Method for manufacturing packaging film and method for manufacturing food packaging film

Abstract

To provide a packaging film 10 having a white ink layer 30 made into biomass, and a method for manufacturing a food packaging film.SOLUTION: The method for manufacturing the packaging film 10 includes a step of laminating the seal layer 40 by extrusion-laminating polypropylene in a molten state on the surface of the base material layer 20 on which the white ink layer 30 is formed. The packaging film 10 has a white ink layer 30 between a base material layer 20 and a seal layer 40. The substrate layer 20 is composed of a stretched polypropylene film. The seal layer 40 is made of non-oriented polypropylene. The seal layer 40 is directly laminated on the white ink layer 30. The white ink layer 30 contains a white pigment that turns black by laser light, a binder resin containing a biomass-derived resin, and an anti-blocking agent having an average particle diameter of 1.0 μm to 7.0 μm. The content of the biomass-derived resin in the white ink layer 30 is 5% by mass to 30% by mass.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing a packaging film having a white ink layer and a method for producing a food packaging film.

Background Art

[0002] In recent years, biomass conversion of gravure inks has been proposed from the viewpoint of environmental conservation (Patent Document 1). Patent Document 1 proposes that a laminated film printed with biomass-converted gravure ink be used as a plastic packaging film.

[0003] It is also proposed to use a laser marking method for printing information such as manufacturer codes and manufacturing dates on laminated films from the viewpoints of excellent visibility, as the marks will not be erased by external friction (Patent Document 2).

Prior Art Literature

Patent Literature

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problem to be Solved by the Invention

[0005] However, when biomass-converted gravure ink is used, color development by laser light on the outer surface becomes difficult, and therefore the current situation is that progress in biomass conversion of the white ink layer in packaging films has been delayed.

[0006] Accordingly, an object of the present invention is to provide a method for producing a packaging film having a biomass-converted white ink layer and a method for producing a food packaging film.

Means for Solving the Problem

[0007] The present invention has been made to solve at least some of the above-mentioned problems and can be realized in the following embodiments or applications.

[0008] [1] One embodiment of the method for manufacturing a packaging film according to the present invention is: A method for manufacturing a packaging film comprising a base layer and a sealing layer laminated on the base layer, The process involves applying white ink to the substrate layer to laminate a white ink layer, The process includes a step of laminating the seal layer by extruding and laminating molten polypropylene onto the surface of the substrate layer on which the white ink layer is formed, The packaging film has a white ink layer between the base material layer and the sealing layer. The aforementioned substrate layer is composed of a stretched polypropylene film. The sealing layer is made of unoriented polypropylene. The sealing layer is directly laminated on the white ink layer. The aforementioned white ink layer comprises a white pigment that turns black when exposed to laser light, a binder resin containing a biomass-derived resin, and an average particle size 3.0 μm It contains an antiblocking agent of ~7.0 μm, The content of biomass-derived resin in the white ink layer is 5% to 30% by mass. the law of nature, The step of laminating the white ink layer involves applying the white ink layer so that its thickness is between 0.5 μm and 2.0 μm. It is characterized by the following:

[0009] [2] In one embodiment of the method for manufacturing the packaging film described above, The aforementioned binder resin is a polyurethane resin. The antiblocking agent is silica. The content of the antiblocking agent in the white ink layer can be 2% to 6% by mass.

[0010] [3] One embodiment of the method for producing a food packaging film according to the present invention is: The packaging film obtained by one embodiment of the method for producing the packaging film described above is characterized in that it is a food packaging film. [Effects of the Invention]

[0011] According to one aspect of the method for producing a packaging film and the method for producing a food packaging film of the present invention, a film in which characters or the like marked by laser light are clear and have good visibility can be obtained even though the film has a biomas-based white ink layer. [Brief Description of Drawings]

[0012] [Figure 1] It is a schematic diagram showing a cross-section of the packaging film according to the present embodiment. [Figure 2] It is a photograph of a printed portion of the sample of Comparative Example 1. [Figure 3] It is a photograph of a printed portion of the sample of Comparative Example 1. [Figure 4] It is a photograph of a printed portion of the sample of Example 1. [Figure 5] It is a photograph of a printed portion of the sample of Example 2. [Mode for Carrying Out the Invention]

[0013] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the embodiments described below do not unduly limit the content of the present invention described in the claims. Furthermore, not all of the configurations described below are necessarily essential constituent requirements of the present invention.

