Modified ethylene-vinyl alcohol resin and method for producing the same

Abstract

Provided is a modified EVOH resin that has suppressed excessive decrease in melting point and includes an aliphatic polyester unit. The average chain length for the aliphatic polyester unit in the modified EVOH resin is at least 1.5.

Description

Technical Field

[0001] The present invention relates to a modified ethylene-vinyl alcohol resin containing an aliphatic polyester unit, and more particularly to a modified ethylene-vinyl alcohol resin having an average chain length of the aliphatic polyester unit of 1.5 or more and a method for producing the same.

Background Art

[0002] Ethylene-vinyl alcohol resin (hereinafter sometimes referred to as "EVOH resin") has very strong intermolecular forces due to hydrogen bonding between hydroxyl groups present in the polymer side chains. Therefore, it has high crystallinity and high intermolecular forces even in the amorphous part, so gas molecules and the like have difficulty passing through a film using the EVOH resin, and the film using the EVOH resin exhibits excellent gas barrier properties.

[0003] However, the EVOH resin is a hard and brittle resin and has the drawback of lacking flexibility. Therefore, when used as a packaging material or a molding material, when repeatedly bent and used, cracks and pinholes are generated due to bending fatigue or the like, and there are problems such as the inability to maintain its excellent performance.

[0004] As a means for solving such problems, a modified EVOH resin in which an aliphatic polyester is grafted to the hydroxyl group of the EVOH resin by a ring-opening polymerization reaction of lactones has been proposed (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, while the modified EVOH resin described in Patent Document 1 is more flexible than the unmodified EVOH resin, its melting point is significantly lower, resulting in poor heat resistance and limiting its use in applications requiring high heat resistance.

[0007] The present invention provides a modified EVOH-based resin in which excessive reduction of the melting point is suppressed. [Means for solving the problem]

[0008] However, in view of these circumstances, the present inventors conducted extensive research and found that the above problem can be solved by making the average chain length of the aliphatic polyester units in a modified EVOH resin containing aliphatic polyester units 1.5 or more.

[0009] In other words, the present invention has the following aspects. [1] A modified ethylene-vinyl alcohol resin containing aliphatic polyester units, A modified ethylene-vinyl alcohol resin in which the average chain length of aliphatic polyester units in the modified ethylene-vinyl alcohol resin is 1.5 or more. [2] A modified ethylene-vinyl alcohol resin according to [1], wherein the modification rate is 1.5 mol% or more. [3] A modified ethylene-vinyl alcohol resin according to [1] or [2], further containing at least one selected from the group consisting of tin, zinc, and titanium, wherein the total content of tin, zinc, and titanium is 25 μg / g or more. [4] The modified ethylene-vinyl alcohol resin according to any one of [1] to [3], wherein the aliphatic polyester unit is a ring-opening polymer of lactones. [5] The modified ethylene-vinyl alcohol resin according to any one of [1] to [4], wherein the modified ethylene-vinyl alcohol resin is a modified product of an ethylene-vinyl alcohol resin using a ring-opening polymerization catalyst of a tin-based compound and / or a zinc-based compound as a polymerization catalyst. [6] A method for producing a modified ethylene-vinyl alcohol resin according to any one of [1] to [5], comprising the step of ring-opening polymerization of lactones in an extruder in the presence of an ethylene-vinyl alcohol resin using at least one ring-opening polymerization catalyst selected from the group consisting of tin compounds, zinc compounds, and titanium compounds. [7] The method for producing a modified ethylene-vinyl alcohol resin according to [6], wherein the ring-opening polymerization catalyst is a ring-opening polymerization catalyst of a tin-based compound and / or a zinc-based compound. [8] A method for producing a modified ethylene-vinyl alcohol resin according to [6] or [7], wherein the amount of the ring-opening polymerization catalyst is greater than 1 part by weight per 100 parts by weight of the lactones. [Effects of the Invention]

[0010] The modified EVOH resin of the present invention is a modified EVOH resin containing aliphatic polyester units, and since the average chain length of the aliphatic polyester units in the modified EVOH resin is 1.5 or more, an excessive decrease in the melting point is suppressed. [Modes for carrying out the invention]

[0011] The configuration of the present invention will be described in detail below, but these are merely examples of preferred embodiments. Note that "X and / or Y (where X and Y are any combination)" means at least one of X and Y, and can mean X only, Y only, or X and Y.

[0012] <Explanation of Modified EVOH Resins> The modified EVOH-based resin of the present invention is a modified EVOH-based resin containing an aliphatic polyester unit. The aliphatic polyester unit is preferably a ring-opening polymer of lactones because the reaction is simple, there is little bleeding or poor adhesion, little evaporation during melt molding, and little contamination of the working environment. It is preferable that the aliphatic polyester unit is bonded to the side chain of the EVOH-based resin from the viewpoint of ensuring gas barrier properties and flexibility. As such a modified EVOH-based resin, for example, a resin obtained by grafting an aliphatic polyester onto an EVOH-based resin is preferably mentioned. Specifically, it can be obtained by a ring-opening polymerization reaction and a graft reaction of lactones in the presence of an EVOH-based resin. The formation of the aliphatic polyester by such a graft reaction uses the hydroxyl group of the EVOH-based resin as the starting end.

[0013] Hereinafter, the graft reaction of lactones in the presence of an EVOH-based resin will be described in detail.

