Polyester resin and method for producing polyester resin

Abstract

To provide a polyester resin that uses bis-2-hydroxyethyl terephthalate as a raw material, and has a small amount of thermally deteriorated substance occurred during a polymerization step.SOLUTION: Polyester resin polymerized by using bis-2-hydroxyethyl terephthalate satisfies the followings (a) to (d): (a) when the total amount of the total acid component is 100 mol%, 50 to 97.5 mol% is terephthalic acid, and 2.5 to 40 mol% is isophthalic acid; (b) when the total amount of the total glycol component is 100 mol%, the content of diethylene glycol is 4.0 mol% or less; (c) carboxyl end group concentration is 40 equivalent / t or less; and (d) the number of foreign matters is 5,000 pcs. / m2 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a polyester resin that uses bis-2-hydroxyethyl terephthalate as a starting material and can be processed into various molded articles, and a method for producing the same. [Background technology]

[0002] Polyester resins, typified by polyethylene terephthalate (PET), have a high melting point, chemical resistance, and are relatively low cost, and are therefore widely used in molded products such as fibers, films, and PET bottles. Obtaining PET by polymerizing bis-2-hydroxyethyl terephthalate (BHET) as a starting material has been investigated (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2005 / 035621 Summary of the Invention [Problem to be solved by the invention]

[0004] However, as in Patent Document 1, polyester resins polymerized using only BHET have problems such as poor thermal stability and mechanical properties due to the large amount of diethylene glycol produced as a by-product. Furthermore, polyester resins are required to have a sufficient reduction in the amount of foreign matter, such as thermal degradation products, generated during polymerization, and to have good color tone, in order to ensure the various properties of the resulting molded products.

[0005] Therefore, an object of the present invention is to solve the above problems and to provide a polyester resin which is obtained by polymerizing BHET as a starting material, which contains small amounts of foreign matter and diethylene glycol in the resin, and which has a good color tone. [Means for solving the problem]

[0006] As a result of extensive research in light of the problems of the prior art, the present inventors have discovered that the above-mentioned object can be achieved by incorporating a specific range of isophthalic acid as a dicarboxylic acid component in a polyester resin polymerized using bis-2-hydroxyethyl terephthalate (BHET) and by undergoing a specific esterification reaction or polycondensation reaction, thereby completing the present invention.

[0007] That is, the present invention relates to the following polyester resin, a method for producing the same, and fibers, molded articles, and films obtained using the polyester resin. (I) A polyester resin polymerized using bis-2-hydroxyethyl terephthalate, which is characterized by satisfying the following (a) to (d): (a) When the total amount of all acid components is taken as 100 mol %, 50 to 97.5 mol % is terephthalic acid and 2.5 to 40 mol % is isophthalic acid. (b) When the total amount of all glycol components is 100 mol%, the content of diethylene glycol is 4.0 mol% or less. (c) The carboxyl end group concentration is 40 equivalents / t or less. (d) Number of foreign particles: 5,000 / m 2 is (II) A method for producing the polyester resin (1), comprising the following steps (1) and (2): (1) A process of adding ethylene glycol and isophthalic acid to molten bis-2-hydroxyethyl terephthalate and carrying out an esterification reaction under heat treatment conditions of 200 to 280°C to obtain a reaction product. (2) adding a polymerization catalyst to the reaction product and carrying out a polycondensation reaction at a temperature of 260 to 290°C under reduced pressure of 1.0 hPa or less; (III) Fibers comprising the polyester resin of (I). (IV) A molded article comprising the polyester resin of (I). (V) A film containing the resin of (I). [Effects of the Invention]

[0008] According to the present invention, by using bis-2-hydroxyethyl terephthalate and containing isophthalic acid as the glycol component in a specific range, it is possible to obtain a polyester resin that has a good color tone and that generates a small amount of foreign matter such as thermal degradation products and a small amount of diethylene glycol as a by-product during polymerization. Furthermore, products (e.g., direct blow-molded articles and binder fibers) obtained from the polyester resin of the present invention can exhibit excellent quality. For example, when a molded article is formed by direct blow molding, whitening due to crystallization is suppressed, and when used as a binder fiber, the tensile strength is good.

[0009] According to the method for producing a polyester resin of the present invention, it is possible to efficiently and reliably produce the polyester resin of the present invention as described above. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is an example of a DSC curve showing crystallization at lower temperatures obtained by DSC for a polyester resin of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] The polyester resin of the present invention is a polyester resin polymerized using bis-2-hydroxyethyl terephthalate, and satisfies the following (a) to (d): (a) When the total amount of all acid components is taken as 100 mol %, 50 to 97.5 mol % is terephthalic acid and 2.5 to 40 mol % is isophthalic acid. (b) When the total amount of all glycol components is 100 mol%, the content of diethylene glycol is 4.0 mol% or less. (c) The carboxyl end group concentration is 40 equivalents / t or less. (d) Number of foreign particles: 5,000 / m 2 is In the present invention, the term "foreign matter" refers to a substance generated by thermal degradation during the esterification reaction or polycondensation.

[0012] The bis-2-hydroxyethyl terephthalate is not particularly limited, and examples thereof include those obtained by crushing used PET products and the like and depolymerizing them with ethylene glycol or the like, those obtained by subjecting terephthalic acid to an esterification reaction with ethylene glycol, and commercially available products.

