JPS6050208B2 - Manufacturing method of polyester for film molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing polyester for film forming, which has few foreign substances and has an excellent surface morphology.

Biaxially stretched films of polyester, particularly polyethylene terephthalate, are widely used in various fields due to their excellent properties such as mechanical strength, electrical insulation, heat resistance, and chemical resistance.

However, in order for polyester to be used advantageously in each of these fields, workability in the forming processes such as melt extrusion, stretching, heat treatment, and winding, as well as secondary processes such as magnetic layer coating, metal vapor deposition, and surface coating, are required. It is necessary that the final product has excellent properties such as workability in the next processing step, product finish, appearance, transparency, surface properties, electrical properties, etc. The characteristics of the base film required to obtain such high-quality polyester film products include the absence of foreign substances in the film, good transparency, and good slipperiness. It will be done.

Here, the foreign matter refers to precipitated particles that have aggregated and become coarse. Foreign matter in the film will cause a decrease in electromagnetic conversion characteristics when used for magnetic tape, a decrease in withstand voltage when used for capacitors, and may cause thread breakage when used for gold and silver. To obtain a base film free of foreign matter, it is required that the resin used as the raw material be free of foreign matter.

The slipperiness is particularly important because it affects the roll-off formation of the wound film, the workability of secondary processing, and furthermore, the quality of the product.

It is well known that in order to improve workability (sliding), fine irregularities are provided on the surface of a film to reduce the coefficient of friction between films and between films and metal. One such method is to roughen the film surface by adding inert fine particles such as calcium carbonate, titanium dioxide, kaolin, or talc to polyester, but it is difficult to obtain fine particles and it is difficult to obtain fine particles. If this happens, the filter will become clogged during extrusion processing, making stable operation difficult. In addition, in order to obtain fine particles with a uniform particle size that do not contain coarse particles, it is generally necessary to crush and classify the coarse particles, and considering the complexity of the process and the yield, this method is not suitable in terms of cost. This will be a significant disadvantage. On the other hand, a method is also known in which fine particles are precipitated within the system using the metal compound residue used as a catalyst.

This method does not require special equipment or complicated operations and can be carried out relatively easily. However, it is difficult to control the size of the precipitated particles, agglomerated particles are easily generated, and the amount of precipitated particles is There are many practical problems that need to be solved, such as fluctuations between the two. In recent years, in order to save energy and reduce costs, the production method for polyethylene terephthalate for film forming has changed from the conventional transesterification of dimethyl terephthalate and ethylene glycol, similar to that used for textiles. A shift is being made to a production method using the so-called direct esterification method, in which terephthalic acid obtained from the raw material is directly reacted with ethylene glycol.

Naturally, when polyester resin for film molding is produced using such a direct esterification method, when the film is molded, the properties that the base film should have as mentioned above, i.e., no foreign matter, no winding, etc. There is a demand for commercial quality polyester resin for film forming with excellent workability and slip properties. In view of the above points, as a result of intensive study, the present inventor has developed the following. At the end of the sterilization reaction, a phosphorus compound is added at a specific time to react with the esterification reaction product for a certain period of time, and then a lithium compound or a lithium compound and a calcium compound are added in specific amounts to create fine irregularities on the film surface. As a result, they discovered a method for producing polyester that provides molded products of excellent quality, with excellent slip properties and little foreign matter in the film, without sacrificing transparency, and completed the present invention.

That is, the present invention provides a method for producing a film-forming polyester in which at least 80% of the repeating structural units are ethylene terephthalate units by esterification reaction and polycondensation reaction using terephthalic acid and ethylene glycol as starting materials. When the esterification reaction reaches 91 to 99%, a phosphorus compound is added and held at a temperature of 240 to 270°C for 5 minutes or more, and then a lithium compound or a mixture of a lithium compound and a calcium compound is converted to A method for producing polyester for film forming, characterized by adding an amount satisfying (1) (in formula (1), P..Ca..L
i is a number representing the mole % of the phosphorus compound, calcium compound, and lithium compound, respectively, with respect to the raw acid component of polyestefyl.

). The present invention will be explained in more detail.

