Cross-linked polyester resin

Abstract

This invention provides a crosslinked polyester resin that exhibits covalent exchange properties at temperatures above 150°C and a gel fraction of 80% by mass or more. The crosslinked polyester resin is obtained by crosslinking polyester units with a compound having two or more epoxy groups, and exhibits covalent exchange properties at temperatures above 150°C and a gel fraction of 80% by mass or more.

Description

[Technical Field]

[0001] The present invention relates to a resin obtained by crosslinking polyester units with a compound having two or more epoxy groups (hereinafter, sometimes referred to as crosslinked polyester resin). [Previous Technology]

[0002] Polymer elastomers obtained by covalent crosslinking cannot typically be reshaped or recycled. This is due to the irreversibility of the covalent crosslinking points. Recently, bond-exchange type dynamic covalent crosslinking resins have attracted attention regarding this issue. Regarding bond-exchange type dynamic covalent crosslinking resins, research results have been reported on the preparation of polyester-based bond-exchange type crosslinking resins from linear general-purpose polyesters [e.g., polybutylene terephthalate (PBT), polyethylene terephthalate (PET)] and polyfunctional alcohols using transesterification reactions (Non-Patent Literature 1, 2). [Prior Art Literature] [Non-Patent Literature]

[0003] [Non-patent literature 1] Yanwu Zhou, et al., Macromolecules. 2017, 50(17), 6742-6751. [Non-patent literature 2] Jianfan Qiu, et al., Macromolecules. 2021, 54(2), 703-712. [Summary of the Invention]

[0004] [The problem that the invention aims to solve]

[0005] The gel fraction of the crosslinking reaction product of a general-purpose polyester whose side chains do not have crosslinking functional groups is limited to about 70%, with the remaining about 30% being a sol component that is not linked into a network structure (uncrosslinked chains). It is believed that if the gel fraction increases, the non-crosslinked components decrease, so the crosslinked resin can be upcycled.

[0006] The gel fraction of the bond-exchange crosslinking resin described in Non-Patent Document 1 is 71-72%, and the gel fraction of the bond-exchange crosslinking resin described in Non-Patent Document 2 is 74.6%, which is slightly higher than the gel fraction of the crosslinking reaction product of a general-purpose polyester whose side chains do not have crosslinking functional groups. However, even for bond-exchange crosslinking resins, the gel fraction is only about 75%. It is hoped that by further increasing the gel fraction, a bond-exchange resin that is more effective for upgrading and recycling can be obtained.

[0007] The object of this invention is to provide a crosslinked polyester resin that exhibits covalent bond exchange properties at temperatures above 150°C and is more effective for upgrading and recycling. [Means for Solving the Problem]

[0008] The present invention, which solves the aforementioned problems, is structured as follows. [1] A crosslinked polyester resin is a resin obtained by crosslinking polyester units with a compound having two or more epoxy groups, and has covalent bond exchange characteristics at a temperature of 150°C or above, and has a gel fraction of 80% by mass or more. [2] The crosslinked polyester resin of [1] contains silicon dioxide particles. [3] The crosslinked polyester resin of [1] or [2], wherein the polyester unit is a polycondensate of a polycarboxylic acid component (A) and a polyol component (B), and is composed of terephthalic acid as the polycarboxylic acid component (A) and an alkanediol having 2 to 4 carbon atoms as the polyol component (B). [4] The crosslinked polyester resin of [3], wherein, with regard to the polycarboxylic acid component (A), it further contains a saturated aliphatic dicarboxylic acid having 5 to 20 carbon atoms. [5] The crosslinked polyester resin of [3] or [4], wherein, with regard to the polyol component (B), it further contains at least one selected from the group consisting of neopentyl glycol, cyclohexanediol, diethylene glycol, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, and hexanediol. [6] The crosslinked polyester resin of any one of [1] to [5] contains an ester exchange catalyst. [7] The crosslinked polyester resin of any one of [1] to [6] has a Young's modulus of 50 MPa or more calculated from the slope of the stress-strain curve at 2% elongation. [8] The crosslinked polyester resin of any one of [1] to [7] has a tensile strength of 10 MPa or more. [Effects of the Invention]

[0009] According to the present invention, a cross-linked polyester resin with covalent bond exchange properties at temperatures above 150°C and a gel fraction of 80% by mass can be obtained, which is more effective for upgrading and recycling.

Implementation Method

[0011] The cross-linked polyester resin of the present invention is a resin obtained by cross-linking polyester units with a compound having two or more epoxy groups, and has covalent bond exchange characteristics at a temperature of 150°C or higher, and a gel fraction of 80% by mass or higher. Because of the high gel fraction, the cross-linked polyester resin of the present invention is more useful for upgrading and recycling.

[0012] 1. Polyester Unit A polyester unit refers to a unit derived from the polyester resin (hereinafter sometimes referred to as pre-crosslinking polyester resin) used as a raw material before crosslinking. The pre-crosslinking polyester resin can be either aliphatic polyester or aromatic polyester. Using aromatic polyester can improve heat resistance. Aliphatic polyester and aromatic polyester can also be used in combination.

[0013] The polyester resin before crosslinking is a polycondensate of polycarboxylic acid component (A) and polyol component (B).

[0014] As for the polycarboxylic acid component (A), for example, it includes dicarboxylic acids, tricarboxylic acids, tetracarboxylic acids, etc., and is preferably a dicarboxylic acid. One or more of the polycarboxylic acid components (A) may be used.