[0013] When bis-2-hydroxyethyl terephthalate is obtained by depolymerization of used PET products or the like, it may contain metal components. The metal component content in bis-2-hydroxyethyl terephthalate is preferably 300 ppm or less, more preferably 150 ppm or less, even more preferably 100 ppm or less, and even more preferably 50 ppm or less, in order to further reduce the amount of foreign matter in the resulting polyester resin and improve various properties. The metal components are, for example, derived from metal catalysts contained in the used PET products that are the raw material, but are not limited thereto.

[0014] The polyester resin of the present invention has a diethylene glycol content of 4.0 mol% or less, preferably 3.0 mol% or less, and more preferably 2.0 mol% or less, when the total amount of all glycol components is taken as 100 mol%. The polyester resin of the present invention obtained by the production method of the present invention uses ethylene glycol as one of the raw materials, and diethylene glycol may be generated as a by-product during this process. By keeping the diethylene glycol content at 4.0 mol% or less, a polyester resin with low levels of foreign matter (described below) and excellent transparency can be obtained, making it possible to efficiently produce molded products such as fibers, injection-molded articles, various blow-molded articles, sheets, and films. The lower limit of the diethylene glycol content can be, for example, 0.5 mol%, but is not limited thereto.

[0015] In the polyester resin of the present invention, when the total amount of all glycol components is taken as 100 mol%, the ethylene glycol (EG) content is preferably 80 mol% or more, and more preferably 90 mol% or more. If the EG content is less than 80 mol%, the amount of diethylene glycol produced as a by-product increases, and various physical properties such as heat resistance may be deteriorated.

[0016] The polyester resin of the present invention has a foreign matter content of 5,000 particles / m as measured by the method described in the Examples below. 2 less than 1000 pieces / m 2 More preferably, it is 500 pieces / m or less. 2 More preferably, it is 300 particles / m or less. 2 It is particularly preferable that the amount of foreign matter is below 100%. By sufficiently reducing the amount of foreign matter, a polyester resin can be obtained that has excellent properties (transparency, mechanical properties) of the resulting molded article and excellent processing operability in the spinning step or film-forming step. The lower the lower limit of the amount of foreign matter, the better.

[0017] The polyester resin of the present invention has remarkably excellent transparency, and when molded into a molded piece (e.g., 90 mm in length, 50 mm in width, and 10 mm in thickness) using direct blow molding, the haze is 4.0% or less, preferably 3.0% or less, and more preferably 2.0% or less. The method for determining haze will be described later in the Examples.

[0018] In the polyester resin of the present invention, when the total amount of all dicarboxylic acid components is taken as 100 mol%, the content of isophthalic acid (IPA) is 2.5 mol% to 40 mol%, and preferably 4.0 mol% to 38 mol%. If the IPA content is less than 2.5 mol%, the transparency during molding and the adhesiveness of fibers will be poor, while if it exceeds 40 mol%, the crystallinity of the resulting resin composition will be reduced and it will become amorphous, making it difficult to melt-spin, stretch, and turn into fibers.

[0019] In particular, the copolymerization amount of isophthalic acid can be adjusted to a more preferred range within the range of 2.5 to 40 mol % depending on the application of the resulting polyester resin, and for example, when used for molding purposes, the copolymerization amount of isophthalic acid is preferably 2.5 to 20 mol %, more preferably 3 to 10 mol %, and even more preferably 4 to 8 mol %. By copolymerizing 2.5 to 20 mol% isophthalic acid, the crystallization rate of the polyester resin can be adjusted to a level suitable for direct blow molding, preventing whitening due to crystallization during direct blow molding. If the copolymerization amount of isophthalic acid is less than 2.5 mol%, the crystallization rate of the resin composition will be too fast, and the molded product will crystallize and whiten during direct blow molding, resulting in poor transparency. On the other hand, if the copolymerization amount of isophthalic acid exceeds 20 mol%, the resin composition will become amorphous, making it more susceptible to blocking during high-temperature drying or solid-state polymerization.

[0020] Furthermore, when used as a binder fiber, the copolymerization amount of isophthalic acid is preferably 10 to 40 mol%, and more preferably 20 to 38 mol%. By copolymerizing 10 to 40 mol% of isophthalic acid, the melting point of the polyester resin can be lowered and the polyester resin can be made amorphous, making it suitable for binder applications. If the copolymerization amount of isophthalic acid is less than 10 mol%, the melting point of the resin will be high, which may make it unsuitable for binder fiber applications. On the other hand, if the copolymerization amount of isophthalic acid exceeds 40 mol%, the crystallinity of the resulting resin composition will decrease and the resin will become amorphous, which may make it difficult to melt-spin and draw the resin into fibers.

[0021] The polyester resin of the present invention is preferably composed mainly of polyethylene terephthalate (PET), specifically, when the total amount of all acid components is taken as 100 mol %, 50 to 97.5 mol % is terephthalic acid. The content of PET in the polyester resin of the present invention is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90 to 100% by mass.

[0022] In particular, in the production method of the present invention described below, a PET that is usually a polycondensation product of ethylene glycol and terephthalic acid and copolymerized with isophthalic acid can be obtained, but the following components may also be copolymerized as other acid components or glycol components. Two or more of these components may be contained.

[0023] Examples of the acid component include 5-sulfoisophthalic acid, phthalic acid, phthalic anhydride, naphthalenedicarboxylic acid, adipic acid, sebacic acid, 1,4-cyclohexanedicarboxylic acid, dodecanedioic acid, and other dimer acids, as well as trimellitic anhydride, trimellitic acid, pyromellitic acid, 1,4-cyclohexanedicarboxylic acid, sebacic acid, dimer acids, ε-caprolactone, itaconic acid, and phosphorus-based compounds (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 2-(9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-yl)-methylsuccinic acid bis-(2-hydroxyethyl)-ester, and 2-carboxyethylphenylphosphinic acid).

