JP2507724B2 - Method for producing flame resistant polyester - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a flame-resistant polyester, and more particularly to a method for producing a flame-resistant polyester having thermotropic liquid crystallinity with high intrinsic viscosity. It is a thing.

(Prior Art) Conventionally, polyester has been widely accepted as a general molded product, but many polyesters have insufficient mechanical properties such as bending strength and bending elastic modulus. Therefore, it was not suitable for fields requiring high physical properties.

In recent years, there has been an increasing demand for materials excellent in strength, rigidity, heat resistance, chemical resistance, etc. regardless of whether they are fibers, films or molded products.

Already, as a pioneer of polyester with such high physical properties, WJ Jackson has been
-Thermotropic liquid crystalline polyester (LCP) composed of -hydroxybenzoic acid (4HBA) has been reported, and attention has been paid to such thermotropic liquid crystalline polyester. This thermotropic liquid crystalline polyester has mechanical properties that are several times higher than those of ordinary polyesters that do not exhibit thermotropic liquid crystalline properties, and we have found a new possibility for highly functional polymers.

In general, this thermotropic liquid crystalline polyester is produced by polyethylene terephthalate (PE
It is produced by bringing T) into contact with 4-acetoxybenzoic acid (4HBA-A) to depolymerize PET by an acidolysis reaction, and then polycondensing the depolymerized product in the second step.

By the way, in recent years, there has been an increasing demand for flame resistance of various plastic products from the viewpoint of fire prevention. In particular, it is said that the PET / 4HBA type LCP is inferior in flame resistance to the aromatic type LCP, and therefore, establishment of a countermeasure therefor is urgently needed.

Conventionally, various methods for imparting flame resistance to polyesters have been proposed, and it is considered effective to add a phosphorus compound to the polyester.

For example, Japanese Patent Publication No. 55-41610 discloses a method of producing a flame-resistant polyester by adding a specific phosphorus compound and copolymerizing the same. However, in this method, a polyester having a high degree of polymerization is produced. Requires that the phosphorus compound to be added be a compound having a divalent ester-forming functional group in advance. In that case, depending on the kind of the component constituting the portion having the ester-forming functional group to be selected, the phosphorus compound to be added may be added. Because of the high price and extremely difficult manufacturing, there was an economic problem in the end.

Also, Japanese Patent Publication No. 56-9178 proposes a method of blending a phosphorus compound having a specific structure with a polyester. In this method, a functional group capable of depolymerizing the polyester, such as a PH bond, is provided. When a phosphorus compound is used, the degree of polymerization of the polyester is remarkably reduced, or the ends of the polyester are blocked, thereby deteriorating the physical properties of the obtained polyester, which is not practical.

(Problems to be Solved by the Invention) The present invention is intended to provide a method for economically producing a polyester which can impart flame resistance to the polyester without deteriorating the physical properties, and further has thermotropic liquid crystallinity. is there.

(Means for Solving Problems) As a result of earnest research on a method for producing a flame-resistant polyester having thermotropic liquid crystallinity which does not have the above-mentioned problems, the present inventors have found that an unsaturated compound is previously added to the main chain of the polyester. Copolymerized with the specific P-
The present inventors have found that it is extremely effective to add a phosphorus compound having an H bond to the unsaturated bond, and arrived at the present invention.

That is, the present invention comprises an aromatic oxycarboxylic acid component represented by the following formula (I) and an alkylene terephthalate component, the molar ratio of both is 30:70 to 95: 5, and the intrinsic viscosity is 0.5 or more. When the thermotropic liquid crystalline polyester is produced, an unsaturated compound having an ester-forming functional group is copolymerized so as to be 0.5 to 10 mol% with respect to all repeating units constituting the thermotropic liquid crystalline polyester, and then, The gist is a method for producing a flame-resistant polyester, which comprises reacting a phosphorus compound represented by the following formula (II).

(In the formula, Ar represents a divalent aromatic group. However, the aromatic ring may be substituted with a substituent. Further, R is a hydrogen atom, a hydroxyl group or a lower acyl group, and R ₁ and R ₂ are hydrogen. An atom, an alkyl group, an aryl group, an alkoxy group, and an allyloxy group, which are the same or different groups and R ₁ and R ₂ may form a ring with each other.) According to the method of the present invention The intrinsic viscosity [η] of the produced polyester is at least 0.5 dl / g or more, preferably 0.5 to 1.
0 dl / g, optimally 0.6-0.8 dl / g. Intrinsic viscosity [η]
If is less than 0.5 dl / g, various physical and mechanical properties such as the desired bending properties will be inferior.

