Laminated film

Abstract

To provide a technology useful for increasing the biomass degree of a laminated film having ultraviolet absorption capability.SOLUTION: An adhesive composition includes a polyisocyanate, a polyol, a glycol-lignin alkylene oxide adduct, and an organic solvent.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a laminated film. [Background technology]

[0002] Laminated films having an adhesive layer are used as films for packaging materials, etc. For example, Patent Document 1 describes the use of a laminate having a base film, an adhesive layer, and a sealant film in this order as a packaging material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-102513 Summary of the Invention [Problem to be solved by the invention]

[0004] Laminated films are sometimes required to have ultraviolet absorption ability, for example, to protect the contents of packaged goods from deterioration due to ultraviolet light, etc. Furthermore, in recent years, laminated films are sometimes desired to have a high biomass content.

[0005] An object of the present invention is to provide a technique useful for increasing the biomass content of a laminated film having ultraviolet absorbing properties. [Means for solving the problem]

[0006] According to one aspect of the present invention, there is provided an adhesive composition comprising a polyisocyanate, a polyol, a glycol lignin alkylene oxide adduct, and an organic solvent.

[0007] According to another aspect of the present invention, there is provided an adhesive composition according to the above aspect, wherein the proportion of hydroxyl groups contained in the glycol lignin alkylene oxide adduct is in the range of 30 mol % or more and 95 mol % or less of the total amount of hydroxyl groups contained in the solid content.

[0008] According to yet another aspect of the present invention, there is provided an adhesive composition according to any of the above aspects, wherein the proportion of the glycol lignin alkylene oxide adduct in the total amount of solids is in the range of 1% by mass or more and 40% by mass or less.

[0009] According to yet another aspect of the present invention, there is provided the adhesive composition according to any of the above aspects, wherein the glycol lignin alkylene oxide adduct is derived from a softwood.

[0010] According to yet another aspect of the present invention, there is provided an adhesive composition according to any one of the above aspects, wherein the organic solvent comprises tetrahydrofuran and ethyl acetate.

[0011] According to yet another aspect of the present invention, there is provided a laminated film comprising a resin substrate and an adhesive layer provided on one surface of the resin substrate, the adhesive layer being made of a dried or cured product of the adhesive composition according to any of the above aspects.

[0012] According to yet another aspect of the present invention, there is provided the laminated film according to the above aspect, wherein the adhesive layer has a thickness in the range of 1 μm or more and 10 μm or less.

[0013] According to yet another aspect of the present invention, there is provided the laminate film according to any one of the above aspects, further comprising a laminate layer supported on the resin substrate via the adhesive layer.

[0014] According to yet another aspect of the present invention, there is provided a laminate film according to the above aspect, which has a transmittance of 75% or less for light having a wavelength of 330 nm.

[0015] According to yet another aspect of the present invention, there is provided a method for producing a laminated film, which includes applying the adhesive composition according to any of the above aspects to one surface of a resin substrate to obtain an adhesive layer.

[0016] According to yet another aspect of the present invention, there is provided a method for producing a laminated film according to the above aspect, further comprising providing a laminate layer on the adhesive layer. [Effects of the Invention]

[0017] The present invention provides a technique that is useful for increasing the biomass content of a laminated film having ultraviolet absorbing properties. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a cross-sectional view showing a part of a laminated film according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] The following describes embodiments of the present invention. The embodiments described below are more specific embodiments of any of the above aspects. The following features can be incorporated into each of the above aspects, either singly or in combination.

[0020] Furthermore, the embodiments described below are merely examples of configurations for embodying the technical idea of ​​the present invention, and the technical idea of ​​the present invention is not limited to the following matters. Various modifications can be made to the technical idea of ​​the present invention within the technical scope defined by the claims.

[0021] <1> Laminated Film Fig. 1 is a cross-sectional view showing a portion of a laminated film according to one embodiment of the present invention. Note that the term "film" is sometimes used interchangeably with the term "sheet" depending on the thickness, but here no distinction is made based on thickness. That is, the term "film" here refers to an article having a thin layer shape and flexibility, and does not include the concept of thickness.

[0022] The laminated film 1 shown in Fig. 1 includes a resin substrate 10, a laminate layer 20, and an adhesive layer 30. The laminated film 1 can be used, for example, as a packaging material or a surface protection member.

[0023] The resin substrate 10 is a film containing a resin layer. The resin substrate 10 may have a single-layer structure or a multi-layer structure. When the resin substrate 10 has a multi-layer structure, the resin substrate 10 may consist of only a plurality of resin layers, or may consist of one or more resin layers and one or more non-resin layers.

[0024] The resin layer is, for example, a film made of a resin, such as a biaxially oriented polypropylene (BOPP) film, a polyethylene terephthalate (PET) film, an oriented polyamide (OPA) film, a cold rolled polypropylene (CPP) film, a linear low-density polyethylene (LLDPE) film, or a low-density polyethylene (LDPE) film.

[0025] The non-resin layer is, for example, a layer made of an inorganic material. The layer made of an inorganic material is, for example, a metal foil such as an aluminum foil, or a vapor-deposited layer such as an aluminum vapor-deposited layer or an aluminum oxide vapor-deposited layer.

