Laminate

Abstract

To provide a laminate capable of easily peeling an object to be peeled off from a substrate by immersion in warm water.SOLUTION: A laminate comprises a substrate (A) and a coating layer on at least one side of the substrate, wherein the coating layer contains an amphoteric polymer containing a structural unit derived from the amphoteric monomer; and a light transmittance at 550 nm of pure water containing 1 mass% of the amphoteric polymer is 40% or more at 80°C, and a light transmittance at 550 nm of pure water containing 1 mass% of the amphoteric polymer is 5.0% or less at 30°C.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a laminate comprising a substrate (A) and a coating layer. More specifically, the present invention relates to a laminate suitable as a laminate for recycling. [Background technology]

[0002] In recent years, the importance of material recycling and paper recycling, which are methods for recycling resources, has been increasing. Material recycling is a recycling method in which waste materials are reused as resin materials for new products, while paper recycling is a recycling method in which waste paper and other materials from households are collected as recyclable waste and reused as new recycled paper by paper manufacturers, etc. These recycling methods allow for the cyclical use of limited resources, thereby reducing resource consumption and the amount of waste sent to landfills, and contributing to a lighter environmental load.

[0003] In paper recycling, newspapers, magazines, etc. have been used as concrete examples of recycled paper. Paper recycling is generally achieved by carrying out a deinking process to remove the ink contained in waste printing paper such as newspapers and magazines. For example, Patent Document 1 discloses a method for dissolving ink by stirring it in an alkaline aqueous solution in a deinking process for removing ink from printed matter.

[0004] In material recycling, when recycling such waste materials, it is necessary to separate them by type and material quality. By separating waste materials, it is possible to select the appropriate recycling method according to the type and material quality of the material. If waste materials can be separated and recycled in the appropriate way, problems in the recycling process caused by the mixing of different types of materials can be prevented. Furthermore, by separating waste materials, it is easier to obtain recycled materials and raw materials from waste materials of the same material, which can result in improving the quality of new products obtained after recycling. In this regard, Patent Document 2 discloses that when a laminated film provided with a coating layer containing a compound having an acidic group is immersed in an alkaline solution, the laminated film can be easily separated into a single layer film. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-146644 [Patent Document 2] International Publication No. 2020 / 066652 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the techniques disclosed in Patent Documents 1 and 2 enable ink removal or single-layer separation using an alkaline aqueous solution, but require a further washing step after treatment with the alkaline aqueous solution. This requires not only alkaline chemicals but also dedicated washing equipment, which poses challenges in terms of cost, work efficiency, and even washing wastewater treatment.

[0007] The present invention has been made to solve the above-mentioned problems of the prior art. That is, an object of the present invention is to provide a laminate that allows an object to be peeled off easily from a substrate by immersion in warm water. [Means for solving the problem]

[0008] As a result of extensive investigations into solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by providing a coating layer on at least one surface of the substrate (A), and by the coating layer containing an amphoteric polymer having specific properties.

[0009] That is, the present invention is summarized as follows [1] to

[14] .

[0010] [1] A laminate having a coating layer on at least one side of a substrate (A), the coating layer contains an amphoteric polymer containing constitutional units derived from amphoteric monomers, The light transmittance of pure water containing 1% by mass of the amphoteric polymer at a wavelength of 550 nm is 40% or more at 80°C, and A laminate in which the light transmittance at 30°C of pure water containing 1% by mass of the amphoteric polymer at a wavelength of 550 nm is 5.0% or less.

[0011] [2] The laminate according to [1], further comprising a substrate (B) different from the coating layer, in which the substrate (A), the coating layer, and the substrate (B) are laminated in this order.

[0012] [3] The laminate according to [1] or [2], wherein the substrate (A) comprises one or more selected from the group consisting of cellulose ester, cellulose acetate, polyester, polystyrene, polyethylene, poly(vinyl acetate), saponified poly(vinyl acetate), polypropylene, polycarbonate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyamide, polyimide, polyether, polyvinyl chloride, polysulfonamide, silicone, glass, aluminum, copper, titanium, steel, iron, and stainless steel.

[0013] [4] The laminate according to any one of [1] to [3], wherein the amphoteric monomer contains a compound represented by the following formula (1):

[0014] [ka]

[0015] (In formula (1), R 1 is a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 20 carbon atoms, and X is -O- or -NR 2 - and Y + Ha-S + R 3-or-N + R 4 R 5 - and Z - Ha-SO3 - Or -PO2(OR 6 ) - where n is an integer from 1 to 8, and m is an integer from 1 to 5. 2 , R 3 , R 4 , R 5 and R 6 are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

[0016] [5] The laminate according to [4], wherein the amphoteric monomer contains a compound represented by the following formula (2):

[0017] [ka]

[0018] (In formula (2), R 1 ,X,n,m,R 4 and R 5 are R in the formula (1), respectively. 1 ,X,n,m,R 4 and R 5 is equivalent to

[0019] [6] The laminate according to any one of [1] to [5], wherein the amphoteric polymer further contains a structural unit derived from an ethylenically unsaturated monomer other than the structural unit derived from the amphoteric monomer.