[0014] [EVOH-based resin] First, the EVOH-based resin, which is a raw material of the modified EVOH-based resin of the present invention, will be described. The EVOH-based resin used in the present invention is usually a thermoplastic resin obtained by saponifying an ethylene-vinyl ester copolymer, which is a copolymer of ethylene and a vinyl ester monomer. Generally, vinyl acetate is used as the vinyl ester monomer from an economic perspective. As the polymerization method, any known polymerization method, such as solution polymerization, suspension polymerization, emulsion polymerization, etc., can be used, but generally solution polymerization using methanol as a solvent is used. The saponification of the obtained ethylene-vinyl ester copolymer can also be carried out by a known method. That is, the EVOH-based resin mainly contains an ethylene structural unit and a vinyl alcohol structural unit, and contains a small amount of vinyl ester structural units remaining without being saponified.

[0015] The content of the ethylene structural unit in the EVOH resin used in the present invention is usually 20 to 60 mol%, preferably 25 to 50 mol%, particularly preferably 29 to 45 mol%. When such content is too low, the flexibility tends to deteriorate, and when it is too high, the gas barrier property tends to be insufficient. The content of such ethylene structural unit can be measured, for example, in accordance with ISO14663.

[0016] The saponification degree of the vinyl ester component in the EVOH resin is usually 80 to 100 mol%, preferably 90 to 99.99 mol%, particularly preferably 99 to 99.99 mol%. When such saponification degree is too low, the flexibility tends to deteriorate. The saponification degree of such vinyl ester component can be measured, for example, in accordance with JIS K6726 (however, for EVOH resin, in a solution uniformly dissolved in a water / methanol solvent).

[0017] The melt flow rate (MFR) (210 °C, load 2160 g) of the EVOH resin is usually 1 to 50 g / 10 min, preferably 1.5 to 25 g / 10 min, particularly preferably 2 to 20 g / 10 min. When the MFR is too large, the barrier property tends to deteriorate, and when it is too small, the flexibility tends to deteriorate.

[0018] As the EVOH resin, as long as the average value satisfies the above requirements, two or more kinds of EVOH resins with different ethylene content, saponification degree, and MFR may be mixed and used.

[0019] Furthermore, the EVOH-based resin used in the present invention may further contain structural units derived from the following comonomers. These comonomers include α-olefins such as propylene, isobutene, α-octene, α-dodecene, and α-octadecene; hydroxyl group-containing α-olefins such as 3-buten-1-ol, 4-penten-1-ol, and 3-buten-1,2-diol, and hydroxyl group-containing α-olefin derivatives such as their esters and acylated products; unsaturated carboxylic acids or their salts, partially alkyl esters, fully alkyl esters, nitriles, amides, or anhydrides; unsaturated sulfonic acids or their salts; vinylsilane compounds; vinyl chloride; and styrene.

[0020] Furthermore, EVOH-based resins that have undergone "post-modification" such as urethaneization, acetalization, cyanoethylation, or oxyalkyleneization can also be used.

[0021] Among the modified products described above, EVOH-based resins in which primary hydroxyl groups are introduced into the side chains by copolymerization are preferred because they have good secondary moldability, such as in stretching and vacuum / pressure molding, and among these, EVOH-based resins having a 1,2-diol structure in the side chains are preferred.

[0022] [Lactones] The lactones are not particularly limited as long as they are lactones in which the number of carbon atoms constituting the ring that forms an aliphatic polyester by ring-opening polymerization is 3 to 10. Such lactones, when they do not have substituents, are represented by the following general formula (1), where n is an integer from 2 to 9. Preferably, n is 4 to 5. Also, the alkylene chain -(CH2) in the following formula (1) n - Any of the carbon atoms may have at least one substituent such as a lower alkyl group, lower alkoxy group, cycloalkyl group, phenyl group, or aralkyl group having approximately 1 to 8 carbon atoms.

[0023] [ka]

[0024] Examples of lactones include β-propiolactones, γ-butyrolactones, ε-caprolactones, and δ-valerolactones.

[0025] Examples of β-propiolactones include β-propiolactone and dimethylpropion lactone.

[0026] Examples of γ-butyrolactones include butyrolactone, γ-valerolactone, γ-caprolactone, γ-capryloractone, γ-laurolactone, γ-palmitractone, γ-stearolactone, crotonolactone, α-angelicalactone, and β-angelicalactone.

[0027] Examples of ε-caprolactones include monoalkyl-ε-caprolactones such as ε-caprolactone, monomethyl-ε-caprolactone, monoethyl-ε-caprolactone, monodecyl-ε-caprolactone, monopropyl-ε-caprolactone, and monodecyl-ε-caprolactone; dialkyl-ε-caprolactones in which two alkyl groups are substituted on carbon atoms other than the ε position; trialkyl-ε-caprolactones in which three alkyl groups are substituted on carbon atoms other than the ε position; alkoxy-ε-caprolactones such as ethoxy-ε-caprolactone; cycloalkyl-lactones such as cyclohexyl-ε-caprolactone; aralkyl-ε-caprolactones such as benzyl-ε-caprolactone; and aryl-ε-caprolactones such as phenyl-ε-caprolactone.

[0028] Examples of δ-valerolactones include 5-valerolactone, 3-methyl-5-valerolactone, 3,3-dimethyl-5-valerolactone, 2-methyl-5-valerolactone, and 3-ethyl-5-valerolactone.

[0029] These lactones can be used individually or in combination of two or more.

[0030] Among these, the lactones used in the present invention are not particularly limited, but from the viewpoint of reactivity, ε-caprolactones and δ-valerolactones are preferred, and ε-caprolactones are even more preferred because they are inexpensive and readily available.

