FR2570077A1 - Process for the preparation of polyester - Google Patents

Abstract

Improvement to the preparation of polyethylene terephthalate and of copolyesters consisting predominantly of ethylene terephthalate units. This improved process is characterised by the following succession of stages: - reaction of a dicarboxylic acid, essentially terephthalic acid, or one of its lower alkyl esters with essentially an aliphatic diol, in the presence of a magnesium compound and/or a calcium compound at least partially soluble in the diol; - distillation of the excess aliphatic diol after addition of a phosphorus compound capable of inhibiting the catalytic action of the magnesium compound and/or of the calcium compound; - polycondensation of the diol dicarboxylate obtained above, in the presence of an alkali metal germanate. The polyester obtained by the process of the invention has a higher conductivity than that obtained with other prior processes, as well as a decreased or eliminated presence of insoluble catalyst residues, which makes it particularly well suited to the preparation of thin films, especially for applications in the fields of magnetic tapes.

Description

PROCESS FOR PREPARING POLYESTER
The present invention relates to an improvement in the preparation of polyester.

 More specifically, the invention relates to the preparation of polyesters or copolyesters mainly constituted by ethylene terephthalate units.

 These polyesters or copolyesters, which we will call for convenience polyethylene terephthalate (or PET) in the present text, are polymers with interesting properties and are known and widely used for many years especially in the manufacture of fibers and films .

There are many variants of polyethylene terephthalate preparation processes which are divided into two main types - the direct esterification of terephthalic acid (optionally
associated with other dicarboxylic acids) by ethylene glycol or
ethylene oxide, followed by polycondensation of the terephthalate of
bis (2-hydroxyethyl) obtained - transesterification between a dialkyl terephthalate (the most
often dimethyl terephthalate) and ethylene glycol, followed by
as previously by a polycondensation phase of the terephthalate of
bis (2-hydroxyethyl).

 Among the catalysts commonly used in the transesterification phase, there may be mentioned compounds of manganese, zinc, titanium, lithium, magnesium or calcium, generally in the form of their carboxylic acid salts, their halides or their hydroxides.

 During subsequent removal of excess ethylene glycol and during polycondensation, the transesterification catalysts tend to promote undesirable side reactions and degradation reactions.

 To overcome this disadvantage it is generally recommended to introduce at this stage a phosphorus compound, often called stabilizer, whose function is to neutralize the harmful effect of these catalysts.

 For the next phase of the various processes for the preparation of polyethylene terephthalate, many polycondensation catalysts are also known. The most frequently cited and used include antimony oxides, organtitan compounds, germanium oxides.

 US Pat. No. 2,998,412 lists a series of known catalysts serving for one of the two process phases or for the two phases successively.

 When the polyethylene terephthalate is used for the preparation of films, one of the important characteristics that it must possess is an electrical conductivity sufficiently high to allow electrostatic plating on the casting drum. Indeed, the process commonly used to prepare films consists in extruding the polyester in the molten state through a die on a rotary cooling drum.

 In order to ensure good contact of the extruded sheet on the casting drum, said sheet passes between the die and the drum in the vicinity of a wire-shaped or knife-blade electrode subjected to a high voltage. The static electric charge created on the sheet not yet solidified causes it to press against the casting drum during its solidification.

 In view of the high voltages required by the high velocity of aoulée, there are problems of electric arcs between the electrodes and the surface of the drum. These problems to be solved require a polyester having a very good conductivity, provided by any catalysts or additives it contains.

 One of the objects of the process according to the present invention is precisely to provide a polyethylene terephthalate having a greater conductivity than that of polyesters obtained by previous methods, and thus making it possible to prepare better quality films, especially for applications such as audio tapes, video or packaging.

 Another advantage of the invention lies in obtaining a polyester having a level of insoluble catalytic residues particularly low, if not zero; this eliminates or at least greatly reduces the risk of surface defects of the thin films that can be prepared from said polyester.

 Indeed, for certain applications, such as magnetic tapes, especially video tapes, and capacitors, the thin film (a few micrometers thick) must be practically free of surface defects; one of the causes of these defects is the insoluble catalytic residues. The method according to the invention therefore makes it possible to essentially eliminate this source of defects.

 Finally, the process according to the invention leads to a polyester having a good appearance, as well as a good transparency.