[0020] [7] The laminate according to [6], wherein the ethylenically unsaturated monomer is at least one of a (meth)acrylate and a (meth)acrylamide having a hydroxy group or a tertiary amide bond.

[0021] [8] The laminate according to any one of [1] to [7], wherein the amphoteric polymer contains 80 to 100 mass % of structural units derived from the amphoteric monomer based on the total mass of the amphoteric polymer.

[0022] [9] The laminate according to any one of [6] to [8], wherein the amphoteric polymer contains 0 to 20% by mass of structural units derived from the ethylenically unsaturated monomer relative to the total mass of the amphoteric polymer.

[0023]

[10] The laminate according to any one of [1] to [9], wherein the amphoteric polymer is partially soluble in pure water at a temperature of 60°C or higher and 100°C or lower.

[0024]

[11] The laminate according to any one of [2] to

[10] , wherein the substrate (B) is an ink layer, a resin layer, or paper.

[0025]

[12] The laminate according to

[11] , wherein the resin type of the resin layer includes one or more selected from the group consisting of cellulose ester, cellulose acetate, polyester, polystyrene, polyethylene, poly(vinyl acetate), saponified poly(vinyl acetate), polypropylene, polycarbonate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyamide, polyimide, polyether, polyvinyl chloride, polysulfonamide, and silicone.

[0026]

[13] The laminate according to any one of [1] to

[12] , wherein the substrate (A) is a recyclable laminate that is reused.

[0027]

[14] The laminate according to

[12] or

[13] , wherein the resin layer is a recyclable laminate that can be reused. [Effects of the Invention]

[0028] The coating layer of the laminate of the present invention can be easily peeled off and removed from the substrate by simply immersing it in warm water. That is, in the laminate of the present invention, the coating layer provided on the substrate contains an amphoteric polymer whose solubility in water is temperature-dependent and whose solubility in water varies depending on the temperature, and therefore the laminate can be used without any problems at room temperature. When recovering the substrate, the coating layer can be easily and efficiently peeled off and removed from the substrate simply by immersing the laminate in warm water, and the substrate can be effectively reused after the coating layer has been removed. Therefore, according to the present invention, it is possible to reduce the number of processing steps, processing equipment, and chemicals used for separating and recovering the substrate from the laminate, and to reduce processing costs. DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention will be described in detail below. However, the following description is an example of an embodiment of the present invention, and the present invention is not limited to the following description as long as it does not deviate from the gist of the present invention. Unless otherwise specified, in this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits, and "A to B" means A or more and B or less. In the present invention, the term "monomer" refers to an unpolymerized compound, and the term "structural unit" refers to a unit derived from a monomer formed by polymerization of the monomer. The structural unit may be a unit formed directly by a polymerization reaction, or may be a unit in which a portion of the unit has been converted into a different structure by processing the polymer. Hereinafter, the term "structural unit" may be simply referred to as "unit." Additionally, "parts by mass" indicates the number of parts by weight of a particular component. In this specification, "(meth)acrylic" means either or both of "acrylic" and "methacrylic." The same applies to "(meth)acrylate" and "(meth)acryloyl."

[0030] <Laminate> The laminate of the present invention comprises a coating layer (hereinafter, sometimes referred to as the "coating layer of the present invention") described below, and this coating layer contains an amphoteric polymer (hereinafter, sometimes referred to as the "amphoteric polymer of the present invention") that includes a structural unit derived from an amphoteric monomer. An essential constituent requirement of the laminate is that pure water containing 1% by mass of this amphoteric polymer has a light transmittance of 40% or more at 80°C and 5.0% or less at 30°C for light with a wavelength of 550 nm. That is, the high light transmittance at a wavelength of 550 nm of pure water containing the amphoteric polymer of the present invention means that the amphoteric polymer has high solubility in pure water and that the aqueous solution of this amphoteric polymer has high transparency. On the other hand, this low light transmittance means that the amphoteric polymer of the present invention has low solubility in pure water, and the transparency of the amphoteric polymer aqueous solution or amphoteric polymer dispersion is low. That is, this regulation of light transmittance indicates that the solubility of the amphoteric polymer of the present invention in pure water is temperature dependent.

[0031] The light transmittance in the present invention is specifically measured by the method described in the Examples section below.

[0032] <Ampholytic polymer> The amphoteric polymer of the present invention is an amphoteric polymer containing one or more structural units derived from amphoteric monomers, and the light transmittance at a wavelength of 550 nm of pure water containing 1% by mass of this amphoteric polymer is 40% or more at 80°C and 5.0% or less at 30°C. In the amphoteric polymer of the present invention, the amphoteric moieties on the side chains form intramolecular or intermolecular ionic bonds, and the strength of these ionic bonds changes with heat. Therefore, the amphoteric polymer of the present invention has the property that its solubility in pure water changes depending on the temperature, and therefore has sufficient water resistance at room temperature, while being easily soluble in warm water, which makes it possible to peel off the ink printed on the coating layer and the substrate (B) provided on the coating layer.

