JP7615568B2 - Manufacturing method of adhesives, packaging materials, and recycled substrates - Google Patents

Description

The present invention relates to an adhesive used to form a removable adhesive layer for recycling a sealant substrate from a packaging material, a packaging material comprising the adhesive, and a method for producing a recycled substrate from the packaging material.

In recent years, packaging, plastic bottles, and other plastic products made from plastic film have been discarded and dumped into the ocean as garbage, causing environmental pollution. These plastic products break down in seawater and become submicron-sized fragments (microplastics), which float in the seawater. If these plastics are ingested by marine organisms such as fish, they will be concentrated in their bodies, and there are concerns that they may affect the health of seabirds and humans that consume these marine organisms as food. In addition, harmful substances originating from inks, adhesives, and coating layers adhere to the surface of the microplastics generated from the packaging, which is of further concern from the perspective of environmental conservation. In order to improve this problem, various efforts to reduce microplastics have been launched.

The main examples of the above-mentioned plastic products include food packaging packages that use plastic substrates. In these packages, various plastic substrates are used as film substrates, such as polyester (PET) substrates, nylon (NY) substrates, and polypropylene (OPP, CPP) substrates. These plastic substrates are given a pattern layer using gravure ink, flexographic ink, or other printing inks, and are then bonded to a sealant substrate via an adhesive or the like to form a laminate, which is then cut and heat-sealed to form a package.

Attempts to reduce the amount of microplastics in the above-mentioned packages include (1) replacing the plastic base material with "paper" made from wood, a renewable resource, (2) recycling the plastic base material by converting it into a single monomaterial (polyolefin), and (3) recycling the plastic base material by removing impurities.

The above-mentioned (1) is promising in terms of safety and recyclability, but is inferior in many aspects to conventional plastic substrates in terms of performance, such as gas barrier properties, water vapor barrier properties, and water resistance.
Regarding (2) above, technology is being developed to cover the weaknesses of polyolefins with functional coating agents such as barrier coating agents, but since polyolefins are inferior in performance to conventional plastic substrates in terms of retort suitability and light blocking properties, it is not easy to replace them with polyolefins. Furthermore, there is also the issue that inks, functional coating agents, adhesives, etc. between polyolefin substrates become impurities when recycling polyolefins.

As for the above (3), attempts have been made to remove the pattern layer on the outer surface of the package, which becomes an impurity during the recycling process, with an alkaline aqueous solution.
For example, Cited Document 1 discloses a technique in which an undercoat layer made of an acrylic resin or a styrene-maleic acid resin is provided on a plastic substrate, and a printed layer disposed on the undercoat layer is removed with alkaline water. Patent Document 2 discloses a technique in which an ink containing a polyurethane resin or an acrylic resin having an acidic group as a binder resin is printed, and the printed layer is removed with alkaline water. However, these techniques only remove the surface-printed ink on the outside of the package, and do not allow the sealant substrate to be peeled off from the other substrates in the laminate.

In packaging materials in which a base material containing a plastic layer and a printed layer such as a picture layer is laminated with a sealant base material using an adhesive, a technology for peeling the sealant base material from the other base materials and recycling the sealant base material, which is particularly thick and accounts for a large proportion of the entire packaging material, is an important technology that can be used industrially to promote plastic recycling and contribute to environmental conservation. However, no technology has yet been reported that combines the required performance of a laminating adhesive with the function of peeling the sealant base material from other base materials.

JP 2001-131484 A Japanese Patent Application Publication No. 11-209677

The objective of the present invention is to provide an adhesive with excellent releasability that allows the pattern layer, etc., to be easily removed from the packaging material and the sealant substrate to be easily recovered, a packaging material that includes the adhesive, and a method for producing a recycled substrate from the packaging material.

As a result of extensive research into the above-mentioned problems, the inventors discovered that the problems could be solved by using the laminating adhesive described below, and arrived at the present invention. The present invention relates to the following inventions [1] to [11].

[1] An adhesive that forms a removable adhesive layer constituting a packaging material in which a substrate 1 having a plastic layer and a pattern layer, a removable adhesive layer, and a sealant substrate 2 are laminated from the outside in this order, and the substrate 1 is peeled off to recycle the sealant substrate 2, the adhesive comprising a polyester polyol component and at least one polyisocyanate component selected from the group consisting of aliphatic polyisocyanates and aralkyl polyisocyanates, and the adhesive has an acid value of 5 to 40 mgKOH/g.

[2] The adhesive described in [1], in which the number average molecular weight of the polyester polyol component is 5,000 to 15,000.

[3] The adhesive according to [1] or [2], in which the acid value of the polyester polyol component is 10 to 40 mg KOH/g.

[4] The adhesive described in any one of [1] to [3], wherein the polyester polyol component contains an acid anhydride-modified polyester polyurethane polyol.

[5] The adhesive described in any one of [1] to [4], wherein the polyester polyol component contains a polyester polyol having a number average molecular weight of 5,000 to 15,000 and a polyester polyol having a number average molecular weight of less than 3,000.

[6] The adhesive according to any one of [1] to [5], further comprising 0.01 to 5 mass% of a phosphorus oxyacid or a derivative thereof based on the solid content of the adhesive.

[7] The adhesive described in any one of [1] to [6] further contains fine particles having an average particle size of 1 to 10 μm.

[8] The adhesive according to [7], in which the content of the microparticles is 0.1 to 10 mass% based on the solid content of the adhesive.

[9] A packaging material having a structure in which a substrate 1 having a plastic layer and a pattern layer, a removable adhesive layer formed from the adhesive described in any one of [1] to [8], and a sealant substrate 2 are laminated from the outside in this order.

[10] The packaging material described in [9], in which the sealant substrate 2 is a layer formed by extrusion lamination, and the thickness of the removable adhesive layer is 0.01 to 1 μm.

[11] A method for producing a recycled substrate, comprising the step of immersing a packaging material in a basic aqueous solution, the packaging material comprising a substrate 1 having a plastic layer and a pattern layer, a removable adhesive layer formed from the adhesive described in any one of [1] to [8], and a sealant substrate 2, laminated in this order from the outside, the basic aqueous solution contains a basic compound in an amount of 0.5 to 20% by mass of the entire basic aqueous solution, and the temperature of the basic aqueous solution during immersion is 25 to 120°C.

The present invention provides an adhesive with excellent releasability that allows the pattern layer, etc., to be easily removed from the packaging material and the sealant substrate to be easily recovered, a packaging material that includes the adhesive, and a method for producing a recycled substrate from the packaging material.

The adhesive of the present invention is an adhesive used to form a removable adhesive layer for recycling a sealant substrate 2 by peeling off a substrate 1 from a packaging material having a configuration in which a substrate 1 having a plastic layer and a pattern layer, a removable adhesive layer, and a sealant substrate 2 are laminated in this order from the outside, and is characterized in that it contains a polyester polyol component and at least one polyisocyanate component selected from the group consisting of aliphatic polyisocyanates and aralkyl polyisocyanates, and has an acid value of 5 to 40 mgKOH/g.
In this adhesive, the ester bond derived from the polyol and the aliphatic structure derived from the polyisocyanate improve the affinity for an alkaline aqueous solution, so that the substrate 1 and the substrate 2 can be easily peeled off in an alkaline aqueous solution.
When the adhesive has an acid value of 5 mgKOH/g or more, the acid value neutralizes the alkali, making it easy to peel the substrate 1 and substrate 2 in an alkaline aqueous solution. When the acid value is 40 mgKOH/g or less, the adhesion and water resistance between the substrate 1 and substrate 2 are good. As a result, the adhesive exhibits excellent releasability and the sealant substrate can be recovered while maintaining the adhesive strength and retort resistance required of a laminating adhesive.
The present invention will be described in detail below, but these are merely examples of the embodiments of the present invention, and the present invention is not limited to these details as long as it does not depart from the gist of the present invention.