[0015] Examples of dicarboxylic acids include: aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid; aliphatic dicarboxylic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, tetradecanedicarboxylic acid, hexadecanedicarboxylic acid (octadecanoic acid), octadecanedicarboxylic acid (eicosanoic acid), and dimer acids; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, tetrahydrophthalic acid, hexahydroisophthalic acid, and 1,2-cyclohexenedicarboxylic acid; and dicarboxylic acids containing unsaturated groups such as terpene-maleic acid adducts. Among these dicarboxylic acids, aromatic dicarboxylic acids and aliphatic dicarboxylic acids are preferred. One or more dicarboxylic acids may be used from this group.

[0016] Examples of tricarboxylic acids include: aliphatic tricarboxylic acids such as 1,3,5-pentanetricarboxylic acid; alicyclic tricarboxylic acids such as 1,3,5-cyclohexanetricarboxylic acid; aromatic tricarboxylic acids such as trimellitic acid and pyromellitic acid. These tricarboxylic acids may also be acid anhydrides. One or more of these tricarboxylic acids may be used.

[0017] Examples of tetracarboxylic acids include 1,2,4,5-phenyltetracarboxylic acid and 3,3',4,4'-diphenylketonetetracarboxylic acid. These tetracarboxylic acids may also be acid anhydrides. One or more of these tetracarboxylic acids may be used.

[0018] Regarding the polyol component (B), examples include: ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol (also known as neopentyl glycol), 2,2-diethyl-1,3-propanediol, 2-n-Butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 3-methyl-1,6-hexanediol Aliphatic diols include: 4-methyl-1,7-heptanediol, 2-methyl-1,8-octanediol, 3-methyl-1,8-octanediol, 4-methyl-1,8-octanediol, 4-propyl-1,8-octanediol, and 1,9-nonanediol; alicyclic polyols include: 1,4-cyclohexanediol, 1,2-cyclohexanediethanol, 1,3-cyclohexanediethanol, 1,4-cyclohexanediethanol, tricyclodecanediols, and hydrogenated bisphenols; and aromatic diols such as bisphenol A. Among monomeric polyols, aliphatic diols are preferred.

[0019] As a polyol component (B), it may also be a polyether polyol (polyether diol), such as diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, polyolefin diol, polytetramethylene glycol, etc.

[0020] As a polyol component (B), it may be, for example, a polyester polyol modified with ethylene glycol of terephthalic acid [e.g., bis-2-hydroxyethyl terephthalate (BHET)], a polyester polyol modified with propylene glycol of terephthalic acid, a polyester polyol modified with ethylene glycol of isophthalic acid, a polyester polyol modified with propylene glycol of isophthalic acid, a polyester polyol modified with ethylene glycol of phthalic acid, a polyester polyol modified with propylene glycol of phthalic acid, etc. (preferably an aromatic polyester polyol).

[0021] One or more of the polyol components (B) may be used.

[0022] As a polyol component (B), it is preferably a form that includes at least one selected from monomeric polyols (especially aliphatic diols) and polyester polyols (especially aromatic polyester diols), and more preferably a form that includes at least monomeric polyols (especially aliphatic diols).

[0023] The polyester unit is preferably composed of terephthalic acid as a polycarboxylic acid component (A) and an alkanediol with 2 to 4 carbon atoms as a polyol component (B).

[0024] As long as terephthalic acid is the main component of the polycarboxylic acid component (A), the amount of terephthalic acid is, for example, 50 mol% or more, preferably 70 mol% or more, and more preferably 80 mol% or more when the total amount of polycarboxylic acid component (A) is set to 100 mol%.

[0025] Examples of alkyldiols having 2 to 4 carbon atoms include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, and 1,4-butanediol. One or more of these may be used. Ethylene glycol is preferred among these.

[0026] As long as the alkyldiol with 2 to 4 carbons is the main component of the polyol component (B), the amount of the alkyldiol with 2 to 4 carbons is, for example, 50 mol% or more, preferably 70 mol% or more, and more preferably 80 mol% or more when the total amount of the polyol component (B) is set to 100 mol%.

[0027] When the polyester unit is composed of terephthalic acid as a polycarboxylic acid component (A) and alkanediols with 2 to 4 carbon atoms as a polyol component (B), the polycarboxylic acid component (A) should preferably contain saturated aliphatic dicarboxylic acid with 5 to 20 carbon atoms.

[0028] Saturated aliphatic dicarboxylic acids with 5 to 20 carbon atoms may include, for example, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, tetradecanedicarboxylic acid, hexadecanedicarboxylic acid (octadecanoic acid), octadecanedicarboxylic acid (eicosaic acid), etc. One or more of these may be used.

[0029] When the total amount of the polycarboxylic acid component (A) is set to 100 mol%, the amount of the saturated aliphatic dicarboxylic acid with 5 to 20 carbon atoms is preferably 5 mol or more and preferably 50 mol or less.

[0030] When the polyester unit is composed of terephthalic acid as a polycarboxylic acid component (A) and an alkyl diol having 2 to 4 carbon atoms as a polyol component (B), the polyol component (B) preferably contains at least one selected from the group consisting of neopentyl glycol, cyclohexanediol, diethylene glycol, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, and hexanediol. The total amount of neopentyl glycol, cyclohexanediol, diethylene glycol, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, and hexanediol, when the total amount of polyol component (B) is set to 100 mol%, is preferably 5 mol% or more and preferably 50 mol% or less.