[0026] The thickness of the resin substrate 10 is preferably in the range of 7 μm to 150 μm, more preferably in the range of 10 μm to 90 μm, and even more preferably in the range of 12 μm to 80 μm.

[0027] The laminate layer 20 is supported on the resin substrate 10 via an adhesive layer 30. The laminate layer 20 is, for example, a sealant layer. The sealant layer is, for example, a CPP film, an LLDPE film, or an OPP film. The thickness of the laminate layer 20 is preferably within the range described above for the thickness of the resin substrate 10.

[0028] The laminate layer 20 does not have to be a sealant layer, and the laminate layer 20 may be omitted.

[0029] The adhesive layer 30 is provided on one surface of the resin substrate 10. The adhesive layer 30 is interposed between the resin substrate 10 and the laminate layer 20. The adhesive layer 30 is made of a cured product of an adhesive composition described below. Such an adhesive layer 30 has ultraviolet absorption ability. Note that if the laminate layer 20 is omitted, the adhesive layer 30 may be made of a dried product of the adhesive composition described below.

[0030] The adhesive layer preferably has a thickness in the range of 1 μm to 10 μm, and more preferably has a thickness in the range of 2 μm to 5 μm.

[0031] The laminate film 1 may further include one or more other layers. For example, the laminate film 1 may further include a primer layer between the resin substrate 10 and the adhesive layer 30. The laminate film 1 may also further include a printed layer on the resin substrate 10 or between adjacent layers.

[0032] The laminate film 1 has a transmittance of 75% or less for light with a wavelength of 330 nm in one example, 70% or less in another example, and 65% or less in yet another example. This transmittance is preferably 0%, but may be 50% or more, or even 60% or more. The transmittance can be appropriately set depending on the level of UV blocking ability required of the laminate film 1. Furthermore, this transmittance can be adjusted by, for example, changing the amount of glycol lignin alkylene oxide adduct in the adhesive layer 30, the type and amount of other UV absorbers in the adhesive layer 30, the amount of UV absorbers in other layers, the thickness of each layer, etc.

[0033] The laminate film 1 can be produced, for example, by the following method. First, the adhesive composition is applied to one surface of the resin substrate 10 to form a coating film, and this coating film is dried to obtain the adhesive layer 30. Next, the laminate layer 20 is provided on the adhesive layer 30. Specifically, the laminate layer 20 is thermocompression bonded to the resin substrate 10 with the adhesive layer 30 sandwiched therebetween. In this way, the adhesive layer 30 is cured, and the laminate layer 20 is supported on the resin substrate 10 via the adhesive layer 30.

[0034] <2> adhesive composition The adhesive composition used for the adhesive layer 30 in the laminated film 1 contains a polyisocyanate, a polyol, a glycol lignin alkylene oxide adduct, and an organic solvent.

[0035] <2.1> Polyisocyanate Examples of polyisocyanates include polyisocyanate monomers, polyisocyanate derivatives, and isocyanate-terminated prepolymers. The adhesive composition may contain multiple types of polyisocyanates.

[0036] Examples of polyisocyanate monomers include aliphatic polyisocyanates, aromatic polyisocyanates, araliphatic polyisocyanates, and alicyclic polyisocyanates.

[0037] Examples of aliphatic polyisocyanates include trimethylene diisocyanate, 1,2-propylene diisocyanate, butylene diisocyanate (tetramethylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate), 1,5-pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), 2,4,4-trimethylhexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and 2,6-diisocyanate methylcaprate.

[0038] Examples of aromatic aliphatic polyisocyanates include xylylene diisocyanate derivatives, such as xylylene diisocyanate (1,3-xylylene diisocyanate or 1,4-xylylene diisocyanate) (XDI), tetramethyl xylylene diisocyanate (1,3-tetramethyl xylylene diisocyanate or 1,4-tetramethyl xylylene diisocyanate) (TMXDI), ω,ω'-diisocyanato-1,4-diethylbenzene, and polyol-modified xylylene diisocyanate obtained by reacting xylylene diisocyanate with trimethylolpropane.

[0039] The proportion of the xylylene diisocyanate derivative in the polyisocyanate may be 10% by mass or more, 20% by mass or more, 30% by mass or more, or 40% by mass or more, from the viewpoint of improving the reactivity with the polyol contained in the base resin. Increasing this proportion can increase the reactivity.

[0040] Examples of alicyclic polyisocyanates include 1,3-cyclopentane diisocyanate, 1,3-cyclopentene diisocyanate, cyclohexane diisocyanate (1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate), 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (isophorodiisocyanate) (IPDI), methylcyclohexane diisocyanate (methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate), and norbornane diisocyanate (NBDI).

[0041] Examples of polyisocyanate derivatives include polymers of the above-mentioned polyisocyanate monomers, allophanate-modified products, polyol-modified products, polyol-modified products produced by the reaction of a monomer with an alcohol, biuret-modified products, urea-modified products, oxadiazinetrione-modified products, carbodiimide-modified products, uretdione-modified products, and uretonimine-modified products.

[0042] The isocyanate-terminated prepolymer is a urethane prepolymer having at least two isocyanate groups at the molecular terminals. The isocyanate-terminated prepolymer can be obtained by subjecting a polyol to a urethane reaction with at least one member selected from the group consisting of a polyisocyanate monomer, a polyisocyanate derivative, and an isocyanate-terminated prepolymer.