More precisely, the present invention can be defined as an improved polyester preparation process characterized by the following succession of phases - reaction of a dicarboxylic acid, consisting essentially of
terephthalic acid, or one of its lower alkyl esters with
essentially an aliphatic diol having 2 to 4 carbon atoms,
in the presence of a magnesium compound and / or a calcium compound,
at least partially soluble in the diol - distillation of the excess aliphatic diol after addition of a compound
phosphorus capable of inhibiting the catalytic effect of the magnesium compound
and / or the calcium compound: - polycondensation of the diol dicarboxylate obtained above, in
presence of an alkaline mental germanate
By the term lower alkyl is meant according to the current definition the allyl groups, linear or branched, having 4 carbon atoms such as methyl, ethyl, n-propyl, isopropyl or butyl.

Due to many applications of polyethylene terephthalate, the process according to the invention is preferably applied to the preparation of this polyester. Thus terephthalic acid or methyl terephthalate will be used alone or in mixture with less than 20% by weight of one or more other diacids such as orthopntalic, isophthalic, naphthalenedicarboxylic-2,5, naphthalenedicarboxylic acid-2, 6-naphthalenedicarboxylic-2,7, diphenyldicarboxylic, hexahydroterephthalic, adipic, succinic, sebacic, azelaic or one or more methyl esters of these diacids. In the same way, the diol used will be ethylene glycol, alone or mixed with less than 20% by weight of other diols, such as, for example, 1,3-propanediol, 1,4-butanediol or 2-dimethyl-2-butanediol. , 2-1,3-propanediol or 1,4-cyclohexanedimethanol
preferably this polyester prepared by the process of the invention will comprise at least 90% by weight of ethylene terephthalate units.

 The molar ratio between the aliphatic diol and the dicarboxylic acid or its lower alkyl ester may vary within wide limits. Generally this molar ratio is equal to or greater than 1.

 Preferably the ratio will be 1.5 to 2.5 in the case of the transesterification of a lower alkyl ester of dicarboxylic acid and it will be 1.1 to 1.3 in the case of a direct esterification of the dicarboxylic acid. dicarboxylic acid.

 The temperature at which the direct esterification reaction or the transesterification reaction is carried out is known.

Generally, the direct esterification is carried out between 200 ° C. and 290 ° C. while the transesterification is carried out between 1500 ° C. and 250 ° C.

 Usually the pressure at which one operates is first atmospheric pressure, or a higher pressure up to 10 bar, and then this pressure is reduced to facilitate the removal of excess diol.

 Among the magnesium or calcium compounds used in the esterification or transesterification phase, mention may in particular be made of magnesium acetate, magnesium oxalate, magnesium propionate, magnesium butyrate, magnesium benzoate , magnesium chloride, magnesium bromide, magnesium iodide, magnesium hydroxide, magnesium alcoholates such as magnesium ethylene glycolate, calcium acetate, calcium oxalate, propionate calcium, calcium butyrate, calcium benzoate, calcium chloride, calcium bromide, calcium iodide, calcium hydroxide and calcium alkoxides such as calcium ethylene glycolate.

 The magnesium compounds are generally preferentially used and among them magnesium acetate is more particularly preferred.

Generally, the amount of catalyst employed is expressed
moles of metal atoms (t or Ca) based on the weight of polyester
final.

 Thus the usual amounts of catalyst are from 0.5 to 40 moles of magnesium and / or calcium atoms per 106 grams of final polyester.

 Preferably, 2 to 10 moles of magnesium and / or calcium atoms are used per 106 grams of final polyester.