<Removable Adhesive Layer>
The adhesive of the present invention is used to form a removable adhesive layer. "Removal" refers to the adhesive layer being removed from the sealant substrate 2 by neutralization, dissolution, etc. with a basic aqueous solution, and includes both cases: (1) the removable adhesive layer is dissolved and the sealant substrate 2 and substrate 1 are peeled off, and (2) the adhesive layer and substrate 1 are peeled off from the sealant substrate 2 by neutralization, dissolution, etc.
Since the present invention aims to obtain the sealant substrate 2 after detachment as a recycled substrate or regenerated substrate, it is preferable to remove as much of the adhesive layer and substrate 1 as possible from the sealant substrate 2. Specifically, it is preferable that at least 50% by mass or more of the removable adhesive layer is detached in the area or thickness direction out of 100% by mass of the removable adhesive layer. It is more preferable that 60% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more is detached.

The basic compound used in the basic aqueous solution is not particularly limited, and examples of the basic compound that can be suitably used include, but are not limited to, sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH) ₂ ), ammonia, barium hydroxide (Ba(OH) ₂ ), and sodium carbonate ( _Na2CO3 ). More preferably, the basic compound is at least one selected from the group consisting of sodium hydroxide and potassium _hydroxide .

The mechanism of detachment is assumed to be that in a packaging material containing a removable adhesive layer (for example, in an embodiment such as a plastic layer/pattern layer/removable adhesive layer/sealant substrate 2), a basic aqueous solution penetrates through gaps between layers and comes into contact with the removable adhesive layer, causing the adhesive layer to dissolve and become detached from substrate 2. Therefore, it is preferable to carry out the detachment process when the packaging material has been cut and the cross section has been exposed, i.e., when the removable adhesive layer has been exposed.

<Adhesive>
The adhesive of the present invention that forms a removable adhesive layer is characterized in that it contains a polyester polyol component and at least one polyisocyanate component selected from the group consisting of aliphatic polyisocyanates and araliphatic polyisocyanates, and has an acid value of 5 to 40 mgKOH/g.

[Polyester polyol component]
The polyester polyol component can be selected from conventionally known polyester polyols, and may be used alone or in combination of two or more kinds.
The polyester polyol component is not limited to the following, but may be, for example, a dibasic acid 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, itaconic anhydride, or a dialkyl ester thereof, or a mixture thereof (hereinafter also referred to as a carboxyl group component);
For example, 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 other diols or mixtures thereof (hereinafter also referred to as hydroxyl group components),
or polyester polyols obtained by ring-opening polymerization of lactones such as polycaprolactone, polyvalerolactone, and poly(β-methyl-γ-valerolactone).
The above carboxyl group components and hydroxyl group components may be used in combination of two or more kinds.

The polyester polyol component may be a polyester polyurethane polyol reacted with a diisocyanate, or may be one further reacted with an acid anhydride.
Examples of diisocyanates 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, trimellitic ester anhydride, etc. Examples of the trimellitic ester anhydride include ethylene glycol bisanhydrotrimellitate, propylene glycol bisanhydrotrimellitate, etc.

In particular, it is preferable that the polyester polyol component contains an acid anhydride modified polyester polyurethane polyol. The polyester polyol component has urethane bonds, which allows it to exhibit excellent heat resistance and adhesiveness. When the polyester polyol component is an acid anhydride modified polyester polyol, it is possible to precisely control the acid value, and it is preferable that a polyester polyol component having a suitable acid value range as described below can be easily obtained.

The adhesive of the present invention has an acid value of 5 to 40 mgKOH/g, so it is preferable that the polyester polyol component has an acid value, and the acid value of the polyester polyol component is preferably 8 mgKOH/g or more, more preferably 10 mgKOH/g or more. The acid value of the polyester polyol component is preferably 40 mgKOH/g or less. When the polyester polyol component has the above acid value, the adhesive layer formed from the adhesive of the present invention containing the polyester polyol component exhibits excellent releasability while maintaining adhesive strength, making it optimal for recycling sealant substrates from packaging materials.

When the polyester polyol component contains multiple polyester polyols, the acid value of the polyester polyol component can be determined from the acid value of each polyester polyol and its mass ratio.

The polyester polyol component preferably has a number average molecular weight (Mn) of 3,000 to 20,000, more preferably 5,000 to 15,000, and particularly preferably 7,000 to 12,000, from the standpoint of heat sterilization resistance of the adhesive layer and coatability.
When the number average molecular weight (Mn) of the polyester polyol component is 3,000 or more, not only the coatability but also sufficient retort suitability can be exhibited, and when it is 20,000 or less, not only the coatability but also the release property is improved, which is preferable.

In order to satisfy various physical properties required for the packaging material, a plurality of polyester polyols may be used in combination as the polyester polyol component. When the polyester polyol component contains a plurality of polyester polyols, the number average molecular weight of the polyester polyol component can be determined from the number average molecular weights of the respective polyester polyols and their mass ratios.
The number average molecular weight in this specification is a value calculated in terms of standard polystyrene using a GPC (gel permeation chromatography) "Shodex GPC System-21" manufactured by Showa Denko KK and using tetrahydrofuran as a solvent.

The polyester polyol component preferably contains a polyester polyol having a number average molecular weight of 5,000 to 15,000, and further preferably contains a polyester polyol having a number average molecular weight of less than 3,000 in order to improve adhesion to the substrate.
The content of the polyester polyol having a number average molecular weight of less than 3,000 is preferably 0 to 30% by mass, more preferably 0 to 20% by mass, based on the total amount of the polyester polyol component. When it is 30% by mass or less, retort resistance is not decreased, which is preferable.

From the viewpoints of adhesive performance and releasability, the polyester polyol component may contain the following three types of polyol components.
First polyol component: polyester polyol having an acid value of 10 mg/KOH or more; Second polyol component: polyester polyol having a number average molecular weight of less than 3,000; Third polyol component: polyester polyol having a number average molecular weight of 5,000 or more (however, this does not include the case where the second polyol component and the third polyol component are the first polyol component).

The first polyol component has a role of imparting releasability, the second polyol component improves adhesion to a substrate and contributes to improving coatability, and the third polyol component has a role of improving retort properties.
The content of the first polyol component is preferably 50% by mass or more based on the total amount of the polyester polyol component from the viewpoint of exerting sufficient releasing property. The first polyol component is preferably a polyester polyurethane polyol modified with an acid anhydride, and more preferably has a number average molecular weight of 5,000 to 10,000 and an acid value of 15 mgKOH/g to 40 mgKOH/g.
The second polyol component preferably has an acid value of 5 mg KOH/g or less, more preferably 1 mg KOH/g or less.
The third polyol component is preferably a polyester polyurethane polyol modified with an acid anhydride, and more preferably has a number average molecular weight of 5,000 or more and 10,000 or less, and an acid value of 5 mgKOH/g or less.

(Other polyols)
The adhesive of the present invention may contain other polyols in addition to the polyester polyol component. The polyols that may be contained in addition to the polyester polyol component are not particularly limited, and examples thereof include polycarbonate polyols, polycaprolactone polyols, polyether polyols, polyolefin polyols, acrylic polyols, silicone polyols, castor oil-based polyols, and fluorine-based polyols. These may be used alone or in combination of two or more kinds.

[Polyisocyanate component]
The adhesive of the present invention contains, as a polyisocyanate component, at least one polyisocyanate component selected from the group consisting of aliphatic polyisocyanates and araliphatic polyisocyanates. The polyisocyanate component can be selected from conventionally known aliphatic polyisocyanates and araliphatic polyisocyanates, and two or more of them may be used in combination.

