Polyester resin pellet and method for producing polyester resin

Abstract

To provide a polyester resin pellet and a polyester resin production method which prevent fusion between pellets observed during PEF crystallization, thereby enabling preliminary crystallization to progress efficiently in a solid-state polymerization reaction step.SOLUTION: This polyester resin pellet has 2,5-furan dicarboxylic acid units and ethylene glycol units, characterized in that the pellet has a spherical shape.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to polyester resin pellets having 2,5-furandicarboxylic acid units and ethylene glycol units, and a method for producing the polyester resin. [Background technology]

[0002] In the context of global environmental issues, there is hope for a shift from plastics made from petroleum-derived raw materials to plastics made from renewable resources, and aliphatic polyesters such as polylactic acid and polybutylene succinate are being used. In addition, polyester resins such as polyethylene furanoate (PEF), made from 2,5-furandicarboxylic acid and ethylene glycol, have been developed as polyesters made from 2,5-furandicarboxylic acid, which can be produced from renewable resources. PEF is expected to be used as a replacement for PET in various molded products such as bottles, films, and fibers, and has characteristics such as gas barrier properties, making it a plastic that is expected to grow in the future.

[0003] In the manufacturing stage of PEF, it is sometimes desirable to carry out solid-state polymerization after melt polymerization to adjust the molecular weight, as with PET. When carrying out solid-state polymerization, usually, preliminary crystallization is carried out at a temperature lower than that of the solid-state polymerization reaction before carrying out the solid-state polymerization reaction in order to prevent the resin pellets from fusing together. However, because PEF crystallizes more slowly than PET, the pellets are prone to melting together during pre-crystallization, which can result in problems such as the pre-crystallization taking a long time, problems caused by agglomerated pellets, and a heavy load on the manufacturing process. Patent Document 1 (Example 3) describes the step of breaking down aggregates after PEF is heated and crystallized.

[0004] On the other hand, PEF pellets are hard and brittle, and are vulnerable to impacts, which can lead to cracks, chips, and fine powder. If small particles or powder get mixed into the pellets, it can cause problems during molding. In addition, small particles and powder can increase the molecular weight too much when subjected to solid-state polymerization, which can cause problems during molding and impair the appearance of the molded product. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special table 2017-508048 Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above problems, an object of the present invention is to provide a polyester resin pellet and a method for producing a polyester resin, which can efficiently advance preliminary crystallization in the solid-state polymerization reaction step by preventing fusion between pellets that occurs during crystallization of PEF. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above problems, and as a result have completed the present invention. [1] A polyester resin pellet having a 2,5-furandicarboxylic acid unit and an ethylene glycol unit, characterized in that the shape of the pellet is spherical. [2] The polyester resin pellets according to the above [1], wherein at least one of an average value and a median value of sphericity of the spherical pellets is 0.7 to 1.0. [3] The polyester resin pellet according to the above [1] or [2], further comprising 0.1 to 50% by weight of a polyalkylene ether glycol having 5 to 20 carbon atoms and a number average molecular weight of 500 to 6,000. [4] A method for producing a polyester resin having 2,5-furandicarboxylic acid units and ethylene glycol units, comprising the steps of producing spherical pellets and crystallizing the pellets by heating. [5] The method for producing a polyester resin according to the above [4], wherein the spherical pellets are obtained by extruding a molten resin into air or water and cutting the resin. [6] The method for producing a polyester resin according to the above [4] or [5], wherein the spherical pellets are heated at a temperature of 100° C. or higher and 200° C. or lower to crystallize the pellets. [7] The method for producing a polyester resin according to any one of the above [4] to [6], wherein the intrinsic viscosity (IV) is improved by further heating to a temperature of 170° C. or higher and 215° C. or lower. [8] The method for producing a polyester resin according to any one of the above [4] to [7], wherein the polyester resin contains a crystal nucleating agent. [9] The method for producing a polyester resin according to any one of the above [4] to [8], wherein the polyester resin further contains 0.1 to 50% by weight of a polyalkylene ether glycol having 5 to 20 carbon atoms and a number average molecular weight of 500 or more and 6,000 or less. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Representative embodiments for carrying out the present invention will be described in detail below, but the present invention is not limited to the following embodiments as long as they do not depart from the gist of the present invention. In this specification, when a numerical value or physical property value is enclosed by "~", the value before and after the "~" is included.

[0009] [Polyester resin pellets] The polyester resin pellets of the present invention are polyester resin pellets having 2,5-furandicarboxylic acid units and ethylene glycol units, and are characterized in that the pellets have a spherical shape. The spherical shape of the pellets reduces the contact area between the pellets, making it possible to prevent the resin pellets from fusing together. On the other hand, conventional pellets are cylindrical, and fusion between pellets cannot be avoided, so it is necessary to peel off the fused pellets during the preliminary crystallization stage, which places a large burden on the manufacturing process. In the conventional manufacturing method, the resin is drawn out in a strand shape, cooled and solidified in water, etc., and then the strand-shaped resin is cut to produce the resin, which has a cylindrical shape, and it is believed that this is the reason why fusion between the pellets occurs. In contrast, the present invention solves the above problem by forming the pellets into a spherical shape using a production method that will be described in detail later.

[0010] The polyester pellets are spherical, but are not necessarily perfect spheres, and may be flat within the scope of the effects of the present invention. For example, ellipsoidal or rugby ball shapes also fall under the spheres of the present invention. For spherical pellets, it is preferable that at least one of the average and median sphericity is 0.7 to 1.0. If the sphericity is within the above range, the effects of the present invention are easily achieved. From the above viewpoints, the sphericity is more preferably in the range of 0.73 to 1.0, and even more preferably in the range of 0.75 to 1.0. The sphericity is measured by the method described in the Examples.

[0011] [Polyester resin] The polyester resin of the present invention is characterized by having a polyester resin mainly composed of 2,5-furandicarboxylic acid units and ethylene glycol units.