[0043] <2.2> Polyol The polyol has, for example, a number average molecular weight of 400 or more and two or more hydroxyl groups in one molecule. The polyol preferably does not have an aromatic ring in the molecule.

[0044] Polyisocyanate has two or more isocyanate groups in one molecule. Polyol and polyisocyanate are the main components of the base resin and curing agent, respectively, and react with each other to produce polyurethane. The number average molecular weight of the polyol is, for example, 10,000 or less.

[0045] The polyol may contain one or more selected from the group consisting of polyester polyols and polyether polyols. Among these, from the viewpoint of increasing adhesive strength in a high-temperature environment, the polyol preferably contains a polyester polyol, and more preferably contains an aliphatic polyester polyol.

[0046] Polyester polyols can be obtained, for example, by a condensation reaction between a polyhydric alcohol and a polybasic acid, its alkyl ester, its acid anhydride, or its acid halide. Alternatively, polyester polyols can be obtained by a transesterification reaction. Examples of polyhydric alcohols include low-molecular-weight diols, low-molecular-weight triols, and low-molecular-weight polyols having four or more hydroxyl groups.

[0047] Examples of low molecular weight diols include ethylene glycol, propylene glycol, trimethylene glycol, 1,4-butylene glycol, 1,3-butylene glycol, 1,2-butylene glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, neopentyl glycol, 1,6-hexanediol, 2,2-diethyl-1,3-propanediol, 3,3-dimethylolheptane, and 2-ethyl-2-butyl-1,3-propanediol.

[0048] Examples of low molecular weight triols include glycerin, 2-methyl-2-hydroxymethyl-1,3-propanediol, 2,4-dihydroxy-3-hydroxymethylpentane, 1,2,6-hexanetriol, trimethylolethane, trimethylolpropane, 2-methyl-2-hydroxymethyl-1,3-propanediol, 2,4-dihydroxy-3-(hydroxymethyl)pentane, and 2,2-bis(hydroxymethyl)-3-butanol.

[0049] Examples of low molecular weight polyols having four or more hydroxyl groups include tetramethylolmethane, pentaerythritol, dipentaerythritol, D-sorbitol, xylitol, D-mannitol, and D-mannite.

[0050] Examples of the alkyl ester of a polybasic acid include methyl esters and ethyl esters of a polybasic acid. Examples of the acid anhydride include acid anhydrides derived from a polybasic acid. Specific examples of the acid anhydride include oxalic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, 2-alkyl (having 12 to 18 carbon atoms) succinic anhydride, tetrahydrophthalic anhydride, and trimellitic anhydride.

[0051] Examples of the acid halide include those derived from the above-mentioned polybasic acids. Specific examples of the acid halide include oxalic acid dichloride, adipic acid dichloride, and sebacic acid dichloride.

[0052] The polyether polyol is, for example, a polyalkylene oxide. The polyether polyol can be obtained, for example, by addition reaction of an alkylene oxide such as ethylene oxide and / or propylene oxide with a low molecular weight polyol as an initiator. Specific examples of the polyether polyol include polyethylene glycol, polypropylene glycol, and polyethylene polypropylene glycol (random or block copolymer). Specific examples of the polyether polyol also include polytetramethylene ether glycol obtained by ring-opening polymerization of tetrahydrofuran.

[0053] <2.3> Organic solvents The organic solvent may be any solvent capable of dissolving the solids contained in the adhesive composition and easily drying a coating film made of the adhesive composition. Examples of the organic solvent include one or more solvents selected from the group consisting of tetrahydrofuran, ethyl acetate, acetone, methyl ethyl ketone, toluene, cyclohexanone, 2-acetoxy-1-methoxypropane, chloroform, and N,N-dimethylformamide. In one example, the organic solvent is a mixture containing tetrahydrofuran and ethyl acetate.

[0054] When a water-dispersible polyisocyanate is used as the polyisocyanate, an alcohol-based organic solvent such as methanol or 2-propanol can be used in addition to the organic solvents described above. Furthermore, water can also be contained.

[0055] <2.4> Glycol lignin alkylene oxide adduct The glycol lignin alkylene oxide adduct can be obtained, for example, by the method described in JP-A-2021-147409.

[0056] A glycol lignin alkylene oxide adduct is a modified lignin having a structure in which an alkylene oxide is added to at least some of the hydroxyl groups of glycol lignin, which is formed by substituting some of the hydroxyl groups of lignin with glycol chains. Here, the "glycol chain" in glycol lignin may include not only glycol chains derived directly from glycol solvents, but also glycol chains whose chain length is extended by polycondensation of two or more glycol solvent molecules. Furthermore, the term "(poly)alkylene glycol" is used as a concept that encompasses polyalkylene glycols such as monoalkylene glycols and dialkylene glycols, and a "(poly)alkylene glycol chain" is a (poly)alkylene glycol in which one of the terminal hydroxyl groups is ether-bonded to the lignin skeleton.

