JP7521278B2 - Method for producing flexible packaging laminate - Google Patents

Description

The present invention relates to a method for producing a flexible packaging laminate for use in foods, medicines, cosmetics, detergents, miscellaneous goods, etc.

Conventionally, solvent-free, two-component curing polyurethane adhesives have been widely used as adhesives for the production of flexible packaging for foods, medicines, cosmetics, detergents, miscellaneous goods, etc. Such solvent-free adhesives usually use low molecular weight polyisocyanates and polyols to keep the viscosity low, and have low initial cohesive strength, requiring aging for a certain period of time or more. From the perspective of production efficiency, there is a demand for shortening the aging time.

However, solvent-free adhesives are generally made by retaining a mixed solution of polyisocyanate and polyol on a roll and applying it to a substrate using a roll coater. Therefore, when catalysts or other substances are added to improve curing performance, there are problems in that the pot life is significantly shortened and the adhesive thickens on the roll, causing a deterioration in appearance.

To address the above-mentioned problems, Patent Document 1 discloses a technique in which polyisocyanate and polyol are applied to separate substrates and then the substrates are bonded together.
Furthermore, Patent Document 2 discloses a technique in which a mixture of polyol and polyisocyanate is applied to a first plastic substrate, a catalyst is formed in dots on a second substrate, and the two substrates are then bonded together.

On the other hand, it is known that solventless adhesives that use low molecular weight polyisocyanates and polyols can have their hiding power reduced during aging due to the penetration of low molecular weight components into the ink layer, causing the ink layer to swell. Low molecular weight polyisocyanates in particular tend to easily penetrate the ink layer and cause it to swell. When the hiding power of the ink layer decreases, a darkening phenomenon occurs, in which the metal vapor deposition or metal foil can be seen through, especially when the packaging material is laminated with metal vapor deposition film or metal foil and viewed from the outside.

However, the methods described in Patent Documents 1 and 2 cannot prevent the low molecular weight components contained in the adhesive from penetrating into the ink layer, and cannot suppress the decrease in the concealing ability of the ink layer, such as the darkening phenomenon.

International Publication No. 2019/082683 International Publication No. 2019/167638

The object of the present invention is to provide a method for producing a laminate for flexible packaging that can increase the curing speed of the adhesive without deteriorating the pot life, shorten the aging time, and suppress the decrease in the concealment property of the printed layer, such as the darkening phenomenon.

As a result of extensive research into resolving the above-mentioned issues, we discovered that the following embodiment can resolve the above-mentioned issues, and have now completed the present invention.

The present invention relates to a method for producing a flexible packaging laminate having a first substrate, a printing layer, an adhesive layer, and a second substrate in this order, the method including the following steps 1 and 2:
Step 1: A step of forming a layer (X) containing a polyol (A1) and a catalyst on the printed layer of a first substrate having a printed layer provided thereon. Step 2: A step of applying a mixed liquid of a polyol (A2) and a polyisocyanate (B) onto the layer (X), and contacting and pressing with a second substrate.

The present invention relates to a method for producing the flexible packaging laminate, in which the thickness of the layer (X) is 0.1 to 1.0 μm.

The present invention relates to a method for producing the flexible packaging laminate, in which the polyol (A1) has a viscosity of 1 to 50 mPa·s in a 10% by mass ethyl acetate solution at 25°C.

The present invention relates to a method for producing the flexible packaging laminate, in which the number average molecular weight of the polyol (A1) is 5,000 to 30,000.

The present invention relates to a method for producing the flexible packaging laminate, which is characterized in that a mixed liquid containing polyol (A1), a catalyst, and an organic solvent is applied onto the printed layer of the first substrate on which the printed layer is provided, and then the organic solvent is removed to form the layer (X).

The present invention relates to a method for producing the flexible packaging laminate, in which the second substrate includes at least one material selected from the group consisting of a metal-deposited film and a metal foil.

The present invention relates to a method for producing the flexible packaging laminate, in which the catalyst is at least one selected from the group consisting of metal catalysts and tertiary amine catalysts.

The present invention relates to a method for producing the flexible packaging laminate, which includes step 0, which is performed before step 1, of forming a printed layer on a first substrate to obtain a first substrate provided with a printed layer, and is characterized in that steps 0, 1, and 2 are performed inline.

The present invention provides a method for producing a laminate for flexible packaging that can increase the curing speed of the adhesive without deteriorating the pot life, shortens the aging time, and suppresses the decrease in the concealment property of the printed layer, such as the darkening phenomenon.

The present invention is a method for producing a flexible packaging laminate having, in this order, a first substrate, a printed layer, an adhesive layer containing a cured product of a polyol and a polyisocyanate, and a second substrate, and is characterized by having the following steps 1 and 2:
Step 1: A step of forming a layer (X) containing a polyol (A1) and a catalyst on the printed layer of a first substrate having a printed layer provided thereon. Step 2: A step of applying a mixed liquid of a polyol (A2) and a polyisocyanate (B) onto the layer (X), and contacting and pressing with a second substrate.

