Acid-modified polyester-based resin and laminate

Abstract

To provide an acid-modified polyester-based resin that enables production of a laminate excellent in adhesion, in a laminate which is excellent in working handleability and contains a polyvinyl alcohol-based resin layer and a biodegradable resin layer.SOLUTION: An acid-modified polyester-based resin contains an aliphatic compound having a conjugated double bond.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an acid-modified polyester resin, more specifically, to an acid-modified polyester resin preferably used for an adhesive layer between a polyvinyl alcohol resin layer (hereinafter, polyvinyl alcohol is referred to as "PVA") and a biodegradable resin layer such as polylactic acid, etc. The present invention also relates to a laminate having a layer containing the acid-modified polyester resin. [Background technology]

[0002] Plastics are widely used as packaging materials because of their excellent moldability, strength, water resistance, transparency, etc. Examples of plastics used in such packaging materials include polyolefin resins such as polyethylene and polypropylene, vinyl resins such as polystyrene and polyvinyl chloride, and aromatic polyester resins such as polyethylene terephthalate. However, these plastics are poorly biodegradable, and if dumped in the natural environment after use, they may remain for a long time, damaging the scenery and causing environmental destruction.

[0003] In response to this, in recent years, biodegradable resins that are biodegraded or hydrolyzed in soil or water and are useful for preventing environmental pollution have attracted attention and are being put to practical use. Examples of such biodegradable resins include aliphatic polyester resins, cellulose acetate, and modified starch. As packaging materials, polylactic acid, condensation polymers of adipic acid / terephthalic acid / 1,4-butanediol, and condensation polymers of succinic acid / 1,4-butanediol / lactic acid are used because of their excellent transparency, heat resistance, and strength.

[0004] However, aliphatic polyester resins such as polylactic acid have insufficient oxygen gas barrier properties and therefore cannot be used alone as packaging materials for contents that may be subject to oxidative deterioration, such as food and medicines.

[0005] In view of this, a laminate has been proposed in which a coating layer made of PVA, which has excellent gas barrier properties and is also biodegradable, is formed on at least one surface of a polylactic acid film (see, for example, Patent Document 1).

[0006] Furthermore, by using a PVA-based resin that can be melt-formed, a biodegradable laminate that can be co-extrusion laminated and even stretched has been proposed, in which a gas barrier layer made mainly of a PVA-based resin having a 1,2-diol structure in its side chain is sandwiched on both sides between aliphatic polyester layers having a melting point difference of 20°C or less from the gas barrier layer (see, for example, Patent Document 2).

[0007] However, since the surface characteristics of the polylactic acid resin layer and the PVA resin layer are significantly different, the two layers have poor adhesion, and it is difficult to obtain a practical interlayer adhesive strength by directly laminating the two layers. For example, Patent Document 1 proposes surface activation treatments such as corona discharge treatment, frame treatment, and ozone treatment for polylactic acid films, as well as anchor coating treatment, but these are still not satisfactory and there is room for improvement.

[0008] In addition, in Patent Document 2, although the interlayer adhesion between the polylactic acid-based resin layer and the PVA-based resin layer is somewhat improved by co-extrusion lamination, this is still insufficient for practical use.

[0009] Therefore, in order to obtain good interlayer adhesion between the polylactic acid-based resin layer and the PVA-based resin layer, it is necessary to provide an adhesive layer between the two layers. Furthermore, in order to utilize the biodegradability of the polylactic acid-based resin and the PVA-based resin, the adhesive layer used in the laminate containing them is also required to be biodegradable.

[0010] In view of these circumstances, it has been proposed to use a polyester resin having polar groups, which is obtained by graft reacting a biodegradable polyester resin with an α,β-unsaturated carboxylic acid or its anhydride, as an adhesive layer (see, for example, Patent Document 3). [Prior art documents] [Patent documents]

[0011] [Patent Document 1] JP 2000-177072 A [Patent Document 2] JP 2009-196287 A [Patent Document 3] JP 2013-212682 A Summary of the Invention [Problem to be solved by the invention]

[0012] However, in the technique of Patent Document 3, the resin has a low melt flow rate (MFR), which causes poor fluidity during multilayer film formation, leading to poor processing and handling properties and sometimes reduced adhesiveness, which poses problems.

[0013] Under these circumstances, the present invention aims to provide an acid-modified polyester-based resin that has a high MFR and excellent processing and handling properties, and that, for example, when used as an adhesive layer for both a PVA-based resin layer and a biodegradable resin layer in a laminate containing both layers, can give a laminate that is excellent in both processing and handling properties during film formation and adhesion properties. [Means for solving the problem]

[0014] However, after extensive research, the inventors of the present invention have discovered that the above problems can be solved by using an acid-modified polyester resin containing an aliphatic compound having a conjugated double bond in an acid-modified polyester resin.

[0015] That is, the present invention provides the following <1> ~ <6> Regarding.

[0016] <1> An acid-modified polyester resin comprising an aliphatic compound having a conjugated double bond. <2> Having at least one structural unit selected from the structural units represented by the above general formulas (1) to (3), <1> The acid-modified polyester resin according to claim 1. <3> A biodegradable polyester resin is graft-reacted with an α,β-unsaturated carboxylic acid or an anhydride thereof. <1> or <2> The acid-modified polyester resin according to claim 1. <4> The composition contains at least one structural unit selected from the structural units represented by the general formulas (1) to (3) in a total amount of 50 mol % or more. <2> The acid-modified polyester resin according to claim 1. <5> <1> ~ <4> 1. A laminate having at least one layer containing the acid-modified polyester resin according to any one of 1 to 8. <6> A laminate having an adhesive layer provided between a polyvinyl alcohol-based resin (B) layer and a biodegradable resin (C) layer, The adhesive layer is <1> ~ <4> 13. A laminate comprising the acid-modified polyester resin according to claim 12. Effect of the Invention

[0017] When the acid-modified polyester resin of the present invention is used as an adhesive layer for both a PVA resin layer and a biodegradable resin layer in a laminate containing both layers, for example, a laminate excellent in both appearance and adhesiveness can be obtained. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The configuration of the present invention will be described in detail below, but these are merely examples of preferred embodiments. In this specification, "mass" is synonymous with "weight".