[0057] In one example, a glycol lignin alkylene oxide adduct is a modified lignin in which the benzylic hydroxyl groups of lignin are replaced with glycol chains, and an alkylene oxide is added to the phenolic hydroxyl groups to form a (poly)alkylene glycol chain. In addition to the reaction of alkylene oxide adding to the phenolic hydroxyl groups to form a (poly)alkylene glycol chain, a reaction of alkylene oxide to extend the chain length of the glycol chain that replaced the benzylic hydroxyl group of lignin can occur.

[0058] Glycol lignin is derived from lignocellulose, which is the main component of woody or herbaceous biomass, and therefore the glycol lignin alkylene oxide adduct is a biomass-derived substance. Therefore, a laminate film 1 in which the adhesive layer 30 contains a glycol lignin alkylene oxide adduct can achieve a higher biomass content than a similar laminate film that omits the glycol lignin alkylene oxide adduct.

[0059] Furthermore, glycol lignin alkylene oxide adducts have ultraviolet absorbing properties, and therefore the laminate film 1 in which the adhesive layer 30 contains a glycol lignin alkylene oxide adduct has ultraviolet absorbing properties.

[0060] Furthermore, glycol lignin alkylene oxide adducts exhibit high solubility in various organic solvents, and therefore do not form aggregates in the adhesive composition or adhesive layer 30, nor do they cause a decrease in laminate strength due to the aggregates.

[0061] Lignocellulose, the raw material for glycol lignin, can be obtained from, for example, coniferous trees, broad-leaved trees, and grasses. The structure of lignin contained in lignocellulose varies depending on the type of plant from which the lignocellulose was obtained. For example, lignin derived from coniferous trees is guaiacyl lignin (G lignin) formed by the polymerization of coniferyl alcohol. Lignin derived from broad-leaved trees consists of G lignin and syringyl lignin (S lignin) formed by the polymerization of sinapyl alcohol. Lignin derived from grasses consists of p-hydroxyphenyl lignin (H lignin) formed by the polymerization of p-coumaryl alcohol, G lignin, and S lignin. To minimize variation in properties, it is preferable that the lignocellulose be derived from a coniferous tree, i.e., that the glycol lignin alkylene oxide adduct be derived from a coniferous tree.

[0062] In glycol lignin, the glycol chain substituting the benzylic hydroxyl group can be derived from one or more glycol solvents selected from the group consisting of ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, polyethylenepolypropylene glycol, glycerin, and polyglycerin. One or more ethyleneoxy groups in the polyethylene glycol may be substituted with a propyleneoxy group. One or more propyleneoxy groups in the polypropylene glycol may be substituted with an ethyleneoxy group. The glycol chain may be a polymer of the above-mentioned glycol solvent.

[0063] The number of carbon atoms of the alkylene oxide added to glycol lignin is preferably 2 to 18, more preferably 2 to 8. Examples of such alkylene oxides include aliphatic epoxides such as ethylene oxide, propylene oxide (e.g., 1,2-epoxypropane), isobutylene oxide, 1-butene oxide, 2-butene oxide, trimethylethylene oxide, tetramethylethylene oxide, butadiene monoxide, dipentaneethylene oxide, and dihexaneethylene oxide; alicyclic epoxides such as trimethylene oxide, tetramethylene oxide, tetrahydrofuran, and octylene oxide; and aromatic epoxides such as styrene oxide and 1,1-diphenylethylene oxide. The alkylene oxide is preferably ethylene oxide, propylene oxide, or butylene oxide (1-butene oxide or 2-butene oxide), and more preferably ethylene oxide.

[0064] The amount of phenolic hydroxyl groups in a glycol lignin alkylene oxide adduct can be used as an index of the degree of modification by alkylene oxide. The amount of phenolic hydroxyl groups per gram of the glycol lignin alkylene oxide adduct is preferably less than 1.0 mmol, more preferably less than 0.5 mmol, and even more preferably less than 0.3 mmol. The amount of phenolic hydroxyl groups can be measured by differential ionization spectroscopy.

[0065] The ratio of the mass of glycol chains to the mass of lignin is an index showing the amount of glycol chains introduced into the lignin, and this ratio is preferably in the range of 0.4 to 4.0, more preferably in the range of 0.8 to 3.5, and even more preferably in the range of 1.5 to 3.0.

[0066] Here, the ratio of the mass of glycol chains to the mass of lignin can be obtained by the following method.

[0067] First, solutions with different lignin concentrations are prepared by dissolving lignin in a specific solvent. Next, the UV absorbance of these solutions is measured. For example, UV light with a wavelength of 280 nm is used. Then, a calibration curve showing the relationship between UV absorbance and lignin concentration (mass%) is created.

[0068] Next, a solution is prepared by dissolving the glycol lignin alkylene oxide adduct in the same solvent as above. The ultraviolet absorbance of this solution is then measured under the same conditions as above. The result is compared with the calibration curve to determine the lignin concentration (mass%) of this solution.

[0069] The glycol chain concentration (mass%) is then obtained by subtracting the amount of solvent (mass%) and the lignin concentration (mass%) in this solution from 100 mass%, and the glycol chain concentration (mass%) is then divided by the lignin concentration (mass%) to obtain the ratio of the glycol chain mass to the lignin mass.

[0070] The weight-average molecular weight of the glycol lignin alkylene oxide adduct is preferably in the range of 1,000 to 200,000, more preferably in the range of 1,000 to 100,000, and even more preferably in the range of 5,000 to 100,000. Here, the weight-average molecular weight is a value determined by GPC (gel permeation chromatography) from a calibration curve using polyethylene oxide as a standard substance for preparing the calibration curve.

