, zinc oxide and/or iron oxide can be used. The average particle size (primary particle size) of zinc oxide is preferably 0.01 to 1 μm, and more preferably 0.01 to 0.7 μm. The average particle size (primary particle size) of iron oxide is preferably 0.01 to 1 μm, and more preferably 0.1 to 0.7 μm.

(Coloring Agent)
The light-shielding printed layer may contain a colorant. Examples of the colorant include dyes, pigments, and other colorants. Among them, it is preferable to contain a pigment, and the pigment may be either an inorganic pigment or an organic pigment. Examples of inorganic pigments include yellow lead, titanium yellow, red iron oxide, cadmium red, ultramarine, and cobalt blue, and examples of organic pigments include soluble azo, insoluble azo, azo, phthalocyanine, halogenated phthalocyanine, anthraquinone, anthranthrone, dianthraquinonyl, anthrapyrimidine, perylene, perinone, quinacridone, thioindigo, dioxazine, isoindolinone, quinophthalone, azomethine azo, flavanthrone, diketopyrrolopyrrole, isoindoline, and indanthrone pigments. In addition, any pigment indicated by the C.I. Pigment Number in the Color Index may be used.

(urethane resin)
The urethane resin contained in the white printed layer and the light-shielding printed layer contains a constituent unit derived from a polyester polyol, which is a condensate of a dibasic acid and a diol, and the dibasic acid contains at least one selected from the group consisting of sebacic acid, succinic acid, and dimer acid. The urethane resin contained in the white printed layer and the urethane resin contained in the light-shielding printed layer may be the same or different, but from the viewpoint of trapping properties, it is preferable that the urethane resin of each layer contains a constituent unit derived from the same dibasic acid. In addition, from the viewpoint of hot lamination strength, it is more preferable that the urethane resin of each layer contains a constituent unit derived from sebacic acid, and it is even more preferable that the ratio of the constituent unit derived from sebacic acid is the highest in the dibasic acid constituting the urethane resin of each layer.

The urethane resin is not limited to the following, but examples thereof include urethane resins obtained by reacting a urethane prepolymer obtained by reacting a polyisocyanate with a polyol, and then reacting a chain extender such as a polyamine and, if necessary, a reaction terminator, etc. The urethane resin may have urea bonds in addition to urethane bonds.
In order to obtain a structural unit derived from a polyester polyol which is a condensation product of a dibasic acid and a diol, a polyester polyol which is a condensation product of a dibasic acid and a diol is used as the polyol.

The urethane resin content is preferably 5 to 50% by mass, and more preferably 10 to 40% by mass, out of 100% by mass of the white ink. Also, the urethane resin content is preferably 5 to 90% by mass, and more preferably 10 to 80% by mass, out of 100% by mass of the white printed layer. Having the urethane resin content in this range results in good adhesion to the substrate.

The content of the urethane resin is preferably 5 to 50% by mass, and more preferably 10 to 40% by mass, of 100% by mass of the light-shielding ink. Also, the content is preferably 10 to 90% by mass, and more preferably 20 to 80% by mass, of 100% by mass of the light-shielding printed layer. Having the urethane resin content in this range results in good adhesion to the substrate.

(Polyisocyanate)
The polyisocyanate preferably contains a diisocyanate. Examples of the diisocyanate include aliphatic diisocyanates such as tetramethylene diisocyanate, isopropylene diisocyanate, methylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate; cyclohexane-1,4-diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate, lysine diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, methylcyclohexane diisocyanate, m-tetramethylxylylene diisocyanate, and dimers in which the carboxyl groups of dimer acids are converted to isocyanate groups. alicyclic diisocyanates such as diisocyanates; and aromatic diisocyanates such as α,α,α',α'-tetramethylxylylene diisocyanate, 1,5-naphthylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyldimethylmethane diisocyanate, 4,4'-dibenzyl isocyanate, dimethyldiphenylmethane diisocyanate, tetramethyldiphenylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, m-xylylene diisocyanate, p-xylylene diisocyanate, o-xylylene diisocyanate, and 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate. Among these, from the viewpoints of easy reaction control and good balance of the performance of the resulting urethane resin, alicyclic or araliphatic diisocyanates are preferred, and isophorone diisocyanate and α,α,α',α'-tetramethylxylylene diisocyanate are particularly preferred. At least one diisocyanate may be used, or two or more diisocyanates may be used in combination.

(Polyol)
The polyol is essentially a polyester polyol, which is a condensate of a diol and a dibasic acid including at least one selected from the group consisting of sebacic acid, succinic acid, and dimer acid. In addition, polyester polyols not including the dibasic acid, polyether polyols, polycarbonate polyols, and polyolefin polyols can be used in combination. The content of the polyester polyol-derived structural unit in the total mass of the urethane resin is preferably 50% by mass or more (main component), more preferably 60% by mass or more, and even more preferably 70% by mass or more. In addition, it is particularly preferable that the dibasic acid is sebacic acid.

The number average molecular weight of the polyol is preferably 500 to 10,000. Here, the number average molecular weight of the polyol is calculated from the hydroxyl value, which is the amount of hydroxyl groups in 1 g of resin calculated by esterifying or acetylating the hydroxyl groups in the resin and back titrating the remaining acid with an alkali, converted into mg of potassium hydroxide, and is a value measured according to JIS K0070. When the number average molecular weight of the polyol is 10,000 or less, the ink has excellent blocking resistance to plastic substrates. Also, when the number average molecular weight of the polyol is 500 or more, the flexibility of the urethane resin coating is excellent, and the ink has excellent adhesion to plastic films. For these reasons, the number average molecular weight of the polyol is more preferably 1,000 to 5,000.

The polyol is preferably a diol. A diol is a compound having two hydroxyl groups in one molecule. Examples of the diol include polyester polyol, polyether diol, polycarbonate, polybutadiene glycol, and other polyols. At least one diol may be used, and two or more diols may be used in combination.

(Polyester polyol)
The polyester polyol has as its essential component a polyester polyol which is a condensate of a dibasic acid including at least one selected from the group consisting of sebacic acid, succinic acid, and dimer acid with a diol, but it is also possible to use other polyester polyols in combination.

Diols suitable for use in polyester polyols include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2-methyl-1,3-propanediol, 3,3,5-trimethylpentanediol, 2,4-diethyl-1,5-pentanediol, 1,12-octadecanediol, 1,2-alkanediol, 1,3-alkanediol, 1-monoglyceride, 2-monoglyceride, 1-monoglycerin ether, 2-monoglycerin ether, dimer diol, and hydrogenated dimer diol. In addition, it is preferable to use a combination of a linear diol such as ethylene glycol, 1,4-butanediol, or 1,3-propanediol with a branched diol such as propylene glycol, neopentyl glycol, or 3-methyl-1,5-pentanediol. The linear diol imparts crystallinity, while the branched diol imparts flexibility, and the balance between these improves the adhesion between the ink and the plastic substrate and the solubility of the ink composition in the solvent.