[0019] In addition, in this specification, "biodegradable" means meeting the conditions specified in JIS K 6953-1:2011 (ISO 14855-12005).

[0020] [Acid-modified polyester resin (A)] The acid-modified polyester resin (A) of the present invention is characterized by containing an aliphatic compound having a conjugated double bond.

[0021] If the content of the aliphatic compound having a conjugated double bond in the acid-modified polyester resin (A) of the present invention is less than 0.01 wt%, the MFR of the obtained biodegradable acid-modified polyester resin tends to decrease due to an increase in the viscosity of the resin in the extruder during the graft reaction.

[0022] If the content of the aliphatic compound having a conjugated double bond in the acid-modified polyester resin (A) of the present invention is more than 20 wt %, the graft reaction does not proceed sufficiently, and sufficient adhesive strength tends not to be exhibited.

[0023] It is presumed that the effect of the present invention is achieved by the aliphatic compound having a conjugated double bond capturing excess radicals during the graft reaction.

[0024] From the viewpoint of adhesiveness, the content of such an aliphatic compound having a conjugated double bond is preferably 0.01 to 20 wt%, more preferably 0.10 to 15 wt%, even more preferably 0.15 to 10 wt%, and particularly preferably 0.20 to 5 wt%.

[0025] The above aliphatic compound having a conjugated double bond will be described in detail below. Specific examples of aliphatic compounds having a conjugated double bond include isoprene, monoterpene, retinol, α-carotene, β-carotene, lycopene, lutein, astaxanthin, and the like, as well as compounds having a carboxylic acid such as sorbic acid and muconic acid, and their esters and metal salts. The aliphatic compounds having these conjugated double bonds may be used not only alone but also in combination of two or more kinds.

[0026] In order to incorporate the above aliphatic compound having a conjugated double bond, the following (i) to (vii) can be mentioned, for example. (i) A method in which an α,β-unsaturated carboxylic acid, a radical initiator, and an aliphatic compound having a conjugated double bond are mixed in advance with a polyester resin as a raw material, and then the mixture is melt-kneaded in a kneader to cause a reaction. (ii) A method in which an α,β-unsaturated carboxylic acid, a radical initiator, and an aliphatic compound having a conjugated double bond are blended with a polyester resin in a molten state in a kneader, and the resulting mixture is melt-kneaded to react with the polyester resin. (iii) A method in which α,β-unsaturated carboxylic acids, a radical initiator, and an aliphatic compound having a conjugated double bond are dissolved in a solvent in the raw material polyester resin, and the resulting mixture is reacted in solution. (iv) A method in which α,β-unsaturated carboxylic acids, a radical initiator, and an aliphatic compound having a conjugated double bond are dissolved in a solvent and mixed in a suspension state with a polyester resin as a raw material to cause a reaction. (v) A method in which an acid-modified polyester resin and an aliphatic compound having a conjugated double bond are dry-blended, then melted and kneaded. (vi) A method in which an acid-modified polyester resin and an aliphatic compound having a conjugated double bond are dissolved in a solvent and mixed in the form of a solution. (vii) A method in which a laminate containing an acid-modified polyester resin layer and an aliphatic compound layer having a conjugated double bond is pulverized, melted and kneaded. Although the methods (i) to (iv) can be carried out by thermal reaction alone, it is preferable to use a radical initiator in order to increase reactivity. As the reaction method, a solution reaction, a reaction in a suspension, a reaction in a molten state without using a solvent, etc. (melting method), etc. can be mentioned, and among them, the melting method is preferable. The method (vii) is mainly used for recycling the ends of laminates. Among these, the methods (i) and (ii) are preferred from the viewpoints of exerting the effects of the invention and productivity.

[0027] The acid-modified polyester resin (A) of the present invention preferably has at least one structural unit selected from the structural units represented by the following general formulas (1) to (3).

[0028] [ka]

[0029] [In formula (1), l is an integer of 2 to 8, and preferably an integer of 3 to 5.]

[0030] [ka]

[0031] [In formula (2), m is an integer of 2 to 10, and preferably an integer of 3 to 5.]

[0032] [ka]

[0033] [In formula (3), n is an integer of 2 to 9, and preferably an integer of 3 to 5.]

[0034] From the viewpoint of ease of biodegradability, the acid-modified polyester resin (A) of the present invention is preferably composed of at least one structural unit selected from the structural units represented by the above general formulas (1) to (3), but may contain other structural units for the purpose of controlling heat resistance, strength, biodegradability, etc.

[0035] The total content of at least one type of structural unit selected from the structural units represented by the general formulas (1) to (3) is usually 50 mol % or more, preferably 70 mol % or more, and more preferably 90 mol % or more.

[0036] When the acid-modified polyester resin (A) of the present invention has at least one structural unit selected from the structural units represented by the above general formulas (1) to (3), it can be obtained by condensation polymerization of at least one selected from the group consisting of an aliphatic dicarboxylic acid, an aliphatic diol compound, and other components by a known method, and further modifying the resulting resin with an acid.

[0037] Examples of the aliphatic dicarboxylic acid include succinic acid, glutaric acid, adipic acid, 1,5-pentanedicarboxylic acid, and 1,6-hexanedicarboxylic acid. In particular, succinic acid and adipic acid are preferred from the standpoint of moldability and flexibility.

