JP7554337B2 - Coating composition for forming oxygen barrier layer, laminate, method for removing oxygen barrier layer, and method for recovering substrate - Google Patents

Description

The present invention relates to a coating composition for forming an oxygen barrier layer, a laminate, a method for removing the oxygen barrier layer of the laminate, and a method for recovering the substrate of the laminate. More specifically, the present invention relates to a coating composition for forming an oxygen barrier layer used for a laminate having, for example, a first substrate and an oxygen barrier layer, and also to a coating composition for forming an oxygen barrier layer used for a laminate having a first substrate and a second substrate, for example, the first substrate, the second substrate, and the oxygen barrier layer. The laminate of the present invention, which is formed using the coating composition for forming an oxygen barrier layer of the present invention, can be widely used in large quantities as a film packaging material, and is excellent in the removal of the oxygen barrier layer from the laminate as described above. This technology is useful for environmental conservation, and is expected to contribute to the recycling of substrates and the effective use of resources.

For example, for packaging materials (packaging materials) for food packaging and packaging materials for toiletry products, it is necessary to prevent oxidation of the food contained therein and deterioration of the products contained therein, such as moisturizers and shampoos, so films with excellent oxygen barrier properties are used. Various methods have been conceived, proposed, and implemented to provide a film with oxygen barrier properties. For example, Patent Document 1 proposes providing a coating layer of a specific material composition on the deposition layer surface of a deposition film in which a metal deposition layer is provided on a substrate film. Patent Document 2 also proposes a coating liquid using a resin containing a specific polyvinyl alcohol and a specific polyacrylic acid as a coating liquid for forming a gas barrier layer, and proposes a coating film formed from the coating liquid to be used as a gas barrier layer, and a laminate including the coating film and the substrate.

In response to the recent problem of global warming, the applicant has proposed various methods for producing polyhydroxyurethane resins as a groundbreaking technology for synthesizing useful resins using carbon dioxide as a material. Among these, the applicant has proposed an aqueous dispersion composition in which polyhydroxyurethane resin and clay minerals are well-composite-dispersed in water, which can be used as a resin for forming a film in water-based paints and coating agents (see Patent Document 3). This aqueous dispersion composition is an aqueous dispersion in which clay minerals, which are known to improve gas barrier properties (low oxygen permeability), are well-dispersed in water, and by using this, a film with superior gas barrier properties, for example, a laminate in which an oxygen barrier layer is formed on a substrate film, can be easily produced.

In addition, in recent years, excessive consumption of plastic products has become a social issue, and in view of the problem of the depletion of finite petroleum resources and the adverse effects of waste on living organisms, there is a demand to recycle plastic films that have been used once and reuse them as plastic films from the perspective of effective resource utilization and global environmental conservation. In particular, plastic films used as packaging materials for food and toiletry products are consumed in large quantities and discarded in large quantities, so if this plastic film could be easily recycled, it is expected that the amount of discarded plastic film could be significantly reduced, which would be extremely useful.

Japanese Patent Application Publication No. 8-318591 Patent No. 7060946 Patent No. 6813338

However, for example, film packaging (containers) made of plastic film for food or toiletry products packaging is required to have various properties such as oxygen barrier properties and aroma retention properties, and therefore, instead of a structure made of a single layer of plastic film, many of them are formed of a laminate made of various functional material layers such as an oxygen barrier layer, a pattern layer, and a metal layer. For example, in the case of plastic film for food or toiletry products packaging, a laminate is formed in which an oxygen barrier layer is provided on the entire surface of the plastic film substrate in order to prevent oxidation and deterioration of the items contained inside. Therefore, when recycling the plastic film used as the substrate from a film packaging made of such a laminate, it is necessary to remove the oxygen barrier layer formed on the entire surface of the substrate and recover it as a single plastic film. Furthermore, in order to reuse the plastic film recovered after use as a film packaging for food packaging or toiletry products, it is necessary for the recycled film to exhibit physical properties that satisfy the various required properties. However, there were problems in that it was difficult to obtain a recycled film that could be reused for packaging from a laminate with the structure described above in a simple manner, and to obtain a recycled film that met all the various required performance requirements.

Therefore, the object of the present invention is to provide a coating composition for forming an oxygen barrier layer having a new structure, which can form a laminate having a structure in which at least the oxygen barrier layer can be easily removed from a laminate having, for example, a first substrate and an oxygen barrier layer having low oxygen permeability, excellent oxygen barrier properties, and excellent adhesion, and can be made into a recycled film in a simple manner. Another object of the present invention is to provide a coating composition for forming an oxygen barrier layer having a new structure, which can form a laminate having at least the oxygen barrier layer can be easily removed from a laminate having excellent laminate strength, which is composed of, for example, a first substrate, a second substrate, and an excellent oxygen barrier layer having low oxygen permeability, and can be made into a recycled film in a simple manner and can be recovered. Hereinafter, in order to distinguish between embodiments, a laminate having a so-called surface-printed structure having an oxygen barrier layer (coating film) made of a first substrate and the coating composition of the present invention is also referred to as "Laminate-1". In addition, a laminate having a so-called laminate structure, which has a first and second substrate and an oxygen barrier layer (coating film) made of the coating composition of the present invention, is also called "Laminate-2."

In the present invention, the functional layer provided to impart various required performance to the plastic film (substrate) used for packaging materials for food, toiletry products, etc. is called the "oxygen barrier layer" as a representative example of oxygen barrier property among the various performances required for plastic films. A plastic film with low oxygen permeability exhibits good oxygen barrier properties, but in the present invention, it is also an object of the present invention to have another required performance, good aroma retention, by simultaneously achieving low permeability for the aroma applied to the item contained inside. In other words, the film packaging having the oxygen barrier layer in the present invention means that it has at least good oxygen barrier properties and aroma retention. Here, if the "aroma retention" of the film packaging is insufficient, the aroma of the item contained inside will leak out to the outside, causing the problem of odor transfer to other products, so realizing "aroma retention" is also an important technical issue for film packaging for food, toiletry products, etc.

The above object can be achieved by the present invention, which provides the following coating composition for forming an oxygen barrier layer.
[1] A coating composition for forming an oxygen barrier layer, comprising a polyurethane resin and a layered clay mineral,
The polyurethane resin has a hydroxyl value of 100 to 400 mgKOH/g and an acid value of 15 to 70 mgKOH/g;
The average aspect ratio of the layered clay mineral is 150 to 350;
A coating composition for forming an oxygen barrier layer, characterized in that the ratio of solids in the polyurethane resin and the layered clay mineral is 100:1 to 100:35 on a mass basis.

Preferred forms of the above-mentioned coating composition for forming an oxygen barrier layer include the following.
[2] The coating composition for forming an oxygen barrier layer according to the above [1], wherein the particle size of the layered clay mineral is 1.0 to 20 μm.
[3] The coating composition for forming an oxygen barrier layer according to the above [1] or [2], wherein the weight average molecular weight of the polyurethane resin is 10,000 to 1,200,000.
[4] The coating composition for forming an oxygen barrier layer according to any one of the above [1] to [3], wherein the polyurethane resin is a polyhydroxyurethane resin which is a reaction product of a cyclic carbonate compound which is a reaction product of an epoxy compound and carbon dioxide, and a polyamine.
[5] The coating composition for forming an oxygen barrier layer according to any one of the above [1] to [4], further comprising an epoxy compound as a curing agent.
[6] The coating composition for forming an oxygen barrier layer according to any one of the above [1] to [5], which is used for forming an oxygen barrier layer of a laminate film.

