JP7690749B2 - Polyester composition and method for producing same - Google Patents

Description

The present invention relates to a polyester composition and a method for producing the same.

Polyesters have excellent mechanical properties, thermal properties, chemical resistance, electrical properties, and moldability, and are used in a variety of applications. Among polyesters, polyethylene terephthalate (hereinafter referred to as PET) is particularly excellent in transparency and processability, and is therefore widely used in applications requiring high quality, such as optical films and release films. A technique is known for improving the transportability and releasability of release films, in which an appropriate amount of particles are mixed into polyester to form fine protrusions on the film surface. A typical release film is required to have smoothness that maintains releasability while preventing defects in the release film from being transferred to the release object when the release object is placed on the release film. In addition, in the release of liquid crystal polarizing plates, the release film undergoes a crossed Nicol test while still attached to the polarizing plate, so it is desired to reduce foreign matter in the release film so as not to interfere with the crossed Nicol test.

However, due to the activity of the particles themselves, the particles may denature at high temperatures and become foreign matter, and the amount of COOH terminal groups in the polyester composition may increase, resulting in poor hydrolysis resistance.

In response to these issues, studies have been carried out as shown in the following documents.
Patent Documents 1 and 2 describe that by incorporating an alkali metal phosphate in a polyester resin, the hydrolysis resistance is improved.
Patent Document 3 discloses a technique for providing a polyester composition having excellent particle dispersibility and heat resistance by using surface-treated particles.

WO2014/021095 publication JP 2013-189521 A Japanese Patent Application Publication No. 8-143756

As in the conventional technology described above, there was a problem that merely improving the hydrolysis resistance of the polyester composition was insufficient to suppress the formation of foreign matter in the particles. Furthermore, merely suppressing the formation of foreign matter in the particles was not enough to prevent thermal decomposition and hydrolysis when the polyester was melted. Furthermore, the decomposition reaction of the polyester could not be suppressed by merely using surface-treated particles. In other words, the conventional technology for improving hydrolysis resistance and surface treatment of particles was not able to achieve both the hydrolysis resistance of the polyester composition and the stabilization of the particles.

The object of the present invention is to provide a polyester composition that suppresses aggregation and coarse foreign matter formation of calcium carbonate particles and has excellent hydrolysis resistance, and a method for producing the same.

As a result of intensive research aimed at solving the above problems, the present inventors have found a polyester composition which is excellent in hydrolysis resistance and which suppresses aggregation and formation of coarse foreign matter of calcium carbonate particles, and a method for producing the same, thereby completing the present invention.
The object of the present invention is achieved by the following means.
(1) A polyester composition containing calcium carbonate particles and phosphorus atoms (element), using phosphoric acid and an alkali metal phosphate, and satisfying the following formulas (I), (II), (V), and (VI).
0.2≦R≦0.8 (I)
0.38/R ² ≦P ₁ (II)
Free calcium atom (element) content ≦ 5 ppm (V)
0.01 ppm≦Sodium atom (element) content (weight ratio relative to polyester composition)≦30 ppm or less (VI)
R: volume average diameter of calcium carbonate particles (μm)
_P1 : phosphorus atom (element) content contained in isolated particles obtained by isolating the polyester composition by the method described below (wt%: weight ratio to the isolated particles)
(Isolation method: The polyester composition is dissolved in o-chlorophenol at 150° C. for 1 hour, then centrifuged at a centrifugal acceleration of 40,900 G at 20° C. for 1 hour, dichloromethane is added to the obtained solid, and centrifuged under the same conditions to obtain a solid. Dichloromethane is again added to the obtained solid, and centrifuged under the same conditions. This centrifugation with dichloromethane is carried out a total of three times, and the obtained solid is called isolated particles.)
(The free calcium atom (element) content is determined by dissolving the polyester composition in o-chlorophenol at 150° C. for 1 hour, centrifuging the mixture at a centrifugal acceleration of 40,900 G at 20° C. for 1 hour, collecting the resulting supernatant by decantation, adding acetone to cause precipitation, collecting the precipitate by filtration, and drying in vacuum at 150° C. for 12 hours, thereby obtaining the calcium atom (element) content in the polymer.)
(2) The polyester composition according to (1), having a calcium atom (element) content of 100 ppm or more (weight ratio relative to the polyester composition).
(3) The polyester composition according to (1), in which the increase in the amount of carboxylic acid terminal group ΔCOOH before and after wet heat treatment in saturated water vapor at 155° C. for 4 hours is 80 eq/t or less.
(4) The polyester composition according to (1), wherein the polyester is polyethylene terephthalate.
(5) A method for producing a polyester composition by subjecting a dicarboxylic acid or a dicarboxylic acid ester and a diol to an esterification reaction or an ester exchange reaction, followed by a polycondensation reaction, the method comprising adding, as a mixed slurry, a compound containing calcium carbonate particles and a mixed solution of phosphoric acid and an alkali metal phosphate before completion of the polycondensation reaction, so as to satisfy the following formulae (III), (IV), and (VII):
0.2≦R≦0.8 (III)
0.38/R ² ≦P ₂ (IV)
0.01 ppm≦sodium atom (element) content (weight ratio relative to polyester composition)≦30 ppm or less (VII)
R: volume average diameter of calcium carbonate particles (μm)
_P2 : Amount of phosphorus atoms (element) added as mixed slurry (wt%: weight ratio to calcium carbonate)
(6) The method for producing a polyester composition according to (5), wherein the amount of calcium carbonate particles added is 100 ppm or more (weight ratio to the polyester composition) in terms of calcium atoms (element).
(7) The method for producing a polyester composition according to (5), wherein the polyester is polyethylene terephthalate.

The polyester composition obtained by the present invention suppresses aggregation and coarse foreign matter formation of calcium carbonate particles and has excellent hydrolysis resistance.

The present invention is described in detail below.