[0038] Examples of the aliphatic diol compound include ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol, and 1,4-butanediol is particularly preferred from the standpoint of moldability and flexibility.

[0039] Specific examples of other components include hydroxy acids such as 4-hydroxybutyric acid, 5-hydroxyvaleric acid, and 6-hydroxyhexanoic acid; those derived from aromatic dicarboxylic acids such as terephthalic acid and isophthalic acid; those derived from dicarboxylic acids having less than two alkylene chains such as oxalic acid and malonic acid; those derived from hydroxycarboxylic acids having less than two alkylene chains such as glycolic acid and lactic acid; and other components known as copolymerization components for polyester resins.

[0040] The weight average molecular weight of the acid-modified polyester resin (A) of the present invention is usually 50,000 to 500,000, preferably 100,000 to 200,000, and particularly preferably 140,000 to 180,000. If the weight average molecular weight is too large, the melt viscosity tends to increase and melt molding tends to become difficult, and conversely, if the weight average molecular weight is too small, the molded product tends to become brittle.

[0041] The weight average molecular weight mentioned above is a weight average molecular weight converted into the molecular weight of standard polystyrene, and is measured by using a high performance liquid chromatography (manufactured by Tosoh Corporation, "HLC-8320GPC") with two columns: TSKgel SuperMultipore HZ-M (molecular weight exclusion limit: 2 x 106, theoretical plate number: 16,000 plates / column, packing material: styrene-divinylbenzene copolymer, packing particle size: 4 μm) in series.

[0042] The acid-modified polyester resin (A) of the present invention is obtained by graft polymerizing an α,β-unsaturated carboxylic acid or its anhydride (hereinafter, the α,β-unsaturated carboxylic acid or its anhydride may be referred to as "α,β-unsaturated carboxylic acids") onto the raw material biodegradable polyester resin (A'), and the biodegradable acid-modified polyester resin (A) has good adhesive properties.

[0043] Specific examples of α,β-unsaturated carboxylic acids include α,β-unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid; α,β-unsaturated dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, citrus acid, tetrahydrophthalic acid, crotonic acid, and isocrotonic acid, or their anhydrides. Preferably, anhydrides of α,β-unsaturated dicarboxylic acids are used.

[0044] These α,β-unsaturated carboxylic acids may be used not only as a single type but also as a combination of two or more types.

[0045] The method of graft-polymerizing the α,β-unsaturated carboxylic acid to the raw material polyester resin (A') is not particularly limited, and a known method can be used. Although only a thermal reaction is possible, it is preferable to use a radical initiator in order to increase reactivity. In addition, the reaction method can be a solution reaction, a reaction as a suspension, a reaction in a molten state without using a solvent (melting method), etc., and among them, the melting method is preferable.

[0046] The raw material polyester resin (A') may be obtained by synthesis or may be a commercially available product. When synthesizing, a known method for producing polyesters may be adopted. In addition, the polyester resin (A') is not limited to one type, and two or more types of polyester resins having different types of constituent units, ratios of constituent units, production methods, physical properties, etc. may be blended and used.

[0047] Examples of polyester-based resins include polybutylene adipate terephthalate (hereinafter sometimes referred to as "PBAT"), polybutylene succinate terephthalate (hereinafter sometimes referred to as "PBST"), polybutylene succinate adipate (hereinafter sometimes referred to as "PBSA"), polybutylene succinate (hereinafter sometimes referred to as "PBS"), polybutylene sebacate terephthalate (hereinafter sometimes referred to as "PBSeT"), polybutylene succinate adipate terephthalate (hereinafter sometimes referred to as "PBSAT"), polycaprolactone (hereinafter sometimes referred to as "PCL"), and the like.

[0048] Examples of commercially available raw material polyester resins (A') include "Ecoflex" manufactured by BASF, which mainly comprises a condensation polymer of adipic acid / terephthalic acid / 1,4-butanediol, and "BioPBS" manufactured by Mitsubishi Chemical, which mainly comprises a condensation polymer of succinic acid / 1,4-butanediol or a condensation polymer of succinic acid / adipic acid / 1,4-butanediol. These biodegradable polyester resins (A') may be used not only alone, but also in combination of two or more kinds.

[0049] The melting method will now be described in detail. As the melting method, a method in which the raw material polyester resin (A'), α,β-unsaturated carboxylic acids, and a radical initiator are mixed in advance and then melt-kneaded in a kneader to react, or a method in which α,β-unsaturated carboxylic acids and a radical initiator are added to the biodegradable polyester resin (A') in a molten state in a kneader can be used.

[0050] As a mixer used when premixing the raw materials, for example, a Henschel mixer, a ribbon blender, etc. can be used, and as a kneader used for melt kneading, for example, a single-screw or twin-screw extruder, a roll, a Banbury mixer, a kneader, a Brabender mixer, etc. can be used.

[0051] The temperature during melt kneading may be set appropriately within a temperature range that is equal to or higher than the melting point of the raw material biodegradable polyester resin (A') and does not cause thermal degradation, preferably 100 to 250°C, more preferably 160 to 230°C.

[0052] The amount of α,β-unsaturated carboxylic acid is usually 0.0001-5 parts by weight, preferably 0.001-1 part by weight, more preferably 0.02-0.45 parts by weight, based on 100 parts by weight of the raw material polyester resin (A'). If the amount is too small, a sufficient amount of polar groups is not introduced into the polyester resin (A'), and the interlayer adhesion, especially the adhesion to the PVA resin layer, tends to be insufficient. If the amount is too large, the α,β-unsaturated carboxylic acid that has not been graft-polymerized may remain in the resin, which tends to cause poor appearance.