The phosphorus compounds used to inhibit the effect of these catalysts, when the esterification or transesterification stage is complete, are known for most of them and are generally referred to as stabilizers. These are essentially the alkyl esters of phosphoric acid and phosphorous acid, phosphonic acid, alkylphosphonic and phenylphosphonic acids and their respective esters and alkyl alkylphosphonoalkanoates. As examples of such phosphorus compounds mention may in particular be made of phosphate
trimethyl, triethyl phosphate, tributyl phosphate,
triphenyl phosphate, monomethyl phosphate, phosphate
dimeethyl, monoethyl phosphate, diethyl phosphate,
monobutyl phosphate, dibutyl phosphate, phosphite
trimethyl, tributyl phosphite, triethyl phosphite,
triphenyl phosphite, monomethyl phosphite, phosphite
dimethyl, monoethyl phosphite, diethyl phosphite, monobutyl phosphite, dibutyl phosphite, phosphonic acid,
methylphosphonic acid, dimethyl methylphosphonate, diethyl methylphosphonate, ethylphosphonic acid,
dimethyl ethyl phosphonate, diethyl ethyl phosphonate, phenyl phosphonic acid, dimethyl phenyl phosphonate, diethyl phenyl phosphonate, diphenyl phenyl phosphonate, dimethyl benzyl phosphonate, benzyl phosphonic acid, diethyl benzyl phosphonate, methyl methyl phosphono acetate, the
methylphosphonoacetate, butyl methylphosphonoacetate,
methyl ethyl phosphonoacetate, ethyl ethyl phosphonoacetate,
butyl ethylphosphonoacetate, dimethylphosphonoacetate
methyl, ethyl dimethylphosphonoacetate, propyl dimethylphosphonacetate, butyl dimethylphosphonoacetate, methyl diethylphosphonoacetate, ethyl diethylphosphonoacetate, propyl diethylphosphonacetate, butyl diethylphosphonoacetate, methyl methylphosphonopropionate, methyl dimethylphosphonopropionate ethyl ethylphosphonopropionate, ethyl diethylphosphonopropionate, ethyl methylphosphonopropionate, ethyl dimethylphosphonopropionate, methyl ethylphosphonopropionate, methyl diethylphosphonopropionate, methyl dimethylphosphonobutyrate, ethyl dimethylphosphonobutyrate, diethylphosphonobutyrate methyl, diethylphosphonobutyrate ethyl.

 These phosphorus compounds can be used alone or as mixtures of several of them.

 The amount of phosphorus compound used in the process according to the invention may be expressed by the P / M ratio, M being the sum of the number of moles of magnesium and / or calcium atoms involved and the number of moles of alkali metal atoms provided by the alkaline germanate and P representing the number of moles of phosphorus atoms of the phosphorus compound. This P / M ratio is generally from 0.1 to 0.8. This ratio is preferably from 0.2 to 0.6.

 When the transesterification catalyst is a calcium carboxylate, it is necessary, in order to obtain a polyester without precipitate due to the insoluble catalytic residues, to also respect a molar ratio P / Ca, between the number P of moles of phosphorus atoms of the phosphorus compound and Ca the number of moles of calcium atoms of the calcium compound, between 0.3 and 0.9.

 Among the phosphorus compounds which are suitable for carrying out the process according to the invention, those which are more particularly preferred are the lower dialkyl phosphonates, the lower dialkyl alkyl phosphonates, the lower dialkyl phenyl phosphonates and the lower alkyl phosphonates. lower alkyl.

 The catalyst used for the polycondensation phase in the present process is an alkali metal germanate such as sodium, potassium or lithium germanate. Such alkali metal germanates are prepared by known methodes, such as, for example, by reacting the oxides or carbonates of the corresponding levels with germanium dioxide.

 The amount of alkali metal germanate employed can vary widely. In general it is such that the number of moles of germanium atoms engaged per 106 gramms of final polyester is 0.2 to 10; preferably the number of moles of germanium atoms engaged is 0.3 to 3.0 for 106 g of final polyester.

 The alkali metal germanate is usually introduced into the reaction medium at the beginning of the polycondensation phase, either in the form of a powder or in the form of a solution or of a suspension, for example in a small amount of the diol used for the preparation of the dicarboxylate alkylene.

 It can also be present in the medium as early as the transesterification stage.

 Generally, the polycondensation phase is conducted at a temperature of 270 ° C. and preferably at a temperature of 275 ° C. to 285 ° C.

 The process of the invention can be carried out batchwise or continuously according to known conventional techniques. Significantly improved results are obtained in particular by operating continuously.

 Different compounds that it is desired to use in the polyester, such as fillers for example, can be introduced before or during the polycondensation phase.

 As previously stated, one of the advantages of the pressing process is to provide a polyester having a higher conductivity (ie lower resistivity) than previously prepared polyesters which allows for excellent veneer electrostatic, when said polyester is used for the preparation of films.

 The resistivity of the polyester is measured on polyester granules. The method used will be described in the examples which follow.