[0014] 1. Packaging film The packaging film 10 according to the present embodiment will be described with reference to Figure 1. Figure 1 is a schematic diagram showing a cross-section of the packaging film 10 according to the present embodiment.

[0015] As shown in Figure 1, the packaging film 10 comprises a base layer 20 and a sealing layer 40 laminated on the base layer 20. The packaging film 10 has a white ink layer 30 between the base layer 20 and the sealing layer 40.

[0016] The packaging film 10 is used for packaging the items to be packaged. The packaging film 10 can be used for packaging, for example, in the form of a bag, by heat sealing with heat while the sealing layers 40 are overlapping and facing each other.

[0017] 1.1. Base material layer The base layer 20 is made of stretched polypropylene (OPP) film. The base layer 20 constitutes the outer surface 12 of the packaging film 10. By making the base layer 20 of stretched polypropylene, the packaging film 10 can be made with excellent mechanical and chemical strength. The thickness of the base layer 20 is not particularly limited as long as it has the tensile strength, rigidity, puncture resistance, etc. required for the packaging film 10, but for example it is 6 μm to 100 μm, preferably 9 μm to 50 μm, and more preferably 15 μm to 25 μm.

[0018] 1.2. Sealing layer The sealing layer 40 is made of unoriented polypropylene (CPP) laminated to the base layer 20 by extrusion lamination. The sealing layer 40 is on the inner surface of the packaging film 10. The seal layer 40 constitutes surface 14. The seal layer 40 has heat-sealing properties. The seal layer 40 melts and fuses with other opposing seal layers 40 when superimposed on each other by heat. Because the seal layer 40 has heat-sealing properties, it can be used as a bag-shaped packaging material. The thickness of the seal layer 40 is, for example, 5 μm to 100 μm, preferably 5 μm to 50 μm, and more preferably 10 μm to 20 μm.

[0019] The sealing layer 40 is formed by extrusion lamination of molten polypropylene onto the surface of the film-like substrate layer 20 on which the white ink layer 30 is formed. Extrusion lamination allows for the mass production of soft packaging films, but it tends to result in weaker adhesion to the substrate layer 20 compared to dry lamination.

[0020] 1.3. White ink layer The white ink layer 30 comprises a white pigment 32 that turns black when exposed to laser light, a binder resin 34 containing a biomass-derived resin, and an antiblocking agent 36 with an average particle size of 1.0 μm to 7.0 μm. The white ink layer 30 is formed on all or at least a portion of one surface of the substrate layer 20. A printed layer, such as a pattern or text information, may be formed between the white ink layer 30 and the substrate layer 20. The white ink layer 30 develops black text or patterns when irradiated with laser light from a laser marker. The white ink layer 30 is formed on the substrate layer 20, for example, by gravure printing. The thickness of the white ink layer 30 is, for example, 0.5 μm to 5.0 μm, preferably 1.5 μm to 2.0 μm. The coating amount of the white ink layer 30 is, for example, 1 g / m². 2 ~10g / m 2 Preferably 3 g / m 2 ~8g / m 2 That is the case.

[0021] The white pigment 32 can be a known pigment that turns black when exposed to laser light, such as titanium dioxide, barium sulfate, magnesium oxide, calcium carbonate, zinc oxide, or lead white. Titanium dioxide is preferred from the viewpoint of color development. However, titanium dioxide tends to weaken the adhesion between the white ink layer 30 and the seal layer 40. The laser light used in the laser marker can be a YAG (yttrium aluminum garnet) laser, YVO4 laser, or FAYb laser with an oscillation wavelength of around 1064 nm, with the FAYb laser being preferred. Examples of information that can be printed with the laser marker include the date of manufacture, expiration date, quality control number, lot number, and expiration date.

[0022] The binder resin 34 can be a known resin used in gravure printing of white inks, such as polyurethane, acrylic, or epoxy resins. The binder resin 34 can be a polyurethane resin. The binder resin 34 contains a biomass-derived resin, preferably a biomass-derived biomass polyurethane resin. As a biomass ink using biomass polyurethane resin, for example, LP Bio from Toyo Ink SC Holdings Co., Ltd. can be used. Furthermore, it can be used in combination with existing gravure inks (and the binder resin).