The polyester in the present invention refers to a polyester obtained using terephthalic acid and ethylene glycol as main starting materials, but other third components may be mixed as raw materials.

The third component includes one or more aromatic dicarboxylic acids such as isophthalic acid and naphthalene dicarboxylic acid, and one type of glycol such as alkylene glycols such as propylene glycol and tetramethylene glycol, and polyalkylene glycols such as polyethylene glycol. or 2
More than one species can be used. In any case, the polyester of the present invention refers to a polyester in which at least 80% of the repeating structural units are ethylene terephthalate units. Further, impurities such as 4-carboxybenzaldehyde and acetic acid are added to terephthalic acid, which is a raw material for direct esterification, in an amount of, for example, 3000 ppm or less as 4-carboxybenzaldehyde.
There is no problem even if the content is 3000 ppm or less as acetic acid; rather, even if such unpurified crude terephthalic acid is used, a high-quality polyester suitable for film formation with excellent color tone etc. can be obtained.

The direct esterification reaction in the present invention refers to using the above-mentioned terephthalic acid and ethylene glycol as the main starting materials, and reducing the molar ratio of ethylene glycol to terephthalic acid from 1.0 to 1.0 to 270°C at normal or elevated pressure. 3
It means an esterification reaction carried out continuously or batchwise in the presence or absence of a catalyst, in the presence or absence of a lower glycol ester of terephthalic acid. The closer the molar ratio of ethylene glycol to terephthalic acid is to 1, the more advantageous it is, but from the viewpoint of the fluidity of the terephthalic acid ethylene glycol slurry, it should be 1.05 to 2. Stiffness is preferred. The composition of the lower glycol ester compound obtained by the direct esterification reaction varies depending on the reaction conditions, such as temperature, pressure, and the equivalent ratio of ethylene glycol and terephthalic acid used, but generally the number average degree of polymerization is 3 to 3. The main compounds are monomorphic compounds. The phosphorus compound used in the present invention is preferably one or more selected from the group consisting of phosphoric acid, phosphorous acid, methyl ester, ethyl ester, phenyl ester, and one-half ester thereof, and in particular phosphoric acid. Methyl ester, ethyl ester and phenyl ester are preferred.

Furthermore, the lithium compound used in the present invention may be one that is soluble in ethylene glycol, such as acetic acid,
Examples include salts of aliphatic carboxylic acids such as propionic acid and alcoholic acid, salts of aromatic carboxylic acids such as benzoic acid and p-methylbenzoic acid, and alcoholates of alcohols such as methyl alcohol, ethyl alcohol, etc. . Among these, lithium aliphatic carboxylates are particularly preferred, and lithium acetate is particularly preferred. Further, the calcium compound used in the present invention is not particularly limited as long as it is soluble in ethylene glycol.

For example, salts of aliphatic carboxylic acids such as acetic acid, propionic acid, butyric acid, salts of aromatic carboxylic acids such as benzoic acid and p-methylbenzoic acid, and even lucium glycolate such as ethylene glycol, propylene glycol, etc. I can list many. The timing of addition of the phosphorus compound is such that the esterification reaction rate is 91% to 99%, more preferably 93% to 98%.
% point. When the esterification reaction rate is less than 91%,
Since the esterification reaction is insufficient, the polymerization time is delayed in the next polycondensation step, and the precipitated particles become coarse and agglomerated, which is not preferable. In addition, if it exceeds 99%, the esterification reaction takes a long time, and the time for the next polycondensation reaction is almost the same as in the case where the esterification reaction rate is 99% or less, which is not practical. is necessary. The amount of the phosphorus compound added is relatively determined by the amounts of the lithium compound or lithium compound and calcium compound added next, but is selected between 0.05 and 2 mol% based on the acid component of the polyester raw material. .

More preferably, it is 0.05 to 1.2 mol%. Adding too much of a phosphorus compound is undesirable because it lowers the softening point of the polyester.

The lithium compound and the calcium compound can be used in any amount, but preferably, the lithium compound is used in an amount of 0.05 to 0.5 mol % based on the polyester raw acid component. When a calcium compound is used in combination, the amount thereof is 0.5 mol % or less based on the acid component of the polyester raw material.