(Aliphatic polyisocyanate)
The aliphatic polyisocyanate is not limited to the following, but may be a compound derived from a well-known aliphatic diisocyanate or alicyclic diisocyanate.
Examples of aliphatic polyisocyanates that can be used in the present invention include aliphatic diisocyanates such as 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- or 2,2,4-trimethylhexamethylene diisocyanate, and 2,6-diisocyanate methyl caproate;
Alicyclic diisocyanates such as 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (hereinafter, isophorone diisocyanate), 4,4'-methylenebis(cyclohexyl isocyanate), methyl 2,4-cyclohexane diisocyanate, methyl 2,6-cyclohexane diisocyanate, 1,4-bis(isocyanatemethyl)cyclohexane, and 1,3-bis(isocyanatemethyl)cyclohexane;
Alternatively, polyisocyanates such as allophanate type, nurate type, biuret type, and adduct type derivatives derived from the above-mentioned aliphatic diisocyanates or alicyclic diisocyanates, or complexes thereof; and the like.
The aliphatic polyisocyanate is preferably a polyisocyanate derived from hexamethylene diisocyanate (hereinafter also referred to as HDI), which can easily ensure a balance of laminate properties.

(Aromatic aliphatic polyisocyanates)
The araliphatic polyisocyanate is not limited to the following, but a compound derived from a well-known araliphatic diisocyanate can be used.
Examples of the araliphatic polyisocyanate that can be used in the present invention include araliphatic diisocyanates such as 1,3- or 1,4-xylylene diisocyanate or a mixture thereof, ω,ω'-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis(1-isocyanato-1-methylethyl)benzene or a mixture thereof;
Alternatively, polyisocyanates such as derivatives of the above-mentioned araliphatic diisocyanates or complexes thereof; and the like.

(Other polyisocyanate components)
The adhesive of the present invention may contain other polyisocyanates in addition to the above-mentioned aliphatic polyisocyanates and araliphatic polyisocyanates. Examples of other polyisocyanates include aromatic diisocyanates such as toluene diisocyanate and diphenylmethane diisocyanate, or polyisocyanates such as derivatives of the above-mentioned diisocyanates or complexes thereof.

[Other ingredients]
The adhesive of the present invention may contain other components in addition to the above-mentioned polyester polyol component and at least one polyisocyanate component selected from the group consisting of aliphatic polyisocyanates and araliphatic polyisocyanates. The other components may be blended with either the polyester polyol component or the polyisocyanate component, or may be added when blending the polyol component and the polyisocyanate component.

(Silane coupling agent)
The adhesive of the present invention may further contain a silane coupling agent in order to enhance hot water resistance. Examples of the silane coupling agent include trialkoxysilanes having a vinyl group, such as vinyltrimethoxysilane 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 amount of the silane coupling agent added is preferably 0.1 to 5 mass%, more preferably 0.5 to 3 mass%, based on the solid content of the adhesive.

(Phosphorus oxyacid or its derivative)
The adhesive of the present invention may further contain a phosphorus oxyacid or a derivative thereof in order to enhance acid resistance. Among the phosphorus oxyacids or derivatives thereof, the phosphorus oxyacid may be any one having at least one free oxyacid, and examples thereof include phosphoric acids such as hypophosphorous acid, phosphorous acid, orthophosphoric acid, and hypophosphoric acid, and condensed phosphoric acids such as metaphosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, polyphosphoric acid, and ultraphosphoric acid. In addition, examples of derivatives of phosphorus oxyacids include those partially esterified with alcohols in a state in which at least one free oxyacid remains. Examples of these alcohols include aliphatic alcohols such as methanol, ethanol, ethylene glycol, and glycerin, and aromatic alcohols such as phenol, xylenol, hydroquinone, catechol, and phloroglucinol. Two or more types of phosphorus oxyacids or derivatives thereof may be used in combination. The amount of phosphorus oxyacid or its derivative added is preferably 0.01 to 10 mass %, more preferably 0.05 to 5 mass %, and particularly preferably 0.1 to 1 mass %, based on the solid content of the adhesive.

The adhesive of the present invention may contain the above-mentioned phosphorus oxyacid or a derivative thereof in order to improve releasability and increase the recyclability of the sealant substrate. From the viewpoint of the strength and releasability of the packaging material, the content of the phosphorus oxyacid or a derivative thereof is preferably 0.01 to 5 mass% based on the solid content of the adhesive.
More specifically, the amount of phosphorus oxyacid is more preferably 0.01 to 1 mass %, and even more preferably 0.01 to 0.5 mass %, based on the solid content of the adhesive. When the amount is 0.01 mass % or more, the strength of the packaging material is maintained while the releasability is improved. When the amount is 1 mass % or less, the strength of the packaging material is excellent.
The amount of the phosphoric acid derivative is preferably 0.01 to 5 mass %, more preferably 0.1 to 3 mass %, based on the solid content of the adhesive. When the amount is 0.01 mass % or more, the strength of the packaging material is maintained while the releasability is improved. When the amount is 5 mass % or less, the strength as a packaging material is superior.

(Leveling agent or defoamer)
The adhesive of the present invention may further contain a leveling agent or an antifoaming agent in order to improve the appearance of the laminate. Examples of the leveling agent include 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, and lecithin.
Examples of the defoaming agent include known ones such as silicone resin, silicone solution, copolymers of alkyl vinyl ether, alkyl acrylate, and alkyl methacrylate.

(Reaction accelerator)
The adhesive of the present invention may further contain a reaction accelerator to promote the urethanization reaction. Examples of the reaction accelerator include metal catalysts such as dibutyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate, and dibutyltin dimaleate; tertiary amines such as 1,8-diaza-bicyclo(5,4,0)undecene-7 and 1,5-diazabicyclo(4,3,0)nonene-5,6-dibutylamino-1,8-diazabicyclo(5,4,0)undecene-7; and reactive tertiary amines such as triethanolamine. One or more reaction accelerators selected from these groups may be used.

The adhesive of the present invention may contain various additives to the extent that the effect of the present invention is not impaired. Examples of additives include inorganic fillers such as silica, alumina, mica, talc, aluminum flakes, and glass flakes, layered inorganic compounds, stabilizers (antioxidants, heat stabilizers, UV absorbers, hydrolysis inhibitors, etc.), rust inhibitors, thickeners, plasticizers, antistatic agents, lubricants, antiblocking agents, colorants, fillers, crystal nucleating agents, and catalysts for adjusting the curing reaction.

Furthermore, in order to improve releasability and increase the recyclability of the sealant substrate, the adhesive of the present invention may contain, as the additive, fine particles having an average particle size of 1 to 10 μm. It is presumed that the inclusion of such fine particles maintains the strength of the packaging material due to an anchoring effect on the substrate, while reducing the contact area between the adhesive and the substrate, thereby improving releasability.
When the average particle size is 1 μm or more, the strength of the packaging material is maintained while improving the release property. When the average particle size is 10 μm or less, the strength of the packaging material can be maintained. In this specification, the average particle size means the median size measured by a particle size distribution measuring device using a laser diffraction/scattering method.
The fine particles having an average particle size of 1 to 10 μm are not particularly limited, and examples thereof include inorganic fillers such as silica, alumina, mica, talc, aluminum flakes, and glass flakes, as well as aluminum hydroxide, precipitated barium sulfate, magnesium carbonate, calcium carbonate, zeolite, and resin beads such as acrylic beads and urethane beads.

From the viewpoint of the strength and releasability of the packaging material, the blending amount of the microparticles is preferably 0.1 to 10 mass % based on the solid content of the adhesive, and more preferably 0.5 to 5.0 mass %. When the blending amount is 0.5 mass % or more, the strength of the packaging material is maintained while the releasability is improved. When the blending amount is 5.0 mass % or less, the strength as a packaging material is superior.

The adhesive of the present invention is preferably formulated by combining the phosphorus oxygen acid or its derivative with the fine particles having an average particle size of 1 to 10 μm. By using the above in combination, the detachment property and removal rate are further improved.

The adhesive of the present invention can be used as a solvent-free type when its viscosity is 100 to 10,000 mPa·s, preferably 100 to 5,000 mPa·s at room temperature to 150°C, preferably room temperature to 100°C. If the viscosity of the adhesive is higher than the above range, it may be diluted with an organic solvent. As the organic solvent, for example, esters such as ethyl acetate, ketones such as methyl ethyl ketone, aromatic hydrocarbons such as toluene and xylene, etc., which are inactive to the polyisocyanate component, are preferably used, and can be appropriately selected and used.