As another embodiment, the present invention provides the following laminate.
[7] A laminate comprising an oxygen barrier layer formed on a first substrate, the oxygen barrier layer being made of the coating composition for forming an oxygen barrier layer according to any one of [1] to [6] above.

Preferable forms of the above-mentioned laminate include the following.
[8] The laminate according to the above [7], wherein the first substrate is made of any polyolefin-based resin.
[9] The laminate according to the above [7] or [8], wherein the first substrate is made of a recycled material that has been recovered after being used once.
[10] The laminate according to any one of the above [7] to [9], further comprising a first and a second substrate formed by laminating an adhesive layer and a second substrate in this order on the oxygen barrier layer formed on the first substrate.
[11] The laminate according to the above [10], wherein the second substrate is made of at least one resin selected from the group consisting of polyolefin resins, polyester resins, and nylon resins.
[12] The laminate according to the above [10] or [11], wherein the first substrate and/or the second substrate is made of a recycled material that has been recovered after being used once.

As another embodiment, the present invention provides a method for removing an oxygen barrier layer, which is described below.
[13] A method for removing an oxygen barrier layer from a laminate comprising a first substrate and an oxygen barrier layer made of the coating composition for forming an oxygen barrier layer according to any one of [1] to [6] above, or from a laminate comprising the first substrate, a second substrate, and the oxygen barrier layer, the method comprising the step of removing the oxygen barrier layer from the laminate using an alkaline solution.

As another embodiment, the present invention provides a method for recovering a substrate, as described below.
[14] A method for recovering a substrate, comprising removing an oxygen barrier layer from a laminate comprising a first substrate and an oxygen barrier layer formed from the coating composition for forming an oxygen barrier layer according to any one of [1] to [6] above, or a laminate comprising the first substrate, a second substrate, and the oxygen barrier layer, and recovering at least the first substrate, the method comprising the step of removing the oxygen barrier layer from the laminate using an alkaline solution.

According to the present invention, it is possible to provide a coating composition for forming an oxygen barrier layer, which exhibits excellent oxygen barrier properties (including aroma retention) with low oxygen permeability and is capable of forming an oxygen barrier layer in which the formed coating film exhibits excellent release properties. In addition, the oxygen barrier layer having the above-mentioned excellent functions formed with the coating composition for forming an oxygen barrier layer of the present invention has excellent adhesion to the substrate, and when formed into a laminate with a laminate structure, it also has excellent laminate strength. Therefore, according to the present invention, it is possible to provide a laminate that realizes excellent oxygen barrier properties, for example, a film packaging body having good oxygen barrier properties and aroma retention. At the same time, it is possible to provide a laminate in which the oxygen barrier layer constituting the laminate exhibits excellent adhesion and also exhibits good release properties from the substrate, enabling the recycling of the substrate film. In addition, according to the present invention, it is also possible to provide a laminate having a laminate structure with excellent lamination strength in addition to having the above-mentioned excellent properties, and a film packaging body made of the laminate. Furthermore, according to a preferred embodiment of the coating composition for forming an oxygen barrier layer of the present invention, which uses a polyhydroxyurethane resin made from carbon dioxide as a raw material, in addition to the above, it is possible to form a more stable and excellent oxygen barrier layer, and it is also possible to provide a coating composition for forming an oxygen barrier layer that is useful from the viewpoint of global environmental conservation, which can contribute to solving the problem of global warming. Furthermore, according to the study by the present inventors, by using a resin having a hydroxyl value specified in the present invention as a polyurethane resin, a more specific example being a material such as a polyhydroxyurethane resin, it is possible to vapor-deposit a metal or metal oxide such as aluminum or silica directly onto the formed oxygen barrier layer. As a result, according to the present invention, an excellent effect in terms of production is obtained in that it is not necessary to provide a primer as an undercoat.

The present invention will be described in detail below, taking preferred embodiments for carrying out the present invention into consideration. However, the present invention is not limited to the following embodiments. The coating composition for forming an oxygen barrier layer of the present invention (hereinafter, may be simply referred to as the "coating composition") contains a polyurethane resin and a layered clay mineral, the polyurethane resin having a hydroxyl value of 100 to 400 mg KOH/g and an acid value of 15 to 70 mg KOH/g, the layered clay mineral having an average aspect ratio of 150 to 350, and further, the ratio of solids in the polyurethane resin to the layered clay mineral is 100:1 to 100:35 by mass.

The coating composition for forming an oxygen barrier layer of the present invention is used to form an oxygen barrier layer in a laminate (laminate-1) in which an oxygen barrier layer is formed on a first substrate (sometimes referred to as substrate-1), or in a laminate (laminate-2) having an oxygen barrier layer with a first and second substrate (sometimes referred to as substrate-2). These laminates have a remarkable effect that the oxygen barrier layer formed on the first substrate can be easily removed, which was not possible with conventional laminates, and a recyclable plastic film (substrate) can be easily obtained. Furthermore, when the coating composition of the present invention is applied to a laminate having two substrates, a first and a second substrate (a laminate structure), it has a remarkable effect that the oxygen barrier layer formed on the first substrate can be easily removed, and a laminate having excellent laminate strength can be obtained.

Hereinafter, each component constituting the coating composition for forming an oxygen barrier layer of the present invention will be described.
[Polyurethane resin]
The polyurethane resin constituting the coating composition of the present invention must have a hydroxyl value of 100 to 400 mgKOH/g and an acid value of 15 to 70 mgKOH/g. The method for synthesizing the polyurethane resin having the above-mentioned properties used in the present invention is not particularly limited, and it can be easily produced by utilizing a conventionally known method. For example, a synthesis method by reacting a bifunctional cyclic carbonate compound with a polyamine can be used (see, for example, U.S. Patent No. 3,072,613). In the present invention, it is particularly preferable to use a polyhydroxyurethane resin obtained by reacting a cyclic carbonate compound obtained by reacting an epoxy compound with carbon dioxide with a polyamine (see, for example, Japanese Patent No. 6,224,529). Specifically, by using a polyhydroxyurethane resin having a hydroxyl value of 100 to 400 mgKOH/g and an acid value of 15 to 70 mgKOH/g as the polyurethane resin constituting the coating composition of the present invention, an oxygen barrier layer having excellent oxygen barrier properties and aroma retention properties, and a laminate having the oxygen barrier layer and excellent oxygen barrier properties, for example, a film packaging product made of the laminate, can be more stably obtained. Details of the polyhydroxyurethane resin suitable as the polyurethane resin constituting the present invention will be described later.

As described above, the polyurethane resin constituting the coating composition of the present invention has a hydroxyl value of 100 to 400 mgKOH/g. The hydroxyl value is preferably 120 to 350 mgKOH/g, and more preferably 150 to 300 mgKOH/g. Furthermore, it is more preferable to use a polyurethane resin having a hydroxyl value of 170 to 250 mgKOH/g. By using a polyurethane resin having a hydroxyl value in the above range, an oxygen barrier layer having high oxygen barrier properties is formed, and a laminate having excellent oxygen barrier properties and aroma retention properties, for example, a film packaging body made of the laminate, can be obtained. If the hydroxyl value of the polyurethane resin is less than the lower limit of the above range, the oxygen barrier properties and aroma retention properties of the formed oxygen barrier layer are inferior, while if it exceeds the upper limit of the above range, the resin becomes hard, which is undesirable in the following respects. According to the inventors' investigations, particularly when made into a laminate, the adhesion between the first substrate and the oxygen barrier layer in "Laminate-1" is poor, and when made into a laminate film in "Laminate-2," the laminate strength is poor.

