Description
TITLE OF THE INVENTION: POLYESTER RESIN COMPOSITION  PROCESS FOR PRODUCTION OF SAME  AND FILM
TECHNICAL FIELD
[0001]
The present invention relates to a polyester resin composition having good hydrolysis resistance  a process for the production thereof  and a film thereof.
BACKGROUND ART
[0002]
Polyester has been used for various applications because it is superior in mechanical characteristics  thermal characteristics  chemical resistance  electrical characteristics  and moldability.
[0003]
However  since polyester deteriorates with respect to mechanical characteristics due to hydrolysis  various studies have been made in order to control hydrolysis in the case of using it for a long term or in the case of using it under moist conditions. In particular  since films for solar batteries are required to have a lifetime of 20 years or more for outdoor use  they are required to be high in hydrolysis resistance and flame retardancy.
[0004]
For example  a process for producing a polyester containing a phosphoric acid salt of an alkali metal or an alkaline earth metal has been disclosed in Patent Document 1 as a means to enhance hydrolysis resistance.
[0005]
Patent Document 2 discloses a process for producing a polyester containing an inorganic phosphoric acid salt. In the Examples  it is used together with phosphoric acid.
[0006]
Patent Document 3 discloses a polyethylene terephthalate containing a buffer phosphorus compound. In the Examples  it is used together with a phosphorus compound.
PRIOR ART DOCUMENTS
PATENT DOCUMENTS
[0007]
Patent Document 1: JP 2001-114881 A
Patent Document 2: JP 2007-277548 A
Patent Document 3: JP 2008-7750 A
SUMMARY OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
[0008]
However  the use of only a metal phosphate as in the
production process of Patent Document 1 can control the initial
amount of COOH terminal groups  but it is difficult to control increase in the amount of COOH terminal groups due to hydrolysis. Therefore  sufficient hydrolysis resistance cannot be obtained in applications with which long-term durability is required  such as a solar battery application.
[0009]
In the production process of Patent Document 2  since the proportion and the application amounts of phosphoric acid and an inorganic phosphoric acid salt are inappropriate  the inorganic phosphoric acid salt is heterogenized easily and mechanical characteristics of a film deteriorate due to a foreign matter. In addition  the film is superior in short-term hydrolysis resistance  but it is insufficient in long-term hydrolysis resistance  which is required for solar battery applications or the like.
[0010]
In the production process of Patent Document 3  since the type  the proportion  the application amount  and so on of a phosphorus compound are optimi zed insufficiently  products are insufficient in hydrolysis resistance and mechanical characteristics for solar battery applications.
[0011] An obj ect of the present invention is to solve the defects of these conventional technologies and provide a polyester
composition suitable for films superior in hydrolysis
resistance and in mechanical characteristics.
MEANS FOR SOLVING THE PROBLEMS
[0012]
The above-described problems are solved by a polyester resin composition comprising an alkali metal phosphate in an amount of 1.3 mol/ton to 3.0 mol/ton  and phosphoric acid in an amount of 0.4 to 1.5 times (by mole) that of the alkali metal phosphate.
ADVANTAGES OF THE INVENTION
[0013]
According to the present invention  a polyester resin composition that is superior in long-term hydrolysis resistance can be provided. Moreover  by processing the polyester resin composition of the present invention into a biaxially drawn film  it is possible to obtain a film that is suitable for various applications such as magnetic material applications  electrical material applications  e.g.  capacitors  and wrapping applications  and especially solar battery applications with which long-term hydrolysis resistance is required.
EMBODIMENTS OF THE INVENTION
[0014]
The polyester resin composition of the present invention is a polyester resin composition comprising an alkali metal phosphate as a phosphorus compound in an amount of 1.3 mol/ton to 3.0 mol/ton  and phosphoric acid as another phosphorus compound in an amount of 0.4 to 1.5 times (by mole) that of the alkali metal phosphate.
[0015]
From the viewpoint of hydrolysis resistance  it is necessary for the polyester resin composition of the present invention that its acid component should contain an aromatic dicarboxylic acid component in an amount of 95 mol% or more. Especially  a terephthalic acid component is preferred in view of mechanical characteristics. It is also necessary  from the viewpoint of mechanical characteristics and thermal characteristics  that the glycol component should contain a straight-chain alkylene glycol component having 2 to 4 carbon atoms in an amount of 95 mol% or more. Especially  ethylene glycol  which has two carbon atoms  is preferred from the viewpoint of moldability and crystallizability.
[0016]
If the content of a copolymerized component exceeds 5 mol%  this will cause decrease in heat resistance due melting point depression and also cause decrease in hydrolysis resistance due to drop in degree of crystallization.
[0017J
It is necessary from the viewpoint of hydrolysis resistance that the polyester resin composition of the present invention should contain an alkali metal phosphate in an amount of 1.3 mol/ton to 3.0 mol/ton. It is preferably 1.5 mol/ton to 2.0 mol/ton. When the content of the alkali metal phosphate is less than 1. 3 mol/ton  hydrolysis resistance for a long term may be insufficient. On the other hand  when the alkali metal phosphate is contained in a content exceeding 3.0 mol/ton  this is likely to cause heterogenization. [0018J
Examples of the alkali metal phosphate in the present invention include sodium dihydrogen phosphate  disodium hydrogen phosphate  trisodium phosphate  potassium dihydrogen