The adhesive of the present invention is a two-component curing urethane adhesive containing a polyester polyol component and a polyisocyanate component, and the acid value immediately after mixing is 5 mgKOH/g or more, more preferably 7 mgKOH/g or more, and particularly preferably 10 mgKOH/g or more. The acid value of the adhesive of the present invention immediately after mixing is 40 mgKOH/g or less, preferably 30 mgKOH/g or less, and more preferably 20 mgKOH/g or less.

When mixing the polyester polyol component and the polyisocyanate component, mix them so that the equivalent ratio (NCO/OH) of the isocyanate groups of the polyisocyanate to the hydroxyl groups of the polyol is 0.3 to 5.0. It is more preferably 0.3 to 2.0, and particularly preferably 0.5 to 1.5.

The removable adhesive layer is formed from the adhesive of the present invention. A typical method for forming the adhesive layer is to apply the adhesive to one side of a substrate 1 having a plastic layer and a pattern layer, and then, if necessary, to a drying step to volatilize the organic solvent, to bond the substrate to one side of a sealant substrate 2 using a laminator, and to harden the substrate at room temperature or under heating to form a removable adhesive layer.
The sealant substrate 2 may be a layer formed by extrusion lamination. Examples of a method for laminating the sealant substrate 2 by extrusion lamination include a method in which an adhesive is applied to one side of a substrate 1 having a plastic layer and a pattern layer, and an organic solvent is evaporated through a drying process as necessary, and then a molten sealant resin is extruded by a T-die method, the sealant substrate 2 is laminated by a cooling roll, and the sealant substrate 2 is cured at room temperature or under heating to form a removable adhesive layer.
The amount of adhesive applied after drying is optional, but is usually in the range of 0.001 to 6 g/m ² , preferably 1 to 2 g/m ² for solventless types and 1 to 6 g/m ² for solvent types.
When the sealant substrate 2 is a layer formed by extrusion lamination, the coating amount of the adhesive after drying is preferably in the range of 0.01 to 1 g/ ^m2 , and more preferably in the range of 0.05 to 0.5 g/ ^m2 .

<Packaging materials>
The packaging material in the present invention has a configuration in which a substrate 1 having a plastic layer and a pattern layer, a removable adhesive layer formed from the adhesive of the present invention, and a sealant substrate 2 are laminated in this order from the outside, with the removable adhesive layer being provided in contact with the substrate 1, and the sealant substrate 2 being provided on the side of the removable adhesive layer opposite the substrate 1.
The thickness of the removable adhesive layer can be appropriately adjusted depending on the type of adhesive and the sealant substrate 2, but is preferably 1 to 10 μm, and more preferably 1 to 6 μm. In particular, when the sealant substrate 2 is a layer formed by extrusion lamination, the thickness of the removable adhesive layer is preferably 0.01 to 1 μm, and more preferably 0.05 to 0.5 μm.

[Substrate 1]
The substrate 1 is preferably in the form of a film having at least a plastic layer and a pattern layer among the multiple layers constituting the substrate 1. The thickness of the substrate 1 is preferably 5 to 200 μm, more preferably 10 to 100 μm.

(Plastic layer)
Examples of the plastic layer include those generally used in packaging materials, such as polyester resin films such as polyethylene terephthalate, 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; laminates thereof (for example, nylon 6/MXD6/nylon 6, nylon 6/ethylene-vinyl alcohol copolymer/nylon 6) and mixtures thereof. Among these, those having mechanical strength and dimensional stability are preferred.
The plastic layer preferably has a thickness of 5 μm or more and 50 μm or less, and more preferably 10 μm or more and 30 μm or less.

(Pattern layer)
The design layer is a layer on which any desired printed pattern such as letters, numbers, pictures, figures, symbols, patterns, etc. is formed for decoration, display of contents, display of expiration date, display of manufacturer, seller, etc., or for imparting aesthetic appeal, and also includes a solid print layer. The design layer can be formed using conventionally known pigments or dyes, and the method for forming the design layer is not particularly limited.
In general, the design layer is formed using a printing ink containing a colorant such as a pigment or dye. The method for applying the printing ink is not particularly limited, and the printing ink can be applied by a method such as gravure coating, flexo coating, roll coating, bar coating, die coating, curtain coating, spin coating, inkjet, etc. The printing layer can be formed by leaving the ink alone or, if necessary, blowing air, heating, drying under reduced pressure, irradiating with ultraviolet light, etc.
The design layer preferably has a thickness of 0.1 μm or more and 10 μm or less, more preferably 1 μm or more and 5 μm or less, and further preferably 1 μm or more and 3 μm or less.

In addition to the plastic layer and the design layer, the substrate 1 may further comprise another layer, which may be provided either between the plastic layer and the design layer, on the plastic layer or on the design layer.
Other layers that may be present between the plastic layer and the design layer include, for example, a base layer or an anchor layer. Other layers that may be present on the plastic layer or on the design layer include the above-mentioned plastic layer, paper, or a gas barrier layer such as a metal foil or a vapor deposition layer. These other layers may be formed in multiples, and may be laminated via an adhesive layer.
The paper includes natural paper and synthetic paper.
Examples of the gas barrier layer include aluminum foil, as well as vapor-deposited layers of aluminum, silica, alumina, etc. For example, in the case of aluminum foil, a thickness in the range of 3 to 50 μm is preferable from an economical point of view.
As the adhesive layer for laminating another layer, either a known adhesive or the adhesive of the present invention may be used.

[Sealant substrate 2]
Examples of the sealant base material 2 include polyethylenes such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and 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.
From the viewpoint of recyclability, polyethylenes such as low-density polyethylene, linear low-density polyethylene and high-density polyethylene, acid-modified polyethylene, polypropylene, acid-modified polypropylene, copolymer polypropylene and other polyolefin resins are preferred.
From the viewpoint of heat resistance during retort, polypropylene-based resins are preferred, and from the viewpoint of heat sealability, unstretched polypropylene is particularly preferred.
The thickness of the sealant base material 2 is not particularly limited, but is preferably 10 to 150 μm, and more preferably 20 to 70 μm, in consideration of processability into packaging materials, heat sealability, etc. Furthermore, by providing the sealant base material 2 with unevenness having a height difference of about several μm, it is possible to impart slipperiness and tearability to the packaging material.
The method for laminating the sealant substrate is not particularly limited, and examples thereof include a method in which the substrate 1 and the sealant substrate 2 are thermally laminated using the adhesive of the present invention (thermal lamination, dry lamination), and a method in which a sealant resin is melted and extruded onto an adhesive layer using the adhesive of the present invention, and then cooled and solidified to form the sealant substrate 2 (extrusion lamination method).

Examples of the configuration of the packaging material of the present invention are given below, but the present invention is not limited to these.
Biaxially oriented polypropylene (OPP) / pattern layer / removable adhesive layer / non-oriented polypropylene (CPP),
OPP/pattern layer/removable adhesive layer/Al-deposited CPP,
OPP/pattern layer/removable adhesive layer/PE,
Pattern layer/OPP/removable adhesive layer/CPP,
NY/pattern layer/removable adhesive layer/PE,
Pattern layer/NY/Removable adhesive layer/CPP
NY/pattern layer/removable adhesive layer/CPP,
PET/pattern layer/removable adhesive layer/CPP,
Pattern layer/PET/Removable adhesive layer/CPP
PET/pattern layer/adhesive layer/NY/removable adhesive layer/CPP,
Transparent vapor-deposited PET/picture layer/adhesive layer/NY/removable adhesive layer/CPP,
PET/picture layer/adhesive layer/AL/removable adhesive layer/CPP,
PET/picture layer/adhesive layer/AL/removable adhesive layer/PE,
PET/picture layer/adhesive layer/NY/adhesive layer/AL/removable adhesive layer/CPP,
PET/pattern layer/adhesive layer/AL/adhesive layer/NY/removable adhesive layer/CPP.

