JP2011089090A - Polyester resin composition, manufacturing method therefor, and film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester composition suitable for application as a film with excellent hydrolysis resistance and mechanical characteristics over a long term. <P>SOLUTION: The polyester resin composition includes 20 eq/t or less of a carboxylic acid terminal group, 1.3 to 3.0 mol/ton of alkali metal phosphate, and phosphoric acid of an amount 0.4 to 1.5 times that of the alkali metal phosphate in the molar ratio. It is crystalline and has a 37.4 wt.% or less of ester group concentration. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a polyester resin composition having good hydrolysis resistance, a method for producing the same, and a film.

  Polyester is excellent in mechanical properties, thermal properties, chemical resistance, electrical properties, and moldability, and is used in various applications. However, since the mechanical properties of polyester deteriorate due to hydrolysis, various studies have been made to suppress hydrolysis when used over a long period of time or when used in a damp state. In particular, a solar cell film requires a service life of 20 years or more outdoors, and therefore requires high hydrolysis resistance and flame retardancy.

For example, Patent Document 1 describes a method for producing a polyester containing an alkali metal or alkaline earth metal phosphate.
However, the initial COOH end group can be suppressed only with the metal phosphate, but it is difficult to suppress the increase in the COOH end group due to hydrolysis, and applications that require long-term durability, such as solar cell applications However, sufficient hydrolysis resistance cannot be obtained.
Patent Document 2 describes a method for producing a polyester containing an inorganic phosphate, and is used in combination with phosphoric acid in Examples. However, since the ratio of phosphoric acid and inorganic phosphate and the amount applied are inappropriate, inorganic phosphate is easily converted into a foreign substance and has excellent short-term hydrolysis resistance, but it is necessary for solar cell applications. The hydrolysis resistance over a long period of time is insufficient, and the mechanical properties of the film are deteriorated due to foreign matters.

  Patent Document 3 describes polyethylene terephthalate containing buffered phosphorus, and is used in combination with a phosphorus compound in the examples. However, since the types, ratios, and application amounts of phosphorus compounds are optimized and insufficient, hydrolysis resistance and mechanical properties are insufficient for solar cell applications.

JP 2001-144881 A JP 2007-277548 A JP 2008-7750 A

  The object of the present invention is to eliminate these conventional drawbacks and to provide a polyester composition suitable for film applications having excellent hydrolysis resistance and mechanical properties.

That is, the object of the present invention is that the amount of carboxylic acid end groups is 20 eq / t or less, the alkali metal phosphate is 1.3 mol / ton or more and 3.0 mol / ton or less, and the phosphoric acid is alkali metal phosphate. The polyester resin composition is contained in a molar ratio of 0.4 to 1.5 times with respect to the salt and has the following characteristics a) and b).
a) The ester group concentration in the polyester is 37.4 wt% or less b) The heat of crystal fusion ΔHm is 10 J / g or more

  According to the present invention, a polyester resin composition having excellent long-term hydrolysis resistance can be provided. Moreover, by using the composition of the present invention as a biaxially stretched film, it is used for magnetic materials, for electrical materials such as capacitors, for packaging, and particularly for solar cells that require long-term hydrolysis resistance. Can be provided for use.

  The polyester resin composition of the present invention contains 1.3 to 3.0 mol / ton of an alkali metal phosphate, and the phosphoric acid content relative to the alkali metal phosphate is 0.4 to 1.5 times. It is the polyester resin composition which is (mol ratio).

  In the hydrolysis of polyester, it is known that the presence of free protons derived from the carboxylic acid terminal of the molecule accelerates the hydrolysis of the ester. However, by adding these phosphorus compounds in a specific ratio, It can exert a buffering effect on protons that cause decomposition, suppress proton release, and suppress hydrolysis.

  In addition, as a result of intensive studies, we have found that hydrolysis resistance is further improved by combining these phosphorus compounds with the buffer effect and reducing the ester group concentration in the unit weight while maintaining crystallinity. It was.