[0031] The polyester resin before crosslinking should preferably be amorphous. Amorphous means that the exothermic peaks caused by crystallization and the endothermic peaks caused by melting cannot be observed by differential scanning calorimeter (DSC).

[0032] The number average molecular weight (Mn) of the polyester resin before crosslinking is preferably 4,000 to 90,000. Having a number average molecular weight (Mn) of 4,000 or higher improves heat resistance. A number average molecular weight (Mn) of 4,200 or higher is more preferably 10,000 or higher. However, if the number average molecular weight (Mn) of the polyester resin before crosslinking is too high, it will become too hard and brittle. Therefore, the number average molecular weight (Mn) is preferably 90,000 or lower, more preferably 60,000 or lower, and even more preferably 40,000 or lower.

[0033] 2. An epoxy-based crosslinking agent is used to crosslink polyester units with a compound having two or more epoxy groups (hereinafter, sometimes referred to as an epoxy-based crosslinking agent). It is presumed that the carboxyl groups at the carboxylic acid ends of two or more polyester units (including those of polyester units whose molecular weight has been reduced due to hydrolysis) react with two or more epoxy groups in the epoxy-based crosslinking agent to form covalent bonds (ester bonds), thereby forming a crosslinked structure. By crosslinking polyester units with a compound having two or more epoxy groups, a crosslinked polyester resin with covalent bond exchange properties at temperatures above 150°C and a gel fraction of 80% by mass or higher can be obtained. Furthermore, a crosslinked structure can also be introduced by forming a covalent bond (X+Y, ester bond) between the hydroxyl group (X) generated from the reaction of the terminal carboxylic acid of the polyester unit with the epoxy group and the terminal carboxylic acid (Y) of the polyester unit.

[0034] Epoxy crosslinking agents are not particularly limited as long as they have two or more epoxy groups within the molecule. Examples include glycol diglycidyl ether, epoxy propylene ether of alcohols having three or more hydroxyl groups, epoxy resin, epoxy amine compounds having two or more epoxy groups and two or more tertiary amino groups within the molecule, and compounds containing two or more epoxy groups and one tertiary amino group within the molecule. One or more epoxy crosslinking agents can be used from these sources. Epoxy crosslinking agents are preferably epoxy amine compounds having two or more epoxy groups and two or more tertiary amino groups within the molecule, or compounds containing two or more epoxy groups and one tertiary amino group within the molecule, and more preferably epoxy amine compounds having two or more epoxy groups and two or more tertiary amino groups within the molecule.

[0035] As a diol diglycidyl ether, examples include compounds obtained by ether-bonding glycidyl groups to the hydroxyl groups of the diols listed in the polyol component (B), preferably: ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,5-pentanediol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, hydrogenated bisphenol A diglycidyl ether, etc., aliphatic diol diglycidyl ethers; bisphenol A diglycidyl ether, etc., aromatic diol diglycidyl ethers, etc. Among these, aliphatic diol diglycidyl ethers are more preferred. Compounds obtained by ether-bonding glycidyl groups to the hydroxyl groups of the diols listed in polyol component (B) may include one or more of these.

[0036] Examples of epoxy propylene ethers containing alcohols having three or more hydroxyl groups include polyepoxypropylene ethers of aliphatic polyols such as glycerol diepoxypropylene ether, glycerol triepoxypropylene ether, trimethylolpropane diepoxypropylene ether, and trimethylolpropane triepoxypropylene ether (preferably diepoxypropylene ether). One or more of these epoxy propylene ethers containing three or more hydroxyl groups may be used.

[0037] Examples of epoxy resins include cresol varnish-type epoxy resins, phenol varnish-type epoxy resins, and epoxy resins having a dicyclopentadiene backbone. One or more of these epoxy resins may be used.

[0038] Commercially available cresol-formaldehyde varnish-type epoxy resins include, for example, YDCN-700 manufactured by DIC Corporation. Commercially available phenol-formaldehyde varnish-type epoxy resins include, for example, EPICLON N-700A manufactured by DIC Corporation. Commercially available epoxy resins with a dicyclopentadiene backbone include, for example, the HP7200 series manufactured by DIC Corporation.

[0039] Examples of epoxide amine compounds having two or more epoxy groups and two or more tertiary amine groups in the molecule include N,N,N',N'-tetracyclooxypropylm-xylene diamine and 4,4'-methylenebis(N,N-dicyclooxypropylaniline), which have two dicyclooxypropylamine groups and benzene rings.

[0040] N,N,N',N'-Tetracyclooxypropylm-xylenediamine is, for example, sold by Mitsubishi Gas Chemical Co., Ltd. as the multifunctional epoxy compound "TETRAD-X". 4,4'-Methylenebis(N,N-dicyclooxypropylaniline) is, for example, available from Tokyo Chemical Industry Co., Ltd. (TCI).

[0041] As a compound containing two or more epoxy groups and one tertiary amino group, examples include triepoxypropyl-p-aminophenol [also known as N,N-diepoxypropyl-4-(epoxypropyloxy)aniline] and other compounds having one diepoxypropylamino group, an epoxypropyloxy group, and a benzene ring.