metal dihydrogen phosphates and di(alkali metal) hydrogen phosphates. Alkali metal phosphates in which the alkali metal
is Na or K are preferred from the viewpoint of long-term hydrolysis resistance. Particularly preferred are sodium dihydrogen phosphate and potassium dihydrogen phosphate.
[0019J It is necessary from the viewpoint of long-term hydrolysis resistance that the content of the phosphoric acid
in the present invention should be 0.4 to 1.5 times of the alkali
metal phosphate in a molar ratio. It is preferably 0.8 to 1.4 times. If it is less than 0.4 times  the long-term hydrolysis resistance may deteriorate. If it exceeds 1.5 times  a polymerization catalyst will be deactivated by an excess of the phosphoric acid  and as a result polymerization will be delayed
and the amount of terminal COOH groups will increase  so that
hydrolysis resistance may deteriorate.
[0020]
According to calculation from the contents of the alkali metal phosphate and the phosphoric acid  the polyester "resin composition of the present invention contains an alkali metal element in an amount of 1.3 mol/ton to 9.0 mol/ton and phosphorus element in an amount of 1.8 mol/ton to 7.5 mol/ton. In view of the type of a preferred alkali metal phosphate  the composition preferably contains an alkali metal element in an amount of 1. 3 mol/ton to 6.0 mol/ton and phosphorus element in an amount of 1.8 mol/ton to 7.5 mol/ton.
[0021]
From the viewpoint of reduction in the amount of terminal
COOH groups and inhibition of foreign matter formation  it is
preferred that the total content of the phosphorus compounds
contained in the polyester resin composition of the present
invention is 30 ppm to 150 ppm in terms of the amount of
phosphorus element. It is more preferably 60 ppm to 150 ppm.
[0022]
It is preferred that the polyester resin composition of the present invention contains a metal compound whose metal element is at least one member selected from the group consisting of Na  Li  and K  a metal compound whose metal element is at least one member selected from the group consisting of Mg  Ca  Mn  and Co  and a metal compound whose metal element is at least one member selected from the group consisting of Sb  Ti  and Ge  and the total amount of these metal elements is adjusted to 30 ppm or more and 500 ppm or less relative to the whole portion of the polyester resin composition. By adj usting the total amount of the metal elements to this range  the amount of terminal COOH groups can be reduced and heat resistance is improved. It is more preferably 40 ppm to 300 ppm. Na  Li  and K are alkali metal elements. Mg  Ca  Mn  and Co  which are divalent metal elements  give a function as a transesterification catalyst or electrostatic characteristics in film production. Sb  Ti  and Ge  which are metal elements having ability to catalyze polymerization  function as a polymerization catalyst.
[0023]
It is preferred for the polyester resin composition of the present invention from the viewpoint of hydrolysis resistance that the increase in the amount of terminal COOH groups between before and after a wet-heating treatment is 90
eq./ ton (equivalents/ton) or less. It is more preferably 70
eq./ton or less and particularly preferably 50 eq./ton. Specifically  a polymer is shaped by extrusion to form an undrawn sheet having a thickness of 150 ~  which is then
subjected to a humidifying-heating treatment under a saturated
steam atmosphere at 155°C for 4 hours. An increase in the amount of terminal COOH groups between before and after the wet-heating treatment is measured. At this time  the undrawn sheet is needed to be substantially in an amorphous state as a result of being cooled rapidly on a mirror-finished drum or the like. The crystallization state of a polymer has a great influence in the wet-heating treatment. Therefore  a crystallized polymer after drying and after solid phase polymerization is not suitable for evaluating long-term hydrolysis resistance for solar battery applications because hydrolysis is difficult to proceed therein.
[0024J
Moreover  it is preferred that the polyester resin composition is a polyethylene terephthalate resin composition and the increase in the amount of terminal COOH groups is within the above-described range. Since polyethylene terephthalate is lower in crystallizability than polybutylene terephthalate and polybutylene naphthalate  crystallization and whitening just after extrusion do not occur easily. Moreover  since polyethylene terephthalate is lower in glass transition point
and lower in stretch stress than polyethylene naphthalate  it
is superior in film moldability  for example  it permits easy stretch control. A polyethylene terephthalate resin having an increase in the amount of terminal COOH groups falling within the above-described range has long-term hydrolysis resistance in addition to superior characteristics that polyethylene terephthalate inherently has.
[0025]
It is preferred from the viewpoint of mechanical characteristics that the polyester resin composition of the present invention has an intrinsic viscosity of 0.6 to 1.0. It is more preferably 0.7 to 0.9 from the viewpoint of reduction in the amount of terminal COOH groups and heat resistant.
[0026]
It is preferred for the polyester resin composition of the present invention from the viewpoint of hydrolysis resistance that the amount of terminal COOH groups of a polymer just before being supplied to a film production machine is 20 eq./ton or less. It is more preferably 15 eq./ton or less.
[0027]
It is preferred from the viewpoint of inhibition of foreign matter formation that such a polyester resin composition has a nitrogen content of 100 ppm or less. That is  it is preferred to contain substantially no end-capping agent containing nitrogen element  such as carbodiimide and
oxazoline. An end-capping agent reacts with a terminal COOH
group and as a result it easily generates foreign matters  such as a gel  during a reaction  causing deterioration in mechanical characteristics.
[0028J
It is preferred from the viewpoint of retention of elongation  polymerization reactivity  and moldability that the polyester resin composition of the present invention contains a copolymerized component having three or more functionalities in an amount of 0.01 mol% to 1.00 mol% relative to all the acid components. It is more preferably 0.01 mol% to 0.50 mol%.
[0029J
Examples of the copolymerized component having three or more functionalities include polycarboxylic acids such as trimellitic acid  cyclohexanetricarboxylic acid  a biphenyl tetracarboxylic acid  pyromellitic acid  butanetetracarboxylic acid  trimer acids produced by trimerizing long-chain aliphatic carboxylic acids  and their anhydrides and esters; polyhydric alcohols such as glycerol  pentaerythritol  dipentaerythritol  trimethylolpropane  ditrimethylolpropane  trihydroxybenzene  and trihydroxyhexane; and polyhydroxycarboxylic acids such as citric acid  dihydroxybenzenecarboxylic acid  and dihydroxynaphthalene carboxylic acid  and their anhydrides and
esters. In particular  it is preferred from the viewpoint of
retention of elongation and film moldability that the copolymerized component is a copolymerized component having three functionalities. As to the process of adding such a copolymerized component having three or more functionalities  it is preferred from the viewpoint of reactivity and handling property to add it before transesterification in the cases of a polycarboxylic acid ester and a polyhydric alcohol component and to add it in the form of a solution or slurry in ethylene
glycol in the case of a polycarboxylic acid.
[0030]
The process for producing the polyester resin composition of the present invention is a process for producing a polyester resin composition by conducting a polycondensation via esterification or transesterification from an aromatic dicarboxylic acid or an ester-formable derivative of an aromatic dicarboxylic acid and a straight-chain alkylene glycol having 2 to 4 carbon atoms  the process comprising a first step of performing esterification or transesterification  a second step of adding additives such as a polymerization catalyst and a phosphorus compound  and a third step of performing polymerization. As necessity  a fourth step of performing solid phase polymerization may be added.