<Recycled substrate manufacturing method>
The method for producing a recycled substrate of the present invention includes a step of immersing a packaging material having a structure in which a substrate 1 having a plastic layer and a design layer, a removable adhesive layer, and a sealant substrate 2 are laminated in this order from the outside, in a basic aqueous solution. More specifically, the method for producing a recycled substrate of the present invention includes a step of immersing the packaging material in a basic aqueous solution, and a step of peeling the substrate 1 having the plastic layer and the design layer from the packaging material to recover the sealant substrate 2.

The basic aqueous solution preferably contains 0.5 to 20% by mass of the basic compound based on the total amount of the basic aqueous solution, more preferably 1 to 15% by mass, and particularly preferably 3 to 15% by mass. By having the concentration within the above range, the basic aqueous solution can retain sufficient basicity to dissolve or swell the removable adhesive and remove it, thereby peeling off the substrate 1.
The basic aqueous solution penetrates the edge of the packaging material, contacts the removable adhesive layer, and dissolves or swells it, separating the substrate 1 from the substrate 2. Therefore, in order to efficiently proceed with the removal process, it is preferable that the packaging material is cut or crushed so that the removable adhesive layer is exposed on the cross section when it is immersed in the basic aqueous solution. In such a case, the pattern ink layer, substrate, etc. can be removed in a shorter time.

The temperature of the basic aqueous solution when the packaging material is immersed is preferably 25 to 120°C, more preferably 30 to 120°C, and particularly preferably 30 to 80°C. The immersion time in the basic aqueous solution is preferably 1 minute to 24 hours, more preferably 1 minute to 12 hours, and preferably 1 minute to 6 hours. The amount of the basic aqueous solution used is preferably 100 to 1,000,000 times the mass of the packaging material, and it is preferable to stir or circulate the basic aqueous solution to improve the desorption efficiency. The rotation speed is preferably 80 to 250 rpm, and more preferably 80 to 200 rpm.

After the substrate 1 having the plastic layer and the pattern layer is peeled off from the packaging material to recover the sealant substrate 2, the sealant substrate 2 is washed with water and dried to obtain a recycled substrate. The removal rate of the removable adhesive layer on the surface of the sealant substrate 2 is preferably 40% by mass or more, more preferably 70% by mass or more, and particularly preferably 90% by mass or more, out of 100% by mass of the removable adhesive layer.

Therefore, according to the present invention, a recycled base material of the sealant base material can be obtained through the steps of immersing the packaging material in a basic aqueous solution, removing the adhesive layer, peeling the base material 1 having the plastic layer and the pattern layer from the packaging material to recover the sealant base material 2, and rinsing and drying the sealant base material 2. The obtained recycled base material can be processed into pellets using an extruder or the like and reused as recycled resin.

The present invention will be described in more detail 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.

<Measurement of Acid Value>
Approximately 1 g of sample was precisely weighed and placed in a stoppered Erlenmeyer flask, and dissolved in 100 ml of a toluene/ethanol (volume ratio: toluene/ethanol = 2/1) mixture. Phenolphthalein test solution was added as an indicator and the mixture was allowed to stand for 30 seconds. After that, the solution was titrated with 0.1 N alcoholic potassium hydroxide solution until it turned a light pink color, and the acid value was calculated by the following formula.
Acid value (mgKOH/g) = (5.611 x a x F)/S
S: Amount of sample collected (g)
a: Amount of 0.1N alcoholic potassium hydroxide solution consumed (ml)
F: Factor of 0.1N alcoholic potassium hydroxide solution

<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 In the measurement, tetrahydrofuran was used as a solvent, and the value was calculated in terms of standard polystyrene. I asked.

<Production of polyol>
(Production Example 1) Polyester polyol (P-1)
A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping tank and a nitrogen gas inlet tube was charged with 263 parts of ethylene glycol, 468 parts of neopentyl glycol, 472 parts of isophthalic acid and 528 parts of adipic acid, and the temperature was raised to 250 ° C. while stirring under a nitrogen stream. After the reaction was continued until the acid value was 5 or less, the pressure was gradually reduced and the deglycolization reaction was carried out at 1 mmHg for 5 hours to obtain a polyester polyol. The mixture was then diluted with ethyl acetate until the nonvolatile content was 50%, to obtain a solution of polyester polyol (P-1) with a number average molecular weight of 2,500 and an acid value of 0.5 mgKOH / g.

(Production Example 2) Polyester polyol (P-2)
A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping tank and a nitrogen gas inlet tube was charged with 236 parts of ethylene glycol, 263 parts of neopentyl glycol, 202 parts of 1,6-hexanediol, 82 parts of terephthalic acid, 682 parts of isophthalic acid and 236 parts of adipic acid, and the temperature was raised to 250 ° C. while stirring under a nitrogen stream. After continuing the reaction until the acid value was 5 or less, the pressure was gradually reduced and a deglycolization reaction was carried out at 1 mmHg for 5 hours to obtain a polyester polyol. Then, 2 parts of isophorone diisocyanate were gradually added, and the reaction was carried out at 150 ° C. for about 2 hours to obtain a polyester polyurethane polyol. 2.5 parts of trimellitic anhydride were added to 100 parts of this polyester polyurethane polyol, and the reaction was carried out at 180 ° C. for about 2 hours, and then the mixture was diluted with ethyl acetate until the non-volatile content was 50%, to obtain a solution of partially acid-modified polyester polyol (P-2) having a number average molecular weight of 6,000 and an acid value of 14.5 mg KOH / g.

(Production Example 3) Polyester polyol (P-3)
A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping tank and a nitrogen gas inlet tube was charged with 202 parts of ethylene glycol, 331 parts of 2-methyl-1,3-propanediol, 77 parts of 1,6-hexanediol, 262 parts of terephthalic acid, 393 parts of isophthalic acid and 345 parts of adipic acid, and the mixture was heated to 250°C while stirring under a nitrogen stream. After the reaction was continued until the acid value was 5 or less, the pressure was gradually reduced and a deglycolization reaction was carried out at 1 mmHg for 5 hours to obtain a polyester polyol. Thereafter, 2 parts of isophorone diisocyanate was gradually added, and the reaction was carried out at 150°C for about 2 hours to obtain a polyester polyurethane polyol. 0.6 parts of trimellitic anhydride was added to 100 parts of this polyester polyurethane polyol, and the mixture was reacted at 180°C for about 2 hours. The mixture was then diluted with ethyl acetate until the non-volatile content reached 50%, to obtain a solution of partially acid-modified polyester polyol (P-3) having a number average molecular weight of 7,000 and an acid value of 3.6 mgKOH/g.

(Production Example 4) Polyester polyol (P-4)
A reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping tank, and a nitrogen gas inlet tube was charged with 202 parts of ethylene glycol, 253 parts of neopentyl glycol, 247 parts of 1,6-hexanediol, 682 parts of isophthalic acid, 72 parts of adipic acid, and 274 parts of sebacic acid, and the mixture was heated to 250°C while stirring under a nitrogen stream. After the reaction was continued until the acid value was 5 or less, the pressure was gradually reduced, and a deglycolization reaction was carried out at 1 mmHg for 5 hours to obtain a polyester polyol. Thereafter, 20 parts of isophorone diisocyanate was gradually added, and the reaction was carried out at 150°C for about 2 hours to obtain a polyester polyurethane polyol. 3.5 parts of ethylene glycol bis-anhydrotrimellitate was added to 100 parts of this polyester polyurethane polyol, and the mixture was allowed to react at 180°C for about 2 hours. The mixture was then diluted with ethyl acetate until the non-volatile content reached 50%, to obtain a solution of partially acid-modified polyester polyol (P-4) having a number average molecular weight of 8,000 and an acid value of 9.9 mgKOH/g.