[0071] The proportion of hydroxyl groups contained in the glycol lignin alkylene oxide adduct to the total amount of hydroxyl groups contained in the solid content is preferably in the range of 30 mol % to 95 mol %, more preferably in the range of 50 mol % to 90 mol %. The glycol lignin alkylene oxide adduct and polyisocyanate can react with each other to produce polyurethane.

[0072] The amount of hydroxyl groups in the material used can be obtained by multiplying the weight of the material used by the hydroxyl value. The hydroxyl value can be measured in accordance with JIS K1557-1:2007 Method A (acetylation method).

[0073] The proportion of glycol lignin alkylene oxide adduct in the total amount of solids is preferably in the range of 1% by mass to 40% by mass, more preferably in the range of 5% by mass to 35% by mass.

[0074] The molar ratio (NCO / OH) of the isocyanate groups contained in the polyisocyanate to the hydroxyl groups of the polyol and glycol lignin alkylene oxide adduct may be 0.5 or more, 0.6 or more, 0.8 or more, 1 or more, or 1.5 or more. The molar ratio (NCO / OH) may be 10 or less, 5 or less, 4 or less, or 3 or less. Examples of numerical ranges for the molar ratio (NCO / OH) include 0.5 or more and 10 or less, 0.5 or more and 5 or less, 0.8 or more and 4 or less, and 0.6 or more and 3 or less. Such an adhesive composition can form a cured product that has high adhesive strength and excellent flexibility.

[0075] <2.5> Other ingredients In addition to the above-mentioned components, the adhesive composition may further contain one or more additives, such as antioxidants, light stabilizers, fillers, silane coupling agents, catalysts, coatability improvers, leveling agents, nucleating agents, lubricants, release agents, antifoaming agents, plasticizers, surfactants, pigments, dyes, organic fine particles, inorganic fine particles, antifungal agents, and flame retardants.

[0076] <3> effect As described above, the laminate film 1 in which the adhesive layer 30 contains a glycol lignin alkylene oxide adduct can achieve a higher biomass content than a similar laminate film except that the glycol lignin alkylene oxide adduct is omitted. Furthermore, the glycol lignin alkylene oxide adduct has ultraviolet absorption properties. Therefore, the above-described technology is useful for increasing the biomass content of a laminate film with ultraviolet absorption properties.

[0077] Furthermore, lignosulfonic acid is insoluble in organic solvents, while glycol lignin is soluble only in certain organic solvents. In contrast, as described above, glycol lignin alkylene oxide adducts exhibit high solubility in a variety of organic solvents. Therefore, glycol lignin alkylene oxide adducts do not form aggregates in the adhesive composition or adhesive layer 30. Therefore, the adhesive composition is easy to handle, and the laminate film 1 does not suffer from a decrease in laminate strength due to aggregation of the glycol lignin alkylene oxide adduct. Furthermore, the use of glycol lignin alkylene oxide adducts increases the freedom of choice of organic solvent.

[0078] As described above, the adhesive composition used to form the adhesive layer 30 is a polyurethane adhesive containing polyisocyanate and polyol. The polyurethane adhesive can be cured at a lower temperature than other adhesives such as phenolic adhesives. [Example]

[0079] The following describes tests carried out in connection with the present invention.

[0080] (1) Solubility test of lignin derivatives (1.1) Preparation of lignin derivative LD1 As the lignin derivative LD1, a glycol lignin alkylene oxide adduct was prepared by a method similar to that of Preparation Example 2 described in JP 2021-147409 A. Here, the alkylene oxide was ethylene oxide, and the mass ratio of glycol lignin (GL) to ethylene oxide (EO) (GL / EO mass ratio) was 1 / 2. Furthermore, the lignin derivative LD1 had a phenolic hydroxyl group content of 0.11 mmol per gram, a ratio of the glycol chain mass to the lignin mass of 1.69, and a weight-average molecular weight of 6,200.

[0081] (1.2) Preparation of lignin derivative LD2 Lignin derivative LD2 was prepared as a glycol lignin alkylene oxide adduct obtained by the same method as in Preparation Examples 3 to 5 described in JP 2021-147409 A. Here, the alkylene oxide was ethylene oxide, and the GL / EO mass ratio was 1 / 4. Furthermore, lignin derivative LD2 had a phenolic hydroxyl group content of 0.15 mmol per gram, a glycol chain mass to lignin mass ratio of 2.81, and a weight-average molecular weight of 6,800.

[0082] (1.3) Preparation of lignin derivative LD3 As the lignin derivative LD3, glycol lignin obtained by the following method was prepared.

[0083] First, 230 parts by mass of commercially available polyethylene glycol (PEG400) having a mass average molecular weight of 400 and 0.68 parts by mass of sulfuric acid as an acid catalyst were placed in a reaction vessel, and the mixture was stirred.

[0084] Next, 46 parts by mass of bone-dry cedar wood flour was added to the reaction vessel, and the temperature was raised to 140° C. under normal pressure, after which stirring was continued at this temperature for 90 minutes.