[0031]
In the first step  the esterification or
transesterification can be performed by a conventional method
using  for example  terephthalic acid  or dimethyl terephthalate and ethylene glycol. For example  when performing transesterification  a transesterification catalyst  such as magnesium acetate  calcium acetate  manganese acetate  and cobalt acetate  can be used  and antimony trioxide  which is a polymerization catalyst  and the like may also be added. In the esterification  generation of diethylene glycol as a by-product is inhibited and also hydrolysis resistance is
improved if an alkali metal such as potassium hydroxide has been added in an amount of several ppm.
[0032]
The second step is a step of adding additives such as a polymerization catalyst and a phosphorus compound at a stage between the point of time when the esterification or transesterification has been substantially completed and the point of time when the intrinsic viscosity reaches 0.4.
[0033]
As a polymerization catalyst  a solution of germanium dioxide in ethylene glycol  antimony trioxide  titanium alkoxide  titanium chelate compounds  and so on can be used.
[0034]
It is necessary from the viewpoint of hydrolysis resistance that an alkali metal phosphate in an amount of 1.3 mol/ton to 3.0 mol/ton is added as the phosphorus compound. A
preferred addition amount is 1.5 mol/ton to 2.0 mol/ton. When
the addition amount of the alkali metal phosphate is less than
1.3 mol/ton  hydrolysis resistance for a long term may be insufficient. On the other hand  when the alkali metal phosphate is added in an amount exceeding 3.0 mol/ton  this is likely to cause heterogenization. Moreover  from the viewpoint of inhibition of foreign matter formation and long-term hydrolysis resistance  it is necessary to add phosphoric acid as the phosphorus compound in an amount of 0.4 to 1.5 times (by mole) that of the alkali metal phosphate. A preferred addition amount is 0.8 to 1.4 times. If it is less than 0.4 times  the long-term hydrolysis resistance may deteriorate. If it exceeds 1.5 times  a polymerization catalyst will be deactivated by an excess of the phosphoric acid  and as a result polymerization will be delayed and the amount of terminal COOH groups will increase  so that hydrolysis resistance may deteriorate. In particular  it is desirable from the viewpoint of heat resistance and long-term hydrolysis resistance to adjust the amount of an alkali metal element to
1.3 mol/ton or more and 6.0 mol/ton or less and the amount of phosphorus element to 1.8 mol/ton or more and 7.5 mol/ton or less.
[0035J As to the process of adding phosphoric acid and the alkali metal phosphate  it is preferred  from the viewpoint of
long-term hydrolysis resistance  to add and mix them after
dissolving them in ethylene glycol or the like beforehand. As to the kinds of the solvent or dispersing medium to be used at this time  it is preferred from the viewpoint of heat resistance and hydrolysis resistance to use the same alkylene glycol as the straight-chain alkylene glycol having 2 to 4 carbon atoms contained in the polyester resin composition of the present invention. If another kind of alkylene glycol is used  heat resistance may deteriorate due to occurrence of copolymerization.
[0036]
In particular  it is preferred from the viewpoint of inhibition of foreign matter formation to adjust the mixed liquid at this time to an acidic pH of 2.0 to 6.0. More preferably  the pH is 4.0 to 6.0.
[0037]
It is preferred from the viewpoint of polymerization reactivity to add the phosphorus compound at an interval of 5 minutes or more from the addition of the polymerization catalyst  and it may be added either before or after •the addition of the polymerization catalyst.
[0038]
Examples of other additives include magnesium acetate for the purpose of imparting electrostatic characteristics  calcium acetate as a co-catalyst  and hindered phenol type
antioxidants  which may be added as far as they do not impair the effect of the present invention. Particularly  in the case of having experienced esterification  further addition of ethylene glycol such that the total amount of ethylene glycol may become 1.5 to 1.8 times the amount of terephthalic acid in molar ratio is effective for improving hydrolysis resistance because it can reduce terminal eOOH groups.
[0039J
On the other hand  in order to impart slipping property to a film  it is possible to add various types of particles or incorporate internally formed particles using a catalyst.
[0040J
In the third step  the polymerization can be performed by a conventional method. Moreover  in order to reduce the amount of terminal eOOH groups  it is effective to adjust the polymerization temperature up to a temperature that is 30De higher than the melting point of a polyester resin composition  and perform the solid phase polymerization of the fourth step after temporarily forming chips at an intrinsic viscosity of
0.5 to 0.6. [0041J
In the fourth step  it is preferred to perform a solid phase polymerization at a solid phase polymerization temperature that is not higher than a temperature 30De lower than the melting point of the polyester resin composition and
not lower than a temperature 60°C lower than the melting point of the polyester resin composition  and a degree of vacuum of
0.3 Torr or less. [0042]
The thus-obtained polyester resin composition can be subjected  after drying  to extrusion using a conventional extruder and a conventional T die and biaxial stretching. At this time  feed of chips to the extruder is preferably performed under anitrogen atmosphere. The shorter the time taken before being extruded through the T die  the better; it is preferred  from the viewpoint of inhibition of increase of terminal COOH groups  to adjust the time to 30 minutes or shorter as a standard.
[0043]
The thus-produced film which is made of the polyester resin composition of the present invention is not only low in content of terminal COOH groups and superior in short-term hydrolysis resistance but also superior in long-term hydrolysis resistance  which is needed for such application as films for solar batteries  etc.  due to the action of phosphoric acid and the alkali metal phosphate.
EXAMPLES
[0044]
(A. Intrinsic viscosity) Measurement was conducted at 25°C using o-chlorophenol
solvent.
[0045]
(B. Determination of the amount of phosphorus in a polymer)
Measurement was conducted using a fluorescent X-ray analyzer (Model No.: 3270) manufactured by Rigaku Corporation. [0046]
(C. Determination of the amount of alkali metal in a polymer)
Measurement was carried out by an atomic absorption method (Polarized Zeeman Atomic Absorption Spectrophotometer 180-80  manufactured by Hitachi  Ltd.  flame: acetylene-air).
[0047]
(D. The amount of terminal COOH groups)
Measurement was carried out by the method of Maulice. (Document: M. J. Maulice  F. Huizinga  Anal. Chim. Acta  22 363 (1960)) . [0048]
(E. Evaluation of hydrolysis resistance)
A polymer was fed to a single screw extruder  extruded through a T die at 280°C into a sheet form  and rapidly cooled on a mirror-finished drum controlled to a temperature of 20°C  so that a l50-f-IJIl thick undrawn sheet that was substantially in an amorphous state was obtained.
The resulting undrawn sheet was treated at 155°C in
a saturated steam for 4 hours.
The increase in the amount of terminal COOH groups was evaluated on the basis of the difference between before and after the treatment of the undrawn sheet
(L~COOH ) [0049J
(F. Calculation of a retention of elongation)
Using a biaxially drawn film  a degree of film elongation was measured before and after a PCT (pressure cooker test) treatment performed at 125°C  100%RH for 48 hours  and then a retention of elongation after the treatment relative to the sample before the treatment was calculated in percentage.
The degree of film elongation was measured under the following conditions by using an Instron type tensile tester in accordance with the method specified in ASTM-d882.
• Measuring instrument: film strength and elongation
measuring instrument "Tensilon AMF/RTA-lOO" manufactured by Orientec Co.  Ltd.
• Sample size: 10 mm in width and 100 mm in length
• Tensile speed: 200 mm/minute
• Measuring environment: 23°C  65%RH