[0012] <2,5-furandicarboxylic acid unit> The proportion of 2,5-furandicarboxylic acid units contained in the polyester resin of the present invention (hereinafter sometimes referred to as "2,5-furandicarboxylic acid units according to the present invention" or simply "2,5-furandicarboxylic acid units") is not particularly limited, but is preferably 50 mol % or more, more preferably 70 mol % or more, even more preferably 80 mol % or more, and particularly preferably 90 mol % or more, based on the excellent heat resistance of the polyester resin, relative to the total dicarboxylic acid units. The upper limit is 100 mol %. From an environmental perspective, it is preferable that the 2,5-furandicarboxylic acid unit is a unit derived from biomass.

[0013] <Ethylene glycol unit> The proportion of ethylene glycol units in the polyester resin of the present invention (hereinafter sometimes referred to as "ethylene glycol units according to the present invention" or simply "ethylene glycol units") is not particularly limited, but is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, and particularly preferably 90 mol% or more, based on the total diol units, in order to provide excellent heat resistance to the polyester resin. The upper limit is 100 mol%. From an environmental standpoint, it is preferable that the ethylene glycol unit is a unit derived from biomass.

[0014] <Polyalkylene ether glycol> The polyester resin of the present invention may contain 0.1 to 50% by weight of a polyalkylene ether glycol having 5 to 20 carbon atoms and a number average molecular weight of 500 or more and 6000 or less, based on the weight of the polyester resin. The polyalkylene ether glycol may be added to a reactor together with the polyester raw material in the polyester resin production process, or may be added during the production process, or may be kneaded with the PEF resin using a kneader.

[0015] By containing polyalkylene ether glycol, the melting point of the polyester resin can be prevented from decreasing, and the crystallinity can be improved. Since the crystallization during production is accelerated, the load in the preliminary crystallization step during solid-phase polymerization can be reduced, and a molded product with improved stretch orientation can be obtained. The content of polyalkylene ether glycol is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, and the upper limit is preferably 30% by weight or less, more preferably 10% by weight or less.

[0016] Specific examples of the polyalkylene ether glycol include polyhexamethylene ether glycol, polyheptamethylene ether glycol, polyoctamethylene ether glycol, polynonaether glycol, polydecamethylene ether glycol, polyundecamethylene ether glycol, and polydodecamethylene ether glycol. The polyalkylene ether glycol may have a branched structure.

[0017] The melting point of the polyalkylene ether glycol is preferably 40° C. or higher. When the melting point is 40° C. or higher, the effect of improving the crystallization of PEF is large. The melting point is preferably 45° C. or higher, and more preferably 50° C. or higher. From an environmental standpoint, it is preferable that the polyalkylene ether glycol is derived from biomass.

[0018] <Other units> The polyester resin of the present invention may have units such as dicarboxylic acid units other than 2,5-furandicarboxylic acid units (hereinafter, sometimes referred to as "other dicarboxylic acid units") and diol units other than ethylene glycol units (hereinafter, sometimes referred to as "other diol units") (hereinafter, these units may be collectively referred to as "other units"). Examples of the other dicarboxylic acid units include aromatic dicarboxylic acid units other than furandicarboxylic acid (hereinafter, sometimes referred to as "other aromatic carboxylic acid units") and aliphatic dicarboxylic acid units. Examples of the other diol units include aliphatic diol units other than ethylene glycol and aromatic diol units. When the polyester resin of the present invention has other units, it may have only one type of unit or two or more types of units.

[0019] Examples of other aromatic dicarboxylic acid units include units derived from terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, and the like. When the polyester resin of the present invention has an aliphatic dicarboxylic acid unit, the carbon number is preferably 2 to 36, more preferably 4 to 36, from the viewpoint of excellent mechanical properties of the polyester resin. In addition, a chain-like dicarboxylic acid unit is preferable, and a straight-chain dicarboxylic acid unit is more preferable. Specific examples thereof include units derived from oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecane diacid, dodecane diacid, tridecane diacid, tetradecane diacid, pentadecanedioic acid, hexadecanedioic acid, heptadecanedioic acid, octadecanedioic acid, nonadecanedioic acid, eicosane diacid, docosane diacid, fumaric acid, maleic acid, itaconic acid, dimer acid, and 1,4-cyclohexanedicarboxylic acid.

[0020] In terms of providing the polyester resin with excellent heat resistance and mechanical properties, the other diol units preferably have a carbon number of 3 to 20, more preferably 3 to 10. Furthermore, chain diol units are preferred, and linear diol units are even more preferred. Specifically, diethylene glycol, triethylene glycol, 1,3-propanediol, 1,2-propanediol, 2,3-propanediol, 2,2-dimethyl-1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,3-pentanediol, 2,4-pentanediol, 1,6-hexanediol, and units derived from chain diols such as nonanediol, 2,5-hexanediol, 1,2-hexanediol, 1,7-heptanediol, 1,2-octanediol, 1,8-octanediol, 2-ethyl-1,3-hexanediol, 1,9-nonanediol, 1,2-nonanediol, 2-methyl-1,8-octanediol, and 1,10-decanediol; and units derived from alicyclic diols such as 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, and isosorbide.

[0021] When the polyester resin of the present invention has other dicarboxylic acid units or diol units, the proportion of each of these units is preferably 20 mol % or less, and more preferably 10 mol % or less, based on all dicarboxylic acid units or diol units, in order to provide the polyester resin with excellent crystallinity and heat resistance.