[0031] <Method for producing modified EVOH-based resin> The modified EVOH-based resin of the present invention is typically obtained by a process of ring-opening polymerization of lactones in an extruder in the presence of the EVOH-based resin using at least one ring-opening polymerization catalyst selected from the group consisting of tin-based compounds, zinc-based compounds, and titanium-based compounds. For example, an EVOH-based resin, lactones, and at least one ring-opening polymerization catalyst selected from the group consisting of tin-based compounds, zinc-based compounds, and titanium-based compounds are mixed in a predetermined ratio in an extruder, and the EVOH-based resin is brought to a molten state and the reaction is carried out at a predetermined reaction temperature and time. By this method, a modified EVOH-based resin having an average chain length of 1.5 or more aliphatic polyester units can be produced. Furthermore, the polymerization reaction is preferably a graft reaction.

[0032] The amount of lactones used in the EVOH-based resin can be appropriately selected to obtain the desired aliphatic polyester unit content, but typically, the amount of lactones is 1 to 200 parts by weight, preferably 10 to 150 parts by weight, and particularly preferably 20 to 100 parts by weight, per 100 parts by weight of the EVOH-based resin. If the amount used is too small, flexibility tends to be insufficient, and if the amount used is too large, gas barrier properties tend to decrease.

[0033] As the ring-opening polymerization catalyst, at least one ring-opening polymerization catalyst selected from the group consisting of tin-based compounds (also referred to as "tin-based catalysts"), zinc-based compounds (also referred to as "zinc-based catalysts"), and titanium-based compounds (also referred to as "titanium-based catalysts") can be used. Specifically, examples include tin alkoxides such as dibutyldibutoxytin, tin ester compounds such as dibutyltin diacetate; zinc chelates such as zinc(II) acetylacetonate and zinc acetylacetonate hydrate, zinc alkoxides such as zinc i-propoxide and zinc t-butoxide; organic titanates such as tetraisopropyl titanate and tetrabutyl titanate; and metal complexes of tin, zinc, or titanium. Among these, tin-based compounds and / or zinc-based compounds are preferred in terms of flexibility, and it is more preferable to selectively use either tin-based compounds or zinc-based compounds.

[0034] The amount of catalyst used is usually 0.01 to 10 parts by weight, preferably 0.1 to 5 parts by weight, and particularly preferably 0.15 to 3 parts by weight, per 100 parts by weight of lactones. Furthermore, from the viewpoint of ensuring the rate of modification, it is also preferable that the amount of catalyst be greater than 1 part by weight per 100 parts by weight of lactones. If the amount used is too small, the rate of modification tends to decrease, and if the amount used is too large, the composition ratio of the modified EVOH-based resin tends to fluctuate, and the effects of the present invention tend not to be achieved.

[0035] When a graft reaction is performed as a polymerization reaction, the reaction temperature is usually 50 to 250°C, preferably 100 to 240°C, and more preferably 150 to 230°C, which is the temperature at which the resin reaches a melted state. If the reaction temperature is too high, the modified EVOH-based resin tends to degrade due to heat. On the other hand, if the reaction temperature is too low, the graft reaction of the EVOH-based resin does not proceed, and the resin tends to remain unmodified.

[0036] The initial temperature for each material in a graft reaction is typically room temperature, for example, between 10 and 40°C.

[0037] The reaction time in the graft reaction is typically 1 second to 1.5 hours, preferably 3 seconds to 1.25 hours, more preferably 5 seconds to 1 hour, and particularly preferably 7 seconds to 45 minutes. If the reaction time is too long, the modified EVOH resin will degrade due to heat, leading to an extreme increase in viscosity and the formation of thermally degraded products within the modified EVOH resin, which tends to cause gel formation during film formation. On the other hand, if the reaction time is too short, the graft reaction of the EVOH resin will not proceed, and it tends to remain unmodified.

[0038] The manufacturing equipment includes extruders such as single-screw extruders, twin-screw extruders, Banbury mixers, kneaders, and brabenders (for example, the TEX series from Japan Steel Works, the HYPERKTX series from Kobe Steel, Ltd., the TEM series from Shibaura Machinery Co., Ltd., and the KRC kneader series from Kurimoto Iron Works Co., Ltd.), and can be used that can continuously perform the ring-opening polymerization reaction of EVOH-based resin by melt kneading (referred to as a continuous process). It should be noted that the modified EVOH-based resin of the present invention cannot be manufactured using conventional batch-type stirring equipment such as stirring apparatus or flasks that cannot continuously perform the ring-opening polymerization reaction of EVOH-based resin. Extruders used in a continuous process have strong shear force during melt kneading, which accelerates the ring-opening polymerization reaction, allowing for continuous ring-opening polymerization of EVOH-based resin, thereby enabling the production of the modified EVOH-based resin of the present invention.

[0039] In the batch method, various raw materials are charged into the reaction apparatus all at once, and then the modified EVOH-based resin is synthesized by reacting them at a predetermined temperature while raising the temperature and stirring. The input of raw materials and the discharge of the modified EVOH-based resin are not carried out simultaneously. The continuous process is a method of continuously synthesizing modified EVOH-based resins by sequentially feeding various raw materials into an extruder and reacting them while stirring at a predetermined temperature, with the feeding of raw materials and the discharge of modified EVOH-based resins occurring simultaneously.

[0040] The average chain length of aliphatic polyester units in the modified EVOH resin is 1.5 or more, preferably 1.6 to 3, more preferably 1.6 to 2.5, and particularly preferably 1.6 to 2.3. If the average chain length of aliphatic polyester units is too short, the melting point tends to decrease too much. Furthermore, the average chain length of the aliphatic polyester units in the modified EVOH resin is 1 It can be calculated from the H-NMR measurement results.