[0053] The radical initiator is not particularly limited, and known radical initiators can be used. For example, organic or inorganic peroxides such as t-butyl hydroperoxide, cumene hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, 2,5-dimethyl-2,5-bis(t-butyloxy)hexane, 3,5,5-trimethylhexanoyl peroxide, t-butyl peroxybenzoate, benzoyl peroxide, m-toluoyl peroxide, dicumyl peroxide, 1,3-bis(t-butylperoxyisopropyl)benzene, dibutyl peroxide, methyl ethyl ketone peroxide, potassium peroxide, and hydrogen peroxide; azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(isobutylamide)dihalide, 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] and azodi-t-butane; and carbon radical generators such as dicumyl. These may be used alone or in combination of two or more kinds.

[0054] The amount of the radical initiator to be added is usually 0.00001 to 5.0 parts by weight, particularly 0.0001 to 1.0 part by weight, and especially 0.002 to 0.5 part by weight, per 100 parts by weight of the raw material polyester resin (A').

[0055] If the amount of the radical initiator is too small, the graft reaction may not occur sufficiently, and the effects of the present invention may not be obtained. If the amount of the radical initiator is too large, the polyester resin may decompose to reduce its molecular weight, and the adhesive strength may tend to be insufficient due to insufficient cohesive force.

[0056] [PVA resin (B) layer] The PVA-based resin (B) layer is preferably used as a gas barrier layer of the laminate of the present invention described below, and particularly preferably provides gas barrier properties to the laminate of the present invention. The PVA resin (B) layer is preferably laminated to a biodegradable resin (C) layer described below on at least one surface thereof via a layer (adhesive layer) containing the acid-modified polyester resin (A) described above.

[0057] The PVA resin (B) layer used in the present invention is a layer mainly composed of the PVA resin (B), and usually contains 70% by weight or more of the PVA resin (B), preferably 80% by weight or more, and more preferably 90% by weight or more. The upper limit is 100% by weight. If the content is too low, the gas barrier property tends to be insufficient.

[0058] The PVA resin (B) used in the present invention is a resin mainly composed of vinyl alcohol structural units, which is obtained by saponifying a polyvinyl ester resin obtained by polymerizing a vinyl ester monomer, and is composed of vinyl alcohol structural units and vinyl ester structural units corresponding to the degree of saponification.

[0059] Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, and vinyl versatate, with vinyl acetate being economically preferred.

[0060] The average degree of polymerization (measured according to JIS K6726) of the PVA resin (B) used in the present invention is usually 200 to 1800, particularly 300 to 1500, and particularly preferably 300 to 1000.

[0061] If the average polymerization degree is too low, the mechanical strength of the PVA resin (B) layer tends to be insufficient, whereas if the average polymerization degree is too high, the flowability and moldability tend to decrease when the PVA resin (B) layer is formed by hot melt molding, and shear heat may be abnormally generated during molding, making the PVA resin (B) susceptible to thermal decomposition.

[0062] The PVA resin (B) used in the present invention has a degree of saponification (measured according to JIS K6726) of usually 80 to 100 mol %, particularly preferably 90 to 99.9 mol %, and even more preferably 98 to 99.9 mol %. If the degree of saponification is too low, the gas barrier properties tend to decrease.

[0063] In the present invention, the PVA-based resin (B) may be one obtained by copolymerizing various monomers during the production of a polyvinyl ester-based resin and then saponifying the copolymer, or one of various modified PVA-based resins obtained by introducing various functional groups into unmodified PVA by post-modification.

[0064] Examples of monomers used for copolymerization with vinyl ester monomers include olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, and α-octadecene; hydroxyl-containing α-olefins such as 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, and 3,4-dihydroxy-1-butene; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, and itaconic acid; salts, monoesters, or dialkyl esters of the same; nitriles such as acrylonitrile and methacrylonitrile; diacetone acrylate; Examples of suitable vinyl acetates include amides such as olefin sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, and the like, and salts thereof; alkyl vinyl ethers, dimethylallyl vinyl ketone, N-vinylpyrrolidone, vinyl chloride, vinyl ethylene carbonate, 2,2-dialkyl-4-vinyl-1,3-dioxolane, glycerin monoallyl ether, and 3,4-diacetoxy-1-butene, and other vinyl compounds; substituted vinyl acetates such as isopropenyl acetate and 1-methoxyvinyl acetate; vinylidene chloride, 1,4-diacetoxy-2-butene, and vinylene carbonate.

[0065] In addition, examples of modified PVA-based resins into which functional groups have been introduced by post-modification include those having acetoacetyl groups by reaction with diketene, those having polyalkylene oxide groups by reaction with ethylene oxide, those having hydroxyalkyl groups by reaction with epoxy compounds, and those obtained by reacting aldehyde compounds having various functional groups with PVA.

[0066] The content of modified species in such modified PVA-based resins, i.e., constituent units derived from various monomers in the copolymer or functional groups introduced by post-reaction, cannot be generally determined because the characteristics vary greatly depending on the modified species, but is usually 1 to 20 mol %, and a range of 2 to 10 mol % is preferably used.

[0067] Among these various modified PVA-based resins, in the present invention, a PVA-based resin having a structural unit having a 1,2-diol structure in a side chain, as represented by the following general formula (4) (hereinafter, sometimes referred to as a "1,2-diol structural unit"), is preferably used because it facilitates melt molding in the production method of the laminate of the present invention described below.

[0068] [ka]

[0069] In addition, R1 to R4 in the 1,2-diol structural unit represented by the general formula (4) each independently represents a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms.

[0070] Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, and a tert-butyl group. If necessary, the alkyl group may have a functional group such as a halogen group, a hydroxyl group, an ester group, a carboxylic acid group, or a sulfonic acid group.