  That is, the ester group concentration in the polyester of the present invention needs to be 37.4 wt% or less, and preferably 36.5 wt% or less. Further, the heat of crystal fusion ΔHm needs to be 10 J / g or more, more preferably 15 J / g or more, and most preferably 20 J / g or more. In general, polyethylene terephthalate is widely used as a polyester from the viewpoint of cost merit, but using a monomer with a large molecular weight reduces the probability of undergoing hydrolysis by reducing the ester group concentration per unit weight, The combined use with a phosphorus buffer compound synergistically improves hydrolysis resistance. However, simply reducing the ester group concentration does not improve the hydrolysis resistance, and these effects are manifested by the crystalline nature of the resin. This is presumably because the molecular chains are constrained by crystallinity and the hydrolysis reaction rate is suppressed. The crystal melting calorie of the present invention is a calorific value determined when the temperature is raised at a heating rate of 10 ° C./min after being melted in a differential scanning calorimeter and cooled in an amorphous state with liquid nitrogen.

  The polyester resin composition of the present invention preferably has a Tg (glass transition temperature) of 77 ° C. or higher, more preferably 100 ° C. or higher. By being in this range, compared with the polyester resin composition having a low Tg, the hydrolysis resistance can be slightly improved, although not as great as the influence of the ester group concentration and crystallinity.

  The polyester resin composition of the present invention needs to contain 1.3 mol / ton or more and 3.0 mol / ton or less of an alkali metal phosphate from the viewpoint of hydrolysis resistance, and further 1.5 mol / ton. It is preferable that it is ton or more and 2.0 mol / ton or less. When the content of the alkali metal phosphate is less than 1.3 mol / ton, the hydrolysis resistance in the long term may be insufficient. Moreover, when content of alkali metal phosphate exceeds 3.0 mol / ton, it will become easy to turn into a foreign material.

  Examples of the alkali metal phosphate in the present invention include sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, lithium dihydrogen phosphate. , Dilithium hydrogen phosphate, and trilithium phosphate. Among them, sodium dihydrogen phosphate and potassium dihydrogen phosphate are preferable from the viewpoint of long-term hydrolysis resistance.

  The content of phosphoric acid in the present invention is required from the viewpoint of long-term hydrolysis resistance to be 0.4 to 1.5 times in molar ratio with respect to the alkali metal phosphate, Is preferably 0.5 times or more and 1.4 times or less, and more preferably 0.8 times or more and 1.4 times or less. If it is less than 0.4 times or more than 1.5 times, the buffering effect cannot be exerted on protons in the polyester composition, and the long-term hydrolysis resistance is lowered. It tends to indirectly reduce the hydrolysis resistance of the product.

  Moreover, it is preferable to contain 0.01 mol / t or more and 50 mol / t or less of phosphorus compounds other than the said phosphoric acid and an alkali metal phosphate. Hydrolysis resistance can be further improved by using phosphoric acid and a phosphorous compound outside the alkali metal phosphate as a heat stabilizer while suppressing protons in the polyester with phosphoric acid and alkali metal phosphate. . If it is less than 0.01 mol / t, the hydrolysis resistance cannot be further improved, and if it is 50 mol / t or more, the mechanical properties of the polyester resin are deteriorated and bleeding is likely to occur. Also, from the viewpoint of production, the polymerization catalyst is deactivated, the polymerization reaction is delayed, and the COOH end groups are increased, so that the hydrolysis resistance of the product tends to be indirectly lowered, which is not preferable. The phosphorus compound used in combination may be any phosphoric acid, phosphorous acid-derived OH terminal, or any compound that does not have these metal salts. Trimethyl phosphate, triethylphosphonoacetate, dimethylphenylphosphonate, tetrakis (2 , 4-tert-butylphenyl) (1,1-biphenyl) -4,4′-diylbisphosphonite, tetrakis (2,4-tert-butylphenyl-5-methyl) (1,1-biphenyl) -4 , 4′-diylbisphosphonite, bis (4-methyl-2,6-di-tert-butylphenyl) pentaerythritol diphosphite, tris (2,4-tert-butylphenyl) phosphite, 4,4- Examples include isopropylidene-di-phenol-di-phosphite-di-alkyl (C = 12 to 16).

  The total amount of the phosphorus compound contained in the polyester resin composition in the present invention is preferably 30 ppm or more and 150 ppm or less in terms of phosphorus element, from the viewpoint of reducing COOH and suppressing foreign matter formation, and more preferably 60 ppm or more and 150 ppm or less. It is preferable.