[0041] The modification rate in modified EVOH-based resins is typically 1 mol% or more, preferably 1.5 mol% or more, more preferably 2 to 30 mol%, particularly preferably 2.5 to 20 mol%, and more preferably 3 to 15 mol%. This modification rate represents the proportion of the structural units of the EVOH-based resin that are grafted with aliphatic polyester. If the modification rate in the modified EVOH-based resin is too low, flexibility tends to deteriorate, and if the modification rate in the modified EVOH-based resin is too high, the melting point tends to decrease too much. Furthermore, the modification rate in modified EVOH-based resins is 1 It can be calculated from the H-NMR measurement results.

[0042] In modified EVOH resins, the relationship between the modification rate (mol%) and the average chain length (number) of aliphatic polyester units is preferably such that the average chain length value < modification rate value. More specifically, the ratio of modification rate value to average chain length is usually 0.6 to 20, preferably 1.1 to 15, even more preferably 1.3 to 10, particularly preferably 1.5 to 5, and even more preferably 2 to 3.5. By having "average chain length value < modification rate value," the effect of suppressing an excessive decrease in the melting point while maintaining high flexibility can be further enhanced.

[0043] The melting point of modified EVOH resins is typically 40 to 200°C, preferably 60 to 180°C, more preferably 80 to 160°C, particularly preferably 90 to 150°C, and more preferably 100 to 140°C. If the melting point of the modified EVOH resin is too high, it tends to decrease flexibility. If the melting point of the modified EVOH resin is too low, it tends to decrease gas barrier properties and becomes difficult to use in applications requiring heat resistance. When aliphatic polyesters are grafted, the intermolecular forces, such as hydrogen bonds between hydroxyl groups in the EVOH-based resin skeleton, weaken. Therefore, as the modification rate of the modified EVOH-based resin increases, the melting point of the modified EVOH-based resin tends to decrease. The melting point of modified EVOH resins can be measured using a differential scanning calorimeter.

[0044] The modified EVOH resin of the present invention has an average chain length of 1.5 or more aliphatic polyester units, and it is preferable that the modification rate is 1.5 mol% or more, as this allows for high flexibility and suppression of excessive decrease in the melting point. To satisfy both the average chain length and the degree of modification, it is necessary to selectively use a ring-opening polymerization catalyst consisting of a tin-based compound and / or a zinc-based compound among the ring-opening polymerization catalysts used in production, and to carry out the reaction in a continuous manner using an extruder. Furthermore, it is more preferable to selectively use a tin-based compound or a zinc-based compound among the ring-opening polymerization catalysts.

[0045] The modified EVOH resin of the present invention is a modified EVOH resin obtained by using at least one ring-opening polymerization catalyst selected from the group consisting of tin-based compounds, zinc-based compounds, and titanium-based compounds as a polymerization catalyst, and is preferably a modified EVOH resin obtained by using a ring-opening polymerization catalyst of a tin-based compound and / or a zinc-based compound. Therefore, the modified EVOH resin of the present invention usually contains at least one selected from the group consisting of tin, zinc, and titanium, and it is preferable that it contains tin and / or zinc. The total content of tin, zinc, and titanium in the modified EVOH resin is typically 25 μg / g or more, preferably 100 to 1,000,000 μg / g, more preferably 200 to 1,000,000 μg / g, particularly preferably 500 to 50,000 μg / g, and more preferably 1,000 to 10,000 μg / g. Such content levels make it easier to achieve the effects of the present invention.

[0046] The modified EVOH resin of the present invention may contain, to the extent that it does not impair the effects of the present invention (for example, 5% by weight or less of the modified EVOH resin), compounding agents commonly used in EVOH resins, such as heat stabilizers, antioxidants, antistatic agents, colorants, ultraviolet absorbers, lubricants, plasticizers, light stabilizers, surfactants, antibacterial agents, drying agents, antiblocking agents, flame retardants, crosslinking agents, curing agents, foaming agents, nucleating agents, antifogging agents, biodegradable additives, silane coupling agents, oxygen absorbers, etc. These compounding agents may be used individually or in combination of two or more.

[0047] As the heat stabilizer, for the purpose of improving various physical properties such as heat stability during melt molding, organic acids such as acetic acid, propionic acid, butyric acid, lauric acid, stearic acid, oleic acid, and behenic acid, or their alkali metal salts (sodium, potassium, etc.), alkaline earth metal salts (calcium, magnesium, etc.), and zinc salts may be added; or inorganic acids such as sulfuric acid, sulfurous acid, carbonic acid, phosphoric acid, and boric acid, or additives such as their alkali metal salts (sodium, potassium, etc.), alkaline earth metal salts (calcium, magnesium, etc.), and zinc salts may be added. Furthermore, these additives may be used individually or in combination of two or more types. Of these, it is particularly preferable to add acetic acid, boric acid and its salts, boron compounds, acetates, and phosphates.

[0048] When acetic acid is added, the amount added is usually 0.001 to 1 part by weight, preferably 0.005 to 0.2 parts by weight, and particularly preferably 0.01 to 0.1 parts by weight, per 100 parts by weight of the modified EVOH resin. If the amount of acetic acid added is too small, the effect of the acetic acid content tends not to be sufficiently obtained, and conversely, if it is too large, it tends to be difficult to obtain a uniform film.