[0033] The weight-average molecular weight (Mw) of the amphoteric polymer of the present invention is not particularly limited, but is preferably from 400,000 to 10,000,000. When the weight-average molecular weight (Mw) of the amphoteric polymer is within the above range, the solubility of the amphoteric polymer in pure water at 30°C or below is reduced, improving the practical utility at room temperature.

[0034] In the present invention, the weight-average molecular weight (Mw) refers to the absolute molecular weight obtained by separating a polymer using a size exclusion chromatograph and detecting the eluted components with a light scattering detector and a differential refractive index detector. The absolute molecular weight at each elution position (elution time or elution volume) is determined using a light scattering detector and a differential refractive index detector in combination. The weight average molecular weight (Mw) in the present invention means a value measured by connecting a size exclusion chromatograph, a light scattering detector, and a differential refractive index detector in series. More specifically, the weight average molecular weight (Mw) can be measured by the method described in the Examples section below.

[0035] The zwitterionic polymer of the present invention has a light transmittance at a wavelength of 550 nm of pure water containing 1% by mass of the polymer of the present invention of 40% or more at 80°C and 5.0% or less at 30°C. Furthermore, the light transmittance at a wavelength of 550 nm through pure water containing 1% by mass of the amphoteric polymer of the present invention is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, and particularly preferably 80% or more at 80° C., because this increases the dissolution rate in warm water. There is no particular upper limit to this light transmittance, but it is usually about 90%. On the other hand, the light transmittance at a wavelength of 550 nm of pure water containing 1% by mass of the amphoteric polymer of the present invention at 30°C is preferably 4.7% or less, more preferably 4.5% or less, and even more preferably 4.3% or less, from the viewpoint of reducing the solubility in pure water at 30°C or less and improving practicality at room temperature. The above upper and lower limits can be combined arbitrarily.

[0036] The difference in light transmittance of a 1% by mass aqueous solution of the amphoteric polymer, expressed as [light transmittance at a wavelength of 550 nm at 80°C] - [light transmittance at a wavelength of 550 nm at 30°C], is preferably 40% or more and 100% or less, and more preferably 60% or more and 100% or less. It is preferable that the difference in transmittance is within the above range, because when a coating layer containing the amphoteric polymer is formed, a sufficient difference can be achieved between the solubility in cold water and the solubility in hot water, which makes the effect of temperature-dependent solubility in the present invention more pronounced.

[0037] Furthermore, the amphoteric polymer of the present invention is preferably partially soluble in pure water at a temperature of 60° C. to 100° C. Here, "soluble in pure water" means that the solubility is 20% by mass or more, and the light transmittance at a wavelength of 550 nm is 1.0% or more.

[0038] (Zwitterionic Monomer) Since the amphoteric polymer of the present invention exhibits solubility in warm water, the amphoteric monomer that forms the amphoteric polymer of the present invention by polymerization is preferably a monomer represented by the following formula (1).

[0039] [ka]

[0040] (In formula (1), R 1 is a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 20 carbon atoms, and X is -O- or -NR 2 - and Y + Ha-S + R 3 -or-N + R 4 R 5 - and Z - Ha-SO3 - Or -PO2(OR 6 ) - where n is an integer from 1 to 8, and m is an integer from 1 to 5. 2 , R 3 , R4 , R 5 and R 6 are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

[0041] In the formula (1), Y + and Z - are easily available, and -N + R 4 R 5 - and -SO3 - Also, R 1 is preferably a hydrogen atom, a methyl group, or a phenyl group; n is preferably 2 to 3; and m is preferably 1 to 3.

[0042] In view of easy availability, the amphoteric monomer is preferably a monomer represented by the following formula (2):

[0043] [ka]

[0044] (In formula (2), R 1 ,X,n,m,R 4 and R 5 are R in the formula (1), respectively. 1 ,X,n,m,R 4 and R 5 is equivalent to

[0045] The amphoteric monomers may be used alone or in combination of two or more.

[0046] Since the light transmittance at a wavelength of 550 nm of a 1% by mass aqueous solution of the amphoteric polymer at 30°C is low, the amphoteric polymer of the present invention preferably contains 80 to 100% by mass, more preferably 90 to 100% by mass, and even more preferably 95 to 100% by mass of structural units derived from the amphoteric monomer, relative to the total mass of the amphoteric polymer.

[0047] Since a 1% by mass aqueous solution of the amphoteric polymer has a high light transmittance at a wavelength of 550 nm at 80°C, it is preferable that the amphoteric polymer of the present invention further contains a structural unit derived from an ethylenically unsaturated monomer other than the amphoteric monomer. In terms of easy availability, the amphoteric polymer of the present invention is preferably one or more of (meth)acrylate and (meth)acrylamide, in which the ethylenically unsaturated monomer has a hydroxy group or a tertiary amide bond. The structural unit derived from the ethylenically unsaturated monomer can be introduced into the amphoteric polymer of the present invention by copolymerizing the amphoteric monomer using an ethylenically unsaturated monomer in the ratio described below.