[0023] (Biomass polyurethane resin) Biomass polyurethane resins have a biomass content greater than 0, as described below. From the perspective of carbon neutrality, the biomass content of biomass polyurethane resins is preferably 40% to 100% by mass, and more preferably 45% to 100% by mass. Preferred biomass polyurethane resins include polyurethane resins obtained by condensation reaction between a polyol and a polyisocyanate, and polyurethane resins (polyurethane urea resins) obtained by reaction (called chain extension) between a polyamine and a urethane prepolymer having isocyanate groups at the terminals, which is a condensation reaction product of a polyol and a polyisocyanate. It is particularly preferable that the polyol contains a high-molecular-weight polyol. Furthermore, it is necessary that one of the polyol, polyisocyanate, or polyamine contains a biomass-derived component. Such biomass polyurethane resins are described, for example, in pamphlet WO2018 / 199085. The material can be manufactured by the method described in Japanese Patent Publication No. 2018-131624, and the residues of the polyol, polyisocyanate, and polyamine become structural units of the biomass polyurethane resin after the condensation reaction.

[0024] The above polymeric polyol contains a polyester polyol obtained by reacting a biomass dibasic acid (described later) as a raw material component, and preferably has a mass-average molecular weight of 400 to 10000. Furthermore, it is preferable that the raw material polyol contains 50% by mass or more of polyester polyol, and even more preferable that it contains 70% by mass or more.

[0025] Furthermore, polymer polyols other than the polyester polyols mentioned above may be used in combination. Examples of such polymer polyols include polyether polyols, polycarbonate polyols, and polyolefin polyols. It is preferable to use these in an amount of 50% by mass or less of the total amount of raw material polyols. From the viewpoint of plate coverage, polyether polyols are preferred as polymer polyols to be used in combination with polyester polyols, and among polyether polyols, polytrimethylene glycol, polytetramethylene glycol, polypropylene glycol, polyethylene glycol, and copolymers thereof are preferred.

[0026] (Polyester polyol) The above-mentioned polyester polyol contains structural units derived from polyester polyols obtained by a condensation reaction between a dibasic acid and a diol, and some or all of the dibasic acid is a biomass dibasic acid. Here, a biomass dibasic acid is a dibasic acid derived from biomass, but in this embodiment, at least one biomass dibasic acid selected from succinic acid, sebacic acid, and dimer acid is essential. The biomass dibasic acid must be contained in 65% by mass or more of the total mass of dibasic acid in the raw material of the polyester polyol, preferably 70% by mass or more, more preferably 85% by mass or more, and even more preferably consisting only of biomass dibasic acid. Furthermore, it is preferable that the total amount of biomass dibasic acid contains 65% by mass or more of at least one biomass dibasic acid selected from succinic acid, sebacic acid, and dimer acid. It is even more preferable that the dibasic acid consists of only at least one selected from succinic acid, sebacic acid, and dimer acid, and a form in which the dibasic acid consists of only one of these is also preferable. At least one biomass dibasic acid selected from succinic acid, sebacic acid, and dimer acid can be obtained as a commercial product, for example, from Ito Oil Co., Ltd.

[0027] The above dibasic acids may include dibasic acids other than biomass dibasic acids, such as adipic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, fumaric acid, oxalic acid, malonic acid, glutaric acid, pimelic acid, superiic acid, azelaic acid, trimellitic acid, pyromellitic acid, etc. Furthermore, this does not exclude succinic acid, sebacic acid, and dimer acid, which are not derived from biomass.

[0028] The above-mentioned diols include both branched and linear diols. This results in better laminate strength in the laminate. Here, a linear diol is a diol having two or more atoms, and includes alkylene glycols, dialkylene glycols, trialkylene glycols, 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 hydrogen.

[0029] Linear diols impart crystallinity, while branched diols impart flexibility. The balance between these two factors results in a tough ink film and high lamination strength when using polyurethane resin as the binder resin 34.

[0030] Examples of the branched diols mentioned above 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 (also referred to as MPD), neopentyl glycol (also referred to as NPG), 1,2-propylene glycol (hereinafter also referred to as PG), 2,4-diethyl-1,5-pentanediol, 1,3-butanediol, and dipropylene glycol.

[0031] In this embodiment, at least one branched diol selected from MPO, MPD, BEPG, NPG, PG, and 2,4-diethyl-1,5-pentanediol is preferred, more preferably NPG and / or BEPG, and particularly preferably BEPG.