Example 1

 In a 7.5 liter stainless steel reactor equipped with stirring, heating means, pressure and temperature control instruments, a distillation column and means for introducing the various reagents, 3300 grams (17 moles) of dimethyl terephthalate (DMr) and then 2003 g (32.3 moles) of ethylene glycol are charged. The mixture is stirred and heated to 150 ° C., 2.15 g of magnesium acetate tetrahydrate (corresponding to 3.1 moles of magnesium ion relative to 106 g of final polyester) are then introduced in the form of a solution. to 10% by weight in ethylene glycol.

 The temperature of the reaction mixture is raised from 150 ° C. to 220 ° C. while the transesterification reaction is carried out and the methanol formed distils.

 Then the temperature is increased from 220 ° C. to 260 ° C. while the excess of ethylene glycol is distilled. when the temperature of the mixture is 225 ° C., 0.67 gram of ethyl diethylphosphonoacetate in solution at 10% by weight in ethylene glycol is added.

 when the temperature reaches 240 ° C., 0.96 grams of sodium germanate (H 3 Na Ge 2 O 6, H 2 O) are added.

 The temperature of the reaction mixture is then increased from 260 ° C. to 285 ° C. in one hour while decreasing the pressure from atmospheric pressure to less than 133 pascals. The polycondensation is carried out for 35 minutes at 285 ° C. under a pressure of less than 133 pascals.

 Q1 obtained a polymer having a viscosity number (IV) of 0.740 deciliter / gram measured at 250C in 1% by weight solution in orthochlorophenol.

 The resistivity of the obtained polymer is measured as follows.

 Some granules of the polyester are melted on a rectangular quartz plate (20 x 55 mm) having a thickness of 3 mm. After melting 2 stainless steel wires having a diameter of 0.6 mm are arranged parallel to 10 mm from each other in the molten polyester.

 A second quartz plate identical to the first is placed over the wires.

 The assembly held by clamps is introduced into an oven heated to 275 C. son is applied to a voltage of 120 volts and measured every 5 minutes the intensity I of the current that passes for 20 minutes.

 the values found for I. are averaged

 The resistivity p is given in ohmmeter by the formula e = I 0.144 (I being expressed in amperes).

 For each polyester whose resistivity is to be measured, two tests are carried out as described above.

 The polyester obtained in Example 1 has a resistivity of 0.11 × 10 6. m.

 The methods used to detect particles from insoluble catalytic residues, which will be able to create surface defects during processing into thin films of the polyester are as follows. These three methods give qualitative results.

a) Optical method
It consists of melting about 40 milligrams of polyester
between 2 plates of glass, then to soak all in water
cold to keep the polyester transparent (no
crystallized).

The observation is then made using an optical microscope, in
reflected light on black background with a magnification of 200. On
qualifies the appearance, number and approximate size of
insoluble particles.

b) chemical method
If the optical method concludes that there are no particles,
then uses the complementary chemical method. It consists of
dissolve polyester at a concentration by weight of approximately 5% in
a 50/50 mixture by weight phenol-dichloroethane. The solution is
filtered on a millipore filter having a passage diameter of
0.1 m.

The filtered solution is analyzed to determine the amount
of the catalyst it contains, which makes it possible to determine whether there is
had or had not separated insoluble particles.

c) Physical method
The manufactured polymer is melted and then filmed on a thickness
maximum of 90 m. The film is then stretched by a coefficient of 3
in its length, then by a coefficient of 3 in its width.

The resulting film (which is less than 10 m thick) is
metallized with gold or aluminum over a thickness of 1 to 2 m. A
photograph of the surface state at magnification 250 then allows
to determine the even minimal presence of precipitate.

 Another important characteristic of the polyester is represented by the rate of free - or terminal - COCH functions it contains. This level of - COCH is determined by dissolving the polyester in orthochlorophenol and measuring the functions - COOH by a standard solution of sodium hydroxide.

 The polyester obtained in Example 1 has a function rate - COCH liters of 26 equivalents - COCH per 106 grams of polyester.

 The various characteristics of Example 1 as well as the results of measurements and observations made on the prepared polyester are collated in Table 1 below.

Example 2

Example 1 is repeated with the same reagents, but with different amounts of catalysts
magnesium acetate (tetrahydrate: 4.30 g
- ethyl diethylphosphonoacetate: 2.08 g
sodium germanate: 0.96 g
Polycondensation time: 50 minutes at 285 C.