(Production Example 5) Polyester polyol (P-5)
In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dropping tank and a nitrogen gas inlet tube, 240 parts of ethylene glycol, 253 parts of neopentyl glycol, 247 parts of 1,6-hexanediol, 682 parts of isophthalic acid, 72 parts of adipic acid and 274 parts of sebacic acid were charged and heated to 250°C while stirring under a nitrogen stream. After the reaction was continued until the acid value was 5 or less, the pressure was gradually reduced and a deglycolization reaction was carried out at 1 mmHg for 5 hours to obtain a polyester polyol. Thereafter, 40 parts of isophorone diisocyanate was gradually added and the reaction was carried out at 150°C for about 2 hours to obtain a polyester polyurethane polyol. 13.0 parts of ethylene glycol bis-anhydrotrimellitate was added to 100 parts of this polyester polyurethane polyol, and the mixture was allowed to react at 180°C for about 2 hours. The mixture was then diluted with ethyl acetate until the non-volatile content reached 50%, to obtain a solution of partially acid-modified polyester polyol (P-5) having a number average molecular weight of 9,500 and an acid value of 32.1 mgKOH/g.

(Production Example 6) Polyester polyol (P-6)
A reactor equipped with a stirrer, a thermometer, a reflux condenser, a dropping tank and a nitrogen gas inlet tube was charged with 283 parts of ethylene glycol, 468 parts of neopentyl glycol, 472 parts of isophthalic acid and 528 parts of adipic acid, and the temperature was raised to 250 ° C. while stirring under a nitrogen stream. After continuing the reaction until the acid value was 5 or less, the pressure was gradually reduced and the deglycolization reaction was carried out at 1 mmHg for 5 hours to obtain a polyester polyol. 3.5 parts of trimellitic anhydride were added to 100 parts of this polyester polyol, reacted at 180 ° C. for about 2 hours, and then diluted with ethyl acetate until the nonvolatile content was 50%, to obtain a solution of partially acid-modified polyester polyol (P-6) having a number average molecular weight of 2,000 and an acid value of 21.1 mgKOH / g.

(Production Example 7) Polyether polyol (P-7)
P-2000 (trade name, manufactured by ADEKA Corporation, bifunctional polyoxypropylene glycol, hydroxyl value 56.1) 81.95 parts, P-400 (trade name, manufactured by ADEKA Corporation, bifunctional polyoxypropylene glycol, hydroxyl value 265.9) 382.3 parts, T-400 (trade name, manufactured by Mitsui Chemicals, Inc., trifunctional polyoxypropylene glycol, hydroxyl value 404) 81.95 parts, dimethylolpropionic acid 19 parts, ethyl acetate 132.91 parts, tolylene diisocyanate 95.53 parts, and 4,4-diphenylmethane diisocyanate 121 parts, dibutyltin laurate 0.22 parts were charged, the temperature was raised to 90 ° C., and the reaction was carried out until the peak of the isocyanate group disappeared in the infrared absorption spectrum. Next, the solution was diluted with ethyl acetate to a non-volatile content of 50%, thereby obtaining a solution of partially acid-modified polyether polyol (P-7) having a number average molecular weight of 9,000 and an acid value of 10.4 mgKOH/g.

<Preparation of Polyisocyanate>
(Production Example 8) Polyisocyanate (C-1)
Coronate 2785 (biuret type polyisocyanate derived from hexamethylene diisocyanate, manufactured by Tosoh Corporation) was diluted with ethyl acetate to adjust the nonvolatile content to 50% and NCO% to 9.6%, to obtain a solution of polyisocyanate (C-1).

(Production Example 9) Polyisocyanate (C-2)
Bestanat T1890/100 (nurate type polyisocyanate derived from isophorone diisocyanate (hereinafter, IPDI), manufactured by Evonik Corporation) was diluted with ethyl acetate to adjust the nonvolatile content to 50% and NCO% to 8.7%, to obtain a solution of polyisocyanate (C-2).

(Production Example 10) Polyisocyanate (C-3)
Takenate D-110NB (trimethylolpropane adduct type polyisocyanate derived from xylylene diisocyanate (hereinafter, XDI), manufactured by Mitsui Chemicals, Inc.) was diluted with ethyl acetate to adjust the non-volatile content to 50% and NCO% to 7.9%, to obtain a solution of polyisocyanate (C-3).

(Production Example 11) Polyisocyanate (C-4)
Coronate L (a trimethylolpropane adduct type polyisocyanate derived from toluene diisocyanate (hereinafter, TDI), manufactured by Tosoh Corporation) was diluted with ethyl acetate to adjust the nonvolatile content to 50% and the NCO% to 8.8%, to obtain a solution of polyisocyanate (C-4).

(Production Example 12) Polyisocyanate (C-5)
Millionate MR-200 (a polymeric polyisocyanate derived from diphenylmethane diisocyanate (hereinafter, MDI), manufactured by Tosoh Corporation) was diluted with ethyl acetate to adjust the nonvolatile content to 50% and NCO% to 8.8%, to obtain a solution of polyisocyanate (C-5).

<Manufacture of adhesive>
[Examples 1 to 23, Comparative Examples 1 to 6]
The polyol solutions and polyisocyanate solutions obtained in Production Examples 1 to 12 above were mixed in the ratios (mass ratios) shown in Tables 2 and 3, and ethyl acetate was added to prepare adhesive solutions with a non-volatile content of 30%.

[Examples 24 to 26]
The polyol solutions and polyisocyanate solutions obtained in Production Examples 1 to 3, 5, 6, and 8 above were mixed in the ratios (mass ratios) shown in Table 4, and ethyl acetate was added to prepare adhesive solutions with a non-volatile content of 13%.

<Adhesive evaluation>
Using the obtained adhesive solution, packaging materials 1 to 3 were produced in the following manner. The obtained packaging materials were subjected to adhesive strength and releasability tests as described below. The results are shown in Tables 2 to 4.

(Production of packaging material 1)
Printing inks (Toyo Ink Co., Ltd., Rio Alpha R39 indigo, R631 white) were each diluted with an ethyl acetate/IPA mixed solvent (mass ratio 70/30) so that the viscosity was 16 seconds (25°C, Zahn cup No. 3). Each diluted printing ink was printed in the order of indigo and white on a corona-treated PET film (thickness 12 μm) using a gravure proofing two-color machine equipped with a solid plate with a plate depth of 35 μm. The printing speed was 50 m/min, and drying was performed at 50°C in each unit to obtain a PET/design layer laminate. The design layer had a thickness of 1 μm.
Next, an adhesive (TM-250HV/CAT-RT86L-60, manufactured by Toyo-Morton Co., Ltd.) was applied to the pattern layer of the obtained laminate using a laminator, and after the solvent was evaporated, the coated surface was attached to a nylon film having a thickness of 15 μm. The thickness of the adhesive layer was 3 μm.
Next, the adhesives obtained in the Examples and Comparative Examples were applied to the nylon film surface of the obtained laminate in the same manner as above, and after the solvent was evaporated, the applied surface was laminated to a 70 μm-thick CPP film that had been subjected to a surface corona discharge treatment. The thickness of the removable adhesive layer was 3 μm.
The obtained laminate was then kept at 40°C for 4 days to obtain a packaging material having a structure of PET (12 μm)/design layer (1 μm)/adhesive layer (3 μm)/NY (15 μm)/removable adhesive layer (3 μm)/CPP (70 μm).

(Production of packaging material 2)
Printing inks (Toyo Ink Co., Ltd., Rio Alpha R39 indigo, R631 white) were each diluted with an ethyl acetate/IPA mixed solvent (mass ratio 70/30) so that the viscosity was 16 seconds (25°C, Zahn cup No. 3). Each diluted printing ink was printed in the order of indigo and white on a corona-treated OPP film (thickness 20 μm) using a gravure proofing two-color machine equipped with a solid plate with a plate depth of 35 μm. The printing speed was 50 m/min, and drying was performed at 50°C in each unit to obtain a laminate of OPP/design layer. The thickness of the design layer was 1 μm.
Next, the adhesive obtained in the Examples and Comparative Examples was applied to the pattern layer of the obtained laminate using a laminator, the solvent was evaporated, and then the coated surface was laminated to a 25 μm thick CPP film that had been surface-corona discharge-treated.
The resulting laminate was then kept at 40° C. for 4 days to obtain a packaging material having a structure of OPP (20 μm)/picture layer (1 μm)/removable adhesive layer (2 μm)/CPP (25 μm).