Alternatively, when using a lithium compound and a calcium compound together, the ratio of the lithium compound to the calcium compound can be selected arbitrarily, but if the molar ratio of the calcium compound to the lithium compound increases to 0.5 or more, turbidity in the resin may occur. This is undesirable because the particle size decreases and the particle size changes to a dendritic type. Preferably, the molar ratio of the calcium compound to the lithium compound is 0.3 to 0.05. In any case, the turbidity in the resin changes depending on the amount of lithium compound used and the ratio of lithium compound to calcium compound, and can be arbitrarily changed depending on the purpose.

The amount of the lithium compound or the total amount of the lithium compound and calcium compound added in the present invention is 1 to A times equivalent to the phosphorus compound.

The equivalent ratio of the metal compound to the phosphorus compound is expressed by the following formula. (1) where PlCa, . Lj is a number representing the mole % of the phosphorus compound, calcium compound, and lithium compound with respect to the acid component of the polyester raw material, and is 5.

In formula (1), when a calcium compound is not used, calculation is performed as Ca=o.

When the amount of the metal compound is equivalent to or more than the phosphorus compound, lithium terephthalate,
Calcium terephthalate and oligomer salts of these metals are produced, and these metal salts of carboxylic acids have a strong tendency to agglomerate, so they become coarse or grow in the form of needles, so they have little effect on improving the slipperiness of the film.

When the amount of the metal compound is less than 113 times the equivalent of the phosphorus compound, it is not preferable because a sufficient amount of precipitated particles cannot be obtained.

Next, the important point in the present invention is that the phosphorus compound is added to the esterification reaction product before the lithium and lithium and calcium compounds are added.

That is, when lithium and metal compounds such as lithium and calcium compounds are added to the esterification reaction product before the phosphorus compound, they react with unreacted terephthalic acid and carboxyl groups in the reaction product oligomer in the reaction system. However, lithium terephthalate, calcium terephthalate, and oligomer salts of these metals are produced.

These oligomer salts have a very strong tendency to agglomerate, and even if a phosphorus compound is added in an amount equal to or more than the same molar amount as the added metal compound, the agglomerated foreign substances cannot be completely eliminated, and they are extruded from the polymerization tank as strands or sheets. Observed as white foreign matter in the resin. The film obtained by molding the resin obtained in this way has good slipperiness and transparency, but due to the presence of foreign matter, the filter is easily clogged, which reduces productivity and operability. becomes an obstacle.

In order to prevent the formation of aggregating oligomeric metal salts as described above, it is necessary to add a phosphorus compound before adding the metal compound. The purpose of the present invention is to provide a polyester for forming a film containing fine precipitated particles and having an excellent surface morphology. It is necessary to add the metal compound after the reaction between the metal compound and the esterification reaction product.

When the phosphorus compound is added to the esterification reaction product and then the metal compound is immediately added, the average particle size of the particles generated in the polyester is 4 to 5p, and the particles obtained using such polyester resin 5 are A film that is exposed to heat reduces its value as a product.

For example, if metal vapor deposition is applied to such a film,
The surface of the vapor-deposited film becomes frosty, and the difference between the front and back becomes large. Furthermore, when used as a base film for magnetic tape, the particle size is large, resulting in poor electromagnetic conversion characteristics and dropouts. Moreover, when used in a capacitor, it causes a decrease in withstand voltage, which is not preferable. It is preferable that the particles thus precipitated in the reaction system have a particle size as small as possible, for example, an average particle size of 1 to 3 μm. Therefore, in the present invention, after adding the phosphorus compound, the esterification reaction product and the
It is necessary to react for 5 minutes or more, preferably at least one powder, at °C, and then add a lithium compound or a lithium compound and a calcium compound. The present inventor added a phosphorus compound to an esterification reaction product, then added a lithium compound or a lithiated fluoride compound and a calcium compound to conduct a polymerization reaction, and particles were precipitated in the polymer. It has been found that the particle size in the polymer changes depending on the time between adding the phosphorus compound to the esterification reaction product and then adding the metal compound.

FIG. 1 is a plot of the average particle diameter versus the time for addition and holding reaction of a phosphorus compound to the esterification reaction product.