The adhesive layer in the present invention is a polyurethane adhesive layer containing a cured product of polyol (A1) and/or polyol (A2) and polyisocyanate (B), and is formed by applying a mixed liquid of polyol (A2) and polyisocyanate (B) onto a layer (X) containing polyol (A1) and a catalyst, contacting a second substrate with the layer and pressing the layer together, and aging the layer.
By the above process, the catalyst contained in the layer (X) diffuses throughout the adhesive layer, and the polyisocyanate (B) as the curing agent penetrates the layer (X) and reacts not only with the polyol (A2) but also with the polyol (A1), achieving rapid curing without deteriorating the pot life. Furthermore, the polyisocyanate (B) that penetrates the layer (X) reacts quickly with the polyol (A1) due to the crosslinking agent contained in the layer (X) to increase its molecular weight, so that penetration into the ink layer is suppressed, and a decrease in the concealment of the printed layer, such as a darkening phenomenon, can be suppressed.
The present invention will be described in detail below.

<Step 1>
The layer (X) in the present invention contains a polyol (A1) and a catalyst.

[Polyol (A1)]
The polyol (A1) may be any compound having two or more hydroxyl groups, and may be selected from known polyols. Examples of such polyols include polyester polyols, polycarbonate polyols, polycaprolactone polyols, polyvalerolactone polyols, polyether polyols, polyolefin polyols, polyurethane polyols, acrylic polyols, silicone polyols, castor oil polyols, fluorine-based polyols, and polyhydroxyalkanes.
Examples of the glycols include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-5-pentanediol, 1,6-hexanediol, neopentyl glycol, methylpentane glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, bishydroxyethoxybenzene, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, and triethylene glycol; polyalkylene glycols having a number average molecular weight of 200 to 3,000; trifunctional or tetrafunctional aliphatic alcohols such as glycerin, trimethylolpropane, and pentaerythritol; and polyols in which the above-mentioned glycols or polyols are added to the above-mentioned trifunctional or tetrafunctional aliphatic alcohols.
From the viewpoints of leveling ability and adhesive performance to a substrate, the polyol (A1) is preferably a polyether polyol or a polyester polyol.

(Polyester polyol)
Examples of polyester polyols include polyester polyols obtained by reacting a carboxyl group component with a hydroxyl group component; and polyester polyols obtained by ring-opening polymerization of lactones such as polycaprolactone, polyvalerolactone, and poly(β-methyl-γ-valerolactone).
Examples of the carboxyl group component include dibasic acids such as terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, phthalic anhydride, adipic acid, azelaic acid, sebacic acid, succinic acid, glutaric acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, maleic anhydride, and itaconic anhydride, or dialkyl esters thereof, or mixtures thereof.
Examples of the hydroxyl group component include diols such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, butylene glycol, neopentyl glycol, dineopentyl glycol, trimethylolpropane, glycerin, 1,6-hexanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol, 3-methyl-1,5-pentanediol, 3,3'-dimethylolheptane, 1,9-nonanediol, polyoxyethylene glycol, polyoxypropylene glycol, polytetramethylene ether glycol, polyether polyol, polycarbonate polyol, polyolefin polyol, acrylic polyol, polyurethane polyol, and mixtures thereof.
The above carboxyl group components and hydroxyl group components may be used alone or in combination of two or more.

(Polyether polyol)
The polyether polyol may be any compound having two or more hydroxyl groups and two or more ether bonds in the molecule. Examples of such 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.
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.

These polyols (A1) may be acid-modified products in which some of the hydroxyl groups in the polyol are acid-modified, or may be products in which carboxyl groups have been introduced by reacting with an acid anhydride, or products in which urethane bonds have been introduced by reacting with a diisocyanate.
Examples of the diisocyanate include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, 1,5-naphthalene diisocyanate, hexamethylene diisocyanate, and hydrogenated diphenylmethane diisocyanate.
Examples of the acid anhydride include pyromellitic anhydride, mellitic anhydride, trimellitic anhydride, and trimellitic ester anhydride. Examples of the trimellitic ester anhydride include ethylene glycol bisanhydrotrimellitate and propylene glycol bisanhydrotrimellitate.
These polyols (A1) may be used alone or in combination of two or more.

The number average molecular weight of the polyol (A1) is preferably 2,000 to 50,000, more preferably 5,000 to 30,000. A number average molecular weight of 5,000 or more is preferable in that it can more effectively prevent penetration of adhesive components such as low-molecular-weight polyisocyanates and suppress a decrease in the hiding power of the printed layer.
In the present invention, the number average molecular weight (Mn) can be determined as a polystyrene equivalent value measured by GPC (gel permeation chromatography) using tetrahydrofuran as a solvent.

The acid value of the polyol (A1) is preferably 0 to 40 mgKOH/g, more preferably 0 to 10 mgKOH/g, and even more preferably 0 to 5 mgKOH/g. The hydroxyl value of the polyol is preferably 1 to 200 mgKOH/g, and more preferably 1 to 150 mgKOH/g.

The viscosity of the polyol (A1) at 25°C when diluted with ethyl acetate to a concentration of 10% by mass is preferably 1 to 50 mPa·s, more preferably 5 to 50 mPa·s. This range is preferable because it allows the layer (X) to be formed on the printed layer as a thin film having a thickness of about 0.1 to 1.0 μm, and it is then possible to control the penetration of low molecular weight components in the mixed liquid that is applied onto the layer (X).

[catalyst]
The catalyst that can be used in the present invention is preferably at least one selected from the group consisting of metal catalysts and tertiary amine catalysts. Examples of the metal catalysts include dibutyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate, and dibutyltin dimaleate. Examples of the tertiary amine catalysts include 1,8-diaza-bicyclo(5,4,0)undecene-7, 1,5-diazabicyclo(4,3,0)nonene-5,6-dibutylamino-1,8-diazabicyclo(5,4,0)undecene-7, and triethanolamine.