The polyester composition of the present invention is a polyester composition that contains calcium carbonate particles and phosphorus atoms (element) and satisfies the following formulas (I) and (II).
0.2≦R≦0.8 (I)
0.38/R ² ≦P ₁ (II)
R: volume average diameter of calcium carbonate particles (μm)
_P1 : phosphorus atom (element) content contained in isolated particles obtained by isolating the polyester composition by the method described below (wt%: weight ratio to the isolated particles)
The polyester composition of the present invention contains calcium carbonate particles, and the volume average diameter R of the particles is required to be 0.2 μm or more and 0.8 μm or less (see formula (II) above). The volume average diameter was measured by subjecting the polyester composition to a plasma treatment to expose the particles, and measuring at least 20 visual fields at a magnification of 5000 times using a Hitachi field emission scanning electron microscope (model number S-4000) and a Nideco SEM-IMAGE ANALYZER (model number Ludex AP), measuring the circle equivalent diameters of at least 200 particles, and calculating by regarding them as pseudo three-dimensional spheres. The lower limit of the volume average diameter R is preferably 0.4 μm or more. By setting it to the above lower limit or more, it is possible to provide a polyester composition free of particle aggregation. In addition, the volume average diameter affects the surface properties when the polyester composition is processed into a film, and particles with a large volume average diameter are a cause of the formation of coarse protrusions on the film surface. Therefore, by setting the volume average diameter to the above upper limit or less, it is possible to obtain a film with reduced coarse protrusions.

The polyester composition of the present invention must contain phosphorus atoms (element). By containing phosphorus atoms (element), it is possible to impart hydrolysis resistance to the polyester composition, and further, by protecting the surface of the calcium carbonate particles with a phosphorus compound, particle aggregation is less likely to occur even when subjected to heat history, making it possible to provide a polyester composition with good particle dispersibility.

The phosphorus atom (element) content P ₁ (wt %: weight ratio to the isolated particles) contained in the isolated particles obtained by isolating the polyester composition of the present invention must satisfy the following formula.
0.38/R ² ≦P ₁ (II)
Here, the upper limit of _P1 is preferably 2.5 wt % or less.
By setting the content within the above range, it is possible to provide a polyester composition in which particle aggregation is suppressed without inhibiting the polymerization reaction of the polyester. The isolation of particles from the polyester composition is performed by the following method. That is, the polyester composition is dissolved in 10 ml of o-chlorophenol per 1 g of the polyester composition at 150° C. for 1 hour, and then centrifuged at a centrifugal acceleration of 40900 G and 20° C. for 1 hour. After separation, the supernatant is removed by decantation, dichloromethane is added to the obtained solid content, the precipitate is stirred, and then centrifuged under the same conditions to obtain a solid content. Dichloromethane is again added to the obtained solid content, the precipitate is stirred, and then centrifuged under the same conditions. The solid content obtained by performing this centrifugation with dichloromethane three times in total is the isolated particle. By mixing and adding the calcium carbonate particles with a phosphorus compound, the phosphorus compound adheres to the particle surface. Since the phosphorus compound attached to the surface has the effect of protecting the particles, it is necessary to add the phosphorus compound according to the surface area of the particles. By containing a phosphorus atom (element) satisfying the formula (II), it is possible to effectively protect the particle surface and suppress the aggregation of the particles and the formation of coarse foreign matter.

The polyester composition of the present invention preferably contains calcium atoms (element) in an amount of 100 ppm or more based on the weight of the polyester composition. By containing calcium atoms (element) in an amount equal to or greater than the above lower limit, the polyester composition has good transportability and releasability when processed into a film.

The content of free calcium atoms (elements) in the polyester composition of the present invention is preferably 10 ppm or less, more preferably 5 ppm or less, based on the weight of the polyester composition. The free calcium content is the calcium content in the polymer from which the particles have been removed, obtained by dissolving 1 g of the polyester composition in 10 ml of o-chlorophenol at 150° C. for 1 hour, centrifuging at a centrifugal acceleration of 40,900 G at 20° C. for 1 hour, decanting the resulting supernatant, adding acetone to precipitate the solution, and filtering the solution to recover the solution. In a film containing calcium carbonate particles, free calcium is generated from the calcium carbonate particles due to the heat history during film formation. This generated free calcium forms by-products with the polyester composition, causing particle aggregation and coarse foreign matter. By protecting the surface of the calcium carbonate particles with a sufficient amount of phosphorus compound, it is possible to prevent calcium from being released from the calcium carbonate particles. By suppressing the amount of free calcium to the above upper limit or less, it is possible to suppress the aggregation of calcium carbonate particles.

In addition, the polyester composition of the present invention preferably contains sodium atoms (elements) in an amount of 0.01 ppm or more and 30 ppm or less based on the weight of the polyester composition. By setting the amount within the above range, the hydrolysis resistance is improved, and the surface protection of the calcium carbonate particles can also be effectively performed.

The hydrolysis resistance of the polyester composition of the present invention is evaluated by the value of ΔCOOH. ΔCOOH is the amount of COOH end group increase when the composition is subjected to wet heat treatment at 155°C for 4 hours under saturated water vapor, and the lower the value of ΔCOOH, the better the hydrolysis resistance. In the polyester composition of the present invention, it is preferable that ΔCOOH is 80.0 or less. When the value of ΔCOOH is 80.0 or less, the hydrolysis resistance is good and the decomposition of polyester, which causes particle aggregation, can be suppressed. The value of ΔCOOH is more preferably 70.0 or less, and even more preferably 60.0 or less.

Next, a method for producing the polyester composition of the present invention will be described.
The method for producing the polyester composition of the present invention uses dicarboxylic acid or its ester and a diol as main raw materials and comprises the following two steps: a first step consisting of (A) an esterification reaction or (B) an ester exchange reaction, and a second step consisting of (C) a polycondensation reaction.

The raw materials for producing the polyester composition of the present invention can be dicarboxylic acids or dicarboxylic acid esters and diols, and it is also possible to use a combination of two or more types.