  The amount of metal element contained in the polyester resin composition in the present invention is at least one alkali metal selected from Na, Li, K, at least one divalent metal selected from Mg, Ca, Mn, Co, And at least one metal having a polymerization catalyst ability selected from Sb, Ti, and Ge is preferably 30 ppm or more and 500 ppm or less as a total amount of metal elements from the viewpoint of low COOH and heat resistance, and more preferably 40 ppm. It is preferably 300 ppm or less.

  In the polyester resin composition of the present invention, various dicarboxylic acid components generally used as an acid component can be used, but 95 mol% or more is an aromatic dicarboxylic acid component from the viewpoint of hydrolysis resistance. Among these, a naphthalenedicarboxylic acid component and a terephthalic acid component are preferable from the viewpoint of mechanical properties. In particular, a naphthalenedicarboxylic acid component is essential from the viewpoint of reducing the ester group concentration. In addition, it is necessary that 90 mol% or more of the glycol component is a linear alkylene glycol component having 2 to 4 carbon atoms from the viewpoint of mechanical properties and thermal properties, and among them, those having 2 carbon atoms from the viewpoint of moldability and crystallinity. Ethylene glycol is preferred. When the copolymerization component other than the main component exceeds 10 mol% in both the dicarboxylic acid component and the glycol component, it causes a decrease in heat resistance due to a melting point drop and a decrease in hydrolysis resistance due to a decrease in crystallinity.

  In order to maintain the elongation and shape of the polyester resin composition of the present invention after molding under wet heat conditions, it is also preferable to copolymerize a polyfunctional component having three or more functional groups. Preferred polyfunctional components include trimethyl trimellitic acid, trimellitic acid, pyromellitic acid, butanetetracarboxylic acid, polyvalent carboxylic acid such as trimer acid obtained by trimerization of long chain aliphatic carboxylic acid, and anhydrides thereof. Examples thereof include polyhydric alcohols such as esters, glycerin, and pentaerythritol, polyhydric hydroxycarboxylic acids such as citric acid, and anhydrides and esters thereof. Particularly, a trifunctional copolymer component is an elongation retention rate, This is preferable from the viewpoint of suppressing gel foreign substances during polymerization. The addition amount is preferably 1.0 mol% or less of either the carboxylic acid component or the glycol component. If it is larger than 1.0 mol%, gelled foreign substances are generated, the viscosity increases rapidly during polycondensation, and chip formation becomes difficult, which is not preferable. A more preferable addition amount is 0.1 mol% or more and 0.5 mol% or less.

  As a method for adding such a tri- or higher functional copolymer component, in the case of a polyvalent carboxylic acid ester and a polyhydric alcohol component, it is polymerized before the transesterification reaction, in the case of a polyvalent carboxylic acid, as an ethylene glycol solution or slurry. It is preferable to add it before the reaction from the viewpoint of handling properties and reduction of gelled foreign matter.

  As the characteristics of the polyester resin composition of the present invention, the increase in the COOH end groups before and after the wet heat treatment is preferably 70 eq / ton or less from the viewpoint of hydrolysis resistance, more preferably 50 eq / ton or less, particularly 40 eq / ton. Ton is preferable. Specifically, after extruding the polymer to form a 150 μm unstretched sheet, it is treated at 155 ° C. for 4 hours in a saturated steam atmosphere, and the amount of increase in COOH end groups before and after this treatment is measured. . At this time, it is necessary that the unstretched sheet is quenched with a mirror drum or the like and is in a substantially amorphous state. The polymer crystallization state has a great influence on wet heat treatment, and the result is greatly different even with the same polymer due to the heat history before wet heat treatment, so it is suitable for evaluating long-term hydrolysis resistance as in solar cell applications. It is necessary to unify in the amorphous state. The smaller the increase in the COOH end group here means that the hydrolysis of the polyester is suppressed, and this is preferable because the hydrolysis resistance is improved in various applications such as resins, films and fibers.

The intrinsic viscosity of the polyester resin composition of the present invention is preferably 0.6 or more and 1.0 or less from the viewpoint of mechanical properties, and more preferably 0.7 or more and 0.9 or less with a low COOH terminal. From the viewpoint of heat treatment and heat resistance. The amount of COOH end groups is preferably 20 eq / ton or less from the viewpoint of hydrolysis resistance, and more preferably 15 eq / ton or less.
Such a polyester resin composition preferably has a nitrogen content of less than 100 ppm from the viewpoint of suppressing foreign matter formation. That is, it is preferable that no end-capping agents such as carbodiimide and oxazoline containing nitrogen element are contained practically. The end-capping agent reacts with the COOH end group. As a result, foreign substances such as gels are easily generated during the reaction, which causes a decrease in mechanical properties.