In the present invention, the thermotropic liquid crystalline polyester mainly comprises an aromatic oxycarboxylic acid component represented by the above formula (I) and an alkylene terephthalate component.

The aromatic oxycarboxylic acid component used in the present invention is a compound represented by the formula (I), for example, 4-
Hydroxybenzoic acid (4HBA), 1-hydroxy-4-naphthoic acid, 4-hydroxy-3-methylbenzoic acid, 4-
Hydroxy-3-chlorobenzoic acid, 2-hydroxy-6
-Naphthoic acid or the like, or lower acetate such as acetic acid ester, propionic acid ester, butyric acid ester, isopropionic acid ester, α, α-dimethylpropionic acid ester, and the like, 4HBA or 4-acetoxybenzoic acid (4HBA- A) is the best. Incidentally, when the aromatic oxycarboxylic acid itself is used as the aromatic oxycarboxylic acid, the amount equal to or more than the amount equivalent to the aromatic oxycarboxylic acid (preferably 1.05 to 1.25) is, of course, used.
It goes without saying that the acid anhydride of lower fatty acid (double equivalent) is also used in combination. Further, in order to obtain the thermotropic liquid crystalline polyester, since it is responsible for the rigid portion of the thermotropic liquid crystalline polyester to be formed, it is basically necessary to select a para-oriented or amphi-oriented compound. As long as the liquid crystallinity of the resulting polyester is not impaired, compounds having ortho, meta, ana, epi, cata, peri, or pros orientation can be copolymerized.

The alkylene terephthalate component referred to in the present invention is mainly based on PET, polybutylene terephthalate (PBT) or their oligomers, monomers, etc., but if necessary, contains a small amount of other components as a copolymerization component. Although PET may be used, PET is particularly preferable, and the preferable intrinsic viscosity of such PET is 0.60 dl / g or less, particularly 0.20 d.
It is about l / g. When the intrinsic viscosity exceeds these ranges and the intrinsic viscosity becomes too high, the randomness of the obtained polyester is apt to be lost, and only the aromatic oxycarboxylic acid component locally forms a homopolyester, which becomes a high melting point crystal and becomes a polyester. In some cases, it is not preferable because it may precipitate from the melt and become foreign matter. In the present invention, the polyalkylene terephthalate can be produced by any conventionally known production method of polyester such as esterification method and transesterification method.

As the unsaturated compound having an ester-forming functional group used in the present invention, a compound having 1 to 4, preferably 2 carboxyl groups or hydroxyl groups is suitable. Specifically, fumaric acid, maleic acid, mesaconic acid,
Dicarboxylic acids such as citraconic acid, glutaconic acid and itaconic acid, or unsaturated dicarboxylic acids consisting of their acid anhydrides, esters, etc., or 2-butene-1,4-diol, 3-butene-1,2-diol, etc. Unsaturated diols and their esters are listed, and maleic acid or its derivative is most preferred.

In the present invention, the ratio of copolymerizing an unsaturated compound having an ester-forming functional group is 0.5 to 1 with respect to all repeating units constituting the thermotropic liquid crystalline polyester.
It is 0 mol%, and when the copolymerization ratio is less than 0.5 mol%, the effect of copolymerization is not substantially exhibited, while on the other hand, 10 mol%
When the amount is larger, the resulting polyester is not preferable because it does not exhibit thermotropic liquid crystallinity and causes undesirable phenomena such as gelation.

Specific examples of the phosphorus compound represented by the formula (II) used in the present invention include the following compounds.

In the present invention, the content ratio of the phosphorus compound represented by the formula (II) is such that when the ratio of the phosphorus compound is too small,
Since the flame resistance of the thermotropic liquid crystalline polyester finally obtained becomes insufficient, on the other hand, if the ratio is too large, the physical properties of the obtained polyester may be impaired. The amount is in the range not exceeding the equivalent amount, and 0.5 to 10 mol%, preferably 2.0 to 7.0, based on all repeating units constituting the entire polyester.
It is suitable to be mol%, optimally 2.5 to 5.0 mol%. The residual amount of the phosphorus compound in the polyester is
Although it varies depending on the type of phosphorus compound, it is usually 70 to 100%, and therefore the addition amount may be selected in consideration of it.