[0071] Furthermore, X in the 1,2-diol structural unit represented by the general formula (4) represents a single bond or a bonding chain. Examples of such a bonding chain include hydrocarbons such as linear or branched alkylene groups having 1 to 6 carbon atoms, linear or branched alkenylene groups having 1 to 6 carbon atoms, linear or branched alkynylene groups having 1 to 6 carbon atoms, phenylene groups, and naphthylene groups (these hydrocarbons may be substituted with halogens such as fluorine, chlorine, and bromine), as well as -O-, -(CHO)t-, -(OCH)t-, -(CHO)tCH2-, -CO-, -COCO-, -CO(CH)tCO-, -CO(CH)CO-, -S-, and -CS Examples thereof include -, -SO-, -SO2-, -NR-, -CONR-, -NRCO-, -CSNR-, -NRCS-, -NRNR-, -HPO4-, -Si(OR)2-, -OSi(OR)2-, -OSi(OR)2O-, -Ti(OR)2-, -OTi(OR)2-, -OTi(OR)2O-, -Al(OR)-, -OAl(OR)-, -OAl(OR)O- and the like (each R is independently any substituent and represents a hydrogen atom or a linear or branched alkyl group having 1 to 6 carbon atoms, and t represents an integer of 1 to 5). Among these, from the viewpoint of stability during production or use, the linking chain is preferably a linear or branched alkylene group having 1 to 6 carbon atoms, particularly a methylene group, or -CH2OCH2-.

[0072] X is most preferably a single bond in terms of thermal stability and stability under high temperature and acidic conditions.

[0073] Among the 1,2-diol structural units represented by general formula (4), a structural unit represented by the following general formula (4') in which all of R1 to R4 are hydrogen atoms and X is a single bond is most preferred.

[0074] [ka]

[0075] Examples of a method for producing such a PVA-based resin having a 1,2-diol structural unit in a side chain include the method described in paragraphs

[0026] to

[0034] of JP-A No. 2015-143356.

[0076] The content of the 1,2-diol structural unit contained in the PVA resin having the 1,2-diol structural unit in the side chain is usually 1 to 20 mol%, more preferably 2 to 10 mol%, particularly preferably 3 to 8 mol%. If the content is too low, it is difficult to obtain the effect of the 1,2-diol structure in the side chain, and conversely, if the content is too high, the gas barrier property at high humidity tends to decrease significantly.

[0077] The content of 1,2-diol structural units in a PVA resin can be determined from the 1H-NMR spectrum (solvent: DMSO-d6, internal standard: tetramethylsilane) of a completely saponified PVA resin. Specifically, the content can be calculated from the peak areas derived from the hydroxyl group protons, methine protons, and methylene protons in the 1,2-diol structural units, the methylene protons in the main chain, and the protons of the hydroxyl groups linked to the main chain.

[0078] The PVA-based resin (B) used in the present invention may be one type or a mixture of two or more types. When the PVA-based resin (B) is a mixture of two or more types, it may be a mixture of the above-mentioned unmodified PVAs, an unmodified PVA and a PVA-based resin having a structural unit represented by general formula (4), a mixture of PVA-based resins having structural units represented by general formula (4) with different degrees of saponification, polymerization, modification, etc., an unmodified PVA, or a PVA-based resin having a structural unit represented by general formula (4). Combinations of resins and other modified PVA-based resins, etc. may be used.

[0079] The PVA-based resin (B) layer used in the present invention may contain, in addition to the PVA-based resin (B), a heat stabilizer, an antioxidant, an ultraviolet absorber, a crystal nucleating agent, an antistatic agent, a flame retardant, a plasticizer, a lubricant, a filler, a lubricant, or a crystal nucleating agent.

[0080] [Biodegradable resin (C) layer] Next, the biodegradable resin (C) layer preferably used as the outer layer of the laminate of the present invention described later will be explained. The biodegradable resin (C) layer is a layer mainly composed of a biodegradable resin (C), and usually contains 70% by weight or more of the biodegradable resin (C), preferably 80% by weight or more, and more preferably 90% by weight or more. The upper limit is 100% by weight.

[0081] Examples of the biodegradable resin (C) include aliphatic polyesters such as polylactic acid (C1), adipic acid / terephthalic acid / 1,4-butanediol condensation polymer (polybutylene adipate terephthalate (C2)), succinic acid / 1,4-butanediol condensation polymer (polybutylene succinate (C3)), and polyglycolic acid; modified starch; casein plastic; and cellulose. These may be used alone or in combination of two or more kinds.

[0082] Among them, polylactic acid (C1) and polybutylene adipate terephthalate (C2) are preferable from the viewpoint of strength, and polybutylene succinate (C3) is preferable from the viewpoint of flexibility and biodegradability.

[0083] Polybutylene succinate (C3) is an aliphatic polyester resin whose main components are succinic acid and 1,4-butanediol.

[0084] The polybutylene succinate (C3) used in the present invention is preferably a succinic acid / 1,4-butanediol copolymer, but may contain copolymerization components other than succinic acid / 1,4-butanediol in an amount that does not impair the properties, for example, 10 mol % or less.

[0085] Examples of such copolymerization components include aliphatic hydroxycarboxylic acids such as glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvaleric acid, 4-hydroxyvaleric acid, and 6-hydroxycaproic acid; lactones such as caprolactone; aliphatic diols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, and 1,4-butanediol; and aliphatic dibasic acids such as succinic acid, oxalic acid, malonic acid, glutaric acid, and adipic acid.

[0086] The weight-average molecular weight of the polybutylene succinate (C3) used in the present invention is usually 20,000 to 1,000,000, and preferably 30,000 to 300,000, and more preferably 40,000 to 200,000. If the weight-average molecular weight is too large, the melt viscosity during hot melt molding tends to be too high, making it difficult to form a good film, and conversely, if the weight-average molecular weight is too small, the mechanical strength of the obtained laminate tends to be insufficient.