  The polyester resin composition of the present invention can be used for other thermoplastic resins such as polyethylene, polypropylene, polystyrene, polycycloolefin, etc., as long as the purpose is not impaired, and inert particles such as talc, silica, carbon black, etc. These additives may contain, for example, end-capping agents such as carbodiimide, oxazoline and epoxy compounds, ultraviolet absorbers, antioxidants, antistatic agents, surfactants, pigments, fluorescent brighteners and the like.

  The polyester resin composition of the present invention is produced by a first step of performing an esterification reaction or a transesterification reaction, a second step of adding an additive such as a polymerization catalyst and a phosphorus compound, and a third step of performing a polymerization reaction. A fourth step of performing a solid phase polymerization reaction may be added as necessary.

  In the first step, for example, terephthalic acid or dimethyl terephthalate and ethylene glycol can be used to perform an esterification reaction or an ester exchange reaction by a known method. For example, when performing a transesterification reaction, a known transesterification reaction catalyst such as magnesium acetate, calcium acetate, manganese acetate, and cobalt acetate can be used, and antimony trioxide as a polymerization catalyst may be added. . In the transesterification reaction, it is preferable to start the transesterification reaction by dissolving the monomer at 150 ° C. or higher, more preferably 180 ° C. or higher in order to dissolve a high molecular weight monomer such as dimethyl naphthalenedicarboxylate. By adding several ppm of alkali metal such as potassium hydroxide during the esterification reaction, diethylene glycol by-product is suppressed and hydrolysis resistance is improved.

  The second step is a step in which an additive such as a polymerization catalyst or a phosphorus compound is added after the esterification reaction or transesterification reaction is substantially completed until the intrinsic viscosity reaches 0.4. .

As the polymerization catalyst, an ethylene glycol solution of germanium dioxide, antimony trioxide, titanium alkoxide, a titanium chelate compound, or the like can be used.
As a phosphorus compound, it is necessary to add an alkali metal phosphate from 1.3 mol / ton to 3.0 mol / ton in terms of hydrolysis resistance. Furthermore, it is necessary to add phosphoric acid 0.4 times or more and 1.5 times or less in terms of moles with respect to the alkali metal phosphate from the viewpoints of suppressing foreign matter formation and long-term hydrolysis resistance. At this time, the alkali metal of the alkali metal phosphate is preferably Na or K from the viewpoint of hydrolysis resistance and suppression of foreign matter formation.

As a method for adding phosphoric acid or alkali metal phosphate, it is preferable from the viewpoint of long-term hydrolysis resistance that the phosphoric acid and alkali metal phosphate are previously dissolved in ethylene glycol and mixed.
In particular, the pH of the mixed solution at this time is preferably adjusted to an acidity of 2.0 or more and 6.0 or less from the viewpoint of suppressing foreign matter formation, and more preferably 4.0 or more and 6.0 or less.
These phosphorus compounds are preferably added at intervals of 5 minutes or more from the polymerization catalyst from the viewpoint of polymerization reactivity, and the addition timing may be after addition of the polymerization catalyst or before addition.

  Examples of other additives include magnesium acetate for the purpose of imparting electrostatic application characteristics, and calcium acetate as a co-catalyst, and can be added within a range that does not hinder the effects of the present invention. In particular, in the case of undergoing an esterification reaction, COOH end groups should be reduced by adding so that the total ethylene glycol is 1.5 times or more and 1.8 times or less in terms of moles relative to terephthalic acid. Therefore, it is effective for improving hydrolysis resistance. On the other hand, various particles may be added to add film slipperiness, or internal precipitation particles using a catalyst may be included.

  In the third step, the polymerization reaction can be carried out by a known method. However, in order to reduce the amount of COOH end groups, the polymerization reaction temperature is set to the melting point of the polyester resin composition + 30 ° C. or less, and the intrinsic viscosity is 0. It is effective to form a chip once at 5 or more and 0.6 or less and perform solid phase polymerization as the fourth step.