In producing the polyester by the method of the present invention, it is necessary to add the unsaturated compound having an ester-forming functional group in advance before adding the phosphorus compound.
There are roughly three types of this method. That is, when a polyalkylene terephthalate is produced, an unsaturated compound is added and copolymerized, and then a phosphorus compound is added, followed by a reaction with an aromatic oxycarboxylic acid, a method in which an aromatic oxycarboxylic acid and a polyalkylene terephthalate are not mixed. A method of reacting a saturated compound and then adding a phosphorus compound, after reacting an aromatic oxycarboxylic acid and an unsaturated compound, and then adding a phosphorus compound,
The method is followed by reaction with polyalkylene terephthalate, and the method is most suitable.

More specifically, when the intrinsic viscosity of the polyalkylene terephthalate obtained by copolymerizing an unsaturated compound becomes 0.5 or more, the reaction system is brought to normal pressure under nitrogen gas, 260 to 310 ° C, preferably 270 to 290 ° C. The phosphorus compound represented by the formula (II) is added at the temperature of, and the reaction is carried out under stirring for 5 to 60 minutes, preferably 10 to 30 minutes. After that, (a) an acyl aromatic oxycarboxylic acid, preferably 0.05 to 0.25 times the equivalent of acetic anhydride, or (b) an aromatic oxycarboxylic acid and the equivalent or more of acetic anhydride, preferably 1.05 to 1.25 times the equivalent. Acetic anhydride was added and the pressure was reduced to 0.01 to 10 torr under a reduced pressure of 260 to 310.
Polycondensation may be carried out at a temperature of ° C, preferably 270 to 290 ° C until a polyester having a predetermined degree of polymerization is obtained.

In the production method of the present invention, it is preferable to use an acid anhydride of a lower fatty acid such as acetic anhydride in combination as described above to effectively acylate the hydroxyl group of the aromatic oxycarboxylic acid, and further, PET or its Oligomer,
Addition of an acid anhydride of a lower fatty acid in an amount exceeding the equivalent number of all glycol terminal groups of the monomer is a preferable method from the viewpoint of improving the reaction rate and suppressing the generation of foreign substances.

The total glycol end groups of PET are 1,200 to 1,500 equivalent / ton-PET when the intrinsic viscosity is 0.1 dl / g, and 600 to 700 equivalent / ton-PET when the intrinsic viscosity is 0.2 dl / g. It is a degree.

Such an acid anhydride of a lower fatty acid is usually an acid anhydride of a lower fatty acid having 1 to 8 carbon atoms, that is, acetic anhydride, propionic anhydride, monochloroacetic anhydride, dichloroacetic anhydride, trichloroacetic anhydride, monobromoacetic anhydride,
Dibromoacetic anhydride, tribromoacetic anhydride, monofluoroacetic anhydride, difluoroacetic anhydride, trifluoroacetic anhydride, bromoacetic anhydride, glutaric anhydride, maleic anhydride, succinic anhydride, β-bromopropionic anhydride, butyric anhydride, iso Butyric acid, propylacetic anhydride, valeric anhydride,
Pivalic anhydride and the like can be mentioned, but acetic anhydride is particularly preferably used from the viewpoint of price and boiling point, and the following description is represented by acetic anhydride (Ac ₂ O).

Since the phosphorus compound represented by the above formula (II) may have some reducibility, the polycondensation catalyst to be added before adding the phosphorus compound is, for example, antimony among those described later. It is better not to use a material that may be deactivated in a reducing atmosphere.

Hereinafter, as an example to which the method of the present invention can be particularly preferably applied, PET which is a copolymer of an unsaturated compound as a first structural unit, and a polyester having a 4HBA residue as a second structural unit is taken as an example, and the structural method of the present invention is further I will explain in detail.

The ratio of the first constitutional unit and the second constitutional unit is a repeating unit molar ratio of 30:70 to 95: 5, preferably 30:70 to 70:30.
Is. If the ratio of the first constitutional unit is too small, a polyester showing clear liquid crystallinity cannot be obtained, and conversely, if it is too large, the melting point becomes too high, which makes production and use difficult.