The dicarboxylic acid of the present invention includes terephthalic acid, 2,6-naphthalenedicarboxylic acid, isophthalic acid, diphenyl 4,4'-dicarboxylic acid, 5-sodium sulfoisophthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, malonic acid, dimer acid, and the like. The dicarboxylic acid ester is the lower alkyl ester, acid anhydride, acyl chloride, and the like of the above-mentioned dicarboxylic acid, and methyl ester, ethyl ester, hydroxyethyl ester, and the like are preferably used. The more preferred embodiment of the dicarboxylic acid or dicarboxylic acid ester in the present invention is terephthalic acid, 2,6-naphthalenedicarboxylic acid, isophthalic acid, or an alkyl ester thereof, since it is possible to obtain a polyester composition having a high melting point and being easily processable into films, fibers, and the like.

The diols of the present invention include aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, butanediol, 2-methyl-1,3-propanediol, hexanediol, and neopentyl glycol; alicyclic diols include saturated alicyclic primary diols such as cyclohexanedimethanol, cyclohexanediethanol, norbornanedimethanol, norbornanediethanol, tricyclodecanedimethanol, tricyclodecanediethanol, decalindimethanol, and decalindiethanol; saturated heterocyclic primary diols containing cyclic ethers such as isosorbide; and other cyclohexacyclic diols. Examples of suitable diols include various alicyclic diols such as cyclopentane, bicyclohexyl-4,4'-diol, 2,2-bis(4-hydroxycyclohexylpropane), 2,2-bis(4-(2-hydroxyethoxy)cyclohexyl)propane, cyclopentanediol, 3-methyl-1,2-cyclopentadiol, 4-cyclopentene-1,3-diol, and adamantanediol, and aromatic diols such as paraxylene glycol, bisphenol A, bisphenol S, styrene glycol, 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene, and 9,9'-bis(4-hydroxyphenyl)fluorene. In addition to diols, polyfunctional alcohols such as trimethylolpropane and pentaerythritol can also be used within the scope of the present invention, provided that the effects of the present invention are not impaired. Ethylene glycol is preferred in that it can fully achieve the effects of the present invention and can provide a polyester composition that is easily processed into films, fibers, and the like.

In the manufacturing method of the present invention, the first step of the esterification reaction (A) is a step in which a dicarboxylic acid and a diol are esterified at a predetermined temperature until a predetermined amount of water is distilled off to obtain a low polymer. When obtaining a low polymer by an esterification reaction, from the viewpoints of esterification reactivity and heat resistance, the molar ratio of dicarboxylic acid to diol (diol/dicarboxylic acid) before the start of the esterification reaction is preferably in the range of 1.05 to 1.40. More preferably, it is in the range of 1.05 to 1.30, and even more preferably, it is in the range of 1.05 to 1.20. By setting it in the above range, it has good reactivity and can suppress the generation of by-products such as dimers of diol, thereby making it possible to improve heat resistance.

The (B) transesterification step is a step in which a dicarboxylate and a diol are transesterified until a predetermined amount of alcohol is distilled off to obtain a low polymer. When a low polymer is obtained by transesterification, the molar ratio of the dicarboxylate and the diol (diol/dicarboxylate) is preferably in the range of 1.7 to 2.3 from the viewpoints of reactivity and heat resistance. By setting the ratio in the above range, the transesterification reaction can be efficiently carried out and the by-production of dimers of the diol can be suppressed, resulting in good heat resistance.

In the second step, the polycondensation reaction (C) is a process for obtaining a polyester composition from the low polymer obtained in the esterification reaction (A) or the transesterification reaction (B).

The manufacturing method of the present invention can be applied to batch polymerization, semi-continuous polymerization, and continuous polymerization.

In the method for producing the polyester composition of the present invention, the catalyst used in the esterification reaction (A) may be a compound such as manganese, cobalt, zinc, titanium, or calcium. However, from the viewpoint of thermal decomposition and generation of foreign matter in the polycondensation reaction stage, it is preferable to carry out the esterification reaction without a catalyst. Here, the esterification reaction (A) proceeds sufficiently even without a catalyst due to the self-catalytic action of the carboxylic acid. In addition, a known transesterification catalyst can be used as the catalyst used in the transesterification reaction (B). Examples of the transesterification catalyst include organic manganese compounds, organic magnesium compounds, organic calcium compounds, organic cobalt compounds, and organic lithium compounds. Specific examples of the transesterification catalyst include carbonates, acetates, benzoates, oxides, and hydroxides, but are not limited to these.

The catalyst used in the polycondensation reaction (C) may be a known polycondensation catalyst, such as a compound of antimony, titanium, aluminum, tin, or germanium.
Examples of the antimony compound include antimony oxide, antimony carboxylate, and antimony alkoxide.
Examples of the titanium compound include titanium chelate complexes, titanium alkoxides, and titanium oxides obtained by hydrolysis of titanium alkoxides.

Examples of aluminum compounds include aluminum carboxylates, aluminum alkoxides, aluminum chelate compounds, and basic aluminum compounds.

Examples of tin compounds include tin compounds with alkyl groups and tin compounds with hydroxyl groups.

Germanium compounds include germanium oxide and germanium alkoxide.

The above metal compounds may be hydrates.
Among these, from the viewpoints of polymerization time and economic efficiency, it is preferable to use an antimony compound as a polycondensation reaction catalyst.
In the method for producing the polyester composition of the present invention, it is necessary that the calcium carbonate particles and the compound containing a phosphorus atom (element) are added as a mixed slurry and that the following formulae (III) and (IV) are satisfied.
0.2≦R≦0.8 (III)
0.38/R ² ≦P ₂ (IV)
R: volume average diameter of calcium carbonate particles (μm)
_P2 : Amount of phosphorus atoms (element) added as a mixed slurry (wt%: weight ratio to calcium carbonate).