[0024] Examples of glycol components include neopentyl glycol, 1,4-butanediol, 1,2-propylene glycol, 1,5-pentanediol, 1,3-propanediol, 1,6-hexamethylenediol, 1,4-cyclohexanedimethanol, dimer diol, butylethylpropanediol, (2-methyl-1,3-propanediol, trimethylolpropane, glycerin, pentaerythritol, polyethylene glycol, and ethylene oxide adducts of bisphenol A or bisphenol S.

[0025] When the polyester resin of the present invention contains a metal component, the content thereof is preferably 1000 ppm or less, more preferably 500 ppm or less, even more preferably 300 ppm or less, and even more preferably 200 ppm or less, since this provides excellent properties.

[0026] The polyester resin of the present invention has a carboxyl terminal group concentration of 40 equivalents / t or less, preferably 35 equivalents / t or less, and more preferably 30 equivalents / t or less. If the carboxyl terminal group concentration exceeds 40 equivalents / t, the viscosity of the molten polymer may decrease, various physical properties such as heat resistance may decrease, and color tone may deteriorate. The lower limit of the carboxyl terminal group concentration may be, for example, about 5 equivalents / t, but is not limited to this.

[0027] The polyester resin of the present invention preferably has an average pressure increase rate of 0.6 MPa / h or less, more preferably 0.5 MPa / h or less, and even more preferably 0.4 MPa / h or less, as measured by the following method. The average pressure increase rate in the present invention is an example of an index of the amount of foreign matter, and a lower average pressure increase rate indicates a lower amount of foreign matter mixed in. The lower limit of the average pressure increase rate can be, for example, about 0.01 MPa / h, but is not limited to this.

[0028] The average pressure rise rate was measured using a pressure rise tester including an extruder and a pressure sensor. The filter was set at the tip of the extruder, polyester resin was melted in the extruder at 300°C, and the melt was extruded from the filter at a discharge rate of 29.0 g / min. The pressure value at the start of extrusion was defined as the "initial pressure value (MPa)" and the pressure value at the point when extrusion was continued for 12 hours was defined as the "final pressure value (MPa)." The average pressure rise rate was calculated based on these pressure values ​​using the following formula A: Average pressure rise rate (MPa / h) = (final pressure value - initial pressure value) / 12) A) This is the method used.

[0029] The extruder, filter, etc. used in the above measurement may be any known or commercially available product as long as it satisfies the requirements of the present invention. If necessary, a reinforcing material may be added to the filter within a range that does not substantially affect the measurement results.

[0030] The intrinsic viscosity of the polyester resin of the present invention is not particularly limited, but is preferably 0.44 to 0.80. Furthermore, the polyester resin of the present invention can also be used for molding purposes by being subjected to a solid-state polymerization process to achieve a high degree of polymerization, as described below. In this case, the intrinsic viscosity of the resulting polyester resin is preferably 0.80 to 1.25.

[0031] The polyester resin of the present invention is crystalline, and the DSC curve showing the crystallization upon cooling determined by DSC preferably satisfies the following formula (1): The larger the b / a ratio, the better the crystallinity upon cooling, but to achieve the intended effects of the present invention, it is preferable that b / a be 0.007 or less. b / a≦0.007(mW / mg·℃)···(1) The method for determining the value of b / a will be described later in the examples.

[0032] The melting point of the resulting polyester resin is not particularly limited, but is preferably 210 to 250°C. In addition, when the polyester resin to be obtained does not have a melting point, it is preferable that the glass transition temperature is 62 to 80°C.

[0033] The method for producing a polyester resin of the present invention includes the following steps (1) and (2). (1) A process of adding ethylene glycol and isophthalic acid to molten bis-2-hydroxyethyl terephthalate and carrying out an esterification reaction under heat treatment conditions of 200 to 280°C to obtain a reaction product. (2) adding a polymerization catalyst to the reaction product and carrying out a polycondensation reaction at a temperature of 260 to 290°C under reduced pressure of 1.0 hPa or less;

[0034] In step (1), the crystallinity of the resulting polyester resin can be controlled by using IPA in addition to BHET as a starting material.

[0035] Furthermore, ethylene terephthalate oligomer may be added as a starting material, if necessary, within the range that does not impair the effects of the present invention.

[0036] The amounts (mass ratio) of the starting materials used in step (1) are not particularly limited as long as the content of IPA in the resulting polyester resin falls within the above-mentioned specific range. For example, it is preferable that (BHET) / (IPA) is 70 / 30 to 97 / 3.

[0037] Although the method for adding IPA or ethylene glycol to BHET is not particularly limited, it is preferable to add the mixture under normal pressure with stirring, and more preferably to add the mixture under purged conditions with a small amount of inert gas (generally nitrogen gas). This prevents oxygen from being mixed in, and more reliably prevents deterioration of color tone.

[0038] The method for melting bis-2-hydroxyethyl terephthalate is not particularly limited. For example, the bis-2-hydroxyethyl terephthalate may be charged into a reaction vessel in a solid state such as flakes, or may be heated and melted to a molten state.

[0039] In step (1), it is preferable to use all raw materials so that the molar ratio (G / A) of (total glycol components) / (total acid components) is 1.1 to 3.0, more preferably 1.5 to 2.8, and even more preferably 2.0 to 2.5. By setting the molar ratio to 1.1 or more, the esterification reaction is facilitated. By setting the ratio to 3.0 or less, the amount of diethylene glycol by-product can be suppressed, and various physical properties such as heat resistance can be maintained.