[0022] As other units, the copolymer may contain a unit derived from an aromatic dihydroxy compound, a bisphenol unit, a hydroxycarboxylic acid unit, a diamine unit, a unit having a trifunctional or higher functional group, or the like. The hydroxycarboxylic acid unit is not particularly limited as long as it is a unit derived from a compound having one hydroxyl group and one carboxyl group in the unit. Specific examples of the hydroxycarboxylic acid unit include units derived from lactic acid, glycolic acid, 2-hydroxy-n-butyric acid, 2-hydroxycaproic acid, 6-hydroxycaproic acid, 2-hydroxy-3,3-dimethylbutyric acid, 2-hydroxy-3-methylbutyric acid, 2-hydroxyisocaproic acid, mandelic acid, salicylic acid, 3-hydroxybenzoic acid, 4-hydroxybenzoic acid, and their esters, acid chlorides, acid anhydrides, etc.

[0023] Examples of the unit having a tri- or higher functional group include a unit derived from at least one tri- or higher functional polyfunctional compound selected from the group consisting of tri- or higher functional polyhydric alcohols; tri- or higher functional polycarboxylic acids or their anhydrides, acid chlorides, or esters; tri- or higher functional hydroxycarboxylic acids or their anhydrides, acid chlorides, or esters; and tri- or higher functional amines.

[0024] Specific examples of trifunctional or higher polyhydric alcohols include units derived from glycerin, trimethylolpropane, pentaerythritol, etc. Specific examples of units derived from trifunctional or higher polyvalent carboxylic acids or anhydrides thereof include units derived from trimesic acid, propanetricarboxylic acid, trimellitic anhydride, pyromellitic anhydride, benzophenonetetracarboxylic anhydride, cyclopentatetracarboxylic anhydride, etc. Specific examples of units derived from trifunctional or higher functional hydroxycarboxylic acids include units derived from malic acid, hydroxyglutaric acid, hydroxymethylglutaric acid, tartaric acid, citric acid, hydroxyisophthalic acid, hydroxyterephthalic acid, etc. Among these, units derived from trimethylolpropane, malic acid, tartaric acid, and citric acid are preferred because of their ease of availability.

[0025] When the polyester resin of the present invention has a unit having a functional group with three or more functionalities, the ratio is preferably high in terms of the melt viscosity of the polyester being moderate and excellent in moldability. On the other hand, it is preferable that the ratio is low in terms of the crosslinking not proceeding excessively, the polyester being easily extracted stably, and excellent in moldability. Therefore, the ratio of the unit having a functional group with three or more functionalities in the polyester resin of the present invention is preferably 0.0001 mol% or more, more preferably 0.001 mol% or more, even more preferably 0.005 mol% or more, and particularly preferably 0.01 mol% or more, based on the total constitutional units constituting the polyester resin of the present invention. The upper limit is preferably 5 mol%, more preferably 4 mol%, and even more preferably 3 mol%.

[0026] In producing the polyester resin of the present invention, a chain extender such as a diisocyanate, an oxazoline, a carbodiimide compound, or an epoxy compound may be used. That is, the polyester resin of the present invention may have a structure derived from the chain extender. When a chain extender is used, in terms of excellent moldability and mechanical properties of the polyester resin, the structure derived from the chain extender in the polyester resin is preferably 10% by weight or less, more preferably 5% by weight or less, and particularly preferably 2% by weight or less.

[0027] <Biomass-derived ingredients> The units constituting the polyester resin of the present invention are preferably units derived from biomass. In this case, alkali metals and periodic table group 2 elements such as Mg and Ca derived from biomass raw materials may be contained in the polyester resin. Here, it is preferable that the amount of these components is small because they may inhibit the polymerization reaction during polyester production. Specifically, the amount of alkali metal is preferably 30 ppm or less, more preferably 20 ppm or less, and even more preferably 10 ppm or less, and the amount of Group 2 elements of the periodic table is preferably 300 ppm or less, more preferably 200 ppm or less, even more preferably 100 ppm or less, and particularly preferably 50 ppm or less.

[0028] [Method of manufacturing polyester resin] The polyester resin of the present invention can be produced by a known method for producing polyester resins by using specific dicarboxylic acids and specific diols in specific amounts so that the dicarboxylic acid units and diol units are the above-mentioned polyester resin of the present invention. Here, the dicarboxylic acid may be a dicarboxylate ester. Examples of the dicarboxylate ester include alkyl esters having 1 to 4 carbon atoms, and among these, methyl ester, ethyl ester, n-propyl ester, isopropyl ester, butyl ester, and the like are preferred, with methyl ester being more preferred.

[0029] The polyester resin can be produced by a general melt polymerization method in which a dicarboxylic acid or a dicarboxylic acid ester and a diol are used to carry out an esterification reaction or an ester exchange reaction, followed by a polycondensation reaction under reduced pressure. In addition, solid-phase polymerization may be carried out following the melt polymerization. When the polyalkylene ether glycol is reacted during the production of the polyester resin, the above-mentioned amount may be charged relative to the amount of the polyester resin to be produced and reacted. It may be charged before the start of the reaction, or may be added during the production process.

[0030] <Raw material molar ratio> In the production of the polyester resin of the present invention, the molar ratio of the total amount of dicarboxylic acid and dicarboxylic acid ester (hereinafter, both may be collectively referred to as "dicarboxylic acid component") to the diol is not particularly limited as long as the polyester of the present invention can be produced. However, in terms of preventing pipe blockage due to generation of sublimate during polyester resin production and facilitating the production of high molecular weight polyester resin, the diol is preferably 0.9 mol or more per mol of the dicarboxylic acid component, more preferably 1.0 mol or more, and even more preferably 1.01 mol or more. On the other hand, it is preferably 4.0 mol or less, more preferably 3.0 mol or less, and even more preferably 2.5 mol or less.

[0031] <Catalyst> The polyester resin of the present invention is preferably produced in the presence of a catalyst. The timing and amount of the catalyst to be added may be appropriately adjusted. That is, the catalyst may be added when the raw materials are charged, or may be added during the production process. Also, the catalyst may be added both when the raw materials are charged and during the production process. The catalyst may be charged either as a single catalyst compound or in a state of being dissolved or dispersed in water, alcohol, or glycol such as ethylene glycol.