[Formation of layer (X)]
The method for forming the layer (X) is not particularly limited, and the layer (X) can be formed by a known method. Examples of the method for forming the layer (X) include gravure coating, flexo coating, roll coating, bar coating, die coating, curtain coating, spin coating, and inkjet coating. The thickness of the layer (X) is preferably 0.1 to 1.0 μm, and more preferably 0.1 to 0.5 μm.
From the viewpoint of setting the thickness of the layer (X) within the above range, the method for forming the layer (X) is preferably a gravure coating method, and a method is suitably used in which a mixed liquid containing the polyol (A1), a catalyst, and an organic solvent is applied, using a gravure coater, onto the printed layer of the first base material on which the printed layer is provided, and then the organic solvent is removed to form the layer (X).

The organic solvent that may be included is not particularly limited, and examples include toluene, xylene, methylene chloride, tetrahydrofuran, methanol, ethanol, isopropyl alcohol, methyl acetate, ethyl acetate, n-butyl acetate, acetone, methyl ethyl ketone, cyclohexanone, toluene, xylol, n-hexane, and cyclohexane.

The catalyst content in layer (X) is preferably 2 to 20% by mass, and more preferably 5 to 15% by mass.

<Step 2>
The production method of the present invention includes a step of applying a mixed liquid of polyol (A2) and polyisocyanate (B) onto layer (X), contacting with a second substrate and pressing. In step 2, the polyol and polyisocyanate contained in layer (X) and the mixed liquid form urethane crosslinks to form an adhesive layer.

[Polyol (A2)]
As for the polyol (A2), the description in the section on polyol (A1) can be used. The number average molecular weight of the polyol (A2) is preferably 1,000 to 10,000, more preferably 1,000 to 8,000, and particularly preferably 1,000 to 5,000. When the number average molecular weight is 1,000 or more, the cohesive force is sufficient, and when it is 10,000 or less, the polyol has fluidity without a solvent and can be applied to a substrate by a roll coater.

[Polyisocyanate (B)]
The polyisocyanate (B) reacts with the polyol (A1) and the polyol (A2) to harden the adhesive. Examples of such polyisocyanate (B) include aromatic polyisocyanates and aliphatic polyisocyanates, and aromatic polyisocyanates or derivatives thereof are preferably used. These polyisocyanates (B) may be used alone or in combination of two or more.

Examples of the aromatic polyisocyanate include m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, or mixtures thereof, 4,4'-toluene diisocyanate, dianisidine diisocyanate, 4,4'-diphenyl ether diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, or mixtures thereof. aromatic diisocyanates such as ω,ω'-diisocyanate-1,4-diethylbenzene, 1,3-bis(1-isocyanate-1-methylethyl)benzene or 1,4-bis(1-isocyanate-1-methylethyl)benzene or mixtures thereof; aromatic triisocyanates such as triphenylmethane-4,4',4'-triisocyanate, 1,3,5-triisocyanate benzene, and 2,4,6-triisocyanate toluene; aromatic polyisocyanates such as 4,4'-diphenyldimethylmethane-2,2'-5,5'-tetraisocyanate;

Examples of the aliphatic polyisocyanate include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2,4,4'-trimethylhexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,6-diisocyanate methylcaproate, 1,3-xylylene diisocyanate, and 1,4-xylylene diisocyanate.

The polyisocyanate (B) may be a derivative derived from the above-mentioned aromatic or aliphatic polyisocyanates, such as, for example, a reaction product of an aromatic or aliphatic polyisocyanate with a known polyol.
Examples of the known polyols include low molecular weight polyols having a molecular weight of less than 200, such as ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 3,3'-dimethylolpropane, cyclohexanedimethanol, diethylene glycol, triethylene glycol, dipropylene glycol, glycerol, trimethylolpropane, pentaerythritol, and sorbitol; and polyols such as polypropylene glycol, polyester polyols, polyether ester polyols, polyester amide polyols, polycaprolactone polyols, polyvalerolactone polyols, acrylic polyols, polycarbonate polyols, polyhydroxyalkanes, castor oil, and polyurethane polyols. Such known polyols may be used alone or in combination of two or more.
The molar ratio of isocyanate groups to hydroxyl groups (moles of NCO/moles of OH) during the reaction of an aromatic or aliphatic polyisocyanate with a known polyol is preferably 2 or more.

The polyisocyanate (B) is preferably a reaction product of a polyisocyanate and polypropylene glycol, and more preferably a reaction product of an aromatic polyisocyanate and polypropylene glycol. The polyisocyanate containing an aromatic skeleton is preferred because it improves heat resistance and can suppress lifting caused by bending the heat-sealed portion. The number-average molecular weight of the polypropylene glycol is preferably 200 to 5,000.

The isocyanate group content in polyisocyanate (B) is preferably 5 to 30% by mass, and more preferably 8 to 25% by mass. By being within the above range, a laminate with a better appearance can be formed when a film substrate with high gas barrier properties is used. The isocyanate group content (mass%) can be determined by titration with hydrochloric acid.