[0040] In step (1), the reaction temperature (particularly the internal temperature of the reactor) is preferably set in the range of 200 to 280°C, more preferably in the range of 230 to 280°C. If the temperature is below 200°C, the reaction time will be long, which may result in poor productivity. In addition, the reaction product may solidify, which may worsen operability or prevent the esterification reaction from proceeding. On the other hand, if the temperature exceeds 280°C, the amount of diethylene glycol produced as a by-product will increase, and the amount of foreign matter due to thermal decomposition will increase.

[0041] The reaction time in step (1) (the reaction time from the end of the introduction of the raw materials) is not particularly limited, but is usually preferably within 4 hours, and more preferably within 2 hours, particularly from the viewpoints of suppressing the amount of diethylene glycol by-product and suppressing deterioration in the color tone of the polyester. The lower limit of the reaction time is not particularly limited, but is, for example, 1 hour.

[0042] The internal pressure in step (1) may be normal pressure, or the reaction may be carried out under pressure as needed. The internal pressure of the reactor is preferably 0 to 0.5 MPa, more preferably 0.05 to 0.3 MPa.

[0043] The reaction apparatus used in the production method of the present invention is not particularly limited, and known or commercially available apparatuses can be used. In particular, although there are no particular problems with the volume, shape of the stirring blades, etc. of the reactor, a commonly used esterification reactor can be used, and in order to efficiently proceed with the depolymerization reaction, it is preferable to use a reactor having a structure equipped with a distillation column that does not distill ethylene glycol out of the system.

[0044] The reaction product obtained in step (1) is a liquid and may be subjected to a filtration step. Filters that can be used for filtration include, for example, metal filters such as stainless steel filters. The filter type is not particularly limited, and examples include screen changer filters, leaf disc filters, candle-type sintered filters, etc. The filtration particle size of the filter is preferably 10 to 25 μm.

[0045] In step (2), a polycondensation catalyst is added to the reaction product, and the reaction product is subjected to a polycondensation reaction at a temperature of 260 to 290° C. under a reduced pressure of 1.0 hPa or less.

[0046] The polycondensation catalyst is not particularly limited, and for example, at least one of a germanium compound, an antimony compound, a titanium compound, a cobalt compound, etc. Alternatively, an organic sulfonic acid compound such as 2-sulfobenzoic anhydride, o-sulfobenzoic acid, m-sulfobenzoic acid, p-sulfobenzoic acid, 5-sulfosalicylic acid, benzenesulfonic acid, o-aminobenzenesulfonic acid, m-aminobenzenesulfonic acid, p-aminobenzenesulfonic acid, p-toluenesulfonic acid, methyl p-toluenesulfonate, 5-sulfoisophthalic acid, or a salt thereof may be used as the polycondensation catalyst.

[0047] The amount of the polycondensation catalyst used is not particularly limited, but for example, it is 5 × 10 -5 It is preferable to set the concentration to 6×10 moles / unit or more. -5 The upper limit of the amount used is, for example, 1 × 10 -3 It can be, but is not limited to, moles / unit.

[0048] When BHET obtained by depolymerizing used PET products is used as a raw material, the polymerization catalyst residue contained in this raw material may also act as a catalyst during the polycondensation reaction. Therefore, it is preferable to adjust the amount of polycondensation catalyst used taking into account the type and content of the polymerization catalyst contained in the raw material BHET.

[0049] During the polycondensation reaction, if necessary, a fatty acid ester capable of adjusting the melt viscosity, a hindered phenol-based antioxidant, or a phosphorus compound capable of suppressing thermal decomposition of the resin can also be added in addition to the polycondensation catalyst.

[0050] Examples of fatty acid esters include beeswax (a mixture mainly composed of myricyl palmitate), stearyl stearate, behenyl behenate, stearyl behenate, glycerin monopalmitate, glycerin monostearate, glycerin distearate, glycerin tristearate, pentaerythritol monopalmitate, pentaerythritol monostearate, pentaerythritol distearate, pentaerythritol tristearate, pentaerythritol tetrastearate, and dipentaerythritol hexastearate. Among these, glycerin monostearate, pentaerythritol tetrastearate, and dipentaerythritol hexastearate are preferred. These can be used alone or in combination of two or more.

[0051] Examples of hindered phenol antioxidants include 2,6-di-t-butyl-4-methylphenol, n-octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate, tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane, tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate, 4,4'-butylidenebis-(3-methyl-6-t-butylphenol), ... Examples of suitable compounds include ethylene glycol-bis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate] and 3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1'-dimethylethyl}-2,4,8,10-tetraoxaspiro[5,5]undecane, but tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane is preferred from the standpoint of effectiveness and cost. These compounds can be used alone or in combination of two or more.

[0052] Examples of phosphorus compounds that can be used include phosphorous acid, phosphoric acid, trimethyl phosphite, triphenyl phosphite, tridecyl phosphite, trimethyl phosphate, tridecyl phosphate, triphenyl phosphate, etc. These compounds can be used alone or in combination of two or more.