[0048] (ethylenically unsaturated monomer) Ethylenically unsaturated monomers are monomers other than zwitterionic monomers. Common (meth)acrylates and vinyl monomers can be used as the ethylenically unsaturated monomer. Among them, ethylenically unsaturated monomers having a hydroxy group or a tertiary amide bond, which are highly soluble in water, are preferred because water can be used as a solvent when copolymerizing with the amphoteric monomer. The number of hydroxy groups and tertiary amide bonds in one molecule of the ethylenically unsaturated monomer is preferably 1 to 5, and more preferably 1 to 3.

[0049] Examples of the ethylenically unsaturated monomer include (meth)acrylamides such as (meth)acryloylmorpholine; hydroxypropyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 3-hydroxypropyl (meth)acrylate; hydroxybutyl (meth)acrylate; glycerol mono(meth)acrylate; neopentyl glycol mono(meth)acrylate; hexamethylene glycol mono(meth)acrylate; trimethylolpropane mono(meth)acrylate; trimethylolethane mono(meth)acrylate; trimethylolpropane mono(meth)methacrylate; trimethylolethane mono(meth)methacrylate; Examples of the vinyl monomer include (meth)acrylates such as acrylate, tetraethylene glycol mono(meth)acrylate, triethylene glycol mono(meth)acrylate, tetraethylene glycol mono(meth)acrylate, pentaerythritol mono(meth)acrylate, dipentaerythritol mono(meth)acrylate, tripentaerythritol mono(meth)acrylate, 1,3-butanediol mono(meth)acrylate, sorbitol mono(meth)acrylate, pentaerythritol-modified mono(meth)acrylate, and 1-hydroxy-4-cyclohexyl (meth)acrylate; and vinyl monomers such as butanediol monovinyl ether and pentaerythritol monovinyl ether. Among these, (meth)acryloylmorpholine and 2-hydroxyethyl (meth)acrylate are preferred because of their good solubility in water. These ethylenically unsaturated monomers may be used alone or in combination of two or more.

[0050] From the viewpoint of reducing the transmittance of a 1% by mass aqueous solution of the amphoteric polymer at 30°C for light having a wavelength of 550 nm, the amphoteric polymer of the present invention preferably contains 0 to 20% by mass, more preferably 0 to 15% by mass, and even more preferably 0 to 10% by mass of structural units derived from ethylenically unsaturated monomers other than the amphoteric monomers, relative to the total mass of the amphoteric polymer.

[0051] (Method for producing amphoteric polymers) The amphoteric polymer of the present invention can be obtained by polymerizing or copolymerizing a monomer raw material containing one or more amphoteric monomers and one or more of the above-mentioned ethylenically unsaturated monomers, which are used as needed. The method for polymerizing the amphoteric polymer in the present invention is not particularly limited, and can be any known method, such as solution polymerization, emulsion polymerization, suspension polymerization, etc. The polymerization reaction is not particularly limited as long as it is carried out under conditions that generate radicals.

[0052] When solution polymerization is performed, it is preferable to use water as the solvent from the viewpoint of the solubility of the amphoteric monomer. When an ethylenically unsaturated monomer having low solubility in water is copolymerized, an alcohol solvent such as methanol or ethanol may be used in combination with water.

[0053] The method for generating radicals is not particularly limited, and for example, a method of irradiating with radiation such as ultraviolet rays, gamma rays, or electron beams may be used, or a method of using a radical initiator used in ordinary radical polymerization may be used. The reaction temperature for the polymerization reaction is also not particularly limited, and is usually, for example, about 15 to 150°C. When a radical initiator is used, examples of the radical initiator include bis(fluoroacyl) peroxides, bis(chlorofluoroacyl) peroxides, dialkyl peroxydicarbonates, diacyl peroxides, peroxy esters, azo compounds, and persulfates. However, since the solvent in which the zwitterionic monomer is easily dissolved is water as the main component, a radical initiator having high solubility, dispersibility, and stability in water is preferred.

[0054] <Coating layer> The coating layer of the present invention is present on at least one surface of the substrate (A), and an essential constituent requirement is that it contains the amphoteric polymer.

[0055] The thickness of the coating layer of the present invention is not particularly limited, but from the viewpoint of uniform application, it is preferably 0.01 μm or more, more preferably 0.1 μm or more, while from the viewpoint of durability in pure water at 30° C. or less, it is preferably 10 μm or less, more preferably 1 μm or less.

[0056] (Method of forming coating layer) The method for forming the coating layer of the present invention is not particularly limited, and any known method can be used. Examples of known methods include Mayer bar coating, reverse roll coating, roller coating, wire bar coating, dip coating, air knife coating, slide coating, curtain coating, knife coating, spray coating, flexographic coating, wound wire coating, slot coating, slide hopper coating, inkjet coating, and gravure coating, and a method of applying a coating liquid for forming a coating layer to the substrate (A) and drying the applied coating liquid to form a coating layer.