A retention of elongation of 50% or more  that corresponds to a lifetime of 20 years or more in a solar
battery application was considered to be acceptable.
[0050J
(G. Nitrogen content)
Measurement was carried out by the Kjeldahl method described in JIS K2609 Crude petroleum and petroleum products-Determination of nitrogen content.
[005lJ (Example 1) First step: 100 parts by mass of dimethyl terephthalate 
57.5 parts by mass of ethylene glycol  0.06 parts by mass of magnesium acetate  and 0.03 parts by mass of antimony trioxide were melted at 150°C under a nitrogen atmosphere. The resulting molten material was heated under stirring to 230°C over 3 hours  thereby distilling methanol out to complete transesterification.
[0052J
Second step: After the completion of the transesterification  an ethylene glycol solution (pH 5.0) prepared by dissolving 0.019 parts by mass (equivalent to 1.9 mol/ton) of phosphoric acid and 0.027 parts by mass (equivalent to 1.7 mol/ton) of sodium dihydrogen phosphate dihydrate in 0.5 parts by mass of ethylene glycol was added. The intrinsic viscosity at this time was less than 0.2.
[0053J The third step: Polymerization was performed at a final
achievement temperature of 285°C and a degree of vacuum of 0.1 Torr  so that a polyethylene terephthalate having an intrinsic
viscosity of 0.52 and 15 eq./ton of terminal COOH groups was obtained.
[0054]
Fourth step: The resulting polyethylene terephthalate was dried and crystallized at 160°C for 6 hours. Then  solid phase polymerization at 220°C  a degree of vacuum of 0.3 Torr  for 8 hours was performed  so that a polyethylene terephthalate
having an intrinsic viscosity of 0.85 and 10.2 eq./ton of
terminal COOH groups was obtained.
[0055]
The polyethylene terephthalate after the solid phase polymerization was fed to an extruder under a nitrogen atmosphere. It was discharged through a T die at an extrusion temperature of 280°C and cooled rapidly on a casting drum (20°C)   so that it was converted into a sheet by an electrostatic application method. This sheet was longitudinally drawn at a
longitudinally drawing temperature of 90°C and a longitudinally
drawing ratio of 3.6 times and then laterally drawn at a laterally drawing temperature of 110°C and a laterally drawing ratio of 3.6 times followed by performing heat treatment at 210°C for 3 seconds  so that a biaxially drawn film was obtained. [0056]
As the filter of the extruder used at this time  a 400-mesh
wire gauze was used. The residence time taken from the polymer
feed to the discharge through the T die was about 5 minutes.
[0057]
Hydrolysis resistance was evaluated  and it was found that the amount of terminal COOH groups of the undrawn sheet before the treatment was 12.0 eq. /ton and the amount of terminal COOH groups after performing a treatment at 155°C under saturated steam for 4 hours was 46.1 eq./ton  which means that the hydrolysis resistance was good. As to a nitrogen content  60 ppm of nitrogen was detected though no nitrogen compounds were added. It is presumed that this was because some nitrogen was incorporated due to the fact that molding was carried out under a nitrogen atmosphere.
[0058]
Moreover  the resulting biaxially drawn film was compared with respect to degree of film elongation before and after treatment at 125°C and 100%RH for 48 hours  and then a retention of elongation was calculated to be 65%.
[0059]
(Example 2)
A polyethylene terephthalate and a biaxially drawn film were obtained in the same manner as in Example 1 except for exchanging sodium dihydrogen phosphate for potassium dihydrogen phosphate.
The resulting film exhibited performance that was almost
equivalent to Example 1 as shown in Table 1.
[0060J
(Examples 3  4  10  and 11  Comparative Examples 1  2  3  5  6  7  and 8)
A polyethylene terephthalate and a biaxially drawn film were obtained in the same manner as in Example 1 except for changing the addition amounts and the mixing ratio of phosphoric acid and sodium dihydrogen phosphate.
[006lJ
In Example 3  the addition amount of an alkali metal phosphate was reduced and the molar ratio of phosphoric acid/alkali metal phosphate was increased in comparison to Example 1. As a result  the increase in the amount of terminal COOH groups detected""between before and after the wet-heating treatment became larger in comparison to Example 1 though characteristics as a film for a solar battery were maintained.
[0062J
In Example 4  the addition amount of an alkali metal phosphate was increased and the molar ratio of phosphoric acid/alkali metal phosphate was reduced in comparison to Example 1. As a result  the retention of elongation decreased while characteristics as a film for a solar battery were maintained though the increase in the amount of terminal COOH groups detected between before and after the wet-heating treatment became smaller in comparison to Example 1.
[0063]
In Example 10  the addition amounts of sodium dihydrogen phosphate and phosphoric acid were reduced and the molar ratio of phosphoric acid/sodium dihydrogen phosphate was reduced in comparison to Example 1. As a result  both the amount of terminal COOH groups and the ~ terminal COOH group increased in comparison to Example 1. A retention of elongation was reduced in comparison to Example 1  but characteristics as a film for a solar battery were maintained.
[0064]
In Example 11  the addition amounts of sodium dihydrogen phosphate and phosphoric acid were increased and the molar ratio of phosphoric acid/sodium dihydrogen phosphate was increased in comparison to Example 1. As a result  the polymerization was elongated  and both the amount of terminal COOH groups and the ~ terminal COOH group increased in comparison to Example
1. A retention of elongation was reduced in comparison to Example 1  but characteristics as a film for a solar battery were maintained.
[0065]
In Comparative Example 1  since phosphoric acid was reduced excessively  the initial amount of terminal COOH groups increased  and the retention of elongation was 35%  which means that performance was insufficient.