The polyester obtained has:
a resistivity of 0.09 × 10 6. m
a viscosity number of 0.760 dl / g
- a rate of free cooe functions of 32 equivalents / 106 g of
polyester.

These different characteristics and measures are shown in Table 1 below.

Example 3

Example 1 is repeated with the following amounts of catalysts:
magnesium acetate (tetrahydrate): 2.15 g
ethyl diethylphosphonoacetate: 1.37 g;
sodium germanate: 0.96 g
Polycondensation time 1 hour at 2850C
The polyester obtained has:
- a resistivity of 0.18 x 106 #. m
a viscosity number of 0.785 dl / g
- a rate of functions - free COCH of 19 equivalents
COOH / 106 g of polyester.

These different characteristics and measures are shown in Table 1 below.

Comparative test
The procedure is as in Example 1, but with the following amounts of catalysts
magnesium acetate (tetrahydrate): 2.15 g
ethyl diethylphosphonoacetate: 2.03 g
sodium germanate s 0.32 g (The molar ratio P / Mg is 0.8 in this test).

Duration of the polycondensation at 285 C: 1 h 20 min.

The polyester obtained
a resistivity of 1.4 x
a viscosity number of 0.710 dl / g
- a rate of free -COCE functions of 31 equivalents coo for
106 g of polyester.

Comparative test b
The procedure is as in Example 1, but with the following amounts of catalysts:
magnesium acetate (tetrahydrate): 2.15 g
- ethyl diethylphosphonoacetate 0.71 g
antimony oxide Sb203: 1.33 g
Duration of the polycondensation at 285 C: 25 min.

The polyester obtained has:
- a resistivity of 0.21 x 106 # .m
a viscosity number of 0.700 dl / g;
a rate of free CO functions of 41 equivalents COCH for
106 g of polyester.

Comparative test c
The procedure is as in Example 1, with the following amounts of catalysts
magnesium acetate (tetrahydrate): 2.15 g
ethyl diethylphosphonoacetate: 2.77 g
- antimony oxide: 1.33 g
Duration of the polycondensation at 285 C: 40 min.

The polyester obtained
a resistivity of 5.7 x 106 # .m
a viscosity index of 0.670 dl / g
a level of free -COOH functions of 13 equivalents -COOH for
106 g of polyester.

Comparative test of
The procedure is as in Example 1, with the following amounts of catalysts
- magnesium acetate, (tetrahydrate): 2.15 g
ethyl diethylphosphonoacetate: 1.07 g
- germanium oxide: 0.70 g
- soda in glycolic solution at 10% by weight (introduced after
germanium oxide): 0.082 g of sodium hydroxide.

Duration of polycondensation at 2850C: 2 hours
The resulting polyester has a resistivity of 0.2 x 10 6 μm;
a viscosity number of 0.720 dl / g;
a rate of free COCH functions of 42 equivalents -COOH for
106 g of polyester.

TABLE 1.