[0057] (Coating liquid) The coating liquid contains the amphoteric polymer. In addition to the amphoteric polymer, the coating liquid may further contain a solvent such as water or a mixture of water and a water-miscible organic solvent. If necessary, the coating liquid may contain other components described below. The method for producing the coating solution is not particularly limited, and examples thereof include a method in which the components are stirred with a conventional stirrer. However, it is preferable to heat the coating solution to a temperature at which the amphoteric polymer dissolves, as this will result in a more uniform coating solution.

[0058] (solvent) Examples of water-miscible organic solvents include alcohols such as methanol, ethanol, n-propanol, and isopropanol; ketones such as acetone and methyl ethyl ketone; polyalkylene glycols such as ethylene glycol, diethylene glycol, and propylene glycol; alkyl ethers such as polyalkylene ether glycol; and lactams such as N-methyl-2-pyrrolidone. These may be used alone or in combination of two or more.

[0059] (Other ingredients) The coating liquid may contain other components in addition to the amphoteric polymer and the solvent, such as inorganic fillers and organic particulates. Inorganic fillers include, for example, amorphous silica, crystalline silica, aluminum trihydrate, kaolin, talc, chalk, bentonite, zeolite, glass beads, calcium carbonate, potassium sodium aluminum silicate, diatomaceous earth, aluminum and magnesium silicates, and mixtures thereof. Titanium dioxide can also be used for certain applications. Examples of organic particulate materials include polyolefin, polystyrene, polyurethane, starch, poly(methyl methacrylate), and polytetrafluoroethylene.

[0060] Furthermore, within the range that does not impair the effects of the present invention, a plasticizer, a weathering agent, an antioxidant, a heat stabilizer, a lubricant, an antistatic agent, a brightening agent, a colorant, a conductive agent, a release agent, a surface treatment agent, a surfactant, a viscosity modifier, and the like may be blended, if necessary.

[0061] The content of the amphoteric polymer in the coating liquid is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, from the viewpoint of excellent solubility in warm water, and on the other hand, from the viewpoint of good dispersibility in the coating liquid, it is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass.

[0062] In order to improve the dispersion stability of the amphoteric polymer, when the coating solution contains other components, the total content of the other components is preferably 0.0001 to 5 mass %, more preferably 0.001 to 3 mass %, and even more preferably 0.01 to 1 mass %, of the total amount of the coating solution.

[0063] In the coating solution, the total content of each component does not exceed 100% by mass of the total amount of the coating solution, and the content of the solvent other than the amphoteric polymer and other components used as needed in the coating solution is the content of the solvent.

[0064] ≪Base material (A)≫ The substrate (A) in the present invention is one of the components of the laminate, and means a layer that supports the coating layer.

[0065] The substrate (A) may be a naturally occurring substance or a synthetic substance, such as cellulose ester, cellulose acetate, polyester, polystyrene, polyethylene, poly(vinyl acetate), saponified poly(vinyl acetate), polypropylene, polycarbonate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyamide, polyimide, polyether, polyvinyl chloride, polysulfonamide, silicone, glass, aluminum, copper, titanium, steel, iron, and stainless steel. The substrate (A) may contain two or more of these materials, and the substrate (A) itself may have a laminate structure.

[0066] There is no particular limitation on the thickness of the substrate (A), and it may be arbitrarily designed depending on the application of the laminate.

[0067] ≪Base material (B)≫ The substrate (B) in the present invention is a constituent member that may be included as one of the laminates. When the substrate (B) is included, it is preferable to laminate the substrate (A), the coating layer, and the substrate (B) in this order.

[0068] Materials for the substrate (B) include naturally occurring substances and synthetic substances, such as cellulose ester, cellulose acetate, polyester, polystyrene, polyethylene, poly(vinyl acetate) and its saponification products, polypropylene, polycarbonate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyamide, polyimide, polyether, polyvinyl chloride, polysulfonamide, silicone, glass, aluminum, copper, titanium, steel, iron, and stainless steel.

[0069] In addition, the substrate (B) may be a coating layer other than the hot water-soluble coating layer between the substrate (B) and the substrate (A), and may be, for example, a layer of ink, paint, a cured product of a thermosetting resin, or a cured product of a photocurable resin. The substrate (B) may also itself have a laminate structure.

[0070] There is no particular limitation on the thickness of the substrate (B), and it may be arbitrarily designed depending on the application of the laminate.

[0071] A laminate having a laminated structure of substrate (A) / coating layer / substrate (B) can be produced by forming a coating layer on substrate (A) by the above-mentioned method, and then printing, applying, laminating, vapor-depositing, plating or pressing substrate (B) onto this coating layer.

[0072] ≪Usage≫ The use form of the laminate of the present invention is not particularly limited. For example, the laminate of the present invention may contain the coating layer and be used to separate and recover the substrate (A). This allows, for example, the substrate (A) after separation and recovery to be recycled. The recycling may be material recycling or may be used as a raw material for chemical recycling. Furthermore, the recycled substrate (A) may be used as the substrate (A) for producing a laminate by forming the coating layer again on the substrate (A). Furthermore, when a substrate (B) different from the coating layer is further provided, the substrate (A) and the substrate (B) can be separated by including the coating layer of the present invention, which allows, for example, the substrates (A) and (B) after peeling to be recycled by appropriately setting the processes and conditions suitable for each of them. In particular, in products where the substrate (A) and the substrate (B) are difficult to separate, the inclusion of the coating layer of the present invention is particularly preferred since it enables them to be easily separated.