The dibasic acid used in the polyester polyol must contain at least one selected from the group consisting of sebacic acid, succinic acid, and dimer acid, but other suitable examples include adipic acid, phthalic anhydride, isophthalic acid, terephthalic acid, maleic acid, fumaric acid, oxalic acid, malonic acid, pimelic acid, azelaic acid, suberic acid, glutaric acid, 1,4-cyclohexyl dibasic acid, and hydrogenated dimer acid. Of the total mass of the dibasic acid, it is preferable that at least one selected from the group consisting of sebacic acid, succinic acid, and dimer acid is contained in an amount of 5 mass% or more, more preferably 10 mass%, and even more preferably 20 mass%. Of these, it is preferable that the dibasic acid contains at least sebacic acid.

Furthermore, a polyol having three or more hydroxyl groups and/or a polycarboxylic acid having three or more carboxyl groups can be used in combination as a raw material for the polyester polyol.

When used in a light-shielding printed layer, the amount of constituent units of sebacic acid in the total mass of the dibasic acid is preferably 20 mass% or more, more preferably 30 mass% or more, and even more preferably 40 mass% or more.
When used in a white print layer, the amount of constituent units of sebacic acid in the total mass of the dibasic acid is preferably 20% by mass or more, more preferably 40% by mass or more, and even more preferably 60% by mass or more.

(Chain extender)
The chain extender is preferably a polyamine. Suitable examples of the polyamine include, but are not limited to, ethylenediamine, propylenediamine, hexamethylenediamine, isophoronediamine, dicyclohexylmethane-4,4'-diamine, and diamines obtained by converting the carboxyl groups of dimer acid to amino groups. These can be used alone or in combination of two or more.

Amino acids can also be used as chain extenders. An amino acid is a compound that has both an amino group and an acidic functional group in one molecule, and suitable examples include glutamine, asparagine, lysine, diaminopropionic acid, ornithine, diaminobenzoic acid, and diaminobenzenesulfonic acid. During the synthesis of the urethane resin, there is a high probability that the acidic group will not react with the isocyanate group, so the acidic group remains in the urethane resin and the acid value can be maintained.

(Reaction stopper)
In the case of a urethane resin that can be produced only by the urethanization step, it is preferable to use a monoalcohol or a monoamine as the reaction terminator, and in the case of a urethane resin that is produced by carrying out a urethanization reaction step in addition to the urethanization step, it is preferable to use a monoamine.
The monoalcohol is preferably a substituted or unsubstituted alcohol, and suitable examples thereof include methanol, ethanol, n-propanol, isopropyl alcohol, and 1-butanol.
The monoamine is preferably a substituted or unsubstituted monoamine, and suitable examples thereof include n-butylamine, n-dibutylamine, octylamine, diethylamine, monoethanolamine, monopropanolamine, diethanolamine, dipropanolamine, etc. As the reaction terminator, the compounds exemplified as the chain extender can also be used, and at least one of them may be used, or two or more of them may be used in combination.

In the production of a urethane prepolymer having an isocyanate group at its end obtained by reacting a polyisocyanate with a polyol, the molar equivalent ratio of NCO of the polyisocyanate to OH of the polyol (molar equivalent of NCO of the polyisocyanate/molar equivalent of OH of the polyol compound) is preferably 1.3 to 3, more preferably 1.5 to 2.

The urethane resin preferably has active hydrogen groups such as hydroxyl groups and/or amino groups. This is to obtain reaction sites with the isocyanate-based curing agent described below. When the urethane resin has hydroxyl groups, the hydroxyl value is preferably 0.5 to 30 mgKOH/g, more preferably 1 to 20 mgKOH/g, and even more preferably 2 to 15 mgKOH/g. When the urethane resin has amino groups, the amine value is preferably 0.1 to 15 mgKOH/g, and even more preferably 1 to 12 mgKOH/g. On the other hand, the acid value of the urethane resin is preferably 5 mgKOH/g or less, and even more preferably 3 mgKOH/g or less. This is because acid groups are difficult to react with the isocyanate-based curing agent described below.

The mass average molecular weight of the urethane resin is preferably 5,000 to 100,000, more preferably 7,000 to 90,000, and even more preferably 10,000 to 80,000. When the urethane resin has the above mass average molecular weight, the printed layer becomes a strong film by crosslinking with the curing agent described below, and sufficient hot lamination strength is obtained.
The mass average molecular weight of the present invention and the molecular weight distribution (Mw/Mn) described later can be measured by gel permeation chromatography (GPC). As an example, Water2690 (manufactured by Waters Corporation) or HLC-8220 (manufactured by Tosoh Corporation) can be used as a GPC device, and PLgel, 5 μm, MIXED-D (manufactured by Polymer Laboratories) or TSKgel Super AW series (manufactured by Tosoh Corporation) can be used as a column. Tetrahydrofuran, 1,2,4-trichlorobenzene, N,N-dimethylformamide (with 0.01N lithium bromide added), etc. can be used as a developing solvent, and the flow rate is preferably 0.5 to 1.5 milliliters/minute. An RI detector or the like can be used for detection, and the measurement can be performed under conditions such as a sample injection concentration of 0.5 to 1.5 milligrams/milliliter and an injection amount of 0.1 to 1.0 microliters. The mass average molecular weight can be determined as a polystyrene equivalent value.

(Molecular Weight Distribution (Mw/Mn) of Urethane Resin)
The molecular weight distribution (Mw/Mn) of the urethane resin is preferably 4 to 12, more preferably 4.5 to 10, and even more preferably 5 to 8. Mw represents the mass average molecular weight, and Mn represents the number average molecular weight. When the molecular weight distribution of the urethane resin is within the above range, the cohesive force and adhesive force are strengthened, and the substrate adhesion and hot lamination strength are improved. Note that Mw, Mn, and Mw/Mn can be determined by gel permeation chromatography (GPC) as described above.

In order to achieve a molecular weight distribution (Mw/Mn) of the urethane resin within the above range, there are methods for appropriately selecting the urethane synthesis raw materials and the solid mass ratio in the urethane resin synthesis, the dripping speed of reactive raw materials such as polyisocyanate in the synthesis reaction, the stirring speed and shape of the stirring blades, and the reaction temperature.

Furthermore, when a chain extension reaction is carried out, it is effective to control the molecular weight distribution within a predetermined range by controlling the dropping speed and temperature range to a certain range, particularly when reacting polyamine with urethane prepolymer. Reaction temperature control is important, and it is preferable to control it to a range of 50 to 130°C in the synthesis of urethane prepolymer, and to control it to a range of 10 to 50°C when reacting polyamine with urethane prepolymer.
In addition, setting the charging ratio of the reaction raw materials to an appropriate ratio is also effective in keeping the molecular weight distribution within a predetermined range. Examples of the charging ratio include the NCO/OH ratio, which is the ratio of the hydroxyl groups of the polyol and hydroxy acid, and the isocyanate groups of the polyisocyanate, and the amino group/NCO ratio, which is the ratio of the amino group of the polyamine and the isocyanate group of the urethane prepolymer. In order to control the molecular weight distribution, it is preferable to use the above-mentioned reaction terminator for the purpose of preventing excessive polymerization reaction.

(Isocyanate-based hardener)
In the packaging material of the present invention, in order to further improve the hot lamination strength and the adhesion to the substrate, the white printed layer and/or the light-shielding printed layer preferably contain a cured product derived from an isocyanate-based curing agent. That is, the white ink forming the white printed layer and/or the light-shielding ink forming the light-shielding printed layer preferably contain an isocyanate-based curing agent. When the urethane resin in the ink has a hydroxyl group, an amino group or other active hydrogen group, the ink crosslinks with the active hydrogen group, and when the urethane resin does not have the active hydrogen group, the ink crosslinks with itself only with the isocyanate-based curing agent, thereby improving the laminate strength.