[0085] The reaction vessel was then cooled. After the temperature reached 40° C. or lower, 280 parts by mass of an aqueous sodium hydroxide solution (0.2 mol / L) was added to the reaction vessel, and the mixture was stirred for 30 minutes.

[0086] Next, the resulting solid component (pulp) was removed using a filter press, and the solution component was recovered.

[0087] Next, sulfuric acid was added to the resulting solution components to adjust the pH to 1.8, thereby obtaining a suspension of glycol lignin.

[0088] The glycol lignin was then recovered by centrifugation. Subsequently, the glycol lignin was washed by suspending it in water and stirring it. The glycol lignin was then recovered from the suspension by centrifugation and the recovered product was dried.

[0089] In this way, lignin derivative LD3 was obtained, which was a lignin modified with polyethylene glycol having a mass-average molecular weight of 400. The lignin derivative LD3 had a phenolic hydroxyl group content of 1.55 mmol per gram, a ratio of the glycol chain mass to the lignin mass of 0.27, and a weight-average molecular weight of 5,400.

[0090] (1.4) Solubility evaluation Each of the lignin derivatives LD1 to LD3 was mixed with an organic solvent to examine its solubility. The organic solvent used was a mixed solvent consisting of 50 parts by mass of tetrahydrofuran and 50 parts by mass of ethyl acetate. The amount of the lignin derivative was 11.1 parts by mass per 100 parts by mass of this mixed solvent. The mixed solvent containing the lignin derivative was stirred at 25°C for 30 minutes. The solubility of the lignin derivative was evaluated based on the presence or absence of solids after stirring. The results are shown in Table 1 below.

[0091] [Table 1]

[0092] As shown in Table 1, the lignin derivatives LD1 and LD2 were completely dissolved in the above mixed solvent, whereas the lignin derivative LD3 was not dissolved in the above mixed solvent.

[0093] (2) Tests on adhesive compositions and laminated films (2.1) Preparation of adhesive composition (2.1.1) Preparation of Adhesive Composition AC1 The lignin derivative LD1, base agent, and solvent were weighed and mixed. After thoroughly stirring the mixture, a curing agent was added. The base agent and curing agent were Takelac® A-626 and Takenate® A-50, manufactured by Mitsui Chemicals, Inc., respectively. Tetrahydrofuran was used as the solvent. Note that both the base agent and curing agent contain ethyl acetate as a solvent. Therefore, a mixed solvent of ethyl acetate and tetrahydrofuran was used as the organic solvent. Furthermore, for 1 part by mass of curing agent, the amount of base agent was 6.2 parts by mass, the amount of lignin derivative LD1 was 0.2 parts by mass, and the amount of tetrahydrofuran was 39 parts by mass.

[0094] This solution was further stirred to prepare adhesive composition AC1 with a solid content of 10% by mass. In adhesive composition AC1, the proportion of hydroxyl groups contained in lignin derivative LD1 (lignin-derived OH ratio) relative to the total amount of hydroxyl groups contained in the solid content was 30 mol %. The proportion of lignin derivative LD1 relative to the total amount of solid content was 4% by mass. The molar ratio (NCO / OH) of isocyanate groups contained in polyisocyanate to hydroxyl groups of polyol and glycol lignin alkylene oxide adduct was 1.4.

[0095] (2.1.2) Preparation of Adhesive Composition AC2 Adhesive composition AC2 with a solids concentration of 10% by mass was prepared in the same manner as described above for adhesive composition AC1, except that the amount of base agent was 4.4 parts by mass, the amount of lignin derivative LD1 was 0.3 parts by mass, and the amount of tetrahydrofuran was 31.3 parts by mass per part by mass of curing agent. In adhesive composition AC2, the lignin-derived OH ratio was 50 mol%, the proportion of lignin derivative LD1 in the total solids was 8% by mass, and the NCO / OH ratio was 1.4.

[0096] (2.1.3) Preparation of adhesive composition AC3 Adhesive composition AC3, with a solids concentration of 10% by mass, was prepared in the same manner as described above for adhesive composition AC1, except that the amount of base agent was 3.5 parts by mass, the amount of lignin derivative LD1 was 0.4 parts by mass, and the amount of tetrahydrofuran was 27.4 parts by mass per part by mass of curing agent. In adhesive composition AC3, the lignin-derived OH ratio was 60 mol%, the proportion of lignin derivative LD1 in the total solids was 12% by mass, and the NCO / OH ratio was 1.4.

[0097] (2.1.4) Preparation of adhesive composition AC4 Adhesive composition AC4, with a solids concentration of 10% by mass, was prepared in the same manner as described above for adhesive composition AC1, except that the amount of base agent was 2.6 parts by mass, the amount of lignin derivative LD1 was 0.4 parts by mass, and the amount of tetrahydrofuran was 23.5 parts by mass per part by mass of curing agent. In adhesive composition AC4, the lignin-derived OH ratio was 70 mol%, the proportion of lignin derivative LD1 in the total solids was 14% by mass, and the NCO / OH ratio was 1.4.

[0098] (2.1.5) Preparation of adhesive composition AC5 Adhesive composition AC5, with a solids concentration of 10% by mass, was prepared in the same manner as described above for adhesive composition AC1, except that the amount of base agent was 1.8 parts by mass, the amount of lignin derivative LD1 was 0.5 parts by mass, and the amount of tetrahydrofuran was 19.7 parts by mass per part by mass of curing agent. In adhesive composition AC5, the lignin-derived OH ratio was 80 mol%, the proportion of lignin derivative LD1 in the total solids was 21% by mass, and the NCO / OH ratio was 1.4.