[0032] The linear diol is preferably an alkylene glycol, and examples of such compounds include ethylene glycol (also written as EG), diethylene glycol, 1,3-propanediol (also written as 1,3-PD), 1,4-butanediol (also written as 1,4-BD), 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 1,4-butynediol, 1,4-butylenediol, diethylene glycol, triethylene glycol, etc. Among these, linear diols with 8 or fewer carbon atoms, preferably 6 or fewer carbon atoms, are preferred, with EG, 1,3-PD, 1,4-BD, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, etc. Furthermore, from the viewpoint of biomass content and physical properties, EG, 1,3-PD, and 1,4-BD are particularly preferred.

[0033] In this embodiment, from the viewpoint of lamination strength, the mass ratio of branched diols to linear diols (branched diol:linear diol) in the total diol of the polyester polyol is preferably 10:90 to 90:10, more preferably 20:80 to 80:20, and even more preferably 30:70 to 70:30.

[0034] Furthermore, branched diol units and linear diol units may each be present in a single polyester polyol, or a mixture of polyester polyols containing only branched diol units and polyester polyols containing only linear diol units may be used as raw materials to produce a biomass urethane resin.

[0035] In this embodiment, diisocyanates are preferred as polyisocyanates, and various known aromatic, aliphatic, or alicyclic diisocyanates can be used as such compounds. For example, 1,5-naphthylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyldimethylmethane diisocyanate, 4,4'-dibenzylu isocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, tolylene diisocyanate, butane-1,4-diisocyanate, hexamethylene diisocyanate, isopropyl diisocyanate, methylene diisocyanate, 2,2,4-tri 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(isocyanate-methyl)cyclohexane, methylcyclohexane diisocyanate, m-tetramethylxylylene diisocyanate, and dimer diisocyanates obtained by converting the carboxyl group of a dimer acid to an isocyanate group. These can be used individually or in combination of two or more. Among them, isophorone diisocyanate and tri Diisocyanate and 4,4'-diphenylmethane diisocyanate are preferred, and isophorone diisocyanate is even more preferred from the viewpoint of solubility.

[0036] The polyamines mentioned above are preferably organic diamines, and examples of such diamines include ethylenediamine, propylenediamine, hexamethylenediamine, isophoronediamine, and dicyclohexylmethane-4,4'-diamine. In addition, amines having a hydroxyl group in the molecule, such as 2-hydroxyethylethylenediamine, 2-hydroxyethylpropyldiamine, 2-hydroxyethylpropylenediamine, di-2-hydroxyethylethylenediamine, di-2-hydroxyethylenediamine, di-2-hydroxyethylpropylenediamine, 2-hydroxypyropyrethylenediamine, and di-2-hydroxypyropyrethylenediamine, can also be used. These organic diamines can be used individually or in combination of two or more, but isophoronediamine is preferred. Furthermore, polyfunctional amines with three or more amino groups, such as diethylenetriamine, iminobispropylamine (IBPA, 3,3'-diaminodipropylamine), N-(3-aminopropyl)butane-1,4-diamine (spermidine), 6,6-iminodihexylamine, 3,7-diazanonane-1,9-diamine, and N,N'-bis(3-aminopropyl)ethylenediamine, are included in the above organic It can also be used in combination with diamines.

[0037] In this embodiment, the polyurethane resin preferably has an amine value. The amine value of the polyurethane urea resin is preferably 1 to 13 mgKOH / g, and within this range, the lamination strength to the base layer 20 and the seal layer 40 tends to improve.

[0038] Monoamines may be used as reaction stoppers in chain extension reactions using polyamines. Examples of reaction stoppers include dialkylamines such as dibutylamine, diethylamine, and dipropylamine, as well as amines having hydroxyl groups such as monoethanolamine, diethanolamine, 2-amino-2-methyl-1-propanol, and tri(hydroxymethyl)aminomethane.