  In the fourth step, it is preferable to perform the solid phase polymerization reaction at a solid phase polymerization temperature of the polyester resin composition having a melting point of −30 ° C. or lower, a melting point of −60 ° C. or higher, and a vacuum of 0.3 Torr or lower.

  The polyester resin composition obtained in this way can be biaxially stretched after being dried and extruded with a normal extruder or T-die. At this time, it is preferable to supply the chip to the extruder under a nitrogen atmosphere, and it is better that the time until extrusion from the T die is short. As a guideline, it is 30 minutes or less to suppress the increase in COOH end group. This is preferable.

  The film made of the polyester resin composition of the present invention thus produced has a low COOH end group and not only good resistance to hydrolysis in a short period of time, but also phosphoric acid and alkali metal phosphate. Due to the effects of the action and crystallinity and the low ester group concentration, the long-term hydrolysis resistance required for applications such as a film for solar cells is also improved.

(A. Intrinsic viscosity)
It measured at 25 degreeC using the o-chlorophenol solvent.

(B. Determination of phosphorus content in polymer)
The measurement was performed using a fluorescent X-ray analyzer (model number: 3270) manufactured by Rigaku Corporation.

(C. Determination of alkali metal content in polymer)
Quantification was performed by atomic absorption analysis (manufactured by Hitachi, Ltd .: polarized Zeeman atomic absorption photometer 180-80, frame: acetylene-air).

(D. COOH end group amount)
Measured by the method of Malice. (Reference M. J. Malice, F. Huizinga. Anal. Chim. Acta, 22 363 (1960))
(E. Evaluation of hydrolysis resistance)
The polymer is supplied to a single-screw extruder, extruded from a T-die at 290 ° C. into a sheet shape, rapidly cooled on a mirror drum temperature-controlled at 20 ° C., and an unstretched sheet having a thickness of 150 μm in a substantially amorphous state. Obtained.
The obtained unstretched sheet was treated at 155 ° C. in saturated steam for 4 hours.
The amount of COOH end group increase was evaluated by the difference (ΔCOOH) before and after processing the unstretched sheet.

(F. Calculation of elongation retention)
Using the biaxially stretched film, the film elongation before and after PCT treatment at 125 ° C., 100% RH, 48 hours was measured, and the elongation retention after treatment with respect to the sample before treatment was calculated as a percentage.

    The elongation of the film was measured under the following conditions using an Instron type tensile tester according to the method defined in ASTM-d882.

Measuring device: Orientec Co., Ltd. film strength measuring device
“Tensilon AMF / RTA-100”
Sample size: width 10mm x test length 100mm
Tensile speed: 200 mm / min Measurement environment: 23 ° C., 65% RH
An elongation retention of 65% or more was regarded as acceptable.

(G. Nitrogen content)
Measured by the Kjeldahl method described in JIS K2609 (Act 1975) Petroleum and petroleum products-nitrogen content test method.

(H. Glass transition temperature (Tg), melting point (Tm), heat of fusion (ΔTm))
Each value was calculated for the chart obtained at the time of temperature increase in the second cycle using the following measuring machine in accordance with JIS K7121 (No. 1987).

Apparatus: Differential scanning calorimeter DSCQ100 (manufactured by TA Instruments)
Measurement conditions: Under nitrogen atmosphere Measurement range: 50-280 ° C
Sample weight: 10 mg (using TA Instruments aluminum pan)
Temperature program:
1st cycle Room temperature → Temperature rise (10 ° C / min) → Hold at 50 ° C for 2 minutes → Temperature rise (10 ° C / min) → Hold at 280 ° C for 5 minutes → Take out from the electric furnace and cool rapidly with liquid nitrogen (cool for 2 minutes) → Raise to room temperature (Leave for 5 minutes)
2nd cycle 50 ° C hold for 2 minutes → temperature rise (10 ° C / min) → 280 ° C → temperature drop (10 ° C / min) → 25 ° C
(I. Ester group concentration)
The ester group concentration in the polyester was calculated as the atomic weight ratio from the monomer charge composition.