[Formation of adhesive layer]
As described above, the adhesive layer in the present invention contains a cured product of polyol (A1) and/or polyol (A2) and polyisocyanate (B), and can be formed by applying a mixed solution of polyol (A2) and polyisocyanate (B) onto a layer (X) containing polyol (A1) and a catalyst, contacting and pressing a second substrate, and aging. When the mixed solution is a solvent-free type, the effects of the present invention, such as the fast curing and reduced hiding power of the printed layer, become more pronounced.
The mixed solution can be produced by mixing and stirring the polyol (A2) and the polyisocyanate (B) by a known method. The molar ratio of isocyanate groups to hydroxyl groups in the mixed solution (NCO moles/OH moles) is preferably 1.2 to 3.0, more preferably 1.5 to 2.5. The content of the polyisocyanate (B) is preferably 40 to 300% by mass, more preferably 70 to 250% by mass, based on the polyol (A2) from the viewpoint of adhesive performance. The mixed solution obtained above can be applied to a substrate using, for example, a nonsol laminator to form an adhesive layer. The amount of the mixed solution applied is preferably about 1.0 to 4.0 g/m ² .

[Other ingredients]
The adhesive layer may contain other components other than the polyols (A1) and (A2) and the polyisocyanate (B) in order to satisfy various physical properties required for the package. These other components may be blended with either the polyol or the polyisocyanate, or may be added when blending the polyol and the polyisocyanate. These other components may be used alone or in combination of two or more.

(Silane coupling agent)
The adhesive layer may contain a silane coupling agent from the viewpoint of improving the adhesive strength to the substrate. Examples of the silane coupling agent include trialkoxysilanes having a vinyl group, such as vinyltriethoxysilane and vinyltriethoxysilane; trialkoxysilanes having an amino group, such as 3-aminopropyltriethoxysilane and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane; and trialkoxysilanes having a glycidyl group, such as 3-glycidoxypropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane and 3-glycidoxypropyltriethoxysilane.
The content of the silane coupling agent is preferably 0.1 to 5 mass %, more preferably 0.2 to 3 mass %, based on the polyol (A2). By setting it in the above range, the adhesive strength to metal can be improved.

(Phosphoric acid or phosphoric acid derivative)
The adhesive layer may contain phosphoric acid or a phosphoric acid derivative from the viewpoint of improving the adhesive strength to the substrate. The phosphoric acid may be any one having at least one free oxygen acid, and may be, for example, phosphoric acids such as hypophosphorous acid, phosphorous acid, orthophosphoric acid, and hypophosphoric acid; condensed phosphoric acids such as metaphosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, polyphosphoric acid, and ultraphosphoric acid; or derivatives of phosphoric acid. In addition, examples of derivatives of phosphoric acid include those obtained by partially esterifying the above-mentioned phosphoric acid with alcohols while leaving at least one free oxygen acid. Examples of the alcohols include aliphatic alcohols such as methanol, ethanol, ethylene glycol, and glycerin; and aromatic alcohols such as phenol, xylenol, hydroquinone, catechol, and phloroglucinol.
The content of phosphoric acid or a derivative thereof is preferably 0.001 to 10 mass %, more preferably 0.005 to 5 mass %, and particularly preferably 0.01 to 1 mass %, based on the mass of the adhesive layer.

(Leveling Agent or Defoamer)
The adhesive layer can further contain a leveling agent or an antifoaming agent to improve the appearance of the laminate.The leveling agent can be, for example, polyether-modified polydimethylsiloxane, polyester-modified polydimethylsiloxane, aralkyl-modified polymethylalkylsiloxane, polyester-modified hydroxyl-containing polydimethylsiloxane, polyetherester-modified hydroxyl-containing polydimethylsiloxane, acrylic copolymer, methacrylic copolymer, polyether-modified polymethylalkylsiloxane, acrylic acid alkyl ester copolymer, methacrylic acid alkyl ester copolymer, or lecithin.The antifoaming agent can be, for example, silicone resin, silicone solution, or copolymer of alkyl vinyl ether, acrylic acid alkyl ester, and methacrylic acid alkyl ester.

(Other additives)
The adhesive layer may contain various additives within a range that does not impair the effects of the present invention. Examples of the additives include inorganic fillers such as silica, alumina, mica, talc, aluminum flakes, and glass flakes, layered inorganic compounds, stabilizers (antioxidants, heat stabilizers, ultraviolet absorbers, hydrolysis inhibitors, etc.), rust inhibitors, thickeners, plasticizers, antistatic agents, lubricants, antiblocking agents, colorants, fillers, and crystal nucleating agents.

<Production of flexible packaging laminate>
The flexible packaging laminate of the present invention comprises, in this order, a first substrate, a printing layer, an adhesive layer including a cured product of a polyol and a polyisocyanate, and a second substrate, and is produced by a production method having the following steps 1 and 2, and is preferably produced by a production method characterized in that it includes the following step 0 before step 1, and steps 0, 1, and 2 are carried out in-line.
Step 0: A step of forming a printed layer on a first substrate to obtain a first substrate provided with a printed layer. Step 1: A step of forming a layer (X) containing a polyol (A1) and a catalyst on the printed layer of the first substrate provided with a printed layer. Step 2: A step of applying a mixed liquid of a polyol (A2) and a polyisocyanate (B) onto the layer (X), contacting it with a second substrate and pressing it together.

By carrying out steps 0 to 2 all in-line, not only can the processes from printing to lamination be carried out in one process, but even if the mixed liquid of polyol (A2) and polyisocyanate (B) is a solvent-free type, the adhesive curing speed can be increased without deteriorating the pot life, shortening the aging time and increasing the production efficiency of the flexible packaging laminate. Furthermore, the flexible packaging laminate has a suppressed decrease in the concealing property of the printed layer.