moles <SEP> Mg <SEP> Moles <SEP> Ge <SEP> Ratio <SEP> Moles <SEP> Na <SEP> Moles <SEP> Sb <SEP> Resistance <SEP> Index <SEP> of <SEP> precipitated <SEP> eq. <SEP> COOH
<tb> for <SEP> for <SEP> molar <SEP> for <SEP> for <SEP> time <SEP> of <SEP> viscosity <SEP> (residues <SEP> for
<tb> Tests <SEP> 106 <SEP> g <SEP> of <SEP> 106 <SEP> g <SEP> of <SEP> P / Mg <SEP> + <SEP> Na <SEP> 106 <SEP> g <SEP> of <SEP> 106 <SEP> g <SEP> of <SEP> polyester <SEP> (in <SEP> d1 / g) <SEP> catalytic <SEP> Aspect <SEP> 106 <SEP> g <SEP> de
<tb> polyester <SEP> polyester <SEP> polyester <SEP> polyester <SEP> (in <SEP> 106 <SEP> ques <SEP> polyester
<tb>#<SEP> .m) <SEP> Insoluble)
<tb> Example <SEP> 3.1 <SEP> 2.1 <SEP> 0.22 <SEP> 1.05 <SEP> 0 <SEP> 0.11 <SEP> 0.740 <SEP> no <SEP> 1 <SEP> 26
<tb> 1
<tb> Example <SEP> 6.2 <SEP> 2.1 <SEP> 0.39 <SEP> 1.05 <SEP> 0 <SEP> 0.09 <SEP> 0.760 <SEP> no <SEP> 2 <SEP > 32
<tb> 2
<tb> Example <SEP> 3.1 <SEP> 2.1 <SEP> 0.45 <SEP> 1.05 <SEP> 0 <SEP> 0.18 <SEP> 0.785 <SEP> no <SEP> 1 <SEP> 19
<tb> 3
<tb> Assay <SEP> 3.1 <SEP> 0.7 <SEP> 0.80 <SEP> 0.35 <SEP> 0 <SEP> 1.4 <SEP> 0.710 <SEP> no <SEP> 1 <SEP> 31
<tb> a
<tb> Assay <SEP> 3.1 <SEP> 0 <SEP> 0.31 <SEP> 0 <SEP> 2.46 <SEP> 0.21 <SEP> 0.700 <SEP> yes <SEP> 2 <SEP > 41
<tb> b <SEP> (very <SEP> end)
<tb> Assay <SEP> 3.1 <SEP> 0 <SEP> 1.25 <SEP> 0 <SEP> 2.46 <SEP> 5.7 <SEP> 0.670 <SEP> yes <SEP> 1 <SEP > 13
<tb> c <SEP> (very <SEP> end)
<tb> Assay3.1 <SEP> 2.1 <SEP> 0.39 <SEP> 0.62 <SEP> 0 <SEP> 0.2 <SEP> 0.702 <SEP> yes <SEP> 5 <SEP> 42
<tb> d <SEP> (coarse)
<tb> Appreciation of the appearance of polyester:

1 <SEP>#<SEP> 2 <SEP>#<SEP> 3 <SEP>#<SEP> 4 <SEP>#<SEP> 5
<tb> very <SEP> good <SEP> good <SEP> average <SEP> bad <SEP> very <SEP> bad
<tb> (colorless <SEP> and <SEP> (yellow)
<tb> brilliant)
<tb> gradual transition from colorless and shiny to yellow.

Example 4

 In a 100-liter stainless steel reactor equipped with stirring, heating means, instruments for controlling the pressure and the temperature, a distillation column and means for introducing the various reagents. 50.0 kg (257.7 moles) of dimethyl terephthalate are charged, followed by 30.4 kg (489.5 moles) of ethylene glycol.

 The transesterification and then polycondensation operation is carried out as described in Example 1.

The charges of various catalysts used are as follows
94.48 calcium acetate: 82.6 g;
ethyl diethylphosphonoacetate: 43.4 g;
sodium germanate: 9.6 g
Duration of the polycondensation at 285 C: 1h 40 min.

The polyester obtained
a resistivity of 0.15 × 10 6 μm;
a viscosity index of 0.745 dl / g
a free COCH function rate of 37 equivalents COOH / 106 g
of polyester.

These different characteristics and measures are shown in Table 2 below:
Example 5

Example 4 is repeated with the following catalysts
94.4% calcium acetate: 82.6 g
ethyl diethylphosphonoacetate: 60.7 g
sodium germanate: 9.6 g
Duration of the polycondensation at 285 C: 1 h. 20 min.

The polyester obtained
a resistivity of 0.31 × 10 6 μm;
a viscosity number of 0.698 dl / g;
a free -COOH function level of 29 equivalents COOH / 106 g
of polyester.

These different characteristics and measures are shown in Table 2 below:
Example 6

Example 4 is repeated with the following catalysts
94.4% calcium acetate: 82.6 g
ethyl diethylphosphonoacetate: 59.6 g
sodium germanate: 9.6 g.

Duration of the pclycondensation at 2850 C: 2 h.

The polyester obtained has:
a resistivity of 0.30 x 106 μm;
a viscosity number of 0.765 dl / g
a free -COOH function level of 28 equivalents COOH / 106 g
of polyester.

These different characteristics and measures are shown in Table 2 below:
Comparative test e
The procedure is as in Example 4, with the following amounts of catalysts:
94.4% calcium acetate: 51.7 g
- ethyl diethylphosphonoacetate: 30.5 g
- antimony oxide: 17.7 g
Duration of the polycondensation at 2850 C: 4 h 09 min.