In the method for producing a polyester composition of the present invention, the volume average diameter R of the calcium carbonate particles to be added must be 0.2 μm or more and 0.8 μm or less. The lower limit is preferably 0.4 μm or more. By setting the volume average diameter at or above the above lower limit, it is possible to provide a polyester composition with excellent particle dispersibility. In addition, the volume average diameter affects the surface properties when the polyester composition is processed into a film, and particles with a large volume average diameter are a cause of the formation of coarse protrusions on the film surface. Therefore, by setting the volume average diameter at or below the above upper limit, it is possible to obtain a film with reduced coarse protrusions.

The amount _P2 of the compound containing a phosphorus atom (element) added to the polyester composition of the present invention needs to be mixed with calcium carbonate particles and added to the polyester composition so as to satisfy the following formula (IV) with respect to the volume average diameter R of the calcium carbonate particles:
0.38/R ² ≦P ₂ (IV)
The upper limit of _P2 is preferably 3.0 wt% or less. By setting it within the above range, it is possible to provide a polyester composition in which particle aggregation is suppressed without inhibiting the polymerization reaction. If the amount of phosphorus added is less than 0.38/ ^R2 relative to the volume average diameter R of the calcium carbonate particles, the particle surface cannot be sufficiently protected, which causes particle aggregation and coarse foreign matter. As the phosphorus compound, phosphoric acid, trimethyl phosphoric acid, ethyl diethyl phosphonoacetate, phosphorous acid, etc. can be used, and it is also possible to use multiple phosphorus compounds in combination. It is particularly preferable that this phosphorus compound is phosphoric acid. By adding a phosphorus compound, the surface of the calcium carbonate particles can be effectively protected, and further hydrolysis resistance can be imparted to the polyester composition.

In addition, in the method for producing the polyester composition of the present invention, it is preferable to add sodium atoms (element) in an amount of 0.01 ppm or more and 30 ppm or less based on the weight of the polyester composition. By setting the amount within the above range, the hydrolysis resistance is improved, and the surface protection of the calcium carbonate particles can also be effectively performed.

The compound containing a sodium atom (element) is not particularly limited. Examples include sodium phosphate, hydroxide, acetate, carbonate, nitrate, and chloride. From the viewpoint of hydrolysis resistance, sodium phosphate is more preferable. Examples of sodium phosphate include sodium dihydrogen phosphate, disodium hydrogen phosphate, and trisodium phosphate. From the viewpoint of hydrolysis resistance, sodium dihydrogen phosphate is particularly preferable. Also, multiple sodium phosphate salts may be used in combination.

It is also preferable to use the above sodium phosphate salt in combination with another compound containing a phosphorus atom (element). It is particularly preferable to mix the sodium phosphate salt and phosphoric acid as a buffer solution. By mixing the buffer solution of sodium phosphate salt and phosphoric acid with the calcium carbonate particle slurry, it is possible to coat the calcium carbonate particle surface and suppress calcium elution from the calcium carbonate particle surface due to heating during polycondensation reaction or melt molding such as film formation.

In the method for producing the polyester composition of the present invention, the calcium carbonate particles and the compound containing phosphorus atoms (element) may be added at any stage of the (A) esterification reaction or (B) ester exchange reaction process, or the subsequent (C) polycondensation reaction process. However, by adding the compound before the end of the polycondensation reaction and after mixing the calcium carbonate particles and the compound containing phosphorus atoms (element), the amount of COOH terminal groups can be reduced and hydrolysis resistance can be improved, and a polyester composition with even better particle dispersibility can be obtained.

The above-mentioned compound containing phosphorus atoms (elements) may be used in combination with other alkali metal compounds. For example, by using potassium hydroxide in combination, the melt resistivity of the polyester required for electrostatically applied film formation can be reduced, improving moldability.

In the method for producing the polyester composition of the present invention, when the method is carried out via (A) an esterification reaction, it is preferable to add an additional glycol component such as ethylene glycol after the esterification reaction and before the calcium carbonate particles and the compound containing phosphorus atoms (element) are added as a mixed slurry. The low molecular weight substance of the polyester composition obtained by the esterification reaction has a higher degree of polymerization than the low molecular weight substance obtained by the transesterification reaction, so that the calcium carbonate particles and sodium phosphate salt are less likely to disperse and foreign matter is more likely to occur. Therefore, foreign matter can be suppressed by adding an additional glycol such as ethylene glycol and temporarily lowering the degree of polymerization by depolymerization.

The amount of glycol such as ethylene glycol added is preferably 0.05 to 0.5 times by mole relative to the total amount of acid components. More preferably, it is 0.1 to 0.3 times by mole. By keeping it within the above range, it is possible to suppress the conversion of the alkali metal phosphate into foreign matter without causing a delay in the polymerization time due to a drop in temperature in the polymerization system.

When calcium carbonate particles and a compound containing phosphorus atoms (element) are added, it is preferable to add them as a slurry from the viewpoint of particle dispersibility. When adding them as a slurry, it is preferable that the particles and the dispersion solvent are mixed thoroughly, so it is preferable to mix for at least 10 seconds. Mixing may be performed using a stirring device such as a stirrer or magnetic stirrer. In addition, it is preferable that the particle dispersion solvent is the same as the diol of the polyester composition, and in the case of PET, it is particularly preferable to use ethylene glycol.

It is preferable to stir the reaction system during and after the addition of calcium carbonate particles and the compound containing phosphorus atoms (element). Stirring helps disperse the additives more uniformly.

In addition, in the method for producing the polyester composition of the present invention, solid-phase polymerization may be performed to obtain a polyester composition with a high molecular weight. The solid-phase polymerization is performed by heating the polyester composition under an inert gas atmosphere or under reduced pressure, although the apparatus and method are not particularly limited. The inert gas may be any gas that is inert to the polyester composition, such as nitrogen, helium, and carbon dioxide, but nitrogen is preferably used from an economical standpoint. In addition, under reduced pressure conditions, a higher vacuum is advantageous because it shortens the time required for the solid-phase polymerization reaction, and specifically, it is preferable to maintain the pressure at 110 Pa or less.

Specific examples of the method for producing the polyester composition of the present invention are given below, but the present invention is not limited to these.