The first substrate is a transparent substrate, and examples thereof include conventionally known plastic films. Examples of the plastic film include those generally used for packaging materials, such as polyester resin films such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polylactic acid (PLA); polyolefin resin films such as polyethylene (PE) and polypropylene (PP); polystyrene resin films; polyamide resin films such as nylon 6 and poly-p-xylylene adipamide (MXD6 nylon); polycarbonate resin films; polyacrylonitrile resin films; polyimide resin films; and laminates thereof (e.g., nylon 6/MXD6/nylon 6, nylon 6/ethylene-vinyl alcohol copolymer/nylon 6) or mixtures thereof. The thickness of the plastic film is preferably 5 to 50 μm.
The first substrate may be a laminate of a plurality of such plastic films, or may be a colorless and transparent vapor-deposited film having a vapor-deposited layer of silica, alumina, or the like.

Examples of the second substrate include the plastic films listed above as the first substrate, as well as sealant substrates, metal-deposited films, and metal foils.
Examples of the sealant substrate include polyethylene such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE) or high-density polyethylene (HDPE), acid-modified polyethylene, polypropylene (PP), acid-modified polypropylene, copolymerized polypropylene, ethylene-vinyl acetate copolymer, ethylene-(meth)acrylic acid ester copolymer, ethylene-(meth)acrylic acid copolymer, and ionomer. The thickness of the sealant substrate is preferably 10 to 150 μm, taking into consideration processability into packaging materials, heat sealability, and the like.
An example of the metal vapor deposition film is an aluminum vapor deposition film, and an example of the metal foil is an aluminum foil.
The second substrate may be a laminate of a plurality of such plastic films, sealant substrates, metallized films, and metal foils. In particular, when the second substrate includes at least one selected from the group consisting of metallized films and metal foils, the manufacturing method of the present invention is preferably used since the darkening phenomenon can be suppressed.

The printing layer is a layer on which any desired printed pattern such as letters, numbers, pictures, figures, symbols, designs, etc. is formed for decoration, display of contents, display of expiration date, display of manufacturer, seller, etc., and for other display or aesthetic purposes, and includes solid printing layers. The printing layer is generally formed using printing ink containing a colorant such as a pigment or dye. There are no particular limitations on the method for forming the printing layer, and examples include gravure coating, flexo coating, roll coating, bar coating, die coating, curtain coating, spin coating, and inkjet methods. The thickness of the printing layer is preferably 0.1 to 10 μm.

The present invention will be specifically described below with reference to examples and comparative examples. In the examples and comparative examples, "parts" and "%" mean "parts by mass" and "% by mass" unless otherwise specified.

[Method for measuring number average molecular weight (Mn)]
The number average molecular weight (Mn) was measured using a GPC (gel permeation chromatography) "Shodex GPC System-21" manufactured by Showa Denko KK GPC is a liquid chromatography that separates and quantifies substances dissolved in a solvent based on the difference in their molecular size. Tetrahydrofuran was used as the solvent, and the molecular weight was determined in terms of polystyrene.

[Method of measuring acid value (AV)]
Approximately 1 g of sample was precisely weighed and placed in a stoppered Erlenmeyer flask, and 100 mL of a toluene/ethanol (volume ratio: toluene/ethanol = 2/1) mixture was added to dissolve it. Phenolphthalein test solution was added as an indicator and allowed to stand for 30 seconds. After that, the solution was titrated with 0.1N alcoholic potassium hydroxide solution until it turned a light pink color. The acid value was calculated using the following formula (1). (Unit: mgKOH/g).
(Formula 1) Acid value (mgKOH/g) = [{(ba) x F x 28.25}/S]
S: Amount of sample collected (g)
a: Amount of 0.1N alcoholic potassium hydroxide solution consumed (mL)
b: Amount of 0.1 N alcoholic potassium hydroxide solution consumed in the blank experiment (mL)
F: Potency of 0.1N alcoholic potassium hydroxide solution

[Method of measuring hydroxyl value (OHV)]
Approximately 1 g of sample was precisely weighed and placed in a stoppered Erlenmeyer flask, and 100 mL of a toluene/ethanol (volume ratio: toluene/ethanol = 2/1) mixture was added and dissolved. Furthermore, exactly 5 mL of an acetylating agent (a solution in which 25 g of acetic anhydride was dissolved in pyridine to a volume of 100 mL) was added and stirred for about 1 hour. Phenolphthalein test solution was added as an indicator and allowed to stand for 30 seconds. After that, the solution was titrated with 0.1N alcoholic potassium hydroxide solution until it turned a light pink color. The hydroxyl value was calculated using the following formula (2). The hydroxyl value was the value in the dry state of the resin (unit: mgKOH/g).
(Formula 2) Hydroxyl value (mg KOH/g) = [{(b-a) x F x 28.25}/S]/(non-volatile content/100) + D
S: Amount of sample collected (g)
a: Amount of 0.1N alcoholic potassium hydroxide solution consumed (mL)
b: Amount of 0.1 N alcoholic potassium hydroxide solution consumed in the blank experiment (mL)
F: Potency of 0.1N alcoholic potassium hydroxide solution D: Acid value (mgKOH/g)

[Method for measuring NCO content (mass%)]
Approximately 1 g of a sample was weighed out and placed in a 200 mL Erlenmeyer flask, and 10 mL of a 0.5 N di-n-butylamine toluene solution and 10 mL of toluene were added to dissolve the sample. Next, phenolphthalein test solution was added as an indicator, and the solution was held for 30 seconds, after which it was titrated with a 0.25 N hydrochloric acid solution until the solution turned a light pink color. The NCO content (mass%) was calculated by the following (Equation 3).
(Formula 3): NCO (mass%) = {(ba) x 4.202 x F x 0.25}/S
Where S is the amount of sample taken (g)
a: Amount of 0.25N hydrochloric acid solution consumed (ml)
b: Amount of 0.25N hydrochloric acid solution consumed in the blank experiment (ml)
F: Potency of 0.25N hydrochloric acid solution