[0073] <Method for removing substrate (A) and / or substrate (B)> The laminate of the present invention can be separated and recovered from the substrate (A) and / or the substrate (B) by simply immersing the laminate in warm water, thereby partially dissolving the amphoteric polymer in the coating layer in the warm water. In this case, the temperature of the hot water used is preferably high for dissolving and removing the amphoteric polymer, but is preferably low for safety and cost reduction during the dissolving and removing process. The temperature of the hot water is preferably 60°C or higher, more preferably 80°C or higher, and is preferably 100°C or lower, more preferably 80°C or lower.

[0074] As described above, the amphoteric polymer in the coating layer of the laminate of the present invention has almost no solubility in water at 30°C. Therefore, when the laminate is used at room temperature, it can be used without any problems even under high humidity conditions or in an environment where it is exposed to water or water droplets. [Example]

[0075] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The measurement methods and evaluations of various measured values ​​shown in this specification were as follows.

[0076] (1) Weight average molecular weight (Mw) The weight average molecular weight (Mw) was measured using a size exclusion chromatograph (GPC) (Viscotek, GPCmax-TDA302) equipped with a light scattering detector and a differential refractive index detector under the following conditions. Guard column: Shodex OHpak SB-G 6B (6.0 mm I.D. x 50 mm) Column: Shodex OHpak SB-806M HQ (8.0 mm I.D. x 300 mm) Mobile phase: 0.1M sodium nitrate aqueous solution Column and detector temperature: 40°C Flow rate: 0.5mL / min Sample concentration: 1 mg / mL (mobile phase) Injection volume 100μL The measurement object (A) for measuring the weight average molecular weight (Mw) was prepared as follows. 20 mg of amphoteric polymer was placed in a 20 mL volumetric flask, and 16 mL of 0.1 M sodium nitrate solution was added. The mixture was left to stand overnight to dissolve. After confirming that the sample had dissolved, another 0.1 M sodium nitrate solution was added to obtain 20 mL of aqueous solution. The resulting aqueous solution was filtered through an aqueous disc filter with a pore size of 0.45 μm, and used as the measurement object (A). A polyethylene oxide standard (Viscotek, molecular weight 24,000) was dissolved in 10 mL of 0.1 M sodium nitrate solution by leaving it to stand at room temperature overnight or longer, and used as a standard sample.

[0077] (2) Light transmittance of pure water containing amphoteric polymer The light transmittance was measured using a UV-3100PC equipped with a cell temperature regulator manufactured by Shimadzu Corporation. The evaluation sample was prepared by adding 1 g of an amphoteric polymer prepared based on the examples and comparative examples described below and 99 g of ion-exchanged water to a glass bottle equipped with a stirrer, heating to 80°C while stirring for 10 minutes, and then cooling to room temperature. 0.7 mL of the evaluation sample was placed in a quartz cell with a lid (thickness (light transmission length): 10 mm), and the cell was attached to a UV-3100PC manufactured by Shimadzu Corporation. The temperature control chiller was set to the specified measurement temperature (30°C or 80°C), and the sample was allowed to settle within a range where the variation in visible light transmittance was within ±5%. The cell was then removed and shaken, and then reattached to the instrument for measurement. The visible light transmittance at a wavelength of 550 nm was measured at each temperature.

[0078] (3) Ink removal A glass bottle equipped with a stirrer was charged with 1 g of an amphoteric polymer prepared based on the examples and comparative examples described below and 99 g of ion-exchanged water, and the mixture was stirred for 10 minutes while heated to 80°C to obtain a solution. A slide glass (76 mm x 52 mm) was treated with ultraviolet light and ozone for 5 minutes using a UV-208 ultraviolet / ozone cleaning device manufactured by Technovision Co., Ltd., and the prepared solution was bar-coated (wet film thickness 60 μm) to produce a laminate including a coating layer. The laminate including the coating layer was dried at 80°C for 5 minutes and cooled to room temperature to prepare an evaluation sample. The total light transmittance of the laminate was measured, and then a 30 mm square was drawn on the coating layer with an oil-based black pen to create a blackened area (ink layer), thereby obtaining a laminate including an ink layer, and the total light transmittance was measured. Thereafter, the laminate was immersed in warm water at 60° C. for 30 minutes, and then taken out, and the total light transmittance of the black painted portion was measured. If the total light transmittance of the blackened area after immersion was 89% or more, the ink removability was rated "good," and if it was less than 89%, the ink removability was rated "poor." The total light transmittance was measured using a haze meter manufactured by Nippon Denshoku Industries Co., Ltd., trade name "NDH2000". This ink removability indicates that the blackened portions have been removed by dissolving the coating layer, and corresponds to an evaluation of the solubility of the coating layer.