[0087] Such weight average molecular weight can be measured by size exclusion chromatography (GPC, gel permeation chromatography) as polystyrene equivalent according to ISO 16014-1 and ISO 16014-3 standards using tetrahydrofuran as eluent and a column (polystyrene gel) heated to 40°C.

[0088] An example of a commercially available product of such polybutylene succinate (C3) is "BioPBS" manufactured by Mitsubishi Chemical Corporation.

[0089] In addition, the biodegradable resin (C) layer used in the present invention may contain, in addition to the biodegradable resin (C), a heat stabilizer, an antioxidant, an ultraviolet absorber, a crystal nucleating agent, an antistatic agent, a flame retardant, a plasticizer, a lubricant, a filler, a lubricant, a crystal nucleating agent, etc.

[0090] [Laminate] The laminate of the present invention has at least one layer containing the acid-modified polyester resin (A) of the present invention (hereinafter, may be referred to as "acid-modified polyester resin (A) layer").

[0091] The acid-modified polyester resin (A) layer is a layer mainly composed of the acid-modified polyester resin (A), and usually contains 70% by weight or more of the acid-modified polyester resin (A), preferably 80% by weight or more, and more preferably 90% by weight or more of the acid-modified polyester resin (A), with the upper limit being 100% by weight.

[0092] The acid-modified polyester resin (A) layer used in the present invention may contain, in addition to the acid-modified polyester resin (A), a heat stabilizer, an antioxidant, an ultraviolet absorber, a crystal nucleating agent, an antistatic agent, a flame retardant, a plasticizer, a lubricant, a filler lubricant, a crystal nucleating agent, etc.

[0093] The laminate of the present invention preferably has a biodegradable resin (C) layer as a layer other than the acid-modified polyester resin (A) layer. Among these, the laminate of the present invention is preferably one which uses a PVA-based resin (B) layer as the gas barrier layer and a biodegradable resin (C) layer as the outer layer.

[0094] The laminate of the present invention is a laminate having an adhesive layer between a PVA resin (B) layer and a biodegradable resin (C) layer, and the adhesive layer preferably contains the biodegradable acid-modified polyester resin (A) of the present invention, and has a layer structure of usually 3 to 15 layers, preferably 3 to 7 layers, and particularly preferably 5 to 7 layers.

[0095] The structure of the laminate of the present invention is not particularly limited, but when the biodegradable resin (C) layer is c, the PVA-based resin (B) layer is b, and the acid-modified polyester-based resin (A) layer (adhesive layer) is a, any combination such as c / a / b, c / a / b / a / c, c / b / a / b / a / b / c, etc. is possible. When there are multiple biodegradable resin (C) layers in the laminate, the multiple biodegradable resin (C) layers may be the same or different. The same applies when there are multiple PVA-based resin (B) layers and when there are multiple acid-modified polyester-based resin (A) layers in the laminate.

[0096] In order to prevent deterioration of the gas barrier performance due to moisture absorption by the PVA-based resin (B) layer, it is usually preferable to provide a layer structure in which a biodegradable resin (C) layer is provided in the PVA-based resin (B) layer in a portion that comes into contact with the outside air or a moisture-containing content.

[0097] The thickness of the laminate of the present invention is usually 1 to 30,000 μm, and is preferably in the range of particularly 3 to 13,000 μm, and particularly 10 to 3,000 μm.

[0098] As for the thickness of each layer constituting the laminate, the thickness of the biodegradable resin (C) layer is usually 0.4 to 14,000 μm, preferably 1 to 6,000 μm, and particularly preferably 4 to 1,400 μm. If the thickness of the biodegradable resin (C) layer is too thick, the laminate tends to be too hard, whereas if the thickness of the biodegradable resin (C) layer is too thin, the laminate tends to be brittle.

[0099] The thickness of the PVA resin (B) layer is usually 0.1 to 1,000 μm, preferably 0.3 to 500 μm, and particularly preferably 1 to 100 μm. If the PVA resin (B) layer is too thick, the laminate tends to be hard and brittle, whereas if the PVA resin (B) layer is too thin, the gas barrier properties tend to be poor.

[0100] The thickness of the acid-modified polyester resin (A) layer (adhesive layer) is usually 0.1 to 500 μm, preferably 0.15 to 250 μm, and particularly preferably 0.5 to 50 μm. If the acid-modified polyester resin (A) layer is too thick, the appearance may be poor, and conversely, if the acid-modified polyester resin (A) layer is too thin, the adhesive strength tends to be weak.

[0101] Furthermore, when there are a plurality of each layer, the ratio of the thickness of the biodegradable resin (C) layer to the thickness of the PVA-based resin (B) layer (thickness of biodegradable resin (C) layer / thickness of PVA-based resin (B) layer) is the ratio of the total thicknesses thereof and is usually 1 to 100, preferably 2.5 to 50. If this ratio is too large, the barrier property tends to be reduced, and if this ratio is too small, the laminate tends to be hard and brittle.

[0102] Furthermore, the thickness ratio of the laminate of the present invention and the acid-modified polyester resin (A) layer (adhesive layer) (thickness of the acid-modified polyester resin (A) layer / thickness of the laminate of the present invention) is the ratio of the total thickness when there are multiple acid-modified polyester resin (A) layers (adhesive layers), and is usually 0.005 to 0.5, preferably 0.01 to 0.3. If this ratio is too large, the appearance tends to deteriorate, and if this ratio is too small, the adhesive strength tends to weaken.

[0103] The laminate of the present invention can be produced by a conventionally known molding method, specifically, a melt molding method or a molding method from a solution state can be used.