[0039] In this embodiment, the gravure or flexographic ink using biomass polyurethane resin can be used in combination with various other resins depending on the application and the materials of the substrate layer 20 and the seal layer 40. Examples of resins that can be used include biomass polyurethane resins other than those listed above, polyurethane urea resins, vinyl chloride copolymer resins, chlorinated polypropylene resins, ethylene-vinyl acetate copolymer resins, vinyl acetate resins, polyamide resins, cellulose-based resins, nitrocellulose resins, acrylic resins, polyester resins, alkyd resins, polyvinyl chloride resins, rosin-based resins, rosin-modified maleic acid resins, terpene resins, phenol-modified terpene resins, ketone resins, cyclized rubbers, chlorinated rubbers, polybutyral, petroleum resins, and modified resins thereof. These resins can be used individually or in combination of two or more, with vinyl chloride copolymer resins and / or cellulose-based resins being particularly preferred. The content of these resins is preferably 1 to 6% by mass in the total mass of the ink. The mass ratio of the polyurethane resin containing the biomass polyurethane resin and the vinyl chloride copolymer resin and / or cellulosic resin is preferably 95:5 to 30:70, more preferably 95:5 to 50:50, and even more preferably 90:10 to 65:35.

[0040] The total amount of the polyurethane resin containing biomass polyurethane resin and the vinyl chloride copolymer resin and / or cellulosic resin is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more, in the total mass of the binder resin.

[0041] <Vinyl chloride copolymer resin> The vinyl chloride copolymer resin is not particularly limited as long as it contains structural units derived from vinyl chloride and structural units derived from other monomers. Among these, vinyl chloride-vinyl acetate copolymer resins and vinyl chloride-acrylic copolymer resins are preferred.

[0042] <Vinyl chloride-vinyl acetate copolymer resin> The vinyl chloride-vinyl acetate copolymer resin is a copolymer of vinyl chloride and vinyl acetate, and its weight-average molecular weight is preferably 5,000 to 100,000, and more preferably 20,000 to 70,000. The structure derived from vinyl acetate monomer is preferably 1 to 30% by mass of the solid content of the vinyl chloride-vinyl acetate copolymer resin, and the structure derived from vinyl chloride monomer is preferably 70 to 95% by mass. In this case, solubility in organic solvents is improved, and adhesion to the substrate, film properties, and laminate strength are also improved.

[0043] Furthermore, to improve solubility in organic solvents, it is even more preferable to have hydroxyl groups derived from vinyl alcohol through saponification or copolymerization, and the hydroxyl value is preferably 20 to 200 mg KOH / g. In addition, the glass transition temperature is preferably 50°C to 90°C.

[0044] <Vinyl chloride-acrylic copolymer resin> The vinyl chloride-acrylic copolymer resin mainly consists of a copolymer resin of vinyl chloride monomer and acrylic monomer. The acrylic monomer preferably contains (meth)acrylate hydroxyalkyl ester to improve adhesion to the substrate layer 20 and the seal layer 40, and solubility in organic solvents. The acrylic monomer may be incorporated into the main chain of polyvinyl chloride in a block or random manner, or it may be graft polymerized into the side chains of polyvinyl chloride. The vinyl chloride-acrylic copolymer resin preferably has a weight-average molecular weight of 10,000 to 100,000, and more preferably 30,000 to 70,000. Furthermore, it preferably has a hydroxyl value of 20 to 200 mg KOH / g, and a glass transition temperature of 50°C to 90°C.

[0045] Furthermore, the structure derived from vinyl chloride monomer in the vinyl chloride-acrylic copolymer resin is preferably 70 to 95% by mass of 100% by mass of the solid content of the vinyl chloride-acrylic copolymer resin. In this case, solubility in organic solvents is improved, and adhesion to the substrate, film properties, and laminate strength are also improved.

[0046] In the following explanation, (meth)acrylic and (meth)acrylate refer to methacrylic and acrylic, methacrylate and acrylate, respectively.

[0047] The above acrylic monomers preferably include those having a hydroxyl group. Examples include hydroxyalkyl esters of (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl (meth)acrylate, as well as glycol mono(meth)acrylates such as polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, and 1,4-cyclohexanedimethanol mono(meth)acrylate, caprolactone-modified (meth)acrylate, and hydroxyethylacrylamide. Among these, 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxypropyl acrylate are more preferred because they improve solubility in solvents. These can be used individually or in combination of two or more. Other acrylic monomers may be included as needed.