In the present invention, polycondensation of polyester having PET as the main constituent component of an unsaturated compound copolymerized to a maximum limit of 0.5 or more, followed by normal pressure of the reaction system under nitrogen gas, 260 to 310 ° C. The phosphorus compound represented by the formula (II) is added at a temperature of preferably 270 to 290 ° C., and the mixture is reacted under stirring for 5 to 60 minutes, preferably 10 to 30 minutes, and then,
4HBA-A and the above-mentioned amount of Ac ₂ O were charged into a reactor, and reaction schedules (a), (b), (c) and (d) described later were prepared.
It is suitable to react in this order. First, (a) react in an inert atmosphere at a temperature not exceeding 150 ° C. for 30 minutes to 4 hours. If the temperature exceeds 150 ° C. or the reaction time is less than 30 minutes, the reaction becomes insufficient and the reaction rate in the polycondensation step may become slow, which is not preferable. On the other hand, 4
Even if the reaction is continued for a time or longer, the effect is only saturated, which is also economically unfavorable. Then, (b) reaction is carried out in an inert atmosphere at a temperature of 150 ° C to 230 ° C for 30 minutes to 8 hours. When the temperature exceeds 230 ° C or the reaction time is less than 30 minutes, the reaction becomes insufficient, the intrinsic viscosity of the finally obtained polyester does not increase, and 4-acetoxybenzoic acid causes homopolyester as described above. It is not preferable because it is formed or 4-acetoxybenzoic acid or Ac ₂ O is scattered. On the other hand, even if the reaction is carried out for 8 hours or more, the effect is not only saturated but also the color tone of the polyester obtained is impaired, which is also not preferable. After that, (c) in an inert atmosphere, from 230 ° C to 250 ° C to 310 ° C.
When the temperature reaches 270 ° C. at the latest, the depressurization is started according to a depressurization schedule such that the full vacuum is 60 minutes or more, preferably 90 minutes. When the temperature exceeds 310 ° C., the color tone of the obtained polyester is only impaired, and when the depressurization schedule is less than 60 minutes, 4-acetoxybenzoic acid scatters, which is not preferable. After that, (d)
Polyester is produced by carrying out a polycondensation reaction while distilling acetic acid (AcOH) in a molten phase for several tens of minutes to several hours under a high reduced pressure of about 0.01 torr to 10 torr at a temperature of usually 260 to 310 ° C. be able to.

In the present invention, other than the above-mentioned two structural units, for example, 2,2-bis (4'-hydroxyphenyl) propane, hydroquinone, resorcin, 4,4'-dihydroxybiphenyl, 1,4-butanediol, 1, 6-hexanediol, cyclohexanedimethanol, pentaerythritol, naphthalic acid, isophthalic acid, phthalic acid, adipic acid, sebacic acid, 2,2-bis (4'-carboxyphenyl) propane, bis (4-carboxyphenyl) methane, Bis (4-carboxyphenyl) ether, trimellitic acid and the like are preferably used as a copolymerization component.

Usually, a catalyst is used in the polycondensation reaction, but in order to produce a polyester by the method of the present invention, for example, one or more compounds selected from various metal compounds or organic sulfonic acid compounds are used. To be

As such a metal compound, a compound such as antimony, titanium, germanium, tin, zinc, aluminum, magnesium, calcium, manganese, sodium, potassium or cobalt is used, while as the organic sulfonic acid compound, sulfosalicylic acid, o-sulfo compound is used. A compound such as benzoic anhydride (OSB) is used, but germanium dioxide (CS) and OSB are particularly preferably used. The amount of the catalyst added is usually 0.1 × 10 ^{−4 to} 100 × 10 ⁻⁴ mol, preferably 0.5 × 10 ⁻⁴ to 50 × 10 ⁻⁴ mol, and most preferably 1 ×, relative to 1 mol of the polyester constitutional unit. 10 ^-4 ~ 10
× 10 ^-4 mol is used.

Further, according to the method of the present invention, for example, as the thermal characteristic value of polyester, a melting point of 200 ° C. or higher, a heat distortion temperature of 60 ° C. or higher, preferably a melting point of 220 ° C. or higher, a heat distortion temperature of 100 ° C. or higher,
Optimally, a polyester having a melting point of 220 to 250 ° C. and a heat distortion temperature of 100 to 130 ° C. is obtained, and such a polyester is preferable because it has both heat resistance and various physical and mechanical property values.

(Function) The reason why a polyester having a high intrinsic viscosity and excellent flame resistance can be economically produced by the method of the present invention has not been fully clarified, but it may be previously unknown in the main chain of the polyester. There is a saturated bond, and then
It is speculated that a phosphorus compound having a P—H bond in the unsaturated bond is pendantly added to the main chain of the polyester, resulting in a polyester having excellent flame resistance without deteriorating the physical properties of the polyester. To be done.