Note that trimethyl phosphate was used as the phosphorus compound. As is clear from this figure, as the holding reaction time increases, the average particle size becomes finer and finally reaches an average particle size of around 1 μm. The time for reacting the esterification reaction product and the phosphorus compound varies slightly depending on the reaction method.

For example, if a large amount of ethylene glycol is present in the system, a shorter time may be required. In addition, when the degree of polymerization is relatively high and there is little free ethylene glycol, it takes time to uniformly mix the phosphorus compound into the reaction system.
The time required to reach the minimum particle size in FIG. 1 is even longer. On the other hand, from the viewpoint of productivity, if the reaction time between the phosphorus compound and the esterification reaction product is too long, the time required to occupy the polymerization tank becomes longer and productivity is lowered, which is not preferable.

Furthermore, the appropriate reaction time varies depending on the type of phosphorus compound used.

Considering these points, it is desirable that the reaction time between the esterification reaction product and the phosphorus compound is within 5 minutes, preferably within 8 degrees, and preferably within 6 degrees.

The reaction temperature is preferably 240 to 270°C.

Generally, direct esterification reaction is carried out at 240°C or higher,
Moreover, the melting point of the obtained oligomer is 230 to 240°C.
In order to obtain a melting point lower than this, ethylene glycol is further required to lower the degree of polymerization, which is undesirable because ethylene glycol is used in excess. For these reasons, it is not practical to add an ethylene glycol solution of a phosphorus compound at a temperature below 240°C.

A high temperature of 5270° C. or higher is undesirable because if it reacts with a phosphorus compound for a long time, the by-product of diethylene glycol increases and the softening point of the polymer decreases. Furthermore, when the temperature reaches such a high temperature, especially when a phosphorus ester compound is used, there is a lot of volatilization outside the system, and the amount of phosphorus compound remaining in the polymer 1' decreases.
This is not preferable because it changes the amount of precipitated particles and the particle size, causing variations in the amount of haze particles. During the reaction and holding with the phosphorus compound, the temperature is gradually increased from 240'C to 240'C.
Raising the temperature to 70°C is preferable from the viewpoint of productivity because it shortens the time required for heating and has little effect on the particle size. The phosphorus compound used in the present invention is preferably used as a 0.5 to 20% by weight solution in ethylene glycol.

Adding the phosphorus compound at too high a concentration, for example, at a concentration of 30% or more, is not preferable because the phosphorus compound is not sufficiently dispersed and mixed into the reaction system, and furthermore, the reaction of the phosphorus compound may cause foreign matter due to the high melting point gel-like compound. It should be avoided as it may cause outbreaks. Known antimony compounds as polymerization catalysts,
One or more of germanium compounds, titanium compounds, tin compounds, cobalt compounds, etc. can be used, but antimony compounds are particularly preferred.

In addition, the polyester obtained by the present invention includes the polyester produced by the present invention. As long as the purpose of the invention is not impaired, a small amount of inorganic particles inert to polyester such as kaolin, talc, silica, calcium carbonate, calcium terephthalate, etc. may be contained.
It may also contain weathering agents, antioxidants, pigments, etc.

As explained in detail above, based on the present invention, a phosphorus compound is added when the esterification reaction reaches 91 to 99%.
A simple operation can be achieved by maintaining the temperature at 40 to 270°C for 5 minutes or more, and then adding the lithium compound or a mixture of a lithium compound and a calcium compound in an amount equivalent to 113 times the amount of the phosphorus compound added. This makes it possible to control the size of the particles precipitated in the polymer, and as a result, it is possible to obtain a molded product with excellent transparency and slippage, as well as good electrical properties and (B) excellent surface properties after vapor deposition.

The present invention will be explained in more detail below with reference to specific examples5.

In addition, "parts" in the examples indicate "parts by weight." The measurement method used is shown below.

Dissolve 2.7y of H liquid haze dipolymer in 20ml of phenol/tetrachloroethane (60/4 rutting amount/weight), and measure with a hazemeter (SR type) manufactured by Nippon Seimitsu Kogaku Co., Ltd.
Measured using a CWL cell.