The acid value of the polyurethane resin constituting the coating composition of the present invention must be 15 to 70 mgKOH/g. It is also preferable that it is 15 to 60 mgKOH/g or 20 to 55 mgKOH/g, and more preferably 30 to 50 mgKOH/g or 35 to 45 mgKOH/g. If the acid value of the polyurethane resin is less than the lower limit, the releasability is poor, and there is another problem that the miscibility with water is reduced and the stability as an emulsion is poor. Regarding the releasability, for example, as shown in Comparative Example 6, the peeling test results when a polyurethane resin having an acid value of 10 mgKOH/g was used showed that the peeling of the coating film was less than 10%. This point will be described later. On the other hand, if the acid value of the polyurethane resin exceeds the upper limit, it is not preferable in terms of a decrease in water resistance. According to the study by the present inventors, by using a polyurethane resin having an acid value within the above range, an oxygen barrier layer with excellent releasability can be obtained.

The weight-average molecular weight of the polyurethane resin is preferably 10,000 to 1,200,000, more preferably 30,000 to 200,000, and even more preferably 50,000 to 100,000. According to the inventors' study, when a polyurethane resin having a weight-average molecular weight of less than 10,000 is used, physical properties such as water resistance may decrease. On the other hand, according to the inventors' study, when a polyurethane resin having a weight-average molecular weight of more than 1,200,000 is used, the laminate strength of the laminate film "Laminate-2" may decrease. According to the inventors' study, by using a polyurethane resin having a weight-average molecular weight within the above range, a laminate that achieves both physical properties such as water resistance and laminate strength and adhesion, and a film packaging body made of the laminate can be obtained.

The content of the polyurethane resin constituting the coating composition of the present invention is preferably 10 to 80% by mass. If the content of the polyurethane resin is less than 10% by mass, the drying speed may decrease when the coating composition is printed or applied as a coating liquid, raising concerns about reduced productivity. On the other hand, since the viscosity of the coating liquid may increase, it is preferable that the content of the polyurethane resin does not exceed 80% by mass. In view of the above, it is preferable that the content of the polyurethane resin is 10% by mass or more, since if it is less than 10% by mass, there is a concern about reduced productivity due to a reduced drying speed during printing, and it is preferable that it does not exceed 80% by mass, since the viscosity of the coating liquid increases.

(Polyhydroxyurethane resin)
As mentioned above, it is preferable to use a polyhydroxyurethane resin synthesized as follows as the polyurethane resin used in the present invention. The polyhydroxyurethane resin is obtained by reacting a cyclic carbonate compound obtained by reacting an epoxy compound with carbon dioxide with a polyamine. The polyhydroxyurethane resin obtained by this synthesis method has a characteristic structure having a hydroxyl group (hydroxy group) in the main chain. An example of a polyhydroxyurethane resin that can be suitably used in the coating composition of the present invention is shown below.

［一般式（１）中、－Ｘ－は、直接結合か、炭素数１～３０の脂肪族炭化水素基、炭素数４～４０の脂環式炭化水素基又は炭素数６～４０の芳香族炭化水素基であり、これらの基の構造中には、エーテル結合、アミノ結合、スルホニル結合及びエステル結合のいずれか、或いは、置換基として、水酸基、ハロゲン原子及び繰り返し単位１～３０の炭素数２～６からなるポリアルキレングリコール鎖のいずれかを含んでもよい。Ｙ－は、炭素数１～１５の脂肪族炭化水素基、炭素数４～１５の脂環式炭化水素基又は炭素数６～１５の芳香族炭化水素基であり、これらの基の構造中には、エーテル結合又はスルホニル結合、或いは、置換基として水酸基及びハロゲン原子のいずれかを含んでもよい。－Ｚ_１－、－Ｚ_２－は、それぞれ独立に、下記式（２）、式（３）、一般式（４）及び一般式（５）からなる群から選ばれる少なくともいずれかの構造を示し、繰り返し単位内及び繰り返し単位間のいずれにおいても、これらの式（２）～（５）から選ばれる２種以上の構造が混在してもよい。また、これらの式（２）～（５）のいずれの式を選択した場合も、右側の結合手は酸素原子と結合し、且つ、左側の結合手はＸと結合し、Ｘが直接結合の場合は、他方のＺの左側の結合手と結合する。］

［一般式（４）又は（５）中、Ｒは、水素原子又はメチル基を示す。］

［一般式（６）中、－Ｗ－は、炭素数１～３０の脂肪族炭化水素基、炭素数４～４０の脂環式炭化水素基又は炭素数６～４０の芳香族炭化水素基であり、これらの基の構造中には、エーテル結合、アミノ結合、スルホニル結合及びエステル結合のいずれか、或いは、置換基として、水酸基、ハロゲン原子及び繰り返し単位１～３０の炭素数２～６からなるポリアルキレングリコール鎖のいずれかを含んでもよい。Ｙ－は、一般式（１）の結合手のあるウレタン構造と結合する部分であって、前記一般式（１）中のＹ－として選択できるものを選択し得る。－Ｖ－は、炭素数１～１０の炭化水素基又は炭素数６～１０の芳香族炭化水素基であり、これらの基の構造中には、酸素原子又は窒素原子を含んでもよい。］ In the coating composition of the present invention, for example, a polyhydroxyurethane resin having a repeating unit represented by the following general formula (1) as a basic structure and a chemical structural portion having a carboxy group represented by the following general formula (6) can be preferably used.

[In general formula (1), -X- represents a direct bond, an aliphatic hydrocarbon group having 1 to 30 carbon atoms, an alicyclic hydrocarbon group having 4 to 40 carbon atoms, or an aromatic hydrocarbon group having 6 to 40 carbon atoms, and the structure of these groups may contain any of an ether bond, an amino bond, a sulfonyl bond, and an ester bond, or any of a hydroxyl group, a halogen atom, and a polyalkylene glycol chain having 1 to 30 repeating units and 2 to 6 carbon atoms as a substituent. Y- represents an aliphatic hydrocarbon group having 1 to 15 carbon atoms, an alicyclic hydrocarbon group having 4 to 15 carbon atoms, or an aromatic hydrocarbon group having 6 to 15 carbon atoms, and the structure of these groups may contain any of an ether bond or a sulfonyl bond, or any of a hydroxyl group and a halogen atom as a substituent. -Z ₁ - and -Z ₂ - each independently represent at least one structure selected from the group consisting of the following formula (2), formula (3), general formula (4) and general formula (5), and two or more structures selected from these formulas (2) to (5) may be mixed either within a repeating unit or between repeating units. In addition, when any of these formulas (2) to (5) is selected, the bond on the right side is bonded to an oxygen atom, and the bond on the left side is bonded to X, and when X is a direct bond, it is bonded to the bond on the left side of the other Z.]

[In general formula (4) or (5), R represents a hydrogen atom or a methyl group.]

[In the general formula (6), -W- is an aliphatic hydrocarbon group having 1 to 30 carbon atoms, an alicyclic hydrocarbon group having 4 to 40 carbon atoms, or an aromatic hydrocarbon group having 6 to 40 carbon atoms, and the structure of these groups may contain any of an ether bond, an amino bond, a sulfonyl bond, and an ester bond, or any of a hydroxyl group, a halogen atom, and a polyalkylene glycol chain having 2 to 6 carbon atoms and 1 to 30 repeating units as a substituent. Y- is a moiety that bonds to the urethane structure having a bond in the general formula (1), and may be selected from those that can be selected as Y- in the general formula (1). -V- is a hydrocarbon group having 1 to 10 carbon atoms or an aromatic hydrocarbon group having 6 to 10 carbon atoms, and the structure of these groups may contain an oxygen atom or a nitrogen atom.]