[0053] In step (2), the polycondensation reaction is carried out at a temperature of 260 to 290°C under reduced pressure of 1.0 hPa or less. If the polycondensation reaction temperature is less than 260°C or the pressure during the polycondensation reaction exceeds 1.0 hPa, the polycondensation reaction time will be long, resulting in poor productivity. In addition, the reaction time will be long, and the amount of diethylene glycol will increase due to thermal history, which may increase the amount of foreign matter. Among these, the polycondensation reaction temperature is more preferably 270°C or higher, as this facilitates the polycondensation reaction. On the other hand, if the polycondensation reaction temperature is too high, the polymer will become discolored due to thermal decomposition, resulting in a deterioration in color tone, and the amount of foreign matter may also increase due to thermal decomposition, so the upper limit of the polycondensation reaction temperature is preferably 290°C or lower.

[0054] In the present invention, if necessary, the polyester resin obtained as described above may be further subjected to a crystallization step, thereby increasing the crystallinity of the polyester resin.

[0055] The crystallization conditions are not particularly limited, but can be carried out by, for example, heat treatment at the crystallization temperature of the polyester resin used or a temperature higher. For example, when the polyester resin is PET, since the crystallization temperature of PET is usually about 130°C, heat treatment can be carried out at a temperature of, for example, 135°C or higher (preferably 140 to 180°C). The heat treatment time can be changed depending on the heat treatment temperature, etc., and can be, for example, about 30 minutes to 20 hours.

[0056] In the present invention, if necessary, the resin obtained in the polycondensation step or the crystallization step can be further subjected to a solid-state polymerization reaction, thereby further increasing the degree of polymerization of the polyester resin and thereby making it possible to obtain physical properties more suitable for molding.

[0057] The conditions for the solid-state polymerization reaction are not particularly limited, but it is preferable to carry out the heat treatment so that the intrinsic viscosity of the resulting polyester resin becomes 0.80 to 1.25 (particularly preferably 0.82 to 1.24). More specifically, for example, the heat treatment can be carried out by heat treating the resulting polyester resin in an inert gas atmosphere at about 180 to 240°C. The heat treatment time depends on the heat treatment temperature, etc., but is usually about 5 to 50 hours.

[0058] In order to reduce the acetaldehyde content, the solid-state polymerization may include, for example, a step of adding an additive that prevents thermal decomposition of PET and a step of crystallization.

[0059] The polyester resin of the present invention may be used for producing various products either as it is or after being mixed with other additives as necessary to form a resin composition.

[0060] Examples of additives include the above-mentioned polymerization catalysts, antioxidants, phosphorus compounds, and the like, as well as colorants, pigments, dispersants, fillers, ultraviolet absorbers, thickeners, antistatic agents, color inhibitors, stabilizers, flame retardants, lubricants, and the like, so long as the additives do not impair the effects of the present invention.

[0061] In particular, a coloring inhibitor can be preferably used. For example, phosphorus compounds such as phosphorous acid, phosphoric acid, trimethyl phosphite, triphenyl phosphite, tridecyl phosphite, trimethyl phosphate, tridecyl phosphate, and triphenyl phosphate can be used. These phosphorus compounds can be used alone or in combination of two or more.

[0062] In addition, in order to suppress coloration due to thermal decomposition of the polyester resin, additives such as cobalt compounds such as cobalt acetate, manganese compounds such as manganese acetate, anthraquinone dye compounds, copper phthalocyanine compounds, etc. may be contained.

[0063] Various types of products can be adopted in the same form as conventional polyester products. The polyester product can be suitably used in the form of, for example, fibers, molded articles, films, etc.

[0064] In the case of fibers, for example, fibers can be produced by a production method including a step of melting a raw material containing the resin of the present invention and spinning it. This makes it possible to produce ultrafine fibers with a single fiber fineness of 0.8 dtex or less (preferably 0.6 to 0.3 dtex). The spinning method can be carried out under known conditions.

[0065] As described above, the polyester resin of the present invention has a low content of foreign matter and also a low content of diethylene glycol, and therefore, troubles such as yarn breakage are unlikely to occur in any of the melt spinning, drawing and heat treatment, and winding steps, and polyester fibers can be produced with good productivity.

[0066] The fiber of the present invention containing the polyester resin of the present invention may be, for example, either a monofilament or a multifilament, and may be either a long fiber or a short fiber. In fiber production, it is generally more difficult to produce a multifilament, but the fiber of the present invention can be a multifilament having, for example, a single yarn fineness of 0.3 to 30 decitex, a single yarn count of 2 to 300, a total fineness of 5 to 350, a strength of 1 to 5 cN / dtex, and an elongation of 10 to 400%. Among these, ultrafine fibers, which are more difficult to produce, can also be obtained.

[0067] In particular, binder fibers using the polyester resin of the present invention have excellent fusibility and adhesion of the fibers because the crystallinity and melting point can be controlled.

[0068] The fiber of the present invention containing the resin of the present invention may be, for example, either a monofilament or a multifilament, and may be either a long fiber or a short fiber. The fiber of the present invention may be used as either a main fiber or a binder fiber. Furthermore, the fiber may be a fiber made only of the resin of the present invention, or a composite fiber made of the resin of the present invention together with another resin.

[0069] When the fiber of the present invention is used as a binder fiber, it may be a fully melted binder fiber using only the resin of the present invention, or a core-sheath binder fiber using the resin of the present invention only in the sheath portion. Furthermore, a colored pigment may be added during melt spinning of the fiber, provided that the effects of the present invention are not impaired. Examples of colored pigments include inorganic pigments such as iron oxide, ultramarine, and titanium oxide, and organic pigments such as cyanine, polyazo, anthraquinone, and carbon black. To achieve the desired color, these colored pigments may be appropriately selected and used alone or in blends. The colored pigment may be added at any stage of the composite fiber spinning process. Examples of the method include the masterbatch method and the liquid color method. However, the masterbatch method is preferred due to the stability during melt spinning and the ease of handling the colored pigment. When using the masterbatch method, either a method of measuring and mixing the raw material pellets and then melt-spinning, or a method of measuring and mixing separately melted polymers and then spinning, may be used.