(Production of packaging material 3)
Printing inks (Toyo Ink Co., Ltd., Rio Alpha R39 indigo, R631 white) were each diluted with an ethyl acetate/IPA mixed solvent (mass ratio 70/30) so that the viscosity was 16 seconds (25°C, Zahn cup No. 3). Each diluted printing ink was printed in the order of indigo and white on a corona-treated PET film (PET) having a thickness of 12 μm using a gravure proofing two-color machine equipped with a solid plate having a plate depth of 35 μm. The printing speed was 50 m/min, and drying was performed at 50°C in each unit to obtain a laminate of PET/design layer. The thickness of the design layer was 1 μm.
Next, the obtained laminate was delivered from the first roll, and the adhesive obtained in the Example was applied onto the design layer using a gravure coater, and the solvent was evaporated to form a removable adhesive layer having a thickness of 0.3 μm. Extrusion polyethylene (LDPE ^EXT ) was extruded from a T-die at 315° C., and then cooled on a cooling roll and taken up.
The resulting laminate was then kept at 40° C. for 4 days to obtain a packaging material having a structure of PET (12 μm)/picture layer (1 μm)/removable adhesive layer (0.3 μm)/LDPE ^EXT (30 μm).

<Evaluation of Packaging Material 1>
(Adhesive strength before retort)
A test piece measuring 15 mm × 300 mm was prepared from the packaging material 1, and the laminate strength (N/15 mm) between NY and CPP was measured using a tensile tester under conditions of a temperature of 20°C and a relative humidity of 65% by T-peel at a peel rate of 30 cm/min.

(Adhesive strength after retort)
A pouch measuring 21 cm x 30 cm was prepared using the packaging material 1, and a sauce containing salad oil, ketchup, and 4.2% vinegar in a mass ratio of 1:1:1 was vacuum-filled as the content. The obtained pouch was subjected to hot water sterilization at 10 rpm, 120°C, 30 minutes, and a pressure of 3 MPa.
A test piece measuring 15 mm×300 mm was prepared from the pouch that had been subjected to the retort treatment, and the laminate strength (N/15 mm) between NY and CPP was measured in the same manner as the adhesive strength before retort.

(Releasability)
Three test pieces measuring 2.0 cm x 2.0 cm were cut out from the pouch after the retort treatment, and were immersed and stirred at a rotation speed of 100 rpm in 50 g of a 2% aqueous solution of sodium hydroxide (NaOH) at 70° C. The time it took for the NY and CPP to peel off was measured, and the peeling was evaluated according to the following criteria.
⊚: Within 20 minutes, all of the NY and CPP peeled off (very good)
○: NY and CPP are completely peeled off within 20 minutes to 1 hour (good)
△: Within 1 hour to 12 hours, the NY and CPP are completely peeled off (usable)
×: No peeling between NY and CPP occurred within 12 hours (unusable)

(Removal rate)
A test piece measuring 2.0 cm x 2.0 cm was cut out from the pouch after the retort treatment, and immersed and stirred in 50 g of a 2% aqueous solution of sodium hydroxide (NaOH) at 70°C for 1 hour at a rotation speed of 100 rpm to peel the NY from the CPP. The test piece was then washed with water and dried to obtain a recycled CPP film measuring 2.0 cm x 2.0 cm.
The recycled CPP film thus obtained was checked for the presence or absence of an absorption peak of the adhesive at a total of five locations, namely, the four edges and the center, on the surface where the removable adhesive layer had been in contact, using FT-IR, and was evaluated according to the following criteria: Films in which the NY and CPP did not peel within one hour were deemed unsatisfactory.
◎: No adhesive absorption peak at all five locations (removal rate is approximately 100%: very good)
○: Adhesive absorption peak is observed in only one of the five locations (removal rate is about 80%: good)
△: Adhesive absorption peaks in 2 to 3 of the 5 locations (removal rate of about 40 to 60%: usable)
×: Adhesive absorption peaks in 4 or more of the 5 locations (removal rate of about 20%: unusable)

<Evaluation of Packaging Material 2>
(Adhesive strength)
A test piece measuring 15 mm × 300 mm was prepared from the packaging material 2, and the laminate strength (N/15 mm) between the OPP and CPP was measured using a tensile tester under conditions of a temperature of 20°C and a relative humidity of 65% by T-peel at a peel rate of 30 cm/min.

(Releasability (1))
A test piece measuring 2.0 cm x 2.0 cm was cut out from the obtained packaging material 2, and was immersed and stirred at a rotation speed of 100 rpm in 50 g of a 2% aqueous solution of sodium hydroxide (NaOH) at 70° C. The time it took for the OPP and CPP to peel off was measured, and evaluated according to the following criteria.
⊚: OPP and CPP are completely peeled off within 20 minutes (very good)
○: OPP and CPP are completely peeled off within 20 minutes to 1 hour (good)
△: The OPP and CPP are completely peeled off within 1 hour to 12 hours (usable)
×: The OPP and CPP are not completely peeled off within 12 hours (unusable)

(Releasability (2))
A test piece measuring 3.0 cm x 3.0 cm was cut out from the obtained packaging material 2, and was immersed and stirred in 50 g of a 2% aqueous solution of sodium hydroxide (NaOH) at 70°C at a rotation speed of 50 rpm. The time it took for the OPP and CPP to peel off was measured, and evaluated according to the following criteria.
⊚: OPP and CPP are completely peeled off within 20 minutes (very good)
○: OPP and CPP are completely peeled off within 20 minutes to 1 hour (good)
△: The OPP and CPP are completely peeled off within 1 hour to 12 hours (usable)
×: The OPP and CPP are not completely peeled off within 12 hours (unusable)

(Removal rate (1))
A test piece measuring 2.0 cm x 2.0 cm was cut out from the obtained packaging material 2, and immersed and stirred in 50 g of a 2% aqueous solution of sodium hydroxide (NaOH) at 70°C for 1 hour at a rotation speed of 100 rpm to peel the OPP and CPP apart, followed by rinsing with water and drying to obtain a recycled CPP film measuring 2.0 cm x 2.0 cm.
The presence or absence of an absorption peak of the adhesive was confirmed using FT-IR at five locations, namely, the four edges and the center, on the surface of the obtained recycled CPP film where the removable adhesive layer had been in contact, and the film was evaluated according to the following criteria. Films in which the OPP and CPP did not peel off within one hour were deemed unsatisfactory.
◎: No adhesive absorption peak at all five locations (removal rate is approximately 100%: very good)
○: Adhesive absorption peak is observed in only one of the five locations (removal rate is about 80%: good)
△: Adhesive absorption peaks in 2 to 3 of the 5 locations (removal rate of about 40 to 60%: usable)
×: Adhesive absorption peaks in 4 or more of the 5 locations (removal rate of about 20%: unusable)

(Removal rate (2))
A test piece measuring 3.0 cm x 3.0 cm was cut out of the obtained packaging material 2, and immersed and stirred in 50 g of a 2% aqueous solution of sodium hydroxide (NaOH) at 70°C for 1 hour at a rotation speed of 50 rpm to peel the OPP and CPP apart, followed by rinsing with water and drying to obtain a recycled CPP film measuring 3.0 cm x 3.0 cm.
The presence or absence of an absorption peak of the adhesive was confirmed using FT-IR at five locations, namely, the four edges and the center, on the surface of the obtained recycled CPP film where the removable adhesive layer had been in contact, and the film was evaluated according to the following criteria. Films in which the OPP and CPP did not peel off within one hour were deemed unsatisfactory.
◎: No adhesive absorption peak at all five locations (removal rate is approximately 100%: very good)
○: Adhesive absorption peak is observed in only one of the five locations (removal rate is about 80%: good)
△: Adhesive absorption peaks in 2 to 3 of the 5 locations (removal rate of about 40 to 60%: usable)
×: Adhesive absorption peaks in 4 or more of the 5 locations (removal rate of about 20%: unusable)

<Evaluation of Packaging Material 3>
(Adhesive strength before boiling)
A test piece measuring 15 mm × 300 mm was prepared from the packaging material 3, and the laminate strength (N/15 mm) between the PET/LDPE ^EXT was measured using a tensile tester under conditions of a temperature of 20° C. and a relative humidity of 65% by T-peel at a peel rate of 30 cm/min.