[0079] (4) Water resistance of the coating layer At the same time as evaluating the ink removability, a black painted area was created, and the total light transmittance was measured. The sample was then immersed in pure water at 30° C. After one hour, it was taken out and the total light transmittance of the black painted area was measured. If the total light transmittance after immersion in pure water at 30°C was 10% or less, it indicated that the coating layer had hardly dissolved, and the water resistance was rated as "Good." If the total light transmittance was greater than 10%, it indicated that the coating layer had dissolved, and the water resistance was rated as "Poor." The total light transmittance was measured using a haze meter manufactured by Nippon Denshoku Industries Co., Ltd., trade name "NDH2000".

[0080] (5) Overall evaluation If all of the following conditions were met, it was marked as "OK"; if any of them were not met, it was marked as "X". (i) Ink removal rating: "Good" (ii) The coating layer has a water resistance rating of "Good."

[0081] The abbreviations for the raw materials used in the examples and comparative examples are as follows: DMAPS: 3-[[2-(methacryloyloxy)ethyl]dimethylammonio]propane-1-sulfonic acid (Tokyo Chemical Industry Co., Ltd.) HEMA: 2-hydroxyethyl methacrylate (Tokyo Chemical Industry Co., Ltd.) ACMO: Acryloylmorpholine (KJ Chemicals Co., Ltd.) APS: Ammonium persulfate (Fujifilm Wako Pure Chemical Industries, Ltd.)

[0082] Example 1 7.5 g of DMAPS and 50.2 g of ion-exchanged water were weighed into a 200 mL three-neck flask, and a magnetic stirrer was added to dissolve the DMAPS. Dry nitrogen was bubbled through the flask at 150 mL / min for 30 minutes, after which 0.037 g of APS was added and stirred until the APS dissolved. The flask was then immersed in a 60°C water bath and stirred for 6 hours. The resulting reaction solution was then reprecipitated in 1 L of methanol, and the precipitated white viscous solid was filtered off. The resulting white viscous solid was air-dried and then dried at 80°C to obtain the zwitterionic polymer. The resulting zwitterionic polymer was then evaluated. The results are shown in Table 1.

[0083] Example 2 145 g of DMAPS, 3.58 g of HEMA, and 920 g of ion-exchanged water were weighed into a 2000 mL four-neck flask and stirred with a mechanical stirrer equipped with a stirring rod and impeller to dissolve the DMAPS. Dry nitrogen was bubbled through the flask at 150 mL / min for 30 minutes, and then 80 g of an aqueous APS solution containing 0.752 g of APS was added dropwise to the flask. The flask was then immersed in a water bath at 60 °C and stirred for 6 hours. A portion of the resulting reaction solution was then reprecipitated in 1 L of methanol, and the precipitated white viscous solid was filtered off. The resulting white viscous solid was air-dried and then dried at 80 °C to obtain the zwitterionic polymer. The resulting zwitterionic polymer was then evaluated. The results are shown in Table 1.

[0084] Example 3 7.5 g of DMAPS, 0.18 g of HEMA, and 51.4 g of ion-exchanged water were weighed into a 200 mL three-neck flask. A stirring bar was added and the mixture was stirred with a magnetic stirrer to dissolve the DMAPS. Dry nitrogen was bubbled through the flask at 150 mL / min for 30 minutes, after which 0.039 g of APS was added and stirred until the APS dissolved. The flask was then immersed in a water bath at 60 °C and stirred for 6 hours. The resulting reaction solution was then reprecipitated in 1 L of methanol, and the precipitated white viscous solid was filtered off. The resulting white viscous solid was air-dried and then dried at 80 °C to obtain the zwitterionic polymer. The resulting zwitterionic polymer was then evaluated. The results are shown in Table 1.

[0085] Example 4 An amphoteric polymer was obtained and evaluated in the same manner as in Example 3, except that the amount of HEMA, APS, and ion-exchanged water were changed to 0.39 g, 0.041 g, and 52.8 g, respectively. The evaluation results are shown in Table 1.

[0086] Example 5 An amphoteric polymer was obtained and evaluated in the same manner as in Example 1, except that the amount of HEMA, APS, and ion-exchanged water used in Example 3 were changed to 0.87 g, 0.046 g, and 56 g, respectively. The evaluation results are shown in Table 1.

[0087] Example 6 142 g of DMAPS, 7.94 g of ACMO, and 920 g of ion-exchanged water were weighed into a 2000 mL four-neck flask and stirred with a mechanical stirrer equipped with a stirring bar and impeller to dissolve DMAPS. Dry nitrogen was bubbled through the flask at 150 mL / min for 30 minutes, and then 80 g of an aqueous APS solution containing 2.311 g of APS was added dropwise to the flask. The flask was then immersed in a water bath at 60 °C and stirred for 6 hours. A portion of the resulting reaction solution was then reprecipitated in 1 L of methanol, and the precipitated white viscous solid was filtered off. The resulting white viscous solid was air-dried and then dried at 80 °C to obtain the zwitterionic polymer. The resulting zwitterionic polymer was then evaluated. The results are shown in Table 1.