[0032] The catalyst can be selected from any catalyst that can be used in the production of polyester, but metal compounds such as germanium, titanium, zirconium, hafnium, antimony, tin, zinc, aluminum, cobalt, lead, manganese, copper, barium, and cadmium are preferred. Among them, germanium compounds, titanium compounds, antimony compounds, tin compounds, zinc compounds, and aluminum compounds are more preferred, and germanium compounds, titanium compounds, and antimony compounds are particularly preferred. Therefore, the polyester resin of the present invention contains germanium, titanium, and antimony derived from the catalyst.

[0033] The titanium compound is not particularly limited. As the titanium compound, tetraalkyl titanate is preferable, and specifically, tetra-n-propyl titanate, tetraisopropyl titanate, tetra-n-butyl titanate, tetra-t-butyl titanate, tetraoctyl titanate, tetraphenyl titanate, tetracyclohexyl titanate, tetrabenzyl titanate, mixed titanates thereof, etc. are mentioned. In addition, titanium (oxy) acetylacetonate, titanium tetraacetylacetonate, titanium (diisopropoxide) acetylacetonate, titanium bis (ammonium lactate) dihydroxide, titanium bis (ethylacetoacetate) diisopropoxide, titanium (triethanolamine) isopropoxide, polyhydroxy titanium stearate, tetrastearyl titanate, titanium lactate, titanium triethanolamine, butyl titanate dimer, etc. are also mentioned. Furthermore, titanium oxide, composite oxides containing titanium and silicon, etc. are also mentioned.

[0034] Among these, tetra-n-propyl titanate, tetraisopropyl titanate, tetra-n-butyl titanate, tetraoctyl titanate, titanium (oxy)acetylacetonate, titanium tetraacetylacetonate, titanium bis(ammonium lactate) dihydroxide, polyhydroxytitanium stearate, tetrastearyl titanate, titanium lactate, butyl titanate dimer, titanium oxide, or titania / silica composite oxide is preferred. Furthermore, tetraisopropyl titanate, tetra-n-butyl titanate, tetraoctyl titanate, titanium (oxy)acetylacetonate, titanium tetraacetylacetonate, polyhydroxytitanium stearate, tetrastearyl titanate, titanium lactate, butyl titanate dimer, or titania / silica composite oxide is more preferred.

[0035] The germanium compound used as the catalyst is not particularly limited. The germanium compound may be an inorganic germanium compound such as germanium oxide or germanium chloride, or an organic germanium compound such as tetraalkoxygermanium. In view of price and availability, germanium oxide, tetraethoxygermanium, and tetrabutoxygermanium are preferred, and germanium oxide is particularly preferred. When a germanium catalyst is used, a polyester resin with little coloring is easily obtained, and when the polyester resin of the present invention is used for an application where little coloring is important, such as an optical application, it is preferable to use a germanium catalyst. In this case, the YI (yellow index) of the polyester resin is preferably 50 or less, more preferably 40 or less, and even more preferably 30 or less. In addition, the b value is preferably 30 or less, more preferably 20 or less, and even more preferably 10 or less.

[0036] The antimony compound used as the catalyst is not particularly limited. Examples of the antimony compound include antimony acetate, antimony oxide, and antimony glycolate. Among these, antimony acetate and antimony oxide are preferred.

[0037] The amount of catalyst used is preferably large in terms of a high polymerization reaction rate and high production efficiency, while it is preferably small in terms of low catalyst cost, low generation of catalyst residue, low coloration, and easy production of polyester resins with excellent melt thermal stability and hydrolysis resistance. Specifically, the amount of the catalyst used is preferably 1 ppm or more, more preferably 3 ppm or more, and even more preferably 5 ppm or more in terms of metal content in the polyester resin produced, and is preferably 500 ppm or less, more preferably 400 ppm or less, and even more preferably 300 ppm or less. In particular, when a titanium compound is used as a catalyst, the amount is preferably small, more preferably 300 ppm or less, more preferably 100 ppm or less, even more preferably 50 ppm or less, and particularly preferably 30 ppm or less. Therefore, the polyester resin of the present invention contains the above-mentioned amount of metal.

[0038] The amount of catalyst used relative to the furan dicarboxylic acid component is, in terms of molar ratio, 3.8 x 10 -6 More than 1.14×10 is preferable. -5 More preferably, 1.9×10 -5 More preferably, 1.14×10 -3 Less than or equal to 3.8×10 is preferred -4 Less than or equal to 1.9×10 is preferable. -4 Less than or equal to 1.14×10 is even better. -4 The following are particularly preferred: In the case of germanium compounds, the -6 More than 7.5×10 is preferable. -6 More preferably, 1.25×10 -5 More preferably, the ratio is 1.25×10 -3 Less than or equal to 1.00×10 is preferred. -3 Less than or equal to 7.5×10 is preferable. -4 The following is even more preferred: For antimony compounds, 1.5 x 10 -6 More than 4.5×10 is preferable. -6 More preferably, 7.5×10 -6 More preferably, 7.5×10 -4 Less than 6.0×10 is preferable. -4 Less than or equal to 4.5×10 is preferable. -4 The following is even more preferred:

[0039] <Additives during polymerization> When producing the polyester resin of the present invention, in order to suppress the by-production of diethylene glycol, it is preferable to add an alkali compound that is commonly known in the production of PET, etc. Specifically, an ammonium hydroxide compound such as tetraethylammonium hydroxide can be mentioned. It is also preferable to use an alkali metal compound such as sodium or potassium, or a compound having an element of Group 2 of the periodic table. Specific examples include compounds of beryllium, magnesium, calcium, strontium, barium, etc., with magnesium and calcium being preferred due to their ease of availability. Compounds of these elements include oxides, chlorides, hydroxides, carbonates, carboxylates, alkoxy salts, etc. Among these, carboxylates are preferred, and acetates are particularly preferred. When these compounds are charged into a reaction vessel, the compounds may be charged alone or may be charged after being dissolved or dispersed in water, alcohol, or glycol such as ethylene glycol. It is preferable to charge the compounds after being dissolved in water or ethylene glycol.