[0048] <Cellulose resin> Examples of cellulosic resins include nitrocellulose, cellulose acetate propionate, cellulose acetate butyrate, hydroxyalkylcellulose, and carboxyalkylcellulose. Examples of alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, and hexyl groups, and the alkyl group may also have substituents. In particular, it is preferable that it be at least one selected from cellulose acetate propionate, cellulose acetate butyrate, and nitrocellulose. The molecular weight is preferably 5,000 to 200,000 by weight average, and more preferably 10,000 to 80,000. Furthermore, it is preferable that the glass transition temperature is 100°C to 160°C. The nitrogen content of the nitrocellulose is preferably 10 to 13% by mass, and more preferably 10.5 to 12.5% ​​by mass.

[0049] The biomass content refers to the proportion of plant-derived and other biomass-derived components contained in a compound. The biomass content is expressed as: Biomass Content = 100 × Mass of Biomass-Derived Components in the Compound / Total Mass of the Compound. However, if the compound is a reaction product of biomass-derived raw materials and non-biomass-derived raw materials, the calculation is performed by converting it to the raw materials before the reaction. For example, in the case of polyester resin (polyester polyol), which is a reaction product of a dibasic acid and a diol, the biomass content = 100 × (biomass dibasic acid + biomass-derived diol) / (all dibasic acids + all diols). Here, "all dibasic acids + all diols" refers to the sum of biomass-derived and non-biomass-derived dibasic acids, and biomass-derived and non-biomass-derived diols.

[0050] The biomass-derived resin content in the white ink layer 30 is between 5% by mass and 30% by mass. If the biomass-derived resin content in the white ink layer 30 is less than 5% by mass, it is undesirable from an environmental protection standpoint, and if it exceeds 30% by mass, it becomes difficult to improve the visibility of characters, etc., when printed with laser light. Here, according to experiments by the inventors, it was found that when biomass-derived resin is included in the binder resin 34, the adhesion between the seal layer 40 and the white ink layer 30 tends to weaken. Laser printing, such as with a laser marker, produces color by delamination between the substrate layer 20 and the white ink layer 30 due to the laser light and carbonization of the white pigment 32 in the delaminated area. If the adhesion between the seal layer 40 and the white ink layer 30 is weak, delamination and carbonization occur on the seal layer 40 side rather than between the substrate layer 20 and the white ink layer 30, which tends to cause blurring or uneven coloring when printed with laser light. Therefore, the packaging film 10 according to this embodiment suppresses peeling and carbonization between the seal layer 40 and the white ink layer 30 by incorporating an antiblocking agent 36 having a predetermined particle size into the white ink layer 30.

[0051] (Antiblocking agent) The antiblocking agent 36 has an average particle diameter of 1.0 μm to 7.0 μm, preferably 2.0 μm to 6.0 μm, and more preferably 3.0 μm to 5.0 μm. The average particle diameter can be measured by, for example, image measurement. The particles of the antiblocking agent 36 are photographed with a transmission electron microscope, and the particle diameters of 50 particles randomly selected from the obtained images are measured by image measurement. The average particle diameter is then calculated by averaging these measurements. An average particle diameter of 1.0 μm or more of the antiblocking agent 36 creates irregularities on the surface of the white ink layer 30 on the seal layer 40 side, improving the adhesion between the white ink layer 30 and the seal layer 40, suppressing peeling and carbonization between the seal layer 40 and the white ink layer 30, and resulting in good color development by laser light between the substrate layer 20 and the white ink layer 30. Furthermore, because the average particle size of the antiblocking agent 36 is 7.0 μm or less, the antiblocking agent 36 is contained within the white ink layer 30 and acts as an anchor coat between the substrate layer 20 and the seal layer 40. It can function while also ensuring the seal strength between the seal layers 40, 40.

[0052] The antiblocking agent 36 can be, for example, silica, PMMA beads, or silicone resin, and is preferably silica. The content of the antiblocking agent 36 in the white ink layer 30 is 2% to 6% by mass. If the antiblocking agent 36 is 2% by mass or more, the effect of suppressing peeling and carbonization caused by laser light between the seal layer 40 and the white ink layer 30 can be obtained. If the antiblocking agent 36 is 6% by mass or less, the adhesive strength required for the packaging film 10 can be obtained between the seal layer 40 and the white ink layer 30.