[0070] When the fiber of the present invention is a staple fiber, it can have, for example, a single filament fineness of 0.5 to 25.0 decitex, a strength of 0.1 to 6.0 cN / dtex, and an elongation of 20 to 600%. As described above, the resin of the present invention has excellent thermal stability due to the diethylene glycol content being less than a specific amount. Therefore, when producing such staple fibers, single filament fusion during the spinning and drawing processes is suppressed, reducing the occurrence of variations in single filament fineness, and highly uniform fibers can be obtained with good operability. Furthermore, in the case of staple fibers used for wetlaid nonwoven fabrics, single filament fusion during the spinning and drawing processes is suppressed, resulting in fibers with good single filament dispersion in water. Furthermore, as described above, the resin of the present invention generates little thermal degradation products, resulting in low levels of foreign matter contamination. The low level of foreign matter improves the quality and strength of products such as nonwoven fabrics obtained when the fiber of the present invention is used as a main fiber or binder fiber.

[0071] The nonwoven fabric obtained using the fiber of the present invention may be dry- or wet-woven, and the basis weight of the nonwoven fabric is not particularly limited. When the fiber of the present invention is used as a binder fiber, the nonwoven fabric may be produced by, for example, a method in which the constituent low-melting-point polyester resin (the resin of the present invention) serves as a thermal adhesive component to integrate the fibers together by thermal bonding, or the constituent fibers may be three-dimensionally entangled with each other before thermal bonding.

[0072] The nonwoven fabric obtained using the fiber of the present invention may contain fibers other than the fiber of the present invention, for example, a nonwoven fabric using the fiber of the present invention as a binder fiber and fibers made of a polyester resin having a melting point higher than that of the resin of the present invention as a main fiber.

[0073] An example of a method for producing a drylaid nonwoven fabric is given below. In this example, the fiber of the present invention is used as a binder fiber and mixed with fibers other than the fiber of the present invention to obtain a drylaid nonwoven fabric. The ratio of the fiber of the present invention to the other fibers when mixed can be appropriately selected depending on the required properties of the nonwoven fabric, and the ratio of the fiber of the present invention is preferably about 10 to 90% by mass. These fibers (fibers that will become the constituent fibers) are fed into a carding machine and defibrated to produce a drylaid web. The obtained web is subjected to a thermal bonding treatment in a continuous heat treatment machine that performs a hot air treatment at a temperature at which the low-melting-point polyester resin that constitutes the fiber of the present invention melts or softens, resulting in a drylaid nonwoven fabric in which the constituent fibers are integrated by thermal bonding.

[0074] An example of a method for producing a wetlaid nonwoven fabric will be described below. As with drylaid nonwoven fabrics, the fiber of the present invention is used as a binder fiber and mixed with fibers other than the fiber of the present invention to obtain a wetlaid nonwoven fabric. The ratio of the fiber of the present invention to the other fibers when mixed can be appropriately selected depending on the required properties of the nonwoven fabric, and the ratio of the fiber of the present invention is preferably about 10 to 90% by mass. These fibers (fibers that will become the constituent fibers) are agitated and defibrated using a pulp disintegrator, and then a wetlaid web is produced using a papermaking machine. The obtained web is subjected to a thermal bonding treatment in a continuous heat treatment machine that performs a hot air treatment at a temperature at which the low-melting-point polyester resin that constitutes the fiber of the present invention melts or softens, resulting in a wetlaid nonwoven fabric in which the constituent fibers are integrated by thermal bonding.

[0075] Molded articles can be produced by applying various molding methods, such as press molding, extrusion molding, pressure molding, and blow molding, using raw materials containing the polyester resin of the present invention. This allows for the provision of various parts, including containers. The polyester resin of the present invention is particularly suitable for the production of blow-molded articles because of its low diethylene glycol content, excellent thermal stability, and excellent transparency. Therefore, a method for producing a molded article can be suitably employed, which includes a step of obtaining a parison from a melt containing the resin of the present invention and a step of blowing gas into the parison. This allows for the production of molded articles, such as containers.

[0076] In the case of a film, a raw material containing the polyester resin of the present invention can be molded by a known film-forming method. For example, a melt of the raw material is extruded through a T-die and then cooled with a casting roll to produce an unstretched sheet. The polyester resin of the present invention has a low content of foreign matter, a low content of diethylene glycol, and excellent thermal stability, so stretching in the MD and TD directions can be performed with good operability. The stretching method may be either uniaxial or biaxial stretching, and as a biaxial stretching method, either simultaneous biaxial stretching or sequential biaxial stretching can be used. As a result, a polyester film can be obtained that has properties such as strength and elongation almost similar to those when virgin polyester resin is used, and also has excellent transparency.

[0077] The thickness of the film is not limited, but can usually be set appropriately within the range of 10 to 50 μm. If necessary, the film can be laminated with other layers (for example, an adhesive layer, a heat seal layer, a surface protection layer, a print layer, a design layer, etc.) to be used as a laminate, and the laminate can be molded to be used as the various molded articles described above. [Example]

[0078] The features of the present invention will be described in more detail below with reference to examples and comparative examples. However, the scope of the present invention is not limited to the examples. Measurements and evaluations were carried out by the following methods. (a) Intrinsic viscosity The measurement was carried out at 20°C using an equal weight mixture of phenol and tetrachloroethane as a solvent.