[0040] The amounts of the ammonium hydroxide compound, the alkali metal compound, and the Group 2 element of the periodic table used are preferably large in order to suppress the by-production of diethylene glycol and to easily obtain a polyester resin with high heat resistance, whereas the amounts are preferably small in order to easily obtain a polyester resin with high molecular weight through fast melt polymerization and solid-phase polymerization. The amount of the ammonium hydroxide compound used is preferably 50 ppm or more, more preferably 100 ppm or more, based on the polyester resin obtained, and is preferably 2000 ppm or less, more preferably 1000 ppm or less.

[0041] The amount of the alkali metal or Group 2 element of the periodic table used is preferably 1 ppm or more, more preferably 3 ppm or more, and even more preferably 5 ppm or more, relative to the amount of the resulting polyester resin, and is preferably 300 ppm or less, more preferably 200 ppm or less, and even more preferably 100 ppm or less. The amount of the catalyst used in the polymerization is preferably 3 mol or less, more preferably 2 mol or less, and even more preferably 1 mol or less, while the amount of the catalyst used in the polymerization is preferably 0.1 mol or more, more preferably 0.2 mol or more, and even more preferably 0.3 mol or more.

[0042] <Esterification reaction or transesterification reaction step> The conditions such as temperature, time, and pressure in the esterification reaction between dicarboxylic acid and diol and the transesterification reaction between dicarboxylic acid ester and diol can be within the range of the conventional polyester production method. The reaction temperature is usually 100°C or higher, preferably 120°C or higher. Also, it is usually 300°C or lower, preferably 290°C or lower, and more preferably 280°C or lower. Within these ranges, the reaction can proceed efficiently. The reaction atmosphere is usually an inert gas atmosphere such as nitrogen or argon. The reaction pressure is usually from normal pressure to 0.3 MPa. The reaction time is usually 1 hour or more, and on the other hand, usually 10 hours or less, preferably 8 hours or less.

[0043] <Polycondensation reaction process> Following the above reaction, a polycondensation reaction is carried out under reduced pressure to further improve the degree of polymerization. The conditions of the polycondensation reaction step, such as temperature, time, and pressure, can be within the ranges of conventionally known polyester production methods. The polycondensation reaction temperature is preferably 230°C or higher, more preferably 235°C or higher, and even more preferably 240°C or higher. On the other hand, it is preferably 300°C or lower, more preferably 290°C or lower, and even more preferably 280°C or lower. By setting the temperature within this range, the polymerization rate is sufficiently ensured, and thermal decomposition, coloration, side reactions, etc. are suppressed, and a polyester resin with a high degree of polymerization is obtained. The polycondensation reaction begins to reduce pressure when a certain temperature is reached, and the final pressure is usually 0.01 x 10 3 Pa or more, 0.05×10 3 Pa or more is preferable. Also, typically 1.4×10 3 Pa or less, 0.6×103 Pa or less is preferable, and 0.3×10 3 A high degree of vacuum is preferable because the short production time makes it difficult for the polyester to undergo a decrease in molecular weight or coloration due to thermal decomposition, and it is easy to produce a polyester with high properties. On the other hand, a low degree of vacuum is preferable because high vacuum equipment is not required.

[0044] The reaction time of the polycondensation reaction is usually 1 hour or more and 15 hours or less. It is preferably 10 hours or less, more preferably 8 hours or less. By using a long reaction time, the reaction proceeds sufficiently, and a polyester resin having a high degree of polymerization and excellent mechanical properties is obtained. On the other hand, by using a short reaction time, the decrease in molecular weight due to thermal decomposition of the polyester can be suppressed, and a polyester resin having excellent mechanical properties can be obtained.

[0045] <Solid phase polymerization process> When producing the polyester resin of the present invention, it is preferable to further carry out a solid-phase polymerization step after the above-mentioned polycondensation reaction step. The method of solid-phase polymerization is not particularly limited, but for example, the polyester resin obtained in the above-mentioned polycondensation reaction step is heated under an inert gas atmosphere or under reduced pressure. The reaction may be carried out with the polyester resin pellets left stationary or with stirring. When stirring, stirring may be carried out by installing a stirring blade in the reaction vessel or by moving the reaction vessel.

[0046] The reaction temperature of the solid-phase polymerization is preferably high in that it is easy to obtain a polyester resin having a high molecular weight. On the other hand, it is preferably low in that it is difficult for the polyester resin to be in a molten state. Therefore, the reaction temperature is preferably 170°C or higher, more preferably 180°C or higher, and particularly preferably 200°C or higher. On the other hand, it is preferably 215°C or lower, and more preferably 210°C or lower. The heating time is preferably 1 hour or more, more preferably 3 hours or more, while, since coloring is less likely to occur, it is preferably 50 hours or less, more preferably 40 hours or less, and even more preferably 30 hours or less.

[0047] Before carrying out the solid-state polymerization reaction, it is preferable to heat and crystallize the polyester resin at a temperature of 100°C or more and 200°C or less. More specifically, it is preferable to start heating at about 100°C and gradually increase the temperature to 200°C, preferably to about 180°C, to pre-crystallize the polyester resin surface. During pre-crystallization, it is preferable to take out the resin as appropriate, cool it, and then stimulate the slightly fused sample to loosen it before continuing the heat treatment, in order to prevent fusion. In the present invention, since spherical pellets are used, fusion between pellets in the pre-crystallization step is unlikely to occur, and the time required for pre-crystallization can be shortened. As described later, the use of a crystal nucleating agent is also preferred in that the time required for preliminary crystallization can be shortened.