A slurry of terephthalic acid and ethylene glycol (1.15 times the molar amount of terephthalic acid) is gradually added to an esterification reactor containing dissolved bishydroxyethyl terephthalate (BHT) at 250°C to allow the esterification reaction to proceed. The temperature in the reaction system is controlled to be 245-250°C, and the esterification reaction is terminated when the reaction rate reaches 95%.

The 255°C esterification product thus obtained is transferred to a polymerization apparatus, and a polycondensation catalyst, additional ethylene glycol, and a mixed slurry of calcium carbonate particles and a compound containing phosphorus atoms (element) are added. During these operations, it is preferable to keep the temperature in the reaction system at 240-255°C to prevent the esterification product from solidifying.

Then, while gradually increasing the temperature inside the polymerization apparatus to 290°C, the pressure inside the polymerization apparatus is gradually reduced from normal pressure to 250 Pa or less to distill off ethylene glycol. The reaction is terminated when a predetermined stirring torque is reached, the reaction system is returned to normal pressure with nitrogen gas, and the molten polyester is discharged into cold water in the form of strands and cut to obtain a polyester composition.

The polyester composition obtained by the present invention can be molded by known molding and processing methods and processed into various products such as films, fibers, bottles, and injection molded products.

When the polyester composition of the present invention is processed into various products, one or more of various additives, such as colorants including pigments and dyes, lubricants, antistatic agents, flame retardants, ultraviolet absorbers, antibacterial agents, nucleating agents, plasticizers, and release agents, can be added within a range that does not impair the effects of the present invention.

The polyester composition of the present invention has excellent hydrolysis resistance and particle dispersibility, and generates little decomposition or particle agglomeration during melt molding or processing. Therefore, it can be used in a variety of products, including films, fibers, bottles, and injection molded products, and can be used in high-quality films, such as optical films and release films.

The film may be a single film made of the polyester composition of the present invention or a laminated film having at least one layer of the polyester composition of the present invention. In particular, in the case of a laminated film, a laminated film having a layer made of the polyester composition of the present invention on at least one surface is preferred. When a layer made of the polyester composition of the present invention is present on the film surface, it is possible to suppress the formation of aggregated foreign matter and coarse protrusions derived from particles.

Molded articles made from the polyester composition of the present invention have excellent thermal stability and color tone, and are therefore useful as agricultural materials, horticultural materials, fishing materials, civil engineering and construction materials, stationery, medical supplies, automotive parts, electrical and electronic parts, and other applications, and are particularly suitable for biaxially stretched films as release process films and optical films.

The present invention will be described in more detail below with reference to examples. The physical properties in the examples were measured by the following methods. The methods described below are for the polyester composition of the present invention, but in the case of a molded product made of multiple resins, such as a laminated film, the resins of each layer are isolated by, for example, scraping, and then analyzed.
Moreover, Examples 4, 9, and 10 should be read as Reference Examples.

(1) Amount of COOH terminal groups in polyester composition (unit: eq/t indicates equivalent/t)
The measurement was performed by the method of M. J. Maurice, F. Huizinga, Anal. Chem. Acta, 22, 363 (1960).
That is, 0.5 g of the polyester resin composition is weighed out to within 0.001 g accuracy. 50 ml of a solvent in which o-cresol/chloroform is mixed in a mass ratio of 7/3 is added to the sample, and the mixture is heated until the internal temperature reaches 90°C, after which it is heated and stirred for 20 minutes to dissolve. In addition, the mixed solvent alone is heated separately in the same manner as a blank solution. The solution is cooled to room temperature, and titration is performed with a 1/50N solution of potassium hydroxide in methanol using a potentiometric titrator. Titration is also performed in the same manner on the blank solution of the mixed solvent alone.
The amount of COOH terminal groups in the polyester resin composition was calculated according to the following formula.
COOH terminal group amount (eq/t) = {(V1-V0) x N x f} x 1000/S
Here, V1 is the titration volume (mL) of the sample solution, V0 is the titration volume (mL) of the blank solution, N is the normality (N) of the titration solution, f is the factor of the titration solution, and S is the mass (g) of the polyester resin composition.

(2) Quantitative Determination of Alkali Metal Atoms (Elements) in Polyester Composition (Unit: ppm)
1 g of the polyester composition was placed on a platinum dish and completely incinerated at 700° C. for 1.5 hours. The incinerated product was then dissolved in 20 mL of a 0.25 N aqueous hydrochloric acid solution, and pure water was added to make a 0.1 N aqueous hydrochloric acid solution. This was used as a measurement sample, and quantitative analysis was performed by atomic absorption spectrometry (polarized Zeeman atomic absorption spectrometer model 180-80, manufactured by Hitachi, Ltd., flame: acetylene-air).

(3) Quantitative Analysis of Ca Atoms (Element) and P Atoms (Element) in the Polyester Composition (Unit: ppm)
7 g of the polyester composition was molded into a cylindrical shape using a melt press, and the amount of the cylindrical material was measured using a fluorescent X-ray analyzer (model number: 3270) manufactured by Rigaku Corporation.

(4) Content of free calcium atoms (elements) in the polyester composition (unit: ppm)
30 g of the polyester composition was added to 300 mL of o-chlorophenol, and the mixture was dissolved at 150° C. for 1 hour, and then centrifuged at a centrifugal acceleration of 40,900 G at 20° C. for 1 hour. The resulting supernatant solution was collected by decantation, and 500 mL of acetone was added to cause precipitation. The precipitate was collected by filtration and dried in vacuum at 150° C. for 12 hours, and then quantified by the analytical method in (3).
The centrifuge used was a HITACHI himacCR20G (rotor: R19A).