[0042] As a commercially available product of tricyclooxypropyl-p-aminophenol, for example, jER630 manufactured by Mitsubishi Chemical Co., Ltd. can be used.

[0043] The amount of epoxy crosslinking agent relative to 100 parts by weight of polyester resin before crosslinking is preferably 3 parts by weight or more and 30 parts by weight or less, more preferably 5 parts by weight or more, more preferably 8 parts by weight or more, more preferably 25 parts by weight or less, and more preferably 20 parts by weight or less.

[0044] 3. Covalent Bond Exchange Characteristics Crosslinked polyester resins possess covalent bond exchange characteristics at temperatures above 150°C. Due to these covalent bond exchange characteristics, despite being crosslinked resins, they can still undergo reshaping processes or be recycled using hot pressing. Possessing covalent bond exchange characteristics means satisfying the following two points: 1) Stress relief occurs when a stress relief test is performed at temperatures above 150°C. 2) In the temperature range where the stress relief test is performed, a rubbery, flat region is observed where the lost elastic modulus (E'') is significantly smaller than the stored elastic modulus (E'). A rubbery, flat region means that the region where the lost elastic modulus (E'') is below 90% relative to the stored elastic modulus (E') continues continuously above 100°C.

[0045] Regarding 1) above, stress relief refers to the phenomenon that σ / σ0 reaches 0.7 or less within 1 × 10⁴ seconds during a stress relief test. The temperature at which the stress relief test is conducted is taken as the starting temperature for stress relief. Stress relief is preferably achieved when σ / σ0 reaches 0.7 or less within 5 × 10³ seconds. σ0 represents the initial stress, and σ represents the stress. The stress relief test is preferably conducted under a passive gas environment (e.g., N₂ gas environment) with a vertical stress of 10 N and under shear strain in a linear region.

[0046] 4. Gel Fraction The gel fraction of the crosslinked polyester resin is 80% by mass or higher. A high gel fraction indicates a low non-crosslinked component, making it easier to upgrade and recycle. The gel fraction is calculated by immersing the sample in a solvent that exhibits high solubility for the uncrosslinked polyester resin, drying the resulting sol solution and the remaining gel component separately, and letting the mass of the sample remaining after drying the sol solution be wsol and the mass of the sample remaining after drying the gel component be wgel. The value fgel is calculated according to the following formula. The gel fraction of the crosslinked polyester resin is preferably 85% by mass or higher, and more preferably 90% by mass or higher. fgel = wgel / (wgel + wsol) × 100

[0047] 5. Crosslinked polyester resins containing silica particles preferably contain silica particles. The presence of silica particles increases the strength (Young's modulus) of the crosslinked polyester resin. Furthermore, the heat resistance also improves. This improvement is presumably due to the inherently high elasticity of silica particles and the formation of an adsorbed phase between the silica particles and the polymer.

[0048] Silicon dioxide particles can be surface-modified functional particles or surface-nonfunctional particles without surface modification.

[0049] Regarding the size of the silicon dioxide particles, for example, the diameter is preferably 5 nm or more and 20 nm or less, more preferably 7 nm or more, more preferably 10 nm or more, more preferably 18 nm or less, and more preferably 16 nm or less.

[0050] The amount of silicon dioxide particles relative to 100 parts by weight of the polyester resin before crosslinking is preferably 5 parts by weight or more and 35 parts by weight or less, more preferably 10 parts by weight or more, more preferably 15 parts by weight or more, more preferably 30 parts by weight or less, and more preferably 25 parts by weight or less.

[0051] 6. The polyester resin with ester exchange catalyst should preferably contain an ester exchange catalyst. By containing an ester exchange catalyst, the ester exchange reaction and the epoxy ring-opening reaction will proceed simultaneously, which can promote the crosslinking of polyester units and epoxy crosslinking agents.

[0052] As a transesterification catalyst, examples include: titanium compounds (tetrabutyl titanate, tetraisopropyl titanate, acetyl acetone titanium oxide, etc.), antimony compounds (tributoxy antimony, antimony trioxide, etc.), germanium compounds (tetrabutoxy germanium, germanium oxide, etc.), scandium compounds (scandium trifluoromethanesulfonate, etc.), zinc compounds (zinc acetate, zinc octanoate, etc.), aluminum compounds (aluminum acetate, aluminum acetate, etc.), and other metal-containing catalysts; trimethylamine, triethylamine, benzyl dimethylamine, diazabicycloundecene, etc. Amines such as DBU, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 1,4-diazabicyclo[2.2.2]octane (DABCO), and 1,5-diazabicyclo[4.3.0]nonene (DBN); quaternary ammonium salts such as tetramethylammonium chloride and triethylbenzylammonium chloride; imidazoles such as 2-ethyl-4-imidazolium; amides; pyridines such as 4-dimethylaminopyridine; phosphines such as triphenylphosphine; and phosphonium salts such as tetraphenylphosphonium bromide. One or more types of ester exchange catalysts may be used. Among these, metal-containing catalysts or amines are preferred. For metal-containing catalysts, scandium compounds or zinc compounds are more preferred. For amines, diazabicycloundecene (DBU), 1,4-diazabicyclo[2.2.2]octane (DABCO), or 1,5-diazabicyclo[4.3.0]nonene (DBN) are more preferred.