[0066]
In Comparative Example 2  since sodium dihydrogen
phosphate was increased excessively  sodium dihydrogen phosphate was heterogenized. As a result  the initial amount of terminal COOH groups decreased  but heterogenized sodium dihydrogen phosphate did not function  the increase in the amount of terminal COOH groups detected between before and after the wet-heating treatment became large  and the retention of elongation was also insufficient.
[0067]
In Comparative Example 3  since no sodium dihydrogen phosphate was added  the initial amount of terminal COOH groups was small  but the increase in the amount of terminal COOH groups detected between before and after the wet-heating treatment became remarkably large  and the retention of elongation was also insufficient.
[0068]
In Comparative Example 5  since no phosphoric acid was added  the heat resistance deteriorated  the increase in the amount of terminal COOH groups detected between before and after the wet-heating treatment became remarkably large  and the retention of elongation was also insufficient.
[0069J
In Comparative Example 6  since sodium dihydrogen phosphate was reduced excessively  the retention of elongation decreased  and characteristics as a film for a solar battery
were insufficient.
[0070]
In Comparative Example 7  since the amount of phosphoric acid was increased so that the molar ratio of phosphoric acid/sodium dihydrogen phosphate was made excessively large  the retention of elongation decreased  and characteristics as a film for a solar battery were insufficient.
[007l] In Comparative Example 8  citric acid in an amount equivalent to 1.9 mol/ton was added instead of phosphoric acid 
so that a 6 terminal COOH group increased greatly  the retention of elongation decreased remarkably  and characteristics as a film for a solar battery were insufficient.
[0072]
(Example 5)
A polyethylene terephthalate and a biaxially drawn film were obtained in the same manner as in Example 1 except for performing the polymerization in the third step until the intrinsic viscosity reached 0.65 and omitting the fourth step.
Since the resulting polyethylene terephthalate was one in which the initial amount of terminal COOH groups was larger than 20 eq. /ton as a result of performing polymerization to an intrinsic viscosity of 0.65 without performing solid phase polymerization  the increase in the amount of terminal COOH groups detected between before and after the wet-heating
treatment became larger though characteristics as a film for a solar battery were maintained. Moreover  the retention of elongation also decreased.
[0073]
(Example 6)
A polyethylene terephthalate and a biaxially drawn film were obtained in the same manner as in Example 1 except for using trisodium phosphate as the alkali metal phosphate and increasing the amount of antimony trioxide. Trisodium phosphate was strong alkali and the pH of its mixed solution with phosphoric acid was 7.5.
As a result  the initial amount of terminal COOH groups decreased and the increase in the amount of terminal COOH groups detected between before and after the wet-heating treatment increased. The retention of elongation decreased though characteristics as a film for a solar battery were maintained.
[0074]
(Example 7)
A polyethylene terephthalate and a biaxially drawn film were obtained in the same manner as in Example 1 except for reducing the addition amounts of magnesium acetate and antimony trioxide.
The initial amount of terminal COOH groups decreased due to the reduction in amount of magnesium acetate and antimony trioxide. This is probably because the heat resistance of the
composition was improved due to the decrease in the content of
the metal compound.
On the other hand  characteristics as a film for a solar battery were maintained though the intrinsic viscosity decreased in correspondence to the reduction in the amount of the catalyst.
[0075J
(Example 8)
A polyethylene terephthalate and a biaxially drawn film were obtained in the same manner as in Example 1 except for shortening the solid phase polymerization time of the fourth step.
Characteristics as a film for a solar battery were maintained though the initial amount of terminal COOH groups and the increase in the amount of terminal COOH groups detected between before and after the wet-heating treatment became larger in correspondence to the reduction in the solid phase polymerization time.
[0076J
(Example 9)
A polyethylene terephthalate and a biaxially drawn film were obtained in the same manner as in Example 1 except for exchanging the polymerization catalyst for titanium diisopropoxide bisethylacetoacetate  and adding no magnesium acetate.
There were no problems with the initial amount of terminal
COOH groups or the increase in the amount of terminal COOH groups detected between before and after the wet-heating treatment  but unevenness in thickness was produced due to the fact that electrostatic application casting became unstable in film production. As a result  characteristics as a film for a solar battery were maintained  but the retention of elongation decreased.
[0077J
(Comparative Example 4)
A polyethylene terephthalate and a biaxially drawn film were obtained in the same manner as in Example 1 except for exchanging phosphoric acid for trimethyl phosphate.
Because of the use of trimethyl phosphate instead of phosphoric acid  the effect of sodium dihydrogen phosphate to inhibit the increase in the amount of terminal COOH groups was weakened  and the increase in the amount of terminal COOH groups detected between before and after the wet-heating treatment became larger. Moreover  the retention of elongation was insufficient.
[0078J
(Comparative Example 9)
A polyethylene terephthalate and a biaxially drawn film were obtained in the same manner as in Example 1 except for exchanging sodium dihydrogen phosphate for sodium phosphite.
Due to th""e exchange of sodium dihydrogen phosphate for