[0079] (b) Isophthalic acid and diethylene glycol content The obtained polyester resin was dissolved in a mixed solvent of deuterated hexafluoroisopropanol and deuterated chloroform in a volume ratio of 1:20, and analyzed using a JEOL "LA-400 NMR" apparatus. 1 H-NMR was measured, and the contents of isophthalic acid and diethylene glycol were determined from the integrated intensity of the proton peaks of each component in the resulting chart.

[0080] (c) Melting point (Tm) Using a differential scanning calorimeter DSC-7 manufactured by PerkinElmer, measurements were carried out in a nitrogen stream at a temperature range of 25 to 280°C and a heating rate of 20°C / min.

[0081] (d) Glass transition temperature (Tg) The measurement was carried out under the same conditions as those for measuring the melting point.

[0082] (e) Carboxyl end group concentration 0.1 g of the obtained polyester resin was dissolved in 10 ml of benzyl alcohol, and 10 ml of chloroform was added to the solution, followed by titration with a 1 / 10 N potassium hydroxide benzyl alcohol solution to determine the viscosity.

[0083] (f) Color tone (b value) Sample pieces (20 pieces) were cut out from the blow-molded article (hollow container) obtained as described in (i) below, and the color tone of the sample pieces was measured using a color difference meter ND-Σ80 manufactured by Nippon Denshoku Industries Co., Ltd. The color tone was determined using a Hunter Lab colorimeter, and the b value was measured and taken as the average value of 20 values. A b value of 3.5 or less was determined to be good color tone. A b value of 3.0 or less is more preferable.

[0084] (g) Amount of foreign matter The number of foreign matters in the obtained resin was measured as follows: A sheet having a thickness of 0.1 mm was produced using a fisheye counter (gel counter) manufactured by Optical Control Systems under the conditions of an extruder temperature of 260 to 290°C, a rotation speed of 50 rpm, a winder temperature of 50°C, and a rotation speed of 5 m / min. 2 The number of foreign particles with a particle size of 25 μm or more per unit area was detected and counted.

[0085] (h) Formability The thickness of the body of blow-molded products (hollow containers) (100 samples) obtained as described in (i) below was measured, and samples with a difference in thickness between the thickest and thinnest parts of up to 0.30 mm were considered to have passed the test. If the number of passing samples was 90 or more, the moldability was evaluated as good (◯).

[0086] (i) Haze of molded products The resulting polyester resin was chipped and dried, and then extruded at 260°C using a direct blow molding machine (manufactured by Tahara) to form a cylindrical parison. While the parison was still softened, it was clamped in a mold to form a bottom, and then blown into a bottle. At this time, the bottom was formed when the parison reached a diameter of 3 cm and a length of 25 cm, and then blow molded to obtain a 350 ml hollow container (direct blow molded product). Haze was evaluated by the following method. Sample pieces (20 pieces) were cut out from the obtained container, and the turbidity was measured using a turbidity meter, Model 1001DP, manufactured by Nippon Denshoku Industries Co., Ltd. (air: haze 0%), and the average value of 20 was taken as the average value. The smaller this value, the better the transparency, and a value of 4% or less was judged to be excellent transparency. A haze of 3.5% or less is more preferable.

[0087] (j) Evaluation of binder fibers Using a spinneret with 2174 holes and a hole diameter of 0.35 mm, melt spinning was carried out at a throughput of 1630 g / min, a core-sheath mass ratio of 50 / 50, a spinning temperature of 270°C, and a spinning speed of 1100 m / min, with a polyethylene terephthalate core with an intrinsic viscosity of 0.70 and a polyester resin obtained in the examples as a sheath. The undrawn yarn obtained was converged to form a 115 ktex tow, which was then drawn at a drawing temperature of 56°C and a draw ratio of 3.5. The tow was then mechanically crimped using a push-in crimper and cut to a fiber length of 51 mm, yielding a heat-bondable sheath-core composite fiber with a fineness of 2.2 dtex. Unitika regular polyester fiber <121> 70% by mass of 1.7T51mm and 30% by mass of the core-sheath type composite fiber (used as binder fiber) obtained as described above were mixed to obtain a nonwoven fabric with a basis weight of 50 g / m after heat treatment.2 The fibers were fed into a carding machine (Yamato Kiko SC-500DI3HC) to produce a web, which was then heat-treated using a continuous heat treatment machine (Tsujii Senki Kogyo NFD-500E2) at an air volume of 57 m / min and 130°C for 1 min to produce a dry-laid nonwoven fabric. The dry-laid nonwoven fabrics thus obtained were evaluated for nonwoven fabric strength by the following method. The obtained nonwoven fabric was cut into samples of 150 mm in the MD direction and 50 mm in the CD direction, and the MD strength of the nonwoven fabric was measured using an autograph (Shimadzu Corporation AG-50KNI) at a tensile speed of 100 mm / min and a chuck distance of 100 mm. The number of samples was n=5. The tensile strength of the obtained nonwoven fabric was evaluated according to the following two levels. ○: Tensile strength 1500cN or more ×: Tensile strength less than 1500cN

[0088] (k) Crystallinity (b / a) The measurements were carried out using a PerkinElmer DSC-7 differential scanning calorimeter in a nitrogen stream at a temperature range of 25 to 280°C and a temperature increase / decrease rate of 20°C / min. The above b / a was determined from a DSC curve showing crystallization upon cooling. As shown in FIG. 1, in the DSC curve of a polyester resin, a is the difference (A1-A2) between the temperature A1 (°C) at the intersection of the tangent line with the maximum slope and the baseline in the DSC curve showing crystallization upon cooling and the temperature A2 (°C) at the intersection of the tangent line with the minimum slope and the baseline, and b is the value obtained by dividing the difference (B1-B2) between the calorific value B1 (mW) of the baseline at the peak top temperature and the calorific value B2 (mW) of the peak top by the sample weight (mg).