(Examples) Hereinafter, the present invention will be described more specifically with reference to Examples.

[Η] of the polymer in the examples was determined from the solution viscosity measured at 20 ° C. in an equal weight mixed solvent of phenol and ethane tetrachloride.

Further, the total glycol end groups of the polyalkylene terephthalate are obtained by subtracting the number of carboxyl end groups described below from the total number of end groups calculated back from the intrinsic viscosity. The carboxyl end group was determined by titrating with 1/10 N sodium hydroxide solution in benzyl alcohol.

The thermotropic crystallinity referred to in the present invention was confirmed with a Leitz polarization microscope with a hot stage.

In addition, the content of phosphorus atoms in the polyester is fluorescent X
It was quantified by the linear method.

The flame resistance was evaluated according to the limiting oxygen index (LOI) according to JIS K 7201 standard.

Example 1 498 g of terephthalic acid (TPA) and ethylene glycol (E
G) 279 g and maleic acid 18.3 g (copolymerization ratio of maleic acid is 5 mol%) in an autoclave.
The esterification reaction was carried out by heating at ℃ for 2.5 hours. Then, using germanium dioxide as a catalyst, 2.5 × 10 ⁻⁴ mol /
An acid component was added, the temperature of the system was raised to 275 ° C. in 1 hour, the system pressure was gradually reduced to 0.1 torr after 1 hour, and the polycondensation reaction was further continued under these conditions. When the intrinsic viscosity of this polyester (PET-1) reached 0.62, the reaction system was brought to normal pressure with nitrogen gas, and the phosphorus compound (HCA) represented by the above formula (h) was added to 16.5 g (to 1 mol of all acid components). (The amount of HCA is 2.36 mol%) was added thereto, and the mixture was stirred at 275 ° C. for 20 minutes. Thereafter, 2,000 equivalents / ton-PET-1 of Ac ₂ O and PET-1 and 1.5 times mole of 4-acetoxybenzoic acid were added, and the mixture was added over 5 hours.
The temperature was sequentially raised to 230 ° C., and the mixture was stirred and mixed for 2 hours.
Next, the temperature was raised to 270 ° C. over a further 2 hours, and then depressurization was started according to a depressurization schedule such that full vacuum (1 torr) was reached for 90 minutes. Finally usually 270 ℃
The polycondensation reaction was carried out in the melt phase under reduced pressure of 0.3 torr for 4 hours at the temperature of.

As a result, a thermotropic liquid crystalline polyester having an intrinsic viscosity of 0.72 was obtained. The LOI of the 1/3 inch thick test piece obtained from this polyester was 33.

Example 2 498 g of terephthalic acid (TPA) and ethylene glycol (E
G) a mixture of 279 g in an autoclave at 260 ° C 2.
The esterification reaction was performed by heating for 5 hours. Next, maleic acid 18.3g (copolymerization ratio of maleic acid is 5mol%)
And germanium dioxide as a catalyst 2.5 × 10 ^-4 mol /
Add an acid component and raise the system temperature to 275 ° C in 1 hour.
The mixture was stirred at 0 ° C for 30 minutes. After that, the reaction was carried out in substantially the same manner as in Example 1.

As a result, a thermotropic liquid crystalline polyester having an intrinsic viscosity of 0.67 was obtained. The LOI of the 1/3 inch thick test piece obtained from this polyester was 32.

Example 3 A thermotropic liquid crystalline polyester was obtained in the same manner as in Example 1 except that the compound of formula (j) was used as the phosphorus compound. The results are shown in Table 1.

Example 4 The copolymerization ratio of maleic acid was 17.6 mol%,
A thermotropic liquid crystalline polyester was obtained by reacting in the same manner as in Example 1 except that A was used in an amount such that HCA was 8.24 mol% with respect to 1 mol of all acid components. The results are shown in Table 1.

Examples 5 to 8 The phosphorus compounds of the above formulas (a), (b), (c) and (e) are used as the phosphorus compounds, and the amount of the phosphorus compounds is 2.5 mol% based on 1 mol of all the acid components. The reaction was carried out in the same manner as in Example 1 except that the thermotropic liquid crystal polyester was obtained. The results are shown in Table 1.