(Adhesive strength after boiling)
A pouch measuring 21 cm x 30 cm was prepared using the packaging material 3, and water was vacuum-filled as the content. The obtained pouch was subjected to a heat treatment at 85°C for 30 minutes.
A test piece measuring 15 mm×300 mm was prepared from the above-mentioned boiled pouch, and the laminate strength (N/15 mm) between PET/LDPE ^EXT was measured in the same manner as the adhesive strength before boiling.

(Releasability)
Three test pieces measuring 2.0 cm x 2.0 cm were cut out from the pouch after the boiling treatment, and were immersed and stirred in 50 g of a 2% aqueous solution of sodium hydroxide (NaOH) at 70°C at a rotation speed of 100 rpm. The time it took for the PET and LDPE ^EXT to peel off was measured, and the peeling was evaluated according to the following criteria.
⊚: Within 20 minutes, the PET and LDPE ^EXT are completely peeled off (very good)
○: The PET and the LDPE ^EXT are completely peeled off within 20 minutes to 1 hour (good)
△: Within 1 hour to 12 hours, the PET and LDPE ^EXT are completely peeled off (usable)
×: No peeling between the PET and the LDPE ^EXT occurred within 12 hours (unusable)

(Removal rate)
A test piece measuring 2.0 cm x 2.0 cm was cut out from the pouch after the boiling treatment, and immersed and stirred in 50 g of a 2% aqueous solution of sodium hydroxide (NaOH) at 70°C for 1 hour at a rotation speed of 100 rpm to peel the PET from the LDPE ^EXT , followed by rinsing with water and drying to obtain a recycled PE film measuring 2.0 cm x 2.0 cm.
The presence or absence of an absorption peak of the adhesive was confirmed using FT-IR for a total of five locations, namely, the four edges and the center, on the surface of the obtained recycled PE film where the removable adhesive layer had been in contact, and the film was evaluated according to the following criteria. Films in which the PET and LDPE ^EXT did not peel off within one hour were deemed unsatisfactory.
◎: No adhesive absorption peak at all five locations (removal rate is approximately 100%: very good)
○: Adhesive absorption peak is observed in only one of the five locations (removal rate is about 80%: good)
△: Adhesive absorption peaks in 2 to 3 of the 5 locations (removal rate of about 40 to 60%: usable)
×: Adhesive absorption peaks in 4 or more of the 5 locations (removal rate of about 20%: unusable)

According to the results in Table 2, the adhesive of the present invention, which contains a polyester polyol component including an acid anhydride-modified polyester polyurethane polyol and at least one polyisocyanate component selected from the group consisting of aliphatic polyisocyanates and araliphatic polyisocyanates and has an acid value of 5 to 40 mgKOH/g, has retort suitability and excellent alkali release properties, and allows the sealant substrate to be easily separated from the packaging material, thereby enhancing the recyclability of the sealant substrate.
In particular, Examples 5, 6 and 11, in which a polyester polyol having a number average molecular weight of less than 3,000 was used in combination, exhibited excellent laminate strength in addition to good alkali release properties and removal rates.

The abbreviations in Table 3 are as follows:
Phosphoric acid: 85% phosphoric acid aqueous solution Phosphoric acid derivative: Phosphanol RL-310, manufactured by Toho Chemical Industry Co., Ltd. Aluminum hydroxide 1: BF013, manufactured by Nippon Light Metal Co., Ltd., average particle size 1 μm
Aluminum hydroxide 2: BX103, manufactured by Nippon Light Metal Co., Ltd., average particle size 5 μm
Aluminum hydroxide 3: BF083, manufactured by Nippon Light Metal Co., Ltd., average particle size 10 μm
Acrylic resin beads: Art Pearl J-7P, manufactured by Negami Chemical Industries, Ltd., average particle size 6 μm

According to the results in Table 3 above, compared to Example 11, Examples 12 to 16, in which phosphoric acid or a phosphoric acid derivative was added, and Example 17, in which fine particles with an average particle size of 1 to 10 μm were added, showed improved desorption. Furthermore, Examples 18 to 23, in which both phosphoric acid and fine particles with an average particle size of 1 to 10 μm were added, showed a tendency for the desorption or removal rate to improve.

According to the results in Table 4 above, the packaging material 3 in which the sealant substrate 2 was laminated by extrusion lamination had a thinner removable adhesive layer than that in the case of conventional dry lamination, but exhibited good alkali releasability and removal rate as well as excellent laminate strength.

Claims (11)

A substrate 1 having a plastic layer and a pattern layer, a removable adhesive layer, and a sealant substrate 2 are laminated in this order from the outside, and an adhesive that forms a removable adhesive layer that constitutes a packaging material in which the substrate 1 is peeled off and the sealant substrate 2 is recycled,
The adhesive comprises a polyester polyol component and at least one polyisocyanate component selected from the group consisting of an aliphatic polyisocyanate and an araliphatic polyisocyanate, the araliphatic polyisocyanate being selected from the compounds listed below:
<A compound selected from 1,3- or 1,4-xylylene diisocyanate or a mixture thereof, ω,ω'-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis(1-isocyanato-1-methylethyl)benzene or a mixture thereof;
and a compound selected from the above-mentioned derivatives and complexes.
The adhesive has an acid value of 5 to 40 mgKOH/g. The adhesive according to claim 1, wherein the number average molecular weight of the polyester polyol component is 5,000 to 15,000. The adhesive according to claim 1 or 2, wherein the acid value of the polyester polyol component is 10 to 40 mg KOH/g. The adhesive according to any one of claims 1 to 3, wherein the polyester polyol component contains an acid anhydride-modified polyester polyurethane polyol. The adhesive according to any one of claims 1 to 4, wherein the polyester polyol component comprises a polyester polyol having a number average molecular weight of 5,000 to 15,000 and a polyester polyol having a number average molecular weight of less than 3,000. The adhesive according to any one of claims 1 to 5 further contains 0.01 to 5 mass% of a phosphorus oxyacid or a derivative thereof based on the solid content of the adhesive. The adhesive according to any one of claims 1 to 6 further comprises fine particles having an average particle size of 1 to 10 μm. The adhesive according to claim 7, wherein the content of the microparticles is 0.1 to 10 mass % based on the solid content of the adhesive. A packaging material having a structure in which a substrate 1 having a plastic layer and a pattern layer, a removable adhesive layer formed from the adhesive according to any one of claims 1 to 8, and a sealant substrate 2 are laminated from the outside in this order. The packaging material according to claim 9, wherein the sealant substrate 2 is a layer formed by extrusion lamination, and the thickness of the removable adhesive layer is 0.01 to 1 μm. A method for producing a recycled substrate, comprising the step of immersing a packaging material in a basic aqueous solution, the packaging material comprising a substrate 1 having a plastic layer and a pattern layer, a removable adhesive layer formed from the adhesive according to any one of claims 1 to 8, and a sealant substrate 2, laminated in this order from the outside;
The basic aqueous solution contains a basic compound in an amount of 0.5 to 20% by mass based on the total amount of the basic aqueous solution, and the temperature of the basic aqueous solution during immersion is 25 to 120° C.