Friction coefficient: Based on the method of ASTM Dl894-63, it has been improved so that it can be measured using a tape-shaped sample.The measurement is carried out in an atmosphere of 21±2°C165±5%, and the measurement conditions are tensile speed. 20T0ftImin
1 chart speed 120TrL. The time was set to 1 min. The sample size is 15mm wide. A piece with a length of 150 Tmm was used. The slipperiness was expressed by the coefficient of static friction. The measurement was carried out using a Nippon Denshoku turbidity meter NDH-Ha type according to the method of Ilmkhezni ASTM DlOO3-61.
Surface properties of deposited film: A film sample was introduced into a vacuum deposition apparatus, and metal aluminum was deposited under a high vacuum of 10-4T0rr or less.

After vapor deposition, a part of the vapor-deposited film was cut out and the appearance of the film surface was visually judged. A case where the entire film surface has a frosty tone is indicated as ×, a case where a slight frosty tone is observed is indicated as Δ, and a case where no frosty tone is observed is indicated as O. Withstand voltage: The dielectric breakdown voltage of a biaxially stretched polyester film having a thickness of 12 μm was measured using a 20K DC dielectric breakdown voltage device manufactured by Iwasa Institute of Electrical Research, with a voltage increase rate of 0.1 KV/sec.

The higher this value is, the better the withstand voltage characteristics are. Observation of precipitated particle size in polymer: The polymer was melted on a cover glass, rapidly cooled, and observed under a microscope to determine the approximate average particle size.

Note that if a 12μ film was made using the polymerized resin as it was, the film haze would be too high, so it was diluted with a resin that does not contain any precipitated particles, and the film haze at 12μ was targeted to be 3%.

Specifically, the resin of the example or comparative example and the resin containing no particles were blended at a ratio of 1:3. In reality, the film haze is slightly off target, but it is not a problem for looking at the relationship between transparency and slipperiness. Example 1 Using a two-stage continuous esterification reactor equipped with a stirring device, a partial condenser, a raw material inlet, and a product outlet, the molar ratio of ethylene glycol to terephthalic acid was set at 1 in the first stage reaction vessel. An ethylene glycol slurry of terephthalic acid prepared in Example 3 was continuously supplied to the system in which the esterification reaction product was present to carry out the esterification reaction.

However, the terephthalic acid used was a purified raw material containing almost no impurities such as 4-carboxybenzaldehyde and acetic acid, which are by-produced during the production of terephthalic acid. The reaction product was continuously taken out of the system, and then charged into the second stage esterification reactor, and 0.2 mole of ethylene glycol was added per unit of terephthalic acid charged to continue the reaction.

The obtained reaction product had an esterification rate of 96% and a number average degree of polymerization of 7.4. The esterification reaction product 10
6 parts (equivalent to 1 (1) part of ethylene terephthalate unit) was charged into a polycondensation reactor, maintained at 260°C, and then 4.67 parts of a 6% by weight solution of trimethyl phosphate in ethylene glycol was added and the mixture was stirred. It held 4 times at 260°C.

Then, 2.67 parts of a 3% by weight solution of calcium acetate monohydrate in ethylene glycol and 3.17 parts of a 6% by weight solution of lithium acetate dihydrate in ethylene glycol were added.
Next, as a polycondensation catalyst, 1% by weight of antimony trioxide was dissolved in ethylene glycol. 3 parts of the liquid was added, and the pressure inside the system was reduced to start the polycondensation reaction.Finally, 0.5?Hgl
The reaction was carried out at 28O'C for about 4 hours. After the stirring power reached a predetermined power, the inside of the system was returned to normal pressure with nitrogen, the pressure was further increased, and the polymer was extracted under a pressure of 2k91G. No foreign matter was observed when the polymer was observed with the naked eye at the time of extraction.

The obtained polymer had an intrinsic viscosity of 0.680 and a solution haze of 36%. As a result of observing the particles in the resin, the particle size was very small, about 1.5 μm, and agglomerated, no coarse particles were observed, and the shape was uniform. Blend the resulting resin 1 with transparent resin 3 that does not contain particles and heat at 290°C.
After being extruded into a sheet from an extruder and rapidly cooled to obtain an amorphous sheet, it was extruded in the longitudinal and transverse directions at a temperature above the glass transition point for 3.
The film was stretched 5 times in increments to form a 12μ film. The obtained film was measured for film haze, slipperiness, surface morphology of the aluminum-deposited surface, withstand voltage, etc.
The results are shown in Table 1.