[0088] (Comparative Example 1) An amphoteric polymer was obtained and evaluated in the same manner as in Example 2, except that the amount of APS added was changed to 1.51 g. The evaluation results are shown in Table 1.

[0089] (Comparative Example 2) 24.9 g of DMAPS, 4.97 g of HEMA, and 150 g of ion-exchanged water were weighed into a 500 mL three-neck flask and stirred with a mechanical stirrer equipped with a stirring rod and impeller to dissolve the DMAPS. Dry nitrogen was bubbled through the flask at 150 mL / min for 30 minutes, and then 50 g of an aqueous APS solution containing 0.174 g of APS was added dropwise to the flask. The flask was then immersed in a water bath at 60 °C and stirred for 6 hours. The resulting reaction solution was then reprecipitated in 1 L of methanol, and the precipitated white viscous solid was filtered off. The resulting white viscous solid was air-dried and then dried at 80 °C to obtain the zwitterionic polymer. The resulting zwitterionic polymer was then evaluated. The results are shown in Table 1.

[0090] [Table 1]

[0091] Table 1 shows that the laminates of Examples 1 to 6, which are laminates of the present invention, have excellent water resistance against water at 30°C, while the coating layer can be easily removed in a warm bath, allowing the substrate (A) to be separated and recovered. In contrast, Comparative Examples 1 and 2, in which the amphoteric polymer does not satisfy the conditions of the present invention, have excellent solubility in hot water but lack water resistance in cold water, making them unsuitable for practical use.

Claims

1. A laminate comprising a coating layer on at least one surface of a substrate (A), the coating layer contains an amphoteric polymer containing constitutional units derived from amphoteric monomers, The light transmittance of pure water containing 1% by mass of the amphoteric polymer at a wavelength of 550 nm is 40% or more at 80°C, and A laminate, wherein the light transmittance at a wavelength of 550 nm through pure water containing 1% by mass of the amphoteric polymer at 30°C is 5.0% or less.

2. The laminate according to claim 1, further comprising a substrate (B) different from the coating layer, wherein the substrate (A), the coating layer, and the substrate (B) are laminated in this order.

3. 2. The laminate according to claim 1, wherein the substrate (A) comprises one or more materials selected from the group consisting of cellulose ester, cellulose acetate, polyester, polystyrene, polyethylene, poly(vinyl acetate), saponified poly(vinyl acetate), polypropylene, polycarbonate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyamide, polyimide, polyether, polyvinyl chloride, polysulfonamide, silicone, glass, aluminum, copper, titanium, steel, iron, and stainless steel.

4. The laminate according to claim 1 , wherein the amphoteric monomer contains a compound represented by the following formula (1): 【Chemistry 1】 (In formula (1), R １ is a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 20 carbon atoms, and X is —O— or —NR ２ - and Y ＋ Ha-S ＋ R ３ -or-N ＋ R ４ R ５ - and Z － Ha-SO ３ － or -PO ２ (OR ６ ) － where n is an integer from 1 to 8, and m is an integer from 1 to 5. ２ , R ３ , R ４ , R ５ and R ６ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

5. The laminate according to claim 4 , wherein the amphoteric monomer contains a compound represented by the following formula (2): 【Chemistry 2】 (In formula (2), R １ , X, n, m, R ４ and R ５ are R in the formula (1), respectively. １ , X, n, m, R ４ and R ５ is synonymous with

6. The laminate according to claim 1 , wherein the zwitterionic polymer further comprises a constituent unit derived from an ethylenically unsaturated monomer other than the constituent unit derived from the zwitterionic monomer.

7. The laminate according to claim 6, wherein the ethylenically unsaturated monomer is at least one of a (meth)acrylate and a (meth)acrylamide having a hydroxy group or a tertiary amide bond.

8. 2. The laminate according to claim 1, wherein the amphoteric polymer contains 80 to 100% by mass of structural units derived from the amphoteric monomer based on the total mass of the amphoteric polymer.

9. 7. The laminate according to claim 6, wherein the amphoteric polymer contains 0 to 20% by mass of the structural units derived from the ethylenically unsaturated monomer, based on the total mass of the amphoteric polymer.

10. The laminate according to claim 1 , wherein the amphoteric polymer is partially soluble in pure water at a temperature of 60° C. or higher and 100° C. or lower.

11. The laminate according to claim 2 , wherein the substrate (B) is an ink layer, a resin layer, or paper.

12. 12. The laminate according to claim 11, wherein the resin type of the resin layer comprises one or more selected from the group consisting of cellulose ester, cellulose acetate, polyester, polystyrene, polyethylene, poly(vinyl acetate), saponified poly(vinyl acetate), polypropylene, polycarbonate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyamide, polyimide, polyether, polyvinyl chloride, polysulfonamide, and silicone.

13. The laminate according to any one of claims 1 to 12, wherein the substrate (A) is a recyclable laminate that is reused.

14. The laminate according to claim 12, which is a recyclable laminate in which the resin layer is reused.

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