[0048] <Reaction Apparatus> A known vertical or horizontal stirred tank reactor can be used as the reactor in which the above-mentioned reaction is carried out. For example, when two steps, an esterification reaction and / or transesterification reaction and a polycondensation reaction, are carried out, one or more reactors may be used. As the reactor in which the polycondensation reaction is carried out, a condenser is preferably connected between a vacuum pump and a pressure reducing exhaust pipe connecting the reactor, and the volatile components and unreacted monomers produced during the polycondensation reaction can be recovered by the condenser. As a reaction apparatus capable of continuously producing a polyester resin, for example, a known vertical stirring polymerization tank, horizontal stirring polymerization tank, thin-film evaporation type polymerization tank, etc. can be used, and it is common to carry out the production in a multi-stage manner by arranging a plurality of reaction tanks.

[0049] A known reaction apparatus can be used as the reaction apparatus for the solid-phase polymerization step. For example, an apparatus equipped with a process in which the crystallization of the resin pellets is promoted while heating in a preliminary crystallization tank equipped with a stirrer, and then the pellets are sent to a drying tank and a solid-phase polymerization tank is known. In the solid-phase polymerization tank, the reaction is carried out under vacuum or in an inert gas flow with or without stirring.

[0050] <Preparation of polyester resin pellets> The preferred method for obtaining pellets of common polyester resins such as PET is to extrude the molten resin into strands, cool them with water to solidify them, and then cut them. The pellets obtained by this method tend to be cylindrical. When the molecular weight of PET resin is further increased by solid-state polymerization, a preliminary crystallization process is carried out in which the pellets are gradually heated from a low temperature to promote crystallization. This prevents the pellets from fusing together. In the case of PEF, which is the polyester resin of the present invention, the crystallization speed is slower than that of PET, so the pellets are more likely to fuse together than with PET, and a longer time is required for pre-crystallization. Also, problems are more likely to occur due to agglomerated pellets. Furthermore, cylindrical PEF pellets are weak against impact and are prone to cracking, chipping, and fine powder. If small particles or fine powder are mixed in, it may lead to problems during molding. In addition, small particles or powders undergo solid-state polymerization at a high rate, resulting in an excessive increase in molecular weight. If a part with a particularly large molecular weight is mixed in, it may cause problems when molding films or the like, or cause damage to the appearance of the molded product.

[0051] The polyester resin pellets of the present invention are spherical in shape. Therefore, they are less likely to fuse when heated. They are also more resistant to impacts and are less likely to crack, chip, or break into fine powder. A method for obtaining spherical pellets includes a method in which the molten resin is extruded and cut, preferably before solidification. After cutting, the resin can be cooled by air or water, and water cooling is more preferable. The temperature for water cooling can be from about 5°C to about 90°C.

[0052] As for the size of the pellets, the maximum width of the pellets is preferably 0.5 mm or more, more preferably 1 mm or more. Also, 7 mm or less is preferable, and 5 mm or less is more preferable. The above size makes it easy to handle, and also makes it easy to adjust the molecular weight by solid-phase polymerization. The above-mentioned cutting system may be applied when the pellets are taken out of the polymerization apparatus after melt polymerization. Also, after producing cylindrical pellets, they may be melted again and repelletized into spherical pellets. At that time, various additives described later may be added.

[0053] [Physical properties of polyester resin] <Intrinsic viscosity> The intrinsic viscosity IV of the polyester resin of the present invention obtained by the above-mentioned method after melt polymerization is usually 0.5 dL / g or more, preferably 0.6 dL / g or more, more preferably 0.7 dL / g or more, and preferably 2.0 dL / g or less, more preferably 1.5 dL / g or less, even more preferably 1.2 dL / g or less, particularly preferably 1.1 dL / g or less, and most preferably 1.0 dL / g or less. A high intrinsic viscosity is preferable in that it is easy to mold high-strength injection-molded products, films, bottles, and other molded products and can shorten the solid-state polymerization time when solid-state polymerization is performed after melt polymerization, while a low intrinsic viscosity is preferable in that it can provide a polyester having an appropriate melt viscosity, shorten the time for the extraction step, and increase the yield of the polyester resin. As described above, the intrinsic viscosity can be further increased by performing a solid-state polymerization process after the melt polymerization. The solid-state polymerization process is also performed in order to prepare polyester resins with various intrinsic viscosities.

[0054] The intrinsic viscosity IV after solid-state polymerization is preferably high in order to efficiently produce molded products such as high-strength injection molded products, films, and bottles. Therefore, it is usually 0.7 dL / g or more, preferably 0.8 dL / g or more, more preferably 0.9 dL / g or more, and even more preferably 1.0 dL / g or more. On the other hand, the intrinsic viscosity after solid-state polymerization is usually 3.0 dL / g or less, preferably 2.5 dL / g or less, more preferably 2.0 dL / g or less, and even more preferably 1.8 dL / g or less. In the present invention, the intrinsic viscosity (IV) of the polyester resin is determined from the solution viscosity measured in phenol / tetrachloroethane (1:1 weight ratio) at a polyester resin concentration of 0.5 g / dL at 30° C. The Huggins constant here is 0.32.

[0055] [Polyester resin composition] The polyester resin of the present invention may contain various additives such as a heat stabilizer, an antioxidant, an antihydrolysis agent, a crystal nucleating agent, a flame retardant, an antistatic agent, a release agent, and an ultraviolet absorber, within a range that does not impair the properties of the polyester resin. These additives may be added to a reaction device before the polymerization reaction of the polyester, or may be added to a conveying device or the like from the start of the polymerization reaction to before the end of the polymerization reaction, or may be added before the product is discharged after the polymerization reaction is completed. Alternatively, they may be added to the product after the discharge. When molding the polyester resin composition of the present invention, in addition to the various additives described above, an impact resistance modifier, a filler, a crystal nucleating agent, a reinforcing agent, an extender, etc. may be added. Examples of impact resistance modifiers include Metablen (manufactured by Mitsubishi Chemical Corporation) and Kane Ace (manufactured by Kaneka Corporation).