As is clear from the results, this example has an excellent relationship between transparency and slippage, and also has good surface properties after vapor deposition and good electrical properties. Comparative Example 1 106 parts of the esterification reaction product obtained in Example 1 (equivalent to 100 parts as ethylene terephthalate) was kept at 260°C and 3.17 parts of a 6% by weight ethylene glycol solution of lithium acetate dihydrate was added. Then, 2.67 parts of a 3% by weight solution of calcium acetate hydrate in ethylene glycol 7-ol was added.

Next, 12 parts of a 3% by weight solution of triethyl phosphate in ethylene glycol were added, and further 3 parts of a 1% by weight ethylene glycol solution of antimony trioxide were added, and 28
0°C0.5T! The polycondensation reaction was carried out for 4 hours under $THg. After the reaction l was completed, the system was returned to normal pressure with nitrogen, and an additional 2 kg was added.
The polymer was extracted from the polymerization tank under a pressure of 1 G. The intrinsic viscosity of the obtained polymer was 0.67, and the solution haze was 40%.
It was hot. When the polymer was observed in a molten state at the time of extraction with the naked eye, numerous white aggregated foreign substances were observed. The polyester was extruded and stretched in the same manner as in Example 1.
A 2μ film was obtained and the film properties were evaluated.

The results are shown in Table 1. Among the properties of the film, the slipperiness and transparency were relatively good, but there were many foreign substances in the film, and when aluminum was vapor-deposited on the film surface, the film surface became frosty, which was undesirable. .

Furthermore, when a filter filtration test was conducted using the obtained polyester, the filter became clogged in about 114 hours compared to conventional polymers.

As is clear from this comparative example, when lithium or a lithium and calcium compound is added to the esterification reaction product before the phosphorus compound is added, agglomerated foreign matter is often generated, and the particle size of the precipitated particles becomes large. , is not preferred because the quality of the film is inferior. Example 2 A polymerization reaction was carried out in the same manner as in Example 1, except that triethyl phosphate was used in place of the trimethyl phosphate used in Example 1 in the amount shown in Table 1, and a film was formed and the properties of the film were evaluated.

The results showed that the particle size in the resin after polymerization was approximately 1.5 μm, with almost no aggregation or coarse particles observed. The film properties were also good in both transparency and slipperiness, and the withstand voltage and surface properties of the vapor-deposited film were also excellent. The results are shown in Table 1.
Examples 3 and 4 Trimethyl phosphate was used as the phosphorus compound in Example 3, and triethyl phosphate was used as the phosphorus compound in Example 4, and the amounts shown in Table 1 were added to the direct esterification product used in Example 1. After holding reaction at 260°C for 1 min,
Polycondensation was carried out in the same manner as in Example 1, except that a lithium compound and a calcium compound were added.

As a result, as shown in Table 1, the diameter of the precipitated particles in the resin was about 3 μm, which was larger than that in Example 1. Although the relationship between transparency and slippage was good, the aluminum vapor-deposited surface had a very slight frosty appearance. The withstand voltage is also lower than that of Example 1.
Example 5 Using terephthalic acid containing 300 ppm of 4-carboxybenzaldehyde in the raw material terephthalic acid,
The equivalent ratio of ethylene glycol to terephthalic acid is 1
．． An ethylene glycol slurry of terephthalic acid No. 15 was charged into the esterification reaction product with an esterification reaction rate of 97% left in advance, and an esterification reaction was carried out by a batch method.

At the end of the reaction, the esterification reaction rate was 97%, and the number average degree of polymerization was 4.9. Approximately 112 parts of the obtained esterification reaction product was subjected to the next polycondensation reaction, and the remainder was used again for the next batch of esterification reaction. A polycondensation reaction was carried out in the same manner as in Example 2, using triethyl phosphate in the amount shown in Table 1 as the phosphorus compound and holding the reaction time with the esterification reaction mixture for 4 minutes.