The polyester obtained
a resistivity of 1.2 × 10 6 μm;
a viscosity number of 0.746 dl / g;
a level of free -COOH functions of 33 equivalents COOH for
106 g of polyester.

These different characteristics and measures are shown in Table 2 below.

Comparative test f
Ch operates as in Example 4, with the following amounts of catalysts
94.4% calcium acetate: 51.7 g
- phosphoric acid: 14.4 g
antimony oxide: 17.7 g. Duration of the polycondensation at 285 ° C.: 4 h 19 min.

The polyester obtained has:
a resistivity of 0.41 × 10 6 μm;
a viscosity number of 0.736 dl / g
- a rate of free COCH functions of 37 COCH equivalents for
106 g of polyester.

Comparative test
The procedure is as in Example 4, with the following amounts of catalysts
94.4% calcium acetate: 82.6 g
ethyl diethylphosphonoacetate: 27.2 g;
- sodium-germanate: 9.6 g.

Duration of the polycondensation at 2850 C: 1 h 45 min.

The polyester obtained has:
a resistivity of 0.15 × 10 6 μm;
a viscosity number of 0.732 dl / g;
- a rate of free COoe functions of 7.3 equivalents
-COOH for 106 g of polyester.

These different characteristics and measures are shown in Table 2 below.

Comparative test h
The procedure is as in Example 4, with the following amounts of catalysts
94.4% calcium acetate: 82.6 g
ethyl diethylphosphonoacetate: 96.3 g:
sodium germanate: 9.6 g.

Duration of the polycondensation at 285 C: 2h 30 min.

The polyester obtained has:
a resistivity of 4.8 × 10 6 μm;
a viscosity index of 0.669 dl / g
a level of free -COOH functions of 39 equivalents
-COOH for 106 g of polyester.

TABLE 2.

moles <SEP> Ca <SEP> Moles <SEP> P <SEP> Moles <SEP> Ge <SEP> Report <SEP> Report <SEP> Moles <SEP> Na <SEP> Moles <SEP> Sb <SEP> Resistance <SEP> Index <SEP> of <SEP> Precipitation <SEP> eq. <SEP> COOH
<tb> for <SEP> for <SEP> for <SEP> molar <SEP> molar <SEP> for <SEP> for <SEP> time <SEP> of <SEP> viscosity <SEP> (residues <SEP> for
<tb> Tests <SEP> 106 <SEP> g <SEP> of <SEP> 106 <SEP> g <SEP> of <SEP> 106 <SEP> g <SEP> of <SEP> P / Ca <SEP> + <SEP> Na <SEP> P / Ca <SEP> 106 <SEP> g <SEP> of <SEP> 106 <SEP> g <SEP> of <SEP> polyester <SEP> (in <SEP> d1 / g) <SEP> Catalyst <SEP> 106 <SEP> g <SEP> of
<tb> polyester <SEP> polyester <SEP> polyester <SEP> polyester <SEP> polyester <SEP> (in <SEP> 106 <SEP> ques <SEP> polyester
<tb># .m) <SEP> insoluble)
<tb> Example <SEP> 10.0 <SEP> 3.97 <SEP> 1.38 <SEP> 0.37 <SEP> 0.40 <SEP> 0.78 <SEP> 0 <SEP> 0.15 <SEP> 0.745 <SEP> no <SEP> 37
<tb> 4
<tb> Example <SEP> 10.0 <SEP> 5.55 <SEP> 1.38 <SEP> 0.52 <SEP> 0.55 <SEP> 0.78 <SEP> 0 <SEP> 0.31 <SEP> 0,698 <SEP> no <SEP> 29
<tb> 5
<tb> Example <SEP> 10.0 <SEP> 5.45 <SEP> 1.38 <SEP> 0.50 <SEP> 0.54 <SEP> 0.78 <SEP> 0 <SEP> 0.30 <SEP> 0.765 <SEP> no <SEP> 28
<tb> 6
<tb> Assay <SEP> 6.25 <SEP> 2.74 <SEP> 0 <SEP> 0.44 <SEP> 0.44 <SEP> 0 <SEP> 2.46 <SEP> 1.2 <SEP > 0.746 <SEP> yes <SEP> 33
<tb> e
<tb> Assay <SEP> 6.25 <SEP> 2.74 <SEP> 0 <SEP> 0.44 <SEP> 0.44 <SEP> 0 <SEP> 2.46 <SEP> 0.41 <SEP > 0.736 <SEP> yes <SEP> 37
<tb> f
<tb> Assay <SEP> 10.0 <SEP> 2.48 <SEP> 1.38 <SEP> 0.23 <SEP> 0.25 <SEP> 0.78 <SEP> 0 <SEP> 0.15 <SEP> 0.732 <SEP> yes <SEP> (very <SEP> 7.3
<tb> g <SEP> rude)
<tb> Assay <SEP> 10.0 <SEP> 8.70 <SEP> 1.38 <SEP> 0.81 <SEP> 0.87 <SEP> 0.78 <SEP> 0 <SEP> 4.8 <SEP> 0.661 <SEP> yes <SEP> (very <SEP> 39
<tb> h <SEP> rude)
<Tb>