<Production of polyol (A1)>
(Production Example 1)
A reaction vessel equipped with a stirrer, a temperature system, a reflux condenser, a dropping tank and a nitrogen gas inlet tube was charged with 217 parts of diethylene glycol (hereinafter referred to as DEG), 310.3 parts of isophthalic acid (hereinafter referred to as IPA), 47.0 parts of ethylene glycol (hereinafter referred to as EG), and 117.2 parts of adipic acid (hereinafter referred to as ADA), and heated to 235 ° C. while stirring under a nitrogen stream. After continuing the reaction until the acid value was 25.0 mg KOH / g or less, the inside of the reaction vessel was gradually depressurized and reacted at 1.3 kPa or less to obtain a polyester polyol-1 (A1-1) having an acid value of 2.5 mg KOH / g, a hydroxyl value of 9.3 mg KOH / g, and a number average molecular weight of about 12,000.

(Production Example 2)
A reaction vessel equipped with a stirrer, a temperature system, a reflux condenser, a dropping tank and a nitrogen gas inlet tube was charged with 291 parts of IPA, 35.8 parts of terephthalic acid (hereinafter referred to as TPA), 98.5 parts of ADA, 59.5 parts of EG, and 103.6 parts of 1,6-hexanediol (hereinafter referred to as 1,6-HD), and heated to 240° C. while stirring under a nitrogen stream. After the reaction was continued until the acid value was 20.0 mgKOH/g or less, the pressure inside the reaction vessel was gradually reduced, and the reaction was continued at 1.3 kPa or less to obtain polyester polyol-2 (A1-2) having an acid value of 4.0 mgKOH/g, a hydroxyl value of 18 mgKOH/g, and a number average molecular weight of about 5,000.

(Production Example 3)
As polyester polyol-3 (A1-3), Vylon 630 (acid value 1.0 mg KOH/g, hydroxyl value 5 mg KOH/g, number average molecular weight about 23,000) manufactured by Toyobo Co., Ltd. was used.

<Production of composition for forming layer (X)>
According to the formulation (parts by mass) shown in Table 1, polyol (A1) was diluted with ethyl acetate to prepare a solution adjusted to a solids concentration of 10%, and the viscosity (mPa·s) at 25° C. was measured using a Brookfield viscometer. Furthermore, a catalyst was mixed according to the formulation (parts by mass) shown in Table 1 to obtain compositions (X-1) to (X-8) for forming layer (X). (X-9) is a composition in which the catalyst was diluted with ethyl acetate.

The abbreviations in Table 1 are as follows.
DOTL: dioctyltin dilaurate DBTDL: dibutyltin dilaurate DBU: diazabicycloundecene

<Production of polyol (A2)>
(Production Example 4)
A reaction vessel was charged with 34 parts of polypropylene glycol having a number average molecular weight of about 400, 19 parts of polypropylene glycol having a number average molecular weight of about 2,000, 34 parts of a triol having a number average molecular weight of about 400 obtained by adding polypropylene glycol to glycerin, and 13 parts of 4,4'-diphenylmethane diisocyanate, and the mixture was heated at 80°C to 90°C for 5 hours while stirring under a nitrogen gas flow to carry out a urethanization reaction. The disappearance of the isocyanate groups was confirmed by IR, and a polyether urethane polyol (A2-1) having a number average molecular weight of 1,500 was obtained.

(Production Example 5)
In a reaction vessel equipped with a stirrer, a temperature system, a reflux condenser, a dropping tank, and a nitrogen gas inlet tube, 46.6 parts of diethylene glycol and 53.4 parts of adipic acid were charged, and the mixture was heated to 220° C. with stirring under a nitrogen stream. After the reaction was continued until the acid value was 10 mgKOH/g or less, the pressure inside the reaction vessel was gradually reduced, and the reaction was continued at 1.3 kPa or less to obtain a polyester polyol-4 having an acid value of 0.3 mgKOH/g, a hydroxyl value of 56 mgKOH/g, and a number average molecular weight of about 2,000.
Next, 85 parts of the obtained polyester polyol-4 and 15 parts of polypropylene glycol having a number average molecular weight of about 400 were mixed and stirred until the solution became homogeneous, thereby obtaining a polyol (A2-2) consisting of polyester polyol and polypropylene glycol.

(Production Example 6)
In a reaction vessel equipped with a stirrer, a temperature system, a reflux condenser, a dropping tank, and a nitrogen gas inlet tube, 7.3 parts of ethylene glycol, 36.7 parts of neopentyl glycol, 21 parts of isophthalic acid, and 34.4 parts of adipic acid were charged, and the mixture was heated to 240° C. with stirring under a nitrogen stream. After the reaction was continued until the acid value was 5.0 mgKOH/g or less, the pressure inside the reaction vessel was gradually reduced, and the reaction was continued at 1.3 kPa or less to obtain a polyester polyol-5 (A2-3) having an acid value of 0.3 mgKOH/g, a hydroxyl value of 121 mgKOH/g, and a number average molecular weight of about 2,000.