[Layered clay minerals]
The coating composition of the present invention is characterized in that it comprises a polyurethane resin having a specific hydroxyl value and a specific acid value as defined in the present invention as described above, and a specific layered clay mineral as described below, and the ratio of solids in the polyurethane resin to the layered clay mineral is 100:1 to 100:35 by mass. The layered clay mineral will be described below.

The layered clay mineral used in the coating composition of the present invention is a material having a layered structure, which is composed of a large number of sheets of silicate minerals having a layered structure stacked together. What is important about the coating composition of the present invention is that a specific layered clay mineral having an average aspect ratio of 150 to 350 is used as the layered clay mineral to be used in combination with the polyurethane resin having the above-mentioned characteristics. The layered clay mineral constituting the present invention must have an average aspect ratio of 150 to 350. In addition, the average aspect ratio is preferably 170 to 330, more preferably 190 to 310, and even more preferably 210 to 290. If the above average aspect ratio is less than the lower limit, the oxygen barrier properties of the coating film formed with the coating composition of the present invention are inferior, while if the above average aspect ratio exceeds the upper limit, thixotropy is manifested, and the adhesion and lamination strength of the coating film are reduced, which is not preferable. According to the inventors' investigations, by using a layered clay mineral having an average aspect ratio in the above range as a component of the coating composition of the present invention, it is surprisingly possible to form an oxygen barrier layer having excellent oxygen barrier properties and aroma retention properties, and to form a laminate having the oxygen barrier layer that is useful as a material for forming film packaging. The "aspect ratio of the layered clay mineral" in the present invention is the value of the planar diameter of the clay mineral particle relative to the thickness of the particle.

The average aspect ratio of the layered clay mineral defined in the present invention is a value measured and calculated by the following procedure. It is an arithmetic mean value obtained by using the aspect ratio values measured for 20 or more particles randomly selected from clay mineral particles observed by a scanning electron microscope (SEM). The aspect ratio for one clay mineral particle was obtained as follows. Using an SEM image of one clay mineral particle, the planar diameter and thickness of the particle were measured, and the aspect ratio was calculated by dividing the measured planar diameter by the measured thickness. In this case, the major axis of the clay mineral particle was used as the planar diameter. The thickness of the particle can be almost the same, but the measured value of the thicker part was used. In the specification of the present invention, the arithmetic mean value of the aspect ratios measured for each of 20 clay mineral particles was used as the average aspect ratio. According to the study by the inventors, an objective average aspect ratio can be obtained by using the aspect ratios of 10 or more, more preferably about 20, randomly selected clay mineral particles.

The layered clay mineral constituting the present invention is preferably one having a particle size of 1.0 μm to 20 μm. The particle size is more preferably 3 μm to 15 μm, and even more preferably 3 μm to 12 μm. The particle size of the layered clay mineral described above is the median diameter (50% particle size) obtained by laser diffraction/scattering particle size distribution measurement. If the particle size is smaller than the above value, sufficient barrier properties may not be exhibited. On the other hand, if the particle size is too large than the above range, adhesion and lamination strength may decrease. According to the studies of the present inventors, by using a layered clay mineral having a particle size within the above range, a laminate that combines physical properties such as water resistance and barrier properties, as well as a film packaging product made of the laminate, can be obtained.

Examples of the layered clay minerals constituting the present invention include montmorillonite, saponite, hectorite, vermiculite, kaolinite, and mica. According to the inventors' studies, montmorillonite, saponite, and mica are particularly preferred. These layered clay minerals can be either natural or synthetic. In addition, a mixture of multiple types of clay minerals such as those listed above can be used.

Specific examples of such layered clay minerals include Benton EW, Benton MA, Benton AD (all manufactured by Rheox Corporation), Kunipia F, Kunipia G, Kunigel VA, Sumecton SA (all manufactured by Kunimine Kogyo Co., Ltd.), Lucentite SWN, Lucentite SWF, Somasif ME (all manufactured by Katakura Co-op Agri Co., Ltd.), Sanbentonite KG-1, Sanbentonite K-1, Sanbentonite KA-1 (all manufactured by Sanbentonite Kogyo Co., Ltd.), etc.

[Ratio of solid content of polyurethane resin to layered clay mineral]
The coating composition for forming an oxygen barrier layer of the present invention is characterized in that the ratio of the solid content of the polyurethane resin to the layered clay mineral is 100:1 to 100:35 on a mass basis. This ratio is more preferably 100:2 to 100:35, and even more preferably 100:10 to 100:35. If the solid content ratio of the polyurethane resin to the layered clay mineral is less than 100:1, sufficient barrier properties are not exhibited. On the other hand, if it exceeds 100:35, it is not preferable because the fluidity, adhesion to the substrate, and laminate strength are poor when the coating composition is used as a coating liquid. According to the study by the present inventors, the coating composition of the present invention, by setting the solid content ratio of the polyurethane resin to the layered clay mineral within the above range, can realize the formation of an oxygen barrier layer that has excellent laminate strength when made into a laminate film corresponding to the above-mentioned configuration of "laminate-2", and also has excellent adhesion to the substrate in "laminate-1" and "laminate-2".

[Curing agent]
In the coating composition of the present invention, a curing agent is also blended as a component other than the polyurethane resin and layered clay mineral described above, which is a preferred embodiment. According to the coating composition of the present invention having a configuration in which a curing agent is blended, a crosslinked coating film can be formed on the first substrate. The oxygen barrier layer formed by the coating composition of the present invention blended with a curing agent becomes a crosslinked coating film, and thus excellent effects can be obtained in terms of adhesion, laminate strength, and water resistance. There is no particular limitation on the curing agent that can be used in the present invention. For example, polyisocyanates, blocked isocyanates, epoxy compounds, metal chelate compounds such as aluminum and titanium, melamine resins, aldehyde compounds, carbodiimides, etc. can be used. Among these, it is preferable to use an epoxy compound as a curing agent.

[solvent]
The coating composition of the present invention may contain an appropriate solvent as necessary as a component other than the polyurethane resin and layered clay mineral described above. Examples of the solvent used in the present invention include water; lower alcohols such as methanol, ethanol, n-propanol, isopropanol, and n-butanol; ketone-based organic solvents such as methyl ethyl ketone and methyl isobutyl ketone; and ester-based organic solvents such as ethyl acetate, n-propyl acetate, isopropyl acetate, and n-butyl acetate. These solvents may be used alone or in combination of two or more.

In the coating composition of the present invention, among the above-mentioned solvents, it is particularly preferable to use a mixed solvent containing water and isopropanol as the main component. The reasons for using such a mixed solvent are as follows. First, by using water as a solvent, it is possible to eliminate the problems of odor and performance deterioration due to residual organic solvents, and to obtain a coating composition with reduced environmental impact. In addition, by using isopropanol as a solvent, when forming an oxygen barrier layer on the substrate 1 to form a laminate, it is possible to obtain manufacturing advantages such as excellent leveling and defoaming properties, and a shorter drying time after applying the coating composition to the substrate 1.

[Other additives]
The coating composition of the present invention may contain various additives as appropriate in accordance with the required properties, other than those described above. Examples of additives that can be used include wax, fatty acid amide, silica, dispersant, leveling agent, defoamer, antioxidant, light stabilizer, ultraviolet absorber, and rheology adjuster.