The mass average molecular weight of isocyanate-based curing agents used in conventional packaging materials is small, less than 500, and they are almost always low-molecular-weight compounds. However, while this is not a problem if the material is simply used as a packaging material, when pearl pigments or metal flakes are included as pigment components, the cohesive strength is insufficient and the properties are not satisfactory. In addition, there are concerns that low-molecular-weight compounds may migrate into the substrate, ink layer, or adhesive layer.

Therefore, in the present invention, the mass average molecular weight of the isocyanate-based curing agent is preferably 500 to 8000, more preferably 600 to 6000, and even more preferably 700 to 4000. Furthermore, the molecular weight distribution (Mw/Mn) of the isocyanate-based curing agent is preferably 2 to 5, even more preferably 2.2 to 4.5, and even more preferably 2.5 to 4. When the mass average molecular weight and Mw/Mn are within the above ranges, it is believed that the cohesive force and adhesive force are strengthened by the action with the urethane resin, improving the substrate adhesion and hot lamination strength.

As an isocyanate-based curing agent, polyisocyanates including adduct type polyisocyanates (adduct bodies), biuret type polyisocyanates (biuret bodies), isocyanurate type polyisocyanates (isocyanurate bodies), etc. are suitable, and examples of adduct bodies, biuret bodies and isocyanurate bodies include adduct bodies obtained by reacting trimethylolpropane or other polyols with diisocyanates, biuret bodies in which diisocyanates are dimerized and linked by biuret bonds, and isocyanurate bodies obtained by the cyclic trimerization reaction of diisocyanates. The diisocyanate may be selected from the above diisocyanates, and among them, tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), hydrogenated diphenylmethane diisocyanate (hydrogenated MDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate, xylylene diisocyanate (XDI), hydrogenated xylylene diisocyanate (hydrogenated XDI), etc. may be preferably used. Adduct type polyisocyanate, biuret type polyisocyanate, and isocyanurate type polyisocyanate may be used in combination, and may also be used in combination with other polyisocyanates.

In order to set the mass average molecular weight and molecular weight distribution (Mw/Mn) of the isocyanate-based curing agent in the above range, it is effective to appropriately set the selection of diisocyanate, polyol, etc., the solid content mass ratio, the dripping speed of reactive raw materials such as polyisocyanate in the synthesis reaction, the stirring speed, the shape of the stirring blade, and the reaction temperature in the isocyanate-based curing agent synthesis. In addition, it is effective to set the dripping speed and temperature range control when reacting polyamine and polyisocyanate to a certain range in order to set the molecular weight distribution in a predetermined range. In addition, setting the charging ratio of the reactive raw materials to an appropriate ratio is also effective in setting the molecular weight distribution in a predetermined range. The charging ratio includes, for example, the NCO/OH ratio, which is the ratio of the isocyanate groups of the polyol and the polyisocyanate, and the amino group/NCO ratio, which is the ratio of the amino group of the polyamine and the isocyanate group of the polyisocyanate. Controlling the reaction temperature is important. In synthesis using polyol and polyisocyanate, it is preferable to control the temperature between 50 and 130°C, and when reacting polyamine and polyisocyanate, it is preferable to control the temperature in the range of 10 to 50°C. In addition, it is preferable to keep the solid content during the reaction at 40 to 80 mass%. As the reaction solvent, it is preferable to use ethyl acetate, normal propyl acetate, or other ester-based organic solvents.

The mass ratio of the urethane resin to the isocyanate-based curing agent (urethane resin:isocyanate-based curing agent) is preferably 99:1 to 60:40, more preferably 98:2 to 65:35, and even more preferably 95:5 to 70:30. When a co-used resin described below is used in addition to the urethane resin, the mass ratio of the total amount of the urethane resin and co-used resin to the isocyanate-based curing agent (total amount of resin:isocyanate-based curing agent) is preferably 99:1 to 60:40, and even more preferably 95:5 to 70:30. Within this range, the effects of crosslinking of the ink and adhesion to the substrate are particularly good, improving substrate adhesion and laminate strength.

<Concomitant Resin>
The white printed layer and/or the light-shielding printed layer preferably contain a co-used resin together with the urethane resin. Examples of the co-used resin include polyolefin resins such as polyethylene resins and chlorinated polypropylene resins, poly(meth)acrylic resins, polyvinyl chloride resins, polyvinyl acetate resins, vinyl chloride-vinyl acetate copolymers, polystyrene resins, styrene-butadiene copolymers, vinylidene fluoride resins, polyvinyl alcohol resins, polyvinyl acetal resins, polyvinyl butyral resins, polybutadiene resins, polyester resins, polyamide resins, alkyd resins, epoxy resins, unsaturated polyester resins, thermosetting poly(meth)acrylic resins, melamine resins, urea resins, phenolic resins, xylene resins, maleic acid resins, cellulose resins such as nitrocellulose, ethyl cellulose, acetyl butyl cellulose, and ethyloxyethyl cellulose, rubber resins such as chlorinated rubber and cyclized rubber, petroleum resins, and natural resins such as rosin and casein.
Among them, at least one resin selected from vinyl chloride copolymer resin, cellulose-based resin and rosin-based resin is preferred, and vinyl chloride copolymer resin is even more preferred.

The vinyl chloride copolymer resin is preferably a vinyl chloride-vinyl acetate copolymer resin, a vinyl chloride-acrylic copolymer resin, a vinyl chloride-vinyl acetate-acrylic copolymer resin, or the like. The mass average molecular weight of the vinyl chloride copolymer resin is preferably 5,000 to 100,000, more preferably 5,000 to 50,000. The content of the constituent units derived from vinyl acetate monomer in 100 mass% of the solid content of the vinyl chloride copolymer resin is preferably 70 to 95 mass%. The glass transition temperature of the vinyl chloride copolymer resin is preferably 50°C to 90°C. The vinyl chloride copolymer resin preferably has a hydroxyl group, and the hydroxyl value is preferably 10 to 200 mgKOH/g. This is because the reactivity with the isocyanate-based curing agent is improved, and the hydroxyl group is preferably derived from a hydroxyl group derived from a vinyl alcohol unit or an acrylic monomer having a hydroxyl group.

In each of the white print layer and the light-shielding print layer, the mass ratio of the urethane resin to the co-used resin (urethane resin:co-used resin) is preferably 95:5 to 30:70, and more preferably 90:10 to 40:60. This is because it improves the adhesion of the ink to the substrate, the coating properties, the laminate strength, etc.

(Liquid medium)
The white ink forming the white printed layer and the light-shielding ink forming the light-shielding printed layer may contain an organic solvent, water, or other liquid medium. Although not limited thereto, suitable organic solvents include toluene and other aromatic organic solvents, methyl ethyl ketone and other ketone-based organic solvents, ethyl acetate, normal propyl acetate, and other ester-based organic solvents, ethanol, isopropanol, normal propanol, and other alcohol-based organic solvents. Water may be contained, and when an organic solvent is used as the main liquid medium, the water content in the ink is preferably 10% by mass or less.