The abbreviations in Table 2 are as follows.
PPG-400: Polypropylene glycol with a number average molecular weight of about 400 PPG-2000: Polypropylene glycol with a number average molecular weight of about 2,000 PPG-400-3 functional: Triol with a number average molecular weight of about 400 obtained by adding polypropylene glycol to glycerin 4,4'-MDI: 4,4'-diphenylmethane diisocyanate

<Production of Polyisocyanate (B)>
(Production Example 7)
6 parts of polypropylene glycol having a number average molecular weight of about 400, 32 parts of polypropylene glycol having a number average molecular weight of about 2,000, 4 parts of triol having a number average molecular weight of about 400 obtained by adding polypropylene glycol to glycerin, 10 parts of polyester polyol-6 having a number average molecular weight of about 2,000 consisting of adipic acid and 1,2-propanediol, and 40 parts of 4,4'-diphenylmethane diisocyanate were charged into a reaction vessel, and the mixture was heated at 80°C to 90°C for 3 hours while stirring under a nitrogen gas flow to carry out a urethane reaction, thereby obtaining a polyisocyanate resin. Next, 8 parts of a biuret of hexamethylene diisocyanate were added, and the mixture was stirred at 70°C or less until the solution became uniform, thereby obtaining a polyisocyanate (B-1) having an isocyanate group content of 10.7%.

(Production Example 8)
20 parts of polypropylene glycol having a number average molecular weight of about 400 and 55 parts of a mixture of 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate (hereinafter, liquid MDI) were charged into a reaction vessel, and the mixture was heated at 80°C to 90°C for 3 hours while stirring under a nitrogen gas flow to carry out a urethane reaction. Then, 25 parts of a mixture of polymeric diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate (hereinafter, crude MDI) was added, and the solution was stirred at 70°C or less until it became uniform, thereby obtaining polyisocyanate (B-2) having an isocyanate group content of 21.5%.

(Production Example 9)
25 parts of HDI billet, 50 parts of hexamethylene diisocyanate nurate (hereinafter, HDI nurate), and 25 parts of isophorone diisocyanate nurate (hereinafter, IPDI nurate) were charged into a reaction vessel, and the mixture was heated to 50° C. to 60° C. with stirring under a nitrogen gas flow to obtain polyisocyanate (B-3) having an isocyanate group content of 20.4%.

The abbreviations in Table 3 are as follows:
PPG-400: Polypropylene glycol with a number average molecular weight of about 400 PPG-2000: Polypropylene glycol with a number average molecular weight of about 2,000 PPG-400-3 functional: Triol with a number average molecular weight of about 400 obtained by adding polypropylene glycol to glycerin 4,4'-MDI: 4,4'-diphenylmethane diisocyanate Liquid MDI: Mixture of 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate HDI biuret: Biuret of hexamethylene diisocyanate HDI nurate: Nurate of hexamethylene diisocyanate IPDI nurate: Nurate of isophorone diisocyanate Crude MDI: Mixture of polymeric diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate

<Preparation of Mixture>
Polyol (A2) and polyisocyanate (B) were mixed in the amounts shown in Table 4 to obtain adhesive mixtures 1 to 3.

<Preparation of Laminate>
[Example 1]
A printing ink (ink 1: Rio Alpha R631 white, manufactured by Toyo Ink Co., Ltd.) was diluted with an ethyl acetate/IPA mixed solvent (mass ratio 70/30) so that the viscosity at 25°C was 16 seconds in Zahn cup #3. The diluted printing ink was printed on a 12 μm-thick polyethylene terephthalate film ("Ester Film E5102" manufactured by Toyobo Co., Ltd., hereinafter referred to as PET) at a printing speed of 150 m/min using a gravure proofing machine equipped with a solid plate with a plate depth of 35 μm, and then dried at 70°C. The thickness of the printed layer was in the range of 0.5 to 1 μm.
Next, the layer (X)-forming composition (X-1) was applied onto the printed layer of the obtained laminate (first substrate) using a dry laminator at a coating speed of 150 m/min, and then dried through an oven at 80° C. to form a layer (X). The thickness of the layer (X) was 0.1 μm.
Next, on the layer (X), a mixed solution 1 of polyol (A2) and polyisocyanate (B) was applied at a coating speed of 150 m/min using a solventless laminator so that the coating amount was adjusted to 2.0 g/ ^m2 . Thereafter, the aluminum vapor deposition surface of a 25 μm thick aluminum vapor deposition CPP film ("2203" manufactured by Toray Industries, Inc., hereinafter referred to as VMCPP) and the mixed solution coated surface of the obtained laminate were bonded together to obtain a laminate having a configuration of PET/printed layer/adhesive layer/VMCPP.

[Examples 2 to 15]
A laminate was obtained in the same manner as in Example 1, except for the changes shown in Table 5.
In Example 14, the printing ink used was (ink 2: LP Bio R631 white, manufactured by Toyo Ink Co., Ltd.), and in Example 15, an aluminum (AL) foil having a thickness of 7 μm was used as the second substrate.

[Comparative Examples 1 to 3]
A laminate was obtained in the same manner as in Example 1, except for the changes shown in Table 5.
In Comparative Example 1, the mixed liquid was directly applied onto the first substrate without forming the layer (X), and in Comparative Example 2, (X-9) containing no polyol (A1) and in which the catalyst was diluted with ethyl acetate was applied onto the printed layer.
In Comparative Example 3, first, a printed layer was formed on PET in the same manner as in Example 1. Onto the printed layer of the obtained laminate, mixed liquid 1 was applied in the same manner as in Example 1. On the other hand, (X-1) was applied and dried on VMCPP in the same manner as in Example 1 to form a layer (X). Next, the mixed liquid applied surface and the layer (X) surface were bonded together to obtain a laminate having a configuration of PET/printed layer/adhesive layer/VMCPP.