[0053] The amount of the ester exchange catalyst relative to 100 parts by weight of the polyester resin before crosslinking is preferably 1 part by weight or more and 20 parts by weight or less, more preferably 1.3 parts by weight or more, more preferably 1.5 parts by weight or more, more preferably 15 parts by weight or less, and more preferably 10 parts by weight or less.

[0054] 7. Crosslinked polyester resin The Young's modulus of the crosslinked polyester resin, calculated from the slope of the stress-strain curve at 2% elongation (measurement temperature: room temperature, e.g., 25°C), should preferably be 50 MPa or higher. More preferably, it should be 70 MPa or higher, and even more preferably 80 MPa or higher.

[0055] The tensile strength of the cross-linked polyester resin should preferably be above 10 MPa. More preferably, it should be above 15 MPa, and even more preferably above 20 MPa.

[0056] The glass transition temperature (Tg) of the crosslinked polyester resin is preferably above 0°C (more preferably above 10°C) and below 25°C.

[0057] The cross-linked polyester resin preferably has reformability at a temperature of 200°C. Reformability means the property that when the cross-linked polyester resin is heated and held at 200°C in a state where it has been deformed into a predetermined shape, it will retain the predetermined shape even after cooling to room temperature. It is believed that the predetermined shape is retained because heat causes transesterification and reforming, and the reformed material retains the predetermined shape even after cooling.

[0058] The cross-linked polyester resin should preferably have the property of dissolving triethylene glycol. Dissolution property refers to the ability of the cross-linked polyester resin to dissolve when immersed in triethylene glycol and heated at 200°C for 20 hours, preferably dissolved when heated at 180°C for 10 hours. Through heating, decrosslinking occurs via a bond exchange reaction between triethylene glycol and the cross-linked polyester resin, making the cross-linked polyester resin soluble in triethylene glycol. This dissolution property allows for the separation and recycling of the constituent components.

[0059] The peak of the loss tangent tanδ of the crosslinked polyester resin with respect to temperature (sometimes called the α-modulation peak) should preferably be above 30°C. The higher the temperature of the α-modulation peak, the higher the heat resistance. A temperature above 35°C for the α-modulation peak is preferable, and above 40°C is even better. The upper limit of the temperature of the α-modulation peak is not particularly limited, for example, it can be below 100°C. The change of the loss tangent tanδ with temperature is obtained by measuring the temperature-dispersive viscoelasticity under N2 atmosphere, with the measurement frequency set to 1Hz and the strain set to 0.05%.

[0060] Cross-linked polyester resins can be used, for example, as molding materials.

[0061] 8. Method for manufacturing cross-linked polyester resin. Cross-linked polyester resin can be manufactured using known methods. For example, a method can be described by dissolving the aforementioned pre-cross-linked polyester resin, the aforementioned epoxy cross-linking agent, and the aforementioned transesterification catalyst in a solvent, then performing vacuum drying to remove the solvent, and heating to cross-link them. Silicon dioxide particles are preferably added at an appropriate stage before cross-linking, for example, before or after the polyester resin is dissolved in the solvent.

[0062] Examples of solvents include: aromatic hydrocarbons such as toluene; ketones such as methyl ethyl ketone and cyclohexanone; nitrogen-containing solvents such as dimethyl acetamide, dimethylformamide, and N-methylpyrrolidone; and ethers such as tetrahydrofuran (THF), 1,4-diane, 1,3-diane, and 1,3-dioxolane. Among these, ethers are preferred.

[0063] The polyester resin before crosslinking can be a commercially available product, or it can be manufactured by polycondensation of the polycarboxylic acid component (A) and the polyol component (B) using known methods. The polycondensation reaction can be carried out with or without a solvent. Known catalysts such as the transesterification catalyst described above can also be used in the polycondensation reaction.

[0064] This application claims the benefit of priority based on Japanese Patent Application No. 2021-131627, filed on August 12, 2021. The entire contents of the description of the aforementioned Japanese Patent Application No. 2021-131627 are incorporated herein by reference. [Example]

[0065] Hereinafter, embodiments will be given to illustrate the present invention in more detail, but the present invention is not limited to the following embodiments. Of course, modifications and implementations can be made within the scope that can suit the foregoing or the following intent, and all such modifications and implementations are included within the technical scope of the present invention.

[0066] (Example 1) A cross-linked polyester resin was prepared using pre-cross-linked polyester resin, epoxy cross-linking agent, silicon dioxide particles, and transesterification catalyst.

[0067] The pre-crosslinking polyester resin (glass transition temperature Tg = 13.6°C, number average molecular weight Mn = 23000, polycarboxylic acid component (A): 70 mol% terephthalic acid, 30 mol% sebacic acid; polyol component (B): 58 mol% ethylene glycol, 42 mol% neopentyl glycol) was a linear amorphous polyester resin without crosslinking functional groups in its side chains. Furthermore, the pre-crosslinking polyester resin did not show exothermic peaks due to crystallization or endothermic peaks due to melting under differential scanning calorimetry (DSC), confirming it as amorphous. The amount of terephthalic acid was 70 mol% when the total amount of polycarboxylic acid component (A) was set to 100 mol%. The amount of sebacic acid was 30 mol% when the total amount of polycarboxylic acid component (A) was set to 100 mol%. The amount of ethylene glycol is 58 mol when the total amount of polyol component (B) is set at 100 mol%. The amount of neopentyl glycol is 42 mol when the total amount of polyol component (B) is set at 100 mol%.