[0049] Furthermore, when adding a boron compound, the amount added is usually 0.001 to 1 part by weight, preferably 0.002 to 0.2 parts by weight, and particularly preferably 0.005 to 0.1 parts by weight, per 100 parts by weight of modified EVOH resin, in terms of boron equivalent (analyzed by ICP emission spectrometry after ashing). If the amount of boron compound added is too small, the effect of adding the boron compound may not be sufficiently obtained, and if it is too large, it tends to be difficult to obtain a uniform film.

[0050] Furthermore, the amount of acetate and phosphate (including hydrogen phosphate) added is typically 0.005 to 0.1 parts by weight, preferably 0.001 to 0.05 parts by weight, and particularly preferably 0.002 to 0.03 parts by weight, per 100 parts by weight of modified EVOH resin, calculated on a metal basis (analyzed by ICP emission spectrometry after ashing). If the amount added is too small, the effect of its inclusion may not be sufficiently obtained, and if it is too large, it tends to be difficult to obtain a uniform film. When two or more salts are added to the modified EVOH resin, it is preferable that the total amount is within the range of the above-mentioned addition amounts.

[0051] When using alkali metal salts as the salt, the amount of alkali metal added is usually 10 to 2000 ppm by weight relative to the modified EVOH resin, preferably 25 to 1000 ppm, and particularly preferably 50 to 500 ppm. If the amount of alkali metal is too high, there is a tendency for poor coloring, and if the amount of alkali metal is too low, there is a tendency for interlayer adhesion to decrease.

[0052] The method for adding acetic acid, boron compounds, acetates, and phosphates to the modified EVOH resin is not particularly limited. Examples include a graft reaction between the EVOH resin obtained by the methods i) to iv) below and lactones, a method of adding the compounds during the ring-opening polymerization of lactones, and a method of treating the modified EVOH resin by the methods v) to vi) below. For example, methods for adding additives such as acetic acid, boron compounds, acetates, and phosphates to EVOH resins include: i) a method in which a porous precipitate of EVOH resin with a water content of 20-80% by weight is brought into contact with an aqueous solution of the additive to incorporate the additive into the porous EVOH resin, and then dried; ii) a method in which the additive is incorporated into a homogeneous solution of EVOH resin (water / alcohol solution, etc.), then extruded into a solidifying solution in the form of strands, and then the resulting strands are cut into pellets and further dried; iii) a method in which the EVOH resin and the additive are mixed together and then melt-kneaded in an extruder or the like; iv) a method in which, during the production of EVOH resin, the alkali (sodium hydroxide, potassium hydroxide, etc.) used in the saponification process is neutralized with organic acids such as acetic acid, and the amount of remaining organic acids such as acetic acid and by-product salts is adjusted by washing with water. To obtain the effects of the present invention more significantly, methods i) and ii), which have excellent dispersibility of additives, and method iv), which includes organic acids and their salts, are preferred.

[0053] Furthermore, for example, methods for adding additives such as acetic acid, boron compounds, acetates, and phosphates to a modified EVOH-based resin include: v) a method of contacting the modified EVOH-based resin with an aqueous solution of the additive to incorporate the additive into the modified EVOH-based resin and then drying it; vi) a method of mixing the modified EVOH-based resin and the additive together and then melt-kneading them in an extruder or the like.

[0054] Furthermore, it is possible to blend two or more different modified EVOH-based resins, or to blend modified EVOH-based resins with regular EVOH-based resins.

[0055] <Applications of Modified EVOH Resins> The modified EVOH resin obtained in this way can be molded into, for example, films, sheets, cups, bottles, etc., by melt molding. The main melt molding methods used are extrusion molding (T-die extrusion, inflation extrusion, blow molding, melt spinning, mold extrusion, etc.) and injection molding. The melt molding temperature is usually selected from the range of 150 to 300°C.

[0056] Molded products can be used as is for various purposes, but they are usually laminated with other substrates to form laminates in order to further increase strength or add other functions. Thermoplastic resins are useful as other substrates for this purpose. Examples of thermoplastic resins include polyethylenes such as linear low-density polyethylene, low-density polyethylene, ultra-low-density polyethylene, medium-density polyethylene, and high-density polyethylene; polypropylene; ethylene-propylene (block and random) copolymers; propylene-α-olefin (α-olefin with 4 to 20 carbon atoms) copolymers; polyolefins such as polybutene and polypentene; grafted polyolefins obtained by graft-modifying these polyolefins with unsaturated carboxylic acids or their esters; ionomers; ethylene-vinyl acetate copolymers; ethylene-acrylic acid copolymers; ethylene-acrylic acid ester copolymers; polyester resins; polyamide resins (including copolymerized polyamides); polyvinyl chloride; polyvinylidene chloride; acrylic resins; polystyrene; vinyl ester resins; polyester elastomers; polyurethane elastomers; halogenated polyolefins such as chlorinated polyethylene and chlorinated polypropylene; aromatic or aliphatic polyketones; and polyalcohols obtained by reduction thereof. However, from the viewpoint of practicality such as the physical properties (especially strength) of laminates, polyolefin resins and polyamide resins are preferred, and polyethylenes and polypropylene are particularly preferred. These thermoplastic resins may be used individually or in combination of two or more types.

[0057] These base resins may contain conventionally known antioxidants, antistatic agents, lubricants, nucleating agents, antiblocking agents, ultraviolet absorbers, waxes, etc., to the extent that they do not impede the spirit of the present invention.