[Method of producing coating composition]
The method for producing the coating composition of the present invention is not particularly limited, and can be produced by a conventionally known production method. For example, a method of adding a specific polyurethane resin defined in the present invention to an aqueous dispersion obtained by dispersing the layered clay mineral defined in the present invention in a mixed solvent containing water in advance can be mentioned. In addition, a method of mixing and dispersing the polyurethane resin, layered clay mineral, and solvent at once is also possible. The method for dispersing the layered clay mineral is not particularly limited, and can be appropriately selected from, for example, a disperser, a roller mill, a ball mill, a pebble mill, an attritor, a sand mill, and a paint conditioner.

[Laminate]
Next, a laminate characterized by being formed of the coating composition of the present invention and having the above-described excellent functionality as an oxygen barrier layer will be described.

(Laminate-1)
Laminate-1, which is one embodiment of the present invention, is characterized by comprising a first substrate and an oxygen barrier layer formed from the coating composition of the present invention. The thickness of the oxygen barrier layer formed on the substrate is not particularly limited, but in the case of a laminate to be applied to a film packaging body, it is, for example, about 0.5 to 3 μm. Laminate-1 may further comprise a layer other than the first substrate and the oxygen barrier layer, and may, for example, comprise a pattern layer made of a printing ink, a deposition layer formed by depositing a metal or a metal oxide such as aluminum or silica, or the like.

According to the study by the present inventors, by using a polyurethane resin having a hydroxyl value with the characteristics specified in the present invention that constitutes the coating composition of the present invention, it becomes possible to directly vapor-deposit aluminum, silica, etc. onto the oxygen barrier layer formed from the coating composition. And, since aluminum, silica, etc. can be directly vapor-deposited onto the oxygen barrier layer, an excellent effect in terms of production is obtained in that a vapor-deposited layer can be easily formed in the production of a laminate. In contrast, in the conventional technology, when a vapor-deposited layer formed by vapor-depositing aluminum, silica, etc. is formed, a primer layer as a base must be formed, which causes a problem of complicated processes. According to the study by the present inventors, the above-mentioned effects can be obtained more stably when, for example, a polyhydroxyurethane resin is used as a polyurethane resin with the characteristics specified in the present invention.

Examples of the laminate structure included in the laminate-1 include a structure in which an oxygen barrier layer specific to the present invention is provided on the surface of a first substrate, and a structure in which an oxygen barrier layer specific to the present invention is provided on the surface of a first substrate having a pattern layer, which has a pattern layer. When preparing the laminate-1 having the above-mentioned structure, for example, the useful oxygen barrier layer described above can be easily produced by applying the coating composition of the present invention and then removing the volatile components. Here, the method of applying the coating composition of the present invention is not particularly limited, and the coating composition can be easily and stably applied by using, for example, a gravure coater, a knife coater, a reverse coater, a bar coater, a spray coater, a slit coater, or the like. The thickness of the oxygen barrier layer constituting the present invention formed on the surface of the first substrate is not particularly limited depending on its use, but considering the releasability of the formed oxygen barrier layer, it is, for example, about 0.5 to 3 μm, more preferably about 1 to 2 μm.

(Laminate-2)
Next, laminate-2, which is one embodiment of the present invention and has a different configuration from laminate-1 described above, will be described. As described above, laminate-1 is characterized by having a first substrate and an oxygen barrier layer formed from the coating composition of the present invention, while laminate-2 is characterized by having a second substrate. That is, laminate-2 of the present invention is a laminate having a configuration including a first substrate, a second substrate, and a specific oxygen barrier layer formed from the coating composition of the present invention, and has a form of a so-called laminate film. Laminate-2 may have a first substrate, a second substrate, and other layers other than the specific oxygen barrier layer. For example, the other layers may include a pattern layer made of a printing ink, an adhesive layer made of an adhesive, and a deposition layer formed by depositing a metal or metal oxide such as aluminum or silica. More specifically, laminate-2 may be in the form of a laminate film in which an adhesive layer and a second substrate are laminated in this order on the specific oxygen barrier layer formed on the first substrate. As described above, the oxygen barrier layer formed from the coating composition of the present invention has the advantage that aluminum, silica, etc. can be directly vapor-deposited on the oxygen barrier layer. Therefore, according to the present invention, the laminate-2 having the vapor-deposited layer can be easily obtained.

When laminate-2 is to be a laminate film having the above-mentioned configuration, it can be easily manufactured, for example, by the following method. First, an adhesive is applied to the surface of the specific oxygen barrier layer of laminate-1 of the present invention manufactured as described above, thereby laminating and forming an adhesive layer, and then a second substrate is laminated onto the adhesive layer to manufacture a laminate film. By making a laminate film of such a configuration, it is possible to obtain a laminate film of laminate-2 having a configuration in which, in addition to the performance realized by laminate-1, other desired functions are added.

(Substrate)
Examples of the substrate 1 or substrate 2 used in the laminate of the present invention having the above-described configuration include plastic films appropriately selected from polyethylenes such as high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), polypropylene, polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), nylon (NY), etc. As the substrate 1 for forming the oxygen barrier layer made of the coating composition of the present invention, it is preferable to use polyolefin films such as polyethylenes and polypropylene among those listed above. In this case, it is preferable to use a film that has been corona-treated. In addition, any of the substrates used in the production of the laminate of the present invention may be made of recycled materials that have been used once as a printed matter and then recovered. In addition, any of the substrates used in the production of the laminate of the present invention may be stretched or unstretched. Furthermore, as the substrate, for example, a substrate on which a metal or metal oxide such as silica, alumina, or aluminum is vapor-deposited, or a substrate on which the vapor-deposited surface is coated with a paint such as polyvinyl alcohol, may be used.

[Method for removing oxygen barrier layer (coating film) from substrate]
The method for removing an oxygen barrier layer (coating film) of the present invention is characterized by comprising a step of immersing a laminate-1 in which an oxygen barrier layer made of the coating composition for forming an oxygen barrier layer of the present invention is formed on a first substrate, or a laminate-2 in which an oxygen barrier layer formed by laminating a first substrate and a second substrate is formed, in an alkaline aqueous solution to remove the oxygen barrier layer from the first substrate. According to the removal method of the present invention, as described above, the coating film formed on the first substrate can be removed in a good state by a very simple method. Examples of the alkaline aqueous solution used above include ammonia water, a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, calcium hydroxide, sodium hydrogen carbonate, potassium hydrogen carbonate, sodium carbonate, potassium carbonate, and other aqueous solutions. Among them, it is preferable to use a sodium hydroxide aqueous solution, which is widely used.

The conditions for immersing the laminate of the present invention in an alkaline aqueous solution are not particularly limited, but it is preferable to determine the concentration, temperature, immersion time, etc. of the alkaline aqueous solution to be used by observing the state in which the coating film formed on the substrate is detached. As the alkaline aqueous solution, it is preferable to use an alkaline aqueous solution having a concentration of, for example, about 1 to 5% by mass. According to the study by the present inventors, for example, when the coating film is detached using an aqueous solution of sodium hydroxide having a concentration of about 1.5 mass percent, a good coating film can be peeled off (detached) by a very simple and quick process of immersing the laminate in an aqueous solution at a temperature of about 40°C to 80°C for a short period of time of about 5 to 30 minutes. More specifically, in the case of a laminate-1 in which a coating film is formed on a first substrate, for example, the laminate-1 is immersed in a 1.5 mass percent aqueous solution of sodium hydroxide and treated by stirring at 40°C for about 5 minutes, whereby the coating film can be peeled off from the substrate 1 and detached in a good state. In the case of a laminate-2 having a first and second substrate, for example, by immersing the laminate-2 in a 1.5 mass percent aqueous solution of sodium hydroxide and stirring at 80°C for about 30 minutes, the coating film can be peeled off from the first substrate and detached in a good condition from the first substrate. Details of the above-mentioned detachment test will be described later.