(Additives)
The white ink forming the white printed layer and the light-shielding ink forming the light-shielding printed layer may further contain any additives as necessary, such as fillers, stabilizers, plasticizers, antioxidants, light stabilizers such as ultraviolet absorbers, dispersants, thickeners, drying agents, lubricants, antistatic agents, crosslinking agents, etc.

(Other ink layers)
In the present invention, the other ink layer refers to a printed layer formed from a printing ink that does not contain the above-mentioned light-shielding pigment. The other ink layer may be located between the substrate and the white printed layer, between the white printed layer and the light-shielding printed layer, or between the light-shielding printed layer and the adhesive layer. From the viewpoint of enhancing the design of the packaging material, the other ink layer is also preferably a colored ink layer formed from a colored ink.

Preferable examples of printing inks include conventional screen inks, gravure inks, flexographic inks, inkjet inks, offset inks, and others. For example, printing inks described in JP-A-2005-298618, JP-A-2006-299136, JP-A-2009-249388, JP-A-2013-127038, JP-A-2017-19991, JP-A-2006-131844, JP-A-2013-40248, JP-A-2007-231148, JP-A-2006-257302, and the like can be suitably used. However, the printing inks are not limited to these. Among them, the use of gravure inks, flexographic inks, and inkjet inks is preferred, and the use of gravure inks and/or flexographic inks is even more preferred.

<Substrate>
The substrate serves as the substrate on the outer layer side of the packaging material, and is preferably made of a light-transmitting material so that the printed layer can be visually recognized from the outside.
The substrate is preferably a plastic film, and specific examples thereof include polyolefin resins such as polyethylene (PE) and polypropylene (PP), cyclic polyolefin resins, polystyrene resins, acrylonitrile-styrene copolymer (AS) resins, acrylonitrile-butadiene-styrene copolymer (ABS) resins, poly(meth)acrylic resins, polycarbonate resins, polyvinyl alcohol resins, ethylene-vinyl alcohol copolymers (EVOH), saponified ethylene-vinyl ester copolymers, polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN), polyamide resins such as various nylons (Ny), polyurethane resins, acetal resins, cellulose resins, and polyvinylidene chloride resins (PVDC). The substrate may be uniaxially or biaxially stretched. It may also be a composite film in which two or more of the above resin films are laminated. It may also be in a form in which a metal oxide such as silica or alumina is vapor-deposited.

The thickness of the substrate is not particularly limited and can be set appropriately depending on the application of the packaging material, but it is usually preferably about 5 to 50 μm, and more preferably 10 to 30 μm.

The substrate preferably has a total light transmittance of 85% or more, more preferably 90% or more, as measured in accordance with JIS K7361-1:1997. In addition, the substrate preferably has a haze of 1.5% or less, more preferably 1.0% or less, and even more preferably 0.5% or less, as measured in accordance with JIS K7136:2000.

<Formation of White Printed Layer and Light-Shielding Printed Layer>
The white printed layer and the light-shielding printed layer can be suitably formed on the substrate using the white ink and the light-shielding ink by a printing method such as screen printing, offset printing, flexographic printing, dry offset printing, gravure printing, inkjet printing, etc. Among these, gravure printing or flexographic printing is more preferable.

<Gravure printing>
(Photogravure version)
A gravure plate is a cylindrical metal plate on which recesses for each color are made by engraving, etching, or laser. There are no restrictions on the engraving or laser used, and they can be set arbitrarily to match the pattern. A line count of 100 to 300 lines is appropriately used, and the higher the line count, the finer the printing. The thickness of the printing layer is preferably 0.1 μm to 100 μm.
(Gravure printing machine)
One printing unit in the gravure press is equipped with the gravure plate and doctor blade. There are many printing units, and printing units corresponding to organic solvent-based printing inks and picture inks can be set, and each unit has an oven drying unit. Printing is performed by rotary printing, and a roll-to-roll printing method is used. The type of plate and the type of doctor blade are appropriately selected according to the specifications.

<Flexographic printing>
(Flexographic plate)
Plates used in flexographic printing include photosensitive resin plates that utilize ultraviolet curing with a UV light source, and elastomer material plates that use a direct laser engraving method. Regardless of the method for forming the image part of the flexographic plate, the screening line count of the plate is 75 lpi or more. Any sleeve or cushion tape can be used to attach the plate.
(Flexographic printing machine)
The flexographic printing press includes a CI type multi-color flexographic printing press and a unit type multi-color flexographic printing press, and the ink supply system includes a chamber system and a two-roll system, and an appropriate printing press can be used.

<Lamination processing>
The packaging material of the present invention can be obtained, for example, by providing an adhesive layer on the printed layer of a printed matter obtained by printing an ink on a substrate, and laminating the adhesive layer with a sealant or an intermediate substrate layer. Representative examples of lamination include extrusion lamination, dry lamination, and non-solvent lamination. Extrusion lamination is a method in which an anchor coating agent is applied as an adhesive assistant on the printed layer of a printed matter, and molten polyethylene resin, molten polypropylene resin, or the like is extruded thereon and simultaneously laminated with a sealant. The dry lamination method and non-solvent lamination method are methods in which an adhesive is applied and dried on the printed layer of a printed matter, and then laminated with a sealant by thermocompression. The difference between the dry lamination method and the non-solvent lamination method is whether or not an organic solvent or other volatile medium is contained.

<Adhesive Layer>
The adhesive layer is preferably an anchor coating agent layer made of an anchor coating agent in extrusion lamination, and is preferably a reactive urethane adhesive layer in dry lamination or non-sol lamination.

(Anchor Coating Layer)
The anchor coating agent used as an adhesive in extrusion lamination is selected from, for example, solvent-soluble or water-soluble polyester resins, isocyanate resins, urethane resins, acrylic resins, polyvinyl alcohol resins, ethylene vinyl alcohol resins, vinyl modified resins, epoxy resins, imine resins, oxazoline group-containing resins, modified styrene resins, modified silicone resins, alkyl titanates, etc., which can be used alone or in combination of two or more. In addition, various additives such as curing agents, catalysts, stabilizers, initiators, etc. may be added to the anchor coating agent layer depending on the resin used.

The anchor coating agent layer can usually have a thickness of about 5 nm to 5 μm. An anchor coating agent layer having such a thickness can be formed on the surface of the printing layer with a uniform thickness that suppresses internal stress. The more preferred thickness of the anchor coating agent layer is 10 nm to 1 μm.
In order to improve the coatability and adhesiveness of the anchor coating agent layer, the surface of the printed layer may be subjected to a corona treatment or the like prior to the formation of the anchor coating agent layer.

(Reactive urethane adhesive layer)
The adhesive layer used during dry lamination or non-solvent lamination processing is preferably a reactive urethane-based adhesive layer consisting of a reactive urethane-based adhesive of a polyol base agent and a curing agent which is an isocyanate compound, and in particular, a solvent-free (non-solvent) urethane-based adhesive layer or a dry laminate-type urethane-based adhesive layer containing an organic solvent is preferred.

(Polyol base)
Suitable examples of the polyol used in the polyol base include polyester polyol, polyether polyol, polylactone polyol, polycarbonate polyol, polyolefin polyol, castor oil polyol, hydrogenated castor oil polyol, dimer diol, and hydrogenated dimer diol. Among these, polyester polyol, polyether polyol, castor oil polyol, and hydrogenated castor oil polyol are more preferred, and polyester polyol and castor oil polyol are even more preferred.