(5) Isolation of calcium carbonate particles from the polyester composition and measurement of the phosphorus element (atom) content in the isolated particles (unit: wt%)
30 g of the polyester composition was added to 300 mL of o-chlorophenol, dissolved at 150° C. for 1 hour, and then centrifuged at 18,000 rpm (40,900 G) and 20° C. for 1 hour. 300 mL of dichloromethane was added to the obtained solid content, the precipitate was stirred, and then centrifuged at a centrifugal acceleration of 40,900 G and 20° C. for 1 hour to obtain a solid content. 300 mL of dichloromethane was added again to the obtained solid content, the precipitate was stirred, and then centrifuged under the same conditions. The solid content obtained by performing this centrifugation with dichloromethane three times in total was used as isolated particles. The phosphorus atom (element) content in the isolated particles was measured using an ICP emission spectrometer (PS3520VDDII manufactured by Hitachi High-Tech Science).
The centrifuge used was a Hitachi himac CR20G (rotor: R19A).

(6) Measurement of volume average particle diameter in polyester composition (unit: μm)
The polyester composition was plasma-treated, and the volume average particle diameter was measured using a Hitachi field emission scanning electron microscope (model S-4000) and a Nideco SEM-IMAGE ANALYZER (model Ludex AP). When analyzing the particle diameter, measurements were performed in 20 or more fields at a magnification of 5000 times, and the circle equivalent diameters were measured from at least 200 particles, which were regarded as pseudo-three-dimensional spheres to calculate the volume average particle diameter.

(7) Heat treatment of polyester composition and evaluation of particle aggregation/coarse foreign matter formation The polyester composition was pretreated by vacuum drying at 150° C. for 3 hours and then at 180° C. for 7.5 hours, followed by heating and melting at 300° C. for 10 hours under nitrogen flow, and then quenching in water. The volume average particle diameter of the obtained composition was calculated by the method of (6) above, and the ratio (volume average diameter after heating/volume average diameter before heating) divided by the volume average diameter before heat treatment calculated in (6) was evaluated as an index of particle aggregation/coarse foreign matter formation (◎ and ◯ were evaluated as pass).
◎: 1.2 or less ○: 1.2 to 1.5
×: 1.5 or more.

(8) Evaluation of Hydrolysis Resistance of Polyester Composition (ΔCOOH)
The polyester composition was subjected to a wet heat treatment in saturated water vapor at 155° C. for 4 hours, and the amount of COOH terminal groups before and after the treatment was measured to calculate the increase in the amount of COOH terminal groups (ΔCOOH=COOH after treatment−COOH before treatment).
The processing apparatus used was PRESSER COOKER 306SIII (manufactured by HIRAYAMA SEISAKUSHO CO., LTD.).

(9) Preparation of biaxially oriented film and three-dimensional roughness measurement [Preparation of PET-A] A slurry consisting of 86 parts by weight of terephthalic acid and 37 parts by weight of ethylene glycol (1.15 times the molar amount relative to terephthalic acid) is gradually added to an esterification reactor containing 105 parts by weight of BHT melted at 250°C, and the esterification reaction is allowed to proceed. The temperature in the reaction system is controlled to 245-250°C, and the esterification reaction is terminated when the reaction rate reaches 95%, to obtain BHT. 105 parts by weight (corresponding to 100 parts by weight of PET) of BHT is charged in a molten state from the esterification reactor into a polymerization apparatus, and the temperature is set to 255°C. To this are added an ethylene glycol solution of manganese acetate tetrahydrate (40 ppm as Mn atoms (element) relative to the weight of the polyester composition), an ethylene glycol slurry of diantimony trioxide (100 ppm as Sb atoms (element) relative to the weight of the polyester composition), and phosphoric acid (35 ppm as phosphorus atoms (element) relative to the weight of the polyester composition). Thereafter, the temperature inside the polymerization apparatus is gradually raised to 290°C, and the pressure is reduced from normal pressure to 250 Pa or less, and the polymerization reaction is carried out until a predetermined stirring torque is exhibited at 290°C. After completion of the polymerization reaction, the reaction system is returned to normal pressure with nitrogen gas, and the molten polyester in the polymerization apparatus is discharged in the form of strands into a water tank, cooled, and then cut to obtain a pellet-shaped polyester composition (intrinsic viscosity 0.62).

[Preparation of biaxially oriented film] 50 parts by weight of PET-A and 50 parts by weight of the polyester composition of the present invention are blended as the resin constituting the A layer, dried under reduced pressure at 160°C for 2 hours, and then fed into the extruder for the A layer. 100 parts by weight of PET-A as the resin constituting the B layer are dried under reduced pressure at 160°C for 2 hours, and then fed into the extruder for the B layer. The respective raw materials are melted at 280°C in the extruder, merged and laminated in a layer merge block, and a two-layer laminate with a layer A/layer B lamination ratio of 2/12.5 is formed. The laminate is extruded onto a casting drum with a surface temperature of 25°C, and a two-layer laminate sheet is produced while applying electrostatic force. The sheet is then preheated with a group of heated rolls, stretched 3.5 times in the longitudinal direction at a temperature of 90°C, and cooled with a group of rolls at a temperature of 25°C to obtain a uniaxially stretched film. While holding both ends of the obtained uniaxially stretched film with clips, it is stretched 4.0 times in the width direction perpendicular to the longitudinal direction in a heating zone at 110°C in a tenter. It is then heat-set for 10 seconds at a temperature of 230°C in a heat treatment zone in the tenter. It is then uniformly cooled in a cooling zone and wound up to obtain a biaxially oriented polyester film with a thickness of 25 μm.

[Measurement of three-dimensional roughness of biaxially oriented film] The obtained biaxially oriented polyester film was cut into 10 cm squares, and 40 visual field measurements were performed using a non-contact optical roughness measuring instrument (NewView7300 manufactured by Zygo) with a measurement area of 139 μm × 104 μm using a 50x objective lens, with the location changed randomly. At this time, the sample was set so that the particle-containing layer was the observation surface. The arithmetic average roughness Ra (unit: nm) was obtained using a bandpass filter with a wavelength of 1.65 to 50 μm by the surface analysis software MetroPro built into the measuring instrument. The Ra required for an optical release film was evaluated according to the following criteria, with ◎ and ○ being considered as passing.
◎: Less than 15.5 ○: 15.5 or more but less than 17.0 ×: 17.0 or more.