[0058] The lamination method for laminating the modified EVOH resin of the present invention with other substrates can be carried out by known methods. For example, methods include melt-extrude lamination of other substrates onto a film, sheet, etc., of the modified EVOH resin of the present invention; conversely, melt-extrude lamination of the resin onto other substrates; co-extrusion of the resin and other substrates; dry lamination of the resin (layer) and other substrates (layers) using known adhesives such as organic titanium compounds, isocyanate compounds, polyester compounds, and polyurethane compounds; and coating of a solution of the resin onto other substrates and then removing the solvent. Among these methods, co-extrusion is preferred from the standpoint of cost and environmental impact.

[0059] The layer structure of the laminate can be any combination, not just a two-layer structure of a / b, but also b / a / b, a / b / a, a1 / a2 / b, a / b1 / b2, b2 / b1 / a / b1 / b2, b2 / b1 / a / b1 / b2, b2 / b1 / a / b1 / a / b1 / b2, etc., when the modified EVOH resin-containing layer of the present invention is a(a1, a2, ...) and the thermoplastic resin-containing layer is b(b1, b2, ...). Furthermore, when the recycled layer containing a mixture of the EVOH resin and thermoplastic resin, obtained by remelting edges and defective products generated during the manufacturing process of the laminate, is called R, it is also possible to have a structure such as b / R / a, b / R / a / b, b / R / a / R / b, b / a / R / a / b, b / R / a / R / a / R / b, etc.

[0060] In the above layer configuration, an adhesive resin layer may be provided between each layer as needed, and any known adhesive resin may be used. Since the adhesive resin will vary depending on the type of resin in layer b, it should be selected appropriately, but typically, a modified olefin polymer containing a carboxyl group can be obtained by chemically bonding an unsaturated carboxylic acid or its anhydride to a polyolefin resin by addition reaction, graft reaction, etc. Examples include maleic anhydride graft-modified polyethylene, maleic anhydride graft-modified polypropylene, maleic anhydride graft-modified ethylene-propylene (block and random) copolymer, maleic anhydride graft-modified ethylene-ethyl acrylate copolymer, maleic anhydride graft-modified ethylene-vinyl acetate copolymer, etc., and one or more of these selected mixtures are preferred. Furthermore, these adhesive resins can be blended with the modified EVOH resin of the present invention, other EVOH resins, rubber / elastomer components such as polyisobutylene and ethylene-propylene rubber, and the resin of layer b. In particular, blending a different polyolefin resin with the base polyolefin resin of the adhesive resin can improve adhesion and is therefore useful.

[0061] The laminate described above is then subjected to (heat) stretching as necessary. Such (heat) stretching refers to the operation of uniformly forming a tube or film-like laminate, which has been heated uniformly, into a tube or film shape using a chuck, plug, vacuum force, compressed air, blow, etc. The stretching may be uniaxial stretching or biaxial stretching, and in the case of biaxial stretching, it may be simultaneous stretching or sequential stretching.

[0062] As for the stretching method, methods with high stretch ratios can be used, including roll stretching, tenter stretching, tubular stretching, stretch blowing, and vacuum pressure forming. In the case of biaxial stretching, either simultaneous biaxial stretching or sequential biaxial stretching can be used. The stretching temperature is usually selected from a range of 40 to 170°C, preferably 60 to 160°C. If the stretching temperature is too low, the stretchability tends to be poor, and if it is too high, it tends to be difficult to maintain a stable stretched state.

[0063] Furthermore, to impart dimensional stability after stretching, heat setting may be performed next. Heat setting can be carried out by well-known means; for example, the stretched film is heat-treated at a temperature of typically 80 to 180°C, preferably 100 to 165°C, for about 2 to 600 seconds while maintaining tension. Furthermore, when using a multilayer stretched film obtained from a laminate containing the EVOH-based resin layer of the present invention as a shrinkable film, in order to impart heat shrinkability, the above-mentioned heat fixing is omitted, and instead, a treatment such as applying cold air to the stretched film to cool and fix it is performed.

[0064] The thickness of the thermoplastic resin layer and adhesive resin layer of the laminate cannot be generalized as it depends on the layer configuration, type of thermoplastic resin, type of adhesive resin, application, packaging form, required physical properties, etc., but the thermoplastic resin layer is usually selected from a range of 10 to 1000 μm, preferably 50 to 500 μm, and the adhesive resin layer is usually selected from a range of 5 to 500 μm, preferably 10 to 250 μm.

[0065] Furthermore, the thickness of the modified EVOH resin-containing layer of the present invention varies depending on the required gas barrier properties, but is usually 5 to 500 μm, preferably 10 to 250 μm, and particularly preferably 20 to 100 μm. If the thickness is too thin, sufficient gas barrier properties tend not to be obtained, and conversely, if it is too thick, the flexibility of the film tends to be insufficient.

[0066] When further extruding another substrate onto the resulting laminate, or when laminating a film, sheet, or other material of another substrate using an adhesive, any substrate other than the thermoplastic resin mentioned above (paper, metal foil, uniaxial or biaxially oriented plastic film (or sheet) and its inorganic compound vapor-deposited product, woven fabric, nonwoven fabric, metallic cotton, wood, etc.) can be used as the substrate.

[0067] The bags, cups, trays, tubes, bottles, and other containers and lids made from the films, sheets, and stretched films obtained as described above are useful as packaging materials for various products, including general foods, condiments such as mayonnaise and dressings, fermented foods such as miso, oily foods such as salad oil, beverages, cosmetics, and pharmaceuticals. [Examples]

[0068] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention. In the examples, "parts" and "%" refer to weight unless otherwise specified.