[0053] 1.4. Method of manufacturing ink The white ink layer 30 is obtained by applying gravure ink to one side of the substrate layer 20 and drying it. The gravure ink used for the white ink layer 30 can be manufactured by dispersing a white pigment 32 in an organic solvent using a disperser with a binder resin 34 or the like, and then mixing the resulting pigment dispersion with the binder resin 34, various additives, and organic solvents. Commonly used dispersers such as roller mills, ball mills, pebble mills, attritors, and sand mills can be used. The particle size distribution of the pigment in the pigment dispersion can be adjusted by appropriately adjusting the size of the grinding media in the disperser, the filling rate of the grinding media, the dispersion processing time, the discharge speed of the pigment dispersion, and the viscosity of the pigment dispersion.

[0054] The viscosity of the gravure ink is preferably in the range of 10 seconds (90 mPa·s) or more (using a Zahn cup #3) at 25°C from the viewpoint of preventing sedimentation of the white pigment 32 and ensuring appropriate dispersion, and 68 seconds (600 mPa·s) or less (from the viewpoint of workability during ink manufacturing and printing). A range of 12 to 20 seconds (100 mPa·s to 180 mPa·s) is even more preferable. The viscosity (mPa·s) above can be the viscosity value measured at 25°C using a Tokimec B-type viscometer.

[0055] (Other additives) Gravure inks may also contain additives such as leveling agents, defoamers, waxes, silane coupling agents, plasticizers, light stabilizers, infrared absorbers, ultraviolet absorbers, fragrances, flame retardants, and curing agents, as needed.

[0056] (Organic solvents) Gravure inks preferably contain an organic solvent as a liquid medium. The organic solvent used is preferably a mixed solvent, and any known organic solvents can be used, including aromatic organic solvents such as toluene and xylene, ketone organic solvents such as methyl ethyl ketone and methyl isobutyl ketone, ester organic solvents such as ethyl acetate, n-propyl acetate, isopropyl acetate, isobutyl acetate, methanol, ethanol, n-propanol, isopropanol, and n-butanol. Among these, organic solvents that do not contain aromatic organic solvents such as toluene and xylene (non-toluene organic solvents) are more preferable. Even more preferable are organic solvents that do not contain aromatic organic solvents and / or ketone organic solvents such as methyl ethyl ketone, and it is preferable that the organic solvent contains an ester organic solvent as a main component (50% or more). A mixture containing both an ester organic solvent and an alcohol organic solvent is particularly preferable.

[0057] (Hardening agent) Gravure inks are also preferably used as two-component gravure inks by adding an isocyanate-based curing agent to improve the lamination strength. Examples of such isocyanate-based curing agents include tolylene diisocyanate (TDI) and diphenylmethane diisocyanate. Polyisocyanates (MDI) and hexamethylene diisocyanate (HDI) can be suitably used in the form of adduct-type polyisocyanates (adduct), biuret-type polyisocyanates (biuret), and isocyanurate-type polyisocyanates (isocyanurate), respectively. Examples include the adduct obtained from the reaction of 1 mole of trimethylolpropane and 3 moles of HDI, the biuret obtained from the reaction of 1 mole of water and 3 moles of HDI, and the isocyanurate obtained from the cyclic trimerization reaction of HDI. When used as a two-component system, the amount of polyisocyanate-based curing agent added is preferably 0.5 to 10% by mass, and preferably 0.5 to 5% by mass, relative to the total amount of gravure ink.

[0058] 1.5. Gravure or flexographic ink printing Gravure ink can be printed on one side of the substrate layer 20 using the gravure printing method. In gravure printing, the ink is diluted with a diluent solvent to a viscosity and concentration suitable for printing and supplied to each printing unit either alone or in a mixture.

[0059] 2. Film for food packaging The food packaging film according to this embodiment is the packaging film 10 described in "1. Packaging Film" above, which is used for packaging food.

[0060] Examples of packaged foods include bread, noodles, rice, tofu, dairy products, soy sauce, miso, confectionery, cream, sauces, mayonnaise, dressings, and supplements.

[0061] For example, a food packaging film can be made by forming a packaging film 10 into a tube and heat-sealing the outer sealing layers 40 together to form a bag.

[0062] Food packaging films need to have the manufacturing date and expiration date printed on them, and in order to make it easy for consumers to pick them up and check them, good color development of the laser printing on the white ink layer 30 is particularly required. In the food packaging film according to this embodiment, blackening occurs on the substrate layer 20 side of the white ink layer 30 due to laser light, resulting in excellent color development of the print and excellent visibility of the print.