Example 1
As a first step, 100 parts by weight of dimethyl naphthalenedicarboxylate, 51.2 parts by weight of ethylene glycol, 0.06 part by weight of magnesium acetate, and 0.03 part by weight of antimony trioxide are melted at 180 ° C. in a nitrogen atmosphere and stirred. However, the temperature was raised to 230 ° C. over 3 hours, and methanol was distilled off to complete the transesterification reaction.

  As the second step, after completion of the transesterification reaction, 0.004 part by weight of triethylphosphonoacetate (equivalent to 0.2 mol / ton) was added, and after 5 minutes, 0.019 part by weight of phosphoric acid (equivalent to 1.9 mol / ton) ) And 0.027 parts by weight of sodium dihydrogen phosphate dihydrate (equivalent to 1.7 mol / ton) were added to an ethylene glycol solution (pH 5.0) dissolved in 0.5 parts by weight of ethylene glycol.

  As a third step, the polymerization reaction was carried out at a final temperature of 285 ° C. and a degree of vacuum of 0.1 Torr to obtain polyethylene naphthalate having an intrinsic viscosity of 0.52 and COOH end groups of 18 eq / ton.

  As a fourth step, the obtained polyethylene naphthalate was dried and crystallized at 160 ° C. for 6 hours, and then solid-phase polymerization was performed at 230 ° C. and a vacuum degree of 0.3 Torr. A polyethylene naphthalate of 12.8 eq / ton was obtained.

  Polyethylene naphthalate after solid-phase polymerization is supplied to an extruder in a nitrogen atmosphere, quenched at a casting temperature (20 ° C.) from a T die at an extrusion temperature of 290 ° C., formed into a sheet by an electrostatic application method, and then longitudinally stretched. After longitudinal stretching at a temperature of 130 ° C. and a longitudinal stretching ratio of 3.6 times, the film was stretched at a transverse stretching temperature of 130 ° C. and a transverse stretching ratio of 3.6 times, and heat-treated at 230 ° C. for 3 seconds to obtain a biaxially stretched film. .

  At this time, the filter of the extruder used a 400-mesh wire mesh, and the residence time was about 5 minutes from the supply of the polymer to the discharge from the T-die.

  When the hydrolysis resistance was evaluated, the COOH end group of the unstretched sheet before treatment was 12.8 eq / ton, and the COOH end group after treatment under saturated steam at 155 ° C. for 4 hours was 38.6 eq / ton. It was good.

  Further, the obtained biaxially stretched film was compared for film elongation before and after treatment at 125 ° C., 100% RH for 48 hours, and the elongation retention was calculated to be 75%.

(Example 2)
Polyethylene naphthalate and a biaxially stretched film were obtained in the same manner as in Example 1 except that sodium dihydrogen phosphate was changed to potassium dihydrogen phosphate. As shown in Table 1, the obtained film exhibited almost the same performance as Example 1.

(Comparative Example 1)
The charge composition of the first step was the same as in Example 1 except that 100 parts by weight of dimethyl terephthalate, 64.5 parts by weight of ethylene glycol, 0.06 parts by weight of magnesium acetate, and 0.03 parts by weight of antimony trioxide were used. Polyethylene terephthalate and a biaxially stretched film were obtained. Although the initial COOH end group amount was small, the ester group concentration was high, so the COOH end group increase amount before and after the wet heat treatment was large, and the elongation retention rate was insufficient.

(Comparative Example 2)
A polyester and a biaxially stretched film were obtained in the same manner as in Example 1 except that the copolymer composition was changed and solid phase polymerization was not performed.

  Since the amount of terephthalic acid copolymerization is large, the crystallinity is lowered (ΔHm is reduced), and the amount of COOH end groups increased before and after wet heat treatment is greatly increased, and the elongation retention rate is also greatly reduced as compared with Example 1. did.

(Examples 3, 4 and Comparative Examples 3, 4, 5)
A polyethylene naphthalate and a biaxially stretched film were obtained in the same manner as in Example 1 except that the addition amount and mixing ratio of phosphoric acid and sodium dihydrogen phosphate were changed.

  In Example 3, as a result of reducing the addition amount of the alkali metal phosphate and increasing the phosphoric acid / alkali metal phosphate molar ratio, the elongation retention was maintained, but the COOH terminal before and after the wet heat treatment. The amount of increase in the group tended to increase.