sodium phosphite  a ~ terminal COOH group tended to increase
and the retention of elongation became insufficient.
[0079J
(Example 12)
Into an esterification apparatus into which 114 parts by mass (equivalent to 100 parts by mass of PET) of bishydroxyethylene terephthalate had been fed beforehand  a slurry composed of 86 parts by mass of terephthalic acid and 37 parts by mass of ethylene glycol was fed over 3 hours by using a snake pump  and esterification was performed while the temperature of the reactant was controlled at 245°C to 255°C.
[0080J
After completion of the esterification  114 parts by mass
(equivalent to 100 parts by mass of PET) of the resulting bishydroxyethylene terephthalate was transferred to a polymerization can  followed by addition of 0.06 parts by mass of magnesium acetate tetrahydrate and 0.03 parts by mass of antimony trioxide  and then a reaction was performed for 30 minutes under stirring  thereby distilling water out. Then  an ethylene glycol solution (pH 5.0) prepared by dissolving
0.019 parts by mass (equivalent to 1.9 mol/ton) of phosphoric acid and 0.027 parts by mass (equivalent to 1.7 mol/ton) of sodium dihydrogen phosphate dihydrate in 0.5 parts by mass of ethylene glycol was added. The intrinsic viscosity at this time
was 0.24. Then  the pressure was reduced while the temperature
was raised from 255°C to 280°C  and polycondensation was performed at an ultimate temperature of 280°C and a degree of vacuum of 0.1 Torr. Thus  a polyethylene terephthalate having an intrinsic viscosity of 0.62 and 18.0 eq. /ton of terminal COOH groups was obtained.
[0081J
The resulting polyethylene terephthalate was dried and crystallized at 160°C for 6 hours and then subjected to solid phase polymerization of 8 hours at 220°C and a degree of vacuum of 0.3 Torr  so that a polyethylene terephthalate having an intrinsic viscosity of 0.85 and 13.1 eq./ton of terminal COOH groups was obtained. Further  a biaxially drawn film was obtained in the same manner as in Example 1. The resulting biaxially drawn film was increased in the amount of terminal COOH groups and L1 terminal COOH group in comparison to Example 1  but it was at a satisfactory level as a film for a solar battery.
[0082J
(Example 13)
A biaxially drawn film was obtained in the same manner as in Example 12 except for adjusting the polymerization temperature to 290°C and the intrinsic viscosity to 0.68 and omitting solid phase polymerization.
In the resulting film  both the amount of terminal COOH groups and the ~ terminal COOH group increased in comparison to Example 12. Although the retention of elongation decreased  characteristics as a film for a solar battery were maintained.
[0083]
(Examples 14  15)
A polyethylene terephthalate and a biaxially drawn film were obtained in the same manner as in Example 1 except for exchanging magnesium acetate for manganese acetate or calcium acetate.
[0084]
In Example 14  due to the use of manganese acetate  the amount of terminal COOH groups after solid phase polymerization was 9.2 eq. /ton  whereas the amount of terminal COOH groups of the undrawn sheet was 9.5 eq./ton  which means that heat resistance was good. Moreover  the increase in the amount of terminal COOH groups decreased in comparison to Example 1  which means that hydrolysis resistance was also good and the product was satisfactory as a film for a solar battery.
[0085]
In Example 15  in which calcium acetate was used  the increase in the amount of terminal COOH groups tended to decrease in comparison to Example 1 and the product was satisfactory as a film for a solar battery.
[0086]
(Examples 16  17)
A polyethylene terephthalate and a biaxially drawn film
were obtained in the same manner as in Example 1 except for adding trime11itic acid trimethyl as a copolymerized component before transesterification.
[0087J
In Example 16  the polymerization time was shortened successfully and the amount of terminal COOH groups tended to decrease because of the fact that trimethyl trimellitate was copolymerized in an amount of 0.05 mol% relative to the whole acid component. The retention of elongation  which was also improved in comparison to Example 1  was a characteristic satisfactory as a film for a solar battery.
[0088J
In Example 17  the polymerization time was shortened more than in Example 16 and the amount of terminal COOH groups tended to decrease because of the fact that trimethyl trimellitate was copolymerized in an amount of 0.05 mol% relative to the whole acid component. Although the melt viscosity was high and the filter pressure and the extrusion torque to be applied tended to increase due to a high intrinsic viscosity in association with crosslinking caused by trimethyl trimellitate  the resulting film was improved in retention of elongation in comparison to Example 1 and Example 16  and it had characteristics satisfactory as a film for a solar battery.
[0089J (Example 18)
A polyethylene terephthalate and a biaxially drawn film were obtained in the same manner as in Example 1 except for adding butanetetracarboxylic acid in the form of an ethylene glycol solution (5 wt%) after transesterification.
The polymerization time was shortened successfully and the amount of terminal COOH groups tended to decrease because of the fact that butane tetracarboxylic acid was copolymerized in an amount of 0.1 mol% relative to the whole acid component. The retention of elongation  which was also improved in comparison to Example 1  was a characteristic satisfactory as a film for a solar battery.
[0090J
In every Example and Comparative Example  a nitrogen content of 60 ppm was detected despite the fact that no nitrogen-containing substance was used as a raw material. This is presumably because a nitrogen compound had remained as an impurity in a raw material such as terephthalic acid or ethylene glycol  or gaseous nitrogen was dissolved in a polyester resin composition during melt-molding in a nitrogen atmosphere.
[0091J [Table 1J