Almost no foreign matter was seen in the obtained resin, and the color tone of the polymer was also good and not much different from Example 2. The solution haze of the resin is 28%, and the particle size is fine, about 1.5μ.
Almost no coarse agglomerated particles were observed.

Furthermore, the film properties were also good as shown in Table 1.

Example 6 A polyester resin was obtained in the same manner as in Example 5.

However, in this example, the raw material terephthalic acid was 4
-carboxybenzaldehyde 1100ppm 1 acetic acid 1
Terephthalic acid containing 500 ppm was used as raw material.

Both the esterification reaction and polycondensation were able to be carried out without any problems. The obtained resin had a slightly yellowish tinge compared to Example 1, but this was not a particular problem for use in film. The particle size of the precipitated particles in the resin was also sufficiently fine, and the film properties were also good. The results are shown in Table 1.
Example 7 Other than using orthophosphoric acid as a phosphorus compound in the esterification reaction product obtained in Example 1 in the amount shown in Table 1, and holding the reaction between the phosphorus compound and the esterification reaction product for 1 gin. A polycondensation reaction was carried out in the same manner as in Example 1 to obtain a polyester.

No aggregated foreign matter was observed in the polymer, and the solution haze was 29.
%, and the average particle size of the precipitated particles was about 2μ.

The polyester was extruded and stretched in the same manner as in Example 1 to prepare a 12μ film, and the film properties were evaluated.

As shown in Table 1, the film properties were good.

Examples 8 and 9 In Examples 1 to 7, a lithium compound and a calcium compound were used together as the metal compound.

In Examples 8 and 9, a lithium compound alone was used as the metal compound, triethyl phosulfate was used as the phosphorus compound, and the reaction holding time was 40 minutes in Example 8, and 1 gin was used in Example 9. A polycondensation reaction was carried out in the same manner as in Example 1, and the resulting polyester resin was formed into a film and the film properties were evaluated. The results are shown in Table 1. It can be seen that even in the case of using lithium compound 7 alone, the particle size becomes smaller as the retention reaction time of the phosphorus compound and the esterification reaction mixture increases, as in the case of using the lithium compound and the calcium compound in combination. The particle size in the resin was approximately 2μ in Example 8 and approximately 3μ in Example 9, and the film properties were also good. Comparative Example 2 Using a batch direct esterification reactor equipped with a stirrer and a partial condenser, the molar ratio of ethylene glycol to terephthalic acid was 1.4 and the pressure was 5 k.
A direct esterification reaction was carried out by a batch method under pressure of 91cT1G.

The esterification reaction product obtained had an esterification rate of 89%. A reaction was carried out in the same manner as in Comparative Example 3 using the esterification reaction product.

That is, triethylene phosphate was used as the phosphorus compound, a metal compound was added 3 minutes after the addition of the phosphorus compound, and then a polycondensation reaction was performed.

It took about 6 hours to reach the specified stirring power, which was a significant extension of the polymerization time compared to the conventional method. Furthermore, in the obtained resin, many aggregated foreign substances were generated, which were presumed to be caused by the terephthalate or oligomer salt of the metal compound added.

The average particle size in the resin was about 4.5 microns. Since this resin produced a large amount of aggregated foreign matter, its quality as a resin for film was clearly inferior, so subsequent film production was not carried out.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the time during which a phosphorus compound is added to a reaction system and the precipitated particle size.

Claims (1)

[Claims] 1. A method for producing a film-forming polyester in which at least 80% of the repeating structural units are ethylene terephthalate units by esterification reaction and polycondensation reaction using terephthalic acid and ethylene glycol as main starting materials. When the esterification reaction rate reached 91 to 99%, a phosphorus compound was added and the mixture was heated at a temperature of 240 to 270°C for 50 minutes.
A method for producing a polyester for film forming, which comprises adding a lithium compound or a lithium compound and a calcium compound in an amount satisfying the following formula (I) after holding the polyester for at least 1 minute. 1/3≦{Ca+(1/2)Li}/P≦1………
(I) (In formula (I), P, Ca, and Li are numbers representing the mol% of the phosphorus compound, calcium compound, and lithium compound, respectively, with respect to the polyester raw acid component)