[Method for recovering substrate]
The method for recovering a substrate of the present invention is a method for recovering a substrate by removing an oxygen barrier layer (coating film) from a laminate-1 in which an oxygen barrier layer made of the coating composition for forming an oxygen barrier layer of the present invention is formed on a first substrate, or a laminate-2 in which an oxygen barrier layer formed by laminating a first substrate and a second substrate is formed, and is characterized by having a step of immersing the laminate in an alkaline aqueous solution to remove the oxygen barrier layer from the substrate. By carrying out the above-mentioned extremely simple and rapid oxygen barrier layer removal method of the present invention, the oxygen barrier layer (coating film) can be removed (peeled off) from the first substrate very easily and quickly. As a result, the coating film is easily peeled off from the first substrate, and the coating film removed from the substrate remains in the alkaline aqueous solution in which the laminate is immersed, and a first substrate from which the coating film has been removed in a good state is obtained. For example, if the coating film is 80% or more peeled off from the first substrate, it is possible to use the substrate as a recycled film simply by cleaning the recovered substrate surface.

The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to these examples. Note that "parts" and "%" in the examples and comparative examples are based on mass unless otherwise specified.

[Production Example 1: Synthesis of cyclic carbonate-containing compound (IA)]
100 parts of bisphenol A diglycidyl ether (trade name: jER828, manufactured by Japan Epoxy Resins Co., Ltd.) with an epoxy equivalent of 192, 20 parts of sodium iodide (manufactured by Wako Pure Chemical Industries, Ltd.), and 100 parts of N-methyl-2-pyrrolidone were charged into a reaction vessel equipped with a stirrer and a reflux condenser with an air opening. Then, carbon dioxide was continuously blown in while stirring, and the reaction was carried out at 100°C for 10 hours. Then, 1400 parts of isopropanol was added to the solution after the reaction was completed, and the reaction product was precipitated as a white precipitate and separated by filtration. The obtained precipitate was recrystallized with toluene to obtain 52 parts of a white powder (yield 42%).

The white powder obtained above was analyzed by a Fourier transform infrared spectrophotometer (FT-IR) FT-720 (trade name, manufactured by Horiba, Ltd., the same device was used in the following manufacturing examples), and the absorption derived from the epoxy group of the raw material at around 910 cm ⁻¹ disappeared, while the absorption derived from the carbonyl of the carbonate group not present in the raw material was confirmed at around 1800 cm ⁻¹ . In addition, as a result of analysis by high performance liquid chromatography (HPLC) LC-2000 (trade name, manufactured by JASCO Corporation, column FinepakSIL C18-T5; mobile phase acetonitrile + water), the peak of the raw material disappeared, a new peak appeared on the high polarity side, and the purity was 98%. In addition, as a result of DSC measurement (differential scanning calorimetry), the melting point was 178 ° C., and the melting point range was ± 5 ° C.

From the above, it was confirmed that this powder is a compound with the structure shown in the following formula, in which cyclic carbonate groups have been introduced by the reaction of epoxy groups with carbon dioxide. This was abbreviated as I-A. The proportion of carbon dioxide-derived components in the chemical structure of I-A was 20.5% (calculated value).

[Production Example 2: Production of carboxyl group-containing polyhydroxyurethane resin]
In a reaction vessel equipped with a stirrer and a reflux condenser with an air opening and capable of vacuum distillation, 22.4 parts of bisphenol A diglycidyl ether (trade name: jER828, manufactured by Japan Epoxy Resins Co., Ltd.), 33.9 parts of hexamethylenediamine (manufactured by Tokyo Chemical Industry Co., Ltd.), and 112 parts of tetrahydrofuran (THF) as a reaction solvent were added and reacted for 12 hours while stirring at a temperature of 60 ° C. Next, 100 parts of the cyclic carbonate-containing compound IA obtained in Production Example 1 were added, and the reaction was carried out for 24 hours while stirring at a temperature of 60 ° C.

The resin solution after the reaction was analyzed by FT-IR, and it was found that the absorption due to the carbonyl group of the cyclic carbonate observed near 1800 cm ^-1 had completely disappeared, and a new absorption due to the carbonyl group of the urethane bond was confirmed near 1760 cm ^-1 . The amine value measured using the obtained resin solution was 41.93 mgKOH/g, calculated as a value of 100% resin content (measured in accordance with JIS K-1557).

Next, this resin solution was diluted with 140 parts of tetrahydrofuran (THF), and then 11.5 parts of maleic anhydride (Tokyo Chemical Industry Co., Ltd.) was added and the reaction was carried out at room temperature. The reaction was terminated when it was confirmed by FT-IR that the peak at 1800 cm ⁻¹ derived from the acid anhydride carbonyl had disappeared.

Next, 7.8 parts of 28% ammonia water was added to the reaction vessel to neutralize the carboxyl groups. Then, 453 parts of ion-exchanged water was gradually added while stirring at room temperature to perform phase inversion emulsification. Next, the reaction vessel was heated to 50°C, the pressure was reduced, and the THF was distilled off to obtain an aqueous dispersion in which the polyhydroxyurethane resin was dispersed in water. The resulting aqueous dispersion was adjusted so that the solid content was 30%. As a result, the aqueous dispersion was uniform in appearance. The hydroxyl value of the resulting polyhydroxyurethane resin was 187 mg KOH/g, the acid value was 40 mg KOH/g, and the weight average molecular weight was 71,000. The resulting polyhydroxyurethane resin is abbreviated as PU-1.

[Production Example 3: Production of Polyurethane Resins PU-2 to PU-6 and PU-8 to PU-10]
Aqueous dispersions of polyurethane resins PU-2 to PU-6 and PU-8 to PU-10 with different hydroxyl values and a solid content of 30% were prepared by the same method as in Production Example 2. As shown in Table 2, PU-9 has a larger hydroxyl value than that specified in the present invention, and PU-10 has a smaller hydroxyl value than that specified in the present invention. Also, PU-8 has a smaller acid value than that specified in the present invention. PU-7 is a commercially available polyurethane resin (manufactured by Dainichiseika Color & Chemicals Co., Ltd.) that does not have a hydroxyl group.

[Preparation of aqueous dispersions A-1 to A-6 of layered clay minerals]
As the aqueous dispersion A-4 of the layered clay mineral, a commercially available dispersion (solid content 8% by mass) in which mica A-4 (average aspect ratio = 264, median diameter = 8 μm) was dispersed in water was used.

Eight parts of each of mica A-1 to A-3, A-5, and A-6, which have different average aspect ratios and median diameters as shown in Table 1, were mixed with 92 parts of water, filled into a container together with glass beads, and dispersed for one hour in a paint conditioner to obtain aqueous dispersions of layered clay minerals A-1 to A-3, A-5, and A-6. The solid content of each of the aqueous dispersions of layered clay minerals obtained was 8% by mass.