<Evaluation of Laminate>
The obtained laminate was subjected to the following evaluations. The results are shown in Table 5.

[Curing speed]
The obtained laminate was peeled between the adhesive layer and VMCPP, and the height of the isocyanate peak (near 2270 cm ^-1 ) of the adhesive layer immediately after lamination was measured using FT-IR. The laminate was then aged at 30°C for 6 hours, and the laminate after aging was similarly peeled between the adhesive layer and VMCPP, and the height of the isocyanate peak of the adhesive layer was measured using FT-IR. The peak near 2980 cm ^-1 derived from _CH3 was used as the reference peak, and the isocyanate residual rate (%) was calculated using the following formula.

Based on the obtained residual isocyanate ratio, the curing speed was evaluated according to the following criteria.
A: Residual isocyanate rate is less than 20% (Next step possible: Good)
B: Residual isocyanate rate is 20% or more and less than 30% (Next process possible: Usable)
C: Residual isocyanate rate is 30% or more and less than 40% (cannot proceed to next process: cannot be used)
D: Residual isocyanate rate is 40% or more (cannot proceed to next process: defective)

[Darking]
The reflection density (L value) of the white printed portion of the obtained laminate was measured from the PET side using an X-Rite. The larger the value, the higher the whiteness, and the more the darkening phenomenon was suppressed. From the measured value, the state of darkening was judged according to the following criteria.
A: L value is 70 or more (good)
B: L value is 65 or more and less than 70 (usable)
C: L value is 60 or more and less than 65 (not suitable for use)
D: L value is less than 60 (bad)

[Adhesive strength]
The obtained laminate was cut into a length of 300 mm and a width of 15 mm to prepare a test piece. Using an Instron tensile tester, the laminate was pulled at a peel rate of 300 mm/min in an environment of 25° C., and the T-type peel strength (N/15 mm) between the PET and VMPET was measured. This test was carried out five times, and the average value was calculated and evaluated according to the following criteria.
A: Peel strength is 1.5 N/15 mm or more (good)
B: Peel strength is 1.0 N/15 mm or more and less than 1.5 N/15 mm (usable)
C: Peel strength is 0.5 N/15 mm or more and less than 1.0 N/15 mm (unusable)
D: Peel strength is less than 0.5 N/15 mm (poor)

According to the evaluation results, the flexible packaging laminate obtained by applying a mixed liquid containing polyol (A2) and polyisocyanate (B) onto a layer (X) containing a catalyst and polyol (A1) exhibited an acceleration of the curing rate due to the catalytic effect and an effect of suppressing a decrease in the concealing property of the printed layer (darkening phenomenon), which is likely to occur due to the penetration of low molecular weight components in the adhesive into the printed layer.
In particular, the curing rate accelerating effect was observed even in a system in which a slow-reactive aliphatic isocyanate was used in the mixed solution as in Example 3, and the production method of the present invention is very useful from the viewpoint of rapid curing. Moreover, Examples 1 to 12, 14, and 15, in which a polyol (A1) having a number average molecular weight of 5,000 or more was used in the catalyst layer (X), were excellent in suppressing the darkening phenomenon.
On the other hand, in Comparative Examples 1 to 3, the low molecular weight components contained in the solvent-free mixed liquid could not be prevented from penetrating into the printed layer, and the darkening phenomenon occurred in all cases.

Claims (7)

A method for producing a flexible packaging laminate having a first substrate, a printing layer, an adhesive layer, and a second substrate in this order, the method comprising the following steps 1 and 2.
Step 1: A step of forming a layer (X) containing a polyol (A1) and a catalyst on the printed layer of the first substrate having the printed layer provided thereon (provided that the thickness of the layer (X) is 0.1 to 1.0 μm).
Step 2: A step of applying a mixed liquid of polyol (A2) and polyisocyanate (B) onto the layer (X), contacting it with a second substrate and pressing it together (the mixed liquid is a solvent-free mixed liquid). The method for producing a flexible packaging laminate according to claim 1 , wherein the polyol (A1) has a viscosity of a 10% by mass solution in ethyl acetate at 25° C. of 1 to 50 mPa·s. The method for producing a flexible packaging laminate according to claim 1 or 2 , wherein the polyol (A1) has a number average molecular weight of 5,000 to 30,000. The method for producing a flexible packaging laminate according to any one of claims 1 to 3, characterized in that a mixed liquid containing a polyol (A1 ) , a catalyst, and an organic solvent is applied onto the printed layer of the first base material having the printed layer provided thereon, and then the organic solvent is removed to form the layer (X). The method for producing a flexible packaging laminate according to any one of claims 1 to 4 , wherein the second substrate comprises at least one selected from the group consisting of a metal-deposited film and a metal foil. The method for producing a flexible packaging laminate according to any one of claims 1 to 5 , wherein the catalyst is at least one selected from the group consisting of metal catalysts and tertiary amine catalysts. The method for producing a flexible packaging laminate according to any one of claims 1 to 6, further comprising, before step 1, step 0 of forming a printing layer on a first substrate to obtain a first substrate provided with a printing layer, and step 0, step 1, and step 2 are carried out in-line.