[0069] <Example 1> [Manufacturing of modified EVOH resins] 100 parts of EVOH resin (ethylene content 44 mol%, saponification degree of vinyl acetate portion 99.8 mol%, MFR 12 g / 10 min (210℃, load 2160 g)), 30 parts of ε-caprolactone (Praxel M, manufactured by Daicel Corporation), and 0.9 parts of 2-ethylhexanoate tin (Neostan U-28, manufactured by Nitto Chemical Co., Ltd.) (3 parts per 100 parts of ε-caprolactone) were put into a twin-screw compounding extruder (TEX30α, manufactured by Japan Steel Works Corporation), transported to a molten section set to a residence time of 2-3 minutes, and reacted while melt-kneading to obtain a modified EVOH resin. The temperature pattern for the twin-screw compounding extruder is as follows: C2=80℃, C3=80℃, C4=150℃, C5=150℃, C6=230℃, C7=230℃, C8=230℃, C9=230℃, C10 =230℃, C11=230℃, C12=230℃, C13=230℃, C14=230℃, C15=230℃, C16=230℃, D=230℃

[0070] <Example 2> A modified EVOH-based resin was obtained using the same manufacturing method as in Example 1, except that the amount of tin 2-ethylhexanoate was 0.3 parts (1 part per 100 parts of ε-caprolactone).

[0071] <Example 3> A modified EVOH-based resin was obtained using the same manufacturing method as in Example 1, except that the amount of ε-caprolactone was 40 parts and tin 2-ethylhexanoate was 1.2 parts (3 parts per 100 parts of ε-caprolactone).

[0072] <Example 4> A modified EVOH-based resin was obtained using the same manufacturing method as in Example 1, except that the amount of ε-caprolactone was 50 parts and tin 2-ethylhexanoate was 1.5 parts (3 parts per 100 parts of ε-caprolactone).

[0073] <Example 5> A modified EVOH-based resin was obtained by the same manufacturing method as in Example 1, except that 0.3 parts (1 part per 100 parts of ε-caprolactone) of zinc acetylacetone monohydrate (Nasem Zinc, manufactured by Nippon Chemical Industries, Ltd.) was used instead of tin 2-ethylhexanoate.

[0074] <Example 6> A modified EVOH-based resin was obtained by the same manufacturing method as in Example 1, except that 0.03 parts (0.1 parts per 100 parts of ε-caprolactone) of tetran-butyl titanate (Orgatics TA-21, manufactured by Matsumoto Fine Chemical Co., Ltd.) was used instead of tin 2-ethylhexanoate.

[0075] <Comparative Example 1> 100 parts of the same EVOH-based resin as in Example 1 and 30 parts of ε-caprolactone were placed in a flask, and then 0.03 parts of tetrabutyl titanate (0.1 parts per 100 parts of ε-caprolactone) were added. The mixture was heated at a rate of 1°C / 2-3 minutes while stirring under a nitrogen atmosphere. The reaction was continued at 180-200°C for 6 hours, and modified EVOH-based resin was obtained by batch.

[0076] [Measurement of degeneration rate and mean chain length] The modification rate and the average chain length of aliphatic polyester units in the modified EVOH resin were determined under the following conditions: 1 The calculation was performed by measuring 1H-NMR.

[0077] (a) 1 H-NMR measurement conditions Equipment: Ascend 400 (400MHz NMR) (manufactured by Bruker) Internal standard: Tetramethylsilane Solvent: d6-DMSO Measured polymer concentration: 5% (0.05g sample, 1mL solvent) Measurement temperature: 50℃ (323K) Irradiation pulse: 45° pulse Pulse interval: 10 sec Total number of times: 16

[0078] (b) Assignment of resonance absorption peaks (I) 0.8~0.9 ppm: -CH3 at the end of modified EVOH resin (II) 1.0~1.9 ppm: -CH2- of the main chain of modified EVOH resin and adjacent -CH2- of aliphatic polyester (III) 2.0 ppm: -CH3 residual acetyl group of modified EVOH resin (IV) 2.1~2.3 ppm: -CH2- adjacent to the carboxyl group of aliphatic polyester (V) 3.3~4.0 ppm: -CH- adjacent to the -OH group of modified EVOH resins, and -CH2- adjacent to the -OH group of aliphatic polyesters (VI) 4.0~4.7 ppm: Modified EVOH resin and the -OH group of the aliphatic polyester, and the -CH2- adjacent to the ester bond of the aliphatic polyester.

[0079] (c) Calculation of the denaturation rate and average chain length of aliphatic polyesters Using the integral values ​​of each resonance absorption peak in (I) to (VI), a system of equations (i) to (vi) was established, and the amount of graft-modified groups C (moles) and the average chain length n (units) of the aliphatic polyester were calculated from the solution to the system of equations. Furthermore, the graft modification rate X (mol%) of the aliphatic polyester was calculated from equation (vii). Equation (i) 3 × M = [Integral value of peak (I)] Equation (ii) (2×M)+(2×A)+(4×E)+(2×O)+(6×n+2)×C=[Integral value of peak(II)] Equation (iii) 3 × A = [Integral value of peak (III)] Equation (vi) 2 × n × C = [Integral value of peak (IV)] Equation (v) O + (2 × C) = [Integral value of peak (V)] Equation (vi) O + (2 × n - 1) × C = [Integral value of peak (VI)] Equation (vii) X = C / (M + A + O + C + E) × 100 Here, M, A, O, C, n, E, X are M: Amount of terminal methyl groups (moles) in modified EVOH resin A: Amount of acetyl groups (moles) in modified EVOH resin O: Amount of hydroxyl groups (moles) in modified EVOH resin C: Amount of modified groups (moles) in aliphatic polyester grafts of modified EVOH-based resins. n: Average chain length of aliphatic polyester (number of strands) E: Amount of ethylene groups (moles) in modified EVOH resin X: Modification rate (mol%) of aliphatic polyester grafts in modified EVOH-based resins It is represented as follows.