The polyol used in the polyol base refers to a resin containing two or more terminal hydroxyl groups, and those having urethane bonds resulting from a reaction with an isocyanate compound are also suitable.

The mass average molecular weight of the polyol base is preferably 2,000 to 100,000, more preferably 10,000 to 80,000, and even more preferably 20,000 to 50,000. The molecular weight distribution (Mw/Mn) of the polyol base is preferably 1.5 to 20.0, and even more preferably 2.0 to 15.0. This is because it improves the leveling properties when applying the adhesive and the adhesion between each layer.

The content of the polyol base in the adhesive layer is preferably 70 to 95% by mass, and more preferably 80 to 90% by mass.

(Polyester polyol)
The polyester polyol is preferably a polyester polyol which is a condensation product of a diol and a dibasic acid.

(Diol)
Suitable examples of the diol include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2-methyl-1,3-propanediol, 3,3,5-trimethylpentanediol, 2,4-diethyl-1,5-pentanediol, 1,12-octadecanediol, 1,2-alkanediol, 1,3-alkanediol, 1-monoglyceride, 2-monoglyceride, 1-monoglycerin ether, 2-monoglycerin ether, dimer diol, and hydrogenated dimer diol. The polyester polyol may be used alone or in combination of two or more. Also usable are diols obtained by ring-opening reaction of cyclic esters (lactones, etc.).

The diol preferably includes both branched diols and linear diols. Here, a linear diol is a diol having two or more atoms, such as alkylene glycol, dialkylene glycol, trialkylene glycol, and other diols. A branched diol is a diol in which at least one hydrogen atom of the hydrocarbon group of an alkylene glycol is substituted with an atom other than a hydrogen atom.

The linear diol imparts crystallinity, while the branched diol imparts flexibility, so the right balance between them makes the urethane adhesive coating tough after the two-part curing process, resulting in high lamination strength and heat resistance.

The branched diols include 2-butyl-2-ethyl-1,3-propanediol (hereinafter also referred to as BEPG), 2-methyl-1,3-propanediol (hereinafter also referred to as MPO), 3-methyl-1,5-pentanediol (hereinafter also referred to as MPD), neopentyl glycol (hereinafter also referred to as NPG), 1,2-propylene glycol (hereinafter also referred to as PG), 2,4-diethyl-1,5-pentanediol, 1,3-butanediol, dipropylene glycol, etc., and at least one branched diol selected from NPG and PG is particularly preferred.

The linear diol is preferably an alkylene glycol, and examples of such compounds include ethylene glycol (also described as EG), diethylene glycol, 1,3-propanediol (also described as 1,3-PD), 1,4-butanediol (also described as 1,4-BD), 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 1,4-butynediol, 1,4-butylenediol, diethylene glycol, and triethylene glycol.
Among these, linear diols having 8 or less carbon atoms, preferably 6 or less carbon atoms, are preferred, such as EG, 1,3-PD, 1,4-BD, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, etc. Furthermore, from the viewpoint of physical properties, EG is particularly preferred.

The branched diol units and the linear diol units may each be present in one polyester polyol, or a polyester polyol containing only branched diol units and a polyester polyol containing only linear diol units may be used as a mixture raw material. Approximately the same effect can be obtained.

(Dibasic acid)
Suitable dibasic acids include adipic acid, phthalic anhydride, isophthalic acid, terephthalic acid, maleic acid, fumaric acid, succinic acid, oxalic acid, malonic acid, pimelic acid, azelaic acid, sebacic acid, suberic acid, glutaric acid, 1,4-cyclohexyl dibasic acid, dimer acid, hydrogenated dimer acid, etc. Among these, adipic acid, succinic acid, and sebacic acid are more preferred, and sebacic acid is even more preferred.

The content of sebacic acid is preferably 10 to 70% by mass, and more preferably 20 to 60% by mass, of the total amount of dibasic acids.

The dibasic acid preferably further contains an aromatic dibasic acid such as isophthalic acid. The content of the aromatic dibasic acid in the total amount of dibasic acids is preferably 25 to 90 mass%, and more preferably 40 to 80 mass%.

In addition, a polyol having three or more hydroxyl groups and a polycarboxylic acid having three or more carboxyl groups can be used in combination as raw materials for polyester polyol.

In addition, a form in which some of the hydroxyl groups of the polyester polyol contain structural units derived from trimellitic anhydride and/or trimellitic ester anhydride is also preferred. Partially acid-modified polyols that have been esterified with trimellitic anhydride and/or trimellitic ester anhydride are suitable. Due to the partial acid modification, the polyols exhibit excellent adhesive strength, hot water resistance, acid resistance, and oil resistance, and there is no deterioration in appearance due to inadvertent bending when stacked after retorting. Furthermore, even when highly acidic or oily foods are filled as the contents of the packaging bag, the decrease in adhesive strength can be suppressed, which contributes to maintaining strength over time.

The polyester polyol may also be a reaction product with a polyisocyanate, in which case it will have a terminal hydroxyl group. As the polyisocyanate, the polyisocyanate described in the explanation of "urethane resin" is preferably used.

(Castor oil polyol)
The castor oil polyol is not particularly limited, and known castor oil, castor oil derivatives, ricinoleic acid, and ricinoleic acid polyols, etc., can be used. One type may be used alone, or two or more types may be used in combination.

Examples of castor oil derivatives include dehydrated castor oil, hydrogenated castor oil, which is a hydrogenated product of castor oil, castor oil fatty acid, dehydrated castor oil fatty acid, castor oil fatty acid condensates, 5 to 50 mole ethylene oxide adducts of castor oil, ricinoleic acid polyol, and castor oil-based polyols.

In particular, from the viewpoint of the stability of the production quality of the polyol, the acid value of the castor oil polyol is preferably in the range of 0.1 to 5.0 mgKOH/g, more preferably in the range of 0.1 to 2.0 mgKOH/g, and even more preferably in the range of 0.1 to 1.0 mgKOH/g. From the viewpoint of various resistances, the content of the castor oil polyol is preferably 3 to 80 mass% based on the total mass of the polyol.

(Polyether polyol)
Suitable examples of polyether polyols include polyalkylene glycols such as polyethylene glycol, polytrimethylene glycol, polypropylene glycol, polytetramethylene glycol, and polybutylene glycol; polyethylene glycol/polypropylene glycol block copolymers; and propylene oxide/ethylene oxide random polyethers. From the viewpoint of coatability due to the viscosity effect during adhesive coating, polyether polyols containing structural units derived from polypropylene glycol are preferred. The number average molecular weight of the polyether glycol is preferably 400 to 10,000, and more preferably 400 to 5,000.

In addition, an addition polymer obtained by addition polymerization of an oxirane compound such as ethylene oxide, propylene oxide, butylene oxide, or tetrahydrofuran to a low molecular weight polyol initiator such as water, ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, or sucrose may be used as the polyether polyol.
Examples of the addition polymer include propylene glycol propylene oxide adducts, glycerin propylene oxide adducts, sorbitol-based propylene oxide adducts, and sucrose-based propylene oxide adducts.