[0099] (2.1.6) Preparation of adhesive composition AC6 Adhesive composition AC6, with a solids concentration of 10% by mass, was prepared in the same manner as described above for adhesive composition AC1, except that the amount of base agent was 0.9 parts by mass, the amount of lignin derivative LD1 was 0.6 parts by mass, and the amount of tetrahydrofuran was 15.8 parts by mass per part by mass of curing agent. In adhesive composition AC6, the lignin-derived OH ratio was 90 mol%, the proportion of lignin derivative LD1 in the total solids was 31% by mass, and the NCO / OH ratio was 1.4.

[0100] (2.1.7) Preparation of adhesive composition AC7 Adhesive composition AC7, with a solids concentration of 10% by mass, was prepared in the same manner as described above for adhesive composition AC1, except that lignin derivative LD2 was used instead of lignin derivative LD1, and the amount of lignin derivative LD2 was 0.1 parts by mass and the amount of tetrahydrofuran was 38.7 parts by mass per part by mass of curing agent. In adhesive composition AC7, the lignin-derived OH ratio was 30 mol%, the proportion of lignin derivative LD2 to the total solids was 2% by mass, and the NCO / OH ratio was 1.4.

[0101] (2.1.8) Preparation of adhesive composition AC8 Adhesive composition AC8, with a solids concentration of 10% by mass, was prepared in the same manner as described above for adhesive composition AC7, except that the amount of base agent was 4.4 parts by mass, the amount of lignin derivative LD2 was 0.2 parts by mass, and the amount of tetrahydrofuran was 30.7 parts by mass per part by mass of curing agent. In adhesive composition AC8, the lignin-derived OH ratio was 50 mol%, the proportion of lignin derivative LD2 in the total solids was 5% by mass, and the NCO / OH ratio was 1.4.

[0102] (2.1.9) Preparation of Adhesive Composition AC9 Adhesive composition AC9, with a solids concentration of 10% by mass, was prepared in the same manner as described above for adhesive composition AC7, except that the amount of base agent was 3.5 parts by mass, the amount of lignin derivative LD2 was 0.3 parts by mass, and the amount of tetrahydrofuran was 26.7 parts by mass per part by mass of curing agent. In adhesive composition AC9, the lignin-derived OH ratio was 60 mol%, the proportion of lignin derivative LD2 in the total solids was 9% by mass, and the NCO / OH ratio was 1.4.

[0103] (2.1.10) Preparation of adhesive composition AC10 Adhesive composition AC10, with a solids concentration of 10% by mass, was prepared in the same manner as described above for adhesive composition AC7, except that the amount of base agent was 2.6 parts by mass, the amount of lignin derivative LD2 was 0.3 parts by mass, and the amount of tetrahydrofuran was 22.7 parts by mass per part by mass of curing agent. In adhesive composition AC10, the lignin-derived OH ratio was 70 mol%, the proportion of lignin derivative LD2 in the total solids was 11% by mass, and the NCO / OH ratio was 1.4.

[0104] (2.1.11) Preparation of adhesive composition AC11 Adhesive composition AC11, with a solids concentration of 10% by mass, was prepared in the same manner as described above for adhesive composition AC7, except that the amount of base agent was 1.8 parts by mass, the amount of lignin derivative LD2 was 0.4 parts by mass, and the amount of tetrahydrofuran was 18.7 parts by mass per part by mass of curing agent. In adhesive composition AC11, the lignin-derived OH ratio was 80 mol%, the proportion of lignin derivative LD2 in the total solids was 17% by mass, and the NCO / OH ratio was 1.4.

[0105] (2.1.12) Preparation of adhesive composition AC12 Adhesive composition AC12, with a solids concentration of 10% by mass, was prepared in the same manner as described above for adhesive composition AC7, except that the amount of base agent was 0.9 parts by mass, the amount of lignin derivative LD2 was 0.4 parts by mass, and the amount of tetrahydrofuran was 14.7 parts by mass per part by mass of curing agent. In adhesive composition AC12, the lignin-derived OH ratio was 90 mol%, the proportion of lignin derivative LD2 in the total solids was 23% by mass, and the NCO / OH ratio was 1.4.

[0106] (2.1.13) Preparation of Adhesive Composition AC13 (Comparative Example) The lignin derivative LD1 was omitted and ethyl acetate was used instead of tetrahydrofuran. Adhesive composition AC13, with a solids concentration of 30% by mass, was prepared in the same manner as described above for adhesive composition AC1, except that the amount of base agent was 8 parts by mass and the amount of ethyl acetate was 9.5 parts by mass per 1 part by mass of curing agent. In adhesive composition AC13, the lignin-derived OH ratio was 0 mol%, the proportion of lignin derivatives in the total solids was 0 mass%, and the NCO / OH ratio was 1.4.