[0068] As an epoxy crosslinking agent, 4,4'-methylenebis(N,N-diepoxypropylaniline) (hereinafter sometimes referred to as 4-Epoxy), a 4-functional epoxy compound, was used. The 4-Epoxy was blended at 10% by weight relative to the polyester resin before crosslinking.

[0069] The silica particles used are products of Nissan Chemical Co., Ltd. The silica particles used are surface-nonfunctional and have a diameter of 12 nm. The silica particles are blended at 20% by weight relative to the pre-crosslinked polyester resin.

[0070] As a transesterification catalyst, diazabicycloundecene (DBU) was used. The DBU was blended at 2% by weight relative to the pre-crosslinked polyester resin.

[0071] The pre-crosslinked polyester resin, 4-Epoxy, silicon dioxide particles, and DBU were uniformly mixed using a solvent casting method employing tetrahydrofuran (THF). After vacuum drying, a crosslinking reaction was carried out by heating at 200°C for 24 hours to obtain a sample. The obtained sample was designated as Sample 1. It is believed that in this reaction, a network was formed due to the transesterification reaction of the pre-crosslinked polyester resin and 4-Epoxy, as well as the ring-opening reaction of the epoxy.

[0072] For sample 1, the dispersion state of silicon dioxide particles was observed under a field emission scanning electron microscope (JSM-7800F manufactured by Nippon Electron Ltd.), and the resulting photograph is shown in Figure 1. The accelerating voltage was set to 5.0 keV, and the magnification was set to 20,000x. Furthermore, platinum-palladium was deposited onto the surface during observation. As shown in Figure 1, there were no visible aggregates of silicon dioxide particles, indicating high transparency.

[0073] (Example 2) Compared with Example 1, without the addition of silicon dioxide particles, the sample was prepared under the same conditions as in Example 1. The obtained sample was designated as Sample 2. It is believed that in this reaction, a network was formed due to the transesterification reaction of the pre-crosslinked polyester resin with 4-Epoxy and the ring-opening reaction of the epoxy.

[0074] (Comparative Example 1) The pre-crosslinking polyester resin used in Example 1 was used directly as Sample 3.

[0075] (Example 3) Surface-functionalized silica particles were used instead of the surface-nonfunctionalized silica particles in Example 1, and the sample was prepared under the same conditions as in Example 1. In Example 3, surface-hydroxyl-functionalized silica particles manufactured by Nissan Chemical Co., Ltd. were used. The diameter of the silica particles was 12 nm. The silica particles were incorporated at a mass ratio of 10% relative to the pre-crosslinking polyester resin. The obtained sample was designated as Sample 4. It is believed that in Example 3, a network was formed due to the transesterification reaction of the pre-crosslinking polyester resin with 4-Epoxy and the ring-opening reaction of the epoxy.

[0076] For sample 4, the dispersion state of silicon dioxide particles was observed under the same conditions as in Example 1, and the resulting photograph is shown in Figure 2. As can be seen from Figure 2, similar to sample 1 (Example 1), there were no visible aggregates of silicon dioxide particles.

[0077] For samples 1 to 4, the number average molecular weight (Mn) was determined as follows.

[0078] (Number Average Molecular Weight (Mn)) Samples 1-4 were dissolved in DMF to achieve a concentration of approximately 0.5% by mass, and filtered through a polytetrafluoroethylene membrane filter with a pore size of 0.5 μm. The resulting sample was used for determination. The number average molecular weight (Mn) was determined by gel permeation chromatography using DMF with added LiBr (0.05% by mass) as the mobile phase and a differential refractometer as the detector. The flow rate was set to 0.5 mL / min, and the column temperature was set to 40°C. The columns used were KF-803, KF-804L, and KF-805L manufactured by Showa Denko Corporation. Monodisperse polymethyl methacrylate was used as the standard material (molecular weight standard). Low molecular weight compounds (oligomers, etc.) with a number average molecular weight (Mn) less than 1000 were discarded and not counted.

[0079] The gel fraction was determined for samples 1-4. The gel fraction was determined by a swelling test. 0.1 g of the sample was immersed in tetrahydrofuran (THF), and after 24 hours, the extracted sol solution was transferred to another sample vial. The remaining gel component was immersed in THF again, and the same operation was performed three times. Let wsol be the mass of the sample remaining after drying the sol solution, and wgel be the mass of the sample remaining after drying the gel component. The gel fraction fgel was calculated according to the following formula. As a result, the gel fraction of sample 1 was 94.4% by mass, the gel fraction of sample 2 was 95.5% by mass, the gel fraction of sample 3 was 0% by mass (completely dissolved), and the gel fraction of sample 4 was 95.3% by mass. fgel = wgel / (wgel + wsol) × 100

[0080] (1) Glass transition temperature (Tg) The glass transition temperature (Tg) of samples 1 to 3 was determined. A DSC7020 (manufactured by HITACHI High-Tech) was used for the determination. The temperature range was from -50°C to 200°C, and the heat flow was measured in a N2 atmosphere at a temperature change rate of 10°C / min to determine the glass transition temperature (Tg). The results of the DSC determination are shown in Figure 3. The vertical axis shows the heat flow, and the horizontal axis shows the temperature (°C). The Tg of sample 1 was 17.6°C, the Tg of sample 2 was 21.7°C, and the Tg of sample 3 was 13.6°C. It is believed that the higher temperatures of samples 1 and 2 compared to sample 3 are due to the formation of cross-linked structures, which restricts molecular motion.