[0063] The present invention is not limited to the embodiments described above, and various further modifications are possible. For example, the present invention includes configurations that are substantially identical to the configurations described in the embodiments (for example, configurations with the same function, method, and result, or configurations with the same purpose and effect). The present invention also includes configurations in which non-essential parts of the configurations described in the embodiments are replaced. The present invention also includes configurations that produce the same effects or achieve the same purpose as the configurations described in the embodiments. Furthermore, the present invention includes configurations that add known technology to the configurations described in the embodiments. [Examples]

[0064] The following describes embodiments of the present invention, but the present invention is not limited to these embodiments.

[0065] (A) Preparation of packaging film [Preparation of white ink] A white ink was obtained by using biomass ink (LP Bio, manufactured by Toyo Ink SC Holdings Co., Ltd.) as a base, and adding a predetermined amount of silica particles as an antiblocking agent to adjust the viscosity and ensure that the "content of AB agent in the white ink layer" was as shown in Table 1 below.

[0066] [Table 1]

[0067] [Preparation of the base layer] Each of the prepared white inks was gravure printed onto one side of a stretched polypropylene (OPP) film (20 μm thick) that served as the base layer, at a printing speed of 150 m / min to 160 m / min and a drying temperature of 60°C.

[0068] [Creation of a sealing layer] Samples of packaging films for Comparative Example 1 and Examples 1 and 2 were obtained by extrusion lamination molding of molten polypropylene (film thickness 15 μm) onto a surface coated with white ink.

[0069] (B) Laser printing Samples of packaging films from Comparative Example 1 and Examples 1 and 2 were printed using a FAYb laser, and the visibility of the printed characters was evaluated. The laser settings were a scan speed of 9000 mm / s, laser power of 40% to 60%, and pulse period in the range of 15 μs to 30 μs.

[0070] Figure 2 is a photograph of the Comparative Example 1 sample taken from the substrate layer side, and Figure 3 is a photograph of the same sample taken from the seal layer side. As shown in Figure 2, the characters in Comparative Example 1 had thin lines and poor visibility from the substrate layer side. Also, as shown in Figure 3, when viewed from the seal layer side, the lines of the characters in Comparative Example 1 appeared wider and the characters were blurred.

[0071] Figure 4 is a photograph of the sample from Example 1 taken from the substrate layer side. As shown in Figure 4, the characters in Example 1 had thicker lines, were clearer, and had better visibility compared to the characters in Comparative Example 1.

[0072] Figure 5 is a photograph of the sample from Example 2 taken from the substrate layer side. As shown in Figure 5, the characters in Example 2 have thicker lines and are clear both when viewed from the substrate layer and the seal layer, exhibiting superior visibility compared to the characters in Comparative Example 1. [Explanation of Symbols]

[0073] 10…Packaging film, 12…Outer surface, 14…Inner surface, 20…Base layer, 30…White ink layer, 32…White pigment, 34…Binder resin, 36…Antiblocking agent, 40…Seal layer

Claims

1. A method for manufacturing a packaging film comprising a base layer and a sealing layer laminated on the base layer, The process involves applying white ink to the substrate layer to laminate a white ink layer, The process includes a step of laminating the seal layer by extruding and laminating molten polypropylene onto the surface of the substrate layer on which the white ink layer is formed, The packaging film has a white ink layer between the base material layer and the sealing layer. The aforementioned substrate layer is composed of a stretched polypropylene film. The sealing layer is made of unoriented polypropylene. The sealing layer is directly laminated on the white ink layer. The aforementioned white ink layer comprises a white pigment that blackens upon laser light, a binder resin containing a biomass-derived resin, and an antiblocking agent with an average particle size of 3.0 μm to 7.0 μm. The content of biomass-derived resin in the white ink layer is 5% by mass to 30% by mass. A method for manufacturing a packaging film, wherein the step of laminating the white ink layer is to apply the white ink layer so that its thickness is 0.5 μm to 2.0 μm.

2. In claim 1, The aforementioned binder resin is a polyurethane resin. The antiblocking agent is silica. A method for manufacturing a packaging film, wherein the content of the antiblocking agent in the white ink layer is 2% by mass to 6% by mass.

3. A method for manufacturing a food packaging film, wherein the packaging film obtained by the method for manufacturing the packaging film according to claim 1 or claim 2 is a food packaging film.

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