(Isocyanate Compounds)
In the reactive urethane adhesive, the isocyanate compound used as a curing agent is preferably a diisocyanate or a urethane prepolymer which is a reaction product of a diisocyanate and a polyol, and various known aromatic, aliphatic or alicyclic diisocyanates can be used as the diisocyanate. For example, 1,5-naphthylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyldimethylmethane diisocyanate, 4,4'-dibenzyl isocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, tolylene diisocyanate, butane-1,4-diisocyanate, hexamethylene diisocyanate, isopropylene diisocyanate, methylene diisocyanate, 2,2,4-trimethylsilyl diisocyanate, tetra ... Representative examples include methylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, xylylene diisocyanate, isophorone diisocyanate, lysine diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, 1,3-bis(isocyanatemethyl)cyclohexane, methylcyclohexane diisocyanate, m-tetramethylxylylene diisocyanate, and dimer diisocyanate in which the carboxyl group of a dimer acid is converted to an isocyanate group. These can be used alone or in combination of two or more kinds.

The content of the isocyanate compound in the adhesive layer is preferably 5 to 30% by mass, and more preferably 10 to 20% by mass.

There are no limitations on the isocyanate compound that can be used as long as it functions as a curing agent and contains a group that is reactive with the hydroxyl group of the polyol.

As the isocyanate compound, a urethane prepolymer having an isocyanate group at the end can be preferably used. Furthermore, from the viewpoint of preventing yellowing and imparting flexibility to improve adhesion, it is preferable to use aliphatic diisocyanates such as hexamethylene diisocyanate and xylylene diisocyanate, and alicyclic diisocyanates such as isophorone diisocyanate, and from the viewpoint of compatibility with retort resistance, it is preferable to use an adduct such as trimethylolpropane, an isocyanurate, a biuret, or another polyisocyanate compound having three or more functional groups.

In the polyol base and isocyanate compound, the ratio NCO/OH of the isocyanate group derived from the isocyanate compound to the hydroxyl group derived from the polyol used as the polyol base is preferably 1.0 to 8.0, and more preferably 1.5 to 5.0.

<Sealant>
The inner layer of the sealant comes into direct contact with the packaged goods and serves to protect the packaged goods.
In order to make the packaging material into a bag shape, it is preferable that the innermost layer of the sealant has heat sealability. Examples of materials constituting the sealant include polyolefin resins such as low density polyethylene (LDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), ethylene-vinyl acetate copolymer, propylene homopolymer, and ethylene-propylene copolymer, and one or more of these resins can be used. The sealant may be composed of a single layer or may be composed of two or more layers. Note that the sealant is preferably a non-stretched film made of the above resin in order to suppress shrinkage during heat sealing.

The thickness of the sealant is not particularly limited and is set appropriately depending on the application of the packaging material and the type and properties of the packaged item, but is usually preferably 10 to 200 μm. In addition, in the case of pouches (especially retort pouches), the thickness of the sealant is preferably 20 to 150 μm, and more preferably 30 to 100 μm.

<Intermediate Base Material Layer>
The packaging material of the present invention may have an intermediate substrate layer between the light-shielding printed layer and the sealant.
The intermediate substrate layer is a layer that is provided as necessary for the purpose of improving the strength and processing suitability of the packaging material. Examples of the constituent material of the intermediate substrate layer include a plastic film-like substrate. The substrate can be the same as the substrate used for the substrate layer described above.

<Manufacturing method of packaging material>
The method for producing a packaging material of the present invention is a method for producing a packaging material having a substrate, a white printed layer, a light-shielding printed layer, an adhesive layer, and a sealant in this order, and includes a step of forming a white printed layer by gravure printing or flexographic printing a white ink, and a step of forming a light-shielding printed layer by gravure printing or flexographic printing the light-shielding ink on the white printed layer, wherein the light-shielding ink contains at least one type selected from the group consisting of carbon black, aluminum particles, iron oxide, and zinc oxide, the white ink and the light-shielding ink contain a urethane resin, the urethane resin contains a structural unit derived from a polyester polyol which is a condensation product of a dibasic acid and a diol, and the dibasic acid contains at least one type selected from the group consisting of sebacic acid, succinic acid, and dimer acid.

From the viewpoint of achieving both sufficient light-shielding properties and adhesion to the substrate, in the above-mentioned manufacturing method, the amount of the light-shielding ink applied by printing is preferably 0.5 g/ ^m2 or more and less than 5 g/ ^m2 , more preferably 0.6 g/ ^m2 or more and 4.9 g/ ^m2 or less, and even more preferably 0.7 g/ ^m2 or more and 4.5 g/ ^m2 or less, or 4 g/ ^m2 or less.

Furthermore, if necessary, other ink layers may be formed on either the substrate, the white printed layer, or the light-shielding printed layer to improve the design. The adhesive layer may be formed by coating on the printed layer, or may be formed by coating on the sealant.

A preferred embodiment of the method for producing a packaging material of the present invention is, for example, an embodiment in which an adhesive is applied onto the printed layer, and then a sealant is bonded to the printed layer. If the packaging material further has an intermediate substrate layer, a preferred embodiment includes a step of first bonding the printed layer and the intermediate substrate layer with an adhesive, and then bonding the intermediate substrate layer and the sealant to the printed layer. The configuration is arbitrary and is not particularly limited.

The packaging material thus obtained can be cut to a predetermined size, and the edges of the sealants are joined together and heat-sealed to form a bag, to produce a packaging bag. The heat-sealing temperature is preferably 50 to 250°C, and more preferably 80 to 180°C. The heat-sealing pressure is preferably 1 to 5 kg/ ^cm2 . One sheet of packaging material may be folded and the edges may be heat-sealed, or two or more sheets of packaging material may be heat-sealed. Furthermore, the packaging bag made of the packaging material may be one in which all openings are heat-sealed after the contents are packaged.

The present invention will be described in detail below with reference to examples. However, the following embodiments are merely examples of the present invention, and the present invention is not limited to these examples. In the present invention, parts and percentages are as follows:
Unless otherwise noted, all parts by mass and percent by mass are used.
Examples 22 and 23 are reference examples.

<Method for measuring amine value>
The amine value is the number of milligrams of potassium hydroxide equivalent to the amount of hydrochloric acid required to neutralize the amino groups contained in 1 g of resin, and was determined according to the following method in accordance with JIS K0070.
0.5 to 2 g of sample was precisely weighed out (sample solid content: Sg). 50 mL of a mixed solution of methanol/methyl ethyl ketone = 60/40 (mass ratio) was added to the precisely weighed sample to dissolve it. Bromophenol blue was added to the obtained solution as an indicator, and the obtained solution was titrated with 0.2 mol/L ethanolic hydrochloric acid solution (titer: f). The point at which the color of the solution changed from green to yellow was set as the end point, and the titration amount (A mL) at this time was used to calculate the amine value according to the following (Equation 1).
(Formula 1) Amine value = (A x f x 0.2 x 56.108) / S [mg KOH / g]

(Mass average molecular weight Mw, number average molecular weight Mn and molecular weight distribution Mw/Mn)
The mass average molecular weight Mw, number average molecular weight Mn and molecular weight distribution Mw/Mn were measured using a GPC (gel permeation chromatography) device (HLC-8220 manufactured by Tosoh Corporation) and polystyrene as a standard substance. The measurement conditions are shown below.
Columns: The following columns were used in series connection:
Tosoh Corporation TSKgel Super AW2500
Tosoh Corporation TSKgel Super AW3000
Tosoh Corporation TSKgel Super AW4000
Tosoh Corporation TSK gelguard column Super AWH
Detector: RI (differential refractometer)
Measurement conditions: column temperature 40°C
Eluent: tetrahydrofuran Flow rate: 1.0 mL/min

<Method for measuring hydroxyl value>
It was determined according to the method described in JIS K0070.