Examples 9 to 11 Thermotropic liquid crystalline polyesters were obtained in the same manner as in Example 1 except that maleic anhydride, itaconic acid or 2-butene-1,4-diol were used as unsaturated compounds. . The results are shown in Table 2.

Example 12 As an acyl aromatic oxycarboxylic acid, 4-acetoxybenzoic acid and 3-acetoxybenzoic acid were used in a molar ratio of 9: 1.
A thermotropic liquid crystalline polyester was obtained by reacting in substantially the same manner as in Example 1 except that the above was used. The results are shown in Table 3.

Example 13 A thermotropic liquid crystalline polyester was obtained in substantially the same manner as in Example 1 except that 2-acetoxy-6-naphthoic acid (BON6) was used as the acylaromatic oxycarboxylic acid. The results are shown in Table 3.

Example 14 A mixture of 582 g of dimethyl terephthalate (DMT) and 660 g of 1,4-butanediol (BD) and 2.4 × 10 ⁻⁴ mol of tetrabutyl titanate as a catalyst / acid component were charged in an autoclave for transesterification. Then maleic acid
18.3 g (copolymerization ratio of maleic acid 5 mol%) was added,
Thereafter, the reaction was carried out in substantially the same manner as in Example 2 to obtain a thermotropic liquid crystalline polyester. The results are shown in Table 3.

Comparative Example 1 A thermotropic liquid crystalline polyester was obtained in the same manner as in Example 2 except that the amount of maleic acid added was 1.2 g (copolymerization ratio of maleic acid was 0.34 mol%). The intrinsic viscosity of the resulting polyester was only 0.39, and the LOI of the barely obtained sample was 27.

Comparative Example 2 A polyester was obtained by carrying out a reaction in substantially the same manner as in Example 2 except that the amount of maleic acid added was 67.0 g (13.5 mol%), but it did not exhibit thermotropic liquid crystallinity, but exhibited a gel form. It could not be used practically.

Comparative Example 3 A polyester was obtained by reacting in substantially the same manner as in Example 2 except that 20.7 g of triphenyl phosphate was used as the phosphorus compound, but not only did not exhibit thermotropic liquid crystallinity, but also exhibited a gel form for practical use. It could not stand the above use.

(Effect of the Invention) According to the present invention, a thermotropic liquid crystalline polyester having excellent flame resistance can be economically and stably produced without deteriorating excellent physical properties of the polyester. The thermotropic liquid crystalline polyester obtained by the present invention is extremely useful as a material having high physical properties, which is used particularly in applications requiring flame retardancy.

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Claims (6)

(57) [Claims] 1. An aromatic oxycarboxylic acid component represented by the following formula (I) and an alkylene terephthalate component, the molar ratio of both is 30:70 to 95: 5 and the intrinsic viscosity is 0.5.
In producing the above thermotropic liquid crystalline polyester, an unsaturated compound having an ester-forming functional group is copolymerized to be 0.5 to 10 mol% with respect to all repeating units constituting the thermotropic liquid crystalline polyester, Then, a method for producing a flame-resistant polyester, which comprises reacting a phosphorus compound represented by the following formula (II). (In the formula, Ar represents a divalent aromatic group. However, the aromatic ring may be substituted with a substituent. Further, R is a hydrogen atom, a hydroxyl group or a lower acyl group, and R ₁ and R ₂ are hydrogen. And R ₁ and R ₂ may form a ring with each other, which are the same or different groups selected from the group consisting of an atom, an alkyl group, an aryl group, an alkoxy group and an aryloxy group.) 2. A flame-resistant polyester according to claim 1, wherein the polyalkylene terephthalate component is reacted with the unsaturated compound, the phosphorus compound is added, and then the aromatic oxycarboxylic acid component is reacted. Production method. 3. The method for producing a flame-resistant polyester according to claim 1, wherein the unsaturated compound is maleic acid or its ester-forming derivative. 4. The method for producing a flame-resistant polyester according to claim 1, wherein the phosphorus compound is a compound represented by the following formula (III). (In the formula, the benzene ring may be substituted with a substituent.) 5. The method for producing a polyester according to claim 1, wherein the aromatic oxycarboxylic acid component is a 4-hydroxybenzoic acid component. 6. When the intrinsic viscosity of the polyester reaches 0.5 or more, the phosphorus compound represented by the formula (II) is added in an amount not exceeding the equivalent amount of the unsaturated bond of the unsaturated compound, and then the polycondensation is completed. The method for producing a polyester according to claim 1, wherein the polyester is produced.