[Preparation of aqueous dispersion B-1 of layered clay mineral]
Mica B (average aspect ratio = 55, median diameter = 4 μm) was used, 8 parts of mica B was mixed with 92 parts of water, and the mixture was filled into a container together with glass beads and dispersed in a paint conditioner for 1 hour to obtain aqueous dispersion B-1 of a layered clay mineral. The solid content of the aqueous dispersion B-1 of the layered clay mineral thus obtained was 8 mass%.

[Preparation of aqueous dispersions B-2 and B-3 of layered clay minerals]
Aqueous dispersions of layered clay minerals with a solid content of 8% by mass, B-2 and B-3, were prepared in the same manner as in the above-mentioned production examples, except that the formulations were as shown in Table 1. The properties of each layered clay mineral used are summarized in Table 1. Table 1 also lists mica A-4 constituting aqueous dispersion A-4. The average aspect ratio and median diameter shown in Table 1 are values measured by the method described above.

[Example 1]
As shown in Table 3-1, 56.25 parts of the aqueous dispersion A-4 of the layered clay mineral having a solid content of 8% described above, 50 parts of the polyhydroxyurethane resin having a solid content of 30% prepared in the previous Production Example 2 (abbreviated as PU-1 in the table), 12.4 parts of water, and 3.1 parts of isopropanol (IPA) were mixed to obtain a coating composition for forming an oxygen barrier layer in this example. The solid content ratio of the polyurethane resin to the layered clay mineral in the obtained coating composition was 100:30 on a mass basis.

[Examples 2 to 15, Comparative Examples 1 to 8]
The coating compositions for forming an oxygen barrier layer of Examples 2 to 15 and Comparative Examples 1 to 8 were obtained in the same manner as in Example 1, except that the raw materials for preparation were blended as shown in Table 3 (Table 3-1 to Table 3-3) and Table 4 (Table 4-1, Table 4-2), respectively. The curing agent used in Example 6 was Denacol EX-614B (product name, manufactured by Nagase Chemtec Corporation: sorbitol polyglycidyl ether).

Table 2 summarizes the properties of the polyurethane resins used in preparing the coating compositions for forming oxygen barrier layers in the examples and comparative examples. As shown in Table 2, PU-7 has a hydroxyl value of 0 mgKOH/g, and PU-8 has an acid value of 10 mgKOH/g. Both are polyurethane resins with hydroxyl and acid values outside the ranges specified in the present invention, and were used in the comparative examples. Furthermore, PU-9 has a hydroxyl value larger than that specified in the present invention, and PU-10 has a hydroxyl value smaller than that specified in the present invention, and both were used in the comparative examples.

<Evaluation>
For the coating compositions of the Examples and Comparative Examples, laminates were formed and evaluated according to the following evaluation methods and criteria.
[Preparation of Laminate-1 and Laminate-2]
First, each of the coating compositions obtained above was applied to a 50 μm-thick HDPE (high density polyethylene) film (product name: HS31, manufactured by Tamapoly Co., Ltd.) used as the substrate 1 using a bar coater #16, and dried at 40° C. for 24 hours to prepare a printed matter in which an oxygen barrier layer (hereinafter also referred to as a coating film) was formed on the substrate 1. The printed matter corresponds to a "laminate-1" called a surface print, in which a coating film made of each coating composition was formed on the substrate 1, which is a polyolefin-based substrate.

Further, on each of the printed materials prepared above, an adhesive was applied to a dry weight of 3 g/ ^m2 , and the adhesive was laminated with LLDPE (low density polyethylene), and cured at 40°C for 48 hours to obtain "Laminate-2". The adhesive used was a mixture of "Seikabond E-263" and "Seikabond C-75N" (trade names of Dainichiseika Chemicals Mfg. Co., Ltd.) in a ratio of 10:1. The laminate-2 obtained as described above is a so-called laminate form in which an adhesive layer and LLDPE, which is a second polyolefin-based base material, are laminated in this order on the oxygen barrier layer constituting the laminate-1. The "Laminate-1" or "Laminate-2" obtained above was used as a laminate for evaluation test, and was evaluated according to the following method and criteria. The evaluation results for each laminate made using the coating composition for forming an oxygen barrier layer of the embodiment of the present invention are summarized in Table 3. The evaluation results of the laminates having coating films formed using the coating compositions of the comparative examples, which were similarly evaluated, are shown in Table 4.

(Evaluation Method and Criteria)
[Adhesion]
For the "Laminate-1" for evaluation test obtained above, the adhesion of the oxygen barrier layer (coating film) formed on the surface of the substrate 1 was evaluated using the following evaluation method and evaluation criteria. Specifically, Cellotape (registered trademark) (manufactured by Nichiban Co., Ltd., 12 mm width) was attached to the coating film surface of "Laminate-1", and the appearance of the oxygen barrier layer (coating film) when it was peeled off in one go was evaluated using the following evaluation criteria. In the present invention, an evaluation of ◯ or higher was judged to be practical.

[Evaluation Criteria]
◎: 90% or more of the coating film remains on the substrate. ○: 70% or more but less than 90% of the coating film remains on the substrate. △: 30% or more but less than 70% of the coating film remains on the substrate. ×: Less than 30% of the coating film remains on the substrate.

[Desorption test]
Using the "Laminate-1" for evaluation test obtained above, a peeling test was performed on the oxygen barrier layer (coating film) formed on the substrate 1 to evaluate the releasability by the following evaluation method. Specifically, the "Laminate-1" was added to a 1.5 mass percent aqueous solution of sodium hydroxide, and stirred at 40°C for 30 minutes, and the peeling (detachment) state of the "oxygen barrier layer (coating film)" formed on the substrate 1 was evaluated by visual observation and evaluated according to the following criteria. In addition, for the "Laminate-2" for evaluation test, the detachment performance of the coating film was evaluated in the same manner as in the evaluation method performed for the "Laminate-1", except that the "Laminate-2" was added to a 1.5 mass percent aqueous solution of sodium hydroxide and stirred at 80°C for 30 minutes.

The evaluation results are summarized in Table 3. In the case of the present invention, the evaluation of the detachment test indicates that the greater the degree of peeling (detachment) of the coating film, the better the quality. In the present invention, an evaluation of 0 or higher was determined to make it easier to separate and recover the substrate due to the improved detachment performance of the formed coating film.

[Evaluation Criteria]
◎: 80% or more of the coating film has peeled off. ○: 50% or more but less than 80% of the coating film has peeled off. △: 10% or more but less than 50% of the coating film has peeled off. ×: Less than 10% of the coating film has peeled off.

[Lamination strength]
As mentioned above, the "Laminate-2" evaluated was a laminate for evaluation test obtained by aging (curing) at 40°C for 48 hours after lamination. The laminate strength of this "Laminate-2" was measured by measuring the load when peeling at 180° at a tensile speed of 100 mm/min, and evaluated according to the following criteria using the measured value. In the present invention, a rating of △ or higher was judged to be practical.

[Evaluation Criteria]
◎: Load exceeds 1.0N/15mm ○: Load exceeds 0.6N/15mm and is 1.0N/15mm or less △: Load is 0.4N/15mm or more and 0.6N/15mm or less ×: Less than 0.4N/15mm

[Oxygen Transmission Rate (OTR)]
The oxygen permeability of each of the thus obtained "Laminate-1" and "Laminate-2" for evaluation test was measured in accordance with JIS K-7126. An OX-TRAN2-22H (trade name, manufactured by MOCON) was used as the oxygen permeability measuring device. Evaluation was performed according to the following criteria. In the present invention, an evaluation of △ or higher indicates that the formed coating film effectively functions as an oxygen barrier layer and is practical.