<Method of measuring acid value>
It was determined according to the method described in JIS K0070.

[Synthesis Example 1-1] (Synthesis of polyester polyol A1)
26 parts of 1,3-propanediol (hereinafter also abbreviated as 1,3-PD), 26 parts of neopentyl glycol (hereinafter also abbreviated as NPG), 48 parts of sebacic acid, and 0.002 parts of tetrabutyl titanate were charged into a round-bottom flask equipped with a stirrer, a thermometer, a water divider, and a nitrogen gas inlet tube, and esterification was carried out for 8 hours at 230° C. under a nitrogen stream while removing water generated by condensation. After confirming that the acid value of the polyester was 15 or less, the degree of vacuum was gradually increased by a vacuum pump to terminate the reaction. As a result, a polyester polyol (A1) having a number average molecular weight of 2000, a hydroxyl value of 56.1 mgKOH/g, and an acid value of 0.3 mgKOH/g was obtained.

[Synthesis Examples 1-2 to 1-7] (Synthesis of Polyester Polyols A2 to A7)
Polyester polyols A2 to A7 were obtained in the same manner as in Synthesis Example 1-1, except that the raw materials and charging ratios were changed to those shown in Table 1.

Comparative Synthesis Example 1-8 (Synthesis of Polyester Polyol A8)
A polyester polyol A8 was obtained in the same manner as in Synthesis Example 1-1, except that the raw materials and charging ratios were changed to those shown in Table 1.

[Synthesis Example 2-1] (Synthesis of polyester-based urethane resin B1)
A four-neck flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube was charged with 23.6 parts of Polyester Polyol A1, 4.68 parts of isophorone diisocyanate (hereinafter also abbreviated as IPDI), 7.5 parts of ethyl acetate, and 0.003 parts of tin 2-ethylhexanoate, and reacted for 6 hours at 120°C under a nitrogen stream, followed by addition of 7.5 parts of propyl acetate and cooling to obtain a solution of a terminal isocyanate prepolymer. Next, the obtained solution of isocyanate-terminated prepolymer was gradually added at room temperature to a mixture of 1.60 parts of isophorone diamine (hereinafter also abbreviated as IPDA), 0.12 parts of dibutylamine (hereinafter also abbreviated as DBA), 34 parts of ethyl acetate and 21 parts of isopropyl alcohol (hereinafter also abbreviated as IPA), and then the mixture was reacted at 50°C for 1 hour to obtain a polyester-based urethane resin B1 solution having a solid content of 30%, a mass average molecular weight of 70,000, an amine value of 4 mgKOH/g and a molecular weight distribution (Mw/Mn) of 5.5.

[Synthesis Examples 2-2 to 2-7] (Synthesis of polyester-based urethane resins B2 to B7)
Polyester-based urethane resins B2 to B7 were obtained in the same manner as in Synthesis Example 2-1, except that the raw materials and charging ratios were changed to those shown in Table 2.

Comparative Synthesis Example 2-8 (Synthesis of Polyester-Based Urethane Resin B8)
A polyester-based urethane resin B8 was obtained in the same manner as in Synthesis Example 2-1, except that the raw materials and charging ratios were changed to those shown in Table 2.

[White Ink Preparation Example 3-1] (Preparation of Ink C1)
35 parts of titanium oxide, 10 parts of urethane resin B1 solution, and 20 parts of a mixed solvent (n-propyl acetate/IPA=70/30 (mass ratio)) were stirred and mixed and dispersed using a sand mill, and then 20 parts of the urethane resin B1 solution and 15 parts of a mixed solvent (propyl acetate/isopropyl alcohol=70/30 (mass ratio)) were stirred and mixed to obtain white ink C1.

[White Ink Preparation Examples 3-2 to 3-8] (Preparation of Inks C2 to C8)
White inks C2 to C8 were obtained in the same manner as in White Ink Preparation Example 3-1, except that the raw materials and charging ratios were changed to those shown in Table 3.
Vinyl chloride-vinyl acetate resin solution (vinyl chloride-vinyl acetate copolymer resin with a hydroxyl value of 140 mg KOH/g and a mass average molecular weight of 50,000, a 30% solids solution)

[Comparative Preparation Examples 3-9 to 3-10] (Preparation of Inks C9 to C10)
White inks C9 to C10 were obtained in the same manner as in White Ink Preparation Example 3-1, except that the raw materials and charging ratios were changed to those shown in Table 3.
Polyether-based urethane resin (mass average molecular weight 70,000, solids content 30% solution)

[Light-shielding ink preparation example 4-1] (Preparation of ink D1)
10 parts of carbon black, 10 parts of urethane resin B1 solution, and 20 parts of a mixed solvent (n-propyl acetate/IPA=70/30 (mass ratio)) were stirred and mixed and dispersed using a sand mill, and then 20 parts of the urethane resin B1 solution and 40 parts of a mixed solvent (propyl acetate/isopropyl alcohol=70/30 (mass ratio)) were stirred and mixed to obtain a light-shielding ink D1.

[Light-shielding ink preparation examples 4-2 to 4-11] (Preparation of inks D2 to D11)
Light-shielding inks D2 to D11 were obtained in the same manner as in Light-shielding ink Preparation Example 4-1, except that the raw materials and charging ratios were changed to those shown in Table 4.
Vinyl chloride-vinyl acetate resin solution (a 30% solids solution of vinyl chloride-vinyl acetate copolymer resin with a hydroxyl value of 140 mg KOH/g and a mass average molecular weight of 50,000)
Zinc oxide: zinc oxide particles (average particle size 200 nm, primary particle size 25 nm, oil absorption 24 ml/100 g)
Iron oxide: iron (III) oxide particles (average particle size 200 nm)

[Comparative Preparation Examples 4-12 to 4-13] (Preparation of Inks D12 to D13)
Light-shielding inks D12 to D13 were obtained in the same manner as in Light-shielding ink Preparation Example 4-1, except that the raw materials and charging ratios were changed to those shown in Table 4.
Polyether-based urethane resin (mass average molecular weight 70,000, solids content 30% solution)

[Example 1] (Preparation of packaging material E1)
White ink C1 and light-shielding ink D1 were gravure printed on the inner surface treatment layer of a 12 μm thick plastic film G1 (polyethylene terephthalate film E5100 manufactured by Toyobo Co., Ltd.) and dried to obtain a printed matter having a printed layer with a dry thickness of 1.5 μm including the white printed layer and the light-shielding printed layer. In addition to a solid plate with a plate depth of 100%, printing was also performed on a gradation plate with a plate depth of 0 to 100% to evaluate trapping properties. Using this printed matter, the substrate adhesion and appearance were evaluated.