[0080] [Measurement of flexibility] A 150 μm thick film was punched into a dumbbell shape (Type 3), and a tensile test was performed using a tensile testing machine (Shimadzu Corporation's AGS-X desktop precision universal testing machine). The flexibility was evaluated from the modulus at a constant elongation obtained from the tensile test (measurement conditions conformed to JIS K6251).

[0081] [Evaluation of flexibility] 1: Excellent (very soft) 2: Good (soft) 3: Intermediate 4: Poor (hard) 5: Extremely poor quality (extremely hard) Note that the flexibility evaluation is a relative evaluation with the flexibility of Example 1 set to "3". All evaluations from 1 to 5 indicate that the flexibility is superior to that of unmodified EVOH-based resin (softer than unmodified EVOH-based resin).

[0082] [Measuring the melting point] The melting point of the obtained modified EVOH resin was measured by thermal analysis using differential scanning calorimetry (DSC-Q2000, manufactured by T.A. Instruments).

[0083] Table 1 below shows the average chain length (number of chains), modification rate (mol%), flexibility evaluation results, and melting point (°C) measurement results of the modified EVOH resins obtained in Examples 1 to 6 and Comparative Example 1.

[0084] [Table 1]

[0085] Table 1 shows that in Examples 1-6, where a polymerization catalyst consisting of a tin-based compound, a zinc-based compound, or a titanium-based compound was used and the graft reaction was carried out continuously using a twin-screw extruder, the decrease in melting point was suppressed. Among the polymerization catalysts, Examples 1-5, which used tin-based or zinc-based compounds, exhibited high modification rates and excellent flexibility. On the other hand, Comparative Example 1, in which a batch-type graft reaction was carried out using 0.1 parts of a titanium-based catalyst per 100 parts of ε-caprolactone, showed a high rate of denaturation, but the average chain length was short and the melting point was significantly lower. These results show that when a graft reaction is carried out in a continuous manner using a twin-screw extruder with a polymerization catalyst of a tin-based compound, a zinc-based compound, or a titanium-based compound, a modified EVOH-based resin with a suppressed decrease in melting point can be produced. Furthermore, when a graft reaction is carried out in a continuous manner using a twin-screw extruder with a polymerization catalyst of a tin-based compound or a zinc-based compound, a modified EVOH-based resin that achieves both excellent flexibility and melting point maintenance can be produced. On the other hand, it is clear that a modified EVOH-based resin with a suppressed decrease in melting point cannot be produced when a batch process is used.

[0086] While the above embodiments illustrate specific forms of the present invention, these embodiments are merely illustrative and should not be interpreted restrictively. Various modifications that are obvious to those skilled in the art are intended to fall within the scope of the present invention. [Industrial applicability]

[0087] The modified EVOH resin of the present invention possesses gas barrier properties while suppressing an excessive decrease in the melting point, making it widely useful as a barrier material for various applications, including those requiring heat resistance.

Claims

1. A modified ethylene-vinyl alcohol resin containing aliphatic polyester units, A modified ethylene-vinyl alcohol resin in which the average chain length of aliphatic polyester units in the modified ethylene-vinyl alcohol resin is 1.5 or more, and the modification rate calculated from the following formula (vii) is 1.5 mol% or more. Formula (vii) X=C / (M+A+O+C+E)×100 Here, M, A, O, C, E, X are, M: Amount of terminal methyl groups (moles) in modified ethylene-vinyl alcohol resin A: Amount of acetyl groups (moles) in modified ethylene-vinyl alcohol resin O: Amount of hydroxyl groups (moles) in modified ethylene-vinyl alcohol resin C: Amount of modified groups (moles) in aliphatic polyester grafts of modified ethylene-vinyl alcohol resins. E: Amount of ethylene groups (moles) in modified ethylene-vinyl alcohol resin X: Modification rate (mol%) of aliphatic polyester grafts in modified ethylene-vinyl alcohol resins It is represented as follows.

2. The modified ethylene-vinyl alcohol resin according to Claim 1, wherein the total content of tin and zinc in the modified ethylene-vinyl alcohol resin is 25 μg / g or more and 1,000,000 μg / g or less.

3. The modified ethylene-vinyl alcohol resin according to claim 1 or 2, wherein the aliphatic polyester unit is a ring-opening polymer of lactones.

4. The modified ethylene-vinyl alcohol resin according to any one of claims 1 to 3, wherein the modified ethylene-vinyl alcohol resin is a modified product of an ethylene-vinyl alcohol resin using a ring-opening polymerization catalyst of a tin-based compound and / or a zinc-based compound as the polymerization catalyst.

5. A method for producing a modified ethylene-vinyl alcohol resin according to any one of claims 1 to 4, comprising the step of ring-opening polymerization of lactones in an extruder in the presence of an ethylene-vinyl alcohol resin using at least one ring-opening polymerization catalyst selected from the group consisting of tin compounds and zinc compounds.

6. The method for producing a modified ethylene-vinyl alcohol resin according to claim 5, wherein the amount of the ring-opening polymerization catalyst is more than 1 part by weight per 100 parts by weight of the lactones.

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