[Evaluation Criteria]
◎: Less than 1.0 ml/ ^m2 ·atm·day ○: 1.0 ml/ ^m2 ·atm·day or more, but less than 10 ml/ ^m2 ·atm·day △: 10 ml/ ^m2 ·atm·day or more, but less than 200 ml/ ^m2 ·atm·day ×: 200 ml/ ^m2 ·atm·day or more

[Aroma retention]
The "Laminate-1" obtained as described above was used to form a coating film made of a coating composition on a substrate 1, and the aroma retention obtained by this coating film was evaluated using the following evaluation method and evaluation criteria. Specifically, three types of commercially available shampoo, fabric softener, and body soap with different aromas shown below were used as aroma sources in each of the prepared metal containers, and 1 g of each aroma source was placed in each container. Then, the openings (20 cm ² ) of the metal containers containing the different aroma sources were covered with the "Laminate-1" to be evaluated, with the coating film side (test print) facing the inside of the container, and the periphery of the opening was sealed with paraffin to prepare samples for the aroma retention evaluation test. Each of the evaluation test samples obtained as described above was placed in an aluminum-deposited nylon (NY) bag, sealed, and the "aroma retention" was evaluated based on the level of aroma in the NY bag at 25°C after 24 hours.

The aroma inside the NY bag was evaluated by a sensory test conducted by three neutral panelists, and was rated according to the following criteria. The sensory test was conducted under the condition that the evaluation of the majority of the three panelists was adopted as the evaluation result. However, the evaluation results of the sensory test by the three panelists were all consistent, and no individual evaluations were made. The evaluation results are summarized in Tables 3 and 4. Furthermore, when an evaluation test of aroma retention was conducted on "Laminate-2" in the same manner as above, the same effect was obtained as when "Laminate-1" was used, and it was confirmed that "Laminate-2" also exhibits good aroma retention.

[Source of aroma]
·shampoo:
Product name: Pantene Micellar Pure & Rose Water (manufactured by P&G)
・Fabric softener:
Product name: Lenor Super Deodorizer Fresh Green Scent (P&G)
・Body soap:
Product name: Dove Peach & Sweet Pea (Unilever)

[Evaluation Criteria]
◎: No scent detected at all 〇: Almost no scent detected △: Can distinguish type of scent ×: Strong scent detected

[Example of use] (Evaluation of packaging material made of laminate-2)
Using the "Laminate-2" for evaluation test used previously in the evaluation, the second substrates of the Laminate-2 were overlapped and heat-sealed to obtain a bag-shaped package. The same evaluation test as that previously performed on the Laminate-2 was performed on each of the obtained packages. As a result, it was confirmed that the effects of the present invention described above could be obtained even with the packages after heat sealing.

[Examples of recovery and reuse of base materials]
The coating composition for forming an oxygen barrier layer of Example 1 prepared above was used to form an oxygen barrier layer on the HDPE (high density polyethylene) film of substrate 1, and the laminate 2 was bonded to the laminate 1 with an adhesive to form a laminate 2 of LLDPE (low density polyethylene). The releasability of the oxygen barrier layer and whether each substrate 1 after the releasability was confirmed for the laminate 1 and the laminate 2. Specifically, as in the above-described desorption test, the laminate 1 was added to a 1.5 mass percent aqueous solution of sodium hydroxide and stirred at 40° C. for 30 minutes to remove the oxygen barrier layer (coating film) formed on the substrate 1, and the laminate 2 was added to a 1.5 mass percent aqueous solution of sodium hydroxide and stirred at 80° C. for 30 minutes to remove the oxygen barrier layer (coating film) formed on the substrate 1. Then, after "Laminate-1" and "Laminate-2" were pulled out of the aqueous sodium hydroxide solution and washed with water, visual observation confirmed that the oxygen barrier layer had been detached and removed in a good condition from the substrate 1 of each laminate. Furthermore, for "Laminate-1," in which the coating film could be detached well under milder conditions than for "Laminate-2," the conditions for the detachment treatment were further relaxed, and "Laminate-1" was placed in a 1.5 mass percent aqueous sodium hydroxide solution and stirred at 40°C for 5 minutes to detach the "oxygen barrier layer (coating film)" formed on the substrate 1. As a result, it was confirmed that the coating film could be detached well under these conditions as well.

After the above-mentioned coating film removal treatment was performed, strands were made from the substrate 1 recovered using a twin-screw extruder, which was then cooled with water and crushed with a cutter to obtain pellets. The resulting pellets were pressed in a hot press to produce a sheet. When the produced sheet was visually observed, it was confirmed to be a transparent sheet. This means that the substrate can be recovered from the laminate in a simple manner, and the recovered substrate 1 can be recycled as is.

Claims (14)

A coating composition for forming an oxygen barrier layer, comprising a polyurethane resin and a layered clay mineral,
The polyurethane resin has a hydroxyl value of 100 to 400 mgKOH/g and an acid value of 15 to 70 mgKOH/g;
The layered clay mineral has an average particle size of 1.0 to 20 μm and an aspect ratio of 160 to 350;
A coating composition for forming an oxygen barrier layer, characterized in that the ratio of solids in the polyurethane resin and the layered clay mineral is 100:1 to 100:35 on a mass basis. The coating composition for forming an oxygen barrier layer according to claim 1, wherein the layered clay mineral is at least one selected from the group consisting of montmorillonite, saponite, hectorite, vermiculite, kaolinite and mica. The coating composition for forming an oxygen barrier layer according to claim 1, wherein the weight average molecular weight of the polyurethane resin is 10,000 to 1,200,000. The coating composition for forming an oxygen barrier layer according to claim 1, wherein the polyurethane resin is a polyhydroxyurethane resin, which is a reaction product of a cyclic carbonate compound, which is a reaction product of an epoxy compound and carbon dioxide, and a polyamine. The coating composition for forming an oxygen barrier layer according to any one of claims 1 to 4 further comprises an epoxy compound as a curing agent. The coating composition for forming an oxygen barrier layer according to any one of claims 1 to 4, which is used to form an oxygen barrier layer of a laminate film. A laminate comprising an oxygen barrier layer formed on a first substrate, the oxygen barrier layer being made of a coating composition for forming an oxygen barrier layer according to any one of claims 1 to 4. The laminate according to claim 7, wherein the first substrate is made of any polyolefin-based resin. The laminate according to claim 7, wherein the first substrate is made of recycled material that has been recovered after being used once. The laminate according to claim 7, further comprising a first and second substrate formed by laminating an adhesive layer and a second substrate in this order on the oxygen barrier layer formed on the first substrate. The laminate according to claim 10, wherein the first substrate is made of any polyolefin-based resin. The laminate according to claim 10, wherein the first substrate and/or the second substrate are made of recycled materials that have been used once and then recovered. A method for removing an oxygen barrier layer from a laminate comprising a first substrate and an oxygen barrier layer made of the coating composition for forming an oxygen barrier layer according to any one of claims 1 to 4, or from a laminate comprising the first substrate, a second substrate, and the oxygen barrier layer, the method comprising removing the oxygen barrier layer from the laminate using an alkaline solution. A method for recovering a substrate, comprising removing the oxygen barrier layer from a laminate comprising a first substrate and an oxygen barrier layer made of the coating composition for forming an oxygen barrier layer according to any one of claims 1 to 4, or from a laminate comprising the first substrate, a second substrate, and the oxygen barrier layer, to recover at least the first substrate, the method comprising the step of removing the oxygen barrier layer from the laminate using an alkaline solution.