Next, a laminate adhesive solution was prepared by mixing 8 parts of polyol resin H1 (TM-250HV, manufactured by Toyo-Morton Co., Ltd.) and 1 part of isocyanate compound I1 (CAT-RT86-60, manufactured by Toyo-Morton Co., Ltd.) and adding ethyl acetate to adjust the non-volatile content to 30%, and the resultant was applied onto the printed layer, dried, and laminated with intermediate substrate layer J1 (oriented nylon (Ny), thickness 15 μm) using a laminator. Next, the laminate adhesive solution was applied to the surface of the intermediate substrate layer, dried, and laminated with sealant K1 (CPP, unoriented polypropylene film, thickness 60 μm, surface corona discharge treatment) using a laminator, and the resulting mixture was kept at 40° C. for 1 day to prepare packaging material E1.
The packaging material E1 of Example 1 has, from the outer layer side, a substrate, a white printed layer, a light-shielding printed layer, a first adhesive layer, an intermediate substrate layer, a second adhesive layer, and a sealant, in that order.

[Examples 2 to 23] (Preparation of packaging materials E2 to E23)
Printed matters and packaging materials E2 to E23 of Examples 2 to 23 were obtained in the same manner as in Example 1, except that inks having the raw materials and blending ratios shown in Table 5 were used. In Examples 15, 16, and 17, an isocyanate curing agent (TLA-100, isocyanurate type manufactured by Asahi Kasei Corporation, solid content 70% by mass) was mixed with the ink so that the mass ratio of the ink to the isocyanate curing agent was ink/isocyanate curing agent = 100/1, and printing was performed.

[Comparative Examples 1 to 5] (Preparation of Packaging Materials F1 to F5)
Printed matters and packaging materials F1 to F5 of Comparative Examples 1 to 5 were obtained in the same manner as in Example 1, except that the raw materials and inks having the blending ratios shown in Table 6 were used.

(Measurement and Evaluation)
The following measurements and evaluations were carried out on the printed matter and packaging materials of the Examples and Comparative Examples. The results are shown in Tables 5 and 6.

(Light blocking properties)
For the packaging materials obtained in the Examples and Comparative Examples, the maximum transmittance in the 380 to 780 nm region was measured using a Shimadzu UV3600 ultraviolet-visible-near infrared spectrophotometer to evaluate the light-blocking ability in the visible region.
<Evaluation criteria>
5 (Excellent): Maximum transmittance is less than 1.0%. 4 (Good): Maximum transmittance is 1.0% or more but less than 2.0%. 3 (Acceptable): Maximum transmittance is 2.0% or more but less than 3.0%. 2 (Unacceptable): Maximum transmittance is 3.0% or more but less than 4.0%. 1 (Poor): Maximum transmittance is 4.0% or more. Note that 3 to 5 are in the range where there are no problems in practical use.

(Adhesion to substrate)
For the prints obtained in the Examples and Comparative Examples, 3 hours after printing, a 12 mm wide adhesive tape (cellophane tape manufactured by Nichiban Co., Ltd.) was applied to the printed surface, and the appearance of the printed surface was visually judged when the tape was quickly peeled off. The judging criteria were as follows:
<Evaluation criteria>
5 (Excellent): The ink film on the printed surface does not peel off at all.4 (Good): The area of the ink film peeled off is between 1% and 5%.3 (Fair): The area of the ink film peeled off is between 5% and 20%.2 (Unacceptable): The area of the ink film peeled off is between 20% and 50%.1 (Poor): The area of the ink film peeled off is 50% or more.Note that 3 to 5 are in the range where there are no problems in practical use.

(Appearance (trapping ability))
The appearance (trapping property) of the overlapping portion of the white ink layer/light-shielding ink layer of the printed matter obtained in the examples and comparative examples was evaluated using a microscope (VHX-5000) manufactured by Keyence Corp. The evaluation was performed on the gradation printed matter.
It should be noted that Comparative Examples 4 and 5 were not evaluated because they did not have the overlapping portion.
<Evaluation criteria>
5 (Excellent): Printing unevenness occurs at a plate depth of less than 70%.4 (Good): Printing unevenness occurs at a plate depth of 70% or more but less than 80%.3 (Fair): Printing unevenness occurs at a plate depth of 80% or more but less than 90%.2 (Unacceptable): Printing unevenness occurs at a plate depth of 90% or more but less than 100%.1 (Poor): The overlapping light-blocking ink is all halftone dots and does not wet out or spread at all.Note that 3 to 5 are in the range where there are no problems in practical use.

(Hot lamination strength)
The packaging materials obtained in the Examples and Comparative Examples were cut into 15 mm widths, and the printed layer was peeled off from the substrate surface. The peel strength (lamination strength) was then measured in an environment of 60°C using an Intesco 201 universal tensile tester.
<Evaluation criteria>
5 (Excellent): Tensile strength is 1.0 N/15 mm or more; 4 (Good): Tensile strength is 0.6 N/15 mm or more and less than 1.0 N/15 mm; 3 (Fair): Tensile strength is 0.4 N/15 mm or more and less than 0.6 N/15 mm; 2 (Unacceptable): Tensile strength is 0.2 N/15 mm or more and less than 0.4 N/15 mm; 1 (Poor): Tensile strength is less than 0.2 N/15 mm. Note that 3 to 5 are in the range where there are no problems in practical use.

The above results show that the object of the present application can be achieved by using the packaging material of the present invention. When there is no white printing layer or light-shielding printing layer, the light-shielding property or hot lamination strength is inferior, and when the white printing layer and the light-shielding printing layer do not contain a urethane resin containing a structural unit derived from sebacic acid, succinic acid, or dimer acid-based polyester polyol, the results show that at least one of the adhesion to the substrate, the appearance, and the hot lamination strength is inferior.

Claims (4)

A packaging material having a substrate, a white printed layer, a light-shielding printed layer, an adhesive layer, and a sealant in this order,
The white printing layer contains a white pigment,
the light-shielding printed layer contains at least one pigment selected from the group consisting of carbon black, aluminum particles, iron oxide, and zinc oxide,
Both the white printed layer and the light-shielding printed layer contain a urethane resin,
the urethane resin contains a structural unit derived from a polyester polyol which is a condensation product of a dibasic acid and a diol,
The packaging material, wherein the dibasic acid contains 5% by mass or more of sebacic acid based on the total mass of the dibasic acid . The packaging material according to claim 1 , wherein the white printed layer and/or the light-shielding printed layer comprises a cured product derived from an isocyanate-based curing agent. A method for producing a packaging material having a substrate, a white printed layer, a light-shielding printed layer, an adhesive layer, and a sealant in this order, comprising:
A step of forming a white printing layer by gravure printing or flexographic printing with white ink;
and forming a light-shielding printed layer by gravure printing or flexographic printing a light-shielding ink on the white printed layer,
the light-shielding ink contains at least one selected from the group consisting of carbon black, aluminum particles, iron oxide, and zinc oxide;
Both the white ink and the light-shielding ink contain a urethane resin,
the urethane resin contains a structural unit derived from a polyester polyol which is a condensation product of a dibasic acid and a diol,
The method for producing a packaging material, wherein the dibasic acid contains 5% by mass or more of sebacic acid based on the total mass of the dibasic acid . The method for producing a packaging material according to claim 3 , wherein the amount of the light-shielding ink applied by printing is 0.5 g/ ^m2 or more and less than 5 g/ ^m2 .