Claims (12)

 presence of an alkali metal germanate.  polycondensation of the diol dicarboxylate obtained above, in  magnesium and / or calcium compound  phosphorus compound capable of inhibiting the catalytic effect of the compound  - distillation of the excess aliphatic diol after addition of a  calcium, at least partially soluble in the diol  carbon, in the presence of a magnesium compound and / or an OompDsé  essentially an aliphatic diol having 2 to 4 carbon atoms  terephthalic acid, or a lower alkyl ester thereof with  reaction of a dicarboxylic acid, consisting essentially of  following succession of phases  1) Improved method of polyester preparation characterized by the 2) Method according to claim 1 characterized in that in the phase  esterification or transesterification a compound of the  magnesium such as in particular magnesium acetate, oxalate  magnesium, magnesium propionate, magnesium butyrate,  magnesium benzoate, magnesium chloride, bromide  magnesium, magnesium iodide, magnesium hydroxide,  magnesium alcoholates such as magnesium ethylene glycolate. 3) Process according to claim 1 characterized in that in the phase  esterification or transesterification a compound of the  calcium such as in particular calcium acetate, calcium oxalate,  calcium propionate, calcium butyrate, benzoate  calcium, calcium chloride, calcium bromide, iodide  calcium, calcium hydroxide and calcium alkoxides such as  calcium ethylene glycolate. 4) Process according to claim 2 characterized in that the compound of  magnesium used is magnesium acetate. 5) Process according to any one of claims 1 to 4 characterized in  what the esterification compound or transesterification  represents from 0.5 to 40 moles of magnesium and / or calcium atoms  for 106 grams of final polyester and preferably 2 to 10 moles  for 106 grams of final polyester. 6) Process according to any one of claims 1 to 5 characterized in  what the phosphorus compound used is selected from a group  essentially comprising the alkyl esters of phosphoric acid  and phosphorous acid, phosphonic acid, acids  alkylphosphonic and phenylphosphonic acids and their esters  respective alkyl-phosphonoalkanoates. 7) Method according to claim 6 characterized in that the compound '  phosphorus used is preferably a diaikyl phosphonate  lower, a dialkyl lower alkyl dialkylphosphonate, a  lower dialkyl phenylphosphonate, or lower alkyl  lower alkyl phosphonoacetate. 8) Process according to any one of claims 1 to 7 characterized in  the amount of alkali metal germanate used is such  that the number of moles of germanium atoms engaged for 106 g of  final polyester is 0.2 to 10 and preferably 0.3 to 3. 9) Method according to any one of claims 1 to 8 characterized in  what the P / M ratio between the number P of moles of phosphorus atoms  of the phosphorus compound and M which is the sum of the number of moles of atoms  magnesium and / or calcium and the number of moles of  alkali metal provided by the alkaline germanate is from 0.1 to 0.8 and  preferably from 0.2 to 0.6. 10) Method according to one of claims 1, 3 and 5 to 9 characterized in  what the P / Ca ratio between the number P of moles of atoms of  phosphorus of the phosphorus compound and Ca the number of moles of  calcium of the calcium compound is between 0.3 and 0.9. 11) Method according to any one of claims 1 to 10 characterized  in that the prepared polyester comprises at least 90% by weight of  ethylene terephthalate units. 12) Method according to any one of claims 1 to 11 characterized  in that the molar ratio of the aliphatic diol to the acid  dicarboxylic acid or its lower alkyl ester is equal to or greater than  to 1.