  On the other hand, in Example 4, the addition amount of the alkali metal phosphate was increased and the molar ratio of phosphoric acid / alkali phosphate was reduced, and as a result, the increase in the COOH end group before and after the wet heat treatment tended to decrease. However, the elongation retention rate was maintained but tended to decrease.

  In Comparative Example 3, the amount of sodium dihydrogen phosphate added was excessive, so that sodium dihydrogen phosphate became a foreign substance. As a result, the initial COOH end group tended to decrease, but the foreign sodium dihydrogen phosphate did not function, and the increase in COOH end group before and after wet heat treatment tended to increase, and the elongation retention rate Was insufficient.

  In Comparative Example 4, sodium dihydrogen phosphate and phosphoric acid were not added, and the amount of triethylphosphonoacetate added was increased. Since the buffering effect was not exhibited, the amount of COOH end group increase before and after the wet heat treatment tended to increase, and the elongation retention rate was insufficient.

  In Comparative Example 5, since the phosphoric acid ratio was too small, the increase in the COOH end group before and after the wet heat treatment tended to increase, and the elongation retention was insufficient.

(Example 5)
The polymerization reaction in the third step was performed until the intrinsic viscosity reached 0.55, and a polyethylene naphthalate and a biaxially stretched film were obtained in the same manner as in Example 1 except that the fourth step was omitted.
Since the obtained polyethylene naphthalate had an intrinsic viscosity of 0.55 without performing solid phase polymerization, the initial COOH end groups were somewhat high, and the increase in COOH end groups before and after wet heat treatment tended to be large. Although it showed excellent elongation retention, it tended to decrease slightly.

(Example 6)
A polyethylene naphthalate and a biaxially stretched film were obtained in the same manner as in Example 1 except that triethylphosphonoacetate was not added. As a result, initial COOH end groups and COOH end groups increased slightly before and after wet heat treatment, and the elongation retention rate tended to decrease slightly.

(Example 7)
In the same manner as in Example 1 except that 0.021 part by weight of trimethylphosphoric acid (equivalent to 1.5 mol / ton) was used instead of triethylphosphonoacetate, and trisodium phosphate was used instead of sodium dihydrogenphosphate. A phthalate and a biaxially stretched film were obtained. Trisodium phosphate was a strong alkali, and the pH of the mixed solution with phosphoric acid was 7.5. As a result, both the initial COOH end groups and the increase in COOH end groups before and after the wet heat treatment tended to decrease. Further, the elongation retention was slightly good but good.

(Example 8)
Polyethylene naphthalate and a biaxially stretched film were obtained in the same manner as in Example 1 except that the polymerization catalyst was changed to titanium diisopropoxide bisethyl acetoacetate and magnesium acetate was not added. There were no problems with the initial COOH end groups and the increase in COOH end groups before and after wet heat treatment. Moreover, since the electrostatic application castability at the time of film formation slightly decreased, a slight thickness unevenness occurred, but there was no problem. As a result, the elongation retention was good although it tended to decrease slightly.

Example 9
As a first step, the charged composition was 100.3 parts by weight of dimethyl naphthalenedicarboxylate, 0.5 parts by weight of trimethyl trimellitic acid, 51.3 parts by weight of ethylene glycol, 0.06 parts by weight of magnesium acetate, 0.03 parts of antimony trioxide. A polyester and a biaxially stretched film were obtained in the same manner as in Example 1 except that the amount was in parts by weight.

  Compared to Example 1 in which a trifunctional cross-linking copolymer component (trimethyl trimellitic acid) was not used, the initial amount of COOH end groups and the increase in COOH end groups before and after wet heat treatment were almost the same, but the elongation was maintained. The rate was great and excellent.

(Example 10)
In the first step, the charged composition was 96.8 parts by weight of dimethyl naphthalenedicarboxylate, 4.0 parts by weight of dimethyl terephthalate, 51.8 parts by weight of ethylene glycol, 0.06 parts by weight of manganese acetate, 0.03 parts by weight of antimony trioxide. A polyester and a biaxially stretched film were obtained in the same manner as in Example 1 except that the parts were used.

  Due to the terephthalic acid copolymerization, the crystallinity was lowered (ΔHm was reduced), and the amount of COOH end group increase before and after wet heat treatment was slightly larger than that of Example 1, but good and excellent elongation retention was exhibited. .