[0081] (2) Temperature-dispersed viscoelasticity was measured using a DMS6100 (manufactured by HITACHI High-Tech) in a cooling mode within a temperature range of 190°C to -50°C. The measurement was conducted in an N2 atmosphere with a temperature change rate of 3°C / min, a measurement frequency of 1Hz, and a strain of 0.05%. The test piece used for the measurement was a strip with a thickness of 1mm, a length of 15mm, and a width of 4mm.

[0082] Figure 4(a) shows the temperature dependence of the storage elastic modulus (E') and loss tangent tanδ of samples 1 and 2 obtained in Examples 1 and 2; Figure 4(b) shows the temperature dependence of the storage elastic modulus (E') and loss tangent tanδ of sample 3 obtained in Comparative Example 1; and Figure 5 shows the temperature dependence of the storage elastic modulus (E') and loss tangent tanδ of sample 4 obtained in Example 3. Figure 5 also shows the data of sample 1 obtained in Example 1 for comparison. In Figures 4(a), (b) and 5, the vertical axis represents the storage elastic modulus E' (Pa), and the horizontal axis represents the temperature (°C).

[0083] In Figures 4(a), (b) and 5, the solid line represents the temperature dependence of the storage elastic modulus (E'), and the dashed line represents the temperature dependence of the loss tangent tanδ. For samples 1 and 2, a tanδ peak originating from segment easing (α-easing peak) is visible in the region of approximately 40–50 °C. For sample 3, an α-easing peak is visible at approximately 25 °C. The samples are in a glassy state at a lower temperature than this peak region, and in a rubbery state at a higher temperature. For sample 3, no rubbery flat region was observed, and the storage elastic modulus (E') above 40 °C decreased significantly with increasing temperature. This is typical behavior of amorphous uncrosslinked polymers. In contrast, samples 1 and 2 showed a rubbery flat region, and no sharp decrease in the storage elastic modulus (E') (plateau elastic modulus) was observed. This indicates the formation of a crosslinked network and that the crosslinking density remains unchanged even at high temperatures. Similar to sample 1, sample 4 exhibits a tanδ peak (α-moderate peak) originating from the segmental easing in the approximately 40–50 °C region. The storage modulus (E') of sample 4 is lower than that of sample 1. This is believed to be due to the difference in silica particle content, specifically, the silica particle content of sample 1 is 20%, while that of sample 4 is 10%. Like sample 1, sample 4 maintains a stable, rubbery, flat region even at high temperatures, without a sharp decrease in the storage modulus (E') (plateau modulus). This is believed to indicate the formation of a cross-linked network with no change in cross-linking density even at high temperatures. These results suggest that, regardless of the surface functional groups of the silica particles, a stable cross-linked network is formed in this design.

[0084] Regarding the value of the storage elastic modulus (E') in the rubbery flat region, it is 9.1 MPa for sample 1, 3.1 MPa for sample 2, 2.5 MPa for sample 3, and 5.4 MPa for sample 4. Comparing the storage elastic modulus (E') of sample 1 and sample 2, it can be seen that the filler effect obtained by incorporating silicon dioxide particles is increased by approximately 3 times.

[0085] (3) Tensile tests were conducted using an AGS-500NX (manufactured by SHIMADZU) at room temperature. During the test, dumbbell-shaped test pieces with a thickness of 1 mm, a gauge width of 4 mm, and a gauge length of 13 mm were used, and the tensile test speed was set to 10 mm / min. The tensile strength was 23.4 MPa for specimen 1, 21.0 MPa for specimen 2, 0.28 MPa for specimen 3, and 20.8 MPa for specimen 4. Figure 6 shows the stress-strain curves of specimens 1-3, and Figure 7 shows the stress-strain curve of specimen 4. The vertical axis shows the stress (MPa), and the horizontal axis shows the strain (%). As can be seen from Figure 6, although specimen 3 can achieve high elongation, the stress is significantly smaller. That is, it exhibits viscous behavior. It was also observed that the storage modulus (E') of specimens 1 and 2 was significantly higher than that of specimen 3.

[0086] Regarding the Young's modulus estimated from the slope at 2% strain, it was 150 MPa for specimen 1, 91 MPa for specimen 2, 1.75 MPa for specimen 3, and 144 MPa for specimen 4. It is believed that the difference in Young's modulus between specimen 1 and specimen 2 is due to the addition of silicon dioxide particles. Furthermore, regarding the maximum stress, specimen 1, which contained silicon dioxide particles, had the highest stress, confirming the strength increase due to the presence of silicon dioxide particles.

[0087] (4) Stress relief tests were conducted using an MCR302 (manufactured by Anton Paar). Stress relief tests were performed on specimens 1-3 at temperatures of 100°C, 180°C, 190°C, or 200°C, and on specimen 4 at temperatures of 100°C, 170°C, 180°C, or 190°C. During the tests, a disc-shaped test piece with a diameter of 8 mm and a thickness of 0.5 mm was used. The tests were conducted in an N2 atmosphere, with a vertical stress of 10 N and a shear strain set at 3% of the linear region.