[0089] Example 1 93.8 parts by mass of bis-2-hydroxyethyl terephthalate was charged into an esterification reactor, and then, with the agitator of the esterification reactor (hereinafter referred to as "ES can") rotating, 3.4 parts by mass of ethylene glycol (EG) and 2.8 parts by mass of isophthalic acid (IPA) were added in a mixed state. At this time, the molar ratio of total glycol components / total acid components (hereinafter sometimes referred to as "G / A") in the raw materials was 2.06. The depolymerization reaction was then carried out under heat treatment conditions at 260°C for 1 hour, yielding a depolymerization product with a melt viscosity of 60 mPa·s at 260°C. The obtained depolymerization product was then pressure-fed to a polycondensation reactor (hereinafter referred to as a PC can) through a candle filter with a mesh size of 20 μm set between the esterification reactor and the polycondensation reactor. After that, 2.0 × 10 antimony trioxide was added as a polymerization catalyst. -4 The PC can was then decompressed for 60 minutes, and the melt polymerization reaction was carried out at a final pressure of 0.5 hPa and a temperature of 280°C for 3 hours, yielding a polyester resin with an intrinsic viscosity of 0.57.

[0090] Examples 1 to 7, Comparative Examples 1 to 6 In Example 1, the charged composition and the temperature in step (1) or (2) were changed as shown in Table 1 to obtain polyester resins.

[0091] In Comparative Example 2, the esterification reaction temperature was low, so the reaction did not proceed in step (1), and a polyester resin was not obtained. In Comparative Example 3, the polycondensation reaction temperature was low, so that the polymerization did not proceed in step (2), and a polyester resin was not obtained.

[0092] The polyester resin obtained in Example 1 and master chips of polyethylene terephthalate resin containing 1.5% by mass of silica particles were melt-kneaded in an extruder, fed to a T-die, extruded into a sheet, wrapped around a metal drum, cooled, and wound up to produce an unstretched sheet. Next, the edges of this unstretched sheet were held with clips in a tenter-type simultaneous biaxial stretching device, and simultaneously biaxially stretched at 180°C with a stretch ratio of 3.0 times in the MD direction and 3.3 times in the TD direction, followed by heat treatment with a relaxation rate of 5% in the TD direction, resulting in a biaxially stretched PET resin film with a thickness of 15 μm.

[0093] The polyester resins obtained in the examples and comparative examples and the evaluation results thereof are shown in Tables 1 and 2. [Table 1]

[0094] [Table 2]

[0095] Examples 1 to 7 The polyester resins obtained in Examples 1 to 7 had low amounts of diethylene glycol (DEG) by-product, low carboxyl end group concentrations (COOH end group amounts), low color tone b values, and suppressed generation of foreign matter. Furthermore, the moldability and transparency of the molded products were sufficient for practical use. As shown in Table 2, when the polyester resins obtained in Examples 3 and 4 were used as binder fibers to obtain nonwoven fabrics, the nonwoven fabrics had excellent tensile strength.

[0096] In Comparative Example 1, the esterification reaction temperature was high, and therefore the amount of DEG by-product and the number of foreign matters in the obtained polyester resin were large, and the resin was inferior.

[0097] The polyester resin obtained in Comparative Example 4 had a high polycondensation reaction temperature, resulting in a large amount of DEG by-product, a large number of impurities, and a large amount of COOH terminal groups, and had poor color tone. Furthermore, when used as a binder fiber to obtain a nonwoven fabric, the tensile strength was poor.

[0098] The polyester resin obtained in Comparative Example 5 had a high content of isophthalic acid, which resulted in a large amount of DEG by-product and COOH terminal groups. Furthermore, the polyester resin had poor moldability and, when used as a binder fiber to obtain a nonwoven fabric, the tensile strength was poor.

[0099] The polyester resin obtained in Comparative Example 6 had a low content of isophthalic acid, and therefore the molded product had a high haze value and poor transparency.

Claims

1. A polyester resin polymerized using bis-2-hydroxyethyl terephthalate, which is characterized by satisfying the following (a) to (d): (a) When the total amount of all acid components is taken as 100 mol %, 50 to 97.5 mol % is terephthalic acid and 2.5 to 40 mol % is isophthalic acid. (b) When the total amount of all glycol components is 100 mol %, the content of diethylene glycol is 4.0 mol % or less. (c) The carboxyl terminal group concentration is 40 equivalents / t or less. (d) The number of foreign particles is 5,000 / m 2 is

2. A method for producing the polyester resin according to claim 1, comprising the following steps (1) and (2): (1) A step of adding ethylene glycol and isophthalic acid to molten bis-2-hydroxyethyl terephthalate and carrying out an esterification reaction under heat treatment conditions of 200 to 280°C to obtain a reaction product. (2) A step of adding a polymerization catalyst to the reaction product and carrying out a polycondensation reaction at a temperature of 260 to 290°C and a reduced pressure of 1.0 hPa or less.

3. A fiber comprising the polyester resin of claim 1.

4. A molded article comprising the polyester resin of claim 1.

5. A film comprising the resin of claim 1.

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