(Example 11)
A polyester and a biaxially stretched film were obtained in the same manner as in Example 1 except that the copolymer composition was changed and solid phase polymerization was not performed.

  Copolymerization of terephthalic acid and trimethyltrimellitic acid resulted in a decrease in crystallinity (ΔHm decreased) and increased COOH end group increase before and after wet heat treatment compared to Example 1, but excellent elongation retention Showed the rate.

(Example 12)
As a first step, the charge composition was 100 parts by weight of dimethyl naphthalenedicarboxylate, 63.5 parts by weight of 1,4-butanediol, and 0.021 parts by weight of tetra-n-butoxytitanium, and an ester exchange reaction was performed at 210 ° C. Thereafter, a polyester and a biaxially stretched film were obtained in the same manner as in Example 1 except that the polymerization temperature was 262 ° C. The increase in COOH end groups before and after the wet heat treatment was small, and a good elongation retention rate was exhibited.

(Comparative Example 6)
Polyethylene naphthalate and a biaxially stretched film were obtained in the same manner as in Example 1 except that solid-state polymerization was not performed and the polymerization time was shortened.

  Since the initial amount of COOH end groups was large, the amount of increase in COOH end groups before and after the wet heat treatment was significantly increased as compared with Example 1, and the elongation retention was also greatly reduced.

Claims (12)

Carboxylic acid terminal group amount is 20 eq / t or less, alkali metal phosphate is 1.3 mol / ton or more and 3.0 mol / ton or less, and phosphoric acid is 0.4 times with respect to alkali metal phosphate. A polyester resin composition comprising a molar ratio of 1.5 times or less, naphthalenedicarboxylic acid as a dicarboxylic acid component, and having the following characteristics a) and b).
a) The ester group concentration in the polyester is 37.4 wt% or less b) The heat of crystal fusion ΔHm is 10 J / g or more 2. The polyester resin according to claim 1, wherein the polyester resin has a glass transition temperature of 77 ° C. or more, and an increase in carboxylic acid terminal end before and after wet-heat treatment at 155 ° C. for 4 hours under saturated steam is 70 eq / ton or less. Composition. 3. The polyester resin composition according to claim 1, comprising a phosphorus compound other than phosphoric acid and an alkali metal phosphate, in an amount of 0.01 mol / t to 50 mol / t. The polyester resin composition according to any one of claims 1 to 3, wherein the nitrogen element content is less than 100 ppm. A diol component is ethylene glycol, The polyester resin composition of any one of Claims 1-4 characterized by the above-mentioned. The polyester resin composition according to any one of claims 1 to 5, wherein the copolymer component contains 0.01 to 1.0 mol% of a trifunctional or higher functional crosslinking component. It has at least one alkali metal compound selected from Na, Li and K, at least one divalent metal compound selected from Mg, Ca, Mn and Co, and a polymerization catalytic ability selected from Sb, Ti and Ge. The polyester resin composition according to any one of claims 1 to 6, comprising at least one metal compound in a total amount of metal elements of 30 ppm to 500 ppm and a phosphorus compound in terms of phosphorus element of 30 ppm to 150 ppm. object. In the method for producing a polyester resin composition in which naphthalenedicarboxylic acid or an ester-forming derivative of naphthalenedicarboxylic acid is an essential component as a dicarboxylic acid component, and a polycondensation reaction is performed via an esterification reaction or an ester exchange reaction, an esterification reaction or an ester exchange reaction Between the time when the intrinsic viscosity reaches 0.4 after the liquid crystal is substantially finished, the phosphoric acid and alkali metal phosphate are converted to 0.4 times or more and 1.5 times as phosphoric acid / alkali metal phosphate. The method for producing a polyester resin composition according to claim 1, wherein the polyester resin composition is added in the following molar ratio. The method for producing a polyester resin composition according to claim 8, wherein phosphoric acid and alkali metal phosphate are added as an alkylene glycol mixed solution, and the pH thereof is 2.0 to 6.0. The method for producing a polyester resin composition according to claim 8 or 9, wherein the alkali metal of the alkali metal phosphate is Na or K. The method for producing a polyester composition according to any one of claims 8 to 10, wherein the polymerization method is a transesterification method, and the temperature rise start temperature of the transesterification reaction is 180 ° C or higher. The film for solar cells formed by shape | molding the polyester resin composition of any one of Claims 1-7.