[0104] Examples of melt molding methods include a method in which an acid-modified polyester resin (A) and a PVA-based resin (B) are sequentially or simultaneously melt extrusion laminated onto a film or sheet of a biodegradable resin (C); a method in which an acid-modified polyester resin (A) and a biodegradable resin (C) are sequentially or simultaneously melt extrusion laminated onto a film or sheet of a PVA-based resin (B); and a method in which the biodegradable resin (C), the acid-modified polyester resin (A), and the PVA-based resin (B) are co-extruded.

[0105] As a molding method from a solution state, there can be mentioned a method in which a solution of an acid-modified polyester resin (A) dissolved in a good solvent is solution-coated onto a film or sheet of a biodegradable resin (C), and after drying, an aqueous solution of a PVA resin (B) is solution-coated.

[0106] Among them, the melt molding method is preferred, and the co-extrusion method is particularly preferred, since it can be produced in one step and can give a laminate with excellent interlayer adhesion. When using such a melt molding method, it is preferred to use a PVA resin having a 1,2-diol structural unit in the side chain as the PVA resin (B).

[0107] Specific examples of the co-extrusion method include the inflation method, the T-die method, the multi-manifold die method, the feed block method, and the multi-slot die method. The shape of the die that can be used may be a T-die, a round die, or the like. The melt molding temperature during melt extrusion is usually 140 to 250°C, and preferably in the range of 160 to 230°C.

[0108] The laminate of the present invention may be further subjected to a heat stretching treatment, and such a stretching treatment is expected to improve the strength and gas barrier properties.

[0109] In particular, in the laminate of the present invention, when a PVA resin having a 1,2-diol structural unit in the side chain is used as the PVA resin (B), the stretchability is good.

[0110] For the stretching treatment, a known stretching method can be used. Specific examples of such methods include uniaxial stretching and biaxial stretching, in which both edges of a multilayer structure sheet are gripped and expanded; die forming methods such as deep drawing, vacuum forming, pressure forming, and vacuum pressure forming, in which a multilayer structure sheet is stretched using a die; and methods in which a preformed multilayer structure such as a parison is processed using a tubular stretching method, stretch blow method, etc.

[0111] As such a stretching method, when a film or sheet-like molded product is intended, it is preferable to employ a uniaxial stretching method or a biaxial stretching method.

[0112] In the case of a die forming method such as deep drawing, vacuum forming, pressure forming, or vacuum pressure forming, it is preferable to uniformly heat the laminate using a hot air oven, a heater type oven, or a combination of both, and stretch the laminate using a chuck, a plug, vacuum force, compressed air force, or the like.

[0113] When the object is to produce a molded product such as a cup or a tray having a drawing ratio (depth of molded product (mm) / maximum diameter of molded product (mm)) of usually 0.1 to 3, it is preferable to adopt a mold molding method in which a mold is used for stretching processing, such as a deep drawing method, a vacuum forming method, a pressure forming method, or a vacuum pressure forming method.

[0114] The laminate of the present invention thus obtained has strong adhesive strength between any of the layers, for example, between the biodegradable resin (C) layer and the acid-modified polyester resin (A) layer, and between the PVA resin (B) layer and the acid-modified polyester resin (A) layer.

[0115] Moreover, the acid-modified polyester resin (A), the biodegradable resin (C) and the PVA resin (B) are all biodegradable, and the laminate of the present invention having at least one layer of the acid-modified polyester resin (A) also has excellent biodegradability.

[0116] Since the laminate of the present invention is biodegradable, it is suitable for use in products that can be disposed of directly in compost, such as coffee capsules (coffee bean containers for capsule-type coffee makers), shrink films, and other food and beverage containers.

[0117] Furthermore, when the laminate of the present invention has a PVA-based resin (B) layer, the PVA-based resin (B) layer can be removed by dissolving it in water, and only the remaining water-insoluble resin can be recycled. EXAMPLES

[0118] The present invention will be described below with reference to examples. However, the present invention is not limited to the description of the examples as long as it does not depart from the gist of the present invention. In the examples, "parts" and "%" are by weight.

[0119] [Example 1] [Preparation of Acid-Modified Polyester Resin (A)] As the raw material polyester resin (A'), 100 parts of polybutylene succinate adipate (PBSA) ("BioPBS FD92PM" manufactured by Mitsubishi Chemical Corporation), which is a condensation polymer of succinic acid / adipic acid / 1,4-butanediol, 0.40 parts of maleic anhydride, and 2,5-dimethyl-2,5-bis(t-butyloxy)hexane ("Trigonox" manufactured by Nouryon Chemical Co., Ltd.) as a radical initiator were used. A dry blend of 0.44 parts of sorbic acid as an aliphatic compound having a conjugated double bond, 0.46 parts of sorbic acid as an aliphatic compound having a conjugated double bond, and 0.46 parts of 3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionic acid (BASF's "Irganox 1010") as an antioxidant was then melt-kneaded under the following conditions in a twin-screw extruder, extruded into a strand shape, cooled with water, and cut with a pelletizer to obtain cylindrical pellets of acid-modified polyester resin (A).

[0120] Twin Screw Extruder Diameter (D): 15mm, L / D:60 Screw rotation speed: 200 rpm Mesh: 60 / 90 / 60mesh Processing temperature: 160℃

[0121] [Measurement of MFR] The melt flow rate (MFR) was measured by Method A in accordance with JIS K 7210 (1999). The measurement temperature was 210°C and the load was 2160g. The results are shown in Table 1.

[0122] [Preparation of PVA resin (B)] A reaction vessel equipped with a reflux condenser, a dropping funnel, and a stirrer was charged with 68.0 parts of vinyl acetate, 23.8 parts of methanol, and 8.2 parts of 3,4-diacetoxy-1-butene, and 0.3 mol % (relative to the charged vinyl acetate) of azobisisobutyronitrile was added, and the temperature was raised under a nitrogen stream while stirring to start polymerization. When the polymerization rate of vinyl acetate reached 90%, m-dinitrobenzene was added to terminate the polymerization, and then methanol vapor was blown in to remove unreacted vinyl acetate monomer from the system, yielding a methanol solution of the copolymer.