Example 1
A slurry consisting of 86 parts by weight of terephthalic acid and 37 parts by weight of ethylene glycol (1.15 times the molar amount relative to terephthalic acid) was gradually added to an esterification reactor charged with 105 parts by weight of BHT melted at 250° C. to allow the esterification reaction to proceed. The temperature in the reaction system was controlled to be 245 to 250° C., and the esterification reaction was terminated when the reaction rate reached 95%, yielding BHT.
105 parts by weight (corresponding to 100 parts by weight of PET) of BHT was charged in a molten state from the esterification reactor into the polymerization apparatus, and the temperature was set to 255° C. An ethylene glycol solution of manganese acetate tetrahydrate (24 ppm as Mn atom (element) relative to the weight of the polyester composition) and an ethylene glycol slurry of diantimony trioxide (255 ppm as Sb atom (element) relative to the weight of the polyester composition) were added. Thereafter, 5 parts by weight of ethylene glycol (0.15 times the molar ratio relative to the terephthalic component) were added to proceed with depolymerization, and then an ethylene glycol solution of phosphoric acid (49 ppm as P atom (element) relative to the weight of the polyester composition) and sodium dihydrogen phosphate dihydrate (16 ppm as Na atom (element) and 23 ppm as P atom (element) relative to the weight of the polyester composition) and an ethylene glycol slurry (volume average diameter 0.8 μm) with a concentration of calcium carbonate particles of 20 wt % were all mixed and stirred for 60 seconds to form a homogeneous slurry, which was then added. (1 part by weight as calcium carbonate).
Thereafter, the temperature in the polymerization apparatus was gradually increased to 290° C., and the pressure was reduced from normal pressure to 250 Pa or less, and the polymerization reaction was allowed to proceed until a predetermined stirring torque was observed at 290° C. After the polymerization reaction was completed, the reaction system was returned to normal pressure with nitrogen gas, and the molten polyester in the polymerization apparatus was discharged in the form of strands into a water tank, cooled, and then cut to obtain a polyester composition in the form of pellets. The properties of the obtained polyester composition are shown in Table 1.
The polyester composition obtained in Example 1 had no particle aggregation or formation of coarse foreign matter and was excellent in hydrolysis resistance, and therefore had physical properties suitable for optical films and release films.

(Examples 2 to 4, Comparative Examples 1 and 2)
A polyester composition was obtained in the same manner as in Example 1, except that the volume average diameter of the calcium carbonate particles and the amount of the compound containing a phosphorus atom (element) were changed as shown in Table 1. The properties of the obtained polyester composition are shown in Table 1.

The polyester compositions obtained in Examples 2 to 4 were free from particle aggregation or formation of coarse foreign matter and had excellent hydrolysis resistance, and therefore had properties suitable for optical films and release films.
The polyester composition obtained in Comparative Example 1 had a small volume average diameter of calcium carbonate particles, and particle aggregation was observed, and was therefore unacceptable.
The polyester composition obtained in Comparative Example 2 had a large volume average diameter of calcium carbonate particles, and when molded into a film, large protrusions were formed, resulting in failure.

(Examples 5 to 8, Comparative Example 3)
A polyester composition was obtained in the same manner as in Example 1, except that the amount of the compound containing a phosphorus atom (element) was changed as shown in Table 2. The properties of the obtained polyester composition are shown in Table 2.

The polyester compositions obtained in Examples 5 to 8 had a slight increase in volume average diameter after heat treatment due to an increase in phosphorus atoms (element), but they did not suffer from particle aggregation or coarse foreign matter formation and had excellent hydrolysis resistance, so they had physical properties suitable for optical films and release films.
The polyester composition obtained in Comparative Example 3 had a small amount of the compound containing a phosphorus atom (element) added, and the phosphorus atom (element) content in the calcium carbonate particles isolated from the polyester composition was small, so that aggregation of particles and formation of coarse foreign matter occurred, and the hydrolysis resistance was also poor, resulting in failure.

(Examples 9 to 10, Comparative Example 4)
A polyester composition was obtained in the same manner as in Example 1, except that the type of compound containing a phosphorus element (atom) was changed as shown in Table 3. The properties of the obtained polyester composition are shown in Table 3.
Although the polyester compositions obtained in Examples 9 and 10 showed some particle aggregation due to differences in the acidity of the phosphorus species used, they had excellent hydrolysis resistance and physical properties suitable for optical films and release films.
In the polyester composition obtained in Comparative Example 4, only phosphoric acid was added by mixing it with calcium carbonate particles, and calcium ions were eluted from the calcium carbonate particles, the content of free calcium atoms (element) was increased, and the content of phosphorus atoms (element) in isolated particles was also low.

(Examples 11 to 12)
A polyester composition was obtained in the same manner as in Example 1, except that the amount of calcium carbonate particles and the amount of the compound containing a phosphorus atom (element) were changed as shown in Table 3. The properties of the obtained polyester composition are shown in Table 3.
The polyester compositions obtained in Examples 11 and 12 showed some aggregation and formation of coarse foreign matter when the amount of particles added was increased, but had physical properties suitable for optical films and release films.