[0056] The filler may be inorganic or organic, and one type of filler may be used alone, or two or more types may be used in combination. Examples of inorganic fillers include anhydrous silica, mica, talc, titanium oxide, calcium carbonate, diatomaceous earth, allophane, bentonite, potassium titanate, zeolite, sepiolite, smectite, kaolin, kaolinite, glass, limestone, carbon, wollastonite, calcined perlite, silicates such as calcium silicate and sodium silicate, hydroxides such as aluminum oxide, magnesium carbonate and calcium hydroxide, salts such as ferric carbonate, zinc oxide, iron oxide, aluminum phosphate and barium sulfate, etc. These may be used alone or in combination of two or more. In the case of a polyester composition containing an inorganic filler, the content of the inorganic filler in the polyester composition is usually 1% by weight or more, preferably 3% by weight or more, and more preferably 5% by weight or more, and usually 80% by weight or less, preferably 70% by weight or less, and more preferably 60% by weight or less.

[0057] Examples of organic fillers include raw starch, processed starch, pulp, chitin, chitosan, coconut shell powder, bamboo powder, bark powder, kenaf powder, straw powder, etc. Also included is nanofiber cellulose, which is made by defibrating fibers such as pulp to the nano level.

[0058] As the crystal nucleating agent, talc, boron nitride, silica, layered silicate, polyethylene wax, and polypropylene wax are preferable, and boron nitride, talc, and polyethylene wax are more preferable. Boron nitride is more preferable. The crystal nucleating agent may be used alone or in combination of two or more kinds. When the nucleating agent is an inorganic material, the smaller the particle size, the better the nucleating effect. The average particle size of the inorganic nucleating agent is preferably 5 μm or less, more preferably 3 μm or less, even more preferably 1 μm or less, and particularly preferably 0.5 μm or less. The average particle size of the nucleating agent is preferably 0.1 μm or more.

[0059] The amount of the crystal nucleating agent is preferably large in terms of the crystallization promotion effect and the time required for preliminary crystallization being easily shortened. On the other hand, it is preferable that the amount is small in terms of the mechanical properties and flexibility of the polyester resin or polyester resin composition. Therefore, the amount of the crystal nucleating agent is preferably 0.001% by weight or more, more preferably 0.01% by weight or more, and even more preferably 0.1% by weight or more, based on the polyester resin. The amount of the crystal nucleating agent is preferably 30% by weight or less, more preferably 10% by weight or less, even more preferably 5% by weight or less, and particularly preferably 1% by weight or less. In addition, fillers other than those used as nucleating agents, such as inorganic fillers used to improve rigidity, organic stabilizers used as heat stabilizers, and foreign matter mixed in during the production process or molding process of the polyester resin, may also act as crystal nucleating agents.

[0060] The polyester resin of the present invention may be blended with a resin other than the polyester resin of the present invention (hereinafter, sometimes referred to as "other resins".) The other resins are not particularly limited, and examples thereof include polyester resins other than the polyester resin of the present invention, polycarbonate resins, polyamide resins, polyethylene resins, polypropylene resins, and other general-purpose thermoplastic resins.

[0061] [Uses of polyester resin composition] The polyester resin and polyester resin composition of the present invention can be molded by various molding methods applicable to general-purpose plastics. Examples of molding methods include compression molding (compression molding, lamination molding, stampable molding), injection molding, extrusion molding and co-extrusion molding (film molding by an inflation method or a T-die method, laminate molding, pipe molding, electric wire / cable molding, molding of profiled materials), hollow molding, calendar molding, foam molding (melt foam molding, solid-phase foam molding), solid molding (uniaxial stretch molding, biaxial stretch molding, roll rolling molding, stretch-oriented nonwoven fabric molding, thermoforming (vacuum forming, pressure forming), plastic processing, powder molding (rotational molding), various nonwoven fabric moldings (dry method, adhesion method, entanglement method, spunbond method, etc.), and the like.

[0062] The polyester resin and polyester resin composition of the present invention are particularly preferably applied to injection molded articles, extrusion molded articles, foam molded articles, and blow molded articles.Specific forms of the polyester resin and polyester resin composition of the present invention are particularly preferably applied to various parts, films, containers, and fibers in the electric and electronic fields and automobiles. These molded articles can also be subjected to secondary processing according to various purposes in order to impart surface functions such as chemical functions, electrical functions, magnetic functions, mechanical functions, friction / wear / lubrication functions, optical functions, and thermal functions. Examples of secondary processing include embossing, painting, adhesion, printing, metallizing (plating, etc.), machining, and surface treatment (antistatic treatment, corona discharge treatment, plasma treatment, photochromism treatment, physical vapor deposition, chemical vapor deposition, coating, etc.). EXAMPLES

[0063] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples as long as the gist of the invention is not exceeded. The methods for measuring various physical properties and the like are as follows.

[0064] [Intrinsic viscosity (IV)] The polyester resins obtained in the examples and comparative examples were dissolved in phenol / 1,1,2,2-tetrachloroethane (1:1 weight ratio) at a concentration of 0.5 g / dL, and the viscosity was determined from the solution viscosity measured at 30° C. The Huggins constant was 0.32.