• COOH terminal group: a value of a chip before shaping
• L1.COOH: the increase in the number of COOH terminal groups between before and after a wet-heating treatment of an undrawn sheet

.
[0092J [Table 2J

• COOH terminal group: a value of a chip before shaping
• i\COOH: the increase in the number of COOH terminal groups

between before and after a wet-heating treatment of an undrawn sheet
[0093] [Table 3]
Example 7
Example 8
Example 9 Alkali metal phosphate
Sodium
Sodium
Sodium dihydrogen
dihydrogen
dihydrogen phosphate
phosphate
phosphate Addition amount
1.7
1.7
1.7
(mol/ton) Phosphoric acid/alkali
1.12
1.12
1.12 metal phosphate pH
5.0
5.0
5.0 Alkali metal
Na
Na
Na Amount of alkali metal
39
39.1
39 (ppm) Divalent metal
-Amount of divalent
Mg
Mg
-metal (ppm) Polymerization
45
68
Sb
Sb
Ti catalyst metal Amount of
209
251
10 polymerization catalyst metal (ppm) Total amount of metal
293
358
49 (ppm) Amount of phosphorus
112
112
112 (ppm) Nitrogen content (ppm)
60
60
60 Intrinsic viscosity
0.82
0.65
0.80 COOH terminal group
8.3
14.6
10.5
(eq./t) LiCOOH terminal group
30.2
45.2
34.6
(eq. It) Retention of
70
55
65 elongation (% )
• COOH terminal group: a value of a chip before shaping
• LiCOOH: the increase in the number of COOH terminal groups

between before and after a wet-heating treatment of an undrawn sheet
[0094] [Table 4]
ComparativeComparative
Comparative Example 1
Example 2
Example 3 Alkali metal phosphate
Sodium
Sodium
-
dihydrogen phosphate dihydrogen
phosphate Addition amount
-(mol/ton) Phosphoric
3.5
1.7
-acid/alkali metal phosphate pH
0.54
0.24
-Alkali metal
5.5
4.0
NaNa
-
81Amount of alkali metal
39
-
(ppm) Divalent metal
Mg
Mg
Mg Amount of divalent
68
68
68 metal (ppm) Polymerization
Sb
Sb
Sb
catalyst metal Amount of
251
251
251 polymerization catalyst metal (ppm) Total amount of metal
400
358
319 (ppm) Amount of phosphorus
124
65
59 (ppm) Nitrogen content (ppm)
60
60
60 Intrinsic viscosity
0.85
0.85
0.85 COOH terminal group
10.2
15.5
17.9
(eq. It) Li.COOH terminal group
90.3
85.6
120.5
(eq. It) Retention of
20
35
10 elongation (%)
• COOH terminal group: a value of a chip before shaping
• Li.COOH: the increase in the number of COOH terminal groups between before and after a wet-heating treatment of an undrawn sheet
• COOH terminal group: a value of a chip before shaping
• ~COOH: the increase in the number of COOH terminal groups between before and after a wet-heating treatment of an undrawn

[0095J [Table 5J

39
sheet
[0096]
[Table 6]

• COOH terminal group: a value of a chip before shaping
• L""iCOOH: the increase in the number of COOH terminal groups

between before and after a wet-heating treatment of an undrawn sheet
[0097J [Table 7]
Example 13 Example 14
Example 15 Alkali metal phosphate
Sodium Sodium
Potassium dihydrogen
dihydrogen dihydrogen
phosphate phosphate
phosphate Addition amount
1.7
1.7
1.7
(mol/ton) Phosphoric acid/alkali
1.12
1. 12 1.12
metal phosphate pH
5.0
5.0
5.0 Alkali metal
Na Na
Na Amount of alkali metal
39 39 39
(ppm) Divalent metal
Mg Mn
Ca
Amount of divalent
40
156 113
metal (ppm) Polymerization
Sb Sb Sb
catalyst metal Amount of
251 251 403
polymerization catalyst metal (ppm) Total amount of metal
340 446 358
(ppm) Amount of phosphorus
112 112 112
(ppm) Nitrogen content (ppm) 60 60 60
Intrinsic viscosity
0.68
0.83
0.83 COOH terminal group
25
9.2
11. 0
(eq. It) il.COOH terminal group
92
32.1
33.3
(eq. It) Retention of
50 65
65 elongation (% )
• COOH terminal group: a value of a chip before shaping
• il.COOH: the increase in the number of COOH terminal groups between before and after a wet-heating treatment of an undrawn sheet
• COOH terminal group: a value of a chip before shaping
• boCOOH: the increase in the number of COOH terminal groups