Example 13
Dimethyl terephthalate (101.0 parts by weight) and ethylene glycol (64.6 parts by weight, twice the molar amount of dimethyl terephthalate) were weighed and charged into an ester exchange reactor. The contents were dissolved at 150°C, and then an ethylene glycol solution of manganese acetate tetrahydrate (24 ppm as Mn atom (element) relative to the weight of the polyester composition) and an ethylene glycol slurry of diantimony trioxide (255 ppm as Sb atom (element) relative to the weight of the polyester composition) were added and stirred. Methanol was distilled off while increasing the temperature to 240°C, and the ester exchange reaction was terminated when a predetermined amount of methanol was distilled off. Thereafter, the reactants were transferred to a polymerization apparatus, and an ethylene glycol solution of phosphoric acid (49 ppm as P atom (element) relative to the weight of the polyester composition) and sodium dihydrogen phosphate dihydrate (16 ppm as Na atom (element) and 23 ppm as P atom (element) relative to the weight of the polyester composition) and an ethylene glycol slurry with a concentration of calcium carbonate particles of 20 wt% were all mixed and stirred for 60 seconds to form a homogeneous slurry, which was then added. (1 part by weight as calcium carbonate). After the addition, the temperature inside the polymerization apparatus was gradually raised to 290°C, and the pressure was reduced from normal pressure to 250 Pa or less, and the polymerization reaction was carried out until a predetermined stirring torque was observed at 290°C. After the polymerization reaction was completed, the reaction system was returned to normal pressure with nitrogen gas, and the molten polyester in the polymerization apparatus was discharged into a water tank in the form of a strand, cooled, and then cut to obtain a pellet-shaped polyester composition. The properties of the obtained polyester composition are shown in Table 3.
The polyester composition obtained in Example 14 was free from particle aggregation or formation of coarse foreign matter and had excellent hydrolysis resistance, and therefore had physical properties suitable for optical films and release films.

(Comparative Example 5)
In the same manner as in Example 1, 105 parts by weight (corresponding to 100 parts by weight of PET) of BHT was charged in a molten state from the esterification reactor into the polymerization apparatus, and the temperature was adjusted to 255° C. An ethylene glycol solution of manganese acetate tetrahydrate (24 ppm as Mn atom (element) relative to the weight of the polyester composition) and an ethylene glycol slurry of diantimony trioxide (255 ppm as Sb atom (element) relative to the weight of the polyester composition) were added. Thereafter, 5 parts by weight of ethylene glycol (0.15 times the molar amount relative to the terephthalic component) were additionally added to proceed with depolymerization, and then a mixed ethylene glycol solution of phosphoric acid (49 ppm as P atom (element) relative to the weight of the polyester composition) and sodium dihydrogen phosphate dihydrate (16 ppm as Na atom (element) and 23 ppm as P atom (element) relative to the weight of the polyester composition) was added. After the phosphorus compound was added, an ethylene glycol slurry with a concentration of calcium carbonate particles of 20 wt % was added (1 part by weight as calcium carbonate). Thereafter, the temperature inside the polymerization apparatus was gradually increased to 290° C., and the pressure was reduced from normal pressure to 250 Pa or less, and the polymerization reaction was carried out until a predetermined stirring torque was observed at 290° C. After completion of the polymerization reaction, the pressure inside the reaction system was returned to normal with nitrogen gas, and the molten polyester inside the polymerization apparatus was discharged in the form of strands into a water tank, cooled, and then cut to obtain a polyester composition in the form of pellets.
The obtained polyester composition did not have the particle surface protected by the phosphorus compound, contained a large amount of free calcium components, and furthermore, the particle shape was not maintained by heat treatment, causing particle aggregation, and the three-dimensional roughness when processed into a biaxially oriented film was unacceptable.

Claims (7)

A polyester composition containing calcium carbonate particles and phosphorus atoms (element), using phosphoric acid and an alkali metal phosphate, and satisfying the following formulas (I), (II), (V), and (VI).
0.2≦R≦0.8 (I)
0.38/R ² ≦P ₁ (II)
Free calcium atom (element) content ≦ 5 ppm (V)
0.01 ppm≦Sodium atom (element) content (weight ratio relative to polyester composition)≦30 ppm or less (VI)
R: volume average diameter of calcium carbonate particles (μm)
_P1 : phosphorus atom (element) content contained in isolated particles obtained by isolating the polyester composition by the method described below (wt%: weight ratio to the isolated particles)
(Isolation method: The polyester composition is dissolved in o-chlorophenol at 150° C. for 1 hour, then centrifuged at a centrifugal acceleration of 40,900 G at 20° C. for 1 hour, dichloromethane is added to the obtained solid, and centrifuged under the same conditions to obtain a solid. Dichloromethane is again added to the obtained solid, and centrifuged under the same conditions. This centrifugation with dichloromethane is carried out a total of three times, and the obtained solid is called isolated particles.)
(The free calcium atom (element) content is determined by dissolving the polyester composition in o-chlorophenol at 150° C. for 1 hour, centrifuging the mixture at a centrifugal acceleration of 40,900 G at 20° C. for 1 hour, collecting the resulting supernatant by decantation, adding acetone to cause precipitation, collecting the precipitate by filtration, and drying in vacuum at 150° C. for 12 hours, thereby obtaining the calcium atom (element) content in the polymer.) The polyester composition according to claim 1, wherein the calcium atom (element) content is 100 ppm or more (weight ratio relative to the polyester composition). The polyester composition according to claim 1, in which the increase in carboxylic acid end groups ΔCOOH before and after 4 hours of wet heat treatment at 155°C in saturated water vapor is 80 eq/t or less. The polyester composition according to claim 1, wherein the polyester is polyethylene terephthalate. A method for producing a polyester composition by subjecting a dicarboxylic acid or a dicarboxylic acid ester and a diol to an esterification reaction or an ester exchange reaction, followed by a polycondensation reaction, the method comprising adding, as a mixed slurry, a compound containing calcium carbonate particles and a mixed solution of phosphoric acid and an alkali metal phosphate before completion of the polycondensation reaction, so as to satisfy the following formulae (III), (IV), and (VII):
0.2≦R≦0.8 (III)
0.38/R ² ≦P ₂ (IV)
0.01 ppm≦sodium atom (element) added amount (weight ratio to polyester composition)≦30 ppm or less (VII)
R: volume average diameter of calcium carbonate particles (μm)
_P2 : Amount of phosphorus atoms (element) added as mixed slurry (wt%: weight ratio to calcium carbonate) The method for producing a polyester composition according to claim 5, wherein the amount of calcium carbonate particles added is 100 ppm or more (weight ratio to the polyester composition) in terms of calcium atoms (element). 6. The method for producing a polyester composition according to claim 5, wherein the polyester is polyethylene terephthalate.