[0065] [Sphericity] The pellets obtained in each Example and Comparative Example were placed on a horizontal plane and photographed using a digital camera placed parallel to the plane. The contours of the pellets were detected from the photographed images using the OpenCV library, and the contours were approximated as an ellipse. Any method may be used for image processing. For 60 pellets, the major axis and the area within the contour of the pellets in the ellipse approximation were calculated using the images processed as described above, and the sphericity was calculated using the following formula, and the average and median values ​​are shown in Table 1. Sphericity = (4 × area) / (π × square of major axis)

[0066] Manufacturing Example 1 A reaction vessel equipped with a stirrer, a nitrogen inlet, a heater, a thermometer, and a rectification column was charged with 42.85 kg of 2,5-furandicarboxylic acid, 30.6 L of 1,2-ethanediol, and 14.3 g of a 35% aqueous solution of tetraethylammonium hydroxide as raw materials, and the inside of the reaction vessel was filled with nitrogen. Next, heating and stirring were started, the temperature was raised to 100° C. to 200° C. over 2 hours, and the reaction was carried out at 200° C. for 2 hours and 30 minutes, and the distillate was collected to allow the esterification reaction to proceed. Then, the mixture was transferred to a reactor equipped with a pressure reduction port, and 888.5 g of a 1,2-ethanediol solution in which 2.0% by weight of tetrabutyl titanate was dissolved was added. The temperature was raised to 260°C over 2 hours, and the pressure was gradually reduced so that the pressure reached about 130 Pa in 1.5 hours, and then the pressure was maintained at 130 Pa. When 3 hours and 50 minutes had elapsed since the start of the pressure reduction, the stirring was stopped, the pressure was restored, and the polycondensation reaction was terminated to obtain polyester A. Polyester A was extracted in the form of a strand from the bottom of the reaction vessel, cooled through a cooling water tank, and then cut by a pelletizer to obtain cylindrical pellets. The obtained pellets were called pellet A (Comparative Example 1). The intrinsic viscosity of polyester A was 0.74 dL / g.

[0067] Manufacturing Example 2 Polyester A was kneaded at 240°C using a twin-screw kneading extruder (HK-25D, manufactured by Parker Corporation) and granulated using an underwater cutter EPU10 (manufactured by EPCON). The die plate had a diameter of 2.9 mm x 1 hole. The resin was extruded from the die into water, cut instantly, and separated from the water to obtain pellets. The water temperatures were 11°C, 25°C, and 80°C. These pellets were designated as pellets B-1 (Example 1), pellets B-2 (Example 2), and pellets B-3 (Example 3).

[0068] The sphericity of each pellet determined by the above method is shown in Table 1. [Table 1]

[0069] It was confirmed that in Production Example 2, spherical pellets were obtained at all water temperatures.

[0070] Examples 1 to 3 and Comparative Example 1 (Heat treatment test) The pellets A and pellets B-1 to B-3 obtained above were each placed in a 28-mesh mesh basket in an amount of 8 g. They were then placed in an inert oven (Yamato Scientific 410I), and heat-treated under the conditions shown in Table 1 while nitrogen was circulated at 30 L / min. The evaluation criteria were as follows. The results are shown in Table 1. ○: No fusion △: Melted but can be loosened ×: Melted and cannot be loosened

[0071] (Impact resistance test) 1 kg each of pellet A (Comparative Example 1) and pellet B-2 (Example 2) was collected and placed in a plastic bag and the bag was closed. Both ends of the plastic bag were held by hand and the bag was vibrated back and forth 300 times. After that, the occurrence of fragments and fine powder derived from the pellets was observed. The evaluation criteria were as follows. ○: No debris or fine powder is observed on the surface of the plastic bag. ×: Fragments or fine powder were observed on the surface of the plastic bag.

[0072] [Table 2]

[0073] The results in Table 2 support the idea that spherical pellets are less likely to fuse when heated than cylindrical pellets. It was also found that spherical pellets are less likely to crack or produce fine powder when subjected to impact. [Industrial Applicability]

[0074] According to the present invention, it is possible to easily increase the molecular weight of a polyester resin having 2,5-furandicarboxylic acid units and ethylene glycol units, and to obtain a molded article having high mechanical properties. In addition, it is possible to obtain a polyester resin having both heat resistance and mechanical properties such as strength. Polyethylene furanoate (PEF), a polyester resin containing 2,5-furandicarboxylic acid units and ethylene glycol units, is expected to be used as an alternative to PET for various molded products such as bottles, films, and fibers. In addition, it has excellent gas barrier properties and can be produced from renewable resources, making it highly valuable.

Claims

1. A polyester resin pellet having a 2,5-furandicarboxylic acid unit and an ethylene glycol unit, the pellet being characterized in that the shape of the pellet is spherical.

2. 2. The polyester resin pellet according to claim 1, wherein at least one of an average value and a median value of sphericity of the spherical pellets is 0.7 to 1.

0.

3. 3. The polyester resin pellet according to claim 1, further comprising 0.1 to 50% by weight of a polyalkylene ether glycol having 5 to 20 carbon atoms and a number average molecular weight of 500 to 6,000.

4. A method for producing a polyester resin having 2,5-furandicarboxylic acid units and ethylene glycol units, comprising the steps of producing spherical pellets and crystallizing the pellets by heating.

5. The method for producing a polyester resin according to claim 4, wherein the spherical pellets are obtained by extruding a molten resin into air or water and cutting the resin.

6. The method for producing a polyester resin according to claim 4 or 5, wherein the spherical pellets are heated at a temperature of 100° C. or more and 200° C. or less to crystallize the pellets.

7. The method for producing a polyester resin according to any one of claims 4 to 6, further comprising heating to a temperature of 170°C or higher and 215°C or lower to improve the intrinsic viscosity (IV).

8. The method for producing a polyester resin according to any one of claims 4 to 7, wherein the polyester resin contains a crystal nucleating agent.

9. The method for producing a polyester resin according to any one of claims 4 to 8, wherein the polyester resin further contains 0.1 to 50% by weight of a polyalkylene ether glycol having 5 to 20 carbon atoms and a number average molecular weight of 500 to 6000.

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