[0123] Next, the above methanol solution was further diluted with methanol to adjust the concentration to 45%, and charged into a kneader, and while maintaining the solution temperature at 35°C, a 2% methanol solution of sodium hydroxide was added in a ratio of 10.5 mmol per mol of the total amount of vinyl acetate structural units and 3,4-diacetoxy-1-butene structural units in the copolymer to carry out saponification. As the saponification proceeded, the saponified product precipitated, and when it became particulate, it was filtered off, thoroughly washed with methanol, and dried in a hot air dryer to produce a PVA-based resin (B) having 1,2-diol structural units in the side chains.

[0124] The degree of saponification of the obtained PVA resin (B) was 99.2 mol % as analyzed based on the amount of alkali consumed for hydrolysis of the remaining vinyl acetate and 3,4-diacetoxy-1-butene.

[0125] The average degree of polymerization of the PVA resin (B) was analyzed in accordance with JIS K 6726 and was found to be 450. The content of the 1,2-diol structural unit represented by general formula (4) was 6 mol % as calculated from the integrated value measured by 1H-NMR (300 MHz proton NMR, d6-DMSO solution, internal standard: tetramethylsilane, 50°C).

[0126] [Preparation of Laminate] Using polybutylene succinate (C3) ("BioPBS FZ91PM" manufactured by Mitsubishi Chemical Corporation), PVA resin (B), and acid-modified polyester resin (A), a three-type, five-layer laminate of polybutylene succinate (C3) layer / acid-modified polyester resin (A) layer / PVA resin (B) layer / acid-modified polyester resin (A) layer / polybutylene succinate (C3) layer was produced in a five-type, five-layer multilayer film-forming device equipped with five extruders. The thickness of the obtained laminate was 100 μm, and the thicknesses of the individual layers were 30 μm / 10 μm / 20 μm / 20 μm / 30 μm. The set temperatures of each extruder and cooling device were as follows.

[0127] Set temperature (C1~C3: cylinders, H: head, AD: adapter, D1~5: dies.) Polybutylene succinate (C3): C1 / C2 / H / AD=140 / 160 / 160 / 160℃ PVA resin (B): C1 / C2 / C3 / H / AD=190 / 200 / 210 / 200 / 190℃ Acid-modified polyester resin (A): C1 / C2 / C3 / H / AD=180 / 200 / 210 / 200 / 190℃ Dice: D1 / D2 / D3 / D4 / D5=190 / 190 / 190 / 190 / 190℃ Cooling temperature: 7℃

[0128] [Adhesion Strength Evaluation] The laminate obtained above was cut into a rectangular shape with a width of 15 mm, and the adhesive strength at the interface between the layers was measured using a 50 N load cell of a tensile tester "AG-IS 5kN" (manufactured by Shimadzu Corporation). The test speed was set to 100 mm / min, and the average of five measurements was used as the adhesive strength value. The measurement was performed in an environment of 23°C / 50% RH. The results are shown in Table 1.

[0129] [Comparative Example 1] to [Comparative Example 2] In the preparation of the acid-modified polyester resin (A) of Example 1, an acid-modified polyester resin (A) was prepared in the same manner as in Example 1, except that an aliphatic compound having a conjugated double bond was added as shown in Table 1, and a laminate was prepared. The appearance of the obtained laminate was evaluated in the same manner as in Example 1. The results are shown in Table 1. The amount of the aliphatic compound having a conjugated double bond added was adjusted based on the number of moles relative to the biodegradable polyester resin.

[0130] [Table 1]

[0131] The acid-modified polyester resin (A) of the present invention suppressed the decrease in MFR, and the laminate of Example 1 in which it was used had excellent adhesive strength. On the other hand, the laminates of Comparative Examples 1 and 2, which used a polyester resin that did not contain an aliphatic compound having a conjugated double bond, were poor in achieving both MFR and adhesive strength. [Industrial Applicability]

[0132] The acid-modified polyester resin (A) of the present invention can be suitably used as an adhesive layer between a PVA resin (B) layer and a biodegradable resin (C) layer. The obtained laminate is biodegradable and therefore can be suitably used for products that can be disposed of as is in the compost, such as coffee capsules (coffee bean containers for capsule-type coffee makers), shrink films, and other food and beverage containers.

Claims

1. An acid-modified polyester resin comprising an aliphatic compound having a conjugated double bond.

2. The acid-modified polyester resin according to claim 1, which has at least one structural unit selected from the structural units represented by the following general formulas (1) to (3): 【Chemistry 1】 [In formula (1), l is an integer from 2 to 8.] 【Chemistry 2】 [In formula (2), m is an integer from 2 to 10.] 【Chemistry 3】 [In formula (3), n is an integer from 2 to 9.]

3. 3. The acid-modified polyester resin according to claim 1, which is obtained by graft-polymerizing an α,β-unsaturated carboxylic acid or an anhydride thereof onto a biodegradable polyester resin.

4. 3. The acid-modified polyester resin according to claim 2, which contains at least one structural unit selected from the structural units represented by the general formulas (1) to (3) in a total amount of 50 mol % or more.

5. A laminate having at least one layer containing the acid-modified polyester resin according to any one of claims 1 to 4.

6. A laminate having an adhesive layer provided between a polyvinyl alcohol-based resin (B) layer and a biodegradable resin (C) layer, A laminate, wherein the adhesive layer contains the acid-modified polyester resin according to any one of claims 1 to 4.

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