[0098] [Table 8]

between before and after a wet-heating treatment of an undrawn sheet
[0099] [Table 9J Example l7
Example 16
E.xample 18 Copolymerized
TMTM
TMTM
BTCA component Copolymerized amount
0.5
(mol% ) Alkali metal phosphate
0.05
Potassium
Sodium
Sodium dihydrogen
dihydrogen
dihydrogen phosphate
phosphate
phosphate Addition amount
l.7
l.7
l.7
(mol/ton) Phosphoric acid/alkali
l. 12
l.12
l. 12
metal phosphate pH
5.0
5.0
5.0 Alkali metal
Na
Na
Na Amount of alkali metal
39
39
39 (ppm) Divalent metal
Mg
Mg
Mg Amount of divalent
68
68
68 metal (ppm) Polymerization
Sb
Sb
Sb catalyst metal Amount of
251
251
251 polymerization catalyst metal (ppm) Total amount of metal
358
358
358 (ppm) Amount of phosphorus
112
112
112 (ppm) Nitrogen content (ppm)
60
60
60 Intrinsic viscosity
O. 90
0.85
0.80 COOH terminal group
9.2
8.5
9.1
(eq. It) Li.COOH terminal group
32.8
33.0
33.2
(eq. It) Retention of
82 elongation (% )
72
• COOH terminal group: a value of a chip before shaping
• Li.COOH: the increase in the number of COOH terminal groups between before and after a wet-heating treatment of an undrawn sheet
• TMTM: trimethyl trimellitate
• BTCA: butane tetracarboxylic acid

CLAIMS
1. A polyester resin composition comprising an alkali metal phosphate in an amount of 1.3 mol/ton to 3.0 mol/ton  and phosphoric acid in an amount of 0.4 to 1.5 times (by mole) that of the alkali metal phosphate.
2. The polyester resin composition according to claim 1  wherein the polyester of the polyester resin composition is polyethylene terephthalate  and the increase in COOH between before and after a wet-heating treatment performed at 155°C for 4 hours under saturated steam is 90 eq./ton or less.
3. A polyester resin composition comprising an alkali metal element in an amount of 1.3 mol/ton to 6.0 mol/ton  and phosphorus element in an amount of 1.8 mol/ton to 7.5 mol/ton  wherein the polyester of the polyester resin composition is polyethylene terephthalate  and the increase in COOH between before and after a wet-heating treatment performed at 155°C for 4 hours under saturated steam is 90 eq./ton or less.
4. The polyester resin composition according to anyone of claims 1 to 3  wherein the content of nitrogen element is less than 100 ppm.

5. The polyester resin composition according to anyone
of claims 1 to 4  wherein the amount of COOH terminal groups is 20 eq./ton or less.
1. The polyester resin composition according to anyone of claims 1 to 5  wherein the polyester resin composition comprises a metal compound whose metal element is at least one member selected from the group consisting of Na  Li  and K  a metal compound whose metal element is at least one member selected from the group consisting of Mg  Ca  Mn  and Co  and a metal compound whose metal element is at least one member selected from the group consisting of Sb  Ti  and Ge  wherein the total amount of the metal elements is 30 ppm to 500 ppm relative to the polyester resin composition as a whole  and the phosphorus compound is contained in an amount of 30 ppm to 150 ppm in terms of the amount of phosphorus element relative to the polyester resin composition as a whole.
2. The polyester resin composition according to any one of claims 1 to 6  wherein the polyester resin composition comprises at least one member selected from the group consisting of polycarboxylic acid components having three or more functionalities  polyhydric alcohol components having three or more functionalities  and polyhydroxycarboxylic acid components having three or

more functionali ties in an amount of 0.01 mol% to 1.0 mol%
relative to all the acid components.
1. A film for a solar battery produced by shaping the polyester resin composition according to anyone of claims 1 to 7.
2. A process for producing a polyester resin composition by conducting polycondensation via esterification or transesterification from an aromatic dicarboxylic acid or an ester-formable derivative of an aromatic dicarboxylic acid and a straight-chain alkylene glycol having 2 to 4 carbon atoms  wherein an alkali metal phosphate in an amount of 1.3 mol/ton to 3.0 mol/ton and phosphoric acid in an amount of 0.4 to 1.5 times (by mole) that of the alkali metal phosphate are added at a stage between the point of time when the esterification or transesterification has been substantially completed and the point of time when the intrinsic viscosity reaches 0.4.
3. The process for producing a polyester resin composition according to claim 9  wherein the phosphoric acid and the alkali metal phosphate are added in the form of a mixed solution in alkylene glycol and the pH of the solution is 2.0 to 6.0.
4. The process for producing a polyester resin composition according to claim 9 or 10  wherein the alkali metal of the alkali metal phosphate is Na or K.
5. The process for producing a polyester resin composition according to anyone of claims 9 to 11  wherein the polyester of the polyester resin composition is polyethylene terephthalate.

ABSTRACT
A method for the production of a polyester resin composition by conducting polycondensation via esterification or transesterification  wherein an alkali metal phosphate in an amount of 1.3 mol/ton to 3.0 mol/ton and phosphoric acid in an amount of 0.4 to 1.5 times (by mole) that of the alkali metal phosphate are added at a stage between the point of time when the esterification or transesterification has been substantially completed and the point of time when the intrinsic viscosity reaches 0.4. A polyester resin composition obtained by the process exhibits excellent long-term hydrolysis resistance and excellent mechanical characteristics.