[0107] (2.1.14) Preparation of Adhesive Composition AC14 (Comparative Example) Adhesive composition AC14, with a solids concentration of 30% by mass, was prepared in the same manner as described above for adhesive composition AC1, except that the base agent was omitted, and the amount of lignin derivative LD1 was 0.6 parts by mass and the amount of tetrahydrofuran was 2.9 parts by mass per part by mass of curing agent. In adhesive composition AC14, the lignin-derived OH ratio was 100 mol%, the proportion of lignin derivative LD1 in the total solids was 44% by mass, and the NCO / OH ratio was 1.4.

[0108] (2.1.15) Preparation of Adhesive Composition AC15 (Comparative Example) Adhesive composition AC15, with a solids concentration of 30% by mass, was prepared in the same manner as described above for adhesive composition AC1, except that the base resin was omitted, lignin derivative LD2 was used instead of lignin derivative LD1, and the amount of lignin derivative LD2 was 0.5 parts by mass and the amount of tetrahydrofuran was 2.6 parts by mass per part by mass of curing agent. In adhesive composition AC15, the lignin-derived OH ratio was 100 mol%, the proportion of lignin derivative LD2 to the total solids was 41% by mass, and the NCO / OH ratio was 1.4.

[0109] (2.2) Manufacturing of laminated film The adhesive compositions AC1 to AC15 were used to produce laminate films LF1 to LF15, respectively. Specifically, each of the laminate films LF1 to LF15 was produced by the following method.

[0110] First, a polyester film (P60K#12 manufactured by Toray Industries, Inc.) with a thickness of 12 μm was prepared as the resin substrate, and an unstretched polypropylene film (RXC-22 manufactured by Mitsui Chemicals Tocello, Inc.) with a thickness of 60 μm was prepared as the laminate layer.

[0111] Next, the adhesive composition was applied to the corona-treated surface of the resin substrate using a wire bar. The resin substrate was then placed in an oven set at 80°C, and the coating was dried for 1 minute. In this manner, an adhesive layer with a thickness of 3 μm was obtained. Visual inspection of the adhesive layer revealed no agglomerates, regardless of whether any of the adhesive compositions AC1 to AC15 was used.

[0112] Next, the laminate layer was attached to the resin substrate with the adhesive layer sandwiched between them so that the corona-treated surface of the laminate layer was in contact with the adhesive layer, and then aged at 50°C for 3 days to obtain a laminated film.

[0113] (2.3) Evaluation of laminated film (2.3.1) Laminate strength For each of the laminate films LF1 to LF15, the laminate strength was measured in accordance with "7.2 Tensile strength and tensile elongation at break test" described in JIS Z1707:2019.

[0114] Specifically, 15 mm-wide strip-shaped test pieces were first cut from each of the laminate films LF1 to LF15. Next, the laminate strength was measured using a Shimadzu EZ-LX compact benchtop tensile tester manufactured by Shimadzu Corporation. In this measurement, peeling was induced at the interface between the adhesive layer and the laminate layer at one end of each test piece, and the two peeled portions were held in a jig. The peeling speed was 300 mm / min.

[0115] As shown in Table 2, the laminate films LF14 and LF15 had a lamination strength of 0 N / 15 mm. In contrast, the laminate films LF1 to LF13 had a lamination strength of more than 2 N / 15 mm.

[0116] [Table 2]

[0117] (2.3.2) Ultraviolet transmittance The transmittance of each of the laminated films LF1 to LF15 to ultraviolet light with a wavelength of 330 nm was measured using a UV-2600 manufactured by Shimadzu Corporation.

[0118] As shown in Table 2, the laminate films LF1 to LF12, LF14 and LF15 had lower transmittance to ultraviolet light with a wavelength of 330 nm than the laminate film LF13. [Explanation of symbols]

[0119] 1... laminated film, 10... resin substrate, 20... laminate layer, 30... adhesive layer

Claims

1. An adhesive composition comprising a polyisocyanate, a polyol, a glycol lignin alkylene oxide adduct, and an organic solvent.

2. 2. The adhesive composition according to claim 1, wherein the proportion of hydroxyl groups contained in the glycol lignin alkylene oxide adduct is in the range of 30 mol % to 95 mol % of the total amount of hydroxyl groups contained in the solid content.

3. 2. The adhesive composition according to claim 1, wherein the glycol lignin alkylene oxide adduct has a proportion of 1% by mass or more and 40% by mass or less of the total solid content.

4. 2. The adhesive composition of claim 1, wherein the glycol lignin alkylene oxide adduct is derived from a softwood.

5. The adhesive composition according to claim 1 , wherein the organic solvent comprises tetrahydrofuran and ethyl acetate.

6. 6. A laminated film comprising a resin substrate and an adhesive layer provided on one surface of the resin substrate, the adhesive layer comprising a dried or cured product of the adhesive composition according to claim 1.

7. The laminated film according to claim 6, wherein the adhesive layer has a thickness in the range of 1 μm to 10 μm.

8. The laminated film according to claim 6 , further comprising a laminate layer supported on the resin substrate via the adhesive layer.

9. 9. The laminated film according to claim 8, which has a transmittance of 75% or less for light having a wavelength of 330 nm.

10. A method for producing a laminated film, comprising applying the adhesive composition according to claim 1 to one surface of a resin substrate to obtain an adhesive layer.

11. The method for producing a laminated film according to claim 10, further comprising providing a laminate layer on the adhesive layer.

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