[0088] Figure 8(a) shows the results of the stress relief measurement of sample 1. The vertical axis shows the stress (σ) after normalization with the initial stress (σ0), and the horizontal axis shows the elapsed time (seconds). As can be seen from Figure 8(a), no significant stress relief was observed at the measurement temperature of 100°C, while significant stress relief was observed at high temperatures above 180°C. It is believed that this is because a transesterification reaction occurs at high temperatures, resulting in stress dispersion. Furthermore, it can be seen that if the measurement temperature is further increased from 180°C, the rate of stress relief increases with increasing temperature. It is believed that this is because the transesterification reaction is activated by temperature.

[0089] Figure 8(b) shows the results of stress relief tests conducted on specimens 1 and 2 at a temperature of 200°C. As can be seen from Figure 8(b), the presence or absence of silica particles does not have a significant impact on the stress relief behavior.

[0090] Figure 9 shows the results of the stress relief test for sample 4. As can be seen from Figure 9, no significant stress relief was observed at the test temperature of 100°C, while significant stress relief was observed at temperatures above 170°C. This is believed to be because an ester exchange reaction occurs at high temperatures, resulting in stress dispersion. Furthermore, it can be seen that if the test temperature is further increased from 170°C, the rate of stress relief increases with increasing temperature. This is believed to be because the ester exchange reaction is activated by temperature. From these results, it can be concluded that the bond exchange in the crosslinking network is activated regardless of the surface functional groups of silicon dioxide.

[0091] (5) Re-forming processability The re-forming processability of sample 1 was evaluated according to the following procedure. A strip of sample 1 (30 mm in length, 4 mm in width, and 0.3 mm in thickness) was wound around the outer surface of a glass bottle with a diameter of 0.8 mm, and the two ends of the wound sample 1 were attached to the glass bottle with tape. With sample 1 fixed to the outer surface of the glass bottle, it was kept at a temperature of 200°C for 20 hours and then cooled to room temperature. After cooling, sample 1 was removed from the outer surface of the glass bottle. As a result, sample 1 maintained the curved shape, showing re-forming processability. On the other hand, general cross-linked samples did not show such properties and would return to their original shape before being wound if removed from the outer surface of the glass bottle. It is believed that the re-forming processability of this system is due to the loss of elasticity during the network rearrangement caused by the transesterification reaction.

[0092] (6) Decomposability The decomposability of sample 1 was evaluated according to the following procedure. Sample 1 (5 mm in length, 5 mm in width, and 0.3 mm in thickness) was immersed in 30 mL of triethylene glycol, and heated to 180 °C using a reflux apparatus. As a result, sample 1 began to dissolve after 1 hour and almost completely dissolved after 10 hours. It is believed that this decomposition is due to the exchange between the hydroxyl groups of the alcohol solvent under heating and the ester bonds in sample 1. [Industrial Applicability]

[0093] The cross-linked polyester resin of the present invention can be applied to resin materials, film materials, elastomer materials, gel (gel) materials, etc., which are composed of polymers. [Simplified Explanation of the Diagram]

[0010] [Figure 1] Figure 1 is a photograph of sample 1 obtained in Example 1 taken under a field emission scanning electron microscope. [Figure 2] Figure 2 is a photograph of sample 4 obtained in Example 3 taken under a field emission scanning electron microscope. [Figure 3] Figure 3 is a graph showing the results of heat flow measurement. [Figure 4] Figure 4 is a graph showing the temperature dependence of storage modulus (E') and loss tangent tanδ. Figure 4(a) shows the results for samples 1 and 2, and Figure 4(b) shows the results for sample 3. [Figure 5] Figure 5 is a graph showing the temperature dependence of storage modulus (E') and loss tangent tanδ, and shows the results for samples 1 and 4. [Figure 6] Figure 6 is a graph showing the stress-strain curves of samples 1 to 3. [Figure 7] Figure 7 is a graph showing the stress-strain curve of sample 4. [Figure 8] Figure 8 is a graph showing the temperature dependence of stress relief curves. Figure 8(a) shows the stress relief curve of specimen 1, and Figure 8(b) shows the stress relief curves of specimens 1 and 2. [Figure 9] Figure 9 is a graph showing the temperature dependence of stress relief curves, and shows the stress relief curve of specimen 4.

Claims

1. A crosslinked polyester resin, which is a resin obtained by crosslinking polyester units with a compound having two or more epoxy groups, contains silicon dioxide particles, has covalent bond exchange characteristics at a temperature of 150°C or above, and has a gel fraction of 80% by mass or above.

2. The cross-linked polyester resin as claimed in claim 1, wherein, The polyester unit is a polycondensation compound of a polycarboxylic acid component (A) and a polyol component (B), and is composed of terephthalic acid as the polycarboxylic acid component (A) and an alkanediol having 2 to 4 carbon atoms as the polyol component (B).

3. The cross-linked polyester resin as claimed in claim 2, wherein, Regarding this polycarboxylic acid component (A), it contains saturated aliphatic dicarboxylic acids with 5 to 20 carbon atoms.

4. The cross-linked polyester resin as claimed in claim 2, wherein, Regarding the polyol component (B), it further contains at least one selected from the group consisting of neopentyl glycol, cyclohexanediol, diethylene glycol, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, and hexanediol.

5. The cross-linked polyester resin of claim 1 contains an ester exchange catalyst.

6. The cross-linked polyester resin of claim 1 has a Young's modulus of 50 MPa or higher, calculated from the slope of the stress-strain curve at 2% elongation.

7. The cross-linked polyester resin of claim 1 has a tensile strength of 10 MPa or more.

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